The Hybrid cochlear implant: a review

Abstract

The Hybrid S or 'short-electrode' cochlear implant was developed to treat patients with a severe to profound hearing loss limited to the high frequencies. The short electrode is implanted into just the base or high-frequency region of the cochlea, with the goal of preserving residual low-frequency hearing. As a result, electric stimulation can be combined with acoustic stimulation in the same ear (and the opposite ear); this is one instance of 'acoustic plus electric' (A + E) stimulation. In this paper, we will review the latest findings from the first two stages of the clinical trial for the Hybrid concept in the United States. Generally, we will review surgical techniques, clinical trial criteria, residual hearing preservation, improvements in speech perception in quiet, and predictive factors for patient benefit. We will also discuss the significant benefit of A + E stimulation for speech perception in noise and musical measures of melody and instrument recognition, as well as valuable insights into central auditory nervous system plasticity gained from the use of a very short electrode array.

Figure 1

Iowa/Nucleus clinical trial audiometric and other inclusion criteria (see box). Light gray shows the Phase I audiometric range, and dark gray shows additional audiometric range appended in Phase II. Speech inclusion criteria for Phase II are shown with Phase I criteria in parentheses.

Figure 2

Postoperative hearing preservation results for subjects in multicenter clinical trial. A. Low-frequency threshold shifts (averaged over 125–750 Hz) in the implant ear as a function of preoperative hearing threshold for all subjects in the multicenter clinical trial at one month post-implantation (initial activation). B. Long-term threshold shifts at least 12-months after implantation. Plotted as in B.

Figure 3

Comparison of speech in noise for Hybrid patients, long-electrode patients, hearing-impaired patients, and normal-hearing subjects. The values shown are signal-to-noise ratios (in dB) for 50% correct recognition of spondee words in competing backgrounds of steady noise (black bars) or competing talkers (white bars). Subjects are sorted according to degree of hearing loss (average of 500, 1000, and 2000 Hz) and also if they are listening through a traditional long-electrode cochlear implant or Hybrid cochlear implant. Figure reprinted with permission (Gantz et al. Audiol Neurotol; 2006; 11 (suppl 1):63–68) courtesy of S Karger AG, Basel.