Atrial fibrillation is an irregular and often rapid heart rate that occurs when the two upper chambers of your heart (atria) experience chaotic electrical signals.
Your heart consists of four chambers â two upper chambers (atria) and two lower chambers (ventricles). Within the upper right chamber of your heart (right atrium) is a group of cells called the sinus node. This is your heart's natural pacemaker. The sinus node produces the impulse that normally starts each heartbeat.
Normally, the impulse travels first through the atria and then through a connecting pathway between the upper and lower chambers of your heart called the atrioventricular (AV) node. As the signal passes from the sinus node through the atria, they contract, pumping blood from your atria into the ventricles below. As the signal passes through the AV node to the ventricles, it signals the ventricles to contract, pumping blood out to your body.
In atrial fibrillation, the upper chambers of your heart (atria) experience chaotic electrical signals. As a result, they quiver. The AV node â the electrical connection between the atria and the ventricles â is bombarded with impulses trying to get through to the ventricles.
The ventricles also beat rapidly, but not as rapidly as the atria, as not all the impulses get through. The reason is that the AV node is like a highway on-ramp â only so many vehicles can get on at one time.
The result is a fast and irregular heart rhythm. The heart rate in atrial fibrillation may range from 100 to 175 beats a minute. The normal range for a heart rate is 60 to 100 beats a minute.
Possible causes of atrial fibrillation
Abnormalities or damage to the heart's structure are the most common cause of atrial fibrillation. Possible causes of atrial fibrillation include:
- High blood pressure
- Heart attacks
- Coronary artery disease
- Abnormal heart valves
- Heart defects you're born with (congenital)
- An overactive thyroid gland or other metabolic imbalance
- Exposure to stimulants, such as medications, caffeine, tobacco or alcohol
- Sick sinus syndrome â improper functioning of the heart's natural pacemaker
- Lung diseases
- Previous heart surgery
- Viral infections
- Stress due to pneumonia, surgery or other illnesses
- Sleep apnea
However, some people who have atrial fibrillation don't have any heart defects or damage, a condition called lone atrial fibrillation. In lone atrial fibrillation, the cause is often unclear, and serious complications are rare.
Atrial flutter is similar to atrial fibrillation, but the rhythm in your atria is more organized and less chaotic than the abnormal patterns common with atrial fibrillation. Sometimes you may have atrial flutter that develops into atrial fibrillation and vice versa.
The risk factors for and the symptoms and causes of atrial flutter are similar to those of atrial fibrillation. For example, strokes are also a concern in someone with atrial flutter. As with atrial fibrillation, atrial flutter is usually not life-threatening when it's properly treated.