ECG Blog #391 — Asymptomatic but Irregular ...

This patient was seen in the office — and during his exam, was found to have an “irregular heart beat”. He was not symptomatic with the ECG shown in Figure-1.

• How would YOU interpret this ECG?
• As the primary care clinician — What would YOU do?
•    Extra Credit (which is a HINT to the Answer! ):  How many beats are recorded on the ECG in Figure-1?

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

MY Thoughts on Today’s Case:

This ECG was sent to me for my interpretation. Even without knowing clinical details — I thought it an illustrative case.

• As always — I like to start by focusing on the long lead rhythm strip — which shows a bigeminal rhythm — in that there are repetitive 2-beat groups (See ECG Blog #232 for review of the concept of “bigeminy” ).

QUESTION:

• Did YOU realize that the long lead II rhythm strip at the bottom of the tracing is not simultaneous with each of the leads for the entire the 12-lead tracing? 
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• IF not — Please take another LOOK at Figure-1.

ANSWER:

I’ve labeled today’s tracing in Figure-2. Before going further — I’d highlight these points:

• There are 11 beats in the long lead rhythm strip (The simple step of numbering the beats ensures there will be no confusion about which beat(s) we are talking about.
• Each of the 2-beat groups begins with a sinus P wave (ie, RED arrows before beats #1,3,5,7,9).
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• Note that the QRS complex of beats #1 and #2 in the long lead II rhythm strip occur directly under the QRS of beats #1 and 2 in leads I,II,III. This tells that there is simultaneous recording of these 2 beats in these 4 leads (vertical BLUE lines extending upward in Figure-2 from beats #1 and #2 in the rhythm strip).
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• In contrast — QRS complexes in the other 9 leads do not line up with corresponding beats below them in the long lead II rhythm strip (vertical PINK lines extending upward from the long lead rhythm strip). This is because only beats #1 and 2 are simultaneously recorded in other leads. In fact, these same first 2 beats in today’s tracing are repeated in the 9 remaining leads of ECG #1.

NOTE: I’ve labeled ECG #1 accordingly in Figure-2. 

• The advantage of the type of monitoring system used in today’s tracing — is that we get to see what beats #1 and #2 in the long lead II rhythm strip look like in all 12 leads.
• The disadvantage of this monitoring system — is that we have no idea what beats #3-thru-11 look like in any lead other than in the long lead II rhythm strip.

Editorial Comment: It is often very helpful to have the option of viewing P wave and QRS morphology in more than a single lead. For example — If part of the QRS complex lies on the baseline in the 1 lead that you are monitoring — then you might be misled into thinking that the QRS complex is narrow — when in fact other simultaneously-recorded leads would clearly show that the QRS is wide.

• For this reason — I generally favor the more commonly used monitoring system, in which each of the beats in the long lead rhythm strip are shown in the 3 simultaneously-recorded leads above them.
• That said — today's tracing illustrates an exception in which it turns out to be advantageous that we see the appearance of the first 2 beats in each of the 12 leads, as we will see momentarily.

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The CASE Continues:

Take another LOOK at Figure-2. 

• What is the reason for today's bigeminal rhythm? (ie, Why does every-other-beat occur earlier-than-expected?).
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• HINT: The most helpful lead to answer this question is lead V1.

Figure-2: I've labeled the ECG from Figure-1 — to show that the first 2 beats in the long lead II rhythm strip occur simultaneously with beats #1 and #2 in leads I,II,III — but we do not see any simultaneously-recorded leads for the remaining 9 beats in the long lead II (See text).

PEARL #1: As discussed in ECG Blog #232 — it helps to consider the differential diagnosis of a bigeminal rhythm. When there is sinus conduction of the 1st beat in each pair of the bigeminal rhythm (as we see in the long lead II rhythm strip in Figure-2) — Consider the following:

• Sinus rhythm with atrial or junctional bigeminy (ie, every-other-beat is a PAC or a PJC).
• Sinus rhythm with atrial trigeminy — in which every-third P wave is a PAC that is "blocked" (non-conducted).
• SA ( = Sino-Atrial) Block.
• Mobitz I, 2nd-Degree AV Block ( = AV Wenckebach) with 3:2 AV conduction.
• Mobitz II, 2nd-Degree AV Block.

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Beyond-the-Core: Technically, there are a few additional causes of a bigeminal rhythm that need not be considered in today's case, because the rhythm is either not strictly supraventricular — or — because the 1st beat in each group is not sinus-conducted. These additional causes include:

• Ventricular bigeminy (ie, every-other-beat is a PVC).
• Atrial fibrillation, atrial tachycardia or atrial flutter with Wenckebach conduction.
• "Escape-Capture" (the 1st beat in each group is a junctional or ventricular escape beat — followed by a conducted beat).

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PEARL #2: As discussed in ECG Blog #389 — the saying, "Birds of a Feather Flock Together" — serves as a helpful reminder of an important concept in arrhythmia interpretation. 

• The meaning of this English proverb, "Birds of a Feather ... " — is that people of similar type, interest or character tend to mutually associate.
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• The relationship to cardiac arrhythmias of the saying, "Birds of a Feather" — is that IF we see other clear evidence on an arrhythmia of a frequent-occurring phenomenon — then additional less evident findings in that same patient probably reflect the same phenomenon.
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• Application to Today's Tracing: There are 5 groups of 2 beats in the long lead II rhythm strip from today's tracing. As seen in Figure-2 — QRS morphology of the 2nd beat in each of these 5 groups is not the same (ie, the QRS of beat #6 is clearly wider and different-looking than the QRS of beats #2,4,8 and 10). That said — since each of these 5 groups begin with a similar-looking sinus P wave — and since the timing (coupling interval) of the 2nd beat in each of these 5 groups is virtually the same — by the "Birds of a Feather" concept, the etiology of the wider and different-looking beat #6 will probably be the same etiology as whatever beats #2,4,8 and 10 turn out to be.

PEARL #3: In keeping with the differential diagnosis for a bigeminal rhythm reviewed in PEARL #1 — there are 2 findings that confirm the etiology of beat #2 in today's tracing. These are:

• Finding #1: In simultaneously-recorded leads V1,V2,V3 — there clearly is a PAC (Premature Atrial Contraction) seen before beat #2 in each of these 3 leads (BLUE arrows in Figure-3). Of note — this PAC before beat #2 is really only seen in leads V1,V2,V3, and not in the other 9 leads. As emphasized in ECG Blog #211 — the BEST way to prove aberrant conduction is by demonstration of a premature P wave (PAC) preceding the widened complex.
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• Finding #2: As emphasized below in today's ADDENDUM — aberrantly conducted beats typically manifest some form of conduction block, most commonly with RBBB (Right Bundle Branch Block) morphology. The rSR' morphology of beat #2 in lead V1 (with S wave descending below the baseline and a taller right "rabbit ear" = R' deflection) — with wide terminal S waves in lateral leads I and V6 — is classic for RBBB aberration.

BOTTOM Line: The etiology of the bigeminal rhythm in today's tracing is atrial bigeminy (ie, every-other-beat is a PAC). QRS morphology of the even-numbered beats in the long lead II rhythm strip in Figure-3 varies — because the 2nd beat in each group is being conducted with different degrees of RBBB aberration.

• Factors predisposing the 2nd beat in each group to aberrant conduction are: i) Early occurrence of PACs during the RRP (Relative Refractory Period); and/or, ii) The Ashman phenomenon (in which an increase in the preceding R-R interval facilitates aberrant conduction by prolonging the RRP of the beat after the pause) — See the ADDENDUM below!

PEARL #4: Twelve leads are better than one. The premature P waves preceding each of the even-numbered beats in Figure-3 are not well seen in the long lead II rhythm strip. As a result — we would not have been able to confidently make the diagnosis of atrial bigeminy without the use of simultaneously-recorded leads V1,V2,V3 that allowed ready identification of the premature P wave before beat #2.

• Although today's patient was asymptomatic with the rhythm shown in ECG #1 — having this frequent amount of PACs is of potential concern, and may increase the risk of developing atrial fibrillation. 
• Optimal management entails trying to "find and fix" the cause of these frequent PACs (ie, stimulants including sympathomimetic drugs, cocaine, alcohol, excess caffeine — electrolyte disturbance — excess stress or anxiety — dehydration — inadequate sleep — anemia or other illness). If no easily "fixable" cause is found — further evaluation including chest X-ray and/or Echo may be indicated.

Figure-3: BLUE arrows in simultaneously-recorded leads V1,V2,V3 highlight the premature P wave that confirms that beat #2 is a PAC conducted with RBBB aberration (See text).

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Acknowledgment: My appreciation to Ku-Lang Chang (from Gainesville, Florida) for the case and this tracing.

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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 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.
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• ECG Blog #232 — Reviews the concept of Bigeminy.
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• ECG Blog #389 — Reviews the "Birds of a Feather" concept.
• ECG Blog #253 — Another case using the "Birds of a Feather" principle.
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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 due to Aberrant Conduction.
• ECG Blog #33 — Example of PACs with varying degrees of Aberrant Conduction.
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• ECG Blog #70 — for Review of the Ashman Phenomenon.
• See ECG Blog #212 — for Step-by-Step discussion of another case with the Ashman Phenomenon.
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• See ECG Blog #211 — Reviews WHY some early beats and some SVT rhythms are conducted with Aberration (and why the most common form of aberrant conduction manifests RBBB morphology).
• See ECG Blog #253 — Reviews a case with multiple aberrantly-conducted beats.

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ADDENDUM (8/19/2023) In the following 3 Figures — I post written summary from my ACLS-2013-ePub regarding the basics of Aberrant Conduction.

ECG Media PEARL #28 (4:45 minutes Video) — Reviews WHY some early beats and some SVT rhythms are conducted with Aberration (and why the most common form of aberrant conduction manifests RBBB morphology).

• CLICK HERE — for a PDF of this 6-page file on the basics of Aberrant Conduction that appears in Figures-4, -5, -6.

 

Figure-4: Aberrant Conduction — Refractory periods/Coupling intervals (from my ACLS-2013-ePub).

 

Figure-5: Aberrant Conduction (Continued) — QRS morphology/Rabbit Ears.

 

Figure-6: Aberrant Conduction (Continued) — Example/Summary.

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ECG Media PEARL #29 (8:00 minutes Audio) — Reviews WHAT the Ashman Phenomenon is — HOW to use it clinically?

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ECG Media PEARL #67 (9:10 minutes Audio) — Applies the wisdom from 2 of my favorite sayings to the "art" of ECG interpretation. These 2 sayings are = "Birds of a Feather" and "Forest from Trees".