Determinants of successful ablation of idiopathic ventricular tachycardias with left bundle branch block morphology from the right ventricular outflow tract

The aim of the study was to define the factors that may predict the outcomes of radiofrequency ablation from the right ventricular outflow tract (RVOT) in patients with idiopathic VT with a QRS morphology of LBBB. Endocardial mapping and RF ablation from the RVOT were performed in 35 patients (14 men, mean age 41 ± 14 years), and VT was successfully ablated in 30 patients. There was no significant difference with regard to clinical characteristics and electrophysiological findings between patients with successful and failed ablation. The VTs with successful ablation showed an rS (n = 16) or QS (n = 14) pattern in lead V₁, and all five VTs with failed ablation showed an rS pattern in lead V₁. Although the absence of an R wave in lead V₁ did not differ between patients with successful and failed ablation (P = 0.13), the absence of an R wave in lead V₁ predicted VT successfully ablated from the RVOT (positive predictive value 100%; negative predictive value 24%). The VTs with successful ablation had a median precordial transitional zone at lead V₄ (range V₃-V₆), whereas all five VTs with failed ablation had precordial transition zones at lead V₃ (P = 0.004). Furthermore, a presence of an R wave in lead V₁ associated with a precordial transition zone at lead V₃ predicted VT not successfully ablated from the RVOT (positive predictive value 100%; negative predictive value 100%). In conclusion, some VTs with LBBB and inferior or normal axis cannot be ablated from the RVOT. The presence of an R wave in lead V₁ associated with a precordial transition zone at lead V₃ suggest that some VTs may not arise from the RVOT.