913-115 Uptake and Retention of Radiolabled lodophenylpentadecanoic Acid (IPPA) in a Rabbit Model of Acute Myocardial Infarction

When radiolabeled iodophenylpentadecanoic acid (IPPA) is administered to patients with stable coronary artery disease, hibernating myocardium can be detected. However, the uptake and retention of IPPA within acutely infarcted and stunned myocardium has not been critically examined. Accordingly, we evaluated the initial distribution and retention of IPPA in infarcted and viable myocardium from the risk area (RA) of 7 rabbits. The left circumflex artery was occluded for 1 hour during which Nb-95 labeled microspheres (MS) were injected to define the RA. Following 1 hour of reperfusion, Ru-103 labeled MS and 1–123 IPPA were injected. To allow partial myocardial clearance of the 1123 IPPA, a 40 minute period without intervention was observed after which Cr-51 labeled MS and 1–125 IPPA were injected. The hearts were harvested 5 minutes later to determine the retention of 1–123 IPPA and initial uptake of 1–125 IPPA. Hearts were cut into segments which were individually incubated in Nitro Blue Tetrazolium baths to determine viability. The MS and IPPA activity for the normal, the infarcted RA and the viable RA was measured and normalized to the mean activity of the entire left ventricle, and is displayed as follows: Reperfusion Blood Flow IPPA Distribution/Blood Flow At 1hour At 1.7 hour 1–123 Rentention 1–125 Uptake Normal 0.99 ± 0.10 1.11 ± 0.16 1.01 ± 0.08 1.01 ± 0.26 RA-Viable 1.17 ± 0.22 0.86 ± 0.17 * 0.94 ± 0.20 0.97 ± 0.15 RA-Infact 1.14 ± 0.38 0.73 ± 0.24 * 0.94 ± 0.30 0.94 ± 0.16 * p l 0.05 Despite a significant decrease in blood flow within the RA at the end of the experiment, the retained 1–123 IPPA reflected the blood flow at the time of its injection. We conclude that following acute coronary occlusion and reperfusion, the initial distribution of IPPA is related to flow and does not reflect the severity of myocardial injury, In addition, the cardiac retention of IPPA cannot be used to identify acutely infarcted or stunned myocardium, Therefore, during the immediate peri-infarction period, IPPA uptake and kinetics cannot be used to determine the viability of reperfused myocardium.