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Causes
By Mayo Clinic staff
Your heart consists of four chambers — 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 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 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, the ventricles 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 — the electrical connection between the atria and the ventricles — is overloaded with impulses trying to get through to the ventricles. The ventricles also beat rapidly, but not as rapidly as the atria. The reason is that the AV node is like a highway on-ramp — only so many cars 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
- 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 or tobacco, or to alcohol
- Sick sinus syndrome — improper functioning of the heart's natural pacemaker
- Emphysema or other 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
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 symptoms, causes and risk factors of atrial flutter are similar to those of atrial fibrillation. For example, strokes are a concern in someone with atrial flutter. As with atrial fibrillation, atrial flutter is usually not life-threatening when it's properly treated.
- Atrial fibrillation and flutter. Heart Rhythm Society. http://www.hrspatients.org/patients/heart_disorders/atrial_fibrillation/default.asp. Accessed Dec. 8, 2010.
- Atrial fibrillation. National Heart Lung and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/af/af_all.html. Accessed Dec. 8, 2010.
- Thomas MC, et al. Blood pressure control and the risk of incident atrial fibrillation. American Journal of Hypertension. 2008;21:1111.
- ACC/AHA/ESC Writing Committee members. 2006 guidelines for the management of patients with atrial fibrillation. Europace. 2006;8:651.
- Singer DE, et al. Antithrombotic therapy in atrial fibrillation: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008;133:546S.
- Connolly S, et al. Dabigatran versus warfarin in patients with atrial fibrillation. New England Journal of Medicine. 2009;361:1139.
- FDA approves Pradaxa to prevent stroke in people with atrial fibrillation. U.S. Food and Drug Administration. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm230241.htm. Accessed Dec. 8, 2010.
- Cardioversion. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/crv/crv_all.html. Accessed Dec. 8, 2010.
- Catheter ablation. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/health/dci/Diseases/ablation/ablation_all.html. Accessed Dec. 8, 2010.
- Cheng J, et al. Surgical approaches to prevent recurrent atrial fibrillation. http://www.uptodate.com/index. Accessed Dec. 8, 2010.
- Maze procedure for treatment of atrial fibrillation. University of Southern California Keck School of Medicine. http://www.cts.usc.edu/mazeprocedure.html. Accessed Dec. 1, 2010.
- Arrhythmia medications. American Heart Association. http://americanheart.org/presenter.jhtml?identifier=18. Accessed Nov. 30, 2010.
- Wann LS, et al. 2011 ACCF/AHA/HRS focused update on the management of patients with atrial fibrillation (updating the 2006 guideline): A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation. 2010; In press. Accessed Dec. 20, 2010.
- FDA approves Xarelto to prevent stroke in people with common type of abnormal heart rhythm. U.S. Food and Drug Administration. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm278646.htm. Accessed Dec. 1, 2011.
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