Saturday, February 12, 2022

ECG Blog #283 — VT or SVT with Aberrancy?

The ECG in Figure-1 was sent to me with the following question: VT or SVT with Aberrancy? 

  • How would you answer?
  • How certain are you of your answer?

Figure-1: Is the rhythm VT or SVT with Aberrancy? 

My THOUGHTS regarding the ECG in Figure-1:

My initial impression of the ECG in Figure-1 (formed within the first 2-3 seconds of seeing this tracing) — is that the rhythm is very fast, and that the QRS is obviously wide.

  • Clinically — The 1st priority in assessing this patient would be to determine hemodynamic status. This is because IF this patient was hemodynamically unstable with this ECG — then regardless of what the rhythm happens to be — synchronized cardioversion becomes immediately indicated!

For the purpose of reviewing my diagnostic approach to rhythm interpretation — Let’s work on the assumption that the patient is hemodynamically stable. My thought process for assessing this rhythm (using the Ps, Qs, 3R Approach) — was the following:

  • The rhythm in Figure-1 is fast and Regular.
  • By the Every-other-Beat Method (See ECG Blog #210) — the ventricular Rate of the rhythm is ~180-190/minute (ie, The R-R interval of every-other-beat [BLUE numbers in lead I of Figure-2] is just over 3 large boxes [RED numbers] — therefore Half the rate = 300 ÷ 3.2 ~90-95/minute X 2 ~180-190/minute for the estimated heart rate).
  • Sinus P waves are absent (since there is no clearly upright conducting P wave in lead II).
  • The QRS is obviously Wide (ie, Looking at those leads in which the QRS looks widest — there should be no doubt that QRS duration in leads like aVR and V1 is at the least, longer than 3 little boxes in duration = more than 0.12 second).

Putting It All Together:
Assessment of the first 4 parameters in the Ps, Qs, 3R Approach tells us that this hemodynamically stable patient is in a regular WCT ( = Wide-Complex Tachycardia) at ~180-190/minute, without clear sign of sinus P waves.
  • As emphasized in the supplementary material of the ADDENDUM below — the differential diagnosis of a regular WCT rhythm of uncertain etiology should be assumed to be VT (Ventricular Tachycardia)until proven otherwise. This is because statistically — at least 80-90% of all such rhythms will turn out to be VT even before you get to analyze specific findings in the ECG.

  • PEARL #1: Because of this high statistical likelihood that a regular WCT rhythm without sinus P waves will turn out to be VT — Our "mindset" should be that we need to prove that the rhythm is not VT, rather than the other way around. This KEY point is often forgotten by all-too-many emergency providers.

  • As suggested in Figure-4 (below in the Addendum) — the remaining 10-20% of regular WCT rhythms will be divided into: i) An SVT (SupraVentricular Tachycardia) rhythm with either preexisting BBB or aberrant conduction, as the reason for QRS widening; or, ii) Something else! (ie, WPW, hyperkalemia, and/or some form of toxicity).

Figure-2: I've labeled Figure-1 to facilitate calculation of Rate — and to highlight retrograde atrial activity (See text).

Use of Axis and QRS Morphology:
We can often increase our degree of certainty about the etiology of a regular WCT rhythm by attention to: i) The frontal plane Axis during the tachycardia; and, ii) Assessment of QRS Morphology (See Figure-5 and Figure-6 below in the Addendum):
  • PEARL #2: Assessing frontal plane Axis during a regular WCT rhythm is EASY to do and, may be diagnostic. IF there is "extreme" Axis deviation (as determined by the finding of an all negative QRS in either lead I or in lead aVF— this strongly suggests that the rhythm is VT. 
  • Note in Figure-2 — that the QRS complex is entirely negative in each of the 3 inferior leads during the tachycardia. This degree of extreme axis deviation increase statistical likelihood of VT to over 90%!
  • To Emphasize It does not count if you have marked left or right axis deviation (ie, with a small initial r wave in either lead aVF or in lead I). The above Axis criterion is only helpful diagnostically IF there is "extreme" Axis deviation (as defined by an entirely negative QRS in either lead I or in lead aVF).

  • PEARL #3: In general — aberrant conduction is most likely to resemble some form of conduction defect (of either bundle branch block and/or a hemiblock pattern). In contrast — VT is more likely to manifest a less well defined QRS morphology that looks different from known forms of conduction block (this concept discussed in more detail in ECG Blog #211). Exceptions exist (!) — but appreciation of this general concept goes a long way toward understanding what to look for when assessing a 12-lead tracing obtained during a regular WCT rhythm.
  • Note in Figure-2 — that QRS morphology during the tachycardia is not typical for any known form of conduction defect: i) The upright QRS in lead V1 rules out LBBB conduction; iiLack of any R wave at all in the inferior leads is against LAHB conduction; iii) QRS morphology in leads I, II and III looks nothing like LPHB conduction; and, iv) Although the upright QRS in lead V1 might be consistent with RBBB in a patient with underlying heart disease — as suggested below (in Figure-6 of the Addendum) — QRS morphology in lead V1 if anything, is more consistent with VT. In addition — the lack of any S wave in lead aVL, and the all negative (QS) complexes in leads V3-thru-V6 are not consistent with what we'd expect with RBBB conduction.

  • PEARL #4: The last 2 of the 3 "Simple" Rules suggested in Figure-5 of the Addendum — further support even greater likelihood that the rhythm in Figure-2 is VT because: i) The QRS complex in lead V6 is all negative (which suggests an origin of the rhythm in the ventricular apex — which essentially defines the rhythm as VT); and, ii) QRS morphology is "ugly", therefore much more likely to be originating from outside of the conduction system.

  • BOTTOM LINE: Considering ECG features in the above 3 Pearls — statistical likelihood that the regular WCT rhythm shown in Figure-2 is VT are well over 95%!

Are there Retrograde P-Waves?
The last component in the 5-parameter Ps, Qs, 3R Approach is more difficult to ascertain in today's tracing. This is the 3rd "R" — which is to determine IF there is any atrial activity that might be Related to neighboring QRS complexes.

  • I believe there is atrial activity in today's tracing — in the form of retrograde P-waves that are seen after every-other QRS complex (slanted RED lines in Figure-2).
  • Note that the R-P' interval is constant ( = the distance from the preceding QRS — to the negative notch present in each of the inferior leads, as well as in leads V3 and V6). The fact that this negative notch reliably appears every-other beat — but is definitely not present for beats in between — confirms that this 2:1 VA (ie, retrograde) conduction is real!

PEARL #5: There seems to be a common belief that the presence of retrograde P waves in a regular WCT rhythm favors a supraventricular etiology for the rhythm. This is not so!
  • It is true that identification of AV dissociation during a regular WCT rhythm confirms that the rhythm is VT (See ECG Blog #133 and Blog #151 for examples of this).
  • That said — identification of 1:1 VA (retrograde) conduction during a regular WCT rhythm confirms nothing, because both VT and reentry SVT rhythms may manifest 1:1 retrograde conduction.

Advanced Point = PEARL #6: This case is different! The ECG in Figure-2 shows retrograde conduction — but not after every beat. Instead, retrograde conduction manifests 2-to-1 VA block (ie, only every-other ventricular beat is followed by a retrograde P wave — as shown by the slanted RED lines in Figure-2).
  • Beyond-the-Core: You will not often see a regular WCT rhythm with retrograde conduction and VA block! If ever you do (as we see in Figure-2) — this does provide some diagnostic information. This is because neither ATach (Atrial Tachycardia) nor AVRT (with participation of an accessory pathway) are able to sustain tachycardia when there are fewer P waves than QRS complexes (ie, when there is VA block). Instead — both of these rhythms are dependent on atrial participation (atrial activation) to sustain the tachycardia.
  • Identification of retrograde VA block therefore narrows down the differential diagnosis of a regular WCT rhythm to VT vs QRS widening from BBB or aberrant conduction with a fast junctional tachycardia or with a reentry SVT rhythm such as AVNRT, in which the reentry circuit does not depend on atrial participation (because the reentry circuit is contained entirely within the AV Node).

The Post-Conversion Tracing:
Sometimes, definitive diagnosis of a regular WCT rhythm will not be possible during the tachycardia. However, in some of these cases — comparing the 12-lead ECG obtained during tachycardia with a follow-up ECG obtained after conversion to sinus rhythm may allow a definitive retrospective diagnosis of the WCT rhythm.

  • The patient in today's case was electrically cardioverted. The resultant rhythm is shown in the bottom Panel of Figure-3

  • What are YOUR thoughts on comparing the 2 tracings in Figure-3?

Figure-3: Comparison of the initial WCT rhythm (TOP tracing) — with the 12-lead ECG obtained after electrical cardioversion (BOTTOM tracing).


I reviewed the post-cardioversion ECG (ie, ECG #2 in Figure-3) — in the last ECG Blog that I published (This is the tracing presented in ECG Blog #282). The interpretation in Blog #282 was: Sinus rhythm with a PVC — QRS widening from LBBB (or IVCD, depending on your terminology) — marked LVH — QRS "fragmentation" in multiple leads — probable prior infarction — and nonspecific ST-T wave abnormalities that were probably not acute.

  • As was emphasized in ECG Blog #282 — the combined findings in ECG #2 of QRS "fragmentation" in multiple leads + the LBBB with abnormal Q waves in leads V4,V5 + the marked LVH, taken together strongly suggest severe underlying heart disease. This of itself — significantly increases statistical likelihood that the regular WCT rhythm in ECG #1 was VT.
  • QRS morphology during the WCT rhythm ( = ECG #1) looks very different in many leads from QRS morphology after conversion to sinus rhythm. While this doesn't prove that the WCT was VT — it does further increase the likelihood of VT.
  • Beat #11 in the post-conversion tracing is a PVC. If this PVC would have manifested identical QRS morphology as was seen during the WCT rhythm — then this would have proven VT. However, QRS morphology of this PVC in ECG #2 for simultaneously-recorded leads V1, V2, V3 and lead II is not the same as QRS morphology of the WCT rhythm. As a result — beat #11 in ECG #2 is of no help diagnostically.

BOTTOM LINE: Considering all of the information presented in today's case — I estimated a ~99% likelihood that the WCT rhythm was VT.


Acknowledgment: My appreciation to Abdullah Al Mamum (from Dhaka, Bangladesh) for allowing me to use this case and this tracing.



Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #185 — Reviews my System for Rhythm Interpretation, using the Ps, Qs & 3R Approach.

  • ECG Blog #210 — Reviews the Every-Other-Beat (or Every-Third-Beat) Method for estimation of fast heart rates — and discusses another case of a regular WCT rhythm.

  • ECG Blog #220Step-byStep assessment of a regular WCT Rhythm to distinguish between VT vs SVT with preexisting BBB or aberrant conduction.

  • ECG Blog #196 — Reviews another Case with a Regular WCT Rhythm. 
  • ECG Blog #197 — Reviews the concept of Idiopathic VT, of which Fascicular VT is one of the 2 most common types. 
  • 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 ECG Media Pearl #21 in this blog post.
  • ECG Blog #211 — WHY does Aberrant Conduction occur?
  • ECG Blog #42 — Reviews additional QRS morphology features for distinguishing beteen VT vs SVT with preexisting BBB or aberrant conduction.
  • mmm
  • ECG Blog #133 and ECG Blog #151— for examples in which AV dissociation confirmed the diagnosis of VT.



ADDENDUM (2/10/2022):

I've reproduced below from ECG Blog #196 — a number of helpful figures and my Audio Pearl (ECG-MP-13a) on assessment of the regular WCT rhythm: VT vs SVT with either preexisting BBB or aberrant conduction: 


Figure-4 : This is my LIST #1: Causes of a Regular WCT (Wide-Complex Tachycardia) of Uncertain Etiology (ie, without clear sign of sinus P waves).

Figure-5: Use of the "3-Simple Rules" for distinction between SVT vs VT.

Figure-6: Use of Lead V1 for assessing QRS morphology during a WCT rhythm.


NOTE: The KEY concepts from today's case are summarized in this 13-minute ECG Audio Pearl (ECG MP-13a).


Today’s ECG Media PEARL #13a (12:20 minutes Audio) — reviews “My Take” on assessing the regular WCT (Wide-Complex Tachycardia), when sinus P waves are absent — with tips for distinguishing between VT vs SVT with either preexisting BBB or aberrant conduction.

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