Studies Link Heart Attacks to Moderate Air Pollution
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.
Epidemiologists in about 70 cities around the world consistently have found that more people die and are hospitalized during periods 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 Environmental Protection Agency’s pulmonary toxicology branch.
The sudden-death phenomenon has been reported for nearly a decade. Only within 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 emerging research shows.
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 particularly acute for elderly people 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 U.S. Environmental Protection Agency.
In the past year, about a dozen major scientific studies have turned up heart pattern changes in animals exposed in laboratories and in elderly people tested in nursing homes. Several more studies are about to be published.
Skepticism Turns to Suspicion
According to one groundbreaking study of 100 patients in Boston, conducted by the Harvard School of Public Health, when particle pollution increased, elderly people with pacemakers suffered more arrhythmia.
In another study, 26 seniors 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.
“I started out skeptical, but I’m starting to think there’s something really there,” said Brigham Young University epidemiologist Arden Pope, who studied elderly patients in Provo, Utah. “We have strongly suggestive evidence now that there’s an impact on the heart.”
Robert McWherter is about as vulnerable to particle pollution as anyone can get. He’s 80, suffers from heart disease and chronic bronchitis, and lives in Indio, a desert town with high levels of microscopic particles from dust whipped up by spring winds. Like many retirees, McWherter moved to the Coachella Valley to protect his health, unaware that particulates there may be harming his heart.
“My heart muscle is pretty well shot,” said McWherter, who has undergone both a quadruple and a triple bypass but stays in shape by walking outdoors and lifting weights in a gym.
McWherter is one of 23 cardiac patients in the Coachella Valley who are wearing heart monitors one day a week for three months. They are volunteers in a new state study testing whether elderly people in the desert are endangered on high-particle days.
In March, during the worst of the windy season, McWherter’s heart monitor detected skipped beats. No one knows whether the particles were to blame, but taking part in the experiment probably saved his life because the abnormalities were found. McWherter wound up being fitted for a pacemaker.
Some environmental health researchers and doctors say cardiologists should advise patients such as McWherter to avoid exertion on days with high particulate counts. In the Coachella Valley, particulate pollution peaks in the spring. In the Los Angeles Basin, it peaks in the fall and winter, when many residents mistakenly believe the sky is clean because traditional smog strikes most heavily in the summer.
But Denton of Cedars-Sinai, 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, who is a consulting cardiologist for the state’s Coachella Valley test. “Maybe in a year or so it could [warrant doctors’ warnings], if we get better data.”
In much of the research on the heart rhythm theory, animals have served as scientific surrogates.
Rats with simulated heart disease died from arrhythmia when exposed to single doses of highly concentrated smokestack particles in EPA tests. The rats started out with normal heartbeats, but within half an hour their hearts went haywire, skipping beats and contracting prematurely.
Fashioning Tests for Human Volunteers
The rats were exposed to pollution levels hundreds of times higher than what any person would encounter. But in another experiment, dogs with simulated coronary artery disease showed “very significant changes in EKGs” after breathing elevated levels of particulates no higher than those found in many U.S. cities, said Daniel Greenbaum, director of the Health Effects Institute, a Massachusetts research group that funded the study at Harvard.
Studies of rats and dogs, however, have limited value because their hearts differ from human hearts. As a result, scientists are now fashioning creative experiments using human volunteers.
An as yet unpublished EPA study offers some of the most compelling evidence so far that particles can affect heart rhythm. Elderly 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 showed no heart changes, even at the highest doses.
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.
A similar study is underway at Rancho Los Amigos Medical Center in Downey, where elderly volunteers are being exposed both to clean air and to air with 200 micrograms of ultra-fine particles per cubic meter--the Los Angeles Basin’s “worst-case scenario.”
Experiments like this are the closest that science comes to proving a cause and effect between pollution and heart effects.
Researchers are just now 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.
Examining Particle Size, Content
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.
Particulates may be dangerous because of fragments of metals such as iron that are contained in soot. But some researchers believe it is the size of the particles, not the content, that causes the harm, and that microscopic road dust could be just as hazardous as truck exhaust.
Air pollution regulators say they need the answers to help them decide how to target efforts to clean up particulate pollution. Billions of dollars from corporate and public interests--from utilities to the trucking industry--are at stake.
To public health officials, the new findings are disturbing because they suggest that moderate, everyday concentrations of a pollutant can be lethal.
But epidemiologist Pope says if the link between air particles and heart attacks is proved, “it’s incredibly good news.”
“We already know that about half of us die of cardiopulmonary disease, and if this is true about particulates, we have found a preventable cause,” he said.
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Pollution and the Heart
A regular heartbeat is vital because it determines the amount of blood that surges into the arteries. If the pattern is erratic or the beat is too slow or fast, it could be life-threatening. Microscopic solids in the air, called particulates, seem to interfere with the body’s ability to control its heart rate and rhythm.
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* Nerves help keep the heart beating in a regular, rhythmic pattern.
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* Electrical impulses shoot out from a node in the upper section of the heart. This stimulates a heartbeat--contraction of thick muscular walls--that forces blood out of the heart.
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* According to one theory, when particles are inhaled, it stimulates a reflex response in the autonomic nervous system that alters the heart rate and lowers heart rate variability --the heart’s ability to respond to exercise or stress. Such changes are often associated with fatal heart attacks in people with cardiac disorders.
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* The inhaled particles also provoke immune cells and cause inflammation in the lungs and heart that might exacerbate heartbeat disturbances.
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Source: U.S. Environmental Protection Agency/Experimental Toxicology Division
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Particle Pollution
Fine particulates have fouled the Los Angeles Basin’s air for decades, especially in the Riverside area. Here are peak concentrations per year for 1990-98, measured in micrograms of particles per cubic meter of air.
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* What’s in Particulates
* Nitrate: Mostly from cars and diesel trucks
* Organic carbon: From auto and truck exhaust and from petroleum-based solvents and paints
* Elemental carbon: Mostly from diesel engines
* Ammonium: From animal waste
* Sulfate: From factories and motor vehicles
* Other: Mostly dust, soil and salt
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RIVERSIDE
Nitrate: 41%
Organic carbon: 18%
Ammonium: 17%
Sulfate: 9%
Elemental carbon: 8%
Other: 7%
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Source: South Coast Air Quality Management District
