Differentiation of Transiently Ischemic from Infarcted Myocardium by Serial Imaging after a Single Dose of Thallium‐201

Myocardial 201TI uptake and regional blood flow by the microsphere technique were determined in anesthetized dogs undergoing either 20 min of coronary occlusion and 100 min of reperfusion (N = 10) or 120 min of occlusion (N = 4). In both groups, 201TI was injected intravenously after 10 min of occlusion. In transiently occluded dogs, regional flow at the time of 201TI administration was reduced to 8 ± 3% of normal flow in endocardial layers of the central ischemic zone. After 100 min of reperfusion, flow values were not significantly different from normal. 201TI activity after reperfusion rose to 56 ± 5% of normal, demonstrating that redistribution of the radionuclide occurred during the reflow period. In animals with persistent occlusion, there was a significant relationship between 201TI uptake and flow (r = 0.95) and no evidence of redistribution of 2lTl during the two hour occlusion period. In another five dogs receiving 201TI, serial gamma camera images obtained during reperfusion showed increasing uptake of the tracer in apical defects which returned to normal by 4 hours of reflow.Thirteen patients with stable angina received 2 mCi of 201TI intravenously at peak exercise, and multiple gamma camera images obtained serially. All demonstrated zones of diminished 201TI uptake 10 min after exercise. Defects which partially or completely disappeared within 1–6 hours postexercise corresponded to areas supplied by coronary arteries with significant stenoses. Persistent defects were present in regions of old myocardial infarction. Six additional patients with acute myocardial infarction demonstrated 201TI myocardial defects which showed no significant change over 6 hours.Thus, redistribution of 201TI into ischemic myocardium was demonstrated during transient coronary occlusion in dogs and after exercise stress in man. Sequential imaging after a single dose of 201TI at the time of exercise may provide a means for distinguishing between transient perfusion abnormalities or ischemia and myocardial infarction or scar.