Re: Trifascicular blocks vs 3rd degree blocks

[Guest guest]

The combination of RBBB, LAFB and long PR interval has been called

'trifasicular' block and implies that conduction is delayed in the third

fascicle (in this case the left posterior fascicle) and a permanent

pacemaker may be needed. However there are other causes of a long PR

interval such as delayed conduction in the AV node or atrium so

'trifascicular block' is not a true ECG diagnosis.

From ECG library http://www.ecglibrary.com/trifas.html

This is what I learned and teach. The only true trifasicular block is

blockage of the RB, LAF, LPF--a complete AV block. There are too many causes

of PR prolongation to declare the third fascicle blocked (drugs, disease,

metabolic states) and functionally must be treated as an complete AV block.

Is the block in the AV node, is it in one of the three fascicles that

remains unblocked? Is it a toxic state? What is the clinical significance?

Without electrophysiological studies you cannot tell. The difference between

" book medicine " and the " practice of medicine " can be quite different.

BEB

[Guest guest]

Exactly, I think we have been saying the same thing all along...

My original point was that since we are unable to always know exactly what is

causing the 3rd degree block (tri-block, meds or just plain old AV dysfunction),

a trial dose of atropine may be helpful and as referenced is a Class IIa

recommendation in the ACLS guidelines. This would only apply however to narrow

QRS complexes that are more likely to be related to an infranodal block, as

opposed to wide QRS complexes caused by fascicular blocks where atropine will

not be effective.

Many people come into my ACLS classes saying that atropine will not work for 3rd

degree block (CHB) but I advise them, that it MAY help CHB, depending on its

etiology.

Thank you for the discussion!

Nick

RE: Trifascicular blocks vs 3rd degree blocks

The combination of RBBB, LAFB and long PR interval has been called

'trifasicular' block and implies that conduction is delayed in the third

fascicle (in this case the left posterior fascicle) and a permanent

pacemaker may be needed. However there are other causes of a long PR

interval such as delayed conduction in the AV node or atrium so

'trifascicular block' is not a true ECG diagnosis.

From ECG library http://www.ecglibrary.com/trifas.html

This is what I learned and teach. The only true trifasicular block is

blockage of the RB, LAF, LPF--a complete AV block. There are too many causes

of PR prolongation to declare the third fascicle blocked (drugs, disease,

metabolic states) and functionally must be treated as an complete AV block.

Is the block in the AV node, is it in one of the three fascicles that

remains unblocked? Is it a toxic state? What is the clinical significance?

Without electrophysiological studies you cannot tell. The difference between

" book medicine " and the " practice of medicine " can be quite different.

BEB

[Guest guest]

,

Would you address the issue of why atropine is recommended to be given with

caution in Mobitz II and 3rd degree blocks because it might increase or

exacerbate the block? I understand that it doesn't work in the ventricles so

would

not be likely to speed up a 3rd degree with a ventricular escape rhythm. But

why would it increase the degree of block in a Mobitz II?

Mr. Grady wants to know.

[Guest guest]

I asked an EKG expert who I am influenced by for some help on this subject. He

provided a quote from Dr. Chou's book Electrocardiography in Clinical Practice:

" Trifascicular block may be suspected if there is a permanent block in one

fascicle and an intermittent block in the other two fascicles. For example, if

a patient with a chronic RBBB has a pattern of left anterior fascicular block

and left posterior fascicular block on different occasions, the presence of

disease in all three fascicles is implied. If the block in one of the three

fascicles is incomplete, the ECG shows a bifascicular block with first- or

second-degree AV block is caused by involvement of the third fascicle because

the conduction delay may be at the level of the AV node or the His bundle.

A complete trifascicular block results in a complete AV block. The escape

pacemaker often originates in the region of the left or right posterior

fascicle, resulting in an escape rhythm with a pattern of RBBB plus left

posterior fascicular block or RBBB plus left anterior fascicular block,

respectively.

A definitive diagnosis of trifascicular block requires His bundle recording.

Levitas and Haft compared the results of His bundle recording in 89 patients

with PR prolongation and bifascicular block with those of 172 patients with a

normal PR interval and bifascicular block. Variable degrees of HV interval

prolongation were recorded in the two groups. The authors concluded that it is

difficult to determine whether trifascicular block is present in the individual

patient from the body-surface ECG. "

It was also commented on that the term 'trifascicular block' is going out of

favor. 'Bilateral bundle branch block' is now being used to describe blocks of

both the main right and main left bundle branches. BBBB=4-B's for all 4

fascicles... easy enough to remember.

My bad for using that term. Just wanted to share this last piece of info with

you. Thank you, I have learned a lot from this researching this discussion.

Regards

Nick