#lpfb

[emresident]

Bundles, LAFB, and LPFB

[emresident]

LAFB, LPFB

LAFB

What is happening?

left bundle branch composed of  left anterior fascicle and left posterior fascicle

LAFB - anterior fascicle blocked

initial impulse downward and rightward, then upward/leftward

EKG:

-left axis deviation (+I, -avF, -II)

-look at II, III, avF: rS (small r, deep S)

-look at I, avL: small q waves, tall R waves

-avL: prolonged R wave to peak time

-increased QRS voltage in limb leads

-slight QRS widening (80-110)

LPFB

What is happening?

-initial vector upward and leftward, then vector downward and rightward

-less common than LAFB (many bundles of fibers, more resistant)

EKG

Right axis deviation (-I, +avF)

no RVH, no other cause for Right axis deviation

look at I, avL: rS (small r, deep S)

llook at II, III, avF: small Q, tall R. Also prolonged R wave to peak time  in avF

QRS normal or slightly prolonged (80-110)

increased QRS voltage in limb leads

Bifascicular block

Technically LBBB = bifascicular block as both fascicles are blocked

RBBB + LAFB (RBBB + LAD)

OR RBBB + LPFB (RBBB + RAD)

significance - conduction to ventricles from 1 remaining fascicle