Pandemic Lockdowns, Cleaner Air Tied to Reduced MIs

Marlene Busko

November 29, 2021

When skies were blue and air pollution was reduced during stay-at-home lockdowns in the United States at the beginning of the COVID-19 pandemic, fewer ST-elevation myocardial infarctions (STEMI) occurred, a new study suggests.

The researchers examined the link between air pollution and STEMI in 29 US states from January 1, 2019 to April 30, 2020, which included the lockdown period, roughly March 11 to March 30. During that time, there were virtually no vehicles on the roads or planes in the skies, and thus exhaust emissions and air pollution decreased. 

On days when air pollution was lower, as measured by levels of inhalable fine particulate matter up to 2.5 micrometers wide (PM2.5 ), the number of STEMIs was also lower.  

Each 10 µg/m3 reduction in PM2.5 levels was associated with 6% fewer STEMIs or 3.7 fewer STEMIs per 100 person-years, after adjusting for US census division, day of week, month, and year.

These findings by Sidney Aung, a fourth-year medical student at the University of California San Francisco, and colleagues were presented at the American Heart Association (AHA) 2021 Scientific Sessions. 

"While more pollution is known to increase STEMI risk, this demonstration of the reciprocal relationship provides the most direct evidence that efforts to reduce ambient pollution can prevent the most severe forms of myocardial infarctions," they conclude.

Natural Experiment  

The pandemic-related shutdown was a "a unique opportunity" to investigate how a short period of cleaner air might be associated with fewer severe heart attacks, senior author Gregory M. Marcus, MD, professor and associate chief of cardiology for research, University of California San Francisco, told theheart.org | Medscape Cardiology in an email.

"And, indeed, as pollution fell, we found a concomitant reduction in the most serious forms of heart attack," he said.

However, the researchers acknowledge that this was an observational study, so it cannot show cause and effect, and other unknown factors might explain the decrease in MI.

Nevertheless, "these data suggest that a reduction in particulate matter with the shutdown may be at least partly responsible for the drop in heart attacks," said Marcus.

These findings can inform people "about the possible immediate health impacts of pollution so that they can push for cleaner air initiatives," Aung told theheart.org | Medscape Cardiology.

"We also hope this [work] inspires other investigators to corroborate these findings and conduct further research," he said.

"The links between air pollution levels and, in particular, particulate matter <2.5 microns and cardiovascular disease has been studied for over two decades," Sanjay Rajagopalan, MD, who co-authored an editorial about a study in China that linked air pollution with risk of fatal MIs, commented to theheart.org | Medscape Cardiology.

"Quasi-experimental studies," he noted, "have also firmly demonstrated that reductions in air pollution levels due to serendipitous natural experiments such as reduction in traffic or closure of coal-fired power plants and corresponding reductions in air pollution translate into reductions in overall mortality and cardiovascular events."

"However, this data is perhaps one of the few in the United States suggesting a reduction in MI as a consequence of COVID-19-related reduction in air pollution levels," added Rajagopalan, director of the Cardiovascular Research Institute at Case Western Reserve University, Cleveland, Ohio, and a professor in CWRU's School of Medicine.  

The data "provide another layer of evidence that reductions in air pollution levels are immediately meaningful, and societal measures to reduce air pollution levels can have a huge impact," he noted.

The findings "clearly suggest that urgent action is needed to switch from fossil fuel energy sources to clean energy sources," to benefit people's health as well as the planet, Rajagopalan summarized.

AHA spokesperson Joel D. Kaufman, MD, MPH, professor in the departments of Environmental and Occupational Health Sciences, Medicine, and Epidemiology, at the University of Washington, Seattle, echoed these comments in an AHA video. Kaufman is chair of the writing group for AHA's 2020 policy statement "Guidance to Reduce the Cardiovascular Burden of Ambient Air Pollutants."

"If these results hold up," Kaufman said, "it reinforces the benefits of air pollution reduction as a cost-effective way to improve health."

"It also means that reducing fossil fuel combustion, which we need to do anyway to combat climate change, might mean tremendous health benefits now, even if the climate benefits take a few years to accrue."

NEMSIS, EPA Data  

The researchers determined the number of STEMIs and the level of PM2.5 in the period between January 1, 2019 and April 30, 2020, for 29 US states that had data available.

They obtained STEMI numbers from the National Emergency Medical Services Information System (NEMSIS) database, population data from the US census, and PM2.5 levels from the Environmental Protection Agency (EPA) website.

States that imposed lockdowns implemented them around March 13, 2020, soon after the director of the World Health Organization labeled COVID-19 a pandemic on March 11, and then lifted the lockdowns a few weeks later around March 30.

There were 60,722 STEMIs in the 29 states during the 16 months of the study.

For each 10 µg/m3 reduction in PM2.5, there were 6% fewer STEMIs, (rate ratio 0.94, 95% CI, 0.90 - 0.99, P = .016) and 373.8 fewer STEMIs per 10,000 person-years (95% CI, 69.4 - 678.1), after variable adjustments.

Aung and Rajagopalan have disclosed no relevant financial relationships. Marcus has received research grants from Medtronic, Jawbone Health, Eight Medical, and Baylis and owning shares from InCarda Therapeutics; and has received honoraria from InCarda Therapeutics, iRhythm Technologies, and Johnson & Johnson. Kaufman has received research grants from the National Institutes of Health and the EPA.

American Heart Association (AHA) 2021 Scientific Sessions: Abstract P2315. Presented November 13, 2021.

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