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Evaluation of Myocardial Infarct Size Before and After Reperfusion: Dual-Tracer Imaging with Radiolabeled Antimyosin Antibody

Cardiac Unit, Division of Nuclear Medicine and Department of Pathology, Massachusetts General Hospital and Harvard Medical School
Center for Drug Targeting and Analysis, Northeastern University, Boston, Massachusetts

Correspondence: For correspondence or reprints contact: Ban An Khaw, PhD, Center for Drug Targeting and Analysis, Mugar-205, Bouvé College of Pharmacy and Health Sciences, Northeastern University, Boston, MA 02115.

ABSTRACT

Antimyosin antibody is a specific marker of myocardial necrosis that is based on the loss of integrity of the sarcolemmal membrane. Because antimyosin can be labeled with several different radiotracers, gamma imaging performed with antimyosin labeled with two different radionuclides can be used to quantify infarct size before and after an intervention such as reperfusion. Methods: Twelve open-chested anesthetized dogs were evaluated both at the end of 1.5 hr of occlusion of the left anterior descending coronary artery and following reperfusion. Antimyosin Fab radiolabeled with either ¹²³I or ¹²³In was injected by intracoronary administration over 3 min at the end of the occlusion interval, and the coronary sinus was drained continuously for 7 min to prevent recirculation of the antibody. One hour after reperfusion, a second injection of antimyosin Fab (labeled with a different isotope from the first) was administered as before. Six dogs were given intracoronary trifluoperazine (150 µg/kg of body weight) simultaneously with reperfusion, and another six dogs received saline as the control. The infarct size in grams before and after reperfusion was assessed by antimyosin antibody uptake in ex vivo images of 1-cm thick slices of the hearts. The mean infarct sizes before (W1) and after (W2) reperfusion were then calculated as the percent of infarcted myocardium/ventricular myocardial mass. Results: There was a significant increase in the mean percent infarct size after reperfusion in the control group (W2 = 16.73 ± 4.0, W1 = 14.92 ± 3.88; p = 0.029). The mean infarct size was uniformly smaller with trifluoperazine intervention (W2 = 12.33 ± 2.03, W1 = 16.34 ± 2.78; p = 0.004). The difference between the mean change in the infarct sizes in the two groups was highly significant (p = 0.002). Conclusion: Dual imaging of the extent of myocardial necrosis before and after an intervention (reperfusion) in the same animal demonstrated the utility of antimyosin imaging to document changes in the extent of necrosis.

Key Words: myocardial infarct size • antimyosin antibody • myocardial reperfusion

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