Saturday, February 17, 2024

ECG Blog #417 — AFib with Aberrancy?

The ECG in Figure-1 was obtained from a previously healthy middle-aged man — who presented to the ED (Emergency Department) for shortness of breath. 

  • How would YOU interpret the ECG shown in Figure-1?
  • Given the irregular irregularity of beats #4-through 17 — Is this a run of AFib (Atrial Fibrillation) with aberrant conduction?

Figure-1: The initial ECG in today's case.

Initial Thoughts on the ECG in Figure-1:
Today's ECG is challenging because despite the marked change in QRS morphology beginning with beat #4 — monomorphic VT (Ventricular Tachycardia) is usually a regular (if not, at least fairly regular) rhythm. This raises the question if beats #4-thru-17 might represent a run of AFib with aberrant conduction?
  • HINT: The KEY to interpreting today's rhythm lies with assessment of atrial activity. What do YOU see?


Does this Earlier Tracing Help?
Another ECG had been recorded on today's patient shortly before the ECG shown in Figure-1
  • Does this earlier tracing (shown in Figure-2) help to determine the etiology of the run of irregular wide beats in Figure-1?

Figure-2: A 2nd ECG in today's case. This tracing was recorded shortly before ECG #1. Does this earlier tracing help to determine the etiology of the wide beats?


My Approach to Today's Rhythm:
Atrial activity is present in association with each of the beats in both of today’s tracings. This atrial activity provides the KEY clue for determining the etiology of the wide beats. 
  • Using calipers facilitates the process.

  • HINT: We need to look for P waves not only in front of the wide beats — but also during and just after the wide QRS complexes in order to complete our search for atrial activity. 

I’ve put both tracings together in Figure-3.
  • How do the colored arrows provide the answer?

Figure-3: I’ve put both tracings in today’s case together — and have labeled atrial activity with colored arrows.

The ANSWER to Today’s Rhythm:
The first 3 beats in ECG #1 are sinus conducted — with RED arrows highlighting on-time sinus P waves.
  • Note that a 4th on-time sinus P wave occurs just before the 1st wide beat in the long lead II rhythm strip seen in Figure-3 ( = the 4th RED arrow in ECG #1 that appears just before beat #4).
  • Note also that a subtle negative deflection occurs at the very end of the 2nd wide QRS complex ( = the 1st YELLOW arrow in the long lead II rhythm strip of ECG #1). This YELLOW arrow represents a retrograde P wave.
  • KEY Point: The above events prove that beat #4 and beat #5 are PVCs (Premature Ventricular Contractions).

Several points should be emphasized regarding ECG #1:
  • The reason we know that the subtle negative deflection ( = that 1st YELLOW arrow in ECG #1) that appears at the end of beat #5 is definitely a retrograde P wave — is that we see no such negative deflection at the end of beat #4. This is as expected — because an on-time sinus P wave appears just before beat #4, and this renders the atria refractory to retrograde conduction.
  • Of interest — retrograde P waves (highlighted by YELLOW arrows) are seen at the very same point (ie, just after the QRS complex) of beats #6-thru-17.
  • Further support that the subtle negative deflections at the end of the wide beats are indeed retrograde P waves — is forthcoming from our ability to see these retrograde P waves in other leads in the 12-lead tracing (= YELLOW arrows in multiple other leads in ECG #1).
  • Returning to the long lead II rhythm strip in ECG #1 Beat #17 is followed by a brief pause, after which the 5th RED arrow in this tracing highlights resumption of sinus rhythm with beat #18.

  • PEARL #1: The polarity of a P wave that appears shortly after a QRS complex helps to distinguish between sinus P waves, PACs (Premature Atrial Contractions) and retrograde P waves. Sinus P waves should be positive in lead II. They are often (albeit not always) negative in lead V1. PACs may either be positive or negative. But retrograde P waves should be negative in inferior leads (II,III,aVF— and positive in leads aVR and V1 (as seen by the YELLOW arrows in ECG #1).

  • PEARL #2: The fact the 4th sinus P wave in ECG #1, as shown in Figure-3 ( = the 4th RED arrow in the long lead rhythm strip) is completely on-time, and is followed by a wide beat that is preceded by a PR interval too short to conduct — proves that beat #4 is a PVC. (Since the PR interval before beat #4 is too short to conduct normally — this means that beat #4 must be coming at least in part, from below the AV Node).

  • PEARL #3: QRS morphology of wide beats #5-thru-17 is very similar to QRS morphology of beat #4. This strongly suggests that despite the irregularity of beats #4-thru-17 — this represents a run of irregular VT.

  • PEARL #4: Beat #4 is a fusion beat. As noted in PEARL #3 — QRS morphology of beat #4 looks very similar (but is not identical) to QRS morphology of beats #5-17 (ie, The R wave of beat #4 is slightly shorter than the R wave of each of the 13 wide beats that follow it). To prove “fusion” — there should be a logical reason for a beat to manifest an intermediate morphology between sinus-conducted beats and pure ventricular beats — and this logical reason is present in ECG #1 — because the on-time 4th RED arrow sinus P wave (that is seen just before beat #4) has no more than a very brief moment of time to conduct to the ventricles before ventricular beat #4 arises. (For more on fusion beats — See ECG Blog #128 and Blog #129).  
  • KEY Clinical Point: The finding of a fusion beat — provides further support that not only is beat #4 in ECG #1 at least in part of ventricular etiology — but also, that each of the wide beats that look like beat #4 ( = beats #5-17) are also of ventricular etiology, such that we have proven that beats #4-thru-17 represent a run of irregular VT! (See ECG Blog #133).

PEARL #5: One of the main reasons I chose today’s case is to emphasize that although monomorphic VT is usually a regular rhythm — it is not always a regular rhythm (See the ECG Media Pearl in today’s ADDENDUM below)
  • Most of the time when monomorphic VT is not regular — the amount of “irregularity” is minimal. That said — Today’s case represents an example in which we know the rhythm is VT despite the marked irregularity that we see in ECG #1.

  • The reason most monomorphic VT manifests a regular (or at least almost regular) R-R interval — is that this rhythm is most often the result of a stable reentrant circuitThere may be a brief "warm-up" or "cool-down" period until a regular R-R interval is established (in which case there is gradual acceleration or deceleration of the rate — either at the beginning or the end of an otherwise regular run of VT).
  • The above said — On occasion, there may be focal triggered activity that results in the marked irregularity of the monomorphic VT seen in ECG #1 (Zhang et al — Circulation 139:1750-1752, 2019). 

  • P.S.: The reason for specifying the monomorphic form of VT as the VT rhythm that is usually regular — is that by definition, PMVT (PolyMorphic Ventricular Tachycardia) is a very irregular VT rhythm that quickly leads to hemodynamic instability (See ECG Blog #231).


Regarding ECG #2 in Figure-3:
  • As noted earlier — the bottom tracing in Figure-3 was recorded shortly before ECG #1. What additional information is provided by ECG #2 — that was not evident in ECG #1?

In addition to further confirmation that the wide beats in today’s 2 tracings are ventricular in etiology — ECG #2 provides insight to the potential cause of the today’s VT rhythm.
  • In Figure-3 — Beats #1,28, 10 and 15 in ECG #2 are PVCs, with beats #1 and 2 forming a ventricular couplet ( = 2 PVCs in a row). We know these 5 wide beats are all of ventricular etiology — because the underlying atrial rhythm continues throughout this tracing despite these wide beats (ie, the 2 PINK arrow P waves slightly deform the initial upslope of the R wave of beats #8 and 10 — therefore with a PR interval too short to conduct. The 3 WHITE arrow P waves are contained within the QRS of wide beats #1,2,15 — thereby making it impossible for these P waves to conduct).

 12 leads are better than one! 

  • Although we see no evidence that WHITE arrow P waves are hidden within the wide QRS beats #1,2 and 15 in the long lead rhythm strip of ECG #2 — We do see a precisely on-time positive notch in lead V6 (2nd RED arrow in this lead). This confirms that regular P waves do continue throughout today's rhythm. 
  • The above observation illustrates the concept of how use of simultaneous leads can provide insight not forthcoming from a single lead (in this case — looking for evidence of atrial activity not only in the long lead rhythm strip — but also in simultaneously-recorded leads V4,V5,V6).

 Most of the time, assessment of ST-T wave morphology of ventricular beats will not be a reliable indicator of a recent or acute event. As a result — We are only able to reliably assess ST-T wave morphology for acute changes in leads I,II,III of ECG #1, because these are the only 3 leads in which we see ST-T waves for sinus-conducted beats. These 3 leads suggest left axis deviation consistent with LAHB (Left Anterior HemiBlock) for sinus-conducted beats #1,2,3 — with nonspecific ST-T wave flattening, but no acute changes.

  • In contrast to our inability to optimally assess ECG #1 for ischemic changes — the chest leads in ECG #2 clearly show suspicious changes for a recent acute event in sinus-conducted beats #11,12,13 (that manifest abnormal straightening of the ST segment takeoff in anterior leads V2,V3) — and — in sinus-conducted beats #14 and 16 (that show ST segment coving with symmetric T wave inversion in leads V4,V5,V6 — as well as a small amount of residual ST elevation in lead V4).

  • Clinical IMPRESSION: Given the minimal amount of ST elevation in the chest leads of ECG #2 — in association with symmetric T wave inversion in leads V4,V5,V6 — I suspect reperfusion T waves following recent LAD (Left Anterior Descending) coronary artery occlusion as the cause of the irregular VT and PVCs that we see in today’s 2 ECGs.


LADDERGRAM Illustration:
To facilitate appreciation of the mechanism of today’s arrhythmia — I’ve added laddergrams for ECG #1 and ECG #2 in Figure-4.
  • Following 3 sinus-conducted beats — beat #4 in ECG #1 (TOP laddergram) is a fusion beat ("F"), after which a run of irregular VT is seen ( = beats #5-thru-17). After a brief (post-ectopic) pause — sinus rhythm resumes with beat #18.
  • YELLOW arrows in ECG #1 represent retrograde P waves that are conducted back to the atria.
  • Note that I show the point of fusion for beat #4 at a relatively high point in the ventricles. Because QRS morphology of beat #4 closely resembles QRS morphology during the run of VT (with the main difference in morphology being slightly less R wave amplitude for the fusion beat) — the ventricular impulse contributing to beat #4 passes through most of the ventricles before encountering the sinus-conducted contribution to beat #4.

  • In ECG #2 (BOTTOM laddergrambeats #1,2; 8, 10 and 15 represent PVCs. These 5 ventricular impulses conduct only a short distance backward (ie, into the AV Nodal Tier) before encountering the downward directed sinus-conducted impulses that prevent retrograde conduction of these PVCs from reaching the atria.
Figure-4: Laddergram illustration for the 2 ECGs in today’s case.


Acknowledgment: My appreciation to Seung-Lyul Shin (from Incheon, South Korea) for the case and this tracing.




Related ECG Blog Posts to Today’s Case:

  • ECG Blog #185 — Reviews my System for Rhythm Interpretationusing thPs, Qs & 3R Approach.

  • ECG Blog #198Can VT be Irregular?
  • ECG Blog #403 (ECG Video) — Case of a regular WCT rhythm.

  • ECG Blog #128 and ECG Blog #129 — Reviews the concept of Fusion beats.
  • ECG Blog #393 — Case of multiple Fusion beats.
  • ECG Blog #133AV Dissociation, Fusion prove VT ...
  • ECG Blog #382 — Another case in which Fusion confirms PVCs.

  • ECG Blog #204 — Reviews the ECG diagnosis of the Bundle Branch Blocks (RBBB/LBBB/IVCD). 
  • ECG Blog #203 — Reviews ECG diagnosis of Axis and the Hemiblocks. For review of QRS morphology with the Bifascicular Blocks (RBBB/LAHB; RBBB/LPHB) — See the Video Pearl in this blog post.

  • ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).

  • ECG Blog #38 and Blog #85 — Review of Fascicular VT.
  • ECG Blog #278 — Another case of a regular WCT rhythm in a younger adult.
  • ECG Blog #35 — Review of RVOT VT.
  • ECG Blog #42 — Comprehensive review of criteria for distinguishing VT vs Aberration.

ADDENDUM (2/17/2024)

ECG Media PEARL #15 (5 minutes Audio) — Is Monomorphic VT a regular rhythm? — with attention to the 2 Caveats that emhasize how: i) Fast AFib may look regular; andii) Monomorphic VT is not always perfectly regular.


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