Mapping and Ablation of Ventricular Tachycardia From the Left Upper Fascicle

Abstract

Triggered activity or localized reentry in the fascicular system can give rise to premature impulses or ventricular tachycardia (VT). The diagnosis of fascicular rhythms relies on the recording of the His bundle potential before the onset of surface ventricular activation.1 Radiofrequency catheter ablation can be performed successfully by identification of the earliest fascicular potential (FP).2 The following cases illustrate how the comparison of the FP-V interval between sinus rhythm (SR) and VT can help to identify the successful ablation site. ### Case 1 A 50-year-old man presented with symptoms of fatigue and frequent premature ventricular contractions (PVC) that were refractory to medical therapy. Left ventricular systolic function was normal as measured by echocardiography. On a 12-lead ECG, the PVCs were relatively narrow with an incomplete right bundle branch block morphology and normal axis, suggestive of origin from the proximal left fascicular system (Figure 1A). Electrophysiology study and mapping were performed during PVCs with a 4-mm catheter electrode via a retrograde aortic approach. Right bundle branch block was noted because of inadvertent mechanical block of the right bundle branch during manipulation of the right ventricular catheter. The ablation catheter was positioned near the distal His bundle or proximal left bundle with H-V (His-V) interval of 52 ms during SR and 24 ms during PVCs (Figure 2A). The catheter was then positioned at the proximal left anterior fascicle (LAF) with recordings of FP-V (fascicular potential-V) interval of 38 ms during SR and PVCs (Figure 2C). Radiofrequency was applied at this site with 30 W at 60°C that resulted in complete elimination of PVCs and LAF block (Figure 1B). The proximal left posterior fascicle (LPF) and distal LAF were also mapped before radiofrequency application. FP-V interval was measured as 29 ms during SR versus 17 ms during PVCs at the site of the proximal …