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Atrial fibrillation (A-fib or AF) is the most common type of sustained cardiac arrhythmia. It occurs when there are too many electrical signals that normally control the heartbeat, causing the upper chambers of the heart (the atria) to beat extremely rapidly (more than 400 beats per minute) and quiver (fibrillate). This is felt as an always irregular, sometimes rapid heartbeat.
What happens during atrial fibrillation?
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A normal heartbeat begins with an electrical impulse from the sinus node, a single point in the heart's right atrium (upper chamber). During atrial fibrillation, electrical impulses fire rapidly from multiple sites in both atria, triggering 400 or more atrial contractions per minute.
The ventricles (lower chambers), overwhelmed with so many impulses from the atria, don't have time to fill and pump as they should, beating 80 to 160 times per minute in an irregular, rapid and inefficient heartbeat. Blood tends to pool in the upper chambers of the heart, increasing the risk of blood clot formation within the heart.
Blood clots can travel from the heart into the bloodstream and into the brain, resulting in a stroke.
An arrhythmia centered in the upper chambers of the heart is called a supraventricular tachycardia (SVT) — literally, "fast heartbeat above the ventricle." Atrial fibrillation is the most common type of SVT, affecting more than 3 million people in the United States alone. Atrial fibrillation is most common in people over the age of 50, especially white men, and in those who have other types of heart disease. Sometimes atrial fibrillation occurs in young, otherwise healthy individuals.
Watch a Johns Hopkins health seminar on atrial fibrillation.
What are the symptoms of atrial fibrillation?
Atrial fibrillation may cause no symptoms at all, or it may cause any of the following:
Some people have atrial fibrillation between periods of completely normal heartbeats (intermittent or paroxysmal AF). Others are in atrial fibrillation for seven days or longer (persistent AF).
What causes atrial fibrillation?
For many people, the underlying cause of atrial fibrillation is more serious than the arrhythmia itself. The major causes are:
Age: more common over 50
Gender: more common in men
Race: more common in Caucasians
Coronary heart disease (coronary artery disease)
Rheumatic heart disease (caused by rheumatic fever)
Hypertension (high blood pressure)
Thyrotoxicosis (an excess of thyroid hormones)
Certain other arrhythmias — atrial flutter and atrial tachycardia — may later develop into atrial fibrillation if not treated.
How is atrial fibrillation diagnosed?
Your doctor may suspect that you have atrial fibrillation based on your medical history and symptoms. The doctor will check your heart rate and rhythm, together with your pulses. In atrial fibrillation the pulse, which reflects the activity of the ventricles, is often mismatched with the heart sounds because not all of the atrial beats are reaching the ventricles.
The diagnosis of atrial fibrillation can usually be confirmed with an electrocardiogram (ECG or EKG). However, because atrial fibrillation tends to come and go, an office ECG may be normal. If this is the case, your doctor may give you an ECG monitor to wear at home that will record your heart rhythm over time. These include:
Holter Monitor — a portable ECG you wear continuously for one to seven days to record your heart rhythms over time
Event Monitor — a portable ECG you wear for one or two months, which records only when triggered by an abnormal heart rhythm or when you manually activate it
Implantable Monitor — a tiny event monitor inserted under your skin, worn for several years to record events that only seldom take place.
How is atrial fibrillation treated?
Some people with atrial fibrillation will return to normal rhythm without treatment. Otherwise, the first focus of treatment is to find and treat the underlying cause. If the cause is thyrotoxicosis, treatment may consist of medications or surgery. For most patients no specific reversible cause can be identified.
Doctors may approach the treatment of atrial fibrillation using various strategies:
Medications to prevent blood clots, called anticoagulants or blood thinners. The most important risk of atrial fibrillation is the development of a stroke, which can be lethal. Atrial fibrillation increases the risk of stroke fivefold. Many patients with atrial fibrillation, especially those over the age of 65, require lifelong anticoagulation to prevent strokes and prolong life.
Catheter ablation, to address the most common trigger for atrial fibrillation: cells in the pulmonary veins that produce their own electrical signal. This type of ablation creates a ring of scar tissue where the veins enter the heart, blocking electrical signals from the veins.
Maze procedure, in which heart muscle is cut in strategic places to create a "maze" of scar tissue that prevents electrical signals from passing through. Learn more about the minimally invasive maze procedure at Johns Hopkins, also known as minimally invasive radiofrequency ablation.
Cardioversion, in which the heart is carefully shocked into rhythm while the person is under anesthesia. Although this procedure is effective in restoring normal sinus rhythm, it does not prevent further recurrences of atrial fibrillation. Therefore, it is generally combined with antiarrhythmic drug therapy or catheter ablation. Learn more about cardioversion at Johns Hopkins.
Learn more about arrhythmias or visit the Johns Hopkins Electrophysiology and Arrhythmia Service.