Post Fascicular Ventricular Tachycardia (Belhassen VT)

Post Fascicular Ventricular Tachycardia (Belhassen VT)

Introduction

Post fascicular ventricular tachycardia (PFVT), commonly called fascicular VT or Belhassen VT, is a distinct form of idiopathic left ventricular tachycardia. It typically occurs in young patients without structural heart disease and is characteristically verapamil sensitive.

Unlike scar-related VT seen in structural cardiomyopathy, PFVT originates from the specialized conduction system of the left ventricle—most often the posterior fascicle of the left bundle branch.

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Historical Background

This arrhythmia was first clearly described and treated successfully with verapamil by Hein J. J. Wellens and later characterized by Menashe Belhassen, hence the term Belhassen tachycardia.

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Epidemiology

Typically affects young males (15–40 years)

Structurally normal heart

Accounts for 10–15% of idiopathic VTs

Often misdiagnosed as SVT with aberrancy

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Mechanism

PFVT is a re-entry tachycardia involving the Purkinje system.

Most common mechanism:

Re-entry circuit between:

Abnormal Purkinje tissue

Posterior fascicle

Adjacent ventricular myocardium

Why verapamil works:

The circuit is calcium-dependent, unlike most VTs which are sodium-dependent. This explains the dramatic response to IV verapamil.

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Types of Fascicular VT

1. Posterior Fascicular VT (Most Common – 90–95%)

Origin: Left posterior fascicle

ECG:

RBBB morphology

Left axis deviation

2. Anterior Fascicular VT

RBBB morphology

Right axis deviation

3. Upper Septal Fascicular VT (Rare)

Narrow QRS or near-normal morphology

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ECG Characteristics

Classic ECG Pattern:

Relatively narrow QRS (120–140 ms)

RBBB pattern

Left axis deviation (posterior type)

AV dissociation may be subtle

Capture/fusion beats may be present

Differentiation from SVT with aberrancy:

Feature Fascicular VT SVT with RBBB

Age Young Any

Structural disease Usually absent Variable

Response to Adenosine No Often yes

Response to Verapamil Yes Variable

AV dissociation May be present Absent

Important: Hemodynamically stable patient with RBBB + LAD in a young person → Think Fascicular VT.

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Clinical Presentation

Palpitations

Dizziness

Presyncope

Rarely syncope

Usually hemodynamically stable

Often triggered by:

Exercise

Stress

Sympathetic activation

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Acute Management

Hemodynamically Stable

First-line:

IV Verapamil (slow administration)

Avoid:

Amiodarone (less effective acutely)

Adenosine (usually ineffective)

DC shock unless unstable

Hemodynamically Unstable

Immediate synchronized cardioversion

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Long-Term Management

1. Catheter Ablation (Definitive Therapy)

Success rate: >90–95%

Low recurrence

Curative in most cases

Mapping identifies:

Purkinje potential preceding QRS

Successful ablation eliminates fascicular signal

2. Medical Therapy

Oral verapamil

Beta blockers (less effective)

Preferred approach in young patients: Early ablation

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Electrophysiology Study Findings

Inducible with atrial or ventricular pacing

Purkinje potentials precede QRS by 20–40 ms

Entrainment confirms re-entry mechanism

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Differential Diagnosis

SVT with aberrancy

Bundle branch re-entry VT

Outflow tract VT

Scar-related VT

Clue toward fascicular VT: Young patient + structurally normal heart + RBBB/LAD morphology + verapamil sensitivity.

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Prognosis

Excellent prognosis

No increased sudden cardiac death risk in structurally normal heart

Rare progression to cardiomyopathy if incessant

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Key Teaching Points

Fascicular VT = Verapamil-sensitive VT

Most common type → Posterior fascicle

ECG → RBBB + Left axis deviation

Mechanism → Re-entry involving Purkinje system

Ablation → Highly successful and curative

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Practical Clinical Algorithm

Young patient with regular wide QRS tachycardia:

1. Check stability

2. If stable + RBBB/LAD morphology → Consider Fascicular VT

3. Give IV verapamil

4. If recurrent → Refer for EP study and ablation