Sudden cardiac arrest refers to a sudden arrest of the blood circulation due to loss of heart function caused by myocardial infarction, trauma, and intoxication, and if not corrected within 10 minutes, irreversible damage proceeds even if spontaneous circulation is recovered[1]. The number of patients who experience sudden cardiac arrest in Korea is increasing each year to 61.6 per 100,000 population, with 25,909 in 2010, 30,771 in 2015, and 31,652 in 2020; the survival rate of cardiac arrest patients in Korea is lower than that of patients in developed countries[2,3]. The low survival rate of patients with sudden cardiac arrest in Korea is attributed to the delayed performance of cardiopulmonary resuscitation (CPR) and defibrillation during the pre-hospital phase[4].

To increase the resuscitation potential of patients with cardiac arrest, the American Heart Association proposed the following six stages of Out-of-Hospital Chain of Survival (Figure 1): recognition of cardiac arrest and activation of the emergency response system, early cardiopulmonary resuscitation (CPR) with an emphasis on chest compressions, rapid defibrillation, advanced resuscitation by emergency medical services and other healthcare providers, post-cardiac arrest care, and recovery (including additional treatment, observation, rehabilitation, and psychological support)[5] (fig 1). Among these, the main factors affecting the survival rate of patients who experienced out-of-hospital sudden cardiac arrest are the presence of bystander CPR, the implementation of rapid defibrillation, and the arrival time and treatment of paramedics[6-8].

In order to increase the bystander CPR rate, efforts have been made to spread awareness on the necessity of CPR to the public through campaigns such as Kids Save Lives and World Restart a Heart of the European Resuscitation Council and CPR awareness week of the ASA, and CPR training[9,10]. Korea also implements CPR training in various methods to increase the resuscitation rate of sudden cardiac arrest patients; with these efforts, the overall implementation rate of CPR is increasing every year, but the survival rate remains lower than that in developed countries[11,12]. Some studies have reported increasing disparities between regions[13]. Therefore, this study aimed to analyze the characteristics of emergency medical services by administrative district using the raw data of patients who experienced out-of-hospital sudden cardiac arrest collected from the Korea Disegase Control and Prevention Agency (KDCA) and provide the fundamental data for establishing a system to improve the recovery rate of out-of-hospital sudden cardiac arrest patients.

Sudden cardiac arrest refers to a condition in which the mechanical activity of the heart ceases, and no signs of circulation are detected[15]. The implementation of initial bystander CPR and early defibrillation in out-of-hospital sudden cardiac arrest patients is a major factor that may increase the survival rate in this group[6,7]. In Korea, although the rate of CPR implementation is increasing due to the expansion of CPR training for the general public to improve the resuscitation rate of patients who experience sudden cardiac arrest, the implementation rate of CPR by the general public remains low compared with the rates of 34.8% in Japan, 27%-56% in the United States, 77% in Sweden, and 40.3% in Norway, and with the global average of 32%[12]. This study also showed that the implementation rate of CPR by the general public was only 22.1%, which was lower compared with that in other countries. In particular, bystander CPR and the use of a rapid automated external defibrillator (AED) are important to increase the survival rate of patients who experienced out-of-hospital sudden cardiac arrest; the survival rate of patients increases by more than six times when AED by the general public are performed together[16-19]. In the initial rhythm of cardiac arrest patients, VF and pulseless VT were found to have a higher 24-hour survival rate and survival discharge rate than those with asystole and pulseless electrical activity (PEA)[20]. Moreover, patients with VF and pulseless VT in the initial stages of cardiac arrest had five times higher neurological prognoses than those with asystole and PEA. Globally, improvement of the return of spontaneous circulation and good neurological outcomes (cerebral performance category scale, CPC) in out-of-hospital sudden cardiac arrest patients are recognized as important public health issues[12]. The CPC scale is divided into 5 categories, with CPC 1 defined as normal, CPC 2 as mild or moderate disability, CPC 3 as severe disability, CPC 4 as coma or vegetative state, and CPC 5 as brain death or death[14]. According to the results of overseas studies, good neurological outcomes (corresponding to CPC 1 and 2 scores and the return to daily life after cardiac arrest) was observed in 12% of cardiac arrest patients in Norway, 6.9% in the United States, and 6.0% in Japan, while the results of domestic studies were relatively low (0.66%-1.6%)[20-22]. As a measure to improve the neurological outcomes of patients who experienced out-of-hospital sudden cardiac arrest, the neurological outcomes was good when pre-hospital defibrillation was performed by the general public or paramedics[23]. This study also reported good neurological outcomes (CPC score of 1-2) when the paramedics performed defibrillation at the pre-hospital phase. Therefore, it is necessary to continuously educate and recommend the use of AED to the general public and emergency medical practitioners to increase the neurological outcomes of patients who experienced out-of-hospital sudden cardiac arrest. In order to strengthen the capabilities of paramedics and efficiently operate the emergency medical system, Korea has been operating a Smart Advanced Life Support pilot project since 2015 and 119 Special Emergency Medical Services Team (hereinafter referred to as Special Emergency Medical Services Team) since 2019. Paramedics are performing professional cardiac resuscitation, including the administration of epinephrine and amiodarone, under direct medical guidance from an emergency physician at the site for cardiac arrest patients. The implementation of professional cardiac resuscitation in the field increased the survival rates of severe and sudden cardiac arrest patients; when the outcome was compared between before and after implementing professional cardiac resuscitation, the survival discharge rates have improved, and discharge with good neurological outcomes has been reported[24]. Some studies have reported that the economic status of communities, presence of teaching hospitals, size of beds, and number of emergency medical institutions per million population are the factors affecting the survival rate of out-of-hospital patients who experienced sudden cardiac arrest[25]. Such differences in survival rates by region are attributed to the fact that the more urbanized regions have higher implementation rate of bystander CPR and have greater access to high-level emergency medical institutions such as regional emergency medical centers and local emergency medical centers; therefore, the out-of-hospital survival chain is operating appropriately[26]. In this study, a significant difference was observed in the administrative district when the factors and characteristics of out-of-hospital sudden cardiac arrest were analyzed by administrative district, including one metropolitan city, six megalopolises, and eight provinces. In the future, it may be necessary to establish measures to reduce the regional disparities so that appropriate treatment of patients with sudden cardiac arrest can be provided at the government level.

This study aimed to contribute to the establishment of a system to increase the rate of return of spontaneous circulation in patients who experienced sudden cardiac arrest by analyzing its impact on the return of spontaneous circulation in the studies population. The implementation of out-of-hospital defibrillation by paramedics resulted in an excellent neurological outcomes. In addition, the implementation rate of emergency medical services differed according to the characteristics and factors of patients who experienced sudden cardiac arrest by administrative district. Therefore, appropriate measures will be required to reduce the disparity in the implementation rate of emergency medical services by the administrative district.