Left anterior (superior) fascicle
Fascicles, Purkinje, muscle · LAD septals only
Long, thin division of the left bundle running across the outflow tract to the anterolateral papillary muscle and the anterosuperior LV wall. A single arterial supply and a slender trunk exposed to outflow-tract pressure make it the most frequently blocked part of the ventricular conduction system.
Traced from the start
Detail
- Supplies
- Anterosuperior and lateral LV free wall through its Purkinje ramifications; normal activation proceeds superiorly and leftwards from it
- Arterial supply
- LAD septal perforators only — no collateral source
- Anatomy
- Long, thin, subendocardial, lying in the high-pressure LV outflow region
When it goes wrong
Block of the anterior fascicle from anterior MI, hypertension, aortic valve disease, cardiomyopathy or degenerative fibrosis (also common in the healthy elderly)
LAFB: left axis deviation −45° to −90°, qR in I and aVL, rS in II, III, aVF, QRS under 120 ms, R-wave peak time in aVL above 45 ms — the commonest cause of left axis deviation; poor R-wave progression may mimic anterior infarction
LAFB plus RBBB after anterior MI
The commonest bifascicular block; with new Mobitz II or a lengthening PR it heralds complete heart block
Practise this structure
2 questions in the bank tagged Cardiac Conduction.
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