Saturday, May 15, 2021

ECG Blog #224 — Recognize this Familiar Picture?

The 12-lead ECG and long lead II rhythm strip shown in Figure-1 was obtained from a middle-aged woman with severe new-onset chest pain. She was hemodynamically stable at the time this ECG was recorded.

  • How would YOU interpret this tracing?
  • What is the rhythm?


Figure-1: ECG obtained from a middle-aged woman with new-onset chest pain (See text).




NOTE #1: Some readers may prefer at this point to listen to the 3:45 minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-1. Feel free at any time to review to My Thoughts on this tracing (that appear below ECG MP-41a).


Today's ECG Media PEARL #41a (3:45 minutes Audio) — Reviews HOW to recognize within seconds (!!!) a Mobitz I ( = AV Wenckebach) 2nd-degree AV Block in which there is ongoing Inferior STEMI.



MY Initial Approach to the ECG in Figure-1:

There are a number of important ECG findings in this case. Although I used a Systematic Approach (as I always do) to interpret both the cardiac rhythm and the 12-lead ECG (See ECG Blog #185 and Blog #205 for details on my approach) — I did allow myself the "luxury" of about 10 seconds to take in the principal findings. KEY Point: A total of 10 seconds was all I needed to arrive at the probable diagnosis:

  • Knowing this patient had new-onset chest pain — my "eye was immediately captured" by the marked inferior lead ST elevation with reciprocal ST depression in lead aVL. This is an obvious acute Inferior STEMI. And, as is so often the case — there is anterior ST depression consistent with acute Posterior involvement (Total Time to see this ~5 seconds)
  • My "eye" was next "captured" by Group Beating (ie, alternate long-short intervals) in the long lead II rhythm strip. Duration of each of the shorter R-R intervals looks similar — and duration of most longer R-R intervals also looked very similar. Virtually all of the longer R-R intervals are preceded by a P wave with a similar (albeit long) PR interval — which means that each of these longer R-R intervals end with a conducted beat! (Total Time to make these observations = another  ~5 seconds).

PEARL #1: In my experience, the combination of acute inferior MI + Group Beating, in which P waves are seen, and each longer R-R interval ends with a conducted beat = Mobitz I, 2nd-Degree AV Block almost all of the time! 

  • Given acuity of this patient (who presented with new-onset chest pain!) — Knowing within minimal time that acute intervention will be needed (ideally, cath lab activation for acute reperfusion) — is essential for optimal outcome!


Applying a Systematic Approach to the ECG in Figure-1:

I'll dissect the rhythm in the long lead II momentarily. For now, seeing that the QRS complex is narrow — tells us that the rhythm is supraventricular — which means that we can systematically assess QRST morphology for acute changes.

  • Intervals (PR, QRS, QTc) — I'll address the PR interval with discussion of the rhythm (below). The QRS is narrow. The QTc is difficult to assess because of continual change from short-to-long R-R intervals — but at most, the QTc is borderline prolonged.
  • Axis: Normal (about +30 degrees).
  • Chamber Enlargement: Assuming normal standardization — there is probable LVH (ie, there appears to be overlap of the R wave in lead V6 with the R wave in lead V5 — so that I'd estimate R wave amplitude in lead V6 at more than 20 mm).


Regarding Q-R-S-T Changes:

  • Q Waves: Large Q waves are seen in each of the inferior leads (II, III, aVF) — especially in lead III.
  • R Wave Progression: Transition (where height of the R wave exceeds depth of the S wave in the chest leads) is slightly delayed (occurs between lead V4-to-V5). That said — there is appropriate progression of R wave amplitude as one moves from lead V1 toward lead V3.
  • ST-T Wave Changes: There is marked ST segment elevation in each of the inferior leads. Significant ST-T wave depression is seen in virtually all remaining leads, except for lead aVR. The "magic" mirror-image opposite picture of reciprocal ST-T wave depression is seen in lead aVL — as compared to the shape of the elevated inferior lead ST segments. 

IMPRESSION: As discussed in ECG Blog #184 — identifying the "magic" mirror-image opposite ST-T wave relationship between lead aVL and lead III in a patient with new chest pain is virtually diagnostic of acute coronary occlusion.

  • We suspect acute RCA (Right Coronary Artery) occlusion because: i) Statistically — between 80-90% of patients have a "right dominant" circulation, in which the RCA rather than the LCx (Left Circumflex) coronary artery is responsible for supplying the inferior wall of the left ventricle; andii) The ECG findings of more ST elevation in lead III > II — together with the finding of marked ST-T wave depression in lead aVL strongly favor the RCA as the "culprit artery".
  • The finding of deep Q waves in each of the inferior leads suggests that this inferior STEMI is already established.
  • Tall voltage in lead V6 suggests probable LVH.
  • Diffuse ST-T wave depression in leads I, aVL and in all 6 chest leads — is consistent with a combination of: i) Reciprocal changes; ii) LV "strain" in lateral leads; iii) Probable posterior wall extension; andiv) Diffuse ischemia.
  • As an observational sign — the extra peaking of inferior lead T waves, on top of elevated inferior lead ST segments is consistent with "hyperacute" changes. The biphasic T waves in leads V5 and V6 (with terminal positivity at the end of the ST depression seen in these leads) — has the appearance of being a "reciprocal" effect to the hyperacute inferior T waves.


Looking CLOSER at the Cardiac Rhythm:

I have often emphasized that the simple act of labeling P waves tremendously facilities seeing even complex relationships between atrial activity and neighboring QRS complexes.

  • PEARL #2: I fully acknowledge that I did not initially see all of the P waves in Figure-1. When looking for atrial activity when I suspect an underlying regular P wave rhythm (as I did in today's case) — I start by a quick "scan" of the tracing, in an attempt to identify a place in the rhythm where I can be fairly certain that I see 2 P waves in a row (YELLOW arrows in Figure-2).
  • Setting my calipers to a P-P interval defined by the distance between these 2 YELLOW arrows — I found I was able to "walk out" regular atrial activity (RED arrows) — with 2 possible exceptions (WHITE arrows).
  • PEARL #3: Not only is it "logical" that sinus P waves are almost certainly hiding under the WHITE arrows — but applying the concept of "simultaneous leads" allows us to prove that this is so. In addition to greater peaking of the T wave of beat #9 in the long lead II — WHITE arrows in simultaneously-recorded anterior leads show deeper negative peaking of the T wave in lead V1, and "tell-tale" notching in leads V2 and V3. While the P wave that occurs just after beat #8 is even more subtly hidden — the 1st WHITE arrow in lead V1 points to an angulation at the top of the S wave upstroke that no other S wave in lead V1 shows. Use of simultaneous leads is an invaluable technique for detecting and/or confirming subtle atrial activity that is only evident in selected leads.



Figure-2: I've labeled P waves from Figure-1 with colored arrows (See text).


Drawing the LADDERGRAM:

Now that we've established the presence of regular atrial activity — I've drawn a Laddergram to illustrate the mechanism for the rhythm in today's case (Figure-3)

  • RED arrows in the Atrial Tier in Figure-3 show the regular occurrence of P waves, seen here at the rapid rate of ~130/minute.
  • There are 5 groups of 2 beats — and 1 group of 3 beats ( = beats #9,10,11). Within each group — the PR interval increases until a beat is dropped. Therefore — the rhythm is 2nd-Degree AV Block, Mobitz I — primarily with 3:2 AV conduction, and in the one 3-beat group, with 4:3 AV conduction.
  • P.S. There is also 1st-Degree AV Block, as explained below.


Figure-3: Laddergram illustration of the mechanism for the rhythm in today's case (Please see ECG Blog #188 for review of how to read and/or draw Laddergrams).


Understanding the LADDERGRAM Better:

The reason recognition of Wenckebach conduction is difficult in today's case — is that the atrial rate is fast, and as a result, most P waves are hidden within the ST segments. To facilitate following the laddergram I drew in Figure-3 — I've selectively colored P waves according to their role in the arrhythmia (Figure-4).

  • KEY clues for deciphering this arrhythmia are: i) Recognizing the group beating, which in the setting of acute inferior STEMI immediately tells you that the rhythm will probably be Mobitz I; andii) Looking at the P waves that occur at the end of each of the short pauses (ie, Looking at the 5 red P waves and the 1 pink P wave in Figure-4).
  • All of the red P waves have the identical PR interval. This tells us that each of these red P waves must be conducting, albeit with a prolonged PR interval (of ~0.35 second). These red P waves result in the 1st conducted beat in each of the 5 2-beat groups (and they conduct with 1st-Degree AV Block).
  • The 2nd P wave in each of the groups is light blue. As seen in the laddergram — each of these light blue P waves is conducted to the ventricles, albeit with a slighty longer PR interval than was seen for the red P waves.
  • The 3rd P wave in each of the 2-beat groups is yellow. These yellow P waves occur very early in the ST segment — and as a result, they are not conducted to the ventricles.
  • There is a brief pause following each of these yellow P waves — after which is seen a red P wave that conducts with the same prolonged PR interval to start the next cycle.
  • Events are slightly different for the one 3-beat group ( = beats 9,10,11). This group begins with a pink P wave — which for reasons I can't explain, is conducted with a shorter PR interval than is seen for each of the red P waves.


Figure-4: Use of colored arrows to illustrate the mechanism of the rhythm in Figure-3.



In SUMMARY: Adopting the mindset that IF you see group beating in a long lead rhythm strip in a patient with obvious acute inferior MI — the chances are high that this group-beating rhythm is AV Wenckebach ( = Mobitz I, 2nd-degree AV Block).

  • IF P waves are seen with the same PR interval before each of the pauses — you have virtually confirmed your diagnosis.
  • Final confirmation is forthcoming if you can now "walk out" regular P waves that may have been hiding within elevated ST segment.
  • Clinically — Prompt recognition of Mobitz I in association with acute inferior MI helps optimize treatment. I bet you'll be making this diagnosis now within seconds!



Acknowledgment: My appreciation to Abdullah Al Mamum and Shomi Ganguly (from Dhaka, Bangladesh) for making me aware of this case and allowing me to use this tracing.



Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #185 — Systematic Approach to Rhythm Interpretation. 
  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation. 
  • ECG Blog #188 — Reviews HOW to Read and Draw Laddergrams
  • ECG Blog #184 — Reviews the "Magical" Lead 3-Lead aVL Relationship with acute OMI (Occlusion-based Myocardial Infarction). 
  • ECG Blog #55 — Reviews a Case similar to the one presented today!
  • ECG Blog #164 — Reviews another Step-by-Step Laddergram demonstration.


  1. This is beautiful! I initially thought it was some sort of atrial Bigemminy and I scrolled through the post but I came back to it to dissect it myself. Your explanation was enlightening.

    1. THANK YOU for the kind words. I'm delighted that this post was insightful to you! — :)

  2. Given that there is still a prolonged PR interval after the non-conducted P wave should you not add first degree AV block to the list of diagnoses. My interpretation would be sinus tachycardia, first degree AV block, mobitz 1 second degree AV block with 3:2 conduction, Inferior STEMI with probable posterior and RV infarct.

  3. Excellent teaching points. A point of clarification: Shouldn't first degree AV block be also added to your interpretation, in addition to the second degree Mobitz 1 you beautifully explained?

    1. @ Dr. Adil Al Riyami — You are completely correct, that in addition to 2nd-degree, Mobitz I — there is also 1st-degree AV block as a result of the markedly prolonged PR interval for the P waves with the RED arrows in Figure-4. It is COMMON for 1st-degree AV block to accompany Mobitz I in association with acute inferior MI.

      I initially didn't not want to further "complicate" my explanation — but your point is excellent — and I have just now ADDED 1st-degree AV block to my diagnoses. THANK YOU — :)

  4. Nice presentation.
    Very effective one.
    Thanks for enlightening me.

    1. My THANKS to YOU for allowing me to use this case! — :)