Tc-99m sestamibi defect magnitude predicts the amount of viable myocardiumafter coronary reperfusion despite the presence of severe residual stenosis

Background. Whether technetium-99m-labeled methoxyisobutyl isonitrile (Tc-9 9m sestamibi) imaging early after reperfusion can detect the amount of salv aged viable myocardium in the presence of a severe residual stenosis remain s controversial. Methods and Results. Nine dogs underwent total left anterior descending cor onary artery (LAD) occlusion for 40 to 180 minutes followed by reperfusion through a flow-limiting stenosis, They were divided into 2 groups based on infarct size (group 1, <15% of risk area; group 2, <greater than or equal t o>15%), Triphenyl tetrazolium chloride infarct size was measured by planime try, and regional flow was quantified by radiolabeled microspheres. Mean in farct size was 9.3% +/- 3.0% of risk area in group 1 versus 51.1% +/- 4.8 % in group 2 (P <.01). Tc-99m sestamibi was injected 30 minutes after reperf usion, when the LAD flows were comparable for group 1 (9 +/- 2 mt min-l) an d group 2 (9 +/- 1 mt min(-1)), Left circumflex coronary artery flows were 33 +/- 5 and 32 +/- 9 mL min(-1) for groups 1 and 2, respectively. Despite administration of Tc-99m sestamibi during diminished residual LAD flow afte r reperfusion, defect magnitude on ex vivo images in group 1 was significan tly less severe than that in group 2, which had larger infarcts (0.71 +/- 0 .02 vs 0.42 +/- 0.05, P <.01). This reflects greater salvage and more viabi lity in group 1. Conclusion. Resting perfusion imaging with Tc-99m sestamibi accurately dete rmined viability of the infarct zone despite reperfusion through a residual stenosis, Tc-99m sestamibi imaging may prove useful in the clinical settin g for the prediction of the amount of salvaged myocardium.