Cardiac Effects of Isoproterenol during Graded Myocardial Ischemia

Abstract

Conflicting results of isoproterenol administration to patients with ischemic heart disease suggest that the effect of isoproterenol on cardiac function is related to the severity of myocardial ischemia. Myocardial oxygen consumption (MVO₂) was therefore reduced by graded reductions in coronary blood flow before and after coronary administration of isoproterenol in 9 anesthetized dogs. When coronary blood flow was reduced by less than 50 per cent of control value, cardiac output and maximal value of left ventricular pressure rise (dP/dt) were higher with isoproterenol than without at similar values of MVO₂. When coronary blood flow was further reduced, however, cardiac output and dP/dt were depressed by isoproterenol. Myocardial lactate production was at any MVO₂ value higher during isoproterenol administration than during control periods, and stimulation of myocardial glycolysis by isoproterenol might –- at least in part –- explain an improved cardiac function during moderate ischemia. From these experimental results we conclude that isoproterenol exerts a therapeutic effect only at moderate degrees of myocardial ischemia.

Key Words:

• Contractility
• coronary insufficiency
• coronary perfusion
• inotropy
• ischemic ventricular dilatation
• myocardial anaerobiosis
• myocardial infarction
• myocardial oxygen consumption