Aim: 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.
Conclusion: 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.