VT begets VT—and other bad stuff—in patients treated with CRT-D

Abstract

Clinical trials have helped clarify the role of cardiac resynchronization therapy (CRT) in patients with heart failure. Early trials demonstrated reduction in mortality and heart failure hospitalization in patients with electrical dyssynchrony and moderate to severe functional impairment, and more recent trials showed that these benefits extend to heart failure patients even with mild symptoms. Most patients with a class 1 or 2 indication for CRT also have an appropriate indication for an implantable cardioverterdefibrillator (ICD) on the basis of the presence of ischemic or nonischemic cardiomyopathy, so the vast majority of CRT is delivered via a CRT with defibrillator (CRT-D). In fact, the Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy (MADIT-CRT) study randomized 1820 patients with cardiomyopathy of any etiology with left ventricular ejection fraction ≤30%, QRS duration ≥130 ms, and mild heart failure (New York Heart Association class I or II) to either standard ICD or CRT-D, and it showed that CRT-D leads to improved outcome compared with ICD alone in this population. The MADIT-CRT study design has enabled the investigators to also examine the effect of CRT on ventricular arrhythmic events. In a recent report, this group showed that CRT-D was associated with a 29% reduction in the risk of a first episode of ventricular tachyarrhythmic events compared with ICD alone. Importantly, this arrhythmia risk reduction was not homogeneous across the entire study population. Among patients with left bundle branch block (LBBB), CRT-D conferred a 42% reduction in the risk of first arrhythmic event compared with standard ICD, but in nonLBBB patients, CRT-D provided no such advantage, a finding that mirrors the general lack of clinical response to CRT seen in non-LBBB patients. Conversely, one might wonder what effect arrhythmic events have on subsequent outcome in CRT-D treated patients compared with that in standard ICD recipients. In this issue of HeartRhythm, Kutyifa et al addresses this very question, once again taking the advantage of the rich database provided by the MADIT-CRT trial. These investigators sought to evaluate the prognostic value of ventricular tachyarrhythmias, categorized as slow ventricular tachycardia