Idiopathic left ventricular tachycardia with a change from left to right axis deviation during radiofrequency catheter ablation.

A 62 year-old-woman presented with a right bundle branch block (RBBB) and left axis deviation (LAD) tachycardia. Radiofrequency (RF) energy was delivered to the left posterior fascicle (LPF) where 2 presystolic Purkinje potentials (P1 and P2) preceding onset of the QRS complex were recorded. During RF energy applications, the QRS morphology of the tachycardia changed from RBBB and LAD to RBBB and right axis deviation without termination of the tachycardia. The Purkinje potential was observed following the QRS complex during the tachycardia because of conduction block of the LPF distal to the reentry circuit due to RF catheter ablation.