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Wednesday, 5 June 2013

LAD + RBBB = Bifascicular Block - #ECGclass Case31

This 44yr old lady comes to see you in surgery complaining of stabbing left side chest pains. 
They are like 'a sharp needling pain' and last for a few seconds at a time. 
They don't radiate, and occur only and at rest, and never on exertion. 
She never experiences dizzy spells, or faints.
She is an anxious lady by nature, and has a lot of social problems, but her father died in his 50's of a heart attack and she is worried about her heart. 
She has been getting these transient pains, on and off for several years. 


What do you think of the history?


Update 1
You note that she is a smoker, and takes low dose Citalopram for her long standing anxiety/depression, but is on no other medications. 

Examination is entirely normal. She is normotensive, with a strong, regular pulse rate of 80bpm. 
You note from her records that she had bloods taken 3 months ago for 'tiredness', which were all normal (including FBC, ferritin, Thyroid and glucose). 

Clinically, you are confident these symptoms do not represent any significant underlying pathology,  but would you do an ECG anyway?


Update 2
You decide you will. 
Here it is:




What are you going to tell her when she calls back for the reassurance? ;-)

Update 3 
There are a couple of things to bear in mind here.

  • Her symptoms are long standing, and are not suggestive of cardiac disease. Clinically, you were not worried.
  • Citalopram might ring alarm bells for you, given its propensity to prolong the QT interval. History should be sought about other medications, including over-the-counter preparations which may interact. Whilst this is unlikely to explain her symptoms, it's worth checking the QT interval.

         See latest MHRA guidelines on safe maximum doses of Citalopram and interactions with other       drugs which prolong to QT interval.

QT interval in this ECG is probably best seen in lead I or II (tip - always select the most normal     looking lead for calculations!) and is probably about 0.36 seconds (9 small squares) but certainly   less than 0.44 secs (11 small squares) . It's normal. 


So what about the rest of the ECG?

Update 4
We can see P waves and the rhythm is regular. So this represents a sinus rhythm originating from the SA node.

What about the QRS complexes?

They look a bit odd, don't they. 
Looking in particular at the precordial leads, they are broadish - although barely, if at all, more than 0.12 seconds (Remember - they should be less than 0.11 seconds (under 3 small squares) in a rapid, healthy conduction pathway; but need to be > 0.12 seconds (over 3 small squares) to diagnose a complete Left or Right Bundle branch block.

This 'in between' duration is often called a incomplete bundle branch block.
So all you have to decide is, is it right or left?

Note the terminal R wave in V1 and V2 (rR') and V3 (rSR).
This pattern fulfils the criteria for Right Bundle Branch block.

Remember the menomics for BBB's:
MaRRow - RIGHT = M in V1 and W in V6
WiLLiaM -  LEFT    = W in V1 and M in V6

But we know it's not quite of broad enough duration to be a complete RBBB, so we call this an Incomplete RBBB. 

But that's not all. 
What about the axis?


Update 5
In a flash, you pull out your sticky-backed Axis calculator from your pocket, and calculate that this is a Left Axis Deviation (LAD). (It's somewhere between -30 and -60 degrees).

A RBBB alone would not generate a LAD.

When we see a Right Bundle Brach Block (RBBB) with a Left Axis Deviation (LAD), we call this a Bifascicular block. 

In other words, 2 of the 3 conducting fasicles of the Bundle of His have conduction delays. Remember the 3 fasicles? - The Right bundle branch has no divisions, but the Left bindle branch has two - an anterior and posterior fasicle:

A left Anterior Fasicular Block (LAFB) gives a Left Axis Deviation (LAD). This is also called Left anterior Hemiblock)
A Left Posterior Fasicular Block (LPFB) gives a Right Axis Deviation (RAD). 

See 'GP Notebook' for a brief, clear explanation of bifascicular blocks, and links to left anterior and left posterior fasicular blocks (LAFB and LPFB)

So this lady has a RBBB+LAD = Bifascicular Block.


But what does this mean to her?
Both RBBB and Bifascicular block can be seen in healthy hearts. 
However, there is an association with underlying cardiac disease.

Possible causes of LAFB 

LAFB can be seen in about 4% presentation with acute myocardial infarction (usually anterior or inferior). Clearly this well lady is not presenting with an acute MI. So what else?

LAFB can also be seen with hypertensive heart disease, aortic valve disease, cardiomyopathies and degenerative fibrotic disease of the myocardium. 

Possible causes of RBBB

  • Atrial Septal Defect
  • Coronary and Hypertensive disease
  • Pulmonary Embolism
  • Congestive Heart failure
  • Cardiac Surgery
  • Idiopathic degenerative Disease
  • Anteroseptal MI
  • Pericarditis or Myocarditis
(Pretty much the same list can be shared with LBBB, but replacing the 'Pulmonary Embolism' with 'Aortic Stenosis'). 

So What next?
You look through her notes, and see that she had an ECG 6 yrs ago for a brief spell of palpitations. 
On reviewing her old ECG it looks exactly the same as today's. 
Given that this lady is clinically well and has no cardiac history. Significant underlying disease is unlikely, but an ECHO might be prudent.

She went on to have an ECHO which was normal. 
Are any further investigations necessary?

Probably not. 
She has long standing ECG changes, with no alarming symptoms of syncope or dizzy spells.
Her ECHO is reassuringly normal. 

However, there is a small tendency for bifascicular block to progress to a more sinister heart block. 
If she develops any new symptoms in the future - such as syncope or dizzy spells, then she needs urgent investigation and pacing would be indicated.

In Summary

Clinical judgement is important.  
There would have been a good case for not doing an ECG here! But you did. 
Whilst this dug up a whole heap of work for you, and worry for her, it didn't alter her ultimate management. These findings are incidental.

None the less, you will ready to act in a flash, next time, if she re-presents with dizzy spells...


Criteria for RBBB

  • The heart Rhythm must originate above the ventricles to activate normal conduction
  • The QRS complex must be broad (> 0.10 secs in Incomplete RBBB, and > 0.12 secs in Complete RBBB)
  • There should be a terminal R wave in V1  (This might be R, rR', rsR', rSR or qR)
  • There should be a slurred S wave in leads I and V6
In Bundle Branch Block, the T wave should be 'discordant' (i.e. deflected in the opposite direction) to the terminal deflection of the QRS complex. 


Thank you. :)
Full summary of interactive Twitter discussion will be shared next week. 




2 comments:

  1. Great cases! FYI, of my EM residents recommended a nice site to help with ECG interpretation.

    The focus is EM, but it has a bunch of nice markups of common emergency rhythms and a useful quiz tool.

    Cheers,
    Paul

    ReplyDelete
  2. Thanks Paul. That's a really useful link - thanks for sharing it! I will pass it on to others.
    H.

    ReplyDelete