The effect of external cardiac pacing on stroke volume.

To evaluate the hemodynamic effects of external cardiac pacing, ten subjects with normal left ventricular function were paced at rates approximating their resting heart rates using an external pacemaker while continuous-wave Doppler measurements from the aortic outflow were recorded. The Doppler flow velocity integral was used as an index of stroke volume and the product of heart rate and flow velocity integral was used as an index of cardiac output. At a pacing rate 13% faster (range -5% to 32%) than the rate during sinus rhythm, the mean index of stroke volume was reduced 24% from 17.7 cm to 13.5 cm (P less than 0.0002). However, the faster rate during external pacing partially compensated for the reduced stroke volume resulting in an index of cardiac output that was 14% lower compared to the prepaced index (1,297 vs 1,121 cm [P less than 0.02]). Thus, in subjects with normal LV function, external pacing results in a small drop in cardiac output that may be partially overcome by increasing the pacing rate.