Main Air Pollutants and Myocardial Infarction: A Systematic Review and Meta-Analysis

Study Questions:

What is the association between short-term exposure to major air pollutants (ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and particulate matter ≤10 μm [PM10] and ≤2.5 μm [PM2.5] in diameter) on myocardial infarction (MI) risk?

Methods:

EMBASE, Ovid MEDLINE in-process and other nonindexed citations, and Ovid MEDLINE (between 1948 and November 28, 2011), and EBM Reviews–Cochrane Central Register of Controlled Trials and EBM Reviews–Cochrane Database of Systematic Reviews (between 2005 and November 28, 2011) were searched for a combination of keywords related to the type of exposure (air pollution, ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, PM10, and PM2.5) and to the type of outcome (MI, heart attack, acute coronary syndrome). Two independent reviewers selected studies of any study design and in any language, using original data and investigating the association between short-term exposure (for up to 7 days) to one or more air pollutants and subsequent MI risk. Selection was performed from abstracts and titles and pursued by reviewing the full text of potentially eligible studies. Descriptive and quantitative information was extracted from each selected study. Using a random-effects model, relative risks (RRs) and 95% confidence intervals (CIs) were calculated for each increment of 10 μg/m3 in pollutant concentration, with the exception of carbon monoxide, for which an increase of 1 mg/m3 was considered.

Results:

After a detailed screening of 117 studies, 34 studies were identified. All the main air pollutants, with the exception of ozone, were significantly associated with an increase in MI risk (carbon monoxide: 1.048; 95% CI, 1.026-1.070; nitrogen dioxide: 1.011; 95% CI, 1.006-1.016; sulfur dioxide: 1.010; 95% CI, 1.003-1.017; PM10: 1.006; 95% CI, 1.002-1.009; and PM2.5: 1.025; 95% CI, 1.015-1.036). For ozone, the RR was 1.003 (95% CI, 0.997-1.010; p = 0.36). Subgroup analyses provided results comparable with those of the overall analyses. Population-attributable fractions ranged between 0.6% and 4.5%, depending on the air pollutant.

Conclusions:

The authors concluded that all the main air pollutants, with the exception of ozone, were significantly associated with a near-term increase in MI risk.

Perspective:

This meta-analysis demonstrates a significant association between all analyzed pollutants, with the exception of ozone, and MI risk. Although the calculated relative risks were relatively low, the population-attributable fractions were not negligible because the majority of the population is exposed to air pollution in industrialized countries. Additional prospective research is indicated to determine whether interventions that effectively improve air quality are associated with a decreased incidence of MI and other cardiovascular conditions.

Clinical Topics: Acute Coronary Syndromes

Keywords: Risk, Acute Coronary Syndrome, Myocardial Infarction, Particulate Matter, Nitrogen Dioxide, Sulfur Dioxide, Ozone, Incidence, Developed Countries, Population, Carbon Monoxide, Cardiovascular Diseases


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