Causes and consequences of heart failure after prophylactic implantation of a defibrillator in the multicenter automatic defibrillator implantation trial II.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy may be associated with an increased risk for heart failure (HF). The present study evaluated the frequency, causes, and consequences of HF after ICD implantation.

METHODS AND RESULTS: We performed a retrospective analysis of the clinical factors and outcomes associated with postenrollment HF events in 1218 patients enrolled in the Multicenter Automatic Defibrillator Implantation Trial II. The adjusted hazard ratios (HRs) of ICD:conventional therapy for first and recurrent HF events were 1.39 (P=0.02) and 1.58 (P<0.001), respectively. The risk was increased among patients who received single-chamber or dual-chamber ICDs. Development of HF was associated with an increased mortality risk (HR, 3.80; P<0.001). Among patients who received a single-chamber ICD, there was a similar survival benefit before and after the development of HF (HR, 0.59 and 0.61, respectively; P=0.92 for difference), whereas among patients with dual-chamber devices, there was a significant reduction in survival benefit after HF (HR, 0.26 and 0.83, respectively; P=0.01 for difference). Within the defibrillator arm of the trial, patients who received life-prolonging therapy from the ICD had an increased risk for first and recurrent HF events (HR, 1.90; P=0.01 and 1.74; P<0.001, respectively).

CONCLUSIONS: Patients with chronic ischemic heart disease who are treated with either single-chamber or dual-chamber ICDs have improved survival but an increased risk of HF. The present data suggest that ICD therapy transforms sudden death risk to a subsequent HF risk. These findings should direct more attention to the prevention of HF in patients who receive an ICD.