February 8, 2016

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Atrial Fibrillation (AFib)

What is the electrical function of the heart?

With each beat of the heart, an electrical discharge (current) passes through the electrical system of the heart. The electrical discharge causes the muscle of the atria and ventricles to contract and pump blood. The electrical system of the heart consists of the SA node (sinoatrial node), the AV node (atrioventricular node) and special tissues in the atria and the ventricles that conduct the current.

The SA node is the heart's electrical pacemaker. It is a small patch of cells located in the wall of the right atrium; the frequency with which the SA node discharges determines the rate at which the heart beats. The electrical current passes from the SA node, through the special tissues of the atria and into the AV node.

The AV node serves as an electrical relay station between the atria and the ventricles. Electrical signals from the atria must pass through the AV node to reach the ventricles.

The electrical discharges from the SA node cause the atria to contract and pump blood into the ventricles. The same discharges then pass through the AV node to reach the ventricles, traveling through the special tissues of the ventricles and causing the ventricles to contract. In a normal heart, the rate of atrial contraction is the same as the rate of ventricular contraction.

At rest, the frequency of the electrical discharges originating from the SA node is low, and the heart beats at the lower range of normal (60 to 80 beats/minute). During exercise or excitement, the frequency of discharges from the SA node increases, increasing the rate at which the heart beats. Continue Reading

Reviewed on 5/27/2015
Atrial Fibrillation Quiz