Wednesday, March 18, 2020

A 32 year old woman with chest pain has a prehospital ECG

A 32 year old woman with chest pain has a prehospital ECG:
What do you think?
Is it really "due to ventricular hypertrophy," as the computer says?

This was texted to me and my response was:

"Leads are reversed.  Correct them and I think you will find a STEMI (or OMI).  Either inferoposterior or posterolateral."

The QRS is negative in I, II, and aVL and positive in aVR, all of which makes for a bizarre axis.  Normally you can determine if it is truly lead placement by looking at P-waves, which should be upright in lead II.  Here it is difficult to see them.  But another way is to see if the QRS is negative in the lateral precordial leads.  Here the QRS is positive.

This could also be seen if a right sided ECG is recorded in someone with dextrocardia (this would be extremely unusual!)

There is ST Elevation in aVR and STD in I, II, and aVL.  Clearly there should be ST Elevation in lateral leads and ST depression in the right sided lead aVR.

I believe that the right and left arm leads are reversed, but in any case lead reversal is certain.

So they corrected the lead placement:

Here the leads are placed correctly:
Clearly a Posterolateral STEMI now.
The computer diagnosed it this time.

This lead placement problem was not diagnosed by the medics.  This resulted in a prolonged Door to Balloon Time.  The resident did see it.  The faculty did not, and learned a lot.


Culprit was a 100% Occlusion of OM-1 (first obtuse marginal off the circumflex).

Learning Points

1.  Young Women do have Acute MI.  See here for more cases:

2. Beware Lead placement!  The computer will not always see it.  STEMI can be missed.  See Ken's detailed comments below.

MY Comment by KEN GRAUER, MD (3/18/2020):
Recognition of technical errors is an often ignored, yet extremely important aspect of optimal ECG interpretation. That such technical errors remain prominent in everyday practice is immediately evident from random sampling of a series of tracings in any of the many international ECG internet forums. As a result — we like to periodically publish clinical examples of lead misplacement. To review a number of these — GO TO:

There are many similarities between Todays Case — and the February 11, 2020 post on Dr. Smith’s ECG Blog. Both patients presented with acute chest pain — which adds to the challenge of recognizing superimposed lead misplacement.
  • By far — the most common lead reversal is mix-up of the LA (Left Armand RA (Right Arm) electrodes. This is the mix-up that occurred in both the Feb. post and in today’s case. Figure-1 (which I’ve adapted from the superb LITFL web page on this subject) — reviews the essentials of LA-RA reversal.

Figure-1: LA-RA Lead Reversal — adapted from LITFL (See text).

With the essentials from Figure-1 of LA-RA lead reversal in mind — Let’s TAKE ANOTHER LOOK at the initial ECG in this case (Figure-2):

Figure-2: The initial ECG in the ED — with features of LA-RA lead reversal written below the tracing (See text).

CHALLENGE — TRY TO ENVISION what this initial ECG (in Figure-2) would have looked like IF the limb leads were correctly placed.

ANSWER: In the bottom tracing of Figure-3 ( = ECG #1Boutlined in RED) — I have made the following changes:
  • Lead I from ECG #1A has been inverted in ECG #1B.
  • Leads II and III have switched positions.
  • Leads aVL and aVR have switched positions.
  • Lead aVF and the chest leads were left unchanged.

NOTE: As per Dr. Smith — correction of LA-RA lead reversal reveals acute postero-lateral OMI. This diagnosis is based on the following ECG features that we see in ECG #1B:
  • Sinus rhythm (there now is an upright P wave in lead II of ECG #1B).
  • Hyperacute ST-T waves in high-lateral leads I and aVL (as determined by T waves in these leads that are much fatter-at-their-peak and wider-at-their-base than expected).
  • Reciprocal ST depression in each of the inferior leads — which is most marked in lead III, in which the shape of the depressed ST-T wave is a mirror-image opposite picture of the hyperacute ST-T wave in lead aVL.
  • Anterior lead changes suggestive of acute posterior OMI — in the form of unexpectedly tall R waves in leads V2, V3 and a characteristic shape to the ST segment depression seen in leads V2 and V3, consistent with a positive Mirror Test (See My Comment in the February 16, 2019 post for illustration of the Mirror Test).

Figure-3: Comparison of the initial ECG in the ED ( = ECG #1A) — with what this ECG would look like IFi) Lead I was inverted; ii) Leads II and III switched places; andiii) Leads aVR and aVL switched places (See text).

KEY POINTS: As per Dr. Smith — This case is remarkable for lead misplacement in the initial ECG, that occurs in association with acute OMI. I’ll add the following points that have helped me to rapidly recognize this most common technical error of LA-RA lead reversal:
  • You should never normally see global negativity (of the P wave, QRS complex and T wave) in lead I. If ever you do — then the diagnosis is either: i) Limb lead reversal; or, ii) Dextrocardia. Dextrocardia is rare (lead reversal is far more common!). With dextrocardia — there is reverse R wave progression (with much more rapid loss of R wave amplitude than what we see in ECG #1A).
  • Lead aVR — most often manifests a predominantly negative QRS complex (often, but not always accompanied by a negative P and T wave). But the combination of a predominantly negative QRS in lead I with an upright QRS and upright T wave in lead aVR is distinctly unusual. IF lead I looks like you expect aVR to look — and, aVR looks like you expect lead I to look — then suspect LA-RA lead reversal!
  • The P wave should be upright in lead II when there is sinus rhythm. IF you do not see an upright P wave in lead II — then you either have: i) a non-sinus rhythm; ii) some type of lead reversal; or, iii) dextrocardia. Note that NO P wave is seen in lead II of ECG #1A (although P waves are seen in leads I, III, aVL and aVF of this tracing). Then note that in ECG #1B — that an upright P wave now is seen in lead II, as expected with normal sinus rhythm.
  • Finally — Please remember the easy-to-find superb web page on LITFL — that describes key findings in the 7 most common lead reversals: Simply put in, LITFL Lead Reversal into the Search bar — and this web page link will instantly come up!


  1. nice explaianation Dr.Ken and Dr.Smith
    at first sight the first ECG looks Dextrocardia to me. as the R waves are progressively smaller in chest leads.
    is there any way we can diagnose by ECG in this scenario not Dextrocardia but simple limb lead reversal.

    1. Excellent question! ECG examples of true dextrocardia are few and far between — because the condition is rare. So virtually none of us get to see a large sampling of cases. Here’s one (from LITFL — ) — and it provides a “textbook example” of reverse R wave progression (Note that R wave amplitude is greatest in lead V1, and then progressively decreases as one moves across the chest). That is DIFFERENT than the ECG in this case, in which the R wave becomes taller as one moves from V1-to-V2 — and the very tall R wave is still present in lead V3! If you Google, “dextrocardia ecgs” — you’ll be taken to this site = dextrocardia.ecg — on which are a number of ECG examples you can quickly review. Most seem to show the pattern from the LITFL case I reference above — but some do not. The problem is that there are a huge number of anatomic variants in which not only the heart, but other organs, great vessels, etc. may all be transposed — as well as the possibility that the patient living with dextrocardia may develop other underlying conditions (ie, bundle branch block, heart failure with chamber enlargement, etc.) — all of which can make such variants of dextrocardia ever so much more challenging to recognize. Clinically, the 1st things to do are: i) Ask the patient (Many with dextrocardia will know their heart is on the “wrong” side … ); ii) Listen to the chest to see if heart sounds are on the right; iii) Get a chest x-ray, which usually will definitively answer the question! and iv) Repeat the ECG, verifying correct lead placement. If still suspicious for dextrocardia — Repeat the ECG with chest leads placed on the right (ie, V1R, V2R, etc.). Hope that helps — :)

    2. @ Kiran — I just published a case of Dextrocardia on my ECG Blog — GO TO — — In this post, I've added information specific to recognized the various types of dextrocardia — :)

  2. In this situations, the R/S ratio is more reliable and important than the absolute height of the R wave.
    k. Wang.

    1. Hi K. I'm not sure to what condition you are referring to regarding use of the R/S ratio (ie, dextrocardia or posterior infarction?) — Nor if you are referring to the R/S ratio in leads V1 or V2 (or V3)? And sometimes I think it depends on what the entire ECG is showing (ie, in ECGs 1A and 1B above — I thought the disproportionately tall [ie, R/S ratio] in lead V2 provided clear indication that supported acute posterior involvement). I'd welcome clarification from you regarding your comment — :) THANKS as always!

  3. A very good example ... not only of an LA/RA lead wire switch but also a reminder to examine the ECG again AFTER the ECG is performed correctly! On several occasions during my long career I have had to point out blatant abnormalities AFTER the wires were rearranged and the ECG repeated. People so often assume there is only ONE major problem per ECG.

    A rule of thumb I use is that if the P wave in Lead II is the tallest, it is originating in the sinus node and the acquisition of the ECG is OK (as far as LA/RA attachments). If the P wave in Lead III is the tallest upright P wave, then suspect a LA/RA lead wire switch (as in this ECG). If the P wave in Lead I is the tallest, then suspect a LA/LL lead wire switch. Of course, there can be exceptions - especially with advanced emphysema which can result in the tallest P wave being in aVF at times. But otherwise, it's a pretty good rule.

    I'm wondering if Dr. Wang was referring to the fact that when we talk about "poor R wave progression" we are REALLY talking about R/S ratio progression. It is the R/S RATIO that progresses under NORMAL circumstances - not just the R wave HEIGHT.

    BTW, Ken, that was an excellent discussion of distinguishing dextrocardia from a lead wire switch. Thanks for an excellent review!

    1. THANKS so much Jerry! K just sent in clarification of his remark. While of course true that one has to review all 12 leads on the tracing — you, myself & K all agree that the R/S ratio (rather than R wave height) is the most important thing! — :)

  4. Ken, disregard my response to your question and replace it with this revised one: "In both dextrocardia and posterior MI"

    1. Thanks for clarifying K! I agree with you! — :)


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