Thursday, March 29, 2018

I saw this ECG only after the patient was discharged....

I was reading ECGs on the computer system when this one came up:
What do you think?

There is apparent ST elevation in III, with reciprocal ST depression in aVL.  At first glance, it looks like an inferior STEMI.

It also has a wavy pattern reminiscent of hypokalemia.  See these cases:

Prehospital Ventricular Fibrillation in a Young Woman. What is the Diagnosis?

But it looks very bizarre.  And I knew why. 

I looked to see what the patients symptoms were, and she was a 30-something woman with symptoms listed as "chest burning."

Then I saw that..... It was I who had seen and discharged this patient! 

It turns out she had complained to me only of cough and SOB, and had an asthma exacerbation, and we (I and an advanced practice provider) had treated her for an asthma exacerbation.  Her chest burning was only during coughing.  I had not known that she had an ECG recorded in triage.

The computer diagnosis was "Non-specific ST-T abnormality."   We immediately show all ECGs to faculty physicians in triage, but somehow this one did not get seen.

It had not occurred to me that she needed an ECG, and so I had not looked to see if she had had one.

The advance practice provider who was primarily responsible for the patient had not noticed the ECG abnormality.

So look at the ECG closely:

The 2 most bizarre leads are leads I and III.  aVR, aVL, and aVF also have ST-T abnormalities.

But lead II is completely normal.

How is this possible?

Only if there is artifact of one electrode, specifically the left arm electrode.

This diagram shows how limb leads are produced from the 3 electrodes:
Leads I - III are calculated like this:
Lead I: voltage difference between right arm and left arm electrode
Lead II: voltage difference between right arm and left leg electrodes
Lead III: voltage difference between left arm and left leg electrodes.

The augmented leads are calculated like this:
 aVR: from right arm electrode + average of left arm and left leg
aVL: left arm electrode + average of right arm and left leg
aVF: left leg electrode + average of right arm and left arm.

Notice that:
Lead II does not depend on the left arm electrode.
All other leads do depend on the left arm electrode.

Since, lead II is completely normal, there was a problem with the left arm electrode.

I was 99% certain that these ECG abnormalities were entirely due artifact.  But I wanted to be 100% certain, so we tried to call the patient back.  She said she would return, but she did not.

See this recent case:  Bizarre (Hyperacute??) T-waves


  1. thanks , nice teaching . But i think you mean , DII does not repond on left arm and not right arm

  2. Steve...

    Shouldn't the voltage of aVF = LL - (RA + LA/2)? Those should be minus (-) signs instead of (+) signs. Wilson's Central Terminal established a voltage difference to create the VL, VR and VF leads which, obviously, are really bipolar like the standard leads. It was the removal of the measured lead from the average for the negative pole that resulted in the leads being "augmented" by 50%.

    1. Jerry,
      Good point. I wasn't using the + sign appropriately. I meant it only as an "and" sign. that these are the electrodes that are involved in the calculation.
      I should fix that to be a true equation.

  3. Of course an electrode problem on the left arm. (Loose?)
    Potassium imbalance mostly look best in lead V3-V4.
    Not in I-aVL-III.


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