T2-based area-at-risk and edema are influenced by ischemic duration in acute myocardial infarction

The purpose of our study was to assess whether T2 MRI identifies the infarcted myocardium or the true area-at-risk (AAR) and whether edema is present in the salvageable region following acute myocardial infarction (MI). The study involved a porcine model of MI with a coronary occlusion model of either 60 min or 90 min. Imaging was performed on a 3T MRI pre-occlusion and at day 3 post-MI. Prior-MI, myocardial perfusion territory (MPT) maps were obtained under MRI via direct intracoronary injection of contrast agent. Post-MI, edema extent was quantified by T2 mapping while infarction and microvascular obstruction (MVO) were assessed by late gadolinium enhancement (LGE). Anatomically registered short-axis slices were analyzed for MPT, T2-AAR and infarct areas and T2 relaxation values. Animals were divided into groups with (MVO+) and without MVO (MVO-). T2-AAR area was significantly greater than infarct area in both groups. In the MVO+ group, T2-AAR and MPT were comparable and highly correlated, whereas, in the MVO- group, T2-AAR significantly underestimated MPT without any trend. T2 values in the salvageable myocardium were found to be significantly higher than those in remote myocardium. Our methodology offers the advantage that all images are acquired within the same MRI reference as opposed to complex co-registration with gross pathology. Our study suggests that edema may expand beyond the infarct zone over the entire ischemic bed. T2-AAR may be more clinically relevant than true AAR by perfusion territory since it identifies the "salvageable" myocardium.