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.