Study procedure
Antiarrhythmic medications were stopped for at least five half-lives before the procedure. Isoproterenol 1~5 µg/min was administered intravenously to provoke the clinical VAs if necessary. An 8F saline irrigating catheter (Thermocool, Biosense Webster, Diamond Bar, CA, USA) was advanced to the RVOT region under fluoroscopy through the femoral vein. A long sheath (SL1, Swartz or Preface) was used to facilitate catheter stability. For mapping of the PSCs, the reversed U-curve of the catheter was created in the bifurcation of PA, then pulled back into the PSCs, and confirmed by angiography by injecting contrast through the irrigating tube of the catheter (Figure 2). Pulmonary valve-ventricle junction (PVVJ) was determined by the resistance while retracting the catheter. Before ablation, the angiography was performed again to confirm the catheter’s location.
Activation mapping was completed by a three-dimensional mapping system (CARTO 3, Biosense Webster, Diamond Bar, CA, USA). Bipolar and unipolar electrograms were filtered at 30 to 500 Hz and 0.05 to 400 Hz. Local activating time (LAT) was determined by the correlation of earliest rapid downstroke of unipolar signal with the first sharp peak of the bipolar electrogram. The earliest ventricular activation (EVA) site had the longest time interval from LAT to ECG reference. The distance from EVA site to PVVJ was measured on CARTO3. IA targets were selected from the EVA sites with the steepest Q waves in the unipolar and bipolar electrogram.11 If the assigned strategy could not engage the target, the less earlier and closest sites on the PVVJ were alternatives.