Atrial fibrillation (AF or afib) is the most common cardiac arrhythmia (abnormal heart rhythm) and involves the two upper chambers (atria) of the heart. Its name comes from the fibrillating (i.e. quivering) of the heart muscles of the atria, instead of a coordinated contraction. It can often be identified by taking a pulse and observing that the heartbeats don't occur at regular intervals. However, a conclusive indication of AF is the absence of P waves on an electrocardiogram (ECG), which are normally present when there is a coordinated atrial contraction at the beginning of each heart beat. Risk increases with age, with 8% of people over 80 having AF.

In AF, the normal electrical impulses that are generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles that generate the heartbeat. The result is an irregular heartbeat which may occur in episodes lasting from minutes to weeks, or it could occur all the time for years. The natural tendency of AF is to become a chronic condition. Chronic AF leads to a small increase in the risk of death.

Atrial fibrillation is often asymptomatic, and is not in itself generally life-threatening, but may result in palpitations, fainting, chest pain, or congestive heart failure. People with AF usually have a significantly increased risk of stroke (up to 7 times that of the general population). Stroke risk increases during AF because blood may pool and form clots in the poorly contracting atria and especially in the left atrial appendage (LAA). The level of increased risk of stroke depends on the number of additional risk factors. If a person with AF has none, the risk of stroke is similar to that of the general population. However, many people with AF do have additional risk factors and AF is a leading cause of stroke.

Atrial fibrillation may be treated with medications which either slow the heart rate or revert the heart rhythm back to normal. Synchronized electrical cardioversion may also be used to convert AF to a normal heart rhythm. Surgical and catheter-based therapies may also be used to prevent recurrence of AF in certain individuals. People with AF are often given anticoagulants such as warfarin to protect them from stroke.

For more information about Atrial fibrillation, read the full article at Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.