Heart Attacks Follow Dirty Air Like Clockwork

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Cardiovascular harms from air pollution may occur almost immediately, before dwindling over the hours after exposure, according to a Chinese study.

Based on data from over a million people, time of acute coronary syndrome (ACS) symptom onset tended to track closely with local short-term elevations in fine particulate matter (PM2.5), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO), according to Haidong Kan, PhD, of Fudan University in Shanghai, and colleagues.

The strongest association between ACS and ambient pollution was within the hour of transient pollutant exposure. Thereafter, it dropped to nonsignificance by 15 to 29 hours, they noted in Circulation.

Additionally, the risk of ACS generally rose with increasing concentrations of air pollutants — the strongest link being for NO2, which is primarily released into the air from the burning of fuel.

In contrast, transient exposure to coarse particulate matter (PM2.5-10) — matter around the size of traffic dust and pollen — and ozone (O3) did not appear to trigger ACS.

“As the largest developing country, China faces one of the most severe air pollution problems and the largest disease burden of ACS in the world,” Kan’s group pointed out.

“Notably, the national average concentrations of hourly PM2.5 (44.3 μg/m3), PM2.5-10 (35.1 μg/m3), and NO2 (33.7 μg/m3) before the index hour are well beyond the recently updated World Health Organization (WHO) Global Air Quality Guidelines 2021 (annual average, PM2.5: 5 μg/m3; PM10 minus PM2.5: 10 μg/m3; NO2: 10 μg/m3),” they wrote.

As such, they suggested tighter limits on air quality guidelines.

A recent study found that the U.S. has seen PM2.5 pollution drop by 40% from 2000 to 2016, an improvement that occurred disproportionately in white communities.

For the current time-stratified case-crossover study, which was based on a nationwide ACS registry, the authors included 1,292,880 individuals who presented to hospitals with ACS in 318 Chinese cities.

Kan and colleagues used pollution data that had been gathered hourly from 2015 to 2020 at environmental monitoring stations located a median 2.6 km away from each hospital. This served as a proxy for the ambient air pollution experienced by each patient hour-by-hour. For the 33% of patients who had sufficient address records, a median 6.1 km separated the location of patients with ACS onset and the treating hospital.

The link was stronger in cold weather, in people older than 65 years, and — notably — those without a history of smoking or chronic cardiorespiratory diseases.

“It is possible that these individuals were at high risk of ACS due to other reasons, making the contributions from air pollutants less relevant. It is also possible that the effects of air pollutants might have been masked or attenuated by medications or other risk factors. While the results of these stratified analyses are interesting, some were based on small samples, and therefore they must be interpreted cautiously and require independent confirmations,” Kan and team wrote.

Another caveat to the study was the potential for exposure misclassification and residual confounding.

Nevertheless, the authors suggested that this analysis fixes a lot of the issues with previous studies on pollution and ACS.

“Most previous studies have assessed the associations by fitting aggregate cases of ACS-related events and exposures at the daily timescale through time-series analyses. Consequently, these studies have always been challenged by concerns about ecological fallacy, exposure misclassification, and the inability to inform biological mechanisms without identifying the most relevant time windows of exposures for ACS onset,” the group noted.

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    Nicole Lou is a reporter for MedPage Today, where she covers cardiology news and other developments in medicine. Follow

Disclosures

The study was funded by grants from the National Natural Science Foundation of China, Shanghai Three-year Action Plan, and Shanghai Xuhui District Science and Technology Commission.

Kan’s group had no disclosures.

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