127 Timing of cardiovascular MRI after acute myocardial infarction: effect on estimates of infarct characteristics and prediction of late ventricular remodelling

Background The pathophysiological remodelling processes associated with acute myocardial infarction (AMI) evolve over time and the optimal acute imaging time point to predict medium-term surrogates for outcome has not been established. This study aimed to define the evolution of infarct characteristics by cardiovascular magnetic resonance (CMR), and to assess whether CMR data acquired at “day 2” or at “1 week” post-AMI are stronger predictors of infarct size and left ventricular (LV) function measured at 3 months.

Methods Fifty-seven patients were recruited with first presentation ST elevation AMI treated successfully with primary percutaneous coronary intervention. Cine, T2- weighted and late gadolinium enhancement CMR imaging were performed at days 2, 7, 30 and 90 after index presentation.

Results Infarct size and extent of myocardial oedema decreased significantly between “day 2” and “1 week” (mean %LV-scar (SD) 27.2 (13.9) vs 21.6 (14.1), p<0.001 and %LV-AAR (Area At Risk) (SD), 37.9 (15.2) vs 32.3 (14.3), p=0.003). These changes were accompanied by a significant improvement in LV ejection fraction (%LVEF (SD), 41.7 (9.6) vs 44.6 (10.1), p<0.001). CMR data acquired at “1 week” were better predictors of LVEF and infarct size at “3 months” than data collected at “day 2”.

Conclusions The extent of myocardial oedema and infarct size decrease significantly during the first week after reperfusion for AMI and these changes are associated with a significant improvement in LVEF over the same interval. These findings have implications for the timing of CMR studies in the early post-infarct period. We found that the percentage myocardial salvage index did not change significantly between “day 2” and “1 week”. Therefore, accurate assessment of the efficacy of reperfusion therapy can be made up to one week after revascularization. In addition, CMR data acquired at “1 week” were better predictors of CMR endpoints measured at “3 months”. Thus, we conclude that the optimal time point to image patients post-reperfusion therapy for AMI is at 1 week.