Hourly air pollution exposure and emergency department visit for acute myocardial infarction: Vulnerable populations and susceptible time window.

Although short-term exposure to air pollution can trigger sudden heart attacks, evidence is scarce regarding the relationship between sub-daily changes in air pollution level and the risk of acute myocardial infarction (AMI). Here we assessed the intraday effect of air pollution on AMI risk and potential effect modification by pre-existing cardiac risk factors. Hourly data on emergency department visits (EDVs) for AMI and air pollutants in Brisbane, Australia during 2013-2015 were acquired from pertinent government departments. A time-stratified case-crossover analysis was adopted to examine relationships of AMI risk with hourly changes in particulate matters (aerodynamic diameter ≤ 2.5 μm (PM2.5) and ≤10 μm (PM10)) and gaseous pollutants (ozone and nitrogen dioxide) after adjusting for potential confounders. We also conducted stratified analyses according to age, gender, disease history, season, and day/night time exposure. Excess risk of AMI per 10 μg/m3 increase in air pollutant concentration was reported at four time windows: within 1, 2-6, 7-12, and 13-24 h. Both single- and multi-pollutant models found an elevated risk of AMI within 2-6 h after exposure to PM2.5 (excessive risk: 12.34%, 95% confidence interval (CI): 1.44%-24.42% in single-pollutant model) and PM10 within 1 h (excessive risk: 5.21%, 95% CI: 0.26%-10.40% in single-pollutant model). We did not find modification effect by age, gender, season or day/night time, except that PM2.5 had a greater effect on EDVs for AMI during night-time than daytime. Our findings suggest that AMI risk could increase within hours after exposure to particulate matters.