Bundle of His and bundle branches

Fasciculus atrioventricularis

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What it is

The ventricular conduction pathway: the bundle of His runs from the AV node through the top of the septum and splits into a right bundle branch (reaching the RV via the moderator band) and a fan-like left bundle branch with anterior and posterior fascicles that end in Purkinje fibres.

Function

Spreads the impulse rapidly (up to 4 m/s) down the septum to the apex and papillary muscles so the ventricles contract from apex to base.

Size

His bundle ~1 cm long and 1–4 mm thick; bundle branches a few millimetres wide (exaggerated here for visibility).

Clinical note

Block of either bundle branch widens the QRS complex on the ECG (right or left bundle branch block).