Left atrial electroanatomical mapping and catheter ablation
procedure
Patients were under conscious sedation. Transesophageal echocardiography
was performed in all subjects to exclude LA thrombus. The procedure has
been described in details elsewhere.10,12 After a
single transseptal puncture, an activated clotting time (ACT) more than
300 seconds was maintained by intravenous heparin bolus (100 IU/kg) and
infusion. A 20‐pole catheter (Pentaray, interelectrode spacing 2-6-2 mm,
Biosense Webster) and an open‐tip irrigated radiofrequency (RF) catheter
with tip‐integrated contact force (CF) sensor (Thermocool SmartTouch, D
curve, 1‐6‐2mm; Biosense Webster) were used for mapping and ablation,
respectively. After reconstructing the three‐dimensional geometry of the
left atrium (LA) (Carto 3; Biosense Webster), high‐density bipolar
voltage mapping was performed during AF using the 20‐pole multielectrode
mapping catheter. In patients presented in sinus rhythm, burst atrial
pacing from distal coronary sinus (CS) at a cycle length of 200 to 150ms
was used to induce atrial fibrillation (AF). The Biosense Webster
Confidense module process was used to collect points with the following
filter settings: (a) force >6 g; (b) catheter stability,
acquiring points when the catheter location was stable (position
stability 2.5mm); (c) density 1mm, minimizing acquisition points when
the catheter is not being moved or collecting denser points if a higher
setting is chosen; (d) tissue proximity indicator, which uses impedance
measurements to determine the electrode proximity to cardiac tissue. The
CS was mapped with a steerable decapolar catheter (DECANAV,
interelectrode spacing 2-8-2 mm, Biosense Webster). As the ablation
catheter has a different electrode size and spacing and generally
underestimates the true electrogram voltage compared with the
multielectrode catheters, we made every attempt to collect all points
using the multipolar catheter rather than the ablation catheter to
maintain consistency within the map. Criteria for an adequate LA shell
were more than 2000 points (mean number of points: 2323±862) that were
homogenously distributed to delineate the entire chamber of the LA. We
mapped regions with low‐amplitude signals with greater point density to
more precisely delineate the extent of endocardial electroanatomic scar
areas. With a band pass filter set at 30 to 500 Hz, each acquired point
was classified according to the peak‐to‐peak bipolar electrogram
voltage. Two different cut-off values of bipolar signal amplitude were
investigated for scar fibrotic area characterization. Areas displaying
low amplitude bipolar signals ≤0.25 mV (1st low
voltage definition) and ≤0.4 mV (2nd low voltage
definition) were defined as scar fibrotic regions. We divided the LA
into the following regions: (1) left PV‐LA junction; (2) right PV‐LA
junction; (3) roof; (4) posterior; (5) inferior; (6) anterior (including
LA appendage); and (7) left septum (Figure 1 ). Confluent
regions of bipolar low voltage were measured using the standard surface
area measurement tool on the CARTO 3 software. The proportion of the
mapped LA surface exhibiting low voltage bipolar signals was expressed
as a percentage of the overall mapped LA surface area, except the four
PVs. All measurements were performed during the index ablation
procedure.
HCM patients underwent pulmonary vein antral isolation (PVAI) with
intention to minimize not isolated posterior and roof line, while
non-HCM patients PVAI only. Point‐by‐point ipsilateral PVAI was
performed using the real‐time automated display of radiofrequency
applications (Visitag; Biosense Webster) with predefined settings for
catheter stability (2.5mm for 10 seconds) and minimum CF (60% of time
>7 g). Radiofrequency energy was delivered in a
power‐controlled mode with maximum 40W for 20 seconds on the posterior
wall and maximum 40W for 30 seconds on the anterior wall and the roof of
the LA (irrigation of 30 ml/min) (EP Shuttle ST, Stockert GmbH,
Freiburg, Germany). If we could not terminate AF to a regular rhythm
(sinus rhythm or atrial tachycardia), we performed electrical
cardioversion. Entrance and exit block of the PVs as well as
bidirectional block of the roof line were confirmed after sinus rhythm
was restored.