Comparative study of myocardial ischemia during angina at rest and on exertion using thallium-201 scintigraphy

To compare the results of thallium-201 myocardial scintigraphy during angina at rest with those observed during effort angina, 81 patients were selected in whom the existence of acute myocardial ischemia was indicated both by typical transient S-T segment or T wave changes and by typical anginal pain. In these patients, scintigrams were obtained during 58 attacks of angina on effort (group 1) and during 40 attacks of angina at rest (group 2); 16 patients were studied during both types of angina. The attack at rest was spontaneous in 20 patients and induced by ergonovine maleate in 20 patients.In the presence of S-T segment elevation or transient normalization of inverted T waves, scintigrams were positive in all 24 studies at rest and in 19 of 20 studies during exercise. By contrast, in the presence of S-T segment depression scintigrams were positive in 14 (95 percent) of 15 studies during angina at rest, but in only 20 (53 percent) of 38 during angina on effort. Neither the degree of S-T segment changes nor their duration after injection of thallium was significantly different in resting studies relative to exercise studies, but the heart rate and double product were consistently higher during exercise.The marked difference in sensitivity in detecting ischemia in angina at rest with S-T segment depression compared with detection during exertional angina, even in the same patients, suggests that different pathogenetic mechanisms are responsible for the attack. Conversely, a similar mechanism operating in angina at rest and on exertion during S-T segment elevation and normalization of T waves is suggested by the similarity of thallium-201 scintigraphic findings in this situation. The findings are compatible with the hypothesis of a regional reduction in myocardial blood flow in angina at rest, independently of the direction of S-T segment change, and in exertional angina with S-T segment elevation or normalization of inverted T waves; they suggest an inadequate increase in myocardial blood flow in angina on effort with S-T segment depression.