[Pathophysiology of pacing in patients with atrial fibrillation]

The limited efficacy of and side effects associated with antiarrhythmic drug therapy have led to renewed interest in non-pharmacologic treatment options for paroxysmal atrial fibrillation. In addition to catheter ablation of the initiating ectopic atrial beats, electrical stimulation of the atrium is a new and promising method to reduce the frequency of arrhythmia recurrences. Recent studies have confirmed the importance of both the initiating triggers and the electrophysiologic substrate for the recurrence and perpetuation, respectively, of atrial fibrillation. Bradycardia and pauses, atrial premature beats, and early recurrence of atrial fibrillation all seem to play an important role for (re-)initiation of an episode. Results from single-site atrial pacing in the high right atrium have shown a reduction of atrial fibrillation episodes and progression into chronic atrial fibrillation in selected groups of patients (brady-tachycardia syndrome and vagally induced atrial fibrillation). Therefore, specific preventive pacing algorithms (atrial overdrive pacing, rate smoothing or rate acceleration after detection of atrial premature beats and termination of a mode-switch) and new pacing sites have recently been investigated in order to address all of these initiation mechanisms and to increase the efficacy of pacing. In studies published so far, the specific pacing algorithms seem to add benefit compared to atrial-based demand (AAI or DDD) pacing alone. Finally, attempts are being made to terminate recurrences of atrial tachycardia or atrial flutter with antitachycardia pacing algorithms in order to avoid progression into atrial fibrillation. Based on experimental and clinical evidence, the initial phase of the majority of atrial tachyarrhythmia recurrences is not 'leading circle reentry'. Most episodes start relatively regular and seem to have an excitable gap, allowing capture and pace termination.