The deadly consequences of wildfires may stretch beyond the people directly in harm's way. Smoke-polluted air may also fuel a spike in cardiac arrests, a new U.S. government study finds.
Looking at the impact of California wildfires in recent years, researchers with the U.S. Environmental Protection Agency found a clear pattern: As smoke from the fires rolled in, more people fell victim to cardiac arrest.
Within days of heavy smoke exposure, counties' cardiac arrest rates rose by as much as 70%.
The findings add to evidence that wildfires can harm the heart. An earlier EPA study linked California wildfires to short-term spikes in heart attacks and strokes.
It has long been known that air pollution can raise the risks of sometimes-fatal heart complications in vulnerable people. But it's important to study the effects of wildfires specifically, said Aruni Bhatnagar, chief of environmental medicine at the University of Louisville in Kentucky.
"The mix of pollutants in forest fire is very different from that of pollutants common in urban environments," said Bhatnagar, who also directs the American Heart Association Tobacco Regulation Center.
And a growing number of people are being exposed to those pollutants. According to the EPA, roughly 57 million Americans were exposed to wildfire smoke at least once between 2004 and 2009 — a number that is projected to rise to 82 million by mid-century.
So there is a "great need," Bhatnagar said, to understand how smoke exposure affects rates of heart complications.
The current study focused on cardiac arrest, where an electrical malfunction in the heart prevents it from pumping blood to the body. It is quickly fatal without emergency medical attention to restore the heart's normal rhythm.
The EPA researchers analyzed more than 5,300 cases of cardiac arrest in 14 California counties between 2015 and 2017. To see how those cases correlated with wildfire smoke, they used a federal database with information on smoke "plumes" seen by satellite.
Overall, the study found, the risk of cardiac arrest rose on days with heavy smoke density, and remained elevated for up to three days. The strongest effect was seen two days later. At that point, the risk of cardiac arrest was 70% higher, compared with days with no smoke exposure.
The findings were published April 15 in the Journal of the American Heart Association. And they're in line with what's known about particulate matter — extremely fine air pollutants that can be inhaled deep into the lungs.
"These particles can create an inflammatory reaction in the lungs and throughout the body," said Ana Rappold, an EPA scientist who worked on the study.
"The body's defense system may react to activate the fight-or-flight system, increasing heart rate, constricting blood vessels and increasing blood pressure," Rappold explained in a journal news release. "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."
There were signs that people in low-income communities were more vulnerable. Cardiac arrests rose in those areas even on days with less-dense smoke.
It's not clear why, but Rappold said lower-income people may be less likely to have air conditioning or portable air filters.
For the most part, Bhatnagar said, cardiac arrest strikes people who already have heart disease, or at least risk factors for it. In this study, the ill effects of smoke exposure were strongest among people age 65 and older — though the risk also tended to go up among 35- to 64-year-olds.
One possibility, Rappold said, is that many people in that age range may be outside, exerting themselves, on smoky days.
But when wildfires are raging, Bhatnagar said, people living in affected areas should pay attention to local health authorities' messages.
"Either stay indoors with air conditioning or, if possible, evacuate if the air quality index is dangerous for sensitive individuals," he said.
People with existing heart disease — or risk factors like diabetes and high blood pressure — should be especially careful, according to Bhatnagar. He advised talking to your doctor, and possibly taking extra precautions, like using an indoor air filter and wearing a mask if you must go outside.