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Contrast-enhanced MR Delineation of Stunned Myocardium with Administration of MnCl₂ in Rats¹

¹ From the Department of Radiology, University of California San Francisco, 505 Parnassus Ave, San Francisco, CA 94143. From the 2001 RSNA scientific assembly. Received March 4, 2002; revision requested May 24; final revision received April 30, 2003; accepted May 20. Address correspondence to M.F.W. (e-mail: mike.wendland@radiology.ucsf.edu).

PURPOSE: To determine whether stunned myocardium can be delineated at magnetic resonance (MR) imaging with differential cellular uptake of manganese ions.

MATERIALS AND METHODS: Twenty-one adult Sprague-Dawley rats underwent either (a) a sequence of three episodes of 10 minutes of coronary artery occlusion and 12 minutes of reflow (group 1, n = 9); (b) a single episode of 10 minutes of occlusion followed by reflow (group 2, n = 6), designed to produce different degrees of myocardial stunning; or (c) a single episode of 2 minutes of occlusion followed by reperfusion (group 3, n = 6), designed to produce no stunning. Ventricular wall thickening was measured on spin-echo (SE) MR images. MnCl₂ (0.025 mmol/kg) was intravenously infused for 10 minutes. Highly T1-sensitive inversion-recovery (IR) SE images were obtained to detect subtle regional differences in manganese accumulation. Hearts were stained at sacrifice to define area at risk and to test for myocardial infarction. Significance of differences in mean values was evaluated with repeated-measures analysis of variance.

RESULTS: All hearts were free of infarction, as detected with triphenyltetrazolium chloride staining. On IR SE images, the hearts from rats in groups 1 and 2 exhibited clearly delineated regions of diminished manganese uptake in the expected territory of the occluded artery. The circumferential extent of the manganese-defined defect (45.5% ± 5.6) was similar to that of the area at risk (46.8% ± 7.5). Systolic wall thickening in the defect was significantly (P < .01) less than in the nonischemic myocardium (2.7% ± 3.3 vs 31.2% ± 7.5 and 10.0% ± 4.8 vs 28.6% ± 6.5, respectively, for groups 1 and 2). The hearts from rats in group 3 demonstrated no wall thickening deficit or abnormal zone on manganese-enhanced images.

CONCLUSION: Stunned myocardium was delineated with MnCl₂-enhanced MR imaging as a hypoenhanced zone. This finding suggests that Ca²⁺ channel activity is diminished in stunned myocardium.

© RSNA, 2004

Index terms: Animals • Contrast media, experimental studies • Magnetic resonance (MR), contrast media, 511.12143 • Myocardium, MR, 511.121411

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