Atrial pacing therapies for prevention of atrial fibrillation in patients with implantable defibrillators.

Atrial fibrillation (AF), atrial flutter and atrial tachycardia (AT) occur frequently in patients following implantation of an implantable cardioverter defibrillator (ICD) for the treatment of ventricular tachyarrhythmias. Some new generation ICDs have incorporated atrial antitachycardia pacing therapy (ATP) and atrial pacing algorithms designed specifically for the prevention of AF. In the GEM III AT clinical evaluation, atrial ATP efficacy for termination of AF and AT was assessed. Overall ATP efficacy for AF/AT, based on device classification, was 40% when adjusted using the Generalized Estimating Equations to account for correlated data that arises from utilizing multiple episodes in some patients. However, many episodes of AF/AT were noted to terminate within 10 minutes of onset. Applying a more conservative definition of efficacy, termination within 20 sec of delivery of the last atrial ATP, efficacy for termination of AF/AT was 26%. 50 Hz burst pacing was shown to have minimal efficacy for termination of AF and modest incremental benefit following ramp or burst pacing therapies for AT. These observations provide a more realistic expectation of the value of atrial ATP in the ICD population with AF. Atrial ATP terminates some episodes of AT but previously reported efficacy rates of 40-50% are exaggerated and in part reflect spontaneous terminations of some AF/AT episodes.