Ventricular tachycardia vs SVT with abberrancy
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"ventricular tachycardia" AND "supraventricular tachycardia" AND "differentiation"
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I now have all the essential content. Let me compile the comprehensive answer.
Ventricular Tachycardia vs. SVT with Aberrancy
This is one of the classic ECG dilemmas. Both present as wide-complex tachycardia (WCT) - QRS duration ≥ 120 ms with rate > 100 bpm. The key principle from Rosen's Emergency Medicine is: treat any new wide-complex tachycardia as VT until proven otherwise.
The Fundamental Distinction
| Feature | VT | SVT with Aberrancy |
|---|---|---|
| Origin | Below the bundle of His (ventricular myocardium) | Above the AV node; wide QRS from bundle branch block (fixed or rate-related) |
| Substrate | Usually structural heart disease (scar, cardiomyopathy) | Usually normal or near-normal heart |
| Hemodynamics | Can be stable OR unstable | Usually stable (but not always) |
Critical point: Hemodynamic stability does NOT exclude VT. Many patients in sustained VT are hemodynamically stable. Never use blood pressure or pulse quality to diagnose the rhythm.
SVT with a baseline wide QRS = permanent BBB (right or left). The QRS is wide in sinus rhythm too.
SVT with aberrancy = functional (rate-related) BBB - the bundle branch becomes refractory at fast rates, so conduction is blocked transiently. The QRS is narrow at baseline. - Frameworks for Internal Medicine, p. 89
ECG Features Favoring VT
1. AV Dissociation
Independent P waves and QRS complexes marching at different rates. P waves are best seen in the inferior limb leads (II, III, aVF) and V1-V2. This is pathognomonic for VT when present - but only visible in ~10% of VT cases. - Tintinalli's, p. 158
2. Capture Beats and Fusion Beats
- Capture beat: A sinus impulse briefly "captures" the ventricle via the normal conduction system during VT - produces a narrow, early QRS complex among the wide beats. Strongly supports VT.
- Fusion beat: Simultaneous activation from the ventricular focus AND a sinus impulse - produces a QRS intermediate in morphology between the VT beat and the sinus beat.
Both are diagnostic of VT. See ECG tracings below - panel D shows capture (large arrow) and fusion (small arrow) beats:
3. QRS Duration
- QRS > 160 ms strongly favors VT (bundle branch blocks rarely produce QRS > 140-160 ms)
- In RBBB-pattern WCT: QRS > 140 ms favors VT
- In LBBB-pattern WCT: QRS > 160 ms favors VT
4. Axis Deviation
- Northwest (extreme) axis (-90° to ±180°, "no-man's land") = strongly favors VT
- Left axis deviation in RBBB-pattern tachycardia favors VT
5. Concordance
- Positive concordance (all precordial leads V1-V6 upright) = strongly favors VT
- Negative concordance (all leads negative) = virtually diagnostic of VT
6. QRS Morphology
- R wave in aVR: An initial R wave in aVR favors VT (Vereckei criterion)
- In RBBB pattern: Monophasic R, QR, or RS in V1; small R with deep S ("rS") in V6 favors VT
- In LBBB pattern: Broad R (>30 ms) or slurred downstroke in V1 or V2; Q wave in V6 favors VT
Validated Algorithmic Approaches
Brugada Criteria (1991) - Most Widely Used
Apply the following in sequence (any single "Yes" = VT diagnosis):
- No RS complex in any precordial lead? → Yes = VT
- RS interval > 100 ms in any precordial lead? → Yes = VT
- AV dissociation present? → Yes = VT
- Morphology criteria for VT in V1-V2 and V6? → Yes = VT
Only if all four are "No" → diagnose SVT with aberrancy
Original sensitivity 98.7%, specificity 96.5%, though subsequent ED validation shows ~92-94% sensitivity. - Rosen's Emergency Medicine, p. 1059
Vereckei aVR Algorithm (2008)
Uses only lead aVR - diagnose VT if any are present (analyzed in sequence):
- Initial R wave in aVR
- Initial r or q wave > 40 ms in aVR
- Notch on the initial descending limb of a predominantly negative QRS
- vi/vt ratio < 1 (velocity at terminal 40 ms is faster than initial 40 ms - means faster at end, paradoxical for aberrancy)
Griffith Criteria (1994)
Diagnoses SVT with aberrancy only if QRS morphology is classic for BBB (not atypical):
- LBBB: rS or QS in V1/V2, time to S nadir < 70 ms, no Q wave in V6
- RBBB: rsR' in V1, RS in V2, R > S in V1
- AV dissociation absent
Pava Lead II Criterion (2010) - Simplest
- Time from QRS onset to R-wave peak in lead II > 50 ms → VT
Summary Table of Algorithms
| Algorithm | Approach | Favors VT | Favors SVT |
|---|---|---|---|
| Brugada (1991) | Sequential, precordial leads | Any 1 of 4 criteria | None of 4 criteria |
| Griffith (1994) | Morphology check | Not classic BBB | Classic LBBB or RBBB morphology |
| Vereckei (2008) | aVR only | Any 1 of 4 aVR criteria | None of 4 criteria |
| Pava (2010) | Lead II R-peak time | R-peak time > 50 ms | R-peak time ≤ 50 ms |
Source: Tintinalli's Emergency Medicine, p. 158
Clinical Context Clues
| Clinical Feature | Favors |
|---|---|
| Age > 35, prior MI, structural heart disease | VT |
| Symptoms present since childhood or in young patient | SVT |
| Prior ECG showing same QRS morphology during SVT | SVT with BBB |
| History of WPW | SVT with pre-excitation |
| Irregular wide-complex tachycardia | AFib with aberrancy or pre-excitation |
| Completely regular | Either (though VT is usually very regular) |
Special Cases
Pre-excited AFib (WPW + AFib): Presents as irregularly irregular WCT with variable QRS morphology and very rapid rates (> 200/min) - can degenerate to VFib. Never give AV nodal blockers (adenosine, beta-blockers, verapamil, digoxin) - they force all conduction down the accessory pathway and can be lethal.
Antidromic AVRT: Regular WCT in WPW where the impulse travels anterograde down the accessory pathway and retrograde up the His-Purkinje system. Looks like VT but patient often young and otherwise healthy.
Management
Hemodynamically unstable (any rhythm):
- Immediate synchronized DC cardioversion
Hemodynamically stable:
- If diagnosis is VT or unknown: procainamide (drug of choice - works for both VT and most SVT); amiodarone or lidocaine as alternatives
- If confirmed SVT with aberrancy: adenosine (diagnostic and therapeutic)
- Never give verapamil or adenosine to an undifferentiated WCT - verapamil can cause cardiovascular collapse in VT
Key rule from Tintinalli's (p. 145): Procainamide is the antiarrhythmic of choice for stable wide-complex tachycardia of uncertain etiology because it is effective for both VT and SVT.
Memory Aid: Features That Are Essentially Diagnostic of VT
- AV dissociation
- Capture beats
- Fusion beats
- Northwest axis ("no-man's land")
- QRS concordance (positive or negative)
- QRS > 160 ms
The more of these present, the more certain the diagnosis. Absence of all Brugada criteria is the only validated path to diagnosing SVT with aberrancy.
Sources: Frameworks for Internal Medicine, p. 89-90 | Tintinalli's Emergency Medicine, pp. 145, 158 | Rosen's Emergency Medicine, pp. 1059-1060
Explain the 4th step in brug algorithm ada
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Here is the detailed breakdown of Brugada Step 4.
Brugada Step 4 - Morphology Criteria for VT in V1 and V6
This step is reached only after all three prior steps are negative (RS complexes are present, RS interval is ≤100 ms, and no AV dissociation is seen). It asks: does the QRS morphology in V1 and V6 look like typical VT rather than a clean bundle branch block pattern?
The logic is that aberrantly conducted SVT tends to produce "classic" RBBB or LBBB patterns, whereas ventricular activation from an ectopic focus produces atypical, abnormal-looking morphologies that don't fit a clean BBB template.
The criteria split depending on whether the WCT has an RBBB-like or LBBB-like appearance in V1.
If the QRS in V1 looks RBBB-like (predominantly positive / biphasic with an R')
V1 - favors VT if:
- Monophasic R (single tall R wave, no notch, no secondary deflection)
- QR pattern (initial Q followed by R)
- RS pattern where R > S (but not a clean rsR' or triphasic pattern)
In other words: any pattern that is not a classic triphasic rsR' (rabbit-ear pattern). A true RBBB aberrancy should produce rsR' or rSR' in V1.
V6 - favors VT if:
- rS pattern (small r, deep S) - S wave deeper than R wave
- QS pattern (entirely negative)
- QR pattern
A clean RBBB aberrancy should produce a broad R with no deep S in V6 (or qRS at most). An rS or QS in V6 during a supposed RBBB pattern means the lateral wall is activating from below-normal - pointing to VT. - Tintinalli's Emergency Medicine, p. 158
If the QRS in V1 looks LBBB-like (predominantly negative)
V1 or V2 - favors VT if any of the following:
- r wave > 30 ms wide (broad, slurred initial r - slow conduction through myocardium, not fast conduction through Purkinje)
- Notched or slurred downstroke of the S wave (delayed, irregular descent)
- Time from QRS onset to nadir of S wave > 70 ms (prolonged time to S-wave nadir)
A clean LBBB aberrancy should have a narrow, sharp initial r (or no r at all) and a rapid, clean descent to the S-wave nadir in < 70 ms.
V6 - favors VT if:
- Any Q wave present (QR or QS pattern)
A clean LBBB aberrancy should give a monophasic R with no Q in V6. A Q wave in V6 with an LBBB-pattern tachycardia is pathological and strongly suggests ventricular origin.
Summary Table
| Lead | RBBB-pattern WCT | LBBB-pattern WCT |
|---|---|---|
| V1 - VT morphology | Monophasic R, QR, or RS (not rsR') | r width > 30 ms, slurred S descent, or onset-to-S-nadir > 70 ms |
| V6 - VT morphology | rS, QS, or QR | Q wave (QR or QS) |
The Underlying Concept
The whole step rests on one idea: aberrant conduction still uses the His-Purkinje system (just one branch is blocked), so depolarization is still partially fast and orderly - producing "textbook" BBB shapes. VT activates the ventricles cell-to-cell through myocardium, which is slow and disorganized - producing wide, slurred, atypical shapes that don't fit a clean BBB template.
Think of it this way:
- Classic rsR' in V1 with qRS in V6 = fast Purkinje-based conduction = aberrant SVT
- Monophasic R in V1 with rS in V6 = slow myocardial spread = VT
Sources: Tintinalli's Emergency Medicine, pp. 158-159 | Rosen's Emergency Medicine, pp. 1059-1060
Can u give few ecgs for to test me for svt with abberrancy and vt
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I have all the material I need. Here's your ECG quiz - real tracings from Braunwald's, Rosen's, and Goldman-Cecil, presented one at a time with clues. Scroll past the ECG only when you're ready for the answer.
ECG Quiz - VT vs SVT with Aberrancy
ECG 1
From Goldman-Cecil Medicine
Look at tracing B. Wide-complex tachycardia. Regular rhythm. Small arrows are marked on the tracing. Rate is fast.
Question 1: What do the arrows indicate, and what is the diagnosis of tracing B?
Question 2: In tracing C - look at the 8th beat. It looks slightly different from the others. What is it, and what does it prove?
||ECG 1 Answers: B: The arrows mark dissociated P waves marching at their own rate, independent of the wide QRS complexes. This is AV dissociation - pathognomonic of VT (nonsustained monomorphic VT). C: The 8th beat is a fusion beat - a sinus impulse and a ventricular beat occurring simultaneously, producing an intermediate-morphology QRS. This is diagnostic of VT. The tracing shows sustained monomorphic VT with dissociated P waves (arrows) and a fusion beat at beat 8.||
ECG 2
From Rosen's Emergency Medicine, Fig 65.36A - Three VT tracings using the Brugada algorithm
Focus on tracing A (top). 12-lead wide-complex tachycardia. Look at V1-V6.
Question: You are applying the Brugada algorithm. In the precordial leads, you measure the RS complexes. The RS interval (onset of R to deepest S) appears to be greater than 100 ms in at least one lead. P waves are also visible in V1 (arrows marked P). What step of Brugada gives you the diagnosis, and what is it?
||ECG 2 Answer: Step 2 of the Brugada criteria is positive: RS interval > 100 ms. Stop here - the diagnosis is VT. You do NOT need to proceed further. Bonus: Step 3 (AV dissociation) is also positive - the P arrows show independent atrial activity. And V6 morphology is also consistent with VT. Multiple criteria are met, but Step 2 alone is sufficient.||
ECG 3
From Rosen's, same figure - tracing B
Question: In tracing B, RS complexes are present but RS duration is ≤100 ms. AV dissociation is not clearly visible. You proceed to Brugada Step 4 (morphology). You note: S wave is notched in V1, and V6 shows a QR pattern. What is the diagnosis and which Brugada step got you there?
||ECG 3 Answer: Step 4 (morphology criteria) is positive. Notched S in V1 = atypical LBBB-pattern morphology (slurred/notched S downstroke - slow myocardial conduction, not clean Purkinje-based BBB). QR in V6 with an LBBB-pattern tachycardia = Q wave in V6 = VT morphology criterion. Diagnosis: VT. Both V1 and V6 satisfy the Step 4 morphology criteria for VT.||
ECG 4
From Braunwald's Heart Disease, Fig 67.8 - the comprehensive flow diagram
This is a full diagnostic flow diagram with real ECG examples at each branch point. Look at the bottom row - V1 shows a clean rSR' (classic RBBB "rabbit-ear") or a clean rS with sharp S downstroke (classic LBBB).
Question: The patient at the bottom of the algorithm passes all four Brugada steps as negative. V1 shows a classic triphasic rsR' pattern consistent with a clean RBBB. What is the diagnosis?
||ECG 4 Answer: When all four Brugada criteria are negative AND V1 shows typical RBBB or LBBB morphology, the diagnosis is SVT with aberrancy (or SVT with baseline wide QRS). This is the ONLY pathway to an SVT diagnosis using the Brugada algorithm. Classic rsR' in V1 = fast, clean Purkinje conduction = the RBBB bundle branch is simply blocked, not a ventricular origin rhythm.||
ECG 5 - Bonus Challenge
From the same Braunwald's figure, middle rows
Question: Look at the aVR row in the diagram. Three aVR morphology examples are shown, each with a prominent initial positive deflection (initial R wave) or broad initial deflection > 40 ms. What algorithm does this represent, and what is the diagnosis if aVR shows a monophasic R wave?
||ECG 5 Answer: This is the Vereckei aVR algorithm. An initial R wave in aVR = the impulse is traveling away from the aVR lead at the start (away from the right shoulder, toward the left foot) = abnormal initial activation = VT. A monophasic R in aVR is Step 1 of the Vereckei criteria and is diagnostic of VT. Normal supraventricular conduction (whether with RBBB or LBBB) starts with septal depolarization from left to right, which produces a predominantly negative initial deflection in aVR - not a positive one.||
How did you do? Let me know which ones you want to discuss further, and I can walk through the morphology step by step. I can also quiz you on more tracings - torsades de pointes, fascicular VT (which mimics SVT), or WPW-related wide-complex tachycardias.
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