Friday, January 3, 2014

ECG Blog #81 — Tall R Wave in V1 ...

There is a tall R wave in lead V1 of the ECG that is shown below (
Figure-1). No history is available.
  • What is the likely cause of this Tall R Wave in Lead V1?

Figure-1: 12-lead ECG showing a tall R wave in lead V1. What is the likely cause of this tall R wave? 

Normal Appearance of the QRS in Lead V1
When the rhythm is supraventricular — the QRS complex in lead V1 should be predominantly negative under normal circumstances. This is because this right-sided lead (V1) normally sees electrical activity as moving away from V1 (or toward the large left ventricle). This concept is illustrated in schematic Figure-2.
  • The finding of predominant positive activity in lead V1 (an R wave that equals or exceeds the S wave in this right-sided lead) is not “normal”. This is the premise on which one of our 6 “Essential Lists” in ECG Interpretation is based (Figure-3 below).

Figure-2: Transverse (cross-sectional) view of the heart — illustrating precordial lead appearance in leads V1-through-V6. Transition occurs in the above Figure between lead V2-to-V4. Note that the QRS complex in lead V1 is predominantly negative under normal circumstances (red box). Septal depolarization normally moves left-to-right (small black arrow). The major component of ventricular activation moves to the left and posteriorly (large red arrow) — which reflects the relative size and anatomic position of the left ventricle. This explains why lead V1 normally sees predominant electrical activity as moving away from this right-sided lead. 

LIST #6: Causes of a Tall R Wave in Lead V1
It is easy to overlook the finding of a tall (or relatively tall) R wave in lead V1. It is equally easy to overlook the finding of early transition — in which the R wave in precordial leads V2 or V3 becomes disproportionately tall much sooner than expected.
  • The KEY to not overlooking the ECG findings of a tall R wave in lead V1 or early transition — is to routinely apply a Systematic Approach to your ECG interpretation. This is our purpose for including the “R” component (looking for R Wave progression) when assessing for Q-R-S-T” Changes.
  • The purpose of our LIST #6 which we present in Figure-3 — is to facilitate recall of the principal causes of a disproportionately tall R wave in lead V1. The best way not to overlook any of the causes — is to work through each of the entities on this list whenever you recognize that the R wave in lead V1 is taller than you expect.
  • NOTE: Awareness of these causes is especially important — because computerized ECG interpretations typically fail to pick up a taller-than-expected R wave in leads V1,V2,V3.

Figure-3: The Common Causes of a Tall R Wave in Lead V1 = LIST #6Normal variant is a diagnosis of exclusion. 

Taking a Closer Look at LIST #6:
The way to narrow down which of the entities on List #6 is likely to be the cause of a tall R wave in lead V1 — is to look for associated findings in the remaining leads.
  • WPW — Look for the QRS to be wide with delta waves and a short PR interval.
  • RBBB — Look for the QRS complex to be wide with an rSR’ (or equivalent) in lead V1 and wide terminal S waves in leads I,V6.
  • RVH Look for ECG criteria of RVH including right or indeterminate axis; RAA (Right Atrial Abnormality); tall R wave in V1; RV “strain”; persistent precordial S waves  (See ECG Blog #77).
  • Posterior MI — Look for ECG evidence of associated inferior infarction and for a positive “mirror test” (See ECG Blog #56).
  • Hypertrophic CardiomyopathySee below.
  • Normal Variant — to be considered only after the above 5 causes have been ruled out. Thus, the diagnosis of “normal variant” as the reason for a disproportionately tall R wave in lead V1 — is a diagnosis of exclusion!

  • P.S. My List in Figure-3 is not all-inclusive. For example — uncommon conditions such as dextrocardia or a mix-up in the chest leads could also result in an unexpectedly tall R wave in lead V1. Other entities (ie, a drug toxicity, hyperkalemia, Brugada syndrome) — may also alter the appearance of the QRS complex in lead V1, but these entities will usually be suggested by the clinical history.

HOW to Recognize Hypertrophic Cardiomyopathy on ECG? 
Be aware of the 5th cause in List #6 of a Tall R in Lead V1 — which is HCM (Hypertrophic CardioMyopathy). Although not overly common — HCM is an important potential cause of sudden death (especially in young athletes). Echo is diagnostic! On the other hand — ECG findings are highly variable. These may include a moderately tall R wave in lead V1 which suggests prominent septal forces. It might also include deep septal Q waves; LVH by voltage; IVCD/LBBB — or no ECG changes at all. The reason for emphasizing awareness of HCM is the risk of sudden death that HCM poses among previously healthy young adults. While cost concerns prohibit mass screening by Echo of all young adults — Echo is indicated when there is a history of syncope during exercise; with a positive family history for early sudden death; when a non-innocent murmur is heard — or when a pre-participation ECG reveals abnormal findings that may be consistent with the diagnosis.

Returning to FIGURE-1: What is the Cause of the Tall R in V1?
Let’s apply List #6 to the ECG in Figure-1 (reproduced below in Figure-4). The QRS complex looks to be slightly wide. The rhythm appears to be sinus — as suggested by the presence of an upright P wave in lead II. The PR interval in lead II looks normal. The QT is not prolonged. The most remarkable finding on this tracing — is the very tall R wave in lead V1. This is clearly not expected — and should prompt consideration of the 6 entities in LIST #6 as a possible explanation.
  • We suspect that the answer will probably also explain: i) the marked left axis (and/or QS complex in inferior leads); and ii) ST flattening and shallow T inversion seen in multiple leads.

Figure-4: We reproduce Figure-1 of this ECG showing a tall R wave in lead V1What is the likely cause?

ANSWER to Figure-4:
No history is available. The rhythm in Figure-4 appears to be sinus. The QRS looks slightly wide. As we work through List #6 (Figure-3) — We note the following:
  • This is clearly not a “normal variant” tracing. Other than the tall R wave in lead V1 — there is really nothing to suggest RVH (no right axis; no RAA; no RV “strain” in lead V1). And although it almost looks as if there are inferior Q waves — this is not the usual picture of inferior infarction, and the “mirror test” is not suggestive of posterior infarction.
  • Finally — the patient does not have RBBB. There is no rSR’ in lead V1 — and no S wave is seen in lead I. The QRS complex is also not as wide as is generally seen with bundle branch block.
  • The patient has WPW! It is important to appreciate that the QRS complex is not always overly wide with WPW. This is because there may occasionally be simultaneous conduction down both normal and accessory pathway — which will result in only partial pre-excitation. It is because of awareness of LIST #6 — that one looks extra hard for delta waves whenever the finding of a tall R wave in V1 is seen. Close inspection reveals such delta waves are seen (red and blue arrows in Figure-5).

Figure-5: Arrows highlight delta waves that were subtly present in the ECG shown in Figure-4. The QRS complex with WPW will not always be overly wide — as there may only be partial pre-excitation (if impulses are simultaneously conducted down normal and accessory pathway). Although the PR interval looks to be normal in lead II of this tracing — it appears to be short in leads V4,V5,V6 (red arrows in these leads). Delta waves are present. They are negative in the inferior leads (blue arrows) — and positive in other leads in which they are seen (red arrows). No delta wave is evident in leads aVR, aVL or V2. 

For more information  GO TO:

  • See ECG Blog #93 ( = Basic Concepts #6 — for Review of the Systematic Approach to ECG interpretation.
  • CLICK HERE — to download a pdf of Section 10.41 on Causes of a Tall R Wave in Lead V1 (from our ECG-2014-ePub).


  1. Very nice. I like these examples that are not standard, and in this case show that there is a gray area between WPW-wide QRS and normal-narrow QRS. Thanks a lot.

  2. How would you explain LAD in the setting of type A WPW? Thanks in advance!

    1. Thank you Tim for your comment. There are 2 potential explanations for the point your raise in your excellent question. #1 - There is only partial preexcitation in this case - because the QRS is not all that wide (ie, a portion of the impulse utilizes the accessory pathway to produce the delta waves we see - whereas a portion uses the normal AV nodal pathway - in which case there might be some left axis deviation as this patient's baseline when they are conducting normally and not using their accessory pathway.

      Otherwise - QRS morphology with preexcitation will depend on the location of the accessory pathway. I review how to determine WHERE the AP (Accessory Pathway) is based on QRS morphology when the QRS is wide in my Blog-76 (GO TO - ). You'll note that Step A-1 in Blog-76 is based on whatthe relative inferior lead amplitudes are. If the net sum of the amplitudes in the three inferior leads is neg 1 or neg 2 - then you'll have a left axis with the AP either being postero-septal or in the postero-lateral LV free wall.

    2. If the above link doesn't work - try this one -

  3. Great case... Thank you
    Why do you say it's not the usual picture of inferior infarction (before you called it WPW)??

    1. This doesn’t look like inferior infarction because there appear to be tiny-but-present initial r waves in leads II and III, with a very wide S wave that just isn’t what is generally seen with inferior infarction. Then one has a subtle initial slurring in lead I ( = delta wave) — and finally in the chest leads the more obvious delta waves that confirm this is WPW.

  4. Would it be possible to draw a transversal cut containing all the depol. vectors? Would help a lot.

    1. Hi. I'm not sure what you mean by a "transversal cut containing all depol vectors?" Perhaps you are referring to a vectorcardiogram — a tool that used to be used, but really isn't in general practice any more. That said, even with such a cut showing "all vectors" — since we are dealing with preexcitation (ie, WPW) — invasive EP (electrophysiologic) mapping is really needed in order to plot the location of the accessory pathway here in this patient with incomplete preexcitation ...

    2. Oh, I guess you are right and it is called vectorcardiogram, I am sorry, I did not know that. How come it is not used anymore? I drew one by myself (which probably contains some mistakes - that is why I was asking for one) and I think it improved my understanding of the precordial leads.
      By the way, I have "A practical guide to ECG interpretation" on my wishlist :-)

    3. I suspect not enough providers knew how to interpret vectorcardiograms — which are quite challenging to read ... The essentials can be assessed from a standard 12-lead ECG. If you are interested in derivations of the waveforms — you may find my ECG Video on QRST Changes = — of interest. If you click on SHOW MORE below the video on YouTube, you'll find a linked Contents — :)

  5. Thank you very much! I am going to watch the video now. The initial question remains though, if you ever come across a vectorcardiogram in the transversal plane showing all the vectors, please link or upload it here, I'd love to have an all-in-one picture. :-)
    One more question (I already asked via a comment here but it seems that comment disappeared): I tried googling for a fully labelled (physiological) 12-lead ECG but couldn't find any; by "fully labelled" I mean all waves (not only the ones from lead II) should be labelled - also, if you have a decent picture I would be very happy if you provided one because I, as well as my colleagues, believe it would make life as a beginner/ student way easier.
    And once more I thank you very much, even though I am right now only at the beginning of my ECG studies I can tell your website is amazing!

  6. Hi. I don't know what you mean by "fully labeled". But my ECG video on QRST Changes ( has illustrations in it of the path of conduction (not of each individual vector, but of generalized depolarization forces. Hope that helps.

  7. Thank you very much for this informative lecture.
    I want to ask.
    According to your algorithm in
    ECG Interpretation Review #76 (Anterior Infarction – WPW – AP – Accessory Pathway - Localization)
    The AP location appear to be posteroseptal,am I right?

    1. Yes — If I were to follow my algorithm for localization of the AP (from my ECG Blog #76 — — I would start with STEP A-1 (since the QRS is predominantly upright in V1). I’d then measure the sum of delta wave polarities in the 3 inferior leads — which is -3, because delta waves are negative in each of these leads — which suggests a LEFT-sided and POSTERIOR AP — and since the R wave in lead I is ≥0.8 mV — this suggests a left-sided Postero-Septal AP — :) — THAT SAID — Please realize that delta waves in this example are subtle, so there is NOT complete pre-excitation — so localization of the AP by this method may be a bit less accurate — :)