Who Needs Physiologic Pacing and Why?

Various pacing technologies have been developed during the past 50 years since the first pacemaker was implanted in 1958. Dual-chamber pacing, rate responsiveness, programmable and rate-responsive atrioventricular (AV) intervals, alternative-site pa0cing, and new multichamber pacing devices are all attempts to mimic normal cardiac physiology as much as feasible. The categories of alternative-site and multichamber pacing will not be addressed in this review. The term physiologic pacing refers to dual-chamber (DDD and DDDR) and atrium-based pacing (AAI and AAIR) in contrast to the ventricle-based mode of pacing (VVI and VVIR). Both AAI/R and DDD/R pacing preserve the synchrony of atrial and ventricular contraction, and therefore resemble the normal cardiac function more closely than does VVI/R pacing. Despite this physiological superiority of AAI and DDD pacing, VVI pacemakers are still used in a large proportion of patients with sick sinus syndrome. Physician’s reluctance toward implantation of more physiological pacemakers may be related to difficulties with implantation of an atrial lead, the higher device cost of DDD units, and the more complex programming and follow-up of such pacemakers. Moreover, the lack of large-scale prospective randomized trials to document which pacing mode is superior probably also contributes significantly.