To determine if incomplete redistribution at 4 h in exercise tomographic thallium-201 studies is always due to a myocardial scar, 141 patients were evaluated before and after a total of 160 successful percutaneous transluminal coronary angioplasty procedures. Thallium studies were analyzed using polar "bull's-eye" maps. For both immediate and delayed images, abnormalities were quantified as a thallium score by calculating a standard deviation-weighted sum of pixels > 2.5 SD below gender-matched normal limits. One hundred forty-four of 160 studies indicated abnormalities before angioplasty. Of these 144, incomplete redistribution occurred in 111 (77%): 16 (14%) in patients with and 95 (86%) in patients without prior Q wave myocardial infarction. After angioplasty, improvement in delayed image score occurred in 8 (50%) of 16 patients with prior infarction and 72 (76%) of 95 patients without prior infarction (p < 0.05). After angioplasty, delayed images were normal in 1 (6%) of 16 patients with prior infarction and 32 (34%) of the 95 without (p < 0.05). Before angioplasty. delayed image scores were positively correlated with scores in the immediate postexercise images in patients with (r = 0.84) and those without (r = 0.69) prior infarction. To determine if additional delayed images could help differentiate scar from ischemia, an 8 to 24 h delayed image was obtained in each of 40 other patients with incomplete redistribution at 4 h. Of 28 patients with prior infarction, 15 had no redistribution and 13 had further redistribution at 8 to 24 h. Of 12 patients without prior infarction, 1 had no redistribution, 7 had further redistribution and 4 had complete redistribution. Thus, 4 h delayed thallium image defects frequently do not signify myocardial infarction. Their severity is proportional to immediate poststress abnormalities. Additional imaging at 8 to 24 h is recommended in patients with incomplete redistribution and no evidence of prior infarction. © 1988.
Cloninger, K. G., DePuey, E. G., Garcia, E. V., Roubin, G. S., Robbins, W. L., Nody, A., … Berger, H. J. (1988). Incomplete redistribution in delayed thallium-201 single photon emission computed tomographic (SPECT) images: An overestimation of myocardial scarring. Journal of the American College of Cardiology, 12(4), 955–963. https://doi.org/10.1016/0735-1097(88)90461-5