Rapid increases in nitrogen oxides are associated with acute myocardial infarction: A case-crossover study

Aims High concentrations of air pollutants are associated with increased risk for myocardial infarction. The European Union has defined statutory limits for air pollutants based on upper absolute concentrations. We evaluated the association between rapid changes in air pollutants and the risk of myocardial infarction independently of absolute concentrations. Methods and results Using a hospital-based case-crossover study, effects of 24h changes of nitrogen oxides (NO_X/2), particulate matter (PM₁₀), and ozone on the risk of myocardial infarction was assessed in 693 patients. In the overall population, increases of NO_X of more than 20 µg/m³ within 24 h were associated with an increase in the risk of myocardial infarction by up to 121% (odds ratio (OR) 2.21, 95% confidence interval (CI) 1.19-4.08). Comparably, rapid increases of NO₂ of more than 8 µg/m³ tended to increase myocardial infarction risk by 73% (OR 1.73, 95% CI 0.91-3.28) while myocardial infarction risk decreased by 60% after a decrease of NO₂ concentration of more than 8 µg/m³ (OR 0.4, 95% CI 0.21-0.77), suggesting a close-to-linear association. While results for ozone concentrations were ambiguous, rapid change in PM₁₀ was not associated with myocardial infarction risk. Conclusion Dynamics and extent of increase in nitrogen oxide concentrations may be an independent risk factor for myocardial infarction. As there are currently no European Union statutory limits reflecting this dynamic variation of air pollutants on a daily basis, the results urgently call for confirming studies in different geographical regions to verify the observations.