Abstract 16618: Pre-Gadolinium Inversion-Recovery Sequence: A Novel and Reliable Magnetic Resonance Method for Assessing Area at Risk

Abstract

Introduction: Non-invasive assessment of area at risk (AAR) during myocardial infarction (MI) is of paramount importance in cardioprotection studies. T2-weighted (T2W) magnetic resonance imaging (MRI) is commonly used to quantify myocardial AAR but it is extensively limited by high susceptibility to artifacts. We postulated that edema-induced increase of T1 time in the acute phase of MI could be detected by a precontrast, inversion-recovery (IR), T1-weighted (T1W) sequence

Methods: Acute MI was induced in 9 Yorkshire pigs by balloon occlusion of the proximal LAD for 60 minutes. MRI was performed at 1 week. AAR was quantified as regions with signal intensity >2 standard deviations above that of remote myocardium prior to contrast injection in both conventional T2W and novel IR-T1W approaches. MI size was measured by standard late gadolinium enhancement. At 1 month dobutamine-MRI was performed; prior to euthanasia a balloon catheter was inflated at the original occlusion site, and Evans blue dye was injected to quantify AAR

Results: AAR derived from the precontrast IR-T1W sequence encompassed 38.5±5.7% of left ventricular (LV) mass, and did not differ from T2W-derived AAR (39.4±5.8% of LV) or Evans blue-derived AAR (40.64±3.8% of LV; p=NS for both). There was a strong correlation in edema between IR-T1W and T2W (r=0.97, p<0.01); Evans blue and IR-T1W (r=0.75, p<.05); and Evans blue and T2W (r=0.79, p<0.05). AAR detected by both IR-T1W and T2W was larger than scar size (33.8±7.8% of LV, p<0.05 for both) allowing for quantification of salvaged myocardium. IR-T1W-estimated myocardial salvage correlated positively with the change in LV ejection fraction from 1 week to 1 month (r=0.71, p<0.05) and with dobutamine-contractile reserve (r=0.73, p<0.05). Furthermore, IR-T1W-estimated myocardial salvage inversely correlated with parameters of postMI LV remodeling: LV mass at 1 month (r=-0.8, p<.05) and cardiomyocyte hypertrophy (r=-0.73, p<.05), better than T2W-salvage (r=-0.65 and r=-0.61, respectively)

Conclusions: IR-T1W imaging is a novel approach that reliably and accurately quantifies AAR similar to conventional T2W-MRI and Evans blue. IR-T1W-estimated myocardial salvage accurately predicts postMI LV remodeling and recovery of systolic function