Correlation between stimulation levels and ECAP thresholds for audiometry-based fitting in cochlear implants

Persons whose speech recognition with hearing aids at 65 dB_SPL, WRS₆₅(HA), is inadequate but whose maximum monosyllabic word recognition score (WRS_max) is still measurable may benefit from a cochlear implant (CI). Using a validated prediction model, one can estimate word recognition with a CI, WRS₆₅(CI), for these patients. The aim of this study was to investigate the relationship between electrically evoked compound action potentials (ECAP) and stimulation parameters of the CI system.

In this prospective study, 37 patients were included. The WRS₆₅(CI) was determined after 6 and 12 months and compared with the predicted WRS₆₅(CI). The correlation of minimum and maximum electrical stimulation with the ECAP was investigated.

All patients showed a significantly better WRS₆₅(CI) after 12 months compared with the preoperatively determined WRS₆₅(HA). The proportion of patients whose WRS₆₅(CI) fell short of the predicted value by more than 20 percentage points was 19% after 6 months and 5% after 12 months. In the patient population, there was a closer correlation of the ECAP thresholds with the maximum than with the minimum electrical stimulation.

For patients whose speech understanding with hearing aids is inadequate-even with a very high preoperative WRS_max in moderately severe hearing loss-CI fitting appears to be a promising treatment option. The predictive model enables individual treatment planning. Its application contributed to a quality of care that was higher than was found in an earlier retrospective study. The correlation found between stimulation intensity and ECAP in a cohort of patients with achieved predicted values supports the hypothesis that a fitting procedure based on ECAP and audiometry is a promising approach.