PP1517 - Can Alternate Electrode Montages Dethrone the Infra-Orbital Montage for Recording Ocular VEMP?

Abstract:
Several studies have found larger response amplitudes of ocular vestibular-evoked myogenic potentials (oVEMP) when recorded using belly-tendon (BT), chin-referenced (CR), and sternum-referenced (SR) electrode montages than the popularly used inferior orbicular (IO) montage; however, not without the potential confounds due to the sequential recording. To avoid these confounding factors, 36 healthy young adults underwent simultaneous oVEMP recording from IO, BT, CR, and SR electrode montages. Excellent test-retest reliability, coupled with significantly shorter latency, larger amplitude, higher SNR, and better response morphology makes the BT montage better for a clinical recording of oVEMP than all other montages.

Summary:
The last decade has witnessed several attempts to identify the most appropriate electrode placement site to improve the recordability of ocular vestibular evoked myogenic potential (oVEMP). A vast majority of the published literature found larger response amplitudes for alternate electrode montages like belly-tendon (BT), chin-referenced (CR), and/or sternum-referenced (SR) montages than the popular Infra-orbital (IO) montage. However, in a number of these studies, the comparisons between the electrode montages were based on the sequential recordings of oVEMP for different montages (Vanspauwen et al., 2017; Piker et al., 2018). This could predispose the findings to confounding variables such as fatigue or changes in gaze angle between the recordings. Nonetheless, even those using simultaneous recording have found better responses for various alternate montages than the IO montage (Piker et al., 2011; Sandhu et al., 2013; Makowiec et al., 2017). However, no study has yet compared all alternate electrode montages in a simultaneous recording paradigm to eliminate other confounding factors. Also, no study has systematically compared all these electrode montages for their test-retest reliability, waveform morphology, and signal-to-noise ratio. Therefore, the present study aimed at investigating the effects of various electrode montages on oVEMP’s response parameters and determining the test-retest reliability of each of these. Thirty-six young healthy adults (age range: 20-30 years) underwent contralateral oVEMP recording using IO, BT, CR, and SR electrode montages simultaneously. Following the finding of non-normal data distribution (Shapiro-Wilk’s test, p< 0.05), Friedman’s non-parametric test showed a significant difference in all response parameters among the electrode montages. The pair-wise analyses were performed using the Wilcoxon signed-rank test with an α-correction. BT montage had a significantly shorter latency, larger amplitude, and higher SNR (p < 0.008). These findings could be attributed to the differences in the placement of active and reference electrodes. In BT montage, both active and reference electrodes are on the muscle itself, thus reducing the conduction time (Makowiec et al., 2017). In addition, this could reduce the dissipation of energy as the recording electrodes placed along the orientation of the muscle help to pick up the maximal EMG activity generated at the site (Sheykholeslami, 2015; Zuniga et al., 2010). Coupled with the above, a smaller spatial distance between the recording electrodes would reduce the chances of contamination from other EMG noises and therefore explains a significantly higher SNR with the BT montage, especially compared to CR and SR montages (Ertl et al., 2015). Finally, the rating of the waveform morphology on a 5-point Likert scale by 3 experienced audiologists showed significantly better morphology for BT montage than all others (p < 0.008). This might be due to higher SNR and response amplitudes for BT montage than all others. All the known electrode montages investigated in the current study showed excellent test-retest reliability ( >0.8 on the Cronbach’s α test and Intraclass correlation coefficient using the mixed effects model). Thus, based on the above findings, it is suggested to use BT montage over the popularly used IO montage for a better clinical recording of oVEMP which might enhance the chances for responses in challenging cases.