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Fascicular Ventricular Tachycardia

Fascicular tachycardia, Belhassen-type VT, verapamil-sensitive VT, Infrafascicular tachycardia, Idiopathic fascicular left ventricular tachycardia

Fascicular Ventricular Tachycardia

• Accounts for only 10% of idiopathic VTs
• Mechanism is re-entry
• Re-entry involves one fascicle and the adjacent myocardium
• Fast pathway is the fascicle (anterior or posterior)
• Slow pathway is the adjacent myocardium near the fascicle
• Primarily occurs in men aged 15-40 years
• Referred to as verapamil-sensitive ventricular tachycardia
• Responds well (terminates) after administration of verapamil
  
  
• Fascicular VT is often referred to as:
• Verapamil-sensitive VT (responds well to Verapamil)
• Belhassen's VT (described once by Belhassen)
• Idiopathic left ventricular VT (re-entry occurs in the left ventricle)
  
  
• According to the location of re-entry, we recognize 3 types of fascicular VT:
• Posterior Fascicular VT
• The most common (95%)
• Re-entry is in the posterior fascicle
• On ECG, there is left anterior hemiblock + right bundle branch block (RBBB)
• Anterior Fascicular VT
• Rare (5%)
• Re-entry is in the anterior fascicle
• On ECG, there is left posterior hemiblock + RBBB
• Upper Septal Fascicular VT
• Very rare (1%)
• Re-entry involves both fascicles and the adjacent myocardium
• On ECG, there are narrow QRS complexes and a pattern of left bundle branch block (LBBB) or RBBB
• It is a ventricular tachycardia with narrow QRS complexes
  
  

Sinus Rhythm

• During sinus rhythm, the impulse spreads anterogradely through the fascicles
• of the left bundle branch, and activates the left ventricle
• During propagation through the fascicle, the impulse emerges
• into re-entry (into the adjacent myocardium)
• The impulse emerges from both the proximal and distal parts of the fascicle
• However, the impulse does not start re-entering because in the slow pathway
• the impulses meet during the refractory period and reset
• A normal sinus rhythm is observed on the ECG

Upper Septal Fascicular Tachycardia

• Slow re-entry pathway is the adjacent myocardium in the area of the fascicles
• The impulse progresses anterogradely through both the anterior and posterior fascicles
• The left ventricle is activated through both fascicles (similar to sinus rhythm)
• The impulse retrogrades through the slow pathway (myocardium of the septum)
• Enters the bifurcation of the fascicles
• The His bundle is not part of the re-entry circuit
• Narrow QRS complexes (<0.12s) are produced
• Despite being a ventricular tachycardia
• Sometimes referred to as narrow-complex ventricular tachycardia

ECG and Fascicular Tachycardia

• Characteristic features of ventricular tachycardia
  
  
• Posterior Fascicular Tachycardia
• The ventricles are activated from the posterior fascicle
• Pattern of right bundle branch block
• Left anterior hemiblock
  
  
• Anterior Fascicular Tachycardia
• The ventricles are activated from the anterior fascicle
• Pattern of right bundle branch block
• Left posterior hemiblock
  
  
• Upper Septal Fascicular Tachycardia
• The ventricles are activated from the septal area
• Pattern of right bundle branch block (rarely left bundle branch block)
• Heart axis is normal
• Narrow QRS complexes (despite being ventricular tachycardia)
• The ventricles are activated from the ventricular septum within 0.12s
• Often referred to as narrow-complex ventricular tachycardia
• Differential Diagnosis of Ventricular Tachycardia
• Fascicular tachycardia is often confused with supraventricular tachycardia with bifascicular block
• For more accurate diagnosis and localization of re-entry, electrophysiological testing is used

Posterior Fascicular Ventricular Tachycardia

• Heart Rate 150/min.
• QRS complexes are borderline wide (0.12s)
• Right Bundle Branch Block
• rsR (V1)
• Deep and wide S (V6)
• Left Posterior Hemiblock
• Negative QRS (II, aVF)
• Positive QRS (I)
• On the ECG, we see basic features of ventricular tachycardia
• AV Dissociation
• In the continuous II lead, we see P waves that deform QRS complexes
• Merged Contraction (6th QRS complex on the continuous II lead)
• It is Fascicular Tachycardia (re-entry is in the left posterior fascicle)

Septal Fascicular Ventricular Tachycardia (Narrow Complex Ventricular Tachycardia)

• In both ECG recordings (A, B), septal fascicular ventricular tachycardia is observed
  • Compared to sinus rhythm
• Patient A
  • Narrow QRS complexes 100ms
  • QRS complexes are identical to sinus rhythm, except for a new S wave in I, V5, V6
  • Right axis deviation (120º)
• Patient B
  • Narrow QRS complexes 90ms
  • QRS complexes are identical to sinus rhythm, except for a new rSR configuration in V1
  • Normal heart axis (60º)
• Tachycardias did not respond to adenosine, they ceased after administration of verapamil
• This is septal ventricular tachycardia (verapamil-sensitive)
  • Definitive diagnosis is via electrophysiological study
• Fascicular septal ventricular tachycardia is very rare
  • It has narrow QRS complexes despite being a ventricular tachycardia
  • Because the ventricles activate from the re-entry area of the ventricular septum within 0.12s