Mapping Myocardial Salvage Index by Extracellular Volume Fraction: Are We There Yet?

Abstract

In ST-segment–elevation myocardial infarction (STEMI) patients treated by primary percutaneous coronary intervention (PPCI), the myocardial salvage index (MSI) provides a more sensitive measure for assessing the efficacy of novel cardioprotective therapies, than an absolute reduction in myocardial infarct (MI) size. Knowledge of the MI size and the size of the area at risk (AAR) are prerequisites for measuring the MSI, and both may be obtained by cardiovascular magnetic resonance (CMR) in reperfused STEMI patients, with the MSI shown to predict clinical outcomes after PPCI.1 CMR is considered the gold standard imaging modality for quantifying MI size, and it can also delineate the edema-based AAR, with T2- and T1-mapping CMR emerging as the most robust techniques,2 although no consensus has yet been reached. See Article by Garg et al In this issue of Circulation: Cardiovascular Imaging , Garg et al3 report on a potentially novel approach for quantifying the AAR, chronic MI size, and MSI in a study of 50 STEMI patients reperfused by PPCI, based on extracellular volume fraction (ECV) maps from an acute CMR scan. The study derived specific ECV cutoff values on an acute CMR scan (performed at a median of 48 hours post-PPCI) in a subset of 10 patients, to delineate the AAR (when compared with T2-STIR imaging), and chronic MI size (when compared with late gadolinium enhancement [LGE]) on a follow-up scan performed at 3 months post-PPCI). Using acute ECV cutoff values of >33% to delineate the AAR and >46% to delineate chronic MI size, they concluded that acute ECV maps could be used to reliably quantify AAR, chronic MI size, and MSI. Being able to accurately quantify MI size using a …