Friday, November 12, 2021

ECG Blog #261 (51a) — How Many P Waves?

The 12-lead ECG and long lead II rhythm shown in Figure-1 was obtained from a middle-aged man, who presented with shortness of breath. That said — he was hemodynamically stable at the time this tracing was done.

  • What is the rhythm? — Are you certain?
  • How many P waves are there?


Figure-1: 12-lead ECG and long lead II rhythm strip, obtained from a middle-aged man with shortness of breath.



NOTE #1: Some readers may prefer at this point to listen to the 7:40 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-51a).


Today’s ECG Media PEARL #51a (7:40 minutes Audio) — Reviews of "Some Simple Steps to Help Interpret Complex Rhythms" ).



NOTE #2: As I will show below — attention to the simple steps reviewed in the above Audio Pearl allowed me to diagnose this rhythm in less than 15 seconds.



My Sequential Thoughts for Interpreting this Tracing:

As always — I began my systematic approach to the rhythm with assessment of the PsQs and 3Rs (as discussed in detail in ECG Blog #185).

  • We are told that despite being "short of breath" — the patient in today's case was hemodynamically stable. Therefore — we have the "luxury" of a little bit of time to figure out the rhythm.
  • When applying the Ps, Qs, 3R System — You do not have to go in sequence. Therefore, in today's case — I looked first at QRS width. The fact that the QRS is clearly narrow in all 12 leads tells us that the rhythm is SupraVentricular!
  • The rhythm is obviously fast, but not Regular. As a result, the Rate of the ventricular rhythm will vary — but it looks like in parts of the tracing, the rate attains ~120-130/minute.
  • In my rapid systematic approach to rhythm interpretation — I like to spend a couple seconds when the rhythm is irregular by "stepping back" a bit from the tracing to observe IF there is a "pattern" to the rhythm that repeats. In the long lead II rhythm strip in Figure-1 — I see Group Beating (ie, groups of 3 or 4 beats — with each group separated by a short pause of approximately the same duration).


NOTE #3: Despite technical shortcomings in today's tracing (ie, baseline artifact in some leads — with significant angling, and therefore distortion of measurements)I feel this tracing still is adequate for interpretation.



Continuing with the Ps, Qs & 3R Approach in the long lead II rhythm strip (Figure-2):

  • P waves are present! — although I was initially not able to make out a regular atrial rhythm. But looking in front of each of the QRS complexes that end each of the short pauses (ie, in front of beats #2, 5, 9, 12 and 16 in Figure-2) — there is an upright P wave with the same PR interval! Therefore — at least some P waves are Related to neighboring QRS complexes!
  • PEARL #1: The finding of group beating in an SVT rhythm in which each of the relative pauses are approximately equal in duration and preceded by a P wave with the same PR interval — is most often the result of Wenckebach conduction. Awareness of this Pearl literally allowed me to suspect AV Wenckebach within seconds of seeing this tracing.
  • PEARL #2: One of the most common causes of AV Wenckebach, especially when the atrial rate is rapid — is acute inferior MI (See ECG Blog #55Blog #154Blog #168Blog #224). Therefore — I always consider this possibility with rhythms such as that seen in Figure-2. That said — quick overview of the 12-lead tracing in Figure-1 does not suggest acute changes. The isolated Q wave in lead III is non-diagnostic — and this middle-aged patient was not having chest pain. I therefore suspected a primary arrhythmia, rather than an ischemic cause for the tachycardia.


Figure-2: For clarity — I've numbered the beats in the long lead II rhythm strip from Figure-1.


PEARL #3: For there to be AV Wenckebach — there should be an underlying regular atrial rhythm. Use of calipers allowed me to confirm this within seconds (Figure-3):

  • When regular P waves are not initially obvious — the way in which I search for them, is to look for one or more places on the tracing where I can definitely see evidence of at least 2 P waves in a row (RED arrows in Figure-3).

Figure-3: RED arrows show what appears to be 2 P waves in a row in 2 places on this tracing. Artifact and angling (distortion) of this tracing make it impossible to tell if similar consecutive P waves are also occurring between beats #11-12 and between #15-16.

Using the P-P interval determined by consecutive RED arrows in Figure-3 — I was able to walk out indication of regular P waves throughout the long lead II rhythm strip (PINK arrows in Figure-4).

  • Support that the ARROWS in Figure-4 truly represent the occurrence of regular P waves throughout this tracing — is forthcoming from that extra peaking seen in the T waves of beats #2,3 — 5,6,7 — 9,10 — and 12,13. In contrast, there is no such peaking for the T waves of beats #1, 4, 8, 11 and 14, because P waves do not coincide with the T waves for these beats. Given the tall amplitude and peaking of those P waves that we clearly see (ie, the P waves before beats #2, 5 and 9) — it is easy to imagine how P waves that occur at the same time as T waves would produce "extra peaking" in this tracing.


Figure-4: RED and PINK arrows suggest that there is an underlying regular atrial rhythm at ~130-140/minute (See text).


Putting IAll Together: One of the "Take Home" points from today's tracing is that application of a series of the Simple Steps highlighted in today's Audio Pearl allowed me complete the above assessment in ~15 seconds. I concluded the following:

  • The underlying rhythm in today's case is Atrial Tachycardia (ATach) at ~130-140/minute (regular-occurring RED and PINK arrows in Figure-4).
  • "Common things are common" — and ATach is commonly associated with Wenckebach conduction. Recognition of group beating led me to immediately suspect Wenckebach conduction in today's case — and this was supported by the finding of a constant PR interval that repeats at the end of each of the relative pauses (ie, the constant PR interval before beats #2, 5, 9, 12 and 16).
  • Use of calipers allowed me to confirm the regular atrial rhythm.
  • Wenckebach conduction can be visually confirmed by progressive increase in the PR interval within each group of beats — until a beat is dropped (ie, the P waves that occur just after the QRS complex of beats #1, 4, 8, 11 are not conducted). The next cycle then begins with shortening of the PR interval (ie, before beats #2, 5, 9 and 12).
  • Although inferior infarction is a common cause of group beating with Wenckebach — there is no suggestion of recent infarction on today's 12-lead ECG. Chances are good that IF the ATach is controlled — that Wenckebach conduction will resolve.




To clarify the mechanism in today’s rhythm — I've drawn a laddergram with step-by-step annotations. I begin with Figure-5

  • NOTE: For review of the Basics for HOW to read (and drawladdergrams  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 14 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. We accomplish this by first connecting those P waves that are most evident, and which we know (because of the constant PR interval) that these P waves are being conducted to the ventricles (BLUE lines in the AV Nodal Tier).


Figure-8: I've next connected the other P waves in this first group of beats in this tracing. As can be seen from progressive increase in the amount of inclination within the AV Nodal Tier until the P wave occurring just after beat #4 is non-conducted (BLUE lines) — this appearance in the laddergram is perfectly consistent with AV Wenckebach. Following the dropped beat — the PR interval shortens with conduction of beat #5.


Figure-9: I've completed the laddergram by connecting all atral impulses with neighboring QRS complexes in the Ventricular Tier that seem most likely to be conducting. Note that this laddergram appearance is consistent with ATach with AV Wenckebach showing 4:3 and 5:4 AV conduction (ie, 4 P waves for the groups with 3 QRS complexes — and 5 P waves for the one 4-beat group = beats #5,6,7,8)



Final POINT: Rather than calling the rhythm in Figure-9 some form of 2nd-degree AV "block" — I favor considering this rhythm as Atrial Tachycardia with Wenckebach conduction. This type of Wenckebach conduction is often physiologic, as a result of the rapid atrial rate. It often does not represent a specific conduction defect — and Wenckebach conduction will often resolve if the ATach is controlled.




Acknowledgment: My appreciation to Pisey Chantha and Phearo Pheap (from Phnom Penh, Cambodia) for the case and these tracings.



Relevant ECG Posts to Today's Case:


  1. Thank you so much ! Very clear , very helpful .

  2. Dr Gobinda Kanti Paul MD cardiologyNovember 16, 2021 at 10:58 AM

    I learned elaborately with nice explanation.
    Thanks a lot, Sir.

    1. @ Dr. Gobinda Kanti Paul — THANK YOU for the kind words! — :)