Autonomic Dysfunction and Silent Myocardial Ischaemia on Exercise Testing in Diabetes Mellitus

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Abstract
The incidence and mechanism of painless myocardial ischaemia on exercise testing in diabetic patients is not clear. Therefore, two studies were performed. Retrospectively, all exercise tests carried out in our hospital during the past 5 years were reviewed for silent ischaemia. Prospectively, diabetic patients with known or suspected coronary artery disease underwent autonomic function testing and a second exercise test. Of 1653 exercise tests reviewed, 247 were positive (ST depression > 0.1 mV). Of the 29 diabetic patients with positive tests 20 (69%) had painless ST depression, compared with 77 (35%) of the 218 non-diabetic patients (p < 0.001). The diabetic patients with painful and painless ST depression were comparable for age, sex, therapy, but the 20 with no pain on exercise testing had a longer duration of diabetes and a higher incidence of microvascular complications than the 9 with pain (70 vs 22%, p < 0.05). In the prospective study, 12 of 30 diabetic patients with positive exercise tests had pain in association with ST depression and 18 had no pain. Six patients had mild and 12 severe autonomic neuropathy on formal testing. Twelve had no autonomic dysfunction. Eleven (92%) of 12 patients with severe neuropathy had painless ST depression, compared with 7 (39%) of 18 without severe neuropathy (p < 0.01). Thus, silent myocardial ischaemia on exercise testing is common among patients with diabetes mellitus and is associated with severe autonomic dysfunction.