Hearing Preservation Outcomes with Different Cochlear Implant Electrodes: Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422

Abstract

Objectives: In recent years, it has been possible to preserve hearing after cochlear implantation in patients with significant amounts of low-frequency residual hearing. Due to the dimensions and characteristics of the cochlear implants (CIs) Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422, both can be used to preserve residual hearing. The aim was to investigate the degree and progression of hearing preservation over a longitudinal postoperative period in a large consecutive cohort of implanted patients with preoperative residual hearing who received either the Nucleus Hybrid-L24 or the Nucleus Freedom CI422 implant. The intention was to examine potential characteristics and triggers of resulting postoperative hearing loss which may support a differentiation of CI candidacy criteria for a certain implant type. Methods: A retrospective data analysis of patient files on consecutively implanted subjects presenting with a severe-to-profound sensorineural hearing loss at frequencies >1,500 Hz and substantial residual hearing at frequencies ≤1,500 Hz, implanted with a Nucleus Hybrid-L24 (n = 97) or a CI422 implant (n = 100), was undertaken. A single-subject repeated-measure design comparing the mean threshold shift for pure-tone thresholds under headphones up to 24 months after implantation was used. Results: Hearing preservation is observed in the majority of subjects with either implant (250-1,500 Hz frequency range). Hybrid-L24 patients exhibited a median hearing loss of 10 dB at initial fitting (n = 97) and of 15 dB after 24 months (n = 51). A 14.4-dB decrease in median hearing loss at initial fitting (n = 100) and a 30-dB decrease after 24 months (n = 28) was observed with the CI422 electrode. At initial fitting, 54.6% of the Hybrid-L24 (n = 97) and 49.0% of the CI422 (n = 100) subjects showed a mean threshold shift <15 dB. After 24 months, 58.8% (Hybrid-L24, n = 51) and 28.6% (CI422, n = 28) of the patients showed a mean threshold shift <15 dB. Conclusions: The results indicate that residual hearing was preserved for the majority of implanted patients with the Hybrid-L24 and the CI422 implant. Patients implanted with the Hybrid-L24 implant demonstrate greater stability and less median hearing loss over time than those with the CI422 implant. Assessments of onset and stability of hearing loss prior to implantation are important factors to consider during candidacy evaluation for electrode selection to potentially maximize the performance outcome for each patient.