Seasonal variation in morbidity and mortality related to atrial fibrillation

Objective To determine whether there is seasonal variation in hospitalisations and deaths due to atrial fibrillation (AF) and to examine possible contributors to such variability. Methods We used the linked Scottish Morbidity Record scheme, which provides individualised morbidity and mortality data for the entire Scottish population. Results Between 1990 and 1996, there were a total of 33,582 male and 34,463 female hospitalisations related to AF. Significantly more admissions occurred in winter compared to summer (P<0.0001). In women, the peak number of admissions (106 per day) occurred in December (12% more than average) and the lowest number (89) in June (6% less than average). The respective figures for men were 10% more (101), 2% less (90). In both sexes, the greatest variation occurred in those aged >85 years—peak winter rates being 35–39% higher than average. A similar phenomenon was evident in relation to mortality in these patients. The average number of men who died during December was 22% higher, and in August 12% lower, than average, P<0.001. In women, the equivalent figures were 28% higher (December) and 14% lower (August), P<0.001. The winter peak of AF admissions did not, however, coincide with the lowest temperatures, and other factors such as seasonal variation in respiratory infection, may account for the monthly variation observed in hospitalisations for AF. Conclusions There is substantial seasonal variation in AF hospitalisations and deaths, particularly in the elderly.