Emory Scientists Link Atrial Fibrillation with Decrease in Nitrous Oxide: Finding Could Hold Key to Increased Risk of Stroke

Emory University
Tuesday, 11 November 2003

Emory research presented at the Abstract Oral Sessions of the American Heart Association's Scientific Sessions today entitled "Atrial Fibrillation Causes Increased Oxidative Stress and Decreased Nitric Oxide Bioavailability in the Left Atrial Appendage" offers a possible explanation for one of the most serious, and sometimes deadly, complications associated with the heart rhythm disorder known as atrial fibrillation (AF) -- stroke.

AF, which is characterized by a rapid and irregular beat originating from the upper chambers of the heart, is the most common sustained heart rhythm disorder. According to the Centers for Disease Control (CDC), an estimated 2.2 million adults in the United States have been diagnosed with this arrhythmia. A-fib increases the risk for heart disease and stroke, both leading causes of death in the United States. AF associated stroke is known to be due almost exclusively to blood clot ( hrombus) formation in the left atrial appendage (LAA), a small, thumb-shaped pouch in the heart's left upper chamber.

"Previous studies have indicated that more than 90 percent of non-rheumatic AF-related strokes are the result of blood clots that form in the LAA and then travel to blood vessels leading to the brain, causing stroke, " says Emory Heart Center and Atlanta Veterans Administration Medical Center cardiologist Samuel C. Dudley, MD, who headed the Emory research team. "The mechanisms underlying AF perpetuation and localized formation of LAA thrombus continue to be poorly understood. However, we recently found that AF is associated with decreased endocardial nitric oxide (NO) in the LAA . We believe that may play a role in blood clot formation."

The Emory researchers, working with pig hearts, examined atrial tissue (from the upper chambers of the heart) from animals that had experienced induced AF and compared them with the hearts of control animals. They found that superoxide (O2) levels were twice as high in the LAA of animals with AF compared with controls and this increase in O2 was associated with a significant decrease in NO.

"Nitrous oxide is known to have has antithrombotic properties that can protect against blood clots, so we believe these changes may explain the predisposition to LAA thrombus in people with AF," says Dr. Dudley. "These findings may provide new avenues for the study of therapeutic interventions in humans with AF."

For more information, or to contact Emory University, see their website at: whsc.emory.edu