Italian Study Links Daily Air Pollution Levels to OHCA

Day-to-day concentrations of a variety of air pollutants are positively linked to the incidence of out-of-hospital cardiac arrest (OHCA), new Italian data indicate.

Multiple studies have shown connections between air pollution and heart and lung disease, especially with cumulative exposure, but data linking it to OHCA—a condition with more-urgent implications—have been limited.

Presenting the findings during a dedicated session on sudden cardiac death at the European Society of Cardiology Congress 2021, Francesca Gentile, MD (Fondazione IRCCS Policlinico San Matteo, Pavia, Italy), said her results indicate that “people who live in a very polluted area may be considered more susceptible to cardiac arrest. And air pollutant monitoring could be helpful in the future to predict a higher incidence of cardiac arrest, specific to geographical areas.

“Everyone, especially those at high risk, should be aware that air pollution exposure has harmful effects and when possible should modify their behavior to protect their own health,” she stressed.

In their paper, simultaneously published in PLoS ONE, the researchers write: “Just as genetics, lifestyle, and diet have a well-established role in CVD, environmental pollution is now playing an increasingly important role as well. In an era of precision medicine, air pollution exposure assessment may have a role in predicting OHCA susceptibility, especially for patients affected by other comorbidities. The warning during high-[pollution] days should be addressed to these people in particular, even if to date there is no evidence about the role of previous hospitalizations in modifying the association between the risk of OHCA and short-term increases in pollutant concentration.”

‘A Modifiable Risk Factor’

For the study, Gentile and colleagues analyzed 2019 OHCA rates in southern Lombardy, Italy—encompassing around 1.5 million people and known for being particularly polluted due to industry and population growth—and the corresponding levels of the following air pollutants: fine particulate matter (PM₁₀, PM_2.5), benzene (C₆H₆), carbon monoxide (CO), nitrogen dioxide (NO₂), sulphur dioxide (SO₂), and ozone (O₃).

The median age of OHCA patients was 80, and 57% were male. Overall, 19% survived the OHCA, but only 7.4% were alive at hospital discharge.

Concentrations of all pollutants were significantly higher on days with high reported incidence of OHCA (> 0.3 cases per 100,000 people), except for ozone, which appeared to have an inverse relationship. However, after adjusting for temperature, all pollutants including ozone showed a significant dose-response relationship. Additionally, multivariate analysis correcting for temperature, humidity, and day-to-day concentration changes confirmed strong associations with OHCA with all pollutants.

Multivariate Analysis of OHCA Odds and Pollutants

Other research has indicated the potential negative implications of cumulative air pollution exposure, but Gentile told TCTMD that the day-to-day concentrations are a more likely trigger for OHCA.

“To the best of our knowledge, this is the first study to have provided a significant dose-response relationship between such a large number of air pollutants and an increased risk of OHCA,” the authors write. “The identification of the shape of the exposure-curve is a key issue in decision-making and strategic thinking in public health.”

Specifically, Gentile said, a warning system for ambulances that alerts them to bad pollution—and potential increases in OHCA—“would be useful in order to reduce emergency medical service response times in the case of cardiac arrest.”

She added that air pollution exposure should be “seen as a modifiable risk factor for cardiovascular disease” and physicians might consider advising some patients to stay indoors on particularly polluted days. However, who those specific patients might be remains to be seen.