Noninvasive prediction of ultimate infarct size at the time of acute coronary occlusion based on the extent and magnitude of collateral-derived myocardial blood flow

Background-We hypothesized that by detecting regions with adequate collater al-derived myocardial blood flow (MBF) within the risk area (RA), we could predict ultimate infarct size (IS) at the time of coronary occlusion. Methods and Results-Group 1 dogs (n= 15) underwent coronary occlusion witho ut reperfusion, whereas group 2 dogs (n=6) underwent both occlusion and rep erfusion. RA was measured with aortic root injections of microbubbles. Myoc ardial contrast echocardiography (MCE) was performed with high mechanical i ndex intermittent harmonic imaging at pulsing intervals (PIs) of <1 to 30 c ardiac cycles during an intravenous infusion of microbubbles (Sonozoid). MB F was measured with radiolabeled microspheres, and postmortem tissue staini ng was used to determine IS. Pei-fusion defect size (PDS) on MCE varied wit h the PT and was largest at a PI of 2.6 +/- 0.4 seconds, where it correlate d well with RA (r=0.82). PDS was smallest at a PI of greater than or equal to 10.6 +/-1.5 seconds, where it correlated closely with IS (r greater than or equal to0.92). Areas that underwent necrosis could be identified early after coronary occlusion as having the lowest microvascular flow velocity ( beta) and MCE-derived MBF (AX beta). The results were similar with or witho ut reperfusion. Because of variability in collateral-derived MBF, there was no correlation between RA and ultimate IS (P=0.37). The extent of regional dysfunction also correlated poorly with IS (r=0.31). Conclusions-MCE can be used immediately after coronary occlusion to define ultimate IS by measuring the magnitude and spatial extent of collateral-der ived residual MBF within the RA. Thus, it could help individualize risk and management in acute myocardial infarction.