PARTS OF THE CONDUCTION SYSTEM

The sinus node, a group of cells in the upper part of the right atrium, is the normal origin of the electrical impulse.

It is the heart's natural pacemaker. The impulse is channeled into the adjacent cells of the conduction system. This channeling, in effect, produces an electrical current that then passes from cell to cell down through the distant portions of the conduction system.

The second part of the conduction system is the electrical pathways in the atrium through which this electrical current preferentially travels on its journey throughout the atria and down to the ventricles.

The third portion of the conduction system is the atrioventricular (AV) node, which is a cluster of cells in the center of the heart between the atria and the ventricles. The AV node is like a gate that slows down the electrical current before it is allowed to pass through to the ventricles. This conduction delay at the AV node ensures that the atria contract a short time before the ventricles.

After it leaves the AV node, the current travels into specialized conduction tissue called the His-Purkinje system. This system of branching pathways of specialized electricity-conducting tissue rapidly distributes the current throughout the muscle cells of the left and right ventricles.

The interval from the initiation of the electrical impulse in the sinus node to completion of its delivery through the conduction system to the myocardial cells is brief, averaging about 1/4 second when the heart is beating 72 beats per minute. More than half of this time is due to the built-in delay at the AV node.

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Cardio & Blood