ECG Interpretation: ECG Blog #490 — Which Lead is Most Revealing?

The ECG in Figure-1 is from a young adult woman with known diabetes, who presented to the ED (Emergency Department) for a syncopal episode. The patient was alert, without chest pain, and hemodynamically stable at the time ECG #1 was recorded.

QUESTIONS:

How would you interpret the ECG in Figure-1?
Is the syncopal episode likely to be responsible for the abnormal findings in ECG-1 — OR — Should the cath lab be activated?

Figure-1: The initial ECG in today's case — obtained from a young adult woman with syncope. (To improve visualization — I've digitized the original ECG using PMcardio).

My Thoughts on Today's CASE:

While it is true that CNS Catastrophes may account for some of the most unusual ECG findings (See Goldberger et al — J Electrocard 47(1):80-83, 2013) — this patient's syncope (from whatever etiology this patient's syncope may have been caused by) is not the cause of the diffuse and dramatic ST-T wave changes that we see in ECG #1:

While significant overlap of QRS complexes in a number of the leads from Figure-1 complicate assessment of ST-T wave deviations — it should be apparent that there is dramatic ST elevation in lead aVR, with equally "eye-catching" ST depression in other limb leads — and less (but still considerable) ST depression depression in all chest leads.

PEARL #1: Did YOU notice that each of the 7 QRST complexes in lead III look normal? (See Figure-2). Awareness that when there appear to be dramatic (albeit bizarre-looking) ST-T wave deflections in 2 of the 3 standard limb leads (which are leads I,II,III) — but for which the 3rd standard limb lead is "spared" from this bizarre ST-T wave morphology — the cause if these bizarre ST-T wave deflections is usually Artifact.

We can establish with greater certainty that artifact is the cause of these dramatic (bizarre) ST-T wave changes as the result of "something" occurring in 1 of the patient's 4 extremities — IF the relative size of these abnormal deflections obeys Einthoven's Laws (See below).

PEARL #2: Artifact is common in clinical practice. The BEST way not to overlook artifact — is to be aware of how frequently it actually occurs! I’ll suggest the following CLUES that are relevant to the presence of Artifact in today’s case:

Clue #1: Already highlighted in PEARL #1 — in that despite unusual ST-T wave deviations in 2 of the 3 standard leads — the 3rd standard lead is spared! (and lead III is spared from artifact in Figure-2! ).
Clue #2: The shape of the abnormal ST segments is bizarre. This unusual shape does not “fit” with the clinical situation. Although today’s patient does have diabetes — she is younger-than-usual for having an acute cardiac event — and, there is no history of chest pain (ie, Syncope without chest pain is not a common presentation of an acute MI). Finally — it’s hard to imagine that there would be this amount of ST-T wave deviation with an acute MI in a hemodynamically stable young adult who presents with syncope but no chest pain (and hard to imagine there would be this amount of ST-T wave deviation with a CNS catastrophe in an alert, hemodynamically stable patient).
Clue #3: The bizarre ST-T wave shape in leads with ST depression (and also in lead aVR with ST elevation) — occurs at a fixed interval with respect to the preceding QRS complex (Figure-2). This tells us that whatever is producing these deflections must be related to cardiac contraction (and/or to arterial pulsation).

Figure-2: I've colored in maximal artifact deflections in RED — and lesser amplitude artifact deflections in BLUE and GREEN (See text).

KEY Clue #4: In Figure-2, we can see that the distribution of ST-T wave deflections precisely follows the location and relative amount of amplitude distortion predicted by Einthoven’s Triangle.

The amount of ST-T wave distortion is approximately equal in 2 of the limb leads (ie, leads I and II) — and not seen at all in the 3rd limb lead (ie, no artifact is seen in lead III). By Einthoven’s Triangle (See the picture below of Einthoven's Triangle next to the link for today’s ECG Media Pearl) — the finding of equal ST segment amplitude artifact in Lead I and Lead II, localizes the “culprit” extremity to the RA ( = Right Arm) electrode.
The absence of any artifact at all in lead III is consistent with this — because, derivation of the standard bipolar limb lead III is determined by the electrical difference between the LL ( = Left Leg) and LA ( = Left Arm) electrodes, which will not be affected if the source of the artifact is the right arm.
As I discuss in detail in my MP-18 Audio Pearl below — the finding of maximal amplitude artifact in unipolar lead aVR confirms that the right arm is the “culprit” extremity.

Click on this image to hear the Audio Pearl!

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ECG Media PEARL #18 (7:45 minutes Audio) — On recognizing Artifact — and — using Einthoven’s Triangle to determine within seconds the “culprit” extremity causing the Artifact on your ECG.

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The CASE Continues:

A short while later — the ECG was repeated (See Figure-3).

QUESTION: How can you explain the change in appearance that we see in Figure-3 between ECG #1 and the repeat ECG #2 done ~10 minutes later?

Figure-3: Comparison between the initial ECG — and the repeat ECG recorded ~10 minutes later.

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ANSWER: The dramatic ST-T wave deviations that we saw in ECG #1 — have now totally resolved in ECG #2! Other than sinus tachycardia and some baseline artifact in a few leads — this repeat ECG is unremarkable.

Note in particular that lead III has not changed in the repeat ECG compared to the initial tracing!
KEY Point: It is the complete resolution of abnormal ST-T wave deflections that were seen in ECG #1 — that confirms the deflections that had been seen in ECG #1 were the result of Artifact produced by contact of the RA electrode lead with a pulsating artery (sometimes known as "PTA" = Pulse-Tap Artifact).

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Acknowledgment: My appreciation to Tayfun Dilek Demir (from Antalya, Turkey) for these tracings and this case.

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ADDENDUM (8/2/2025):

For More Material — I have added this Tab on Lead Reversals & Artifact — to the Menu at the top of every page in this ECG Blog:

— Where to find this LINK in the Top Menu! —

All-too-often lead reversals, unsuspected artifact, and other "technical misadventures" go unrecognized — with resultant erroneous diagnostic and therapeutic implications.

In the hope of facilitating recognition of these cases — I am developing an ongoing listing on this page with LINKS to examples that I’ve published in this ECG Blog, as well as in Dr. Smith’s ECG Blog where I frequently write commentaries.

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NOTE: I reproduce below in Figures 4, 5 and 6 — the 3-page article by Rowlands and Moore (J. Electrocardiology 40: 475-477, 2007) — which is the BEST review I’ve seen on the physiology explaining the relative size of artifact amplitude deflections when the cause of the artifact is a single extremity. These principles are illustrated by the colored deflections in Figure-3:

As noted by the equations on page 477 in the Rowlands and Moore article: i) The amplitude of the artifact is maximal in the unipolar augmented electrode of the “culprit” extremity — which is lead aVR in Figure-3 (RED outline of the elevated ST segment in this lead); and, ii) The amplitude of the artifact in the other 2 augmented leads (ie, leads aVL and aVF) is about 1/2 the amplitude of the artifact in lead aVR (BLUE outline of the marked ST depression in leads aVL and aVF).
Similarly — the amplitude of the artifact deflections in the 6 unipolar chest leads in Figure-3 is also significantly reduced from the maximal amplitude seen in leads I, II and aVR (GREEN outline of the ST depression seen in each of the 6 chest leads).

BOTTOM LINE: You will see artifact frequently in real-life practice. With a little practice, you can immediately KNOW with 100% certainty that the bizarre deflections on a tracing like this one are the result of artifact, and are related to arterial pulsations in one of the extremities.

Nothing else shows fixed relation to the QRS complex in the mathematical relationships described above, in which there is equal maximal artifact deflection in 2 of the 3 limb leads (with no artifact at all in the 3rd limb lead) — in which maximal artifact in the unipolar augmented lead will be seen in the extremity electrode that shares the 2 limb leads that show maximal artifact (as according to Einthoven’s Triangle).
In Other Words: When the cause of artifact originates from a single extremity — the relative amount of artifact will be:

Maximal in 2 of the 3 standard limb leads.
Absent in the 3rd standard limb lead — and ...
Maximal in the unipolar augmented electrode of the “culprit“ extremity (which as per the RED outline in Figure-3 — is lead aVR).
PEARL #3: Appreciation of these electrophysiologic principles allowed me to instantly identify lead aVR as the “culprit” extremity in today’s case — because this is the augmented lead with maximal artifact!