Scintigraphic quantification of myocardial ischemia: a new approach.

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Abstract
To develop a quantitative scintigraphic measurement of ischemia, 201Tl scintigrams were recorded by the 7-pinhole tomographic technique immediately after exercise and 3 h 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 h tracer distribution and of the 3 h clearance rate were generated for each of 3 left ventricular sections. A circumferential profile of the 3 h clearance rate (initial counts minus 3 h 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 3 sections the area (in arbitary units) between the exercise and 3 h profiles and the area by which the clearance profile fell below the lower limits of normal for clearance derived from the normal subjects. 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 age-predicted 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 1 of 9 with < 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 1-, 2- and 3-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 anteriography score designed to reflect the potential for ischemia based on the coronary anatomy (r = 0.78, P < 0.001) and with an index of ischemia generated from the exercise ECG (r = 0.72, P < 0.001). A continuous and quantitative scintigraphic index of myocardial ischemia evidently can be derived from analysis of the postexercise distribution and clearance of 201Tl. 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.

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