title: Heat, heat waves, and out-of-hospital cardiac arrest.
abstract: OBJECTIVE
  Cardiac arrest is one of the common presentations of cardiovascular disorders and a leading cause of death. There are limited data on the relationship between out-of-hospital cardiac arrest (OHCA) and ambient temperatures, specifically extreme heat. This study investigated how heat and heat waves affect the occurrence of OHCA.
  
  
  METHODS
  Seven major cities in Korea with more than 1 million residents were included in this study. A heat wave was defined as a daily mean temperature above the 98th percentile of the yearly distribution for at least two consecutive days.
  
  
  RESULTS
  A total of 50,318 OHCAs of presumed cardiac origin were identified from the nationwide emergency medical service database between 2006 and 2013. Ambient temperature and OHCA had a J-shaped relationship with a trough at 28°C. Heat waves were shown to be associated with a 14-% increase in the risk of OHCA. Adverse effects were apparent from the beginning of each heat wave period and slightly increased during its continuation. Excess OHCA events during heat waves occurred between 3PM and 5PM. Subgroup analysis showed that those 65years or older were significantly more susceptible to heat waves.
  
  
  CONCLUSIONS
  Ambient temperature and OHCA had a J-shaped relationship. The risk of OHCA was significantly increased with heat waves. Excess OHCA events primarily occurred during the afternoon when the temperature was high. We found that the elderly were more susceptible to the deleterious effects of heat waves.
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Si-Hyuck
authors.initials: SH
authors.lastname: Kang
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Il-Young
authors.initials: IY
authors.lastname: Oh
authors.affiliation: Department of Environmental Health and Institute of Health and Environment, Graduate School of Public Health, Seoul National University, Seoul, Republic of Korea.
authors.forename: Jongbae
authors.initials: J
authors.lastname: Heo
authors.affiliation: Department of Biostatistics and Epidemiology, Graduate School of Public Health & Asian Institute of Energy, Environment, and Sustainability, Seoul National University, Republic of Korea.
authors.forename: Hyewon
authors.initials: H
authors.lastname: Lee
authors.affiliation: Laboratory of Emergency Medical Services, Biomedical Research Institute, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Jungeun
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Boramae Medical Center, Seoul, Republic of Korea.
authors.forename: Woo-Hyun
authors.initials: WH
authors.lastname: Lim
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Youngjin
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Eue-Keun
authors.initials: EK
authors.lastname: Choi
authors.affiliation: Department of Environmental Health and Institute of Health and Environment, Graduate School of Public Health, Seoul National University, Seoul, Republic of Korea.
authors.forename: Seung-Muk
authors.initials: SM
authors.lastname: Yi
authors.affiliation: Department of Emergency Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Do Shin
authors.initials: do S
authors.lastname: Sang
authors.affiliation: Department of Biostatistics and Epidemiology, Graduate School of Public Health & Asian Institute of Energy, Environment, and Sustainability, Seoul National University, Republic of Korea.
authors.forename: Ho
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Tae-Jin
authors.initials: TJ
authors.lastname: Youn
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: In-Ho
authors.initials: IH
authors.lastname: Chae
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Republic of Korea. Electronic address: seil@snu.ac.kr.
authors.forename: Seil
authors.initials: S
authors.lastname: Oh
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002947:Cities / Q000453:epidemiology*; D018592:Cross-Over Studies; D004632:Emergency Medical Services / Q000639:trends; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000175:diagnosis* / Q000453:epidemiology*; D056910:Republic of Korea / Q000453:epidemiology; D012307:Risk Factors
keywords: Cardiac arrest; Epidemiology; Heat waves; Weather