Self-assessment of cochlear health by new cochlear implant recipients: daily impedance, electrically-evoked compound action potential and electrocochleography measurements over the first three postoperative months

A recent study from our research group showed that experienced cochlear implant (CI) users can independently perform their own cochlear health (CH) recordings at home, thanks to advances in CI telemetry. This allows measurements to be taken at regular intervals and over long periods of time. Whilst this is not yet currently available in routine clinical practice, the wealth of data that can be generated in this way has numerous potential applications, including helping to maximise the benefit patients receive from CIs by allowing clinicians to tailor CI programming strategies based on each individual’s own responses, explaining some of the variation in CI outcomes and creating tools to evaluate the safety and efficacy of novel adjunctive treatments for hearing loss. In this project, we assessed the stability of early post-implantation electrode impedances, electrically-evoked compound action potentials (eCAPs) and electrocochleography (ECochGs) in a group of newly implanted CI recipients. Specifically, eight subjects used the Active Insertion Monitoring system by Advanced Bionics to take the three recordings on a daily basis at home for three months, starting from the first day after CI surgery. Group level measurement validity was 93.7% for impedances, 93.1% for eCAPs and 83.7% for ECochGs. Impedances gradually increased over the first ten days and likely associated with the initial intracochlear inflammatory response to the electrode array, before decreasing and immediately after CI switch-on and, subsequently stabilizing thereafter. eCAP thresholds also showed good long-term stability over time and some subjects consistently displayed absent thresholds at one or more electrodes, potentially indicating regions of poor neural health. Since subjects were expected to have very little residual hearing, having met UK NICE guidelines for cochlear implantation, it was unsurprising that most ECochG thresholds did not reach the signal-to-noise criterion of 2:1 adopted by the AIM system. For the very small number of subjects that did show a considerable proportion of valid thresholds, these were relatively stable. We conclude that eCAPs and electrode impedances are promising objective measurements for evaluating CH in newly implanted CI recipients.