748-5 Collateral Flow Determination During Coronary Occlusion with Tc-99m-Sestamibi: Validation in a Closed Chest Canine Model

The purpose of this study was to determine whether tomographic imaging with Tc-99m-Sestamibi (MIBI) can identify collateral flow during coronary occlusion as measured by radiolabelled microspheres. Seven anesthetized mongrel dogs underwent 40 minutes of proximal coronary occlusion by a percutaneous 3.0 balloon catheter. At 30 minutes of occlusion, microspheres were injected via a transseptal left atrial catheter; simultaneously, 30 mCi of MIBI were injected intravenously. Tomographic imaging was performed 45 minutes after reperfusion. Following sacrifice 2–4 hours after reperfusion, the heart was sliced into 5 short-axis slices which were placed on the camera face for imaging. Tissue activity of MIBI and microspheres were determined for 2gm segments(n=417) in a well counter. Coliateral flow by MIBI was calculated by the ratio of minimum/maximum counts (severity) for each pathologic and tomographic slice (n=29) using previously published methods. Area at risk was 19–48% of the left ventricle. Tissue MIBI activity was highly correlated with myocardial blood flow in myocardial segments for each dog (r=0.89–0.98, median r=0.95). This correlation remained significant when only severely ischemic segments (<0.3ml/gm/min blood flow, n=77). were analyzed (r=0.85, p<0.0001). There was a significant correlation between the lowest values of blood flow in the ischemic zone of each pathologic slice and MIBI collateral flow estimates for pathologic (r=0.85, p<0.0001) and tomographic (r=0.78, p<0.0001) short-axis slices.Conclusion(1) Two to 4 hours after reperfusion, MIBI tissue levels closely parallel myocardial blood flow measured during occlusion within the ischemic zone. (2) When MIBI is injected during occlusion, the severity of the tomographic perfusion defect acquired after reperfusion is determined primarily by collateral flow in the ischemic zone