Fascicular blocks

Question 1

What are the two fascicles in the left bundle?

Answer 1

-anterior, superior
-inferior, posterior

Question 2

What is the cause of left anterior fascicular block?

Answer 2

There is a block in the anterior, superior fascicle and so the impulse has to travel inferiorly first.
The anteriosuperior then activated by conduction from the posteroinferior

Question 3

What waveform results from impulse travelling inferiorly first?

Answer 3

An R wave in II,III and aVF

Question 4

What waveform results from impulse then travelling through the superior part?

Answer 4

R wave in I, aVR and aVL, S wave in II, III and aVF

Question 5

Why is the wave larger when travelling through this superior part?

Answer 5

It is travelling through slower, ordinary myocardium rather than specialised conducting tissues.

Question 6

What is the QRS axis in left anterior fascicular block?

Answer 6

LAD (superiorly directed)

Question 7

What is the cause of left posterior fascicular block?

Answer 7

Block in posteroinferior so impulse has to travel through high lateral first.

Question 8

Which waveform is seen due to impulse travelling superiorly first?

Answer 8

R wave in high lateral (I, aVL and aVR)

Question 9

Which waveform is seen in II, III and aVF?

Answer 9

A negative q wave

Question 10

What is the QRS axis for left posterior fascicular block?

Answer 10

RAD

Question 11

When can a diagnosis be made for left PFB?

Answer 11

Only in absence of other causes of RAD (LVH, strain and lateral MI)

Question 12

What is trifascicular block defined as?

Answer 12

-RBBB or LAFB/ LPFB WITH 1st degree HB

Question 13

Do you treat trifascicular block?

Answer 13

No, don’t treat but document