title: Diurnal, weekly and seasonal rhythm of out of hospital cardiac arrest in Sweden.
abstract: OBJECTIVE
  To describe the diurnal, weekly and seasonal rhythm among patients suffering from out of hospital cardiac arrest in Sweden.
  
  
  METHODS
  All patients in Sweden between 1990 and 1999 participating in a National Registry covering 65% of all patients suffering from out of hospital cardiac arrest where cardiopulmonary resuscitation (CPR) was attempted. Only patients with a cardiac arrest of a cardiac aetiology and aged > 18 years were included in the survey.
  
  
  RESULTS
  10,868 patients fulfilled inclusion criteria. In terms of the diurnal rhythm, there was a progressive increase in the development of cardiac arrest from 06:00 h, reaching a peak at about 10:00 h. Thereafter, there was a progressive decline until 05:00 h. The diurnal rhythm was more marked among patients aged > 65 years and among patients in whom the arrest occurred outside home. There was a weekly rhythm with an increased incidence of cardiac arrest on Mondays. This was particularly evident among patients aged < 66 years and among men. A cardiac arrest occurred most frequently in January and December. This was particularly observed in the large cities.
  
  
  CONCLUSIONS
  We found that out of hospital cardiac arrest of a cardiac etiology has a diurnal, weekly and seasonal rhythm occurring most frequently in the morning hours, on Mondays and in December and January. Age, sex and place of arrest influence these rhythms.
authors.affiliation: Division of Cardiology, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. johan.herlitz@hjl.gu.se
authors.forename: Johan
authors.initials: J
authors.lastname: Herlitz
authors.forename: Mikael
authors.initials: M
authors.lastname: Eek
authors.forename: Mikael
authors.initials: M
authors.lastname: Holmberg
authors.forename: Stig
authors.initials: S
authors.lastname: Holmberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006323:Heart Arrest / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010507:Periodicity; D012621:Seasons; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors