Noninvasive assessment of coronary artery bypass patency: determination of myocardial thallium-201 washout rates.

This prospective study was undertaken to investigate the response of thallium-201 washout rates to coronary artery bypass surgery. Thirty-four patients with coronary heart disease were studied before and after coronary artery bypass grafting, 27 patients with normal coronary arteries serving as controls. All patients underwent cardiac catheterization and thallium-201 serial imaging, including assessment of myocardial washout rates. Pre-operatively, thallium-201 washout rates yielded a considerably higher sensitivity in detection of coronary artery disease, without significant loss of specificity compared to qualitative evaluation of serial static thallium-201 scintigrams. Post-operatively, 50 of 57 segments supplied by a patent graft showed normal washout rates, while in 9 out of 11 segments an occlusion of the graft was indicated by decreased washout rates. Compared to pre- and post-operative qualitative interpretation of static thallium-201 images, the post-operative assessment of washout rates increased both sensitivity (82% vs. 64%) and specificity (88% vs. 77%) for the evaluation of bypass graft patency. Thus, quantitative assessment of thallium-201 washout rates improves the diagnostic reliability of noninvasive detection of myocardial ischaemia with regard to the evaluation of coronary artery bypass graft patency.