Transient defects of resting thallium scans in patients with coronary artery disease

Defects on resting thallium-201 (²⁰¹Tl) scans in patients who do not have evidence of acute myocardial ischemia have been thought to represent myocardial scar. The authors' study of 20 patients with stable but severe coronary artery disease (CAD), including nine with ECG evidence of myocardial scar, was undertaken to reexamine the significance of such defects. Imaging was performed in two views, beginning within 10 minutes after Tl administration and repeated over a 2-4 hour period. Images in each of the two projections were divided into three zones, for a total of 120 zones in 20 patients. An initial defect was present in 43 zones in 15 patients, while five patients demonstrated totally normal studies. On later scans 18 defects persisted while 25 filled in. Twelve of 18 persistent defects were associated with ECG evidence of infarction, compared with only six of 25 transient defects (p < 0.01). Correlation with angiographic left ventricular wall motion was possible for 12 of 18 persistent defects and 18 of 25 transient defects. Six of 12 persistent defects, compared with only one of 18 transient defects, were associated with akinesia/dyskinesia (p < 0.01). In addition, 17 of 18 transient defects were associated with either normal left ventricular wall motion (12 defects) or hypokinesia (five defects). Finally, 23 of 25 transient defects, compared with only 41 of 77 normal zones, were associated with severe CAD (p < 0.001). Thus, in resting patients with stable CAD: 1) serial imaging reveals that many initial defects fill in over time; 2) initial resting defects on Tl scans may not indicate myocardial scar; and 3) transient defects are usually associated with severe CAD, but normal or only mildly abnormal left ventricular wall motion.