Tuesday, January 17, 2023

A 60 year old with chest pain

A 60 year old with chest pain presented to the ED.

Here is his first ECG:

What do you think?

It looks bizarre, doesn't it?  There are lots of ST-T abnormalities, but they just don't look recognizable.  

Whenever you see a bizarre ECG, look at leads I, II, and III.  See if one of them does NOT look bizarre.  In this case, lead I does not look bizarre, but all other leads do.

I immediately recognized this as pulse tapping artifact.  This is when one of the limb leads is placed near an artery and it affected either by the mechanical action of the artery or possibly by the electrical conduction of the blood in the artery.

Since lead I looks relatively normal, that means that the right arm and left arm electrodes must be OK.  It is the left leg electrode that is abnormal.

A single affected electrode will affect ALL other 11 leads!!  So if the left leg electrode is affected, it will of course affect leads II and III.  But also all of the augmented leads because Wilson's central terminal is affected by all electrodes, but only by half as much.  The precordial leads use the limb leads as grounding, so they also are affected, but not as much as leads II and III.  

So I asked the tech to record the ECG again, but move the left leg electrode.

This is the result:

The bizarre morphology is gone.

Since learning about pulse tapping artifact, I have seen more than one case per month of this.  I believe it is far more common than I ever knew.

My Comment by KEN GRAUER, MD (1/17/2023):
As per Dr. Smith — pulse-tap artifact used to be a "new" phenomenon to us (as well as to virtually all medical providers). This is no longer the case!
  • In the December 5, 2022 post of Dr. Smith's ECG Blog — We show 4 additional cases of this pulse-tap artifact. There are many more cases — reflecting the interesting phenomenon in medicine when we find ourselves going for years without awareness of a particular entity — until it is brought to our attention. Thereafter, we find ourselves seeing this entity all the time — finally realizing that the entity probably had always been there, but went undetected by us because we simply did not yet know the entity existed ...

  • I reference below to LINKS from a number of additional cases of various artifacts that I've encountered. The BEST way to get good at recognizing artifact — is to be aware of how amazingly common artifact is in practice — to lower your threshold when a tracing for whatever reason "looks weird" — to return to the bedside and LOOK at the patient (scratching, shivering, tremor, etc. make for wonderful sources of artifact) — to reposition the leads (sometimes best if YOU do this yourself!) — and to promptly repeat the ECG. You'll be surprised at how often those "weird deflections" magically disappear!

NOTE: The reasons I especially liked today's case are: i) The patient presented with chest pain — so the importance of distinguishing artifact from reality can not be overstated! — ii) Artifactual deflections in today's case are rounded, therefore not as obviously distorted as in many cases of artifact (ie, easier to overlook!); — iii) The repeat tracing in this patient with chest pain was not "normal" — although it was nevertheless obvious on repeating the ECG that the most marked deflections had "magically" disappeared after repositioning the left leg electrode; — and, iv) Today's tracing also shows a bizarre "bigeminal" form of artifact that I have not seen before!
  • For clarity in Figure-1 — I've labeled today's initial tracing, and have put it together with the repeat ECG.

  • Do you know why the largest artifactual deflections in ECG #1 are RED? Why are the smallest artifactual deflections GREEN?

  • HINT: In My Comment at the bottom of the page in the August 26, 2022 post in Dr. Smith's ECG Blog — I work through via application of Einthoven's Triangle, the physiologic rationale for the relative size of artifactual deflections (depending on where the "culprit extremity" is).

Figure-1: Comparison between the initial ECG — and the repeat ECG in today's case after repositioning the LL ( = Left Leg) electrode(To improve visualization — I've digitized the original ECG using PMcardio).

My Thoughts on ECG #1:
The rhythm in ECG #1 is sinus — with clearly upright sinus P waves with fixed PR interval preceding each QRS in the long lead II rhythm strip.
  • Did YOU Notice the change in both the baseline — as well as in the size of the ST-T wave alternating every-other-beat in the long lead II rhythm strip?

KEY Point: As emphasized by Samaniego et al (Emerg Med J 20: 356-357, 2003) — there are 2 main sources of artifact — which are "physiologic" vs "non-physiologic" sources:
  • Non-Physiologic Artifact Sources — include 60 hertz cycle interference (from AC current devices in the area) — and/or cable or electrode malfunction (ie, loose or broken wire, loose electrode lead connection, etc.).
  • Physiologic Artifact Sources include patient movement and/or voluntary or involuntary muscular activity (ie, tremor, shivering, scratching, coughing, hiccups, distressed breathing, etc.).

  • Bottom Line: I simply did not know how to explain WHY any of the above physiologic sources of artifact would result in such perfect alternation of the ECG baseline and artifactual distortion of the ST-T wave for all even-numbered beats in ECG #1, but not for the odd-numbered beats!

What is the "Culprit" Extremity in ECG #1? 
As per Dr. Smith — the "culprit" extremity in today's case is the LL electrode. As I review in the August 26, 2022 post of Dr. Smith's ECG Blog — when the cause of artifact is attributable to a single extremity, it is EASY to quickly determine the "culprit" extremity:
  • single extremity is suggested as the cause of artifact when the amount of artifactual ST segment deviation is approximately equal in 2 of the 3 standard limb leads (ie, outlined in RED in leads II and III of ECG #1) — and not seen at all in the 3rd standard limb lead (ie, the ST segment is neither elevated nor depressed in lead I of ECG #1).

  • By Einthoven's Triangle (See Figure-2) — the finding of equal ST segment amplitude artifact in Lead II and Lead III, localizes the "culprit" extremity to the LL ( = Left Leg) electrode.
  • The absence of ST elevation or depression in lead I is consistent with this — because, derivation of the standard bipolar limb lead I is determined by the electrical difference between the RA and LA electrodes, which will not be affected if the source of the artifact is the left leg.

  • By Einthoven's Triangle — the finding of maximal amplitude artifact in unipolar lead aVF confirms that the left leg is the "culprit" extremity (highlighted in RED in lead aVF of ECG #1).

Finally, as I discuss in My Comment in the August 26, 2022 post (which applies the electrophysiologic principles of Rowlands & Moore: J. Electrocardiology 40:475,477, 2007):
  • The amplitude of the artifact from a single extremity source, is maximal in the unipolar augmented electrode of the "culprit" extremity (which as per the RED outline in Figure-1 — is lead aVF).
  • The amplitude of the artifact in the other 2 augmented leds (ie, leads aVR and aVL) — is about 1/2 the amplitude of the artifact in lead aVF (BLUE outline of the elevated ST segments in leads aVR and aVL of ECG #1).
  • The amplitude of the artifact deflections in the unipolar chest leads is even more reduced (to ~1/3 the size of the artifact in leads II,III,aVF — as suggested by the GREEN outline of the curved ST segment elevations in each of the 6 chest leads in ECG #1).

  • PEARL: Nothing else shows a 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 ST segment deviation 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-2: Use of Einthoven's Triangle to determine the electrical voltages in the 3 standard limb leads.

Today's Case CONCLUSION:
Take another LOOK at Figure-1. It was after Dr. Smith suggested repeating the initial ECG after repositioning the LL electrode — that ECG #2 was recorded.
  • In your mind's eye — Wouldn't ECG #1 look like ECG #2 if we took away the artifactual deflections highlighted in RED, BLUE and GREEN?
  • That said — there is nonspecific ST-T wave flattening in multiple leads of ECG #2, as well as T wave inversion in lead V2. There are also fairly large U waves in leads V3 and V4. Finally — significant baseline artifact persists in leads II and III of ECG #2, suggesting there may still be some patient movement localized to the left leg.

  • MY Impression of ECG #2: Keeping in mind that the patient in today's case presented with chest pain — the nonspecific ST-T wave flattening in multiple leads, with T wave inversion in lead V2 could be ischemic — albeit clearly not suggestive of an acute event! Serum K+/Mg++ levels need to be checked — as hypokalemia/hypomagnesemia are common causes of nonspecific ST-T wave flattening with U waves.

  • Finally — Did YOU Notice that there is no longer alternate beat variation in the long lead II baseline, nor in ST-T wave morphology. MY Theory: Given that we know the source of ST-T wave artifact in ECG #1 arises from the LL extremity — I suspect the type of patient movement causing this artifact was such that LL electrode skin contact was compromised every-other-beat. Repositioning the LL electrode must have resolved this problem.


REFERENCE: For those interested in More on Recognition of ECG Artifact:

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