Associations between PM(2.5) and Heart Rate Variability Are Modified by Particle Composition and Beta-Blocker Use in Patients with Coronary Heart Disease

BACKGROUND: It has been hypothesized that ambient particulate air pollution is able to modify the autonomic nervous control of the heart, measured as heart rate variability (HRV). Previously we reported heterogeneous associations between particulate matter with aerodynamic diameter < 2.5 μm (PM(2.5)) and HRV across three study centers. OBJECTIVES: We evaluated whether exposure misclassification, effect modification by medication, or differences in particle composition could explain the inconsistencies. METHODS: Subjects with coronary heart disease visited clinics biweekly in Amsterdam, the Netherlands; Erfurt, Germany; and Helsinki, Finland for 6–8 months. The standard deviation (SD) of NN intervals on an electrocardiogram (ECG; SDNN) and high frequency (HF) power of HRV was measured with ambulatory ECG during paced breathing. Outdoor levels of PM(2.5) were measured at a central site. In Amsterdam and Helsinki, indoor and personal PM(2.5) were measured during the 24 hr preceding the clinic visit. PM(2.5) was apportioned between sources using principal component analyses. We analyzed associations of indoor/personal PM(2.5), elements of PM(2.5), and source-specific PM(2.5) with HRV using linear regression. RESULTS: Indoor and personal PM(2.5) were not associated with HRV. Increased outdoor PM(2.5) was associated with decreased SDNN and HF at lags of 2 and 3 days only among persons not using beta-blocker medication. Traffic-related PM(2.5) was associated with decreased SDNN, and long-range transported PM(2.5) with decreased SDNN and HF, most strongly among persons not using beta blockers. Indicators for PM(2.5) from traffic and long-range transport were also associated with decreased HRV. CONCLUSIONS: Our results suggest that differences in the composition of particles, beta-blocker use, and obesity of study subjects may explain some inconsistencies among previous studies on HRV.