3.3 Left atrial voltage mapping
Following PVI, detailed voltage mapping using a 20-pole circular
catheter with 1-mm electrodes (LassoNaV®, Biosense
Webstar) or a 20-pole multielectrode catheter arranged in 5 soft
radiating spines (Pentaray®, Biosense Webster) was
performed during 100-beat-per-minute paced rhythm from the high right
atrium. Mapping points were automatically acquired using the CARTO
confidence module with the following settings: cycle length filtering,
±30 msec; localize activation time stability, < 3 msec;
position stability, < 2 mm; and density, < 1 mm.
Left atrial geometry was created using the fast-anatomical mapping
module. Mapping was continued to fill all color gaps on the voltage map
with an interpolation threshold of 17 mm for fill threshold and 10 mm
for color threshold. If poor contact between the circular mapping
catheter and endocardium surface was suspected, mapping using the
ablation catheter was added with a point acquisition setting of contact
force ≥ 5 g. The band pass filter was set at 30 to 500 Hz.
LVAs were defined as areas with a bipolar peak-to-peak voltage
< 0.50 mV covering > 5 cm2 of
left atrium. On the voltage map, the bipolar voltage color bar was set
to range from 0.10 to 0.50 mV and scar level was set at < 0.05
mV. The left atrium was divided into six regions - septal, anterior,
roof, posterior, inferior, and lateral - as reported
previously.5
After this procedure, constant burst pacing was performed for 5 s at
each cycle length, starting with 300 ms and a subsequent decrement of 20
to 200 ms or the shortest cycle length that resulted in 1:1 atrial
capture. This was followed by a high-dose isoproterenol provocation test
(infusion of 5, 10, and 20 µg/min isoproterenol for 2 min each) to
induce AF or atrial tachycardia. If atrial flutters or non-PV AF
triggers were observed spontaneously or induced by atrial burst stimuli
or isoproterenol infusion, additional ablation were performed. Ablation
of induced and spontaneously developing AF-triggering ectopies and
atrial tachycardia was attempted at the earliest activation site for AF
trigger or centrifugal atrial tachycardia, and across the reentrant
circuit for macro-reentrant atrial tachycardia. Ablation targeting LVAs,
linear ablations and/or ablation guided by complex fractionated
electrograms were performed at the discretion of attending operators.
3.4 Whole left atrial
electrophysiological degeneration
Whole left atrial electrophysiological degeneration was assessed by the
mean regional voltage at each region and left atrial total conduction
velocity.12
Mean regional voltage was calculated by averaging 10 points evenly
selected across the region. ROC analysis was used to estimate a best
cut-off value of mean regional voltage to predict AF recurrence. The
extension of mean regional voltage reduction was assessed by the number
of regions with a mean regional voltage < the region-specific
cut-off value.
Left atrial conduction velocity
was calculated as left atrial anterior conduction distance divided by
conduction time between the start (septum) and end of the propagation
wave front (lateral mitral annulus) in the left atrium, as reported
previously.12 Anterior conduction distance was
measured manually by tracing the pathway of the propagation wave front
from the start point to the end point in the anterior left atrium.