About 3 million Americans suffer from the most common type of abnormal heart rhythm, atrial fibrillation, and that number is likely to double by 2035, new research shows.

Atrial fibrillation occurs when the two upper chambers of the heart, the atria, stop contracting in a coordinated, steady fashion and instead begin to quiver. People may experience brief bouts of atrial fibrillation, or it can be a permanent condition.

Atrial fibrillation increases the risk of stroke five-fold, according to the American Heart Association, and it can also lead to congestive heart failure and chronic fatigue.

The new research, based on national health care claims data and compiled by the Healthcare Division of Thomson Reuters, was funded by Sanofi-Aventis, maker of the atrial fibrillation drug Multaq. Sanofi-Aventis also has a research consulting agreement with Thomson Reuters, which is the parent company of Reuters Health.

Dr. Gerald V. Naccarelli of Pennsylvania State University in Hershey and colleagues from Thomson Reuters and Sanofi-Aventis looked at claims data from July 2004 to December 2005 on nearly 22 million people 20 and older.

Around 1 percent of these individuals had atrial fibrillation, translating into about 3 million people in the US, Naccarelli and his team found.

People with atrial fibrillation were more likely to have high blood pressure and coronary artery disease than people who didn't have the abnormal heart rhythm, the researchers found; their risk of congestive heart failure was more than four times greater, while they were about three times more likely to have had a stroke.

By 2025, the researchers estimate, about 5 million people in the US will have atrial fibrillation. They predict that number will reach 7.6 million by 2050.

In a 2001 study based on data from 1996-1997, Naccarelli and his team note, another team of researchers came up with lower estimates for the prevalence of atrial fibrillation: around 2.4 million in 2005, 3.8 million in 2035, and 5.6 million in 2050.

The researchers suggest that the current study may be more accurate because atrial fibrillation prevalence could have risen more since the late 1990s than would have been expected based on aging and population growth alone.

SOURCE: American Journal of Cardiology, December 2009.

Medicine