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 Centre, 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 US 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 US 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 behaviour of air pollution can be complicated, explained Dr. Robert A. Kloner of the University of Southern California, in Los Angeles.