Relation between short-term fine-particulate matter exposure and onset of myocardial infarction

Background: Epidemiologic studies have reported increases in the incidence of cardiovascular morbidity and myocardial infarction (MI) associated with increases in short-term and daily levels of fine-particulate matter air pollution, suggesting a role for particulate matter in triggering an MI. Methods: We studied the association between onset time of MI and preceding hourly measures of fine-particulate matter using a case-crossover study of 5793 confirmed cases of acute MI. We linked data from a community-wide database on acute MI from 1988-1994 in King County, Washington, with central site air pollution monitoring data on fine-particulate matter determined by nephelometry. We compared air pollution exposure levels averaged 1 hour, 2 hours, 4 hours, and 24 hours before MI onset to a set of time-stratified referent exposures from the same day of the week in the month of the case event. Results: The estimated relative risk for a 10-mug/m(3) increase in fine-particulate matter the hour before MI onset was 1.01 (95% CI = 0.98-1.05). Analyses of pollutant levels at the other time points demonstrated a similar lack of association. No increased risk was found in all cases with preexisting cardiac disease (odds ratio = 1.05; 0.95-1.16). Stratification by known cardiovascular risk factors (hypertension, diabetes, and smoking status) also did not modify the relation between fine-particulate matter and MI onset. Conclusion: Although a very small effect cannot be excluded, there was no consistent association between ambient levels of fine-particulate matter and risk of MI onset.