Atrial Fibrillation

Atrial Fibrillation (A Fib) Overview

Atrial fibrillation (A fib) is an irregular and often rapid heart rhythm. The irregular rhythm, or arrhythmia, results from abnormal electrical impulses in the upper chambers (atria, singular=atrium) of the heart that cause the heartbeat (ventricle contraction) to be irregular and usually fast. The irregularity can be continuous, or it can come and go. Some individuals, especially patients on medications, may have atrial fibrillation constantly but not have a rapid (>100 heartbeats per minute) rate at rest. Variations of A fib may be termed paroxysmal, persistent, or permanent (these are further described below). A fib is the most common heart arrhythmia.

Normal heart contractions begin as an electrical impulse in the right atrium. This impulse comes from an area of the atrium called the sinoatrial (SA) or sinus node, the “natural pacemaker” that causes the normal range of regular heartbeats. Normal heartbeats proceed as follows:

    • The electrical impulse originates in the SA node of the right atrium. As the impulse travels through the atrium, it produces a wave of muscle contractions. This causes the atria to contract.
    • The impulse reaches the atrioventricular (AV) node in the muscle wall between the two ventricles. There, it pauses, giving blood from the atria time to enter the ventricles.
    • The impulse then continues into the ventricles, causing ventricular contraction that pushes the blood out of the heart, completing a single heartbeat.

In an adult person with a normal heart rate and rhythm the heart beats 50-100 times per minute at rest (not under stress or exercising).

atrial fibrillation

Figure 1. Picture of electrical pathways of the heart

      • If the heart beats more than 100 times per minute, the heart rate is considered fast (tachycardia).
      • If the heart beats less than 50 times per minute, the heart rate is considered slow (bradycardia).


In atrial fibrillation, multiple sources of impulses other than only from the SA node travel through the atria at the same time. The reason that these sources develop are not completely understood, but cardiac muscles in the pulmonary veins have electrical generating properties and may be one source of these extra impulses.

      • Instead of a coordinated contraction, the atrial contractions are irregular, disorganized, chaotic, and very rapid. The atria may contract at a rate of 400-600 beats per minute. The blood flow from the atria to the ventricles is often disrupted.
      • These irregular impulses reach the AV node in rapid succession, but not all of them make it past the AV node. Therefore, the ventricles beat more slowly than the atria, often at fairly fast rates of 110-180 beats per minute in an irregular rhythm.
      • The resulting rapid, irregular heartbeat causes an irregular pulse and sometimes a sensation of fluttering in the chest.

Atrial fibrillation can occur in several different patterns.

      • Intermittent (paroxysmal): The heart develops atrial fibrillation and typically converts back again spontaneously to normal (sinus) rhythm. The episodes may last anywhere from seconds to days.
      • Persistent: Atrial fibrillation occurs in episodes, but the arrhythmia does not convert back to sinus rhythm spontaneously. Medical treatment or cardioversion (electrical treatment) is required to end the episode.
      • Permanent: The heart is always in atrial fibrillation. Conversion back to sinus rhythm either is not possible or is deemed not appropriate for medical reasons. In most cases, the rate is reduced by medications and the patients are placed on anticlotting medication for their lifetime.

Atrial fibrillation, often called A Fib, atrial tachyarrhythmia, or atrial tachycardia, is one of the very common heart rhythm disorders.

      • It affects about 4% of the population, mostly people older than 60 years. This amounts to more than 2.6 million people in the U.S. People older than 40 have about a 25% chance of developing A fib in their lifetime.
      • The risk of developing atrial fibrillation increases as we get older. About 10% of people older than 80 years have atrial fibrillation.

For many people, atrial fibrillation may cause symptoms but does no harm.

    • Complications like blood clot formation, strokes, and heart failure can arise, but appropriate treatment reduces the chances that such complications will develop.
    • If treated properly, atrial fibrillation infrequently causes serious or life-threatening problems.

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