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Reviewed by the Faculty of Harvard Medical School

Atrial Fibrillation

What Is It?

Atrial fibrillation is a type of cardiac arrhythmia, which is an abnormal heart rate or rhythm. Atrial fibrillation causes a rapid and irregular heartbeat, during which the upper two chambers of the heart that receive blood (the atria) quiver or "fibrillate" instead of beating normally.

During a normal heartbeat, the electrical impulses that cause the atria to contract come from a small area of the right atrium called the sinus node. During atrial fibrillation, however, these impulses come from all over the atria, triggering 300 to 500 contractions per minute in the heart's upper chambers. Normally, the atrioventricular node would receive these impulses and send them to the lower two chambers of the heart that do the pumping (the ventricles). During atrial fibrillation, however, the atrioventricular node becomes overwhelmed by all of the impulses it receives from the atria, and only lets a minority of the electrical impulses through to reach the ventricles. Still, there are so many impulses bombarding the atrioventricular node that the result is an irregular and rapid heartbeat, 80 to 160 beats per minute. A normal heartbeat is 60 to 100 beats per minute.

The rapid and irregular heartbeat caused by atrial fibrillation cannot pump blood out of the heart efficiently. As a result, some people get short of breath and even faint when they first go into atrial fibrillation. A serious longer-term problem is that, because the walls of the atria are quivering instead of contracting, blood tends to pool along those walls, allowing formation of blood clots. These blood clots can travel from the heart into the bloodstream and circulate through the body. Ultimately, they may become lodged in an artery, causing pulmonary embolism, stroke and other disorders.

The major factors that increase the risk of atrial fibrillation are:

  • Age
  • Coronary artery disease
  • Rheumatic heart disease (caused by rheumatic fever)
  • High blood pressure (hypertension)
  • Diabetes
  • An excess of thyroid hormones (thyrotoxicosis)

In many people, the cause of atrial fibrillation is more serious than the arrhythmia itself.

Symptoms

Atrial fibrillation often doesn't cause any symptoms. When symptoms occur, they can include:

  • Palpitations (awareness of a rapid heartbeat)
  • Fainting
  • Dizziness
  • Weakness
  • Shortness of breath
  • Chest pain caused by a reduced blood supply to the heart muscle (angina pectoris)
Some people with atrial fibrillation have periods of completely normal heartbeats. Diagnosis

Your doctor will ask about your family history of cardiovascular disorders and will review your personal medical history, including any possible risk factors for atrial fibrillation. Your doctor also will ask you to describe your specific heart symptoms, including any possible triggers for your palpitations, dizziness or shortness of breath.

Your doctor will examine you and will check your heart rate and rhythm, and your pulse. In atrial fibrillation, the pulse often doesn't match the heart sounds that your doctor hears through a stethoscope.

The diagnosis of atrial fibrillation usually can be confirmed with an electrocardiogram (EKG). However, because atrial fibrillation tends to come and go, a regular EKG may be normal. If this is the case, a test called ambulatory electrocardiography may be done. During this test, the patient wears a portable EKG machine called a Holter monitor, usually for 24 hours. If the frequency of your symptoms is less common, your doctor may use an "event recorder," which can be worn by you for several days or even weeks in an attempt to capture your heart rhythm at the time you feel an irregular beat.

Expected Duration

How long atrial fibrillation lasts depends on the cause. For example, if atrial fibrillation is caused by a disease such as coronary heart disease, rheumatic heart disease, hypertension or thyrotoxicosis, the abnormal rhythm may go away when the disease is treated. However, atrial fibrillation that has no known cause, or that results from a long-standing cardiac disorder, is often a lifelong condition.

Prevention

Atrial fibrillation resulting from coronary artery disease can be prevented by taking these actions to modify your risk factors:
  • Eat a low-fat diet.
  • Control cholesterol and high blood pressure.
  • Quit smoking.
  • Do not drink more than two alcoholic drinks per day.
  • Control your weight.
  • Get regular exercise.

Some causes of atrial fibrillation cannot be prevented.

Treatment

Treatment depends on the cause. If the cause is coronary artery disease, treatment may consist of lifestyle changes, medications that treat high blood cholesterol and high blood pressure and/or procedures, such as angioplasty and coronary artery bypass surgery. Atrial fibrillation caused by thyrotoxicosis can be treated with medication or surgery. Atrial fibrillation caused by rheumatic heart disease may be treated by surgery to replace damaged heart valves.

The irregular heartbeat can be treated with medications, such as beta blockers (atenolol, metoprolol) diltiazem hydrochloride (Cardizem), digoxin (Lanoxin) or verapamil (Tarka), which slow the heart rate. In addition, people with atrial fibrillation often are given medications to prevent blood clots that can lead to stroke, pulmonary embolism and other complications. This usually includes anticoagulant medications (blood thinners), such as aspirin and warfarin (Coumadin).

Another treatment option is electrical cardioversion, a procedure that delivers an electrical shock to the heart to restore normal heart rhythm. Although this procedure works in most cases, between 50% and 75% of patients eventually develop atrial fibrillation again. Drugs such as amiodarone (Cordarone), procainamide (Procan SR, Promine, Pronestyl) or quinidine (Cardioquin, Quinaglute Dura-tabs, Quinidex Extentabs, Quin-Release) may be given to try to prevent atrial fibrillation from returning.

Research studies in the last few years indication that "conversion" of patients from atrial fibrillation back into a normal rhythm using drugs and/or electrical shocks does not prolong lives. Therefore, a reasonable approach to patients with atrial fibrilation due to a non-curable cause is to put them indefinitely on a blood thinning medication to prevent blood clots, as long as they are not having symptoms from their atrial fibrillation. If they are having symptoms even with medications to control their heart rate, then "cardioversion" back to sinus rhythm is worth trying.

When medications are not successful in controlling a patient's symptoms or heart rate, a procedure called catheter radiofrequency ablation sometimes can be done. In this procedure, an area of tissue in the atrioventricular node is destroyed to prevent excess electrical impulses from moving from the atria to the ventricles. The procedure often completely blocks all electrical impulses. A pacemaker is then implanted to control heart rate and rhythm. Another surgical procedure involves producing scars in the upper chambers of the heart to reduce the ability of abnormal electrical activity to spread and cause atrial fibrillation.

When To Call A Professional

Call your doctor if you have any of the symptoms of atrial fibrillation, including palpitations, faintness, dizziness, weakness, shortness of breath or chest pain.

Prognosis

When a cause of atrial fibrillation is identified and treated, the arrhythmia often goes away. Atrial fibrillation is less likely to go away in people who have long-standing rheumatic heart disease or any condition in which the atria are enlarged. When atrial fibrillation does not go away or returns frequently, the risk of a stroke or other complication can be reduced by using anticoagulant medications.

Additional Info

American Heart Association (AHA)
7272 Greenville Ave.
Dallas, TX 75231
Toll-Free: 800-242-8721
http://www.americanheart.org/

National Heart, Lung and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: 301-592-8573
TTY: 240-629-3255
Fax: 301-592-8563
E-Mail: NHLBIinfo@rover.nhlbi.nih.gov
http://www.nhlbi.nih.gov/

American College of Cardiology
Heart House
9111 Old Georgetown Road
Bethesda, MD 20814-1699
Phone: 301-897-5400
Toll-Free: 800-253-4636, ext. 694
Fax: 301-897-9745
E-Mail: resource@acc.org
http://www.acc.org/

Last updated November 22, 2008



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