Atrial fibrillation (AF) is a rapid and irregular heart rhythm (arrhythmia) caused by faulty electrical signals from the upper chambers of the heart (atria). Electrical signals should normally originate only from the sinus node (the heart’s natural pacemaker), creating a steady heart rhythm – about 60 to 100 beats per minute. AF is marked by rapid electrical signals that come from the atria, causing them to quiver instead of contract properly. These electrical signals may increase the heart rate to 100 to 175 beats per minute or more. 

AF is the most common type of sustained arrhythmia, affecting 2 million people each year in the United States alone. The American Heart Association (AHA) notes that hospitalizations for AF have tripled since 1985. The risk of developing atrial fibrillation increases dramatically with age. As a result, approximately 70 percent of patients with atrial fibrillation are between the ages of 65 and 85 years old.

Not all abnormal heartbeats are a sign of AF. Skips, pauses or unusually strong/irregular heartbeats (palpitations) commonly occur in people with no history of heart problems. Some are related to more serious cardiac problems, while others are not.  A rhythm that is closely related to atrial fibrillation is atrial flutter, in which a very rapid but regular electrical signal in the atria causes a very rapid heartbeat. It is common for patients to experience episodes of atrial fibrillation at some times and atrial flutter at others. Like atrial fibrillation, atrial flutter increases the risk of stroke. According to the AHA, it leads to more than 54,000 deaths in the United States each year. People who experience abnormal or irregular heartbeats are encouraged to speak with their physician.

There are several dangerous conditions associated with atrial fibrillation. Among the most common is the risk of blood clots forming in the atria as they quiver. If part of a clot breaks off and leaves the heart via the arteries, it can become lodged in blood vessels that supply the brain, lungs or other parts of the body with blood. Depending upon where the traveling blood clot (embolus) becomes lodged, the patient could experience symptoms ranging from cold feet to a stroke. Atrial fibrillation is also associated with heart failure.

The risk associated with atrial fibrillation depends on the duration of the condition. The American College of Cardiology, along with the AHA, has proposed the following classification system for atrial fibrillation:

• Paroxysmal atrial fibrillation, in which the arrhythmia lasts less than seven days and usually less than 24 hours and may be recurrent.
  
  
• Persistent atrial fibrillation, in which the arrhythmia lasts longer than seven days, but the abnormal rhythm can be stopped with treatment (e.g., cardioversion with a defibrillator).
  
  
• Permanent atrial fibrillation, in which the arrhythmia lasts longer than one year and has either not responded to treatment or treatment has not been attempted.
  
  
• Lone atrial fibrillation, in which the arrhythmia, either paroxysmal or persistent, occurs in people without any other form of heart disease.

The treatment course depends on the length of the atrial fibrillation, the patient’s medical history and if there are any other factors (e.g., coronary heart disease) present.

A quite different (and life-threatening) condition is ventricular fibrillation (VF). Ventricular fibrillation involves a quivering of the ventricles instead of the atria. Unlike atrial fibrillation, ventricular fibrillation is life threatening because it results in a heart rate of 350 beats per minute or higher. Because of these rapid, chaotic contractions, the heart is unable to pump blood to the body. Untreated, ventricular fibrillation can result in sudden cardiac death within minutes. Treatment for ventricular fibrillation involves shocking the heart back into a normal rhythm with a defibrillator. Among high-risk patients, implantable cardioverter defibrillators continuously monitor the heart and deliver a shock when necessary.

Some patients have a condition that allows extra impulses to travel between the atrium and ventricles (this is known as Wolf Parkinson White syndrome). In this case, atrial fibrillation is considered a risk factor for ventricular fibrillation, and episodes of atrial fibrillation can lead to a life-threatening ventricular arrhythmia.