Ablation procedure
The ablation procedure, previously described in detail,10 was performed under general anesthesia. A single transseptal puncture was created under fluoroscopic and intracardiac echocardiographic guidance (Acuson, AcuNav, Biosense Webster, Diamond Bar, CA). A 28-mm cryoballoon catheter (Arctic Front Advance, Medtronic, Minneapolis, USA) was introduced into the LA through a steerable sheath (Flexcath Advance, Medtronic) with a circular mapping catheter (Achieve, Medtronic), and cryothermal energy was applied through a cryoballoon, occluding each PV. The compound motor action potentials of the diaphragm, provoked by phrenic nerve pacing, were continuously monitored during CBA of the right PV to prevent phrenic nerve injury. PVI was confirmed using a dual-decapolar circular mapping catheter (EPstar Libero, Japan Lifeline, Tokyo, Japan). If successful PVI was not achieved solely with a cryoballoon, touch-up ablation was performed using an irrigated RF catheter (FlexAbility or TactiCath, Abbott, Illinois). After successful PVI, linear ablation of the LA roof was performed using a cryoballoon. An Achieve catheter was inserted into the left and right superior PVs; the cryoballoon was shifted along the LA roof by changing the direction of the steerable sheath and adjusting the position of the cryoballoon and sheath, ensuring that each cryoballoon location overlapped with the previous location. After CBA of the LA roof, complete conduction block was confirmed based on activation and voltage maps created via an electrical, impedance-based mapping system (Ensite NavX, Abbott, Illinois), using a duo-decapolar circular mapping catheter (EPstar Libero, Japan Lifeline, Tokyo) (Figure 2 ). If complete conduction block was not obtained after CBA, we then performed touch-up ablation using an irrigated RF catheter. Cryothermal energy was then applied for 180–240 s at the surgeon’s discretion. We performed CBA under luminal esophageal temperature (LET) monitoring using esophageal temperature probes (Esophaster, Japan Lifeline, Tokyo) with a cutoff value of 15°C. RF applications were prematurely interrupted when the LET reached 39°C.