Hemiblocks (fascicular blocks)

Question 1

What is a Hemiblock?

Answer 1

Blockage of one of two main division of the LBBB

Question 2

What are the divisions of the LBBB called?

Answer 2

Anterior division (superior)
Posterior Division (inferior)

Question 3

What are the names of the two hemiblocks and which one is more common?

Answer 3

Left anterior hemiblock (LAH)- more common

Left posterior hemiblock (LPH)

Question 4

Which vessel supplies the AV node and also gives branches to the posterior division of the left bundle?

Answer 4

Right Coronary artery

Question 5

What coronary artery supplies the right bundle as well as the anterior division of the left bundle?

Answer 5

Anterior descending branch of the left coronary artery

Question 6

In which direction is the QRS complex in leads I and III in a Left anterior hemiblock (LAH)

Answer 6

I- Downward Q and upright R wave

III- upright Q downward facing R wave

Question 7

In what direction is the QRS facing in leads I and III in a Left posterior hemiblock?

Answer 7

I- upward facing Q and downward facing R wave

III- downward facing Q and upward facing R wave

Question 8

What are the criteria for left anterior hemiblock? (5)

Answer 8

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

Question 9

What are the criteria for left posterior hemiblock? (6)

Answer 9

Right axis deviation (usually > +120)
Small R in leads I and aVL, small Q in II, III and aVF
Usually normal QRS duration (slightly widened Q1S3)
Late intrinsicoid deflection in aVF (>0.045 s)
Increased QRS voltage in limb leads
No evidence for right ventricular hypertrophy

Question 10

What is the etiology of LAH?

Answer 10

Disease in conduction system

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

Question 11

What is the etiology of a left posterior hemiblock (LPH)?

Answer 11

Disease in the Conduction