Congestive Heart Failure Telemonitoring:
Non-invasive telemonitoring for congestive heart failure involves the trans-telephonic transmission of weight, blood pressure (BP), heart rate (HR) and rhythm to a remote monitoring center. The Trans-European Network-Home-Care Management System (TEN-HMS) study is a randomized controlled clinical trial comparing home telemonitoring (HTM) to nurse telephone support (NTS) and usual care (UC) for patients with heart failure who are at high-risk of hospitalization or death. The study found that patients assigned to HTM did not have significantly fewer days dead or hospitalized (the primary study endpoint) than patients assigned to NTS or UC. In this study, 426 patients recruited from hospitals in the Netherlands, the United Kingdom, and Germany with a recent (within the past 6 weeks) hospital admission for heart failure and left ventricular ejection fraction (LVEF) less than 40 % were assigned randomly to HTM, NTS, or UC in a 2:2:1 ratio. Patients were taking at least 40 mg per day of furosemide or equivalent, and at least 1 marker of increased risk. Home telemonitoring consisted of twice-daily patient self-measurement of weight, BP, HR, and rhythm with automated devices linked to a cardiology center. The NTS consisted of specialist nurses who were available to patients by telephone. Primary care physicians delivered UC. The primary end point was days dead or hospitalized with NTS versus HTM at 240 days. The investigators reported that, during 240 days of follow-up, there was no statistically significant difference in the days that were lost as the result of death or hospitalization for UC, NTS, and HTM. The number of admissions and mortality were similar among patients randomly assigned to NTS or HTM, but the mean duration of admission was less in patients assigned to HTM. The investigators concluded that “[f]urther investigation and refinement of the application of HTM are warranted because it may be a valuable role for the management of selected patients with heart failure.”
Heart failure guidelines from the National Institute for Clinical Excellence (2003) stated that “[m]ore complex remote monitoring (such as telemonitoring) of patients with heart failure is in its infancy, but shows promise for the future.”
In a systematic review, Chaudhry et al (2007) examined the evidence on telemonitoring in patients with chronic heart failure. Interventions included telephone-based symptom monitoring (n = 5), automated monitoring of signs and symptoms (n = 1), and automated physiologic monitoring (n = 1). Two studies directly compared effectiveness of 2 or more forms of telemonitoring. Study quality and intervention type varied considerably. Six studies suggested reduction in all-cause and heart failure hospitalizations (14 % to 55 % and 29 % to 43 %, respectively) or mortality (40 % to 56 %) with telemonitoring. Of the 3 negative studies, 2 enrolled low-risk patients and patients with access to high quality care, whereas 1 enrolled a very high-risk Hispanic population. Studies comparing forms of telemonitoring demonstrated similar effectiveness. However, intervention costs were higher with more complex programs (8,383 dollars per patient per year) versus less complex programs (1,695 dollars per patient per year). The authors concluded that the evidence base for telemonitoring in heart failure is currently quite limited. Furthermore, an editorial published in the British Medical Journal (Grancelli and Ferrante, 2007), which addressed another systematic evidence review found similar results with simple telephone interventions compared to complex congestive heart failure telemonitoring.
Dang et al (2009) evaluated the evidence base for the use of home telehealth remote monitoring in elderly with congestive heart failure (CHF). The search was restricted to randomized controlled trials using either automated monitoring of signs and symptoms or automated physiologic monitoring. For this review, telephone-based monitoring of signs and symptoms was not considered remote monitoring. Studies were also excluded if they did not present outcomes related to healthcare utilization. A total of 9 studies met selection criteria, with interventions that varied greatly. Four 3-arm studies directly compared the effectiveness of 2 different interventions to usual care. Six of the 9 studies suggested a 27 % to 40 % reduction in overall admissions. Two 2-arm studies demonstrated a 40 % to 46 % reduction in HF-related admissions while 2 other 3-arm studies showed similar trends; however, this was not statistically significant. Three of 9 studies suggested a significant reduction in mortality (30 % to 67 %) and 3 studies showed significant reduction in healthcare utilization costs. Two studies suggested a 53 % to 62 % reduction in bed days of care. Two studies showed significant reduction in the number of Emergency Department visits. Three 2-arm studies and 1 3-arm study demonstrated significant overall improvement in outcomes with use of telemonitoring. Available data suggest that telemonitoring is a promising strategy. The authors stated that more data are needed to determine the ideal patient population, technology, and parameters, frequency and duration of telemonitoring, and the exact combination of case management and close monitoring that would assure consistent and improved outcomes with cost reductions in CHF.
Mortara and co-workers (2009) assessed the feasibility of a new system of HTM. The HTM system was used to monitor clinical and physiological parameters, and its effectiveness (compared with usual care) in reducing cardiac events in heart failure (HF) patients was evaluated. Measurements were patient-managed. From 2002 to 2004, a total of 461 HF patients (age 60 +/- 11 years, New York Heart Association class 2.4 +/- 0.6, left ventricular ejection fraction 29 +/- 7 %) were enrolled at 11 centers and randomized (1:2) to either usual outpatient care or HTM administered as 3 randomized strategies: (i) monthly telephone contact; (ii) strategy 1 plus weekly transmission of vital signs; and (iii) strategy 2 plus monthly 24-hr recording of cardiorespiratory activity. Patients completed 81 % of vital signs transmissions, as well as 92 % of cardio-respiratory recordings. Over a 12-month follow-up, there was no significant effect of HTM in reducing bed-days occupancy for HF or cardiac death plus HF hospitalization. Post-hoc analysis revealed a heterogeneous effect of HTM in the 3 countries (Italy, Poland, and the United Kingdom) with a trend towards a reduction of events in Italy. The authors concluded that Home or Hospital in Heart Failure Study indicated that self-managed HTM of clinical and physiological parameters is feasible in HF patients, with surprisingly high compliance. Whether HTM contributes to a reduction of cardiac events requires further investigation.
Schmidt and colleagues (2010) reviewed the current status of health services research on telemonitoring, focusing on patients with chronic CHF. The Medline database was selectively searched for articles appearing from June 2001 to May 2008, with an emphasis on randomized, controlled trials. The available scientific data on vital signs monitoring are limited, yet there is evidence for a positive effect on some clinical endpoints, particularly mortality. However, any possible improvement of patient-reported outcomes, such as the quality of life, still remains to be demonstrated. The authors concluded that these findings suggested that telemonitoring is effective, yet there is no evidence for superior outcomes with any particular model of care incorporating telemonitoring (i.e., monitoring of vital signs versus structured telephone monitoring). A valid criticism is that the individual components of HTM have not yet been separately tested in order to compare their individual effects.
Polisena and associates (2010) conducted a systematic review of the literature about HTM compared with usual care. An electronic literature search was conducted to identify studies of HTM use in CHF patients. A total of 21 original studies on HTM for patients with CHF were included (n = 3,082). A random effects model was used to compute treatment effectiveness to measure the average effect of the intervention across all studies where the quantitative pooling of results was appropriate. Home telemonitoring reduced mortality (risk ratio = 0.64; 95 % confidence interval [CI]: 0.48 to 0.85) compared with usual care. Several studies suggested that HTM also helped to lower the number of hospitalizations and the use of other health services. Patient quality of life and satisfaction with HTM were similar or better than with usual care. Moreover, the authors stated that more studies of higher methodological quality are needed to provide more precise information regarding the potential clinical effectiveness of home telehealth interventions.
Koehler et al (2011) examined if physician-led remote telemedical management (RTM) compared with usual care would result in reduced mortality in ambulatory patients with CHF. A total of 710 stable CHF patients in New York Heart Association (NYHA) functional class II or III with a LVEF of less than or equal to 35 % and a history of HF decompensation within the previous 2 years or with a LVEF of less than or equal to 25 % were enrolled in this study. Patients were randomly assigned (1:1) to RTM or usual care. Remote telemedical management used portable devices for ECG, BP, and body weight measurements connected to a personal digital assistant that sent automated encrypted transmission via cell phones to the telemedical centers. The primary end point was death from any cause. The first secondary end point was a composite of cardiovascular death and hospitalization for HF. Baseline characteristics were similar between the RTM (n = 354) and control (n = 356) groups. Of the patients assigned to RTM, 287 (81 %) were at least 70 % compliant with daily data transfers and no break for greater than 30 days (except during hospitalizations). The median follow-up was 26 months (minimum 12), and was 99.9 % complete. Compared with usual care, RTM had no significant effect on all-cause mortality (hazard ratio, 0.97; 95 % CI: 0.67 to 1.41; p = 0.87) or on cardiovascular death or HF hospitalization (hazard ratio, 0.89; 95 % CI, 0.67 to 1.19; p = 0.44). The authors concluded that in ambulatory patients with CHF, RTM compared with usual care was not associated with a reduction in all-cause mortality.
A systematic evidence review (Molloy et al, 2012) examined interventions to enhance adherence to medications in patients with heart failure identified randomized controlled studies of intensified interventions. The review found that all of the six studies of intensified patient care that used direct patient contact intervention showed a significant positive effect on adherence. However, of the five studies of intensified patient that used telephone or telemonitoring programs, only one led to increased adherence.
An assessment by the California Technology Assessment Forum (Tice, 2011) found that home telemonitoring for patients with heart failure does not meet CTAF TA Criterion 3 through 5 for safety, effectiveness and improvement in health outcomes. CTAF's systematic review of the literature identified 17 trials that randomized 6352 patients to evaluate the efficacy of home telemonitoring. The settings, patient populations, interventions, control groups, outcomes and length of follow-up varied widely between the studies. Because of the heterogeneity in the trials and their outcomes,CTAF performed no formal metaanalysis. The CTAF assessment noted that two large, high quality trials that randomized 2363 patients were published near the time of the CTAF assessment (Tele-HF, TIM-HF) (citing Chaudhry, et al., 2010 and Koehler, et al., 2011). CTAF noted that neither study found any benefit to home monitoring compared with usual care. Mortality was 11% in both groups in one study and 15% in both groups in the other study. In both studies, hospitalization rates were slightly higher in the home telemonitoring groups (Tele-HF 49% versus 47%; TIM-HF 44% versus 39%). The CTAF assessment observed that there were not even trends in favor of home telemonitoring. At the time of the CTAF assessment, there are at least two additional large studies that have yet to be published (TEHAF, OptiLink-HF); the CTAF assessment noted that preliminary results from one of the studies were negative. The CTAF assessment noted that the strongly positive findings in some of the randomized trials suggest that there are subgroups of patients with HF who benefit from some form of telemonitoring. The CTAF assessment stated, however, that the published literature to date does not clearly identify which patients are mostlikely to benefit and what combination of home monitoring technologies are required to obtain optimal results.
Kitsiou et al (2013) evaluated the methodology, quality, and reporting characteristics of prior reviews that have investigated the effects of HTM interventions in the context of chronic diseases. Ovid MEDLINE, the Database of Abstract of Reviews of Effects (DARE), and Health Technology Assessment Database (HTA) of the Cochrane Library were electronically searched to find relevant systematic reviews, published between January 1966 and December 2012. Potential reviews were screened and assessed for inclusion independently by 3 reviewers. Data pertaining to the methods used were extracted from each included review and examined for accuracy by 2 reviewers. A validated quality assessment instrument, R-AMSTAR, was used as a framework to guide the assessment process. A total of 24 reviews, 9 of which were meta-analyses, were identified from more than 200 citations. The bibliographic search revealed that the number of published reviews has increased substantially over the years in this area and although most reviews focus on studying the effects of HTM on patients with CHF, researcher interest has extended to other chronic diseases as well, such as diabetes, hypertension, chronic obstructive pulmonary disease, and asthma. Nevertheless, an important number of these reviews appear to lack optimal scientific rigor due to intrinsic methodological issues. Also, the overall quality of reviews did not appear to have improved over time. While several criteria were met satisfactorily by either all or nearly all reviews, such as the establishment of an a priori design with inclusion and exclusion criteria, use of electronic searches on multiple databases, and reporting of studies characteristics, there were other important areas that needed improvement. Duplicate data extraction, manual searches of highly relevant journals, inclusion of gray and non-English literature, assessment of the methodological quality of included studies and quality of evidence were key methodological procedures that were performed infrequently. Furthermore, certain methodological limitations identified in the synthesis of study results have affected the results and conclusions of some reviews. The authors concluded that despite the availability of methodological guidelines that can be utilized to guide the proper conduct of systematic reviews and meta-analyses and eliminate potential risks of bias, this knowledge has not yet been fully integrated in the area of HTM. Moreover, they stated that further efforts should be made to improve the design, conduct, reporting, and publication of systematic reviews and meta-analyses in this area.
Pandor and colleagues (2013) examined the clinical effectiveness and cost-effectiveness of HTM or structured telephone support (STS) strategies compared with usual care for adult patients who have been recently discharged (within 28 days) from acute care after a recent exacerbation of HF. A total of 14 electronic databases (including MEDLINE, EMBASE, PsycINFO and The Cochrane Library) and research registers were searched to January 2012, supplemented by hand-searching relevant articles and contact with experts. The review included randomized controlled trials (RCTs) or observational cohort studies with a contemporaneous control group that included the following remote monitoring (RM) interventions: (i) TM (including cardiovascular implanted monitoring devices) with medical support provided during office hours or 24/7; (ii) STS programs delivered by human-to-human contact (HH) or human-to-machine interface (HM). A systematic review and network meta-analysis (where appropriate) of the clinical evidence was carried out using standard methods. A Markov model was developed to evaluate the cost-effectiveness of different RM packages compared with usual care for recently discharged HF patients. Tele-monitoring 24/7 or using cardiovascular monitoring devices was not considered in the economic model because of the lack of data and/or unsuitability for the United Kingdom (UK) setting. Given the heterogeneity in the components of usual care and RM interventions, the cost-effectiveness analysis was performed using a set of costing scenarios designed to reflect the different configurations of usual care and RM in the UK. The literature searches identified 3,060 citations; 6 RCTs met the inclusion criteria and were added to the 15 trials identified from the previous systematic reviews giving a total of 21 RCTs included in the systematic review. No trials of cardiovascular implanted monitoring devices or observational studies met the inclusion criteria. The methodological quality of the studies varied widely and reporting was generally poor. Compared with usual care, RM was beneficial in reducing all-cause mortality for STS HH [hazard ratio (HR) 0.77, 95 % credible interval (CrI): 0.55 to 1.08], TM during office hours (HR 0.76, 95 % CrI: 0.49 to 1.18) and TM 24/7 (HR 0.49, 9 5% CrI: 0.20 to 1.18); however, these results were statistically inconclusive. The results for TM 24/7 should be treated with caution because of the poor methodological quality of the only included study in this network. No favorable effect on mortality was observed with STS HM. Similar reductions were observed in all-cause hospitalizations for TM interventions, whereas STS interventions had no major effect. A sensitivity analysis, in which a study was excluded because it provided better-than-usual support to the control group, showed larger beneficial effects for most outcomes, particularly for TM during office hours. In the cost-effectiveness analyses, TM during office hours was the most cost-effective strategy with an estimated incremental cost-effectiveness ratio (ICER) of £11,873 per quality-adjusted life-year (QALY) compared with usual care, whereas STS HH had an ICER of £228,035 per QALY compared with TM during office hours. Structured telephone support HM was dominated by usual care. Similar results were observed in scenario analyses performed using higher costs of usual care, higher costs of STS HH and lower costs of TM during office hours. The authors concluded that despite wide variation in usual care and RM strategies, cost-effectiveness analyses suggested that TM during office hours was an optimal strategy (in most costing scenarios). However, clarity was lacking among descriptions of the components of RM packages and usual care and there was a lack of robust estimation of costs. The y stated that further research is needed in these areas.
Invasive Congestive Heart Failure Monitoring:
Implantable hemodynamic monitoring devices have features that allow remote monitoring of hemodynamic data in patients with HF. The Chronicle Implantable Hemodynamic Monitor (IHM) is approximately the size of a pacemaker. The device consists of an implantable monitor and a transvenous lead carrying a pressure sensor. The pressure-sensing lead continuously measures intra-cardiac pressure, body temperature, physical activity, and HR. It contains integrated circuitry, a lithium silver vanadium oxide battery with an approximate life of 3 years, and a bi-directional telemetry transmission coil hermetically sealed in a titanium can. The Chronicle IHM has an investigational device exemption in the United States, which allows use of the device in clinical trials.
Bourge et al (2008) reported on the outcomes of the COMPASS-HF (Chronicle Offers Management to Patients with Advanced Signs and Symptoms of Heart Failure) study, a randomized, single-blinded, multi-center controlled study of the Chronicle IHM in 274 persons with NYHA class III or IV CHF. All study subjects had an emergency room visit or at least 1 prior HF-related hospitalization within 6 months of entering the study. The 274 successfully implanted patients were randomized to receive either optimal medical care alone (n = 140) or optimal medical care guided by results from hemodynamic measurements provided by the Chronicle IHM (n = 134). For the first 6 months, all IHM patients transmitted monitoring data weekly. Physicians for the control group were blocked from receiving IHM data. After 6 months, all physicians received IHM information for patient care. The primary end point of the study was a statistically significant reduction in treatment events, as defined by hospitalizations for HF, or emergency or urgent care center visits requiring intravenous therapy. Patients whose physicians had access to IHM data had 22 % lower HF-related events; however this difference in the primary study end point was not statistically significant (p = 0.33). However, in the NYHA class III subgroup, there was a statistically significant 41 % reduction in the event rate for those patients whose physicians were accessing IHM data. The class IV (severe) subgroup did worse than the control group. The event rate over the course of the 6 months was 0.70 for IHM-monitored patients whose physicians could see the data, compared to 0.89 for the control group. Patients whose physicians had access to IHM data also had 21 % fewer hospitalizations. The relative risk of HF hospitalizations was 0.79 in the group with access to IHM data compared to the blocked access group, a difference that was statistically significant. A retrospective analysis of the time to first HF hospitalization showed a 36 % reduction (p = 0.03) in the relative risk of a HF-related hospitalization in the IHM group. In addition, the group whose physicians had access to IHM data had a 46 % increase in the proportion of patients who improved over the 6 months and a 34 % reduction in the proportion who worsened, compared to 35 % and 51 % in the control group, respectively. Primary safety related study end points were met, including freedom from system-related complications and freedom from pressure-sensor failure. System-related complications occurred in 8 % of the 277 patients who underwent implantation, and all but 4 complications were successfully resolved. There were no pressure-sensor failures after 6 months.
The Canadian Agency for Drugs and Technologies in Health's assessment on implantable hemodynamic monitoring (the Chronicle IHM System) (Ho, 2008) stated that preliminary evidence from observational studies suggested a potential for reducing hospitalizations with the use of right ventricle implantable hemodynamic monitoring (IHM). The assessment noted, however, although a multi-center, randomized controlled trial (COMPASS-HF) showed a reduction in hospitalizations in the IHM group, the results were not statistically significant and the U.S. FDA panel concluded the trial failed to meet its primary efficacy end point. The assessment noted that, in the COMPASS-HF study, the most common device-related complication was lead dislodgement. The report stated that large randomized controlled trials are needed to demonstrate the clinical utility of IHM, particularly in terms of its impact on reducing hospitalization and improving patient outcomes.
Abraham (2013) noted that HF represents a major public health concern, associated with high rates of morbidity and mortality. A particular focus of contemporary HF management is reduction of hospital admission and re-admission rates. While optimal medical therapy favorably impacts the natural history of the disease, devices such as cardiac resynchronization therapy devices and implantable cardioverter defibrillators have added incremental value in improving HF outcomes. These devices also enable remote patient monitoring via device-based diagnostics. Device-based measurement of physiological parameters, such as intra-thoracic impedance and HR variability, provide a means to assess risk of worsening HF and the possibility of future hospitalization. Beyond this capability, implantable hemodynamic monitors have the potential to direct day-to-day management of HF patients to significantly reduce hospitalization rates. The use of a pulmonary artery pressure measurement system has been shown to significantly reduce the risk of HF hospitalization in a large RCT, the CardioMEMS Heart Sensor Allows Monitoring of Pressure to Improve Outcomes in NYHA Class III Heart Failure Patients (CHAMPION) trial. Observations from a pilot study also supported the potential use of a left atrial pressure monitoring system and physician-directed patient self-management paradigm; these observations are under further investigation in the ongoing LAPTOP-HF trial.
Automated Oscillometer Blood Pressure Monitors:
Barker et al (2000) stated that according to the criteria of the British Hypertension Society, neither the Dinamap 8100 nor the Omron M1 can be recommended for use in children in clinical situations in which accuracy of the absolute measurement is required.
Beaubien and colleagues (2002) reported that the Dinamap yields inaccurate estimates of both systolic and diastolic BP even under standardized, and thus optimal, conditions. This inaccuracy is exaggerated at higher BP (over 160/90 mm Hg), although the number of measurements at higher pressures was small. The authors recommended that this device not be used when accurate BP measurement is needed for therapeutic decision-making.
Chang and colleagues (2003) evaluated the variability in observed BP associated with use of the Dinamap monitor (Dinamap PRO 100) and estimated the contributions of various factors to that variability. In 60 volunteers (30 aged 23 to 35 years and 30 aged 54 to 82 years), the authors obtained 30 simultaneous paired BP measurements in both arms at 1-min intervals. Variability, defined as the between-arm difference in BP measurements, was analyzed using a mixed-effects linear regression model. A total of 1,800 paired BP measurements were obtained. These researchers found that only 50 % of paired simultaneous BP measurements obtained were in agreement within 4 mm Hg for systolic BP or within 3 mm Hg for diastolic BP. Residual variability, attributable to the intrinsic inaccuracy of the device, accounted for 64 to 82 % of the total systolic and diastolic BP variability. The majority of variability in BP measurement was due to the device as used under the study conditions.
Textor et al (2003) reported that 26 % (62 of 238) potential donors with excellent kidney function were mis-classified as hypertensive with clinic oscillometric measurements (Dinamap) alone. Ramanathan et al (2003) claimed that there is no role for standard automated oscillometric devices (Dinamap) in the calculation of ankle-brachial pressure index in the vascular clinic.
Afzali et al (2004) examined if there are differences in BP measurements taken using either automated oscillometric machines (Dinamap BP8800 and Omron Hem 713) or a random zero Hawskley sphygmomanometer in stable healthy renal transplant outpatients. These investigators concluded that there were no significant observer bias or cardiovascular artifacts. Intra-machine variability was small. Blood pressure measurements using Dinamap and Omron could lead to a difference of up to 30 mm Hg higher or 15 mm Hg lower than Hawskley random zero BP readings. Though widely used for convenience, automated oscillometric measures of BP in the renal transplant clinic are not optimal.
Dannevig et al (2005) concluded that BP should preferably be measured invasively in severely ill neonates and preterm infants, being aware of pitfalls with measurements using different oscillometer monitors and the size/arm circumference of the infant.
The BpTRU™ is an automated device that takes serial BP measurements in a physician’s office. The Canadian Agency for Drugs and Technologies in Health (Allison, 2006) stated that preliminary data from non-randomized, uncontrolled studies suggested that the average of 5 BP measurements by means of the BpTRU, taken while the patient is alone, more reliably reflects resting BP compared to standard manual measurements taken with a stethoscope and sphygmomanometer. Moreover, the report noted that more controlled studies are needed to compare BpTRU measurements at specific interval settings to standard measurements taken by trained clinicians across a spectrum of patients. This evidence is needed before specific recommendations can be made in guidelines regarding which BP monitor should be used preferentially in a physician’s office.
Fischell et al (2010) conducted the first clinical studies of intracardiac ST-segment monitoring in ambulatory humans. The authors reported that intracardiac monitoring was performed in 37 patients at high risk for acute coronary syndromes and the implanted monitor continuously evaluated ST segments as sensed by a conventional pacemaker right ventricle apical lead. Patients were alerted to detected ischemic events. The patients were followed for a median of 1.52 years. Four patients had ST segment changes of greater than or equal to 3 standard deviations of their normal daily range, in the absence of an elevated heart rate. In combination with immediate hospital monitoring, the results led to angiogram and/or intravascular ultrasonographic confirmation of thrombotic coronary occlusion/ruptured plaque. The authors concluded that shifts exceeding 3 standard deviations from a patient’s daily intracardiac ST-segment range may be a sensitive/specific marker for thrombotic coronary occlusion and that patient alerting was associated with a median alert-to-door time of 19.5 minutes for patients at high risk of recurrent coronary syndromes, who typically present with 2 to 3 hour delays.
The AngelMed Guardian is an implantable device which records cardiac data and detects ischemic events through use of a standard pacemaker intracardiac lead placed in the right ventricular apex. The AngelMed Guardian detects acute ischemic events by analyzing ST-segment shifts, and if a shift is detected as greater than a heart rate-dependent programmable threshold, the device will generate an emergency alert signal. As of 2009, the AngelMed Guardian had been implanted in 55 people in the United States and Brazil (Hopenfeld et al, 2009).
The AngelMed Guardian remains an investigational device in the United States (AngelMed, 2012). Currently, a prospective, randomized multicenter study of subjects with a high-risk of having a myocardial infarction (MI) due to acute coronary syndrome or bypass surgery is underway. Subjects are being recruited in to the AngelMed for Early Recognition and Treatment of STEMI (ALERTS) Study, which has an open-label, crossover design; the primary efficacy objective is to determine whether the Guardian System reduces the composite of cardiac or unexplained death, new Q-wave MI and time-to-door for a confirmed occlusive event at a medical facility (Angel Medical Systems, 2012).