Electrocardiographic Characteristics of Left Ventricular Outflow Tract Tachycardia

Abstract

Catheter ablation of idiopathic left ventricular outflow tract tachycardia (LVOT‐VT) is rare because a safe ablation technique at this site has not been described, and serious complications may occur. This study compared the QRS morphology of LVOT‐VT with that of idiopathic right ventricular outflow tract tachycardia. A comparison was made between the electrocardiographic characteristics of LVOT‐VT originating from the supravalvular region of a coronary cusp (Supra‐Ao group) with those of LVOT‐VT originating from the infravalvular endocardial region of a coronary cusp of the aortic valve within the LV (Infra‐Ao group). After precise mapping of the right ventricle, left ventricle, pulmonary artery, coronary cusps, and proximal portion of the anterior interventricular vein, there were 17 patients in whom VT was thought to be located at the LVOT by both activation and pace mapping. They were divided between a Supra‐Ao group (n = 8), and an Infra‐Ao group (n = 9). Analysis of the 12‐lead electrocardiogram (ECG) revealed an S wave in lead I in all 17 patients. A precordial R wave transition was also observed at V₁ or V₂ in 16 patients (94%). In 7 of 8 patients (88%) with Supra‐Ao LVOT‐VT, no S wave was observed in either V₅ or V₆. In contrast, an Rs pattern was observed in both V₅ and V₆, or in V₆ only, in 100% of the patients with Infra‐Ao LVOT‐VT. A LVOT‐VT should be suspected when the ECG shows an S wave in lead I and an R/S ratio greater than 1 in lead V₁ or V₂, versus a coronary cusp location if there is no S wave in either lead V₅ or V₆.