Conduction of the Heart (1)

Conduction of the Heart
Sinus Node

The normal cardiac impulse originates in the sinus node, a structure located in the long superior portion of the right atrium at its juncture with the superior vena cava. Conduction from the sinus node is thought to occur over internodal pathways, although this is controversial. Three internodal pathways are described below.

 second Atrial Conduction and Internodal Pathways
The anterior internodal pathway arises at the cranial end of the sinus node. It divides into branches, one to the left atrium (Bachman’s bundle) and the other along the right side of the interatrial septum to the AV node.

• The middle internodal pathway arises along the endocardial surface of the sinus node and descends through the interatrial septum to the AV node.

• The posterior internodal pathway arises from the caudal end of the sinus node and approaches the AV node at its posterior aspect.

The speed of conduction through the atria via these pathways is approximately 1000 mm/