Saturday, November 30, 2024

ECG Blog #458 — Complete Heart Block?


I was sent this tracing — and told that providers thought that the rhythm was 3rd-degree (ie, complete) AV block.
  • Do YOU agree?

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


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NOTE: The tracing in Figure-1 is an 8-lead rhythm strip (and not a complete 12-lead ECG). This offers the advantage of providing 8 leads with simultaneously-recorded viewpoints of the same 7 beats that we see in this tracing. 
  • Note also that the 3rd lead from the top is lead -aVR (and not +aVR) — with this negative perspective of lead aVR providing an electrical viewpoint of +30 degrees (which corresponds to an electrical viewpoint located between leads I and II )
  • The reason we see lead -aVR in today's tracing, is that this ECG is provided by Dr. Magnus Nossen — who is from Norway, where the Cabrera Format is the standard for ECG recordings (Please check out ECG Blog #365 for potential advantages of the Cabrera Format).
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MY Thoughts on the Rhythm in Figure-1:
Regarding the clinical question posed by today's case — I immediately recognized that ECG #1 was unlikely to represent complete AV block — simply because the ventricular response is not regular.
  • PEARL #1: While exceptions exist, most of the time when the rhythm is complete AV block — the escape rhythm will be regular (or at least fairly regular). This truism generally holds regardless of whether the escape rhythm originates from the AV Node — from the His — or from the ventricles.
  • PEARL #2: My favorite follow-up to PEARL #1 — is that the best clue in a tracing with AV block that at least some on-time P waves are being conducted — is if one or more of the otherwise regular QRS complexes occur earlier-than-expected (which strongly suggests that the reason this QRS occurs earlier-than-expected — is that this QRS is being conducted to the ventricles). As a result, rather than "complete" AV block — this tells us that some form of 2nd-degree AV block is almost certain to be present.

The “Quick Answer” to Today’s Rhythm:
Even without calipers, as we look at the rhythm in Figure-1 — it should take no more than seconds to recognize that there are P waves that look to be too far away from neighboring QRS complexes to conduct — BUT — that at least beat #4 occurs a little bit earlier than expected. This suggests that beat #4 is probably conducted (albeit with a long PR interval) — such that this rhythm is unlikely to be complete AV block.
  • To Emphasize: Regardless of whether the rhythm in Figure-1 represents 2nd- or 3rd-degree AV block — the overall ventricular rate is slow (in the 40s/minute) — so that IF this patient is symptomatic and no “fixable” cause of the bradycardia is found — pacing might still be needed. 

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The "Longer" Answer: = What then is going on?
As always — I favor systematic assessment of the cardiac rhythm by the PsQs3R Approach (See ECG Blog #185 for review).

Returning to Figure-1 — I look for the Ps, Qs and 3Rs:
  • P waves are clearly present in today's rhythm. Although small in amplitude — these P waves are fairly well seen in lead II
  • In Figure-2 — I've highlighted with RED arrows those sinus P waves that we definitely see.

PEARL #3:
 One of the KEY features of 2nd- or 3rd- degree AV block — is that the atrial rhythm will usually be regular (or at least almost regular — if there is an underlying sinus arrhythmia).
  • Awareness of this feature helps to exclude potential mimics of AV block, such as non-conducted PACs (in which case the atrial rhythm will clearly be “off” — much more obviously than by the limited irregularity of a ventriculophasic sinus arrhythmia).
  • HINT: Using calipers facilitates (and expedites) the search to determine if an underlying regular atrial rhythm is present.

LOOK again at Figure-2. Considering the RED arrow sinus P waves in this tracing that we know are definitely present:
  • Don’t the small extra deflections under the 2 PINK arrows (occurring just after the QRS complex of beats #5 and #7) correspond to a location where you’d expect to see P waves if there was an underlying regular sinus rhythm?
  • Isn’t the T wave of beat #2 slightly more peaked than all other T waves in the long lead II rhythm strip (under the WHITE arrow)?
  • Therefore — Haven’t we just established that it is almost certain that an underlying regular sinus rhythm is present in Figure-2?

Figure-2: Identifying the partially hidden P waves.


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Continuing with the Ps, Qs3Rs ... ( = Looking at the QRS):
  • PEARL #4: "More leads are better than one!"

Although I generally favor starting with lead II in rhythm analysis — the QRS complex does not look much different from one beat-to-the-next in this lead.
  • Confession: I was in fact initially misled in my interpretation of today's rhythm — beause I forgot to apply PEARL #4 ...
  • Then I looked more closely at lead V5. 

In Figure-3 — I highlight the most helpful CLUE for solving today's complex arrhythmia — which is the changing QRS morphology for the 7 beats in Figure-3:
  • Overall — The QRS complex is clearly wide (at least 3 little boxes, or ≥0.12 second in duration).
  • The most logical reason for the changing QRS morphology that is best seen in lead V5 — is that some beats are conducted (albeit with some form of conduction defect) — while other beats arise from a ventricular "escape" focus.

Figure-3: The KEY to solving today’s arrhythmia — is to appreciate that the changing QRS morphology is most easily seen in lead V5. I’ve added RED arrows in both leads II and V5 to highlight the underlying regular sinus rhythm in both of these leads.

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The Next STEPS …
From this point on — I focus on the long lead V5 rhythm strip that I’ve labeled in Figure-4:
  • RED arrows show the fairly regular underlying sinus rhythm (albeit with some ventriculophasic sinus arrhythmia) — that we worked out above in Figure-2.
  • 3 different QRS shapes are seen in Figure-4i) Beats #1,3,5,7 look similar (with a widened RSr’ complex); — ii) Beats #2 and 4 look similar (each with a fragmented RR’ complex); — and, iii) Beat #6 resembles beats #2 and 4 — but lacks the distinct, wide terminal S wave that the other 2 beats have.
  • The last KEY finding results from application of PEARLS #1 and 2 — for which we need to carefully measure all R-R intervals (as I’ve done in msec. in Figure-4).

QUESTION:
  • Which QRS complexes in Figure-4 are most likely to represent escape beats?

Figure-4: Focusing on the lead V5 rhythm strip — RED arrows highlight the underlying sinus arrhythmia — with R-R intervals measured in msec.


Which Beats in Figure-4 represent Ventricular Escape?
Ventricular escape beats are most easily recognized by the presence of: i) A different QRS morphology compared to sinus-conducted beats; — ii) A longer preceding R-R interval; — and, iii) The absence of a preceding P wave with a PR interval that is likely to conduct.
  • The 3 QRS complexes in Figure-4 with the longest preceding R-R intervals are beats #3, 5 and 7 (with preceding R-R intervals of 1400 msec. — 1410 msec. — and 1400 msec., respectively).
  • Beat #3 is preceded by a P wave with a PR interval that looks too short to conduct. Beats #5 and 7 are both preceded by P waves with PR intervals that look too long to conduct.
  • QRS morphology of each of these 3 beats is the same (an RSr’ complex) — which suggests that beats #3,5,7 are all ventricular escape beats with a preceding R-R interval of ~7 large boxes (corresponding to a ventricular escape rate of ~43/minute).
  • Beat #1 is also most probably a ventricular  escape beat — because it manifests the same RSr’ morphology as do beats #3,5,7. 
  • Advanced Point: Even though beat #1 in Figure-4 is preceded by a P wave with a seemingly reasonable PR interval (of ~0.18 second) — this PR interval is probably still too short to conduct because of the degree of underlying AV block in today’s tracing.

Which Beats in Figure-4 are probably Conducted?
Applying PEARL #2 — beats #2 and 4 both occur significantly earlier-than-expected (ie, with preceding R-R intervals of 1340 msec. and 1280 msec., respectively). This suggests that both of these beats are conducted.
  • PEARL #5: Knowing that beats #2 and 4 are conducted allows us to deduce 2 more important points: i) That the QRS morphology of conducted beats looks like the RSr’ complex of beats #2 and 4; — and, ii) That despite their markedly prolonged PR intervals — the P waves preceding beats #2 and 4 are conducting because of how early these beats occur — which implies a significant degree of AV block is present.

This leaves us with beat #6 as the only unaccounted QRS complex:
  • Note that QRS morphology of beat #6 is intermediate between the QRS morphology of escape beats #1,3,5,7 — and sinus-conducted beats #2 and 4. This suggests that beat #6 is a Fusion beat (See ECG Blog #128 — for more on fusion beats).
  • Support that beat #6 truly is a fusion beat — is forthcoming from the finding of its relatively longer preceding R-R interval (of 1380 msec.) and — a preceding P wave with a PR interval that would seem likely to be able to conduct.

Putting Together the Longer” Answer:
By the Ps, Qs, 3R Approach — the rhythm in Figure-4 is slow (average rate ~40/minute) — slightly irregular — with an underlying sinus arrhythmia and several different widened QRS morphologies — for which some P waves are conducting, but others are not.
  • The rhythm in Figure-4 — therefore represents some form of 2nd-degree AV block, with significant bradycardia.

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What about the Other Leads?
As noted earlier — today's tracing is not a 12-lead ECG. That said, this rhythm recording shows all 6 limb leads and 2 of the chest leads — such that enough leads are present to provide insight to the clinical situation.
  • It's important to rule out an acute event.

In Figure-5 — I focus on QRST morphology of the 2 conducted beats in this tracing ( = beats #2 and #4) — since it is much more difficult to assess for acute changes with escape or fusion beats.
  • The rsR' complex in lead V1 — in association with wide terminal S wave in lead I, and to a lesser extent in lead V5 — is consistent with underlying RBBB (Right Bundle Branch Block).
  • The predominantly negative QRS complex in lead I — in association with the presence of a qR pattern in inferior leads II,III,aVF — is consistent with LPHB (Left Posterior HemiBlock) — so that there is bifascicular block (RBBB/LPHB).
  • Extra notching in multiple leads (ie, especially in leads I,II,V5) indicates fragmentation, which is often a sign of previous scarring with significant underlying heart disease.
  • The above said — assessment of ST-T wave changes in the 8 leads shown in Figure-5 does not suggest acute changes.

Figure-5: Assessing today's tracing for ECG findings (including whether or not there was recent infarction). To facilitate assessment — I focus on the 8 leads that we see in the 2 sinus-conducted beats ( = beats #2 and #4). Doing so suggests there is RBBB/LPHB — but there are no acute ST-T wave changes.



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The LADDERGRAM: 
For clarity over the next 5 Figures — I work out what I believe is the most plausible mechanism for today's complex arrhythmia:


Figure-6: It is usually easiest to begin a laddergram by filling in the Atrial Tier — which I've done with near-vertical lines for the 10 P waves in this tracing. I have also filled in the information we derived regarding the Ventricular Tier — in that beats #2 and #4 are conducted — beats #1,3,5,7 are ventricular escape beats — and beat #6 is a fusion beat.
= = = = = = = = = = = = =
Now the challenge begins — as we try to "solve" the laddergram by figuring out which of the P waves in the Atrial Tier are being conducted to the ventricles.




Figure-7: Since beats #2 and 4 are conducted — I've drawn in slanted BLUE lines connecting those P waves presumed to be conducting to the ventricles (albeit these P waves are conducting with very prolonged PR intervals). Since beat #6 is a fusion beat — I've also connected the P wave before it to represent the supraventricular component of this fusion.




Figure-8: This leaves us with a series of P waves about which we don't know if AV block prevents conduction to the ventricles — or — if those P waves would have conducted had there not been escape beats blocking their path of conduction.




Figure-9: I thought it most logical to postulate that the RED butt ends in the AV Nodal Tier were the result of AV block preventing conduction — whereas the BLUE butt ends indicate P waves that probably would have conducted, had it not been for escape beats #1,3,5,7 blocking their path to the ventricles.




Figure-10: Finishing my proposed laddergram (and color-coding the P waves in the lead V5 rhythm strip) — RED arrow P waves represent sinus conduction — YELLOW arrow P waves are non-conducted because of AV block — and PINK arrow P waves are accompanied by a question mark because I can not prove these P waves would have been able to conduct had it not been for the ventricular escape beats.
= = = = = = = = = = = = =
BOTTOM Line: This patient with bifascicular block (RBBB/LPHB) — has some form of 2nd-degree AV block, in which there is marked bradycardia (effective rate in the 40s) — and for which those P waves that do conduct, do so with marked 1st-degree AV block. Unless some "fixable" cause of this conduction disturbance can be found — the patient will probably need a pacemaker.



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Acknowledgment: My appreciation to Magnus Nossen (from Fredrikstad, Norway) for the case and these tracings.

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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.

    • ECG Blog #164 and ECG Blog #251 —Review of Mobitz I 2nd-Degree AV Block, with detailed discussion of the "Footprints" of Wenckebach.
    • ECG Blog #236 — Reviews in our 15-minute Video Pearl #52 how to recognize the 2nd-Degree AV Blocks (including "high-grade" AV block)
    • ECG Blog #186 — Reviews when to suspect 2nd-Degree, Mobitz Type I.

    • ECG Blog #404 — Walks you through a step-by-step approach to this AV block case (with links to a VIDEO of this case, and to Blog #344 for more details).

    • ECG Blog #352 — emphasizes that 1st-degree AV block with a very long PR interval may have hemodynamic consequences.



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    ADDENDUM (12/1/2024) — RP/PR Reciprocity ... 

    I received a comment today on this tracing from David Richley, who is well known to most ECG enthusiasts who frequent any of the many ECG internet forums. Dave always offers the most astute commentary on complex arrhythmia interpretation. 

    • NOTE: What follows below goes beyond-the-core! But for those readers who love complex arrhythmia diagnosis — I think you'll find what follows is both fascinating and extremely useful in complex tracings such as the one in today's case!


    Dave writes the following:

    • Dear Ken — I enjoyed your latest ECG blog and I fully agree with your analysis. In addition to all the points you make, I think this is a great example of RP/PR Reciprocity — in which the PR interval of the conducted beats is inversely proportional to the preceding RP interval (Please see Figure-11 below).

    • When I have presented similar ECGs in class, the question that is occasionally asked is: If these are conducted beats — How come the PR intervals are all different? 
    • The answer is RP/PR Reciprocity: The ventricular escape beats conduct retrogradely into (but not through) the AV node, and render it refractory to stimulation. When subsequently a sinus impulse arrives at the AV node — the speed with which it conducts depends on the relative refractoriness of the node. 

    • PEARL #6: The longer the RP interval — the more time the AV node has to recover, and the shorter the PR interval will be. Obviously, if the sinus impulse is very early (very short RP interval) — the AV node will be in its ARP (Absolute Refractory Period), and the impulse will fail to conduct at all. 

    Figure-11: Submitted by David Richley — in which he calculates the RP and PR intervals for the 3 conducted beats in today's tracing. Note that there is RP/PR Reciprocity — in that the shortest RP interval ( = 720 msec.) results in the longest PR interval ( = 640 msec.).
    And, the longest RP interval ( = 960 msec.) results in the shortest PR interval ( = 400 msec.).


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    PEARL #7: = the "Footprints" of Wenckebach:
    David Richley's astute observation regarding today's case brings up a KEY concept known as the "Footprints" of Wenckebach — that I've discussed in many prior ECG Blog posts (You'll find many of these Wenckebach tracings with illustrative laddergrams in my ECG Blog #188).
    • In addition to group beating (that many readers are familiar with) — there are a number of other characteristics that suggest a periodicity consistent with some form of Wenckebach conduction. Marriott has colorfuly labeled these characteristics as the "Footprints" of Wenckebach.
    • To Emphasize: Wenckebach conduction does not always manifest each of these findings. That said — the recognition that several of these characteristics are present goes a long way toward suggesting the diagnosis! (and this is the reason I suspected within seconds — that some form of Wenckebach conduction was present in today's case)

    These are the "Footprints" to look for:
    • Group beating.
    • Lengthening of the PR interval until a beat is dropped — after which the cycle resumes and the PR interval shortens.
    • A regular atrial rhythm (ie, a regular, or at least fairly regular P-P interval).
    • The pause that contains the dropped beat is less than twice the shortest R-R interval.
    • Progressive shortening of the R-R interval within groups of beats, until a beat is dropped.
    • RP/PR Reciprocity (as explained above by David Richley).

    Today's case is extremely challenging — because none of the PR intervals of the conducting beats are the same. There is however group beating — a fairly regular atrial rhythm — and (as per Figure-11) — RP/PR Reciprocity!
    • As always — My appreciation to David Richley for reminding me of the importance of RP/PR Reciprocity that Dr. Barney Marriott first taught me decades ago!

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    Additional LINKS of Interest:
    • ECG Blog #164 — the "Footprints" of Wenckebach.
    • ECG Blog #236 — has a 15-minute ECG Video Pearl on the 2nd-degree AV blocks (I begin talking about the "Footprints" at ~1:20 in this video).
    • ECG Blog #235 — in the ADDENDUM to this Blog #235 (at the bottom of the page) — David Richley adds more Pearls regarding advanced AV block diagnosis.

    • ECG Blog #188 — in which I provide LINKS to over 115 laddergrams (many showing step-by-step analysis) — of which there are many examples of Wenckebach conduction.
    • NOTE: I have added a LINK to facilitate finding this Laddergram page (See the TOP bar of the MENU just below my Blog name at the top of every page in my Blog! ).









    Saturday, November 23, 2024

    ECG Blog #457 — Is Anything Conducting?


    I was sent the ECG shown in Figure-1 — told only that that it was from an acutely ill patient on a ventilator, who was being evaluated for bradycardia. His providers thought this rhythm was complete AV block.


    QUESTIONS: 
    • How would you interpret the ECG in Figure-1?
    • Is the rhythm complete AV block?

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


    MY Thoughts on Figure-1: 
    The "Short" Answer to the question of whether today's rhythm represents complete AV block is no! The "good news" — is that I knew within seconds that today's rhythm was unlikely to represent complete AV block — because there is group beating!
    • Most of the time when there is complete AV block — the ventricular response will be regular (or at least almost regular). This is because most escape rhythms (be they from the AV node; the His; the ventricles) — tend to be surprisingly regular — unless altered by hyperkalemia, acidosis or other toxicity.
    • So, while exceptions are always possible — the presence of the regular irregularity (ie, group beating, in the form of alternating short-long intervals of comparable duration) — makes it highly unlikely that there is no conduction, as would be expected if 3rd-degree AV block was present.
    • NOTE: If there is any doubt on visual inspection about the regular irregularity in Figure-1 — using calipers allows you within seconds to verify comparable duration for the RED arrow R-R intervals — and comparable duration for the slightly longer BLUE arrow R-R intervals (shown in Figure-2).

    • PEARL #1: The presence of group beating — should always suggest the possibility of Wenckebach conduction. While there are other potential causes of group beating (ie, atrial bigeminy; blocked PACs, etc.) — recognizing this finding (as we see in Figure-2) is a "tip-off" to be on the alert for possible 2nd-degree AV block, Mobitz Type I. And, as soon as we recognize group beating — We know that the rhythm is probably not complete AV block!

    Figure-2: Alternating short-long R-R intervals (highlighted by RED and BLUE markers of comparable duration) — indicate group beating in today's rhythm.


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    The "Longer" Answer: What is the Rhythm?
    As always — I favor assessment of the cardiac rhythm by the Ps, Qs, 3R Approach as a time-efficient, user-friendly systematic way to recall the 5 KEY Parameters (See ECG Blog #185 for review of this concept).

    Returning to Figure-1 — I look for the Ps, Qs and 3Rs:
    • P waves are clearly present.
    • The QRS complex is clearly narrow in all 12 leads.
    • The rhythm is not Regular — because as we have already determined there is group beating.
    • As a result of this group beating — the Rate is not constant, but since R-R intervals are between 4-to-6 large boxes in duration — the overall heart rate is reasonable (between 55-70/minute).
    • Which leaves us with having to assess the 5th Parameter — which is "Related" (ie, Whether any of the P waves that are present are "related" and therefore conducting any of the neighboring QRS complexes?).

    ===========================
    In Figure-3 — We look closer at the Ps, Qs and 3Rs:
    • RED arrows in Figure-3 show that there is an underlying regular sinus rhythm (upright P waves with minimal variation in the P-P interval thoughout the long lead II rhythm strip).

    • PEARL #2: Note that there are more P waves than QRS complexes in Figure-3 (ie, a total of 15 RED arrow P waves — but only 10 QRS complexes). This means that at least some of these P waves are not conducting — and, since P waves are regular (ie, All P waves are "on-time" — which means there are no blocked PACs) — this tells us that the reason some of these "on-time" P waves are not conducting, is that there is some form of 2nd-degree AV block!

    PEARL #3: Now step back for a moment — and take another LOOK at the long lead rhythm strip in Figure-3. Doesn't the simple act of labeling all P waves in today's rhythm facilitate assessment of the 5th Parameter? Assessing this 5th Parameter is KEY to solving today's rhythm = Are any of the P waves in Figure-3 conducting?
    • HINT: To answer this question — LOOK in Figure-3 at the PR intervals in front of each beat in the long lead II rhyhm strip. Are any of these PR intervals the same?

    Figure-3: I've labeled all P waves in today's rhythm with RED arrows.


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    ANSWER: Are any of the P waves in Figure-3 conducting?
    In Figure-2 — We saw that there is group beating with alternating shorter and slightly longer R-R intervals.
    • Figure-4 highlights that each of the PR intervals that end the slightly longer R-R intervals in today's rhythm are the same! (ie, BLUE arrows in front of beats #1,3,5,7 and #9 in Figure-4 show that these PR intervals are all identical = 0.40 second). This proves that each of these P waves in front of beats #1,3,5,7,9 is conducting!

    • PEARL #4: The findings of group beating + a regular underlying sinus rhythm in which there are more P waves than QRS complexes — but in which each short "pause" in the rhythm (ie, each of the slightly longer R-R intervals in Figure-4) ends with a sinus P wave that conducts with the same PR interval — all but confirms that today's rhythm is some form of 2nd-degree AV Block, Mobitz Type I (ie, AV Wenckebach).

    The findings noted in PEARL #4 constitute several of the "Footprints" of Wenckebach (discussed more in ECG Blog #251).
    • While at this point in my assessment — I was all-but-certain that today's rhythm represented some for of Mobitz I (which really is all that we need to know for optimal clinical management) — I had not yet demonstrated cycles with progressive increase in the PR interval until an on-time sinus P wave is dropped (as should be seen with typical AV Wenckebach).
    • To prove my theory — I needed to construct a laddergram (See below).

    Figure-4: BLUE arrows highlight that the PR intervals in front of beats #1,3,5,7,9 are identical — therefore confirming that each of the P waves in front of these beats is conducting!


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    What about the 12-Lead ECG?
    At this point (before looking closer at today's rhythm with use of a laddergram) — We should consider the 12-lead ECG (shown above the long lead II rhythm strip in Figure-3 that I show again below).
    • There is low voltage in the limb leads (QRS amplitude ≤5 mm in all limb leads — with potential causes of low voltage discussed in more detail in ECG Blog #272).
    • As already noted — the QRS is narrow in all 12 leads.
    • Considering the slow rate — the QTc does not look to be prolonged.
    • The frontal plane axis is normal (about +60 degrees).
    • There is no chamber enlargement.
    • There are QS waves in leads V1-thru-V4. This suggests there has been anterior infarction at some point in time. That said — there is non-specific ST-T wave flattening in many leads that does not appear to be acute.

    Another LOOK at Figure-3: What about the 12-lead ECG?



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    The LADDERGRAM: 
    Returning to a more in-depth look at today's rhythm — the BEST way to prove that this rhythm is 2nd-degree AV block of the Mobitz I (AV Wenckebach) Type — is to construct a laddergram. I illustrate this in Figures-5 thru -10:

    Figure-5: Laddergram STEP-1. It is usually easiest to begin a laddergram by filling in the Atrial TierBLUE arrows show the onset of P waves as my reference point for drawing in atrial activity. Because conduction through the atria is generally rapid — I drew in near-vertical lines in the Atrial Tier.



    Figure-6: Laddergram STEP-2. I next fill in the Ventricular Tier.
     
    BLUE arrows show the onset of each QRS complex as my reference point for each of the QRS complexes in this tracing. 

    Note that I drew in near-vertical lines for each of the 10 QRS beats in the Ventricular Tier. (If the 12-lead ECG were to show bundle branch block with a wide QRS complex — I would then draw more angled lines in the ventricular tier to reflect slower conduction as impulses passed through the ventricles).

    KEY
     Point:
     The "EASY part" for constructing most laddergrams consists of these first 2 STEPS (
    as shown in Figures-5 and -6)
    Now the challenge begins  which is trying to "solve" the laddergram by figuring out which of the P waves in the Atrial Tier are being conducted to the ventricles.




    Figure-7: We are now ready to begin solving the laddergram. I do this by connecting those P waves from the Atrial Tier — to those QRS complexes that I feel it most logical for these P waves to conduct to (BLUE lines that I've drawn within the AV Nodal Tier).



    Figure-8: It seems logical that the next P waves to conduct to the ventricles are those that are highlighted by BLUE arrows in Figure-8. It should now be easy to see that conduction of this 2nd P wave in each group takes a bit longer to be conducted, which is the principal characteristic of Wenckebach conduction (BLUE lines that I've drawn within the AV Nodal Tier).



    Figure-9: By the process of elimination — this means that the remaining YELLOW arrow P wave in each group is not conducted (ie, there are no unconnected QRS complexes left). This therefore "completes" the laddergram — by the "butt end" that I've added to the remaining YELLOW arrow P waves.



    Figure-10: Final laddergram — with P waves color-coded.
    Within each group, the 1st P wave (light BLUE arrows) conducts with a prolonged PR interval = 0.40 second. The 2nd P wave (dark BLUE arrows) conducts with an even longer PR interval — and then the 3rd P wave in each group (YELLOW arrows) is non-conducted — after which, the cycle begins again with the next light BLUE arrow. Thus, the rhythm = 2nd-degree AV Block, Mobitz Type I (AV Wenckebach) with 3:2 AV conduction (because there are 3 P waves for every 2 P waves that are conducted).



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    Acknowledgment: My appreciation to Jean Max Figueiredo (from Iguaçu, Brazil) 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 my System for Rhythm Interpretation, using thPs, Qs, 3R Approach.
    • 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 #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 — and ECG Blog #344 — for review of some cases that illustrate "AV block problem-solving".
    • ECG Blog #251  Reviews the concepts of Wenckebach periodicity and the "Footprints" of Wenckebach.
    • ECG Blog #164 — Reviews a case of typical Mobitz I 2nd-Degree AV Block (with detailed discussion of the "Footprints" of Wenckebach)
    • ECG Blog #236 — for an ECG Video Pearl on the 3 Types of 2nd-degree AV block.
    • ECG Blog #344 — thoroughly reviews the Types of 2nd-degree AV block (Mobitz I vs Mobitz II vs 2:1 AV Block).

    • ECG Blog #63 Mobitz I, 2nd-degree AV block with junctional escape.
    • ECG Blog #195 — reviews Isorhythmic AV Dissociation.

    • 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 #405 — ECG Video presentation that reviews the distinction between AV Dissociation vs Complete (3rd-degree) AV Block (For a LINKED Contents to this ECG Video — Click on MORE in the Description under the video on YouTube).