Catheter ablation procedure
Catheter ablation was performed under general anesthesia using an intravenous administration of propofol and dexmedetomidine. A single-use supraglottic airway device (i-gel, NIHON KOHDEN, Tokyo, Japan) was inserted in all eligible patients, and an esophageal temperature thermocouple catheter (Esophaster, Japan Lifeline, Tokyo, Japan) was inserted through this airway device into the esophagus for continuous monitoring of the luminal esophageal temperature. Vascular access was acquired through the right internal jugular and femoral veins. A 20-pole catheter (BeeAT, Japan Lifeline, Tokyo, Japan) was inserted into the coronary sinus for electrogram recording, atrial pacing, and defibrillation. Two transseptal punctures were performed; one for a 12-Fr inner-diameter deflectable sheath (CardioFocus, MA, USA) and VGLA catheter and the other for a circular mapping catheter. Heparin was given as intravenous boluses followed by a constant infusion to maintain an activated clotting time of >300 seconds during the ablation procedure.
An EnSite NavX navigation system (St. Jude Medical, St. Paul, MN, USA) was used for 3-dimensional mapping. A mapping catheter (EPstar libero, Japan Lifeline, Tokyo, Japan) was used to construct the geometry of the LA and each PV. The bipolar electrogram filters were set between 30 and 500 Hz.
The first generation VGLA catheter (HeartLight, CardioFocus, MA, USA) was inserted into the LA, and expanded trying to occlude each PVs. The laser balloon (LB) was inflated in a slow fashion to maximize the contact between the LB and cardiac tissue according to the size and shape of the target PV orifice. An LCPV isolation was performed with a maximal dilated LB (balloon size 9). If the LCPV could not be completely occluded with the maximal size of the LB, the LB was further inserted into the distal superior and inferior branches of the LCPV for the sake of isolating the distal branches the LCPV individually. The laser console uses aluminum gallium arsenide as a semiconductor laser element and emits a therapeutic laser with a wavelength of 980 nm. The laser energy level was titrated according to the degree of tissue exposure between 5.5 and 12 W using the LightTrackTM software (CardioFocus, MA, USA). Every energy application was applied for 20 to 30 seconds depending on the applied laser energy. The area adjacent to the blood was applied with 5.5 W for 30 seconds in order to avoid an LB rupture. The laser energy was applied continuously overlapping each lesion by 50% around each PV ostium. The VGLA was prematurely terminated when the luminal esophageal temperature reached 39℃. The VGLA was performed in a sequence of the LSPV (or LCPV), LIPV, RSPV, and RIPV.
A 10-pole catheter was placed in the right subclavian vein or superior vena cava to pace the right phrenic nerve. The compound motor action potentials (CMAPs) were continuously measured, and the operators confirmed the tactile feedback of the diaphragmatic contractions during the VGLA of the RSPV or RIPV. The threshold for capturing the right-sided diaphragm was recorded, and phrenic nerve pacing was performed at a rate of 40 pulses per minute at an output exceeding the pacing threshold by 10%8). The VGLA was prematurely discontinued when the operator felt a reduction in the diaphragmatic contractions or the CMAP amplitude decreased by more than 30%9).
After the initial encirclement by the LB, the electrical isolation status of each PV was assessed. If all PVs were electrically isolated, dormant conduction was evaluated by an administration of adenosine triphosphate (ATP). The VGLA was subsequently applied at the electrical gap sites for touch-up ablation when the PVI was unsuccessful despite the initial encircling by the LB. When a PVI could not be successfully accomplished with only the VGLA, an irrigated RF catheter (TactiCath, Abbott, Illinois, USA) was used for touch-up ablation to eliminate all gap conduction sites. A successful PVI was defined as entrance and exit conduction block between the LA and PVs. After a successful initial PVI, it was reassessed 15 minutes after the last application. A voltage map of the PVs and LA was acquired before and after the PVI using a CARTO 3D mapping system (Figure 1 ).
A cavotricuspid isthmus ablation was also performed when atrial flutter was observed during the catheter ablation procedure or according to the discretion of the operator. No eligible patients underwent catheter ablation of non-PV foci. The RF energy was delivered with a maximum power of 35 W, and the catheter tip temperature was limited to 42 °C. The ovality index was calculated according to the method of a previous report based on the CT image: 2 * (maximal diameter − minimal diameter) / (maximal diameter + minimal diameter)10).