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Antiarrhythmic drugs (except amiodarone) were withdrawn at least 5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.