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Exactly What Is Atrial Fibrillation?

What Is Atrial Fibrillation

A good date to learn more about Afib is today - Atrial fibrillation (also known as Afib) is the most common type of heart arrhythmia. Arrhythmia is a problem with the rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with irregular rhythm.

Atrial Fibrillation occurs when rapid, disorganized electrical signals cause the atria (AY-tree-uh), the two upper chambers of the heart, to fibrillate. The term "fibrillate" means to contract very fast and irregularly.

In Atrial Fibrillation, blood pools in the atria and isn't pumped completely into the ventricles, the heart's two lower chambers. As a result, the heart's upper and lower chambers don't work together as they should.

Often, people who have Atrial Fibrillation may not feel its symptoms. However, even when Afib is not noticed, Atrial Fibrillation can increase the risk of stroke. In some people, Atrial Fibrillation can cause chest pain or heart failure, particularly when the heart rhythm is very rapid.

Atrial Fibrillation may occur rarely or every now and then, or it may become a persistent or permanent heart rhythm lasting for years.

Understanding the Heart's Electrical System

To understand Atrial Fibrillation, it helps to understand the heart's internal electrical system. The heart's electrical system controls the rate and rhythm of the heartbeat.

With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The process repeats with each new heartbeat.

Each electrical signal begins in a group of cells called the sinus node or sinoatrial (SA) node. The SA node is located in the right atrium. In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute. (This rate may be slower in very fit athletes.)

From the SA node, the electrical signal travels through the right and left atria. This causes the atria to contract and pump blood into the ventricles.

The electrical signal then moves down to a group of cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here, the signal slows down just a little, allowing the ventricles time to finish filling with blood.

The electrical signal then leaves the AV node and travels to the ventricles. This causes the ventricles to contract and pump blood out to the lungs and the rest of the body. The ventricles then relax, and the heartbeat process starts all over again in the SA node.

Understanding Heart Electrical Issues involving Atrial Fibrillation

In Atrial Fibrillation, the heart's electrical signals don't begin in the SA node. Instead, they begin in another part of the atria or in the nearby pulmonary veins. The signals don't travel normally, and they may spread throughout the atria in a rapid, disorganized way. This can cause the atria to fibrillate.

The abnormal electrical signals flood the AV node with electrical impulses. As a result, the ventricles also begin to beat very fast. However, the AV node can't conduct the signals to the ventricles as fast as they arrive. So, even though the ventricles may be beating faster than normal, they aren't beating as fast as the atria.

Thus, the atria and ventricles no longer beat in a coordinated way. This creates a fast and irregular heart rhythm. In Atrial Fibrillation, the ventricles may beat 100 to 175 times a minute, in contrast to the normal rate of 60 to 100 beats a minute.

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When this happens, blood isn't pumped into the ventricles as well as it should be. Also, the amount of blood pumped out of the ventricles to the body is based on the randomness of the atrial beats.

The body may get rapid, small amounts of blood and occasional larger amounts of blood. The amount will depend on how much blood has flowed from the atria to the ventricles with each beat.

Most of the symptoms of Atrial Fibrillation are related to how fast the heart is beating. If medicines or age slow the heart rate, afib symptoms are minimized.

Atrial Fibrillation may be brief, with AF symptoms which may come and go and end on their own. Or, the condition may be persistent and require treatment. Sometimes Atrial Fibrillation is permanent, and medicines or other treatments can't restore a normal heart rhythm.

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.


People who have Atrial Fibrillation can live normal, active lives. For some people, treatment can cure Atrial Fibrillation and restore normal heart rhythms.

For people who have permanent Atrial Fibrillation, treatment can successfully control symptoms and prevent complications. Treatments include medicines, medical procedures, and lifestyle changes.

Types of Atrial Fibrillation

Paroxysmal Atrial Fibrillation

In paroxysmal (par-ok-SIZ-mal) atrial fibrillation (Atrial Fibrillation), the abnormal electrical signals and rapid heart rate begin suddenly and then stop on their own. Symptoms can be mild or severe and last for seconds, minutes, hours, or days.

Persistent Atrial Fibrillation

Persistent Atrial Fibrillation is a condition in which the abnormal heart rhythm continues until it's stopped with treatment.

Permanent Atrial Fibrillation

Permanent Atrial Fibrillation is a condition in which a normal heart rhythm can't be restored with the usual treatments. Both paroxysmal and persistent Atrial Fibrillation may become more frequent and, over time, result in permanent Atrial Fibrillation.

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What Causes Atrial Fibrillation?

Atrial fibrillation (Atrial Fib) occurs when the electrical signals traveling through the heart are conducted abnormally and become very rapid and disorganized.

This is the result of damage to the heart's electrical system. The damage most often is the result of other conditions, such as coronary heart disease (also called coronary artery disease) or high blood pressure, affecting heart health.

Sometimes, the cause of Atrial Fibrillation is unknown.

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Who Is At Risk for Atrial Fibrillation?

More than 2 million people in the United States have atrial fibrillation (Atrial Fibrillation). It affects both men and women.

The risk of Atrial Fibrillation increases as you age. This is mostly because as you get older, your risk for heart disease and other conditions that can cause Atrial Fibrillation also increases. However, about half of the people who have Atrial Fibrillation are younger than 75.

Atrial Fibrillation is uncommon in children.

Major Risk Factors

Atrial Fibrillation is more common in people who have heart diseases or conditions, such as:

  • Coronary heart disease
  • Heart failure
  • Rheumatic heart disease
  • Structural heart defects, such as mitral valve disorders
  • Pericarditis (a condition in which the membrane, or sac, around your heart is inflamed)
  • Congenital heart defects
  • Sick sinus syndrome (a condition in which the heart's electrical signals don't fire properly and the heart rate slows down; sometimes the heart will switch back and forth between a slow rate and a fast rate)

Atrial Fibrillation also is more common in people who are having heart attacks or who have just had surgery.

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Other Risk Factors

Other conditions that increase Atrial Fibrillation risk include hyperthyroidism (too much thyroid hormone), obesity, high blood pressure, diabetes, and lung disease.

Other factors also can increase your risk of Atrial Fibrillation. For example, drinking large amounts of alcohol, especially binge drinking, increases your risk. Even modest amounts of alcohol can trigger Atrial Fibrillation in some people. Caffeine or psychological stress also may trigger Atrial Fibrillation in some people.

Some evidence suggests that people who have sleep apnea are at greater risk for Atrial Fibrillation. Sleep apnea is a common disorder in which you have one or more pauses in breathing or shallow breaths while you sleep.

Metabolic syndrome also increases your risk of Atrial Fibrillation. People who have this condition have a group of risk factors that increase their risk of heart disease and other health problems.

Recent research suggests that people who receive high-dose steroid therapy are at increased risk of Atrial Fibrillation. This therapy, which is commonly used for asthma and certain inflammatory conditions, may act as a trigger in people who already cardiac dysrhythmia, irregular heartbeat and other afib risk factors.

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Warning Signs and Symptoms of Afib and Irregular Heartbeats

Atrial fibrillation (A-Fib) often causes the ventricles to contract faster than normal. When this happens, the ventricles don't have enough time to fill completely with blood to pump to the lungs and body.

This inefficient pumping can cause signs and symptoms, such as:

  • Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)
  • Shortness of breath
  • Weakness or difficulty exercising
  • Chest pain
  • Dizziness or fainting
  • Fatigue (tiredness)
  • Confusion

Atrial Fibrillation Complications

Atrial Fibrillation has two major complications— stroke and heart failure.

Stroke and Mini strokes

During Atrial Fibrillation, the atria don't pump all of the blood to the ventricles. Some blood pools in the atria. When this happens, a blood clot (also called a thrombus) can form.

If the clot breaks off and travels to the brain, it can cause a stroke. (A clot that forms in one part of the body and travels in the bloodstream to another part of the body is called an embolus.)

Blood-thinning medicines to reduce the risk of stroke are a very important part of treatment for people who have Atrial Fibrillation.

Atrial Fibrillation and Stroke

The illustration shows how a stroke can occur during atrial fibrillation. If a clot (thrombus) forms in the left atrium of the heart, a piece of it can dislodge and travel to an artery in the brain, blocking blood flow through the artery. The lack of blood flow to the portion of the brain fed by the artery causes a stroke.

The illustration shows how a stroke can occur during atrial fibrillation. If a clot (thrombus) forms in the left atrium of the heart, a piece of it can dislodge and travel to an artery in the brain, blocking blood flow through the artery. The lack of blood flow to the portion of the brain fed by the artery causes a stroke.

Heart Failure

Heart failure occurs when the heart can't pump enough blood to meet the body's needs. Atrial Fibrillation can lead to heart failure because the ventricles are beating very fast and aren't able to properly fill with blood to pump out to the body.

Fatigue and shortness of breath are common symptoms of heart failure. A buildup of fluid in the lungs causes these symptoms. Fluid also can build up in the feet, ankles, and legs, causing weight gain.

Lifestyle changes, medicines, and sometimes special care (rarely, a mechanical heart pump or heart transplant) are the main treatments for heart failure.

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