Idiopathic Left Bundle-Branch Block–Shaped Ventricular Tachycardia May Originate Above the Pulmonary Valve

BACKGROUND: Idiopathic left bundle-branch block (LBBB)-like ventricular tachycardia (VT) is considered to originate in the right ventricular outflow tract (RVOT) or from the aortic root. Both regions are derived from the embryonic outflow tract. We now report that also the pulmonary trunk can give rise to VT, suggesting a common etiology of these tachycardias. METHODS AND RESULTS: We studied 6 patients with symptomatic idiopathic LBBB-VT using electrophysiological mapping techniques. The VT origin was determined by analyzing the electrograms and the angiographic location of the catheter tip at the successful ablation site or the earliest activation site. Eight VTs were induced. Two VTs, with a mean earliest endocardial activation time of -5 and -20 ms and optimal pace mapping, were successfully ablated in the RVOT. In the remaining 6 VTs, the earliest activation site was found in the pulmonary artery, and, at this site, a sharp potential was present -38+/-12 ms before the QRS in 5 VTs. The mean earliest endocardial activation time in the RVOT was -1+/-2 ms. Ablation was attempted in 5 of 6 VTs and resulted in an acutely successful procedure. After a mean follow-up of 10+/-4 months, 1 of 5 patients had a recurrence. CONCLUSIONS: The site of origin of idiopathic LBBB-VT can be in the root of the pulmonary artery, suggesting a myocardial connection from this site to the RVOT. If no good criteria for ablation in the RVOT are found, detailed mapping of the pulmonary artery should be performed.