General principle
Patients were established on oral anticoagulation for at least one month prior to ablation. Unfractionated heparin was administered before transseptal puncture, with a target activated clotting time of 300 to 400 s. All procedures were carried out under conscious sedation. The Rhythmia system (Boston Scientific, Marlborough, MA) or the CARTO-3 HD-coloring system (Biosense Webster, Diamond Bar, CA) was used for the high-density mapping. Three catheters were inserted via the right femoral vein: (1) a steerable decapolar catheter (Dynamic XT, Boston Scientific) inside the coronary sinus (CS) and the great cardiac vein (GCV); (2) an irrigated tip catheter (IntellaNav, Boston Scientific; or Thermocool SmartTouch, Biosense Webster) for ablation; and (3) a multipolar catheter (Orion, Boston scientific; or Pentaray, Biosense Webster) to build the anatomy and record the electrograms of the left atrium (LA) and right atrium (RA). A steerable long sheath (Agilis, St Jude Medical, St Paul, MN) was used to optimize catheter stability during mapping and ablation. Points were automatically acquired when: (1) the tachycardia cycle length (TCL) was stable (± 10 ms); (2) the time variation of a reference electrogram from the CS catheter was stable (± 5 ms); and (3) the beat-to-beat catheter motion was limited (< 4 mm with CARTO-3, and < 1 mm with Rhythmia). The low-voltage electrogram and noise threshold were defined as an amplitude of < 0.5 mV and < 0.03 mV, respectively. Point-by-point radiofrequency ablation was performed using power control mode and normal saline irrigation, with the following settings: (1) 30-50 W during 15-30 s at the endocardial aspect of the atria; and (2) 20-25 W during 15-20 s inside the CS or the GCV.