Observational analysiS of out-of-hospital Cardiac Arrest occurRence and temporal variability patterns in subpopulation of southern POLand from 2006 to 2018: OSCAR-POL registry.

Background: Temporal variability of out-of-hospital cardiac arrest (OHCA) occurrence was presented in previous studies, however, the data regarding long-term observation is scarce. The aim of this study was to investigate the temporal variability of OHCA occurrence during a long-time period and analyze the circadian pattern within particular timeframes.

Methods: The retrospective analysis of 5058 OHCA cases was made covering the period from January 1st, 2006 to December 31st, 2018. Circadian, weekly, monthly and seasonal variabilities were investigated. The circadian variability of OHCA occurrence was assessed within particular years, seasons of the year, and days of the week.

Results: The highest OHCA incidence was observed between 08:00 and 08:59 and the lowest between 01:00 and 01:59 (7.1% vs. 1.6%, p < 0.001). After division into 6-h intervals, a significantly lower number of OHCA cases occurred between 00:00 and 05:59 (12.3%) in comparison to the highest number observed in between 06:00 and 11:59 (12.3% vs. 33.5%, p < 0.001). The highest OHCA occurrence was observed on Monday (14.9%), however, no weekly variability was found (p = 0.557). The highest OHCA occurrence was observed in the winter and lowest in the summer (27.4% vs. 22.8%, p < 0.001). Significant circadian variability was observed for every day of the week, every season and year during the observation period (p < 0.001).

Conclusions: Circadian, monthly and seasonal variability of OHCA occurrence was confirmed in the long-term observation with no differences between particular days of the week. Significant circadian variability was observed within days of the week, seasons of the year, and particular years.