[Use of a rate responsive pacemaker in sick sinus syndrome].

In this study of 10 patients with sick sinus syndrome, we examined the benefits of a single-chamber ventricular pacing system that utilizes a sensor to detect the QT interval and then adjusts the heart rate. Changes in exercise tolerance capacity and cardiac function were evaluated when the pacing mode was changed from rate-variable mode (VVIR) to fixed-rate mode (VVI). Anaerobic threshold (AT), peak VO2 and cardiac output were measured in VVIR, during short-term VVI(VVI-S), which occurred two hours after the pacing mode was changed, and during long-term VVI (VVI-L), which occurred one month after the pacing mode was changed. 8 of 10 cases (80%) had their own beats during exercise. The AT and peak VO2 during VVI-S were not different from those during VVIR. However, AT and peak VO2 during VVI-L were significantly lower than those during VVIR pacing. (Respectively, 11.7 +/- 2.4 vs. 16.4 +/- 3.3, p < 0.01; 21.5 +/- 5.9 vs. 24.6 +/- 6.2, p < 0.01). At AT and peak VO2, there were no differences in cardiac output between VVIR and VVI-S, or between VVIR and VVI-L(NS). Physiologic changes in heart rate and cardiac output after exercise during VVIR were greater than those during VVI pacing. The present study suggests the above-mentioned changes after exercise effect, oxygen consumption in the peripheral circulation, which might lower exercise tolerance capacity in the chronic phase. The rate-variable pacing mode might improve exercise tolerance capacity and may be of benefit for patients with sick sinus syndrome.