Definition: The atrioventricular (AV) node is a key part of the heart's electrical system, helping transmit the heart's electrical impulse from the atria to the ventricles.
The AV node is a tiny "button" of cells that is located near the center of the heart, at the junction of the atria and the ventricles. After an electrical impulse is generated by the sinus node, it spreads across the atria, causing the atria to beat. The AV node then "gathers" that electrical impulse and, after a brief delay, allows it to pass through to the ventricles. The brief delay in the AV node permits the atria to finish beating and emptying into the ventricles, before the ventricles begin to beat.
The AV node is richly innervated by the vagus nerve. Stimulation of the vagus nerve strongly slows the conduction of electrical impulses through the AV node. This feature of the AV node is useful when attempting to stop episodes of supraventricular tachycardia (SVT).
Disease of the AV node can cause either a delay, or a partial or complete block, in the transmission of electrical impulses from the atria to the ventricles - a condition known as "heart block." If heart block becomes severe enough, significant bradycardia can result, and insertion of a pacemaker may be required.
