Atrioventricular Node

Description

The atrioventricular node (or AV node) is located in the base of the right atrium close to the interatrial septum. The AV node is a group of highly specialized cardiac muscle fibers that depolarize and produce action potentials. These electrical impulses are generated automatically in a rhythmic fashion, occurring roughly 40–50 times per minute. Typically, the basal rhythm of the AV node is masked by the higher pace of the SA node, but in pathologic situations, the AV node can take over pacemaker function for the heart.

Like most of the cells of the cardiac conduction system, and unlike typical myocardial cells, the cells of the AV node have few myofibers and are only weakly contractile.

The AV node receives input from the SA node via the three internodal tracts. Additionally, it receives sympathetic and parasympathetic inputs from the cardiac plexus to increase or decrease the rate of firing, respectively. All of these inputs modulate the rate at which the AV node fires an action potential. Once depolarized, the AV node transmits its action potential unidirectionally to the AV bundle, and from there throughout the ventricles (Katz, 2010; Anderson et al., 2009).