Time course of thallium-201 redistribution after transient myocardial ischemia

The mechanism and time course of thallium-201 (201Tl) redistribution after transient myocardial ischemia was investigated in 27 anesthetized dogs given 1.5 mCi of 201Tl intravenously 10 minutes after occlusion of the left anterior descending coronary artery. Coronary reperfusion (RP) was accomplished 10 minutes after 201Tl administration. Transmural myocardial biopsies were obtained in situ from normal (N) and ischemic (IS) regions during occlusion and 5 minutes (four dogs), 20 minutes (eight dogs), 90 minutes (six dogs), 4 hours (five dogs) and 6 hours (four dogs) after RP. There was a twofold rise in 201Tl activity (counts/10 min/mg) in the IS region after only 5 minutes of reflow with as yet no detectable change in 201Tl concentration in the N zone. In dogs undergoing 90 minutes of RP, 201Tl activity was 700 +- 150 (SEM) in the IS zone during occlusion and markedly increased (p < 0.001) to 3200 +- 100 at 90 minutes of reflow. During this period 201T1 activity in the N region decreased only slightly, from 7000 +- 800 to 6000 +- 450 (NS). In dogs that underwent 6 hours 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, bbaTl activity in the N zone +- 1200 to 3900 +- 400 over the 6 hours of reflow, reflecting the magnitude of thallium washout after ischemia. This near-equalization of 201Tl activity between N and IS zones was already apparent by 4 hours of RP. These data indicate that 201Tl redistribution after transient myocardial ischemia is related to both delayed accumulation of 201Tl into ischemic myocardial segments and to a more rapid washout of the radionuclide from normal segments