[High incidence of false positive results of thallium-201 myocardial stress scintigraphy for the evaluation of artery bypass graft patency after CABG].

We have often experienced false positive results of the stress Thallium-201 myocardial scintigraphy (TL) for the evaluation of artery bypass graft patency after coronary artery bypass surgery (CABG). The purpose of this study is to clarify the frequency and the clinical significance of this findings. Sixty-two patients undergoing coronary angiography (CAG) after CABG were studied. These patients had undergone at total of 156 bypasses (artery grafts 108, saphenous vein grafts 48, mean bypass grafts number 2.65/cases), and the mean period from CABG to TL was 41.6 +/- 34 days. The territories of stress induced ischemia were divided into 3 territories; left anterior descending (LAD), right coronary artery (RCA), and left circumflex (LCX) territories. Patency of the bypass grafts was estimated on the absence of transient perfusion defect (TPD) on TL images. The incidence of false positive results was higher in Dipyridamole TL (38%) than in Exercise TL (18%) and higher in LAD territories (38%) than in RCA (11%) and LCX (13%) territories. All false positive cases showed no evidence of chest pain and significant ST-T change during stress TL test. High incidence of false positive results of stress TL test was observed for the evaluation of artery bypass graft patency after CABG.