Abstract 2006: Contrast-Enhanced MRI in the Hyperacute Phase of ST-Elevation Myocardial Infarction Predicts Late Myocardial Recovery

Abstract

Left ventricular ejection fraction (EF) late after myocardial infarction determines whether patients will benefit from cardioverter/defibrillator (CV/D) implantation. At present, patients with acute ST elevation myocardial infarction (STEMI) are evaluated several months later to determine EF and CV/D indication following initial recovery. We determined whether contrast-enhanced MRI (CE-MRI) in the hyperacute phase of STEMI could predict late myocardial recovery. 50 patients with STEMI underwent CE-CMR within 12 hours of primary angioplasty (median 4h). All had follow-up CE-CMR >6 months later. Global and segmental left ventricular function, morphology, perfusion and necrosis were determined and assessed by validated techniques (QMass, Medis, the Netherlands). In the hyperacute phase of STEMI, a greater cardiac output (4.2 vs 3.4 L/min, p=0.01) was measured due to significantly greater heart rate (72 vs 57 bpm, p<0.01) despite similar stroke volumes (59 vs 60mL, p=NS) compared to >6 months later. On average, LVEF did not significantly change from hyperacute STEMI to recovered phase (51 vs 54%, p=NS) but systolic wall thickening increased on average from 41 to 50% (p=0.01) due to compensatory increased systolic thickening of non-infarct related segments. LV mass decreased from 120 to 105 g (p=0.01) due to a decrease in mean wall thickness driven by infarct segment wall thinning (9.2 vs 8.4mm, p<0.01). Microvascular function improved significantly (time to 50% enhancement on first-pass CE-MRI: 24.3 vs 21.7ms, p=0.03). Contrary to prior reports of “scar shrinkage” comparing necrosis in the first week after STEMI and 6 months later, necrosis relative to total myocardial volume did not differ between the hyperacute phase and >6 months (20 vs 18%, p=0.46). Furthermore, the transmural extent of necrosis, a potent predictor of functional recovery, did not significantly change from the hyperacute to the recovered phase of STEMI (mean 17 vs 14%, p=0.38). CE-MRI in the hyperacute phase of STEMI is a powerful predictor of long-term myocardial function and necrosis which could prove useful for very early risk stratification and future targeting of appropriate therapies.