Fascicular VT

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: George Leef MD

Synonyms and Keywords: verapamil sensitive VT

Overview

Fascicular VT (aka verapamil sensitive VT) is a type of idiopathic VT. Most VT is seen in structurally abnormal hearts, but VT can sometimes be seen in hearts with no structural defects (~10% of cases of VT). VT is called idiopathic in these circumstances. Fascicular VT is a benign rhythm caused by re-entry involving one of the fascicles of the conduction system.

Epidemiology

Seen in healthy young patients, male predominance.

Presentation

Fascicular VT usually presents with palpitations or syncope/pre-syncope. Exercise or emotional stress can act as triggers to bring on episodes of palpitations.

Pathophysiology

Fascicular VT is caused by a re-entry involving one of the fascicles of the conduction system.

Risk Factors

None known.

Diagnosis

Fascicular VT can be difficult to diagnose since it has an atypically narrow QRS complex for a rhythm of ventricular origin. It is commonly mistaken for an SVT with aberrant conduction.

The QRS is narrower than other VTs (~120-140ms) because the arrhythmia still makes partial use of the normal conduction system.
The QRS typically has a RBBB pattern, since the rhythm originates from one of the fascicles in the LV (and therefore travels left to right, as in a RBBB).
Left-axis deviation is seen if the posterior fascicle is involved (similar to a left anterior hemiblock)
- This is the most common form of fascicular VT
Right-axis deviation is seen if the anterior fascicle is involved (similar to posterior hemiblock)
There is a rare form called upper septal fascicular VT, which is associated with narrow QRS and normal axis.
As in all VT, there is A-V dissociation and fusion/capture beats may be observed

Treatment

Fascicular VT is usually highly responsive to treatment with verapamil (hence its alternative name "verapamil sensitive VT"). IV verapamil can be used to terminate the arrhythmia acute, and PO verapamil used for chronic treatment.

If the patient continues to have symptoms or cannot tolerate verapamil treatment, catheter ablation of the re-entrant circuit can be performed. Ablation of this arrhythmia has a very high success rate.

Prognosis

Fascicular VT is a benign condition with an excellent prognosis.

References

Francis J, Venugopal K, et al. Idiopathic fascicular VT. Indian Pacing Electrophysiol J. 2004 Jul-Sep; 4(3): 98–103.
Bennin C, Ali R, Wannenburg T. Idiopathic left anterior fascicular tachycardia presenting after aortic valve replacement. J Am Coll Cardiol. 2014; 63.