Electrode impedance fluctuations coincide with post-operative hearing loss and vertigo in cochlear implant recipients.

Fluctuations in cochlear implant impedance are associated with inner ear pathology after implantation. The current research explores whether these fluctuations coincide with episodes of hearing loss and/or vertigo, with a comparison between lateral wall and peri-modiolar electrode arrays. Seven-hundred and seventy recipients of Cochlear's slimstraight, lateral wall electrode (CI422) or peri-modiolar (CI512) electrode were investigated for impedance fluctuations. Impedance fluctuations were defined as a median rise of ≥ 4 kΩ across all intra-cochlear electrodes from baseline measurements taken two weeks after switch-on. Medical records were analysed from 193 of the 770 patients selected so that a comparable number would have impedance fluctuations as did not, for both electrode types. The slim straight, lateral wall electrode was found to fluctuate in impedance at a small, but significantly higher rate than the peri-modiolar array (17% vs 12% respectively). Impedance fluctuations were found to significantly correlate with medical events (either hearing loss, vertigo, or tinnitus). Overall, in the "fluctuation" group, 42 out of 75 patients (56%) demonstrated a clinical event during the impedance fluctuation, whereas 26 out of 118 patients (22%) of the "non-fluctuation" group had a clinical event. This significant difference existed with both implant type. The Positive Predictive Value (PPV) of the impedance fluctuation being associated with a clinical event is 0.56, and the Negative Predictive Value (NPV) is 0.78. There were no significant differences in the demographics of those who had an impedance fluctuation compared with those who did not. These results support the relationship between fluctuations in cochlear implant impedances and post-operative clinical events, including the loss of residual hearing and vertigo. Monitoring cochlear implant impedance may be a method for early detection, and so the prevention, of these events in the future. [ABSTRACT FROM AUTHOR]