Air pollution, generated from sources such as burning fossil fuels and wildfire smoke, is a leading environmental health threat worldwide. In a new study from UHN, researchers found that long-term exposure to air pollution is associated with myocardial fibrosis—scarring of heart muscle that can lead to poor outcomes for cardiovascular disease.
The majority of the global population lives in areas with air pollution levels exceeding World Health Organization air quality limits. Fine particulate matter with a 2.5-μm or smaller diameter (PM2.5) is the most thoroughly studied component of air pollution. These tiny airborne particles can be inhaled deep into the lungs and are associated with an increased risk of cardiovascular diseases such as heart attack and stroke. However, exactly how PM2.5 affects the heart’s structure and function remains unclear.
A team led by Dr. Kate Hanneman used cardiac MRI to non-invasively measure fibrosis in the heart muscle and determine its relationship to long-term exposure to PM2.5. They analyzed cardiac MRI scans from 694 patients, including 493 with dilated cardiomyopathy—a condition where the heart becomes enlarged and weakened—and 201 with healthy hearts.
The team measured diffuse myocardial fibrosis—when scar tissue abnormally accumulates throughout the heart muscle—using a specialized MRI technique called T1 mapping. They also calculated each person’s average daily PM2.5 exposure in the year preceding MRI imaging, based on air quality measurements near their homes.
Results showed a clear trend: for every small increase in PM2.5 levels, both patients with heart disease and healthy individuals had more heart muscle scarring. The effect was strongest in women, smokers, and people with high blood pressure.
These findings suggest that long-term air pollution exposure could damage heart tissue, potentially increasing the risk of future heart problems. With wildfires becoming more frequent, these results highlight the need for public health measures to reduce air pollution and for individuals to limit exposure whenever possible.
Dr. Jacques Du Plessis, who was a clinical cardiovascular imaging fellow at the University of Toronto, is the first author of the study.
Dr. Kate Hanneman, Clinician Scientist at UHN and Associate Professor in the Department of Medical Imaging at the University of Toronto, is the corresponding author of the study.
This work was supported by UHN Foundation.
Dr. Kate Hanneman has received payment or honoraria for lectures, presentations, speakers’ bureaus, manuscript writing or educational events from Sanofi, and is an associate editor for Radiology and Radiology: Cardiothoracic Imaging. For a full list of competing interests, see the manuscript.
Du Plessis J, DesRoche C, Delaney S, Nethery RC, Hong R, Thavendiranathan P, Ross H, Castillo F, Hanneman K. Association between Long-term Exposure to Ambient Air Pollution and Myocardial Fibrosis Assessed with Cardiac MRI. Radiology. 2025 Jul;316(1):e250331. doi: 10.1148/radiol.250331.