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.