Wednesday, November 23, 2022

ECG Blog #346 — Recurrent Palpitations

The ECG in Figure-1 — was obtained from a young woman with a history of recurrent palpitations over several years. She was hemodynamically stable at the time this tracing was recorded. ECGs, Echo and Holter monitoring on previous admissions had been normal.
  • What is YOUR differential diagnosis of the rhythm? 
  • What treatment is indicated?

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:
The "good news" regarding today's case — is that this young adult woman with a history of presumably similar prior episodes — was hemodynamically stable at the time the ECG in Figure-1 was recorded.
  • By definition — the fact that this patient was hemodynamically stable in association with the rhythm in Figure-1 means — that there was at least some time to contemplate the rhythm and formulate a plan for optimal management. Despite the fast rate in today's case — immediate cardioversion is not necessarily needed since the patient is stable!

  • To Emphasize: While true that many patients in sustained VT promptly deteriorate — others do not. I'm aware of many cases of sustained VT in which the patient remained awake, alert and hemodynamically stable for hours (and even days!). 
  • BOTTOM Line: As long as you are right there at the bedside (ready to cardiovert at any moment should the patient deteriorate) — an initial trial of antiarrhythmic therapy is reasonable for a patient who remains hemodynamically stable despite sustained VT.

WHAT THEN is the Rhythm in Figure-1?
As always, once establishing that the patient in front of you is hemodynamically stable — I favor assessment of the rhythm by the Ps, Qs, 3R Approach (See ECG Blog #185):
  • The rhythm in ECG #1 is fast and Regular. I estimate the Rate to be ~200/minute.
  • I see no sign of atrial activity (ie, No P waves)
  • The QRS complex during the tachycardia is wide (I measure ≥0.12 second = 3 little boxes in duration).

IMPRESSION: The above parameters define the rhythm in Figure-1 as a regular WCT ( = Wide-Complex Tachycardia) at ~200/minute, without clear sign of atrial activity.
  • As emphasized in many of my prior ECG Blogs (especially in ECG Blog #220) — the finding of a regular WCT rhythm without clear sign of atrial activity should always be assumed to be VT until proven otherwise (Statistical odds that a regular WCT rhythm without sinus P waves is VT — are ~80% in a previously healthy younger adult — and attain ~90% when the patient is older and has underlying heart disease).

PEARL #1: 80-to-90% is not 100%! Although we need to assume VT for any regular WCT rhythm without P waves until proven otherwise — sometimes the rhythm will be supraventricular!
  • Assessment of QRS morphology helps greatly to narrow down the likelihood that a given WCT rhythm is either VT or an SVT (SupraVentricular Tachycardia) with preexisting BBB (Bundle Branch Block) or aberrant conduction (See ECG Blog #196 for details).

  • As emphasized in ECG Blog #211 — The chances of a WCT rhythm being supraventricular increase significantly IF — QRS morphology is consistent with one of the known forms of conduction block (ie, RBBB; LBBB; LAHB or LPHB; or RBBB with one of the hemiblocks).

Take another LOOK at the ECG in Figure-1:
  • Does QRS morphology look like LBBB conduction?
  • Is the rhythm in this tracing VT? — or — Is this SVT with LBBB conduction?

Figure-2: Take another LOOK at the ECG in today's case!

Is there Typical LBBB Morphology in ECG #1?
As emphasized in ECG Blog #204 — the 3 KEY leads for the ECG diagnosis of the bundle branch blocks are right-sided lead V1 — and left-sided leads I and V6.
  • Assessment of these 3 KEY leads during the WCT rhythm in today's case is consistent with LBBB morphology — because we do see an all upright QRS in lateral leads I and V6 — and the QRS is predominantly negative in right-sided lead V1.

PEARL #2: The reason I favor focusing on leads I, V1, V6 — is that doing so allows rapid recognition of typical BBB morphology in a matter of seconds. However, when applying this concept to assessment of QRS morphology during a regular WCT rhythm — I look for a number of additional ECG findings that render QRS morphology during the WCT to be either more or less likely the result of VT.

  • When assessing for LBBB Morphology: VT becomes more likely if one or more of the following atypical ECG findings are seen during the WCT: i) If the QRS complex is not all upright in both high-lateral leads (ie, not only in lead I — but also in lead aVL); ii) If the QRS complex is not predominantly negative in at least the first 4 chest leads (ie, not only in V1,V2 — but also in V3,V4); and, iii) If there are unexpected Q waves in lateral and/or in anterior leads — especially if these initial unexpected Q waves are wide.

  • When assessing for RBBB Morphology: SVT becomes more likely if QRS morphology is completely typical for this conduction defect — which means: i) There is a completely typical rsR' complex in lead V1 (ie, with an s wave that descends below the baseline — and a taller right "rabbit ear" R' wave)andii) There are upright R waves with wide terminal S waves in lateral leads I and V6.

We have previously shown cases for the diagnostic dilemma that arises when QRS morphology of a WCT resembles RBBB conduction (See ECG Blog #323ECG Blog #38and ECG Blog #85). In contrast — today's case highlights the dilemma when QRS morphology for a regular WCT resembles LBBB conduction.
  • To Emphasize: None of the "rules" for assessing QRS morphology during regular WCT rhythm are perfect. Exceptions always exist. For example — QRS morphology may be dramatically altered in a "baseline" ECG in patients who have significant underlying heart disease. In such cases — QRS morphology will not resemble a "typical" conduction defect when heart rate increases.
  • PEARL #3: When possible — Try to find a prior ECG on the patient! Doing so will occasionally allow you to make a definitive diagnosis of a supraventricular rhythm IF — QRS morphology on the baseline ECG is identical to QRS morphology during the WCT. Then after successful treatment — Be sure to obtain a post-conversion 12-lead ECG for comparison purposes.

Returning to Today's CASE:
Although the ECG in Figure-2 superficially resembles LBBB conduction — there are some atypical features. As noted above in PEARL #2:
  • Although the QRS complex in lead V6 is perfectly consistent with LBBB conduction (because the QRS is tall and all upright in this lead) — the QRS in lead I is of much smaller amplitude (and the QRS is barely positive in several of the complexes in lead I). In lead aVLthe QRS is all negative! Therefore — QRS morphology in leads I and aVL is not typical for LBBB conduction.

  • In the chest leads — the QRS is predominantly negative (as it should be with LBBB conduction) in leads V1 and V2. However, the QRS abruptly becomes all positive beginning in lead V3 — which is clearly much earlier that expected with LBBB conduction!

  • Putting It All Together: As emphasized above — Statistical odds that a regular WCT rhythm without clear sign of sinus P waves will turn out to be VT are ~80-90% even before you look at the ECG. Thus, we begin from the premise that the regular WCT in today's case should be assumed  VT until proven otherwise. Add to this the 2 atypical features for LBBB conduction described above — and statistical odds that the rhythm in Figure-2 is VT are over 90%!

  • PEARL #4: In view of the fact that the patient in today's case is a younger adult without underlying heart disease (ie, normal Echo on prior admissions) — the rhythm most probably is Idiopathic VT. As summarized in the ADDENDUM below — approximately 10% of patients who present with VT do not have ischemic or underlying structural heart disease. Short- and longterm treatment (as well as prognosis) of such patients differs greatly compared to that for the ~90% of patients with ischemic or structural forms of VT.

  • As discussed in Figure-3 — QRS morphology for the VT rhythm in today's case manifests a LBBB pattern in the chest leads (ie, with predominant negativity in V1,V2 — and a completely positive QRS in lateral chest leads) — but with a vertical (inferior) axis in the frontal plane (ie, marked QRS positivity in the inferior leads compared to lead I). This suggests the OT (Outflow Track) form of VT. Early transition to an all positive QRS already by lead V3 in the chest leads suggests LVOT (Left Ventricular Outflow Track) VT

  • With Respect to Treatment: Regardless of whether today's rhythm is RVOT VT or LVOT VT — both of these forms of idiopathic VT tend to be "Adenosine-responsive". Adenosine would therefore be my initial drug of choice for treatment of today's patient in the ED.


Acknowledgment: My appreciation to Mubarak Al-Hatemi (from Qatar) for the case and this tracing.





ADDENDUM (11/23/2022):

  • KEY features of Idiopathic VT are summarized in Figure-3.

Figure-3: Review of KEY features regarding Idiopathic VT (See text).

ECG Media PEARL #14 (8 minutes Audio) — What is Idiopathic VT?WHY do we care? Special attention to the 2 most common forms = RVOT (Right Ventricular Outflow Track) Vand Fascicular VT.  



Additional Relevant ECG Blog Posts to Today’s Case:

  • ECG Blog #185 — Reviews my System for Rhythm Interpretationusing 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 #220 — Review of the approach to the Regular WCT (Wide-Complex Tachycardia).
  • ECG Blog #196 — Reviews another Case with a Regular WCT Rhythm. 

  • 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 #211 — WHY does Aberrant Conduction occur?

  • ECG Blog #197 — Review of Fascicular VT.
  • ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).

  • ECG Blog #323 — Review of Fascicular VT.
  • 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.


  1. Replies
    1. Close — but not quite. Unlikely to be RVOT VT because transition in the chest leads occurs EARLY (between V2-to-V3). Please take a look at Figure-3 in the Addendum — in which I discuss the more common types of idiopathic VT — :)