What do implantable cardioverter/defibrillators teach us about the mechanisms of sudden cardiac death?

Abstract

Almost two decades of experience with the ICD have resulted in a better understanding of the nature of life-threatening ventricular tachyarrhythmias. The most pertinent achievements in this respect stem from clinical follow-up observations in patients with important clinical entities such as dilated cardiomyopathy or the Brugada syndrome. For instance, patients with dilated cardiomyopathy presenting with syncope and a negative electrophysiological study have been shown to have a high incidence of appropriate usage of their ICD. On the other hand, relative little has been gained from the extensive electrogram storage capabilities of third and fourth generation ICDs. Basically, careful evaluation of these electrograms has confirmed previous anecdotal data obtained from analysis of Holter recordings of patients who died suddenly while wearing the ECG recorder. In most instances, VT/VF episodes are triggered by relatively late-coupled premature beats whereas short--long--short sequences have been observed only in few patients. One future research avenue concerns the more detailed analysis of changes in cardiac autonomic tone preceding the occurrence of sustained ventricular tachyarrhythmias which can be assessed from the electrogram storage of the ICD.