ECG Blog #447 — A "Prophetic" P Wave ...

I was sent the ECG shown in Figure-1 — being told only that providers on the case suspected AFib (Atrial Fibrillation) with RBBB (Right Bundle Branch Block) aberrancy.

QUESTIONS:

• Is the wide tachycardia that is seen best in the chest leads, too irregular to be VT (Ventricular Tachycardia)?
•    — How certain are YOU of your answer?

Figure-1: The initial ECG in today's case. (To improve visualization — I've digitized the original ECG using PMcardio).

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PEARL #1: Before reviewing my approach to today's challenging arrhythmia — it's important to clarify a commonly misunderstood concept: Although monomorphic VT is usually a regular (or at least almost regular) rhythm — it is not always regular!

• As reviewed in ECG Blog #231 — QRS morphology in VT may manifest a number of different forms. These include: i) Monomorphic VT — in which there is a similar (if not identical) QRS appearance throughout the episode of VT; ii) Polymorphic VT (PMVT) — in which QRS morphology continually changes from 1 beat-to-the-next (and which when associated with a long QTc interval — is known as Torsades de Pointes); and, iii) Several VT forms that are much less common in practice (ie, Pleomorphic VT — Bidirectional VT).
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• As noted in ECG Blog #444 — Reasons why monomorphic VT may not be regular include: i) There may be a "warm-up" period of slower and gradually accelerating ventricular beats before the VT becomes regularized; ii) There may be a "cool-down" period in which after the regular run of VT, the rate of VT progressively slows until the VT run finally resolves (these concepts thoroughly illustrated and explained in ECG Blog #417); and, iii) There may be more than a single VT reentry circuit sharing the same exit pathway — and/or the speed of conduction over the reentry circuit may vary (Oreto et al — Am Heart J 124(6):1506-11, 1992).

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MY Thoughts on the Rhythm in Figure-1:

The format used to record today's ECG provides a continuous rhythm strip recording that shows 21 consecutive beats. As seen in Figure-1 — the first 9 beats are displayed in each of the simultaneously-recorded limb leads — with the last 12 beats displayed in each of the simultaneously-recorded chest leads.

• PEARL #2: When confronted with a number of different ECG features on a single rhythm strip — I favor starting with the easier part(s) of the tracing. I save for last those parts of the tracing that are more difficult to interpret.
• Therefore — I began my interpretation by first identifying the 3 consecutive sinus-conducted beats ( = beats #6,7,8).
• Note that I placed colored arrows over the initial part of these sinus P waves in leads I and II (See Figure-2). And note that a precisely on-time 4th arrow appears just before beat #9. 
• KEY Point: It is the presence of this 4th precisely-on-time P wave that solves today's arrhythmia — because before we see the end of this 4th P wave, the rhythm is interrupted by a run of wide beats that continues until the end of this tracing!
• Note the 2 vertical dotted BLUE lines that I have added to Figure-2. These dotted lines mark the beginning of the QRS complex for beats #4 and #9 in each of the simultaneously-recorded limb leads. My purpose in drawing these dotted lines — is to show that in lead I, the initial part of the QRS complex for beats #4 and #9 is isoelectric and falls on the baseline.
• Focusing our attention now on lead I — it should be apparent that the 4th on-time RED arrow clearly occurs before the QRS of beat #4 — and that there clearly is not enough time for this 4th P wave to conduct to the ventricles. This defines the presence of AV Dissociation — which proves that beat #4 must be of ventricular etiology (ie, something "else" other than a sinus-conducted beat, must have occurred to produce widened beat #9). For more on the diagnostic significance of identifying AV dissociation in wide tachycardia — See ECG Blog #133 and ECG Blog #151.
• Since the presence of AV dissociation proves that beat #9 is of ventricular etiology — all other beats in Figure-2 that look the same as beat #9 must also be of ventricular etiology ( = beats #1-thru-5). And, since the run of consecutive wide beats that begins with beat #9 continues after the lead switch (that marks the change from limb leads to chest leads) — this run of VT (that begins with beat #9) continues throughout the rest of this rhythm strip!
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• PEARL #3: In addition to AV Dissociation — there are 2 additional features regarding QRS morphology of the wide beats in Figure-2 that prove the runs of wide beats represent VT. These are: i) Extreme axis deviation (since the QRS in lead I is all negative); — and, ii) Positive QRS concordance in all 6 chest leads (ie, When the QRS is either all positive or all negative in all 6 chest leads — this is virtually 100% predictive of VT).

BOTTOM Line: Today's case provides the best example I have seen that shows how monomorphic VT may sometimes be surprisingly irregular throughout its entire duration.

Figure-2: I've labeled P waves in the initial ECG. Note how irregular the run of VT that begins with beat #9 is, throughout its entire duration! 

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Acknowledgment: My appreciation to Javed Iqbal (from Leiah, Punjab, Pakistan) for the case and these tracings.

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ADDENDUM (9/13/2024): 

• I've reproduced below from ECG Blog #196 — a number of helpful figures and my Audio Pearl on assessment of the regular WCT rhythm.

 

Figure-5 : My LIST #1 = Causes of a Regular WCT (Wide-Complex Tachycardia) of uncertain Etiology (ie, when there is no clear sign of sinus P waves).

Figure-6: Use of the "3-Simple Rules" for distinction between SVT vs VT.

Figure-7: Use of Lead V1 for assessing QRS morphology during a WCT rhythm.

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ECG Media PEARL #13a (12:20 minutes Audio) — reviews “My Take” on assessing the regular WCT (Wide-Complex Tachycardia), when sinus P waves are absent — with tips to distinguish between VT vs SVT with either preexisting BBB or aberrant conduction.

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Additional Relevant ECG Blog Posts to Today’s Case:

• ECG Blog #185 — Reviews my System for Rhythm Interpretation, using the Ps, Qs & 3R Approach.
• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #210 — Reviews the Every-Other-Beat (or Every-Third-Beat) Method for estimation of fast heart rates — and discusses another case of a regular WCT rhythm. 
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• ECG Blog #220 — Review of the approach to the regular WCT ( = Wide-Complex Tachycardia).
• ECG Blog #196 — Another Case with a regular WCT rhythm.
• ECG Blog #263 and Blog #283 and Blog #361 — more WCTs.
• ECG Blog #444 — a monomorphic VT rhythm that is not regular.
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• ECG Blog #197 — Reviews the concept of Idiopathic VT, of which Fascicular VT is one of the 2 most common types. 
• ECG Blog #346 — Reviews a case of LVOT VT (a less common idiopathic form of VT).
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• ECG Blog #204 — Reviews the ECG diagnosis of the Bundle Branch Blocks (RBBB/LBBB/IVCD). 
• ECG Blog #203 — Reviews ECG diagnosis of Axis, the Hemiblocks — and  the Bifascicular Blocks.
• ECG Blog #211 — WHY does Aberrant Conduction occur?
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• ECG Blog #42 — Review of criteria to distinguish between VT vs Aberration.

• Working through a case of a regular WCT Rhythm in this 80-something woman — See My Comment in the May 5, 2020 post on Dr. Smith’s ECG Blog. 
• Another case of a regular WCT Rhythm in a 60-something woman — See My Comment at the bottom of the page in the April 15, 2020 post on Dr. Smith’s ECG Blog. 
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• Review of the Idiopathic VTs (ie, Fascicular VT; RVOT and LVOT VT) — See My Comment at the bottom of the page in the September 7, 2020 post on Dr. Smith’s ECG Blog.
• Review of a different kind of VT (Pleomorphic VT) — See My Comment in the June 1, 2020 post on Dr. Smith’s ECG Blog (as well as ECG Blog #231).