AB291. SPR-18 Correlation of sacral nerve lead targeting and urological efficacy: motor mapping, electrode position, and stimulation amplitude

Objective: Sacral neuromodulation (SNM) is a clinically used therapy for refractory urge frequency and incontinent patients. Using a recently developed sheep model, this preclinical study retrospectively evaluated the relationship between implanted sacral lead locations, motor threshold (MT) values, motor mapping, and acute urological efficacy to determine if acute location and physiological measurements are correlated.

Methods: Twelve female polypay sheep were implanted with bilateral InterStim^® devices (Model 3058) connected to quadripolar leads (model 3889) placed in the S2-4 foramina with S3 as the ideal target. CT scans at post-op and ≥12 months later were used for 3D rendering using MedCAD points placed on the sacrum and lead contacts to compare coordinates across animals. Acute cystometry was performed to test responses to SNM (0.21 ms PW, 10 Hz) at maximum tolerable amplitude (MTA). MT values were obtained by visual identification of the first motor response and the motor reflex was mapped to an anatomical map.

Results: Sheep were categorized as responders (n=6; 50%) or non-responders (n=6; 50%) based on ≥50% increase in bladder capacity to acute SNM. There was a significant difference in motor mapping areas between responders (peri-anal contacts) and non-responders (activation of leg) (chi-square; P<0.05). Higher MTA values correlated with larger bladder capacity increases (Pearson correlation; P<0.05). Contact position correlated with urological response (ANOVA; P<0.05). A generalized Procrustes analysis on the 17 leads in S3 (remainder in S2 or S4) showed variability of distributions was higher in distal contacts (0 & 1, mean distance to center 7.3±1.8 mm, left & 6.8±1.3 mm, right) than proximal (2 & 3, mean distance to center 5.8±0.86 mm, left & 4.3±0.35 mm, right (ANOVA; alpha =0.05; F_(3,64) =20.55; P<0.0001).

Conclusions: (I) Responder sheep showed motor responses in peri-anal areas significantly more often than non-responders; (II) MTA weakly correlated with increased bladder capacity; (III) activation of lead contacts proximal to the sacral foramen produced more reliable urological results than did activation of distal contacts. These results suggest well-positioned leads will elicit specific responses that could be essential to effective SNM therapy. Future work will characterize changes over time to provide a temporal correlation of this relationship.

Funding Source(s): Medtronic

Keywords: Neuromodulation; sheep; bladder; motor mapping; lead targeting