Wildland Fire-Related Smoke PM and Cardiovascular Disease Emergency Department Visits in the Western United States.

Background: The impact of short-term exposure to fine particulate matter with a diameter ≤2.5 μm (PM) due to wildland fire smoke on the risk of cardiovascular disease (CVD) remains unclear. We investigated the association between short-term exposure to wildfire smoke PM and emergency department visits for acute CVD in the western United States from 2007 to 2018.

Methods: We analyzed 49 759 958 emergency department visits for primary or secondary diagnoses of atrial fibrillation (AF), acute myocardial infarction, heart failure, stroke, and total CVD across 5 states. Daily smoke, nonsmoke, and total PM were estimated using a 1-km resolution satellite-driven multistage model and were aggregated to the zip code level. A case-crossover study design was used, adjusting for temperature, relative humidity, and day of the year.

Results: The mean smoke PM was 1.27 (interquartile range, 0-1.29) μg/m. A 10-μg/m increase in smoke PM was associated with a minuscule decreased risk for AF (odds ratio, 0.994 [95% CI, 0.991-0.997]), heart failure (odds ratio, 0.995 [95% CI, 0.992-0.998]), and CVD (odds ratio, 0.997 [95% CI, 0.996-0.998]) but not for acute myocardial infarction and stroke. Adjusting for nonsmoke PM did not alter these associations. A 10-μg/m increase in total PM was linked to a small increased risk for all outcomes except stroke (odds ratio for CVD, 1.006 [95% CI, 1.006-1.007]). Associations were similar across sex and age groups.

Conclusions: Short-term wildfire smoke PM exposure was unexpectedly associated with a slightly lower risk of CVD emergency department visits. Whether these findings are due to methodological issues, behavioral changes, or other factors requires further investigation.