Left posterior (inferior) fascicle
Fascicles, Purkinje, muscle · LAD + PDA (dual)
Short, broad fan of fibres passing to the posteromedial papillary muscle and the inferoposterior LV wall, lying in the low-pressure inflow region. Its breadth and dual coronary supply make isolated block rare — when it is present it implies extensive disease.
Traced from the start
Detail
- Supplies
- Inferoposterior LV wall through its Purkinje ramifications
- Arterial supply
- Dual: LAD septal perforators and septal branches of the posterior descending artery (RCA)
- Anatomy
- Short, thick, fan-shaped; sheltered in the inflow tract near the mitral valve
When it goes wrong
Block of the posterior fascicle (extensive ischaemia, almost always with RBBB)
LPFB: right axis deviation beyond +90°, rS in I and aVL, qR in III and aVF, QRS under 120 ms — diagnose only after excluding RV hypertrophy, acute pulmonary embolism, lateral infarction, tricyclic overdose and limb-lead reversal
Verapamil-sensitive re-entry within the posterior fascicle and adjacent Purkinje network (idiopathic fascicular VT, structurally normal hearts, young males)
Relatively narrow VT (120–140 ms) with RBBB morphology and left axis deviation, often misdiagnosed as SVT with aberrancy; adenosine-resistant, terminates with IV verapamil; ablation is curative
Practise this structure
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