Hemodynamics and exercise capacity during pacemaker stimulation.

This review summarizes the present knowledge concerning the hemodynamic and myocardial effects of various pacing modalities with special reference to the importance of heart rate variability and atrioventricular synchronization. An adequate increase in heart rate, irrespective of atrioventricular synchronization, seems to be the most important denominator for cardiac output and exercise tolerance. Atrioventricular synchronization will add some hemodynamic benefit, which is most pronounced at rest. The importance of a rate-adaptive atrioventricular delay and a normalized ventricular activation sequence remains, however, to be fully established. Myocardial oxygen consumption does not differ during fixed rate ventricular pacing, atrial synchronous or non-synchronous rate-adaptive ventricular pacing, neither at rest nor during exercise, despite a higher cardiac output during the rate-adaptive modes. This indicates a more "economic" cardiac work with rate-adaptive pacing. Fixed rate ventricular pacing, on the other hand, may have negative long-term effects on myocardial function due to an increased cardiac sympathetic activity compared with rate-adaptive ventricular pacing, in particular during exercise. It is concluded that the majority of pacemaker-dependent patients will benefit from restored rate variability, with the atrial electrogram still being the most appropriate trigger for rate-adaptive ventricular pacing. When the atrial signal cannot be used or when it is unreliable, however, other rate-triggering signals can be used with comparable results regarding hemodynamics and exercise tolerance.