Variability in response to norepinephrine in acute myocardial infarction

Abstract

Twenty-seven patients with acute myocardial infarction were studied by infusion of graded levels of norepinephrine at rates of 1 to 3, 3 to 5, 5 to 8 and 8 to 10 <i>μ</i>g/min. Twelve patients subsequently died of pump failure during hospitalization. Control levels of stroke work produced excellent separation between survivors and nonsurvivors. The magnitude of maximal stroke work response during norepinephrine infusion in the two groups was also significantly different, but did not further separate the groups. However, the maximal percent change in stroke work in the two groups was similar, thus suggesting that, even in the presence of large infarcts, the remaining viable myocardium remains responsive to inotropic agents. Qualitatively the response of survivors and nonsurvivors was similar at low dose rates, but at a rate of 8 to 10 <i>μ</i>g/min, survivors exhibited predominantly an increase in stroke volume with little change in peripheral vascular resistance, whereas nonsurvivors showed predominantly an increase in peripheral vascular resistance with little change in stroke volume. We conclude that the initial level of ventricular function determines both the nature and magnitude of response to inotropic agents in acute myocardial infarction. Clinically, the usefulness of norepinephrine in this disease may be limited, since patients most likely to receive the drug would be expected to respond with a small increase in flow and a significant increase in afterload.