resonance imaging (CMR) using T1 MOLLI maps before and after contrast. We repeatedly measured infarct ECV in STEMI survivors, and assessed the relationships between ECV, peak troponin T and baseline infarct size. Methods Acute STEMI survivors were enrolled in a singlecentre cohort study (BHF MR-MI study -NCT02072850). Contrast-enhanced CMR was performed at 1.5 Tesla (Siemens MAGNETOM Avanto) 2 days and 6 months post-MI. T1 mapping with MOLLI was performed before and 15 min after contrast (0.15 mmol/kg gadoterate meglumine). ECV analysis was performed by outlining regions of interest (ROIs) in infarcted myocardium and left ventricular (LV) blood pool. ROIs were representative of the infarct including microvascular obstruction. ECV was calculated as the relaxation rate (R1=1/T1) for myocardium and LV blood pool before vs. after contrast, corrected for haematocrit. Infarct size was measured using late gadolinium images and expressed as a percentage of LV mass. Infarct ECV at baseline and follow up was compared with peak troponin T measured at presentation and infarct size at baseline. Peak troponin T was log-transformed to improve normality and linearity. Results 201 STEMI patients (mean age 58 ± 11 years; 156 (77%) male) were enrolled. Infarct ECV was similar at baseline and follow-up (51.3 ± 9.5% vs. 50.3 ± 12.0%, p = 0.097). Peak troponin T was widely variable (4256.7 ug/L ± 4020.8 ug/ L). Peak troponin T was positively associated with infarct ECV at baseline (p < 0.001) and follow-up (p < 0.001). Infarct size at baseline was 18 ± 13% of LV mass and was positively associated with infarct ECV at baseline (p < 0.001) and follow-up (p < 0.001) ( Table 1). Background The clinical significance of infarct extracellular volume (ECV) post-STEMI is unknown. ECV can be estimated by cardiac magnetic resonance imaging (CMR) using T1 MOLLI maps. We measured infarct ECV in STEMI survivors, and assessed the relationships between ECV and markers of MI severity. Methods STEMI survivors were enrolled in a single-centre cohort study (BHF MR-MI study -NCT02072850). Culprit artery flow was described by thrombus in myocardial infarction (TIMI) classification. CMR was performed at 1.5 Tesla (Siemens MAGNETOM Avanto) 2-days and 6-months post-MI, including T1-mapping with MOLLI before and 15-minutes after contrast (0.15 mmol/kg gadoterate meglumine). ECV was analysed by outlining regions-of-interest (ROIs) in infarcted myocardium, including microvascular obstruction, and left ventricular (LV) blood pool. ECV was calculated as the relaxation rate (R1=1/ T1) for myocardium and LV blood pool before vs. after contrast, corrected for haematocrit. ECV was compared with TIMI-flow pre-and post-percutaneous coronary intervention (PCI) and STsegment resolution. A reduction in ST-segment voltage of ‡70% was considered complete ST-resolution and <70% was considered incomplete ST-resolution. Results 201 STEMI patients (age 58 ± 11 years; 156 (77%) male) were enrolled. Infarct ECV was similar at baseline and follow-up (51.3 ± 9.5% vs. 50.3 ± 12.0%, p...
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