COR LOE Recommendations I B-NR In patients with verapamil-sensitive, idiopathic LVT related to interfascicular reentry for whom antiarrhythmic medications are ineffective, not tolerated, or not the patient s preference, catheter ablation is I B-NR In patients with sustained hemodynamically tolerated verapamil-sensitive, idiopathic LVT related to interfascicular reentry, intravenous verapamil is recommended for IIa C-LD In patients with recurrent verapamil-sensitive idiopathic LVT, chronic therapy with oral verapamil can be useful.S8.3-7 S8.3-10 Recommendation-Specific Supportive Text 1. Idiopathic LVT is due to reentry involving a portion of the LV Purkinje system, usually the left posterior fascicle as the retrograde limb of the circuit and an incompletely defined segment of LV tissue as the anterograde limb, a portion of which is verapamil CLINICAL STATEMENTS AND GUIDELINES These VTs are typically sustained with a QRS that has a right bundle-branch block configuration with a superior axis. Less frequently an inferior axis VT or a relatively narrow QRS VT occurs as a result of alternate reentry paths, also involving a part of the Purkinje system. Beta block- ers or verapamil typically terminate these arrhyth- mias, but they fail to prevent recurrences in some The target of catheter ablation for the most common form is usually the distal insertion of the anterograde limb of the Purkinje system along the inferior portion of the LV septum near its junc- tion with the left posterior fascicle. Catheter abla- tion is acutely successful in >90% of patients with a risk of recurrence of approximately 10%. This VT may resemble fascicular VA that are due to a focal mechanism in the left anterior or left posterior fas- cicles of the LV His-Purkinje system. These fascicular arrhythmias usually have a focal mechanism with the target of catheter ablation being the site of earliest electrical activation recorded with a presystolic fas- cicular potential. 