[The mediating effect of electrocardiographic indicators in the association between exposure to fine particulate matter and its element constituents and blood pressure].

Objective: To evaluate the mediating effect of electrocardiographic (ECG) indicators in the association between short-term exposure to fine particulate matter (PM_2.5) and blood pressure and to explore the key PM_2.5 element constituents that produce the mediating effect. Methods: Based on a cross-sectional survey across 10 cities in the Beijing-Tianjin-Hebei region and surrounding areas, PM_2.5 and its element constituents were collected from the nearest air monitoring superstation. Blood pressure and ECG indicators of participants were obtained through physical examinations. A multivariate linear regression was used to evaluate the effect of short-term exposures to PM_2.5 on blood pressure. A mediation analysis was used to identify the mediating effect of ECG indicators in the association between exposure to PM_2.5 and its element constituents and blood pressure. Results: The age of the 1 793 participants was (65.1±13.3) years, and 885 (49.4%) were males. During the study period, the daily mean concentration of PM_2.5 was (70±45) μg/m³, and the systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and pulse pressure (PP) were (139±20), (82±11), (101±13), and (57±17) mmHg (1 mmHg=0.133 kPa), respectively. The results of the multivariate linear regression showed that for every 10 μg/m³ increase in PM_2.5 on the same day (lag 0), DBP increased by 0.15 (95%CI: 0.02-0.28) mmHg, and PP decreased 0.18 (95%CI: 0.36-0.01) mmHg. The exposure to 14 elemental constituents, such as Ga, Co and Se, was associated with an increase in DBP, while the exposure to 17 elemental constituents, such as Cs, Se and Ag, was associated with a decrease in PP. At lag 0, the PM_2.5-induced increase in DBP was mediated by the QRS interval (mediation percentage of 18.98%), and the PM_2.5-induced decrease in PP was mediated by the QT interval (mediation percentage of -6.31%). The exposure to K, Br, Pb, Zn, Ca, Co, Pd, Cu, and As constituents was associated with increases in DBP mediated by prolonged QRS interval. The exposure to Pb, Zn, K, and As constituents was associated with decreases in PP mediated by prolonged QRS interval. Conclusion: ECG indicators such as QRS interval may mediate the association between short-term exposure to PM_2.5 and its element constituents and blood pressure.