Idiopathic left ventricular tachycardia (ILVT) with right bundle branch block and left axis deviation originates from the left posterior fascicle—Purkinje fiber network. Scar-related ventricular tachycardias (VTs) with Purkinje fibers as a part of the reentry circuit have also been described in patients with structural heart disease.

Nine patients with fascicular VT (left posterior, n = 8; left anterior, n = 1) with preserved left ventricular ejection fraction (60 ± 10 %) underwent cardiac magnetic resonance imaging (MRI) including functional analysis and delayed enhancement magnetic resonance imaging (DE-MRI). No definite structural abnormalities were detected by DE-MRI in four patients. DE-MRI revealed unifocal or multifocal areas of fibrosis or scar in three patients corresponding to the regions where typical Purkinje potentials guided successful ablation of the sustained fascicular VT. A false tendon extending from the free wall to the septum was found in one patient. Moderate reduction of left ventricular ejection fraction associated with septal or multifocal left ventricular fibrosis was detected in two patients with ventricular bigeminy originating from the left posterior fascicle. During the follow-up of 29 ± 22 months after successful catheter ablation in the nine patients, one patient with septal fibrosis detected by DE-MRI had VT recurrence and received an implantable cardioverter defibrillator.

Detection of local areas of fibrosis or scar by DE-MRI may help to distinguish idiopathic fascicular tachycardia from scar-related fascicular VT in patients with preserved left ventricular function.