Comparison of exercise performance of six rate-adaptive right ventricular cardiac pacemakers.

Single chamber cardiac pacemakers capable of automatically adjusting the rate according to body requirements have become an important means of physiologic pacing in patients with bradycardias. Such pacemakers are dependent on a nonatrial sensor of physiologic needs to optimize the rate response. Fifty rate-adaptive right ventricular pacemakers were implanted in 46 patients with a mean age of 60 +/- 4 years (mean +/- standard error of the mean). There were 2 types of activity-sensing pacemakers (Activitrax and Sensolog 702), the QT-sensing pacemakers (TX2 and Quintech), 2 types of respiratory-sensing pacemakers (Biorate [RDP3 and MB1] and Meta) and a rate-adaptive pacemaker that senses right ventricular dP/dt (Deltatrax). The rate responses of a group of 9 volunteers of similar age (62 +/- 2 years) were also included for comparison. Improvement in exercise duration in the rate-adaptive mode compared to the constant-rate ventricular pacing (VVI) mode was achieved during randomized symptom-limited treadmill exercise (from 26 to 49%). Compared with the sinus responses, the activity-sensing pacemakers responded most appropriately in speed. However, their rate responses were not related to workload and had lower correlations with estimated oxygen consumption (r = 0.7 and 0.47 for Activitrax and Sensolog, respectively). Respiratory-sensing pacemakers responded more appropriately in magnitude (r greater than 0.8) although their rate responses were slower. All pacemakers studied either showed no response or a reverse-rate response to the Valsalva maneuver. It is concluded that the currently available rate-adaptive ventricular pacemakers improve exercise performance compared with VVI pacemakers in patients with bradycardias.(ABSTRACT TRUNCATED AT 250 WORDS)