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Right bundle branch

Bundle branches · LAD septals (proximal)

Thin, long, unbranched cord running subendocardially down the right side of the muscular septum, entering the moderator band and reaching the anterior papillary muscle before fanning into the right ventricular Purkinje network. Its slender single trunk is easily interrupted, so RBBB is common and often benign.

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)
  5. Right bundle branch

Detail

Conduction velocity
~2 m/s; the RV free wall is activated slightly after the septum and LV apex
Arterial supply
Proximal part by LAD septal perforators (with a contribution from the AV nodal artery); distal part by RCA branches — so proximal RBBB accompanies anteroseptal MI
Course
Septal surface, then the moderator band (septomarginal trabecula), the anterior papillary muscle and the RV free wall
Refractoriness
Longest refractory period of the bundle branches, so it is the branch that fails first at fast rates

When it goes wrong

Block of the right bundle — normal variant; RV strain from PE, ASD or pulmonary hypertension; anteroseptal MI; myocarditis; Chagas disease; degenerative fibrosis

RBBB: QRS 120 ms or more, RSR' ('M') in V1–V2, broad slurred S in I, aVL, V5–V6, T inversion in V1–V3; ST segments can still be interpreted for infarction; new RBBB in anterior MI signals a large infarct and high risk of complete block

Rate-dependent functional block of the right bundle

Aberrant conduction of early supraventricular beats — the Ashman phenomenon in AF, where a long–short cycle produces an RBBB-shaped beat that is not a ventricular ectopic

RBBB combined with LAFB (bifascicular block), degenerative or ischaemic

RBBB with left axis deviation; if PR is also prolonged ('trifascicular' pattern) or syncope occurs, conduction hangs on one fascicle — electrophysiology assessment or pacing

Practise this structure

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