Background The natural history and clinical significance of myocardial extracellular volume (ECV) in infarcted myocardium post-STEMI is uncertain. ECV can be estimated by cardiac magnetic resonance imaging (CMR). We measured infarct ECV of STEMI survivors, and assessed the relationships with clinical findings.

Methods STEMI survivors were enrolled in a cohort study (BHF MR-MI study – NCT02072850). CMR was performed at 1.5 Tesla (Siemens MAGNETOM Avanto) 2 days and 6 months post-MI. T1 MOLLI mapping was performed pre- and 15 min post-contrast (0.15 mmol/kg gadoterate meglumin). ECV was calculated as the difference in relaxation rate (R1 = 1/T1) for myocardium and LV blood pool pre- vs. post-contrast, corrected for haematocrit (HCT). The percentage change in infarct ECV was calculated (%ΔECV).

Results 129 patients (59 ± 11 years; 98 (76%) male) were included. Infarct ECV at baseline and follow-up was similar (49.5(9.3)% vs. 49.4 ± = (10.9)%; p = 0.904). The within-subject change in ECV varied markedly (1.0% (20.0%)). In multiple linear regression, TIMI coronary flow grade 2 pre-PCI, TIMI coronary flow grade 3 pre-PCI, a history of previous PCI and initial infarct size were independently associated with%ΔECV (all p < 0.05). At 6 months, LV end-diastolic volume increased on average by 2(25) ml. An increase in infarct zone ECV was associated with an increasing LV end-diastolic volume (0.30 (0.11, 0.48); p = 0.002).

Conclusion %ΔECV is associated with measures of MI severity, and portends worsening LV volume. Infarct ECV represents a novel biomarker for infarct characterisation in STEMI patients.