A systematic review of air pollution and incidence of out-of-hospital cardiac arrest Tiew-Hwa Katherine Teng, 1,2 Teresa A Williams, 1,3,4 Alexandra Bremner, 5 Hideo Tohira, 3 Peter Franklin, 5 Andrew Tonkin, 6 Ian Jacobs, 1,3,4 Judith Finn 1,3,4,6 ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/jech- 2013-203116). For numbered affiliations see end of article. Correspondence to Dr Tiew-Hwa Katherine Teng, Discipline of Emergency Medicine, The University of Western Australia, Crawley, WA 6009, Australia; katherine.teng@uwa.edu.au Received 18 July 2013 Revised 12 September 2013 Accepted 18 September 2013 To cite: Teng T-HK, Williams TA, Bremner A, et al. J Epidemiol Community Health Published Online First: [ please include Day Month Year] doi:10.1136/jech-2013- 203116 ABSTRACT Introduction Studies have linked air pollution with the incidence of acute coronary artery events and cardiovascular mortality but the association with out-of-hospital cardiac arrest (OHCA) is less clear. Aim To examine the association of air pollution with the occurrence of OHCA. Methods Electronic bibliographic databases (until February 2013) were searched. Search terms included common air pollutants and OHCA. Studies of patients with implantable cardioverter defibrillators and OHCA not attended by paramedics were excluded. Two independent reviewers (THKT and TAW) identified potential studies. Methodological quality was assessed by the Newcastle-Ottawa Scale. Results Of 849 studies, 8 met the selection criteria. Significant associations between particulate matter (PM) exposure (especially PM 2.5 ) and OHCA were found in 5 studies. An increase of OHCA risk ranged from 2.4% to 7% per interquartile increase in average PM exposure on the same day and up to 4 days prior to the event. A large study found ozone increased the risk of OHCA within 3 h prior to the event. The strongest risk OR of 3.8–4.6% per 20 parts per billion ozone increase of the average level was within 2 h prior to the event. Similarly, another study found an increased risk of 18% within 2 days prior to the event. Conclusions Larger studies have suggested an increased risk of OHCA with air pollution exposure from PM 2.5 and ozone. BACKGROUND Out-of-hospital cardiac arrest (OHCA) is a signifi- cant public health issue affecting an estimated 310 000 Americans/year. 1 While OHCA incidence and outcome vary around the globe, 2 case fatality is consistently high, with overall survival to hospital discharge usually less than 10%. 2 Thus, there is an imperative to better understand factors that ‘trigger’ the onset of cardiac arrest. There is increasing evidence to support the associ- ation of ambient air pollution with overall cardio- vascular mortality and morbidity. 3–5 Exposure to higher than usual levels of airborne air pollutants over a few hours to several days has been reported to increase the risk of myocardial infarction, 4 arrhythmia, 6–8 stroke 9–12 and heart failure, 13–16 par- ticularly in susceptible patients. 12–18 Inconsistent results have been found in the relationship between OHCA and air pollution. 3 However, there has not been a systematic review of these studies and the aim of our paper is to identify, evaluate and sum- marise the studies of air pollution and OHCA to examine the hypothesis that air pollution is asso- ciated with the incidence of OHCA. METHODS Search strategy A literature search was performed to identify studies that had analysed the association between OHCA attended by emergency medical services (EMS) and exposure to any air pollutant of interest (see Exposure section) in any lag period. The follow- ing bibliographic databases were searched (by authors THKTand TAW): MEDLINE (1946-February 2013); EMBASE (1980–February 2013), CINAHL (1982– February 2013), AUSTHealth (1997–February 2013) and the Cochrane Library (2004–February 2013). Scopus and Biosis Previews were searched for add- itional environmental science literature. Regional electronic bibliographic databases: Chinese Biomedical Literature Database (CBM), China Knowledge Resource Integrated Database (Cnki), CiNii ( Japan), KoreaMed (Korea), IndMED (India) and LILACS (for Latin America and the Carribean) were also examined. Reference lists of relevant review articles and journals were hand-searched, and “Google” and “Google Scholar” search engines were used to search the internet. Terms were mapped to the appropriate MeSH/ EMTREE subject headings and “exploded”: [“cardiac arrest” OR “heart arrest” OR “sudden cardiac death”] AND [“air pollution” OR “air pol- lutants” OR “particulate matter” OR “airborne par- ticles” OR “fine particles” OR environmental exposure” OR “soot” OR “elemental carbon” OR “ carbon monoxide” OR “nitrogen dioxide” OR “nitrogen oxides” OR “ozone” OR “sulfur dioxide” OR “ sulphur dioxide”] (see online supplementary appendix 1). Study selection Inclusion criteria were comparative studies and arti- cles published in any language in peer-reviewed journals that examined the relationship between air pollution and OHCA in adults and children, including neonates. Exposures from ambient air- borne pollutant levels: particulate matter (PM) <2.5 m in aerodynamic diameter (PM 2.5 ), PM 10 , ultrafine particles (UFP), nitrogen oxides (NO x ), ozone, sulfur dioxide (SO 2 ) and carbon monoxide (CO) were included. Animal studies, toxicological studies, summaries, commentaries, reviews, case reports, editorials, duplicates and articles only published in abstract form were excluded. Studies of patients with implantable cardioverter defibrillators and OHCA not attended by EMS personnel were also Teng T-HK, et al. J Epidemiol Community Health 2013;0:1–7. doi:10.1136/jech-2013-203116 1 Review JECH Online First, published on October 7, 2013 as 10.1136/jech-2013-203116 Copyright Article author (or their employer) 2013. Produced by BMJ Publishing Group Ltd under licence.