Localization of radiolabeled cardiac myosin-specific antibody in myocardial infarcts. Comparison with technetium-99m stannous pyrophosphate.

The myocardial uptake of radioiodinated (Fab')2 fragments of antimyosin antibody [125I-(Fab')2] was compared with simultaneously administered 99mTc-pyrophosphate (Tc-PYP) in dogs undergoing coronary occlusion for 24 (N=6) or 72 hours (N=5). Relative concentrations of both agents in normal and infarcted myocardium were related to regional blood flow as determined by distribution of 55Sr-labeled microspheres in the same animals. There was an inverse exponential relationship between 125I-(Fab')2 localization and regional blood flow in 24 hr (r=-0.64) and 72 hr (r=-0.80) occluded animals. The greatest uptake of 125I-(Fab')2 was observed in subendocardial layers of the center of the infarct where regional flow was most severely impaired (1-10% of normal flow). Maximal localization of Tc-PYP was observed in subepicardial layers in samples from the periphery of the infarct where flow was only moderately reduced (31-50% of normal). Differences in distribution of these two agents in ischemic myocardium are probably related to differences in kinetics of exit from the blood pool.