Pathophysiology of atrial fibrillation (AF)

A healthy 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.

The Electrical Problem in Atrial Fibrillation

The heart's electrical signals don't begin in the SA node.

Commonly begin in the left atria or in the nearby pulmonary veins.

The signals don't travel normally and spread throughout the atria in a rapid, disorganized way causing the atria to fibrillate (quivering)

The firing of these impulses results in a very rapid and disorganized heartbeat.

The rate of impulses through the atria can range from 300 to 600 beats per minute

As the AV node limits the number of impulses it allows to travel to the ventricles, the pulse rate is often less than 150 beats per minute, but this is fast enough to cause symptoms.

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 AF, the ventricles may beat 100 to 175 times a minute.

As only a small amount of blood enters the ventricles, the normal force created by the cardiac muscles decreases and only a small amount of blood is ejected from the heart. (frank-starling law of the heart)

The body gets rapid, small amounts of blood and occasional larger amounts of blood.

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

AF may be brief, with symptoms that come and go and end on their own. Or, the condition may be persistent and require treatment.

Sometimes AF is permanent, and medicines or other treatments can't restore a normal heart rhythm.

Tends to become a chronic disease as molecular and structural changes occur and makes it hard to achieve sinus rhythm

Video at http://www.nhlbi.nih.gov/health/dci/Diseases/af/af_what.html

References : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC546076/ , http://www.webmd.com/heart-disease/atrial-fibrillation/heart-disease-atrial-fibrillation-basics , http://www.mayoclinic.com/health/atrial-fibrillation/DS00291 , http://www.medscape.com/infosite/atrial-fibrillation/article-2