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The ability of artériographie, electrocardiographic, and physiologic indices of exercise testing to predict the reversibility of the persistent defect visualized on poststress and early (2-4 h) thallium-201 redistribution imaging was assessed in 35 consecutive patients who had arteriography within 6 months of their scintigraphic study. Postexercise, early, and late (24-72 h) redistribution images were scored on a scale of 0-3. Moderate to complete late redistribution (scores 2 and 3) was found in 23 (66%) patients (group I). Of these patients in group I, 19 had no significant early redistribution (group IA). There was little or no late redistribution (0-1) in 12 patients (group II). Late redistribution of thallium-201 in persistent myocardial defects was prevalent in the culprit vascular distribution in patients with Q wave myocardial infarction, but was more prevalent in patients without the presence of Q waves on the electrocardiogram. No difference was found between groups I and II, respectively, in exercise time, angina pectoris on exertion, rate-pressure product, ischemic electrocardiographic changes, and number of coronary vessels with > 50% luminal narrowing. The degree of stenosis of the culprit artery did not correlate with the presence of late redistribution. Except for a trend in group IA patients to have more frequent angina pectoris on exertion, similar results were obtained comparing group IA with group II. We conclude that neither symptomatic, hemodynamic, and electrocardiographic variables of standard treadmill testing nor the degree of stenosis of the culprit coronary artery by coronary cineangiography can distinguish patients who manifest evidence of ischemia and viability by late-redistribution imaging of persistent myocardial defects following single-dose administration of thallium- 201.

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The decade of the 1990s witnessed a paradigm shift in the use of nuclear cardiology beyond diagnostic applications to prognostic assessments that were incremental to those provided by clinical, exercise, electrocardiographic, and arteriographic data. [1][2][3] The value of radionuclide tomographic perfusion and function imaging as a gatekeeper for coronary arteriography to define revascularization options has been confirmed by a large study of its cost-effectiveness of routine compared with selective use of coronary arteriography by use of single photon emission computed tomography (SPECT) imaging with the Economics of Noninvasive Diagnosis (END) study. 4 A further paradigm shift has been the understanding of the past decade that the vast majority of myocardial infarctions occur in areas of the coronary artery associated with hemodynamically nonocclusive stenoses. 5 We now recognize that prognostically important stress-induced perfusion defects reflect not only the hemodynamic effects of focal stenoses but also the effects of diffuse atherosclerosis 6,7 and vasomotor changes. 8,9 The dynamic vasomotor changes and abnormal endothelial function may not be visible on routine diagnostic coronary arteriography unless vasodilator stress is used. 9 Both the extent and severity of stressinduced perfusion defects contribute to the identification of the coronary event risk associated with plaque burden of the coronary tree. For example, an extensive mild ischemic defect might equal or exceed the risk of a smaller, more severe stress-induced defect. 10 The mechanistic understanding that has resulted from these findings over the past decade has positioned nuclear cardiologists to address 2 further developments in the clinical application of the field to meet public health needs.The first development is the ability of radionuclide myocardial perfusion scintigraphy (MPS) to detect preclinical risk of coronary events in high-risk asymptomatic populations, as has been reviewed recently. 11 The high-risk asymptomatic populations studied to date with MPS include apparently healthy adult subjects with type 2 diabetes mellitus, 12 subjects with siblings or parents with coronary artery disease (CAD), 8,13,14 and subjects with multiple coronary risk factors. 14,15 These asymptomatic subjects tend to have mild perfusion defects related to predominantly mild stenoses and stress-inducible vasomotor changes. 8,9,13 Earlier observations with quantitative coronary arteriography correlated the number and severity of coronary risk factors with reduced stress-induced dilation or provocation of spasm. 16 Risk, rather than symptoms, is considered to drive the predictive accuracy of MPS.The second development is the ability to monitor changes in myocardial perfusion associated with therapeutic effects of lifestyle and medical therapy associated with the healing of the endothelium. Starting in 1994, Gould et al 17,18 first described short-term (90-day) and long-term (5-year) improvements in stress perfusion with lifestyle changes by positron emiss...