Identification of distinct electrocardiographic patterns from the basal left ventricle: Distinguishing medial and lateral sites of origin in patients with idiopathic ventricular tachycardia

Background: Idiopathic ventricular tachycardias (IVTs) can originate from the basal left ventricle (LV). Objective: To determine if using magnetic electroanatomic mapping (MEAM) for accurate localization (1) unique ECG morphologies on pace maps from medial and lateral sites in basal LV could be identified and (2) this ECG information would facilitate VT localization. Methods: In 12 patients with structurally normal hearts undergoing ablation for IVT, detailed MEAM of LV was constructed in sinus rhythm and pace-mapping was done from the septal-parahisian (S-P) region, aortomitral continuity (AMC), and superior, superolateral, and lateral mitral annular (MA) locations. Pace maps were analyzed for ECG morphologies in limb leads and transition patterns in precordial leads. Results: Medial pacing sites (S-P and AMC) compared with lateral sites (superolateral and lateral MA) demonstrated narrower QRS complexes (134 ± 24 msec vs. 182 ± 18 msec; P < .05) with initial negative forces in lead V₁ and predominantly positive forces in lead I (amplitude 0.59 ± 0.27 mV vs. 0.16 ± 0.34 mV; P < .05). The ratio of QRS complexes in leads II and III was >1 for all (12 of 12) S-P pace maps and 11 of 12 lateral MA pace maps but remained ≤1 for pace maps from 10 of 12 AMC locations, 11 of 12 superior MA locations, and 10 of 11 superolateral MA locations. Using these ECG criteria, a blinded reviewer was able to accurately localize the site of origin (SOO) of clinical arrhythmia (successful ablation site on MEAM) in 10 of 12 cases (83%) of IVT originating from basal LV. Conclusion: Pace maps from basal LV endocardium manifest site-dependent ECG morphologies that can help differentiate medial from lateral locations and can predict the SOO of clinical arrhythmias from this region.