Cardiac performance and metabolism in shock due to acute myocardial infarction in man: response to catecholomines and mechanical cardiac assist.

Abstract

SummarySystemic hemodynamics and myocardial metabolism were studied in 21 patients in shock due to acute myocardial infarction. The response to isoproterenol was determined in six, to l‐norepinephrine in eight, and to intra‐aortic counterpulsation in 10 patients. Before treatment, cardiac index was markedly reduced, averaging 1.35 L/min/m2. Mean aortic pressures ranged between 40 and 65 mm Hg, while systemic vascular resistance varied widely, averaging 1,575 dynes‐sec‐cm−5. 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 extraction (mean 78%) and with lactate production (mean 9%). Isoproterenol increased cardiac index and heart rate an average of 0.85 L/min/m2 and 25 beats/min. Coronary blood flow rose an average of 12 ml/100 g/min in face of unchanged mean aortic pressure, while diastolic aortic pressure fell uniformly. Myocardial lactate metabolism deteriorated. 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 improve. Intra‐aortic 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 towards normal values (mean 15% and 61%). Cardiac index increased an average of 0.45 L/min/m2. Conclusion: Hemodynamics and myocardial metabolism 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. L‐norepinephrine improved myocardial perfusion and oxygenation, while cardiac output remained unchanged. Nevertheless, l‐norepinephrine appears to be the vasoactive agent of choice in the initial treatment of coronary shock. Intra‐aortic counterpulsation changed myocardial metabolism towards 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.