Middle-term nitrogen dioxide exposure and electrocardiogram abnormalities: A nationwide longitudinal study

Background: Recently, professionals, such as those from the World Health Organization, have recommended a rigorous standard for nitrogen dioxide (NO₂), a typical urban air pollutant affected by regular traffic emissions, based on its short-term and long-term cardiorespiratory effects. However, the association between middle-term NO₂ exposure and cardiovascular disorders remains unknown. Objectives: This study was conducted to examine the relationship between NO₂ exposure and its middle-term cardiovascular risks indicated by electrocardiogram (ECG) abnormalities. Method: We included 61,094 subjects (132,249 visits) with repeated ECG observations based on longitudinal data from the China National Stroke Screening Survey (CNSSS). The NO₂ exposure concentration was derived from a predictive model, measured as the monthly average concentration in the 6 months of preceding the ECG measurement. We used the generalized estimation equation to assess the association between NO₂ exposure and ECG abnormalities. Result: For each 10 µg/m³ increase in monthly average NO₂ concentration, the odds ratio of ECG abnormalities was 1.10 (95% confidence interval [CI] 1.09–1.12) after multiple adjustments. Stratified regression analyses of urban and rural residents showed associations between middle-term NO₂ exposure and ECG abnormalities in urban (OR 1.09 [95% CI 1.08–1.11]) and rural residents (OR 1.14 [95% CI 1.10–1.19]). The association was robust within different subpopulations. Associations generally remained statistically significant (OR 1.03 [95% CI 1.02–1.05]) after extra adjustment for PM_2.5. Exposure-response relationship analysis revealed a nearly linear relationship between NO₂ exposure and the risk for ECG abnormalities. Conclusion: Using the variation in ECG signals as a potentially reversible indicator for subclinical risk in cardiovascular systems, our study provides additional evidence on the increased risk posed by middle-term NO₂ exposure. Our study showed that policies controlling for NO₂ concentrations are beneficial to prevent cardiovascular diseases among Chinese adults.