EXERTIONAL MYOCARDIAL ISCHEMIA IN DIABETES - A QUANTITATIVE-ANALYSIS OF ANGINAL PERCEPTUAL THRESHOLD AND THE INFLUENCE OF AUTONOMIC FUNCTION

Patients with diabetes are prone to silent myocardial infarction and silent exertional ischemia. Although the mechanism is not clear, it may reflect a specific impairment of the sensory innervation of the heart. To test this hypothesis, anginal perceptual threshold was measured in 32 diabetic patients and 36 nondiabetic control patients, all of whom had typical exertional angina. Anginal perceptual threshold was defined as the time from onset of 0.1 mV ST depression to the onset of chest pain during treadmill stress electrocardiography. Although ST depression occurred earlier in the diabetic than in the nondiabetic group (111 ± 82 versus 216 ± 162 s, p < 0.005), the anginal perceptual threshold in the diabetic group was delayed by a mean of 86 s (149 ± 76 versus 63 ± 59 s, p < 0.001), with 95% confidence intervals of 53 to 119 s. Autonomic function tests were abnormal in the diabetic group, and in both groups regression analyses (using a third order polynomial) showed marked prolongations of anginal perceptual threshold as the heart rate responses to the Valsalva maneuver decreased to below the normal range (r = 0.5, p < 0.001). There was a similar though less pronounced relation between anginal perceptual threshold and the heart rate responses to deep breathing (r = 0.3, p < 0.02). These data suggest that prolongation of the anginal perceptual threshold may be caused by autonomic neuropathy involving the sensory innervation of the heart. To test sensory function, median nerve conduction studies were performed in 19 patients (10 diabetic and 9 nondiabetic). These confirmed that sensory function was subclinically impaired in the subgroup with diabetes, as reflected by increased latency (3.2 ± 0.6 versus 2.5 ± 0.4 ms, p < 0.05) and reduced signal amplitude (6.3 ± 4.2 versus 9.1 ± 1.7 μV, p < 0.05) and conduction velocity (45.0 ± 8.5 versus 55.2 ± 5.0 m/s, p < 0.01) relative to the nondiabetic subgroup. Thus, in patients with diabetes, anginal perceptual threshold is prolonged in association with autonomic and sensory neuropathy. The data suggest that altered perception of myocardial ischemia results from damage to the sensory innervation of the heart, representing a previously unrecognised feature of diabetic neuropathy. © 1990.