Air pollution in US could substantially increase risk of death from infections in heart transplant recipients
Recipients of heart transplants who live in areas where air pollution levels are very high have a 26% greater risk of death due to infection.
The researchers measured particulate matter (PM2.5) air pollution levels in areas where the heart transplant recipients lived and analyzed whether they reached above the national limits for clean air in the US. Air pollution could increase death risk after a heart transplant, found the research team from Case Western Reserve University School of Medicine and other institutes.
More than 2,000 heart transplantations are performed in the US annually. Despite medical advancements, deaths post-transplantation remains high, reaching 50% by 11 years post-surgery, says the study published in the Journal of the American College of Cardiology.
"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," says the study's senior author Dr. Sanjay Rajagopalan, professor of medicine at Case Western Reserve University School of Medicine.
The immune system may see the donor heart as a foreign object and try to reject it, which can damage the heart. Accordingly, every heart transplant recipient receives medications to prevent rejection -- called immunosuppressants.
According to experts, heart transplant recipients are vulnerable to infections due to immunosuppression caused by organ transplantation. Researchers found that air pollution exposure resulted in inflammatory responses and increases in blood pressure and insulin resistance, as well as a weakened immune system.
"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," says Dr. Rajagopalan.
Air pollution has been linked to a higher risk of cardiovascular deaths for patients with heart disease or a history of heart failure. Heart transplant recipients, says the team, represent a particularly vulnerable population to air pollution exposure.
For their analysis, the researchers examined data from a total of 21,800 patients from the United Network for Organ Sharing/Organ Procurement and Transplantation Network (UNOS/OPTN). All adults over the age of 18, who underwent heart transplantation between 2004 and 2015, were included. The patients were an average age of 52 -- 75% were male, 69% white, and 39% had heart failure due to prior ischemic heart disease.
The team analyzed the patients' residential ZIP codes to determine air pollution exposure levels based on location.
The researchers compared the PM2.5 levels in the air (commonly produced from power plants, motor vehicles, or airplanes) of each patient's ZIP code against the US National Ambient Air Quality Standards (NAAQS) applied to outdoor air throughout the country.
The US Environmental Protection Agency (EPA) has set NAAQS for six principal pollutants, which are called "criteria" air pollutants. This includes particle pollution (PM), ozone, nitrogen dioxide, lead, carbon monoxide, and sulfur dioxide. The standards are reviewed periodically and may be revised.
According to the analysis, approximately 21.9% of heart transplant recipients were living in areas where PM2.5 levels exceeded NAAQS limits for clean air. The team says ZIP codes that had higher air pollution had larger populations, higher percentages of minorities, a larger number of households, and higher unemployment rates.
"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 (microgram per cubic meter) increase in PM2.5 levels. After a follow-up of 4.8 years, 23.9% of patients died. The association between air pollution and mortality was consistent across all examined subgroups," says the study.
In an accompanying editorial comment, Dr. C. Arden Pope III, professor of economics at Brigham Young University, says that the study makes an important contribution to our understanding of the health effects of air pollution.
He writes, "It used a straightforward approach to evaluate the health effects of air pollution in a unique cohort of individuals in a vulnerable health state. It provides intriguing evidence that exposure to air pollution substantially contributes to mortality risk in cardiac transplant patients."