DEAR MAYO CLINIC:

What is atrial fibrillation? What causes it, and what are the treatment options for those who have it?

ANSWER:

Atrial fibrillation is an irregular heart rhythm that involves the upper heart chambers (atria). During an episode of atrial fibrillation, the atria beat out of rhythm very quickly, up to 400 beats per minute. Fortunately, this rapid rate is slowed to about 70 to 150 beats per minute as the impulse travels to the lower chambers, the ventricles, which then pump blood to the body. The episode may last minutes to several days and individuals with atrial fibrillation should seek medical care promptly.

In many cases, the condition is caused by the presence of abnormal cells in the heart that produce extra heartbeats and trigger the irregular rhythm. Also, factors such as high blood pressure, diabetes and obesity can increase the risk of atrial fibrillation. Treatment usually involves a combination of lifestyle changes, medication and, in some cases, surgery or catheter ablation.

Most people who have atrial fibrillation are predisposed to it due to abnormal heart cells -- which may be present from birth -- located in the left atrium where the pulmonary veins, which drain blood from the lungs, join the heart. These abnormal cells can create spontaneous electrical activity that can cause extra beats (premature atrial beats) and throw the heart into atrial fibrillation.

Not everyone who has the abnormal heart cells experiences atrial fibrillation, however. Although it's not clear why some of those cells create electrical activity and others don't, a variety of factors appear to make cell activity more likely. For example, stimulants or other substances that increase adrenalin -- including caffeine, alcohol, diet pills and smoking -- can irritate the heart and make the extra cells fire more frequently. In addition, when the atria enlarge -- as can happen in a person who has high blood pressure -- the risk of atrial fibrillation rises. A leaking heart valve, diabetes and an overactive thyroid gland (hyperthyroidism) can also cause atrial fibrillation. About 5 percent of the time, no cause can be identified.

Atrial fibrillation typically does not lead to a heart attack, but it is a significant risk factor for stroke. In about 30 percent of new stroke patients seen in hospital emergency departments, atrial fibrillation caused the stroke.

People with atrial fibrillation have an increased risk of stroke because during an episode of atrial fibrillation, blood cannot easily flow through the atria. Instead, the blood pools, particularly in the left atrial appendage -- a small structure located off the left atrium -- creating an ideal environment for blood clot formation. Approximately 90 percent of blood clots that form due to atrial fibrillation start in the left atrial appendage. A clot that breaks loose and travels in the bloodstream to the brain can cause a stroke.

The first goal of treatment for atrial fibrillation is to decrease the risk of stroke

For some, that risk can be adequately reduced by taking aspirin as an anti-clotting agent and by decreasing episodes of atrial fibrillation through lifestyle changes. These changes may include reducing caffeine and alcohol intake, losing weight, quitting smoking, and controlling high blood pressure, diabetes or other medical conditions that can lead to atrial fibrillation. If the stroke risk is significant, a stronger blood thinning medication, such as warfarin, may be necessary.

For people who can't take blood thinners because of another medical condition, or for those who have a stroke despite using warfarin, another option to reduce stroke risk is a surgical procedure that blocks off or removes the left atrial appendage. With this procedure, blood clots can no longer form there.

The second goal of treatment is to restore and maintain normal heart rhythm

Lifestyle changes that decrease or eliminate atrial fibrillation risk factors can effectively reduce atrial fibrillation in some people. For those who continue to experience atrial fibrillation frequently or have bothersome symptoms, such as shortness of breath, weakness or fatigue, medications to maintain a normal heart rate may be helpful.

If medication doesn't effectively control atrial fibrillation, a procedure known as radiofrequency catheter ablation may be necessary. During this procedure, radiofrequency energy is directed through a catheter inserted in a vein and placed in the left atrium to destroy the abnormal heart cells that cause premature atrial beats, which can lead to atrial fibrillation.

When reviewing treatment options, keep in mind that atrial fibrillation affects people differently. Some have significant symptoms and are fearful of engaging in exercise or other activity, lest they trigger an atrial fibrillation episode. Others experience infrequent bouts of atrial fibrillation and are not bothered by symptoms. In all patients, the risk of stroke needs to be assessed and reduced to an acceptable level. Once that's done, the overall aim of treatment should be to maintain a comfortable quality of life. -- Stephen Hammill, M.D., Cardiovascular Diseases, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

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