Electromyographic Responses Across Different Pulse-Widths of Sacral Neuromodulation in Sheep

In rodents, we reported that short pulse-width (PW) neuromodulation might provide more efficient therapy delivery than traditional 0.21 msec PW. Using fully implanted, commercialized systems in the sheep, the goal of this study was to characterize the relationship of electromyographic (EMG) responses of the external anal sphincter (EAS) to different PWs of sacral neuromodulation (SNM).

In seven sheep, InterStim® quadripolar tined leads were implanted adjacent to the S3 nerve root bilaterally to deliver SNM and two pairs of intramuscular leads were placed on either side of the EAS for EMG sensing. The EMG responses to SNM with different PWs were examined using variable intensities in both anesthetized and conscious conditions.

The EMG responses from ipsilateral EAS (I_EAS ) and contralateral EAS (C_EAS ) were compared. The area under the curve of EMG responses from I_EAS were significantly stronger than that from C_EAS. The late component EMGs were more sensitive to nerve stimulation with a higher response amplitude in awake sheep. The response threshold-PW relationship from the I_EAS as ascertained visually and with EMG in anesthetized and awake sheep were fitted with a monoexponential nonlinear regression; the resulting chronaxies were of 0.05 msec (n = 6), and 0.04 msec (n = 6), and 0.04 msec (n = 8), respectively.

In both anesthetized and awake conditions, a similar motor response may be evoked in the EAS at PWs much shorter (0.04-0.05 msec) than the 0.21 msec typically used with SNM. Potential battery savings manifested by shorter PW would provide more efficient therapy delivery and increased longevity of the stimulator.