Abstract 12020: Overestimation of the Ischemic Area-at-Risk Despite Partial Resolution of Myocardial Edema Twenty-Four Hours After Myocardial Infarction in Swine

Abstract

Objective: Accurate delineation of the ischemic area-at-risk (AAR) is essential for precise quantification of tissue salvage following myocardial infarction (MI), but time-dependent changes in tissue composition may influence the AAR when it is measured after reperfusion. Based on evidence that post-MI edema declines 24 hours after reperfusion, we utilized serial contrast-enhanced computed tomography (CT) to determine if this is an optimal timepoint for retrospective assessment of the AAR in swine. Methods: Swine (n=7) were subjected to a 75-minute LAD occlusion, during which an initial CT scan was performed to assess the pre-reperfusion AAR. A second CT scan was performed during re-occlusion of the LAD 24 hours later to determine the post-reperfusion AAR. Echocardiography was performed at baseline as well as 1 hour and 24 hours after reperfusion to assess end-diastolic wall thickness (EDWT) as an index of post-MI edema. Infarct size was quantified via post-mortem TTC staining and expressed relative to pre- vs. post-reperfusion AAR values. Results: Dynamic changes in EDWT were observed throughout the reperfusion period, consistent with marked edema early after reperfusion and a subsequent decline 24 hours later ( Table; top ). Despite partial resolution of edema 24 hours after reperfusion, a significant ~25% increase in the AAR was observed at this timepoint vs. pre-reperfusion values ( Table; bottom ). As a result, infarct size differed significantly if expressed relative to the pre-reperfusion AAR (91.7 ± 9.2 %) vs. the post-reperfusion AAR (70.9 ± 8.3 %, p<0.01). Conclusion: The ischemic AAR is overestimated relative to pre-reperfusion values when measured retrospectively 24 hours after reperfusion, despite partial resolution of myocardial edema at this timepoint. These results illustrate how variability in post-infarction edema may complicate the assessment of relative infarct size and myocardial salvage when the AAR is measured after reperfusion.