Air pollution is associated with increased cardiac events

Even healthy people exposed to ultrafine particulate pollution associated with traffic and fossil-fuel combustion for just two hours show changes in heart rhythm and evidence of clot formation that may herald the potential for serious cardiac events, according to research from the Environmental Protection Agency.

The study was published in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

"We wanted to look at the specific effects that these ultrafine particles have on healthy individuals as these particles are deposited more deeply and with greater efficiency into the lower respiratory tract and may have effects beyond the pulmonary system," said lead author of the study, James Samet, Ph.D. senior principal investigator with the clinical research branch of the National Health and Environmental Effects Research Laboratory, of the EPA.

Dr. Samet and colleagues exposed 19 healthy 18-to-35 year-old volunteers to the concentrated levels of ambient ultrafine particles from Chapel Hill, North Carolina. The subjects exercised intermittently in a sealed chamber while breathing either filtered air or air containing particulate matter concentrated to about 20 times the ambient levels, which is on par with the ambient concentrations in heavily polluted cities such as Mexico City or Beijing. They then compared the effects of each exposure on markers of coagulation,lung inflammation, pulmonary function andcardiac electrophysiology

"We discovered that there was little to no inflammatory response to speak of in the lungs and airways," said Dr. Samet. "But there were prothrombotic and cardiovascular effects that include evidence of alterations in autonomic cardiovascular control and cardiac repolarization."

Specifically, there were changes in the subject's QT interval, which is represented by the sharp spike and following hump on an EKG. The QT interval is the time during which the heart cells "recover" their polarization after having discharged during the contraction phase, in preparation for the next beat. Changes in the QT interval indicate a change in heart rhythm that may be too subtle to detect by pulse rate variability alone.

Air pollution is known to be associated with increases in cardiac events and even deaths. These may be precipitated by a number of factors, including cardiac arrhythmia. Another cause may be thrombosis— clotting that can lead to occlusion of vital vessels such as the coronary arteries. Dr. Samet and colleagues found that following exposure to ultrafine particulate matter, subjects had an increase in levels of D-dimer in their blood. D-dimer is a product of blood clots and its presence is taken as evidence of clot formation.

"This study provides additional evidence that exposure to the smallest particles in the ambient air is associated with a disregulation of cardiac rhythm as well as prothrombotic effects that may be of significant concern, especially for susceptible individuals", said Dr. Samet. "Additional studies are underway to confirm these findings and expand our mechanistic understanding of the cellular and molecular events that underlie the adverse health effects of exposure to ambient particulate matter."

Source: American Journal of Respiratory and Critical Care Medicine