Agents In Acute Myocardial Infarction Research Articles

Evaluation of 99mtechnetium stannous pyrophosphate as an imaging agent in acute myocardial infarction.

Serial 99mTc pyrophosphate scintigrams were obtained 7 hr to 15 days after experimental acute myocardial infarction produced by permanent or transient coronary occlusion. Scintigrams were interpreted visually and the increased radioactivity in the precordial image was quantitated and compared to extent of infarction found histologically. Results of these studies indicate: 1) 99mTc pyrophosphate imaging is an extremely sensitive for detection of acute myocardial infarction, i.e., infarction in excess of 1% of the left ventricular mass was detected. 2) Early detection of acute infarction is a function of blood flow since 7 hr after infarction scans were negative after permanent occlusion but were strongly positive after transient occlusion. 3) Radioactivity in the precordial image was inversely related to extent of infarction after permanent occlusion and directly related to extent of infarction after transient occlusion. 4) 99mTc pyrophosphate localized in areas with significant histologic infarction but the distribution of radioactivity was not proportional to extent of infarction.

Variability in response to norepinephrine in acute myocardial infarction

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.