Particulate Air Pollution and Risk of Cardiovascular Events Among Adults With a History of Stroke or Acute Myocardial Infarction

BACKGROUND: Previous studies have found associations between fine particulate matter <2.5 µm in diameter (PM(2.5)) and increased risk of cardiovascular disease (CVD) among populations with no CVD history. Less is understood about susceptibility of adults with a history of CVD and subsequent PM(2.5)‐related CVD events and whether current regulation levels for PM(2.5) are protective for this population. METHODS AND RESULTS: This retrospective cohort study included 96 582 Kaiser Permanente Northern California adults with a history of stroke or acute myocardial infarction. Outcome, covariate, and address data obtained from electronic health records were linked to time‐varying 1‐year mean PM(2.5) exposure estimates based on residential locations. Cox proportional hazard models estimated risks of stroke, acute myocardial infarction, and cardiovascular mortality associated with PM(2.5) exposure, adjusting for multiple covariates. Secondary analyses estimated risks below federal and state regulation levels (12 µg/m(3) for 1‐year mean PM(2.5)). A 10‐µg/m(3) increase in 1‐year mean PM(2.5) exposure was associated with an increase in risk of cardiovascular mortality (hazard ratio [HR], 1.20; 95% CI, 1.11–1.30), but no increase in risk of stroke or acute myocardial infarction. Analyses of <12 µg/m(3) showed increased risk for CVD mortality (HR, 2.31; 95% CI, 1.96–2.71), stroke (HR, 1.41; 95% CI, 1.09–1.83]), and acute myocardial infarction (HR, 1.51; 95% CI, 1.21–1.89) per 10‐µg/m(3) increase in 1‐year mean PM(2.5). CONCLUSIONS: Adults with a history of CVD are susceptible to the effects of PM(2.5) exposure, particularly on CVD mortality. Increased risks observed at exposure levels <12 µg/m(3) highlight that current PM(2.5) regulation levels may not be protective for this susceptible population.