Benefits of physiologic atrioventricular synchronization for pacing with an exercise rate response

Although the loss of atrioventricular (AV) synchronization may diminish resting cardiac output, previous studies have not shown any impact on exercise capacity as long as an exercise rate response is present. To test the impact of suboptimal atrial activation during treadmill exercise, 12 patients with normal sinoatrial node function and dual chamber pacemakers were evaluated in pacemaker modes with normal AV intervals allowing maximal atrial contribution to ventricular filling and with the shortest programmable nonphysiologic AV delay. During a double-blinded randomized crossover protocol, exercise performance was improved with physiologic AV filling in comparison with nonphysiologic AV filling: (1) mean increase in exercise time was 16 +/- 16% (mean +/- standard deviation) (p less than 0.05); (2) time to anaerobic threshold was increased by 23 +/- 28% (p less than 0.05); and (3) the level of perceived exertion during comparable stages of exercise was decreased. In 3 patients, exercise time was greater by greater than 35% in the physiologic AV filling mode. Resting echo-Doppler parameters of left atrial and ventricular function did not predict benefit from AV synchronization during exercise. During exercise with rate-responsive pacing an appropriate AV relation is beneficial, and in a subset of patients this benefit may be striking.