Ambient nitrogen dioxide is associated with emergency hospital visits for atrial fibrillation: a population-based case-crossover study in Reykjavik, Iceland

Background In Iceland air quality is generally good; however, previous studies indicate that there is an association between air pollution in Reykjavik and adverse health effects as measured by dispensing of medications, mortality, and increase in health care utilisation. The aim was to study the association between traffic-related ambient air pollution in the Reykjavik capital area and emergency hospital visits for heart diseases and particularly atrial fibrillation and flutter (AF). Methods A multivariate time-stratified case-crossover design was used to study the association. Cases were those patients aged 18 years or older living in the Reykjavik capital area during the study period, 2006–2017, who made emergency visits to Landspitali University Hospital for heart diseases. In this population-based study, the primary discharge diagnoses were registered according to International Classification of Diseases, 10th edition (ICD-10). The pollutants studied were NO 2 , PM 10 , PM 2.5 , and SO 2, with adjustment for H 2 S, temperature, and relative humidity. The 24-h mean of pollutants was used with lag 0 to lag 4. Results During the study period 9536 cases of AF were identified. The 24-h mean NO 2 was 20.7 μg/m 3 . Each 10 μg/m 3 increase in NO 2 was associated with increased risk of heart diseases (ICD-10: I20-I25, I44-I50), odds ratio (OR) 1.023 (95% CI 1.012–1.034) at lag 0. Each 10 μg/m 3 increase in NO 2 was associated with an increased risk of AF (ICD-10: I48) on the same day, OR 1.030 (95% CI: 1.011–1.049). Females were at higher risk for AF, OR 1.051 (95% CI 1.019–1.083) at lag 0, and OR 1.050 (95% CI 1.019–1.083) at lag 1. Females aged younger than 71 years had even higher risk for AF, OR 1.077 (95% CI: 1.025–1.131) at lag 0. Significant associations were found for other pollutants and emergency hospital visits, but they were weaker and did not show a discernable pattern. Conclusions Short-term increase in NO 2 concentrations was associated with heart diseases, more precisely with AF. The associations were stronger among females, and among females at younger age. This is the first study in Iceland that finds an association between air pollution and cardiac arrhythmias, so the results should be interpreted with caution.