Heart Transplantation

Number: 0586

Table Of Contents

Policy

Scope of Policy

This Clinical Policy Bulletin addresses heart transplantation.

1. Medical Necessity

   1. Human Heart Transplantation

      Aetna considers heart transplantation medically necessary for any of the following conditions (not an all-inclusive list) when the member meets the transplanting institution's protocol eligibility criteria.  

      1. In the absence of a protocol, Aetna considers heart transplantation medically necessary for heart failure with irreversible underlying etiology, including  the following indications when the selection criteria listed below are met and none of the absolute contraindications is present:

         1. Cardiac arrhythmia
         2. Cardiac re-transplantation due to graft failure
         3. Cardiomyopathy due to nutritional, metabolic, hypertrophic or restrictive etiologies
         4. Congenital heart disease
         5. End-stage ventricular failure
         6. Idiopathic dilated cardiomyopathy
         7. Inability to be weaned from temporary cardiac-assist devices after myocardial infarction or non-transplant cardiac surgery
         8. Intractable coronary artery disease
         9. Myocarditis
         10. Post-partum cardiomyopathy
         11. Right ventricular dysplasia/cardiomyopathy
         12. Valvular heart disease.

      2. Selection Criteria for Human Heart Transplantation 

         For members off protocol, all criteria listed below must be met:

         1. New York Heart Association (NYHA) classification of heart failure III or IV (see Note below) - does not apply to pediatric members; and
         2. Member has potential for conditioning and rehabilitation after transplant (i.e., member is not moribund); and
         3. Life expectancy (in the absence of cardiovascular disease) is greater than 2 years; and
         4. No malignancy (except for non-melanomatous skin cancers or low grade prostate cancer) or malignancy has been completely resected or (upon individual case review) malignancy has been adequately treated with no substantial likelihood of recurrence with acceptable future risks; and
         5. Adequate pulmonary, liver and renal function; and
         6. Absence of active infections that are not effectively treated; and
         7. Absence of uncontrolled HIV infection, defined as:
            
            
            1. CD4 count greater than 200 cells/mm³ for greater than 6 months; and
            2. HIV-1 RNA (viral load) undetectable; and
            3. On stable anti-viral therapy greater than 3 months; and
            4. No other complications from AIDS, such as opportunistic infections (e.g., aspergillus, tuberculosis, coccidiodomycosis, resistant fungal infections) or neoplasms (e.g., Kaposi's sarcoma, non-Hodgkin's lymphoma); and
               
         8. Absence of active or recurrent pancreatitis; and
         9. Absence of diabetes with severe end-organ damage (neuropathy, nephropathy with declining renal function and proliferative retinopathy); and
         10. No uncontrolled and/or untreated psychiatric disorders that interfere with compliance to a strict treatment regimen; and
         11. No active alcohol or chemical dependency that interferes with compliance to a strict treatment regimen.

         Note: NYHA Class III and Class IV for heart failure are defined as follows:

         Table 1: NYHA Class III and Class IV for heart failure

         Class	Classification
         Class III:	Persons with cardiac disease resulting in marked limitation of physical activity.  They are comfortable at rest.  Less than ordinary activity (i.e., mild exertion) causes fatigue, palpitation, dyspnea, or anginal pain.
         Class IV:	Persons with cardiac disease resulting in inability to carry on any physical activity without discomfort.  Symptoms of cardiac insufficiency or of the anginal syndrome may be present even at rest.  If any physical activity is undertaken, discomfort is increased.

      3. Contraindications

         Heart transplant is considered not medically necessary for persons with any of the following contraindications:

         1. Presence of irreversible end-organ diseases (e.g., renal, hepatic, pulmonary) (unless person is to undergo dual organ transplantation, e.g., heart-lung, heart-kidney, etc.); or
         2. Presence of severe pulmonary hypertension with irreversibly high pulmonary vascular resistance; or
         3. Presence of a recent intra-cranial cerebrovascular event with significant persistent deficit; or
         4. Presence of bleeding peptic ulcer; or
         5. Presence of hepatitis B antigen; or
         6. Presence of diverticulitis; or
         7. Presence of immediately life-threatening neuromuscular disorders; or
         8. Presence of HIV/AIDS with profound immunosuppression (CD4 count of less than 200 cells/mm3); or
         9. Presence of AL amyloidosis (although amyloidosis is considered a contraindication to heart transplantation, exceptions may be made in circumstances where curative therapy of amyloidosis has been performed or is planned (e.g., stem cell transplantation in primary amyloidosis, liver transplantation in familial amyloidosis)).

   2. Total Artificial Heart

      Aetna considers the use of a total artificial heart (e.g., ABIOCOR Total Artificial Heart, SynCardia™ temporary Total Artificial Heart (formerly known as CardioWest Total Artificial Heart)) as permanent treatment (destination therapy) (i.e., as an alternative to heart transplantation) experimental, investigational, or unproven because its safety and effectiveness for this indication has not been established.

      Aetna considers a U.S. Food and Drug Administration-approved total artificial heart (e.g., CardioWest Total Artificial Heart, SynCardia Systems) medically necessary when used as a bridge to transplant for transplant-eligible members who are at imminent risk of death (NYHA Class IV) due to biventricular failure who are awaiting heart transplantation. See CPB 0654 - Ventricular Assist Devices.

   3. AlloMap™ Molecular-Expression Blood Test

      Aetna considers the AlloMap gene expression profile medically necessary for monitoring rejection in heart transplant recipients more than 2 months post-heart transplant.

      Aetna considers the AlloMap gene expression profile experimental, investigational, or unproven for all other indications because its clinical value has not been established.

2. Experimental, Investigational, or Unproven

   Aetna considers the following procedures experimental, investigational, or unproven because the clinical value, safety, and/or effectiveness has not been established:

   1. Xenotransplantation of the Heart

      Cardiac xenotransplantation (e.g., porcine xenografts);

   2. Breath Test for Heart Transplant Rejection

      Heartsbreath Test (Menassana Research, Inc) for diagnosing heart transplant rejection and for all other indications;

   3. Cytokine Gene Polymorphism Testing

      Cytokine gene polymorphism testing for evaluating graft rejection following heart transplantation;

   4. Immune Repertoire Sequencing Assay

      Immune repertoire sequencing assay for measurement of the isotype and clonal composition of the circulating B cell repertoire to detect acute allograft rejection in heart transplant recipients;

   5. myTAIHEART Testing

      myTAIHEART test (TAI Diagnostics, Inc., Milwaukee, WI) for evaluating graft rejection following heart transplant and all other indications;

   6. Measurement of Cardiac Troponins

      Measurement of cardiac troponins for diagnosis of acute cellular rejection following heart transplantation, and for assessing prognosis of primary graft failure in heart transplant recipients;

   7. Measurement of Donor-Derived Cell-Free DNA (Allosure)

      Measurement of donor-derived cell-free DNA (Allosure, Prospera Test) of transplant recipients for monitoring of rejection;

   8. Heart Molecular Microscope Diagnostic System (MMDx-Heart)

      Heart Molecular Microscope Diagnostic System (MMDx-Heart) for evaluation of cardiac transplant rejection;

   9. TransMedics Organ Care System

      TransMedics Organ Care System for preservation and transport of donor heart;

   10. Machine Learning and Artificial Intelligence

       The use of machine learning and artificial intelligence in cardiac transplantation.

   11. Prospera Heart

       The Prospera Heart test for detection of acute rejection, including antibody-mediated rejection (AMR) and acute cellular rejection (ACR) in heart transplantation.

3. Related Policies

   1. CPB 0654 - Ventricular Assist Devices - for left ventricular assist devices as destination therapy for persons with severe heart failure

Background

Heart transplantation has become a commonly used therapeutic option for the treatment of end-stage heart disease.  It has been projected that patients who receive cardiac transplants have an in-hospital mortality rate of less than 5 %, a 1-year survival rate of about 85 %, and a 5-year survival rate of 75 % to 80 %.  Moreover, 90 % of cardiac transplant patients lead a relatively normal lifestyle having no limitations in their activity and 40 % return to work.

In adults, cardiac transplantation is most frequently performed for patients with cardiomyopathy (about 50 %), coronary artery disease (about 40 %), valvular disease (about 4 %), re-transplantation following a failed primary transplantation (about 2 %) and congenital heart disease (about 2 %).

In children, the most common indications for cardiac transplantation are congenital heart disease (about 47 %), dilated cardiomyopathy (about 45 %), and re-transplantation (about 3 %).  Moreover, survival in children with dilated cardiomyopathy relies on accurate diagnosis and aggressive treatment.  The literature indicates that patients may respond to conventional treatment for heart failure or may deteriorate, requiring mechanical support.  Extracorporeal membrane oxygenation (see CPB 0546 - Extracorporeal Membrane Oxygenation (ECMO)) has been used effectively for mechanical support in children until improvement occurs or as a bridge to transplantation.  For individuals who are listed to receive a heart transplant, the mortality rate while waiting for a donor organ averages approximately 20 %.  Survival after transplantation is good, with an intermediate survival rate of about 70 %.

The New York Heart Association (NYHA) classification of heart failure is one of the many parameters used for selecting heart recipients.  It is a 4-tier system that categorizes patients based on subjective impression of the degree of functional compromise.  The 4 NYHA functional classes are as follows:

Contraindications to cardiac transplantation include irreversible end-organ diseases (e.g., renal, hepatic, pulmonary), active malignancy or infections, systemic diseases (e.g., autoimmune, vascular), chronic gastro-intestinal disease (e.g., diverticulitis, active or recurrent pancreatitis, bleeding peptic ulcer), psychiatric disorders, and intra-cranial cerebrovascular disease.  Amyloidosis has also been considered a contraindication to cardiac transplantation due to the high likelihood of development of amyloid in the transplanted organ.  Good outcomes of cardiac transplantation have been reported after curative liver transplantation for familial amyloidosis or stem cell transplantation for primary amyloidosis.  HIV infection is not an absolute contraindication to cardiac transplantation if the HIV infection is well-controlled.  Because of the potential impact of transplant-related immunosuppression, it is especially important for HIV-infected transplant recipients to be followed by an HIV-AIDS multi-disciplinary team with expertise in this area.

Cardiac transplantation is currently the only proven curative treatment for end-stage heart disease, but the supply of donor hearts has not kept pace with the demand.  Therefore, surgical techniques such as reduction ventriculoplasty, trans-myocardial laser revascularization (see CPB 0163 - Transmyocardial and Endovascular Laser Revascularization), myo-reduction operations (see CPB 0182 - Ventricular Remodeling Operation (Batista Procedure) and Surgical Ventricular Restoration (Dor Procedure)) or dynamic cardiomyoplasty are employed to maintain heart function or provide a bridge to heart transplantation.  In addition, ventricular assist devices (see CPB 0654 - Ventricular Assist Devices) and the total artificial heart have been approved by the Food and Drug Administration (FDA) for use as a bridge to transplant in selected persons who are awaiting heart transplantation.

Renlund (2004) explained that a variety of devices can be used as a bridge to heart transplant.  The selection of a device depends on the type of heart failure, as well as the size of the patient, the surgeon's experience, and the institutional preference.  Implantable left ventricular assist devices, which channel blood from the left ventricle to the pump and back to the aorta, are generally inadequate for bridging to transplantation in patients with severe biventricular heart failure.  The replacement of both ventricles with a TAH may be warranted when replacement of both ventricles may be warranted in severe biventricular failure (Renlund, 2004).  Such circumstances frequently arise in patients with severe aortic insufficiency, intractable ventricular arrhythmias, an aortic prosthesis, an acquired ventricular septal defect, or irreversible biventricular failure requiring a high pump output.  Para-corporeal devices, with the pump placed outside of the body, can provide an alternative to either the ventricular assist device for supporting 1 ventricle, or to the TAH for supporting both ventricles.

Xenotransplantation of the Heart

The scarcity of donor organs has also resulted in intense research on xenotransplantation.  As a consequence of physiological compatibility as well as infectious consideration, pig is the most likely source of xenotransplantation.  The advent of transgenic pigs expressing human complement regulatory proteins and new immunosuppressive therapies have provided early promising results in the laboratory.  However, more research is needed to advance porcine xenotransplantation to clinical trials.

The Heartsbreath Test

Menssana Research, Inc. (Fort Lee, NJ) has received a humanitarian device approval (see note below) for the Heartsbreath Test for evaluation of heart transplant rejection.  According to the FDA-approved product labeling, the product is to be used as an aid in diagnosis of grade 3 heart transplant rejection in patients who have received heart transplants within the preceding year (FDA, 2004).  The labeling states that the Heartsbreath test is intended to be used as an adjunct to, and not as a substitute for endomyocardial biopsy.  The labeling states that the use of the Heartsbreath Test is limited to patients who have had endomyocardial biopsy within the previous month.

The Heartsbreath test assesses heart transplant rejection by measuring the amount of methylated alkanes, a marker of oxidative stress, in the patient's breath.  Heart transplant rejection appears to be accompanied by oxidative stress which degrades membrane polyunsaturated fatty acids, creating methylated alkanes, which are excreted in the breath as volatile organic compounds.  The value generated by the Heartsbreath Test is compared to the results of a biopsy performed the previous month to measure the probability of the implant being rejected.

According to the FDA (2004), the Heartsbreath test's greatest potential value may be in helping to separate less severe organ rejection (grades 0, 1, and 2) from more severe rejection (grade 3).  The FDA-approved labeling states that the Heartsbreath test should not be used for patients who have received a heart transplant more than 1 year ago, or who have grade 4 heart transplant rejection because the Heartsbreath test has not been evaluated in these patients.

The FDA's Humanitarian Device Approval of the Heartsbreath Test was based on the results of a multi-center clinical study entitled Heart Allograft Rejection: Detection with Breath Alkanes in Low Levels (HARDBALL), which compared the sensitivity and specificity of the Heartsbreath Test with myocardial biopsy reading by a single pathologist at the transplant site (usually a general pathologist) in distinguishing grade 3 heart transplant rejection from lesser grades of rejection, using biopsy reading by 2 cardiac pathologists as the gold standard for comparison (Phillips et al, 2004; FDA, 2004).  In this study, 1,061 breath samples were collected from 539 heart transplant recipients prior to scheduled endomyocardial biopsy.  Compared to the gold standard, the Heartsbreath Test had a sensitivity of 59.5 %, a specificity of 58.8 %, a positive- predictive value of 5.6 % and a negative-predictive value of 97.2 %.  The biopsy reading by the general pathologist had a sensitivity of 42.4 %, a specificity of 97.0 %, a positive- predictive value of 45.2 %, and a negative-predictive value of 96.7 %.  The investigators concluded that the Heartsbreath Test was more sensitive but less specific for grade 3 heart transplant rejection than a biopsy reading by a single general pathologist, but the negative-predictive values of the 2 tests are similar.  Therefore, a screening breath test may provide supportive information to help identify heart transplant recipients who are at low-risk for grade 3 rejections (Phillips et al, 2004).

In a report of the HARDBALL study results published in the New England Journal of Medicine, the investigators explained that the major potential benefit of the Heartsbreath test is in reducing the number of heart biopsies (Phillips et al, 2004).  If the breath analysis is negative, a biopsy is not needed because, with a negative-predictive value of 97 %, this test accurately predicts where there is not any organ rejection.  If the breath analysis is positive, however, the patient will need a biopsy to determine whether there is rejection, because the Heartsbreath test, with a positive-predictive value of 6 %, does not accurately predict the presence of rejection.  The investigators explained that the low positive-predictive value of this test means that it does not predict the presence of rejection.

A commentary on the HARDBALL study (Williams and Miller, 2002) noted that the study results are "difficult to evaluate" because of a "surprising inconsistency" between the biopsy interpretations of the general pathologist at the transplant site and the biopsy interpretation by the 2 cardiac pathologists used as the gold standard.  The commentary also noted that only 9 of 42 biopsies with grade 3 rejection were predicted by the Heartsbreath test.  Finally, the commentary stated that there needs to be further study of the effect of concurrent illness, such as hemodynamic compromise and infection, on the Heartsbreath test, because such illnesses could theoretically decrease the sensitivity and specificity of the Heartsbreath or any other test that is a marker of oxidative stress.

The FDA-approved product labeling of the Heartsbreath test states that the effectiveness of this device for diagnosis of grade 3 heart transplant rejection "has not been demonstrated" (FDA, 2004).  The FDA, however, approved this device based on the Center for Devices and Radiological Health conclusion that the probable benefit of this test outweighs the risk.  The FDA approval also was based on the assumption that this test would not be used as a substitute for a heart biopsy, as has been suggested by the HARDBALL study investigators (Phillips et al, 2004), but to be used as a confirmatory test in combination with myocardial biopsy to detect grade 3 heart transplant rejection (FDA, 2004).  The Humanitarian Device Exemption for the Heartsbreath was not referred to the FDA's Clinical Chemistry and Clinical Toxicology Devices Panel for review and recommendation because the Heartsbreath is used as an adjunct to myocardial biopsy rather than replacing myocardial biopsy.

According to the FDA, the major benefit of the Heartsbreath test is that it may reduce the risk of a patient getting the wrong treatment because of an erroneous biopsy report:

The FDA states that the major risk of the Heartsbreath Test is a result that conflicts with a biopsy report.  According to the FDA, this risk, however, can be minimized by recommending secondary biopsy review of any discordant results by a 2nd pathologist prior to considering any change in treatment.

A HUD may only be used in facilities that have an Institutional Review Board (IRB) to supervise clinical testing of devices and after the IRB has approved the use of the device to treat or diagnose the specific disease.

On December 8, 2008, the Centers for Medicare and Medicaid Services (CMS) issued a decision memorandum in response to a formal request for Menssana Research, Inc., to consider national coverage of the Heartsbreath test as an adjunct to the heart biopsy to detect grade 3 heart transplant rejection in patients who have had a heart transplant within the last year and an endomyocardial biopsy in the prior month.  The CMS determined that the evidence does not adequately define the technical characteristics of the test nor demonstrate that Heartsbreath testing to predict heart transplant rejection improves health outcomes.

AlloMap Molecular Expression Blood Test

The AlloMap molecular expression blood test was developed by XDx Expression Diagnostics.  The test evaluates the expression of 20 genes, about half of which are directly involved in rejection while the remainder provide other information needed for rejection risk assessment.  It is hoped that the results of this test will reduce the number of endomyocardial biopsies.  Among the proposed benefits are the AlloMap test's ability to differentiate mild rejection for which histological findings may be the least accurate and the potential for monitoring physiological responses to steroid weaning.  It has been recognized that the test is not effective in monitoring rejection within the first 6 months of transplantation, and it is yet unclear what a high AlloMap score might mean in the setting of no histological rejection.

In a multi-center study called CARGO (Cardiac Allograft Rejection Gene Expression Observational study), Deng et al (2006) examined gene expression profiling of peripheral blood mononuclear cells to discriminate International Society of Heart and Lung Transplantation (ISHLT) grade 0 rejection (quiescence) from moderate/severe rejection (ISHLT greater than or equal to 3A).  Patients were followed prospectively with blood sampling at post-transplant visits.  Biopsies were graded by ISHLT criteria locally and by 3 independent pathologists blinded to clinical data.  Known allo-immune pathways and leukocyte microarrays identified 252 candidate genes for which real-time polymerase chain reaction (PCR) assays were developed.  An 11 gene real-time PCR test was derived from a training set (n = 145 samples, 107 patients) using linear discriminant analysis, converted into a score (0 to 40), and validated prospectively in an independent set (n = 63 samples, 63 patients).  The test distinguished biopsy-defined moderate/severe rejection from quiescence (p = 0.0018) in the validation set, and had agreement of 84 % (95 % confidence interval [CI]: 66 % to 94 %) with grade ISHLT greater than or equal to 3A rejection.  Patients over 1 year post-transplant with scores below 30 (approximately 68 % of the study population) are very unlikely to have grade greater than or equal to 3A rejection (negative-predictive value  = 99.6 %).  Gene expression testing can detect absence of moderate/severe rejection, thus avoiding biopsy in certain clinical settings.  The authors concluded that more research is needed to establish the role of molecular testing for prediction of clinical event prediction and management of immunosuppression.  Furthermore, an editorial (Halloran et al, 2006) that accompanied the CARGO study questioned the biological plausibilty of this technology and emphasized the need for replication of these findings.

In a subsequent study, the investigators from the CARGO study (Starling et al, 2006) provided recommendations regarding the use of the gene expression profiling (GEP) test.  However, none of the recommendations received Class I classification and/or Level A evidence.

Candidates for GEP Testing

Class IIa:

• GEP testing can be used in clinically stable cardiac transplant recipients who are 15 years of age or older and 6 months or more post-transplant to identify patients at low-risk for moderate/severe (Grade greater than or equal to 3A/2R) cellular rejection.  (Level of Evidence: B)
• At the time of GEP testing, a thorough history and physical examination should be obtained/performed by an appropriately trained transplant physician, and a non-invasive assessment of cardiac allograft function utilizing echocardiography should be performed to evaluate allograft function.  (Level of Evidence: C)

Class III:

• GEP testing should not be used in patients at high-risk for acute rejection or graft failure, including those with (a) signs/symptoms of cardiac allograft dysfunction or hemodynamic compromise (including LVEF less than 40 % and cardiac index less than 2 L/min), (b) recurrent Grade greater than or equal to 3A/2R cellular rejection (greater than or equal to 2 episodes within the past year), or (c) a history of Grade greater than or equal to 3A/2R cellular rejection within the preceding 6 months or antibody-mediated rejection within the preceding 12 months.  (Level of Evidence: C)
• GEP testing should not be performed in pregnant women, in patients who have had a blood transfusion in the previous 30 days, or in patients who have received hematopoietic growth factors affecting leukocytes within the previous 30 days.  (Level of Evidence: C)
• GEP testing should not be used to rule out rejection in patients who have received high-dose steroids (intravenous bolus or oral augmentation) within the past 21 days or who are currently on greater than or equal to 20 mg/day of prednisone equivalent.  (Level of Evidence: C)
• Molecular testing should not be used in patients less than 15 years of age.  (Level of Evidence: C)

Classification of Recommendations

Class I: Conditions for which there is evidence and/or general agreement that a given procedure/therapy is beneficial, useful, and/or effective.

Class II: Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure/therapy.

Class IIa: Weight of evidence/opinion is in favor of usefulness/efficacy.

Class III: Conditions for which there is evidence and/or general agreement that a procedure/therapy is not useful/effective and in some cases may be harmful.

Level of Evidence

A: Data are derived from multiple randomized clinical trials or meta-analyses.

B: Data are derived from a single randomized trial, or nonrandomized studies.

C: Only consensus opinion of experts, case studies, or standard of care.

Starling and colleagues (2006) noted that while the performance of the GEP test has been validated in a large number of transplant recipients, the clinical outcomes associated with using a GEP-based strategy to monitor for rejection are currently unknown.  A multi-center randomized clinical study is currently underway to assess a GEP-based strategy, compared to a biopsy-based strategy, for evaluating rejection in cardiac transplant patients who are 2 to 5 years post-transplant.  This study will examine the impact of these 2 strategies with respect to clinical outcomes (e.g., graft dysfunction, death, and clinically apparent rejection), incidence of biopsy-related complications, quality of life, as well as resource utilization.

The AlloMap was assessed by the California Technology Assessment Forum (CTAF, 2006), which concluded that this technology does not meet CTAF's assessment criteria.  The CTAF assessment stated that GEP offers the potential for a non-invasive test that may replace endomyocardial biopsy as the gold standard for transplant rejection.  However, given the history of poor reproducibility of other GEP in the recent past, it is prudent to require independent confirmation of the CARGO Study results before widespread adoption of the AlloMap gene expression profile to detect early rejection in cardiac transplant recipients.  This is particularly true given the post-hoc change in the threshold used to define a positive test result in the study and the small size of the primary validation study.  Additionally, there are no studies published to date comparing the clinical outcomes of patients monitored with GEP to those of patients monitored with endomyocardial biopsies.

A subsequent randomized, controlled study of the AlloMap GEP concluded that, among selected patients who had received a cardiac transplant more than 6 months previously and who were at a low-risk for rejection, a strategy of monitoring for rejection that involved AlloMap GEP, as compared with routine biopsies, was not associated with an increased risk of serious adverse outcomes and resulted in the performance of significantly fewer biopsies.  In the Invasive Monitoring Attenuation Through Gene Expression (IMAGE) study (Pham et al, 2010), investigators randomly assigned 602 patients who had undergone cardiac transplantation 6 months to 5 years previously to be monitored for rejection with the use of GEP or with the use of routine endomyocardial biopsies, in addition to clinical and echocardiographic assessment of graft function.  The investigators performed a non-inferiority comparison of the 2 approaches with respect to the composite primary outcome of rejection with hemodynamic compromise, graft dysfunction due to other causes, death, or re-transplantation.  During a median follow-up period of 19 months, patients who were monitored with GEP and those who underwent routine biopsies had similar 2-year cumulative rates of the composite primary outcome (14.5 % and 15.3 %, respectively; hazard ratio with GEP, 1.04; 95 % CI: 0.67 to 1.68).  The 2-year rates of death from any cause were also similar in the 2 groups (6.3 % and 5.5 %, respectively; p = 0.82).  Patients who were monitored with the use of GEP underwent fewer biopsies per person-year of follow-up than did patients who were monitored with the use of endomyocardial biopsies (0.5 versus 3.0, p < 0.001).

Mehra and Uber (2007) stated that clinicians have entered a new era for managing heart transplant recipients with the use of multi-marker GEP.  Early after transplantation, when steroid modification is the main concern, gene expression testing might aid in optimizing the balance of immunosuppression, defraying the occurrence of rejection, and avoiding crisis intervention.  Late after transplantation, the reliance on endomyocardial biopsy could be reduced.  These advances, if continually validated in practice, could result in decreased immunosuppression complications, lesser need for invasive surveillance, and more clinical confidence in immunosuppressive strategies.

An editorial accompanying the IMAGE trial (Jarcho, 2010) commented that the most notable implication of the IMAGE trial may be the evidence it offers that calls into question the importance of any form or routine screening for the early detection of rejection in the longer term after transplantation.  The editorialist explained that, of 34 rejection episodes identified in the GEP group in the trial, only 6 were detected solely on the basis of the GEP test.  All other episodes of rejection were associated with clinical manifestations of heart failure or echocardiographic evidence of allograft dysfunction.  "This observation suggests that, even if rejection is not identified until graft dysfunction is present, the clinical outcomes may not be substantially worse than when rejection is detected early."  Other limitations of the trial include the fact that the investigators only enrolled patients who had undergone transplantation at least 6 months previously, a group that was a much lower risk of rejection than patients within 6 months of transplantation.  In addition, the non-inferiority margin was wide; the actual 95 % CI was consistent with as much as a 68 % increase in risk with the GEP strategy.

A re-assessment of the AlloMap by the California Technology Assessment Forum (Tice, 2010), considering the results of the IMAGE trial, concluded that this technology meets CTAF's assessment criteria.  The CTAF assessment stated that the AlloMap GEP has a high negative-predictive value, but a low positive-predictive value.  Thus, it may be useful to avoid biopsy in stable patients, but the high false-positive rate precludes its use to definitively diagnose acute cellular rejection.  The assessment states that endomyocardial biopsies will still need to be performed in all patients with elevated AlloMap scores and all patients with clinical signs of rejection.  CTAF found that the IMAGE trial provides data supporting the non-inferiority of a monitoring strategy for heart transplant patients incorporating the AlloMap GEP in lieu of routine endomyocardial biopsy.  However, the data only support such strategies in patients more than 1 year post-transplant.  CTAF stated that more data are needed to confirm the tests utility earlier in the post-transplant period when the majority of endomyocardial biopsies are performed.

Kobashigawa et al (2015) noted that EMB is considered the gold standard in rejection surveillance following HTX; however, it is invasive, and with risk of complications.  A previous study suggested that the GEP blood test was non-inferior to EMB between 6 and 60 months post-transplant.  As most rejections occur in the first 6 months, these researchers carried out a randomized, single-center, pilot study of GEP versus EMB starting at 55 days post-transplant (when GEP is valid).  A total of 60 HTx recipients meeting inclusion criteria were randomized beginning at 55 days post-transplant to either GEP or EMB arms.  A positive GEP of 30 or higher between 2 and 6 months, or 34 or higher after 6 months, prompted a follow-up biopsy.  The primary endpoint included a composite of death/re-transplant, rejection with hemodynamic compromise or graft dysfunction at 18 months post-transplant.  A co-primary endpoint included change in 1st-year maximal intimal thickness by IVUS, a recognized surrogate for long-term outcome.  Corticosteroid weaning was assessed in both the groups.  The composite endpoint was similar between the GEP and EMB groups (10 % versus 17 %; log-rank p = 0.44). The co-primary endpoint of 1st-year IVUS change showed no difference in mean maximal intimal thickness (0.35 ± 0.36 versus 0.36 ± 0.26 mm; p = 0.944).  Steroid weaning was successful in both the groups (91 % versus 95 %).  The authors concluded that in this pilot study, GEP starting at 55 days post-transplant appeared comparable with EMB for rejection surveillance in selected HTx patients and did not result in increased adverse outcomes.  GEP also appeared useful to guide corticosteroid weaning.  Moreover, these researchers stated that larger randomized trials are needed to confirm these preliminary findings.  They acknowledged that this trial was not powered and that the small sample size left these researchers unable to draw firm conclusions regarding the non-inferiority of early GEP use compared with EMB use.  This study was also limited by the few primary endpoints experienced as only 8 patients reached the composite primary endpoint.  However, based on these findings, these investigators felt that the findings of this pilot study would serve as proof of concept (POC) for a future large-scale trial.

Crespo-Leiro et al (2016) stated that a non-invasive GEP test for rejection surveillance of HTx recipients was originated in the U.S.  A European-based study, Cardiac Allograft Rejection Gene Expression Observational II Study (CARGO II), was carried out to further clinically validate the GEP test performance.  Blood samples for GEP testing (AlloMap, CareDx, Brisbane, CA) were collected during post-transplant surveillance.  The reference standard for rejection status was based on histopathology grading of tissue from EMB.  The AUC-ROC, NPVs, and PPVs for the GEP scores (range 0 to 39) were computed.  Considering the GEP score of 34 as a cut-off (greater than 6 months post-transplantation), 95.5 % (381/399) of GEP tests were true negatives, 4.5 % (18/399) were false negatives, 10.2 % (6/59) were true positives, and 89.8 % (53/59) were false positives.  Based on 938 paired biopsies, the GEP test score AUC-ROC for distinguishing ≥ 3A rejection was 0.70 and 0.69 for ≥ 2 to 6 and > 6 months post-transplantation, respectively.  Depending on the chosen threshold score, the NPV and PPV range from 98.1 % to 100 % and 2.0 % to 4.7%, respectively.  The authors concluded the GEP test performance characteristics in this CARGO II study were consistent with previous CARGO findings.  The low prevalence of ACR contributed to the high NPV and limited PPV of GEP testing.  Taken together with clinical trial evidence that equivalent clinical outcomes may be attained in patients managed with GEP compared with patients managed with biopsies for ACR surveillance, the CARGO II results further validated that GEP testing may be used as part of a non-invasive surveillance strategy to rule out ACR in HTx recipients.  The choice of threshold score for practical use of GEP testing to rule out rejection should consider overall clinical assessment of the patient’s base[1]line risk for rejection.

The authors stated that this study had several drawbacks.  First, this trial excluded GEP data and biopsies from visits earlier than 55 days post-transplantation; therefore, the analyses did not inform the clinicians regarding GEP performance or rejection incidence in the first 54 days post-transplantation.  Second, because patients treated for rejection within the prior 30 days were excluded, these researchers may have under-estimated the incidence of rejection that might be found in the entire population.  Third, in this study, not all GEP tests had paired biopsy results.  Because of the very small number and proportion of clinically suspected, biopsy confirmed, rejections of grade ≥ 3A (2R), rejections discovered during routine surveillance and rejections confirmed with biopsies performed for clinical suspicion were pooled together in the analyses.  These reference rejection cases, a combination of clinically silent and clinically suspected rejection, may not have identical GEP signatures.  Although the GEP test is intended for use in a surveillance setting, the discovery of sub-clinical rejection is dependent on the frequency of surveillance that varied at the participating centers.  Fourth, the histology grading is an imperfect reference standard for diagnosis of rejection, although it remains the clinical SOC for diagnosis of rejection in HTx.  Fifth, the central pathology feature of this study did not reflect practical clinical care: no clinician relies on obtaining additional histopathology reports from “blinded” independent pathologists to decide on treatment of a patient.  These investigators used the central biopsy reading in this study to enhance the accuracy of diagnostic classification of the reference cases.  Lastly, the question remains whether GEP scores can be potentially used to optimize a post-transplant immune-suppression regimen.  This study was not designed to address that question; these researchers stated that future studies should be carried out to examine the clinical utility of the GEP test to guide immunosuppression medication intensity to improve long-term outcomes in transplant recipients.

Dual Non-Invasive Testing for Acute Cellular Rejection

Henricksen et al (2023) noted that dd-cfDNA and GEP offer non-invasive alternatives to rejection surveillance following HTx; however, there is little evidence on the paired use of GEP and dd-cfDNA for rejection surveillance.  These researchers carried out a retrospective, single-center analysis of adult HTx recipients.  A GEP cohort, transplanted from January 1, 2015 through December 31, 2017 and eligible for rejection surveillance with GEP was compared to a paired testing cohort, transplanted July 1, 2018 through June 30, 2020, with surveillance from both dd-cfDNA and GEP.  The primary outcomes were survival and rejection-free survival at 1 year post-transplant.  A total of 159 patients were included, 95 in the GEP and 64 in the paired testing group.  There were no differences in baseline characteristics, except for less use of induction in the paired testing group (65.6 %) compared to the GEP group (98.9 %) ; p < 0.01.  At 1-year, there were no differences between the paired testing and GEP groups in survival (98.4 % versus 94.7 %, p = 0.23) or rejection-free survival (81.3 % versus 73.7 %; p = 0.28).  The authors concluded that compared to post-transplant rejection surveillance with GEP alone, pairing dd-cfDNA and GEP testing was associated with similar survival and rejection-free survival at 1 year while requiring significantly fewer biopsies.  Moreover, these researchers stated that the use of ongoing non-invasive rejection surveillance beyond 1 year post-transplant remains uncertain.

The authors stated that this study had several drawbacks.  First, this was a retrospective, single-center review of 2 different protocols for non-invasive rejection surveillance, which were implemented based on the discretion of the treating clinicians.  While some patients were excluded from the analysis, this was mainly because they were followed at another center, rather than being ineligible for testing.  There was not a standard protocol for reacting to the results of the non-invasive surveillance.  An isolated GEP result triggered a biopsy when above threshold; however, when paired with dd-cfDNA, a biopsy was often deferred when the dd-cfDNA level was below the detection  threshold.  Second, clinicians could perform a biopsy if they felt it was clinically indicated, even in the setting of normal rejection surveillance; however, this was quite rare.  Biopsies were considered linked to non-invasive rejection surveillance if they were performed within 2 weeks of the non-invasive testing; thus, the biopsy results may not have reflected the pathology at the precise time of the non-invasive testing. However, these investigators believed this also represented a “real world” scenario as clinicians do not typically receive non-invasive test results until 3 to 4 days after the tests were obtained.  Third, this was a single-center study, and the authors’ transplant center’s population may not be generalizable to the broader HTx recipient population.

Khush et al (2024) stated that molecular testing with GEP and dd-cfDNA is increasingly used in the surveillance for ACR following HTx; however, the performance of dual testing over each test individually has not been established.  In addition, the impact of dual non-invasive surveillance on clinical decision-making has not been widely examined.  These researches evaluated 2,077 subjects from the Surveillance HeartCare Outcomes Registry who were enrolled between 2018 and 2021 and had verified biopsy data and were categorized as dual negative, GEP positive/dd-cfDNA negative, GEP negative/dd-cfDNA positive, or dual positive.  The incidence of ACR and follow-up testing rates for each group were evaluated.  Positive likelihood ratios (LRs+) were calculated, and biopsy rates over time were analyzed.  The incidence of ACR was 1.5 % for dual negative, 1.9 % for GEP positive/dd-cfDNA negative, 4.3 % for GEP negative/dd-cfDNA positive, and 9.2 % for dual-positive groups.  Follow-up biopsies were performed after 8.8 % for dual negative, 14.2 % for GEP positive/dd-cfDNA negative, 22.8 % for GEP negative/dd-cfDNA positive, and 35.4 % for dual-positive results.  The LR+ for ACR was 1.37, 2.91, and 3.90 for GEP positive, dd-cfDNA positive, and dual-positive testing, respectively.  From 2018 to 2021, biopsies performed between 2 and 12-months post-transplant declined from 5.9 to 5.3 biopsies/patient, and 2nd-year biopsy rates declined from 1.5 to 0.9 biopsies/patient.  At 2 years, survival was 94.9 %, and only 2.7 % had graft dysfunction.  The authors concluded that dual molecular testing showed improved performance for ACR surveillance compared to single molecular testing.  These investigators stated that the use of dual non-invasive testing was associated with lower biopsy rates over time, excellent survival, and low incidence of graft dysfunction.

The authors stated that this study had several drawbacks.  First, it was possible the 15  sites not included had different patient outcomes and interpretation of molecular testing results; however, given that the entire registry’s clinical characteristics and molecular testing patterns were similar to the included subjects, this is unlikely.  Second, EMBs and molecular testing associated with AMR were excluded from the molecular testing performance characteristics analyses, in part because the GEP test was not developed or tested for AMR surveillance.  However, most  surveillance occurred in the 1st-year post-transplant, at a time when the overall risk of AMR in most patients is lower than ACR, and sub-clinical AMR often goes untreated, with up to 75 % of sub-clinical AMR episodes not receiving treatment.  Furthermore, untreated sub-clinical AMR may not have prognostic implications.  Nevertheless, future SHORE publications assess the relationship between non-invasive testing, AMR, and clinical outcomes following HTx.  Third, the assessment of test characteristics included biopsies performed at any time post-transplant.  Given the decline in incidence of ACR over time, the biopsy yield for any molecular test combination will likely be impacted by the time period analyzed.  Fourth, biopsies carried out on the same day or less than 3 days after the molecular test were excluded from the clinical impact of GEP/dd-cfDNA results assessment to examine the impact the molecular test result had on the decision to proceed with follow-up testing, resulting in an under-estimate of the biopsy follow-up rate associated with each molecular test combination.  This also led to the exclusion of many early post-transplant biopsies/paired molecular testing results.  While the response to molecular test results could be different in this period, with an overall higher follow-up biopsy rate, these researchers expected the pattern to be similar with dual positives resulting in the most follow-up biopsies, dual-negative results the fewest, and discordant results an intermediate number of biopsies.  Fifth, in the primary analysis, these investigators did not account for multiple tests being drawn from within the same patient, which could impact the estimates of sensitivity, specificity, and LR+.  However, subject-level and sample-level test performances were similar, suggesting a significant bias was unlikely.  Sixth, SHORE was designed to examine the real-world performance of molecular testing.  The study design did not require all molecular test results to be paired with a biopsy.  Other clinical factors such as patient symptoms and other diagnostic test results may have influenced a clinician’s decision to conduct or forego a biopsy; thus, impacting the yield of biopsies paired with each category of molecular test results.   Seventh, the sensitivity and specificity paired analysis included  molecular testing that, in some cases, was carried out up to 2 weeks before the EMB; however, this methodology may yield a more accurate representation of the molecular test performance characteristics because abnormalities in molecular testing results often precede biopsy findings.  Lastly, core interpretation of biopsies was not carried out, and previous studies have reported high false positive rates with local EMB interpretation.  However, had the biopsies been centrally reviewed, these researchers expected that there would have been an overall reduction in false negative rates of molecular testing with a corresponding increase in sensitivity for GEP, dd-cfDNA, and combination testing along with small concomitant increases in positive LRs.  Regardless, as it is not standard clinical practice to have biopsies centrally reviewed, these findings remain valid as to what clinicians can expect to find on requested local biopsies in response to molecular testing results.

Total Artificial Heart

Cytokine Gene Polymorphism Testing

Yongcharoen et al (2013) performed a systematic review and meta-analysis with the aim of assessing the association between cytokine gene polymorphisms and graft rejection in heart transplantation.  These researchers identified relevant studies from Medline and Embase using PubMed and Ovid search engines, respectively.  Allele frequencies and allele and genotypic effects were pooled.  Heterogeneity and publication bias were explored.  Four to 5 studies were included in pooling of 3 gene polymorphisms.  The prevalence of the minor alleles for TNF α -308, TGF β 1-c10, and TGF β 1-c25 were 0.166 (95 % CI: 0.129 to 0.203), 0.413 (95 % CI: 0.363 to 0.462), and 0.082 (95 % CI: 0.054 to 0.111) in the control groups, respectively.  Carrying the A allele for the TNF α -308 had 18 % (95 % CI of OR: 0.46 to 3.01) increased risk, but this was not significant for developing graft rejection than the G allele.  Conversely, carrying the minor alleles for both TGF β 1-c10 and c25 had non-significantly lower odds of graft rejection than major alleles, with the pooled ORs of 0.87 (95 % CI: 0.65 to 1.18) and 0.70 (95 % CI: 0.40 to 1.23), respectively.  The authors concluded that there was no evidence of publication bias for all pooling; an updated meta-analysis is needed when more studies are published to increase the power of detection for the association between these polymorphisms and allograft rejection.

Furthermore, an UpToDate review on "Acute cardiac allograft rejection: Diagnosis" (Eisen and Jessup, 2014) does not mention cytokine gene polymorphism testing as a management tool.

Statin Use Following Heart Transplantation/for the Management of Graft Vessel Disease

Som and colleagues (2014) noted that graft vessel disease (GVD) is a significant cause of morbidity and mortality in cardiac allograft recipients.  Hyperlipidemia is a risk factor for GVD, and the majority of patients will display abnormal lipid profiles in the years following transplant.  This systematic review aimed to establish the clinical impact of statins in cardiac allograft recipients, critically appraising the literature on this subject.  These investigators performed a literature search for randomized studies assessing statin use in cardiac allograft recipients.  The Cochrane Central Registry of Controlled Trials, Medline, Embase, clinicaltrials.gov, and the Transplant Library from the Centre for Evidence in Transplantation were searched.  The primary outcome was presence of GVD.  Secondary outcomes included graft and patient survival, acute rejection, and adverse events.  Meta-analysis was precluded by heterogeneity in outcome reporting and therefore narrative synthesis was undertaken.  A total of 7 randomized controlled trials (RCTs) were identified.  The majority of RCTs demonstrated some risk of bias, and methods of outcome measurement were variable.  Studies reporting incidence or severity of GVD suggested that statins do confer benefit.  Survival benefit from statin use is modest.  There is a low incidence of adverse events attributable to statins.  There was no difference in the overall number of episodes of rejection.  The authors concluded that while the methodological quality of evidence describing the use of statins in cardiac allograft recipients is limited, the available evidence suggested benefit from their use.  These findings need to be validated by well-designed studies.

Greenway and colleagues (2016) hypothesized that statin therapy would reduce the incidence of rejection, cardiac allograft vasculopathy (CAV) and post-transplant lymphoproliferative disease (PTLD).  This study was a retrospective review of 964 pediatric (aged 5 to 18 years) heart transplant recipients in the multi-center Pediatric Heart Transplant Study registry from 2001 to 2012.  Patients were excluded if they were undergoing re-transplantation, survived less than 1 year post-transplant, or had missing data regarding statin use.  The effects of statins beyond the 1st year were estimated by Kaplan-Meier and Cox regression multi-variable analysis for freedom from PTLD, rejection requiring treatment, any severity of CAV, and survival.  Statin use was variable among participating centers with only 30 % to 35 % of patients greater than or equal to 10 years of age started on a statin at less than 1 year post-transplant.  After the 1st year post-transplant, statin-treated children (average age at transplant of 13.24 ± 3.29 years) had significantly earlier rejection (hazard ration [HR] 1.42, 95 % CI: 1.11 to 1.82, p = 0.006) compared with untreated children (transplanted at 12 ± 3.64 years) after adjusting for conventional risk factors for rejection.  Freedom from PTLD, CAV and overall survival up to 5 years post-transplant were not affected by statin use, although the number of events was small.  The authors concluded that statin therapy did not confer a survival benefit and was not associated with delayed onset of PTLD or CAV.  Early (less than 1 year post-transplant) statin therapy was associated with increased later frequency of rejection.  The authors stated that these findings suggested that a prospective trial evaluating statin therapy in pediatric heart transplant recipients is needed.

Vallakati and associates (2016) performed a meta-analysis of published studies to evaluate the role of statins in post-cardiac transplant patients, specifically examining the effects on hemodynamically significant/fatal graft rejection, coronary vasculopathy, terminal cancer, and overall survival.  These investigators searched PubMed, Cochran Central, and Web of Science databases using the search terms "cardiac transplant" or "heart transplant", and "statin" for a literature search.  A random-effects model with Mantel-Haenszel method was used to pool the data. They identified 10 studies, 4 RCTs, and 6 non-randomized studies, which compared outcomes in heart transplant recipients undergoing statin therapy to statin-naive patients.  A pooled analysis of 9 studies reporting mortality revealed that the use of statins was associated with significant reduction in all-cause mortality (OR, 0.26; 95 % CI: 0.20 to 0.35; p < 0.0001).  Statins also decreased the odds of hemodynamically significant/fatal rejection (OR, 0.37; 95 % CI: 0.21 to 0.65; p = 0.0005), incidence of coronary vasculopathy (OR, 0.33; 95 % CI: 0.16 to 0.68; p = 0.003), and terminal cancer (OR, 0.30; 95 % CI: 0.15 to 0.63; p = 0.002).  The authors concluded that the evidence from a pooled analysis suggested that statins improve survival in heart transplant recipients.  They stated that statins may prevent fatal rejection episodes, decrease terminal cancer risk, and reduce the incidence of coronary vasculopathy; however, additional prospective studies are needed to further examine and explain this association.

Immune Repertoire Sequencing Assay

In a proof-of-concept diagnostic accuracy study, Vollmers et al (2015) hypothesized that measuring the B-cell repertoire would enable assessment of the overall level of immunosuppression after heart transplantation. These researchers implemented a molecular-barcode-based immune repertoire sequencing assay that sensitively and accurately measures the isotype and clonal composition of the circulating B cell repertoire.  They used this assay to measure the temporal response of the B cell repertoire to immunosuppression after heart transplantation.  The authors selected a subset of 12 participants from a larger prospective cohort study (ClinicalTrials.gov NCT01985412) that is ongoing at Stanford Medical Center and for which enrollment started in March 2010.  This subset of 12 participants was selected to represent post-heart-transplant events, with and without acute rejection (6 participants with moderate-to-severe rejection and 6 without).  These researchers analyzed 130 samples from these patients, with an average follow-up period of 15 months.  Immune repertoire sequencing enabled the measurement of a patient's net state of immunosuppression (correlation with tacrolimus level, r = -0.867, 95 % CI: -0.968 to -0.523, p = 0.0014), as well as the diagnosis of acute allograft rejection, which is preceded by increased immune activity with a sensitivity of 71.4 % (95 % CI: 30.3 % to 94.9 %) and a specificity of 82.0 % (95 % CI: 72.1 % to 89.1 %) (cell-free donor-derived DNA as non-invasive gold standard).  To illustrate the potential of immune repertoire sequencing to monitor atypical post-transplant trajectories, these investigators analyzed 2 more patients, 1 with chronic infections and 1 with amyloidosis.  They stated that a larger, prospective study will be needed to validate the power of immune repertoire sequencing to predict rejection events, as this proof-of-concept study is limited to a small number of patients who were selected based on several criteria including the availability of a large number of samples and the absence or presence of rejection events.  The authors concluded that if confirmed in larger, prospective studies, immune repertoire sequencing assay for measurement of the isotype and clonal composition of the circulating B cell repertoire has potential applications in the tailored management of post-transplant immunosuppression and, more broadly, as a method for assessing the overall activity of the immune system.

myTAIHEART Testing

myTAIHEART (TAI Diagnostics, Inc., Milwaukee, WI.) is a non-invasive laboratory test which measures the donor fraction of cell-free DNA (cfDNA) in blood plasma as a marker for transplanted organ injury. The myTAIHEART test is intended to aid in the identification of heart transplant recipients who have a low probability of moderate/severe acute cellular rejection (Grade 2R or higher) at the time of testing in conjunction with standard clinical assessment. This test is indicated for use in heart transplant recipients who are 2 months of age or older and at least 1 week post-transplant (≥7 days) (TAI, 2018).

The myTAIHEART test quantitates the donor fraction of cfDNA via cfDNA quantitative genotyping by quantitative PCR by multiplexed allele specific PCR of greater than 50 single nucleotide polymorphism targets. An algorithm is used to report risk of allograft rejection (AMA, 2018). This measurement distinguishes "donor specific" cfDNA originating from the engrafted heart versus "self specific" cfDNA originating from the recipient’s native cells. The myTAIHEART test reports the ratio of donor specific cfDNA to total cfDNA as the donor fraction (%) and categorizes the patient as at low or increased risk of moderate/severe acute cellular rejection: low donor fractions indicate less damage to the transplanted heart and a lower risk for rejection, while increased donor fractions indicate more damage to the transplanted heart and an increased risk for rejection. Per TAI Diagnostics, patients treated for rejection within 28 days of sample collection may have variably elevated donor fractions. Clinical judgment will be required for interpretation of results. A heart transplant recipient with a negative result should continue to be monitored according to standard clinical care. All results should be interpreted in the context of the patient’s clinical findings, history, and laboratory results (TAI, 2018).

The myTAIHEART is currently for use in single organ post-transplant patients. It is not intended for those who are pregnant, have another transplanted organ, have post-transplant lymphoproliferative disease, currently have cancer, or have had cancer within the previous 2 years, or for those who are on mechanical circulatory support (TAI, 2018).

This lab test is certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA).The myTAIHEART has not been cleared or approved by the US FDA, as the FDA "has determined that such clearance or approval is not necessary" (TAI, 2018).

Hidestrand et al (2014) stated that targeted quantitative genotyping of circulating donor specific cell free DNA (DScf-DNA) constitutes a sensitive, rapid, and cost-effective non-invasive tool potentially suitable for rejection surveillance as an alternative to endomyocardial biopsy (EMB). The authors note that the current gold standard for monitoring rejection is catheter based EMB which can be associated with risk and expense, and that DScf-DNA has been proposed as a marker for cellular injury caused by rejection. Hidestrand and colleagues evaluated this genotyping method for DScf-DNA percentage in pediatric cardiac transplant recipients in a prospective blinded pilot study. Fifty-three samples from 32 patients were analyzed and divided between 3 scenarios. Scenario 1 included cf-DNA levels from 26 patients undergoing 38 scheduled surveillance EMBs. Thirty-two (84 %) samples contained less than 1 % DScf-DNA. No patient with DScf-DNA less than 1 % had pathological rejection. DScf-DNA levels exceeded 1 % in 6 samples with the highest percentage DScf-DNA associated with asymptomatic biopsy proven rejection. The remaining 5 samples had negative biopsies. Scenario 2 included 7 samples from 6 patients prior to unscheduled diagnostic EMB to rule out rejection based on clinical criteria. Six had DScf-DNA levels greater than 1 % and one sample contained DScf-DNA less than 1 %. Four of the six were associated with biopsy proven rejection; the other two patients had significant coronary artery vasculopathy on angiography. The single symptomatic patient with low percentage DScf-DNA had high levels of Tcf-DNA, implying that the dominant pathology was global rather than confined to the donor organ. This patient was diagnosed with culture positive sepsis, the accompanying EMB was negative for rejection and coronary angiography was normal. Scenario 3 included 4 patients with biopsy proven rejection. All pre-treatment samples collected at diagnosis contained DScf-DNA greater than 1 % (sensitivity 100 %). Following IV immunosuppressive therapy, all patients demonstrated significantly decreased %DScf-DNA. The authors note that 3 to 4 days after discontinuing augmented immunosuppression, the percent DScf-DNA rebounded in 3 of the 4 patients. DScf-DNA was compared to other candidate non-invasive laboratory variables (BNP, Troponin, CRP) as well as echocardiographically determined LVEF in predicting rejection on biopsy; DS-cfDNA had the highest sensitivity and specificity (100 % / 84 %). The authors concluded that DScf-DNA may be sufficiently sensitive to detect rejection and injury to the donor organ earlier than currently available methods; however, the results of their study are based on limited sample size. A larger validation study is needed.

Agbor-Enoh et al (2017) state that previous studies have shown that quantitation of donor-derived cell-free DNA (%ddcfDNA) by unbiased shotgun sequencing is a sensitive, non-invasive marker of acute rejection after heart transplantation. The authors evaluated the reproducibility of %ddcfDNA measurements across technical replicates, manual vs automated platforms, and rejection phenotypes in distinct patient cohorts. The author observed concordance of technical-replicate %ddcfDNA measurements across 2 independent laboratories, as well as across manual and automated platform (p < 0.001). The %ddcfDNA measurements in distinct heart transplant cohorts had similar baselines and error rates. The %ddcfDNA temporal patterns associated with rejection phenotypes were similar in both patient cohorts; however, the quantity of ddcfDNA was significantly higher in samples with severe vs mild histologic rejection grade (p < 0.001). The authors concluded that %ddcfDNA assay is precise and reproducible across laboratories and in samples from 2 distinct types of heart transplant rejection. Agbor-Enoh and colleagues stated that their findings pave the way for larger studies to assess the clinical utility of quantitation of donor-derived cell-free DNA as a marker of acute rejection after heart transplant.

Ragalie et al (2018) state that the novel assay to calculate donor fraction of cell-free DNA in heart transplant has excellent sensitivity for acute cellular rejection and utility in ruling out cardiac allograft vasculopathy (CAV). The authors presented their blinded pilot study which included 158 blood samples collected from heart transplant recipients at a single center prior to endomyocardial biopsy (EMB) and coronary angiography. Donor fraction (DF) of cf-DNA was quantified using a targeted approach and compared to biopsy and angiography results using two distinct methods, with donor genotype (Method 1), and without donor genotype (Method 2) (TAI Diagnostics). By Method 1, median DF was 0.11% (IQR 0.06-0.21%) in CR0 associated samples, 0.37% (IQR 0.15-0.72%) in CR1 associated samples, and 0.97% (IQR 0.88-1.06%) in CR2 associated samples (p=0.027). Empirical optimal cut-point of DF for ruling out CR2 rejection was 0.87% (p=0.009) and area under the curve (AUC) was 0.97. Sensitivity was 100% and specificity was 93%. By Method 2, median DF was 0.25% (IQR 0.17-0.39%) in CR0 associated samples, 0.89% (IQR 0.44-5.35%) in CR1 associated samples, and 1.22% (IQR 1.04-5.18%) in CR2 associated samples (p<0.001). Empirical optimal cut-point for ruling out CR2 rejection was 0.89% (95% CI 0.46-1.70%). AUC was 0.95. Sensitivity was 100% and specificity was 89%. 116 samples were associated with coronary angiography. By Method 1, median DF was 0.09% (IQR 0.06-0.20%) for samples not associated with CAV and 0.47% for CAV associated samples (p=0.05). By Method 2, median DF was 0.27% for samples not associated with CAV and 0.55% for CAV associated samples (p=0.057). The authors found a stepwise DF increase among CR0, CR1, and CR2 associated biopsies, suggesting progressive allograft injury with increasing rejection grades. Paired sample analysis demonstrates the ability to use this assay in the absence of donor genotyping.

A review in UpToDate on "Acute cardiac allograft rejection: Diagnosis" (Eisen, 2017) states that in cardiac transplant recipients, a rise in peripheral blood donor-derived cell-free DNA was shown to occur after graft injury from acute cellular rejection. The authors cite a prospective study in which donor-derived cell-free DNA rose in peripheral blood in 44 adult and 21 pediatric heart transplant recipients at the time of International Society for Heart and Lung Transplantation (ISHLT) Grade 2R acute cellular rejection or ISHLT Grade 2 antibody-mediated rejection. A group using a somewhat different approach to donor-derived cell-free DNA quantification in the peripheral blood noninvasively detected allograft damage from acute cellular rejection and from cardiac allograft vasculopathy in 26 heart transplant recipients. The authors concluded that "further research is needed to determine the utility of quantification of donor-derived cell-free DNA in the peripheral blood as a noninvasive diagnostic technique for detecting acute cellular rejection and other forms of cardiac allograft injury".

Measurement of Cardiac Troponin for Diagnosis of Acute Cellular Rejection Following Heart Transplantation

In an UpToDate chapter on diagnosis of acute cardiac allograft rejection, Eisen (2019) stated that the clinical efficacy of cardiac troponins as a marker for detection of acute rejection has not been established.

Fitzsimons and colleagues (2018) noted that acute cellular rejection (ACR) is a common complication in the 1st year following heart transplantation (HT).  Routine surveillance for ACR is undertaken by EMB.  Measurement of cardiac troponins (cTn) in serum is an established diagnostic test of cardiac myocyte injury.  In a systematic review, these investigators examined if cTn measurement could be used to diagnose or exclude ACR.  PubMed, Google Scholar and the JHLT archive were searched for studies reporting the result of a cTn assay and a paired surveillance EMB.  Significant ACR was defined as International Society for Heart and Lung Transplantation (ISHLT) Grade greater than or equal to 3a / greater than or equal to 2R.  Considerable heterogeneity between studies precluded quantitative meta-analysis.  Individual study sensitivity and specificity data were examined and used to construct a pooled hierarchical summary receiver-operator characteristic (ROC) curve.  A total of 12 studies including 993 patients and 3,803 EMBs, of which 3,729 were paired with cTn levels, had adequate data available for inclusion.  The overall rate of significant ACR was 12 %.  There was wide variation in diagnostic performance; cTn assays demonstrated sensitivity of 8 % to 100 % and specificity of 13 % to 88%  for detection of ACR.  The positive predictive value (PPV) was low but the negative predictive value (NPV) was relatively high (79 % to 100 %).  High-sensitivity cTn assays had greater sensitivity and NPV than conventional cTn assays for detection of ACR (sensitivity: 82 %  to 100 % versus 8 % to 77 %; NPV: 97 % to 100 % versus 81 % to 95 %, respectively).  The authors concluded that cTn assays did not have sufficient specificity to diagnose ACR in place of EMB.  However, hs-cTn assays may have sufficient sensitivity and NPV to exclude ACR and limit the need for surveillance EMB.  These investigators stated that further research is needed to evaluate this strategy.

The International Society of Heart and Lung Transplantation guidelines for the care of heart transplant recipients (Costanzo et al, (2010) state that "The use of brain natriuretic peptide (BNP), troponin I or T, or C-reactive protein (CRP) levels for acute heart allograft rejection monitoring is not recommended".

Liu et al (2022) noted that cTn is well known as a highly specific marker of cardiomyocyte damage; and has significant diagnostic accuracy in many cardiac conditions.  However, the value of elevated recipient troponin in diagnosing adverse outcomes in heart transplant recipients is uncertain.  These investigators searched Medline (Ovid), Embase (Ovid), and the Cochrane Library from inception until December 2020.  They generated summary sensitivity, specificity, and Bayesian areas under the curve (BAUC) using bi-variate Bayesian modelling, and standardized mean differences (SMDs) to quantify the diagnostic relationship of recipient troponin and adverse outcomes following cardiac transplant.  These researchers included 27 studies with 1,684 cardiac transplant recipients.  Patients with AR had a statistically significant late elevation in standardized troponin measurements taken at least 1 month post-operatively (SMD 0.98, 95 % CI: 0.33 to 1.64).  However, pooled diagnostic accuracy was poor (sensitivity 0.414, 95 % CI: 0.174 to 0.696; specificity 0.785, 95 % CI: 0.567 to 0.912; BAUC 0.607, 95 % CI: 0.469 to 0.723).  The authors concluded that late troponin elevation in heart transplant recipients was associated with acute cellular rejection in adults; however, its stand-alone diagnostic accuracy was poor.  These researchers stated that further investigation is needed to examine its performance in predictive modelling of adverse outcomes following cardiac transplant.

Measurement of Donor-Specific Cell-Free DNA for Monitoring Transplant Recipients of Rejection

Knight and colleagues (2019) noted that there is increasing interest in the use of non-invasive biomarkers to reduce the risks posed by invasive biopsy for monitoring of solid organ transplants (SOTs).  One such promising marker is the presence of donor-derived cell-free DNA (dd-cfDNA) in the urine or blood of transplant recipients.  These investigators systematically reviewed the published literature investigating the use of cfDNA in monitoring of graft health following SOT.  Electronic databases were searched for studies relating cfDNA fraction or levels to clinical outcomes, and data including measures of diagnostic test accuracy were extracted.  Narrative analysis was performed.  A total of 95 articles from 47 studies met the inclusion criteria (18 kidneys, 7 livers, 11 hearts, 1 kidney-pancreas, 5 lungs, and 5 multi-organs).  The majority were retrospective and prospective cohort studies, with 19 reporting diagnostic test accuracy data.  Multiple techniques for measuring dd-cfDNA were reported, including many not requiring a donor sample; dd-cfDNA fell rapidly within 2 weeks, with baseline levels varying by organ type.  Levels were elevated in the presence of allograft injury, including acute rejection and infection, and return to baseline following successful treatment.  Elevation of cfDNA levels was observed in advance of clinically apparent organ injury.  Discriminatory power was greatest for higher grades of T cell-mediated and acute antibody-mediated rejection (AMR), with high negative predictive values (NPVs).  The authors concluded that cell-free DNA is a promising biomarker for monitoring the health of SOTs.  These researchers stated that future studies will need to define how it can be used in routine clinical practice and determine clinical benefit with routine prospective monitoring.

Khush and associates (2019) noted that standardized dd-cfDNA testing has been introduced into clinical use to monitor kidney transplant recipients for rejection.  This report described the performance of this dd-cfDNA assay to detect allograft rejection in samples from HT recipients undergoing surveillance monitoring across the United States.  Venous blood was longitudinally sampled from 740 HT recipients from 26 centers and in a single-center cohort of 33 patients at high risk for AMR.  Plasma dd-cfDNA was quantified by using targeted amplification and sequencing of a single nucleotide polymorphism (SNP) panel.  The dd-cfDNA levels were correlated to paired events of biopsy-based diagnosis of rejection.  The median dd-cfDNA was 0.07 % in reference HT recipients (2,164 samples) and 0.17 % in samples classified as acute rejection (35 samples; p = 0.005).  At a 0.2 % threshold, dd-cfDNA had a 44 % sensitivity to detect rejection and a 97 % NPV.  In the cohort at risk for AMR (11 samples), dd-cfDNA levels were elevated 3-fold in AMR compared with patients without AMR (99 samples, p = 0.004).  The authors concluded that standardized dd-cfDNA test identified acute rejection in samples from a broad population of HT recipients.  The reported test performance characteristics will guide the next stage of clinical utility studies of the dd-cfDNA assay.

Bienkowski et al (2020) stated that heart transplantation allows for a long-term management of patients with end-stage heart failure.  After the surgery, organ rejection is monitored with EMB, which is an invasive, but not always informative procedure; thus, there is a pressing need for a new, safe, yet reliable, diagnostic method.  These researchers presented a pilot study confronting liquid biopsy based on donor-specific cfDNA with the protocol EMB.  The study was carried out on 21 blood samples matched with EMB (graded according to ACR scale) from 9 patients after heart transplantation.  Genotyping was performed on genomic DNA from donors and recipients for 10 single-nucleotide polymorphisms (SNPs); cfDNA isolated from plasma was analyzed with digital droplet PCR to detect donor-specific alleles.  From 21 analyzed EMB, 4 were graded as 0R and 17 as 1R.  Liquid biopsy was successfully carried out in each sample for all informative SNPs (median of 3 per patient).  These investigators observed a high homogeneity of the results between SNPs in each sample (inter-class correlation coefficient of greater than 0.9).  The authors concluded that there is a undeniable need for an alternative, non-invasive diagnostic procedure of early transplant rejection and investigation of donor-derived cfDNA appeared to be the promising choice.  The very high sensitivity is particularly enticing to consider liquid biopsy as a potential screening tool.  Its minimal invasiveness may allow for more frequent examination and, thus, tighter monitoring.  The reliable assessment of its clinical utility requires an adequately powered and properly designed multi-center study.

Gondi et al (2021) reported a single-center experience of combined GEP and dd-cfDNA testing for acute rejection (AR) surveillance.  GEP and dd-cfDNA were tested together starting at 2 months after orthotopic heart transplant (OHT).  After 6 months, combined testing was obtained before scheduled EMB, and EMB was canceled with a negative dd-cfDNA.  This approach was compared to using a GEP-only approach, where EMB was canceled with a negative GEP.  These researchers examined for frequency of EMB cancellation with dd-cfDNA usage.  A total of 153 OHT patients over a 13-month period underwent 495 combined GEP/dd-cfDNA tests; 82.2 % of dd-cfDNA tests were below threshold.  Above threshold results identified high-risk patients who developed AR.  A total of 378 combined tests greater than or equal to 6 months post-OHT resulted in cancellation of 83.9 % EMBs as opposed to 71.2 % with GEP surveillance alone.  There were 2 ACR and 2 AMR episodes, and no significant AR at greater than or equal to 6 months.  The authors concluded that routine dd-cfDNA testing alongside GEP testing yielded a significant reduction in EMB volume by re-classifying GEP (+) patients into a lower risk group, without reduction in AR detection.  The addition of dd-cfDNA identified patients at higher risk for AR.  Moreover, these researchers stated that this early experience and lessons learned may guide the future clinical use and investigation of dd-cfDNA testing following OHT.

The authors stated that this study had several drawbacks.  Most importantly, this was a single-center experience with an overall low rate of AR; thus, these findings may not be broadly applicable to all OHT patients.  Furthermore, the perception of AR rate may be skewed by use of the EMB to establish diagnosis, as EMB can be subject to institution-specific variability in diagnostic concordance and subjectivity in grading criteria.  However, these investigators followed a consistent surveillance protocol, and did not selectively exclude high-risk OHT patients.  A second drawback was the protocol allowing clinician discretion in EMB performance, especially in the group with GEP (+) and dd-cfDNA (-).  However, these patients were determined to be at a higher risk for OHT.  This discretion was intentional because this was the authors’ first experience with dd-cfDNA use and they wanted to err on the side of caution with these patients.  These researchers believed this reflected the real-world management of patients where testing results are considered in the context of a patient’s history and risk factors.  Finally, although GEP variability scoring has been examined as a method of AR risk stratification, these investigators did not include it as part of their testing protocol.  First, this was not their standard of care previously, and they did not feel it would be appropriate to retrospectively calculate variability scores.  Second, GEP variability score entailed 4 consecutive GEP results beginning at 1-year post-OHT.  This meant that these researchers could not use this score until the 24-month visit, and they had a limited number of encounters between 24 to 36 months. Therefore, the inclusion of GEP variability scores would not alter the calculated EMB frequency in the GEP only surveillance strategy.  The Surveillance Heartcare Outcomes (SHORE) Registry, a multi-center, observational registry that will prospectively evaluate clinical outcomes using a combined testing approach, will further elucidate the use of combined testing in a broader population.

Agbor-Enoh et al (2021) stated that after heart transplantation, EMB is used to monitor for acute rejection (AR).  Unfortunately, EMB is invasive and its conventional histologic interpretation has limitations.  In a prospective, multi-center, cohort study, these researchers examined the performance of a sensitive blood biomarker -- percent donor-derived cell-free DNA (%ddcfDNA) -- for detection of AR in cardiac transplant recipients.  This trial recruited heart transplant subjects and collected plasma samples contemporaneously with EMB for %ddcfDNA measurement by shotgun sequencing.  Histopathology data were collected to define AR, its 2 phenotypes (acute cellular rejection, ACR, and antibody-mediated rejection, AMR) and controls without rejection.  The primary analysis was to compare %ddcfDNA levels (median and inter-quartile range [IQR]) for AR, AMR and ACR to controls and to determine %ddcfDNA test characteristics using receiver-operator characteristics analysis.  The study included 171 subjects with median post-transplant follow-up of 17.7 months (IQR: 12.1 to 23.6), with 1,392 EMB, and 1,834 ddcfDNA measures available for analysis.  Median %ddcfDNA levels decayed after surgery to 0.13 % (0.03 to 0.21) by 28 days.  %ddcfDNA increased again with AR compared to controls values (0.38, IQR = 0.31 to 0.83, versus 0.03, IQR = 0.01 to 0.14 p < 0.001).  The rise was detected 0.5 and 3.2 months before histopathological diagnosis of ACR and AMR.  The area-under-the- receiver-operator characteristics curve (AUROC) for AR was 0.92.  A 0.25 %ddcfDNA threshold had a negative predictive value (NPV) for AR of 99 % and would have safely eliminated 81 % of EMB.  %ddcfDNA showed distinctive characteristics comparing AMR to ACR, included 5-fold higher levels (AMR greater than or equal to 2; 1.68 %, IQR = 0.49 to 2.79 % versus ACR grade greater than or equal to 2R; 0.34 %, IQR = 0.28 to 0.72 %), higher AUROC (0.95 versus 0.85), higher guanosine-cytosine content, and higher percentage of short ddcfDNA fragments.  The authors concluded that %ddcfDNA detected AR with a high AUROC and NPV.  Monitoring with ddcfDNA, demonstrated excellent performance characteristics for both ACR and AMR and led to earlier detection than the EMB-based monitoring.  This study supported the use of %ddcfDNA to monitor for AR in heart transplant patients and paved the way for a clinical utility study.

The authors stated that the use of cell-free DNA to detect heart allograft acute rejection has drawbacks.  It will not completely eliminate the need for endomyocardial biopsies; however, it can eliminate approximately 80 % of the biopsies currently carried out following heart transplant.  Investigators need to perform additional clinical studies, including a RCT, to confirm these promising findings, but they are using the blood test to further study the mechanisms underlying AR and examine why African Americans tend to have higher rates of transplant rejection, with the goal of eliminating this health disparity.  If future testing in a clinical trial validates the safety and efficacy of this test, it could become a routine tool used to monitor heart transplant patients for early stages of rejection.  The exact timeline for clinical availability of this new test is unclear.

Furthermore, an UpToDate review on “Heart transplantation in adults: Diagnosis of acute allograft rejection” (Eisen, 2021) listed “donor-derived cell-free DNA” as an investigational method.  It states that “Further research is needed to determine the utility of quantification of dd-CF DNA in the peripheral blood as a noninvasive diagnostic technique for detecting ACR and other forms of cardiac allograft injury”.

Kim et al (2022) stated that EMB, the reference surveillance test for AR in HTX recipients, is costly, invasive, and shows significant inter-observer variability.  Recent studies indicated that dd-cfDNA, obtained non-invasively from blood, is associated with AR and could reduce the frequency of EMB surveillance.  These researchers examined the performance characteristics of a novel test for detecting AR in adult HTX recipients.  Plasma samples with contemporaneous EMBs were obtained from HTX recipients.  A clinically available SNP-based massively multiplexed-PCR dd-cfDNA assay was employed to measure dd-cfDNA fraction.  dd-cfDNA fractions were compared with EMB-defined rejection status and test performance was assessed by constructing ROC curves and calculating accuracy measures.  A total of 811 samples from 223 patients with dd-cfDNA testing and contemporaneous EMB were eligible for the study.  dd-cfDNA fraction was significantly higher in AR (median of 0.58 %, IQR, 0.13 % to 1.68 %) compared to non-AR (median of 0.04 %, IQR, 0.01 % to 0.11 %, p < 0.001).  ROC analysis produced an AUC-ROC of 0.86 (95 % CI: 0.77 to 0.96).  Defining samples with dd-cfDNA fraction ≥ 0.15 % as AR yielded 78.5 % sensitivity (95 % CI: 60.7 % to 96.3 %) and 76.9 % specificity (95 % CI: 71.1 % to 82.7 %).  PPVs and NPVs were 25.1 % (95 % CI: 18.8 % to 31.5 %) and 97.3 % (95 % CI: 95.1 % to 99.5 %) respectively, calculated using the cohort AR prevalence of 9.0 % (95 % CI: 5.3 % to 12.8 %) with adjustment for repeat samples.  The authors concluded that this novel dd-cfDNA test detected AR in HTX recipients with good accuracy and holds promise as a non-invasive test for AR in HTX recipients.  Moreover, these researchers stated that prospective, controlled studies are needed to confirm the clinical utility of dd-cfDNA assessment in the management of HTX recipients.

The authors stated that this study had several drawbacks, which entailed the study cohort was restricted to 2 HTX programs in the U.S.  The prevalence of AR, especially AMR, was higher than in some other cohorts.  The assessment for AR included immunofluorescence staining for C4d in patients perceived to be at higher risk of AMR -- those with donor-specific antibodies (DSA), history of AMR or a clinical suspicion of AMR.  In 1 center, immunofluorescence staining for C4d was routinely performed up to 2 months post-transplant.  Furthermore, as enrollment in the study was based on a scheduled biopsy, there may have been a selection bias for patients with previous history or suspicion of AMR, who would be more frequently biopsied at the authors’ centers.  The higher prevalence of AR in this cohort compared with the overall transplant population might have implications for generalizing the findings of this study to patient cohorts with a different risk of rejection.  There was also a limited number of sequential samples.  These investigators anticipated that the results of the Quantitative Detection of Circulating Donor-Specific DNA in Organ Transplant Recipients, an NIH-supported observational study that includes about 1,000 samples, will provide corresponding complementary information to address these drawbacks.

Another potential drawback when measuring dd-cfDNA fraction was the effect of recipient-derived cfDNA, which could be influenced by factors such as infection and BMI.  Some have suggested that dd-cfDNA quantity (cp/ml) may be a better marker than dd-cfDNA fraction, as it is independent of changes in background cfDNA.  A recent study in kidney transplantation incorporated recipient cfDNA levels for detecting rejection, which increased sensitivity, albeit in a small cohort.  A “2-threshold” algorithm was employed, which combined a cut-off for dd-cfDNA fraction with a cut-off for absolute quantity of dd-cfDNA.  In the present study, a post-hoc analysis using dd-cfDNA quantity indicated that incorporation of this measure could increase the sensitivity of the assay.  Finally, this study, and indeed most studies evaluating novel tests for rejection, is limited by the use of EMB as the comparator.  While histology is a commonly accepted gold standard, its variability may lead to an under-estimation of performance of the test under investigation.  One option would be to follow patients for several months after blood draw and use clinical outcomes data to confirm or refute the accuracy of individual biopsy reads.  Alternatively, tissue gene expression profiling may also be a more appropriate comparator, as a previous study showed, in a small series of adult heart transplant patients, that concordance between dd-cfDNA and intra-graft mRNA transcripts was better than between dd-cfDNA and histology.

In a retrospective, single-center study, Kewcharoen et al (2022) described the use of GEP and dd-cfDNA in HTX recipients more than 1-year post-transplantation.  Subjects were patients who were more than 1-year post-transplantation and deemed to be at elevated clinical risk for rejection; both GEP and dd-cfDNA were collected every 3 months.  Baseline characteristics including GEP, dd-cfDNA levels, rejection episodes, and number of biopsies were obtained.  Since July 2019, there were 18 patients being followed with GEP and dd-cfDNA who were more than 1-year post-transplantation; 9 EMBs had been carried out in 7 patients: 3due to elevated GEP (greater than or equal to 34), 1 due to elevated dd-cfDNA (greater than or equal to 0.20 %), 2 due to elevations of both GEP and dd-cfDNA, 2 due to clinical rejection and 1 to follow-up a post-rejection episode.  One of the 2 biopsies due to elevations of both GEP and dd-cfDNA showed ACR grade 2R.  None of the biopsies due to either an elevation in the GEP or dd-cfDNA revealed any significant rejection.  The authors concluded that the use of both GEP and dd-cfDNA led to an increased number of EMB in patients more than 1-year post-transplantation.  These researchers stated that further studies are needed to validate these findings and examine long-term consequences of these diagnostic tests in this population.

Afzal et al (2022) noted that dd-cfDNA has rapidly become part of rejection surveillance following orthotopic HTX; however, some patients show elevated dd-cfDNA without clinical evidence of rejection.  In a retrospective, single-center study, these investigators analyzed 35 HTX recipients at their center who experienced elevated (0.20 % or higher) dd-cfDNA in the absence of clinical rejection, out of a total 106 recipients who had dd-cfDNA results available during the 1st year.  The median time to 1st elevated dd-cfDNA level was 46 days, and the highest dd-cfDNA recorded within 1 year was 0.31 % (IQR, 0.23 to 0.45).  A total of 22 (63 %) patients experienced infections (cytomegalovirus (CMV) or other), and 16 (46 %) presented with de-novo DSA.  Cluster analysis revealed 4 distinct groups characterized by (a) subclinical rejection with 50 % CMV (n = 16), (b) non-CMV infections and the longest time to 1st elevated dd-cfDNA (187 days) (n = 8), (c) right ventricular dysfunction (n = 6), and (d) women who showed the youngest median age (45 years) and highest median dd-cfDNA (0.50 %) (n = 5).  The authors concluded that this analysis brought up several ideas for future research in this rapidly evolving field of non‐invasive monitoring of graft rejection.  Comparison of dd‐cfDNA and histology assessment with molecular microscope (intra-graft mRNA transcripts) is another aspect that the authors is currently evaluating.  They stated that further prospective, multi-center studies are needed to examine if confounding clinical characteristics exist; thus, facilitating the patient guided care and the improved specificity of this vital non‐invasive graft surveillance tool.

The authors stated that this study had several limitations.  First, as inherent to any retrospective analysis from a single center with a relatively small sample size, it is unknown if the characteristics analyzed were generalizable.  Due to the retrospective nature of this study, associations between dd‐cfDNA results and infectious complications could not be studied, since the samples were not drawn concurrently.  Despite this being the largest sample reported to-date, a multi‐center study with programs that use similar surveillance modalities and protocols is needed.  Second, it was possible that elevated AlloSure values were connected to factors not evaluated in the study; however, this study reflected the authors’ clinical experience with a large number of variables that has not been described to-date.  Third, there was well-known subjective variability in pathology interpretation that could not be accounted for in a retrospective study; this cohort could reflect subclinical rejection at the time of the collected elevated AlloSure scores.

Rodgers et al (2023) stated that dd-cfDNA testing is an emerging screening modality for non-invasive detection of acute rejection (AR).  In a retrospective, observational study, these researchers compared the testing accuracy for AR of 2 commercially available dd-cfDNA and gene-expression profiling (GEP) testing in heart transplant (HTx) recipients.  This trial enrolled only HTx patients who underwent standard and expanded single nucleotide polymorphism (SNP) dd-cfDNA between October 2020 to January 2022.  Comparison with GEP was also carried out.  Assays were compared for correlation, accurate classification, and prediction for AR.  A total of 428 samples from 112 unique HTx patients were used for the study.  A positive standard SNP correlated with the expanded SNP assay (p < 0.001).  Both standard and expanded SNP tests showed low sensitivity (39 %, p = 1.0) but high specificity (82 % and 84 %, p = 1.0) for AR.  GEP did not improve sensitivity and showed worse specificity (p < 0.001) compared to standard dd-cfDNA.  The authors found no significant difference between standard and expanded SNP assays in detecting AR.  They reported improved specificity without change in sensitivity using dd-cfDNA in place of GEP testing.  These researchers stated that prospective controlled studies are needed to address how to best implement dd-cfDNA testing into clinical practice.

The authors stated that this study had several drawbacks.  First, this was a retrospective study from a single center and may not necessarily represent the experience of other centers with a different patient demographic. In particular, black patients were under-represented in this trial population compared to the UNOS database in the current era.  However, the AR prevalence remained low (4.4 %) with a 44 % black patient cohort in a recent study.  Second, the vast majority of samples obtained for this study were drawn early post-HTx with a median sample time of 114 days from HTx; therefore, conclusions from samples obtained further out from HTx could not be confidently made.  Third, the time difference between standard and expanded SNP testing may also be a confounding variable; however, the median time difference was only 1 day in this trial; and these investigators found similar results in their sensitivity analysis restricting the sample time difference to 3 days.  Fourth, despite the larger number of samples used, this study remained under-powered to detect smaller differences between standard and expanded SNP testing that may exist.  Fifth, the sensitivity, specificity, PPV, and NPV calculated for standard dd-cfDNA + GEP were performed on a 316-sample subset of the matched dataset.  Although this still accounted for 74 % of the matched dataset, selection bias was a potential confounder in the analysis of the results.  Sixth, this study employed cut-offs recommended by previous studies or based on University of California-San Diego Health’s experience, and it was possible that clinicians will eventually adopt more nuanced cut-offs based on the clinical context of individual patients.

Feingold et al (2023) noted that EMB-led surveillance is common following pediatric heart transplantation (HT), with some centers performing periodic surveillance EMBs indefinitely after HT.  Donor derived cell-free DNA (dd-cfDNA)-led surveillance offers an alternative; however, knowledge about its clinical and economic outcomes, both key drivers of potential utilization, are lacking.  Using single-center recipient and center-level data, these researchers described clinical outcomes before and since transition from EMB-led surveillance to dd-cfDNA-led surveillance of pediatric and young adult HT recipients.  These data were then used to inform Markov models to compare costs between EMB-led and dd-cfDNA-led surveillance strategies.  Over 34.5 months, dd-cfDNA-led surveillance decreased the number of EMBs by 81.8 % (95 % CI: 76.3 % to 86.5 %) among 120 HT recipients (median age of 13.3 years).  There were no differences in the incidences of graft loss or death among all recipients followed at the authors’ center before and following implementation of dd-cfDNA-led surveillance (graft loss: 2.9 versus 1.5 per 100 patient-years; p = 0.17; mortality: 3.7 versus 2.2 per 100 patient-years; p = 0.23).  Over 20 years from HT, dd-cfDNA-led surveillance is projected to cost $8,545 less than EMB-led surveillance.  Model findings were robust in sensitivity and scenario analyses, with cost of EMB, cost of dd-cfDNA testing, and probability of elevated dd-cfDNA most influential on model findings.  The authors concluded that dd-cfDNA-led surveillance showed promise as a less invasive and cost saving alternative to EMB-led surveillance among pediatric and young adult HT recipients.

The authors stated that their analysis had several drawbacks.  Foremost, the clinical outcomes these investigators reported were from a single center over a short follow-up time.  Although their current experience with dd-cfDNA-led surveillance shows similar a proportion referred for reflex RHC/EMB and similar outcomes to their initial experience, the numbers remain small and many patients in the current protocol were also in the initial experience.  The cost-benefit the authors predicted in the base-case model was relatively small given the time over which it was realized and the comparatively high cost of care after HT.  However, cost savings were 1.6- to 2.9-fold greater in the scenario analyses that these researchers modeled.  In particular, beginning dd-cfDNA-led surveillance at 6 weeks post-HT, after only 1 surveillance RHC/EMB at 2 weeks, was the most cost-saving scenario these researchers modeled for all time-points following HT.  Furthermore, when any of the scenarios the authors modeled, including the base-case, was considered from the perspective of multiple recipients per center applied across many HT centers, there is the potential for multi-million dollars of cost savings.

In the cost-effectiveness model, utility estimates for both surveillance modalities may be over-estimates.  Others have reported quality of life ratings among adults who received HT in childhood closer to 0.75.  Substituting this utility in their cost-effectiveness analysis would lower the total QALYs ascribed to each strategy but not impact the difference in QALYs between the strategies or the dominance of the dd-cfDNA-led surveillance strategy.  These investigators did not include cost of B-type natriuretic peptide and donor-specific antibody assessments at the time of each surveillance RHC/EMB or dd-cfDNA in their models.  While the practice around obtaining these assessments is not standardized, for modeling purposes these investigators would expect the assessments to occur at the same times under each strategy and thus equally increase costs for both strategies while maintaining the same cost savings for the dd-cfDNA-led strategy.  For centers that performed surveillance RHC/EMB less often than the authors modeled, use of dd-cfDNA assessments at the frequency the authors modeled may result in increased costs and number of RHC/EMB procedures at their center given the anticipated 16 % to 23 % of reflex EMBs that will be triggered using dd-cfDNA-led surveillance based on their data and of others.

Finally, the use of modeling is necessarily limited by the choice of variables included in the model and the alternative scenarios analyzed.  It was not possible to analyze every conceivable cost, event, or alternative scenario.  These researchers conceded that other surveillance protocols using only surveillance by echocardiography and clinical intuition after 1 year from HT may be less expensive than the scenarios they have analyzed.  The validity of such protocols following pediatric HT has also not been demonstrated in clinical practice to the authors’ knowledge.  Because a high proportion of pediatric HT centers reported using periodic surveillance EMB ad infinitum as recently as 2014 (the most recent such survey published), the authors believed there is value in their comparison of EMB-led surveillance to dd-cfDNA-led surveillance to the HT community.  These investigators also acknowledged that the monetary and quality of life (QOL)-related costs of repeated, invasive RHC/EMB in children may be under-estimated in their analysis.  This was intentional; had the authors over-estimated these, they would have biased their analysis toward dd-cfDNA-led surveillance; thus, complicating the interpretation of their findings.

Furthermore, an UpToDate review on “Heart transplantation in adults: Diagnosis of allograft rejection” (Eisen, 2023) states that “Testing for rejection in symptomatic patients -- In symptomatic patients with a history of alterations to immunosuppression, evidence of new cardiac abnormalities on initial testing, or whose symptoms are unexplained and suspicious for rejection, we typically perform an endomyocardial biopsy to assess for rejection. In these patients, a gene expression profiling (GEP) test or a donor-derived cell-free (dd-CF) DNA test are not substitutes for an endomyocardial biopsy”.

Kobashigawa et al (2023) noted that in HTx, the use of biomarkers to detect the risk of rejection has been evolving.  In this setting, it is becoming less clear as to what is the most reliable test or combination of tests to detect rejection and examine the state of the allo-immune response.  Thus, a virtual expert panel was organized in heart and kidney transplantation to evaluate emerging diagnostics and how they may be best employed to monitor and manage transplant patients.  This manuscript covers the heart content of the conference and is a work product of the American Society of Transplantation's Thoracic and Critical Care Community of Practice.  This paper examined currently available and emerging diagnostic assays and defined the unmet needs for biomarkers in HTx.  Highlights of the in-depth discussions among conference participants that led to development of consensus statements were included.  This conference should serve as a platform to further build consensus within the heart transplant community regarding the optimal framework to implement biomarkers into management protocols and to improve biomarker development, validation, and clinical utility.  Ultimately, these biomarkers and novel diagnostics should improve outcomes and optimize QOL for HTx patients.

The ISHLT guidelines for the care of heart transplant recipients (Velleca et al, 2023) states that cell-free DNA are short, extracellular fragments of DNA released into the circulation from both the donor graft and recipient cells.  During both cellular and antibody mediated rejection, a greater amount of donor-derived cell-free DNA (DD cf-DNA) is released in the blood from the damaged graft in the setting of myocyte necrosis and apoptosis.  Shotgun sequencing of the purified DNA allows for quantification of recipient versus donor DNA fragments via SNPs (single nucleotide polymorphisms) which vary between donor and recipient.  A rise in the percentage of DD cf-DNA in the recipient’s blood has been observed before acute rejection.  Promising results have been reported in observational studies in adults and some teenagers.  As a result, some centers have adopted DD cf-DNA for rejection surveillance and to reduce the number of EMBs during 3 months to 1-year post-transplantation.  The guidelines noted that consideration should be given to remote drawing of blood samples that entail GEP and donor-derived cfDNA assays.  The guidelines stated that this home-based testing can potentially reduce the need for surveillance endomyocardial biopsy and thus limit hospital visits.  Such options should be considered when applicable.  Level of Evidence = C (Consensus of opinion of the experts and/or small studies, retrospective studies, registries).

In a prospective, observational, multi-center study, Deshpande et al (2024) examined the performance of a clinically available cfDNA assay in a large cohort of pediatric and adult HTx recipients, and assessed the performance at specific cut-points in detection of rejection.  This trial enrolled pediatric and adult heart transplant recipients from 7 centers.  Biopsy-associated plasma samples were used for cfDNA measurements.  Pre-determined cut-points were tested for analytic performance.  A total of 487 samples from 160 subjects were used for the analysis.  There were significant differences for df-cfDNA values between rejection [0.21 % (IQR 0.12 to 0.69)] and healthy samples [0.05 % (IQR 0.01 to 0.14), p < 0.0001].  The pediatric rejection group had a median df-cfDNA value of 0.93 % (IQR 0.28 to 2.84) compared to 0.09 % (IQR 0.04 to 0.23) for healthy samples (p = 0.005).  Overall NPV was 0.94 while it was 0.99 for pediatric patients.  Cut-points of 0.13 % and 0.15 % were tested for various types of rejection profiles and were appropriate to rule out rejection.  The authors concluded that the findings of this study suggested that pediatric patients with rejection exhibited higher levels of circulating df-cfDNA compared to adults and supported the specific cut-points for clinical use in pediatric and adult patients with overall acceptable performance.  Moreover, these researchers stated that larger studies with extended follow-up, perhaps incorporating additional ways to characterize biopsy tissue, would be helpful to further understand and optimize the use of df-cfDNA as a non-invasive surveillance tool for HTx recipients.  These investigators stated that future studies should focus on strategies to differentiate between cellular-mediated rejection and AMR as well as improving the understanding of time related changes in circulating cfDNA.

The authors stated that it is important to note that for both pediatric and adult patients without evidence of rejection, the median df-cfDNA was low between 0.03 % for adults and 0.09 % for pediatric patients in this trial; therefore, it appeared that pediatric patients with rejection generated a higher df-cfDNA.  Examining this concept in future studies is important.  A higher df-cfDNA would mean higher concentrations of genomic equivalents of donor-derived DNA were present in pediatric patients with rejection, and suggested that it could be possible to reduce plasma volume  requirements in pediatric patients.  This will overcome an important current limitation of commercial assays that require relatively large volume.  These researchers also noted that there is also a “natural” variation in the df-cfDNA levels depending on the time since transplant.  In the early post-transplant period, a higher level of circulating cfDNA was detected which then settled to essentially undetectable levels over the first few months.  Over time, there was also a gradual decrease in total circulating cfDNA, which could result in a higher donor fraction.  It is important to gather better data regarding the optimal threshold based on the natural history of total and df-cfDNA in HTx recipients.  Using true quantification of donor-derived cfDNA rather than or in addition to the donor fraction may provide further information for clinicians.  The present trial, which had a significant portion of new transplants, did not provide long term follow-up to examine this impact.  These investigators noted that similar to the limitations of other clinical studies, including the authors’ previous DNA-based transplant rejection test (DTRT) study, the diagnosis of rejection based on local biopsy read could be challenging.  The patients were enrolled at highly experienced transplant centers; thus, local biopsy read was a reasonable approach; however, a central biopsy core could help reduce center-based variation.  Even the gold standard “biopsy” in itself has limitations because diagnosis at the lower ends of rejection (ACR 1 and AMR1) could show significant clinical and pathologic variation; thus, these researchers provided distribution of df-cfDNA to show the distribution across levels of biopsy rejection.  The biggest challenge continues to be that the number of samples for individual/specific types of rejection was small (e.g., there was only 1 sample for pediatric AMR2 without ACR).  This limited the ability to differentiate df-cfDNA differences between ACR and AMR.  Finally, the cut-points examined in this trial represented those appropriate for the assay used in the study.  As such, the cut-points would vary by assay and every test will necessitate its own validation.

Computed Tomography Angiography for Evaluation of the Coronary Arteries Following Heart Transplantation

Khan and Jang (2012) stated that cardiac/coronary allograft vasculopathy (CAV) is a significant cause of morbidity and mortality after cardiac transplantation and requires frequent surveillance with conventional catheter-based coronary angiography (CCAG).  Multi-detector row computed tomography (MDCT) has been shown to be effective in assessing atherosclerosis in native coronary arteries.  These investigators reviewed the literature to determine the accuracy of MDCT in CAV assessment.  They carried out an English-language literature search using Embase, OVID, PubMed, and Cochrane Library databases; studies that directly compared MDCT with CCAG and/or intravascular ultrasound (IVUS) for the detection of coronary artery stenosis or significant intimal thickening in cardiac transplant patients were analyzed.  Data were pooled to obtain weighted sensitivities, specificities, and diagnostic accuracies.  Negative and positive predictive values (NPV/PPV) were calculated.  A total of 7studies with a sum of 272 patients were included in this review.  There were 3 studies examining 16-slice MDCT and 4 studies looking at 64-slice MDCT in CAV.  Using per-segment analysis, MDCT assessed between 91 % and 96 % of all coronary segments when evaluating for stenosis.  Pooled estimates for sensitivity and specificity for MDCT ranged from 82 % to 89 % and 89 % to 99 %, respectively, while NPV was 99 %.  Per-patient analysis revealed a sensitivity of 87 to 100 % and NPV of 96 to 100 %; PPV was less than 50 % for 64-slice MDCT in both per-segment and per-patient analysis.  When compared with IVUS, MDCT had a sensitivity of 74 to 96 % and specificity of 88 to 92 % in assessment of intimal thickening; NPV and PPV were 80 to 81 % and 84 to 98 %, respectively.  The authors concluded that the high sensitivity and NPV of MDCT suggested that it may be a useful, non-invasive screening tool to rule out CAV.

Mittal et al (2013) examined the diagnostic accuracy of cardiac computed tomographic angiography (CTA) without the use of β-blockers compared with that of invasive angiography for the detection of CAV in HTX recipients.  Heart transplant recipients (n = 138) scheduled for routine invasive angiography were prospectively enrolled to undergo CT to evaluate coronary artery calcification and retrospectively gated cardiac CTA with a 64-section scanner.  The cardiac CTA images were systematically analyzed for image quality.  Degree of CAV was assessed by using a 15-coronary segments model.  The area under the receiver operating characteristic curve, sensitivity, specificity, NPV and PPV values of cardiac CTA for detection of CAV with any degree of stenosis and greater than or equal to 50 % stenosis were calculated.  Coronary artery calcification was absent in 82 patients, 5 (6 %) of whom had CAV with 50 % or more stenosis.  Interpretable image quality was obtained in 130 (96 %) of the 136 patients who completed the study and 1,900 (98 %) of 1,948 segments.  At the patient level, cardiac CTA had an area under the receiver operating characteristic curve, sensitivity, specificity, PPV and NPV of 0.880 (95 % confidence interval [CI]: 0.819 to 0.941), 98 %, 78 %, 77 %, and 98 %, respectively, for diagnosis of CAV with any degree of stenosis, but for CAV with 50 % or more stenosis, the corresponding values were 0.942 (95 % CI: 0.885 to 1.000), 96 %, 93 %, 72 %, and 99 %, respectively.  None of the 61 patients with normal cardiac CTA results had CAV on the basis of invasive angiographic images.  The authors concluded that the findings of this study showed that cardiac CTA compared favorably with invasive angiography in detecting CAV in HTX recipients and may be a preferable screening technique because of its non-invasive nature.  The absence of coronary artery calcification alone was not reliable enough for excluding CAV.

Wever-Pinzon et al (2014) noted that CAV limits long-term survival after heart transplantation (HTX), and screening for CAV is performed on annual basis.  Coronary computed tomography angiography (CCTA) is currently not recommended for CAV screening due to the limited accuracy reported by early studies.  Technological advances, however, might have resulted in improved test performance and might justify re-evaluation of this recommendation.  In a meta-analysis, these researchers evaluated the diagnostic accuracy of CCTA for detecting CAV in comparison with conventional coronary angiography (CCAG) alone or with IVUS.  They carried out a systematic review of Medline, Cochrane, and Embase for all prospective trials assessing CAV using CCTA using a standard approach for meta-analysis for diagnostic test and a bi-variate analysis.  A total of 13 studies evaluating 615 patients (mean age of 52 years, 83 % men) and 9,481 segments fulfilled inclusion criteria.  Patient-based analyses comparing CCTA versus CCAG for the detection of any CAV (greater than luminal irregularities) and significant CAV (stenosis greater than or equal to 50 %), showed mean weighted sensitivities of 97 % and 94 %, specificities of 81 % and 92 %, a NPV of 97 % and 99 %, a PPV of 78 % and 67 %, and diagnostic accuracies of 88 % and 94 %, respectively.  There was a strong trend toward improved sensitivity (97 % versus 91 %, p = 0.06) and NPV (99 % versus 97 %, p = 0.06) to detect significant CAV with 64-slice compared with 16-slice CCTA.  A patient-based analysis of 64-slice CCTA versus IVUS showed a mean weighted sensitivity and specificity of 81 % and 75 % to detect CAV (intimal thickening greater than 0.5 mm), whereas the PPV and NPV were 93 % and 50 %, respectively.  The authors concluded that CCTA using currently available technology is a reliable non-invasive imaging alternative to coronary angiography with an excellent sensitivity, specificity, and NPV for the detection of CAV.

Gunther et al (2018) stated that CAV is an accelerated form of atherosclerosis unique to HTX patients.  These investigators examined the detection of significant coronary artery stenosis and CAV, determinants of image quality, and the radiation dose in CCTA of HTX patients with 64-MDCT.  A total of 52 HTX recipients scheduled for invasive coronary angiography (ICA) were prospectively enrolled and underwent CCTA before ICA with IVUS.  Interpretable CCTA images were acquired in 570 (95 %) coronary artery segments greater than or equal to 2 mm in diameter.  Sensitivity, specificity, and PPV and NPV of CCTA for the detection of segments with significant stenosis (lumen reduction greater than or equal to 50 %) on ICA were 100 %, 98 %, 7.7 %, and 100 %, respectively; 12 significant stenoses were located in segments with un-interpretable image quality or vessel diameter less than 2 mm; only 1 was eligible for intervention; IVUS detected CAV (maximal intimal thickness greater than or equal to 0.5 mm) in 33/41 (81 %) patients; CCTA and ICA identified CAV (any wall or luminal irregularity) in 18 (44 %) and 14 (34 %) of these 33 patients, respectively.  The mean estimated radiation dose was 19.0 ± 3.4 mSv for CCTA and 5.7 ± 3.3 mSv for ICA (p < 0.001).  The authors concluded that CCTA with interpretable image quality had a high NPV for ruling out significant stenoses suitable for intervention.  The modest detection of CAV by CCTA implied a limited value in identifying subtle CAV.  The high estimated radiation dose for 64-MDCT was of concern considering the need for repetitive examinations in the HTX population.

An UpToDate review on "Clinical manifestations, diagnosis, and prognosis of cardiac allograft vasculopathy" (Gustafsson, 2019) states that "Early detection of CAV is challenging because symptoms of myocardial ischemia secondary to CAV are typically absent or atypical due to afferent and efferent allograft denervation.  Although there is evidence for reinnervation in some patients by 5 years after transplantation, the degree of reinnervation is generally incomplete.  As a result, patients with CAV seldom experience classic angina pectoris.  Premonitory symptoms associated with exertion such as chest pain, dyspnea, diaphoresis, gastrointestinal distress, presyncope, or syncope are often missing or atypical, so symptoms do not provide a reliable warning of disease.  This was illustrated by a study of 22 cardiac transplant recipients with 25 acute myocardial infarctions at a mean of 3.9 years after transplantation.  The most common symptoms were weakness (16), dyspnea (11), and palpitations (8); only 2 patients had chest pain, 3 patients had arm pain, and 3 patients had no symptoms … Use of multi-slice computed tomography coronary angiography to potentially replace invasive cardiac catheterization in evaluating CAV is an area of active investigation".

Furthermore, EviCore’s clinical guideline on "Cardiac Imaging Policy" (version 1.0.2019) states that "There is insufficient evidence to support routine use of coronary computed tomography angiography (CCTA) in the evaluation of the coronary arteries following heart transplantation".

Heart Molecular Microscope Diagnostic System (MMDx-Heart)

The Heart Molecular Microscope Diagnostic System (MMDx-Heart) refers to mRNA gene expression analysis of 1,283 genes utilizing microarray; it measures mRNA transcript levels in transplant heart biopsy tissue, with allograft rejection and injury algorithm reported as a probability score.

Halloran and colleagues (2017) noted that the emergence of molecular systems offers opportunities for improving the assessment of rejection in heart transplant biopsy specimens.  These researchers developed a microarray-based system for assessing heart transplant EMB specimens.  They analyzed 331 protocol or for-cause EMB specimens from 221 subjects in 3 centers (Edmonton, Bologna, and Paris).  Un-supervised principal component analysis (PCA) and archetype analysis used rejection-associated transcripts (RATs) shown in kidney transplants to be associated with antibody-mediated rejection (ABMR) or T cell-mediated rejection (TCMR), or both.  They compared EMB specimens to kidney biopsy specimens, rejection status in both was simplified to TCMR, ABMR, or no rejection.  The pattern of RAT expression was similar in EMB and kidney specimens, permitting use of RATs to assign scores and group ("cluster") membership to each EMB, independent of histology.  Three clusters emerged in EMB specimens, similar to kidney specimens: TCMR, ABMR, and no rejection.  This allowed each EMB specimen to be given 3 scores and assigned to 1 cluster by its highest score.  There was significant agreement between molecular phenotype-archetype scores or clusters-and both histologic diagnoses and donor-specific antibody; AUC estimates for predicting histologic TCMR, ABMR, and no rejection by molecular assessment were lower in EMB specimens than in kidney specimens, reflecting more uncertainty in EMB specimens, particularly in histologic diagnosis of TCMR.  The authors concluded that rejection-associated transcripts can be used to estimate the probability of TCMR and ABMR in heart transplant specimens, providing a new dimension to improve the accuracy of diagnoses and an independent system for recalibrating the histology guidelines.  These findings need to be validated by well-designed studies.

Furthermore, an UpToDate review on "Acute cardiac allograft rejection: Diagnosis" (Eisen, 2019) lists "Molecular microscopy" as one the of the investigational methods for non-invasive detection of rejection.

Antiplatelet Therapy for Reducing the Development of Cardiac Allograft Vasculopathy

Aleksova and colleagues (2021) noted that cardiac allograft vasculopathy (CAV) is mediated by endothelial inflammation, platelet activation and thrombosis.  Antiplatelet therapy may prevent the development of CAV.  In a systematic review and meta-analysis, these researchers examined the evidence on the effect of antiplatelet therapy following HT.  Central (Ovid), Medline (Ovid), Embase (Ovid) were searched from inception until April 30, 2020.  Outcomes included CAV, all-cause mortality, and CAV-related mortality.  Data were pooled using random-effects models.  A total of 7 observational studies including 2,023 patients, mean age of 52 years, 22 % women, 47 % with ischemic cardiomyopathy followed over a mean of 7.1 years proved eligible for this study.  All studies compared acetylsalicylic acid (ASA) to no treatment and were at serious risk of bias.  Data from 1,911 patients in 6 studies were pooled in the meta-analyses.  The evidence is very uncertain regarding the effect of ASA on all-cause or CAV-related mortality.  ASA may reduce the development of CAV (RR 0.75, 95 % CI: 0.44 to 1.29) based on very low certainty evidence.  Two studies that conducted propensity-weighted analyses showed further reduction in CAV with ASA (HR 0.31, 95 % CI: 0.13 to 0.74).  The authors concluded that there is limited evidence that ASA may reduce the development of CAV.  These researchers stated that definitive resolution of the impact of antiplatelet therapy on CAV and mortality will require randomized clinical trials.

TransMedics Organ Care System

On September 7, 2021, the FDA granted premarket approval (PMA) of TransMedics Organ Care System (OCS) Heart System for use with organs from donors after brain death (DBD).  The OCS Heart System is indicated for the preservation of DBD donor hearts deemed unsuitable for procurement and transplantation at initial evaluation due to limitations of prolonged cold static cardioplegic preservation (e.g., more than 4 hours of cross-clamp time).  This indication is based on the results of the OCS Heart EXPAND Trial, the associated OCS Heart EXPAND Continued Access Protocol (CAP) and the OCS Heart PROCEED II Trial.

However, there is currently insufficient evidence to support the use of TransMedics Organ Care System (OCS) Heart System for heart transplantation.

Koerner et al (2014) stated that cold ischemia associated with cold static storage is an independent risk factor for primary allograft failure and survival of patients after orthotopic heart transplantation.  The effects of normothermic ex-vivo allograft blood perfusion on outcomes after orthotopic heart transplantation compared to cold static storage have been studied.  In a prospective, non-randomized, single-center study, normothermic ex-vivo allograft blood perfusion has been performed using an organ care system (OCS) (TransMedics, Andover, MA).  Included were consecutive adult transplantation patients who received an orthotopic heart transplantation (oHTx) without a history of any organ transplantation, in the absence of a congenital heart disorder as an underlying disease and not being in need of a combined heart-lung transplantation.  Furthermore, patients with fixed pulmonary hypertension, ventilator dependency, chronic renal failure, or panel reactive antibodies greater than 20 % and positive T-cell cross-matching were excluded.  Inclusion criteria for donor hearts was age of less than 55 years, systolic blood pressure (SBP) of greater than 85 mmHg at the time of final heart assessment under moderate inotropic support, heart rate of less than 120 bpm at the time of explantation, and left ventricular ejection fraction (LVEF) of greater than 40 % assessed by an transcutaneous echo/Doppler study with the absence of gross wall motion abnormalities, absence of left ventricular hypertrophy, and absence of valve abnormalities.  Donor hearts that were conventionally cold stored with histidine-tryptophan-ketoglutarate solution (Custodiol; Koehler Chemie, Ansbach, Germany) constituted the control group.  The primary endpoint was the recipients' survival at 30 days and 1 and 2 years after their heart transplantation.  Secondary endpoints were primary and chronic allograft failure, non-cardiac complications, and hospital length of stay (LOS).  Over a 2-year period (January 2006 to July 2008), a total of 159 adult cardiac allografts were transplanted; 29 were assigned for normothermic ex-vivo allograft blood perfusion and 130 for cold static storage with HTK solution.  Cumulative survival rates at 30 days and 1 and 2 years were 96 %, 89 %, and 89 %, respectively, whereas in the cold static storage group survival after oHTx was 95 %, 81 %, and 79 %.  Primary graft failure was less frequent in the recipients of an oHTx who received a donor heart that had been preserved with normothermic ex-vivo allograft blood perfusion using an OCS (6.89 % versus 15.3 %; p = 0.20).  Episodes of severe acute rejection (23 % versus 17.2 %; p = 0.73), and cases of acute renal failure requiring hemodialysis (25.3 % versus 10 %; p = 0.05) were more frequent diagnosed among recipients of a donor heart that had been preserved using the cold static storage.  The hospital LOS did not differ (26 days versus 28 days; p = 0.80) in both groups.  The authors concluded that normothermic ex-vivo allograft blood perfusion in adult clinical orthotopic HTx contributed to better outcomes after transplantation in regard to recipient survival, incidence of primary graft dysfunction, and incidence of acute rejection.

Saez et al (2014) noted that a severe shortage of available donor organs has created an impetus to use extended criteria organs for HTx.  Although such attempts increase donor organ availability, they may result in an adverse donor-recipient risk profile.  The TransMedics OCS allows preservation of the donor heart by perfusing the organ at 34° C in a beating state, potentially reducing the detrimental effect of cold storage and providing additional assessment options.  These researchers described a single-center experience with the OCS in high-risk HTx procedures.  A total of 30 hearts were preserved using the OCS between February 2013 and January 2014, 26 of which (86.7 %) were transplanted.  Procedures were classified as high risk based on donor factors, i.e., transport time more than 2.5 hours with estimated ischemic time longer than 4 hours, LVEF less than 50 %, left ventricular hypertrophy (LVH), donor cardiac arrest, alcohol/drug abuse, coronary artery disease (CAD), or recipient factors, i.e., mechanical circulatory support or elevated pulmonary vascular resistance (PVR), or both.  Donor and recipient ages were 37 ± 12 years and 43 ± 13 years, respectively.  Allograft cold ischemia time was 85 ± 17 mins; and OCS perfusion time was 284 ± 90 mins.  The median intensive care unit (ICU) stay was 6 days; 1 death (3.8 %) was observed over the follow-up: 257 ± 116 (109 to 445 days).  There was preserved allograft function in 92 % of patients, with a mean LVEF of 64 % ± 5 %.  The authors concluded that the use of the OCS was associated with markedly improved short-term outcomes and transplant activity by allowing use of organs previously not considered suitable for transplantation or selection of higher risk recipients, or both.

The authors stated that the major drawback of this study was the analysis of a small cohort of patients from a single center who underwent HTx using the OCS as a method of allograft preservation / assessment.  Moreover, because some of these donors would not have been considered suitable for transplantation, on ethical grounds the donor hearts could not be randomized to standard of care (SOC) preservation / cold storage.  Long-term follow-up is also needed, especially in the group of patients who received allografts with LVH, reduced LVEF, or palpable CAD, because such risk factors may have an as yet undetectable impact on long-term outcome.  Conversely, it is conceivable that the minimization of total cold ischemic time by the OCS may limit re-perfusion injury and favorably influence the long-term progression of allograft vasculopathy.  These researchers stated that a single-arm, Food and Drug Administration (FDA)-approved, multi-center, non-randomized trial is currently under way in the U.S. and will examine the rate of use of extended criteria donor hearts and early outcomes after transplantation.

Ardehali et al (2015) stated that the TransMedics OCS is the only clinical platform for ex-vivo perfusion of human donor hearts.  The system preserves the donor heart in a warm beating state during transport from the donor hospital to the recipient hospital.  In a prospective, randomized, multi-center, open-label,  non-inferiority trial (PROCEED II), these researchers examined the clinical outcomes of the OCS compared with standard cold storage of human donor hearts for transplantation.  This trial was carried out at 10 heart-transplant centers in the U.S. and Europe.  Eligible heart-transplant candidates (aged of greater than 18 years) were randomly assigned (1:1) to receive donor hearts preserved with either the OCS or standard cold storage.  Subjects, investigators, and medical staff were not masked to group assignment.  The primary endpoint was 30-day patient and graft survival, with a 10 % non-inferiority margin.  These investigators did analyses in the intention-to-treat (ITT), as-treated, and per-protocol populations.  Between June 29, 2010, and September 16, 2013, these researchers randomly assigned 130 patients to the OCS group (n = 67) or the standard cold storage group (n = 63); 30-day patient and graft survival rates were 94 % (n = 63) in the OCS group and 97 % (n = 61) in the standard cold storage group (difference 2.8 %, 1-sided 95 % upper confidence bound 8.8; p = 0.45); 8 (13 %) patients in the OCS group and 9 (14 %) patients in the standard cold storage group had cardiac-related serious adverse events (SAEs).  The authors concluded that HTx using donor hearts adequately preserved with the OCS or with standard cold storage yielded similar short-term clinical outcomes.  Moreover, these researchers stated that the metabolic assessment capability of the OCS needs further study.  It should be noted that the RCT portion of the PROCEED II trial found no significant differences between ex-vivo perfusion and standard cold storage.

Sato et al (2019) noted that the OCS represents an alternative to the current standard of cold organ storage that sustains the donor heart in a near-physiologic state.  Previous reports showed that this system had significantly shortened the cold ischemic time from standard cold storage (CS).  However, the effect of reduced ischemic injury against the coronary vascular bed has not been examined by intra-vascular ultrasound (IVUS).  Between August 2011 and February 2013, HTx candidates enrolled in the PROCEED II Trial were randomized to either CS or OCS.  IVUS was performed at 4 to 6 weeks (baseline) and repeated 1 year after transplantation.  The change in maximal intimal thickness (MIT) and other clinical outcomes were examined.  A total of 39 patients were randomized and underwent HTx by OCS (n = 16) or CS (n = 18).  Of these, 18 patients (OCS: n = 5, CS: n = 13) with paired IVUS were examined.  There were no significant differences in the change of MIT and other clinical outcomes between the groups.  The authors concluded that the incidence of cardiac allograft vasculopathy in donor hearts preserved with the OCS versus CS was similar; these results suggested that this ex-vivo allograft perfusion system is a promising and valid platform for donor HTx.

Schroder et al (2019) noted that the OCS Heart EXPAND Trial is a prospective, multi-center trial to examine the effectiveness of the OCS to resuscitate, preserve and evaluate donor hearts that may not meet current standard donor heart criteria for transplantation to potentially improve donor heart utilization for transplantation.  Donor hearts were eligible if they met any of the following characteristics: expected total ischemic time of greater than or equal to 4 hours or expected total ischemic time of greater than or equal to 2 hours plus at least one of the following risk factors: LVH, EF 40 to 50 %, downtime of greater than or equal to 20 mins, and age of greater than 55 years.  Hearts were perfused and examined on OCS Heart System from donor to recipient.  Hearts were eligible for transplantation if the following criteria were met -- final OCS Heart arterial lactate of less than 5 mmol/L and stable OCS perfusion parameters within recommended ranges.  The primary effectiveness endpoint was a composite endpoint of patient survival at 30 days and absence of ISHLT severe primary heart graft dysfunction (PGD) (left or right ventricle) in the first 24 hours post-transplantation.  The secondary endpoint was the rate of ECD heart utilization after preservation and assessment on the OCS Heart System.  A total of 93 eligible donor hearts with a mean UNOS match run of 66 declines were assessed on OCS Heart.  Donor categories were as follows: x-clamp time of greater than or equal to 4 hours 37 %, LVH 23 %, EF 40 to 50 % were 23 %, downtime of greater than or equal to 20 mins 28 %, older age 13 % and 33 % met multiple inclusion criteria; 75 of the 93 donor hearts were successfully transplanted resulting in a utilization rate of 81 %.  Mean OCS perfusion time was 6.35 hours.  Incidence of severe LV or RV PGD at 24 hours was 10.7 %; 30-day and 6-month survival were 94.7 % and 88 % respectively.  The authors concluded that the use of OCS Heart System resulted in high utilization of ECD hearts with excellent short-term post-transplant outcomes, most notably a low rate of PGD.  These results provided clinical evidence supporting its use in ECD heart preservation and assessment; and may significantly increase donor utilization for transplantation.  Moreover, it should be noted that the EXPAND Trial reported on short-term outcomes; and it did not include a standard cold storage group for comparison.

Fleck et al (2021) noted that pediatric HTx recipients with congenital heart defects require complex concomitant surgical procedures with the risk of prolonging the allograft's ischemic time.  Ex-vivo allograft perfusion with the TransMedics OCS may improve survival of these challenging patients.  In a retrospective, single-center study, a consecutive series of 8 children with allografts preserved using the OCS was compared with 13 children after HTx with CS of the donor heart from March 2018 to March 2020.  Median recipient age in the control group was 18 months (range of 1 to 189) versus 155 months (range of 83 to 214) in the OCS group, and the baseline differences between the 2 groups were not significant; 50 % of the children in the OCS group had complex congenital heart defects (versus 15 % of the control subjects).  Median operation time during HTx in the OCS group was 616 mins (range of 270 to 809) versus 329 mins (range of 283 to 617).  Because of the time of ex-vivo allograft perfusion (265 mins [range of 202 to 372]) median total ischemia time was significantly shorter in the OCS group: 78 mins (range of 52 to 111) versus 222 mins (range of 74 to 326).  The incidence of primary graft, renal, or hepatic failure did not differ between the groups.  Graft function and the occurrence of any treated rejection at follow-up revealed no significant difference between the 2 groups; 1-year survival was 88 % in the OCS group (versus 85 % in the CS group).  The authors concluded that ex-vivo allograft perfusion enabled complex pediatric HTx, yielding outcomes as positive as those of children whose donor hearts were stored in ice-cold solution.  This was a small (n = 8 for the OCS group), retrospective study with short-term (1 year) follow-up.

The Ontario Health (Quality) technology assessment on “Portable normothermic cardiac perfusion system in donation after cardiocirculatory death” (2020) states that “Outcomes for people who received hearts donated after cardiocirculatory death using a portable normothermic cardiac perfusion system appear to be similar to those for people who received hearts donated after brain death.  However, the quality of this evidence is very low.  Given the lack of clinical and economic evidence on long-term outcomes, we were unable to establish the cost-effectiveness of a portable normothermic cardiac perfusion system.  We estimate that publicly funding a perfusion system for donor heart preservation after cardiocirculatory death over the next 5 years would cost about $5.6 million.  Although the people we spoke with had no direct experience with a perfusion system, people waiting for a heart transplant expressed hope that the technology could increase the potential donor pool.  Family members of organ donors believed the technology could increase the likelihood of a successful heart transplant”.

The American College of Cardiology (ACC)’s webpage on “Improving Heart Transplantation by Expanding the Donor Pool” (ACC, 6/2/2021) noted that “ex-vivo perfusion technologies such as the OCS may soon be applied to donation after circulatory death heart transplant, a paradigm with the potential to significantly expand the donor pool … The technologies are also promising for other areas of donor management that could improve heart transplantation.  For example, ex vivo perfusion may afford an opportunity to administer therapies to the donor heart prior to transplantation to improve the metabolic state of the heart after an insult such as recent cardiac arrest, or to modify the immunologic state of the heart and minimize rejection in the recipient.  These are active areas of research”.  https://www.acc.org/latest-in-cardiology/articles/2021/06/01/18/33/improving-heart-transplantation-by-expanding-the-donor-pool.

A clinical trial entitled “A Study to Evaluate the Effectiveness of The Portable Organ Care System (OCS™) Heart from Donors After Circulatory Death Heart” is ongoing (but closed for enrollment) in the Mayo Clinic (Jacksonville, FL). The objective of this trial is to examine the effectiveness of the OCS Heart System to resuscitate, preserve and evaluate hearts donated after circulatory death for transplantation to increase the pool of donor hearts available for transplantation. 

According to Medscape webpage on “OCS Heart System Earns Hard-Won Backing of FDA Panel” (Wendling, 2021), the Circulatory System Devices Panel of the Medical Devices Advisory Committee voted 12 to 5, with 1 abstention, that the benefits of the OCS Heart System outweigh its risks.  The panel voted in favor of the OCS Heart being effective (10 yes, 6 no, and 2 abstaining) and safe (9 yes, 7 “no”, 2 “abstaining”) but not without mixed feelings.  James Blankenship, MD, a cardiologist at the University of New Mexico, Albuquerque, voted yes to all 3 questions but said, "If it had been compared to standard of care, I would have voted no to all three.  But if it's compared to getting an [left ventricular assist device] LVAD or not getting a heart at all, I would say the benefits outweigh the risks".  Marc R. Katz, MD, chief of cardiothoracic surgery, Medical University of South Carolina, Charleston, also gave universal support, noting that the rate of heart transplantations has been flat for years.  "This is a big step forward toward being able to expand that number.  Now all that said, it obviously was a less than perfect study and I do think there needs to be some constraints put on the utilization". 

In the PMA, the OCS Heart System is indicated for donor hearts with 1 or more of the following characteristics: An expected cross-clamp or ischemic time of at least 4 hours because of donor or recipient characteristics; or an expected total cross-clamp time of at least 2 hours plus 1 of the following risk factors:

• Donor age of 55 years or older
• History of cardiac arrest and downtime of at least 20 mins
• History of alcoholism
• History of diabetes
• Donor ejection fraction of less than or equal to 50 % but greater than or equal to 40 %
• History of left ventricular hypertrophy
• Donor angiogram with luminal irregularities but no significant coronary artery disease.

Several members voiced concern about "indication creep" should the device be approved by the FDA; and highlighted the 2-hour cross-clamp time plus wide-ranging risk factors.  "I'm a surgeon and I voted no on all three counts", said Murray H. Kwon, MD, Ronald Reagan UCLA Medical Center, Los Angeles.  "As far as risk/benefit, if it was just limited to one group -- the 4-hour-plus -- I would say yes, but if you're going to tell me that there's a risk/benefit for the 2-hour with the alcoholic, I don't know how that was proved in anything".  Kwon was also troubled by lack of proper controls and by the 1/4 of patients who ended up on mechanical circulatory support in the first 30 days after transplant.  "I find that highly aberrant".  Joaquin E. Cigarroa, MD, head of cardiovascular medicine, Oregon Health & Science University, Portland, said the unmet need for patients with refractory, end-stage heart failure is challenging and quite emotional, but also voted no across the board, citing concerns about a lack of comparator in the EXPAND trials and overall out-of-body ischemic time.  "As it relates to risk/benefit, I thought long and hard about voting yes despite all the unknowns because of this emotion, but ultimately, I voted no because of the secondary 2-hours plus alcoholism, diabetes, or minor coronary disease, in which the ischemic burden and ongoing lactate production concern me" he said.  

Pinnelas and Kobashigawa (2022) stated that HTx is the gold standard for treatment for select patients with end-stage heart failure, yet donor supply is limited.  Ex-vivo machine perfusion is an emerging technology capable of safely preserving organs and expanding the viable donor pool.  The TransMedics OCS is an investigational device that mimics physiologic conditions while maintaining the heart in a warm, beating state rather than cold storage.  The use of OCS allows increased opportunities for using organs from marginal donors, distant procurement sites, donation after cardiac death, and in recipients with complex anatomy.  In the future, bioengineering technologies including use of mesenchymal stem cells, viral vector delivery of gene therapy, and alternate devices may further broaden the field of ex- vivo machine perfusion.

Furthermore, an UpToDate review on “Heart transplantation in adults: Donor selection and organ allocation” (Mancini, 2022) states that “Strategies to expand donor organ supply -- Potential strategies to expand the supply of donor organs include technologic advances for extending the time limit for organ transport, accepting some DCD, as well as individualized relaxation of traditional criteria for transplantation … A portable heart perfusion system is under investigation as a potential technology for extending the time limits of organ transport and increasing donor supply.  The only system that has been studied clinically for human cardiac allograft preservation is the Transmedics Organ Care System, which provides normothermic blood-based perfusion of the beating donor heart.  In the PROCEED trial, 130 patients receiving standard donor organs were randomly assigned to usual cold preservation or normothermic machine perfusion.  There were comparable 30-day patient and graft survival rates in the two groups.  This trial has been followed by the EXPAND trial, in which donors with high-risk factors (such as older age, presence of LV hypertrophy, and LV ejection fraction between 40 to 50 %) are being randomly assigned to cold versus warm preservation.  The potential advantages of this system include increasing the number of donors (potentially including resuscitated metabolically abnormal donors) and extending safe transport times, thus easing the logistics of transplant surgery, and potentially being able to pretreat patients with cyto-protective and immune-modulatory agents.  Disadvantages include its expense and the work intensive nature of the technology”.  The Transmedics Organ Care System is not mentioned in the “Summary and Recommendations” section of this UTD review.

Electrocardiography for Monitoring Transplant Recipients of Rejection

Hashim et al (2022) noted that in cardiac transplant recipients, the electrocardiography (ECG) is a non-invasive measure of early allograft rejection.  ECG can predict an ACR; thus, shortening the time to recognition of rejection.  Earlier diagnosis has the potential to reduce the number and severity of rejection episodes.  These investigators carried out a systematic literature review to identify and select studies on the use of ECG in diagnosing cardiac transplant rejection in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.  Studies included reported sensitivity and specificity of ECG readings in heart transplant recipients during the 1st post-transplant year.  Data were analyzed with Review manager version 5.4; p-value was used in testing the significant difference.  After the removal of duplicates, 98 studies were eligible for screening.  After the full-text screening, a total of 17 studies were included in the review based on the above criteria.  A meta-analysis of 5 studies was performed.  The authors concluded that in heart transplant recipients, a non-invasive measure of early allograft rejection has the potential to reduce the number and severity of rejection episodes by reducing the time and cost of surveillance of rejection and shortening the time to recognition of rejection.  Moreover, these researchers stated that there is heterogeneity among studies included in the meta‐analysis; therefore, preventing conclusive results.  They stated that more clinical trials are needed to render final conclusion regarding the use of ECG as a measure in detecting heart transplant rejections.

Machine Learning and Artificial Intelligence in Cardiac Transplantation

In a systematic review, Naruka et al (2022) examined available evidence on the use of artificial intelligence (AI) and machine learning (ML) in the field of cardiac transplantation.  In addition, based on the challenges identified, these researchers provided a series of recommendations and a knowledge base for future research in the field of ML and heart transplantation.  These investigators carried out a systematic database search of original studies that examined the use of ML and/or AI in heart transplantation in Embase, Medline, Cochrane database, and Google Scholar, from inception to November 2021.  The search yielded 237 studies, of which 13 were included in this review, featuring 463,850 patients.  Three main areas of application were identified: First, ML for predictive modeling of heart transplantation mortality outcomes.  Second, ML in graft failure outcomes.  Third, ML to aid imaging in heart transplantation.  The results of the included studies suggested that AI and ML are more accurate in predicting graft failure and mortality than traditional scoring systems and conventional regression analysis.  Major predictors of graft failure and mortality identified in ML models included hospital LOS, immunosuppressive regimen, recipient's age, congenital heart disease, and organ ischemia time.  Other potential benefits included analyzing initial laboratory investigations and imaging, assisting a patient with medication adherence, and creating positive behavioral changes to minimize further cardiovascular risk.  The authors concluded that ML showed promising applications for improving heart transplantation outcomes and patient-centered care, nevertheless, there remain important drawbacks relating to implementing AI into everyday surgical practices.  Moreover, these researchers stated that this study also identified the need for higher quality, more granular, and extensive databases since the models are only as good as the initial information that is fed into them.  More importantly, the heterogeneity in data restricted the use of such models to adults over the age of 60 years.  They stated that more prospective, multi‐center and nationwide datasets are needed to address these concerns whereby parameters involved in heart transplantation are collected, regardless of the traditionally perceived importance.

The authors stated that this systematic review had 2 main drawbacks.  First, much of the data included in this systematic review were from retrospective, observational studies, which were conducive to bias and confounding.  Second, due to the different databases used by each individual study, a meta‐analysis was unachievable due to the heterogeneity in the variables included, and due to the type of ML models that were employed.  To test the full potential of ML models and AI, larger, multi‐center prospective studies are needed.  Further investigations will need to consider a broader range of variables, especially those which are commonly not included due to the perceived lack of importance (e.g., the immunosuppression regimen post‐transplantation).

Induction Therapy

Kugathasan et al (2024) stated that induction therapy (IT) utility in HTx remains contested.  Commissioned by a clinical-practice guidelines panel to examine the safety and effectiveness of IT in adult HTx recipients, these investigators carried out a systematic review and network meta-analysis (NMA).  They searched for studies from January 2000 to October 2022, reporting on the use of any IT agent in adult HTx patients.  Based on patient-important outcomes, these researchers conducted frequentist NMAs separately for RCTs and observational studies with adjusted analyses, and examined the certainty of evidence using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach.  From 5,156 publications identified, these investigators included 7 RCTs and 12 observational studies, and reported on 2 contemporarily-used IT agents-basiliximab and rATG.  The RCTs provided only very-low certainty evidence and was uninformative of the effect of the 2 agents versus no IT or one another.  With low certainty in the evidence from observational studies, basiliximab may increase 30-day (OR 1.13; 95 % CI: 1.06 to 1.20) and 1-year (OR 1.11; 95 % CI: 1.02 to 1.22) mortality compared to no IT.  With low certainty from observational studies, rATG may decrease 5-year cardiac allograft vasculopathy (OR 0.82; 95 % CI: 0.74 to 0.90) compared to no IT, as well as 30-day (OR 0.85; 95 % CI: 0.80 to 0.92), 1-year (OR 0.87; 95 % CI: 0.79 to 0.96), and overall (HR 0.84; 95 % CI: 0.76 to 0.93) mortality compared to basiliximab.  The authors concluded that with low and very-low certainty in the synthetized evidence, these NMAs suggested possible superiority of rATG compared to basiliximab, but did not provide compelling evidence for the routine use of these agents in HTx recipients.

The authors stated that the main drawback of this trial  was the small number of contemporarily relevant RCTs available.  Furthermore, despite the multi-center design of a few studies, only a small number of subjects were included, making the NMAs for the outcomes examined to be under-powered, which may have prevented the identification of potential benefits with the use of IT.  In contrast to previous meta-analyses, this NMAs only combined studies with comparable outcomes at specific time-points.  While their more judicious approach strengthened the interpretation of data, it may have further diminished the statistical power to show significant differences.  In addition, although these researchers had planned to carry out specific sub-group analyses for the outcomes evaluated, they were limited by the number of studies available, subjects included, and the inconsistent reporting of the characteristics of interest.  Thus, these investigators were unable to examine different risk factors that may render IT to be more therapeutically strategic in specific patient populations with specific risk profiles.  For example, younger age, black race, reliance on ventricular assist device (VAD) support, higher levels of sensitization, and longer allograft ischemia times are known to be independently associated with a higher risk of mortality and rejection, and it was possible that IT could result in benefit in several of these subgroups, as suggested previously.  However, controversies surrounding the benefit of IT among those deemed to be at high-risk exist.  These researchers stated that given the inherent weaknesses of observational studies, the small sample size, and short follow-up periods of RCTs, and the uncertainty in the available evidence, further investigations are needed to ascertain the long-term effects of IT and help identify patient populations who may reap the highest benefit with IT.

Foroutan et al (2024) noted that the use of IT agents in the early post-HTx period remains controversial.  The following recommendations aim to provide guidance on the use of IT agents, including basiliximab and thymoglobulin, as part of routine care in HTx.  These investigators recruited an international, multi-disciplinary panel of 15 stake-holders, including patient partners, transplant cardiologists and surgeons, nurse practitioners, pharmacists, as well as methodologists.  They commissioned a systematic review on benefits and harms of IT on patient-important outcomes, and another on patients' values and preferences to inform their recommendations.  These researchers employed the GRADE approach to summarize their findings, rate certainty in the evidence, and develop recommendations.  The panel considered the balance between benefits and harms, certainty in the evidence, and patient's values and preferences, to make recommendations for or against the routine post-operative use of basiliximab or thymoglobulin.  The panel made recommendations on 3major clinical problems in HTx.  First, they suggested against the routine post-operative use of basiliximab compared to no IT.  Second, they suggested against the routine use of thymoglobulin compared to no IT.  Third, in patients for whom IT is appeared desirable, these investigators suggested the use of thymoglobulin as compared to basiliximab.  The authors concluded that this report highlighted gaps in available evidence and provided directions for clinical research to better understand the use of IT agents in the early post-HTx period, resulting in improved management and care.  These researchers stated that provision of higher quality evidence of overall effects of the agents, and examination of possible subgroup effects, will require large, rigorous, randomized trials.

Furthermore, an UpToDate review on “Heart transplantation in adults: Induction and maintenance of immunosuppressive therapy” (Pham, 2024) states that “The overall strategy of deciding whether to use induction therapy and identifying an optimal regimen to achieve a state of early intense immunosuppression remains controversial.  Approximately 40 to 50 % of heart transplant programs currently employ a strategy of augmented immunosuppression (induction therapy) during the early postoperative period.  Several antilymphocyte antibodies that target specific epitopes on the surface of both B and T cells have been used as part of induction therapy … Induction therapy may be of benefit in the subset of patients with the highest risk of acute rejection (pre-sensitized patients, young patients, female patients, and African American patients) and in patients with impaired renal function to allow delayed initiation of calcineurin inhibitors (CNIs) post-transplantation”.

Prospera Heart

The Prospera Heart test (Natera, Inc., San Carlos, CA) is a commercially available donor-derived cell-free DNA (dd-cfDNA) assay for the detection acute rejection, including antibody-mediated rejection (AMR) and acute cellular rejection (ACR) in heart transplantation. From a single blood test, the assay amplifies cfDNA by using a single nucleotide polymorphism (SNP)-based massively multiplexed-polymerase chain reaction followed by next-generation sequencing to measure the percentage of dd-cfDNA in transplant recipient’s blood. Donor versus recipient cfDNA is differentiated by targeting over 13,000 SNPs across ethnicities and using advanced bioinformatics. The result is reported as the percentage of dd-cfDNA in the transplant recipient’s blood, a predictor of acute rejection.

Kim and colleagues (2022) conducted a study to examine the performance characteristics of a novel test for detecting acute rejection (AR) in adult heart transplant (HTx) recipients.

Plasma samples with contemporaneous endomyocardial biopsy (EMB) were taken from HTx recipients. EMB is the reference surveillance test for AR in HTx recipients. The investigators used a clinically available single nucleotide polymorphism (SNP)-based massively multiplexed-polymerase chain reaction (PCR) dd-cfDNA assay (i.e., the Prospera test) to measure dd-cfDNA fraction. The dd-cfDNA fractions were evaluated with EMB-defined rejection status and test performance was assessed by constructing receiver operating characteristic (ROC) curves and calculating accuracy measures.

In total, 811 samples from 223 patients with dd-cfDNA testing and contemporaneous EMB were included in the study. The dd-cfDNA fraction was significantly higher in AR (median 0.58%, interquartile range [IQR], 0.13%-1.68%) compared to non-AR (median 0.04%, IQR, 0.01%-0.11%, correct p value [pc]< 0.001). ROC analysis created an area under the curve (AUC-ROC) of 0.86 (95% confidence interval [CI], 0.77-0.96). Defining samples with dd-cfDNA fraction ≥ 0.15% as AR yielded 78.5%  sensitivity (95% CI, 60.7%-96.3%) and 76.9% specificity (95% CI, 71.1%-82.7%). Positive and negative predictive values were 25.1% (95% CI, 18.8%-31.5%) and 97.3% (95% CI, 95.1%-99.5%) respectively, calculated using the cohort AR prevalence of 9.0% (95% CI, 5.3%-12.8%) with adjustment for repeat samples.

The investigators concluded that the novel dd-cfDNA test detects AR in HTx recipients with good accuracy and holds promise as a noninvasive test for AR in HTx recipients.

Rogers and colleagues (2023) conducted a retrospective, observational study comparing the testing accuracy for acute rejection of two commercially available dd-cfDNA and gene-expression profiling (GEP) testing in heart transplant (HTx) recipients.

Patients underwent standard and expanded single nucleotide polymorphism (SNP) dd-cfDNA. The investigators performed a comparison with GEP and assays were compared for correlation, accurate classification, and prediction for AR.

The study included 428 samples from 112 unique HTx patients. A positive standard SNP correlated with expanded SNP assay (p < .001). Both standard and expanded SNP tests showed low sensitivity (39%, p = 1.0) but high specificity (82% and 84%, p = 1.0) for AR. GEP did not improve sensitivity and showed worse specificity (p < .001) compared to standard dd-cfDNA.

The investigators found no significant difference between standard and expanded SNP assays in identifying AR. Additionally, they showed improved specificity without change in sensitivity using dd-cfDNA in place of GEP testing. They noted that prospective controlled studies are warranted to determine appropriate implementation of dd-cfDNA testing into clinical practice.

References