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 collateral-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 without reperfusion, whereas group 2 dogs (n=6) underwent both occlusion and reperfusion. RA was measured with aortic root injections of microbubbles. Myocardial contrast echocardiography (MCE) was performed with high mechanical index intermittent harmonic imaging at pulsing intervals (PIs) of <1 to 30 cardiac cycles during an intravenous infusion of microbubbles (Sonozoid). MBF was measured with radiolabeled microspheres, and postmortem tissue staining was used to determine IS. Perfusion defect size (PDS) on MCE varied with the PI and was largest at a PI of 2.6±0.4 seconds, where it correlated well with RA (r=0.82). PDS was smallest at a PI of ≥10.6±1.5 seconds, where it correlated closely with IS (r≥0.92). Areas that underwent necrosis could be identified early after coronary occlusion as having the lowest microvascular flow velocity (β) and MCE-derived MBF (A×β). The results were similar with or without 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-derived residual MBF within the RA. Thus, it could help individualize risk and management in acute myocardial infarction.