EVALUATION OF MYOCARDIAL INFARCT SIZE BEFORE AND AFTER REPERFUSION - DUAL-TRACER IMAGING WITH RADIOLABELED ANTIMYOSIN ANTIBODY

Antimyosin antibody is a specific marker of myocardial necrosis that i s based on the loss of integrity of the sarcolemmal membrane. Because antimyosin can be labeled with several different radiotracers, gamma i maging performed with antimyosin labeled with two different radionucli des can be used to quantify infarct size before and after an intervent ion such as reperfusion. Methods: Twelve open-chested anesthetized dog s were evaluated both at the end of 1.5 hr of occlusion of the left an terior descending coronary artery and following reperfusion. Antimyosi n Fab radiolabeled with either I-123 or In-111 was injected by intraco ronary 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 in jection of antimyosin Fab (labeled with a different isotope from the f irst) was administered as before. Six dogs were given intracoronary tr ifluoperazine (150 mu g/kg of body weight) simultaneously with reperfu sion, and another six dogs received saline as the control. The infarct size in grams before and after reperfusion was assessed by antimyosin antibody up take in ex vivo images of 1-cm thick slices of the hearts . The mean infarct sizes before (W1) and after (W2) reperfusion were t hen calculated as the percent of infarcted myocardium/ventricular myoc ardial mass. Results: There was a significant increase in the mean per cent 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 uni formly smaller with trifluoperazine intervention (W2 = 12.33 +/- 2.03, W1 = 16.34 +/- 2.78; p = 0.004). The difference between the mean chan ge 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 demo nstrated the utility of antimyosin imaging to document changes in the extent of necrosis.