Even moderate air pollution routinely found in many U.S. cities may trigger sudden deaths by changing heart rhythms in people with existing cardiac problems, according to extensive new scientific research.
The finding, backed by more than a dozen studies on humans and animals, suggests that heart attacks, not lung disease, may be the most serious medical threat posed by air pollution.
The culprits appear to be tiny pieces of soot called particulates. Scientists caution that the link between heart problems and air pollution remains a strong likelihood--not a certainty. More research is underway.
But the emerging evidence could have particular importance for the Los Angeles region, where residents breathe some of the worst concentrations of ultra-fine particulates in the nation, largely because of diesel trucks.
Severe particulate pollution also exists in many other urban and desert areas, including the Coachella Valley, Philadelphia, Chicago, New York City, Salt Lake City and Phoenix, which in 1998 surpassed Riverside for the nation's highest particulate levels.
Research continues to show that air pollution can cause serious lung problems. But as an overall threat to public health, the danger to the heart appears to be more weighty because of the sheer numbers of people with heart disease. Cardiovascular disease is the No. 1 killer in the United States, responsible for nearly half of all deaths.
Changes in heart rhythm that occur after breathing particle pollution are subtle on an electrocardiogram, and a healthy person is unaffected. But for someone with a compromised or diseased heart--especially an elderly person--the impact could have deadly consequences, researchers say.
"When particulate pollution increases, the heart rate seems to go up a little bit and the variability in the heart rate seems to go down. Those are things classically seen [in people] with heart failure," said Dr. Timothy Denton, a cardiologist at Cedars-Sinai Medical Center in Los Angeles.
Experts have estimated that particulate pollution may cause 1% of heart disease fatalities in the United States. That fraction is small but would amount to 10,000 deaths a year. In Los Angeles County, on average, 77 residents die from cardiovascular disease each day.
"If you believe the calculations, particulate-related death is a serious public health problem--more serious than any other pollutant like ozone or sulfur dioxide or carbon monoxide," said Dr. Henry Gong, a USC medical professor who is a leading expert on the health effects of air pollution.
