Hemiblocks (Fascicular Blocks) (Johnston)

Question 1

Hemiblock is

Answer 1

• term for blockage of one of two main divisions of left bundle branch
• LBBB– anterior division (superior) or posterior division (inferior)
• Left anterior hemiblock (LAH) more common than left posterior hemiblock (LPH)

Question 2

The AV node blood supply is from

Answer 2

-RCA so problems/occlusions with RCA will lead to AV-nodal conduction disturbances

Question 3

Hallmarks of LAHs are

Answer 3

-Deep QS complexes in Leads II, III and AVF with left axis deviation

Question 4

Left posterior hemiblocks associated with what kind of axis? Left anterior hemiblocks associated with?

Answer 4

• LPH =RIGHT axis deviation

- LAH= LEFT axis deviation

Question 5

Criteria for LAH

Answer 5

• Left axis deviation (usually greater than -60)
• Small Q in leads 1 and AVL, small R in II, III, and aVF
• Usually normal QRS duration
• Late intrinsic deflection in aVL (>0.045 s)
• Increased QRS voltage in limb leads

Question 6

Criteria for LPH

Answer 6

• Right axis deviation
• small R in leads I and aVL, small Q in II, III and aVF
• Usually normal QRS duration
• Late intrinsic deflection in AVF (>0.045 sec)
• Increased QRS voltage in limb leads
• No evidence for RVH

Question 7

Etiology of LAH

Answer 7

• Disease in conduction system

- Often associated with MI (left anterior descending–LAD occlusion)

Question 8

Criteria for LAH

Answer 8

• Left axis deviation (usually > -60; others > -45)
• Small Q leads in I and AVL
• Small R in leads II, III and AVF
• Usually normal QRS duration or slightly widened Q1S3 (Q in I and S in III)

Question 9

LAD associated with

Answer 9

• MI or other heart disease
• Normal or slightly widened QRS
• Q1S3 widened

Question 10

Etiology of LPH

Answer 10

• Less common

- Disease in conduction system

Question 11

Criteria of LPH

Answer 11

• RAD usually greater or equal to 120 degrees
• Small R in leads I and AVL
• Small Q in leads II, III and AVF
• S1Q3 (S in I and Q in III)