QT interval length and diabetic autonomic neuropathy.

QT interval length was measured in ECG recordings from three groups of age-matched male subjects: 36 normal subjects, 41 diabetic patients without (DAN-ve), and 34 with (DAN+ve) autonomic neuropathy. ECG samples were selected from previously recorded 24-h ECGs on the basis of a clearly defined T wave and a steady RR interval over 2 min of around 750 ms (80 beats min-1). There were no significant differences in RR interval between the groups. The two diabetic groups had slightly longer QT measurements (normal 365 +/- 14 (+/- SD) ms, DAN-ve 373 +/- 18 ms, DAN+ve 375 +/- 23 ms, p = 0.05), and corrected QT (QTc) values (normal 423 +/- 15 ms, DAN-ve 430 +/- 20 ms, DAN+ve 435 +/- 24 ms, p = 0.05). Ten diabetic patients fell above our defined upper limit of normal for QTc (greater than mean + 2SD). There was a significant correlation in the DAN-ve group between the QT indices and 24-h RR counts (QT r = -0.38, p less than 0.01; QTc r = -0.40, p less than 0.01). We conclude that there are some small alterations in QT interval length in the steady state in diabetic autonomic neuropathy. The changes appear to be due to autonomic impairment, rather than diabetes per se.