Aim This was a population-based retrospective cohort study of OHCA. This study intends to retrospectively analyze the data of pre-hospital emergency system in Guangzhou for 10 years, explore the incidence trend of OHCA in Guangzhou for 10 years; Through further analysis, we try to explore the time distribution characteristics of OHCA in order to understand the epidemiological characteristics and rules of OHCA in super large cities in southern China.

Methods The pre-hospital traffic data in the main urban area of Guangzhou Emergency Medical Command Center database from 2011 to 2020 were collected. The cases diagnosed as "cardiac arrest" and "sudden death" were screened, and the cases with non-cardiac causes in the diagnosis were deleted. The crude incidence rate and age-standardized incidence rate of OHCA were calculated. Joinpoint software was used to calculate the changing nodes in the OHCA incidence trend, and the AnnualPercent Change (APC) and Average AnnualPercent Change (Average AnnualPercent Change, APC) of OHCA incidence were calculated. AAPC). The OHCA data were grouped according to the six main urban areas, and the crude incidence rate, ASIR and changing trend of the six main urban areas were calculated. The data of OHCA were grouped by age, and the crude incidence rate, ASIR and changing trend of each age group were calculated. The data information was divided into groups according to 24 hours a day, 7 days a week, and four seasons. The number of OHCA cases in different time periods was statistically described. The data were imported into SPSS 26.0 for analysis, and Mann-Kendall test was used to evaluate the statistical significance of the time trend. Time rhythm variability was tested for mean distribution using chi-square goodness of fit test.

Inclusion Criteria:

Cases in the database with a secondary diagnosis containing the diagnostic keywords "cardiac arrest" and "sudden death"

Exclusion Criteria:

1. cases where the diagnosis of "cardiac arrest" and "sudden death" includes a diagnosis of a non-cardiac cause such as asphyxiation, suicide, drowning, advanced cancer, trauma, shock, poisoning, cerebral vascular accident, etc;
2. cases with duplicate records of sex, age, time of call, pick-up address and initial diagnosis

Cases in the database with a secondary diagnosis containing the diagnostic keywords "cardiac arrest" and "sudden death".Data were collected from the GZ-EMS Command Centre's dispatch system database of pre-hospital data for the central urban districts of City.