Atrial Fibrillation (AFib)

What is atrial fibrillation?

Atrial Fibrillation

Atrial fibrillation, or AFib, is the most common type abnormal heart rhythm (arrhythmia). Normally, a specific group of cells begins the signal to start your heartbeat. These cells are in the sinoatrial (SA) node. This node is in the right atrium, the upper right chamber of the heart. The signal quickly travels down the heart’s conducting system. It travels to the upper-left filling chamber of the heart (left atrium) and to the left and right ventricle, the 2 lower pumping chambers of the heart. As it travels, the signal triggers the chambers of the heart to contract. The atria contract with each heartbeat to move blood into the ventricles.

During AFib, the signal to start the heartbeat is disorganized. This causes the atria to quiver (fibrillate). The disorganized signals are then transmitted to the ventricles. It causes them to contract irregularly and sometimes quickly. The contraction of the atria and the ventricles is no longer coordinated. The amount of blood pumped out to the body will vary with each heartbeat. The ventricles may not be able to pump blood efficiently to the body.

The quivering atria can lead to blood pooling. This pooling can cause blood clots to form inside the heart. Most clots form inside the left atrium. That's because the left atrium has a pouch (left atrial appendage) in the muscle wall. This pouch is often large with several lobes. Blood can pool and form clots inside the lobes. This increases the risk of forming blood clots. These clots can then be pumped out of the heart and travel to the brain, causing a stroke. This is why AFib greatly increases the risk for stroke.

Doctors classify AFib in 3 ways:

  • Parosyxmal. Sometimes AFib occurs briefly and then goes away on its own. It may last for seconds, minutes, hours, or up to 7 days before returning to a normal rhythm.
  • Persistent. This is AFib that does not go away on its own. Treatment may be used to return the heart to normal rhythm. It lasts for 7 days or longer. AFib that lasts longer than a year is called long-standing persistent atrial fibrillation.
  • Permanent. Afib may be called permanent when a decision is made to no longer control the heart’s rhythm or despite best efforts, normal rhythm can't be restored.

AFib is common in adults. The risk increases with age. It is more common in men than in women.

Atrial Fibrillation (AFib)

What causes atrial fibrillation?

AFib can happen from any type of problem that changes the way the heart handles electricity. Sometimes the cause is unknown. There is a range of things that can increase this risk. Some of the risks include:

  • Older age
  • High blood pressure
  • Coronary artery disease
  • Heart failure
  • Rheumatic heart disease from a past Streptococcus infection
  • Heart valve defects such as mitral valve prolapse with regurgitation
  • Pericarditis
  • Congenital heart defects
  • Sick sinus syndrome
  • Hyperthyroidism
  • Obesity
  • Diabetes
  • Lung disease
  • Obstructive sleep apnea
  • Metabolic syndrome
  • High-dose steroid therapy

AFib is also more likely to happen during an infection or right after surgery. Stress, caffeine, and alcohol may also set off attacks. People who do a lot of repeated vigorous endurance exercises, such as running marathons, can develop atrial fibrillation.

Certain people may be at greater risk of developing AFib. This is because of differences in genes they inherited from their parents. This is not yet fully understood.

What are the symptoms of atrial fibrillation?

AFib can cause different symptoms. This is especially true when it is not treated. These can include:

  • The feeling that your heart is skipping beats or beating too hard (heart palpitations)
  • Shortness of breath
  • Chest pain
  • Dizziness or fainting
  • Weakness and tiredness (fatigue)
  • Confusion
  • Swelling in the feet, ankles, and legs

Sometimes AFib has no symptoms. The first symptom of atrial fibrillation may be symptoms of a stroke.


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