Association Between Long-term Ambient PM2.5 Exposure and Cardiovascular Outcomes Among US Hemodialysis Patients
Background: Ambient PM2.5 is an ubiquitous air pollutant with established adverse cardiovascular effect in the general population. However, quantitative estimates of PM2.5 exposure’s impact on health outcomes in susceptible populations are limited. This study aimed to assess long-term PM2.5 exposure’s impact on cardiovascular (CV) events and cardiovascular disease (CVD)-specific mortality among patients receiving maintenance in-center hemodialysis (HD). Methods: Using data from the United State Renal Data System (USRDS) registry, we conducted a retrospective open cohort study to assess the PM2.5 exposure’s long-term CVD effects among patients who initiated in-center HD 2011 to 2016. Annual-average ambient PM2.5 was calculated based on daily PM2.5 ZIP code-level estimates for patients based on the ZIP codes of the dialysis clinics visited during the 365-day prior to the outcome. The outcomes of CV event and CVD-specific mortality were ascertained through December 2016. We used discrete time hazards models to estimate hazards ratios (HRs) per 1 µg/m3 increase in annual-average PM2.5 adjusting for temperature, humidity, day of the week, season, age at baseline, race, employment status, and geographic region. Effect measure modification was assessed for age, sex, race, and baseline comorbidities. Results: Among 314,079 hemodialysis patients, a 1 µg/m3 increase in the annual-average PM2.5 was associated with increased hazard rates in CV events (HR: 1.012, 95% CI: 1.010, 1.015) and CVD-specific mortality (1.015, 95% CI: 1.009, 1.021). The association was more pronounced for people who initiated dialysis at an older age, and patients with COPD at baseline. Minimal evidence of effect modification was observed across levels of race, and other baseline comorbidities. Conclusion: Long-term ambient PM2.5 exposure was positively associated with CV outcomes among patients receiving maintenance in-center HD. Patients with advanced age and COPD appeared to be more susceptible to long-term PM2.5 adverse effects.