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Air pollution may increase mortality risk after heart transplant

Heart transplant recipients living in high pollution areas are more likely to die from infections

Ingrid Torjesen

Tuesday, 10 December 2019

Heart transplant recipients who live in areas where PM2.5 air pollution levels reached above national limits for clean air had a 26% higher risk of mortality due to infection, according to a study* published in the Journal of the American College of Cardiology.

The study used data from the United Network for Organ Sharing/Organ Procurement and Transplantation Network (UNOS/OPTN) on all patients over age 18 who underwent heart transplantation between 2004 and 2015 – a total 21,800 patients. Their average age was 52, 75% were male, 69% white and 39% had heart failure due to prior ischemic heart disease. Air pollution exposure was determined according to the patients' residential ZIP codes.

The study authors compared the PM2.5 levels in the air of each patient's ZIP code against the U.S. National Ambient Air Quality Standards (NAAQS) applied to outdoor air throughout the country. Approximately 21.9% of heart transplant recipients were living in areas where PM2.5 levels exceeded NAAQS limits for clean air. ZIP codes that had higher air pollution had larger populations, higher percentages of minorities, a larger number of households and higher unemployment rates.

After a median follow-up of 4.8 years, 5,208 patients (23.9%) had died. Heart transplant recipients who had long-term exposure to air pollution over several years had a 26% heightened risk for mortality due to infection for every 10 μg/m3 increase in PM2.5 levels. The association between air pollution and mortality was consistent across all examined subgroups.

"Given the fact that organ transplantation adds a tremendous cost to society, we had an interest in understanding if previously unknown environmental detriments adversely affected the outcomes of these patients," said Sanjay Rajagopalan, professor of medicine at Case Western Reserve University School of Medicine and the study's senior author. "Long-term exposure to air pollution appears to pose amplified risks for heart transplant recipients. We found an association between PM2.5 and mortality in these transplant patients."

Heart transplant recipients are vulnerable to infections due to immunosuppression caused by organ transplantation. The study authors found that air pollution exposure resulted in inflammatory responses and increases in blood pressure and insulin resistance, as well as a weakened immune system.

*Al-Kindi SG, Sarode A, Melissa Zullo M, et al. Ambient Air Pollution and Mortality After Cardiac Transplantation. Journal of the American College of Cardiology. 9 December 2019. DOI: 10.1016/j.jacc.2019.09.066

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