ChoiceHub
Sign in

Bundle of His (atrioventricular bundle)

Bundle of His · 40–60/min AVN artery + LAD septal

Continuation of the AV node as an insulated cable 1–2 cm long that penetrates the central fibrous body and runs along the inferior margin of the membranous interventricular septum before splitting into the bundle branches. It is the sole physiological conduit across the fibrous skeleton, so damage anywhere along or below it is 'infranodal' and unpredictable.

Traced from the start

  1. Sinoatrial node
  2. Internodal pathways (anterior, middle, posterior)Right atrial myocardium
  3. Atrioventricular node
  4. Bundle of His (atrioventricular bundle)

Detail

Intrinsic rate
40–60/min proximally (part of the AV junction), falling to 20–40/min in the distal His–Purkinje tissue
Conduction velocity
1–2 m/s: fast-response Na+ cells wrapped in a fibrous sheath that prevents lateral spread
Arterial supply
Dual: the AV nodal artery (RCA) and the first septal perforator of the LAD — relatively ischaemia-resistant, but exposed by large anteroseptal infarcts
Course
Penetrating portion through the central fibrous body, then a branching portion on the crest of the muscular septum beneath the membranous septum, directly below the non-coronary and right coronary aortic cusps

When it goes wrong

Intermittent conduction failure within or below the bundle — Lenègre's idiopathic fibrosis, Lev's calcification of the fibrous skeleton in the elderly, anteroseptal MI, sarcoidosis, cardiac surgery

Mobitz II: constant PR then a suddenly dropped QRS without warning, usually with a wide QRS (block below the His in ~75%); abrupt progression to complete block, Stokes–Adams syncope or asystole — admit, temporary pacing, then permanent pacemaker; atropine does not help and may worsen the conduction ratio

Complete infranodal block (anterior MI with septal necrosis, degenerative conduction disease)

Third-degree block with a slow, unreliable ventricular escape: wide QRS at 20–40/min, syncope, cannon 'a' waves, variable S1 intensity; poor prognosis, urgent pacing

Surgery or intervention beside the membranous septum — aortic valve replacement or TAVI, VSD closure, septal myectomy, alcohol septal ablation, tricuspid annuloplasty

Iatrogenic complete heart block or new LBBB; a permanent pacemaker is needed in a proportion

Aortic valve endocarditis extending into the root

New PR prolongation or heart block signals a peri-annular abscess — an indication for urgent surgery

Practise this structure

2 questions in the bank tagged Cardiac Conduction.

A 24-year-old man presents with two hours of palpitations. He is alert, has no chest pain, and his blood pressure is 124/76 mmHg. The radial pulse is regular at…

Foundations · common

A 46-year-old labourer is freed after six hours trapped beneath a collapsed brick wall. Both thighs are tense, swollen and tender, and he cannot move his toes.…

Foundations · middle twist