In 17 dogs with acute myocardial infarcts produced by ligation of the proximal left anterior descending coronary artery, a comparative study was made of myocardial scintigrams obtained with technetium 99m stannous pyrophosphate (99Tc(m) PYP) and thallium 201 (201Tl), tissue levels of 99Tc(m) PYP and 201Tl uptake, histopathologic alterations, and regional myocardial perfusion measured with radioactive microspheres. Nine of the 10 hearts examined histologically had transmural infarcts with outer peripheral, inner peripheral, and central zones characterized by distinctive histopathologic features. A progressive reduction in myocardial blood flow was demonstrated between normal myocardium and the centers of the infarcts, and correlated well with progressive reduction in 201Tl uptake in the same regions. Marked 99Tc(m) PYP concentration occurred in areas with partial to homogeneous myocardial necrosis and residual perfusion located in the outer peripheral regions of the infarcts. The latter areas also were characterized by the presence of muscle cell calcification. The patterns of distribution of 99Tc(m) PYP and 201Tl explained the filling defects on 201Tl myocardial scintigrams and the doughnut patterns on 99Tc(m) PYP myocardial scintigrams in dogs with transmural infarcts. One dog with a subendocardial infarct had a small homogeneous area of activity on the 99Tc(m) PYP myocardial scintigram, and showed marked uptake of 99Tc(m) PYP in subendocardial areas of extensive necrosis and calcification still receiving some coronary perfusion. Thus, the data indicate that the status of regional myocardial perfusion is a key determinant for the occurrence of distinctive patterns of myocardial necrosis and for the scintigraphic detection of acute myocardial infarcts with 99Tc(m) PYP and 201Tl.
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