Avidity of technetium 99m glucarate for the necrotic myocardium: In vivo and in vitro assessment

BackgroundSimilar to other99mTc-based infarct-avid agents,99mTc-glucarate localizes in myocardial infarcts. Whether severely ischemic viable myocytes sequester99mTc-glucarate is uncertain. To assess the infarct specificity, in vitro and in vivo studies were performed.Methods and ResultsH9C2 embryonic rat cardiocytes cultured under normoxia (N) or hypoxia (H) for 24 hours in 7.5 μCi99mTc-glucarate were compared with necrotic cardiocytes. Mean H/N ratio (3.0±0.004, mean±SD) was significantly less than that of the necrotic/N ratio (39.9±6.5,p<0.01). Reperfused myocardial infarction (MI) in 4 dogs confirmed by201Tl, (0.5 to 1.0 mCi) scintigraphy were imaged serially, with simultaneously injected mixture of99mTc-glucarate and111In-antimyosin Fab. Infarcts were detected scintigraphically within 4 to 10 minutes with99mTc-glucarate.111In-antimyosin required more than 1 hour. Myocardial distribution at 5 hours showed a direct correlation between99mTc-glucarate and111In-antimyosin uptake (r=0.99,p<0.0001). Both99mTc-glucarate (r=−0.777,p<0.0001) and111In-antimyosin (r=−0.775,p<0.0001) were inversely related to201Tl distribution.ConclusionsThe near perfect correlation between99mTc-glucarate and111In-antimyosin uptake (r=0.99) in reperfused canine MI and the insignificant glucarate uptake by viable cardiocytes in vitro attest to the avidity of99mTc-glucarate for the necrotic myocardium and favor its use as a specific early marker of myocyte necrosis in acute MI.