EKG LAD and left bundle branch block

[blazing]

Hey all:

Not sure if anyone else read the Dubin book, but one problem says that if a patient has a left bundle branch block, then the left axis deviation is not very reliable. What does it mean that it's not very reliable?

It also says ST segment and T waves are also unreliable in left bundle branch block. Why?

Thanks

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[NickNaylor]

You have dysfunctional tissue that can't conduct correctly which results in changes in the EKG. By "not very reliable" I'm assuming he means that you have a deviation but it is unlikely to be due to a cause you might otherwise think of (e.g., LVH). In the setting of a LBBB, he might be suggesting that it might be better to get more advanced testing (e.g., echo) to identify anatomical abnormalities rather than relying on an EKG alone. With respect to ST/T waves, it's not unusual to have abnormal waves with a bundle block. Again, I'm guessing by "not reliable" he means that you might have abnormal waves that aren't necessarily suggestive of pathology you might otherwise think about (e.g., T wave inversion with MI, ST elevation/depression).

 

[e30ftw]

you have LAD because the ventricles are being activated in sequence from R>L instead of at the same time. So the QRS deflection in II is usually going to be negative causing "LAD".

LBBB is associated with appropriate discordance of ST segments in the anterior leads. There can be up to 5mm of appropriate STE as long as it is discordant.

diagnosing STEMI in LBBB is a well discussed clinical scenario.

Sgarbossa developed his criteria which are probably the most well-known today.

The most important thing to remember is that concordance is bad. Positive QRS and Positive STE is STEMI in LBBB if > or = to 1mm.
negative QRS deflection and ST depression is STEMI in anterior leads.

discordance needs to be > 5mm with appropriate ischemic morphology.

http://lifeinthefastlane.com/ecg-library/basics/sgarbossa/