ATRIAL FIBRILLATION

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The Normal Heart Rhythm:

The normal heart consists of 4 chambers, the right and left atria (upper chambers), and the right and left ventricles (lower chambers).  During each heartbeat, the 2 atria contract, pushing blood into the ventricles, this is followed by the 2 ventricles contracting, pushing blood to the lungs and to the rest of the body.

This coordinated contracting of the heat is directed by the heart's electrical system.  The electrical impulses begin in an area called the sino-atrial (SA) node, found in the upper part of the right atrium.  When the SA node fires, an electrical impulse passes through the right and left atria, causing them to contract.

The electrical impulses then travel to the atrioventricular (AV) node and through the Bundle of His, before spreading through the muscles of the ventricles, thereby causing them to contract.  The AV node acts like an electrical bridge, slowing down the electrical impulse before passing it on to the ventricular muscles.

Blood from the right ventricle gets pumped into the pulmonary (lung) system, whilst blood from the left ventricle gets pumped to the rest of the body.

A normal heart has a constant, regular rhythm, beating at about 60 to 100 times per minute, when at rest.

What Is Atrial Fibrillation?

Atrial fibrillation (AF) is a common rhythm abnormality of the heart.  Over the years, the incidence of atrial fibrillation is increased, in both the developed and developing world.  If you have AF, electrical impulses do not arise normally in the SA node as described above.  Instead, many impulses begin simultaneously and spread through the atria and compete for a chance to travel through the AV node.  This results in a very rapid, disorganized and irregular heartbeat.

The rate of impulses through the atria can range from 300 to 600 beats per minute.  Fortunately, as these impulses pass through the AV node, they get slowed down, and the resulting pulse rate is often less than 150 beats per minute. 

Classification of Atrial Fibrillation

1. Paroxysmal AF - this means that the episodes of AF terminate spontaneously and usually last less than 7 days.

2. Persistent AF - episodes of atrial fibrillation lasting more than 7 days.

3. Permanent AF - this refers to AF which failed cardioversion (ie. conversion to normal rhythm) or in which cardioversion was not attempted.

4. Non-valvular AF - AF which occurs in the absence of any disease involving the heart valves.

5. Lone AF - this refers to AF occurring in a young person with no evidence of any significant disease.