Atrial fibrillation

What Is Atrial Fibrillation?

Atrial fibrillation (A-tre-al fi-bri-LA-shun), or AF, is the most common type of arrhythmia (ah-RITH-me-ah). An arrhythmia is a problem with the rate or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm.

AF occurs when rapid, disorganized electrical signals cause the atria (AY-tree-uh), the two upper chambers of the heart, to fibrillate. The term "fibrillate" means to contract very fast and irregularly.

In AF, blood pools in the atria and isn't pumped completely into the ventricles (VEN-trih-kuls), the heart's two lower chambers. As a result, the heart's upper and lower chambers don't work together as they should. Most of the time, AF results in symptoms of rapid heart beat, or palpitations. Other symptoms include sweating, dizziness, shortness of breath, especially with activity, fatigue, chest pain or fainting. Pooling of blood in the atria can result in clots forming. If blood clots forming in the heart exit into the bloodstream and travel to the brain, blocking a blood vessel in the brain, a stroke can result.

Often, people who have AF may not feel symptoms. However, even when not noticed, AF can increase the risk of stroke. In some people, AF can cause chest pain or heart failure, particularly when the heart rhythm is very rapid.

AF may occur rarely or every now and then, or it may become a persistent or permanent heart rhythm lasting for years.

The animation below shows atrial fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.

The animation shows how the heart's electrical signal begins in a place other than the sinoatrial node, causing the atria to beat very fast and irregularly.

Understanding the Electrical Problem in Atrial Fibrillation

In AF, the heart's electrical signals don't begin in the SA node. Instead, they begin in another part of the atria or in the nearby pulmonary veins. The signals don't travel normally, and they may spread throughout the atria in a rapid, disorganized way. This can cause the atria to fibrillate.

The abnormal electrical signals flood the AV node with electrical impulses. As a result, the ventricles also begin to beat very fast. However, the AV node can't conduct the signals to the ventricles as fast as they arrive. So, even though the ventricles may be beating faster than normal, they aren't beating as fast as the atria. The ventricles are generally beating irregularly in atrial fibrillation.

Thus, the atria and ventricles no longer beat in a coordinated way. This creates a fast and irregular heart rhythm. In AF, the ventricles may beat 100 to 175 times a minute, in contrast to the normal rate of 60 to 100 beats a minute.

When this happens, blood isn't pumped into the ventricles as well as it should be. Also, the amount of blood pumped out of the ventricles to the body is based on the randomness of the atrial beats.

The body may get rapid, small amounts of blood and occasional larger amounts of blood. The amount will depend on how much blood has flowed from the atria to the ventricles with each beat.

Most of the symptoms of AF are related to how fast the heart is beating. If medicines or age slow the heart rate, the symptoms are minimized.

AF may be brief, with symptoms that come and go and end on their own. Or, the condition may be persistent and require treatment. Sometimes AF is permanent, and medicines or other treatments can't restore a normal heart rhythm.

How Is Atrial Fibrillation Treated?

Treatment for atrial fibrillation (AF) depends on how severe or frequent the symptoms are and whether you already have heart disease. General treatment options include medicines, medical procedures, and lifestyle changes.

The goals of treating AF include:

  • Preventing blood clots from forming, thereby reducing the risk of stroke.
  • Controlling how many times a minute the ventricles contract. This is called rate control. Rate control is important because it allows the ventricles enough time to completely fill with blood. With this approach, the irregular heart rhythm continues, but the person feels better and has fewer symptoms.
  • Restoring a normal heart rhythm. This is called rhythm control. Rhythm control allows the atria and ventricles to work together to efficiently pump blood to the body.
  • Treating any underlying disorder that's causing or raising the risk of AF—for example, hyperthyroidism (too much thyroid hormone).


Cardioversion - Electrical cardioversion is a procedure used to restore a fast or irregular heartbeat to a normal rhythm. For the procedure, low-energy shocks are given to your heart to trigger a normal rhythm. You're temporarily put to sleep before the shocks are given.

Catheter Ablation - Catheter ablation may be used to restore a normal heart rhythm when medicines or electrical cardioversion don't work. During this procedure, a wire is inserted through a vein in the leg or arm and threaded to the heart. Radiofrequency energy is sent through the wire to destroy abnormal tissue that may be disrupting the normal flow of electrical signals. Dr. Gallik does this procedure in a hospital.

Pacemakers - A pacemaker is a small device that's placed in the chest or abdomen to help control abnormal heart rhythms. If the lower chamber of the heart is beating too slow in atrial fibrillation, this device uses electrical pulses to prompt the heart to beat at a normal rate. A pacemaker will not alter the upper chamber rhythm of atrial fibrillation, however.

Information provided by National Heart, Lung and Blood Institute

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