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.