ECG Blog #475 — Aberrant SVT?

The ECG in Figure-1 was obtained from an older man with a history of coronary disease — who presented to the ED (Emergency Department) alert, but complaining of chest tightness since the previous night.

• The consulting cardiologist interpreted this tracing as SVT (SupraVentricular Tachycardia) with QRS widening due to aberrant conduction.

QUESTIONS:

• How would YOU intepret the ECG in Figure-1?
•   — Do you agree with the cardiologist?
•       — What would you do?

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

MY Thoughts on the ECG in Figure-1:

The rhythm in Figure-1 is a regular WCT (Wide-Complex Tachycardia) at ~210/minute — without clear sign of atrial activity.

• PEARL #1: I find it helpful at this point to consider statistics — with the fact that this patient is an older man with known coronary disease meaning that before we look closer at the ECG in Figure-1 — the statistical odds are at least 90% that this regular WCT will turn out to be VT.
• As a result, we need to assume VT until proven otherwise (and treat the patient accordingly). This means that the diagnosis of SVT with aberrant conduction has to be proven before being accepted. If aberrant conduction cannot be proven — then assume VT.
• 
  
• PEARL #2: The easiest way to rule out VT would be IF a prior ECG was available on this patient, in which QRS morphology during sinus rhythm was identical to the morphology of the wide QRS during the WCT rhythm. Realistically, it will not be often that such a baseline tracing will be found at the time that providers are at the bedside treating the patient. (Instead — it is much more common for a baseline tracing to only become available after acute treatment of the WCT rhythm). 

Factors in favor of VT:

Many diagnostic criteria have been described to facilitate distinction between VT vs SVT (that is, SVT with QRS widening from either rate-related aberrant conduction or preexisting bundle branch block). I've synthesized those criteria that I favor in the ADDENDUM below. With regard to the regular WCT in today's case:

• There is extreme Axis deviation (ie, The QRS complex is all negative in each of the inferior leads — as shown by the BLUE arrows in Figure-2). More than this — the QRS is also almost all negative in lead I, such that this is an extreme indeterminate Axis (BLUE arrow in lead I). Barring some form of severe underlying heart disease in which a baseline tracing in sinus rhythm shows identical QRS morphology — the frontal plane axis deviation seen in ECG #1 is almost always indicative of VT.
• The QRS is all negative in left-sided lead V6 — which almost always indicates a ventricular origin. Much more than this — QS complexes are seen in 4 consecutive chest leads (leads V3,V4,V5,V6). It's hard to imagine a scenario in which this finding will be seen in a supraventricular rhythm (RED arrows in leads V3-thru-V6).
• Very wide and deep Q waves (such as the RED arrow Q wave in lead V2) — are rarely seen in a supraventricular rhythm.
• The QRS is all positive in lead aVR (BLUE arrow in this lead). This implies that the electrical impulse must be beginning at the apex — which indicates a ventricular rhythm.
• 
  
• Conclusion: Any one of the above 4 bullets by itself would strongly suggest that this regular WCT is VT. The presence of all 4 of these findings to me overwhelmingly suggests (ie, with a 98-99% likelihood) that the rhythm in Figure-2 is VT.
• 
  
• Note #1: Many observers would call attention to the predominantly positive QRS complex in lead V1, saying that this finding suggests RBBB aberration. As illustrated in Figure-7 of the Addendum below — QRS morphology in lead V1 is predictive of a supraventricular etiology only if a triphasic rsR' complex is present, in which the s wave descends below the baseline, and there is a taller, terminal "right rabbit ear". At best — there is only a 2-phasic complex (qR) in lead V1 — which means that QRS morphology in lead V1 is simply not predictive.
• Note #2: Although difficult to tell because of the presence of baseline artifact — there appears to be fragmentation in multiple leads of Figure-2 (best seen in the notched S wave in lead V3 — but also seen in the inferior leads and in V4,V5. While not diagnostic — the presence of fragmentation suggests there is "scaring", which predisposes to the substrate for the origin of ventricular rhythms.

 

Figure-2: I've labeled today's initial ECG.

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The CASE Continues:

It turns out that today's patient was hypotensive at the time he presented to the ED with the rhythm shown in Figure-2. As a result — synchronized cardioversion with 100J was promptly administered with resumption of sinus rhythm.

• Several Troponin values were normal.
• 20 minutes later — the ECG was repeated (See Figure-3).

Figure-3: Comparison between the WCT — and the repeat 12-lead after synchronized cardioversion.

MY Thoughts on Figure-3:

The ECG recorded ~20 minutes after synchronized cardioversion shows return to sinus rhythm (with upright P waves in each of the inferior leads).

• QRS amplitude (especially in the limb leads) — is markedly reduced in ECG #2. This may be a sign of cardiac "stunning" following an MI or cardiac arrest (See ECG Blog #272 — for more on Causes of Low Voltage).
• The presence of significant baseline artifact complicates interpretation of ECG #2. That said, while similarities exist in QRS morphology between ECG #1 and ECG #2 — the post-cardioversion frontal plane axis is no longer indeterminate — and the predominant R wave in lead V1 is no longer present. 
• ST segment coving with terminal T wave inversion is seen in the inferior and lateral chest leads of ECG #2.

Impression: While not definitive — I thought the post-cardioversion ECG was different enough with respect to QRS morphology to support our diagnosis of sustained VT for the WCT rhythm.

• T wave inversion as seen in ECG #2 is not uncommon following a sustained tachyarrhythmia (sometimes called a "Memory Effect" — or "post-tachycardia" syndrome). In most cases when not due to a new infarction — this post-tachycardia T wave inversion resolves over the ensuing hours (and almost alwlays within 1-2 days).
• The normal Troponin values are reassuring that the cause of this VT episode was not an acute MI.

The Final ECG:

The patient stabilized. Review of his medical chart revealed a recent 12-lead ECG that had been done ~2 weeks earlier (See Figure-4).

• How would you interpret this recent ECG?

Figure-4: A recent ECG done ~2 weeks earlier.

MY Thoughts on the ECG in Figure-4:

Unfortunately — I do not know details of the circumstances surrounding the recent ECG in Figure-4 that was found in this patient's chart. That said:

• Baseline artifact with markedly reduced limb lead voltage is present in ECG #3 — so this is not a new finding.
• Also previously present is poor R wave progression with reduced voltage in the chest leads.
• What is different in this earlier tracing, compared to ECG #2 that was recorded after cardioversion out of the WCT rhythm — is diffuse ST segment coving with deeper T wave inversion across more of the chest leads.

Impression: I interpreted these different findings in ECG #3 — as consistent with reperfusion T waves resulting from a recent MI (that perhaps had occurred 2-to-3 weeks earlier). Thus — ongoing ischemia could have served as the substrate that precipitated the sustained episode of VT discussed in today's case.

• If not recently done — cardiac cath would seem to be indicated.

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Acknowledgment: My appreciation to Chun-Hung Chen = 陳俊宏 (from Taichung City, Taiwan) for the case and this tracing.

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Additional Relevant ECG Blog Posts to Today’s Case:

• ECG Blog #185 — Reviews my System for Rhythm Interpretation — with use of 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. 
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• ECG Blog #220 — Review of the approach to the regular WCT ( = Wide-Complex Tachycardia).
• ECG Blog #196 — Another Case with a regular WCT.
• ECG Blog #263 and Blog #283 — Blog #361 — Blog #384 — and Blog #460 — and Blog #468 — More WCT Rhythms ...
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• ECG Blog #197 — Reviews the concept of Idiopathic VT, of which Fascicular VT is one of the 2 most common types. 
• ECG Blog #346 — Reviews a case of LVOT VT (a less common idiopathic form of VT).
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• 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.
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• ECG Blog #211 — WHY does Aberrant Conduction occur?
• ECG Blog #301 — Reviews a WCT that is SupraVentricular! (with LOTS on Aberrant Conduction).
• ECG Blog #445 and Blog #361 — Another regular WCT rhythm ...
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• 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 — Criteria to distinguish VT vs Aberration.
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• ECG Blog #133 and ECG Blog #151— for examples in which AV dissociation confirmed the diagnosis of VT.
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• Working through a case of a regular WCT Rhythm in this 80-something woman — See My Comment in the May 5, 2020 post on Dr. Smith’s ECG Blog. 
• Another case of a regular WCT Rhythm in a 60-something woman — See My Comment at the bottom of the page in the April 15, 2020 post on Dr. Smith’s ECG Blog. 
• A series of 3 challenging tracings with QRS widening (See My Comment at the bottom of the page in the March 6, 2025 post on Dr. Smith's ECG Blog).
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• Review of the Idiopathic VTs (ie, Fascicular VT; RVOT and LVOT VT) — See My Comment at the bottom of the page in the September 7, 2020 post on Dr. Smith’s ECG Blog.
• Review of a different kind of VT (Pleomorphic VT) — See My Comment in the June 1, 2020 post on Dr. Smith’s ECG Blog.

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ADDENDUM (3/29/2025):

• I've reproduced below from ECG Blog #361 — a number of helpful figures and my Audio Pearl on assessment of the regular WCT rhythm.

Figure-5 : My LIST #1 = Causes of a Regular WCT (Wide-Complex Tachycardia) of uncertain Etiology (ie, when there is no clear sign of sinus P waves).

Figure-6 Use of the "3-Simple Rules" for distinction between SVT vs VT.

Figure-7: Use of Lead V1 for assessing QRS morphology during a WCT rhythm.

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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.

ECG Media PEARL #28 (4:45 minutes Video) — Reviews WHY some early beats and some SVT rhythms are conducted with Aberration (and why the most common form of aberrant conduction manifests RBBB morphology).

• CLICK HERE — to download a PDF of this 6-page file on Aberrant Conduction.