The effect of transient ischemia with reperfusion on thallium clearance from the myocardium.

Publisher Website
Google Scholar
Abstract
Serial myocardial imaging after a single dose of Tl is often used in evaluating patients with coronary disease. Because the appearance of the image is related to myocardial Tl content, it is important to know if transient ischemia occurring after tracer administration will influence the rate of myocardial Tl clearance. Mongrel dogs (13) (8 study dogs and 5 controls) were studied as follows. The left anterior descending (LAD) coronary artery and the anterior interventricular vein (AIV) were isolated. A catheter was inserted in the AIV to collect venous blood draining from the myocardium in the LAD distribution. A snare was positioned around the LAD proximal to the tip of the AIV catheter. Tl was given i.v. and paired samples of arterial and AIV blood were obtained every 10 min for 1 h to determine Tl activity and K and H ion concentration. The LAD was then occluded for 10 min and paired blood samples were obtained. The snare was released and paired blood samples were obtained beginning 10 s, 4, 10 and 20 min after reperfusion. Regional myocardial blood flow at the time of Tl administration and during the coronary occlusion was determined by the microsphere technique. After 20 min of reperfusion, the dog was sacrificed. The hearts were sectioned and counted for Tl and microsphere activity. During the coronary occlusion, the rate of Tl clearance (.mu.Ci/min .times. 10-2) from myocardium drained by the AIV (-1.1 .+-. 0.3, mean .+-. standard error of the mean) was similar to the rate just before occlusion (-0.68 .+-. 0.21, P = not significant [NS]), and to the rate during the 1st min of reperfusion (-0.77 .+-. 0.55, P = NS). Compared with the rate (milliequivalent [mEq]/min .times. 10-3) just before occlusion (-0.55 .+-. 0.61) a significant (P < 0.001) increase in K output (-7.15 .+-. 1.04) by myocardium in the AIV distribution was observed during the coronary occlusion. H ion output (meq/min .times. 10-11) also increased significantly (P < 0.05) during the occlusion (-12.26 .+-. 0.94) compared with the rate just before occlusion (-6.98 .+-. 0.78). At postmortem examination, the ratio of Tl activity in the ischemic zone to that of the normal zone (1.01 .+-. 0.01) did not differ significantly from the ratio of Tl activity of the LAD to that of the circumflex region (1.04 .+-. 0.05) in control dogs in which no occlusion was performed. Transient ischemia occurring after Tl administration evidently does not influence the normal rate of Tl clearance from the myocardium and may not be detected on serial scans.