ECG Blog #489 — Wide Tachycardia in a 20yo

The ECG in Figure-1 — was obtained from a previously healthy 20-ish year old woman with palpitations. She reports a number of prior episodes. The “good news” — is that she was hemodynamically stable in the ED (Emergency Department) at the time ECG #1 was recorded.

QUESTIONS:

• How would you interpret the ECG in Figure-1?
• How certain are you of your diagnosis?
• Did the fact that this patient was hemodynamically stable at the time this ECG was recorded influence your diagnosis?
• How would you treat this patient?

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NOTE: Feel free to skip down to the ANSWER below — or to work through my sequential approach with My Thoughts on Today's CASE:

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Figure-1: The initial ECG in today's case — obtained from a hemodynamically stable 20-ish year old woman with palpitations. (To improve visualization — I've digitized the original ECG using PMcardio).

My Thoughts on Today’s CASE:

Applying the Ps, Qs and 3Rs (See ECG Blog #185) — the rhythm in Figure-1 is fast (~180/minute) — regular — with a wide QRS — and without clear sign of atrial activity. This defines the rhythm as a regular WCT (Wide-Complex Tachycardia). As per the LINKS to other cases that are found at the bottom of this page — the principal differential diagnosis is between:

• VT (Ventricular Tachycardia) — or —
• SVT (SupraVentricular Tachycardia) with either of the following: i) Preexisting BBB (Bundle Branch Block); or ii) Aberrant conduction as a result of the rapid rate.

On rare occasions — "something else" (ie, hyperkalemia, sodium channel blocker toxicity — or other toxicity) may result in a regular WCT rhythm. That said — in a previously healthy young adult (as in today's case) — the main consideration is to distinguish between VT vs SVT with either preexisting BBB or rate-related aberrant conduction. 

KEY Points to consider include the following:

• Statistically, in an unselected adult population — at least 80% of regular WCT rhythms without sign of atrial activity will turn out to be VT. The likelihood of VT increases to ~90% if the patient is an older adult with underlying heart disease.
• These statistics do differ when the patient is a younger adult without underlying heart disease. It's important to appreciate that idiopathic VT is more common in this population than many providers realize — although the percentage of such patients who present with a regular WCT that turns out to be VT will be less than the 80% that is seen with older adults (See Figure-4 and the Audio PEARL in the ADDENDUM below for more on idiopathic VT).
• QRS morphology may allow for greater precision in predicting WCT etiology — especially IF ECG features predictive of either VT or SVT are present. That said, even in cases in which QRS morphology is suggestive — it is rare to attain 100% certainty prior to our need to begin treatment.
• PEARL #1: Much (most) of the time — we will need to begin treatment before we are certain of the diagnosis. Remember that if at any time during the process, the patient shows signs of becoming hemodynamically unstable — that synchronized cardioversion is immediately indicated. That said, in the absence of diagnostic certainty — empiric treatment based on our best hunch diagnosis is reasonable.
• PEARL #2: There are some ECG features that may allow for near-100% certainty in diagnosis. These include AV dissociation, capture and fusion beats. That said — these definitive ECG feaures will rarely be present with faster WCT rhythms, which are the most difficult ones to assess (Although I always look for these definitive ECG features — it is unlikely that we will find them in today's regular WCT at 180/minute). The failure to see AV dissociation, capture or fusion beats does not help diagnostically if none of these signs are seen (These ECG signs only help if present).
• PEARL #3: On occasion — Availability of a prior ECG may prove invaluable for ruling out VT by demonstrating an identical QRS morphology during sinus rhythm as was seen during the WCT rhythm. Unfortunately — it is rare that a prior ECG will be readily available at the time you are dealing with the WCT patient in front of you.
• PEARL #4: Hemodynamic stability during the WCT rhythm does not rule out VT. While true that patients with sustained VT are much more likely to decompensate than those who remain in a persistent SVT rhythm — these generalities do not always hold true. Some patients in sustained VT remain hemodynamically stable for hours — or even longer (with documentation of occasional cases of sustained VT having persisted for days — with providers around the bedside refusing to believe this to be possible). Therefore — hemodynamic stability can not be used to rule out VT.

What About Today's CASE?

As stated — today's patient is a previously healthy young adult with a history of "palpitations" — who presented to the ED hemodynamically stable in a regular WCT rhythm at 180/minute.

• Given this patient's young age and previously healthy status — ischemic VT is highly unlikely. But this patient could have idiopathic VT = the form of VT that is seen in ~10% of VT cases, in which VT occurs without any underlying heart disease (See Figure-4 in the Addendum below).
• As noted above — AV dissociation, capture and fusion beats are not seen (ie, There is no sign of atrial activity, so no AV dissociation — and — there is no "break" in the rhythm, so no capture or fusion beats).
• PEARL #5: Aberrant conduction most often presents as rate-related QRS widening that manifests a QRS morphology that resembles some form of known conduction defect (ie, either RBBB, LBBB, LAHB, LPHB, or RBBB with a hemiblock). This is because the refractory periods of the various conduction fascicles are not the same. In most patients — the refractory period of the right bundle branch tends to be the longest, which is why RBBB conduction is the most common form of rate-related aberrancy. But any conduction pattern may be possible with rate-related aberrancy (See ECG Blog #211 — for more on the WHY of aberrant conduction).
• PEARL #6: As discussed in Figure-4 — fascicular VT is one of the most common forms of idiopathic VT. Because of its origin near the left anterior or the left posterior hemifascicle — QRS morphology with fascicular VT resembles either RBBB/LAHB or RBBB/LPHB conduction. That said — my favorite clue that a WCT rhythm may turn out to be fascicular VT — is that there are some atypical ECG features of RBBB conduction!

Aberrant QRS Morphology in Lead V1:

Although exceptions exist — one would expect rate-related RBBB aberrancy to manifest a typical QRS morphology given that today's patient is an otherwise healthy young adult. In contrast — aberrant RBBB conduction in an older adult with underlying heart disease would be more likely to manifest a less typical QRS morphology (ie, "scar" from ischemic heart disease and/or cardiomyopathy being more likely to alter QRS morphology).

• As shown in the upper right insert in Figure-2 (and as is discussed in more detail in Figure-3 from the Addendum below) — typical RBBB conduction manifests a characteristic pattern in the 3 KEY leads that I rely on for recognition of the Bundle Branch Blocks (See ECG Blog #204 — for my user-friendly approach to diagnosis of BBB and IVCD within seconds!).
• With typical RBBB conduction — there is a distinct triphasic rsR' complex in right-sided lead V1 (with taller right rabbit ear — and S wave that descends below the baseline — consistent with A or B in Figure-2).
• The other characteristic feature of RBBB conduction — is the presence of wide terminal S waves in left-sided leads I and V6.
• PEARL #7: For practical purposes — the only QRS morphology with high specificity for SVT is the presence of the above described morphology (as shown in A or B in Figure-2). Although there are exceptions — any other QRS morphology (ie, C,D,E,F in Figure-2) favors VT.

Figure-2: QRS morphology is not quite "typical" for RBBB aberration.

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ANSWER: Applying QRS Morphology to Today's CASE:

I immediately thought ECG #1 in today's case was most likely to represent left posterior Fascicular VT.

• Although the widened, predominantly positive complex in lead V1 resembles RBBB conduction — QRS morphology in lead V1 is clearly more atypical than I'd expect for RBBB conduction in an otherwise healthy young adult. This is because instead of the expected triphasic QRS in lead V1 — we see an initial q wave with a slurred predominant R wave that manifests a taller left 'rabbit ear' (that most resembles pattern F in the insert in Figure-2).
• A similar qR pattern is seen in lead V2 — such that we never see any triphasic pattern.
• Wide terminal S waves are seen in left-sided leads I and V6 — but the QRS in the 3rd left-sided lead aVL looks very different than the QRS in lead I, and totally lacks a terminal S wave. Otherwise — QRS morphology in the inferior leads is perfectly consistent with LAHB conduction.

BOTTOM Line: Primarily on the basis of the very atypical QRS morphology in lead V1 in this otherwise healthy young adult — I thought QRS morphology to be most consistent with fascicular VT.

• PEARL #8: As discussed in Figure-4 — IV Verapamil is the treatment of choice for fascicular VT. The "beauty" of using IV Verapamil for this indication — is that this drug is also effective for treating the vast majority of reentry SVT rhythms, such that there is little downside to using IV Verapamil for treatment of today's WCT rhythm.
• NOTE: The caution with regard to using IV Verapamil or IV Diltiazem to treat a regular WCT rhythm — is that if the rhythm turns out to be an ischemic VT, that the vasodilating and negative inotropic action of these medications may precipitate deterioration of ischemic VT to VFib. That said — the previously healthy young adult in today's case is highly unlikely to have ischemic VT.

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CASE Follow-Up.

• The patient in today's case was initially treated with IV Adenosine. This was unsuccessful.
• IV Verapamil was then tried — and successfully converted the WCT to sinus rhythm.
• The patient was referred to EP Cardiology for consideration of ablation of her recurrent fascicular VT.

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Acknowledgment: My appreciation to Insanuddin Ihsan (Kabul, Afghanistan) for allowing me to use this case and these tracings.

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ADDENDUM (7/26/2025):

• In Figure-3 — I review QRS morphology in lead V1 that suggests aberrant conduction.
• In Figure-4 — I summarize KEY features regarding idiopathic VT.

Figure-3: QRS morphology in lead V1 that suggests aberrant conduction vs VT (from my ACLS Pocket Brain-2013).

Figure-4: Review of KEY features regarding Idiopathic VT (See text).

—  —

Today’s 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) VT and Fascicular VT. 

 

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Additional Relevant ECG Blog Posts to Today’s Case:

• ECG Blog #185 — Reviews my System for Rhythm Interpretaion, using the Ps, Qs & 3R Approach.
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• 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 — Reviews another regular WCT.
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• 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 — more regular WCTs.
• ECG Blog #475 — Aberrant SVT?
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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.