QTc-interval, heart rate variability and postural hypotension as an indicator of cardiac autonomic neuropathy in type 2 diabetic patients.

OBJECTIVE: To evaluate the QTc-interval, heart rate variability and postural hypotension in predicting cardiac autonomic neruopathy (CAN) in type 2 diabetes mellitus (DM) patients
METHODS: The comparative cross-sectional study was conducted in the Department of Medicine, Muhammad Medical College Hospital, Mirpurkhas, Sindh, from September 2008 to December 2009. A total of 186 type-2 diabetes mellitus patients with a QTc value of > 440 ms were studied. The QT interval was measured on electrocardiographic (ECG) recordings. The patients with HbA1c levels < or = 7% were considered as well-controlled. A cut-off of 5 years was selected for the known duration of diabetes. The longest and shortest R-R intervals on ECG, and heart rate variability (HRV) were determined. An HRV of less than 20 beats per minute was accepted as CAN. The relationship of postural hypotension (PH) and heart rate variability to the duration and control of diabetes were also evaluated. The relationship of cardiac autonomic neuropathy with diabetes control was also determined. Data was analysed using SPSS 10.0 (Chicago, Illinosis, USA). The comparison of differences in means was calculated by the student t-test and the difference in proportions was compared by the Chi-square test. A p-value of < 0.05 was considered significant.
RESULTS: The mean age was 47 +/- 13 years, and the mean duration of diabetes was 13 +/- 7 years. All cases had QTc prolongation with mean 0.52 +/- 0.19. Median QTc intervals were 0.590 (range. 0.515-0.780) and 0.631 (range 0.530-1.869) for males and females respectively. Cardiac autonomic neuropathy manifestations were prominent in diabetics of +/- 5 years when compared with patients for < 5 years (p < 0.003). The postural hypotension difference increased while the heart rate variation decreased with the duration of diabetes (p < 0.002). The PH on standing was significantly related with the control (p < 0.002) as well as the duration of diabetes (p < 0.002). Heart rate variation with respiration was significantly related to the duration (p < 0.005), but not to the control (p = 0.59) of diabetes. QTc showed a significant correlation with the duration of diabetes, postural hypotension and heart rate variation with respiration (p < 0.005, p < 0.013, p < 0.004) respectively.
CONCLUSIONS: Prolonged QTc interval, heart rate variation and postural hypotension are relatively easy, quick and inexpensive methods to measure cardiac autonomic neuropathy.