ICE and WT measurement
ICE imaging in the LA was performed before starting PVI. The ICE
catheter, equipped with a linear-phased array multifrequency (5.5-10
MHz) transducer, was connected to an Acuson P500 system (SIEMENS,
Munich, Germany). The ICE catheter in the RA was withdrawn after the
trans-septal puncture and then advanced into the LA via the 8.5Fr
deflectable sheath (Agilis NxT, short size). Only the tip (transducer)
of ICE catheter was carefully put out from the deflectable sheath and
was placed in the center of the LA under fluoroscopic guidance: the safe
distance (more than 10 mm) between the tip and the LA endocardium was
always confirmed and maintained throughout manipulation of the ICE
catheter (Figure 2). The ICE catheter was finely rotated without any
deflection (keeping neutral position) around the PV-junctional area to
obtain images perpendicular to the LA/PV surface. When different
angulation of ultrasound beam was required for clear anatomical
visualization, only the deflectable sheath was manipulated and deflected
to change the position of the ICE transducer and the direction of the
ultrasound beam. The snapshots of ICE imaging in each segment for PVI
were obtained during the diastolic phase in eight segments: the
anterior, roof, posterior and bottom of both PVs. The endocardial
boundary (separating the blood pool from myocardium) and the epicardial
boundary (separating the myocardial tissue from other surrounding
tissue) were manually outlined. The distance between the epicardial and
endocardial boundary was measured and defined as the WT. The WT was
measured more than five times in each segment between 5 mm inside and 5
mm outside of the LA-PV junction; the highest and lowest measurements
were discarded and the average of the ≥3 middle values was considered as
the WT in a segment.
To validate the accuracy and reliability of the ICE-based WT
measurements, the LA WTs on cardiac CT were also measured in the same
patient. The cardiac CT-based measurement was performed by cardiologists
who were blinded to the result of the ICE-based measurement; the WT
values were compared between the ICE- and cardiac CT-based measurements.