Abstract
The “redistribution” of Tl-201 administered as a single dose during treadmill exercise and monitored by external imaging may permit differentiation between transient ischemia and old myocardial infarction. The time course of this “redistribution” of Tl-201 was examined in 20 closed chest dogs instrumented with indwelling left atrial catheters and occlusive cuffs placed around the proximal left circumflex coronary artery. In 15 of the dogs Tl-201 and Sr-85 microspheres (15μ) were injected during transient coronary artery occlusion: Five of the dogs were sacrificed 2 min later without releasing the occlusion; five dogs were sacrificed after 30 min and five dogs after 4 h of reperfusion. Five dogs with permanent occlusion of the left circumflex coronary artery were studied 4 h after Tl-201 administration. Compared to normal myocardium Tl-201 activity in regions with>95% flow reductions was decreased by 93.3% in the five dogs sacrificed 2 min after administration. After 30 min of reperfusion this difference was 59.7% and was only 16.5% after 4 h of reperfusion. During the initial 30 min of reperfusion this change in regional distribution was due to a 22% fall in activity in normal myocardium and a 4.4 fold increase in the transiently ischemic myocardium. Activity in normal myocardium declined further by 63% from 30 to 240 min of reperfusion while activity in the transiently ischemic myocardium decreased by 15.5%, although this change was statistically not significant. Thus, early “redistribution” of Tl-201 reflects active uptake of Tl-201 by transiently ischemic tissue and decrease in Tl-201 activity in normal myocadium. During late reperfusion redistribution is primarily due to a more rapid loss of Tl-201 from normal myocardium. We conclude that transient ischemia is visualized best early after stress. Imaging begun late after exercise, e.g., after 30 min, may not permit differentiation between transient ischemia and old myocardial infarction.
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Dr. Schuler is a recipient of a Fulbright Travel Grant and a grant from the Heinrich-Hertz Foundation, Duesseldorf, Germany
This project was supported by Specialized Center of Research on Ischemic Heart Disease, NIH Research Grant HL-17682 by the National Heart, Lung and Blood Institute
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Schelbert, H.R., Schuler, G., Ashburn, W.L. et al. Time-course of ”redistribution” of thallium-201 administered during transient ischemia. Eur J Nucl Med 4, 351–358 (1979). https://doi.org/10.1007/BF00263303
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DOI: https://doi.org/10.1007/BF00263303