Idiopathic fascicular left ventricular tachycardia

Background

• Rare
• Also known as narrow complex ventricular tachycardia, fascicular tachycardia, Belhassen-type VT, verapamil-sensitive VT, or intrafascicular tachycardia
• Reentrant tachycardia seen typically in young patients without structural heart disease

Clinical Features

• Young adult
• Male (60-80%)
• Palpitations
• Dizziness
• Syncope is infrequent

Differential Diagnosis

Narrow-complex tachycardia

• Regular
  • AV Node Independent
    • Sinus tachycardia
    • Atrial tachycardia (uni-focal or multi-focal)
    • Atrial fibrillation
    • Atrial flutter
    • Idiopathic fascicular left ventricular tachycardia
  • AV Node Dependent
    • Paroxysmal supraventricular tachycardia (PSVT)
      • AV node re-entry tachycardia (AVNRT)
      • AV re-entry tachycardia (AVRT)
        • Lown-Ganong-Levine syndrome
        • Wolff–Parkinson–White syndrome
    • Junctional tachycardia
• Irregular
  • Multifocal atrial tachycardia (MAT)
  • Sinus tachycardia with frequent PACs, PJCs, PVCs
  • Atrial fibrillation
    • Atrial fibrillation with RVR
  • Atrial flutter with variable conduction
  • Digoxin Toxicity

Palpitations

• Arrhythmias:
  • Narrow-complex tachycardias
  • Wide-complex tachycardias
  • AV blocks
    • Second Degree AV Block Type I (Wenckeback)
    • Second Degree AV Block Type II
    • Third Degree AV Block
  • Premature atrial contraction
  • Premature junctional contraction
  • Premature ventricular contraction
  • Sick sinus syndrome
  • Wandering atrial pacemaker
• Non-arrhythmic cardiac causes:
  • Acute coronary syndrome
  • Cardiomyopathy
  • Congenital heart disease
  • Congestive heart failure (CHF)
  • Mitral valve prolapse
  • Pacemaker complication
  • Pericarditis
  • Myocarditis
  • Valvular disease
• Psychiatric causes:
  • Panic attack
  • Anxiety
  • Somatic Symptom Disorder
• Drugs and Medications:
  • Alcohol
  • Caffeine
  • Drugs of abuse (e.g. cocaine)
  • Medications (e.g. digoxin, theophylline)
  • Tobacco
• Misc
  • Anemia
  • Hyperthyroidism
    • Thyroid storm
  • Pulmonary embolism
  • Dehydration
  • Sepsis
  • Pheochromocytoma

Evaluation

ECG showing classic RBBB with leftward axis morphology suggestive of posterior fascicle origin.

Typical ECG showing RBBB (lead V1). Unlike outflow tract VT, however, leads AVl and AVr are both positive. A strong superior axis is noted, and the positive R wave dominates in lead one.

ECG during ventricular tachycardia. ECG shows a monomorphic right bundle branch block tachycardia with a QRS duration of 120 ms (narrower than other forms of VT) right axis deviation, an appearance illustrative for fascicular ventricular tachycardia.

ECG after amiodarone infusion. After slowing the heart rate with amiodarone, ECG shows captures (red arrow) and fusion beats (green arrow) suggestive of ventricular tachycardia.

• Assume ventricular tachycardia until proven otherwise
• Often misdiagnosed as SVT with aberrancy
• Look for specific features of VT
  • fusion/capture beats
  • AV dissociation
• ECG findings
  • Monomorphic VT
  • QRS duration <140 ms
  • RS interval 60-80 ms
  • Right Bundle Branch Block
  • Axis deviation depending on classification

Classification

Posterior fascicular VT

• 90-95% of cases
• RBBB
• Left axis deviation

Anterior fascicular VT

• second most common
• RBBB
• Right axis deviation

Upper septal fascicular VT

• rare
• RBBB or LBBB
• Normal axis

Management

Unstable

Synchronized Cardioversion

• Adults: 0.5-1.0 J/kg
• Pediatrics: 0.5-1 J/kg
  • If unsuccessful, increase to 2 J/kg
• Consider sedation prior to cardioversion only if it will not significantly delay the procedure

Stable

Verapamil

• 10 mg over 1 min
  • Only administer in stable patients with an established diagnosis of IFLVT

Digoxin Immune Fab

• IFLVT as a result of Digoxin toxicity is responsive to digoxin immune Fab

External Links

• https://litfl.com/idiopathic-fascicular-left-ventricular-tachycardia/