Shock Occurrence and Survival in 241 Patients With Implantable Cardioverter‐ Defibrillator Therapy

BackgroundThe purpose of this study was to determine the influence of clinical characteristics on shock occurrence and survival in 241 patients with implantable cardioverter-defibrillator (ICD) therapy Methods and ResultsTwo hundred forty-one consecutive patients underwent ICD implantation between November 1982 and November 1991 and were subsequently followed for 26±22 months (intention-to-treat analysis). Actuarial incidence of “appropriate” shocks was 13%, 42%, and 63%, and the incidence of any spontaneous shocks was 15%, 51%, and 76% at 1, 3, and 5 years of follow-up, respectively. Poor left ventricular function (ejection fraction $30%) was associated with an earlier occurrence of both appropriate and any spontaneous ICD shocks (p=0.001). Appropriate and any spontaneous shocks occurred significantly later in patients who presented with cardiac arrest and in patients in whom only ventricular fibrillation but no uniform ventricular tachycardia was induced during preoperative programmed stimulation. In addition, amiodarone treatment at implant was associated with later occurrence of any spontaneous shocks. Cumulative survival from all-cause mortality including perioperative mortality was 84%, 62%, and 57%, and survival from arrhythmic death was 97%, 89%o, and 83% at 1, 3, and 5 years, respectively. Ejection fraction $30% was the best predictor of both total arrhythmic death (p=0.019) and total mortality (p=0.003). Antiarrhythmic therapy with class 1 agents at implant was also associated with a higher total mortality during follow-up (p=0.023) but not with total arrhythmic death. Age, sex, underlying heart disease, clinical presentation, and preoperative response to programmed stimulation did not predict long-term survival. In addition, survival curves were similar for patients with and without spontaneous shocks. ConclusionThe majority of patients receive shocks during long-term follow-up. The occurrence of appropriate or any spontaneous shocks during follow-up is not associated with increased arrhythmic or total mortality consistent with effective prevention of sudden cardiac death with ICD therapy in this high-risk patient population. Although low ejection fraction is the strongest predictor of both shock occurrence and mortality during follow-up, no easy algorithm can be derived from the analyzed clinical characteristics to predict which patients will benefit most from ICD implantation.