In the 24 hours after coronary occlusion, some defects on thallium-201 images decrease in size. This study examined the mechanism of the decrease in defect size in dogs with experimental coronary occlusion. The left anterior descending coronary artery was permanently occluded in chronically instrumented awake dogs. Myocardial blood flow was measured with radioactive microspheres immediately before occlusion, 30 minutes, and 24 hours after occlusion. Thallium-201 was injected and imaging was performed 2 to 6 days before occlusion, 30 minutes, and 24 hours after occlusion. Two dogs, in which less than 1% of the left ventricle was infarcted, had no defects on the 30-minute postocclusion images. In four dogs the thallium-201 images did not change appreciably over 24 hours (group 1), while in three dogs the image defect size decreased (group 2). In groups 1 and 2 respectively the percent increase in blood flow to the hypoperfused area was: subendocardium 9 ± 7% vs 31 ± 15%; subepicardium 26 ± 6% vs 47 ± 2% (p < 0.05). Therefore a decrease in the size of thallium-201 image defects occurred if a sufficient increase in collateral flow to the hypoperfused area took place in the first 24 hours after coronary occlusion. The defects appeared to decrease in size even in the absence of a detectable change in the lateral borders of the hypoperfused area.
Bibliographical noteFunding Information:
From the Department Medical School. This work was supported by a Young Investigator Research Award (grant HL-21298) and by National Institutes of Health Grant HL-20598 from the United States Public Health Service; and by a grant-in-aid from the American Heart Association, with funds contributed in part by the Minnesota Affiliate. for publication March 19, 1982; accepted 26, 1982. Reprint requests: Jeffrey S. Schwartz, M.D., Box 258 Mayo Memorial Bldg., University of Minnesota Medical School, Minneapolis, MN 55455.