The atrioventricular (AV) node is a small cluster of specialised conducting tissue that relays the electrical impulse from the atria to the ventricles. It deliberately slows conduction, creating a brief delay that lets the atria finish emptying before the ventricles contract. Normally it is the only electrical link between atria and ventricles.
| Location | Lower part of the interatrial septum in the right atrium, at the apex of the triangle of Koch, just above the opening of the coronary sinus and the septal leaflet of the tricuspid valve. |
|---|---|
| Parts |
|
| Nerve Supply | Vagus nerve, mainly left (slows conduction); Sympathetic cardiac nerves (speed conduction) |
| Blood Supply | Atrioventricular nodal artery (from the right coronary artery in most people) |
Delays impulse transmission by about a tenth of a second, matching ventricular contraction to atrial filling, and protects the ventricles from very fast atrial rhythms by limiting how many impulses pass. If the SA node fails, it can act as a backup pacemaker at about 40-60 beats per minute.
The PR interval on the ECG largely reflects AV nodal delay. AV nodal re-entrant tachycardia is the most common cause of regular palpitations in otherwise healthy young people and is usually cured by ablating the slow pathway. Drugs such as beta-blockers, calcium channel blockers and digoxin slow AV conduction and are used to control heart rate in atrial fibrillation.
Delay or failure of conduction through the AV node or below, graded first, second or third degree. Complete heart block causes slow rates and fainting and needs a pacemaker.
A fast, regular rhythm caused by an electrical circuit looping within and around the AV node. It starts and stops suddenly and can often be stopped by vagal manoeuvres.
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