Myocardial substrate after cardiac resynchronization therapy and the risk of ventricular arrhythmias

Excerpt

Myocardial remodeling is a central feature of failing hearts. It can take several forms, and the most easily recognizable ones are electrical remodeling (wide QRS complex with or without left bundle branch block) and mechanical remodeling (dilated and hypofunctioning left ventricle). This remodeling results in disorganized left ventricular (LV) contraction, which further promotes heart failure (HF) progression and has been shown to be an independent predictor of adverse cardiac events.1-3 Patients with myocardial remodeling and symptomatic HF that is refractory to medical therapy have been shown to derive symptomatic and mortality benefit from cardiac resynchronization therapy (CRT).4,5 This benefit has been largely thought to be secondary to reduced interventricular conduction delay, reduction in LV size, and consequently improved LV contractility.6 The Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure (COMPANION) trial tested the efficacy of CRT-pacemaker and CRT-defibrillator with medical therapy alone. The trial reported that both CRT-pacemaker and CRT-defibrillator provided significantly better survival and reduced hospitalizations when compared with medical therapy alone.5,7 Though not specifically studied, the logical advantage of a CRT-defibrillator would be arrhythmia prevention and CRT-pacemaker seemed to offer a similar level of survival, suggesting an anti-arrhythmic effect of CRT alone. …