NEW YORK (Reuters Health) - Being in traffic, either in an automobile or on public transportation, increases the risk of heart attack in susceptible individuals, German researchers report.

At this point, it remains unclear to what extent stress or air pollution contribute to this association, note Dr. Annette Peters, from the GSF-National Research Center for Environment and Health in Neuherberg, and colleagues.

"Nevertheless," they say, "patients who are at risk for (heart disease) are likely to profit from recent efforts to improve the air quality in urban areas with the use of cleaner vehicles and improved city planning."

Previous reports have suggested that traffic exposure may worsen cardiovascular disease, but it was unclear if such exposure could actually be a triggering event for heart attacks, according to the report in The New England Journal of Medicine.

The findings are based on a study of 691 subjects who had survived at least 24 hours after a heart attack and were able to provide information on events that may have triggered the attack. Patient diaries were reviewed to assess activities in the four days prior to their heart attack symptoms.

Being involved in traffic nearly tripled the risk of heart attack in the hour that followed, the researchers note. Moreover, as time spent in cars, on motorcycles or bicycles, or on public transportation increased, so did the risk of heart attack.

In a related editorial, Dr. Peter H. Stone, from Harvard Medical School in Boston, comments that the association identified in the current study "suggests that...air pollution from traffic may have led to" a breakdown in plaque that had built up in blood-vessels, which ultimately caused the heart attack.

SOURCE: The New England Journal of Medicine, October 21, 2004.

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