Air pollution and emergency department visits for ischemic heart disease in Montreal, Canada.

OBJECTIVES: We examined the associations between emergency department (ED) visits for ischemic heart disease (IHD) and short-term elevations in ambient air pollutants (CO and NO(2)).
MATERIALS AND METHODS: A hierarchical clusters design was used to study ED visits (n = 4979) for ischemic heart disease (ICD-9: 410-414) that occurred at a Montreal hospital between 1997 and 2002. The generalized linear mixed models technique was applied to create Poisson models for the clustered counts of ED visits for IHD. The analysis was done by gender for two age categories, all patients and patients aged over 64 years.
RESULTS: The results are presented as an excess risk increase associated with the interquartile range (IQR) of daily average of the pollutant concentration. The results for NO(2) (IQR = 9.5 ppb) were 5.9% (95% CI: 2.1-9.9) for all patients and 6.2% (95% CI: 1.2-11.4) for males; for patients aged over 64: 7.1% (95% CI: 2.5-11.9) for all patients, 9.1% (95% CI: 2.8-15.7) for males, and 6.5% (95% CI: 0.7-12.7) for females (for exposure lagged by 1-day). The results for CO (IQR = 0.2 ppm): 5.4% (95% CI: 2.3-8.5) for all patients, and 7.5% (95% CI: 3.6-11.6) for males. For patients aged over 64 years, 4.9% (95% CI: 1.3-8.7) for all patients, and 7.5% (95% CI: 2.6-12.6) for males. The results show the associations for the same day exposures.
CONCLUSIONS: The short-term effects of nitrogen dioxide and carbon monoxide are associated significantly with daily ED visits for ischemic heart disease. For NO(2) the associations are stronger for patients aged over 64 years. As indicated by our results, it is likely that vehicular traffic, a producer of NO(2) and CO, contributes to an increased number of ED visits for IHD.