title: Seasonality, incidence and prognosis in atrial fibrillation and stroke in Denmark and New Zealand.
abstract: OBJECTIVE
  There are relatively few large studies of seasonal variation in the occurrence of stroke in patients with atrial fibrillation (AF). We investigated the seasonal variation in incidence rates of hospitalisation with stroke in patients from Denmark and New Zealand.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  Nationwide hospital discharge data from Denmark and New Zealand.
  
  
  METHODS
  243 381 (median age 75) subjects having a first-time hospitalisation with AF in Denmark and 51 480 (median age 76) subjects in New Zealand constituted the study population. Subjects with previous hospitalisation with stroke were excluded.   PRIMARY AND SECONDARY EFFECT MEASURES:  Peak-to-trough ratio of the seasonal variation in incidence rates of stroke in AF patients adjusted for an overall trend was primary effect measure and was assessed using a log-linear Poisson regression model. Secondary effect measures were incidence rate ratios of AF and 30-day case fatality for stroke patients.
  
  
  RESULTS
  Incidence rates of AF per 1000 person-years in Denmark increased by 5.4% (95% CI 5.3% to 5.7%) for patients aged <65 and 5% (95% CI 4.9% to 5.1%) for patients aged ≥65, whereas the increase was 0.2% (95% CI -0.2% to 0.6%) for patients aged <65 and 2.6% (95% CI 2.4% to 2.8%) for patients aged ≥65 in New Zealand. In Denmark 36 088 subjects were hospitalised with stroke, and 7518 subjects in New Zealand, both showing peaks during winter with peak-to-trough ratios of 1.22 and 1.27, respectively and a decreasing trend. The 30-day case fatality risk for stroke patients having AF is now (2000-2008) about 20% in both countries.
  
  
  CONCLUSIONS
  Although incidence rates of hospitalisation with stroke in patients with AF have decreased in recent years, stroke remains a common AF complication with a high case fatality risk. The marked winter peak in incidence rates of hospitalisation with stroke in AF patients suggests that there are opportunities to reduce this complication. Further studies are necessary to identify how to optimise treatment of AF and prevention of stroke.
authors.affiliation: Department of Cardiology, Aalborg AF Study Group, Center for Cardiovascular Research, Aalborg Hospital, Aarhus University Hospital, Aalborg, Denmark.
authors.forename: Anette Luther
authors.initials: AL
authors.lastname: Christensen
authors.forename: Lars Hvilsted
authors.initials: LH
authors.lastname: Rasmussen
authors.forename: Michael G
authors.initials: MG
authors.lastname: Baker
authors.forename: Gregory Y H
authors.initials: GY
authors.lastname: Lip
authors.forename: Claus
authors.initials: C
authors.lastname: Dethlefsen
authors.forename: Torben Bjerregaard
authors.initials: TB
authors.lastname: Larsen