Saturday, August 12, 2023

ECG Blog #390 — No Information Provided ...

I was sent the ECG in Figure-1, with a request for my opinion — without the benefit of any history.
  • How would YOU interpret the ECG in Figure-1?
  • What might you suspect clinically?

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

MY Thoughts on the ECG in Figure-1:
In these days of widespread smart phone availability — transmission of ECGs to request expert opinion is an increasingly used practice, that on many occasions occurs in “real time”. 
  • As recipient of numerous daily requests — I am often asked for my interpretation without the benefit of any history. Such was the case for today’s tracing. 

I routinely begin assessment of each 12-lead ECG I encounter — with interpretation of the rhythm. To do this — I apply the Ps, Qs, 3R Approach (See ECG Blog #185for review of my system).
  • The long lead rhythm strip at the bottom of the 12-lead ECG in Figure-1 — shows the Rhythm to be fairly (albeit not completely) regular — at a Rate between ~60-65/minute.
  • The QRS complex is obviously wide.
  • P waves are present. 

  • The 5th Parameter in the Ps,Qs,3R Approach is the 3rd "R" — which is to assess whether the P waves that are present are Related to "neighboring" QRS complexes. From my initial look at the long lead II rhythm strip in Figure-1 — I was not at all certain IF the P waves that I saw were (or were notrelated to neighboring QRS complexes.

 After considering the 5 KEY Parameters — the EASIEST next step for determining the mechanism of a complex rhythm — is to label the P waves. You'll note that I also number the beats — since this instantly allows everyone involved to ensure we are all talking about the same part of the tracing. 
  • Using calipers is the fastest (and most accurate) way to determine if there is an underlying regular rhythm. Set your calipers to the P-P interval of 2 consecutive P waves, the location of which you are certain about (ie, For example — we clearly see a P wave just before beat #1, with a short PR interval — then a 2nd P wave before beat #2, with a slightly longer PR interval — and then a 3rd P wave that falls near the middle of the R-R interval between beats #2-to-3)
  • Now see IF you can "walk out" regular (or at least fairly regular) P waves throughout the rest of the tracing. NOTE: The RED arrows in Figure-2 show that you can! 

Figure-2: I've labeled the P waves in today's tracing (RED arrows).

More PEARLS: Determing IF there is AV Block?
Having worked through the Ps,Qs,3R Approach — we have established that the QRS is wide — there is a fairly regular P wave rhythm (albeit with slight sinus arrhythmia) — and the ventricuar rhythm is fairly (albeit not completely) regular.
  • The fact that the atrial rhythm is almost regular — means that we are not dealing with PACs (which would produce some earlier-than-expected P waves) — and, we are not dealing with sinus pauses, as occur with Sick Sinus Syndrome (as this would produce delay in the P wave rhythm).
  • Instead — Most of the time with 2nd- or 3rd degree AV block — the atrial rhythm will be regular (or at least fairly regular) — as it is in Figure-2.

Are there More P Waves than QRS Complexes?
When the atrial rhythm is regular — IF there are more P waves than QRS complexes — then there must be at least some AV block.
  • In Figure-2 — there are 12 RED arrows ( = 12 P waves).
  • But — there are only 10 beats ( = 10 QRS complexes).
  • Therefore — at least 2 of the P waves are not conducting!

Do Any QRS Complexes occur Earlier-than-Expected?
My favorite "tip-off" that there is at least some conduction of sinus P waves — is IF in an otherwise regular (or almost regular) ventricular rhythm — one or more QRS complexes occur earlier-than-expected.
  • BUT — None of the QRS complexes in Figure-2 occur earlier than expected. This made me immediately suspect that the degree of AV block in today's tracing may be complete.

Are there Any Repetitive PR Intervals?
Another excellent "tip-off" that there is at least some conduction of atrial impulses — is when you see one or more identical PR intervals on the rhythm strip.
  • The caveat to this general rule — is that by chance you may see an occasional seemingly identical PR interval, without there necessarily being any conduction. Monitoring the patient on telemetry for just a little bit longer (ie, another 20-30 seconds) — is usually all that it takes to establish IF one or more PR intervals are truly repeating — in which case, it becomes likely that these beats that manifest the same PR interval are being conducted.

Putting It All Together in a Laddergram:
As stated — both the atrial and ventricular rhythms in today's tracing are essentially regular.
  • There are no "earlier-than-expected" beats.
  • Instead — P waves are "marching through" the QRS complexes. The same PR interval is never seen twice. As a result, none of the P waves appear to be conducting — and, the rhythm appears to be 3rd-degree (complete) AV block.

The laddergram in Figure-3 schematically illustrates the situation.

  • Since the QRS complex is wide and regular, and no P waves are conducting — the escape rhythm must be from the ventricles (probably from the RV). This is consistent with QRS morphology in Figure-2 — which is not suggestive of any known form of bundle branch block (ie, Although the monophasic R wave in lateral chest lead V6 and the negative QS in lead V1 resemble lbbb conduction — We do not see an all positive R wave in lateral lead I, nor do we see predominantly negative QRS complexes continue in the chest leads at least until lead V5 — which makes for ECG findings that are not seen with typical LBBB).

  • As per the laddergram in Figure-3 — None of the RED arrow P waves make it through the AV Nodal Tier to be conducted to the ventricles.

Figure-3: Laddergram illustration of today's rhythm — suggesting there is complete AV block.

The Final PEARL that is Needed:
In addition to seeing fairly regular atrial and ventricular rhythms, but no indication that any of the P waves on the rhythm strip are being conducted — there is one more all-too-often-forgotten criterion that needs to be satisfied before we can make a definitive diagnosis of complete AV block:
  • We need to be able to show that no on-time P waves are being conducted to the ventricles despite having adequate opportunity to do so!
  • For example — the P waves in Figure-3 that occur just after beats #4 and #10 — the P wave that falls within the QRS complex of beat #5 — and the P wave with the very short PR interval just before beat #6 — do not have an "adequate chance" to conduct.
  • In contrast — one would expect that the P waves occurring near the middle of the R-R interval between beats #2-to-3, and between beats #7-to-8, should have been able to conduct (ie, One would expect that there should have been sufficient time for the conduction system to have recovered — yet there is still no conduction of these P waves).

Technically, in order to ensure that on-time P waves have adequate opportunity to conduct, yet still fail to do so — the rate of the escape rhythm should be slow enough (ie, usually <50-55/minute) in order to guarantee that P waves are going to fall at all points within the R-R interval.
  • When the ventricular escape rhythm is faster than 50-55/minute — you will typically need a longer period of monitoring than the ~10 second rhythm strip seen in today's case, in order to ensure that there is truly "complete" AV block (ie, that P waves have truly occurred at all points within the R-R interval — and have had an adequate "chance" to conduct, but failed to do so).
  • The rate of the ventricular escape rhythm in today's case is ~60-65/minute (ie, the R-R interval is a little less than 5 large boxes in duration). This is somewhat faster than the usual ventricular escape rate (which in adults is typically between 20-40/minute) — and it is fast enough that another 20-30 seconds of monitoring would be needed to ensure that there is truly 3rd-degree AV block.

  • P.S.: No history or lab findings were available in today's case. Given QRS widening with an atypical QRS morphology — with complete AV block — and, with peaked T waves in many leads (ie, in lead I; and in V2-thru-V6) — a serum K+ level needs to be checked, since hyperkalemia might produce all of these findings.

Acknowledgment: My appreciation to Bashiruddin Sayeem (from Chittagong, Bangladesh) for the case and this tracing.

Related ECG Blog Posts to Today’s Case:

  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
  • ECG Blog #185 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.

  • ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 80 laddergram cases — many with step-by-step sequential illustration).
  • ECG Blog #192 — The 3 Causes of AV Dissociation.
  • ECG Blog #191 — Reviews the difference between AV Dissociation vs Complete AV Block.

  • ECG Blog #389ECG Blog #373 — and ECG Blog #344 — for review of some cases that illustrate "AV block problem-solving".

ADDENDUM (8/12/2023):
  • What follows below is a 7-page excerpt from my ACLS-2013 Arrhythmias (Expanded Version) book, in which I review the distinction between AV dissociation vs complete AV block.

ECG Media PEARL #9 (4:45 minutes) — reviews the 3 Causes of AV Dissociation — and emphasizes why AV Dissociation is not the same thing as Complete AV Block.

ECG Media PEARL #8 (7:00 minutes Video) — is an ECG video that illustrates the difference between AV Dissociation vs Complete AV Block.


  1. Interesting, all physicians need to recognize "P waves are "marching through" the QRS complexes" and no one illustrates this better than KG. Great Case, Great illustration, Thank you.