VT vs SVT Brugada Algorithm

 

VT vs SVT With Aberrancy

Brugada Algorithm Explained

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Introduction

Wide complex tachycardia (WCT) is defined as a tachycardia with QRS duration ≥120 ms. The two most common causes are:

• Ventricular Tachycardia (VT)

• Supraventricular Tachycardia with Aberrancy (SVT-A)

Distinguishing between them is critical because misdiagnosing VT as SVT can lead to inappropriate therapy and clinical deterioration.

The Brugada Algorithm, introduced by Brugada et al. (1991), is one of the most widely used ECG methods to differentiate VT from SVT with aberrant conduction.

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Brugada Algorithm (Stepwise Approach)

The algorithm consists of 4 sequential ECG questions.

If the answer to any step is YES → Diagnose VT.

If NO → Move to the next step.

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Step 1: Absence of RS Complex in All Precordial Leads

Look at V1–V6.

Check whether any lead has an RS complex.

RS complex = an R wave followed by an S wave.

If no RS complex is present in all precordial leads → VT

This means the QRS complexes are either:

• monophasic R

• monophasic QS

• entirely negative complexes

Why this suggests VT

In VT, ventricular activation does not use the normal His–Purkinje system, resulting in uniform depolarization patterns without RS morphology.

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Step 2: RS Interval > 100 ms

If an RS complex is present, measure the RS interval.

RS interval =

Start of R wave → Lowest point of S wave

Measure in any precordial lead.

If RS interval >100 ms → VT

Reason

Delayed ventricular activation occurs when impulses travel cell-to-cell rather than through Purkinje fibers.

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Step 3: AV Dissociation

Look for atrial and ventricular activity occurring independently.

Signs of AV dissociation include:

• P waves marching independently of QRS

• Capture beats

• Fusion beats

• Variable PR intervals

If AV dissociation is present → VT

Why this occurs

In VT, the ventricles drive the rhythm while the atria continue to depolarize independently via the sinus node.

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Step 4: Morphologic Criteria for VT

If the first three steps are negative, analyze QRS morphology in V1/V2 and V6.

Morphology differs depending on RBBB-like or LBBB-like pattern.

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VT Morphology with RBBB Pattern (V1)

Suggests VT if:

• Monophasic R wave in V1

• Broad R wave (>30 ms)

• RS interval prolonged

• Notch on descending limb of S wave

In Lead V6

• QS or rS complex favors VT

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VT Morphology with LBBB Pattern (V1)

Suggests VT if:

• Initial R wave >30 ms

• Notching of downstroke of S wave

• Prolonged onset to nadir of S wave (>60 ms)

In Lead V6

• QS or rS complex favors VT

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Sensitivity and Accuracy

Original Brugada study reported:

• Sensitivity for VT ≈ 98%

• Specificity ≈ 96%

However, real-world accuracy may be slightly lower, especially in:

• Pre-existing bundle branch block

• Antiarrhythmic drug use

• Fascicular VT

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Practical Clinical Rule

A widely taught emergency rule:

If a wide complex tachycardia is seen in an adult → Assume VT until proven otherwise.

Reasons:

• VT accounts for ~80% of WCT

• Risk of deterioration with wrong therapy

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Limitations of Brugada Algorithm

Despite its usefulness, several limitations exist:

• Requires careful ECG interpretation

• Difficult during very rapid tachycardia

• Less reliable with preexisting BBB

• May fail in fascicular VT or antidromic AVRT

Because of these limitations, other algorithms were developed:

• Vereckei Algorithm

• aVR Algorithm

• Griffith Algorithm

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Key ECG Features Favoring VT (Quick Summary)

Strong indicators of VT include:

• AV dissociation

• Capture beats

• Fusion beats

• Extreme axis deviation

• Concordance in precordial leads

• Very broad QRS (>160 ms)

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Clinical Importance

Correct differentiation between VT and SVT with aberrancy is essential because treatment strategies differ:

VT Management

• Amiodarone

• Procainamide

• Electrical cardioversion

• ICD therapy in structural heart disease

SVT with Aberrancy

• Adenosine

• AV nodal blockers

• Vagal maneuvers

Administering AV nodal blockers in VT can cause hemodynamic collapse.

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Take-Home Message

The Brugada Algorithm remains one of the most practical ECG tools for differentiating VT from SVT with aberrancy.

The key concept is simple:

1. No RS complex → VT

2. RS interval >100 ms → VT

3. AV dissociation → VT

4. VT morphology → VT

If none of these criteria are present, the rhythm is more likely SVT with aberrancy.

However, in clinical practice, treat any uncertain wide complex tachycardia as VT to avoid dangerous mismanagement.