Background: QT rate dependence is one of the major properties of ventricular repolarization, with its circadian and autonomic modulations. The alteration of cardiac autonomic tone occurring in obstructive sleep apnea syndrome (OSAS) patients could explain the altered rate-dependent adaptation of the myocardial repolarization. Thus, we postulated that dynamic alterations in QT interval adaptation could be ameliorated in OSAS patients under continuous positive airway pressure (CPAP) treatment. To assess ventricular repolarization features in patients with OSAS, we compared QT parameters and their dynamicities along RR intervals from 24-hour ECG.
Methods: The study groups consisted of 38 consecutive OSAS patients and 38 healthy age-matched subjects. The syndrome was confirmed for OSAS patients according to standard polysomnographic criteria (apnea plus hypopnea index: 56.9 +/- 28.4/h). A second polysomnography synchronized with 24-hour ECG Holter and realized under efficient CPAP therapy confirmed the control of sleep-related breathing disorder.
Results: QT length related to heart rate was found significantly altered in patients with OSAS compared with controls (QTend/RR slope: -0.126 +/- 0.031 vs -0.173 +/- 0.038; P < 0.01). This flattened relationship was significantly improved with the treatment of the OSAS (-0.151 +/- 0.051; P < 0.01 vs pretreatment status). There was no significant impact of CPAP therapy on ventricular ectopic activity as well as on static repolarization parameters (QT, RT, QTc, RTc) measured separately over daytime and nighttime.
Conclusions: The prognostic implications of such findings and the protective role of CPAP treatment to prevent sudden cardiac death in OSAS need to be evaluated.