ECG Blog #385 — This Patient Arrested Soon After

The ECG in Figure-1 was obtained from a 60-year old woman — who presented to the ED (Emergency Department) for “palpitations”. Her vital signs were normal at the time this triage ECG was recorded. Blood was drawn, and the patient was promptly placed in a room to be seen — but on entering, the ED physician found her unresponsive in cardiac arrest. ROSC (Return Of Spontaneous Circulation) was achieved — but the patient did not recover neurologically.

• How would YOU interpret the ECG in Figure-1?  
• Do you see any indication on this ECG of WHY this patient was about to arrest?

Figure-1: The initial ECG in today's case. Is there any indication on this ECG of WHY this patient shortly after had a cardiac arrest?

Philosophical Overview:

All emergency providers from time-to-time encounter a patient who unexpectedly develops cardiac arrest — despite no obvious indication from their appearance that this was about to happen. This unexpected occurrence always prompts retrospective soul-searching as to whether any clinical signs may have been missed.

• What do YOU see in ECG #1? 

MY Thoughts on ECG #1:

As per my usual approach — I favor beginning my analysis with a brief look at the long lead rhythm strip before I begin to focus on the 12-lead. By the Ps, Qs, 3R Approach (See ECG Blog #185):

• The rhythm in Figure-1 is clearly not Regular. The heart Rate becomes quite slow in places (ie, with a couple of R-R intervals exceeding 6 large boxes in duration).
• The QRS complex is narrow in all 12 leads — which identifies the rhythm as supraventricular.
• P waves are present — with RED arrows in Figure-2 highlighting sinus P waves that are seen in front of most beats (as identified by the similar shape of these P waves, that are upright in lead II with a constant and normal PR interval).

Figure-2: I've labeled sinus P waves in today's tracing with RED arrows. Is there additional atrial activity?

QUESTION:

Take another look at Figure-2.

• How many additional P waves do you see on this tracing?
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•    HINT: There are more P waves than QRS complexes ...

PART #1 of My ANSWER:

In addition to the 8 RED-arrow sinus P waves in Figure-2 — there are 3 conducted PACs (Premature Atrial Contractions) — as I highlight in Figure-3 by the BLUE arrows placed in front of beats #2, 7 and 11.

• Note that these 3 beats ( = beats #2,7,11) each occur earlier-than-expected (ie, They are "premature").
• Although a slight variation is seen in P wave morphology of the sinus-conducted P waves in Figure-3 (ie, the P waves under the RED arrows) — P wave morphology for each of these 3 PACs is clearly different compared to the P waves of sinus-conducted beats (ie, the P waves under the BLUE arrows are notched). This difference in P wave morphology indicates a different site of origin.
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• Subtle Point — Did YOU notice that the QRS complex for each of these PACs is narrow and looks similar but not identical to the QRS morphology of sinus-conducted beats? (ie, The narrow s wave of premature beats #2,7,11 is not as deep as the narrow S wave of sinus-conducted beats). The reason for this slight variation in QRS morphology — is that these PACs are conducted with some degree of aberration (This difference in morphology is perhaps best appreciated by looking at beat #11 in simultaneously-recorded lead V4 in Figure-2).

Figure-3: I've labeled (with BLUE arrows) — the 3 PACs that are conducted in today's tracing.

PART #2: There are still more P Waves!

Did YOU See the 2 pointed deflections contained within the ST-T waves of beats #3 and 4 in Figure-3?

• We know that the 2 pointed deflections that appear under the YELLOW arrows in Figure-4 are real — because none of the other ST-T waves in today's tracing manifest a similar appearance — and — both of these 2 pointed deflections are followed by a pause not seen elsewhere on this tracing. This timing strongly suggests that these pointed deflections under the YELLOW arrows in Figure-4 represent blocked PACs! (that reset the SA node — thereby producing the brief pause that follows these blocked PACs).
• 
  
• PEARL #1: Another reason the 2 pointed deflections in today's tracing are likely to represent blocked PACs — is what I call, "The Birds of a Feather Phenomenon". As discussed in ECG Blog #348 — Since we know that today's rhythm shows an underlying sinus rhythm with PACs under the BLUE arrows — it is likely that other early-occurring deflections consistent with the timing of blocked PACs do in fact represent PACs.
• 
  
• PEARL #2: As cited in ECG Blog #252 — my favorite truism in arrhythmia interpretation is, "The commonest cause of a pause is a blocked PAC". Application of this truism cautions against overdiagnosis of AV blocks — and encourages us to always carefully scrutinize any unanticipated short pause for the possibility of hidden non-conducted atrial activity.

Figure-4: I've labeled (with YELLOW arrows) — the 2 blocked PACs in today's tracing.

What About the 12-Lead ECG?

Take another LOOK at the 12-lead ECG in today's case — which I've reproduced again in Figure-5. This ECG shows:

• A slightly leftward axis (ie, predominantly negative QRS in lead aVF) — but not negative enough to qualify as LAHB (ie, The QRS is still predominantly positive in lead II).
• No chamber enlargement.
• No Q waves.
• Slightly delayed R wave progression (ie, The R wave does not become more positive than the S wave is deep until between V5-to-V6).
• Nonspecific ST-T wave flattening in multiple leads.
• Subtle-but-real U waves (under the GREEN arrows).
• 
  
• IMPRESSION: I see no acute ST-T wave changes in Figure-5. That said — the finding of sinus rhythm with lots of PACs (some non-conducted) + nonspecific ST-T wave flattening in multiple leads + U waves — strongly suggests that there may be an electrolyte imbalance (ie, low K+ and/or low Mg++).

Figure-5: Take another LOOK at today's 12-lead ECG. What do the GREEN arrows suggest?

BACK to Today's CASE:

To recap the clinical presentation of today's case — this 60-year old woman presented to the ED for "palpitations". Vital signs were initially "normal" — but the patient shortly thereafter was found in cardiac arrest. While no one would predict an impending cardiac arrest from the initial tracing seen in Figure-5 — My admittedly retrospective assessment of today's ECG should suggest:

• A probable electrolyte disorder (ie, low K+ and/or low Mg++).
• An underlying sinus rhythm with lots of PACs of at least 2 different shapes. While the rhythm disorder in Figure-5 does not manifest enough irregularity or P wave variability to qualify as MAT — the finding of multiple PACs with more than 1 morphology should suggest similar clinical implications as the MAT rhythm described in ECG Blog #366 — which are for the provider to anticipate either severe pulmonary disease and/or multisystem disorders in a "sick" patient.
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• CASE Follow-Up: Lab work that had been drawn before the cardiac arrest — came back after the arrest. It showed marked hypokalemia with severe acidosis, hypoxemia, and signs of early CO2 retention. The difficult clinical lesson — is that sometimes patients may be sicker than they appear. 

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Acknowledgment: My appreciation to Chun-Hung Chen - 陳俊宏 (from Taichung City, Taiwan) for the case and this tracing.  

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ADDENDUM (7/9/2023) — Additional material relevant to today's case:

 

Figure-3: Summary of KEY points related to MAT.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #185 — Review of the Ps, Qs, 3R Approach for systematic rhythm interpretation.
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• ECG Blog #199 and ECG Blog #366 — for Review of MAT.
• ECG Blog #65 — for an example of MAT in a patient with chronic pulmonary disease (plus more on the differential diagnosis of MAT).
• ECG Blog #200 — for an example of Wandering Atrial Pacemaker.
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• ECG Blog #289 —  Review of U wave recognition (and low K+/Mg++).
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• ECG Blog #348 — Reviews the concept of "Birds of a Feather" (with regard to recognizing aberrantly conducted PACs).
• ECG Blog #252 — The "Commonest Cause of a Pause" is a blocked PAC.
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• ECG Blog #140 — Example of alternating Bifascicular Block Aberration.
• ECG Blog #14 — Example of Blocked PACs.
• ECG Blog #15 — Example of a WCT rhythm with aberrant conduction.
• ECG Blog #33 — Example of PACs with varying degrees of Aberrant Conduction.
• ECG Blog #263 — Differentiation of WCT rhythms (ie, deciding between VT vs Aberrancy?).
• ECG Blog #211 — WHY does Aberrancy occur? (And why the most common form of aberrant conduction manifests RBBB morphology).
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• ECG Blog #70 — Reviews the Ashman Phenomenon (re aberrant conduction).
• ECG Blog #71 — Regarding the Ashman Phenomenon with AFib.

I link to 2 additional 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 MAT:

• The January 5, 2020 post in Dr. Smith’s ECG Blog — for an example of MAT.
• The September 30, 2019 post in Dr. Smith’s ECG Blog — for an example of “MAT”, but without the tachycardia ...