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What is Atrial Fibrillation?

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Atrial fibrillation is a problem with the heart's rhythm, also known as an arrhythmia.

Arrhythmias occur when there is a problem with the heart's electrical system. In the case of atrial fibrillation, the result is that the top chambers of the heart contract irregularly.

Atrial fibrillation can increase the risk of stroke and, in some cases, cause heart failure.

How the heart works

The heart is made up of four chambers: The left and right atria and the left and right ventricles. The electrical signals that control the heartbeat originate in the right atrium, at a spot called the sinus node. This node pulses out an electrical signal, which spreads from the top of the heart to the bottom, causing the muscle to contract as it travels.

The path of this electrical stimulation is important, as it causes blood to move in the proper direction at the proper time. First, the atria contract, sending blood into the ventricles. Next, the signal hits another node, the atrioventricular node, which slows the electrical pulse slightly so the ventricles can finish filling. Then the electrical signal zips down the ventricles, causing them to contract and squeezing blood out of the heart. Oxygenated blood from the left ventricle goes out to the body's tissues, while deoxygenated blood from the right ventricle goes to the lungs to pick up more oxygen.

This process repeats 60 to 100 times a minute, depending on the person's fitness and pulse rate.

 

Causes and consequences of atrial fibrillation

In atrial fibrillation, this electrical signal is disrupted. Instead of spreading normally through the atria, the electrical pulse spreads erratically. This causes fibrillation, or rapid and irregular contraction.

The erratic signals also arrive at the atrioventricular node in a disorganized way, causing the ventricles to beat faster than normal, too. The atria and ventricles are now uncoordinated, so that blood doesn't move in and out of the heart efficiently.

In some cases, fibrillation causes no noticeable symptoms. At other times, palpitations, chest pain, dizziness and shortness of breath warn of atrial fibrillations.

Atrial fibrillation can cause two serious complications. The first is stroke, which results because blood can pool in the atria, forming clots. If one of these clots makes its way to the brain, it can cut off blood flow, causing stroke. The second is heart failure.

Heart failure occurs when the ventricles beat too quickly to fill with blood. In this case, the heart can't push enough blood out to the body. [Top 10 Amazing Facts About Your Heart]

Treating atrial fibrillation

Atrial fibrillation is treated with blood thinners to reduce the risk of stroke-causing clots, as well as medications that slow the heart rate to a normal level and encourage normal rhythm. Treatments are most effective in patients who have had irregular rhythms for less than six months, according to the National Heart, Lung and Blood Institute.

In some cases, doctors may suggest surgical procedures to treat atrial fibrillation. One common treatment is electrical cardioversion, in which doctors administer a series of low-energy shocks to the heart muscle to nudge it back into rhythm. Another procedure, catheter ablation, is used to destroy tissues that might be interfering with the heart's electrical signals. In the most serious cases, catheter ablation is used to completely destroy the atrioventricular node. A pacemaker then replaces the lost electrical cells.

A final option is an open-heart surgery called maze surgery, which uses small cuts or burns to disrupt the abnormal electrical signals.

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Stephanie Pappas

Stephanie interned as a science writer at Stanford University Medical School, and also interned at ScienceNow magazine and The Santa Cruz Sentinel. She has a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science writing from the University of California, Santa Cruz.
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