Value and limitations of myocardial thallium washout rate in the noninvasive diagnosis of patients with triple-vessel coronary artery disease

Abstract

This study tested the hypothesis that recognition of delayed washout of thallium from myocardial scan zones with apparently normal thallium uptake is useful for identifying patients with triple-vessel coronary artery disease (CAD). Exercise thallium stress tests were performed in 21 patients with angiographically proven triple-vessel CAD (≥50% stenosis of all three major vessels). Anterior and left anterior oblique thallium images were obtained 5 to 10 minutes after stress and 2 hours later. Background corrected scans (bilinear interpolative method) were analyzed by computer (radial analysis program) for the presence of initial uptake defects as well as delayed thallium washout. Twenty-five patients with single or double-vessel CAD and 14 patients with normal coronary arteries also were studied to obtain specificity data regarding the diagnosis of triple-vessel coronary disease. In patients with triple-vessel CAD, 50 of 63 (79%) stenosed vessels were detected by combined use of uptake and washout criteria. However, only 8 of 63 (13%) diseased vessels were detected by washout criteria alone. Nevertheless, use of washout criteria did increase the number of patients correctly identified as having triple-vessel disease from seven (identified on the basis of uptake defects alone) to 10. Accordingly, sensitivity using both uptake and washout criteria was 48% (10 of 21 patients). Specificity for the diagnosis of triple-vessel disease using combined uptake and washout criteria was 76% for patients with single- or double-vessel CAD and 95% for normals, and was little different from values obtained based on uptake criteria alone (80% and 100%, respectively). Thus even though relatively few stenosed vessels in patients with triple-vessel CAD are associated with isolated thallium wahout abnormalities, use of washout criteria does increase the sensitivity of the thallium stress test for the detection of such patients and therefore is a worthwhile addition to routine uptake analysis of thallium images of the myocardium.