Friday, August 16, 2013

Right Bundle Branch Block with Biphasic Wave in lead V2?

A middle-age alcoholic presents with weakness and vague abdomimal discomfort.  The patient's previous ECG was from 4 years prior and was completely normal.  Here is the presenting ECG:
There is sinus rhythm and Right Bundle Branch block.  There is a tall R-wave in V2 and V3 and slightly excessive ST depression in lead V2, with a biphasic wave.  What is it?  Is this ischemia?  Is it posterior STEMI?  Answer below.


Here I have annotated the ECG:
The apex of the T-wave is seen in V1 (inverted).  If you draw a line down to V2, you see that the nadir of the negative wave is at the same time as the peak of the T-wave in V1.  The positive wave comes later.  So this positive wave is a U-wave, not a biphasic T-wave.  The arrow  in V5 shows a small hump that is also U-wave.

If the U-wave were really a T-wave, then the QT would be 440ms and the QTc would be 568 ms, which is very long.  Whenever the QT interval seems too long, suspect a U-wave.

The patient had no myocardial ischemia.  The potassium returned at 2.2 mEq/L.

Diagnosis: U-wave from hypokalemia, in the presence of right bundle branch block.

1 comment:

  1. interesting.
    i wonder if there's even more at play; eg, low mag, thiamine deficiency, other.
    but the point is : U waves, think low K. thank you , steve
    does a low K contribute to the RBB?


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