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).