Is this just right bundle branch block?

This ECG was texted to me with the text:

“There is a history of RBBB but we do not have an image to compare this with.  I interpret as RBBB with atrial fib.  Anything else?”

What was my response?

The QRS duration is long: the computer measured it at 212 ms.  I measured it at approximately 180 ms.  Either way, it is is too long for simple RBBB.

My response:  “It is a pretty wide RBBB.  So think about high potassium.”
The minimal ST segment shifts seen throughout are within normal limits, so there is no ischemia here.

The response was: K = 6.3 mEq/L.

The patient was treated for hyperkalemia.  Unfortunately, no post-treatment ECG was recorded.

QRS duration in RBBB and LBBB

RBBB by definition has a long QRS (at least 120 ms).  But very few are greater than 190 ms.  Literature on this is somewhat hard to find, but in this study of patients with RBBB and Acute MI, only 2% of patients with pre-existing RBBB had a QRS duration greater than 200 ms.  This study only reported durations in 10 ms intervals up to 150 ms, but one might extrapolate from it that approximately 10% of patients with baseline RBBB have a QRS duration greater than 160 ms.  194 ms would be quite unusual.

The point of this is that if you see BBB with a very long QRS, you must suspect hyperkalemia.  Then of course the peaked T-waves should tip you off.   Unless a patient has severe hypercalcemia (this should be evident by a short QT on the ECG as seen at the bottom of this post), or severe hyperphosphatemia (which is very unusual), treatment with calcium is harmless if you read an ECG falsely positive for hyperkalemia.

So don’t wait for the laboratory K or you might be resuscitating a cardiac arrest (see the case with ECGs #3 and #4 of this post).

How about LBBB?

In this study of consecutive patients with LBBB who were hospitalized and had an echocardiogram, 13% had a QRS duration greater than 170 ms, and only 1% had a duration greater than 190 ms. 

See this case.

Is This a Simple Right Bundle Branch Block?

Here is a case of RBBB with a K of 7.9 and QRS duration of 194 ms.
This was recorded next day at a K of 3.3:

The QRS duration is 149 ms, much more appropriate for simple RBBB

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