Benefits of Rate-Responsive Pacing in Patients with Sick Sinus Syndrome

The effect of changing a rate-responsive pacemaker program (which reacts to evoked QT interval) to fixed-rate ventricular pacing was studied in 10 patients with sick sinus syndrome (SSS). After the patients had been in the rate-responsive mode (VVIR) for at least one year, the exercise capacity (maximal oxygen consumption [peak VO₂], anaerobic threshold [AT], and cardiac output [CO] at these points) was examined. Three hours later on the same day, the pacemaker was reprogrammed to the fixed-rate pacing (WI) and the exercise capacity was examined again (VVI-S). One month later, a similar exercise test was also done in the VVI mode (VVI-L). There was no significant difference in peak VO₂ and AT between VVIR and VVI-S, but both peak VO ₂ and AT were significantly lower in VVI-L than in WIR. However, there were no significant differences in the CO at peak VO₂ or AT between any of the pacing modes. These findings indicate that a WIR pacemaker should not be reprogrammed to the VVI mode in SSS patients, because the change can cause the exercise capacity to deteriorate.