Friday, October 15, 2021

ECG Blog #257 (19a) — AV Block in a Young Adult?

The 2-lead rhythm strip shown in Figure-1 was obtained from a young adult woman who presented for "palpitatons". No known previous history of heart disease.

  • How would YOU interpret this tracing?
  • Given the above history — What are your clinical considerations?

Figure-1: 2-lead rhythm strip obtained from a young adult woman with "palpitations" (See text).



NOTE #1: Some readers may prefer at this point to listen to the 6:45-minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-1. Feel free at any time to refer to My Thoughts on this tracing (that appear below ECG MP-19a).


Today’s ECG Media PEARL #19a (6:45 minutes Audio) — Reviews a few quick things to look at that allow you to rule in or rule out complete AV Block within seconds.


NOTE #2: Although I lack clinical details for this case (and I don't even have access to a 12-lead ECG on this patient) — the 2-lead rhythm strip that we are provided in Figure-1, and the limited history we are given is still enough for an instructive discussion.




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).

  • P waves — Sinus P waves are present in today's tracing! It was not immediately obvious to me that the atrial rhythm is regular — because many of the P waves either occur within the QRS complex or within the ST-T wave. In Figure-2 — I highlight with RED arrows a number of P waves that I can definitely identify.

Figure-2: I highlight a number of P waves from Figure-1 that I can definitely identify (RED arrows).


PEARL #1: This is the type of tracing for which use of calipers is essential! I know of no other way to determine that the atrial rhythm in Figure-2 is regular.

  • It is virtually impossible to determine the rhythm in Figure-2 unless you establish that the atrial rhythm is regular throughout the tracing.
  • It will literally take you less than 10 seconds to walk out regularly-occurring deflections (corresponding to regular P waves) with the use of calipers (RED arrows in Figure-3). 


Figure-3: Using calipers allows us to establish that the atrial rhythm is regular throughout today's tracing (RED arrows).


Continuing with the PsQs and 3R Approach:

  • The QRS complex in Figure-3 looks wide! (ie, about 3 little boxes = 0.12 second in duration). Unfortunately — we do not have access to a 12-lead ECG on this patient. That said — the predominantly negative morphology of the QRS complex in leads II and III is consistent with LAHB (Left Anterior HemiBlock).


PEARL #2 (Beyond-the-Core): Although the presence of a hemiblock may slightly prolong the process of ventricular depolarization — it usually does not do so by more than 0.01-to-0.02 second. Therefore — the wide QRS complex (that we measured in Figure-3 to be 0.12 second in duration) is longer than we would expect for simple LAHB. This suggests that there may be additional conduction system disease (ie, possible also RBBB = Right Bundle Branch Block).

  • While LAHB is a common ECG fnding in an older adult popultion — it is not commonly seen in otherwise healthy young adults. Therefore, even without seeing a complete 12-lead ECG on the young adult woman in today's can — we can suspect that there may be underlying structural (and/or conduction system) disease.



Technical POINT: IF you look closely at the ECG grid lines in Figure-3 — it should be apparent that the ECG paper is angled (ie, the ECG grid boxes are not completely vertical — this being easiest to see at the beginning and end of the tracing). In addition, there is baseline artifact (more marked in lead II than lead III) — and — the ECG baseline is rising (being several boxes higher for the last few beats in the tracing). 

  • NOTE: While today's tracing is still adequate for interpretation — the above technical factors combine to produce slight distortion of measurements. The reason this is important — is that often the BEST clue that complete AV block is not present, is when one or more ventricular beats occur earlier-than-expected — which is why precise measurements are needed (This concept discussed in detail in today's Audio Pearl that appears above).



Completing systematic assessment with the 3Rs:

  • Accounting for the above technical imperfections — I thought the ventricular rhythm in Figure-3 appeared to be Regular at a Rate of ~60/minute (ie, the R-R interval is ~5 large boxes in duration).
  • As per our caliper measurement (and as per the RED arrows in Figure-3) — the atrial rhythm in today's tracing appears to be Regular at the rapid atrial Rate of ~130/minute.
  • The 3rd "R" is "Related" — as determined by how many (if any) P waves in Figure-3 are related to neighboring QRS complexes.


PEARL #3: I find it easiest to determine if P waves are related to neighboring QRS complexes — by focusing on each QRS complex in the tracing, and looking to see if any PR intervals are constant.

  • In Figure-3 — the PR interval is constantly changing in front of each of the 10 beats on this tracing. This finding — plus the finding that both the atrial and ventricular rates in Figure-3 remain regular throughout the tracing — suggests that none of the P waves are being conducted to the ventrcles.
  • As emphasized earlier — the BEST clue that complete AV block is not present, occurs when one or more ventricular beats occur earlier-than-expected. This does not happen in Figure-3 — because the ventricular rate remains regular throughout the tracing!



Drawing the LADDERGRAM:

A picture tells 1,000 words. The Laddergram that I've drawn in Figure-4 illustrates the mechanism I propose for today's rhythm (See ECG Blog #188 for review on how to read and/or draw Laddergrams). The laddergram in Figure-4 suggests the following:

  • The atrial rhythm is rapid and regular — but none of the P waves are able to penetrate the AV node.
  • propose that the escape rhythm is junctional (regularly-occurring RED circles within the AV Nodal Tier). That said, the QRS complex is wide — and without a complete 12-lead ECG (and without a prior tracing for comparison) — I can not rule out the possibility of a ventricular escape rhythm. I thought the escape rate of ~60/minute with QRS morphology consistent with a LAHB pattern was more suggestive of junctional (rather than ventricular) escape. 

Figure-4: My proposed laddergram for the rhythm in today's case (See text).


DISCUSSION: Today's case raises a number of points worthy of further comment.

  • The atrial rate in Figure-4 is rapid at ~130/minute. This raises the question of whether the atrial rhythm represents sinus tachycardiaor — possibly an ectopic ATach (Atrial Tachycardia). P wave morphology is consistent with sinus tachycardia (ie, rounded P wave shape of normal duration that is upright in lead II) — but an ectopic ATach arising from a site in the atria not far from the SA node could look the same. That said — regardless of P wave origin, significant AV block is present. However, treatment and clinical outcome of this patient may differ depending on the cause of the fast atrial rhythm that we see in Figure-4One wonders IF there may be return of some AV conduction if the atrial rate were to slow down.
  • The KEY requirement for diagnosis of complete AV block — is to establish that none of the regularly-occurring P waves are conducted to the ventricles despite at least some of these P waves having adequate opportunity to do so. For practical purposes — it is difficult to ensure that at least some P waves will have a chance to conduct when the ventricular rate is faster than 50-55 beats per minute. This is because at ventricular rates above 55-to-60 beats per minute — there is too much of a chance that many (if not most) P waves will either fall within the refractory period (when conduction is not expected) — or will have a PR interval that might be too short to conduct in a patient with partial (but not complete) AV block.

BOTTOM LINE: I suspect that complete (3rd-degree) AV block is present in today's case. That said — it is impossible to be 100% certain of this from the single 2-lead rhythm strip shown in Figure-4 because: i) At a rate of ~60/minute — the escape pacemaker may simply be too fast to ensure that at least some P waves fail to conduct despite having adequate opportunity to do so; andii) Angulation of the tracing, baseline artifact and a rising baseline all contribute to slight distortion that detracts from preciseness of measurement. This reduces utility of the essential diagnostic clue that regularity (or lack the thereof) of the R-R interval will usually tell us if complete AV block is (or is not) present. 

  • KEY Point: An additional few minutes of ECG monitoring is all that would probably be needed confirm IF complete AV block was (or was not) present. 
  • Clinically — Even if the degree of AV block turned out not to be complete, it is likely that the degree of AV block is at-least high-grade. As a result — unless a "fixable" cause of this conduction disturbance can be found, a pacemaker will probably still be needed.

What Etiologies to Consider?

It is not common to see complete or high-grade 2nd-degree AV block in a younger adult. As a result — this ECG finding that we see in today's case should prompt consideration of the etiologies listed in Figure-5.

  • NOTE: The fact that the QRS complex in today's case is wide (with at the least, LAHB) — suggests the presence of some form of underlying structural heart disease (especially given the young adult age in this patient).  

Figure-5: Etiologies to consider for AV block in a younger adult.



Acknowledgment: My appreciation to Nelson Nersisyan (from Yerevan, Armenia) for the case and this tracing.





Relevant ECG Blogs to Today's Audio Pearl:

  • ECG Blog #185 — Use of a Systematic Approach to Rhythm Interpretation.

  • ECG Blog #202 — Reviews another case where the question was whether complete AV block was present? (The KEY to this tracing was to recognize the earlier-than-expected beat that is being conducted to the ventricles!)
  • ECG Blog #191 — Is AV Block Complete? (Assessing AV Dissociation).
  • ECG Blog #188 — How to Read (and Draw) Laddergrams.

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