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# Bundle of His

The bundle of His is a short band of conducting fibres that carries each heartbeat signal from the [atrioventricular node](https://durgical.com/en/anatomy/atrioventricular-node/) into the ventricles.

Official name: Atrioventricular bundle

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## What it is

A short cable of conducting fibres carrying the signal from the AV node through the heart's fibrous skeleton into the septum.

## What it does

Passes the beat to the bundle branches.

## Key points

- Normally the only muscular electrical link between atria and ventricles; the fibrous skeleton insulates the rest of the atrioventricular junction
- Runs along the lower edge of the membranous septum on the crest of the muscular septum, just below the aortic valve, so it is at risk in septal defect repair and aortic valve procedures
- Block within or below the bundle tends to be Mobitz II or complete block with a slow, unreliable wide-QRS escape rhythm, and is usually treated with a permanent pacemaker

## Key facts

**Where**
From AV node through right fibrous trigone (central fibrous body) along lower edge of membranous septum

**Function**
Only electrical link through fibrous skeleton; divides at top of muscular septum into right and left bundle branches

## Relations

**Course**
From the AV node it pierces the central fibrous body (right fibrous trigone), runs forward under the membranous septum along the top of the muscular septum and divides into the right and left [bundle branches](https://durgical.com/en/anatomy/right-bundle-branch/)

**Above**
Membranous [interventricular septum](https://durgical.com/en/anatomy/interventricular-septum/); on the left side, the area below the commissure between the right and non-coronary cusps of the aortic valve

## How to find it

In the electrophysiology laboratory a catheter laid across the tricuspid valve at the top of the septum, just below the anteroseptal commissure, records the His spike; in a dissection the bundle is followed from the apex of the triangle of Koch to the crest of the muscular septum.

## Examination

- His bundle electrogram in an electrophysiology study: the His spike separates the AH interval (AV node) from the HV interval (His–Purkinje system); a prolonged HV interval places the block below the node

## On imaging

Not seen on imaging; it is recorded as the His deflection in an electrophysiology study. Its path is inferred from the membranous septum just below the aortic valve, seen on echocardiography and cardiac CT. Before transcatheter aortic valve implantation, CT assesses this septum, since a short one is linked to a higher risk of heart block afterwards.

## Common problems

- Heart block: the signal is slowed or blocked, causing a slow pulse and fainting.
- Re-entry circuits around it cause sudden fast heartbeats (SVT).

## How it is diagnosed

ECG (PR interval), Holter monitor, electrophysiology study.

## Treatment

- Pacemaker for heart block; catheter ablation for SVT.

## Clinical notes

- Heart block after ventricular septal defect closure, aortic valve replacement or transcatheter aortic valve implantation, because the bundle runs just beneath the aortic annulus
- His bundle pacing places the lead on the bundle to use the heart's own conduction system and produce a narrow QRS
- A junctional escape rhythm from the AV junction and His region has a narrow QRS at about 40–60 beats per minute
- Lenègre–Lev disease: age-related fibrosis and calcification of the conduction system and the fibrous skeleton around it, a common cause of heart block in older adults

## Related conditions

- [Tricyclic antidepressant overdose](https://durgical.com/en/conditions/tricyclic-antidepressant-overdose/)
- [Atrioventricular (heart) block](https://durgical.com/en/conditions/atrioventricular-block/)

## Test yourself

Think of the answer, then tap the question to see it.

## What makes the bundle of His unique in the atrioventricular junction?

It is normally the only muscular electrical link between atria and ventricles, piercing the central fibrous body (right fibrous trigone).

## Why is the bundle of His at risk in septal defect repair and aortic valve procedures?

It runs along the lower edge of the membranous septum on the crest of the muscular septum, just below the aortic valve.

## In an electrophysiology study, what does a prolonged HV interval indicate?

A block below the AV node, in the His–Purkinje system; the His spike separates the AH (AV node) from the HV interval.

## What are the QRS width and rate of a junctional escape rhythm?

A narrow QRS at about 40–60 beats per minute, from the AV junction and the His region.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
fasciculus atrioventricularis TA2 3955

**Official Spanish (DeCS)**
Fascículo atrioventricular DeCS D002036

**English (TA2)**
Atrioventricular bundle

**Also called**
truncus fasciculi atrioventricularis · Kent's bundle

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=2069); [Physiology, AV Junction](https://www.ncbi.nlm.nih.gov/books/NBK546663/); [Anatomy, Thorax, Heart](https://www.ncbi.nlm.nih.gov/books/NBK470256/).

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Source: https://durgical.com/en/anatomy/atrioventricular-bundle/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/atrioventricular-bundle/