Factors Affecting the Value of Planar Exercise Thallium Scintigraphy in the Diagnosis of Coronary Artery Disease

Factors influencing the outcome of planar exercise thallium scintgraphy (ExTS) in the diagnosis and management of coronary artery disease were assessed in this study. The scans of 198 patients who had undergone coronary angiograms were reevaluated without a quantitative analysis. The test was performed in 64 patients in 1986, in 88 patients in 1987 and in 46 patients in 1988. The sensitivities were found to be 92 %, 86 % and 95 % with corresponding specificities of 62 %, 84 % and 100 % with respect to the year the test was performed. The overall sensitivity was 90 % with a specificity of 80 %. After reevaluation sensitivity increased to 94 % while the specificity did not change. The reason for false positivity in 5 of 9 patients was found to be errors in the evaluation of normal variants. In the remaining 4 patients, 3 with a proven previous myocardial infarction and 1 with cardiomyopathy, coronary arteries were normal, but the coronary perfusion was abnormal. In the 15 patients with a false negative diagnosis, the reasons were interpretation errors in 6, low image quality in 3, distal vessel disease in 2, and sufficient collateral flow in 1 patients. Perfusion defects in more than one region could be detected in 42 % of patients with two or three-vessel disease. In all patients defects were detected in 78 % of the patients with left anterior descending disease, 55 % in right coronary artery discase, and 39 % in circumflex disease. Thus we concluded that results obtained with two different methods, one displaying the "anatomy", the other reflecting the "function" are not always consistent with each other and the main factor affecting the sensivity of ExTS in detecting individual lesions in the amount o myocardium jeopardized. Experience in interpretation is of paramount importance as to the diagnostic value of exercise thallium scintigraphy.