Influence of stimulus presentation rate on intraoperative ECAP thresholds in cochlear implant users

The objective is to evaluate the influence of the presentation rate on intraoperative ECAP thresholds in cochlear implant users.

The design was data on the ECAP thresholds (t-NRT) as well as the behavioural T- and C-levels have been collected in CI patients of a quaternary otologic referral centre. Measurements of the tNRT thresholds were performed intraoperatively for 250 Hz and 80 Hz presentation rates and correlated to the stabilised T- and C-levels measured at the 5th fitting session, 4-6 months after surgery.

There was a study sample of 35 consecutive CI patients. All patients were users of the Nucleus 24RECA (Freedom) or Nucleus CI512 cochlear implants with the Contour Advance-of-Stylet electrode.

The result showed that the t-NRT thresholds were higher for the 250 Hz pulse rate typically used during the intraoperative stimulation under general anaesthesia than for the 80 Hz rate used typically during the postoperative fitting sessions. This difference was more pronounced for the basal electrodes where it exceeded 10 current levels (CL). Pearson's correlation coefficients between the t-NRT-measurements and the stabilised T- and C-levels r ranged between 0.34 and 0.47.

In conclusion, the magnitude of the ECAP thresholds (t-NRT) recorded intraoperatively depends significantly on the stimulus presentation rate.