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 (VVI) 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 VO2 and AT were significantly lower in VVI-L than in VVIR. 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 VVIR pacemaker should not be reprogrammed to the VVI mode in SSS patients, because the change can cause the exercise capacity to deteriorate.