Nuclear magnetic resonance analysis of acute and chronic myocardial infarction in dogs: Alterations in spin-lattice relaxation times

The purpose of this study was to evaluate the effects of acute and chronic ischemic injury on myocardial spin-lattice relaxation times (T 1) in dogs. Ligation of the left anterior descending coronary artery was performed on 23 dogs which were divided into four experimental groups and killed at 3 hours (n = 6), 4 days (n = 6), 21 days (n = 5), and 56 days (n = 6) after coronary occlusion. T 1 was measured in vitro with a 2.5 kg nuclear magnetic resonance (NMR) spectrometer using tissue from ischemic and control areas of the myocardium. Both the 3-hour and 4-day groups showed prolongations in T 1 ( p < 0.01) for tissue from the ischemic area. In the 21-day group, two infarcts showed an increase in T 1, two showed a decrease in T 1, and one showed no significant change. The 56-day old infarcts had a lower mean value for T 1 than control myocardium ( p < 0.01). The differences in myocardial water content between control and infarcted myocardium were found to parallel changes in T 1 values in each experimental group. Pathologic examination of the myocardial scar from 21- and 56-day-old infarcts revealed extensive fibrosis in the infarcts with lower T 1 values and tissue water contents than control myocardium. We conclude that myocardial edema in 3-hour and 4-day-old infarcts results in association with prolongations in T 1. Twenty-one-day-old infarcts may be edematous (with increased T 1) or fibrotic (with T 1 values lower than normal myocardium), while 56-day-old infarcts are fibrotic and have shorter T 1 values than normal myocardium. This study suggests that NMR imaging may have the capacity to evaluate myocardial edema and help define the duration of ischemic injury.