QT Interval and Sympathetic Nervous System Dysfunction in Diabetic Patients

Abstract

We evaluated autonomic nervous system dysfunction in diabetic patients by an objective and quantitative sympathetic function test using the QT interval. We constructed a regression line of QT interval with respect to R-R interval in 602 healthy controls to obtain a QT interval independent of R-R interval. We also measured ΔQT, which was the difference between the measured and theoretical QT intervals obtained from the regession line in healthy controls. The ΔQT was prolonged by propranolol and should thus reflect sympathetic nervous function. The QT intervals of 59 diabetic patients (NIDDM) were measured. The ΔQT of those patients was compared with that of the 59 age-matched controls. We also examined the relationship between the clinical features of diabetes mellitus and the ΔQT. The regression line was QT (msec)=0.143×R-R (msec)+243. The ΔQT of diabetic patients (17 msec) was significantly greater than that of the 59 age-matched healthy controls (7 msec), though it was not related to the duration of diabetes, diabetic control, or the presence of retinopathy or proteinuria. However, the ΔQT of patients with delayed nerve conduction velocity (22 msec) or orthostatic hypotension (30 msec) was significantly greater than that without these. Significant correlations were found between the ΔQT in diabetic patients and the Valsalva ratio, the Valsalva overshoot, or the plasma concentration of noradrenaline.ΔQT should be useful in the clinical evaluation of sympathetic nervous system dysfunction in diabetic patients.