What We Know, What We Think We Know, and What We Do Not Know at All
The Contemporary Conundrum of Secondary-Prevention Implantable Cardioverter Defibrillator Therapy
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See Article by Ladejobi et al
Despite recent improvements, the overall survival rate for cardiac arrest is abysmal.1–3 For electrophysiologists consulting on cardiac arrest survivors before discharge, the decision to offer a secondary-prevention implantable cardioverter defibrillator (ICD) is often reflexive. The newly updated guideline recommendations for secondary prevention of sudden cardiac death (SCD) do not differ substantially from prior versions: for patients who survive cardiac arrest due to ventricular tachycardia (VT) or ventricular fibrillation (VF), or who experience sustained VT, not due to reversible causes, an ICD is recommended.4 The evidence basis for these recommendations is the 3 secondary prevention trials: AVID (Antiarrhythmics Versus Implantable Defibrillators Trial),5 which showed a significant mortality benefit from ICD therapy, CASH (the Cardiac Arrest Study Hamburg),6 and CIDS (Canadian Implantable Defibrillator Study)7; the latter 2 also demonstrating a similar but nonstatistically significant reduction in mortality afforded by ICD therapy. An individual patient-level pooled meta-analysis confirmed consistency of trial results and a significant reduction in mortality associated with ICD therapy (hazard ratio, 0.72; 95% confidence interval [CI], 0.60–0.87; P=0.0006).8
Despite this seeming simplicity, secondary prevention is in fact much more complex and much less clear than it appears, particularly in the contemporary era of diagnosis and treatment of acute coronary syndromes. Crucial to the decision regarding the benefit of ICD therapy is the concept of a reversible cause—what is it, how do we recognize and treat it, and is the identified cause truly reversible? The angst inherent to this detective work is not new—in 2001, the AVID investigators published an analysis of the AVID registry subgroup composed of patients otherwise eligible for the trial who were not enrolled due to identification of a presumed transient or correctable cause for SCD.9 This group of 274 …