title: The circadian variation of premature atrial contractions.
abstract: OBJECTIVE
  The aim of the study was to assess a possible circadian variation of premature atrial contractions (PACs) in a community-based population and to determine if the daily variation could be used to assess a more vulnerable period of PACs in predicting later incidence of atrial fibrillation (AF).
  
  
  RESULTS
  We studied 638 subjects between the ages of 55 and 75 years from the Copenhagen Holter Study who underwent up to 48 h electrocardiogram recording. Follow-up on cardiovascular endpoints was performed in 2013 with a median follow-up time of 14.4 years. According to previous studies, two subgroups were studied based on a cut-off point of ≥720 PACs/day termed frequent PACs (n = 66) and not frequent PACs with <720 PACs/day (n = 572). Based on median values, a circadian rhythm could not be demonstrated in the population as a whole and the group without frequent PACs. However, a circadian variation was observed in the group with frequent PACs, who had the fewest PACs/h during the night with a nadir at 6 am and then reaching a peak value in the afternoon at 3 pm. Runs of PACs in all subjects showed a similar circadian variation. Both PACs/h and runs of PACs seemed to follow the daily variation in heart rate. After adjusting for relevant risk factors, the risk of AF was equal in all time intervals throughout the day.
  
  
  CONCLUSIONS
  Premature atrial contractions showed a circadian variation in subjects with frequent PACs. No specific time interval of the day was more predictive of AF than others.
authors.affiliation: Department of Cardiology, Copenhagen University Hospital of Bispebjerg, Bispebjerg Bakke 23, Copenhagen DK-2400, Denmark tfc442@alumni.ku.dk.
authors.forename: Bjørn Strøier
authors.initials: BS
authors.lastname: Larsen
authors.affiliation: Department of Cardiology, Copenhagen University Hospital of Bispebjerg, Bispebjerg Bakke 23, Copenhagen DK-2400, Denmark.
authors.forename: Preman
authors.initials: P
authors.lastname: Kumarathurai
authors.affiliation: Department of Cardiology, Copenhagen University Hospital of Bispebjerg, Bispebjerg Bakke 23, Copenhagen DK-2400, Denmark.
authors.forename: Olav W
authors.initials: OW
authors.lastname: Nielsen
authors.affiliation: Department of Cardiology, Copenhagen University Hospital of Bispebjerg, Bispebjerg Bakke 23, Copenhagen DK-2400, Denmark.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Sajadieh
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000453:epidemiology* / Q000209:etiology; D018880:Atrial Premature Complexes / Q000150:complications* / Q000175:diagnosis*; D002940:Circadian Rhythm; D003718:Denmark; D015716:Electrocardiography, Ambulatory; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012008:Recurrence; D012307:Risk Factors
keywords: Atrial fibrillation; Circadian variation; Epidemiology; Premature atrial contractions