Details of Study
The study looked at 48 coronary artery disease patients who lived in the Boston area, all of whom had previously experienced hospital procedures to open up or examine their coronary arteries.
The group of them had been hospitalized because of deteriorating symptoms of stable coronary artery disease, unstable angina, or a heart attack. Their median age was 57 years and more than 80% were men. In addition, 1 out of 4 had diabetes, while 2 out of every 5 had had a heart attack.
The study team followed up with the patients about two to four weeks post-discharge, and then another three more times at interval periods of about 3-months.
Holter monitors, which are portable electrocardiographs, were used to record the participants' heart activity and to help obtain indications of events such as lack of blood flow to the heart or a heart muscle which was inflamed. Should such situations present themselves, a conductivity change, called an "ST-segment depression", would show up on electrocardiograms.
These measurements were then compared with the levels of certain pollutants, including particulate matter with a diameter less than 2.5 micrometers (or 1/10,000th of an inch), also called PM2.5, and black carbon, which is produced during the incomplete combustion of fossil fuels.
For all the pollutants which were included in the analysis, mean 24-hour levels were within the National Air Quality Standard limits. This meant that air quality was generally considered healthy.
Findings of Study
"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., senior author of the study, which involved researchers from the Harvard School of Public Health and the Harvard Medical School 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," added Gold.
Another pollutant associated with ST-segment depression was sulfur dioxide, which can also originate from non-traffic sources. There was no significant correlation obtained between ST-segment depression and the levels of carbon monoxide, although it should be noted that levels of the latter were generally low for this study.
Broadly speaking, these findings are consistent with previous studies, which have shown the link between increased particulate air pollution and risk of heart attack or cardiac death, as well as exposure