Catheter ablation procedure and mapping
After 1 transseptal puncture, 2 long sheaths (Agilis and SL0; Abbott
Medical) were introduced into both superior PV. A HD Grid were placed
transseptally at the antrum of the target PVs. All patients underwent
circumferential PV isolation guided. The circumferential ablation lines
were created under the guidance of a 3-D mapping system (EnSite
Precision system; Abbott Medical). After PV isolation, a detailed
high-density map of LA was constructed by acquiring more than 2000
endocardial points in each patient
during high right atrial pacing at
a rate of 100 bpm using HD Grid and the steerable sheath. Points
acquired following ectopic beats and far-field ventricular electrograms
were excluded from analysis. Automated 3-D mapping system (EnSite
AutoMap module; Abbott Medical) was used to construct the LA geometry,
voltage map, and isochronal activation map. The band pass filter was set
at 30–500 Hz. To ensure the highest accuracy of the acquired atrial
geometry, respiratory gating was performed, and the atrial geometry was
acquired at high adjustment settings. In addition, high-density mapping
was added at sites where LVA was recorded to exactly define the extent
of the LVA. Endocardial contact was ensured by fluoroscopy, electrogram
stability, and the 3-D mapping system. The highest amplitude bipolar
signal among signals within a vicinity of less than 1
mm2 was reflected on the voltage map. Field scaling
was applied to all maps. Every LA map was divided into the following six
segments. The LVA was defined using cut-off values for bipolar
peak-to-peak voltage as the following; mild (<1.3
mV)9, moderate (<1.0
mV)10, and severe LVA (<0.5
mV)11. LVA size was manually measured on each cut-off
value. The proportion of the mapped LA surface exhibiting low voltage
was expressed as a percentage of the overall mapped surface area of LA
within the isolation line, not including the ablation lesions in the
surface area of the LA and anatomical structures such as the PV and
mitral annulus. The mean bipolar voltage of global LA was calculated.
Isochronal activation maps were created using EnSite AutoMap module at
5-ms interval setting during high right atrial pacing at a rate of 100
bpm. An ACZ was identified on the activation map by locating a site with
isochronal crowding of ≥3 isochrones in a 4-mm diameter tag, which are
calculated as ≤27 cm/s. The cut-off value of ACZ was defined according
to a previous report.12 Figure 1 shows a
representative isochronal activation map and voltage maps. Global
activation time for the LA was calculated by subtracting the earliest
from the latest activation within the LA.