Is the Corrected QT Interval a Reliable Indicator of the Severity of Diabetic Autonomic Neuropathy?

Abstract

We investigated whether the corrected QT interval correlated with two other tests for diagnosing autonomic dysfunction in 60 type I diabetic patients with proven peripheral neuropathy. The mean age +/- SD was 48.3 +/- 11.2 yr, the mean duration of diabetes was 24.9 +/- 11.4 yr, and the mean HbA1 was 9.3 +/- 2.4%. All patients underwent three autonomic function tests: 1) the standard five cardiovascular Ewing tests, each scored 0 (normal), 0.5 (borderline), or 1.0 (abnormal). We used the sum of the abnormal findings for the analysis, the cardiovascular autonomic score; 2) measurement of the corrected QT interval taken from a routine electrocardiogram recording; and 3) static and dynamic pupillometry: measurement of dark adapted pupil diameter as percentage of total iris diameter and of pupil constriction latency using an infrared light reflex technique. No significant correlation was found between age, duration of diabetes, or HbA1 and any of the autonomic function tests, except for one between age and cardiovascular autonomic score (r = 0.3202, P = 0.0126). Corrected QT interval did not correlate with cardiovascular autonomic score, pupil diameter, or constriction latency. A significant inverse correlation was found between cardiovascular autonomic score and pupil diameter (r = -0.4861, P < 0.001) and constriction latency (r = 0.3783, P < 0.001). Pupil diameter and constriction latency correlated well (r = -0.4276, P < 0.001). The corrected QT interval did not correlate with cardiovascular autonomic tests nor pupillometry results. The corrected QT interval therefore should not be used for the diagnosis of the severity of diabetic autonomic neuropathy.