MYOCARDIAL ISCHEMIA AND INFARCTION Assessment of Reperfused Myocardial Infarction in the Hyper-Acute Phase with Delayed Enhancement Magnetic Resonance Imaging

Purpose: This study intends to investigate the earliest point which the reperfused infarct size can be accurately measured by delayed enhancement magnetic resonance imaging (deMRI) with the validation of tetrazolium staining as histological gold standard. Methods: Three groups of Sprague-Dawley rats underwent 30 minutes of ischemia by occlusion of the left anterior descending artery. At the end of a designated reperfusion period of 1, 2 or 24 hours, deMRI measurement of infarct size was performed with a spin echo sequence. Corresponding tissue sections from explanted heart were stained with triphenyltetrazolium, and the infarct size was quantitatively compared with deMRI measurements. Results: At 2 and 24 hr after infarction, infarct size determined by deMRI was in good agreement with histology, with a difference of 0.53 ± 3.59% (n = 5) and 1.47 ± 2.19% (n = 7), respectively, of the left ventricular cross section area. However, with 1 hr reperfusion, the area of delayed hyper-enhancement overestimated by 7.58 ± 3.73% (n = 8) compared to tetrazolium staining. In addition, infarct size measured at early points of time (1 and 2 hr) was significantly smaller than at 24 hours. Conclusion: With tetrazolium staining as a reference, deMRI provides accurate infarct size measurement at a time point as early as 2 hrs after reperfused acute infarction. The data will guide the standardization of deMRI protocols for experimental animal studies and have implications for potential clinical applications.