Changing QRS morphology during catheter ablation of outflow tract ventricular tachycardia: what is the mechanism?

A 62-year-old male patient underwent catheter ablation for outflow tract ventricular tachycardia (VT). During radiofrequency catheter ablation in the right ventricular outflow tract, the VT morphology abruptly changed and its exit shifted to the left coronary cusp. Ablation at this site terminated the VT and rendered it non-inducible. Accurate analysis of the 12-lead ECG during catheter ablation may reveal VT exit shift as a possible explanation for unsuccessful catheter ablation of outflow tract VT.