Particulate Air Pollution, Progression, and Survival after Myocardial Infarction

OBJECTIVE Several studies have examined the effect of particulate pollution (PM) on survival in general populations, but less is known about susceptible groups. Moreover, previous cohort studies have been cross-sectional and subject to confounding by uncontrolled differences between cities. DESIGN We investigated whether PM was associated with progression of disease or reduced survival in a study of 196,000 persons from 21 U.S. cities discharged alive following an acute myocardial infarction (MI), using within-city between-year exposure to PM. We constructed city-specific cohorts of survivors of acute MI using Medicare data between 1985 and 1999, and defined three outcomes on follow-up: death, subsequent MI, and a first admission for congestive heart failure (CHF). Yearly averages of PM(10) (particulate matter with aerodynamic diameter < 10 microm) were merged to the individual annual follow-up in each city. We applied Cox's proportional hazard regression model in each city, with adjustment for individual risk factors. In the second stage of the analysis, the city-specific results were combined using a meta-regression. RESULTS We found significant associations with a hazard ratio for the sum of the distributed lags of 1.3 [95% confidence interval (CI), 1.2-1.5] for mortality, a hazard ratio of 1.4 (95% CI, 1.2-1.7) for a hospitalization for CHF, and a hazard ratio of 1.4 (95% CI, 1.1-1.8) for a new hospitalization for MI per 10 microg/m(3) PM(10). CONCLUSIONS This is the first long-term study showing a significant association between particle exposure and adverse post-MI outcomes in persons who survived an MI.