Air Pollution Decreases Risk Of Surviving Heart Transplant: Study

Individuals who live in areas where they are exposed to higher levels of air pollution may have a lower risk of surviving during the years after receiving heart transplant, according to the findings of new research.

In a study published this month in the Journal of the American College of Cardiology, researchers indicate that heart transplant patients had a 26% increased risk of death during the five years after the procedure if they lived in areas with high levels of particulate matter 2.5 (PM 2.5).

It is known that heart transplant patients face an increased risk of death after surgery, but researchers wanted to know if air pollution exposure factored into that risk.

To evaluate the impact, researchers used data from the United Network for Organ Sharing database, focusing on patients who underwent heart transplantation from 2004 to 2015. They linked the data with validated estimates of fine particulate matter concentrations for each calendar year during which a UNOS cardiac transplant recipient was at risk of death, establishing air pollution exposure using zip codes to determine patient residence.

Nearly 22,000 patients were included in the study. On average, patients were 52 at time of implantation and 39% had ischemic etiology of heart failure.

The data indicated patients had an average annual exposure to PM 2.5 of 10.6 μg/m3.

PM 2.5 is a mix of fine particles of soot, dust, chemicals, and biofuel emissions that are smaller than 2.5 micrometers or 30 times smaller than one human hair. Because of its size it is easily inhaled into the lungs and can enter the blood stream, leading to disease, including cardiovascular disease, lung disease, and emphysema.

At follow-up five years later, 5,200 patients, or roughly 24%, had died.

For each 10 μg/m3 increase annually of PM 2.5, patients had a 43% increased risk of death. Even after adjusting for other factors they had a 26% increased risk of dying for each 10 μg/m3 increase in annual exposure.

Patients living in zip codes with more pollution were linked to higher rates of death from all causes five years after transplant.

Researchers said the risk appeared to be driven by the association with infection-related deaths and to deaths from graft failures and malignancy.

The study also indicated the need for future studies focusing on the influence of key environmental factors after heart transplant. The exact mechanism of pollution related mortality is not known, but study authors suggested it may be linked to systemic immune activation or linked to solid organ rejection.

“Insensitivity of effects to time after transplantation suggests that air pollution contributes to multiple time-variant causes of mortality in transplant patients, and points to pervasive systemic effects that await unambiguous identification,” the authors wrote.

There were drawbacks to the study. It was a retrospective study, so it relied on zip codes to average air pollution exposure form where people spent the majority of their time and did not actually measure the levels of air pollution to which people were actually exposed. Additionally, researchers said which aspect of PM 2.5 contributes to the increased risk of death needs to be explored, since PM 2.5 is made of many components, including fossil fuels, biofuels, mixes of soot, organics, nitrates, sulfates, and chemicals.

Air pollution kills 7 million people each year, according to World Health organization research. Even short term exposure at levels below safety standards can lead to health risks, some studies have found.

“This study provides evidence linking air pollution with mortality after heart transplantation,” researchers wrote. “These results suggest an important influence of a key environmental factor in outcomes following heart transplantation, and supports the need for further studies in this population.”