Hemiblocks (Fascicular Blocks)

Question 1

Hemiblock

Answer 1

blockage of one of two main divisions of left bundle branch

• Left bundle branch
– anterior diversion (superior) – posterior division (inferior)

• Hemiblocks
– left anterior hemiblock (LAH) – more common – left posterior hemiblock (LPH)

Question 2

Criteria for Left Anterior Fascicular Block

Answer 2

Left axis deviation (greater than 60 degrees; others > -45 degrees)
Small Q in leads I and aVL, small R in II, III, and aVF
Usually normal QRS duration or slightly widened Q1S3
Late intrinsicoid defection in aVL (>0.045s)
Increased QRS voltage in limb leads

Question 3

Criteria for Left posterior fascicular block

Answer 3

Right axis deviation (>+120 degrees)
Small R in leads I and aVL, small Q in II, III and aVF
Usually normal QRS duration or S1Q3
Late ID in aVF (>0.045 s)
Increased QRS voltage in limb leads
No evidence for right ventricular hypertrophy

Question 4

Etiology of Left Anterior Hemiblock

Answer 4

Disease in conduction system

Often associated with MI - LAD occlusion

Question 5

Etiology of left posterior hemiblock

Answer 5

less common

disease in conduction system