Diurnal cardiac sympathetic hyperactivity after exposure to acute particulate matter 2.5 air pollution

Background: Ambient fine particulate matter (PM2.5) exposure is associated with increased cardiovascular and cardiac arrhythmias events, but the detailed mechanism remains unclear. Objective: We aimed to investigate the effect of PM2.5 (particulate matter < 2.5 μm in aerodynamic diameter) on the cardiac autonomics through a heart rate variability (HRV) analysis. Method: Among 6912 patients who had underwent 24-hour Holter ECG recordings between Oct 1st 2015 and Oct 31st 2016, 46 (25 males, 69.3 ± 12.1 years old) were enrolled with confirmation of living in an environment with a reported PM2.5 level and were classified as elevated (Group 1, >36 μg/m³, 50.73 ± 8.50) or low (Group 2, <11 μg/m³, 6.06 ± 1.00) PM2.5 group. The Holter recordings and HRV parameters were evaluated. Result: The baseline characteristics including the comorbidities and medications were similar between the 2 groups. The Holter ECG parameters were also similar. There were no significant HRV differences between the two groups for the 24-hour interval analysis. However, the LF/HF ratio was significantly higher in Group 1 than Group 2 in the 9 am to 9 pm (p = 0.028), 8 am to 4 pm (p = 0.024), and 4 pm to 12 pm (p = 0.025) periods, respectively, but not for the nocturnal HRV parameters. Conclusion: Our study demonstrated that an elevated PM2.5 exposure had a significant association with an increased daytime LF/HF ratio suggesting a diurnal difference in the response to PM2.5 exposure.