title: Circadian variation of QTc dispersion in children with vasovagal syncope.
abstract: OBJECTIVE
  To assess the validity of QTc dispersion to cardiac autonomic nervous function status.
  
  
  RESULTS
  Prospective comparisons of QTc dispersion measurements in 77 neurally mediated cardiac syncope (NMCS) patients (29 boys, 48 girls, mean age 13.4+/-0.78) were evaluated. Head-up tilt test (HUT) was positive in 38 patients and negative in 39 patients. QTc dispersion was significantly higher early morning and late night in HUT-positive group compared with HUT-negative group (p<0.001). Although there was a circadian rhythm in HUT-positive group, there was no change on the QTc dispersion within a day in the HUT-negative group. QTc dispersion in the HUT-positive group was high in accordance with their high sympathetic nervous stimulation. Moreover, QTc dispersion was higher during late night and early morning than the rest of the day.
  
  
  CONCLUSIONS
  These results may explain why the HUT-positive patients usually have their syncope attacks early in the morning. Additionally, we can use QTc dispersion measurement as a new noninvasive electrocardiographic test to evaluate cardiac sympathetic nervous system in NMCS.
authors.affiliation: Department of Pediatric Cardiology, Medical Faculty, Gazi Hospital, Gazi University, 06500 Beşevler, Ankara, Turkey. pedcar@gazi.edu.tr
authors.forename: Serdar
authors.initials: S
authors.lastname: Kula
authors.forename: Rana
authors.initials: R
authors.lastname: Olgunturk
authors.forename: F Sedef
authors.initials: FS
authors.lastname: Tunaoglu
authors.forename: Berna
authors.initials: B
authors.lastname: Canter
mesh_terms: D000293:Adolescent; D002648:Child; D002940:Circadian Rhythm / Q000502:physiology*; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D018667:Tilt-Table Test