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.