The association between short-term PM2.5 exposure and the incidence of NSTEMI: A case-crossover study

The incidence of acute myocardial infarction (AMI) is on the rise, partly due to exposure to particulate matter (PM). However, the nature of the events and individuals at higher risk is unclear. This study examines the relationship between air pollution exposure, specifically particles with a diameter <2.5 microns (PM2.5), and the occurrence of non-ST-segment elevation myocardial infarction (NSTEMI).

In this case-crossover study, NSTEMI patients in Imam Hossein Hospital during 2021-2024 were considered. PM2.5 particle levels in Tehran during the 24 hours before NSTEMI admission and during three control periods (7, 14, and 21 days earlier) were recorded. Data were analyzed using Stata 17 and conditional logistic regression.

Of 4,686 patients, 216 (4.61%) experienced NSTEMI. The median PM2.5 level was 91.5 μg/m³ (interquartile range = 78-113). PM2.5 levels did not differ between risk and control times (P = 0.740). Median PM2.5 levels were highest in autumn, followed by winter, and lowest in spring (P < 0.001). PM2.5 levels were not strongly associated with the occurrence of NSTEMI (P = 0.268). Considering PM2.5 levels, the occurrence of NSTEMI during winter was 3.42-fold greater than in autumn (OR = 3.42, 95% CI = 1.07-10.59). A significant association between PM2.5 levels and NSTEMI was observed only in winter, where each 1 μg/m³ increase in PM2.5 was associated with slightly reduced odds of NSTEMI (OR = 0.98, 95% CI: 0.97-0.99).

Exposure to PM2.5 was not related to the incidence of NSTEMI. Nevertheless, seasonal factors, particularly in autumn and winter, could be responsible for NSTEMI events.