Breathing in soot and other fine particles from the urban air may increase the risk of suffering a deadly heart stoppage, suggests a new study of more than 8,000 cardiac arrests in New York City.

“As the levels of particulate matter air pollution increased, more cardiac arrests occurred,” lead researcher Dr. Robert A Silverman of the Long Island Jewish Medical Center, in New York, told Reuters Health in an e-mail.

Research had already linked air pollution to health problems such as cardiovascular disease, heart attacks, asthma and chronic lung disease. But Silverman and his colleagues wanted to know if these airborne chemicals, particularly tiny particles and liquid droplets produced by the combustion of cars and coal-fired power plants, might also raise the risk of sudden death from a cardiac arrest - a severe event brought on when the heart muscle’s rhythm becomes erratic. Cardiac arrest accounts for more than 300,000 deaths in the U.S. each year.

When cardiac arrests occur outside of the hospital, victims typically have less than eight percent chance of survival.

So the team compared readings from air quality monitors around New York City with the records of 8,216 out-of-hospital cardiac arrests that happened between 2002 and 2006.

When they looked at fine particulate matter (particles 2.5 micrometer or less in size), they found that the risk of having a deadly cardiac arrest rose by between four and 10 percent with every 10-microgram-per-cubic-meter increase in fine particulates. (To protect public health, the U.S. Environmental Protection Agency has set the safe air quality standard for this pollutant to 35 micrograms per cubic meter.)

The greatest risks appeared in the warm weather seasons. No differences in effects were seen between men and women, or between middle-aged and older individuals.

In addition to the potential hazards of particulate matter, the researchers also examined ozone, sulfur dioxide, carbon monoxide and nitrogen dioxide, but none of these showed a significant association with the risk of cardiac arrest.

“This is not to say that these gaseous pollutants do not affect the heart,” Silverman said. “What we observed was that small particles have the strongest link.”

And, of course, the behavior of air pollution can be complicated, explained Dr. Robert A. Kloner of the University of Southern California, in Los Angeles. Gaseous pollutants will mix with fine particles, he said, essentially becoming part of the particulate matter.

In a separate study, Francesca Dominici of the Harvard School of Public Health, in Boston, and her colleagues recently identified a link between heart failure hospitalizations and rises in particulate matter across several U.S. urban areas. She noted that her team’s results were consistent with the findings from New York.

Despite the density of hospitals in cities, Silverman suggested they might be especially risky places in terms of sudden cardiac death from air pollution. It may take extra time for rescue workers to reach a victim in a tall building or a crowded office complex, and severe pollution may be more common because of congested roadways and oil-burning buildings.

“Being indoors may offer only limited protection since small particles can penetrate into buildings and homes,” said Silverman. He and his colleagues are currently studying whether being in close proximity to vehicle traffic increases the risk of sudden death.

“Bottom line for large cities,” he added, “more pollution, more arrests and very little chance for survival.”

Further, the problem isn’t limited to New Yorkers. The American Lung Association estimates that a third of people in the U.S. live in areas where fine particulate matter reaches unhealthy levels.

“Controlling air pollution may be a preventative way to decrease the number of deaths from heart disease,” noted Silverman, pointing out that the levels of fine particles seen in their study rarely exceeded the current EPA standard of 35 micrograms per cubic meter. “In this sense, the current standard does not adequately protect human health.”

Kloner agreed. “Regulatory acts and strict adherence to clean air standards,” he said, “are the best ways to combat negative cardiovascular effects of air pollution.”

SOURCE:  American Journal of Epidemiology, online August 20, 2010.