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Hyperkalemia in the setting of Left Bundle Branch Block

Posted Oct 06 2012 8:20am
I'm sorry, but there was an error in the previous post and I had to remove it.  Depending on information received, I may be able to repost it.

A dialysis patient presented with vomiting.  He has  known baseline left bundle branch block.  Here is his initial ECGThere is left bundle branch block, with a QRS duration of 220 ms according to the computer analysis.

Here is his previous ECG, recorded with normal postassiumHere, the QRS duration was 160 ms.  So the previous one is widened by 60 ms.

A widened QRS should always make you suspicious of hyperkalemia.  Indeed, the potassium was 7.3 mEq/L.  After therapy, the widening resolved.

Here is a similar case involving right bundle branch block.

What is the normal QRS duration in LBBB?

In this study of consecutive patients with LBBB who were hospitalized and had an echocardiogram, a QRS duration less than 170 ms (n = 262), vs. greater than 170 ms (n = 38), was associated with a significantly better ejection fraction (36% vs. 24%).  Only 13% had a QRS duration greater than 170 ms, and only 1% had a duration greater than 190 ms.

Obviously, if you have a previous ECG for comparison, you can diagnose prolonged QRS in the setting of LBBB easily.  But it is clear that if your patient with LBBB has a QRS duration greater than 190, then there is more going on.

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