Atrial fibrillation (AF or Afib) is an abnormal heart rhythm. The four chambers of the heart usually beat in a steady, rhythmic pattern. Atrial fibrillation means that the atria (upper chambers of the heart) are fibrillating or twitching quickly and creating an irregular rhythm.
The normal heart rate for an adult is between 60 and 100 beats every minute. When the heart is in AF, the atria can beat over 300 times every minute.
The electrical system of the heart is the power source that makes the heartbeat. Electrical impulse travel along a pathway in the heart and make the atria and ventricles work together to pump blood through the heart.
A normal heartbeat begins as a single electrical impulse that comes from the SA node, a small bundle of tissue located in the right atrium. The impulse sends out an electrical pulse that causes both atria to contract (tighten) and move blood into the lower ventricles. The electrical current then passes through a small bundle of tissue called the AV node (the electrical bridge between the upper and lower chambers of the heart), causing the ventricles to squeeze and release in a steady, rhythmic sequence. As the chambers squeeze and release they draw blood into the heart and push it back out to the rest of the body. This is what causes the pulse we feel on our wrist or neck.
AF occurs when the electrical impulse does not follow this order. Instead of one impulse moving through the heart, many impulses begin in the atria and fight to get through the AV node. There are two main factors that allow this abnormal electrical rhythm to occur and continue. First, the structure of the heart chambers and the electrical pathway through the heart may change. This happens more often as we get older. Second, as the electrical pathways change, one or more “triggers” may develop. “triggers” are electrical circuits that send extra impulses at a faster than usual rate. These extra impulses are all trying to get through the AV node and the atria begin to fibrillate, or twitch, in a fast and disorganized way.