Ambient air pollution and emergency department visits and hospitalisation for cardiac arrest: a population-based case–crossover study in Reykjavik, Iceland

OBJECTIVES: To assess the association between traffic-related ambient air pollution and emergency hospital visits for cardiac arrest. DESIGN: Case–crossover design was used with a lag time to 4 days. SETTING: The Reykjavik capital area and the study population was the inhabitants 18 years and older identified by encrypted personal identification numbers and zip codes. PARTICIPANTS AND EXPOSURE: Cases were those with emergency visits to Landspitali University Hospital during the period 2006–2017 and who were given the primary discharge diagnosis of cardiac arrest according to the International Classification of Diseases 10th edition (ICD-10) code I46. The pollutants were nitrogen dioxide (NO(2)), particulate matter with aerodynamic diameter less than 10 µm (PM(10)), particulate matter with aerodynamic diameter less than 2.5 µm (PM(2.5)) and sulfur dioxide (SO(2)) with adjustment for hydrogen sulfide (H(2)S), temperature and relative humidity. MAIN OUTCOME MEASURE: OR and 95% CIs per 10 µg/m(3) increase in concentration of pollutants. RESULTS: The 24-hour mean NO(2) was 20.7 µg/m(3), mean PM(10) was 20.5 µg/m(3), mean PM(2.5) was 12.5 µg/m(3) and mean SO(2) was 2.5 µg/m(3). PM(10) level was positively associated with the number of emergency hospital visits (n=453) for cardiac arrest. Each 10 µg/m(3) increase in PM(10) was associated with increased risk of cardiac arrest (ICD-10: I46), OR 1.096 (95% CI 1.033 to 1.162) on lag 2, OR 1.118 (95% CI 1.031 to 1.212) on lag 0–2, OR 1.150 (95% CI 1.050 to 1.261) on lag 0–3 and OR 1.168 (95% CI 1.054 to 1.295) on lag 0–4. Significant associations were shown between exposure to PM(10) on lag 2 and lag 0–2 and increased risk of cardiac arrest in the age, gender and season strata. CONCLUSIONS: A new endpoint was used for the first time in this study: cardiac arrest (ICD-10 code: I46) according to hospital discharge registry. Short-term increase in PM(10) concentrations was associated with cardiac arrest. Future ecological studies of this type and their related discussions should perhaps concentrate more on precisely defined endpoints.