[Quantitation of coronary artery lesions by 2-4 hour stress-myocardial clearance of thallium-201]

Abstract

The stress-redistribution thallium-201 scintigraphy and thallium-201 washout method have limitations in their ability to detect individual coronary lesions in patients with multivessel coronary artery disease. The purpose of this study is to investigate the value of the quantitative planar method using the dynamics of thallium-201 redistribution after exercise. We observed the patterns of thallium clearance in the late stages (at 2 and 4 hrs) which are characteristic of decreased myocardial blood supply by the obstructed coronary arteries. In 20 subjects, quantitative thallium scintigrams (planar image and circumferential count profile) and blood samples for thallium concentration were obtained immediately, and 2 and 4 hrs after maximal treadmill exercise. Coronary angiography was performed in all subjects, and 16 patients had coronary artery disease (CAD) and four were normal. The rate of thallium clearance from the blood (TCB) was compared with the rate of thallium clearance from each segmental lesion of the myocardium (TCM) between the 2- and 4-hr images. The system adopted for assignment of myocardial regions to individual coronary arteries has been used as an approach to localization of anatomic disease. In the four patients with normal coronary arteries, TCM exceeded TCB in all regions of all images (specificity 100%). Fourteen of the 16 CAD patients had at least one region where TCM was less than TCB (sensitivity 88%). Ten of the 14 patients with multivessel CAD had multiple regions where TCM was less than TCB (sensitivity 71%). All of the six patients without multivessel CAD (four with normal coronary arteries and two with one vessel disease) did not have multiple regions where TCM was less than TCB (specificity 100%). Quantitative thallium scintigraphy showed sensitivities of 86%, 56% and 91% in the left anterior descending artery, the circumflex coronary artery and right coronary artery, respectively. These results showed that decreased TCM in the late stage is characteristic of myocardial regions where blood is supplied by the diseased coronary arteries. This finding may improve diagnostic sensitivity under the condition of multivessel coronary artery disease.