Update on implantable cardioverter-defibrillators - Tips from Other Journals

Author: Richard Sadovsky
Date: Feb 15, 1997

The implantable cardioverter-defibrillator was initially used to treat survivors of cardiac arrest (due to malignant ventricular tachyarrhythmias) who failed to respond adequately to pharmacologic and surgical interventions. Modern models of the device can terminate ventricular tachycardia painlessly in up to 90 percent of cases. Antibradycardia pacing has been added to correct primary and secondary brady-arrhythmias. The recent availability of Holter function and the development of intracardiac electrocardiograms provides the means to verify the appropriateness of device intervention by documenting the preceding rhythm that triggered discharge of the device. Raviele reviews the progress in implantable cardioverter-defibrillator technology, the impact of its use on patients and current indications for its use.

The cardioverter-defibrillator can be implanted transvenously, making thoracotomy unnecessary. The use of biphasic instead of monophasic shock waveform has improved defibrillation efficiency. Most of the devices are small enough that they can be implanted in the chest of most patients like a pacemaker.

The termination of life-threatening ventricular arrhythmias and reduction in sudden deaths show the high efficacy of implantable cardioverter-defibrillators. It is unclear, however, whether the device really reduces total mortality. The mode of death may merely be changed from sudden to nonsudden. Randomized controlled clinical trials are needed to compare the device with the best alternative therapy currently available for ventricular tachycardia/ventricular fibrillation. These therapies include use of amiodarone, sotalol and/or perhaps beta blockers. Studies are in progress comparing the implantable cardioverter-defibrillators with amiodarone. The high cost of placement of the device makes it appropriate for use only in patients most likely to benefit in terms of prolongation of life. Trials comparing the use of amiodarone and placebo in postin-farction patients at high risk for sudden death show no impact on overall survival, while use of the implantable cardioverter-defibrillator showed a reduction in deaths of approximately 55 percent when compared with amiodarone.

Reasonable indications for implantation of a cardioverter-defibrillator are listed in the accompanying table. Prophylactic use of the device in patients theoretically at risk for sudden death (risk of 20 to 30 percent per year) or as a "bridge" to heart transplant is extremely costly and remains investigational. Therapy with the device is not justified in patients with sustained ventricular tachycardia or ventricular fibrillation mediated by reversible factors such as acute ischemia, electrolyte imbalance or drug toxicity. Additionally, the implantable cardioverter-defibrillator is not useful for controlling sporadic cases of hemodynamically well-tolerated sustained ventricular tachycardia, or in recurrent syncope of undetermined cause in patients without inducible tachyarrhythmias.

RELATED ARTICLE: Indications for Implantation of Cardioverter-Defibrillator

1. Persistent inducibility of poorly tolerated sustained ventricular tachycardia or ventricular fibrillation at electrophysiologic study, despite the use of class In drugs (amiodarone, sotalol) and beta blockers, and despite surgical and catheter ablation (when feasible).

2. Spontaneous recurrence of poorly tolerated sustained ventricular tachycardia or ventricular fibrillation despite drug treatment.

3. Spontaneous recurrence of poorly tolerated sustained ventricular tachycardia or ventricular fibrillation in a patient with intolerance or noncompliance with an effective drug regimen.

4. Noninducibility of sustained ventricular arrhythmia at electrophysiologic study in a patient with poorly tolerated sustained ventricular tachycardia or ventricular fibrillation and a markedly reduced left ventricular fraction ([is less than] 30%).

5. Ventricular fibrillation in a patient with no evidence of structural heart disease and no identifiable suppressing triggering factors.

From Raviele A. Implantable cardioverter-defibrillator (ICD) indications in 1996: have they changed? Am J Cardiol 1996;78 (Suppl 5A):21-5.

Raviele A. Implantable cardioverter-defribrillator (ICD) indications in 1996: have they changed? Am J Cardiol 1996;78(Suppl 5A):21-5.

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