Detecting and managing partial shorts in Cochlear implants: A validation of scalp surface potential testing

Abstract

Objective: To investigate the value of scalp surface potentials to identify and manage partial short circuits to ground in cochlear implant electrodes.Design: A retrospective review of patients with suspected partial short circuits.Main outcome measure: Electrical output of individual electrodes was measured using scalp surface potentials for patients reporting a change in hearing function.Electrical output was compared to functional performance and impedance measurements to determine if devices with suspected partial short circuits were experiencing a decrease in performance as a result of reduced electrical output. Electrical output was checked in an artificial cochlea for two implants following explant surgery to confirm scalp surface potential results.Results: All patients with suspected partial short circuits (n = 49) had reduced electrical output, a drop in impedances to approximately ½ of previously stable measurements or to below 2 kΩ, an atypical electrical field measurement (EFI) and a decline in hearing function. Only devices with an atypical EFI showed reduced electrical output. Results of scalp based surface potentials could be replicated in an artificial cochlea following explantation of the device. All explant reports received to date (n = 42) have confirmed partial short circuits, with an additional four devices failing integrity tests. Conclusion:Surface potential measurements can detect partial shorts and had 100% correlation with atypical EFI measurements, which are characteristic of a partial short to ground in this device. Surface potentials can help determine the degree to which the electrode array is affected, particularly when behavioural testing is limited or not possible.

A Multicenter Comparison of 1-yr Functional Outcomes and Programming Differences Between the Advanced Bionics Mid-Scala and SlimJ Electrode Arrays

“…To our knowledge, all patients with confirmed faults were removed. Unfortunately, impedances alone may not reliably detect all early failures (41). Without routine EFI, we cannot rule out the possibility that hearing outcomes or programming may be affected for a minority of the remaining patients in this series.…”

“…Patients who did not use spoken language as their primary mode of communication (5 SlimJ, 7 Mid-Scala) were excluded from all comparison. Patients were also removed if they did not attend their 1-year appointment (6 SlimJ, 9 Mid-Scala), or showed signs of V1 failure (40,41) (6 SlimJ, 23 Mid-Scala; Table 1).…”

Improving the sensitivity of cochlear implant integrity testing by recording electrode voltages with surface electrodes

“…In February 2020, Advanced Bionics corporation recalled Ultra V1 cochlear implants (CIs), due to a vulnerability of the implanted device to moisture ingress. Moisture ingress leads to partial short circuits to the implant's reference electrodes, resulting in reduced amplitude stimuli and reduced sound quality (Eitutis et al, 2022;Gärtner and Lenarz, 2022;Lindquist et al, 2022;McHugh et al, 2022;Schwam et al, 2023;Winchester et al, 2023). Clinicians may observe changes in impedance telemetry, neural response imaging, soundfield aided thresholds and speech perception assessments as the issue progresses.…”

“…Advanced Bionics (AB) provide a test for assessment of electrode function in these devices, Electrical Field Imaging (EFI), which is available via their Active Insertion Monitoring "AIM tablet" (Eitutis et al, 2022) and can be performed in routine cochlear implant audiology clinics. It is the first integrity test that the manufacturer has provided for routine clinical use, beyond standard impedance telemetry.…”

“…The test has some limitations, as the manufacturer's analysis tool warns that it may be inaccurate in cases of partially inserted electrode arrays, recipients with abnormal anatomy and should not be used before 3 months post-surgery. Eitutis et al (2022) and Gärtner and Lenarz (2022) give examples of Ultra V1 CI faults that did not register on the manufacturer's automated analysis tool. The manufacturer has recently reported that the sensitivity of the test falls between 70 and 90% (Boyle, June 2023, personal communication).…”