In people with serious coronary artery disease, tiny particles of air pollution and black carbon from traffic exhaust fumes may cause ST-segment depression, an EKG finding that usually signals an inadequate supply of oxygen and nutrients to the heart muscle, according to a report in Circulation: Journal of the American Heart Association.
For the study, 48 heart patients in the Boston area wore special monitors that checked for ST-segment depression intermittently over the course of a year. When the particles and black carbon in the air increased, so did the instances of ST-segment depression. Effects were greatest within the first month after hospitalization and for patients who had been hospitalized for a heart attack or had diabetes.
Authors note that previous studies have shown exposure to road traffic can trigger heart attacks and that air pollution increases the risk for cardiac death.
The American Heart Association and the American College of Cardiology already recommend that some heart patients, particularly those who have had heart attacks, avoid driving for several weeks, especially in heavy traffic, because of the stress.
"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," Diane R. Gold, MD, the study's senior author and an associate professor of medicine and environmental health at Harvard University, says in a news release.
The study participants were between 43 and 75 years old. Researchers visited them several times at three-month intervals, hooking them up to a monitor for 24-hour stretches. The participants had all been hospitalized for a heart attack, unstable angina, or worsening symptoms of stable coronary artery disease, and had all undergone angioplasty or stent implantation. Most were male, and 25% had diabetes.
It is not known how the carbon and air particles 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," Gold says.