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Atrioventricular bundle (bundle of His)

The atrioventricular (AV) bundle, also known as the Bundle of His, is a critical component of the cardiac conduction system. It originates from the atrioventricular node (AV node) located at the base of the interatrial septum, penetrates the central fibrous body, and continues into the interventricular septum.

The AV bundle is the only electrical connection between the atria and ventricles, transmitting impulses from the AV node to the ventricles. After entering the interventricular septum, it divides into the right bundle branch and left bundle branch. The left bundle further splits into anterior and posterior fascicles, while both branches terminate in the Purkinje fiber network, coordinating ventricular contraction.

Pathological involvement of the bundle of His results in atrioventricular block, bundle branch blocks, and conduction disturbances. It is a target for His bundle pacing, a modern technique in electrophysiology for physiologic ventricular activation.

Synonyms

  • AV bundle

  • Bundle of His

  • His bundle

  • Tractus atrioventricularis

Function

  • Provides the only normal electrical pathway from atria to ventricles

  • Rapidly conducts impulses to ensure synchronous ventricular activation

  • Coordinates atrioventricular timing for effective cardiac output

  • Subdivision into bundle branches enables precise activation of both ventricles

Branches

  • Right bundle branch (RBB) → supplies right ventricle and moderator band

  • Left bundle branch (LBB) → splits into anterior and posterior fascicles for left ventricle

  • Both terminate in Purkinje fibers

MRI Appearance

T1-weighted images:

  • Too small for direct visualization, but appears as part of the low-signal conduction tissue within the membranous interventricular septum

  • Best assessed indirectly with specialized high-resolution cardiac MRI

T2 Cine (Cardiac-gated):

  • Cine imaging delineates interventricular septal motion influenced by conduction

  • Abnormalities such as bundle branch block may manifest as dyssynchronous septal contraction

  • Useful in functional correlation of conduction defects

STIR (Short Tau Inversion Recovery):

  • Highlights edema or inflammation within the septum, which may involve conduction tissue (e.g., myocarditis, sarcoidosis)

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Late gadolinium enhancement (LGE) may demonstrate fibrosis in the basal septum involving the AV bundle

  • Critical in evaluation of infiltrative cardiomyopathies, ischemia, or post-ablation scarring

CT Appearance

Contrast-Enhanced Cardiac CT:

  • Direct visualization of the AV bundle is limited due to its microscopic size

  • Indirectly evaluated by identifying the membranous septum region between atria and ventricles

  • CT can reveal structural correlates of conduction disease (e.g., calcification in membranous septum, post-surgical changes, or device leads in His-bundle pacing)

CT Coronary Angiography (CCTA):

  • Used to evaluate vascular supply to the conduction system (septal branches of LAD)

  • Helps in correlating ischemia or infarction of septal territories with bundle branch dysfunction

CT image

Atrioventricular bundle (bundle of His) anatomy CT axial image -img-00000-00000

MRI image

Atrioventricular bundle (bundle of His) mri image