The usual reason for pacing is to prevent bradycardia, which is most commonly due to sick sinus syndrome or atrioventricular (AV) nodal disease. The need for pacing for either of these indications increases progressively with age. Atrial fibrillation (AF) is the most common serious arrhythmia. The incidence of AF also increases progressively with age, and patients with pacemakers may be even more prone to AF than comparable patients without pacemakers.1 Therefore, there has been continuing interest in discovering whether certain modes of pacing might be effective at preventing AF in patients with pacemakers.
The simplest question to ask is what chamber should be paced to decrease the chance of AF. Most, though not all, retrospective studies indicate that right atrial pacing decreases the incidence of AF compared with pacing in the ventricle.2 Andersen et al.3 compared single chamber right atrial pacing with single chamber right ventricular pacing in patients with sick sinus syndrome. They demonstrated significant benefit for atrial pacing with improved survival and a decreased incidence of thromboembolic events, AF, and congestive heart failure, especially after longer follow-up. The Mode Selection Trial in Sinus Node Dysfunction (MOST),4 in which all patients had dual chamber rate-responsive (DDDR) pacemakers implanted but were randomized to ventricular or dual chamber pacing, showed significant but less striking benefits in the incidence of AF and congestive heart failure. A possible explanation for the difference in the results between the two trials is that unintentional and unnecessary pacing of the right ventricle in the dual chamber group negated some of the benefits of sequential AV pacing compared with ventricular pacing. Two groups have examined the potential benefit of pacing at more than one site in the right atrium with the goal of activating the right and left atrium more synchronously. Saksena et al. found a small but not significant improvement in time to first AF and frequency of AF with dual site atrial pacing compared with conventional high right atrial pacing.5 Friedman et al. documented significant shortening of the P wave duration but observed only a tendency toward less AF with dual site compared with single site atrial pacing in a small study.6 Notable in both these studies is the significant improvement in AF with atrial pacing regardless of whether one or two sites is paced; the incremental benefit of dual site pacing is much smaller. There are theoretical reasons to think that pacing at a single site in the inter-atrial septum might accomplish similar atrial synchronization. Padeletti et al.7 showed that the incidence of AF was less with interatrial septal pacing compared with high right atrial pacing in a randomized prospective trial.