RESUMEN
Fascicular tachycardia is an uncommon idiopathic ventricular tachycardia, originating from the left ventricle; it usually occurs in young male patients, with a high prevalence in south-east Asiatic people. Electrocardiographic aspects of this unique ventricular tachycardia (right bundle branch block morphology and left or right-axis deviation, with a moderate QRS widening) and verapamil sensitivity make it often difficult the differential diagnosis with other forms of supraventricular tachycardia. Reentry is believed to be the operative mechanism of fascicular tachycardia, with the reentrant circuit located in the Purkinje network, in the region of the left posterior or anterior fascicle. The slow conduction zone participating in the reentry circuit, made up of partially depolarized Purkinje fibers, seems to be located in a relatively wide area, from the basal to the apical left interventricular septum. Intravenous verapamil is elective in acute treatment; however oral verapamil shows poor efficacy in preventing tachycardia relapses. Ablative approach is very effective; success is achieved in approximately 90% of patients, with rare complications. Recently diastolic potentials during fascicular tachycardia have been reported and these findings have given rise to new electrophysiological hypotheses and new indications about the successful ablation site.