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Topic

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Atrioventricular Node (AV Node)

The atrioventricular node (AV node) is a key component of the cardiac conduction system, located in the interatrial septum at the apex of the triangle of Koch in the right atrium. This triangle is bordered by the tendon of Todaro, the ostium of the coronary sinus, and the septal leaflet of the tricuspid valve.

The AV node receives impulses from the sinoatrial (SA) node via atrial conduction pathways and serves as the only normal electrical connection between the atria and ventricles. It introduces a physiologic delay in conduction, allowing time for ventricular filling before systole. From the AV node, impulses are transmitted to the atrioventricular bundle (Bundle of His), and subsequently into the right and left bundle branches.

Clinically, the AV node is important in atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular block, and as a target in catheter ablation procedures.

Synonyms

  • AV node

  • Aschoff–Tawara node

  • Atrioventricular conduction node

Function

  • Receives electrical impulses from the atria (via SA node)

  • Provides a physiological delay, ensuring atrial contraction completes before ventricular systole

  • Only normal conduction pathway from atria to ventricles

  • Transmits impulses to the His–Purkinje system for ventricular activation

  • Plays a central role in arrhythmias such as AV block and AV nodal reentry

MRI Appearance

T1-weighted images:

  • AV node itself is too small to resolve directly, but appears as a low-signal region in the interatrial septum near the coronary sinus ostium

  • High-resolution cardiac MRI can localize conduction system regions indirectly by anatomic landmarks

T2 Cine (Cardiac-gated SSFP):

  • Provides functional assessment of atrioventricular conduction and synchronized contraction

  • Cine imaging correlates wall motion and filling with conduction delay but does not visualize the node directly

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Late gadolinium enhancement (LGE): may show fibrosis or scarring in the interatrial septum involving AV nodal tissue

  • Helpful in arrhythmia workup for identifying substrate for heart block or AV nodal dysfunction

MRA (Magnetic Resonance Angiography):

  • Not used for direct AV node visualization

  • May map adjacent coronary venous anatomy (e.g., coronary sinus) relevant to catheter ablation planning

CT Appearance

Contrast-Enhanced CT (Cardiac CTA):

  • AV node is not directly visualized due to its microscopic size

  • Identified indirectly by its location at the triangle of Koch

  • Useful for procedural planning (e.g., ablation, device implantation) by showing anatomical relationships of coronary sinus, tricuspid valve, and atrial septum

CT Delayed Imaging:

  • May demonstrate fibrosis or scarring in the AV nodal region in cases of prior infarction or ablation

CT images

Atrioventricular node (AV node) anatomy CT axial image -img-00000-00000

MRI image

Atrioventricular node (AV node) mri axial image