Abnormal thallium-201 chloride myocardial SPECT findings with noncritical coronary angiography in a patient after coronary artery bypass graft

We report on a patient with a previous CABG and symptoms similar to syndrome X who had normal angiography and significant abnormal 201Tl perfusion. The discrepancy of the two imaging modalities could have occurred because, fundamentally, SPECT is a physiologic measurement that reflects perfusion of the myocardium, while coronary angiography reflects only anatomy, and it is known that anatomy may not predict perfusion well. Coronary angiography may underestimate the severity of coronary disease, atheromatosis involving coronary vascular wall, and its related perfusion. Another possibility is that coronary blood supply was diverted/stolen by 1 proximal branch of the left internal mammary artery during the exercise. Lastly, during stress there was an inability to increase flow reserve, resulting in decreased perfusion pressure to the collateral supply of the septal perforators from the saphenous venous graft to the distal right coronary artery. Stress and delayed 201Tl SPECT imaging provide insight into regional flow, cellular integrity, and viability, providing a valuable technique of assessing the presence of resting and provokable ischemia.