Observational, retrospective study evaluating the temporal variability of out-of-hospital cardiac arrests (OHCA) in the district of Bydgoszcz in a 24-month period

Introduction: The incidence of out-of-hospital cardiac arrests (OHCA) varies periodically. The aim of our study was to assess the temporal variability of OHCA occurrence in adult population of Bydgoszcz district. Material and methods: A retrospective analysis of 782 cases of OHCA, which occurred between January 1st, 2018, and December 31st, 2019, was performed. The temporal variability of OHCA occurrence was assessed during the day (within twenty-four 1-hour periods and four 6-hour time intervals), weeks, months, and seasons of the year. Results: The incidence of OHCA in the analyzed population was 84 per 100,000 inhabitants/year. The highest incidence of OHCA was observed between 08:00 and 08:59 and between 15:00 and 15:59. The lowest number of OHCA occurred at night (n = 84; 10.7%; p < 0.001). During the week, the lowest number of OHCA was noted on Saturday (12.4%) and the highest on Monday (16.5%), with no significant differences between days. The highest incidence of OHCA was observed in winter and the lowest in summer [225 (28.8%) vs. 171 (21.9%), p = 0.006]. December was the month with the highest number of OHCA cases, and July the lowest. Conclusions: The present analysis confirms that the occurrence of OHCA demonstrates circadian, monthly, and seasonal rhythm. The highest incidence of OHCA was in the morning and afternoon, and in winter, especially in December. The lowest occurrence of OHCA was at night and in the summer, particularly in July. There was a weekly pattern with the highest occurrence of OHCA on Mondays; however’ no significant differences between weekdays were achieved.