Long-Term Outcome After Substrate-Based Ablation of LPF VT During SR. Background: Catheter ablation of left posterior fascicular (LPF) ventricular tachycardia (VT) is commonly performed during tachycardia. This study reports on the long-term outcome of patients undergoing ablation of LPF VT targeting the earliest retrograde activation within the posterior Purkinje fiber network during sinus rhythm (SR). Methods: This study retrospectively analyzed 24 consecutive patients (8 female; mean age 26 +/- 11 years) referred for catheter ablation of electrocardiographically documented LPF VT. Programmed stimulation was performed to induce tachycardia, while mapping and ablation was aided by use of a 3D electroanatomical mapping system. Catheter ablation targeted the earliest potential suggestive of retrograde activation within the posterior Purkinje fiber network (retro-PP) recorded along the posterior mid-septal left ventricle during SR if LPF VT was noninducible. Results: Overall, 21/24 (87.5%) patients underwent successful catheter ablation in SR targeting the earliest retro-PP, while 3/24 (12.5%) patients were successfully ablated during tachycardia. In none of the patients, ablation resulted in LPF block. No procedure-related complications occurred. After a median follow-up period of 8.9 (4.810.9) years, 22/24 (92%) patients were free from recurrent VT. Conclusion: In patients presenting with LPF VT, ablation of the earliest retro-PP along the posterior mid-septal LV during SR results in excellent long-term outcome during a median follow-up period of almost 9 years. (J Cardiovasc Electrophysiol, Vol. 23, pp. 11791184, November 2012)