Monday, April 3, 2023

ECG Blog #372 — PVCs or Aberrant?

I was asked for my interpretation of this tracing. No history was provided.
  • How would YOU interpret this long lead II rhythm strip?
  • Are the different-looking beats PVCs or supraventricular impulses conducted with aberration? — orSomething else?

Figure-1: The long lead II rhythm strip for today’s case. No history was available(To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on the Rhythm in Figure-1:
Although no history is provided for today's case — I'll presume the patient is hemodynamically stable with the rhythm in Figure-1, since runs of the wide beats are not sustained. As always — I favor a systematic approach to rhythm interpretation, using the Ps, Qs, 3R memory aid (See ECG Blog #185).
  • PEARL #1: When 2 or more “elements” exist for a given arrhythmia — I find it easiest to start with the easiest element to interpret. In most cases — this entails looking for the underlying rhythm. The 2 elements in today’s rhythm are distinguished by the 2 different QRS morphologies: i) Element #1 (a total of 10 beats) = Beats #2-thru-5; #9,10; #14-thru-17; and, ii) Element #2 (7 beats) = Beats #1; 6,7,8; and 11,12,13 — which are wider and clearly different in appearance than the beats for Element #1.

Focusing first on the 10 beats in Element #1:
  • The QRS complex looks narrow in this single monitoring lead.
  • P waves are present in front of each of the Element #1 beats, with the possible exception of beat #9 (for which it is difficult to know at first glance whether or not a P wave is hidden in the preceding T wave). In Figure-2 — I’ve labeled all P waves in today’s rhythm that I am certain about. Note that each of these P waves is upright in this lead II, with a constant and normal PR interval. Therefore — there is an underlying sinus rhythm.

  • Focusing on the simplest “segment” in today’s rhythm ( = beats #2-thru-5) — the QRS looks to be narrow in this single monitoring lead — sinus P waves with a constant and normal PR interval precede each QRS — and the rhythm is regular at a rate slightly faster than 100/minute.

Figure-2: I've labeled all P waves that I was certain about in Figure-1 — with RED arrows.

  • Are there some additional P waves in Figure-2 that are not labeled because they are partially (or completely) hidden within QRS complexes or ST-T waves?

  • HINT: How might using calipers help to easily answer this question?

  • LOOK at Figure-3 . . . 

Figure-3: I’ve added PINK arrows to indicate where P waves were “hiding”.

Whenever you are confronted by a complex arrhythmia, and you have the “luxury” of a moment of time (because the patient is hemodynamically stable) — using calipers is by far the most time-efficient way to facilitate your interpretation:
  • Simply set your calipers to a P-P interval determined by the distance between any 2 consecutive P waves of similar morphology that you clearly see. In Figure-3 — you can choose the P-P interval between beats #2-3 — or between  #3-4; between #4-5 — or near the end of the rhythm strip, the P-P interval between beats #14-15; 15-16; or 16-17.
  • Once you’ve set your calipers to any one of the above P-P intervals — See if you can “walk out” an underlying regular atrial rhythm. The PINK and RED arrows in Figure-3show that you can! Note that either a definite P wave — orsome “extra” deflection (in either the QRS or ST-T wave) — can be seen under each of the colored arrows in today’s rhythm!

  • NOTE: P wave deflections in Figure-3 are not perfectly regular. Instead — there is slight variation in the P-P interval, consistent with some degree of sinus arrhythmia. Slight variation in the P-P interval as is seen here is not uncommon with complex arrhythmias.

  • To Emphasize: If you use calipers — it should not take you more than 10 seconds (at most!) — to establish that the underlying atrial rhythm in Figure-3 is essentially regular throughout the rhythm strip. Without using calipers — it will take much longer (and even, then you will not know for certain if there truly is an underlying sinus rhythm).

Putting Together What We Know at this Point:
Establishing that the underlying atrial rhythm is regular is KEY to interpreting today’s rhythm. Now that we know this — we can say the following:
  • The underlying rhythm in Figure-3 is sinus tachycardia at ~105/minute.
  • The QRS is narrow for each of the normal sinus-conducted beats (ie, for beats #2-thru-5; #10; and beats #14-thru-17).
  • Since the QRS of beat #9 looks identical to the QRS for all other sinus beats — beat #9 is also a supraventricular beat. Note that a PINK arrow precedes beat #9 in Figure-3 — indicating that an “on-time” sinus P wave is hiding within the T wave of beat #8. This tells us that beat #9 is a sinus-conducted beat, albeit with a slightly longer PR interval compared to the PR interval of all other sinus beats.

Now that we’ve established the diagnosis of Element #1 — I turned my attention to the 7 beats in Element #2 that are wider and look different than sinus-conducted beats (ie, beats #1; 6,7,8; and 11,12,13).
  • These beats — are dissociated from (and completely unrelated to) neighboring sinus beats. We know this — because the PR intervals that occur just before the on-time sinus P waves that deform the initial part of the QRS of beats #6 and 11 are too short to conduct! This proves that each of the beats that look like beats #6 and 11 must be PVCs (Premature Ventricular Contractions)

  • For review of how recognizing AV dissociation proves the presence of PVCsSee ECG Blog #133.

BOTTOM Line: Simply stated — today’s rhythm represents an underlying sinus tachycardia (at ~105/minute) — with frequent PVCs, including 2 salvos of 3 PVCs in a row ( = beats #6-8 and 11-13).
  • To Emphasize: Although my above step-by-step description is written in “slow motion” — In "real time", it should take no more than seconds to arrive at this conclusion using the above approach.


What Does the 12-Lead ECG Show?
I was then shown the 12-lead ECG corresponding to the rhythm strip that we have been assessing (Figure-4).
  • What do we learn from seeing the 12-lead ECG?

Figure-4: The 12-lead ECG that corresponds to the rhythm we have been assessing. (To improve visualization — I've digitized the original ECG using PMcardio).

On Seeing the 12-Lead ECG:
Whenever possible in my interpretation of a complex arrhythmia — I favor obtaining a 12-lead tracing. Doing so may prove invaluable by: i) Confirming your theory about the presence and nature of atrial activity; ii) Confirming whether the QRS is truly wide or narrow; and/or, iii) Sometimes providing indication of the cause of the arrhythmia (ie, hyper- or hypokalemia; acute infarction; etc.). In Figure-4 — We learn the following from seeing the simultaneously-recorded 12-lead tracing:
  • There is no longer any doubt that beats #1; 6,7,8; and 11,12,13 are PVCs! Each of these beats is obviously wide and totally different in morphology than the underlying sinus beats.

  • PEARL #3: ST-T wave morphology is best assessed in sinus-conducted beats. This suggests that the cause of the PVCs in today's rhythm is probably a recent infarction.  ST-T wave changes are nonspecific for sinus beats #2,3,4 (in leads I,II,III) and for sinus beats #5 and 9 (in leads aVR,aVL,aVF) — but there is loss of R wave in lead V2 with some ST elevation in leads V2,V3 for sinus beat #10 — and ST coving with T wave inversion in leads V4,V5 for sinus beats #14-17.


LADDERGRAM Illustration:
Clarification of the mechanism in today's arrhythmia is best explained by laddergram (Figure-5).
  • As I have often emphasized — it takes a little time to get good at drawing laddergrams (See ECG Blog #188)but it is not difficult to learn how to read them!

  • In Figure-5 — Regular sinus P waves are seen conducting in the Atrial Tier.
  • The normally conducted sinus beats are conducted through to the ventricles ( = beats #2,3,4,5; beat #10; and beats #14,15,16,17).
  • Beats #1, 6,7,8; and 11,12,13 are PVCs. These beats originate from the ventricles, and conduct to some degree beyond the AV node — thereby preventing forward conduction of the on-time PINK sinus P waves, that fail to conduct to the ventricles.
  • One of the on-time sinus P waves in Figure-5 (YELLOW arrow) — is able to conduct to the ventricles, but with a longer-than-expected PR interval because it is partially delayed by backward conduction from the PVC before it ( = beat #8). 

  • PEARL #4: Although the PR interval of the on-time YELLOW P wave in Figure-5 is increased — this is not the result of AV block. Instead — it is the result of what is known as "concealed conduction" — in which retrograde conduction from the preceding PVC, while not enough to block forward conduction of the next sinus beat — is enough to slighty prolong the ensuing PR interval. The term "concealed" is used — because we cannot explain this effect on the ensuing PR interval from what is seen on the actual ECG — but instead must infer there is retrograde conduction from the PVC impeding forward conduction of the next on-time sinus impulse (More on concealed conduction in ECG Blog #68).

Figure-5: Laddergram illustration of today's arrhythmia.


Acknowledgment: My appreciation to Dayanand Khanolkar (from Mumbai, India) for the case and this tracing.



Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #205 Systematic Approach to 12-lead ECG Interpretation
  • ECG Blog #185 — Systematic Approach to Rhythm Interpretation.

  • Our approach for distinction between VT vs SVT with either aberrant conduction or preexisting BBB — See ECG Blog #42.
  • For review of the Ashman Phenomenon  See ECG Blog #70.
  • For review of AV Dissociation  See ECG Blog #133 and ECG Blog #335.
  • For review of Fusion Beats  See ECG Blog #128.

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