Exposure to small particles in air pollution can have negative effects on individuals with coronary artery disease by hindering the ability of the heart to conduct electrical signals, The Washington Post reported.

Researchers from Harvard Medical School in Boston said that cars, trucks and industrial plants are the greatest source of air pollution emissions that generates heart attacks, according to the September 9th online issue of Circulation.

For the study, the electrocardiograms of 48 patients were examined. Those people had recently been hospitalized for heart attacks, unstable angina or worsening symptoms of coronary heart disease. 40% of patients had suffered heart attacks, and 25% had struggled with diabetes.

Researchers, led by Dr. Diane R. Gold, an associate professor of medicine and environmental health, monitored the participants in the study for 24 hours, up to 4 times a year, by means of portable electrocardiograph machines, in an attempt to detect changes in the electrical conductivity of the heart called ST-segment depression.

What the report indicates is that instances of ST-segment depression rose with every raise in the particles and black carbon in the air. “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,” Dr. Gold said in a statement.

Likewise, sulfur dioxide, generated on a large scale by combustion, but not from cars, was also linked to a boost in ST-segment depression.

The most significant alterations – correlated to pollution - in St-segment depression were spotted in people recovering from heart attacks, the BBC wrote on its Web site.

Between ST-segment depression and increased levels of carbon monoxide there wasn’t found any link. However, levels of this toxic gas were minimal in the Circulation study.

As maintained by Dr. Gold, the report’s results, “which are definitely sub clinical, may represent a process that increases clinical risk for people with symptomatic coronary artery disease."