Case selection for cardiac resynchronization in atrial fibrillation.

Remarkably little evidence exists that cardiac resynchronization therapy (CRT) is effective in patients who have atrial fibrillation (AF) but who otherwise seem suitable for this treatment. The landmark trials of CRT generally excluded patients with AF because atrioventricular (AV) resynchronization was considered a possibly important mechanism by which CRT might deliver its benefits. The only landmark trial that included many patients with AF confirmed marked benefit among patients in sinus rhythm but no benefit among those with AF. Evidence is lacking that biventricular rather than AV resynchronization is an important mechanism for delivering the benefits of CRT.