ECG Blog #411 — Is it Wenckebach?

How would YOU interpret the tracing in Figure-1 — that was sent to me without additional information?

QUESTIONS:

• What is the rhythm?
• Is there AV dissociation? If so — WHY?
• 
  
• Clinically — HOW would you approach interpretation of this tracing in optimal time-efficient fashion?

Figure-1: The initial ECG in today's case.

KEY Clinical Point:

If I was the medical provider charged with the care of the patient whose ECG is shown in Figure-1 — I would approach this tracing in the following sequential stages:

• I’d first establish that the patient was hemodnamically stable with this ECG and this cardiac rhythm. Assuming this patient is at least momentarily stable — I’d then proceed as follows:
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• I’d take a quick look at the long lead rhythm strip. 
• To EMPHASIZE: The rhythm shown in the long lead II (below the 12-lead tracing in Figure-1) is not a simple arrhythmia — so rather than trying to come up with a precise interpretation of the rhythm — I’d spend no more than 5-to-10 seconds to ensure there is a reasonable, stable-looking heart rate (which there is in Figure-1 — as the rhythm is supraventricular [narrow QRS everywhere] — some P waves are seen — and, a pattern of repetitive group beating (groups of 3 beats), with an average heart rate in the 60-80/minute rate range — appears to be present).
• 
  
• I’d then spend no more than 5-to-10 seconds looking at the rest of the 12-lead ECG to ensure that there is no ongoing emergency in need of immediate care (ie, No acute MI; No hyperkalemia, etc.).

COMMENT:

While I always advocate a systematic approach to both rhythm and 12-lead ECG interpretation — optimal clinical ECG interpretation entails prioritizing those parts of the tracing in front of you that mandate your immediate attention. Later, when you have a moment of time — You can complete your systematic assessment.

• With Regard to the Cardiac Rhythm: Our initial 5-to-10 second assessment of the long lead II rhythm strip should be all that is needed at this instant in time — because this limited amount of time should still allow you to establish: i) That the patient is hemodynamically stable; and, ii) That the rhythm is supraventricular — with at least some P waves, a narrow QRS everywhere — and, an overall heart rate in the 60-80/minute range.
• 
  
• PEARL #1 (Advanced Point): The fact that the QRS complex is narrow, with at least some P waves — and a pattern suggesting group beating — should clue us into: i) The possibility of Wenckebach conduction! — and, ii) That we need to carefully inquire about recent chest pain, paying special attention to the rest of this 12-lead ECG (looking carefully for signs of acute or recent infarction — because AV Wenckebach is common with acute inferior MI). It is much easier to identify Wenckebach conduction IF you are looking for it!

Regarding the 12-Lead ECG:  

Applying the systematic approach I favor for 12-lead ECG interpretation (as detailed in ECG Blog #205):

• Rate & Rhythm: As stated above — there is a regular, supraventricular rhythm with some P waves, group beating, and an acceptable overall ventricular rate between ~60-80/minute.
• Intervals (PR-QRS-QTc): The PR interval varies — the QRS is narrow — the QTc looks normal (Best seen in leads V2,V3). 
• Axis: Normal (about +60 degrees).
• Chamber Enlargement: Depending on age of the patient — voltage for LVH may be present (ie, Deepest S in V1,V2 + tallest R in V5,V6 ≥35 mm — IF the patient is ≥35 years of age).

Regarding Q-R-S-T Changes: 

• Q waves: Small q waves of uncertain significance are seen in the inferior leads.
• R Wave Progression: Normal, with transition (where height of the R wave becomes taller than the S wave is deep) — occurs normally, here by lead V4.
• ST-T wave Changes: Show some nonspecific ST-T wave flattening, and perhaps shallow T wave inversion in lead aVL. The slight amount of ST elevation that we see in lead V2 is common and normal.
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• Clinical IMPRESSION: The ECG in Figure-1 shows nonspecific ST-T wave abnormalities — but nothing that looks acute.

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Looking Closer at the Rhythm in Today's CASE:

As reviewed in ECG Blog #185 — I favor the Ps, Qs, 3R Approach for systematic, time-efficient interpretation of the cardiac rhythm.

• PEARL #2: When looking for P waves — I find it easiest to first identify those P waves that I am certain about. I have done this with RED arrows in Figure-2.
• The presence of multiple, regularly-spaced RED ( = definitely present) P waves in Figure-2 suggests: i) that there is a very good chance that the underlying atrial rhythm will be regular throughout the long lead II rhythm strip; and, ii) that the P-P interval between any 2 consecutive RED arrows will clue us in to where the remaining (partially hidden) P waves can be found. 
• Use of calipers can facilitate confirming that the underlying atrial rhythm in Figure-2 is in fact regular. With calipers — it takes only seconds to confirm this!
• PINK arrows highlight that the on-time beginning little "hump" at the very onset of the QRS of beats #2 and #5 clearly represents 2 additional on-time P waves.
• Completion of our "P wave search" can then be easily accomplished by noting the subtle-but-unmistakeable distortion under the PURPLE arrows toward the end of the T waves of beats #1 and 4 — and at the very onset of the QRS of beats #8 and #11.

Figure-2: I've labeled atrial activity in today's tracing with colored arrows (See text).

PEARL #3: Recognition that true group beating is present, in association with an underlying regular atrial rhythm — strongly suggests there is some type of 2nd-degree AV block in which there is Wenckebach conduction (ie, the presence of an underlying regular P wave rhythm is an essential component of the typical forms of AV block). 

• Focus on this concept facilitates recognizing the 3 true groupings in Figure-3 (within the dotted WHITE rectangles). Note the uncanny similarity in duration of the R-R interval between the first 2 beats in each group (ie, the R-R interval between beats #2-3; 5-6; and 8-9) — as well as for the R-R interval between the last 2 beats in each group (ie, the R-R interval between beats #3-4; 6-7; and #9-10) — as well as for duration of the R-R intervals of the short pauses that separate each of the groups (ie, the R-R interval between beats #1-2; 4-5; 7-8; and 10-11). This amount of symmetry for the relative duration of R-R intervals within each group of beats is not the result of chance!

Figure-3: RED arrows highlight that the atrial rhythm in the long lead II rhythm strip is regular. Note the 3 true groupings (within the dotted WHITE rectangles).

PEARL #4: We know that there is at least transient AV Dissociation in today's rhythm — because the PR interval of some on-time sinus P waves is clearly too short to be able to conduct (ie, Despite their on-time occurrence — the WHITE arrow P waves before beats #2,5,8 and 11 in Figure-4 — do not have enough time for normal conduction through the AV node).

• Since beats #2,5,8 and 11 all manifest a narrow QRS complex — and are not preceded by sinus P waves with a realistic chance of conducting — this means that these 4 QRS complexes are junctional beats.
• Note that each of these beats is preceded by a similar R-R interval of just under 5 large boxes — which corresponds to an ever-so-slightly accelerated junctional escape rate of ~65/minute.
• That said — We have no idea if the WHITE-arrow P waves that appear at the onset of the QRS of beats #2,5,8 and 11 might possibly have conducted — IF they were given a chance to do so (ie, IF the junctional escape rate would have been slower than 65/minute).

PEARL #5: Despite the presence of at least transient AV dissociation — the rhythm in  Figure-4 is not complete AV Block.

• Most of the time when there is complete AV block — the escape rate (be this a junctional or ventricular escape rhythm) will be regular. The obvious irregularity of the ventricular response in Figure-4 — immediately tells us this is not complete AV block.
• QRS complexes that occur earlier-than-expected are likely to be conducted beats! (ie, Beats #4,7 and 10 in Figure-4 are therefore likely to be conducted — and beats #3,6,9 and 12 may also be conducted).

PEARL #6: As per PEARL #4 — we have already established that there is transient AV dissociation in Figure-4 (because beats #2,5,8,11 are clearly not conducted). There appear to be 2 reasons for this transient AV dissociation in today's rhythm:

• As reviewed in ECG Blog #192 — the 3 Causes of AV Dissociation are: i) Default; ii) Usurpation; and, iii) Some form of 2nd- or 3rd-degree AV block. 
• Today's tracing is interesting — in that the reason for transient AV dissociation (ie, non-conduction of the WHITE-arrow P waves in Figure-4) — appears to be a combination of the slightly accelerated junctional beats (beats #2,5,8 and 11) — and the 2nd-degree AV block that leads to the slight pauses after beats #1,4,7 and 10.

PEARL #7: Looking closer in Figure-4 at the P waves in each of the 3-beat groupings — tells us that there is 2nd-degree AV block, Mobitz Type I ( = AV Wenckebach) because of the following findings:

• As already stated — the WHITE-arrow P waves in each group do not conduct to the ventricles — because the PR interval is too short.
• That said — We know that the next P wave in each grouping (ie, the light BLUE-arrow P waves) — does conduct to the ventricles, because the PR interval preceding beats #3,6,9 and 12 are all equal!
• This is followed by the dark BLUE-arrow P waves that are also conducting — but with slight increase in the PR interval compared to the light BLUE PR interval. Once again — We know that the dark BLUE-arrow P waves are conducting — because the PR interval preceding beats #4,7 and 10 are all equal!
• The last P wave in each grouping (ie, the YELLOW-arrow P waves) — are non-conducted — thus completing the AV Wenckebach cycle of progressive PR interval lengthening until a beat is dropped.
• 
  
• Additional typical features of AV Wenckebach in Figure-4 include: i) The narrow QRS (Mobitz II usually has a wide QRS — because of its origin at a lower point in the conduction system); ii) Progressive shortening of the R-R interval within groups (the R-R intervals between beats #3-4; 6-7; and 9-10 — are shorter than the R-R intervals between beats #2-3; 5-6; 8-9); and, iii) The pause containing the dropped beat is less than twice the shortest R-R interval.

Figure-4: I've colored the P waves from Figure-3 (See text).

SUMMARY:

The rhythm in today's case is sinus (ie, regularly-occurring P waves) — with 2nd-degree AV block, Mobitz Type I ( = AV Wenckebach). Each of the 3-beat Wenckebach groups begins with a slightly accelerated junctional beat (which results in transient AV dissociation).

• The overall ventricular rate in today's tracing should be sufficient at ~60-80/minute for adequate perfusion. 
• Although it is common for Mobitz I to be associated with acute inferior MI — the 12-lead ECG in today's case does not suggest any acute ST-T wave changes.

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LADDERGRAM:

To clarify the mechanism for today’s rhythm — I've derived a laddergram with step-by-step description of events. I begin with Figure-5.

• NOTE: For review of the Basics for HOW to read (and draw) laddergrams — See ECG Blog #188).   

Figure-5: The 1st step in laddergram construction — is to represent each of the P waves in the Atrial Tier. Since conduction through the atria is fast — vertical lines are used, drawn from each of the ARROWS that overlie P waves in this tracing.

Figure-6: Since all QRS complexes are narrow — each of the 12 beats in this tracing is supraventricular. Knowing this allows me to draw in conduction within the Ventricular Tier — which I represent with slightly inclined forward-directed lines with an arrow to indicate the downward direction of conduction. 
NOTE: I find Power Point optimal for drawing laddergrams — as it allows ready duplication of laddergram elements and precisely vertical displacement to ensure laddergram elements appear exactly below P waves and QRS complexes in the original rhythm strip.

Figure-7: It's now time to "solve" the laddergram. I begin by a survey of all P waves (RED arrows — which are represented by the RED vertical lines in the Atrial Tier) — and of all 12 QRS complexes (vertical RED lines within the Ventricular Tier) — with the goal of determining which P waves seem most likely to conduct to the ventricles.

Figure-8: "Armed" with the clue that the PR intervals preceding beats #3,6,9 and 12 look to be both normal and equal — I felt comfortable presuming that each of these BLUE-arrow P waves are conducting (which I illustrate with the slanted BLUE lines within the AV Nodal Tier that connect these P waves to the appropriate QRS complexes. 

Figure-9: I then connected the 2nd P wave in each group (highlighted by the dark BLUE arrows) — with the appropriate QRS complexes for beats #4,7 and 10 in the Ventricular Tier (slanted dark BLUE lines within the AV Nodal Tier). Note slight increase in the amount of slanting of these dark BLUE lines, reflecting slight increase in the PR interval since the light BLUE P waves conducted beats #3,6,9 and 12.

Figure-10: I next chose to represent the YELLOW arrow P waves — which clearly are not conducting because they are not followed by any QRS complexes (YELLOW butt ends drawn within the AV Nodal Tier). This left a limited number of P waves and QRS complexes unaccounted for ...

Figure-11: But the PR interval for the WHITE arrow P waves is clearly too short to conduct! (represented by WHITE butt ends drawn within the AV Nodal Tier).

Figure-12: Since neither the YELLOW nor WHITE arrow P waves are conducting — beats #2,5,8 and 11 have to be arising from the AV node! (The dotted RED lines with butt ends indicate retrograde conduction from the slightly accelerated junctional escape beats — that prevent WHITE arrow P waves from being conducted through the AV Nodal Tier).

Figure-13: My completed laddergram illustrating the mechanism for today's rhythm. There is 2nd-Degree AV Block, Mobitz Type I (AV Wenckebach) — in which slightly accelerated junctional escape beats produce 1 beat of AV dissociation until sinus conduction resumes with beats #3,6,9 and 12.

Final Advanced Point: 

Did YOU notice in Figure-13 — that the QRS of each of the junctional beats ( = beats #2,5,8 and 11) is slightly taller than the QRS of the remaining 8 beats on this tracing?

• The above subtle observation can sometimes be a very helpful clue that these slightly different-looking beats are not sinus-conducted — but instead arise from the AV Node.
• The reason escape beats from the AV Node sometimes look slightly different than sinus-conducted beats — is that the precise site of origin within the AV Node from where these beats arise may be slightly different than the path within the AV Node through which sinus-conducted beats pass.
• To Emphasize: This clue is not needed for us to know that beats #2,5,8,11 in today's tracing are junctional beats — since it is obvious that the P waves preceding beats #2,5,8,11 are too close to the QRS to be conducted. But there are times when it will not be readily apparent if a given QRS complex represents a sinus-conducted beat vs junctional escape — in which case, the observation that QRS morphology differs slight may reveal which beats are junctional escape beats (See ECG Blog #63 — for a clinical example of this phenomenon!).

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Acknowledgment: My appreciation to ไกรสร เต็ง (from Bangkok, Thailand) for the case and this tracing.

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Related 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 System for 12-Lead ECG Interpretation.
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• ECG Blog #245 — Reviews ECG diagnosis of LVH.
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• ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 90 laddergram cases — many with step-by-step sequential illustration).
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• ECG Blog #192 — The 3 Causes of AV Dissociation.

• ECG Blog #191 — Reviews the difference between AV Dissociation vs Complete AV Block.
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• ECG Blog #389 — ECG Blog #373 — and ECG Blog #344 — for review of some cases that illustrate "AV block problem-solving".
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• ECG Blog #63 — Reviews a case of 2nd-Degree AV Block, Mobitz Type I with Junctional Escape Beats.
• ECG Blog #267 — Shows step-by-step Laddergrams, with derivation of a case of Mobitz I with more than a single possible explanation.
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• ECG Blog #404 (ECG Video) — applies the Ps,Qs,3R Approach to a case of 2nd-degree AV Block ( = Mobitz I or Mobitz II or Neither).
• ECG Blog #405 (ECG Video) — applies the Ps,Qs,3R Approach to a case of AV Dissociation vs Complete AV Block (What's the difference?).

 

ADDENDUM (1/6/2024):

This 15-minute ECG Video (Media PEARL #52) — Reviews the 3 Types of 2nd-Degree AV Block — plus — the hard-to-define term of "high-grade" AV block. I supplement this material with the following 2 PDF handouts.

—  —

ECG Media PEARL #4 (4:30 minutes Audio): — takes a brief look at the AV Blocks — and focuses on WHEN to suspect Mobitz I.

• Section 2F (6 pages = the "short" Answer) from my ECG-2014 Pocket Brain book provides quick written review of the AV Blocks.
• Section 20 (54 pages = the "long" Answer) from my ACLS-2013-Arrhythmias Expanded Version provides detailed discussion of WHAT the AV Blocks are — and what they are not!

—  — 

ECG Media PEARL #75 (6:10 minutes Audio) — Reviews how to tell IF a Junctional (AV Nodal) Rhythm is pathologic or appropriate?

ECG Blog #410 — How Tall are the T Waves?

QUESTION:

• HOW would YOU interpret the ECG in Figure-1 — if no clinical information was provided? 

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

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The HISTORY in Today's CASE:

The patient in today's case is a teenager who presented to the ED (Emergency Department) in cardiac arrest after electrocution. The ECG in Figure-1 — was obtained following successful resuscitation.

• The "good news" — is that after an extended hospitalization, the patient was finally discharged home, and doing well.

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A Closer Look at Today's ECG:

The rhythm in Figure-1 is sinus — with regular upright P waves with a constant and normal PR interval in lead II.

• At 1st glance of the chest leads — the QRS complex appears to be significantly widened. However, on looking closer at leads V1 and V6 — and especially at the QRS in the limb leads — it becomes apparent that the QRS is probably of normal duration!
• But — IF the QRS is not prolonged — this means that we are looking at perhaps the greatest amount of ST segment elevation in lead V3 that I (and perhaps you) have ever seen! (that attains more than 40 mm in lead V4).
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• As discussed in ECG Blog #364 and ECG Blog #265 — We are looking at "Shark Fin" ST elevation!

Shark Fin Morphology

It's important to be aware of the pattern of "Shark Fin" ST segment elevation — in which the QRS complex looks wide, because it blends in with ST segments that show extreme ST elevation in multiple leads. As a result — the boundary between the end of the QRS complex and the beginning of the ST segment becomes indistinguishable in those leads showing marked ST elevation or depression.

• "Shark Fin" ST segment elevation is most often a sign of severe transmural ischemia that results from acute coronary occlusion. Today's case is different in that profound myocardial injury (from electrocution) rather than acute coronary occlusion is the cause of this ECG pattern.
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• PEARL: The KEY for confirming that "Shark Fin" morphology is the cause of the striking ECG picture in Figure-1 — is to find 1 or 2 leads in which you can clearly define the limits (end point) of the QRS complex. The most helpful leads for clarifying the end point of the QRS in today's case are lead V1 and lead V6. 
• Note in Figure-2 — that I've drawn in a RED line parallel to the heavy ECG grid line in the simultaneously-recorded chest leads. By choosing the end point of the QRS that is clearly visible in leads V1 and V6 — I'm able to define the end point of the QRS complex in the other chest leads ( = leads V2-thru-V5), knowing that the ST segment begins just to the right of this vertical RED line.

Figure-2: I've drawn a vertical timeline downward from the end point of the QRS complex in lead V1 — so as to define the beginning of the ST segment in the other chest leads. Note that this vertical RED line passes through the clearly defined end point of the QRS complex in lead V6 (See text).

BOTTOM Line in Today's CASE:

Since the vertical RED line in Figure-2 marks the end of the QRS complex in each of the 6 chest leads — everything to the right of this RED line represents the markedly elevated "shark fin" shape of ST elevation.

• Alternatively — the shape of the ST elevation in lead V2 might also be consistent with a component of Brugada Phenocopy (See ECG Blog #238). That said, even if true — ST elevation in the remaining chest leads is still virtually certain to represent "shark fin" ST elevation from severe myocardial injury.

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Acknowledgment: My appreciation to Hamdallah Naser (from AL-Najaf, Iraq) for the case and this tracing.

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ADDENDUM (12/30/2023):

• The Audio Pearl below reviews the concept of "shark fin" ST elevation. 

—  — 

ECG Media PEARL #73 (5:40 minutes Audio) — Reviews the concept of "Shark Fin" ST elevation and depression as a sign of extensive acute infarction.

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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 #265 and ECG Blog #364 — Review cases of Shark-Fin ST Elevation.

ECG Blog #409 — Every-Other-Beat ...

 

The ECG in Figure-1 —  was obtained from a patient with palpitations. The patient was hemodynamically stable in association with this rhythm.

QUESTIONS:

• What is the rhythm in Figure-1? 
•   — How certain are you of your answer? 
• 
  
•      —  Why is QRS morphology changing? 

Figure-1: The initial ECG in today's case.

My Interpretation of the ECG in Figure-1:

Since the patient is hemodynamically stable — there is time for systematic assessment of the rhythm. By the Ps, Qs, 3R Approach (See ECG Blog #185):

• The rhythm is fast and QRS complexes are Regular. Since the R-R interval is just under 2 large boxes in duration — I estimate the ventricular Rate to be just over 150/minute.
• 
  
• QRS morphology varies every-other-beat! This is perhaps best seen in lead V1 (but also well seen in leads V3,V4,V6). The QRS is narrow in odd-numbered beats (but the QRS is wide in even-numbered beats).
• 
  
• Sinus P waves appear to be absent — because we do not see a clearly defined upright P wave in lead II. Instead — a negative deflection appears to precede each QRS complex in lead II (and we can see this negative deflection in front of each of the 26 beats in the long lead II rhythm strip).
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• PEARL #1: Although we know these negative deflections in front of the QRS are not sinus P waves (because, as noted above — these deflections are not upright in lead II) — there does appear to be a fixed interval (distance) between these negative deflections and the QRS complex that follows. This suggests these negative deflections represent some other form of atrial activity (that by the 5th parameter in the Ps,Qs,3R Approach) — is Related to neighboring QRS complexes.

Putting It All Together:

By the Ps, Qs, 3R Approach — We have determined that the rhythm in Figure-1 manifests regular QRS complexes at a rate just over 150/minute — with some form of atrial activity that is related to neighboring QRS complexes.

• But WHY is QRS morphology changing every-other-beat? (ie, being narrow for one beat — and then becoming wide for the next beat)?
•   —  Is the rhythm in Figure-1 supraventricular?
•      — What kind of atrial activity is likely to be present? 

PEARL #2: The obvious initial consideration whenever we see wide beats — is that the etiology of such beats may be ventricular. That said (as per PEARL #1) — the fact that each of the 26 beats in the long lead II rhythm strip in Figure-1 are preceded by a negative deflection with a fixed interval between this negative deflection and the QRS complex that follows (BLUE arrows in the long lead II in Figure-2) — is against these wide beats being ventricular in etiology.

• IF the wide beats were ventricular — we would not expect the interval from the negative deflection preceding each QRS to be equal.
• Instead — the fact that the interval from the negative deflection preceding each of the 26 beats in the long lead II rhythm strip remains constant — suggests that each of these 26 beats are being conducted by whatever form of atrial activity these negative deflections represent.

PEARL #3: QRS morphology of the wide beats strongly supports our presumption that all 26 beats in today's initial ECG are supraventricular! (Figure-2).

• QRS morphology of beats #14,16,18 in lead V1 is consistent with RBBB (Right Bundle Branch Block) conduction — because there is an rsR’ morphology, with S wave descending below the baseline and a taller R’ (right-“rabbit ear” deflection).
• QRS morphology of beats #2,4,6 in lead I — and, beats #8,10,12 in lead aVL support RBBB conduction — because these lateral leads each manifest a slender, upright R wave with wide terminal S wave (RED arrows in these leads).
• 
  
• Finally (as shown in Figure-2) — Note that the wide beats in the inferior leads (especially in lead II) manifest a more marked leftward axis, consistent with LAHB (Left Anterior HemiBlock) aberration — which is yet another suggestion that all wide beats are supraventricular!

Figure-2: I've labeled the initial ECG in today's case.

PEARL #4: As emphasized in ECG Blog #204, in which I review derivation of the bundle branch blocks — RBBB is a terminal conduction delay. By this I mean that the initial vectors of ventricular depolarization occur normally when there is RBBB — and only the last part of ventricular depolarization is altered with this conduction defect.

• As a result — the IVS (InterVentricular Septum) and the LV (Left Ventricle) depolarize normally with RBBB conduction — and it is only after the LV has depolarized that the RV (Right Ventricle) now depolarizes via slow conduction through ventricular myocardium (because of the "block" in the right bundle branch). This results in terminal depolarization moving toward the “blocked” RV — which writes a wide, terminal S wave in left-sided leads (with this S wave being wide with complete RBBB — because conduction through myocardium is slow). 
•  
• KEY Point: Awareness that RBBB is a terminal conduction delay, with the initial vectors of ventricular depolarization being normal — may provide yet another clue that widened QRS complexes are aberrantly-conducted supraventricular beats. This concept is perhaps best illustrated for the wide beats in lead V1 of Figure-2 — in which the shape and slope of the tiny initial r-wave, followed by S wave descent in lead V1 looks identical in shape and slope to the beginning deflections of the narrow beats in this lead. 

Advanced PEARL #5 ( = Beyond-the-Core): Did YOU notice that there appears to be a technical “misadventure” in today's initial ECG — in that the QRS complex does not look as one should expect with RBBB conduction for the wide beats in lead V6? (ie, for beats #20,22,24,26 in lead V6 of Figure-2).

• To Emphasize — that this technical mishap is an extremely subtle finding that I did not notice when I first looked at the initial ECG in today’s case. But since RBBB conduction is the result of a terminal delay in ventricular repolarization — there should be a wide, terminal S wave for wide beats #20,22,24,26 in lateral chest lead V6. Instead, there is a fragmented, all-positive QRS complex in lead V6 without any terminal S wave.
• 
  
• My Theory: I suspect that the V6 lead connection may have inadvertently been reversed with the lead connection for either V4 or V5.

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CONTINUED: Putting It All Together:

Now that we’ve established that all 26 beats in today's initial ECG are supraventricular — We can deduce the following:

• There is RBBB conduction every-other-beat in Figure-2. This is a form of rate-related BBB — in which the rapid ventricular rate may not allow sufficient time between each beat for the right bundle branch to recover.
• Usually, rate-related BBB produces QRS widening with every beat — but on occasion, BBB conduction may only occur every-other or every-third beat.
• 
  
• This means that the rhythm in today's initial tracing — is a regular SVT (SupraVentricular Tachycardia) rhythm at ~150/minute, but without clear sign of sinus P waves. PEARL #6 below reviews the differential diagnosis:

PEARL #6: As discussed in ECG Blog #287 — Recognition that the rhythm in today's initial tracing is a regular SVT without clear sign of sinus P waves (ie, without a definite upright P wave in lead II) — should prompt consideration of the following differential diagnosis LIST:

• i) Sinus Tachycardia (IF there is a possibility that sinus P waves might be hiding within the preceding ST-T wave); 
• ii) A Reentry SVT (either AVNRT if the reentry circuit is contained within the AV node — or AVRT if an AP [Accessory Pathway] located outside the AV node is involved); 
• iii) Atrial Tachycardia (ATach);
• iv) Atrial Flutter (AFlutter) with 2:1 AV conduction. 

PEARL #7: By far (!) — the most commonly overlooked entity in the above differential diagnosis LIST is AFlutter (Atrial Flutter) — especially when the ventricular rate is close to ~150/minute (as it is in today's case) — and — when there appear to be negative deflections (rather than upright P waves) in lead II.

• The reason the ventricular rate in untreated AFlutter tends to be close to 150/minute — is that the atrial rate of flutter in patients not on antiarrhythmic medication (that might reduce the flutter rate in the atria) — tends to be very close to 300/minute in adults (ie, usual range ~250-350/minute). 
• Since the most common ventricular response to untreated AFlutter is with 2:1 AV conduction — this results in a ventricular rate HALF as fast as the flutter rate in the atria — and 300 ÷ 2 ~150/minute (usual range ~130-170/minute).
• 
  
• KEY Point: Knowing that the most commonly overlooked arrhythmia is AFlutter — suggests that the BEST way to avoid missing the diagnosis of AFlutter is simply to THINK of AFlutter whenever you have a regular SVT at a rate close to 150/minute (in which you do not clearly see upright sinus P waves in lead II).

PEARL #8: Using calipers facilitates finding the diagnostic "sawtooth" pattern of AFlutter. When looking for AFlutter — I simply set my calipers at precisely HALF the R-R interval — and then look for leads in which I can "walk out" 2:1 conduction.

• I have done this in Figure-3 — in which slanted RED lines in the long lead II rhythm strip highlight negative dips in the baseline that occur at precisely twice the ventricular rate. This corresponds to an atrial rate of ~300/minute (P-P interval ~1 large box in duration).
• The "sawtooth" pattern of the baseline with AFlutter is best appreciated by stepping back a little bit from the rhythm strip. The pattern is best seen in the inferior leads ( = leads II,III,aVF). The other leads that most often manifest readily identifiable 2:1 atrial activity — are leads aVR, V1 and/or V2 — so I favor first checking out these 6 leads whenever looking for AFlutter.
• 
  
• Physiologically — the most commonly observed pattern of AFlutter, known as "Typical" AFlutter — produces 2:1 negative deflections seen in the inferior leads (as seen in Figure-3) — as a result of CCW (CounterClockWise) rotation of a fixed reentrant circuit around the tricuspid valve annulus and through the cavo-tricuspid isthmus. 
• "Atypical" AFlutter patterns may occasionally be seen, in which the rotation direction of the reentrant pathway around the tricuspid valve annulus changes to CW (ClockWise) — in which case smaller positive deflections may be seen.
• Clinically: Initial treatment of AFlutter is the same, regardless of whether the rotation direction is CW or CCW — so this distinction is not important to the emergency provider (Cosio — Arrhythmia & EP Review 6(2):55-62, 2017). The point to remember is that IF you are able to identify regular 2:1 atrial activity at an atrial rate close to 300/minute (with a P-P interval ~1 large box in duration) — then the rhythm is almost certain to be AFlutter.

The CASE Continues:

The patient was treated with IV Amiodarone — which (as shown in Figure-3) successfully converted the AFlutter into normal sinus rhythm.

• Although significant baseline artifact is seen in ECG #2 — regular upright sinus P waves can be seen in the long lead II rhythm strip.
• RBBB is no longer seen after conversion to sinus rhythm — which supports our suspicion that the intermittent RBBB conduction seen every-other-beat during the tachycardia (in Figure-1) was rate-related.
• Note that QRS morphology after conversion to sinus rhythm is very similar to QRS morphology of odd-numbered beats during the tachycardia.
• Note also that modest T wave inversion persists after conversion to sinus rhythm (seen in leads III; and in V1-thru-V4). This most likely reflects a transient and benign "Memory" effect (ie, Not uncommonly — non-ischemic ST-T wave abnormalities may be seen for hours or even days following a sustained tachycardia).

Figure-3: Slanted RED lines in the long lead II rhythm strip of ECG #1 — highlight the "sawtooth" pattern of AFlutter.

And a Final Tracing ...

As a final advanced concept — I add one more tracing in Figure-4.

• ECG #3 was obtained during treatment of this patient's AFlutter — at approximately the same time that ECG #1 was obtained.
• 
  
• As I noted earlier in advanced PEARL #5 — lack of a wide terminal S wave for the wide beats in lead V6 of ECG #1 did not make physiologic sense, given that beats #20,22,24,26 were conducted with RBBB aberration (within the RED rectangle in Figure-4). I suspected some type of lead connection "technical misadventure".
• 
  
• I believe ECG #3, which was obtained during the treatment process — supports my theory. Note that rather than every-other-beat RBBB conduction — rate-realted RBBB aberrancy is seen every beat in ECG #3 — and, a terminal S wave (albeit a notched deflection) is indeed seen in lead V6. As expected — wide terminal S waves are seen in the other lateral leads in ECG #3 ( = in leads I and aVL).

Figure-4: Confirmation of the "technical misadventure" I described earlier in advanced PEARL #5 (See text).

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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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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.
• 
  
• See ECG Blog #240 — for Review on the ECG assessment of the patient with a regular SVT rhythm (including distinction between the various types of SVT reentry).
• 
  
• ECG Blog #287 — for a regular SVT that was AFlutter.
• See ECG Blog #250 — for a regular SVT with ST depression.
• 
  
• ECG Blog #229 — reviews distinction between AFlutter vs ATach (and WHY AFlutter is so commonly overlooked).
• The November 12, 2019 post in Dr. Smith's ECG Blog — in which I review my approach to a Regular SVT rhythm.
• 
  
• ECG Blog #210 — reviews the Every-Other-Beat Method for estimation of heart rate when the rhythm is very fast.
• 
  
• ECG Blog #220 — reviews my LIST #1: Causes of a regular WCT (and how to assess hemodynamic stability).
• 
  
• ECG Blog #242 — Reviews rate-related BBB.
• ECG Blog #32 — More on rate-related BBB.
• 
  
• The August 17, 2020 post by me in Dr. Smith's ECG Blog — in which I review the phenomenon of Bradycardia-dependent BBB (sometimes called "Phase 4" or "paradoxical" block).
• 
  
• ECG Blog #211 — Reviews WHY some early beats and some SVT rhythms are conducted with Aberration (and why aberrant beats usually look like some form of conduction block).
• 
  
• ECG Blog #203 — reviews ECG recognition of the Hemiblocks.
• ECG Blog #204 and ECG Blog #282 — reviews ECG recognition of the Bundle Branch Blocks.

 

ADDENDUM (12/23/2023):

I've presented this material before — but it bears repeating for reference. These concepts should be automatic for assessment of the patient who presents with a regular SVT rhythm.

—  —

ECG Media PEARL #64 (10:50 minutes Audio) — Reviews my LIST #2: Common Causes of a Regular SVT Rhythm.

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—  —

ECG Media PEARL #45 (10:00 minutes Audio) — Why is Atrial FIutter so commonly overlooked? Reviews PEARLS regarding the ECG diagnosis of AFlutter — and — What's "New"? in the field, regarding distinction between AFlutter vs Atrial Tachycardia (5/29/2021).

—  —

ECG Media PEARL #57 (8:00 minutes Audio) — What is rate-related Bundle Branch Block? How does this differ from "aberrant" conduction.