Scintigraphic quantification of myocardial ischemia: a new approach.

This study was undertaken to develop a quantitative scintigraphic measurement of ischemia. We recorded 201TI scintigrams by the seven-pinhole tomographic technique immediately after exercise and 3 hr later in 15 normal subjects with a low likelihood of coronary disease and in 55 catheterized patients with chest pain. Circumferential profiles of the initial and 3 hr tracer distribution and of the 3 hr clearance rate were generated for each of three left ventricular sections. A circumferential profile of the 3 hr clearance rate (initial counts minus 3 hr counts divided by initial counts, expressed as percent) was also generated for each of these sections. A scintigraphic ischemic score (SIS) was then derived by summing for the three sections the area (in arbitrary units) between the exercise and 3 hr profiles and the area by which the clearance profile fell below the lower limits of normal for clearance derived from the normal subj'ects. This summed area was then normalized for the level of stress by dividing by the product of the exercise duration (in minutes) and the fraction of agepredicted maximum heart rate achieved. This SIS was above the 95% confidence limits derived from the normal subjects in 44 of 46 (96%) patients with the significant coronary disease and in only one of nine with less than a 50% obstruction. The SIS was 52 + 58, 233 + 220, 427 325, and 826 551 U (mean SD) for patients without coronary disease and for those with one-, two-, and' three-vessel disease, respectively. The intergroup differences were statistically significant, but there was considerable overlap among individual patients. More importantly, the SIS correlated significantly with a coronary arteriography score designed to reflect the potential for ischemia based on the coronary anatomy (r = .78, p < .001) and with an index of ischemia generated from the exercise electrocardiogram (r = .72, p < .001). These findings suggest that a continuous and quantitative scintigraphic index of myocardial ischemia can be derived from analysis of the postexercise distribution and clearance of 201T1. Such an index should be valuable in determining prognosis and choosing therapy for patients with coronary artery disease and in assessing their response to therapeutic interventions. Circulation 68, No. 4, 747-755, 1983. THALLIUM-201 (207T1) scintigraphy is widely used to detect coronary disease, usually'in conjunction with exercise testing. In addition, many groups have evaluated its ability to localize obstructed vessels and to estimate the extent of anatomic involvement.24 Unfortunately, the scintigraphic results with these latter applications have often been disappointing, at least in part because of the relative nature of the conventional interpretation criteria, which occasionally make it difFrom the Cardiology Service of the Veterans Administration Hospital and the Department of Medicine and the Cardiovascular Research Institute of the University of California, San Francisco. Supported in part by NHLBI grant No. HL28146. Address for correspondence: Barry Massie, M.D., Veterans Administration Medical Center (111 C), 4150 Clement St., San Francisco, CA. Received Feb. 1, 1983; revision accepted May 26, 1983. Dr. Massie is a Clinical Investigator of the Veterans Administration Medical Research Service. ficult to recognize generalized disease.7 Most recently a combined spatial and temporal approach has been used to evaluate 201TI-perfusion scintigrams. This technique has provided an additional sensitivity, especially in the evaluation of patients with extensive disease.8 11 Previous studies have always assessed scintigraphic findings in relation to the anatomic extent of disease, usually classifying patients by number of obstructed vessels without reference to the viability of the perfused myocardium, the severity of the stenosis, or the presence of collaterals. Thus, there is often a poor correlation between coronary anatomy and either symptomatic or electrocardiographic evidence of ischemia. Furthermore, the relationship between the coronary anatomy and the clinical course of ischemic heart disease, while significant, is relatively crude. It would be valuable to have a quantitative measurement Vol. 68, No. 4, October 1983 747 by guest on January 21, 2016 http://circ.ahajournals.org/ Downloaded from