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Atrioventricular node

From Latin: atrium – entrance; ventriculus – small belly
Synonyms: AV node, Aschoff-Tawara node, nodus atrioventricularis
German: Atrioventrikularknoten

1 Definition

The atrioventricular node, or AV node is the secondary pacemaker centre of the heart and is involved in the complex regulation of the heart rate.

2 Anatomy

The AV node is a muscular structure in Koch triangle in the region of the right atrium near the atrial septum. It is difficult to distinguish at a macroscopic level. It is located at the junction to the ventricles and regulates the transmission of impulses through the non-conductive cardiac skeleton in the ventricles. The node pulls the bundle of His towards the apex. The AV node is likely controlled by the sympathetic and parasympathetic systems, which intervene in the complex regulation of the cardiac rhythm. It is usually supplied with blood by the atrioventricular nodal branch from the right coronary artery.

3 Histology

The atrioventricular node is composed of specific cardiac cells (cardiomyocytes), which partially radiate into the connective tissue of the cardiac skeleton. In contrast to the working muscles of the heart, the node cells are relatively devoid of myofibrils and mitochondria.

4 Physiology

The AV node is the secondary stimulation centre of the heart It usually receive the depolarisations propagated via the working muscles of the atria and redirects them to the ventricle after a delay. The time period for this transition is referred to as the atrioventricular conduction time (AV-time). It corresponds to the PQ interval in the ECG. The delay of the excitation in the AV node is necessary to ensure a coordinated contraction of the atria and ventricles. The atrial systole occurs slightly earlier than the ventricular systole, which leads to improved filling of the ventricles.

The AV node also acts as a frequency filter. Under physiological conditions, it does not conduct stimuli above a certain frequency because of the refractory period of the depolarised cardiac muscle cells.

5 Pathophysiology

In the event of a node failure, the AV node can assume the function of the primary rhythm generator and control a heart rate from 40 to 60/min.

An excessive time lag of the impulse conduction through the AV node or a failure of conduction can lead to AV-block, of which there are three stages.

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