Microscopic particles in polluted air can
adversely affect the heart’s ability to conduct electrical
signals in people with serious coronary artery disease, researchers
reported in Circulation: Journal of the American Heart Association.
In a recent study of 48 Boston-area patients, all of whom
had coronary artery disease, 24-hour Holter monitors were
used to examine electrocardiograms for the conductivity change
called an ST-segment depression, which may indicate inadequate
blood flow to the heart or inflamed heart muscle.
The average 24-hour levels for all pollutants included in
the analysis were below accepted or proposed National Air
Quality Standard thresholds, meaning patients were breathing
air considered healthy.
“We found that an elevation in fine particles, from
non-traffic as well as traffic sources, and black carbon,
a marker for traffic, predicted ST-segment depression,”
said Diane R. Gold, M.D., M.P.H., the study’s senior
author and an associate professor of medicine and environmental
health at Harvard University in Boston, Mass. “Effects
were greatest within the first month after hospitalization,
and for patients who were hospitalized for a heart attack
or had diabetes.”
Previous studies have documented that exposure to road traffic
can trigger heart attacks, and that particulate air pollution
increases the risk for cardiac death or heart attack.
“When coal sales were banned in Dublin, Ireland, and
black smoke concentrations declined by 70 percent within the
next 72 months, cardiovascular deaths fell by 10 percent,”
said Gold, citing a study published in 2002.
The ST-segment changes Gold observed were not associated
with symptoms in these patients, all of whom had experienced
in-hospital procedures to examine or open up their coronary
Nevertheless, the findings expand the evidence that air pollution
can affect heart health, either through inflaming the heart
muscle or through reducing blood flow to the heart. It suggests
the need for greater vigilance by physicians and heart patients
in the weeks after discharge from the hospital, researchers
The American Heart Association and the American College of
Cardiology recommend that some heart patients, particularly
those who have had a heart attack, delay driving for two to
three weeks after leaving the hospital and avoid driving in
heavy traffic because of the stress it creates.
“Our study provides additional rationale to avoid or
reduce heavy traffic exposure after discharge, even for those
without a heart attack, since traffic exposure involves pollution
exposure as well as stress,” she said.
The study’s 48 participants had been hospitalized for
either a heart attack, unstable angina or worsening symptoms
of stable coronary artery disease. Their median age was 57
years, 81 percent were male, 40 percent had suffered a heart
attack and 25 percent had diabetes.
Researchers visited the patients two to four weeks after
their discharge, and then three more times at approximately
three-month intervals. At each visit, a portable electrocardiograph
called a Holter monitor recorded the patients’ heart
activity for 24 hours. All participants were monitored on
the first visit, and 35 had monitoring on more than one visit.
Researchers averaged monitor readings over each half-hour,
providing 5,979 half-hour observations. They then examined
the relation of these ECG measurements with levels of several
pollutants, including black carbon, produced by the incomplete
combustion of fossil fuels, and particulate matter (PM2.5)
of less than 2.5 micrometers (about 1/10,000th of an inch)
Researchers obtained the PM2.5 and black carbon readings
at a Harvard School of Public Health monitoring site, an average
distance of 10.9 miles from the participants’ homes.
Among the study’s findings:
- Increased levels of particular pollution – PM2.5
and black carbon (a marker for traffic exhaust) –
were associated with ST-segment depression in the study
- Sulfur dioxide, a pollutant that can have non-traffic
sources, also was associated with ST-segment depression.
- No significant correlation was found between ST-segment
depression and increased levels of carbon monoxide, but
levels of this pollutant were low in this study.
- Patients recovering from a heart attack had greater changes
in ST segment depression on electrocardiograms compared
to other participants. The key question remains –
how breathing air polluted by PM2.5 and black carbon might
cause ST segment depression.
“Further research is needed to evaluate whether the
pollution-related ST-segment depression that we see is related
to increased heart muscle inflammation, reduced oxygen flow,
oxidative stress, or increased risk of arrhythmias,”
“We think that our findings, which are definitely subclinical,
may represent a process that increases clinical risk for people
with symptomatic coronary artery disease,” she said.
The National Institute of Environmental Health Services,
the Environmental Protection Agency, and the National Science
Council funded the study.