Electrocardiographic characteristics of left ventricular outflow tract tachycardia

Catheter ablation of idiopathic left ventricular outflow tract tachycardia (LVOT-VT) is rare because a safe ablation technique at this site has not be en 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 c oronary cusp (Supra-Ao group) with those of LVOT-VT originating from the in fravalvular endocardial region of a coronary cusp of the aortic valve withi n the LV (Infra-Ao group). After precise mapping of the right ventricle, le ft ventricle,pulmonary artery, coronary cusps, and proximal portion of the anterior interventricular vein, there were 17 patients in whom VT was thoug ht to be located at the LVOT by both activation and pace mapping. They were divided between a Supra-Ao group (n = 8), and an lnfra-Ao group (n = 9). A nalysis 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 V- 1 or V-2 in 16 patients (94%). In 7 of 8 patients (88%) with Supra-Ao LVOT- VT, no S wave was observed in either V-5 or V-6 In contrast, an Rs pattern was observed in both V-5 and V-6, or in V-6 only, in 100% of the patients w ith 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 V-1 or V-2, versus a coronary cusp location if there is no S wave in either lead V-5 or V-6.