Exposure to Small Particulate Air Pollution Tied to Obstructive CAD

BOSTON, MA—When exposed to high levels of small particulate air pollution, individuals with stable chest pain and a low-to-intermediate cardiovascular risk are more likely to have obstructive coronary disease on coronary CT angiography (CTA), an analysis of PROMISE trial participants shows.

People who lived in an area with a high versus low average exposure to small particulate matter were more likely to have CT-detected obstructive CAD (15.6% vs 12.5%; P = 0.007), according to Marcel Langenbach, MD (Massachusetts General Hospital, Boston, and University Hospital Cologne, Germany).

A greater risk of obstructive disease remained even after accounting for traditional CV risk factors and socioeconomic determinants of health, he reported here at the 2023 Society of Cardiovascular Computed Tomography (SCCT) meeting.

“Air pollution should be considered as an additional CV risk factor” that can be taken into account, for example, when seeing a patient with stable chest pain who lives in an area with high pollution levels, Langenbach told TCTMD.

Moreover, he concluded during his presentation, this information “could help to build prevention strategies in patients with stable chest pain.”

Speaking with TCTMD, Marcus Chen, MD (National Heart, Lung, and Blood Institute, Bethesda, MD), one of the moderators of the session at which Langenbach presented the results, highlighted some strengths and weaknesses of the study, saying, “It’s great to look at what environmental factors may play a role in coronary artery disease.”

But there are some limitations, he said, pointing to the fact that the coronary CTs in PROMISE were performed back in 2010 and the use of zip codes to derive much of the information used in the study, including socioeconomic variables and exposure to pollution. When assessing CAD, the disease process likely started many years earlier, and an individual could have been living somewhere else at that time, for instance.

“I think environmental factors might play a role” in coronary disease, Chen commented, and unlike things like diet, exercise, or control of blood pressure or diabetes, “environment is something that we unfortunately can’t really control.”

Still, he said, it’s probably premature to recommend including exposure to air pollution as a factor to consider when assessing an individual patient’s risk.

Air Pollution and CAD in PROMISE

Prior research has linked increased exposure to air pollution to greater risks of major adverse cardiovascular events and mortality in the broader population, presumably due to local and systemic inflammatory reactions—which are known to contribute to the development of CAD—sparked when the small particles enter the alveoli and bloodstream.

The PROMISE data set provided an opportunity to assess associations between air pollution and CT-derived metrics of coronary disease, specifically in patients with stable chest pain and a low-to-intermediate CV risk, Langenbach noted.

For the study, the investigators focused on patients in the CT arm of the trial, which showed that use of coronary CTA as a first-line test didn’t improve clinical outcomes compared with functional testing. The analysis included 3,854 participants (mean age 61 years; 48% men) living in 2,020 unique US zip codes; their median atherosclerotic CVD risk was 14.2%.

Zip codes were used to obtain information on socioeconomic determinants of health derived from Agency for Healthcare Research and Quality and US census data, and to identify the nearest US Environmental Protection Agency air pollution monitor. The exposure of interest was annual level of small particulate matter < 2.5 µm (PM_2.5).

Median annual PM_2.5 exposure among the participants was 9.9 µg/m³, with 43.2% living in an area considered to have high exposure (10 µg/m³ or more).

After adjustment for traditional CV risk factors and socioeconomic determinants of health, high pollution exposure was associated with a greater risk of obstructive CAD (adjusted OR 1.35; 95% CI 1.11-1.65), defined as a stenosis > 50%. That relationship was also seen when exposure was considered on a continuous basis—each 1-µg/m³ increase in exposure was associated with a 6% relative increase in the odds of obstructive disease (OR 1.06; 95% CI 1.01-1.11).

PM_2.5 exposure was not, however, associated with the presence or extent of coronary artery calcification (CAC) or the presence of high-risk plaque features. That was a bit of a surprise, Langenbach said, speculating that exposure to small particulate matter might have a greater impact on noncalcified coronary lesions. This might have implications for using imaging to study the issue. “The knowledge that there is no association of air pollution with coronary artery calcium should remind us that [using] only an unenhanced scan of the heart is not enough to uncover potential unhealthy effects of air pollution,” Langenbach said.

Future studies, he said, will assess associations between various socioeconomic determinants of health and PM_2.5 exposure, will assess the potential impacts of air pollution on mortality, and will explore the impact of other types of pollutants on CV health.