Idiopathic fascicular left ventricular tachycardia


  • 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

Differential Diagnosis

Narrow-complex tachycardia



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


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



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



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

Digoxin Immune Fab


See Also

External Links


  1. [1], Reviriego, Sara Moreno. “Idiopathic Fascicular Left Ventricular Tachycardia.” European Society of Cardiology, European Society of Cardiology, 20 Dec. 2010.