Hideki Mitani

Usefulness of plasma beta-endorphin level, pain threshold and autonomic function in assessing silent myocardial ischemia in patients with and without diabetes mellitus

The differences between diabetic and nondiabetic patients with silent myocardial ischemia were investigated. Based on the results of previous exercise testing, a total of 110 patients (15 diabetic and 95 nondiabetic) with exercise-induced myocardial ischemia were divided into the following 3 groups: 15 diabetics with silent myocardial ischemia, 49 nondiabetics with silent myocardial ischemia, and 46 nondiabetics with anginal symptoms. All patients underwent treadmill exercise testing and 24-hour ambulatory electrocardiographic recording. Before and during exercise, blood samples from the antecubital vein were obtained to determine the plasma beta-endorphin levels, and the pain threshold of each patient was measured with the electrical skin stimulation test. Furthermore, with regard to the ambulatory electrocardiographic recording, the mean of the SDs of all normal sinus RR intervals during successive 5-minute recording periods over 24 hours was analyzed and considered as an index of the autonomic function. The plasma beta-endorphin level during exercise was significantly greater in nondiabetic patients with silent ischemia than in diabetic ones. The SD mean was significantly less in the diabetic group than in the 2 nondiabetic ones. The findings suggest that the role of beta endorphin in diabetic patients with silent myocardial ischemia may be less significant than in nondiabetic ones; therefore, a diabetic neuropathy that affects the autonomic pain fibers that innervate the heart may be involved in the mechanism of silent myocardial ischemia in diabetics.

Utility and limitation of treadmill exercise echocardiography for detecting significant coronary stenosis in infarct-related arteries in patients with healed myocardial infarction.

This clinical study examines the diagnostic accuracy of exercise echocardiography for detecting significant coronary stenoses in infarct-related arteries in patients with healed myocardial infarction. Quantitative coronary angiography and exercise echocardiography using treadmill testing were performed within 2 weeks of each other in 123 patients with a prior myocardial infarction. Coronary lumen diameter stenosis > or =50% by quantitative coronary angiography and the lack of a hyperdynamic response on exercise echocardiography was considered significant. For detection of infarct-related coronary lesions, treadmill exercise echocardiography was highly sensitive (91%) but less specific (59%) than for detection of non-infarct-related artery lesions. The 2 groups of patients with large and small infarct sites had similar sensitivity for detection of residual stenosis of the infarct-related artery (88% vs 96%, p = NS); however, the specificity of the small infarct sites for this purpose was significantly higher than that of the large infarct sites (86% vs 33%, p < 0.01). When remote ischemia was detected on exercise echocardiography, the specificity of exercise echocardiography was significantly lower (33% vs 70%, p < 0.05) than when remote ischemia was not present. Thus, although there is high sensitivity, the specificity of treadmill exercise echocardiography for detecting infarct-related artery lesions is limited. However, high specificity is maintained when the infarct size is small and/or remote ischemia is not present.