EKG

Trust No One

When I was a 4th year med student doing a cardiology sub-internship I came up with 5 rules of medicine.  One of them was Trust No One.  This was mostly based on shady admission histories we’d get from the EM resident.  In retrospect it wasn’t really their fault that people like their patients overly-packaged and silver-plattered when delivered from the ED, but that’s a topic for another day.  It does get to the crux of this EKG however (which no one got right on the quiz).

20170626wrongleads
~35 y.o. man with CP

We’ll follow our typical approach.  Looking at the Rate, we count off big boxes, 300, 150, 100, 75, just short of 60; the rate is a little over 60.  Looking at the Rhythm we see P’s before every QRS and no lost P waves; this is Normal Sinus Rhythm.  Now we start at intervals and complexes.  The PR honestly is a little on the short side, but we see no evidence of pre-excitation so that probably just reflects a relatively young heart.

Now we start on the QRS which is where some abnormalities start arising.  We haven’t talked about axis in this series at all; for better or worse axis isn’t frequently evaluated by EP’s.  Let’s take a closer look at lead I:

20170626wrongleadsa

The main deflection of the QRS is down; it’s an S wave.  That isn’t normal.  Lead I can be imagined as a horizontal line drawn from the right arm to the left arm if the arms are outstretched.  The dominant S wave in I means that this EKG has a right axis.

Look again at lead II as well.  This lead has a fairly bizarre low-voltage, nearly isoelectric QRS which is very strange.  II generally shows the rhythm well enough that the computer frequently defaults to it as one of the rhythm strips; here we can barely see the QRS, much less the P wave.

20170626wrongleadsb.jpg

A number of people suggested an inferior STEMI; indeed there is 0.5-1mm of STE in III and 0.5mm in aVF.  In addition there is STD to aVL; it is common for the reciprocal STD to be more prominent than the inferior STE.

At this point though we would have an 35 y.o. patient with a right axis and an inferior STEMI; the abnormalities are mounting up.  There’s another solution, and it returns us to the opening paragraph.  We assume when we’re handed an EKG that it was done correctly.  When things just don’t make sense we must question whether that is true just as you would a diluted blood sample run by the lab.  If you repeat this EKG and ask the tech to pay careful attention to hooking up the limb leads correctly you will see the following EKG from the same patient:

20170626wrongrightg

The axis has corrected itself and what’s more, the inferior STE has as well!  In this case there were probably 3 leads in the wrong place, not just two.

A number of people questioned HOCM on the quiz, likely based on the prominent chest voltages.  This patient doesn’t really meet criteria for LVH, the predominant voltages in V2 and V5 add up to less than 7 big boxes.  12mm of deflection in aVL can also represent LVH, but that will be a positive deflection.  In this case it’s downward and the strong S wave in aVL is another clue that the limb leads just look wrong and should be repeated.  Most (though not all) of the time HOCM patients will have T wave abnormalities in the hypertrophied chest leads, and also commonly (though not always) will have inferior q waves.  We’ll come back to HOCM at an EKG to be named later.  In this case the prominent voltages likely just represent a thin chest wall.

 

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