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 read this articles 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 would suggest 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 to diagnose it .
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 .
- How common is ILBBB in STEMI ?
- How often ILBBB progress to LBBB ?
- ILBBB in dilated cardiomyopathy : Is desynchrony an issue ? (Normal QRS CHF !)
- Is functional rate dependent LBBB in cornary care units same as transient ischemic LBBB ?
- Intermittent LBBB and Incomplete LBBB aren’t they synonymous ?
ILBBB is not that uncommon as one would tend to perceive.
My humble tributes to Barold, Sodi -palleres , and Leo Schamroth . Probably one of 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