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.
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 under way.
Severe particulate pollution exists in many urban and desert areas, including Los Angeles, Philadelphia, Chicago, New York City, Salt Lake City and Phoenix, which in 1998 surpassed Riverside, Calif., with the nation’s highest particulate levels.
Levels of particulate matter in Houston’s air do not exceed the limit set in the current national health standard for that air pollutant.
Environmental experts, however, expect Houston to violate a new and stricter particulate standard if it goes into effect. The new standard was adopted by the Clinton administration but its implementation was halted by a federal appeals court order, which the administration is appealing to the Supreme Court.
Houston now violates the national health standard for only one major air pollutant – ground-level ozone, a respiratory irritant and smog’s main ingredient.
Research continues to indicate 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 a senior citizen – 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 percent of heart disease fatalities in the United States. That fraction is small but would amount to 10,000 deaths a year.
“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 University of Southern California medical professor who is a leading expert on the health effects of air pollution.
Epidemiologists in 70 cities around the world consistently have found that more people die and are hospitalized when particulate pollution rises even a moderate amount.
Rarely does such a clear pattern emerge in epidemiology, and most experts are now convinced that it is not a coincidence.
“For air pollution to have such a substantial impact on public health, and have it show up so consistently, is remarkable,” said Daniel Costa, chief of the U.S. Environmental Protection Agency’s pulmonary toxicology branch.
The sudden-death phenomenon has been reported for nearly a decade. Only during the last year have scientists begun to figure out why.
Tiny, ubiquitous particles of soot – from diesel trucks, cars, industrial plants and perhaps even windblown dust – seem to alter the normal pulsing of the heart, the research indicated.
At pollution levels commonly found in U.S. cities, inhaling particles appears to disrupt the body’s ability to regulate the pumping of blood.
As particulate counts rise on any given day, a vital indicator, called heart rate variability, decreases in some people, disturbing the beat-to-beat variations that are designed to meet the demands of activities ranging from sleep to exercise.
The threat seems acute for senior citizens who have arrhythmia – a life-threatening condition of skipped or premature beats – or the combination of a weak heart and lung disease such as asthma.
One of the most frightening aspects of heart rhythm irregularities is that they can kill quickly, without warning.
“Studies suggest that people are dying relatively rapidly after you see an increase in particles. Sometimes it’s within 24 hours,” said Robert Devlin, chief of human studies at the clinical research branch of the EPA.
In the last year, about a dozen major scientific studies have turned up heart pattern changes in animals exposed in laboratories and in senior citizens tested in nursing homes. Several more studies are about to be published.
According to one ground-breaking study of 100 patients in Boston, conducted by the Harvard School of Public Health, when particle pollution increased, senior citizens with pacemakers suffered more arrhythmia.
In another study, 26 senior citizens at a Baltimore nursing home wore heart monitors for three weeks. Their heart rate variability decreased on and around days when particulate levels were higher, according to a study by the University of North Carolina and the EPA.
Some environmental health researchers and doctors say cardiologists should advise patients who are at risk to avoid exertion on days with high particulate counts.
But Denton, one of the few cardiologists to study the link between heart rhythm and particulates, said the findings are too preliminary to base medical recommendations on them.
“Based upon the data we have, there’s no need (at this time) for us to change a patient’s behavior or treatment,” said Denton.
An as yet unpublished EPA study offers some of the most compelling evidence so far that particles can affect heart rhythm.
Older volunteers were tested in special pollution chambers using air collected in North Carolina. Even when they were exposed to a dose found in many urban areas, their heart rate variability was worse than when they were exposed to clean air. Younger volunteers indicated no heart changes.
Although the changes detected in beat variability “were not huge,” some persisted for at least a day after exposure and they are “very significant” for human health because low heart rate variability often occurs in people who are about to suffer heart attacks, said Devlin, who directed the study.
Researchers are trying to understand how particles could affect the heart.
The most popular theory is that when particles enter the lungs, some part of the nervous system reflexively sends an impulse to the nerve center in the heart that controls contractions. This reflex raises the pulse rate and lowers the variability of the heart rate.
Also, inhaled particles cause lung inflammation, which can release agents into the blood that are carried into the heart. Blood also seems to thicken and clot differently upon exposure, according to some studies.
Chronicle environmental writer Bill Dawson contributed to this story.
The article “Rise in particles alters heart rate, studies find” by Marla Cone appeared in the Los Angeles Times on June 4, 2000