QT dispersion and autonomic nervous system function in patients with type 1 diabetes

Cardiac arrhythmias and markedly increased mortality rate have been demonstrated in patients with diabetic autonomic neuropathy. Abnormal prolonged QT dispersion interval (QTd) is associated with a higher risk of ventricular arrhythmias. The aim of this study was to evaluate the relationship between autonomic dysfunction, QT and JT interval dispersion parameters and ventricular arrhythmias. Twenty-six patients with type 1 diabetes mellitus and 20 healthy subjects as controls were enrolled in the study. Resting 12-lead electrocardiograms were recorded for measurement of QTd, corrected QTd (QTcd), JT dispersion (JTd) and corrected JT dispersion (JTcd). After taking ECG, all patients underwent autonomic function tests. Patients and control group were also evaluated by 24-h Holter monitoring. Fourteen patients were identified who had autonomic dysfunction. QTd, QTcd, JTd, and JTcd values were significantly higher in patients with autonomic dysfunction than both patients without autonomic dysfunction and the control group (QTd: 78±16 vs. 51±13 ms, P=0.002; 78±16 vs. 48±9 ms, P<0.001; QTcd: 91±14 vs. 66±12 ms, P=0.001; 91±14 vs. 61±11 ms, P<0.001; JTd: 81±12 vs. 58±13 ms, P=0.001; 81±12 vs. 49±7, P<0.001; JTcd: 96±15 vs. 73±11 ms, P<0.001; 96±15 vs. 67±8 ms, P=0.001). There was no significant difference between the dispersion parameters in diabetic patients without autonomic dysfunction and the control subjects (P>0.05). Also, patients with autonomic dysfunction had higher Lown classes of ventricular arrhythmias and patients with higher Lown classes of ventricular arrhythmias had more prolonged QTd and QTcd values. The data suggest that diabetic patients with autonomic dysfunction have increased dispersion of ventricular refractoriness, which may be one of the factors contributing to the increased incidence of arrhythmias and sudden death observed in these patients.