A new study from the US suggests that tiny particles of air pollution and black carbon, both tell tale signs of traffic fumes, may hinder heart function among heart attack survivors by changing the way the heart uses electrical signals. The researchers recommended that people with recent heart attacks should avoid being near heavy traffic, and even healthy people should do the same.
The study was conducted by senior author Dr Diane R Gold, an associate professor of medicine and environmental health at Harvard University in Boston, Massachusetts and is published online before print on 8th September in Circulation: Journal of the American Heart Association.
Other studies have shown links between exposure to traffic fumes and heart attacks, and that there is an increased risk of heart attack and cardiac death from exposure to particulate air pollution.
Citing a study published in 2002, Gold said:
“When coal sales were banned in Dublin, Ireland, and black smoke concentrations declined by 70 per cent within the next 72 months, cardiovascular deaths fell by 10 percent.”
For the study, Gold and colleagues enrolled 48 Boston-resident patients aged from 43 to 75 years, all of whom had coronary artery disease. 81 per cent were male, 40 per cent had suffered a heart attack and 25 percent had diabetes.
For about 24 hours, up to 4 times in one year, each patient was fitted with a Holter monitor, a portable electrocardiogram (ECG) device that attaches to the chest with electrodes. The monitor records conductivity changes called “ST-segment depressions”, which can be a sign of inflamed heart muscle or poor blood flow to the heart.
The researchers visited the patients in their homes two to three weeks after discharge, and then about once every three months, for up to a year after after being treated in hospital for heart attack, acute coronary syndrome without heart attack, or stable coronary artery disease without acute coronary syndrome. All patients were monitored with the Holter device on the first visit, and 35 were monitored on more than one visit.
The ECG readings were then averaged over each half hour, giving a total of nearly 6,000 readings in all. The researchers correlated these readings with the levels of several pollutants, such as black carbon, a byproduct of fossil fuel combustion, and air particles smaller than 2.5 micrometers (particulate matter, PM2.5). The air pollution readings came from a Harvard School of Public Health monitoring site, which was situated on average just over 10 miles from patients’ homes.
The results showed that:
- Higher levels of fine particles (PM2.5) and black carbon (a marker for traffic exhaust fumes) consistently preceded ST-segment depressions.
- Sulphur dioxide, an air pollutant that does not necessarily come from traffic fumes, was also linked to ST-segment depression.
- Over the full range of mean black carbon level measured in the previous 24 hours, an increase of a quarter across the range was linked to a 1.5 times greater risk of ST-segment depression greater than or equal to 0.1 mm, and -0.031 mm decrease in half-hour-averaged ST-segment level (continuous outcome).
- There were no significant links between increase in carbon monoxide and ST-segment depression (the authors noted that the levels of this pollutant were low in this study).
- The strongest links occurred within the first month after leaving hospital, and for patients who had heart attacks in hospital or who had diabetes.
The authors concluded that:
“ST-segment depression is associated with increased exposure to PM2.5 and black carbon in cardiac patients. The risk of pollution-associated ST-segment depression may be greatest in those with myocardial injury in the first month after the cardiac event.”
The researchers pointed out in a press statement that the average 24-hour levels for the pollutants included in the analysis were below accepted or proposed National Air Quality Standard thresholds, meaning the patients were breathing air that the authorities considered to be healthy.
Gold said:
“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.”
The authors suggest this study emphasizes the need to keep a close eye on patients leaving hospital after cardiac procedures.
Both the American Heart Association and the American College of Cardiology say some heart patients shouldn’t drive for the first two or three weeks after leaving hospital, particularly if they have had a heart attack. They should also avoid driving in heavy traffic because of the added stress.
Gold said their study added another reason: to avoid exposure to traffic fumes.
However, the study still did not answer the important question of how breathing in fine particles (PM2.5) and black carbon might lead to ST segment depression. Gold said:
“Further research is needed to evaluate whether the pollution-related 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 added.
“Particulate Air Pollution as a Risk Factor for ST-Segment Depression in Patients With Coronary Artery Disease.”
Kai Jen Chuang, Brent A. Coull, Antonella Zanobetti, Helen Suh, Joel Schwartz, Peter H. Stone, Augusto Litonjua, Frank E. Speizer, and Diane R. Gold.
Circulation, Published online before print September 8, 2008.
DOI:10.1161/CIRCULATIONAHA.108.765669
Source: AHA, journal abstract.
Written by: Catharine Paddock, PhD