Quantification of the extent and severity of myocardial ischemia in single-vessel disease using stress-redistribution thallium-201 single-photon emission computerized tomography

Single-vessel coronary artery (CA) disease (SVD) is not uniformly benign: long-term prognosis is likely to be related to the extent (E) and severity (S) of myocardial ischemia (isch). To assess the ability of stress thalium-201 (Tl) single photon emission computerized tomography (SPECT) to quantify E and S of isch, the authors studied 15 patients (pts) without myocardial infarction who had SVD (8 LAD, 4 RCA, and 3 LCX). SPECT cuts were analyzed using maximum count circumferential profiles (CPs) which were compared with previously established normal (nl) limits derived from 20 nl pts. E of isch was defined as the % of the CP points falling below nl, S and depth (D) of ischemia respectively expressed the total and the mean % by which the abnormal points fell below normal limits. Although all pts had SVD, the range of E, S and D of isch was wide (0 to 48% and 0 to 38% and 0 to 20% respectively). CA scores (CS) were derived using a 15-point system accounting for the distribution of the diseased CA, location, and degree of stenosis, and collateral supply. CS varied from 1.2 to 8. E and S significantly correlated with CS (r=.74,p=.001, and r=.78, p=.000, respectively). The 6 pts with a D ≤ .1 had 75% CA stenosis whereas 5 of the 9 pts with D <.1 had only 50-75% stenosis. Thus, the authors conclude that: 1) pts with SVD have highly differing degrees of isch; 2) E, S and D scores from Tl SPECT correlate favorably with the angiographic extent and severity of disease; and 3) SPECT offers potential for quantification of the magnitude of isch and may become a useful, noninvasive prognostic indicator