IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR SHOCKS ARE NOT A SURROGATE FOR SUDDEN CARDIAC DEATH IN SURVIVORS OF MALIGNANT ARRHYTHMIA

Introduction: It was shown that counting of appropriate ICD shocks overestimates approximately twofold the benefit of prophylactic ICDs in patients with nonischemic cardiomyopathy. We investigated this controversial issue of equating ICD therapy with mortality in single-centre population of patients with ICD implanted for secondary prevention of sudden cardiac death (SCD).
Methods: Total of 277 pts (231 M; age 63±12 yrs; 75% ischemic heart disease, LVEF 37±12%) were followed for 39±34 months (median 28 months). Cumulative total mortality, incidence of first appropriate ICD shock, and incidence of combined endpoint (death or first appropriate ICD shock) were analyzed using Kaplan-Meier analysis and Cox regression model of proportional hazards.
Results: Patients experienced 376 appropriate ICD shocks. Total of 62 patients died after 25±22 months following the implantation. Cumulative incidence of death was 13.7% and 23.3% after 2 and 4 years of follow-up, respectively. Similarly, cumulative incidence of first appropriate ICD shock was 32.6% and 39.2% and cumulative incidence of combined endpoint was 39.4% and 49.5% (Figure). When combined endpoint was considered a surrogate for total mortality in the hypothetical absence of defibrillator, ICD therapy was associated with relative risk reduction of -64% for total mortality. In the model, in which random selection of only 25% of all ICD therapies were considered an equivalent of SCD, ICD therapy was associated with relative risk reduction of -27% for total mortality that was more consistent with the findings of other secondary prevention ICD trials.
Conclusions: Approximately 25% of ICD shocks were life-saving in non-selected population of patients with ICD implanted for secondary prevention of SCD. Majority of ventricular arrhythmias would likely have terminated spontaneously in the absence of the ICD.