Electrophysiological study
Electrophysiological studies were performed under deep sedation with intravenous propofol, pentazocine, and hydroxyzine hydrochloride. Body surface electrograms and bipolar intracardiac electrograms were monitored continuously and recorded on an EP-WorkMate recording system (Abbott, Saint Paul, MN, USA). A 6-Fr Duo-Decapolar catheter (BeeAT, Japan Lifeline Co., Ltd., Tokyo, Japan) was placed into the distal coronary sinus and along the lateral wall of the RA. An intracardiac echocardiography catheter CARTO sound (Biosense Webster, Inc., Diamond Bar, CA, USA) was positioned in the RA to guide transseptal punctures. Two long sheaths (SL0, Agilis, Abbott) were passed into the LA, and LA angiography was performed.
Thereafter, LA electroanatomical mapping was performed during pacing from the distal end of a 10-pole catheter (Snake, Japan Lifeline Co., Ltd.) positioned at two different sites of the RA: (1) the RAA, and (2) the RAPW (posteriorly to the fossa ovalis at the level of the RPV carina as depicted by LA angiography). In the case of AF, electrical cardioversion was performed just before LA mapping. RA pacing was performed at twice the diastolic threshold (2-ms pulse width) at cycle lengths of 750 ms. LA activation maps were acquired only if the conduction time between the RA pacing stimulus and the LA was >30 ms, to exclude direct far field capture by RA pacing. During the RA pacing, the LA was mapped with a multielectrode mapping catheter (PentaRay; Biosense Webster, Inc.) and the CARTO 3 system CONFIDENSE mapping module with the continuous acquisition of electroanatomical points. Points were accepted only if they passed all the selected filters, including cycle length stability within 40 ms of the mapped cycle range under RAA or RAPW pacing, local activation time stability with 4 ms, and an electrode position stability within 2 mm. A tissue proximity filter based on catheter location and impedance measurements was used to determine electrode proximity to the cardiac tissue. The steepest negative deflection (-dV/dt) in each distal unipolar signal was used for calculation of the local activation time.