Catheter ablation protocol
The details of the catheter ablation protocol have been previously published[6]. Under uninterrupted anticoagulants, all patients underwent PVI and superior vena cava isolation (SVCI). These were performed with geometric information based on reconstructed 3-D CT imaging system (CARTO 3, Biosense Webster, Inc., Diamond Bar, CA). Two long sheaths with one circular multi-electrode catheter and a 3.5-mm open-irrigated tipped catheter (ThermoCool STSF; Biosense Webster Inc., Diamond Bar, CA, USA) were used as ablation tools. To monitor the esophageal temperature, a multi-electrode esophageal temperature-monitoring probe was employed during the procedure (Esophaster, Japan Lifeline, Tokyo, Japan).
The detail of radiofrequency power was 50 W with an upper limit temperature of 42°C as recently denoted.[5]Disappearance of negative deflection in the unipolar electrogram recorded at the distal tip of the ablation catheter (unipolar signal modification, USM; Figure 1) was adopted as an indicator of sufficient transmural necrosis.[4, 7] RFA was continued for 3–5 seconds after the USM in the segments other than those adjacent to the esophagus (SAE). RF time was limited to 5 s or by the alert of the temperature sensor (upper limit of 39°C) to avoid esophageal injury in the SAE. During each RF application, the modification of the unipolar atrial electrogram was monitored in real-time at a sweep speed of 200 mm/s and filtered with a 0.5–120 Hz by the CARTO system.
To clearly visualize unipolar signals, a 10-polar electrode catheter with an indifferent electrode (DECANAV®, Biosense Webster Inc., Diamond Bar, CA, USA) in the coronary sinus was used, where a reference annotation signal was recorded from the bipolar signals. Targeted lesion distance was <5 mm and contact force (CF) was aimed at 5–20 g (target 10 g) and at <10g in the segments other than SAE and in the SAE, respectively. RFA was stopped at 3 s after the USM in case CF was above 15 g or catheter was perpendicularly placed on the atrial wall. RFA was continued for 5 s after the USM if CF was below 10 g or RFA site was near the carina. Intensive induction of atrial overdrive pacing with isoproterenol infusion and the confirmation of the absence of dormant conduction with adenosine-triphosphate (ATP) infusion was attempted. The confirmation was conducted for at least 20 min after the isolation of the ipsilateral PV pair.