1 Circ Arrhythm Electrophysiol. 2018;11:e006245. DOI: 10.1161/CIRCEP.118.006245 March 2018 Key Words: Editorials ◼ arrhythmias, cardiac ◼ heart arrest ◼ humans ◼ stroke volume Kristen K. Patton, MD Jeanne E. Poole, MD EDITORIAL See Article by Ladejobi et al D espite 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 rec- ommendations 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 (An- tiarrhythmics 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 demonstrat- ing 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 com- plex and much less clear than it appears, particularly in the contemporary era of diagnosis and treatment of acute coronary syndromes. Crucial to the decision re- garding 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 other- wise 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 patients, despite being younger, with a higher ejection fraction, and having had more frequent use of revascularization compared with subjects enrolled in AVID, had a remarkably high mortality of 27% at 3 years. This risk was nearly identical to the antiarrhythmic (non-ICD) group in the AVID trial, and outcome in the correctible cause group was found to be worse after adjustment for clinical variables. 9 The authors fittingly suggested due diligence is required before assumption of a reversible cause. The accompanying editorial emphasized that the identified treatable causes of SCD, myocardial infarction (MI), ischemia, electrolyte imbalance, or antiarrhythmic drug proarrhythmia, may either not be reversible or may not be the cause of a life- threatening ventricular arrhythmia. 10 Thus, for >2 decades, we believed we knew that survivors of VF/sustained hemodynamically compromised VT would benefit from ICD therapy, but clinical discernment for reversible causes was flawed. In this issue of Circulation: Arrhythmia and Electrophysiology, Ladejobi et al 11 delve into this important area in their analysis of a large population of patients who survived What We Know, What We Think We Know, and What We Do Not Know at All The Contemporary Conundrum of Secondary-Prevention Im- plantable Cardioverter Defibrillator Therapy © 2018 American Heart Association, Inc. The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. Correspondence to: Jeanne E. Poole, MD, Division of Cardiology, Department of Medicine, University of Washington School of Medicine, 1959 NE Pacific St, Health Sciences Bldg, Room AA-121B, Seattle, WA 98195. E-mail jpoole@u.washington.edu Downloaded from http://ahajournals.org by on June 13, 2020