Sunday, March 7, 2021

ECG Blog #201 (ECG MP-18) — Should the Cath Lab be Activated?

The ECG shown in Figure-1 was obtained from a woman in her 80s with a history of a recent stroke. She complained of epigastric discomfort while at rehabilitation. 

  • Based on this ECG — Should the cath lab be activated?


Figure-1: ECG obtained on a woman in her 80s, complaining of epigastric discomfort. Should the cath lab be activated?


My Initial Thoughts on Seeing this Tracing:

I was initially concerned about potential marked ST elevation in leads I and II — as well as ST elevation to a lesser extent in lead aVL and in the chest leads. 

  • I was struck by the finding of some elevation of the isoelectric line that begins before the QRS complex in these 2 leads with maximal ST elevation — which I thought looked similar to the appearance of a Spiked Helmet Sign (See LINK to Dr. Smith’s June 28, 2020 post below for my review of the Spiked Helmet Sign)
  • I thought both the shape and the distribution of the ST elevation in leads I and II of ECG #1 to be strange. That said — I thought cardiac cath might be needed to clarify the picture.


The Case Continues:

A 2nd ECG was done 30 minutes after ECG #1. For clarity — I show both of these tracings in the sequence as they occurred in Figure-2.

  • Based on the 2 ECGs in Figure-2 — Do you still want to activate the cath lab?
  • WHY or why not? 


Figure-2: The initial ECG, together with a repeat ECG done 30 minutes later (See text).





The decision was made not to activate the cath lab. It was noted that the abnormal deflections seen in ECG #1 were no longer present in the repeat ECG done 30 minutes later (Figure-2). Among the investigations done at the time:

  • A bedside Echo showed good LV function without wall motion abnormality.
  • Troponin X3 was without meaningful elevation.
  • A 3rd ECG done ~2 hours after ECG #2 remained unchanged from ECG #2.


QUESTION: How do YOU explain the change in appearance that we see in Figure-2 between ECG #1 and ECG #2?



ANSWER: In view of complete resolution of the abnormal ST-T wave deflections that were seen in ECG #1, along with the normal bedside Echo and negative serial troponins — it was felt that 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.



  • CONFESSION: It is good to be humbled every now and then. I fully acknowledge that I initially missed the diagnosis in this case! In retrospect — I should have immediately recognized artifact as the cause — but I didn't ...




Today’s case provides an excellent example of how the 1st time you see an ECG phenomenon — it may pass unrecognized. But after one learns about the phenomenon — it becomes EASY to recognize in the future!

  • I actually was well aware of the phenomenon of contact with a pulsating artery producing marked ST-T wave abnormality. But I had not previously seen as deceptive an example of this phenomenon as occurs in today’s case. Therefore — I fell into the “trap”.


PEARL #1: Artifact is common in clinical practice. The BEST way not to overlook artifact — is to be aware of how common it actually is! I’ll add the following points regarding today’s case:

  • The 1st Clue to Artifact — is that the shape of the elevated ST segments is bizarre. It is unusually straight — and becomes surprisingly pointed at its peak in multiple leads. In the one lead in which the T wave is negative ( = lead aVR) — the deepest part of the inverted T wave is also surprisingly pointed. This is not physiologic. In general, when ECG deflections look bizarre and “unphysiologic” — there is an excellent chance that such deflections are not real!
  • The location of these 2 limb leads showing maximal ST elevation ( = lead I and lead II) — is not anatomic for what should be expected with acute MI, especially in the absence of reciprocal ST depression in other limb leads. It’s hard to imagine what coronary artery might be occluded with ST elevation in the limb leads limited to leads I and II.
  • The bizarre ST-T wave shape in all leads showing ST elevation (and also in lead aVR with T wave inversion) — occurs at a fixed interval with respect to the preceding QRS complex (Figure-3). This tells us that whatever is producing these deflections must be related to cardiac contraction (and/or to arterial pulsation)!

Figure-3: I’ve colored in maximal artifact deflections in RED — and lesser amplitude artifact deflections in GREEN (See text).

PEARL #2: The distribution of the bizarre ST-T wave deflections precisely follows the location and relative amount of amplitude distortion predicted by Einthoven’s Triangle.

  • The bizarre ST elevation is approximately equal in 2 of the limb leads (ie, in leads I and II) — andnot seen at all in the 3rd limb lead (ie, no artifact at all is seen in lead III). By Einthoven’s Triangle (See the picture below for today’s ECG Media Pearl — which shows Einthoven’s Triangle in the righthand corner) — 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 Legand 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.


Today’s 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.




NOTE: I reproduce below in Figures 45 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 inverted T wave in this lead)andii) 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 (GREEN outline of the sharply angled ST-T waves 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 sharply angled ST-T waves in each of the 6 chest leads).


PEARL #3: A final important clue to artifact as the cause of the bizarre ST-T wave deflections we see in ECG #1 — is provided in the long lead II rhythm strip at the bottom of the tracing!

  • Did YOU notice how the artifact comes and goes in this long lead II rhythm strip? Thus, we see maximal artifact in beats #23910 and 15 in this long lead II rhythm strip (including that baseline elevation distortion that begins just before the QRS complex of these beats — and which gives false impression of a spiked Helmet Sign).
  • In contrast — there is no artifactual ST elevation at all in beats #561213 and 17 — and an intermediate amount of artifact distortion in the remaining beats. This changing amount of artifact from one-beat-to-the-next would be consistent with the RA electrode making only intermittent contact with the pulsating artery. I can not think of a physiologic reason other than artifact to explain this beat-to-beat variation in ST-T wave appearance.


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).


Figure-4: Page 475 from the Rowlands and Moore article referenced above (See text).


Figure-5: Page 476 from the Rowlands and Moore article referenced above (See text).


Figure-6: Page 477 from the Rowlands and Moore article referenced above (See text).




Acknowledgment: My appreciation to 林柏 = Po-Chih Lin (from Taiwan) for these tracings and this case.




Additional Relevant ECG Blog Posts to Today’s Case:

  • The June 28, 2020 post in Dr. Smith’s ECG Blog — for review of the Spiked Helmet Sign.  Please scroll down to the bottom of the page at this link to see My Comment.

Regarding ECG Recognition of ARTIFACT:

Finally — I link to several illustrative Cases taken from Dr. Smith’s ECG Blog. For each of these posts — Please scroll down to the bottom of the page to see My Comment. These cases provide insight to assessment for ARTIFACT:

  • The September 27, 2019 post in Dr. Smith’s ECG Blog — in which I use the Rowlands & Moore article, with the above-noted formulas for recognizing the “culprit” extremity.
  • The October 17, 2020 post in Dr. Smith’s ECG Blog — for an example of VT-like artifact
  • The January 30, 2018 post in Dr. Smith’s ECG Blog — for arterial pulsation artifact (Please click on the COMMENTS to this post to see my discussion).

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