Background The impact of short-term exposure to fine particulate matter (PM2.5) 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 PM2.5 and Emergency Department (ED) visits for acute CVD in the Western United States from 2007 to 2018.

Methods ED visits for primary or secondary diagnoses of atrial fibrillation (AF), acute myocardial infarction (AMI), heart failure (HF), stroke, and total CVD were obtained from hospital associations or state health departments in California, Arizona, Nevada, Oregon, and Utah. ED visits included those that were subsequently hospitalized. Daily smoke, non-smoke, and total PM2.5 were estimated using a satellite-driven multi-stage model with a high resolution of 1 km. The data were aggregated to the zip code level and a case-crossover study design was employed. Temperature, relative humidity, and day of the year were included as covariates.

Results We analyzed 49,759,958 ED visits for primary or secondary CVD diagnoses, which included 6,808,839 (13.7%) AFs, 1,222,053 (2.5%) AMIs, 7,194,474 (14.5%) HFs, and 808,396 (1.6%) strokes. Over the study period from 2007-01-01 to 2018-12-31, the mean smoke PM2.5 was 1.27 (Q1: 0, Q3: 1.29) µg/m3. A 10 µg/m3 increase in smoke PM2.5 was associated with a minuscule decreased risk for AF (OR 0.994, 95% CI 0.991-0.997), HF (OR 0.995, 95% CI 0.992-0.998), and CVD (OR 0.9997, 95% CI 0.996-0.998), but not for AMI and stroke. Adjusting for non-smoke PM2.5 did not alter these associations. A 10 µg/m3 increase in total PM2.5 was linked to a small increased risk for all outcomes except stroke (OR for CVD 1.006, 95% CI 1.006-1.007). Associations were similar across sex and age groups.

Conclusion We identified an unexpected slight lower risk of CVD ED visits associated with short-term wildfire smoke PM2.5 exposure. Whether these findings are due to methodological issues, behavioral changes, or other factors requires further investigation.

The authors have declared no competing interest.

This work was supported by the National Heart, Lung, And Blood Institute of the National Institutes of Health under Award Number 1R01ES032140 (Liu) and R01ES027892 (Chang), and the American Heart Association under Award Number 23PRE1020888 (Li). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

This study received approval from the Institutional Review Board (IRB) at Emory University (STUDY00004823), which also granted an exemption from informed consent requirements due to the impracticability of obtaining consent from each individual patient and the minimal risk associated with the study.

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I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

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In accordance with the agreement with each state, the ED visit data is prohibited from sharing to protect health information. The Daymet daily 1 km meteorological data are available in the Oak Ridge National Laboratory data archive (https://doi.org/10.3334/ORNLDAAC/2129). The zip code level wildfire smoke PM2.5 data are available on Figshare (https://doi.org/10.6084/m9.figshare.25016510).

https://doi.org/10.3334/ORNLDAAC/2129

https://doi.org/10.6084/m9.figshare.25016510