Burst Stimulation Evokes Increased Bladder and Urethral Pressure in Patients With Sacral Neuromodulation, Indicating Potential Activation of the Autonomic Nervous System: A Pilot Study.

OBJECTIVES: Currently, sacral neuromodulation (SNM) outcomes are often suboptimal, and changing stimulation parameters might improve SNM efficacy. Burst stimulation mimics physiological burst firing of the nervous system and might therefore benefit patients treated with SNM. The purpose of the present pilot study was to evaluate the effect of various Burst SNM paradigms on bladder and urethral pressure in patients with overactive bladder (OAB) or nonobstructive urinary retention (NOUR). MATERIALS AND METHODS: The bladder was filled to 50% of its capacity under general anesthesia in six patients with an implanted sacral lead for SNM purposes. Bladder pressure, and mid- and proximal urethral pressure were measured using conventional (Con-) SNM and various Burst SNM paradigms (10-20-40 Hz interburst frequency) with increasing amplitudes up to 5 mA for Con-SNM and 4 mA for Burst SNM. RESULTS: Burst SNM caused a substantial increase in both bladder and urethral pressure. In contrast, Con-SNM caused a milder increase in urethral pressure, and only one patient showed a modest increase in bladder pressure. Furthermore, the pressure increase was higher in the proximal urethra than in the midurethra using Burst-SNM, whereas Con-SNM caused comparable increases in proximal and midurethra pressure. CONCLUSIONS: Burst SNM induces bladder contraction compared with Con-SNM and induces higher pressure increases in bladder and proximal urethra than does Con-SNM in patients with OAB or NOUR, indicating a higher degree of autonomic nervous system stimulation. The observed responses could not be fully explained by the total charge of the Burst SNM paradigms, which suggests the importance of individual Burst SNM parameters, such as frequency and amplitude. Future studies should assess the feasibility and efficacy of Burst SNM in awake patients.

Detailed Investigation of Bladder Diary Parameters During Sacral Neuromodulation in Patients With Overactive Symptoms.

AIMS: Sacral neuromodulation (SNM) is a well-accepted, minimally invasive modality for patients with overactive bladder (OAB). Successful response to SNM is defined as at least 50% improvement in key symptoms, evaluated in a bladder diary (BD). BDs provide much useful information on bladder behavior during daily life. The aim of this study is to investigate BD parameter changes during SNM therapy in patients with OAB. MATERIALS AND METHODS: The International Consultation on Incontinence Questionnaires (ICIQ)-BD was filled out by 34 patients with OAB, for three days at baseline and after three weeks of subthreshold sensory stimulation. The patients were considered responders for SNM when 50% improvement was seen in the BD. They underwent implantation of an internal pulse generator (IPG), and subsequently, an ICIQ-BD and a visual analog scale (VAS) evaluating bladder satisfaction during three days were filled out six weeks, six months, and one year after IPG implantation. RESULTS: IPGs were implanted in 29 patients (85%). The BD showed a significant decrease in 24-hour leakage at three weeks from 4.2 to 0.6 (-86%, p < 0.001), similar significant decreases at six weeks and six months, and at one year (-80%). Voided volume (VV) at corresponding bladder sensation codes was not different between baseline and at three weeks of tined-lead procedure (TLP) (p > 0.05), and at six weeks (p > 0.05), six months (p > 0.1), and one year of IPG (p > 0.08). After three weeks of TLP, urgency episodes decreased from 4.8 to 3.4 (-30%, p = 0.025), with 59% reduction at six-weeks IPG (p < 0.001) and 49% at six-months IPG (p = 0.013). At one year, a decrease from 4.7 to 2.3 (52% reduction, p = 0.017) was noted. VAS showed the strongest correlation with urgency (p < 0.001) and frequency (p = 0.006). No significant correlation was found with VV (p = 0.87). CONCLUSIONS: Our study describes how bladder sensation parameters change over time in patients on SNM. VV does not significantly increase, nor does frequency significantly decrease over the first year. Leaks and the percentage of urgency episodes significantly decrease, reaching a plateau level between six-weeks and six-months SNM.

The Influence of Electrode Configuration Changes on the Sensory and Motor Response During (Re)Programming in Sacral Neuromodulation.

OBJECTIVES: This study aimed to assess the neurophysiological basis behind troubleshooting in sacral neuromodulation (SNM). Close follow-up of SNM patients with program parameter optimization has proven to be paramount by restoring clinical efficacy and avoiding surgical revision. MATERIALS AND METHODS: A total of 34 successful SNM patients (28 overactive bladder wet, six nonobstructive urinary retention) with an implantable pulse generator were included. All possible bipolar and monopolar electrode settings were tested at sensory threshold (ST) to evaluate sensory (mapped on a perineal grid with 1 cm2 coordinates) and motor (peak-to-peak amplitude and latency of muscle action potential) responses of the pelvic floor. Pelvic floor muscle electromyography was recorded using a multiple array probe, placed intravaginally. Parametric tests were used for paired data: repeated-measures ANOVA or t-test. A nonparametric test was used for paired data: Friedman ANOVA or Wilcoxon signed rank (WSR) test; p < 0.05 was considered statistically significant. If significant, ANOVA was followed by Dunn-Bonferroni post hoc analysis. RESULTS: Monopolar configurations showed significantly lower STs-1.38 ± 0.73 V vs 1.76 ± 0.89 V (paired t-test: p < 0.0001)-and presented with significantly higher peak-to-peak amplitudes-115.67 ± 79.03 µV vs 90.77 ± 80.55 µV (WSR: p = 0.005)-than bipolar configurations. When polarity was swapped, configurations with the cathode distal to the anode showed significantly lower STs, 1.73 ± 0.91 V vs 1.85 ± 0.87 V (paired t-test: p = 0.003), and mean peak-to-peak amplitudes, 81.32 ± 72.82 µV vs 100.21 ± 90.22 µV (WSR: p = 0.0001). Cathodal changes resulted in more changes in sensory responses than anodal changes (χ2 test: p = 0.044). In cathodal changes only, peak-to-peak amplitudes were significantly higher when the distance between electrodes was maximally spread (WSR: p = 0.046). CONCLUSIONS: From a neurophysiological point of view, monopolar configurations stimulated more motor nerve fibers at lower STs, therefore providing more therapeutic efficiency. Swapping polarity or changing the position of the cathode led to different sensory and motor responses, serving as potential reprogramming options.

A Supervised 3 Weeks Test Phase in Sacral Neuromodulation with a 1-Year Followup.

PURPOSE: We sought to determine whether prolonged interventional test phase increases cumulative success rate and compared success rates between early responders (ie within 1 week) and those in need for reprogramming (due to lack of efficacy) of sacral neuromodulation after 1-year followup. MATERIALS AND METHODS: In a single tertiary center prospective study (August 2015 to November 2018) 90 patients refractory to first line treatment were eligible for sacral neuromodulation, including 48 overactive bladder wet (53%), 8 overactive bladder dry (9%) and 34 nonobstructive urinary retention (38%). Patients were evaluated at weekly intervals during test phase and those not successful were reprogrammed. This could be repeated after the second week. Primary outcome was success rate after 3-week test phase and after 1-year followup. Statistical analysis was done by nonparametric tests for numeric (Mann-Whitney U) and categorical (chi2) data. RESULTS: After 3 weeks of test period 56 patients (62%) were considered successful. Prolonged interventional testing increased cumulative success. A 1-year followup showed no significant difference in success rate between early responders and those in need for reprogramming (chi2, p=0.562). There was no difference in age (Mann-Whitney U, p=0.222), sex (chi2, p=0.952) or indication (chi2, p= 0.975). CONCLUSIONS: A 3-week test phase with close followup increases cumulative success rate. During this supervised 3-week test phase 42% of the initial nonresponders after the first week became successful candidates after reprogramming. Patients who required this additional programming did equally as well as those without need for reprogramming. A supervised 3-week test phase is therefore strongly recommended.

Pelvic floor activation upon stimulation of the sacral spinal nerves in sacral neuromodulation patients.

PURPOSE: To assess the activation of the different parts of the pelvic floor muscles (PFM) upon electrical stimulation of the sacral spinal nerves while comparing the different lead electrode configurations. MATERIAL AND METHODS: PFM electromyography (EMG) was recorded using an intravaginal multiple array probe with 12 electrodes pairs, which allows to make a distinction between the different sides and depths of the pelvic floor. In addition concentric needle EMG of the external anal sphincter was performed to exclude far-field recording. A medtronic InterStim tined lead (model 3889) was used as stimulation source. Standard SNM parameters (monophasic pulsed square wave, 210 microseconds, 14 Hz) were used to stimulate five different bipolar electrode configurations (3+0-/3+2-/3+1-/0+3-/1+3-) up to and around the sensory threshold. Of each EMG signal the stimulation intensity needed to evoke the EMG signals as well as its amplitude and latency were determined. Linear mixed models was used to analyse the data. RESULTS: Twenty female patients and 100 lead electrode configurations were stimulated around the sensory response threshold resulting in 722 stimulations and 12 times as many (8664) EMG recordings. A significant increase in EMG amplitude was seen upon increasing stimulation intensity (P < .0001). Large differences were noted between the EMG amplitude recorded at the different sides (ipsilateral>posterior>anterior>contralateral) and depths (deep>center>superficial) of the pelvic floor. These differences were noted for all lead electrodes configurations stimulated (P < .0001). Larger EMG amplitudes were measured when the active electrode was located near the entry point of the sacral spinal nerves through the sacral foramen (electrode #3). No differences in EMG latency could be withheld, most likely due to the sacral neuroanatomy (P > .05). CONCLUSIONS: A distinct activation pattern of the PFM could be identified for all stimulated lead electrode configurations. Electrical stimulation with the most proximal electrode (electrode #3) as the active one elicited the largest PFM contractions.

Neural pathway of bellows response during SNM treatment revisited: Conclusive evidence for direct efferent motor response.

BACKGROUND: In sacral neuromodulation (SNM) patients, it is thought the bellows response elicited upon sacral spinal nerve stimulation is reflex-mediated. Therefore the mechanism of action of SNM is considered to be at the spinal or supraspinal level. These ideas need to be challenged. OBJECTIVE: To identify the neural pathway of the bellows response upon sacral spinal nerve stimulation. DESIGN, SETTING, AND PARTICIPANTS: Single tertiary center, prospective study (December 2017-June 2019) including 29 patients with overactive bladder refractory to first-line treatment. INTERVENTION: Recording of the pelvic floor muscle response (PFMR) using a camcorder and electromyography (EMG) (intravaginal probe and concentric needles) upon increasing stimulation during lead or implantable pulse generator placement. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The lowest stimulation intensity needed to elicit a visual PFMR and electrical PFMR was determined. Electrical PFMRs were subdivided according to their latency. OUTCOME: the association between visual and electrical PFMRs. Statistical analyses were performed using the weighted kappa coefficient. RESULTS: Three different electrical PFMRs could be identified by surface and needle EMG, corresponding with a direct efferent motor response (R1), oligosynaptic (R2), and polysynaptic (R3) afferent reflex response. Only the R1 electrical PFMR was perfectly associated with the visual PFMR (κ = 0.900). CONCLUSIONS: The visual PFMRs upon sacral spinal nerve stimulation are direct efferent motor responses. A reopening of the discussion on the mechanism of action of SNM is possibly justified.

Pelvic Floor Muscle Electromyography as a Guiding Tool During Lead Placement and (Re)Programming in Sacral Neuromodulation Patients: Validity, Reliability, and Feasibility of the Technique.

PURPOSE: To assess the validity, reliability, and feasibility of electromyography (EMG) as a tool to measure pelvic floor muscle (PFM) contractions during placement and (re)programming of the tined lead electrodes in sacral neuromodulation (SNM) patients. MATERIALS AND METHODS: Single tertiary center, prospective study conducted between 2017 and 2019 consisting of three protocols including a total of 75 patients with overactive bladder (wet/dry) or nonobstructive urinary retention. PFM EMG was recorded using the multiple array probe (MAPLe), placed intravaginally. All stimulations (monophasic pulsed square wave, 210 µsec, 14 Hz) were performed using Medtronic's standard SNM stimulation equipment. During lead implantation, all four lead electrodes were stimulated with fixed increasing stimulation intensities (1-2-3-5-7-10 V). During lead electrode (re)programming, five bipolar lead electrode configurations were stimulated twice up to when an electrical PFM motor response (EPFMR), sensory response, and pain response were noted (i.e., the threshold), respectively. Additionally, amplitude and latency of the EPFMRs were determined. Validity, reliability, and feasibility were statistically analyzed using the intraclass correlation coefficient, weighted Cohen's kappa and linear regression, respectively. RESULTS: Validity: EPFMRs were strongly associated with visually detected PFM motor responses (κ = 0.90). Reliability: EPFMR amplitude (ICC = 0.99) and latency (ICC = 0.93) showed excellent repeatability. Feasibility: linear regression (EPFMR threshold = 0.18 mA + 0.76 * sensory response threshold) showed an increase in the sensory response threshold is associated with a smaller increase in EPFMR threshold, with the EPFMR occurring before or on the sensory response threshold in 83.8% of all stimulations. CONCLUSIONS: Measuring PFM contractions with EMG during placement and (re)programming of lead electrodes in SNM patients is valid, reliable, and feasible. Therefore, the use of PFM EMG motor responses could be considered as a tool to assist in these procedures.

Sacral neuromodulation using the standardized tined lead implantation technique with a curved vs a straight stylet: 2-year clinical outcomes and sensory responses to lead stimulation.

OBJECTIVES: To assess clinical follow-up data over 24 months, comparing the use of a curved vs straight stylet in patients undergoing sacral neuromodulation using the standardized tined lead implantation technique. PATIENTS AND METHODS: We conducted a single tertiary-centre, prospective study between August 2013 and June 2015 involving 40 patients with overactive bladder and 15 with non-obstructive urinary retention refractory to first-line treatment. The primary outcome was successful tined lead procedure according to intention-to-treat analyses at 12 and 24 months. The secondary outcome was number of optimal electrode configurations during programming. Statistical analysis was performed using plain non-parametric tests for numerical and categorical data. RESULTS: Successful tined lead procedures were achieved in 33 of 35 patients (94%) implanted with the curved stylet compared with 13 of 20 patients (65%) implanted with the straight stylet (P = 0.005). Intention-to-treat analyses at 12 and 24 months showed success rates of 94% and 91%, respectively, in the curved stylet group vs 65% and 45%, respectively, in the straight stylet group (P = 0.002 and P < 0.001). In the curved stylet group, 60% and 25% of the electrode configurations were considered optimal and poor, respectively, vs 40% and 37%, respectively, in the straight stylet group (P < 0.001). CONCLUSIONS: The use of the standardized implantation technique with the curved stylet led to more successful tined lead procedures, better success rates after 2 years of follow-up and a greater number of optimal electrode configurations when compared to use of the straight stylet.

Repeatability of tools to assist in the follow up and troubleshooting of sacral neuromodulation patients using the sensory response.

PURPOSE: Sacral neuromodulation (SNM) is an established minimally invasive therapy for functional disorders of the pelvic organs in which electrodes are stimulated in proximity of the sacral spinal nerves. Reprogramming of the electrodes is regularly required and is based on the sensory response. This study assesses the repeatability of a pelvic chart and grading system to enable a more objective assessment of the sensory response upon electrode stimulation. MATERIAL AND METHODS: In 26 SNM patients, with OAB or NOUR, assessment of the sensory response was done using the sensory threshold (ST) and a pelvic chart with 1 cm2 coordinates, each coordinate corresponding with a dermatome and location of sensation (LoS). A grading system was developed based upon the ST and LoS. Repeatability of ST was assessed using a two-way mixed effects, absolute agreement, single rater/measurement intraclass correlation coefficient (ICC), and displayed using a correlation and Bland Altman plot. Repeatability of dermatomes, LoS, and grading system was assessed using kappa correlation coefficient. RESULTS: On average, 1.55 ± 0.85 coordinates were used to point out the area where the stimulation was perceived. The mean amount of coordinates between the area pointed at during the first and second measurement was 0.47 ± 0.74. ST showed excellent repeatability (ICC 0.93, 95%CI 0.90-0.94, P < 0.001). Dermatomes, LoS and grading system showed a substantial to almost perfect agreement (κ = 0.740-0.833, P < 0.001). CONCLUSIONS: The pelvic chart and grading system, using the sensory response upon electrode stimulation, are repeatable tools and can be used to assist in follow up and troubleshooting of SNM patients.