Specificity of Localization of Myosin-specific

The concentration of radioiodinated (Fab')2 fragments of cardiac specific antimyosin antibody in myocardial infarcts has been shown previously to be inversely proportional to regional myocardial blood flow. The myocardial localization of antibody fragments has also been visualized by gamma camera scintigraphy. We now correlate the site of 121I-antimyosin (Fab')2 uptake with histochemical and histologic evidence of myocardial infarction. One millicurie of '21I-antimyosin (Fab')2 was administered intravenously 4 hours after left anterior descending coronary artery ligation to anesthetized dogs. The dogs were allowed to recover for 48 hours. The hearts were then excised, perfused with 1% triphenyl tetrazolium chloride (TTC) and formalin-fixed. One-centimeter-thick transverse slices were cut; gamma scintigrams for 1251I-antimyosin (Fab')2 localization, macroand microautoradiograms and histologic studies were performed. Samples of the remaining tissues were assayed for 1251 activity by gamma scintillation counting. Comparison of areas of 1251_ antimyosin (Fab')2 uptake on scintigrams and macroautoradiograms with TTC infarct location and size showed close correlation. Maximal ratios of '261-antimyosin (Fab')2 between infarcted and normal tissue (48 ± 13 [SEM] ) were in the subendocardium at the infarct center in areas of most severe cellular necrosis. Microautoradiographic studies showed maximal grain density at the region of maximal myocyte necrosis. This study demonstrates that '211-antimyosin (Fab')2 localization is highly specific for necrotic myocardial cells.