Out-of-Hospital Cardiac Arrest in Korea: Who Does Survive?

Abstract

Background Out-of-hospital cardiac arrest (OHCA) is a lethal event that has become a global health problem. Resource allocations for enhancing OHCA survival outcomes should focus on the modifiable and cost-effective determinants to improve OHCA survival outcomes in targeted communities with either a high incidence rate or a low survival rate in Korea. The primary goal of this study is to better understand the epidemiological features of the incidence, potential determinants, and survival outcomes of EMS-assessed OHCA in Korea. The secondary goal of this study was to estimate the true incidence rate of OHCA and compare the incidence rates of OHCA calculated based on a night-time residential population and a population considering day-time transient people as the population at risk. The tertiary goal was to better understand the trends of the epidemiological features of survival outcomes and determinants, the patient-community-EMS-ED factors, of OHCA by the urbanization levels of various communities.

Methods This study was performed within a nationwide emergency medical service (EMS) system with a single-tiered basic-to-intermediate service level and approximately 900 destination hospitals for eligible OHCA cases in Korea (with 48 million people). A nationwide OHCA database, which included informations such as patient demographics, Utstein criteria, EMS and hospital factors, and survival outcomes, was constructed using the EMS run sheets and medical record reviews of eligible OHCAs who were transported by 119 EMS ambulances from 2006 to 2010. The county urbanization levels are classified according to population size, with metropolitan areas (more than 500,000 residents), urban areas (100,000 to 500,000 residents), and rural areas (less than 100,000 residents). The night-time and day-time transient populations were investigated in the 2010 Census. Based on internal migration statistics, day-time population is defined by adding the day-time influx of population to and subtracting the day-time outflow from the night-time population. Conventional age-standardized incidence rates (CASR) and day-time corrected age standardized incidence rates (DASR) for EMS-assessed OHCA per 100,000 person-years were calculated for each county. The primary survival end point was the survival to discharge. The age- and gender-adjusted survival to discharge rates and standardized survival ratios with 95% confidence intervals (CIs) for each urbanization level by year were calculated against the standard patients group. The adjusted odds ratios (ORs) and 95% CIs for survival to discharge for each year were calculated for all patient groups and stratified patient groups by community urbanization after adjusting for the potential risks.

Results A total of 97,291 EMS-assessed OHCAs were analyzed after excluding 14,798 cases because the medical records were not available (N=10,626) or the survival outcomes were unknown (N=4,172). The age- and gender-standardized incidence rates per 100,000 person-years for EMS-assessed OHCAs increased from 37.5 in 2006 to 46.8 in 2010, and the survival to discharge rates were 3.0% for EMS-assessed OHCAs (3.3% for cardiac etiology and 2.3% for non-cardiac etiology) and 3.6% for resuscitation-attempted OHCAs. The age-standardized incidence rates of EMS-assessed OHCAs per 100,000 person-years by gender and occurrence time were 59.4 (34.6 in day-time and 24.8 in night-time) in males and 25.3 (14.9 in day-time and 10.4 in night-time) in females. The difference between the CASR and DASR ranged from 35.4 to -11.6 in males and from 6.1 to -1.0 in females. With the Bland-Altman plots of CASR and DASR by gender, there was a positive linear trend between the average CASR and DASR and the difference between the CASR and DASR in both genders. The difference between the CASR and the DASR increased as the D index increased which means a large day-time transient population and a relatively small night-time residential population. There were significant differences in the potential modifiable determinants by year among the metropolitan, urban, and rural areas: bystander CPR, EMS performance, and the level of the destination hospital. The age- and gender-adjusted survival to discharge rates improved significantly by year in the metropolitan areas (3.6% in 2006 to 5.3% in 2010) but remained low in the urban areas (1.4% in 2006 to 2.3% in 2010) and very low in the rural areas (0.5 in 2006 to 0.8 in 2010). The standardized survival ratios in the metropolitan areas were 1.19 (1.06-1.34) in 2006 and 1.77 (1.64-1.92) in 2010, whereas the standardized survival ratios were less than 1.00 during the five-year period in the urban and rural areas. In the analysis of the effects on the survival to discharge by urbanization level, the adjusted ORs (95% CIs) in 2010 compared to 2006 exhibited significant increases to 1.42 (1.22-1.66) in the metropolitan areas and to 1.58 (1.18-2.11) in the urban areas but did not increase in the rural areas

Conclusion In this nationwide population-based registry study from 2006 to 2010, the age- and gender-standardized incidence rates of EMS-assessed OHCAs increased by year, and the overall survival rate was 3.0%. An accurate estimate of the burden of OHCA is essential to develop effective strategies and to implement appropriate resource planning for community support and high quality prehospital and in-hospital responses to cardiac arrest. The trend of resuscitation efforts and the accessibility of care by year were significantly affected by urbanization level and the survival to discharge rate increased by year in metropolitan and urban communities but did not increase in rural communities. Appropriate strategies for improving outcomes that are not limited by the disparities between communities should be developed and implemented.