Effect of Isoproterenol, l -Norepinephrine, and Intraaortic Counterpulsation on Hemodynamics and Myocardial Metabolism in Shock following Acute Myocardial Infarction

Abstract

The effects of isoproterenol, l -norepinephrine, and intraaortic counterpulsation on hemodynamics and myocardial metabolism were evaluated in shock due to acute myocardial infarction. Before treatment, the cardiac index was markedly reduced, averaging 1.35 liters/min/m 2 . Mean aortic pressures ranged from 40 to 65 mm Hg. Decreases in coronary blood flow (mean, 68 ml/100 g/min) and in myocardial oxygen consumption (mean, 8.11 ml/100 g/min) were associated with abnormally high myocardial oxygen extractions (mean, 78%) and with lactate production (mean, 9%). Isoproterenol increased cardiac index 63% and heart rate 26%. Coronary blood flow rose an average of 12 ml/100 g/min in the face of decreased diastolic aortic pressure. Rate of myocardial lactate production increased. l -Norepinephrine increased mean aortic pressure and coronary blood flow an average of 21 mm Hg and 27 ml/100 g/min. Mean myocardial oxygen consumption rose 2.24 ml/100 g/min. While myocardial lactate production shifted to extraction (mean, 12%), myocardial oxygen extraction remained abnormally high (mean, 73%). Cardiac index did not change. Intraaortic counterpulsation increased mean aortic pressure and coronary blood flow an average of 15 mm Hg and 23 ml/100 g/min. Myocardial oxygen consumption remained essentially unchanged. Both myocardial lactate and oxygen extraction improved toward normal values (15 and 61%). Cardiac index increased an average of 0.45 liters/min/m 2 . Hemodynamics and myocardial metabolism then were markedly abnormal in shock due to acute myocardial infarction. Isoproterenol improved cardiac performance but myocardial oxygenation deteriorated. Therefore isoproterenol does not seem to be helpful in coronary shock. 1 -Norepinephrine improved myocardial perfusion and oxygenation, but did not change cardiac output. It appears to be the vasoactive agent of choice in the initial treatment of coronary shock. Intraaortic counterpulsation changed myocardial metabolism toward normal and improved systemic perfusion. Mortality remained unchanged however during the three different therapeutic interventions emphasizing the importance of early recognition of the shock state and of further aggressive diagnostic and therapeutic management.