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CLINICAL STUDIES

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

Antonio Pacifico, MD, FACC^*, Laura L. Ferlic, MS^* , F.élix R. Cedillo-Salazar, MD^* , Nadim Nasir, Jr, MD, FACC^* , Timothy K. Doyle, MD, FACC^* and Philip D. Henry, MD, FACC^*

^* Texas Arrhythmia Institute, Houston, Texas, USA
Baylor College of Medicine, Houston, Texas, USA

Manuscript received October 20, 1998; revised manuscript received January 28, 1999, accepted March 15, 1999.

Reprint requests and correspondence: Dr. Antonio Pacifico, Texas Arrhythmia Institute, Scurlock Tower, Suite 620, 6560 Fannin, Houston, Texas 77030
apacifico{at}tmh.tmc.edu

OBJECTIVES

The objective of the study was to determine whether the occurrence of shocks for ventricular tachyarrhythmias during therapy with implantable cardioverter-defibrillators (ICD) is predictive of shortened survival.

BACKGROUND

Ventricular tachyarrhythmias eliciting shocks are often associated with depressed ventricular function, making assessment of shocks as an independent 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 either one of two shock types, defined as single (n = 111) or multiple shocks (n = 48) per arrhythmia episode. Endpoints were all-cause and cardiac deaths. A survival analysis using a stepwise proportional hazards model evaluated the influence of two primary variables, shock type and left ventricular ejection fraction (LVEF <35% or >35%). Covariates analyzed were age, gender, NYHA Class, coronary artery disease, myocardial infarction, coronary revascularization, defibrillation threshold and tachyarrhythmia inducibility.

RESULTS

The most complete model retained LVEF (p = 0.005) and age (p = 0.023) for the comparison of any shock versus no shock (p = 0.031). The occurrence of any versus no shock, or of multiple versus single shocks significantly decreased survival at four years, and these differences persisted after adjustment for LVEF. In the LVEF subgroups <35% and <25%, occurrence of multiple versus no shock more than doubled the risk of death. Compared with the most favorable group LVEF 35% and no shock, risk 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.

Abbreviations and Acronyms   AMI = acute myocardial infarction   ATP = antitachycardia pacing   BMI = body mass index   CABG = coronary artery bypass graft   CAD = coronary artery disease   DFT = defibrillation threshold   EGM = electrogram   EPS = electrophysiologic study   ICD = implantable cardioverter-defibrillator   LVEF = left ventricular ejection fraction   MS = subgroup receiving multiple and possibly also single shocks   NS = subgroup receiving no shock   NYHA = New York Heart Association   SCD = sudden cardiac death   SS = subgroup receiving single but not multiple shocks   VF = ventricular fibrillation   VT = ventricular tachycardia

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