Tuesday, July 28, 2020

A Woman with New Dyspnea. Is the extreme left axis deviation, with negative T-wave in lead III, suggestive of RV strain?

MY Comment by KEN GRAUER, MD (7/28/2020):
The ECG in Figure-1 was obtained from a middle-aged woman who presented to the ED with new-onset shortness of breath.
  • QUESTION: Is the inferior lead T wave inversion indicative of RV (Right Ventricular) Strain from acute PE (Pulmonary Embolism)?

Figure-1: ECG obtained from a middle-aged woman who presented to the ED with new dyspnea (See text).

MY THOUGHTS on ECG #1: As always — I favor a systematic approach to ECG interpretation. Without a systematic approach — it might be all-too-easy to overlook that something is “off” here ...
  • Regardless of whichever systematic approach you favor for 12-lead ECG interpretation — the 1st Step should always be to interpret the rhythm. Once you’ve ensured that your patient is hemodynamically stable — the, “Watch Your Ps, Qs and 3Rs” memory aid reminds me of the 5 KEY parameters to assess (CLICK HERE — if interested in more on this Ps, Qs, 3R approach).
  • Although there is no long lead rhythm strip in ECG #1 — the rhythm is regular at a rate of ~80/minute. The QRS complex is narrow.
  • P waves are present — and, these P waves are clearly related to neighboring QRS complexes, because the PR interval is constant. This tells us that P waves are conducting to produce the QRS complex that follows them.
  • Did you recognize that the P wave in lead II is negative?

PEARL #1: If you see P waves that are conducting, but these P waves are negative in lead II — then you do not have a sinus rhythm. The only 2 exceptions to this are: i) If there is dextrocardia; and/orii) If there is some type of lead reversal.
  • PEARL #2: We can easily rule out dextrocardia for ECG #1 — because R wave progression is perfectly normal in the chest leads (there should be reverse R wave progression if the patient had dextrocardia).
  • This leaves us with distinguishing between a low atrial or junctional rhythm (which could be the cause of negative P waves in lead II) — vs some type of lead reversal.

Recognition of Lead Reversal:
Technical errors featuring a variety of lead reversal placements remain a surprisingly common “mishap” of everyday practice. As a result — we like to periodically publish clinical examples of lead misplacement. To review a number of these — GO TO:

PEARL #3 — I’ve summarized in Figure-2 those tips that have helped me most over the years to rapidly recognize tracings in which lead reversal is likely (Taken from My Comment in the February 11, 2020 post in Dr. Smith’s ECG Blog).
  • Applying the tips from Figure-2 to the initial ECG in Figure-1 — not only is the P wave negative in lead II — but lead aVR does not manifest a predominantly negative QRS complex. Instead, the QRS in lead aVR appears to be positive and both the tiny P wave and T wave in this lead also appear to be positive. This shouldn’t normally be ...
  • Increasing my suspicion further that there must be some type of lead reversal in ECG #1 — is the overly similar appearance of the QRST complex in all 3 of the inferior leads.
  • By far — the most common lead reversal is mix-up of the LA (Left Armand RA (Right Arm) electrodes. But this is not the mix-up that occurred in today’s case — because we do not see global negativity (of P wave, QRS and T wave) in lead I (See the February 11, 2020 post).

Figure-2: Tips for recognizing lead reversal. (See text).

PEARL #4 — My favorite on-line “Quick GO-TO” reference for the most common types of lead misplacement comes from LITFL ( = Life-In-The-Fast-Lane). I have used the superb web page they post in their web site on this subject for years. It’s EASY to find — Simply put in, LITFL Lead Reversal in the Search bar — and the link comes up instantly.
  • This LITFL web page describes the 7 most common lead reversals. There are other possibilities (ie, in which there may be misplacement of multiple leads) — but these are less common and more difficult to predict.
  • When I suspect a type of lead reversal that I am less familiar with — I simply review those 7 most common types of lead reversal on the LITFL page — and see if any of the ECG examples they provide seems to apply. In ECG #1 — the key identifying feature that led me to suspect RA-LL reversal was the finding of similar-looking global negativity in each of the 3 inferior leads (See Figure-3).

Figure-3: Features of RA-LL Lead Reversal — adapted from LITFL (See text).

With the essentials from Figure-3 of RA-LL lead reversal in mind — Let’s TAKE ANOTHER LOOK at the initial ECG in this case (TOP tracing in Figure-4):

Figure-4: TOP: The initial ECG in the ED ( ECG #1) — with features of RA-LL lead reversal written below ECG #1. BOTTOM: ECG #2 shows what this initial ECG would look like if corrections were made for RA-LL Lead Reversal (See text).

MY THOUGHTS on ECG #2: Unfortunately (as often occurs) — RA-LL lead reversal went unrecognized in today’s case. As a result, I do not have an actual follow-up ECG. Instead — I constructed ECG #2 in Figure-4 by inverting lead II in ECG #1 — by inverting and switching places for leads I and III — and by switching places for leads aVR and aVF. Isn’t the appearance of P waves, QRS complexes and T waves in the limb leads of ECG #2 now much more logical?
  • The P wave is upright in lead II of ECG #2, as it should be when there is normal sinus rhythm.
  • There is global negativity (of P wave, QRS and T wave) in lead aVR — as most commonly is seen with normal tracings.
  • The appearance of the P waves, QRS complexes and T waves no longer looks so similar in the 3 inferior leads in ECG #2, as it did in ECG #1 when there was RA-LL lead reversal.
  • My Impression of ECG #2: This is a normal ECG. There is normal sinus rhythm — a horizontal (but normal) frontal plane axis of about 0 degrees — and no chamber enlargement. T wave negativity isolated to lead III is not an abnormal finding when the QRS complex is predominantly negative in this lead. There is no longer suggestion of RV strain, since the T wave in leads II and aVF is upright. As stated earlier — R wave progression in the chest leads is normal. T wave inversion isolated in the chest leads to lead V1 is not abnormal. In Summary — This is a normal ECG.


  1. Thanks for interesting case. Noticing the abnormality of lead aVR, the hypothesis of RA-LL reversal is reasonable. However, I would prefer this case is multiple leads misplacement. The reason is that even if we convert RA and LL lead, just like figure 4 ECG#2, it is quite weird to have a negative p in lead III during sinus rhythm (although negative QRS and T could be normal variant). Here is my hypothesis: the LL "electrode" was misplaced at the patient's RA, the RA "electrode" was misplaced at patient's LA, the LA "electrode" was misplaced at patient's LL, and the RL "electrode" was placed properly. Then, the true lead I (patient's RA towards patient's LA) will be LL "electrode" towards RA "electrode, which is the reverse of false lead II (=reverse figure 1 lead II)(P.S. the RA "electrode" towards LL "electrode" will be documented as lead II in the ECG). The true lead II (patient's RA towards patient's LL) will be LL "electrode" towards LA "electrode", which is the reverse of false lead III(=reverse figure 1 lead III)(P.S. the LA "electrode" towards LL "electrode" will be documented as lead III in the ECG). The true lead III (patient's LA towards patient's LL) will be RA "electrode" towards LA "electrode", which is the false lead I(=figure 1 lead I)(P.S. the RA "electrode" towards LA "electrode" will be documented as lead I in the ECG). We then can appreciate that all "p" "QRS" "T" may be upright in lead I, II, III. As for augmented leads, the true aVR is (patient's LA-patient's LL) towards patients RA, equal to (RA "electrode"-LA "electrode") towards LL "electrode", which is the false lead aVF (=figure 1 lead aVF)(P.S. the (RA "electrode"-LA "electrode") towards LL "electrode" will be documented as lead aVF in the ECG). The true aVF is (patient's RA-patient's LA) towards patients LL, equal to (LL "electrode"-RA "electrode") towards LA "electrode", which is the false lead aVL (=figure 1 lead aVL)(P.S. the (LL "electrode"-RA "electrode") towards LA "electrode" will be documented as lead aVL in the ECG). The true aVL is (patient's RA-patient's LL) towards patients LA, equal to (LL "electrode"-LA "electrode") towards RA "electrode", which is the false lead aVR (=figure 1 lead aVR)(P.S. the (LL "electrode"-LA "electrode") towards RA "electrode" will be documented as lead aVR in the ECG). Then, we will have all "p" "QRS" "T" negative in lead aVR, all "p" "QRS" "T" upright in lead aVF, and low voltage but slightly upright "p" "QRS" "T" in lead aVL. Another hypothesis is the LL "electrode" was misplaced at the patient's RA, the RA "electrode" was misplaced at patient's LA, the LA "electrode" was misplaced at patient's RL, and the RL "electrode" was misplaced at patient’s LL. Because RL only serve as a reference and share the same potential with LL, our deduction above won’t change. But this seems to be more unlikely since there were all 4 leads misplacement. The best way to confirm which hypothesis is correct (2 leads reversal Versus 3 or 4 leads reversal), is to obtain the patient’s other ECG and see if there is negative p in lead III. After all, it’s impossible that the patient’s ECGs are all misplacement. Thanks again!

    1. @ jerryjan — THANKS so much for your comment. I will admit that I had trouble following all that you write … That said — I think the important point is one both of us CAN agree on — namely that in addition to the simple single extremity lead mix-ups — on occasion there can be MULTIPLE lead mix-ups — and THOSE can REALLY be difficult to figure out. That said — ideally (and THIS is really the important point) — is that IF providers (and ALSO if ECG technicians) can get more familiar (and better) at rapidly recognizing artifact and technical mishaps such as lead misplacement — then they can IMMEDIATELY do a repeat ECG in which accurate lead placement is verified — and THEN they can CONFIRM that there initially was lead misplacement, and that the repeat ECG is now an accurate one!

      I will ADD one more possibility to your theories. I did initially think of this — but chose not to include it in my initial write-up for fear of overly complication my explanation — namely that you will note in ECG #2 that the P wave is positive and LARGER in lead I than in lead II. This is NOT normally seen with sinus rhythm — so perhaps I am correct after all (ie, that there is RA/LL lead reversal) — but that instead of a sinus rhythm, there was an ectopic atrial rhythm (which after all can be a normal variant rhythm). Then, as you say — the negative P wave, QRS complex and negative T wave in lead III could all be within what may sometimes normally be seen in patients with a horizontal axis and an ectopic atrial rhythm.

      Unfortunately, I have no follow-up to this case (which wasn’t mine). Lead misplacement (of whatever kind … ) just wasn’t recognized — so I have no record of any repeat ECG to show.

      THANKS again jerryjan for your interesting comments! — :)

  2. Sorry for the complicated description. I think it will be easier to explain in a picture, however, I don't know if it would be possible in the comment. Briefly, in my hypothesis (3 leads misplacement), the corrected lead I will be reverse (upside down) of the lead II in ECG#1, the corrected lead II will be reverse of the lead III in ECG#1, and the corrected lead III will be the lead I in ECG#1 with no reverse. Then, the corrected lead I,II,III will be all upright in "p" "QRS" "T". Furthermore, as you mentioned, there will be a larger positive p wave in corrected lead II than corrected lead I. This hypothesis can make the ECG more logical for sinus rhythm. Of course, there is a possibility that it's actually ectopic atrial rhythm. If so, RA-LL reversal would be likely. For sure, it's more important to recognize the misplaced ECG, and get a new correct one immediately! Thanks for replying.

    1. @ jerryjan — I agree. In years past (when I had access to resources) — I would do as you suggested (ie, intentionally try erroneous lead placement combinations to see the result). That said — my purpose here is as you say at the end — the GOAL is to recognize when lead placement may be “off” — so that you can know in which situations an immediate repeat tracing is indicated. THANKS again for your discussion! — :)

  3. you are amazing, Ken
    thank you.

  4. superb discussion of a not so rare problem we find. The Ps, Qs and 3 Rs analysis has helped me a LOT . Thanks profesor Grauer.
    Hector from venezuela

    1. Gracias Hector. Un placer. Estoy feliz que el enfoque sistem├ítico sea ├║til para ti! (Thanks, a pleasure — I'm happy the systematic approach is useful for you! — :)

  5. A quick way to suspect lead errors by D. Rowlands: A) Is there a flat line in I, II? or III B) Does I and aVL look like aVR should (all negative)? - then view chest leads to exclude dextrocardia C) Does II, III and aVF look like aVF shoud? D) P waves in I and aVL > P in II (may or may not be an error)
    Its a very quick method we use which works very well, most of the patients are still connected so the error can be verified (for the explanation concerning single and double errors see https://www.sciencedirect.com/science/article/abs/pii/S0022073607007960?via%3Dihub and https://www.sciencedirect.com/science/article/abs/pii/S0022073611002329)

    1. THANKS Arron! Agree with your Pearls! I like LITFL for their user-friendly illustrations regarding the common limb lead reversals (my Figure-3 is adapted from their site — and the LINK is above in My Comment). Also — In the Sept. 27, 2019 post in Dr. Smith’s ECG Blog — I excerpted the 3 pages of another invaluable Rowlands manuscript (on recognizing which extremity is the “culprit” for artifact) — it’s at this LINK — http://hqmeded-ecg.blogspot.com/2019/09/chest-pain-with-nondiagnostic-ecg-but.html — THANKS again so much for your insightful comment! — :)


DEAR READER: I have loved receiving your comments, but I am no longer able to moderate them. Since the vast majority are SPAM, I need to moderate them all. Therefore, comments will rarely be published any more. So Sorry.

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