Electrophysiological Study and Mapping
Antiarrhythmic drugs (except amiodarone) were withdrawn at least 5 half-lives before the procedures; amiodarone was interrupted one month before the procedure. A deflectable decapolar catheter (Dynamic XT, Boston Scientific) was positioned within the coronary sinus. If the patient was in sinus rhythm at the start of the procedure, burst pacing was performed to induce AT. Atrial mapping was performed with a Navistar Thermocool 3.5-mm D-F curve ablation catheter with Smart Touch technology (Biosense Webster) or multipolar mapping catheters (Pentaray, Biosense Webster Inc.). Bipolar electrograms filtered at 10–400 Hz were recorded. A bipolar signal from the coronary sinus (CS) electrode was used as the timing reference. The anatomy of the atrium was reconstructed, and zones of ESAs and double potentials (DPs) were marked. The following thresholds were used to define a scar: scar, <0.05 mV; scar border zone, between 0.05 and 0.5 mV; and normal, 0.5 mV. DP was defined as a pair of widely split high-frequency potentials separated by a minimum interval of 30 msec. After sequential construction of the map, all points were manually checked and corrected if necessary, especially for activation timing of local fragmented EGMs. A new map was generated to identify a different reentrant circuit if the P-wave morphology or tachycardia CL changed during RF ablation. A functional conduction block (FCB) region was defined as an area showing a conduction block in one AT but not in another AT or in sinus rhythm (Figs. 1-3). The conduction block line was shown as a white line instead of the conduction time interval between two neighboring tissues over 20% of the CL in the Carto system. Entrainment mapping was not performed systematically to avoid terminating or transforming tachycardia. This approach was used only when it was suspected that the ATs were related to epicardial conduction.