The V₂ transition ratio: A new electrocardiographic criterion for distinguishing left from right ventricular outflow tract tachycardia origin

Objectives: We sought to develop electrocardiography (ECG) criteria for distinguishing left ventricular outflow tract (LVOT) from right ventricular outflow tract (RVOT) origin in patients with idiopathic outflow tract ventricular tachycardia (OTVT) and lead V₃ R/S transition. Background: Several ECG criteria have been proposed for differentiating left from right OTVT origin; ventricular tachycardias (VTs) with left bundle branch block and V₃ transition remain a challenge. Methods: We analyzed the surface ECG pattern of patients with OTVT with a precordial transition in lead V₃ who underwent successful catheter ablation. Sinus and VT QRS morphologies were measured in limb and precordial leads with electronic calipers. The V₂ and V₃ transition ratios were calculated by computing the percentage R-wave during VT (R/R+S)_VT divided by the percentage R-wave in sinus rhythm (R/R+S)_SR. Results: We retrospectively analyzed ECGs from 40 patients (mean age 44 ± 14 years, 21 female) with outflow tract premature ventricular contractions (PVCs)/VT. Patients with structural heart disease, paced rhythms, and bundle branch block during sinus rhythm were excluded. The V₂ transition ratio was significantly greater for LVOT PVCs compared with RVOT PVCs (1.27 ± 0.60 vs. 0.23 ± 0.16; p < 0.001) and was the only independent predictor of LVOT origin. In 21 prospective cases, a V₂ transition ratio <0.60 predicted an LVOT origin with 91% accuracy. A PVC precordial transition occurring later than the sinus rhythm transition excluded an LVOT origin with 100% accuracy. Conclusions: The V₂ transition ratio is a novel electrocardiographic measure that reliably distinguishes LVOT from RVOT origin in patients with lead V₃ precordial transition. This measure might be useful for counseling patients and planning an ablation strategy.