Sunday, February 18, 2024

Acute dyspnea in an older woman, is it OMI?

 Written by Willy Frick

A woman in her 90s with a history of end stage renal disease and complete heart block status post dual chamber pacemaker presented from home with acute onset dyspnea. ECG is shown below.

What do you think?

The ST and T wave abnormalities jump off the page, but let's set that aside just for a moment to review the tracing systematically. 

The rate is 60 (and remember, slower heart rates are often seen in OMI). 

Close inspection reveals ventricular pacing spikes, best seen in aVL. Many ECG readers will not comment any further on rhythm once ventricular pacing has been identified, but it is still critical to determine the atrial rhythm. In this case, it is atrial fibrillation. This could be easily overlooked since there is complete heart block, but recognizing the atrial arrhythmia may mean prescribing anticoagulation to prevent stroke.

See this case: 

Computer often fails to diagnose atrial fibrillation in ventricular paced rhythm, and that can be catastrophic

Given that this is a ventricular paced rhythm, we judge the presence or absence of OMI using Smith Modified Sgarbossa Criteria. It is hard to identify exactly how deep the S waves in I and aVL are, but there could be disproportionate ST elevation and hyperacute T waves with reciprocal changes in III and aVF, altogether concerning for high lateral OMI.

The ER immediately contacted cardiology for consideration of emergent catheterization. Cardiology felt that there was baseline artifact and recommended immediate repeat ECG which is shown below.

This ECG actually has even more baseline wander than the first. In addition to having a particularly bizarre T wave morphology, it is curious that among the limb leads, lead II seems to look relatively normal, just as it did in the first ECG. What could explain this very bizarre looking ST-T morphology which completely spares lead II?

The vector mathematics are explained in detail in the above post, but the important point for localization is recognition that lead II is spared. Lead II connects the R arm and L leg, therefore by process of elimination, the problem is with the L arm electrode. (Remember that the R leg is the ground electrode.) On exam, the L arm electrode was overlying the patient's AV fistula. After repositioning the electrode, repeat ECG was obtained showing resolution of the artifact.

Learning points:
  • Arterial pulse tapping artifact causes bizarre ST-T morphology
  • It also characteristically spares exactly one of the limb leads, and the spared lead tells you which electrode is causing the artifact
  • Repeat ECG will reproduce the artifact if the electrodes are not repositioned
  • Ventricular paced rhythm is an incomplete rhythm analysis, you must also determine the atrial rhythm


MY Comment, by KEN GRAUER, MD (2/18/2024): 

Today's patient is a woman in her 90s with a dual-chamber pacemaker — who presents with acute dyspnea. I focus My Comment on a few additional thoughts to Dr. Frick's excellent discussion regarding ECG findings in today's initial ECG (that I have reproduced in Figure-1).
  • Being told that today's patient has a permanent pacemaker is extremely helpful in keying us in to the need to look especially close for pacemaker spikes (that had we not been told the patient had a pacemaker — might be extremely easy to overlook).
  • As I discussed in detail in My Comment at the bottom of the page in the January 13, 2024 post in Dr. Smith's ECG Blog — pacemaker spikes tend to be a high frequency signal. As a result — they are often effectively filtered out by a monitor mode setting of 0.5-to-40 Hz. If this is the filter setting used — then pacer spikes may simply not be visible on ECG. 
  • Instead — a broader passband (typically from 0.05 Hz to 150 Hz) is recommended for diagnostic mode, for which emphasis is on optimally accurate ST segment analysis (and for a much better chance of seeing pacemaker spikes on ECG). We were not told the frequencies used in today's ECGs.
  • As per Dr. Frick — pacemaker spikes are best seen in lead aVL of ECG #1. Knowing this relative location of pacemaker spikes in lead aVL with respect to the QRS complex in this lead facilitates recognizing the even smaller pacemaker spikes present in a number of other leads (within the GREEN circles in Figure-1).

Recognition of PTA (Pulse-Tap Artifact):
Dr. Frick highlights a number of essential points for recognizing PTA. These include:
  • Realization that artifact often produces bizarre ST-T wave morphology.
  • Awareness that one of the 3 standard limb leads is often "spared" from this bizarre ST-T wave morphology (which is lead II in Figure-1).
  • Remembering to look at the patient for a potential cause of artifact (which was the presence of the patient's dialysis AV fistula in her left arm in today's case).
  • Repeating the ECG after repositioning and verifying correct electrode lead placement.

Figure-1: I've labeled the artifact in today's initial ECG.

Finding the "Culprit" Extremity: 
As per Dr. Frick — the "culprit" extremity in today's case is the LA 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 I and III of ECG #1) — and essentially not seen in the 3rd standard limb lead (ie, there is minimal ST segment deviation in lead II of ECG #1).

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

  • By Einthoven's Triangle — the finding of maximal amplitude artifact in unipolar lead aVL confirms that the left arm is the "culprit" extremity (highlighted in RED in lead aVL of ECG #1).
  • By the electrophysiologic principles of Rowlands & Moore (J Electrocardiology 40:475, 2007) — the amplitude of the artifact in the other 2 augmented leads (ie, leads aVR and aVF) — is about 1/2 the amplitude of the artifact in lead aVL (BLUE outline of the depressed ST segments in leads aVR and aVF of ECG #1).
= = = = = = = = = = = = = = = = = = = = =  
  • KEY Take-Home POINT: 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-1is lead aVL). Appreciation of these electrophysiologic principles allowed me to instantly identify lead aVL as the "culprit" extremity in today's case — because this is the augmented lead with maximal artifact!
= = = = = = = = = = = = = = = = = = = = = 
Figure-2: Use of Einthoven's Triangle to determine the electrical voltages in the 3 standard limb leads.

Links to Examples of ARTIFACT:
What follows below is an expanding list of technical "misadventures" — most from Dr. Smith's ECG Blog — some from other sources (NOTE: As I did not previously keep track of these — there are additional examples of artifact sprinkled through Dr. Smith's ECG Blog that I have not yet included here ... ).

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