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Intrathoracic Impedance Monitoring, Audible Patient Alerts, and Outcomes in Patients With Heart Failure
Study Questions:
Does intrathoracic impedance monitoring with patient alerts lead to improved outcomes in chronic systolic heart failure (HF)?
Methods:
Patients (n = 335) with chronic systolic HF (left ventricular ejection fraction ≤35% and New York Heart Association [NYHA] II-IV HF) and an implantable cardioverter defibrillator (with or without cardiac resynchronization [CRT]) underwent unblinded randomization to intrathoracic impedance monitoring using OptiVol versus standard HF care. In the OptiVol arm, an audible tone was activated to alert patients to a reduction in thoracic impedance, suggesting the presence of increased pulmonary fluid. Patients were then instructed to call their physician and treatment was provided according to a standardized intervention algorithm. The primary outcome of interest was a composite of all-cause mortality and HF hospitalizations, assessed using Cox modeling.
Results:
The study was terminated early due to poor enrollment. Of the intended 2,400 patients, 345 were recruited and randomized to OptiVol (n = 168) or standard care (n = 167). The mean ± standard deviation patient age was 64 ± 10 years, 86% were male, and 82% had a CRT component to their ICD. Baseline NYHA was class I in 3%, class II in 60%, class III in 36%, and class IV in 1%. Over a mean 14.9 ± 5.4 months of follow-up, there 131 events (34 deaths, 96 HF hospitalizations, 1 transplant) in 81 patients. Of these patients, 48 events occurred in the OptiVol arm and 33 were in controls (hazard ratio [HR], 1.52; 95% confidence interval [CI], 0.97-2.32; p = 0.06). The risk of HF hospitalization was significantly higher in the OptiVol arm (HR, 1.79; 95% CI, 1.08-2.95), but there was no significant difference in mortality (HR, 1.24; 95% CI, 0.63-2.44; p = 0.54 for OptiVol vs. control). Patients in the OptiVol arm also had more outpatient visits (n = 250) than controls (n = 84; p < 0.0001); 58% (n = 144) of the visits in the OptiVol group were associated with an OptiVol alert and 79% of alerts were the sole reason for a clinic appointment.
Conclusions:
The authors concluded that implantable intrathoracic impedance monitoring does not improve outcomes in patients with chronic HF, and leads to increased practitioner utilization.
Perspective:
Readmissions for HF remain high, and the concept of a device that alerts practitioners to volume retention is intriguing. Like any test, the alert needs to come early enough to allow for successful HF intervention and carry a low false-positive percentage. In this analysis, impedance monitoring through OptiVol technology did not lead to improved outcomes. Rather, it led to increased ‘noise.’ However, the design of this trial may have led to OptiVol’s ‘failure.’ Mandating practitioner-patient contact at the threshold alert without any other clinical information is like mandating contact for a B-type natriuretic peptide threshold. OptiVol should be used in conjunction with other clinical information (e.g., weight, symptoms, labs, arrhythmias, change in activity) to guide HF intervention. Finally, responses to threshold alerts that are thought to be HF related should be heavily directed at neurohormonal blockade and not solely diuretic intervention.
Keywords: Follow-Up Studies, Chronic Disease, Electric Impedance, Diuretics, New York, Heart Failure, Systolic, Systole, Heart Transplantation, Cardiac Resynchronization Therapy, Prostheses and Implants, Incidence, Cardiography, Impedance, Proportional Hazards Models, Outpatients, Heart Failure, Stroke Volume, Confidence Intervals, Defibrillators, Implantable, Natriuretic Peptide, Brain
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