Significance of magnetic resonance signal enhancement in evaluation of myocardial infarction in cats.

Abstract

To correlate magnetic resonance (MR) signal enhancement with pathophysiologic changes occurring during ischemia and reperfusion in evaluation of myocardial infarction in cats. Seven cats were subjected to 150 minutes of occlusion of the left anterior descending coronary artery followed by 90 minutes of reperfusion. Gadolinium (Gd) diethylenetriaminepentaacetic acid-polylysine (molecular weight [mw] = 40 to 50 kd, DP230) contrast-enhanced MR images were acquired with coinjection of poly-L-lysine-fluorescein isothiocyanate (mW = 40 to 50 kd, DP219) as a fluorescent tracer molecule of the contrast agent. Signal intensities on the MR images and fluorescence activities on the resected cardiac specimens were measured. Pathologic examinations by electron and light microscopes and 2,3,5-triphenyltetrazolium chloride histochemical staining were performed on the specimens. Magnetic resonance signal intensity was lower in the center (3.49 +/- 0.36) than in the periphery (4.71 +/- 0.89) of the enhanced area. Fluorescence activities were absent in the normal myocardium; they were scant as nonspecific discrete dots in the center and numerous as specific interstitial distribution in the periphery of the ischemic myocardium. Electron and light microscopic examinations showed severely damaged ultrastructures of the center and moderately distorted ultrastructures of the periphery. The center of the MR signal-enhanced area is the infarct center with severe ultrastructural damages, which also might be an area of little or absent of blood reflow. Conversely, the peripheral-enhanced area is the infarct periphery with moderate myocardial damages.