A 73-year-old male patient has a history of an acute myocardial infarction (MI) 18 months ago that was treated with a drug-eluting stent deployed in the proximal left circumflex coronary artery. He presents to your clinic for a 6-month evaluation. His most recent echocardiogram shows a left ventricular ejection fraction of 45%. He is currently treated with the following cardiovascular secondary prevention medications:
Angiotensin-converting enzyme inhibitor
Beta-blocker
High-intensity statin
Aspirin
He is obese and takes metformin for type II diabetes mellitus, which is well-controlled. He has never smoked and has no history of lung disease. He is on no other medications. He has a strong family history of coronary artery disease (CAD), including a sister who died after her second heart attack at the age of 69. He completed a structured cardiac rehabilitation program and feels well. He walks daily 2-3 miles around the neighborhood with his wife and dog, maintaining a pace such that he can easily carry on a conversation with his wife. He is highly motivated to prevent any further heart problems from occurring and so has instituted a strict vegetarian diet, through which he has lost 30 pounds over the past 18 months. He thinks his stamina is better than ever. He does not use a wood-burning stove for heating or cooking. He has recently been hearing news stories about how air pollution may be bad for the heart and may be especially severe during the winter months. He wonders whether, during days with high levels of air pollution, he should alter his exercise routine to further prevent future cardiovascular events.
Which of the following would you recommend to this patient regarding air pollution and cardiovascular risk?
Show Answer
The correct answer is: C. He is at higher risk for future cardiac events during times of poor air quality. He should follow air quality reports and try to exercise indoors during periods of abrupt rise in fine particulate matter or during times when levels exceed 35.4 mcg/m³.
This patient with a history of CAD and multiple cardiovascular risk factors presents to his cardiologist to discuss how exposure to air pollution may affect his chances of developing future cardiac problems. You may inform the patient that exposure to air pollution, specifically that which contains very small size particles (PM2.5), can increase someone's short-term and long-term risk for cardiovascular events. One of the first clinical studies to identify a significant correlation between long-term exposure to PM2.5 and cardiovascular outcomes was the women's health initiative that demonstrated that an incremental increase of 10 mcg/m3 of PM2.5 was associated with a 24% increase in the incidence of a variety of adverse cardiovascular events, including cardiovascular death, MI, stroke, and coronary revascularization.1 Other studies have also demonstrated that even acute (1-3 days) exposure to elevations in PM2.5 is associated with an increase in the risk of heart failure exacerbations2 and ischemic heart disease events3 in the time period immediately following this increase. In fact, data from a recent meta-analysis have suggested that an incremental increase in any one of several air pollutants (carbon monoxide, nitrogen dioxide, and sulfur dioxide PM2.5 and PM10) is associated with an increase in the relative risk of MI.4 Although the overall relative risk was low given the large number of persons exposed, this adds up to quite a large number of vulnerable subjects. Based on the evidence of the effects of both long- and short-term exposure to air pollution, it is reasonable to advise a patient with known CAD to try to avoid exercising outside during periods of abrupt rise in PM2.5 or during times when levels exceed 35.4 mcg/m3.5 Physicians should refrain from making recommendations against exercise but instead should educate patients who are at higher risk about monitoring the air quality index report and using this information to help dictate how and when to avoid exposure to air pollution.
References
Miller KA, Siscovick DS, Sheppard L, et al. Long-term exposure to air pollution and incidence of cardiovascular events in women. N Engl J Med 2007;356:447-58.
Pope CA 3rd, Renlund DG, Kfoury AG, May HT, Horne BD. Relation of heart failure hospitalization to exposure to fine particulate air pollution. Am J Cardiol 2008;102:1230-4.
Pope CA, Muhlestein JB, Anderson JL, et al. Short-Term Exposure to Fine Particulate Matter Air Pollution Is Preferentially Associated With the Risk of ST-Segment Elevation Acute Coronary Events. J Am Heart Assoc 2015;4:e002506.
Mustafic H, Jabre P, Caussin C. et al. Main air pollutants and myocardial infarction: a systematic review and meta-analysis. JAMA 2012;307:713-21.
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