Impedance and electrically evoked compound action potential (ECAP) changes overtime in patients with cochlear implants

Background: Cochlear implantation referred to as the treatment of choice for hearing rehabilitation in patients with bilateral severe to profound sensorineural hearing loss that is no longer responsive to amplification . The integrity of this CI can be assessed intraoperatively and postoperatively through objective measures which include telemetric measurement of electrode impedance and electrically evoked compound action potential. Aim of the work: To compare electrode impedance values and electrically evoked compound action potential (ECAP) thresholds intraoperatively and postoperatively to asses whether significant changes take place overtime or not.Patient and Methods This study was carried on 25 subjects with age ranging from (3-60) yrs. 21 of the subjects were implanted unilaterally with a MED-EL devices and 4 implanted with cochlear devices. Impedance values and ECAP thresholds were monitored at the time of surgery then postoperatively at 1st day tunning, 1 month, 2 months and 6th months after 1st day tunning.Results: Intraoperative impedance value was the lowest among all readings measured in all electrodes. The highest value was measured at the 1st day tunning after surgery, after which impedance value continued to decrease significantly when compared to the 1st day tunning. ECAP thresholds showed the highest value intraoperatively after which the ECAP continued to decrease. However, the difference between readings was statistically nonsignificant.Conclusion: During surgery, telemetry provides valuable information regarding integrity of electrodes, the electrical output of the implant and the response of the auditory system to electrical stimulation; however, it is not a valuable predictor of post-operative performance.