SVT with Aberrancy - Wide Complex Tachycardia

SVT with Aberration

SVT with aberration refers to a supraventricular tachycardia conducted through the ventricles with abnormal intraventricular conduction, resulting in a wide QRS complex (>120 ms) on ECG.

Although the rhythm originates above the ventricles, conduction delay in the His–Purkinje system makes it appear similar to ventricular tachycardia.

Correct identification is crucial because misdiagnosing SVT with aberrancy as VT (or vice versa) can lead to inappropriate management.

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Mechanisms

Wide QRS during SVT occurs due to abnormalities in ventricular conduction.

1. Pre-existing Bundle Branch Block

A patient with baseline right bundle branch block (RBBB) or left bundle branch block (LBBB) may develop SVT, which will naturally appear as a wide-complex tachycardia.

2. Rate-Dependent Aberrancy

At very fast heart rates, one of the bundle branches may still be in its refractory period, leading to temporary conduction delay.

This is commonly called functional bundle branch block.

3. Ashman Phenomenon

Occurs when a long–short cycle sequence causes aberrant conduction, typically producing RBBB morphology.

It is often seen in atrial fibrillation.

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Common Rhythms That Can Present with Aberration

Several supraventricular rhythms may appear as wide-complex tachycardia:

• Atrial fibrillation

• Atrial flutter

• Atrial tachycardia

• AVNRT

• AVRT

All of these originate above the ventricles but may show wide QRS complexes when conduction is abnormal.

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ECG Characteristics

Typical ECG findings suggesting SVT with aberrancy include:

• Wide QRS complex (>120 ms)

• Typical bundle branch block morphology (RBBB or LBBB pattern)

• Regular or irregular rhythm depending on the underlying SVT

• Presence of P waves related to atrial rhythm

• Absence of AV dissociation

If the QRS morphology is identical to the patient’s baseline bundle branch block pattern, SVT with aberrancy becomes more likely.

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Distinguishing SVT with Aberration from Ventricular Tachycardia

Wide-complex tachycardia should always be presumed ventricular tachycardia until proven otherwise, especially in older patients or those with structural heart disease.

Features favoring SVT with aberrancy:

• Previous ECG showing identical bundle branch block pattern

• Typical RBBB or LBBB morphology

• Response to vagal maneuvers or adenosine

• Absence of AV dissociation

Features favoring ventricular tachycardia:

• AV dissociation

• Capture or fusion beats

• Extreme axis deviation

• Very wide QRS (>160 ms)

• History of myocardial infarction or cardiomyopathy

Multiple ECG algorithms exist to differentiate the two, including the Brugada and Vereckei criteria.

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Clinical Importance

Distinguishing SVT with aberration from ventricular tachycardia is one of the most important challenges in ECG interpretation.

Incorrect diagnosis may lead to:

• Inappropriate drug therapy

• Delay in treatment of ventricular tachycardia

• Hemodynamic deterioration

Therefore, wide complex tachycardia should always be treated as VT unless clear evidence suggests SVT with aberrancy.

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Management

Management depends on hemodynamic stability.

Unstable patient

Immediate synchronized cardioversion is recommended.

Stable patient

Initial steps include:

• Vagal maneuvers

• Adenosine (if regular rhythm)

• AV nodal blocking agents

If there is any diagnostic uncertainty, treating the rhythm as ventricular tachycardia is safest.

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Key Takeaways

• SVT with aberration is supraventricular tachycardia with wide QRS due to abnormal ventricular conduction

• Most commonly caused by bundle branch block or rate-dependent aberrancy

• It can mimic ventricular tachycardia on ECG

• Careful ECG interpretation is essential for correct diagnosis

• When uncertain, assume ventricular tachycardia and treat accordingly