AV node

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The AV node (atrioventricular node) is the heart's secondary pacemaker. It receives the electrical impulses that come from the sinus node via the atrial muscles and forwards them via the conduction system to the heart chambers so that they contract. Read everything you need to know about the AV node!

AV node: control center between the forecourt and the chamber

The AV node is an area of ​​dense, connective tissue-rich muscle fiber networks in the right atrium near the border with the heart chamber (ventricle). It is the only conductive connection between the atrium and the ventricle: the electrical impulses coming from the sinus node via the atrial muscles spread from the AV node via the bundle of His and then via the ventricular limbs and the Purkinje fibers to the outermost heart muscle cells of the ventricles and trigger a contraction of the heart chambers (systole).

The forwarding of the signals at the AV node takes place with a short time delay. This ensures that the atria and ventricles do not contract at the same time, but rather in quick succession. This improves the blood filling of the ventricles: The atrial contraction presses blood from the atria into the ventricles, which in turn contract shortly afterwards and thus press the blood into the outgoing arteries.

AV time

The time it takes for the electrical impulses to pass from the sinus node via the atria and AV node to the ventricles is what doctors call AV time (atrioventricular conduction time). In the ECG it roughly corresponds to the PQ interval.

AV node as a secondary pacemaker

If the sinus node (the heart's primary pacemaker) fails, the AV node can take over. As a secondary pacemaker, however, it sends at a lower frequency than the sinus node, namely 40 to 60 pulses per minute compared to the approximately 70 pulses per minute of the primary pacemaker.

AV node as a frequency filter

The AV node is not only a pure control center between atrium and chamber, but also a frequency filter. If the frequency of the atria is too high (as is the case with atrial fibrillation), it does not allow all the impulses to pass through to the ventricles, thereby protecting them.

Problems around the AV node

The so-called AV block is a form of cardiac arrhythmia in which the AV node is more or less blocked. There are three degrees of severity:

In the case of a first-degree AV block, the transmission of impulses between the atrium and ventricle is delayed, which usually does not trigger any symptoms.

A 2nd degree AV block is a partial conduction block, which means that not all impulses are transmitted to the heart chamber.

A 3rd degree AV block means a complete blockage of the atrioventricular conduction: the excitation of the atrium does not spread to the ventricle. As a substitute, this develops its own rhythm. Overall, the atria and ventricles then contract independently of one another. That is very dangerous. Symptoms range from decreased performance and dizziness to unconsciousness and cerebral seizures to irreversible brain damage and death.

AV block usually develops as part of a disease such as other cardiac arrhythmias, inflammation of the heart muscle (myocarditis), cardiac insufficiency or degenerative changes in the conduction system. Surgical interventions on the heart (such as the insertion of a heart valve) and various medications can also trigger an AV block. In rarer cases it is congenital.

Another health disorder of the AV node is AV node reentry tachycardia: In addition to the AV node, there is a second, functionally separate pathway between the atrium and ventricle. The excitation can circulate through these two pathways between the atrium and the ventricle. This reciprocal circular excitation (reentry) leads to seizure-like palpitations (tachycardy), which can last from seconds to days. AV node reentry tachycardia mostly affects younger, heart-healthy people.

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