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Impedance Development after Hybrid-L Implantation
18 April 2018 (online)
Nowadays, more and more patients with residual hearing especially in the low frequency range receive a cochlear implant (CI). In order to protect the residual hearing, shorter and thinner electrode arrays were developed that enable atraumatic insertion through the round window. One of these is the Hybrid-L electrode which has also smaller stimulation contacts compared to the standard Contour electrode. The Hybrid-L electrode is now clinically available for more than 10 years. Nevertheless, a systematic evaluation of electrode contact impedance data is still missing.
All patients receiving a Hybrid-L implant at MHH and being at least 18 years of age at the time of implantation (N = 137) were extracted from the patient database at the German Hearing Center. Impedance values as measured during clinical routine were evaluated for all active contacts from a few days after implantation until 10 years post implantation (as long as data for the individual patient are available).
On average, impedances increase from about 5 kOhms shortly after implantation to 13 kOhms before the start of electrical stimulation. During electrical stimulation impedances remain fairly constant over years at 6 to 7 kOhms. Impedances are higher on basal contacts compared to middle and apical ones except shortly after implantation. The stimulation effect, the difference between impedance values before and after electrical stimulation, is larger than for standard Contour electrodes.
As the long term impedance values are comparable to the ones with Contour electrodes but the contact areas are smaller, this indicates less tissue growth around the electrode array when using a Hybrid-L electrode.