ECG Blog #455 — VT Until Proven Otherwise?

I was asked to interpret the ECG in Figure-1 — told only that this 30-ish year old man had a history of having undergone a number of operations for CHD (Congenital Heart Disease) as a child. 

QUESTIONS:

• In Figure-1 — Is the rhythm VT — or — SVT with aberrant conduction — or — potentially neither of these possibilities?
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• IF told that this patient was hypotensive in association with the rhythm in Figure-1 — Does It Matter what the specific etiology of this rhythm is? If it does matter — Why does it matter?

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 ECG in Figure-1 shows a regular WCT (Wide-Complex Tachycardia) at ~225/minute, without clear sign of atrial activity.

• QRS morphology — is obviously very abnormal because: i) There is an unusual (indeterminate) frontal plane axis (with predominant negativity in standard leads I,II,III); — ii) There is a monophasic R wave in lead V1 (consistent with RBBB conduction — but lacking the usual triphasic rsR' configuration of RBBB in lead V1); — and, iii) The QRS is essentially all negative in lead V6.
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• NOTE: In most instances — the finding of a regular WCT rhythm with very abnormal QRS morphology, and without clear sign of atrial activity in an adult has to be assumed VT (Ventricular Tachycardia) until proven otherwise. Statistical odds that such a regular WCT rhythm will turn out to be VT are ≥80%.

The above said — I was not convinced today's rhythm was VT.

• PEARL #1: The KEY feature in today's history is that this patient was diagnosed with CHD as a child, and underwent a number of operations for this. As a result — ALL bets are off as to what his "baseline" ECG might look like! Regardless of how atypical QRS morphology might be in Figure-1 — given this history of multiple surgeries for CHD, there is no predictive value forthcoming regarding QRS morphology in Figure-1 (See ECG Blog #422 for another regular WCT case with abnormal QRS morphology in an adult with CHD).
• PEARL #2: Today's case provides an excellent example for which finding a baseline ECG in this adult with CHD would clearly provide insight. It would probably tell us whether the abnormal QRS morphology that we see in Figure-1 is the result of VT vs SVT (ie, with the abnormal QRS morphology being the result of the patients underlying Congenital Heart Disease). 
• PEARL #3: The survival of children with CHD is much higher than most clinicians realize. At the present time, up to 97% of children with CHD live to reach adulthood — and over 75% of children with CHD who reach 18 years of age, go on to live past middle age (Dellborg et al — Circulation 147(12):930-938, 2023). As a result, it should not be surprising that many children who may have been diagnosed with even severe CHD — are living to later present to the ED with complications (such as tachyarrhythmias) as adults.
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• PEARL #4: Looking closer at today's initial ECG — there is a feature in favor of this rhythm being an SVT (SupraVentricular Tachycardia) instead of VT. Note that the initial deflection of the QRS in several leads is narrow (within the dotted RED ovals in leads I, aVL, V5 in Figure-2). Typically with VT — because the impulse arises from the ventricles (away from the conduction system) — the initial deflection of the QRS tends to be slower (wider) than what we see within the dotted RED ovals in Figure-2.

Figure-2: I've labeled KEY findings in today's WCT rhythm.

• PEARL #5: Figure-2 serves as a reminder of the Every-other-Beat (or in this case, Every-Third-Beat) Method for rapid estimation of heart rate. RED numbers show that in order to record 3 beats — it takes 4 large boxes (BLUE numbers). Thus, 1/3 the heart rate = 300 ÷ 4 = 75/minute X 3 = 225/minute (See ECG Blog #210 for more on the Every-other-Beat Method).
• Fast, accurate estimation of heart rate often provides an important clue to the etiology of certain arrhythmias — though in today's case, a rate of ~225/minute has no value for distinguishing VT from SVT rhythms.
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• PEARL #6: We are told that today's patient was hypotensive in association with the rhythm shown in Figure-1. As a result — it does not matter whether this rhythm is VT or an SVT, because initial treatment is the same! Synchronized cardioversion was applied — and successfully converted the patient to the bottom tracing shown below in Figure-3.
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• PEARL #7: The differential diagnosis that is most commonly cited for the regular WCT rhythm in today's case is between VT vs SVT with aberrancy. More than simply a semantic point — it's important to appreciate that the other common reason for an SVT with QRS widening is a preexisting BBB (Bundle Branch Block). This is different than QRS widening that develops because the very rapid heart rate does not allow sufficient time for recovery of conduction properties in a part of the conduction system (ie, rate-related aberrant conduction — for which a narrow QRS will be seen on the baseline tracing and with return to sinus rhythm after conversion of the fast WCT).

QUESTION:

• Now that we see the post-conversion rhythm ( = ECG #2) — Has this changed your interpretation of the cause of the regular WCT in ECG #1?

Figure-3: Comparison of the initial ECG in today's case — with the repeat ECG done after Cardioversion. (To improve visualization — I've digitized the original ECG using PMcardio).

ANSWER:

The post-cardioversion rhythm in ECG #2 is sinus at a rate of ~110/minute — as we clearly see upright P waves in lead II with a constant PR interval of ~0.20 second.

• Doesn't QRS morphology in the post-cardioversion tracing look very much like QRS morphology during the WCT? Although there are slight differences in QRS morphology between the 2 tracings in Figure-3 — there are many more similarities, including: i) The frontal plane axis is markedly leftward — with very similar-looking predominant negativity in leads II,III,aVF; — ii) The appearance of the monophasic R wave in leads V1,V2,V3 is virtually identical in both tracings; — and, iii) There is predominant negativity for the QRS in leads V4,V5,V6 in both tracings — with a nearly identical almost-all-negative QRS in lead V6.
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• BOTTOM Line: I interpreted the marked similarity in QRS morphology during the WCT and after conversion to sinus rhythm — as indicative of today's tachycardia being the result of an SVT with preexisting RBBB/LAHB in this 30-ish year old man with known CHD, and a history of having undergone a series of operations as a child.
• This impression could be confirmed by obtaining a previous baseline ECG on today's patient. That said, regardless of the likely supraventricular etiology of today's WCT — EP study (with potential ablation treatment) is indicated given hypotension associated with the potential life-threatening arrhythmia that we saw in Figure-1.
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• P.S.: As a technical point — the PR interval of 0.20 second seen in the post-conversion tracing in Figure-3 is not "long enough" by the standard arrhythmia definition to qualify as 1st-degree AV block. That said, the PR interval generally shortens with tachycardia. As a result — the PR interval in ECG #2 looks longer-than-it-should-be. Considering this patient's history of severe CHD as a child and the presence of bifascicular block (RBBB/LAHB) after conversion to sinus rhythm — I'd interpret this as probable indication of a PR interval conduction disturbance (and another reason for EP consultation).

 

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Acknowledgment: My appreciation for the anonymous submission of this case.

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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 #422 and Blog #425 — Cases with Congenital Heart Disease in Adults.
• 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 — and Blog #384 — 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 — 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.