Radionuclide methods of identifying patients who may require coronary artery bypass surgery

Myocardial thallium-201 (201Tl) scintigraphy or radionuclide angiography performed in conjunction with exercise stress testing can provide clinically useful information regarding the functional significance of underlying coronary artery stenoses in patients with known or suspected coronary artery disease. Knowledge of type, location, and extent of myocardial 201Tl perfusion abnormalities or the severity of exercise-induced global and regional dysfunction has prognostic value. Risk stratification can be undertaken with either radionuclide technique by consideration of the magnitude of the ischemic response and may assist in the selection of patients for coronary artery bypass graft surgery (CABG). In patients with coronary artery disease, delayed 201Tl redistribution observed on exercise or dipyridamole 201Tl scintigraphy, particularly when present in multiple vascular regions and associated with increased lung 201Tl uptake, has been shown to be predictive of an adverse outcome, whereas patients with chest pain and a normal exercise 201Tl scintigram have a good prognosis with medical treatment. Similarly, a marked fall in the radionuclide ejection fraction from rest to exercise has been found to correlate with high-risk anatomic disease. In one published nonrandomized study, patients with coronary artery disease who demonstrated an abnormal ejection fraction response to exercise preoperatively had a better survival with CABG than with medical therapy. Another important application of radionuclide imaging in patients being considered for CABG (particularly those with a depressed resting left ventricular ejection fraction) is the determination of myocardial viability and potential for improved blood flow and enhanced regional function after revascularization. There are certain limitations of exercise 201Tl scintigraphy and radionuclide angiography that can be reduced by improved methods of quantitation of perfusion and function and further development of tomographic imaging approaches.