Posts Tagged ‘lbbb’

We know  new onset LBBB  creates considerable anxiety . We  experienced a  reverse situation recently . A 72 year old  man who is known to have chronic LBBB  for over  5 years came  to CCU with vague  chest  discomfort .

His   ECG  was  perfectly normal . . . every one  was  curious !

My ECG always looked like this doctor  !  Now you say it has normalised and you say it concerns you  ! I am really worried  doctor  !

What does it mean doctor ?

Cardiologist : I do not know . Any sudden change in rhythm even if it is from abnormal to normal is to be given importance .

Patient : Is  the  going bad ?

Cardiologist :  I do not know

Patient : Should I  get admitted ?

Cardiologist : I think so  but you need to undergo few blood tests and repeat an ECG .

Patient : Oh  what ?  you  are not sure either !  Are you not an expert in heart  disease doctor ?

Cardiologist : I think I am . I wish I have an answer to  your question .

Follow up

This patient was admitted in intermediate care ward and observed for 12 hours .

His enzymes and Troponin were negative . Echo showed normal LV function .

He was discharged later and adviced  a stress test .

What is the the mechanism of normal ECG  here ?

Intermittent LBBB due to rate dependency is common .But this  man  had persistent chronic LBBB for > 5 years which got normalized .That mystified us !

Can transient ischemia of left bundle  accelerate  the conduction ?

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Can there be a small r wave in V1 and V2 in LBBB ?

Yes .

Though we expect the  reversal of septal depolarization that will   extinguish  the initial r in v1 to v3 . It is  preserved in  many. Hence the  presence of small r in v1 to   v3 does not rule out LBBB.

  1. The commonest explanation given is un-masking of RV free wall forces which is   normally  masked by early LV forces .
  2. Another possibility is the   orientation of septum  in pathological states.
  3. Third possibility is  “r” may  actually represent  the  septal q waves as in LVH or old AWMI  .(Counterpart of small  q in lateral leads )

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LBBB is a common ECG abnormality .The ECG is so classical , no one ever misses the diagnosis. But , what we miss  often is the significance of it .

What is the cause of LBBB in a given patient is much more important than the LBBB itself !

Though the commonest cause of LBBB is a benign one (Pure electrical defect without any valvular , myocardial or ischemic heart disease ) , it is prudent to rule out organic LBBB   . The term  organic  here refers to structural or ischemic etiology .


To diagnose STEMI in LBBB we have the much famed  Sgarbosa criteria .It is a too popular to forget in spite of  it’s limited utility . Applying it in an emergency is not easy exercise . Clinical prediction , cardiac enzymes are  safe and could be more accurate. Thanks to  ACC guidelines  , it has simplified our task .You  are encouraged to thrombolyse all cases of  new  onset LBBB* if clinical picture is strongly  suggestive of ACS.(*The term  “presumably new” onset LBBB  was included  , implying  it is better to err on the safe side )


No one knows how to recognise NSTEMI in LBBB. Logic would say, primary ST depression might occur. How sensitive it is , and which  lead to look for is not known.


Here is an  ECG of a patient who came to our OPD  absolutely asymptomatic for a routine review . He is been diagnosed as a case of  dilated  cardiomyopathy with 30% EF and  no evidence of  ongoing  ischemia.If the history is not known he would have been  diagnosed as a ACS.

To diagnose cardiomyopathy in LBBB we have no specific criteria. But  we have found the following useful

  • Extreme left axis deviation > Minus 45-60 degrees/AVR positivity
  • Low voltage QRS , especially in limb leads
  • ST depression is more flatish  than  the typical  secondary ST/T changes of LBBB
  • QRS notching or slurring either in the r wave or s wave.
  • Atrial abnormalites as evidence by wide P waves.
  • Associated VPDs

Further inputs are welcome to differentiate organic from benign LBBB

Counter point : When we have  facility to do  bedside  echo , why should we  scratch our heads ?

Do not waste time , do a spot echo  . . .

Echo can be very useful in ruling out cardiomyopathies and old MI.But  remember , echocardiography is  unpredictable to detect acute septal MI in the presence of LBBB  , as  paradoxical motion of IVS tend to mask the  ischemic wall motion defect .A simple clue is normal systolic wall thickening will be observed in benign LBBB ,  in spite of  paradoxical  motion .This thickening appears as  post systolic beaking  that  face posteriorly . In STEMI and LBBB thinning or absence of thickening is expected.

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Why the qrs complex becomes wide and tall in LBBB ?

The qrs  complex is  wide , due to delayed conduction over non specialized fibres .The qrs  becomes are  tall due to temporal dissociation of RV  and  LV forces ,  which  leaves  the LV forces  unopposed , thus  a tall qrs  is inscribed  , without the neutralizing effect of RV forces.

Is muscle to muscle  conduction a hall mark of LBBB ?

No , it is not . Even though the left bundle is blocked , much of the conduction tend to occur in

specialized  conduction  system  . It depends upon the level of block of LBBB.

What is the mechanism and clinical significance of left axis deviation in isolated LBBB?

The mean qrs axis is surprisingly  not  altered greatly ,  in LBBB . If there is a significant left ward shift  it may imply associated organic LV pathology or involve ment of predominately  left anterior fascicle

What is  the impact of IVS contraction and timing in LBBB ?

In isolated LBBB, it is expected an abnormal septal motion due to altered sequence of septal activation. This results in an abnormal appearance of  septal motion in Mode (Septal beak immediately following qrs complex) .In fact , this sharp downward movement indicate good LV  function  .Absence  of which  is a  good clue  for a pathological LBBB due to structural heart disease

Why does the abnormal  septal motion in LBBB  ,  do not  desynchronize  the normal LV ?

CRT is the much fancied  treatment in patients with LBBB and cardiac failure. In normal ventricles LBBB do not destabilize LV function in spite of septal /free wall desynchronisation  .This is still a mystery how IVS is cope up with the totally unexpected  insult of asking to work in head over heal situation !In spite of  this the ventricle gets used to the altered conduction pattern and the contractile pattern.(Nature’s  at it’s best !)

What are the mechanical disadvantage of LBBB

  • Septal contraction is  ill-timed
  • Mitral  regurgitation

Most isolated chronic LBBBs  do not  confer  any hemodynamic  disadvantage  to LV  – why ?

LBBBs are dangerous looking ECG , but in most patients it is benign , in the absence  0f structural heart disease like valvular , myocardial or ischemic  disease.

Can there be a small r wave in V1 and V2 in LBBB ?

Yes . Though we expect the  reversal of septal depolarization  extinguish  the initial r in v1 to v3 .It is  noted in many. Hence presence of small r in v1 to   v3 does not rule out LBBB. 

  1. The commonest explanation given is un-masking of RV free wall forces which is   normally  masked by early LV forces .
  2. Another possibility is the   orientation of septum  in pathological states.
  3. Third possibility is  “r” may  actually represent  the  septal q waves as in LVH or old AWMI  .(Counterpart of small  q in lateral leads )

How do we explain concordant  pattern  of QRS  v1 to v6  in LBBB ?

We expect the qrs to  transit from QS  complex  to RS ,  at-least by lead  v5/v6 .Some times even V6  shows a RS complex.This is usually due to faulty lead  position or a grossly enlarged  LV,  ie  if we  record V 7 or V8 we will be able to pick up the qs complex.

What will be the morphology of a VPD that is arising  from LV in the presence of  LBBB ?

A premature beat arising  from a  ventricle which is having  a bundle block  is  sort of  electrical blessing !The VPD often bye  passes the block and makes  the conduction near normal  and a normal  qrs may be  recorded. So , when a patient with LBBB suddenly develops a normal qrs beat or  normal qrs tachycardia  one  should consider a VT arising from the  Left ventricle .

And a studious electro physiology fellow  should  be able to answer the following !

What will be the morphology of  VPD if it arises from RV and septum in the presence of  LBBB ?

Kindwall has tried answer  this question

What is the effect of  LBBB on S1 and  S 2 ?

The classical  description in LBBB   is

  • Paradoxical split of S2
  • Wide split of S1

You are supposed to hear  4 components in complete LBBB  !  In reality this does not happen . At best you can hear the reversed  split of  S2 with difficulty .

One  more reason  for the  non manifestation of these splits is  confounding factors like LV dysfunction , MR , PR interval etc .(Each one tend to pull or push  S1 and S 2 in different directions )

Do  patients with LBBB  , are at increased risk for developing  complete heart block   when

beta blockers , calcium blockers etc  are administered ?

Common sense would say yes. Scientific  sense has  no answer .

We know, ventricles are innervated by two bundles  .When only one bundle  is  functional, it means the ventricles  are experiencing  50 % power shutdown .   In CAD  , single vessel blood supply due to a CTO  is considered  dangerous but in electrical  flow it is not so !  In spite of the fact  that  ventricle has numerous  cell cell electromotive conduction   it is  always better to exercise caution  when administering  beta blockers, calcium blockers and digoxin in patients with LBBB . If it is a must periodic  monitoring is advised .(HV interval in isolated LBBB is slightly prolonged ) Never administer beat blocker in a patient with recent onset LBBB and ACS

Also read the related article  in this blog  Incomplete LBBB

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Pacemaker rhythms  result in classical ECG with  LBBB morphology.It is a universally understood  fact that  RV pacing would  produce LBBB and LV pacing a  RBBB pattern in surface ECG.As with any other rules in medicine , it is not 100%  perfect .(May be 70%)

In the process of oversimplification of rules  we have forgotten a simple fact , that is, interventricular  septum is  shared by both the ventricles . ( functionally and electrically )

In due course , cardiologists and electrophysiologists  have  recognised this fact. A pacemaker lead hitching on the IVS  can behave independently and disobey this  golden rule of pacing.(RV-LBBB,LV-RBBB). Depending upon the orientation of the lead and the pressure it exerts  on the tissue  and degree of penetration of the screwing lead into the septum, the resultant   ECG can  either have a complete RBBB pattern ,  partial RBBB or partial LBBBB or combination of both.

Can RBBB pacing be stable ?

Yes.,  provided the the fixity of the lead and other parameters like impedance and pacing threshold are good.

Before labelling RBBB pacing as safe one should rule out pathological RBBB pacing like septal perforation and

accidental entry into LV through foremen ovale.

Is coronary sinus pacing an acceptable alternative  for  long term permanent pacing ?

The answer is generally ” No ” ,  but it needs rethinking.

A coronary sinus pacing may happen accidentally.The leads get located  either in the main stem coronary sinus or it”s tributaries.the morphology of ECG depends upon the branch it enters.Leads when they reach LV aspect result in RBBB morphology.

Can  we do intentional coronary sinus  pacing for complete heart block ?

There are many accepted  references in literature  that terms   RV pacing as unphysiological and has high risk of precipitating or aggravating cardiac failure. So currently , alternate sites of pacing are explored.( Septum, his bundle , biventricualr etc)

It is an irony , in this era of cardiac resynchronisation therapy where we do coronary  vein pacing  , the same concept is not being tried for regular  permanent pacing in special and difficult situations.( Severe TR, Left sided SVC, AC canal defects etc)

Final message

  1. RBBB morphology following  permanent pacing  need not elicit a panic reaction provided all parameters are stable.
  2. In patients  with difficult RV anatomy* ,  who need permanent pacemaker implantation a modified  coronary sinus pacing can be a solution .But as of now no such speciifc leads are available.EP Industry should take a note on this .

*Epicardial pacing is an option in such situations .But it requires surgery.


Safe right bundle branch block pattern during permanent right ventricular pacing Journal of ElectrocardiologyJanuary 1, 2003   Yang, Yung-Nien ; Yin, Wei-Hsian ; Young, Mason Shing

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