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GUEST POST: Pitt Study Linking Fine Particle Pollution to Increased Stroke Risk for AFib Patients “A Call to Action” For All of Us

By Dr. David Eibling, member of GASP’s board of directors

Editor’s Note: GASP is fortunate to have a dedicated board of directors composed of professionals in myriad fields – law, education, science, and medicine. Among them is Dr. David Eilbling, a Pittsburgh ears, throat, and nose doctor. Dr. Eibling recently weighed in on a new University of Pittsburgh study that found a link between exposure to fine particulate matter and strokes in people with atrial fibrillation. We thank him for this guest post.

It has long been known that increased exposure to small particulate air pollution contributes to an increased risk of cardiovascular disease and stroke. Studies have indicated one mechanism is related to an elevated risk of developing clots (thrombosis) as well as reductions in the normal process of dissolving clots (thrombolysis)

The fine particles found in air pollution (known as PM2.5) are about one-50th of the diameter of a human hair, and seem to be particularly active in these effects. This is probably because they pass so readily through the lung lining membranes into the blood, where they impact blood clotting and other normal processes. 

Most of the research correlating the risk of heart attack or stroke with air pollution has been done utilizing average measures of PM2.5 at city-wide or county-wide level. But past studies have shown that these measures may not tell the whole story in Pittsburgh, where there are dramatic differences in levels of PM2.5, even within single zip codes.

Atrial fibrillation (often referred to as AFib or AB) is a condition in which the smaller fore-chambers of the heart known as the atria do not beat at the same rate, instead “quivering” (fibrillating), leading to irregular contraction of the ventricles and a resultant “irregularly irregular” heart rhythm that can easily be detected by feeling one’s pulse. 

Now, newer fitness tracking monitors are able to detect this irregular rhythm, and even warn the wearer. Atrial fibrillation may arise spontaneously or as a response to some cardiac stressors. It is a very common condition that may cause no immediate problems as long as the ventricles continue to efficiently pump blood through the lungs and out to the rest of the body.

One of the well-known complications of AFib is that blood can clot in the “quivering” corners of the atrium because they do not empty with each beat. Pieces of that clot can then break off and, if it is from the left side of the body, travel through the ventricle into the aorta and go wherever the blood takes it. 

Occasionally the clots go to the vessels in the brain, where they block the blood and cause an “ischemic” stroke – which means the portion of the brain supplied by that blood vessel dies because of lack of blood supply. It is for this reason that people with chronic AFib are typically treated with so-called blood thinners (otherwise known as anticoagulants) long term.

The researchers at the University of Pittsburgh who authored this most recent study used data from more than 30,000 people with AFib and compiled it into a database for seven years. When researchers checked their records to see who had suffered a stroke, they discovered that about 5 percent – or 1,500 people – had suffered one between 18 months and six years following their initial diagnosis. 

The key finding of this study, though, is not the fact that 5 percent of the large group of people with AFib suffered a stroke: It’s that researchers used not county-wide, city-wide, or even zip code location data, but much more precise information about the levels of PM2.5 air pollution at, or very near, to their homes. 

This data has only become available recently, and the more precise measurement of location-specific PM2.5 levels has improved our ability to correlate the levels of small particulate air pollution with a specific health risk, in this case, stroke.

The maps in the report are fascinating, and will not be surprising to anyone living in Pittsburgh, as the levels of PM2.5 are much higher along our rivers and valleys than on the hilltops.  Moreover, levels are inversely proportional to average income, meaning the more economically disadvantaged in our community are also breathing higher levels of polluted air.

As you might have already guessed, the risk of suffering a stroke if you have AFib is much higher if you live in an area with higher levels of PM2.5 air pollution. Similar to other medical conditions, this new data permits the calculation of a “dose-response curve.” This means you can begin to calculate the risk of stroke not only based on other factors (such as other cardiac disease or smoking) but also by where you live.

This is a powerful insight, one that ought to serve as an impetus for us to collectively seek strategies to reduce this risk, especially for those most at risk. For more than 70 years Pittsburgh has realized that air pollution is harmful, and despite decades of effort, we are still among the top-10 most polluted areas in the nation. 

Organizations such as Group Against Smog and Pollution (GASP) have worked for years (in GASP’s case 51 years) to encourage our local municipal and county leaders to enact reforms that will reduce air pollution. 

This research from Pitt adds more credence to this effort, providing an accurate estimate of stroke risk for specific groups of individuals, and suggests that the benefits to be achieved by reducing (the dose) of air pollution are potentially measurable.

It is a call to action for all of us.

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