Utility of QTc interval for the diagnosis of cardiac autonomic neuropathy in type 2 diabetes mellitus

Prolonged QTc interval is a rapid objective method for detecting diabetic cardiac autonomic neuropathy (CAN). Diabetic CAN is a well recognized complication of diabetes mellitus type 2, and its incidence has been reported to be 20-40%, but detection of CAN is not a practical screening method for a large number of diabetic patients.

Methods: 65 cases of type 2 diabetes mellitus with no clinical evidence of cardiac disease were subjected to a battery of 5 non-invasive autonomic function tests as recommended by Ewing; these included deep breath test, orthostatic stress (30:15 ratio), Valsalva ratio, diastolic blood pressure rise with sustained hand grip, and postural hypotension on standing. A score of 2 or larger denoted CAN. QT interval was calculated by Atria 3100 interpretive electrocardiograph. The QTc was determined with Bazett's formula, and a value exceeding 440 msec was considered prolonged.

Results: 24 cases of type 2 diabetes mellitus (36.92%) were found to have CAN. QTc prolongation was observed in diabetics (433.89 +/- 30.37 ms) by comparison with control group 421.2 +/- 24.6 ms (F = 4.9, p = 0.03). QTc was much higher in diabetics with CAN (442.4 +/- 32.69 ms) vs. diabetics without CAN (424.48 +/- 23.45 ms). QTc prolongation correlated positively with the degree of cardiac autonomic neuropathy.

Conclusions: The study has shown that QTc prolongation is an easy and specific testing method for diabetic cardiac autonomic failure.