Evaluation of impedance and ECAP thresholds at early processor activation after CI surgery

The cochlear implant (CI) is the standard treatment for severe to profound hearing loss. So far, the processor was initially activated after a standard healing phase of 4-6 weeks following CI surgery. Due to developments in surgery technique, the wound is smaller and heals faster. This enables an early fitting of the processor within a few days after surgery. The aim of this work was the evaluation of impedances and ECAP thresholds after early processor activation in comparison to an activation after the standard healing phase. In total, 31 patients were included in the early fitted intervention group (IG) and 39 patients in the control group (CG). Objective measurements were performed via the CI fitting software. The intracochlear impedance was documented at different appointments: intraoperative, at initial processor activation, after 3, 6 and 12 months of CI usage. Furthermore, the electrically evoked compound action potentials (ECAP) of the hearing nerve were measured intraoperatively and postoperatively after 12 months of CI usage. The results showed significant higher impedances in the CG at initial processor activation than in the IG. After 3 months of CI usage, the impedances in the CG decreased to the values of the IG and showed no significant differences, likewise after 6 and 12 months. The ECAP thresholds showed no significant difference between IG and CG at intraoperative and postoperative measurements. Although there were differences in the impedance at initial activation between IG and CG, long-term follow-up showed no differences in the objective measurements between the groups. Possible effects on the achieved speech recognition need to be investigated in further studies.