Resynchronization therapy in the context of atrial fibrillation: benefits and limitations.

Atrial fibrillation (AF) and heart failure often coexist and are believed to directly predispose to each other. Cardiac resynchronization does not prevent or increase the induction of AF. However, new onset of AF does not seem to diminish the beneficial effects of CRT on symptoms, cardiac function and, more importantly, all-cause mortality if appropriate ventricular rate control by beta-blockers and digoxin is being achieved. While a pharmacological approach to control ventricular rate may be sufficient in most patients with paroxysmal AF or AF of shorter duration in those with permanent AF ablation strategies may be necessary. Observational studies and one randomized trial indicate a potential benefit of CRT in heart failure patients with chronic AF; particularly, biventricular pacing was superior compared to conventional right-univentricular stimulation. However, recent results suggest that even relatively high percentage biventricular capture may be inadequate, and that the benefits of CRT may only be extended to chronic AF patients with previous AV junctional ablation. Well designed and powered clinical trials are required before pacemaker dependency is created in large numbers of heart failure patients.