Air Pollution Increases Risk of Cardiac Arrest: Study

The buildings of downtown Los Angeles, as seen from Pasadena, Calif., are partially obscured in the late afternoon by smog on Nov. 5, 2019. (Mario Tama/Getty Images)

A team of Italian scientists has closely linked air pollution to cardiac arrest, showing that short-term exposure to pollutants such as carbon monoxide, sulfur dioxide, and benzene raised the risk of cardiac arrest outside the hospital.

“In addition to being a threat to the ecosystem, evidence is accumulating that dirty air should be considered a modifiable factor that contributes to cardiovascular disease,” the paper’s first author, Francesca Romana Gentile of the University of Pavia Fondazione and the IRCCS Policlinico San Matteo, said in a press release.

Air pollution is recognized as a threat to human health, with millions of deaths attributed to it each year. In addition, past research has linked air pollution to out-of-hospital cardiac arrest.

Yet Gentile and her colleagues described the relationship between out-of-hospital cardiac arrest and air pollution as “controversial.” According to their paper, published Aug. 25 in PLOS ONE, different studies have reached conflicting conclusions about the role of ozone. Other research couldn’t clearly connect sulfur dioxide levels with out-of-hospital cardiac arrest.

That uncertainty is why they set out to clarify whether and how air pollution impacts the risk of cardiac arrest outside the hospital.

The researchers focused on people living in the southern half of Italy’s Lombardy region. They analyzed 1,582 out-of-hospital cardiac arrest incidents that occurred during 2019.

After finding that cardiac arrest happened outside the hospital at a median daily rate of 0.3 cases per 100,000 inhabitants, they divided days into low and high. Low out-of-hospital cardiac arrest days had rates below the median daily rate, while high incidence days had rates above that median value.

To gauge air pollution, they used information from Italy’s environmental protection agency, which measures daily levels of various pollutants at stations across southern Lombardy. In addition to benzene, carbon monoxide, and sulfur dioxide, the scientists looked into levels of fine particulate matter, nitrogen dioxide, and ozone.

In an initial analysis, the team found that most pollutants were present at higher levels on higher incidence days. Ozone, however, exhibited the opposite trend, with greater ozone levels being linked to lower rates of out-of-hospital cardiac arrest.

But after correcting for temperature, relative humidity, and day-to-day changes in pollutant concentrations, they found that every pollutant they tested, including ozone, raised the risk of out-of-hospital cardiac arrest. Sulfur dioxide had the strongest impact.

“We studied seven common pollutants and found that as the concentration of each rose, the risk of cardiac arrest increased,” Gentile said.

This clear connection between the concentration of each pollutant and the risk of cardiac arrest is known as a dose-response relationship. Gentile and her colleagues think they’re the first to show such a relationship between out-of-hospital cardiac arrest and this array of pollutants.

Their research, they wrote, “confirmed that meteorological factors have to be taken into account when speaking about air pollution,” as cardiac arrest outside the hospital was more frequent during winter, when temperatures are colder.

With the exception of ozone, the pollutants they studied were also present at higher levels in colder weather as a result of home heating and transportation, among other factors.

The team also noted that their strong findings could stem from the high level of pollution in Lombardy, as well as the relatively advanced age of its population.

Gentile hopes her team’s results can translate to better health care.

“The observed relationships between concentrations of individual pollutants and the likelihood of cardiac arrest could be used in future to predict the incidence of this life-threatening condition in specific geographical areas,” Gentile said. “We hope that air pollutant monitoring can improve health service efficiency by being factored into ambulance forecasting models and warning systems.”