Intrathoracic Impedance Monitoring, Audible Patient Alerts, and Outcome in Patients With Heart Failure

Heart failure is associated with frequent hospitalizations, often resulting from volume overload. Measurement of intrathoracic impedance with an implanted device with an audible patient alert may detect increases in pulmonary fluid retention early. We hypothesized that early intervention could prevent hospitalizations and affect outcome.We studied 335 patients with chronic heart failure who had undergone implantation of an implantable cardioverter-defibrillator alone (18%) or with cardiac resynchronization therapy (82%). All devices featured a monitoring tool to track changes in intrathoracic impedance (OptiVol) and other diagnostic parameters. Patients were randomized to have information available to physicians and patients as an audible alert in case of preset threshold crossings (access arm) or not (control arm). The primary end point was a composite of all-cause mortality and heart failure hospitalizations. During 14.9±5.4 months, this occurred in 48 patients (29%) in the access arm and in 33 patients (20%) in the control arm (P=0.063; hazard ratio, 1.52; 95% confidence interval, 0.97-2.37). This was due mainly to more heart failure hospitalizations (hazard ratio, 1.79; 95% confidence interval, 1.08-2.95; P=0.022), whereas the number of deaths was comparable (19 versus 15; P=0.54). The number of outpatient visits was higher in the access arm (250 versus 84; P<0.0001), with relatively more signs of heart failure among control patients during outpatient visits. Although the trial was terminated as a result of slow enrollment, a post hoc futility analysis indicated that a positive result would have been unlikely.Use of an implantable diagnostic tool to measure intrathoracic impedance with an audible patient alert did not improve outcome and increased heart failure hospitalizations and outpatient visits in heart failure patients. Clinical Trial Registration-URL: http://www.clinicaltrials.gov. Unique identifier: NCT 00480077.