WATER-SUPPRESSED ONE-DIMENSIONAL H-1-NMR CHEMICAL-SHIFT IMAGING OF THE HEART BEFORE AND AFTER REGIONAL ISCHEMIA

This study tests the hypothesis that brief periods of ischemia result in an increase in myocardial lipids during early reperfusion. We conducted H-1 NMR spectroscopy to serially measure myocardial lipids before and after regional ischemia. Localized H-1 NMR spectra (spatial resolution of 1.25 mm) were obtained using a one-dimensional chemical shift imaging technique. Two regions, the subendocardium and the subepicardium, were estimated by summing spectral areas from three slices (3.75 mm). Two groups of dogs that underwent a 45 min ischemia and 4 h reperfusion were studied: a group in which the myocardium beneath the surface coil underwent ischemia and reperfusion; and a group in which the ischemic event was distant from the tissue under the surface coil. Microsphere measurements showed significant blood flow reductions in the subepicardium and subendocardium in the ischemic zones during coronary occlusion. Flow returned to baseline values during reperfusion. In the ischemic zone group, the subendocardium, the triglyceride resonance areas decreased by 24% (p<0.05) during reperfusion. However, subepicardial triglyceride areas were unchanged. Subendocardial creatine areas were also unchanged. The non-ischemic zone group subendocardial triglycerides decreased by 33% (p<0.05) following ischemia and reperfusion in the remote region. In contrast to the ischemic group, the subepicardial triglyceride resonance areas decreased by 42% (p<0.05). Subendocardial creatine areas were unchanged. These data show that triglycerides of the ischemic-reperfused subendocardium do not increase during 4 h of reperfusion. Furthermore, they show that the triglycerides resonance areas of the non-ischemic region decrease following remote ischemia and reperfusion. Decreases in the non-ischemic region's triglycerides may reflect enhanced substrate demand resulting from increased work in that portion of the heart.