Reliability of myocardial salvage assessment by cardiac magnetic resonance imaging in acute reperfused myocardial infarction

Myocardial salvage assessed by cardiac magnetic resonance imaging (CMRI) holds promise as a surrogate endpoint in studies comparing different treatment strategies for ST-elevation myocardial infarction (STEMI). The aim of this study was to evaluate the reliability of salvaged myocardium measurements by CMRI. Twenty patients underwent CMRI on 2 consecutive days early after reperfused STEMI to assess the area at risk (AAR) on T2-weighted and final infarct size (IS) on delayed enhancement images. Myocardial salvage index (MSI) was calculated (AAR minus IS). Agreement between scans 1 and 2 for the AAR, IS and MSI were analyzed using Bland-Altman analyses. Inter- and intraobserver reliability were assessed. Paired t testing revealed a trend for a significant difference for MSI between scans 1 and 2 (scan 1: 43.8 +/- A 22.5; scan 2: 45.5 +/- A 22.0; P = 0.052). The average difference for AAR and IS between scan 1 and scan 2 was -0.5 (upper limit of agreement 5.4% of left ventricular [LV] volume; lower limit of agreement -6.4%LV) and 0.1%LV (upper limit of agreement 2.3%LV; lower limit of agreement -2.1%LV). The corresponding calculated MSI measurements showed a mean bias of -1.7 (upper limit of agreement 5.5; lower limit of agreement -8.9). Coefficients of repeatability for interobserver variability were 3.6%LV for AAR, 2.4%LV for IS and 5.4 for MSI. Likewise, for intraobserver variability, coefficients of repeatability were 5.0%LV (AAR), 2.4%LV (IS) and 4.8 (MSI). Assessment of myocardial salvage by CMRI shows acceptable reliability. Further validation studies and trials showing the prognostic value of myocardial salvage by CMRI are needed before routine implementation as a surrogate endpoint in STEMI trials.