title: Corrected QT dispersion and cardiac sympathetic function in patients with obstructive sleep apnea-hypopnea syndrome.
abstract: OBJECTIVE
  Hypoxemia increases corrected QT dispersion (QTcD), which is the difference between the maximum and minimum QT intervals and is a strong risk factor for cardiovascular mortality. The aim of this study was to investigate the QTcD in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS), and the relationship between the QTcD and (123)I-metaiodobenzylguanidine (MIBG) cardiac imaging, which reflects cardiac sympathetic activity.
  
  
  METHODS
  A university hospital.
  
  
  METHODS
  Forty-eight OSAHS patients without cardiac diseases (mean [+/- SD] age, 45.9 +/- 10.8 years; apnea-hypopnea index [AHI] 51.9 +/- 18.5 events per hour) who underwent polysomnography before treatment and on the first night of nasal continuous positive airway pressure (nCPAP) treatment.
  
  
  METHODS
  Before and after nCPAP treatment was started, we measured the QTcD with computer software, before, during, and after sleep, as well as the washout rate of the MIBG administered for cardiac imaging. As a control, QTcD was also measured in the morning from 26 healthy subjects.
  
  
  RESULTS
  Before treatment, the mean QTcD during sleep (65.0 +/- 14.6 ms) was greater than that before sleep (57.0 +/- 13.5 ms; p < 0.0001). Meanwhile, after 1 night of nCPAP therapy, the QTcD during sleep (50.6 +/- 11.4 ms) decreased from that before treatment (p < 0.0001) and was smaller than the QTcD before sleep (56.2 +/- 13.3 ms; p = 0.003). Before treatment, the QTcD during sleep correlated with the AHI (r = 0.38; p = 0.009) and the percentage of time that SaO(2) was < 90% (SaO(2) < 90% time) [r = 0.34; p = 0.018]. The QTcD did not correlate with the body mass index or the washout rate of MIBG. However, the washout rate of MIBG correlated with the AHI and the SaO(2) < 90% time.
  
  
  CONCLUSIONS
  Nocturnal QTcD is increased in OSAHS patients but is decreased by nCPAP therapy independently of cardiac sympathetic function.
authors.affiliation: Department of Respiratory Medicine, Kyoto University Hospital, Kyoto University, Kyoto, Japan.
authors.forename: Takaya
authors.initials: T
authors.lastname: Nakamura
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chin
authors.forename: Ryohei
authors.initials: R
authors.lastname: Hosokawa
authors.forename: Kenichi
authors.initials: K
authors.lastname: Takahashi
authors.forename: Kensuke
authors.initials: K
authors.lastname: Sumi
authors.forename: Motoharu
authors.initials: M
authors.lastname: Ohi
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
mesh_terms: D019797:3-Iodobenzylguanidine; D000328:Adult; D001342:Autonomic Nervous System Diseases / Q000150:complications / Q000175:diagnosis*; D002318:Cardiovascular Diseases / Q000150:complications / Q000000981:diagnostic imaging* / Q000628:therapy; D015331:Cohort Studies; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D011175:Positive-Pressure Respiration / Q000379:methods; D011336:Probability; D011877:Radionuclide Imaging; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012891:Sleep Apnea Syndromes / Q000150:complications / Q000000981:diagnostic imaging* / Q000628:therapy; D018709:Statistics, Nonparametric
chemical_list: D019797:3-Iodobenzylguanidine