Radiofrequency Ablation
All procedures were performed under conscious sedation using fentanyl and midazolam. Invasive arterial blood pressure was monitored. The SoundStarTM catheter (BiosenseWebster, Diamond Bar, CA, USA) was inserted via the left femoral vein and manipulated into the right ventricle (RV). The phased array probe was used to determine the ICE geometries of the RV, LV, and aorta. Endocardial borders and aortic cusps were delineated and transferred into the CARTO system (BiosenseWebster). The hypertrophic septum was intentionally constructed in detail during systole. (Figure 1) A quadripolar catheter was used to indicate the location of the His bundle and for back-up RV pacing. A retrograde aortic approach to the LV was preferred, while trans-atrial septal access was used if the retrograde aortic approach could not reach stable contact. Intravenous heparin (100 unit per kg) was administered to keep the activated clotting time 300-350 s. The locations of the His bundle and left bundle were annotated on the CARTO shell. (Figure 1) RF energy was delivered via a Navistar THERMOCOOL catheter or Smartouch catheter (Biosense Webster). Using a combination of CARTO and intracardiac echo navigation, RF energy was delivered to the SAM-septal contact area (Figure 1), with power of 35 - 50 W for either 30s or no further elevation of arterial BP, limited temperature of 43°C, and irrigation rate at 30 mL/min. Every effort was made to avoid injury to the His bundle/left bundle/fascicles during ablation. The invasive resting LVOT gradients were monitored during the procedure. The procedural endpoint was an LVOT gradient reduction of >50% or complete ablation of the SAM-septal contact area.9Methylprednisolone was administered for the next three days after the procedure to alleviate edema.