Effect of pacing mode on morbidity and mortality: update of clinical pacing trials

Retrospective studies have suggested that, in patients with sick sinus syndrome, it has been recognized that atrial, dual-chamber, or other so-called physiologic modes of pacing are associated with a lower incidence of atrial fibrillation, stroke, heart failure, and death than is single-chamber ventricular pacing. Retrospective data in patients with atrioventricular block are less robust, but still suggest lower mortality and morbidity with dual-chamber pacing compared with ventricular pacing alone. Overall, the reduction in risk of atrial fibrillation with dual-chamber compared with ventricular pacing has been calculated at 62%, and for death 36%. Retrospective studies are, of course, potentially subject to bias, and there may be a tendency to implant cheaper, simpler pacemakers in older, sicker patients, which could explain the apparent difference in outcome. Prospective studies are, therefore, required; results from 3 such studies, in which pacing mode was randomly allocated, have been recently published. These, in general, support the apparent benefit of dual-chamber pacing in patients with sick sinus syndrome, but give equivocal results in patients with heart block. Other trials are in progress, and their results are awaited. Like all good trials, they will, in addition to providing some answers, generate further questions. They should provide the evidence on which cost-effective pacing policies may be based.