Repetitive Monomorphic Tachycardi From the Left Ventricular Outflow Tract: Electrocardiographic Patterns Consistent With Left Ventricular Site of Origin

Objectives. This study sought to characterize the electrocardiographic patterns predictive of left ventricular sites of origin of repetitive monomorphic ventricular tachycardi (RMVT). Background. RMVT typically arises from the right ventricular outflow tract (RVOT) in patients without structural heart disease. The incidence of left ventricular sites of origin in this syndrome is unknown. Methods. Detailed endocardial mapping of the RVOT was performed in 33 consecutive patients with RMVT during attempted radiofrequency ablation. Left ventricular mapping was also performed if pace maps obtained from the RVOT did not reproduce the configuration of the induced tachycardia. Results. Pace maps identical in configuration to the induced tachycardi were obtained from the RVOT in 29 of 33 patients. Application of radiofrequency energy at sites guided by pace mapping resulted in elimination of RMVT in 24 (83%) of 29 patients. In four patients (12%), pace maps obtained from the RVOT did not match the induced tachycardia. All four patients had QRS configuration during RMVT with precordial R wave transitions at or before lead V2. In two patients, RMVT was mapped to the mediosuperior aspect of the mitral valve annulus, near the left fibrous trigone; catheter ablation at that site was successful in both. In two patients, RMVT was mapped to the basal aspect of the superior left ventricular septum. Catheter ablation was not attempted because His bundle deflections were recorded from this site during sinus rhythm. Conclusions. RMVT can arise from the outflow tract of both the right and left ventricles. RMVTs with precordial R wave transition at or before lead V2 are consistent with left ventricular origin.