During the virtual American Heart Association (AHA) scientific sessions in November 2021, the results of a new study highlighting the role of environmental factors in the development of cardiovascular disease were presented. During the lockdowns at the start of the 2019 coronavirus disease (COVID-19) pandemic, there was a decrease in the ST-segment elevation myocardial infarction (STEMI) incidence, but the reasons for this reduction remain a mystery. As of today, increased particulate matter 2.5 (PM 2.5) is a known risk factor for STEMI, although evidence of the reciprocal relationship (decreased PM 2.5 associated with decreased STEMI incidence) has not been shown.
The authors 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. They abstracted daily STEMI events from the National Emergency Medical Services (EMS) Information System (NEMSIS) database. Incidence rates (events per 10,000 person-years) were calculated using US Census population denominators by US Census Divisions. Average daily PM 2.5 data from across the US was collected from the Environmental Protection Agency (EPA) website.
There were 60,722 total STEMI events recorded during the study period. After multivariable adjustment, there were 6% less STEMIs per each 10 µg/m3 reduction in PM 2.5 (rate ratio 0.94, 95% CI 0.90-0.99, p = 0.016). Using the same multivariate adjustment, there were 373.8 less STEMIs per 10,000 person-years for each 10 µg/m3 decrease in PM 2.5 (95% CI 69.4-678.1).
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.
