This is the physiological proof for the presence of the internodal tracts, which have not been clearly demonstrated histologically.

This bundle was named Wenckebach's bundle, and is also known as the middle internodal tract.

The impulse from the sinus node is still conducted via the internodal tracts to the AV node, and thus normal ventricular activation occurs.

After the atria depolarize, the electrical impulse spreads through the internodal tracts and reach the atrioventricular node (AV node).

In the heart's conduction system, Bachmann's bundle, or the interatrial tract, is a branch of the anterior internodal tract that resides on the inner wall of the left atrium.

As the electrical activity is spreading throughout the atria, it travels via specialized pathways, known as internodal tracts, from the SA node to the AV node.

Wenckebach's bundle is one of the three internodal pathways, the others being the "posterior internodal tract" (Thorel's pathway), and the "anterior internodal tract" (some fibers of which also project to Bachmann's bundle, and then into the left atrium).