Decision Making for Implantable Cardioverter Defibrillator Implantation

Risk prediction for sudden cardiac death (SCD) remains one of the most challenging tasks in medicine.1 The dire consequence of not identifying an individual who is otherwise doing well clinically but will succumb to a sudden arrhythmic death that is potentially either preventable or treatable has driven the search for a strategy that will identify these individuals. It has also been recognized that risk stratification is needed in patients who are currently classified into a high-risk group based on a depressed left ventricular ejection fraction, but who may never have an arrhythmic event. Although multiple implantable cardioverter defibrillator (ICD) trials have demonstrated a benefit to ICD therapy when patients were enrolled based primarily on having a depressed left ventricular ejection fraction, the optimal utilization of ICDs remains unclear. Undoubtedly there are a substantial subgroup of these patients that benefit from ICD implantation, but there are also cohorts that will likely not benefit and some may even be harmed by the ICD. To date, no risk stratifiers have been identified that resolve these issues. The challenges and potential approaches to improve risk stratification have been extensively discussed.1–3 In this issue of Circulation: Cardiovascular Imaging , Hachamovitch et al4 have taken on these challenges directly with their study designed to evaluate whether 123I- m IBG imaging has a role as a gatekeeper for ICD use.See Article by Hachamovitch et al During the past several decades, many noninvasive risk stratification techniques have been proposed and evaluated, including predominantly left ventricular functional assessment and ECG-based techniques. The advanced ECG analyses have included heart rate variability, signal averaged ECG, T-wave alternans, among others.5,6 The development of these techniques was based on strong pathophysiologic links to lethal ventricular tachyarrhythmias, namely altered autonomic inputs, abnormally delayed depolarization, …