Atrial fibrillation

Atrial fibrillation is a type of cardiac arrhythmia, which is an irregular heart rate or rhythm. It occurs when the heart’s electrical signals lose their regular pattern, resulting in an irregular and often rapid heart rate. The heart can still pump blood, but less efficiently. An estimated two million Americans are living with atrial fibrillation.

How the heart works

The heart is a pump divided into four chambers – two atria on the top and two ventricles on the bottom. Normally, each heartbeat starts in the right atrium, where your heart’s natural pacemaker is located. This “pacemaker,” called the sinus node, sends an electrical signal throughout the heart, causing it to contract. First the atria contract, pumping blood into the ventricles. A fraction of a second later, the ventricles contract, sending blood throughout the body. Thus, the heart functions like side-by-side two stage pumps. The ventricles are the powerhouse and do the majority of the work. 

In atrial fibrillation, the electrical signals lose their regular pattern. The atria start putting out uncoordinated signals. They pump too fast and unevenly, and won’t contract fully. The ventricles also beat rapidly, though not as fast as the atria. A normal heart rate is 60 to 100 beats per minute. In atrial fibrillation, the heart rate may range from 100 to 160 beats per minute.

There are three forms of atrial fibrillation: paroxysmal, persistent and permanent. In paroxysmal atrial fibrillation, symptoms may come and go. They may last for a few minutes or a few hours, then stop on their own. In persistent fibrillation, symptoms don’t stop until they are treated with medication or electrical cardioversion. Patients with permanent fibrillation always have a heart rhythm that has become atrial fibrillation.

Diagnosing atrial fibrillation

To make a diagnosis of atrial fibrillation, your doctor may conduct an electrocardiogram, echocardiogram, blood tests or Holter monitoring. See the test section for more information.

Atrial fibrillation fact sheet (pdf)