Reviewed by Pedro R. Guevara, MDAtrial fibrillation or flutter is a type of arrhythmia affecting the two upper chambers of the heart. Unlike ventricular fibrillation, which can lead to a heart attack, it usually is not life threatening. However, an attack lasting longer than a few minutes can lead to heart failure, and people with atrial fibrillation are five times more likely to have a stroke than people without it. Approximately 2 million people in the United States experience atrial fibrillation. It is most common in elderly people, but can occur in people of any age.
The heart has four chambers, two upper (atria) and two lower (ventricles). The atria and ventricles work as a team. When the heart beats, blood flows from the atria to the ventricles. From the ventricles it flows to the lungs and the rest of the body, picking up oxygen from the lungs and carrying oxygen and nutrients to be delivered to the body’s organs and tissues.
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Atrial fibrillation occurs when the top two chambers beat abnormally fast; ventricular fibrillation occurs when the bottom two chambers beat abnormally fast. Normally, the heart beats at a rate of about 60-80 beats per minute. During fibrillation, however, the atria beat at a rate of 300-600 beats per minute. Atrial flutter is slightly different. Fluttering atria beat at a more regular rate of 300 beats or less.
When the atria speed up, the ventricles can compensate to a degree, increasing to 120-180 contractions per minute. But because the atria are still beating so much faster, the heart rate becomes irregular. When the atria and ventricles are not working together, the heart cannot pump out as much blood as it needs. Because the ventricles are still functioning, however, and transporting blood to the rest of the body, atrial fibrillation is not as dangerous as ventricular fibrillation.
Short bouts of AF are not necessarily dangerous. Danger increases if the attack lasts longer than a few minutes. Fibrillation can cause a blood clot to form in either atrium and travel to the brain, which can cause stroke. If the attack is prolonged and the ventricles cannot keep up with the atria, heart failure can occur.
Causes
Atrial fibrillation can be caused by lung disease, heart disease, thyroid disease or high blood pressure. Other causes also include: a malfunctioning of the sinus node, which normally regulates electrical impulses to the heart; binge alcohol intake, recreational drugs, stress, caffeine or high fever.
Last updated: Aug-14-07
