Saturday, March 16, 2024

ECG Blog #421 — Has there been a Recent MI?


What if you were asked to interpret the ECG in Figure-1?
  • How would YOU interpret the rhythm?
  • Even without the benefit of any history — Has there been a recent MI?

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


MY Approach to Today’s Tracing:
As always — I favor beginning assessment with a quick look at the long lead rhythm strips at the bottom of the tracing. By the Ps, Qs, 3R Approach (which I review in ECG Blog #185):
  • Lots of P waves are present — being well seen in the long lead II rhythm strip.
  • The QRS complex is narrow in all 12 leads.
  • The rhythm is not Regular. The ventricular Rate varies.
  • The 5th parameter of the Ps,Qs,3R Approach — is the 3rd R, which recalls Related” — or determining if P waves are (or are not) related to neighboring QRS complexes. This last parameter can best be assessed by labeling P waves in the long lead II rhythm strip.


QUESTIONS:
Take a LOOK at Figure-2 — in which RED arrows highlight those P waves that are definitely seen on this tracing.
  • How would YOU describe the regularity (or lack thereof) of P waves in today's rhythm?
  • Are all of the P waves originating from the SA node?

Figure-2: I have labeled the P waves that we definitely see with RED arrows. Is the underlying atrial rhythm regular?


ANSWERS:
We see in Figure-2 — that each of the RED arrow P waves manifest a similar and normal P wave morphology — and, that each of these P waves are upright in the long lead II rhythm strip. We can therefore presume these are normal sinus P waves.
  • With the exception of 2 places in the rhythm strip where we do not see P waves at the point where we might logically expect them — Don’t the RED arrow P waves that we have labeled in Figure-2 otherwise look fairly regular?

  • NOTE: If measured with calipers — We know that the RED arrow P waves in Figure-2 are not precisely regular. But what we are trying to determine, is if there is an underlying sinus mechanism. This includes sinus arrhythmia — in which there is often slight variation in the P-P interval. This slight variation in sinus P wave regularity tends to be greater when a 2nd- or 3rd-degree AV block is present (called ventriculophasic sinus arrhythmia — as shown in ECG Blog #344).

PEARL #1: When many (most) P waves in a given tracing look regular (or at least fairly regular) — but one or two places exist in the rhythm in which P waves are not seen at the point where you expect them — it may be that additional P waves are “hiding”. As a result — I look especially carefully at QRS complexes and ST-T waves that may be hiding part (or all) of the missing P waves.
  • Is there any indication in Figure-2 — that there may be more P waves than the ones we have labeled with RED arrows?

  •     HINT: My answer is shown in Figure-3.


Figure-3: How can we know if additional sinus P waves are “hiding” under the PINK arrows?

PEARL #2: It is much easier to recognize an ECG finding — IF you know that you should be looking for it!
  • Because we know from PEARL #1 that it would be logical for the atrial rhythm to be more regular than suggested by the RED arrows in Figure-2 — we need to pay special attention to the T waves under the PINK arrows in Figure-3 (since this is where we would expect P waves to be “hiding” if the underlying atrial rhythm was sinus arrhythmia).

QUESTION:
  • Is there a difference in ST-T wave morphology for those T waves under the PINK arrows in Figure-3 — compared to all of the other T waves in this long lead II rhythm strip? (ie, Compared to the T waves of beats #1,3,4,6,7,8?).





ANSWER:
The T waves under the PINK arrows in Figure-3 are larger and clearly “fatter” than all other T waves on this tracing.
  • PEARL #3: Perhaps the greatest challenge in interpreting complex rhythms is distinguishing between “real differences” in morphology — vs artifact and/or the normal variation that is commonly seen in P wave, QRS and ST-T wave morphology.

  • The above said — Reasons I know P waves are “hiding” under the PINK arrows in Figure-3 are that: i) It is so much more logical for sinus P waves to be at least fairly regular throughout the tracing — rather than to see the SA node suddenly stop putting out impulses only in 1 or 2 places in today’s tracing; and, ii) There can be little doubt that the T waves under the 2 PINK arrows in Figure-3 are larger and “fatter” than all other T waves on this tracing.


Putting It All Together:
I find it much EASIER to assess a complex rhythm once all sinus P waves have been labeled. For clarity — I have done this in Figure-4.
  • RED arrows highlight all sinus P waves. The slight variation in the P-P interval is consistent with an underlying sinus arrhythmia.
  • Note that there are more P waves (RED arrows) — than QRS complexes in Figure-4. This means that at least some of the on-time sinus P waves are not being conducted to the ventricles — which defines today's rhythm as some form of AV block.

  • PEARL #4: Today's rhythm is not likely to be complete (3rd-degree) AV block. This is because most of the time when there is complete AV block — the escape rhythm will be regular (or at least fairly regular)
  • In my experience — the BEST clue that a QRS complex is being conducted, is when we see a beat occur earlier-than-expected. This is why in Figure-4 — we can immediately suspect that beats #2,5,8 are being conducted to the ventricles. 
  • Since today's rhythm represents some form of AV block — but by PEARL #4, is unlikely to be complete AV block — this rhythm must represent some form of 2nd-degree AV block. Since the QRS complex is narrow — and since we know that the Mobitz I (AV Wenckebach) form of 2nd-degree AV block is so much more common than Mobitz II — we can immediately suspect that today's challenging rhythm represents some form of Mobitz I (For review of how to distinguish the 2nd-degree AV blocks — See ECG Blog #344).

Figure-4: RED arrows highlight all sinus P waves.


Important CONCEPTS:
To EMPHASIZE — I’ve intentionally dissected the above observations regarding today’s rhythm in “slow motion”. With experience — it should take no more than seconds to arrive at this point in our assessment.
  • Today's rhythm is challenging! That said, the KEY point is — that precise determination of the specific kind of AV block is not essential for appropriate clinical management
  • All that clinicians need do — is to recognize the following: i) That the underlying atrial rhythm is sinus arrhythmia; ii) That some form of AV block is present (because not all of the sinus P waves are being conducted); iii) But that 3rd-degree AV block is not likely (because the ventricular rhythm is not regular); and, iv) That statistically — Mobitz I 2nd-degree AV block is by far (well over 90% of the time) the most common form of 2nd-degree AV block, especially when the QRS complex is narrow, as it is in today's rhythm.

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PEARL #5 (Beyond-the-Core): As an advanced point — Figure-5 illustrates how using calipers should facilitate rapid confirmation of the KEY points described above.
  • Using calipers allows us to quickly determine — that the R-R intervals between beats #2-3; 3-4; 5-6; and 6-7 are all equal! (ie, 142 msec.). However, the PR intervals before beats #4 and 7 are clearly too short to conduct! This strongly suggests that each of these beats with the same preceding R-R interval ( = beats #3,4,6,7) — is a junctional escape beat.
  • The identical R-R interval of 142 msec. that precedes each of the above junctional escape beats — corresponds to an appropriate junctional escape rate of just over 40/minute (ie, 300 ÷ 7 large boxes).
  • The reason today's rhythm is so challenging to interpret — is that the frequent occurrence of junctional escape beats serves to mask the typical progressive PR interval lengthening that we would otherwise see with Mobitz I 2nd-degree AV block.
  • That said — seeing how much earlier-than-expected beats #2,5 and 8 occur provides additional support to our supposition that these 3 beats are almost certain to be conducted, albeit with differing prolonged PR intervals. This is why todays rhythm is so challenging to interpret!

Figure-5: Using calipers allows us to quickly determine that the R-R intervals between beats #2-3; 3-4; 5-6 and 6-7 are equal!



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What about Today's 12-Lead ECG?
Whereas precise determination of today's rhythm is not essential for appropriate clinical management — quickly recognizing that some form of Mobitz I 2nd-degree AV block appears to be present tremendously facilitates interpretation of today's 12-lead tracing (that I have reproduced in Figure-6).
  • Overall — there is ST segment flattening with slight ST depression in multiple leads in today's 12-lead tracing.

  • PEARL #6: The most common clinical setting for seeing the Mobitz I form of 2nd-degree AV block is acute or recent inferior and/or posterior infarction. As a result, whenever I see some form of Mobitz I — I immediately search for any possible indication of recent inferior and/or posterior OMI.

  • PEARL #7: Normally, there is a slight amount of gently upsloping ST elevation in leads V2 and V3. When instead of this gently upsloping ST elevation, there is "shelf-like" ST segment flattening — I immediately suspect recent posterior OMI, especially if the patient presents with new or recent chest pain (See ECG Blog #367 — for review of this concept).
  • Therefore — My "eye" was immediately drawn to the abnormal ST segment flattening in lead V2 (within the RED rectangle). Seeing a similar abnormal ST segment shape in neighboring leads V3 and V4 (within the light BLUE rectangles) — confirmed this as a "real" finding.
  • NOTE: Although we are not provided with any history in today's case — knowing that today's rhythm appears to represent some form of Mobitz I strongly supports my supposition that the ST segment flattening with slight depression in leads V2,V3,V4 of Figure-6 should suggest recent posterior OMI until proven otherwise!
  • The finding of additional ST segment flattening in multiple other leads may represent multi-vessel disease.

Figure-6: I've highlighted the KEY leads in today's 12-lead tracing with colored rectangles (See text).

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PEARL #8 (Beyond-the-Core): There will sometimes be slight variation in QRS morphology between sinus-conducted beats and junctional escape beats. At times, this slight difference in QRS morphology provides an important clue as to whether a given beat is conducted — or — represents a junctional escape beat (See ECG Blog #63).
I've emphasized that although the precise mechanism of today's rhythm is complex — all that is needed for appropriate clinical management, is appreciation that some form of Mobitz I 2nd-degree AV block is present.
at some form of Mobitz I 2nd-degree AV block is present.
  • Did YOU notice the slight difference in QRS morphology between the 2 beats in simultaneously-recorded leads V1,V2 and V3 in Figure-6? This difference in QRS shape further supports my earlier conclusion that beat #5 (that occurs earlier-than-expected) is sinus-conducted with a long PR interval — whereas beat #6 (which is preceded by the 142 msec. R-R interval shown in Figure-5) is a junctional escape beat.
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The LADDERGRAM: 
I've emphasized that although the precise mechanism of today's rhythm is complex — all that is needed for appropriate clinical management, is appreciation that some form of Mobitz I 2nd-degree AV block is present.
  • That said — I fully acknowledge that I needed a laddergram to "solve" (ie, explain) each of the ECG findings in today's tracing. I've labeled my proposed laddergram in Figure-7.

Figure-7: I've labeled my proposed laddergram in today's case.


Laddergram Explanation:
  • Beats #2, 5 and 8 are each sinus-conducted, albeit with significantly prolonged PR intervals (since each of these beats occur much earlier-than-expected).
  • Beats #3,4,6 and 7 are junctional escape beats. We arrived at this conclusion by the finding of PR intervals before beats #4 and 7 that are definitely too short to conduct — with the PR intervals before beats #3 and 6 being significantly shorter than each of the sinus-conducted beats — and, with each of these 4 beats that we presume to be junctional escape beats, being preceded by the identical R-R interval of 142 milliseconds. 
  • Although we do not see far enough in front of beat #1 to know what its preceding R-R interval is — the fact that the PR interval before beat #1 is short (and of similar duration as the PR interval preceding junctional beats #3 and 6) — suggests that beat #1 is also a junctional escape beat.
  • YELLOW arrows represent P waves that are not conducted because of the 2nd-degree AV block.
  • We have no idea whether the BLUE arrow P waves might have conducted (perhaps with an increasing PR interval) — IF the junctional escape beats ( = beats #3,4; 6,7) would not have occurred.

  • BOTTOM Line: Today's case illustrates how challenging it can be to recognize certain forms of 2nd-degree AV block of the Mobitz I type (ie, in which there are frequent junctional escape beats). That said — the overall ventricular rate of today's rhythm is between 40-50/minute, which may be enough to maintain hemodynamic stability. 
  • NOTE: We can not say there is "high-grade" AV block in today's tracing — because we never see 2 consecutive on-time sinus P waves that fail to conduct despite having adquate opportunity to do so (ie, We never see 2 consecutive YELLOW arrow P waves).
  • Clinically: The "good news" regarding today's case — is that most of the time with Mobitz I, acute reperfusion (with PCI or thrombolytics) will result in improvement of the associated AV conduction disturbance.

I conclude today's case with the laddergram shown in Figure-8 — in which I've removed the coloration from Figure-7. 


Figure-8: Today's laddergram without coloration.



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Acknowledgment: My appreciation to Danilo Franco (from Italy) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case:

  • ECG Blog #185 — My Ps,Qs,3R System for Rhythm interpretation.
  • ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 100 laddergram cases — many with step-by-step sequential illustration).
  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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  • CLICK HERE for my 6 new ECG Videos (on Rhythm interpretation — 12-lead interpretation with Case Studies for ECG diagnosis of acute OMI).
  • CLICK HERE for my 2 new ECG Podcasts (on ECG & Rhythm interpretation Errors — and — Errors in assessing for acute OMI).
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  • ECG Blog #192 — The Causes of AV Dissociation
  • ECG Blog #191 — Reviews the difference between AV Dissociation vs Complete AV Block.

  • ECG Blog #389 — ECG Blog #373 — for review of some cases that illustrate "AV block problem-solving".
  • ECG Blog #344 — thoroughly reviews the Types of 2nd-degree AV block (Mobitz I vs Mobitz II vs 2:1 AV Block).
  • ECG Blog #267 — Reviews with step-by-step laddergrams, the derivation of a case of Mobitz I with more than a single possible explanation.
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  • ECG Blog #193 — Reviews the Mirror Test for recognition of acute Posterior MI. This blog post also reviews the basics for predicting the "Culprit" Artery — and use of the term, "OMI" ( Occlusion-based MI) as an improvement from the outdated STEMI paradigm.

  • ECG Blog #367A must to review !!! — as this case reinforces the KEY concepts for recognizing subtle acute posterior OMI!

  • ECG Blog #294 — How to tell IF the "culprit" artery has reperfused.
  • ECG Blog #260 — Reviews when a T wave is hyperacute — and the concept of "dynamicST-T wave changes.
  • ECG Blog #230 — How to compare serial ECGs.
  • ECG Blog #337 — an OMI misdiagnosed as an NSTEMI ...
  • ECG Blog #285 — for another example of acute Posterior MI (with positive Mirror Test).
  • ECG Blog #246 — for another example of acute Posterior MI (with positive Mirror Test).
  • ECG Blog #80 — reviews prediction of the "culprit" artery (with another case to illustrate the Mirror Test for diagnosis of acute Posterior MI).
  • ECG Blog #184 — illustrates the "magical" mirror-image opposite relationship with acute ischemia between lead III and lead aVL (featured in Audio Pearl #2 in this blog post).
  • ECG Blog #167 — another case of the "magical" mirror-image opposite relationship between lead III and lead aVL that confirmed acute OMI.
  • ECG Blog #271 — Reviews determination of the ST segment baseline (with discussion of the entity of diffuse Subendocardial Ischemia).
  • ECG Blog #258 — How to "Date" an Infarction based on the initial ECG.
  • The importance of the new OMI (vs the old STEMI) Paradigm — See My Comment in the July 31, 2020 post in Dr. Smith's ECG Blog.



 




Monday, March 11, 2024

ECG Blog #420 — A "Fast" Complete Heart Block?


I was asked to interpret the 2-lead rhythm strip shown in Figure-1 — without the benefit of any history. What are YOUR thoughts?
  • Is there AV block? If so — Is it complete AV block?

Figure-1: You are asked to interpret this 2-lead rhythm strip without the benefit of any history.

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NOTE: Today's rhythm is challenging — especially if you have not seen this type of rhythm before. That said, attention to the sequential PEARLS I present in my discussion below can greatly facilitate recognizing this rhythm within seconds the next time you encounter it!

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MY Thoughts on Today’s Rhythm: 

Assuming that today’s patient is not unstable hemodynamically (and does not require immediate synchronized cardioversion) — We can completely turn our attention to assessment of the rhythm. By the Ps, Qs & 3R Approach (which I review on ECG Blog #185):

  • The Rate of the rhythm in Figure-1 is somewhat fast — averaging ~100/minute (ie, with an R-R interval close to 3 large boxes in duration for most of the tracing).
  • The rhythm is clearly not Regular. The R-R interval is not the same throughout the tracing.
  • It appears that there are at least some P waves, albeit P waves are not seen in all parts of this tracing.
  • Although the QRS complex looks wider than it normally is — the QRS does not measure more than half a large box (ie, not more than 0.10 second) in either of the 2 monitoring leads shown in Figure-1

PEARL #1: Remember the saying, “12 leads are better than one”. The importance of determining whether the QRS complex of a tachycardia is wide or narrow — is that IF the QRS is narrow in all 12 leads, then the rhythm is supraventricular (and we have therefore ruled out the possibility of VT = Ventricular Tachycardia). The more monitoring leads we have available — the more accurate will be our determination about whether the QRS is wide or narrow.

PEARL #2: We only see 2 of the 12 leads of an ECG in Figure-1. This is important to appreciate — since sometimes a part of the QRS complex may lie on the baseline in one or more leads. When this happens — the QRS may “look” to be narrow in the lead(s) you are monitoring, whereas in reality the QRS is actually wide.
  • It is for this reason that I always favor doing a 12-lead ECG as soon as this is feasible for any arrhythmia of uncertain etiology. Clinical management of the patient clearly differs if you can rule out the possibility of a ventricular rhythm. Unfortunately in today’s case — No 12-lead ECG was available.

Assessing the 5th Parameter:
Thus far — We’ve determined the following: 
  • That the Rate of QRS complexes in today’s rhythm is fairly fast — but not quite Regular.
  • That the rhythm is probably supraventricular (because the QRS is not more than half a large box in either of the 2 monitoring leads we are given)
  • That at least some P waves are present.

  • The remaining parameter is the 3rd R — which  is determining IF any of the P waves in today’s rhythm are Related to neighboring QRS complexes. It turns out that this last parameter is KEY to solving today’s arrhythmia.

PEARL #3: The easiest way to assess for this 5th parameter — is to see if there are any PR intervals that repeat. And the BEST way to find any PR intervals that may be repeating — is to seek out any relative pauses in the rhythm — and to check out the PR interval before each beat that ends each pause.
  • NOTE: The “pause” in the rhythm may be brief — and not much longer than the other R-R intervals. Figure-2 illustrates this principle — in which the R-R intervals between beats #4-5; 8-9; and 12-13 are slightly longer than other R-R intervals in today’s tracing.
  • RED arrows highlight the P waves that precede each of the beats that end each of these short pauses. Isn’t the PR interval before beats #5, 9 and 13 equal?

PEARL #4: An important concept in “arrhythmia problem solving” — is based on the saying, “Birds of a Feather flock Together”. By this I mean that IF you see a certain ECG finding a number of times in a given tracing — then if you see a similar phenomenon that is not quite as precise — the chances are that you are seeing the same ECG finding!
  • Take beat #1 in Figure-2 — which occurs at the very beginning of this tracing (which means that we do not know what came before beat #1). As a result, we can not know if beat #1 was preceded by a slight pause in the same way that beats #5, 9 and 13 are all preceded by a slight pause of the same duration. 
  • BUT — Given the repetitive pattern of there being a slight pause after every 4th beat (ie, “Birds of a feather …” ) — and given that the PR interval preceding beat #1 ( = first RED arrow in Figure-2) is equal to the PR interval preceding beats #5,9,13 ( = the other RED arrows in Figure-2) — this is not by chance, and whatever relationship might be occurring between atrial activity and neighboring QRS complexes for beats #5-thru-16 — is almost certain to be the same phenomenon occurring for beats #1-thru-5! 

Figure-2: Applying the concept of “Looking for a slight pause in the rhythm” I’ve labeled the 4 P waves that we clearly see with RED arrows. Note that the PR interval for these 4 P waves is the same!

PEARL #5: It’s time to determine IF there is an underlying regular atrial rhythm — which could be the case IF some P waves are hiding within certain ST-T waves. Figure-3 illustrates How to Look for “Hidden” P waves:
  • Search the tracing looking for 2 P waves in a row that you can clearly see. RED arrows in Figure-3 illustrate 2 such P waves that are clearly seen in today’s rhythm.
  • Using the P-P interval set by these 2 RED arrows locates the next spot to search for a “P wave in hiding”. Isn’t the T wave under the WHITE arrow in Figure-3 “fatter” than most other T waves in this tracing?
  • The reason the T wave under the WHITE arrow is “fatter” — is that this is where the next consecutive P wave occurs.
  • NOTE: Using calipers greatly facilitates the process. Using calipers instantly makes you “smarter” — and allows me to “solve” an arrhythmia such as today’s tracing within seconds that providers who do not use calipers are simply not able to solve.

Figure-3: How to find “hidden” P waves (See text).


Now that we have identified the P-P interval for 3 consecutive P waves (as shown by the 3 arrows in Figure-3) — it should take no more than seconds to “walk out” where the regularly-occurring P waves are located throughout the rest of today’s tracing (Figure-4):

Figure-4: RED arrows highlight where regular atrial activity is located throughout the rhythm in today’s case.

PEARL #6: Try to determine if the underlying atrial rhythm is a “sinus” rhythm — or an ectopic atrial rhythm. This determination is not always easy to make.
  • A sinus rhythm — is defined by the presence of an upright P wave in lead II. This is because when limb lead electrodes are correctly placed — the direction of atrial depolarization as impulses arising from the SA node travel toward the AV node will be oriented close to +60 degrees in the frontal plane, which corresponds to the 60 degree electrical perspective of standard lead II in Einthoven’s Triangle.
  • Therefore — IF P waves are not upright in lead II, then the rhythm is not sinus!
  • The problem is that when P waves are upright in standard lead II (as they are in Figure-4) — then it may be difficult to distinguish between a sinus rhythm vs an ectopic atrial rhythm!

PEARL #7: Determining the atrial rate may help. In Figure-4 — the atrial rate is ~125/minute (which can be quickly estimated by the Every-Other-Beat Method reviewed in ECG Blog #210)

  • By the Every-Other-Beat Method Given that the P-P interval of every-other-P-wave in Figure-4 is just under 5 large boxes in duration — this means that half the atrial rate is slightly faster than 300 ÷ 5 (ie, slight faster than 60/minute) — which means the actual atrial rate is ~125/minute.

  • The PEARL: The finding of a fast and regular atrial rate in association with an irregular supraventricular (narrow-QRS) rhythm — is much more likely to represent ATach (an ectopic Atrial Tachycardia) — than sinus tachycardia. The reason for this finding, is that Wenckebach conduction is commonly seen with ectopic ATach.


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Proving My Theory . . .
Using calipers — I was able to prove within seconds that my suspicion of ATach with Wenckebach conduction was the answer to today's rhythm.
  • For clarity in Figure-5 — I've reproduced Figure-2, in which we see group beating (ie, beats #1-thru-4; #5-thru-8; #9-thru-12; #13-thru-16— with each group separated by a slight pause of similar duration (ie, between beats #4-5; #8-9; #12-13) — with each pause ending with a conducted P wave (ie, the RED arrow P waves, each with an identical PR interval before beats #1,5,9,13). The repetitive pattern of these similarities can not be by chance!
  • As soon as my calipers confirmed the underlying regular atrial rhythm (RED arrows in Figure-4) — I knew today's rhythm had to be ATach with Wenckebach conduction.

Figure-5: I've reproduced Figure-2 to highlight the repetitive pattern of "group beating" in today's rhythm (See text).


Knowing (from Figure-4) where each of the underlying regular P waves are located — allowed me to focus on the 2nd P wave in each group — which I've highlighted with PINK arrows in Figure-6. These PINK arrow P waves are each conducting the 2nd QRS complex in each group of beats (ie, PINK arrow P waves are conducting beats #2,6,10 and 14).
  • Note that the PR interval of each PINK arrow P wave is longer than the PR interval before the 1st beat in each group (highlighted by each RED arrow P wave).

Figure-6: I've highlighted the 2nd P wave in each group with a PINK arrow.


Next, in Figure-7 — I focused on the 3rd and 4th P waves in each group (highlighted by light and dark BLUE arrows, respectively).
  • Note progressive lengthening of the PR interval for each of the colored arrows in each of the 4 groups!

Figure-7: I've highlighted the 3rd and 4th P waves in each group with light and dark BLUE arrows, respectively


Finally, in Figure-8 — I highlight with YELLOW arrows, the location of the next on-time P wave.
  • It is these "on-time" YELLOW arrow P waves that represent the dropped (non-conducted) P wave in each of the Wenckebach cycles in today's rhythm.
  • This is as it should be with Wenckebach conduction — in that these non-conducted YELLOW P waves occur at the beginning of the slight pause between each group — after which the following on-time P wave (ie, the next RED arrow P wave) begins a new cycle with a shorter PR interval.

Figure-8: YELLOW arrows highlight the non-conducted P wave in each group — after which the next Wenckebach cycle begins.


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The Laddergram . . .
The above derivation for today's rhythm is rendered easier to see in Figure-9 by use of laddergram illustration.
  • For clarity in Figure-9 — I've kept the coloration of arrows from Figure-8, to facilitate appreciation of progressive lengthening of each PR interval within each of the groups — until the 5th P wave in each group ( = the YELLOW arrow P waves) are non-conducted — followed at the end of each short pause, by resumption of conduction with PR interval shortening for the 1st beat in the next group (highlighted by each RED arrow P wave).

Figure-9: Laddergram illustration of today's rhythm.


Figure-10 is what today's laddergram looks like without coloration.

Figure-10: Final laddergram.


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FINAL Thoughts on Today's Rhythm:
As per my Note at the beginning of today's case — today's rhythm is a challenging one if you have not seen this entity before. But once you are aware of this arrhythmia presentation — it becomes EASY to recognize within seconds of seeing the tracing.
  • Repetitive patterns are unlikely to be due to chance! Cement this concept in your mind by going back to the original tracing (which is why I once again show Figure-1 below, without any P waves labeled).

  • As you now take another LOOK at this initial tracing — Isn't it now easier to appreciate group beating with a repetitive pattern of similar intervals — in which each of the short pauses are terminated by easily-identifiable P waves with the same PR interval before beats #1,5,9 and 13?
  • IF you used calipers to facilitate recognizing these relationships — Wasn't it EASY to establish within seconds these similarities in intervals?

  • BOTTOM Line: Once you recognize that today's rhythm is supraventricular — with group beating — and with fast, regularly-occurring P waves — that show clear conduction of the 1st P wave at the end of each pause — you have essentially established that the rhythm is ATach with Wenckebach conduction.
  • Today's rhythm is not complete AV block — because complete ( = 3rd-degree) AV block is most often associated with a regular escape rhythm — and the ventricular rhythm in Figure-1 is clearly not regular!
  • The "good news" — is that most of the time when ATach is associated with the group beating pattern of 2nd-degree AV Wenckebach — the conduction defect usually resolves once the ATach is controlled.

Figure-1: Take another LOOK at today's rhythm!

 



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Acknowledgment: My appreciation for the case and this tracing that was anonymously sent to me for my opinion.
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Related ECG Blog Posts to Today’s Case:
  • ECG Blog #185 — reviews the Ps, Qs & 3R Approach (Listen to Audio Pearl #3 in this post).
  • 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).
  • ECG Blog #267 — Reviews with step-by-step laddergrams, the derivation of a case of Mobitz I with more than a single possible explanation.

  • ECG Blog #210 — for review of the Every-Other-Beat Method for rapid estimation of heart rate (See Video Pearl #27 in this post).

  • ECG Blog #229 — reviews distinction between AFlutter vs ATach.
  • The November 12, 2019 post in Dr. Smith's ECG Blog — in which I review my approach to a Regular SVT rhythm.