Time course of thallium-201 redistribution after transient myocardial ischemia.

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Abstract
The mechanism and time course of 201Tl redistribution after transient myocardial ischemia was investigated in 27 anesthetized dogs given 1.5 mCi of 201Tl i.v. 10 min after occlusion of the left anterior descending coronary artery. Coronary reperfusion (RP) was accomplished 10 min after 201Tl administration. Transmural myocardial biopsies were obtained in situ from normal (N) and ischemic (IS) regions during occlusion and 5 min (4 dogs), 20 min (8 dogs), 90 min (6 dogs), 4 h (5 dogs) and 6 h (4 dogs) after RP. There was a 2-fold rise in 201Tl activity (counts/10 min per mg) in the IS region after only 5 min of reflow with as yet no detectable change in 201Tl concentration in the N zone. In dogs undergoing 90 min of RP, 201Tl activity was 700 .+-. 150 (SEM [standard error of the mean]) in the IS zone during occlusion and markedly increased (P < 0.001) to 3200 .+-. 100 at 90 min of reflow. During this period 201Tl activity in the N region decreased slightly from 7000 .+-. 800 to 6000 .+-. 450 (NS). In dogs that underwent 6 h of RP, 201Tl activity in the IS zone increased from 1700 .+-. 500 during occlusion to 3300 .+-. 200 (P < 0.001) after RP. In this group 201TL activity in the N zone significantly decreased from 6400 .+-. 1200 to 3900 .+-. 400 over the 6 h of reflow, reflecting the magnitude of Tl washout after ischemia. This near-equilization of 201Tl activity between N and IS zones was already apparent by 4 h of RP. 201Tl redistribution after transient myocardial ischemia is related to delayed accumulation of 201Tl into ischemic myocardial segments and to a more rapid washout of the radionuclide from normal segments. Qualitatively the serial changes in myocardial 201Tl activity in ischemic and normal myocardium before and after flow restoration in this study, and the time course of Tl redistribution, are similar to the serial scintigraphic changes in patients who receive Tl during exercise stress or spontaneous rest angina.