Simultaneous evaluation of infarct size and cardiac function in intact mice by contrast-enhanced cardiac magnetic resonance imaging reveals contractile dysfunction in noninfarcted regions early after myocardial infarction

Background - The objective of this study was to noninvasively determine the effects of reperfused myocardial infarction (MI) on regional and global left-ventricular (LV) function 24 hours after MI in intact mice with contrast-enhanced cardiac MRI and a single, gradient-echo pulse sequence. Methods and Results - Twenty-three mice received baseline MRI scans followed by either 60 minutes of coronary occlusion ( MI group, n = 15) or thoracotomy without occlusion ( sham group, n = 8). Gadolinium- DTPA - enhanced magnetic resonance (MR) images were acquired 24 hours after surgery. Hearts were then excised for conventional infarct size determination via 2,3,5-triphenyl tetrazolium chloride (TTC) staining. In addition to infarct size, analysis of the MR images yielded left ventricular ( LV) mass, LV end-systolic volume (LVESV), LV end-diastolic volume (LVEDV), LV ejection fraction (LVEF), cardiac output, and percent LV wall thickening (% WTh). Twenty-four hours after surgery, infarct size was 28.1 +/- 1.8% of LV mass by MRI and 27.5 +/- 1.7% by TTC ( P = NS). Bland-Altman analysis revealed close agreement between the results obtained by the 2 methods. MI had little effect on LVEDV but caused a 98% increase in LVESV ( from 11.3 to 22.4 muL, P < 0.05), which resulted in a significant reduction in LVEF ( from 70% to 37%, P < 0.05). Compared with LV regional function at baseline, % WTh 24 hours after MI was significantly depressed, not only in infarcted myocardium but also in regions remote from the infarct zone. In contrast, sham-operated mice showed a small but significant increase in % WTh 24 hours after surgery ( P < 0.05). Conclusions - MRI can accurately assess both infarct size and cardiac function in intact mice early after large, reperfused MI, revealing the existence of contractile dysfunction in noninfarcted regions of the heart.