Role of Coronary Artery Disease and Collateral Circulation in Redistribution of Thallium-201

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Abstract
A total of 19 patients had myocardial perfusion imaging with thallium-201 thallous chloride (Tl-201) immediately after maximal treadmill exercise and 4–6 hours later (redistribution). They also were given rest–stress EKGs and coronary angiograms as part of an evaluation of coronary artery disease. Twenty-six defects were seen on initial postexercise scans in the 19 patients. Of these, 20 were in the region of noninfarcted myocardium and six were in zones of previous myocardial infarction (diagnosis based on the resting EKG). Of the 20 defects in noninfarcted myocardium, 12 were associated with significant obstruction (> 75%) of regional coronary vessels. The remaining eight had normal coronary arteries or ≤ 75% occlusion. Of the 12 defects with significant disease of coronary vessels, eight showed redistribution of Tl-201; there were functional collaterals to the involved vessels in all of these defects. Of the six defects in the region of prior myocardial infarction, no redistribution of Tl-201 was seen in five (one showed only partial redistribution). In this group, the incidence of collateral circulation was similar to that in noninfarcted myocardial cases. A significant association exists between redistribution of Tl-201 and absence of severe obstruction, or the presence of vessel disease, but with functional collaterals to the involved areas in patients with transient myocardial ischemia. Collaterals do not appear to influence redistribution of Tl-201 in zones of myocardial infarction.

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