Friday, April 23, 2021

ECG Blog #217 (ECG MP-34) — Is this VT on this Holter?

The 2-lead rhythm strip shown in Figure-1 was obtained from the Holter monitor of a middle-aged adult.

  • Does this tracing show a 4-beat run of VT or aberrant conduction?
  • How certain are YOU of your diagnosis?


Figure-1: A simultaneously-recorded 2-lead rhythm strip, obtained during Holter monitoring. Does this tracing show a 4-beat run of VT or aberrant conduction?





NOTE #1: Some readers may prefer at this point to listen to the 6:00 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-34).


Today's ECG Media PEARL #34 (6:00 minutes Audio) — Are YOU really seeing AV Dissociation in that WCT Rhythm? (ie, Is the rhythm VT?).




MY Thoughts regarding the Rhythm in Figure-1:

The underlying rhythm in this 2-lead Holter tracing is sinus — as indicated by normal-appearing upright P waves with a fixed PR interval preceding each of the narrow beats (RED arrows in Figure-2).

  • After the first 2 sinus beats — the rhythm is interrupted by a 4-beat run showing a very different QRS morphology (ie, beats #3-thru-6).
  • Sinus rhythm resumes with beat #7 for the last 3 beats in the tracing.


Figure-2: I’ve labeled atrial activity from Figure-1 (See text).

What is the Cause of the 4-Beat Run?

I am 100% certain that the 4 different-looking beats that are seen in Figure-2 constitute a short run of NSVT ( = Non-Sustained Ventricular Tachycardia). My reasons for saying this are the following:

  • Statistically ( = according to the literature) — When the underlying rhythm is sinus, sudden occurrence of a wide run of different-looking beats (as we see in Figure-2) will turn out to be VT at least 80% (if not 90%) of the time. Therefore — Always assume VT until proven otherwise (ie, Our “mindset” should be that we need to prove aberrant conduction — rather than the other way around).
  • There is no reason for aberrant conduction to occur in Figure-2. Aberrant conduction of supraventricular beats is most often seen when the run of wide beats occurs early in the cycle (ie, when the coupling interval is short) — because this increases the chance that the run will begin during the RRP (Relative Refractory Period). But in Figure-2 — the first wide beat ( = beat #3) occurs late in the cycle, at a time when it is very unlikely that the conduction system will still be refractory. Thus, there is no “reason” for aberrant conduction(NOTEFor more on WHY certain supraventricular beats conduct with aberration — Please see ECG Blog #211).
  • QRS morphology for the different-looking beats shows marked QRS widening and a totally different appearance. Supraventricular beats that conduct with aberration often manifest a similar initial direction and slope of the QRS complex — because supraventricular beats often initially conduct down the normal AV nodal pathway until they encounter that part of the conduction system that is refractory. But, as opposed to the rapid R wave upslope that we see for sinus beats in both lead A and lead B of Figure-2 — beats #3-thru-6 show a marked difference in the very initial part of the QRS complex.
  • I am uncertain which specific leads rhythms A and B in Figure-2 correspond to. The most common leads monitored are a standard lead II — and either a right- or left-sided lead (corresponding to lead V1 or MCL-1  or — lead V5 or V6 or MCL-6). Knowing the specific lead(s) used in monitoring helps — because aberrant conduction is much more likely when QRS morphology is consistent with some type of conduction defect (ie, RBBB, LBBB, LAHB, LPHB, or some combination thereof). 
  • I suspect rhythm A corresponds to a lead II recording — in which case the excessively wide initial R wave and terminal S wave fragmentation are not characteristic of LAHB conduction. And, regardless of the lead that rhythm B corresponds to — QRS morphology would not be typical for any known form of conduction defect. Thus, QRS morphology in Figure-2 is atypical for any of the common forms of conduction defects — and, this is another factor against aberrant conduction. (NOTE: This atypical QRS morphology by itself does not rule out the possibility of aberrant conduction — but it does make aberrant conduction less likely).
  • Most Convincingly: There is AV Dissociation in Figure-2! This is subtle — but it is present (PINK arrows). Calipers are needed to find this! — but the notching that is highlighted by PINK arrows in rhythm A — corresponds perfectly to subtle notching that is also seen in rhythm B (as shown by the vertical BLUE timelines) — and — these PINK arrows occur with a P-P interval that is perfectly consistent with the slight underlying sinus arrhythmia. Demonstration that sinus P waves continue on-time throughout the rhythm strip in both leads A and B confirms that there are independent atrial and ventricular rhythms. This constitutes AV dissociation (ie, P waves that transiently are not related to neighboring QRS complexes) — and identification of AV dissociation proves that beats #3-thru-6 constitute a 4-beat run of NSVT.

P.S. — Some Definitions:

  • There are many different names for early-occurring ventricular beats. I favor the term PVC (Premature Ventricular Contraction).
  • 2 PVCs in a row are called a ventricular Couplet.
  • 3 PVCs in a row are called a ventricular Salvo or a “Triplet”. 
  • The definition of “VT” (Ventricular Tachycardia) — is 3 or more PVCs in a row. 


KEY Point: Rather than simply noting the presence of “VT” — it is important to describe the rhythm by a number of KEY parameters. These include: 

  • Duration of the VT run (ie, How many beats or for what period of time does the VT last?)
  • Rate of the VT? 
  • Regularity of the wide rhythm? (ie, Not all VT is regular — as seen for the 4-beat run in today’s case).
  • QRS Morphology? (ie, Do all VT beats look the same — or is there changing morphology?).
  • What happened just before? — and immediately after the VT episode? (ie, Was the patient in sinus rhythm or AFib before VT began? Was there a “post-ectopic” pause after the run terminated?)
  • Are there recurrent episodes of the VT rhythm? 
  • Has there been antiarrhythmic treatment?
  • Importantly: What is the patient's hemodynamic status during the VT episode? (ie, Is the patient symptomatic? Hemodynamically stable or unstable?)


Some Final Terms:

  • NSVT (Non-Sustained VT) —  The occurrence of 3 or more PVCs in a row up until the point when VT becomes “sustained”.
  • Sustained VT — Definitions for what constitutes “sustained” VT vary, depending on duration of the VT episode and/or the number of beats in the run. Most authorities reserve designation as “sustained” VT for runs lasting at least 30 seconds and/or VT that causes hemodynamic instability. 
  • Editorial Comment: My Simplified Definition  IF the run of VT is long enough to give YOU palpitations, then it is probably “sustained” VT.

  • “Slow” vs “Fast” VT — This gets into the definition of whether the VT rhythm is more likely to be associated with hemodynamic consequences or not. In general — AIVR ( = Accelerated IdioVentricular Rhythm or slow” VT) will often be surprisingly well tolerated — whereas fast VT (usually associated with a ventricular rate of at least 130/minute) is much more likely to be associated with hemodynamic consequences. 
  • NOTE: For more on AIVR and “slow” vs “fast” VT — Please check out ECG Blog #108.



In SUMMARY regarding Today’s Case:

  • The rhythm in Figure-1 shows an underlying sinus arrhythmia that is interrupted by a 4-beat run of an irregular NSVT at ~110-130/minute.




Acknowledgment: My appreciation to Zineddine Chleghoum (from Alger, Algeria) for the case and this tracing.



Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #211 — WHY does Aberrant Conduction occur? 
  • ECG Blog #133 — Illustrates use of Fusion beats and AV Dissociation in the diagnosis of VT.
  • ECG Blog #128 — Reviews the concept of Fusion Beats.
  • ECG Blog #129 — Late-cycle (End-diastolic) AIVR and Fusion beats in diagnosis of ventricular beats. 
  • ECG Blog #134 — A very subtle example of AV Dissociation to prove VT.
  • ECG Blog #108 — About AIVR — and review of why retrograde P waves with 1:1 VA conduction do not constitute AV “dissociation”.

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