Objectives This study investigated the relationship between the index of microcirculatory resistance (IMR) and myocardial salvage as determined by T2-weighted and contrast-enhanced cardiac magnetic resonance (CMR) imaging in patients undergoing primary percutaneous coronary intervention (pPCI) for ST elevation myocardial infarction (STEMI).

Background IMR is a simple invasive measure of microvascular function available at the time of pPCI. T2-weighted non-contrast CMR can reveal myocardial oedema, and in the post-infarct population this represents the ischaemic area at risk (AAR). Contrast-enhanced CMR delineates the area of myocardial infarction. The volume of myocardium within the AAR, but not contained within the infarct area is salvaged myocardium.

Methods 108 patients with STEMI underwent invasive coronary physiology measurements during pPCI and had a subsequent CMR scan at a median of 19 h post pPCI. Short axis non-contrast T2-weighted images were acquired and delayed enhancement imaging was performed following administration of intravenous gadolinium (0.1 mmol/kg). AAR was determined and myocardial salvage was calculated as AAR—infarct area.

Results IMR was 29 (21), AAR 32% (13%) and myocardial salvage 6% (9%)—all mean (SD). Spearman rank correlation between IMR and AAR was 0.27 (p 0.02) and between IMR and salvage was −0.31 (p 0.01). IMR was also a multivariate predictor of AAR (p 0.01) and a negative multivariate predictor of myocardial salvage (p 0.02).

Conclusions IMR measured acutely correlates with AAR and correlates negatively with myocardial salvage as determined by MRI.