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The heart is a muscle that functions as a double-sided pump and consists of four chambers. The two upper chambers are called the left and the right atria and the two lower chambers called the right and left ventricles. The right side of the heart pumps blood to the lungs to pick up oxygen, while the left side of the heart pumps blood rich in oxygen to all parts of the body. The left ventricle has to pump in a strong and effective manner to pump the blood to the farthest parts of the body.

The pumping of the heart is regulated by electrical current that originates in the right atrium at the sinoatrial node (SA node) and then travels to both the left atrium and the atrioventricular node (AV node) which coordinates the pumping of the ventricles. This is called normal sinus rhythm (NSR).

Atrial fibrillation (AF) is characterized by an irregular and rapid beating of the heart's atrial chambers and results when the normal electrical conduction system of the atria is not functioning properly. In atrial fibrillation, there is a storm of electrical activity across both atria causing them to fibrillate (quiver) 300-600 times per minute.

Only a small number of these electrical impulses are picked up by the ventricles, but the ventricular rate can approach 180 or higher. Whether at high or low heart rates, the irregular rhythm renders the ventricle unable to pump efficiently. This leads to pooling of the blood within the heart and insufficient amounts of blood being supplied to the body. This can result in a variety of symptoms and problems.

It has been estimated that atrial fibrillation occurs in about 4% of the general adult population and affects approximately 2.2 million people in the United States. About 160,000 new cases of atrial fibrillation are diagnosed each year. Atrial fibrillation occurs about 1.5 times more frequently in males than in females. It is estimated that atrial fibrillation is responsible for over 60,000 strokes each year in the United States.

The prevalence of atrial fibrillation increases with advancing age:

• 2-5% of persons aged 60-69
• 5-14% of persons aged 70-79
• 9-13% of persons aged 80-89
• 22% of persons aged 91 and older