Effects of Heart Rate on Ventricular Performance, Myocardial Contractile State and Coronary Circulation

Abstract

IKEDA, S. Effects of Heart Rate on Ventricular Performance, Myocardial Contractile State and Coronary Circulation. Tohoku J. exp. Med., 1974, 112 (1), 89-100-Effects of heart rate on ventricular performance, myocardial contractile state and coronary circulation were studied under constant cardiac output in right heart by-passed anesthetized dogs. Myocardial contractile state (Vmax) was elevated as heart rate increased, and this was considered to play an important role in impeding further increase of systolic time ratio which would have occurred unless this elevation had occurred. Myocardial oxygen consumption (MV02) was mainly influenced by heart rate, left ventricular systolic peak pressure and the contractile state of the left ventricle, but neither by stroke volume of the left ventricle nor left ventricular work. After administration of propranolol, the left ventricle was deteriorated at tachycardia more than 210 beats per minute, and Vmax did not rise at such a tachycardia. These results suggest that adrenergic beta-receptor plays an important role in augmenting the contractile state of the left ventricle and in preventing it from being deteriorated at tachycardia. heart rate; myocardial contractility; coronary circulation; myocardial oxygen consumption; propranolol Bowditch (1871) reported a staircase phenomenon in the frog ventricle. That is, when the ventricle was stimulated at a constant rate, the strength of contrac tion reached a plateau, and when it was stimulated at a faster or slower rate, the strength reached a higher or lower plateau, respectively. This phenomenon was demonstrated in mammalian cardiac muscles (Woodworth 1902; Abbott and Mommaerts 1959;Blinks and Koch-Weser 1961;Sonnenblick 1962). The effects of heart rate on the intact pumping ventricle have also been examined, but the conclusions are controversial. Sarnoff et al. (1963 and Covell et al. (1967) concluded that myocardial contractility was increased as heart rate increased, while Noble et al. (1966Noble et al. ( , 1969 reported that it was not altered by changes in heart rate in conscious dogs. On the other hand, it is generally accepted that coronary circulation is influenced greatly by heart rate and ventri cular performance.This experiment was designed to ascertain whether the changes in heart rate varies the myocardial contractile state and which factors contribute to alteration of coronary blood flow and myocardial oxygen consumption. Heart rate was changed by atrial pacing, and the left ventricular pressure, its dp/dt and the total coronary venous return were measured in right heart by-passed dogs. The experiment was also performed after administration of propranolol in order to ascertain whether the activation of beta-receptor mediates the effects of heart rate on myo cardial contractile state, ventricular performance and coronary circulation. METHODEight mongrel dogs of both sexes weighing from 12 to 20 kg were anesthetized with pentobarbital sodium (30 mg/kg) given intravenously. Ventilation was provided by a positive pre...