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.