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“Incomplete” left bundle branch block : Our knowledge is as incomplete as LBBB !

Posted Apr 07 2010 11:13pm

LBBB is probably the most important  conduction defect of the heart .When we say LBBB , we visualize a  strikingly  wide bizarre qrs complex .

Left bundle even though is considered  a discrete structure , the fascicles  make it a diffusely spread structure. Many varieties of LBBB with various degrees of involvement occur.

Talking about the basics of  LBBB  electrophysiology  is out of place for the current generation cardiologists,  who  have little spare time as  they sweat it out inside the cathlabs.

In early 1960s and 70s great articles came from pioneers regarding these defects. If we want get a good insight into this please read articles  like this  . (One  from Sodi palleres   ) Who  says LBBB is a dynamic process, where it can occur from mild functional  delay to a total block .

The conduction  properties of left bundle is very much influenced by heart rate.

Law of statistics  says for every complete LBBB  at least three to 4 times incidence of incomplete  LBBB

Then . . .

Why we are not diagnosing ILBBB often ?

  • We miss it
  • Mistake it with LVH
  • We know it  is there , but we do not want  diagnose it .( But what is the big deal in diagnosing ! )



How to diagnose ILBBB?

See  Sodi palleres criteria*

What is the relationship between qrs width and completeness of LBBB ?

Surprisingly and contrary to the belief , the width of the qrs has no linear correlation between severity of LBBB. In fact incomplete  LBBB can occur with even 150ms qrs !

Then ,  what  exactly determine the completeness of LBBB ?

What  matters is , whether the down coming impulse gets blocked  and split in the  left side of the IVS or not ? This causes the  the septal vector to  change  it’s direction ( ie  right to left instead of the normal left to right) It  removes the initial small r wave in v1  and q in v6  in complete LBBB. In  incomplete LBBB these  r and q are  often retained .

What is the differential diagnosis of ILBBB ?

Type B WPW may mimic LBBB and vice versa.

LV hypertrophy .

Differences : See table in  the Barold’s article  linked above .

Unanswered questions

  1. How common is ILBBB in STEMI ?
  2. How often ILBBB progress to LBBB ?
  3. ILBBB in dilated cardiomyopathy : Is desynchrony an issue ? (Normal QRS CHF !)
  4. Is functional  rate dependent  LBBB in cornary care units  same as transient  ischemic LBBB ?
  5. Intermittent LBBB and Incomplete LBBB  aren’t they  synonymous ?

Final message

ILBBB is not that uncommon as one would  tend to perceive. It is the  academic reluctance  to dwell deeper into surface ECG  findings . Let us not  consider  it an inferior job  in this era of  hyped up cardiology care.

My humble tributes to  Barold, Sodi -palleres ,  Schamroth . Probably the best  article on ILBBB is linked below. Reviewed    in 1963 !  Not much data has been added  in the next 47 years as on 2010 .(Rather ,  no body  exists  in this  world of  cardiac sciences to add further data !)


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