Fasicular Blocks

Conduction delays in the left bundle fascicles and between the Purkinge fibers will result in changes to the QRS complex and T waves. Learn more about fascicular blocks here:

Left anterior fascicular block (LAFB) ECG Criteria

Leftward axis
Small Q waves in leads I and aVL (qR)
Small R waves in inferior leads (rS)
QRS may be normal or slightly prolonged (20 ms) from baseline
Late R wave peak in aVL
Increased QRS voltage in limb leads
Poor R-wave progression is common
No other clear reasons for leftward axis

Left posterior fascicular block (LPFB) ECG Criteria

Rightward axis
Small R waves in leads I and aVL (rS)
Small Q waves in inferior leads (qR)
QRS duration usually normal
Late R wave peak in aVF
Increased QRS voltage in limb leads
No evidence of RVH which is much more common than LPFB

Use the following links to learn about different blocks:

Unifascicular Block

Bifascicular Blocks

Trifascicular Blocks

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