[The diagnostic value of the rate-corrected QT interval in long-term type-1 diabetes mellitus]

To assess the relationship between rate-corrected QT interval (QTc interval) and cardiac reflex tests in order to determine the value of QTc interval measurements in the diagnosis of diabetic cardiac autonomic neuropathy.

The QTc interval was measured in the resting ECG of 97 type 1 diabetics (58 women, 39 men; mean age 35 +/- 12 years; duration of diabetes 18 +/- 10 years; HbA1c 7.8 +/- 1.8%). Age-related results were compared with five cardiac function tests (heart rate variation at rest and on forced breathing; 30/15 ratio of heart rate; Valsalva manoeuvre; orthostasis).

The QTc interval was not prolonged ( < or = 440 ms) in 68 patients (70%), while in 29 (30%) it was prolonged ( > 440 ms). No significant differences regarding QTc interval were found between patients with autonomic cardiac neuropathy ( > or = 2 abnormal function tests) and those without ( < 2 abnormal function tests) (QTc interval 436 +/- 25 vs 426 +/- 19 ms). QTc intervals correlated with the coefficients of variation for heart rate variation at rest and on forced breathing and the 30/15 ratio of heart rate (p = 0.001; p = 0.001; p = 0.03), but not with the results of the Valsalva manoeuvre and the orthostasis test.

Prolongation of the QTc interval in longstanding type 1 diabetes does not provide a reliable indication of cardiac autonomic neuropathy and this measure cannot replace conventional reflex tests for its diagnosis.