title: Circadian variation of vasovagal syncope.
abstract: BACKGROUND
  Circadian patterns have been demonstrated for several cardiovascular catastrophes. Chronobiologic factors play a role in the emergence of vasovagal syncope (VVS); however, diurnal variation of syncopal episodes in VVS has not been reported previously.
  
  
  RESULTS
  We assessed daily distribution of the time of syncopal episodes in VVS. Time of syncope could be determined in 80 episodes in 54 patients (32 men and 22 women; mean age 37 years, range 12 to 67). Patients who were prescribed beta blockers or vasodilators, and who had syncopes related to alcohol intake, were excluded from the study. Head-up tilt testing was performed in 53 patients. The distribution of the episodes of VVS in 3-hour intervals differed significantly from uniform occurrence (P < 0.0001), with a peak frequency between 6 A.M. and noon (67.5% of total episodes). In patients who had experienced the initial syncope in the morning, most (78%) of the next syncopal episodes also occurred in the morning. There was no significant correlation between the time of last syncopes and tilt testing results.
  
  
  CONCLUSIONS
  We demonstrated a prominent circadian variation in the frequency of VVS, with a peak in the morning. Recognition of the daily distribution of VVS is useful for patient education and therapeutic strategy.
authors.affiliation: Department of Cardiology, Juntendo University Izunagaoka Hospital, Shizuoka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Mineda
authors.forename: M
authors.initials: M
authors.lastname: Sumiyoshi
authors.forename: T
authors.initials: T
authors.lastname: Tokano
authors.forename: M
authors.initials: M
authors.lastname: Yasuda
authors.forename: K
authors.initials: K
authors.lastname: Nakazato
authors.forename: Y
authors.initials: Y
authors.lastname: Nakazato
authors.forename: Y
authors.initials: Y
authors.lastname: Nakata
authors.forename: H
authors.initials: H
authors.lastname: Yamaguchi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002940:Circadian Rhythm; D000431:Ethanol / Q000009:adverse effects; D005260:Female; D018475:Head-Down Tilt; D006801:Humans; D008297:Male; D008875:Middle Aged; D013575:Syncope / Q000209:etiology*; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology*
chemical_list: D000431:Ethanol