Increased Short-Term Beat-to-Beat QT Interval Variability in Patients with Imparied Glucose Tolerance

Prediabetic states and diabetes are important risk factors for cardiovascular morbidity and mortality. Determination of short-term QT interval variability (STVQT) is a non-invasive method for assessment of proarrhythmic risk. The aim of the study was to evaluate the STVQT in patients with impaired glucose tolerance (IGT). 18 IGT patients [age: 63 +/- 11 years, body mass index (BMI): 31 +/- 6 kg/m(2), fasting glucose: 6.0 +/- 0.4 mmol/l, 120 min postload glucose: 9.0 +/- 1.0 mmol/l, hemoglobin A1c (HbA1c): 5.9 +/- 0.4%; mean +/- SD] and 18 healthy controls (age: 56 +/- 9 years, BMI: 27 +/- 5 kg/m(2), fasting glucose: 5.2 +/- 0.4 mmol/l, 120 min postload glucose: 5.5 +/- 1.3 mmol/l, HbA1c: 5.4 +/- 0.3%) were enrolled into the study. ECGs were recorded, processed, and analyzed off-line. The RR and QT intervals were expressed as the average of 30 consecutive beats, the temporal instability of beat-to-beat repolarization was characterized by calculating STVQT as follows: STVQT = Sigma|QT(n + 1) - QT(n)| (30x root 2)(-1). Autonomic function was assessed by means of standard cardiovascular reflex tests. There were no differences between IGT and control groups in QT (411 +/- 43 vs 402 +/- 39 ms) and QTc (431 +/- 25 vs 424 +/- 19 ms) intervals or QT dispersion (44 +/- 13 vs 42 +/- 17 ms). However, STVQT was significantly higher in IGT patients (5.0 +/- 0.7 vs 3.7 +/- 0.7, P < 0.0001). The elevated temporal STVQT in patients with IGT may be an early indicator of increased instability of cardiac repolarization during prediabetic conditions.