Role of cardiac resynchronization therapy and atrioventricular junction ablation in patients with permanent atrial fibrillation.

State of the art treatment of atrial fibrillation in an individual patient may follow different, complex avenues depending on symptoms, clinical circumstances, and patient preferences. Management may become particularly challenging when atrial fibrillation is associated with other co-morbidities, especially heart failure. Epidemiological studies have shown that heart failure with New York Heart Association (NYHA) functional class II– IV may be complicated by atrial fibrillation in up to 50% of cases, and this association carries a worse prognosis. In these cases, while ventricular rate control may be the first objective based on results of large, multicentre studies, adequate doses of vasoactive medications may not be tolerated and antiarrhythmic medications or ablation to help with rhythm control may be contraindicated or ineffective. In these challenging cases, atrioventricular (AV) junction ablation and cardiac pacing is an alternative treatment option. AV junction ablation, by slowing and regularizing the ventricular rate, has been shown to improve symptoms, quality of life, and cardiac function, as judged by both physiological and structural measurements. It has been recognized that while rate control is achieved with AV junction ablation, ventricular dyssynchrony caused by chronic right ventricular (RV) pacing may adversely affect heart function and impede the salutary effects of rate control and rate regularization. It has been suggested that biventricular pacing may further improve exercise capacity, especially in patients with reduced LV function. Data from large clinical trials have indicated that cardiac resynchronization therapy (CRT) improves heart failure symptoms and exercise tolerance, halts the progression of cardiomyopathy, and decreases heart failure hospitalization and mortality in NYHA class II– IV patients with left ventricular ejection fraction (LVEF) ≤35%, and a QRS duration .120–130 ms. However, most landmark trials only studied patients in sinus rhythm. AV filling cannot be controlled during atrial fibrillation, and biventricular pacing percentage is often suboptimal because the ventricular rate may increase above the programmed pacing rate, limiting the benefits of CRT. Furthermore, a study from Steinberg et al. has shown that pacing counters frequently overestimate the percentage of biventricular pacing in patients with atrial fibrillation. More recently, observational data from a large European registry showed that during a median follow-up of 34 months, mortality was similar in patients who underwent CRT regardless of the presence of underlying atrial fibrillation as long as biventricular pacing was maintained over 85%. A subgroup of patients, who underwent AV junction ablation in order to achieve this goal, had improved symptomatic relief and survival compared with those who were rate controlled using medical therapy. Small, prospective and retrospective studies as well as a meta-analysis drew similar conclusions, whereas other studies suggested that AV junction ablation may not be necessary. Evidence from randomized, controlled trials to guide therapy, however, remains scarce, and the role of AV junction ablation in CRT has not been assessed. All this information has led to the need for a prospective evaluation of this important issue. The study by Brignole et al. is a welcome and important addition to our understanding of CRT in atrial fibrillation. The Ablate and Pace in Atrial Fibrillation trial recruited patients who were referred for AV junction ablation either for treatment of symptomatic atrial fibrillation or for a rate control strategy as part of CRT implantation for heart failure. A total of 186 patients were randomized to RV or biventricular pacing following AV junction ablation. The choice of implantable device back-up was left to the discretion of the implanter and was utilized in 67% of patients with EF ≤35% and 14% with EF .35%. RV leads were placed in