Atrial Fibrillation
AF is the most common type of serious arrhythmia. It’s a very fast and irregular contraction of the atria. AF occurs when the heart’s electrical signal begins in a different part of the atrium than the sinoatrial (SA) node or when the signal is conducted abnormally. When this happens, the electrical signal doesn’t travel through the normal pathways in the atria, but instead may spread throughout the atria in a fast and disorganized manner. This causes the walls of the atria to quiver very fast (fibrillate) instead of beating normally. As a result, the atria aren’t able to pump blood into the ventricles the way they should.
The animation below shows atrial fibrillation. Click the "start" button to play the animation. Written and spoken explanations are provided with each frame. Use the buttons in the lower right corner to pause, restart, or replay the animation, or use the scroll bar below the buttons to move through the frames.
The animation shows how the heart’s electrical signal begins in a different place in the heart, causing the atria to beat very fast and irregularly.
In AF, electrical signals can travel through the atria at a rate of more than 300 per minute. Some of these abnormal electrical signals can travel to the ventricles, causing them to beat too fast and with an irregular rhythm. AF is not usually life threatening, although it can be dangerous when it causes the ventricles to beat very fast.
The two most serious complications of chronic (long-term) AF are stroke and heart failure. Stroke can happen when a blood clot travels to an artery in the brain, blocking off blood flow. In AF, blood clots can form in the atria because some of the blood “pools” in the fibrillating atria instead of flowing into the ventricles. If a piece of a blood clot in the left atrium breaks off, it can travel to the brain, causing a stroke. People with AF are often treated with blood-thinning medicines to reduce the chances of developing blood clots.
Heart failure is when the heart can’t pump enough blood to meet the needs of the body. AF can cause heart failure when the ventricles beat too fast and don’t have enough time to fill with blood to pump out to the body. Heart failure causes tiredness, leg swelling, and shortness of breath.
AF and other supraventricular arrhythmias can occur for no apparent reason. Most of the time, however, they are caused by an underlying condition that damages the heart muscle and its ability to conduct electrical impulses. These conditions include high blood pressure (hypertension), coronary artery disease, heart failure, or rheumatic heart disease.
Other conditions also can lead to AF, including overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. AF also becomes more common as people get older.
Elements of this page courtesy of: National Heart & Lung Institute