In this study, we conducted an assessment to determine the impact of air pollution on the short-term prognosis of STEMI. The results indicate that NO2 might have a significant influence on the risk of in-hospital mortality in Kaohsiung, Taiwan. Among the various air pollutants analyzed, higher levels of NO2 exposure were found to be associated with an elevated risk of in-hospital mortality in patients diagnosed with STEMI, especially during the warm season. In contrast, it was observed that higher levels of PM10 exposure were linked to an elevated risk of in-hospital mortality among patients diagnosed with STEMI specifically during the cold season.
Numerous epidemiological studies have provided evidence supporting the detrimental effects of air pollution on MI. Bañeras et al. conducted a population-based study that included all STEMIs in Barcelona and found that PM2.5, PM10, and NO2 were positively associated with the incidence of STEMI [
2]. In contrast, a separate study that investigated the relationship between air pollution and acute coronary syndrome found that NO2 exposure was positively associated with STEMI incidence, whereas the association between PM2.5, PM10 exposure and STEMI did not reach statistical significance [
17]. A recent article reviewed 56 studies and concluded that PM2.5, PM10, and NO2 were related to an increased risk of hypertension and subsequent MI [
5]. However, few studies have focused on the relationship between short-term outcomes of STEMI and air pollution. In the current study, NO2 was positively associated with the risk of in-hospital mortality in patients with STEMI, especially during the warm season, and PM10 exposure levels were associated with an increased risk of in-hospital mortality in patients with STEMI during the cold season. Numerous toxicological studies have attempted to elucidate the mechanisms underlying health hazards caused by air pollution. In terms of pulmonary toxicity, cell-based studies have shown that exposure to PM activates nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and triggers the NF-κB-mediated inflammatory response, leading to an increase in inflammatory cytokines such as interleukin (IL)-6, IL-8, and IL-1β in human tracheal epithelial cells [
18], while animal experiments have demonstrated that exposure to PM causes infiltration of inflammatory cells in the lungs, thickening of the tracheal epithelium, and alveolar rupture [
8]. These inflammatory substances include cytokines, activated immune cells, and factors that induce vascular activity, such as endotoxins, histamine, and microparticles, which are involved in the inflammatory response and enter extrapulmonary organs through the bloodstream [
19,
20]. In addition, exposure to NO2 has also been found to increase the levels of inflammation markers in the blood, including C-reactive protein (CRP), tumor necrosis factor-α, IL-6, and coagulation-related factors such as fibrinogen, as well as tissue repair marker hepatocyte growth factor [
21]. These inflammatory cytokines and coagulation-related factors may cause vasoconstriction and affect clot formation in vascular endothelial cells [
22]. In contrast, ultrafine particles (UFP) and certain components of PM, such as organic compounds and heavy metals, may directly penetrate the alveolar and capillary barriers of the lungs, enter the systemic circulation, and induce vascular injury [
23,
24]. Furthermore, while causing inflammation in the lungs, the interaction between air pollutants and lung receptors can lead to reflex responses in the autonomic nervous system, resulting in an increased heart rate, vasoconstriction, and other reactions [
25,
26]. Increased heart rate, vasoconstriction, disturbances in vascular endothelial clot formation, and coagulation biomarkers may affect the outcomes of MI. Animal studies have shown that exposure to NO2 can interfere with the regulation of endothelial nitric oxide synthase and intercellular adhesion molecule 1 in vascular endothelial cells, whereas exposure to PM2.5, has been found to interfere with the regulation of the renin-angiotensin system, which regulates blood pressure, possibly leading to increased blood pressure and enhanced coagulation responses [
27,
28].
Our study findings support the existence of a positive correlation between NO2 exposure and the in-hospital mortality rate among patients with STEMI, particularly during the warm seasons. In contrast, PM10 was found to be positively associated with the in-hospital mortality rate among patients with STEMI during the cold season. The effects of air pollution on human health exhibit seasonal variations. For example, Hsu et al. found a significant connection between PM2.5, concentration, and hospitalization for cardiovascular diseases, with a particular emphasis on the winter season [
29]; while Huang et al. found a correlation between elemental carbon in PM2.5 and the risk of chronic obstructive pulmonary disease (COPD) ED visits, particularly during the warm season [
30]. This can be attributed to several factors. First, the sources and composition of PM pollution particles vary across seasons, which may result in different health hazards. For example, PM2.5, measured at roadside locations, contains high levels of metal components, such as copper, zinc, iron, and calcium, from vehicle emissions and road dust, which are more than twice the levels found in urban background locations [
31]. PM is composed of particles of different sizes and chemical characteristics, and its health effects may differ depending on the composition of the components. Altemose et al. collected PM2.5, data before, during, and after the 2008 Beijing Olympics and measured coagulation-related biomarkers in the plasma of 128 volunteers as well as oxidative stress indicators in their exhaled breath. The results showed that PM2.5, generated by automobiles, factories, and biomass burning, is positively associated with lung inflammation-related biomarkers. The increase in oxidative stress was related to emissions from factories and vehicles, while coagulation-related biomarkers, such as the von Willebrand Factor (vWF), were positively associated with the combustion of fossil fuels [
32]. Hwang et al. obtained data from Taiwan’s National Health Insurance program and found a direct correlation between PM2.5 and asthma, especially for nitrate (NO3-) of PM2.5 [
33]. Toxicological evidence also suggests that exposure to water-soluble extracts of PM2.5 could cause a proliferative response in the livers of mice, while insoluble particles can cause an inflammatory response and an increase in apoptosis regulation in the livers of mice [
34]. Secondly, different PM components in particulate matter may interact with gaseous pollutants, resulting in different health risks. For instance, the interaction between sulfate and nitrate in PM2.5 and ozone (O3) may elevate the likelihood of pediatric pneumonia ED visits [
35]. Third, changes in temperature may have an additive effect on health hazards caused by air pollution. For instance, Imaizumi et al. documented a direct correlation between exposure to PM2.5 and morning hypertension, and noted that this effect was strengthened by low temperatures [
36].