Effect of rate on left ventricular volumes and ejection fraction during chronic ventricular pacing.

Resting left ventricular (LV) function was evaluated in 22 patients with permanent ventricular pacemakers. LV ejection fraction and volume indexes were determined by gated blood pool scintigraphy at ventricular pacing rates of 50-100 beats/min. In patients with a normal heart size, increases in pacing rates resulted in significant linear decreases in stroke volume index and ejection fraction. However, end-systolic volume index and cardiac index did not change. Patients with cardiomegaly appeared to respond differently. End-diastolic volume index decreased significantly as the pacing rate was increased from 50 to 100 beats/min. Ejection fraction was significantly reduced only at pacing rates of 90 and 100 beats/min. Mean cardiac index was highest at ventricular pacing rates of 70-90 beats/min. Increases in cardiac index, achieved by increasing the pacing rate, were maintained over a 4.3-month follow-up. Patients with underlying sinus rhythm had a 27% increase in cardiac output in association with an increase in ejection fraction from 55% to 62% when sinus rhythm was compared to ventricular pacing at a rate of 60 beats/min. These data suggest that patients with cardiomegaly have a narrow range of optimal pacing rates at rest.