Stroke Volume and Peripheral Resistance during Infusion of Isoproterenol at a Constant Fixed Heart Rate

Abstract

The effects of isoproterenol on the cardiac dynamics were determined with the dye-dilution technique in 8 patients with complete heart block who had a pacemaker implanted in the left ventricle. The average heart rate was fixed for the group at 68 beats/minute. Constant intravenous infusion of the drug in a dose of 2 [mu]g./minute resulted in 64%, 66%, 68% and 75% increases in cardiac index, stroke index, ventricular work and stroke power, respectively. Mean systemic pressure and peripheral resistance decreased 19% and 48%, respectively. These data emphasize the important contribution of stroke volume and peripheral resistance in the regulation of cardiac output when the heart rate is maintained fixed with a cardiac pacemaker. Exercise and isoproterenol in the same group of patients produced identical effects on the cardiac output and stroke volume. The possible use of isoproterenol in patients with heart failure and with a permanent pacemaker seems to be justified on the basis of an increase in the cardiac output at a fixed heart rate.