66 / 224
780
10 dB of pre-implant levels (often referred to as “complete
hearing preservation”), or within 20 or 30dB (“partial
hearing preservation”). Other studies report the mean or
median low frequency threshold change post-implantation.
Furthermore, outcomes have been reported at a wide range
of follow-up times, further precluding comparison. Finally,
hearing preservation outcomes with specific devices may
be influenced by variations in surgical technique and/or
patient characteristics.
Evidence for the Cochlear Hybrid devices comes primarily
from a series of multicentre clinical studies. The shorter
Hybrid S8 device was evaluated in a US trial reported by
Gantz et al. (12.24). 87 adults were implanted with the
10 mm electrode array in their poorer ear, with preoper-
ative low frequency (125–500Hz) thresholds of 60dB HL or
better. At initial activation, two subjects (1.3%) had lost all
hearing, and in the remaining subjects the low frequency
average thresholds decreased by a mean of 14.8dB. Over
the subsequent 12 months a further 14 subjects lost func-
tional hearing (low frequency thresholds
>
90dB HL), but
there was little change in thresholds for the remaining
subjects. At 12 months post-activation, 80% of the subjects
retained functional low frequency hearing and were able to
utilize EAS.
Lenarz et al. (16) reported on the European Hybrid L24 multi-
centre study, which included 66 adults with severe-pro-
found high frequency hearing loss and with thresholds
<
60dB HL at frequencies below 500Hz. At initial activa-
tion, 89% of subjects showed low frequency hearing pres-
ervation within 30dB of preoperative levels, and in 61%
of subjects thresholds dropped by less than 10dB. By 12
months these proportions were 74% and 43% respectively,
indicating further hearing loss in some subjects. 88% of
subjects retained sufficient hearing to use EAS at the 12
month interval. Outcomes from the US multicentre clinical
trial were reported by Roland et al. (25), which assessed 50
adults with similar preoperative characteristics to those in
the European study. 66% of subjects retained functional
acoustic hearing after 6 months, and the proportions of
subjects with thresholds changes of
<
10dB and
<
30dB
were 25% and 56% respectively.
The largest cohort of recipients of the relatively new
Cochlear Slim Straight (SS) electrode array has been
implanted by Skarzynski and colleagues. Skarzynski et al.
(26) reported on hearing preservation outcomes in 35
adults separated into three groups according to preop-
erative 500 Hz thresholds. Groups A, B and C had 500Hz
thresholds of
<
50dB HL, 50-80dB HL and
>
80 dB HL respec-
tively. For the total cohort, median threshold increase for
low frequencies was 10dB and 15dB at 1 month and 1
year postoperative respectively, with three subjects (9%)
losing all residual hearing. At the one year interval 38% of
subjects had 500Hz thresholds within 10dB of preoper-
ative levels and 79% had thresholds within 30dB. Figure
4 shows the median preoperative and 12 month postop-
erative thresholds for Groups A and B (i.e. subjects who
were typical candidates for EAS). In each panel the upper
trace shows the difference between pre- and postopera-
tive thresholds (Figure 4).
The same group later reported on outcomes from 19
children implanted with the Nucleus CI422 (27). In this
study, hearing preservation was expressed as an overall
percentage (for all audiometric frequencies combined)
comparing pre- and postoperative thresholds and taking
figure 4. Median pre- and postoperative thresholds for two groups of Cochlear Slim Straight
electrode recipients
[REV. MED. CLIN. CONDES - 2016; 27(6) 776-786]
N was 11 and 13 in groups A and B respectively. Redrawn from Skarzynski et al. (26).