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