gms | German Medical Science

Objective: Continuous recording of electromyographic signals (EMG) is an established method for intraoperative monitoring of facial nerve function in cerebello-pontine angle surgery. Since there is no standard electrode montage, we have compared two commonly used methods according to Møller and Kartush with respect to sensitivity to A-train activity, which is closely related to postoperative nerve function.

Methods: A group of 10 patients (8 female, 2 male) with A-train activity during vestibular schwannoma surgery were examined. Continuous EMG from facial muscles was recorded using needle electrodes in montages according to Kartush and Møller with narrow, respectively wide interelectrode distances. Quantity of pathological A-train activity and signal-to-noise ratios were compared between montages.

Results: A-train activity ranged from 0.44s to 421.32s, median 17.36s in the Kartush montage and from 0.98s to 6.16s, median 1.58s in the montage according to Møller. In 7 of 10 patients, Kartush showed an increased amount of traintime compared to Møller. On average, 96% of all A-train activity was seen in the Kartush montage, 37% was exclusively detectable, without detectable correlate in the Møller channel. The Møller setup showed an average of 63% of total A-train activity, only 4% were exclusive. The wide interelectrode distance Møller Montage was found to be significantly more susceptible to artefacts, especially to low frequency and power line noise. Artefacts were the main reason for the Møller setup to fail detecting A-train activity.

Conclusions: Both montages were able to detect A-train activity. The montage according to Møller is however very susceptible to artefacts. Additional artefact filtering is needed which bears the danger of distorting A-train waveforms. For continuous intraoperative monitoring of facial nerve function, narrow inter-electrode distance Kartush montage or adequate filtering should be used.