Abstract
Objective The quantity of A-trains, a high-frequency pattern of free-running facial nerve electromyography,
is correlated with the risk for postoperative high-grade facial nerve paresis. This
correlation has been confirmed by automated analysis with dedicated algorithms and
by visual offline analysis but not by audiovisual real-time analysis.
Methods An investigator was presented with 29 complete data sets measured during actual surgeries
in real time and without breaks in a random order. Data were presented either strictly
via loudspeaker (audio) or simultaneously by loudspeaker and computer screen (audiovisual).
Visible and/or audible A-train activity was then quantified by the investigator with
the computerized equivalent of a stopwatch. The same data were also analyzed with
quantification of A-trains by automated algorithms.
Results Automated (auto) traintime (TT), known to be a small, yet highly representative fraction
of overall A-train activity, ranged from 0.01 to 10.86 s (median: 0.58 s). In contrast,
audio-TT ranged from 0 to 1,357.44 s (median: 29.69 s), and audiovisual-TT ranged
from 0 to 786.57 s (median: 46.19 s). All three modalities were correlated to each
other in a highly significant way. Likewise, all three modalities correlated significantly
with the extent of postoperative facial paresis. As a rule of thumb, patients with
visible/audible A-train activity < 1 minute presented with a more favorable clinical
outcome than patients with > 1 minute of A-train activity.
Conclusion Detection and even quantification of A-trains is technically possible not only with
intraoperative automated real-time calculation or postoperative visual offline analysis,
but also with very basic monitoring equipment and real-time good quality audiovisual
analysis. However, the investigator found audiovisual real-time-analysis to be very
demanding; thus tools for automated quantification can be very helpful in this respect.
Keywords
facial nerve - neurophysiologic monitoring - vestibular schwannoma - facial palsy
- electromyography
