Background
Whether technetium-99m-labeled methoxyisobutyl isonitrile (Tc-99m sestamibi) imaging early after reperfusion can detect the amount of salvaged viable myocardium in the presence of a severe residual stenosis remains controversial.
Methods and Results
Nine dogs underwent total left anterior descending coronary 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, ≥15%). Triphenyl tetrazolium chloride infarct size was measured by planimetry, and regional flow was quantified by radiolabeled microspheres. Mean infarct 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 reperfusion, when the LAD flows were comparable for group 1 (9 ± 2 mL • min-1) and group 2 (9 ± 1 mL • 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 after reperfusion, defect magnitude on ex vivo images in group 1 was significantly 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 viability in group 1.
Conclusion
Resting perfusion imaging with Tc-99m sestamibi accurately determined viability of the infarct zone despite reperfusion through a residual stenosis. Tc-99m sestamibi imaging may prove useful in the clinical setting for the prediction of the amount of salvaged myocardium.