a b s t r a c t

Background: Previous studies on cardiac arrest in mountainous areas were focused on environmental features such as altitude and temperature. However, those are limited to factors affecting the prognosis of patients after cardiac arrest. We analyzed the cardiac arrests in national or provincial parks located in the mountains and determined the factors affecting the prognosis of patients after cardiac arrest.

Methods: This study included all emergency medical service (EMS) treated patients over the age of 40 experienc- ing out-of-hospital cardiac arrests (OHCAs) of presumed cardiac etiology during exercise, between January 2012 and December 2015. The main focus of interest was the location of cardiac arrest occurrence (national mountain parks and provincial parks vs. other sites). The main outcome was survival to discharge and multivariable logistic regression was performed to adjust for possible confounding effects.

Results: A total 1835 patients who suffered a cardiac arrest while exercising were included. From these, 68 patients experienced cardiac arrest in national or provincial parks, and 1767 occurred in other locations. The unadjusted and adjusted ORs (95% CI) for a good cerebral performance scale (CPC) were 0.09 (0.01-0.63) and 0.08(0.01-0.56), survival discharges were 0.13(0.03-0.53) and 0.11 (0.03-0.48).

Conclusions: Cardiac arrests occurring while exercising in the mountainous areas have worse prognosis compared to alternative locations.

(C) 2017

Introduction

Out-of-hospital cardiac arrest (OHCA) is a serious public health con- cern with a low survival rate [1,2]. The reported survival rate of OHCA varies considerably across communities, but generally ranges between 5 and 10% [1,2]. Despite efforts of modern resuscitation science, im- provements in the OHCA survival rate have been minimal for almost 30 years [3]. The Chain of survival refers to a series of actions that it per- formed properly may lead to improved survival outcomes in OHCA. It involves early access, early cardiopulmonary resuscitation (CPR), Early defibrillation, early advanced care and post-resuscitation care [4]. Therefore, the quality of each process, from emergency medical service

* Corresponding author at: School of Medicine, Chonnam National University, 42 Jebong-ro, Dong-gu, Gwangju 61469, Republic of Korea.

E-mail address: [email protected] (H.H. Ryu).

(EMS) access to post-resuscitation care, has a decisive influence on the prognosis of patients experiencing cardiac arrest.

A healthy lifestyle including exercise has been recommended for the general population to reduce the risk of cardiovascular disease. Regular exercise has been shown to play an important role in the primary and secondary prevention of cardiovascular diseases and major cardiovas- cular events [5]. The number of tourists enjoying hikes in mountainous areas is increasing worldwide with approximately 100 million tourists visiting the mountains annually around the globe [6,7]. On the other hand, hiking or climbing mountains usually involves exposure to Low Temperatures, and as the altitude increases, the oxygen concentration in air decreases. The low temperature and lack of oxygen cause cardiac ischemia and increase the likelihood of cardiac arrest [8]. In addition, the risk of an acute cardiac event is transiently increased during and im- mediately after acute, vigorous exercise [9]. Cardiac arrest during exer- cise has a greater impact on the family and community because of the sudden unexpected death as victims are more likely to be healthy and more active. In some studies, cardiac arrest during moderate exercise is associated with favorable Survival outcomes [10]. However, in the

https://doi.org/10.1016/j.ajem.2017.12.040

0735-6757/(C) 2017

case of cardiac arrest in mountainous areas, even if EMS is activated quickly after a cardiac arrest incident, the patient’s prognosis deterio- rates as much more time is spent in locating the incidence site and arrival times are much longer than with a typical location.

Previous reports studying cardiac arrest in mountainous areas were focused on environmental features such as altitude and temperature [7, 11]. Even though the environmental characteristics of mountains affect the occurrence of cardiac arrest, we suggest that there are several factors that influence the prognosis of cardiac arrest patients after the event itself [12].

We aimed to compare the outcomes of patients with cardiac arrest while exercising in the mountainous area with those patients with car- diac arrest while exercising in non-mountainous areas to determine whether prognosis differs according to the location of cardiac arrest occurrence and if that is the case, to investigate what causes such differ- ences in outcome.

Methods

Study design and setting

This study is a retrospective observational study based on a nation- wide, population-based registry, which involves all patients who expe- rienced OHCA and were transported to hospital by EMS with resuscita- tion efforts in South Korea from 2012 to 2015.

The total territory of Korea is 100,284 km², 65% of which is entirely comprised of mountains. Within the mountains, there are currently 16 national parks and 19 provincial parks designated by certain standards such as total area and topographic features. Visitors to national parks and provincial parks increase annually, with N 50 million people visiting each year as of 2015. This has had an effect of raising the number of cases of cardiac arrest in national and provincial parks. Currently, for na- tional and provincial parks employees, Basic Life Support (BLS) training is emphasized and actively conducted, as a result, 74% of all employees completed training by 2014. New employees are required to submit documentary evidence about their completion of education and CPR is included in the evaluations at the time of their hired. In addition, ap- proximately 250 automated electric defibrillators (AEDs) are installed on the main access roads and shelters and managed by a designated ad- ministrator in the park every each year. Parks where incidents occur regularly are covered by rescue teams composed of specialized rescue personnel. In order to reduce incidents occurring during nighttime hiking or climbing, limits to the time of entry are increasingly being ap- plied. Once a cardiac arrest occurs in the mountains, bystanders call the park offices or 119 (The Korean Emergency Number), and trained park staff and 119 rescue workers are dispatched to the scene.

The Korean EMS is a single tiered, government-based system that provides basic-to-intermediate level ambulance services [13,14]. The public access AED program in South Korea began in 2009, and its de- ployment and training are in progress [15]. Upon activation of the EMS, the fire department judges the accessibility of the location of the incident and an ambulance is dispatched. However, if the location is N 30 km from the hospital, or it is expected transport will take more than one hour, a helicopter will be dispatched. The current EMS CPR protocol calls for emergency medical technicians to perform on scene CPR, using an AED every 2 min, for at least 5 min. Intravenous fluid administration and advanced airway management may be option- ally performed by level-1 EMTs. Epinephrine and other intravenous medication for Advanced cardiac life support are not available at the scene. EMTs cannot declare death at the scene unless there are signs of irreversible death (Rigor mortis, dependent rigidity, decapita- tion, transection and decomposition) that are confirmed by direct med- ical control. If there is no return of spontaneous circulation (ROSC) after at least 5 min of CPR, EMTs transport the patients to the closest emer- gency department (ED), while continuing CPR during transport. Thus, almost all cases of OHCAs in Korea are transported to the closest ED.

When a helicopter is dispatched, the selection of a hospital is affected by the helicopter landing facilities of the hospital.

Data sources

The cardiovascular disease surveillance database is a nationwide population based-database of EMS-assessed OHCA patients in Korea. The registry uses standardized definitions and reporting templates known as Utstein-style and comprises data collected from EMS-run sheets and hospital medical records.

Emergency medical service run sheets are completed by EMS per- sonnel and include patient information comprising of demographic, event demographic, ambulance operation information, patient clinical information, treatment such as defibrillation or cardiopulmonary resus- citation (CPR), and transport information such as to which hospital the patient was transported. They are coded and filed electronically in each provincial EMS headquarters.

Hospital medical records were obtained from patients who transported to the ED and include patient clinical information, treat- ment information, hospital care information and outcomes. Medical records were collected by a trained medical record reviewer from the Korean CDC who visited all of the hospitals to evaluate medical records and document hospital outcomes electronically. A Quality management committee (QMC) composed of emergency physicians, epidemiologists, statistical experts, representatives from the fire department, and medical record review experts ensured the quality of the medical record Review process. The quality management committee educated all med- ical record reviewers (approximately 15 reviewers) prior to joining the project, provided a standard manual for data abstraction, monthly feed- back to the reviewers, and consultation on equivocal cases as needed [16].

Study population

This study included the EMS-treated patients with OHCAs of presumed cardiac etiology during exercise between January 2012 and December 2015. The activities at the time of cardiac arrest were based on the EMS run sheets classified as an ‘exercise’. Cases were presumed to be of cardiac etiology if there was no definite evidence of non-cardiac etiology, such as evident trauma. Cases were excluded if there was missing information regarding the neurological status at hospital discharge.

Main outcomes

The primary end point was survival to discharge, and the secondary end point was survival to discharge with a good neurologic function, distinguished by scoring 1 (no neurologic disability) or 2 (moderate dis- ability; able to perform daily activities independently) on the Cerebral Performance Category score, a 5-point scale used to evaluate neu- rologic functioning. The CPC score was measured on the basis of dis- charge summary abstracts or medical record documentation, written by inpatient care doctors. As there was no standard recording frame across different hospitals for coding the CPC score, the coded scores were reviewed and revised by the medical record reviewers of the Korean CDC, who were supervised by the QMC.

Variables and measurements

Our main interest in this study was location of cardiac arrest (moun- tainous area vs. non-mountainous area). The location of the cardiac ar- rest was extracted from information recorded on the EMS run sheets. We collected demographic variables and examined the effect of numer- ous potential confounders: age, gender, residence area (urban vs. rural), co-morbidity (diabetes, hypertension, heart disease, and strokes), a type of primary electrocardiogram (ECG) at the scene (shock-able vs.

non-shock-able), and the number of pre-hospital defibrillations. Variables regarding time include response time interval (RTI), scene time interval (STI), and transport time interval (TTI). RTI (mins) refers to the time interval from when the call was received by the dispatcher to the arrival of the ambulance at the scene of incidence. STI (mins) re- fers to the time interval from ambulance arrival to ambulance departure to appropriate ED, TTI (mins) refers to the time interval from ambulance departure to arrival at the ED.

Statistical analysis

We calculated the OHCA prevalence rate per 1,000,000 visits using annual visit report by the national and provincial parks.

Demographic findings were compared between different event loca- tions using the chi-square test for categorical variables and the indepen- dent t-test for continuous variables. A p value of b 0.05 was regarded as significant. To investigate the associations between the location of car- diac arrest and the prognosis for cardiac arrest during exercise, we built a matched population for a sensitivity analysis as there are various extraneous factors that could influence the location of the cardiac arrest. The matched dataset was extracted by matching patients who had a mountain occurring OHCA with patients who had an OHCA that oc- curred in a location other than the mountains during exercise (1:2 matching ratio), within strata including age (10-year interval), gender, event time (6-hour interval), event year and residence area (rural vs. urban). To estimate the effect of different event locations on the study end point, multivariable logistic regression analysis was used to calcu- late unadjusted and adjusted odds ratios (aORs) and 95% confidence in- tervals (CIs). The model was adjusted for potential confounders including patient factors (age, gender, and comorbidities) and arrest- Environmental factors (time of arrest and ECG identified cardiac rhythm at the scene). All statistical analysis was performed using SAS version

9.4 for Windows (SAS Institute, Cary, SC, USA).

Ethics statements

The study complied with the Declaration of Helsinki, and its protocol was approved by the Seoul National University Hospital Institutional Review Board with a waiver of informed consent (IRB No: 1103-153- 357).

Results

There were 96,653 EMS treated OHCAs in South Korea during the 4- year study period. We initially excluded cases classified as non-cardiac etiology (n = 27,382), non-exercise patients (n = 67,242). From initial review of the data from mountainous areas, we found no cases of car- diac arrest in patients b 40 years of age, therefore, we excluded all pa- tients less than age 40 from the data set (n = 194). Of the remaining 1835 patients, 68 experienced cardiac arrests in a mountainous area at a national or provincial park, and 1767 occurred in other places (Fig. 1).

Demographic findings

The number of visitors was 46 million in spring, 47 million in sum- mer, 65 million in autumn and 37 million in winter. The OHCA in na- tional or provincial parks prevalence rate per 1,000,000 visits was 0.35 and varied by season over the four years. During winter, the number of mountain visitors was minimal, yet the Incidence of cardiac arrest ap- peared to be higher (0.49 cardiac arrest/1 million visits) than in other seasons, however, statistically not significant (Fig. 2).

The demographic findings of cardiac arrests during exercise in

mountainous areas and other places is represented in Table 1. Most of the victims in the mountains were tended to be younger and males. The residence area of patients, co-morbidity and bystander CPR were similar in both groups. Cardiac arrests in the mountains showed a great number of non-Shockable rhythms (76.5% vs. 61.6%), fewer per- formed defibrillations by EMS personnel (25.0% vs. 45.4%), and were more likely to occur in the presence of a witness (76.5% vs. 60.8%). He- licopter transfers were higher for cardiac arrests in the mountains (42.6% vs. 5.5%). The RTI, STI and TTI were significantly delayed in the mountain arrest group. There were no remarkable differences in the level of the hospital where patients were transferred. The rate of pre- hospital ROSC, emergency department ROSC, survival to discharge, and good CPC were all significantly lower in the mountain arrest group than in other places. To account for the nonrandom distribution of patient characteristics between the two groups, a matched dataset was also analyzed. Among 1767 OHCAs that occurred during exercise in a place other than a mountain, 136 cases matched with OHCAs occur- ring in the national and provincial parks. In matched dataset, survival to discharge and a good neurological recovery were also significantly lower in the mountain arrest group (p value b 0.05) (Table 2).

Fig. 1. Study population. EMS: emergency medical service, OHCA: out-of-hospital cardiac arrest;

Main analysis

Fig. 2. The OHCA in the national or provincial parks prevalence rate per 1 million hikers.

Multivariable logistic regression analysis was conducted to test the associations between the location of cardiac arrest and outcomes after adjusting for the confounders. Model 1 was adjusted for gender, age and Model 2 was adjusted for the covariates in Model 1 plus comorbid- ity of patients.

This analysis shows that patients who had an OHCA that occurred in the mountains were less likely to have a good CPC or a good survival to hospital discharge than patients that had an OHCA in other places (Table 3). The unadjusted ORs [95% CI] for survival discharge were

0.13 [0.03-0.53] and for good CPC were 0.09 [0.01-0.63] in the moun- tains. For the original dataset, the multivariable analysis showed that patients who experienced an OHCA that occurred during exercise in na- tional or provincial parks were less likely to survive discharge (adjusted OR [95% CI] in Model 1 and Model 2: 0.10 [0.03-0.42] and 0.11 [0.03-

0.44], respectively) or have a good CPC (adjusted OR [95% CI] in Model 1 and Model 2: 0.07 [0.01-0.49] and 0.07 [0.01-0.51], respectively). For the matched dataset, the multivariable conditional logistic regres- sion analysis showed that patients who had an OHCA which occurred during physical exercises in the national or provincial parks were less

Table 1

Demographics and clinical characteristics of original and matched data in OHCA.

Original data Matched data

Total OHCA in

Mountains

OHCA in other places

OHCA in Mountains

OHCA in other places

	N	%	N	%		N	%	N	%		N	%
Total	1835	100	68	100		1767	100	68	100		136	100
Gender*
Male	1572	85.7	65	95.6		1507	85.3	65	95.6		130	95.6
Age, year*
40-49	303	16.5	16	23.5		287	16.2	16	23.5		32	23.5
50-59	543	29.6	27	39.7		516	29.2	27	39.7		54	39.7
60-69	411	22.4	13	19.1		398	22.5	13	19.1		26	19.1
70-79	407	22.2	11	16.2		396	22.4	11	16.2		22	16.2
80-	171	9.3	1	1.5		170	9.6	1	1.5		2	1.5
Time of arrest**
0 AM-6 AM	83	4.5	3	4.4		80	4.5	3	4.4		7	5.1
6 AM-MD	610	33.2	34	50.0		576	32.6	34	50.0		69	50.7
MD-6 PM	786	42.8	26	38.2		760	43.0	26	38.2		50	36.8
6 PM-MN	356	19.4	5	7.4		351	19.9	5	7.4		10	7.4
Year of arrest
2012	389	21.2	14	20.6		375	21.2	14	20.6		28	20.6
2013	443	24.1	18	26.5		425	24.1	18	26.5		36	26.5
2014	531	28.9	24	35.3		507	28.7	24	35.3		47	34.6
2015	472	25.7	12	17.6		460	26.0	12	17.6		25	18.4
Season of arrest
Spring [3-5]	537	29.3	15	22.1		522	29.5	15	22.1		42	30.9
Summer [6-8]	359	19.6	14	20.6		345	19.5	14	20.6		26	19.1
Autumn [9-11]	466	25.4	21	30.9		445	25.2	21	30.9		32	23.5
Winter [12-2]	473	25.8	18	26.5		455	25.7	18	26.5		36	26.5
Residential area
Metropolitan city	844	46.0	25	36.8		819	46.3	25	36.8		50	36.8
Comorbidity
Hypertension	492	26.8 14		20.6	478		27.1 14		20.6	30		22.1
Diabetes	282	15.4 10		14.7	272		15.4 10		14.7	23		16.9
Heart disease	295	16.1 8		11.8	287		16.2 8		11.8	26		19.1
Stroke	73	4.0 2		2.9	71		4.0 2		2.9	5		3.7
Transportation method**
Helicopter	126	6.9 29		42.6	97		5.5 29		42.6	13		9.6
Witness**
Yes	1126	61.4 52		76.5	1074		60.8 52		76.5	84		61.8
Bystander CPR
Chest compression	1098	59.8 40		58.8	1058		59.9 40		58.8	85		62.5
Pre-hospital defibrillation**
Yes	819	44.6 17		25.0	802		45.4 17		25.0	58		42.6
Initial ECG rhythm**
Shockable	694	37.8 16		23.5	678		38.4 16		23.5	54		39.7

OHCA: out-of-hospital cardiac arrest; CPR: cardiopulmonary resuscitation; ECG: electrocardiogram.

p-Value: * b 0.05, ** b 0.01.

Table 2

Pre-hospital time and Survival outcomes of original and matched data in OHCA.

				Original data						Matched data
	Total			OHCA in mountains			OHCA in other places			OHCA in mountains			OHCA in other places
	N	%		N	%		N	%		N	%		N	%
Total	1835	100		68	100		1767	100		68	100		136	100
RTI (min)**
b10	1128	61.5		5	7.4		1123	63.6		5	7.4		75	55.1
10-20	426	23.2		20	29.4		406	23.0		20	29.4		41	30.1
20-30	131	7.1		19	27.9		112	6.3		19	27.9		7	5.1
30-40	46	2.5		5	7.4		41	2.3		5	7.4		5	3.7
40-50	28	1.5		4	5.9		24	1.4		4	5.9		3	2.2
50-60	27	1.5		2	2.9		25	1.4		2	2.9		2	1.5
N 60	49	2.7		13	19.1		36	2.0		13	19.1		3	2.2
Median (IQR, min)				23(17-45)			7(5-13)			23(17-45)			9(5.5-14)
STI (min)**
b10	1064	58.0	25		36.8	1039		58.8	25		36.8	75		55.1
10-20	589	32.1	24		35.3	565		32.0	24		35.3	40		29.4
20-30	103	5.6	4		5.9	99		5.6	4		5.9	12		8.8
30-40	34	1.9	3		4.4	31		1.8	3		4.4	3		2.2
40-50	18	1.0	4		5.9	14		0.8	4		5.9	2		1.5
50-60	7	0.4	2		2.9	5		0.3	2		2.9	1		0.7
N 60	20	1.1	6		8.8	14		0.8	6		8.8	3		2.2
Median (IQR, min)			11(7-25.5)			8(5-12)			11(7-25.5)			9(5.5-14.0)
TTI (min)**
b10	1172	63.9	31		45.6	1141		64.6	31		45.6	85		62.5
10-20	471	25.7	19		27.9	452		25.6	19		27.9	36		26.5
20-30	115	6.3	11		16.2	104		5.9	11		16.2	8		5.9
30-40	41	2.2	2		2.9	39		2.2	2		2.9	2		1.5
40-50	16	0.9	3		4.4	13		0.7	3		4.4	4		2.9
50-60	6	0.3	1		1.5	5		0.3	1		1.5	0		0.0
N 60	14	0.8	1		1.5	13		0.7	1		1.5	1		0.7
Median (IQR, min)			10(5-20.5)			7(4-12)			10(5-20.5)			7(5.0-13.0)
Survival outcomes
Pre-hospital ROSC**	329	17.9	2		2.9	327		18.5	2		2.9	28		20.6
ED ROSC**	690	37.6	8		11.8	682		38.6	8		11.8	53		39.0
Survival to discharge**	338	18.4	2		2.9	336		19.0	2		2.9	27		19.9
Good CPC**	259	14.1	1		1.5	258		14.6	1		1.5	20		14.7

OHCA: out-of-hospital cardiac arrest; RTI: response time interval; STI: scene time interval; TTI: transport time interval; ROSC: return of spontaneous circulation; ED: emergency depart- ment; CPC: cerebral performance scale; IQR: interquartile range. p-Value: * b 0.05, ** b 0.01.

likely to survive discharge (adjusted OR [95% CI] in Model 1: 0.08 [0.01- 0.42]) or have a good CPC (adjusted OR [95% CI] in Model 1: 0.04 [0.00- 0.43]).

Discussion

This Nationwide observational study evaluated the difference of sur- vival outcomes in patients that suffered cardiac arrests during exercise in mountainous areas and other locations. The OHCA during exercise in mountainous areas was associated with worse neurologic and sur- vival outcomes, and exhibited a higher number of non-shockable

Table 3

Associations between place of occurrence and study outcomes for original and matched data in OHCA.

Original data Matched

data Unadjusted Model 1 Model 2 Model 1

OR (95% CI) OR (95% CI) OR (95% CI) OR (95% CI)

Survival to discharge**

OHCA in mountains 0.13 0.10 0.11 0.12

(0.03-0.53) (0.03-0.42) (0.03-0.44) (0.03-0.51)

OHCA in other places 1.00 1.00 1.00 1.00

Good neurological recovery**

OHCA in mountains 0.09 0.07 0.07 0.08

(0.01-0.63) (0.01-0.0.49) (0.01-0.51) (0.01-0.62)

OHCA in other places 1.00 1.00 1.00 1.00

p-value: * b 0.05, ** b 0.01

rhythms at the scene, fewer performed defibrillation, and significantly longer pre-hospital times, consisting of response time, scene time and transport time than for incidents in other locations. As a result of our study, for the case of mountainous cardiac arrests, it can be inferred that the patient’s prognosis is worse as defibrillation cannot be per- formed at the required time as pre-hospital time increases. Therefore, it is necessary to find a way to reduce the time from the occurrence of cardiac arrest to the implementation of defibrillation.

Most previous studies have shown that the probability of cardiac ar- rest occurrence is higher due to lower temperatures and lack of oxygen in High altitude mountains. Such studies on the prognosis according to the altitude and temperature were mainly applied to mountains over 5000 m [11], yet all the mountains in Korea are b 2000 m. Therefore, for the mountains of Korea, altitude and temperature are unlikely to have a significant impact on the occurrence of cardiac arrest. Among the cardiac arrests that occurred in mountainous areas, there is a case report that presents a promising survival outcome with bystander CPR, fast defibrillation and transfer to an appropriate hospital [17]. However, there are very few studies on the ‘chain of survival’, which represents early EMS activation, CPR by a witness, defibrillation, and rapid and appropriate transfer. Our study, which analyzed cardiac ar- rests in Korean national or provincial parks in the mountains over four years, showed very low rates of cardiac arrest, but with high mortality. For the case of cardiac arrest in mountainous areas, the frequency of CPR by witnesses was similar to other sites, but the implementation of defibrillation was significantly delayed. In past studies on cardiac arrest occurrence during exercise, a greater shock-able rhythm (ventricular tachycardia or ventricular fibrillation) was observed [10,11]. However, in this study, the initial ECG rhythm performed when EMS arrived at

the scene was often a Non-shockable rhythm (asystole or pulseless elec- trical activity). We predict that some of the initially shockable rhythms degraded to be a non-shockable rhythm due to delayed defibrillation, which may have rendered an inferior prognosis. The amount of pre- hospital time affects the prognosis of the patient, but the response time is particularly important in terms of early defibrillation.

Efforts to reduce pre-hospital time, particularly response time, are

ongoing. Most of the patients experiencing cardiac arrest in mountain- ous areas are helicopter dispatched and an AED is placed at the entrance and shelters of national and provincial parks. Despite these efforts, how- ever, survival rates are not significant. As the survival rate is generally known to be reduced by 7 to 10% per minute when defibrillation is delayed after cardiac arrest, preparedness for cardiac arrest in the mountains is currently insufficient [18]. By analyzing the frequency and route of the hiking or climbing routes, more AEDs should be placed on trails and AED kits should be distributed to climbers and it should be considered that most AEDs currently used are often operated above 0

?Celsius [19]. It is also thought that sophisticated technology, such as AED transportation via drones, should be implemented.

Limitations

Several limitations of this study need to be taken into consideration. First, our main exposure, exercise in the mountains, can be subjective as it is based on the run sheets of paramedics. It is possible that those living in the mountains or performing other activities may be partly included. Second, when the cardiac arrests were recorded as to have taken place in the mountains, other factors that could affect the prognosis, such as altitude, were not analyzed. Lastly, we limited our study to national and provincial parks. As these parks are institutionally managed, unlike other common mountain areas, the results of this study may not reflect conditions in all mountains of Korea.

Conclusions

Cardiac arrest during exercise in the mountains has a worse progno- sis compared to those not occurring in mountainous areas. It is necessary to improve factors affecting such poor prognosis of patients experiencing cardiac arrests in the mountains.

Conflict of interest statement

None.

Funding acknowledgments

The study was funded by the Korea CDC for 2012-2015 (Grant no: 2012-E33010-00. 2013-E33015-00. 2014-E33011-00).

Disclosures

None.

Author contributions

Dr. Jung and Ryu has full access to all the data in the study and the responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Jung, Ryu, Shin.

Acquisition, analysis, or interpretation of data: Jung, Ryu, Shin, Ro, Song.

Drafting of the manuscript: Jung, Ryu, Ro, Hong, Kong. Critical revision of the manuscript for important intellectual content:

Jung, Ryu, Ro.

Statistical analysis: Jung, Ryu, Ro, Song, Hong, Park. Administrative, technical, or material support: Ryu, Shin, Ro, Hong. Study supervision: Ryu, Ro, Park, Kong.

Manuscript approval: all authors.

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