PROCEDURE
After obtaining informed consent, all patients underwent an invasive electrophysiologic study (EPS) under moderate sedation with Midazolam and Fentanyl. Programmed electrical stimulation and burst pacing from the high right atrium, coronary sinus, His bundle region, and right ventricle were used to evaluate atrioventricular conduction and exclude other arrhythmias. 3D Electro-anatomic mapping (3DEAM) (Carto 3, Biosense Webster OR EnSite Precision, Abbott) was used in all cases. Femoral venous access was obtained under ultrasound guidance, and an ICE catheter was advanced through femoral access into the RA.  From the home view position, the ICE probe was rotated clockwise to visualize the interatrial septum, and then tilted posteriorly to obtain a long-axis view of the SVC8 (Fig. 2). Slight adjustments using clockwise and counter-clockwise rotation from this position allowed for visualization of the lateral and septal aspects of the AR, identified as a band of atrial myocardium in the region of the SVC–RA junction, typically connecting the CT to the interatrial septum near its superior limbus7 (Fig. 2). Incremental doses of isoproterenol infusion were used to obtain sinus tachycardia. Once stable sinus tachycardia at the highest tolerated isoproterenol dose (up to 10 mgc/min) was observed, 3DEAM of the SVC-RA region were created using a high-definition multipolar catheter (PENTARAY NAV®, Biosense Webster OR Advisor HD GridTM, Abbott) advanced through a deflectable sheath into the RA. In order to obtain accurate activation points in the AR and avoid point extrapolation, manual annotation was used as deemed necessary, to adjust tags under direct ICE visualization. The course of the right PN was localized by pacing at high output (20 mA/1 ms) and tags were manually annotated on the 3DEAM under ICE visualization when diaphragm stimulation was present (Fig. 3). Local activation times were automatically defined from a stable reference atrial electrogram (EGN), to the maximum negative dV/dT at the local unipolar signal on the mapping catheter. RF applications were performed at the earliest activation location in the AR, using an open irrigated-tip catheter with contact force sensing capabilities (THERMOCOOL SMARTTOUCH SF®, Biosense Webster OR TactiCathTM, Abbott). RF power was set at 30 to 40W, with a contact force between 15-20 gm at the operator’s discretion. Each RF application was monitored for an impedance drop of at least 10 Ohms, with elimination of local automaticity induced by RFA continued until a 50% reduction in the amplitude of the local bipolar EGM was obtained. The RF applications were anatomically extended from the earliest region at the AR towards its septal aspect, until the elimination of automaticity at this region and/or obtaining a decrease in HR of 25% on Isoproterenol infusion was achieved (Fig. 4 d,e) (usually coinciding with a change of the P-wave axis on the horizontal plane of the ECG). Anatomic extension of the RF lesions towards the septal AR was performed on all study subjects, independent of the local activation times recorded at this location. Repeat activation and voltage maps were performed if a significant decrease in HR was not obtained with initial RFA and additional RF applications were performed on the earliest site at the AR with careful delineation of the PN on the new map. Post-procedure, patients remained in the hospital overnight under continuous ECG monitoring and were discharged the next day if no complications occurred.
Follow-up included an exercise stress test at 3 months, a 24-hour Holter, 30-day cardiac rhythm monitor or interrogation of an implanted cardiac rhythm monitor at 3, 6, and 12 months, and longitudinal clinic visits to assess symptom status and medication adjustments.