Shocks as predictors of survival in patients with implantable cardioverter-defibrillators

OBJECTIVES The objective of the study was to determine whether the occurren ce of shocks for ventricular tachyarrhythmias during therapy with implantab le cardioverter-defibrillators (ICD) is predictive of shortened survival. BACKGROUND Ventricular tachyarrhythmias eliciting shocks are often associat ed with depressed ventricular function, making assessment of shocks as an i ndependent risk factor difficult. METHODS Consecutive patients (n = 421) with a mean follow-up of 756 +/- 523 days were classified into those who had received no shock (n = 262) or eit her one of two shock types, defined as single (n = 111) or multiple shocks (n = 48) per arrhythmia episode. Endpoints were all-cause and cardiac death s. A survival analysis using a stepwise proportional hazards model evaluate d the influence of two primary variables, shock type and left ventricular e jection fraction (LVEF <35% or >35%). Covariates analyzed were age, gender, NYHA Class, coronary artery disease, myocardial infarction, coronary revas cularization, defibrillation threshold and tachyarrhythmia inducibility. RESULTS The most complete model retained LVEF (p = 0.005) and age (p = 0.02 3) for the comparison of any shock versus no shock (p = 0.031). The occurre nce of any versus no shock, or of multiple versus single shocks significant ly decreased survival at four years, and these differences persisted after adjustment for LVEF. III the LVEF subgroups <35% and <25%, occurrence of mu ltiple versus no shock more than doubled die risk of death. Compared with t he most favorable group LVEF greater than or equal to 35% and no shock, ris k in the group multiple shocks and LVEF <35% was increased 16-fold. CONCLUSIONS In defibrillator recipients, shocks act as potent predictors of survival independent of several other risk factors, particularly ejection fraction. (C) 1999 by the American College of Cardiology.