Background: It has been reported that cardiovascular events occur more frequently in the morning than in the evening. The purpose of the present study was to assess the characteristics of out-of-hospital cardiac arrests due to cardiac cause in a 24-h period in Japanese patients.
Methods and results: Of 2,199 consecutive patients with cardiopulmonary resuscitation outside hospital, 1,293 cardiogenic patients were enrolled. The incidence of cardiac arrests was assessed as hourly data (ie, circadian variation), and investigated for differences in age, gender, and the location at onset. Cardiac arrests had an apparent circadian rhythm that was characterized by 2 long zeniths in the morning and evening. The peak was at 17:00-18:00 hours. Younger patients had more cardiac arrests in the morning than in the evening. In contrast, older patients had more events in the evening than in the morning. The circadian rhythm did not differ in gender. Regarding location, the patient's residence was the most common place for cardiac arrest. In the residence, the bathroom was associated with the evening zenith of circadian variation.
Conclusions: Out-of-hospital cardiac arrests due to cardiac cause in Japanese patients have an apparent circadian variation with 2 long zeniths, with an evening predominance in older patients. Aging affects the evening zenith, in that elderly patients > or =80 years old have a zenith associated with bath time in the evening.