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 #6. Normal 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 Cardiomyopathy — See 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 V1. What 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).