All the Risk You Cannot See

Corresponding author

effects on cardiovascular health. 1 By and large, exposure to this risk factor has steadily declined in North America from an estimated populationweighted annual average of 22 AE 6.4 mg/m 3 in 1981 to 7.9 AE 2.1 mg/m 3 in 2016 due in no small part to 1970 amendments to the Clean Air Act. 2 However, ambient air pollution in the United States has stabilized or in some locales increased likely as a direct result of wildfires since 2016. 3In the summer of 2023, wildfires across Canada and United States enshrouded much of the population in North America in a miasma of smoke and air pollutants, highlighting a reverse in the trend of improving air quality.Due to climate change, conditions needed to cultivate wildfire are anticipated to become more common seasonally and widespread geospatially. 4Thus, we can expect PM 2.5 will have increasing relevance as a cardiovascular risk factor worldwide in the coming years.
As the authors Deo et al 5 point out, PM 2.5 is a wellestablished risk factor for cardiovascular disease as a whole and atherosclerosis in particular. 6The mecha- surgery. 11Whether or not improved adherence to smoking cessation recommendations (20%-25% of the study population reported to be smokers) or more aggressive lipid control (low-density lipoprotein levels of 90 to 95 mg dL across included patients) reduces the impact of PM 2.5 exposure remains unknown and requires further investigation since control of conventional risk factors may diminish the impact of ambient air pollution exposure.
The authors hypothesize that limiting PM 2.5 exposure to a maximum mean of 8 mg/m 3 would result in a 1.7% absolute risk reduction in cardiovascular events and further lowering this level to 5 mg/m 3 eliminates the lion's share of PM 2.5 attributable cardiovascular events.This analysis provides an aspirational policy target with the potential for widespread benefits to the population as a whole.For additional perspective, lowering low-density lipoprotein levels to a mean of roughly 30 mg/dL with evolocumab in high-risk patients enrolled in the Fourier trial resulted in a 1.5% absolute risk reduction in the composite endpoint. 12Of course, the standard limitations to any non randomized control trial apply here and real-world data for a fair comparison is not yet available but the results of this study are provocative and suggest clinicians should take this risk factor seriously and think beyond standard risk factors in high-risk patients.
Though randomized trial data quantifying the magnitude of risk reduction for interventions aimed at this omnipresent risk factor are lacking, some impactful strategies may be relatively straightforward to deploy.Indeed, a randomized crossover trial showed a high efficiency face mask reduced angina and ST-segment depressions in participants with pre-existing coronary artery disease asked to walk through Beijing on a particularly polluted day (PM 2.5 70 mg/m 3 ). 13Even in healthy adults, the use of a respirator and home air filter resulted in small reductions in systolic blood pressure and improved in-

FUNDING SUPPORT AND AUTHOR DISCLOSURES
The author has reported that they have no relationships relevant to the contents of this paper to disclose.

flammatory biomarkers. 1
Though formal recommendations might be premature with outcomes data still lacking, clinicians would not be remiss in suggesting exposure mitigation strategies such as masking or home air filtration for particularly high-risk patients on polluted days.Cardiovascular risk factor modification must be inclusive of not just pathophysiologic factors like insulin resistance or hyperlipidemia but should also be contextualized in socioeconomic status and environmental exposures.To address the risk that we cannot see, individual risk assessment for cardiovascular disease must be expanded beyond Framingham to include societal, economic, and environmental factors that shape outcomes.Future investigations should trial strategies for high-risk patients, like pollution exposure mitigation, to protect patients from this enduring and pervasive risk factor.