MRI study links long-term fine particle exposure to early heart scarring, even below many guideline limits

Even air pollution at levels many consider acceptable may leave a subtle mark on the heart. A study published today in Radiology reports that long-term exposure to fine particulate matter (PM2.5) is associated with early signs of scarring in the heart muscle, a change that can precede heart failure.

Researchers used cardiac MRI to quantify diffuse myocardial fibrosis and examined its association with PM2.5—tiny particles 2.5 micrometers or smaller that can enter the bloodstream through the lungs. Sources of PM2.5 include vehicle exhaust, industrial emissions and wildfire smoke.

“We know that if you’re exposed to air pollution, you’re at higher risk of cardiac disease, including higher risk of having a heart attack,” said senior author Kate Hanneman, M.D., M.P.H., of the University of Toronto and University Health Network.

“We wanted to understand what drives this increased risk at the tissue level.” The team studied 201 healthy controls and 493 patients with dilated cardiomyopathy, a condition that weakens the heart’s ability to pump blood.

Higher long-term exposure to fine particulate pollution was linked with higher levels of myocardial fibrosis in both groups, suggesting that fibrosis may be one mechanism by which air pollution contributes to cardiovascular complications. The largest effects were observed in women, smokers and patients with hypertension.

The findings add to evidence that air pollution acts as a cardiovascular risk factor beyond conventional predictors such as smoking or high blood pressure. “Even modest increases in air pollution levels appear to have measurable effects on the heart,” Dr. Hanneman said.

“Our study suggests that air quality may play a significant role in changes to heart structure, potentially setting the stage for future cardiovascular disease.” The researchers noted that participants’ pollution exposure levels were below many global air-quality guidelines.

They said this reinforces the concern that there may be no safe threshold for long-term exposure. Incorporating a patient’s exposure history—such as outdoor work in areas with poor air quality—could help refine individual risk assessments and address health inequities tied to where people and work.

Dr. Hanneman said public health measures are needed to further reduce long-term exposure.

While air quality has improved in recent years in Canada and the United States, she added, “we still have a long way to go.” The study also underscores the role of imaging in environmental health research: “Medical imaging can be used as a tool to understand environmental effects on a patient’s health,” she said, noting radiology’s potential to identify and quantify pollution-related changes across organ systems.