INFLUENCE OF HEART-RATE ON LEFT-VENTRICULAR EJECTION FRACTION IN HUMAN-BEINGS

The influence of heart rate on left ventricular ejection fraction was examined in 10 recipients of a cardiac allograft and 7 patients who had had aortocoronary bypass surgery. Ventricular volumes and ejection fraction were measured using computer-assisted analysis of motion of surgically implanted mid wall myocardlal markers recorded by cinefluoroscopy during atrial pacing at increments of about 15 beat/min from an average control rate of 83 beats/min to 154 beats/min. A gradual progressive decrease in ejection fraction occurred as heart rate Increased within the physiologic range. For an increase in heart rate of 70 beats/min above the control rate, ejection fraction decreased 31 percent (P < 0.001) and, in general, statistically significant reductions in ejection fraction occurred with increments in heart rate of 30 beats/min or greater. A proportionately greater linear reduction in end-diastolic volume than in end-systolic volume accounted for the inverse relation between ejection fraction and heart rate. The direction and magnitude of the volume changes were similar in patients with aortocoronary bypass surgery and in the allograft recipients, and in the patients with bypass surgery before and after administration of propranolol, suggesting that neural mechanisms acting directly on the heart did not influence this inverse relation importantly. It is concluded that heart rate must be considered in interpreting serial studies of ventricular function based on ejection fraction, especially If heart rate varies more than 30 beats/min between studies. © 1979.