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.