Mortalit Benefits and the Implantable

The automatic implantable cardioverter-defibrillator (ICD) is highly effective in reducing sudden death rates in patients with life-threatening ventricular tachyarrhythmias. However, the magnitude of the ability of the ICD to improve overall survival is less certain. Data supporting the contention that the ICD prolongs survival are reviewed. It is evident that the mortality benefit consequent to the marked reduction in Tnhe automatic implantable cardioverter-defibrillator (ICD) was originally conceived by Mirowski and coworkers' as a device for detecting and terminating potentially lethal ventricular tachyarrhythmias. Since the initial published report of successful resuscitation from ventricular tachycardia and fibrillation in humans 13 years ago, more than 30 000 devices have been implanted, and there have been dramatic advances in ICD technology. Newer devices are fully programmable and capable of antitachycardia pacing, synchronized cardioversion, defibrillation, back-up ventricular demand pacing, and retrieval of stored intracardiac electrograms. There is universal agreement that the device has demonstrated the ability to meet the goal set forth by its inventors, namely, to abort sudden cardiac death caused by ventricular tachyarrhythmias. In highrisk patients who have survived cardiac arrest or have drug-refractory hemodynamically significant ventricular tachyarrhythmias, the ICD is highly effective in reducing sudden death rates, in most studies to 1% and 5% at 1 and 3 years, respectively.2-8 However, while acknowledging this dramatic reduction in sudden death rates, some reports suggest that treatment with the ICD is not paralleled by a proportionate reduction in overall mortality.2,9 Skeptics have seriously questioned the magnitude of the ability of the ICD to improve survival,10-12 giving rise to a controversy described as the implantable defibrillator "backlash."'13 They argue that regardless of the ability of the device to terminate potentially fatal ventricular tachyarrhythmias (which is not in question), it has not been convincingly shown to prolong life compared with alternate therapies, and the cost and morbidity of the technology remain unjustified. In this article, early studies with the ICD and the origins of the survival benefit controversy are reviewed. It is evident that the mortality benefit consequent to the marked reduction in sudden death varies widely across subpopulations in a predictable Received August 2, 1993; revision accepted December 9, 1993. From the Cardiac Arrhythmia Service, Massachusetts General Hospital, Harvard Medical School, Boston. Correspondence to Dr Ruskin, Cardiac Arrhythmia Service, Massachusetts General Hospital, Boston, MA 02114. sudden death varies widely across subpopulations in a predictable manner. This observation reflects the powerful influence of other clinical factors that constrain survival in typical ICD patients. The implications for future studies on the ICD are discussed. (Circulation. 1994;89:1851-1858.)