Effect of isoproterenol and norepinephrine on myocardial function in experimental cardiogenic shock

Abstract

Cardiogenic shock was produced in 18 dogs by the technique of closed-chest coronary embolization with plastic microspheres. Isoproterenol (0.2 μg per kilogram per minute) and norepinephrine (1.0 μg per kilogram per minute) were infused for 15-minute periods into each shocked animal, and the effects on myocardial function were compared. In the dosage employed, isoproterenol and norepinephrine caused a similar increase in both coronary blood flow and myocardial O 2 consumption. Norepinephrine had a significantly greater effect than isoproterenol in raising arterial blood pressure and in increasing left ventricular work as measured by the tension-time index (TTI). Increase in myocardial work was accompanied by a small increase in left ventricular end-diastolic pressure during infusion of norepinephrine, whereas isoproterenol caused a significant fall in this measurement. Both drugs decreased the level of arterial lactate, indicating improved systemic blood flow. Isoproterenol caused no change in the extraction of lactate by the heart, but norepinephrine, in contrast, resulted in the development of a negative A-V lactate difference across the myocardium with net lactate production by the heart, indicating increased anaerobic myocardial metabolism. These data indicate that the infusion of norepinephrine may have a deleterious effect on myocardial function when used in a dosage commonly employed in treating patients with cardiogenic shock. It is suggested that isoproterenol is equally as effective as norepinephrine in improving cardiac performance after acute myocardial infarction, and that its use is less likely to provoke increased myocardial hypoxia.