Wildfire Smoke Linked to Spike in Risk of Out-of-Hospital Cardiac Arrest

New research from California’s Department of Public Health has uncovered a startling link between wildfires and a sharp rise in out-of-hospital cardiac arrests.

Aggregating data from the National Ocean Atmospheric Association’s (NOAA) Hazard Mapping System and the Cardiac Arrest Registry to Enhance Survival (CARES) from 14 California counties, investigators found heavy wildfire smoke increased risk of out-of-hospital cardiac arrests by as much as 70%.

“In recent decades, we experienced a significant increase in large-scale wildfires, therefore, more people are being exposed to wildfire smoke. In order to respond properly, it is important for us to understand the health impacts of wildfire smoke exposure,” said lead investigator Ana Rappold, PhD, a research scientist at the US EPA’s Center for Public Health and Environmental Assessment in the Office of Research and Development, in a statement.

With the devastating wildfires in California and other parts of the world becoming seemingly more frequent, Rappold and colleagues designed the current study to assess the impact of wildfire smoke exposure on risk of out-of-hospital cardiac arrest. With this in mind, investigators designed a case-crossover study designed to evaluate associations between out-of-hospital cardia arrest and wildfire-related Particulate Matter (PM) 2.5, while also characterizing these relationships within subpopulations by age, sex, and socioeconomic status.

Using deidentified data from 14 California counties from 2015-2017 with large wildfires or duration were included in the current study—these counties included Alameda, Amador, Calaveras, Contra Costa, Mariposa, Mendocino, Napa, San Francisco, San Luis Obispo, San Mateo, Santa Barbara, Sonoma, Stanislaus, and Ventura Counties. Investigators restricted their data to only include cases from May to October, the primary wildfire months.

Categorical estimates for smoke plume density were obtained through the NOAA Office of Satellite and Product Operation’s HMS Smoke Product. Smoke plumes detected using this method were assigned an estimated smoke-originated PM2.5 density defined as light (0-10 ug/ m3), medium (10.5—21.5 ug/m3), and heavy (greater than 22 ug/m3).

For comparison, investigators applied conditional logistic regression using control days from 1, 2, 3 and 4 weeks before the case date. Analyses were stratified by pathogenesis, sex, age groups, and socioeconomic status. Investigators categorized age groups as 19-34, 35-64, and 65 years of age and older.

In total, 5336 cases occurred during wildfire months within the study period, of which 16.7% had been exposed to wildfire smoke. During the study period, out-of-hospital cardiac arrest increased in association with heavy smoke across multiple lag days. Specifically, associations appeared significant at lag days 0 (OR, 1.56; 95% CI, 1.05—2.33), 2 (OR, 1.70; 95% CI, 1.18–2.45) and 3 (OR, 1.48; 95% CI, 1.02–2.13).

When examining socioeconomic status, investigators noted the risk in those of lower socioeconomic status was elevated on medium and heavy days but this association did not reach statistical significance. Among those of higher socioeconomic status, elevated odds ere observed with heavy smoke but null results were seen in regard to light and medium smoke. Results also indicated both sexes and age groups 35 years and older were impacted on days classified as having heavy smoke.

“The body's defense system may react to activate the fight-or-flight system, increasing heart rate, constricting blood vessels and increasing blood pressure. These changes can lead to disturbances in the heart's normal rhythm, blockages in blood vessels and other effects creating conditions that could lead to cardiac arrest," said Rappold in the aforementioned statement.

This study, “Out-of-Hospital Cardiac Arrests and Wildfire-Related Particulate Matter During 2015—2017 California Wildfires,” was published in the Journal of the American Heart Association.