Bad Breaths: Atherosclerosis, Adverse Cardiac Outcomes Linked to Air Pollution

Cardiologists have an arsenal of known risk factors they can address when trying to prevent and treat heart disease. Now, new research is suggesting that the air we breathe might also affect cardiac outcomes, especially in patients with previous events.

Ambient air pollution has been previously linked with increased risk of stroke, lung cancer, and blood inflammation and oxidative stress, but no prior study has associated its effects on cardiac outcomes with the addition of angiographic data.

To fill this gap, Hooman Allayee, PhD (University of Southern California, Los Angeles), and colleagues looked at 3 years of longitudinal data from 6,575 Ohio residents who underwent elective diagnostic coronary angiography at the Cleveland Clinic between 2001 and 2007.

By pairing their outcomes with US Environmental Protection Agency data on ambient air pollution throughout the state, the researchers found increased risks of mild (adjusted OR 1.43; 95% CI 1.11-1.83) and severe coronary atherosclerosis (adjusted OR 1.63; 95% CI 1.26-2.11) in CAD patients who had been exposed to increased levels of fine particulate matter (< 2.5 µm) in the preceding 36 months. This effect was more pronounced in patients who had severe versus mild CAD (P for trend = 0.03).

Exposure to higher particulate matter levels also increased a patient’s likelihood of incident MI (HR 1.33; 95% CI 1.02-1.73), but not stroke or all-cause mortality. The relationship between pollution and MI did not change after adjustment for Framingham Adult Treatment Panel III risk score or statin therapy.

Cardiac outcomes were also analyzed based on levels of NO₂, but no associations were found between increased exposure to this pollutant. This was likely due to insufficient data, Allayee told TCTMD, explaining that there were only four devices measuring NO₂ in Ohio during the study period compared with “a lot more” for particulate matter.

The study was published online July 28, 2016, ahead of print in the Journal of the American Heart Association.

Mechanisms Still Unknown

“We’ve known for a long time that [air pollution] affected cardiac disease,” said outside expert Vladimir Hachinski, MD (University Hospital, London, Canada). However, this study confirms “it isn’t simply that you have more heart attack,” he noted, “but that people who have heart disease have more severe ones and have worse outcomes.”

Moreover, Hachinski explained, these findings are “part of an unfolding story that this is much more dangerous than we realized, [and part of] . . . the whole question of fuel use and global warming and so on.”

Also commenting on the study, Hossein Bahrami, MD, PhD, MPH (University of Southern California), said if further research can pinpoint the “exact mechanisms and pathways through which air pollution can increase the risk of myocardial infarction,” then cardiologists will potentially have a new risk factor to use in optimizing patient care. He suggested the possibilities of systemic inflammation and endothelial dysfunction, pointing out that these are uncertain explanations and can’t necessarily be addressed via the current paper.

The practical implications of this evidence are slim for now, Allayee acknowledged. But looking forward he imagined that cardiologists might, before opening their prescription pad, be able to make suggestions not only about diet and exercise but also aimed at reducing exposure to air pollutants. For example, he said, it might be worthwhile to suggest to certain patients: “Minimize your outdoor activity on polluted days, or maybe get an air filter for the house.”

Allayee was careful to highlight, though, that “nobody has gone and shown that if you reduce somebody’s air pollution that it reduces their risk of heart attack. But it’s something that I think clinicians should be aware of and sort of take into consideration as just another piece of data in evaluating a patient.”

While Bahrami agreed, he noted that air pollution exposure is often a “proxy” for socioeconomic status. “You can’t ask people to change their home or go somewhere less polluted, . . . but we can discuss if they can take time off and go to the country, and in general if they could avoid going outside at the time of maximum air pollution,” Bahrami suggested.

Ultimately, clinicians should recognize that air pollution is “much more dangerous than they realized before,” and educating their patients is the “most important single thing” they can do to mitigate that risk, Hachinski said.

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