The Heart Failure Society of America (2010) defines heart failure as "a syndrome caused by cardiac dysfunction, generally resulting from myocardial muscle dysfunction or loss and characterized by either left ventricular (LV) dilation or hypertrophy or both." Heart failure is a major public health problem that affects nearly 6 million Americans each year (Roger et al, 2011). Heart failure (HF) is the cause for 12 to 15 million office visits and 6.5 million hospital days per year and can result from any structural or functional cardiac disorder that impairs the ability of the ventricle to fill with or eject blood (Hunt et al, 2009). Morbidity and mortality from HF remains high despite advances in evaluation and management with rehospitalization rates of 20% at one month and nearly 50% at 6 months (Ritzema et al, 2010). Bui et al (2012) state that the majority of these HF hospitalizations result from worsening congestion in patients previously diagnosed with HF. Arenja et al (2011) prospectively enrolled 610 consecutive patients presenting to the emergency department with acute HF and followed them for 1 year to determine risk stratification for mortality; a total of 201 patients (33%) died within 360 days and the investigators' analysis identified blood urea nitrogen and age as the best single predictors of 1-year mortality.
Kommuri et al (2012) studied the impact of prior HF hospitalizations on long-term mortality in 2,221 HF patients in a prospective cohort study. They found that in otherwise "low-risk" HF inpatients, a history of 2 or more HF hospitalizations within the prior 12 months markedly increases 1-year mortality risk. Bui et al (2012) report that "earlier identification and treatment of congestion together with improved care coordination, management of comorbid conditions, and enhanced patient self-management may help to prevent hospitalizations in patients with chronic HF. Such home monitoring extends from the promotion of self-care and home visitations to telemedicine and remote monitoring of external or implantable devices."
Giordano et al (2011) enrolled 358 HF patients in a 6 month home-based telemanagement (HBT) program and observed that on re-evaluation after 6 months (238 patients) there was a general improvement in clinical, functional, and quality of life (QoL) status and a significant increase in the mean daily dosage of beta-blockers prescribed. Although Giordano et al (2011) concluded that HBT for patients with congestive HF is associated with favorable effects on hospital readmission for cardiovascular reasons and on QoL, they also noted that a more comprehensive multidisciplinary approach would probably be required to obtain favorable effects on total morbidity.
Recent research has focused on the use of ambulatory hemodynamic monitoring in chronic HF patients and continuous implantable hemodynamic monitoring devices have been introduced as a potential means to improve outcomes in these patients. The American College of Cardiology/American Heart Association Guidelines for the Diagnosis and Management of Heart Failure in Adults state that implantable hemodynamic monitors used for the chronic, remote, outpatient monitoring of ventricular filling pressures and other hemodynamic and clinical variables in HF patients are hypothesized to be of benefit as changes in therapy to optimize LV filling pressure may improve outcomes in HF patients (Hunt et al, 2009). One such device used to measure left atrial pressure (LAP) is the HeartPod® system (St Jude Medical, CRMD, Sylmar, CA), which consists of an implantable sensor lead and coil antenna; the sensor module is affixed to the atrial septum by proximal and distal folding nitinol. The implantation procedure is conducted through performing a right heart catherization with a Swan Ganz catheter. After removing the delivery sheath, the proximal lead connector is affixed to the antenna and placed in a subcutaneous pocket anchors (Troughton et al, 2010). Troughton et al. (2010) state that the handheld Patient Advisor Module device, which is used to interrogate the sensor by placing the module in proximity to the device, uses a standard algorithm to compute mean LAP.
The first reported study of an implantable left atrial hemodynamic monitor was conducted by Ritzema et al. (2007) in eight male patients with established heart failure and at least 1 heart failure hospitalization or unplanned outpatient visit for parenteral therapy during the previous 12 months. The eight subjects from this single center were enrolled in a prospective, multicenter, nonrandomized, open-label feasibility clinical trial called the Hemodynamically Guided Home Self-Therapy in Severe Heart Failure Patients (HOMEOSTASIS I). The LAP hemodynamic monitor device (HeartPOD®) was implanted in all patients without device related complications or systemic emboli. The device consisted of an implantable sensor lead coupled with a subcutaneous antenna coil, a patient advisory module (PAM), and the clinician’s personal computer software. The sensor system was implanted into the atrial septum oriented to the left atrium. Twelve-weeks post implantation 87% of device LAP measurements were within + / - 5 mm Hg of simultaneous pulmonary capillary wedge pressure readings over a wide range of pressures (1.6 to 71 mm Hg). Net drift corrected by calibration was -0.2 + / - 1.9 mm Hg. The authors concluded that although ambulatory monitoring of direct LAP was well tolerated, feasible, and accurate at a short-term follow-up, further follow-up and investigation were warranted to evaluate the clinical utility of LAP monitoring in patients with heart failure.
The COMPASS-HF (Chronicle Offers Management to Patients with Advanced Signs and Symptoms of Heart Failure) study was conducted by Bourge et al. (2008) COMPASS-HF was a prospective, multicenter, randomized, single-blind, parallel-controlled trial of 274 New York Heart Association functional class III or IV HF patients who received an implantable continuous hemodynamic monitor. Patients were randomized to a Chronicle implantable continuous hemodynamic monitoring device (Medtronic Inc., Minneapolis, MN) (n = 134) or a control group (n = 140). The investigators concluded that, compared with control patients, the Chronicle group had a nonsignificant 21% reduction (p = 0.33) in the rate of all HF-related events and a 36% reduction (p = 0.03) in the relative risk of a first HF-related hospitalization. The investigators therefore recommended that additional trials be conducted to establish the clinical benefit of implantable continuous hemodynamic monitor–guided care in patients with advanced HF.
Ritzema et al. (2010) conducted a physician-directed patient self-management of left atrial pressure in advanced chronic heart failure study in forty patients with reduced or preserved left ventricular ejection fraction and acute decompensation. All enrolled patients were implanted with an investigational left atrial pressure monitor. Event-free survival was determined over a median follow-up period of 25 months. Survival without decompensation was 1% at 3 years and events decreased in frequency at the first 3 months following implantation (p < 0.012). Mean daily left arterial pressure fell from 17.6 mm Hg during the first 3 months to 14.8 mm during pressure-guided therapy (p = 0.003). There were statistically significant improvements in NYHA class (p < 0.001) and left ventricular ejection fraction (p < 0.001). The authors concluded that physician-directed patient self-management of left atrial pressure has the potential to improve hemodynamic, symptoms, and outcomes in advanced heart failure. The authors also acknowledge, however, that this was a small observational study and that these results suggest that outpatient hemodynamic monitoring linked to a self-management therapeutic strategy could change current management of advanced heart failure and potentially facilitate more optimal therapy and improved outcomes.
Troughton et al (2010) evaluated the HeartPOD® left atrial hemodynamic monitoring system in 84 advanced HF patients. The investigators conducted a prospective, multicenter, observational open-label registry study the results of which showed that comparisons of LAP with pulmonary capillary wedge pressure (PCWP) generally showed a high degree of concordance. The implanted left atrial monitor measurement of LAP differed from PCWP by > 5 mmHg in 20% of readings. However, the authors stated that these disagreements were likely miscalibration of the Swan Ganz catheter, the implanted LAP sensor, or both. Freedom from device failure was 95% at 2 years and 88% at 4 years. There were no instances of device failure or anomaly associated with clinical worsening. The authors concluded that high-fidelity LAP measurements were accurate and closely predicted PCWP over a 12-month period.
St Jude Medical is currently sponsoring a Phase III randomized, open label trial of the HeartPOD™ System or Promote® LAP System. This trial is currently recruiting participants and the primary outcome measures will be safety and efficacy. Safety will be demonstrated by evaluating the freedom from study-related major adverse cardiovascular and neurological events (MACNE) following twelve months of treatment. Effectiveness will be determined by evaluating the reduction in the relative risk of Heart Failure MACNE between the Treatment and Control groups (St. Jude Medical, 2011). The HeartPOD® and Promote® LAP System have not to date received approval for use in the United States by the Food and Drug Administration.