11Listening to the Device: Objective Measures in Troubleshooting

TReading impedance: open, short, and the patterns between

Impedance is the opposition to current flow at a contact, measured by the implant itself; it sums the active electrode, the tissue, and the indifferent electrode in series, so a change in any element changes the reading. An open circuit reads as very high or unmeasurable impedance: a broken wire, a fractured contact, or an electrode sitting in air rather than fluid (as in a partial or extracochlear insertion). A short circuit reads as abnormally low impedance and reflects two contacts electrically joined; affected channels are typically deactivated to avoid unpredictable current spread. Pattern matters more than any single value: a global rise across the whole array suggests fibrosis or device-wide change, an isolated outlier suggests a single-contact fault, and a cluster can localize translocation or fold-over.[2001][2022]

TIntegrity testing: is the hardware sound?

Each manufacturer provides a dedicated integrity test that interrogates the internal electronics independent of the tissue interface and returns a pass/normal or fault status. Averaged electrode voltages (AEV) and the voltage-distribution/electric-field tables map the voltage produced at each contact when a single electrode is stimulated, revealing abnormal current spread or a non-functioning channel. A normal integrity test with abnormal in-vivo behaviour pushes the explanation toward biology or programming; a failed integrity test, or a fault reproducible across coil repositioning, supports a true hardware problem. Coupling quality between the diagnostic coil and the implant must be confirmed first: 'weak,' 'faint,' or 'poor' coupling produces unreliable telemetry that can mimic a fault.[2010][2009]

TECAP and field measures: localizing the fault

The ECAP is recordable in roughly 95% of recipients; an absent or markedly degraded response on channels that previously responded helps separate a neural/interface problem from a working but mis-programmed device. Electrical-field imaging and spread-of-excitation profiles show how current spreads from a stimulated contact; a discontinuity or unexpected mirror-image pattern is the telemetry signature of tip fold-over. Transimpedance-matrix measurements (a panchannel field map) predict fold-over and array malposition objectively, and can flag it on the table before imaging is obtained. Triangulate: impedance localizes the contact, integrity testing isolates the hardware layer, and ECAP/field measures characterize what the array is doing inside the cochlea.[2022][2020][2001]

CDevice problem or not? Putting it together

Decision rule: a device fault is supported by failed integrity testing, reproducible open/short patterns, or field discontinuities; a biological/programming cause is supported by normal hardware telemetry with abnormal behaviour. Objective measures complement but do not replace behavioural data: a child or guarded adult may give unreliable scores, so telemetry can be the deciding evidence. Longitudinal comparison is the most powerful tool: impedance and ECAP drift within known limits over the first months, so deviation from each recipient's own trend is more informative than population norms. Underlying methods for ECAP, impedance, AEV, and field imaging are detailed in the Objective Measures chapter; here they are deployed as a troubleshooting toolkit, not introduced from first principles.[2001][2010][2005]