It is not surprising that the incidence of asymptomatic coronary disease in the diabetic population is significant. Diabetic patients have more silent ST depression and more perfusion abnormalities during exercise stress testing and thallium scintigraphy (24,94-96). The Milan study on atherosclerosis and diabetes (MiSAD) group found that 12% of the 925 asymptomatic patients with type 2 diabetes had ST depression consistent with ischemia during treadmill stress testing. Approximately half of these patients had nuclear scans consistent with coronary artery disease (94,97). Additional smaller studies have reported asymptomatic coronary artery disease by coronary angiography in approximately 8 to 12% of diabetic patients. In addition to silent ischemia, diabetic patients also have a higher incidence of silent MI (98-100). The utility of noninvasive screening was examined in a study of 1900 asymptomatic diabetic patients, in which stress testing with dipyridamole myocardial contrast echocardiography followed by coronary angiography in those with perfusion defects, was performed. The positive predictive value of stress testing was best in those patients with two or more risk factors (as compared to patients with one or less risk factor), with significantly higher rates of three-vessel disease (33% vs. 8%), diffuse disease (55% vs. 18%), and vessel occlusion (31% vs. 4%) in those with additional risk factors (24). However, overall, studies have demonstrated a fairly low positive predictive value of noninvasive stress testing in the general diabetic population, raising concern about the utility of noninvasive screening of the asymptomatic diabetic population (24,97,101,102).
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