Occult myocardial failure and vasopressors in shock

Abstract

Among the causes of refractory hypotension in the surgical patient is unrecognized myocardial failure when the heart has been depressed by anoxia, anesthesia, or endotoxin toxicity. Using the quantification of myocardial contractility provided by the Isometric Time-Tension Index (12, 13, 14), the present study, in dogs, demonstrates that when the myocardium is depressed, a vasopressor agent without cardiac inotropic activity may produce cardiac failure even though resulting in increased arterial blood pressure and coronary flow. However, vasopressors with inotropic action enable the depressed myocardium to compensate for the increased load imposed by peripheral vasoconstriction. The relative merits of mcthoxamine, angiotensin, and levarterenol are compared. Methoxamine has a negligible inotropic effect and does not protect the depressed myocardium. Angiotensin, while possessing a weak inotropic effect, also has a coronary vasoconstrictor action and may be hazardous to the depressed myocardium under some conditions. Only levarterenol has a sufficiently powerful inotropic action to consistantly protect the depressed myocardium against the effects of its own vasoconstrictor action. © 1965 S. Karger AG, Basel.