title: Variability of QT interval duration in obstructive sleep apnea: an indicator of disease severity.
abstract: OBJECTIVE
  To determine OSA-related changes in variability of QT interval duration and in heart rate variability (HRV), and to evaluate the relationship of these parameters to disease severity.
  
  
  METHODS
  Retrospective analysis of diagnostic sleep records.
  
  
  METHODS
  Clinical sleep laboratory in a hospital setting.
  
  
  METHODS
  Twenty patients (12 males and 8 females) without significant comorbidities who were undergoing polysomnography were studied.
  
  
  RESULTS
  Standard heart rate variability measures and QT variability (Berger algorithm) were computed over consecutive 5-minute ECG epochs throughout the night. The effect of sleep stage and the relationship between these parameters and the severity of OSA as determined by the respiratory disturbance index (RDI) were explored. Further, a linear regression model of QT variability was developed. Severity of OSA (RDI) was 49 +/- 28 (range from 17-107) events/ hr. QT variability was the only ECG measure significantly correlated with RDI (both log-transformed; r = 0.6, P = 0.006). Further, QT variability was correlated with the minimum oxygen saturation (r = -0.55, P = 0.01). Sleep stage showed a significant effect on HRV, but not on QT variability. In the regression model, RDI was the strongest predictor of QT variability (R2 increase 38%), followed by high and low frequency power of HRV (R2 increase 10% each).
  
  
  CONCLUSIONS
  Obstructive sleep apnea is associated with changes in QT interval variability during sleep. The variance of beat-to-beat QT intervals correlates more strongly with the severity of OSA (as determined by RDI) than standard measures of heart rate variability, and is correlated with blood oxygenation, but not sleep stage.
authors.affiliation: School of Electrical & Electronic Engineering, Centre for Biomedical Engineering, University of Adelaide, Adelaide, Australia.
authors.forename: Mathias
authors.initials: M
authors.lastname: Baumert
authors.forename: Janet
authors.initials: J
authors.lastname: Smith
authors.forename: Peter
authors.initials: P
authors.lastname: Catcheside
authors.forename: R Douglas
authors.initials: RD
authors.lastname: McEvoy
authors.forename: Derek
authors.initials: D
authors.lastname: Abbott
authors.forename: Prashanthan
authors.initials: P
authors.lastname: Sanders
authors.forename: Eugene
authors.initials: E
authors.lastname: Nalivaiko
mesh_terms: D000328:Adult; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D017286:Polysomnography; D020181:Sleep Apnea, Obstructive / Q000097:blood / Q000175:diagnosis*; D012894:Sleep Stages / Q000502:physiology; D013223:Statistics as Topic
chemical_list: D010100:Oxygen