Incidence of Cochlear Implant Electrode Contacts in the Functional Acoustic Hearing Region and the Influence on Speech Recognition with Electric-Acoustic Stimulation.

Objectives: To investigate the incidence of electrode contacts within the functional acoustic hearing region in cochlear implant (CI) recipients and to assess its influence on speech recognition for electric-acoustic stimulation (EAS) users.

Study Design: Retrospective review.

Setting: Tertiary referral center.

Patients: One hundred five CI recipients with functional acoustic hearing preservation (≤80 dB HL at 250 Hz).

Interventions: Cochlear implantation with a 24-, 28-, or 31.5-mm lateral wall electrode array.

Main Outcome Measures: Angular insertion depth (AID) of individual contacts was determined from imaging. Unaided acoustic thresholds and AID were used to calculate the proximity of contacts to the functional acoustic hearing region. The association between proximity values and speech recognition in quiet and noise for EAS users at 6 months postactivation was reviewed.

Results: Sixty percent of cases had one or more contacts within the functional acoustic hearing region. Proximity was not significantly associated with speech recognition in quiet. Better performance in noise was observed for cases with close correspondence between the most apical contact and the upper edge of residual hearing, with poorer results for increasing proximity values in either the basal or apical direction ( r14 = 0.48, p = 0.043; r18 = -0.41, p = 0.045, respectively).

Conclusion: There was a high incidence of electrode contacts within the functional acoustic hearing region, which is not accounted for with default mapping procedures. The variability in outcomes across EAS users with default maps may be due in part to electric-on-acoustic interference, electric frequency-to-place mismatch, and/or failure to stimulate regions intermediate between the most apical electrode contact and the functional acoustic hearing region.