Evaluation of the SVC-ERP
The ablation catheter was used to pace the anterior, septal, and posterior sides 2 mm above the SVC-RA junction (Figure 1). The lateral side was not paced because of the common site of phrenic nerve stimulation. We used a stimulator (SEC-5104; Nihon Kohden, Tokyo, Japan) to deliver electrical impulses of 2-ms duration at twice the diastolic pacing threshold. The distal electrode of the catheter was the negative pole. Stable pacing sites were considered only if the output threshold was less than 4 V under the contact force range from 5 to 20 g. Surface and intracardiac electrograms filtered at 50–300 Hz were recorded simultaneously using a polygraph (RMC-5000; Nihon Kohden, Tokyo, Japan). After eight stimuli at a basic cycle length of 600 ms, a single extrastimuli coupled at 400 ms was decremented automatically in steps of 20 ms to the ERP 9. The dispersion of the SVC-ERP was defined as the difference between the longest SVC-ERP and the shortest SVC-ERP.