Indications for internal cardioverter defibrillator implantation predict time to first shock and the modulating effect of β-blockers

Background Patients receive implantable cardioverter defibrillator (ICD) for varying indications. Whether these indications influence the time to first ICD shock is suspected but not confirmed. The modulating effect of β-blockers on shock-free survival is not fully elucidated. Method A retrospective analysis of 230 consecutive patients (age 63 ± 14 years, 79% men, 75% ischemic, 70% β-blockers) implanted with an ICD was performed. Patients were divided into 4 groups depending on the ICD indication: groups A (secondary prevention of sudden death), B (left ventricular ejection fraction ≤35% and positive electrophysiology study [EPS]), C (left ventricular ejection fraction ≤35% and negative EPS or no EPS performed), and D (patients who did not meet inclusion criteria for groups A, B, or C). Time to shock was analyzed by the Kaplan-Meier method. Results During a mean follow-up of 489 ± 280 days, 57 (24.7%) patients received 82 shocks (49% appropriate). The 1-year shock-free survival for patients in groups A, B, C, and D were 57%, 77%, 79%, and 91%, respectively (P = .03), for total shocks and 75%, 92%, 92%, and 100%, respectively (P = .007), for appropriate shocks. For patients in group A, the use of β-blockers increased the 1-year shock-free survival from 48% to 61% for total shocks and from 65% to 79% for appropriate shocks. Conclusion Time to first shock is determined by the indication for ICD implantation and is not predicted by the results of EPS. Patients with secondary indications for ICD implantation are at highest risk of shocks and may deserve consideration for prophylactic antiarrhythmic drugs. β-Blockers increase the time to first ICD shock in patients implanted for secondary prevention of sudden death.