Associations between short-term exposure to fine particulate matter and acute myocardial infarction: A case-crossover study

Background: Previous studies evaluated the impact of particle matters (PM) on the risk of acute myocardial infarction (AMI) based on local registries. Hypothesis: This study aimed to evaluate possible short term effect of air pollutants on occurrence of AMI based on a specific case report sheet that was designed for this purpose. Methods: AMI was documented among 982 patients who referred to the emergency departments in Tehran, Iran, between July 2017 to March 2019. For each patient, case period was defined as 24 hour period preceding the time of emergency admission and referent periods were defined as the corresponding time in 1, 2, and 3 weeks before the admission. The associations of particulate matter with an aerodynamic diameter <= 2.5 mu m (PM2.5) and particulate matter with an aerodynamic diameter <= 10 mu m (PM10) with AMI were analyzed using conditional logistic regression in a case-crossover design. Result: Increase in PM2.5 and PM10 was significantly associated with the occurrence of AMI with and without adjustment for the temperature and humidity. In the adjusted model each 10 mu g/m(3) increase of PM10 and PM2.5 in case periods was significantly associated with increase myocardial infarction events (95% CI = 1.041-1.099, OR = 1.069 and 95% CI = 1.073-1.196, and OR = 1.133, respectively). Subgroup analysis showed that increase in PM10 did not increase AMI events in diabetic subgroup, but in all other subgroups PM10 and PM2.5 concentration showed positive associations with increased AMI events. Conclusion: Acute exposure to ambient air pollution was associated with increased risk of AMI irrespective of temperature and humidity.