FACTBOX: Cheney has recurrence of atrial fibrillation

(Reuters) - U.S. Vice President Dick Cheney on Wednesday experienced another bout of atrial fibrillation, an irregular heartbeat in the upper chambers of the heart that raises the risk of stroke. Following are some facts about atrial fibrillation.

* Atrial fibrillation is the most common form of irregular heartbeat, affecting 2.2 million Americans, according to the American Heart Association. It becomes more common with age. Three to 5 percent of people over 65 have this condition.

* Atrial fibrillation can be caused by an underlying heart problem, including hypertension, coronary artery disease and a prior heart attack. It occurs when an electrical disturbance causes the heart's two small upper chambers to beat so quickly that they quiver. This makes them less effective at pumping blood out of the heart, leaving blood to pool and clot and raising the risk of a stroke.

* Atrial fibrillation causes about 15 percent of strokes in the United States, the American Heart Association said.

* Drugs can slow the rapid heart rate associated with atrial fibrillation and blood thinners can reduce the clotting risk.

* An electrical shock is sometimes used to reset the heart to a normal rhythm. Doctors can also use a procedure called radiofrequency ablation in which a surgeon applies radiofrequency energy to destroy tissue that is causing the electrical disturbance. Atrial pacemakers are sometimes used to treat atrial fibrillation.

Sources: American Heart Association, Mayo Clinic

(Reporting by Julie Steenhuysen, editing by Will Dunham)