Friday, February 19, 2016

Why is there ST depression in aVL in this case of Pericarditis?

This ECG is from an article in the New England Journal on pericarditis.  

Acute Pericarditis

Martin M. LeWinter, M.D.
N Engl J Med 2014; 371:2410-2416December 18, 2014DOI: 10.1056/NEJMcp1404070


A reader had read this post on ST depression in lead aVL in pericarditis vs. inferior STEMI

He sent this ECG recorded from a patient with pericarditis and asked why there is ST depression in lead aVL:
There is sinus rhythm with diffuse ST elevation (especially in inferolateral leads, which is typical of pericarditis).  There is diffuse PR depression and Spodick's sign.
There is a tiny amount of reciprocal ST depression in lead aVL.

My answer to the reader is below:

As there are always exceptions to every rule, one must look at every ECG individually.
There is minimal ST depression in aVL, perhaps 0.5 mm.
Put that into the context of the whole ECG: there is very significant ST elevation in inferior leads.  This is not subtle. When there is inferior MI with large ST elevation, there is nearly always marked reciprocal ST depression in aVL.

Proportional Analysis

Always interpret every ECG with proportional analysis.  Everything should be proportional to everything else for any given diagnosis.    In this case, you see very large inferior ST elevation, but only minimal (if any) reciprocal ST depression.  The proportions do not make sense.  This would be exceptionally unusual for inferior MI.

ST axis analysis

The ST elevation is higher in lead II (3mm) than lead III (2mm).  This is also a pretty good ECG sign for pericarditis, as it implies the ST axis is closer to lead II than III, and less than 90 degrees.  When there is ST depression in aVL, the ST axis must be to the right of lead II (greater than 90 degrees).  Thus, the ST axis is between leads II and aVF (60-90 degrees).  However, the fact that there is such minimal ST depression in lead aVL tells us that the ST axis is only BARELY greater than 60 degrees, perhaps 65 degrees.  Thus, it is still very close to the normal axis for pericarditis (up to 60 degrees) and it is unusually leftward for inferior STEMI.

But, as I always say, you diagnose pericarditis at your peril, so always approach this with caution!

Steve Smith

5 comments:

  1. After your explanations I have learned that the proportionality principle is a general and important one when interpreting also an ECG like this. But I wonder whether there are some numeric values as they exist for example for ST/S in LBBB+ami. In other words, in this ECG there is a very tiny ST depression but my answer is: does exist, let say, an STE-inf/STD-avl ratio? Perhaps did you already evaluate this matter?
    More on the topic of proportionality, please. Thanks.

    By reasoning just on this ECG only (that is, without having additional clinical or Echo informations, always helpful), another sign of pericarditis may be the ST-depression in AVR. As you have magistrally explained, the ST vector in pericarditis is between 45° and 60° thus opposite to AVR, therefore very different to that of inferior STEMI. For these reasons there should ALWAYS be ST-depression in AVR in pericarditis. Isn't it? Many thanks.

    Mario Parrinello

    ReplyDelete
    Replies
    1. Mario,
      this ECG still "breaks the rule" of ST depression in aVL. It does so because the ST vector is a bit farther right (65 degrees) than the rule would state that it should be. The proportion thing comes in only because one would not be able to detect this slight ST axis deviation if there was not a lot of ST amplitude.
      aVR is opposite an imaginary lead exactly between I and II (opposite of 30 degrees, which is -210 degrees. Any ST axis that is between -60 and +120 will have ST depression in aVR. This includes all pericarditis and all inferior STEMI!
      Steve Smith

      Delete
  2. I think that the diagnosis in this patient would have been difficult
    We need serial ecg to make sure we did not miss an AMI
    We cannot be so sure from a single ecg
    traditional and basic fact that st depression in pericarditis happens only in avr and v1

    Thanks

    ReplyDelete
  3. The ST elevation in inferior MI is convex upward and not concave. ..besides one would see ST depression in aVL CONCAVE and not convex as a reciprocal change in inferior MI

    ReplyDelete
    Replies
    1. That is not at all a reliable rule and is, in fact, dangerous.

      Delete

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