title: Circadian rhythm of the signal averaged electrocardiogram and its relation to heart rate variability in healthy subjects.
abstract: OBJECTIVE
  To examine the circadian variation in the signal averaged electrocardiogram (saECG) and heart rate variability and investigate their relations in healthy subjects.
  
  
  METHODS
  24 hour ECGs were obtained with a three channel recorder using bipolar X, Y, and Z leads in 20 healthy subjects. The following variables were determined hourly: heart rate, filtered QRS (f-QRS) duration, low and high frequency components of heart rate variability (LF and HF), and the LF/HF ratio.
  
  
  RESULTS
  Heart rate, f-QRS duration, HF, and the LF/HF ratio showed significant circadian rhythms, as determined by the single cosinor method. Heart rate and the LF/HF ratio increased during daytime, and f-QRS duration and HF increased at night. f-QRS duration was negatively correlated with heart rate (r = 0.95, p < 0.001) and the LF/HF ratio (r = 0.94, p < 0.001) and positively with HF (r = 0.93, p < 0.001).
  
  
  CONCLUSIONS
  f-QRS duration has a significant circadian rhythm in healthy subjects and is closely related to the circadian rhythm of autonomic tone.
authors.affiliation: Department of Laboratory Medicine, Oita Medical University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakagawa
authors.forename: T
authors.initials: T
authors.lastname: Iwao
authors.forename: S
authors.initials: S
authors.lastname: Ishida
authors.forename: H
authors.initials: H
authors.lastname: Yonemochi
authors.forename: T
authors.initials: T
authors.lastname: Fujino
authors.forename: T
authors.initials: T
authors.lastname: Saikawa
authors.forename: M
authors.initials: M
authors.lastname: Ito
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D012815:Signal Processing, Computer-Assisted