Saturday, October 6, 2012

Hyperkalemia in the setting of Left Bundle Branch Block

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 ECG:
There 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 postassium:
Here, 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.


  1. Hmmm.. Easy to assume the widened QRS is from the bundle branch block, rather than hyperkalaemia. Especially when a nurse flicks an ECG in front of your nose to sign, without any story that could suggest to you electrolyte disturbance.

  2. Dr. Smith,

    With the deep S wave in V6, would the first ECG not be more accurately interpreted as a Nonspecific Intraventricular Conduction Delay? And therefore another factor leading one to consider hyperkalemia?

    In the second ECG the NIVCD has resolved and there is a typical LBBB pattern with fully upright broad R or RsR waves in both Leads I and V6.

    Mike Sherriff

  3. Mike,

    Good point! Either way, 220 ms is too long for RBBB, LBBB, or IVCD.

    Steve Smith

  4. Dr. Smith

    Lets say you have a patient that you think might have hyperkalemia, but on the ECG you're not 100% sure if it is a preexisting bundle branch block or if the widened QRS is from hyperkalemia. Let's also say you decide to go ahead and treat for hyperkalemia (for example CaCl 1 gram and 2 amps (90 meq) of sodium bicarbonate).

    With the treatment the QRS duration shortens from 169 ms to 149 ms, and the QTc shortens from 534 ms to 492 ms. (The HR decreases from 88 to 82).

    Do the results prove or strongly suggest hyperkalemia? Or can the treatments narrow the QRS of a BBB and shorten the QTc? (I suspect the CaCl would shorten the QTc regardless of the presence or absence of hyperkalemia).


    1. Pay attention to the QRS, not QTc. Calcium will shorten the QRS only in hyperkalemia. Hypercalcemia does not result in a short QRS, only a short QT as a result of a short ST segment. If the QRS is shorted by calcium, it is not a bundle branch block.

      Steve Smith

  5. i have a question LBBB R wave always should be positive in 1 and v6 ? or it can be negative in V6 also ?


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