PHWR Public Health Weekly Report

Out-of-hospital cardiac arrest (OHCA) or sudden cardiac arrest (SCA) is a clinical condition characterized by the abrupt loss of cardiac mechanical activity, resulting in the absence of circulation and loss of normal physiological function. Without prompt intervention, it often results in death or irreversible brain damage. SCA is a leading cause of death worldwide. In high-income countries, collaborative efforts across clinical and public health sectors aim to improve clinical outcomes and prognosis of this condition [1,2]. In the Republic of Korea (ROK), patients with OHCA who are transported to hospitals by public emergency medical services (EMS) are systematically included in a nationwide registry to support evidence-based prevention and survival strategies. According to the Sudden Cardiac Arrest Survey (SCAS), 33,586 cases of OHCA occurred in 2023, with an incidence rate of 65.7 per 100,000 persons [3].

Since 2008, the rates of survival and brain function recovery in patients with OHCA have increased in ROK. Although survival and brain function recovery rates were only 2.5% and 0.8% in 2008, respectively, they increased to 8.6% and 5.6% by 2023 [4,5]. As survival rates continue to improve, the number of long-term survivors is steadily increasing [6]. As the physical, psychological, and social consequences of SCA persist beyond the acute phase, there is growing interest in the long-term survival outcomes of OHCA [7,-9].

In ROK, the national OHCA registry or SCAS has provided reliable data on the incidence and survival-to-discharge outcomes. However, information on long-term survival has remained limited. Since the implementation of the Act on the Prevention and Management of Cardio-cerebrovascular Diseases (CVD Act) in 2017, linkage between SCAS and the National Health Insurance Service (NHIS) claims database has become feasible, establishing a foundation for assessing long-term outcomes among OHCA survivors. This study aims to investigate the long-term survival outcomes of OHCA patients in in ROK using the linkage database.

1. Data Sources

SCAS investigated the clinical characteristics of patients with OHCA who were transported to hospitals by public EMS, based on a review of medical records [10]. Patients were included if (i) the EMS run sheet or the detailed resuscitation form indicated a chief complaint of “cardiac arrest” or “respiratory arrest”; (ii) cardiopulmonary resuscitation (CPR) was performed; or (iii) the detailed resuscitation form was completed. Between 2011 and 2021, a total of 329,943 cases of OHCA were identified, of which 321,352 cases (97.4%) underwent complete medical record review and were included in the registry.

NHIS serves as the sole insurer in ROK’s single-payer healthcare system, with mandatory enrollment for all residents. After medical services are delivered, healthcare providers submit claims electronically, which are compiled into a national administrative database. These health insurance claims contain information on patient demographics, eligibility status, diagnostic codes, treatment details, and prescribed medications [11]. In this study, resident registration numbers (RRNs) collected through SCAS were linked to NHIS claims database in accordance with Article 15 of CVD Act (Linkage Dataset Number: NHIS-2024-1-498). Causes-of-death data from Statistics Korea were also linked using the same identifier.

2. Study Participants

Among the 321,352 cases included in SCAS between 2011 and 2021, 313,494 OHCA cases with valid RRNs were retained after excluding duplicate entries on the same date and were eligible for linkage to NHIS data. Using RRNs, 307,051 cases, representing 306,039 unique patients, were successfully linked to the NHIS data. Patients with missing data on sex or date of birth, or with a recorded date of death preceding the cardiac arrest event, were excluded from the final analysis.

3. Variables and Measurements

From the NHIS database, the most recent eligibility data for each year were retrieved to obtain information on sex, year of birth, insurance type, chronic conditions, and long-term survival status. Age at the time of cardiac arrest was calculated based on the year of birth. Chronic diseases and disorders were identified using diagnostic codes recorded in the claims data within 1 year prior to the date of cardiac arrest. A condition was classified as present if one or more corresponding ICD-10 codes were recorded in the claims and accompanied by at least two outpatient visits or one hospital admission. Chronic diseases and disorders were defined according to the Elixhauser Comorbidity Index [12,13]. Anxiety disorders (ICD-10 codes: F40, F41, and F42) and atrial fibrillation (ICD-10 code: I48) were also included in the analysis. Long-term survival was assessed using the date of death from NHIS data, with follow-up censored at December 31, 2022. From SCAS dataset, the following variables were collected: causes of SCA (medical, non-medical, or unknown); location of arrest (public, non-public, other, or unknown); witness status (witnessed, unwitnessed, or unknown); performance of bystander CPR (performed, not performed, or unknown); and the initial electrocardiogram (ECG) rhythm at EMS arrival (shockable rhythm, pulseless electrical activity, asystole, or unknown).

4. Statistical Analysis

Linkage rates between SCAS and NHIS data were calculated annually. Among the linked OHCA patients, demographic characteristics, chronic conditions, and cardiac arrest profiles were assessed for the years 2011 and 2021. The 1-year, 3-year, and 5-year survival rates were estimated by calendar year. Both crude and standardized survival rates were reported. For standardization, the linked patients in 2011 were used as the reference population, and rates were adjusted by sex and 5-year age groups.

Figure 1 illustrates the data linkage process between SCAS and NHIS claims data from 2011 to 2021. A total of 307,051 OHCA cases (involving 306,039 unique patients) were linked using RRNs. After excluding cases with errors in sex or year of birth or death records in the NHIS eligibility database, 306,253 cases (305,257 patients) were included in the final analysis. The overall linkage rate between SCAS and NHIS data during the study period was 95.3%.

Figure 1. Flowchart of data linkage between SCAS (KDCA) and Health Insurance Claims Database (NHIS) and study population selection
KDCA=Korea Disease Control and Prevention Agency; NHIS=National Health Insurance Service; RRN=resident registration number; SCAS=Sudden Cardiac Arrest Survey; info.=information.

Table 1 presents the demographic distribution and insurance type of patients with OHCA in 2011 and 2021. The number of OHCA cases increased from 23,301 cases in 2011 to 32,149 cases in 2021, a 1.4-fold increase. The male-to-female ratio remained stable at approximately 2:1. In 2021, 63.4% of OHCA patients were male and 36.6% were female. The incidence increased with age. In 2011, the highest proportion of cases occurred among those in their 70s (24.6%), while in 2021, the largest group was those aged 80 and above (32.6%). Regarding insurance type, 55.5% of patients in 2011 were enrolled in employer provided, 34.9% in locally provided, and 9.6% were medical aid beneficiaries. These proportions changed slightly in 2021 to 55.9%, 33.6%, and 10.5%, respectively (Table 1).

Table 1 Demographic characteristics and insurance type of out-of-hospital cardiac arrest patients in 2011 and 2021

	2011	2021
Survey completed patientsa)	24,902	33,041
Successfully linked patientsb)	23,301 (100.0)	32,149 (100.0)
Sex
Male	15,057 (64.6)	20,388 (63.4)
Female	8,244 (35.4)	11,761 (36.6)
Age group (yr)
0–9	308 (1.3)	231 (0.7)
10–19	379 (1.6)	361 (1.1)
20–29	756 (3.2)	845 (2.6)
30–39	1,198 (5.1)	1,100 (3.4)
40–49	2,468 (10.6)	2,218 (6.9)
50–59	3,757 (16.1)	4,191 (13.0)
60–69	3,861 (16.6)	5,754 (17.9)
70–79	5,727 (24.6)	6,973 (21.7)
≥80	4,847 (20.8)	10,476 (32.6)
Insurance typec)
Employer provided	12,927 (55.5)	17,965 (55.9)
Locally provided	8,134 (34.9)	10,814 (33.6)
Medical aid	2,240 (9.6)	3,368 (10.5)
Missing	0 (0.0)	2 (0.0)

Unit: case (%). SCA=sudden cardiac arrest; EMS=emergency medical services; NHIS=National Health Insurance Service. ^a)Among SCA patients transported to hospitals by the 119 EMS, the study included those whose medical record review was completed. ^b)Among SCA patients transported to hospitals by the 119 EMS, the study included those whose medical record review was completed and whose data were successfully linked to the NHIS claims database. ^c)The insurer type was determined based on the most recent eligibility information as of January 1 of the incidence year..

The distribution of chronic diseases and disorders prior to OHCA in 2011 and 2021 among patients in linkage data is shown in Table 2. In 2011, the five most prevalent chronic conditions were hypertension (46.8%), chronic pulmonary disease (25.6%), other neurological disorders (18.3%), uncomplicated diabetes (17.2%), and peptic ulcer disease excluding bleeding (16.9%). A similar pattern was observed in 2021, although congestive heart failure (22.3%) replaced peptic ulcer disease excluding bleeding in the top five (Table 2).

Table 2 The distribution of diseases and disorders among out-of-hospital cardiac arrest in 2011 and 2021

	2011	2021
Successfully linked patientsa)	23,301 (100.0)	32,149 (100.0)
Disease and disorderb)
Congestive heart failure	2,962 (12.7)	7,167 (22.3)
Cardiac arrhythmias	1,708 (7.3)	3,812 (11.9)
Valvular disease	442 (1.9)	708 (2.2)
Pulmonary circulation disorders	267 (1.1)	1,446 (4.5)
Peripheral vascular disorders	2,510 (10.8)	5,354 (16.7)
Hypertension	10,895 (46.8)	17,801 (55.4)
Paralysis	712 (3.1)	793 (2.5)
Other neurological disorders	4,266 (18.3)	8,938 (27.8)
Chronic pulmonary disease	5,954 (25.6)	8,664 (26.9)
Diabetes, uncomplicated	4,013 (17.2)	7,815 (24.3)
Diabetes, complicated	2,417 (10.4)	3,562 (11.1)
Hypothyroidism	620 (2.7)	1,716 (5.3)
Renal failure	1,316 (5.6)	3,133 (9.7)
Liver disease	2,763 (11.9)	6,047 (18.8)
Peptic ulcer disease excluding bleeding	3,941 (16.9)	4,005 (12.5)
HIV/AIDS	5 (0.0)	25 (0.1)
Lymphoma	76 (0.3)	238 (0.7)
Metastatic cancer	899 (3.9)	1,401 (4.4)
Solid tumor without metastasis	2,567 (11.0)	4,766 (14.8)
Rheumatoid arthritis/collagen vascular diseases	584 (2.5)	1,362 (4.2)
Coagulopathy	276 (1.2)	1,682 (5.2)
Obesity	6 (0.0)	19 (0.1)
Weight loss	771 (3.3)	1,259 (3.9)
Fluid and electrolyte disorder	2,043 (8.8)	4,714 (14.7)
Blood loss anemia	88 (0.4)	167 (0.5)
Deficiency anemia	2,814 (12.1)	6,242 (19.4)
Alcohol abuse	521 (2.2)	709 (2.2)
Drug abuse	23 (0.1)	64 (0.2)
Psychoses	670 (2.9)	1,830 (5.7)
Depression	2,696 (11.6)	6,584 (20.5)
Anxiety disorder	2,909 (12.5)	6,095 (19.0)
Atrial fibrillation	1,030 (4.4)	2,680 (8.3)

Unit: case (%). HIV/AIDS=human immunodeficiency viruses/acquired immunodeficiency syndrome; SCA=sudden cardiac arrest; EMS=emergency medical services; NHIS=National Health Insurance Service. ^a)Among SCA patients transported to hospitals by the 119 EMS, the study included those whose medical record review was completed and whose data were successfully linked to the NHIS claims database. ^b)If a patient had at least two outpatient visits or at least one inpatient admission for the respective condition within one year prior to the date of cardiac arrest occurrence, they were considered to have utilized medical services for that condition..

Table 3 presents the characteristics of cardiac arrest events in 2011 and 2021 among patients in the linkage data. In 2011, 70.9% of cases were attributed to medical causes, which increased to 78.2%, possibly influenced by the coronavirus disease 2019 (COVID-19) pandemic. The majority of OHCA events occurred in non-public places in both years, accounting for 65.7% in 2011 and 62.4% in 2021; the proportion in public places decreased from 20.8% to 15.6%. The proportion of witnessed events increased from 38.9% in 2011 to 51.7% in 2021. Additionally, the proportion of bystander-performed CPR events increased from 4.6% in 2011 to 25.1% in 2021. Regarding prehospital initial ECG rhythm, 88.3% of cases were recorded as unknown in 2011. In contrast, in 2021, asystole was most common (64.6%), followed by pulseless electrical activity (23.4%), shockable rhythm (11.0%), and unknown (1.1%; Table 3).

Table 3 Distribution of cardiac arrest characteristics among patients in 2011 and 2021

	2011	2021
Successfully linked patientsa)	23,301 (100.0)	32,149 (100.0)
Cause of arrestb)
Medical	16,518 (70.9)	25,135 (78.2)
Non-medical	6,248 (26.8)	6,875 (21.4)
Missing	535 (2.3)	139 (0.4)
Location of arrestb)
Public place	4,840 (20.8)	5,008 (15.6)
Non-public place	15,302 (65.7)	20,047 (62.4)
Others	736 (3.2)	1,052 (3.3)
Missing	2,423 (10.4)	6,042 (18.8)
Witnessedb)
Yes	9,064 (38.9)	16,607 (51.7)
No	10,147 (43.5)	14,167 (44.1)
Missing	4,090 (17.6)	1,375 (4.3)
Bystander CPRb)
Yes	1,073 (4.6)	8,059 (25.1)
No	1,762 (7.6)	2,932 (9.1)
Missing	20,466 (87.8)	21,158 (65.8)
Initial cardiac rhythmc)
Shokable	464 (2.0)	3,534 (11.0)
Pulseless electrical activity	351 (1.5)	7,509 (23.4)
Asystole	1,910 (8.2)	20,766 (64.6)
Missing	20,576 (88.3)	340 (1.1)

Unit: case (%). CPR=cardiopulmonary resuscitation; SCA=sudden cardiac arrest; EMS=emergency medical services; NHIS=National Health Insurance Service. ^a)Among SCA patients transported to hospitals by the 119 EMS, the study included those whose medical record review was completed and whose data were successfully linked to the NHIS claims database. ^b)Information is based on medical record review of Sudden Cardiac Arrest Survey. ^c)Information is based on the detailed cardiac arrest situation report of 119 EMS..

The temporal trends of long-term survival among patients in the linkage data are shown in Figure 2. The standardized 30-day survival rate gradually increased from 5.3% in 2011 to 8.6% in 2019, followed by a slight decline to 8.3% in 2021 during the COVID-19 pandemic (Figure 2A). The number of patients surviving at least one year increased from 817 in 2011 to 1,695 in 2019, then slightly declined to 1,670 in 2021. The standardized 1-year survival rate rose from 3.5% in 2011 to 6.3% in 2021 (Figure 2B). The standardized 3-year and 5-year survival rates nearly doubled, increasing from 3.0% and 2.7%

Figure 2. Secular trends in yearly numbers of survivors and survivor rate by survival duration
(A) 30-day survival, (B) 1-year survival, (C) 3-year survival, (D) 5-year survival.

in 2011 to 5.8% and 5.4% in 2017, respectively (Figure 2C, D).

Survival to discharge among patients with OHCA has steadily increased in ROK. However, SCAS, which is based on the review of medical records, has limitations in estimating long-term survival rates and evaluating the status of long-term survivors. By linking data from SCAS and NHIS claims database, this study demonstrated that the standardized 1-year survival rate nearly doubled from 3.5% in 2011 to 6.3% in 2021. The standardized 1-year survival rate peaked at 6.7% in 2019, but slightly declined to 6.5% in 2020 and 6.3% in 2021 during the COVID-19 pandemic. The 3-year and 5-year survival rates have shown a continued upward trend. Among the 2017 cohort, 82.3% of 1-year survivors remained alive 5 years later.

This study provides a comprehensive overview of the chronic conditions in patients with OHCA. As the population of cardiac arrest patients continues to age, the prevalence of various chronic diseases steadily increases. The disease burden includes not only cardiovascular diseases such as diabetes, hypertension, peripheral vascular disease, and heart failure, but also chronic pulmonary disease, cancer, depression, and anemia. These findings highlight the need for further research into the associations between SCA and preexisting chronic illnesses and potential prevention strategies. However, since this study included all diagnostic codes from claims data rather than including only principal or secondary diagnoses, the prevalence of comorbidities may have been overestimated.

International interest in the post-survival lives of SCA survivors and their caregivers is growing [8]. Survivors often experience reduced quality of life due to a combination of emotional, physical, social, and financial challenges, yet many receive inadequate management or support [7]. In light of the life expectancy and disease burden among the long-term survivors, there is a growing need in ROK to develop policies and programs that support post-arrest care and recovery.

In the United Kingdom, the “Sudden Cardiac Arrest UK”, and in the United States, the “Cardiac Arrest Survivor Alliance”, are representative organizations supporting survivors. In ROK, efforts have emerged through government-led initiatives. Since 2022, the Korea Disease Control and Prevention Agency (KDCA) and the National Fire Agency (NFA) have organized annual workshops to identify OHCA survivors and facilitate sharing of their recovery experiences. Since 2023, NFA has operated the “119 Reborn Club,” a public awareness campaign centered on cardiac arrest survivors. Additionally, beginning in 2024, the KDCA launched a CPR awareness contest, inviting patients and families to publicly share their experiences with cardiac arrest and recovery. While these efforts are meaningful, ongoing actions are needed to establish an objective understanding of the long-term status of OHCA survivors. Developing a robust, systematic data infrastructure and promoting collaboration between experts and stakeholders will be essential to reduce the disease burden and improve survivors’ quality of life.

Currently, the data linkage between SCAS and NHIS claims database is controlled by the KDCA and NHIS. This centralized governance poses challenges to data accessibility and research utilization. To improve scientific use, institutional reforms should be implemented to allow broader access to linkage data. In addition, routine data linkage and expanded availability would enable continuous monitoring of long-term survival trends and facilitate diverse analyses aimed at improving outcomes and reducing the burden of disease among OHCA survivors.

Ethics Statement: This study received IRB exemption from Seoul National University Hospital (E-2308-076-1458) due to informed consent was not required to use datasets.

Funding Source: This study was supported by the Korea Disease Control and Prevention Agency.

Acknowledgments: All authors would like to express their deepest gratitude to the staffs of big data research and development lab from National Health Insurance Service for data linkage.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: GWVP, JHP, SDS. Data curation: GWVP, JSK, JEL, EHJ. Formal analysis: GWVP. Funding acquisition: KJS, SDS. Methodology: GWVP, JHP. Project administration: JHP, KJS, SDS. Visualization: GWVP, JHP. Writing – original draft: GWVP, JHP, JSK, SDS. Writing – review & editing: GWVP, JHP, JSK, JEL, EHJ.