Washington, September 9 : A recent study of 48 people with coronary artery disease in Boston has revealed that tiny particles in polluted air can adversely affect the heart's ability to conduct electrical signals in such patients.
Appearing in Circulation: Journal of the American Heart Association, the study involved the use of 24-hour Holter monitors 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.
Senior researchers who worked on the project have revealed that the average 24-hour levels for all pollutants included in their 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. Effects were greatest within the first month after hospitalization, and for patients who were hospitalized for a heart attack or had diabetes," said Dr. Diane R. Gold, the study's senior author and an associate professor of medicine and environmental health at Harvard University in Boston, Massachusetts.
The researchers highlighted the fact that previous studied had already established that exposure to road traffic and particulate air pollution increase 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.
"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. Forty percent of them had suffered a heart attack, and 25 percent diabetes.
The 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.
They averaged monitor readings over each half-hour, providing 5,979 half-hour observations, and then examined the relation of these ECG measurements with levels of several pollutants.
It was observed that increased levels of particular pollution - PM2.5 and black carbon (a marker for traffic exhaust) - were associated with ST-segment depression in the study participants.
The team also observed that sulfur dioxide, a pollutant that can have non-traffic sources, was also associated with ST-segment depression.
They did not find any significant correlation was found between ST-segment depression and increased levels of carbon monoxide, but levels of this pollutant were low in this study.
According to them, patients recovering from a heart attack had greater changes in ST segment depression on electrocardiograms compared to other participants.
"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," Gold said.
"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 added.