Ambient fine particulate matter and mortality among survivors of myocardial infarction: population-based cohort study

Background — Survivors of acute myocardial infarction (AMI) are at increased risk of dying within several hours to days following exposure to elevated levels of ambient air pollution. Less is known, however, about the influence of longer-term air pollution exposure on survival after AMI.

Objective — We conducted a population-based cohort study to determine the impact of long-term exposure to fine particulate matter (PM_2.5) on post-AMI survival.

Methods — We assembled a cohort of 8,873 AMI patients who were admitted to one of 86 hospital corporations across Ontario, Canada in 1999-2001. Mortality follow-up for this cohort extended through 2011. Cumulative time-weighted exposures to PM_2.5 were derived from satellite observations based on participants’ annual residence during follow-up. We used standard and multilevel spatial random-effects Cox proportional hazards models, adjusting for potential confounders.

Results — Between 1999 and 2011, we identified 4,016 non-accidental deaths, of which 2,147 were from any cardiovascular disease, 1,650 from ischemic heart disease, and 675 from AMI. For each 10-μg/m³ increase of PM_2.5, the adjusted hazard ratio (HR10) of non-accidental mortality was 1.22 (95% confidence interval (CI): 1.03-1.45). The association with PM_2.5 was robust to sensitivity analyses and appeared stronger for cardiovascular-related mortality: ischemic heart (HR₁₀=1.43; 95%CI: 1.12-1.83) and AMI (HR₁₀=1.64; 95%CI: 1.13-2.40). We estimated that 12.4% of non-accidental deaths (or 497 deaths) could have been averted if the lowest measured concentration in an urban area (4-μg/m³) had been achieved at all locations over the course of study.

Conclusions — Long-term air pollution exposure adversely affects the survival of AMI patients.