Tiny Air Pollutants Linked To Heart Attack

“Studies of hospital admissions and emergency department visits have linked exposure to particulate air pollution with increased risk of cardiovascular diseases,” says study author Murray A. Mittleman, M.D., Dr.PH., director of cardiovascular epidemiology at Boston’s Beth Israel Deaconess Medical Center. “But the current study is the first to examine short-term transient effects of air pollution on the risk of heart attack.”

Between Jan. 1995 and May 1996, researchers interviewed 772 Boston area heart attack patients about four days after their heart attack to establish when their symptoms began. Participants were enrolled in the Determinants of Myocardial Infarction Onset Study, which is aimed at gathering information about factors associated with myocardial infarction, or heart attack. Researchers compared the times heart attack symptoms began with daily air pollution measurements collected in Boston during the study period. They paid special attention to levels of the smaller pollutants.

“These tiny particles are known as PM2.5 because they measure less than 2.5 micrometers in diameter,” explains co-author Douglas W. Dockery, Sc.D., professor of environmental epidemiology at the Harvard School of Public Health. “They are so small that they can get past the normal defense mechanisms in the lungs and penetrate deeply into the air exchange regions, or alveoli.”

Air pollution measurements taken at the time patients said their heart attack symptoms began were compared to measurements taken during “control” periods. Control periods were selected 24 hours apart, starting three days before the date and time heart attack symptoms began.

The risk of heart attack was higher among those with elevated PM2.5 in the two hours before the onset of symptoms. In addition, researchers observed a higher heart attack risk when 24-hour average exposure to PM2.5 was considered, indicating a delayed response to the particles. Data analysis considering both time windows jointly revealed a 48 percent higher risk of heart attack when PM2.5 concentration increased by 25 micrograms per cubic meter of air (µg/m3) in the two-hours before symptoms began. Fine-particulate air pollution is produced primarily by combustion processes in automobile engines, power plants, refineries, smelters and other industry, says Dockery. Larger, more readily

noticed particles of airborne dust and debris from farming, construction work and mining are far less likely to trigger heart attack, he says.

Some recent data suggest that exposure to high levels of PM2.5 may cause increased systemic inflammation, increased plasma viscosity (thicker blood) and an increase in certain proteins in the blood that can cause clots to form, he says.