Stress thallium-201 test for evaluation of artery bypass graft patency after coronary artery bypass surgery

We have often obtained false-positive results on the stress Thallium-201 test (Tl) for the evaluation of artery bypass graft (AG) patency after coronary artery bypass surgery (CABG). The purpose of this study was to determine the frequency and clinical significance of these findings. Seventy-two patients undergoing coronary angiography after CABG were assessed. These patients had undergone a total of 184 bypass grafts (AG 124, saphenous vein grafts 58, 2.61/case), and complete revascularization was performed in all cases. The locations of stress-induced ischemia were divided into 3 territories: left anterior descending artery (LAD), right coronary artery (RCA), and left circumflex artery (LCX). Patency of the bypass grafts was demonstrated by the absence of transient perfusion defect on Tl images. The period from CABG to Tl was 50.8 ± 45 days. The incidence of false-positive results was higher with dipyridamole Tl (39%) than with exercise Tl (28%) and higher in the territory of the LAD (38%) than that of the RCA (17%) and the LCX (19%). In 8 of the 28 false-positive cases, a stress Tl was performed 40.3 months after CABG. In all 8 cases, redistribution had disappeared. In 5 cases, the diameter of the internal mammary arteries had increased. A high incidence of false-positive stress Tl results was observed in evaluation of artery bypass graft patency after CABG. Because of this high incidence of false positive stress Tl results, a limitation in the evaluation of the graft patency should be recognized. (author)