The role of electrodiagnostic techniques in the reprogramming of patients with a delayed suboptimal response to sacral nerve stimulation

Sensing in Sacral Neuromodulation: A Feasibility Study in Subjects With Urinary Incontinence and Retention

OBJECTIVES

Sacral neuromodulation (SNM) therapy standard of care relies on visual-motor responses and patient-reported sensory responses in deciding optimized lead placement and programming. Automatic detection of stimulation responses could offer a simple, consistent indicator for optimizing SNM. The purpose of this study was to measure and characterize sacral evoked responses (SERs) resulting from sacral nerve stimulation using a commercial, tined SNM lead.

MATERIALS AND METHODS

A custom external research system with stimulation and sensing hardware was connected to the percutaneous extension of an implanted lead during a staged (tined lead) evaluation for SNM. The system collected SER recordings across a range of prespecified stimulation settings (electrode configuration combinations for bipolar stimulation and bipolar sensing) during intraoperative and postoperative sessions in 21 subjects with overactive bladder (OAB) and nonobstructive urinary retention (NOUR). Motor and sensory thresholds were collected during the same sessions.

RESULTS

SERs were detected in all 21 subjects. SER morphology (number of peaks, magnitude, and timing) varied across electrode configurations within and across subjects. Among subjects and electrode configurations tested, recordings contained SERs at motor threshold and/or sensory threshold in 75% to 80% of subjects.

CONCLUSIONS

This study confirmed that implanted SNM leads can be used to directly record SERs elicited by stimulation in subjects with OAB and NOUR. SERs were readily detectable at typical SNM stimulation settings and procedural time points. Using these SERs as possible objective measures of SNM response has the capability to automate patient-specific SNM therapy, potentially providing consistent lead placement, programming, and/or closed-loop therapy.

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.

Sacral Neuromodulation Changes Pelvic Floor Activity in Overactive Bladder Patients-Possible New Insights in Mechanism of Action: A Pilot Study

OBJECTIVES

To evaluate if electrodiagnostic tools can advance the understanding in the effect of sacral neuromodulation (SNM) on pelvic floor activity, more specifically if SNM induces changes in pelvic floor muscle (PFM) contraction.

MATERIALS AND METHODS

Single tertiary center, prospective study (October 2017-May 2018) including patients with overactive bladder syndrome undergoing SNM. Electromyography of the PFM was recorded using the Multiple Array Probe Leiden. The procedure consisted of consecutive stimulations of the lead electrodes with increasing intensity (1-3, 5, 7, 10 V). Recordings were made after electrode placement (T0) and three weeks of SNM (T1). Patients with >50% improvement were defined as responders, others as nonresponders. For the analyses, the highest electrical PFM response (EPFMR), defined as the peak-to-peak amplitude of the muscle response, was identified for each intensity. The sensitivity (intensity where the first EPFMR was registered and the normalized EPFMR as percentage of maximum EPFMR) and the evolution (EMFPR changes over time) were analyzed using linear mixed models.

RESULTS

Fourteen patients were analyzed (nine responders, five nonresponders). For nonresponders, the PFM was significantly less sensitive to stimulation after three weeks (T0: 1.7 V, T1: 2.6 V). The normalized EPFMR was (significantly) lower after three weeks for the ipsilateral side of the PFM for the clinically relevant voltages (1 V: 36%-23%; p = 0.024, 2 V: 56%-29%; p = 0.00001; 3 V: 63%-37%; p = 0.0002). For the nonresponders, the mean EPFMR was significantly lower at 8/12 locations at T1 (T0: 109 μV, T1: 58 μV; mean p = 0.013, range <0.0001-0.0867). For responders, the sensitivity and evolution did not change significantly.

CONCLUSIONS

This is the first study to describe in detail the neurophysiological characteristics of the PFM, and the changes over time upon sacral spinal root stimulation, in responders and nonresponders to SNM. More research is needed to investigate the full potential of EPFMR as a response indicator.

Reprogramming Sacral Neuromodulation for Sub-Optimal Outcomes: Evidence and Recommendations for Clinical Practice

Objectives

In some patients treated for urinary or fecal incontinence with sacral neuromodulation (SNM) persistence of symptoms, a reduction in efficacy or adverse effects of stimulation can occur. In such situations, further programming of the SNM device can help resolve problems. Infrequently hardware failure is detected. This article aims to provide practical guidance to solve sub‐optimal outcomes (troubleshooting) occurring in the course of SNM therapy.

Materials and Methods

A systematic literature review was performed. Collective clinical experience from an expert multidisciplinary group was used to form opinion where evidence was lacking.

Results

Circumstances in which reprogramming is required are described. Actions to undertake include changes of electrode configuration, stimulation amplitude, pulse frequency, and pulse width. Guidance in case of loss of efficacy and adverse effects of stimulation, developed by a group of European experts, is presented. In addition, various hardware failure scenarios and their management are described.

Conclusions

Reprogramming aims to further improve patient symptoms or ensure a comfortable delivery of the therapy. Initial changes of electrode configuration and adjustment of stimulation parameters can be performed at home to avoid unnecessary hospital visits. A logical and stepwise approach to reprogramming can improve the outcome of therapy and restore patient satisfaction.

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.

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

OBJECTIVES

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).

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

The role of the neurometer CPT/C in sacral neuromodulation

Objective

The aim of the current research project was to study the role of the Neurometer^® as a tool to predict responders to sacral neuromodulation therapy (SNM).

Material and methods

This was a prospective, open study in male and female patients, aged 18 and over with voiding dysfunction [non-obstructive retention and/or frequency/ urgency syndrome]. The first group underwent a screening test to evaluate percutaneous nerve functions (PNE) and to determine whether they are candidates for SNM with the InterStim^®. Prior to PNE testing, all patients were evaluated with the pain tolerance test (PTT) using the electro-diagnostic Neurometer^® CPT/C device. An InterStim^® implant was placed in patients who were responders to PNE testing underwent. On the other hand, non-responders underwent a staged implant placement. The second group consisted of patients who already had InterStim^® implanted for voiding dysfunction. During the routine office follow-up, the patients implanted with Interstim^® underwent a PTT using the Neurometer^® CPT/C device. All the testing using the Neurometer CPT/C was performed on the day of the PNE for the first group, and the day of the routine follow-up visit for the second group. All of the results for the Neurometer^® testing were kept blinded from the PNE results, and those of the outcome of the follow-up visit. The study received approval by the Research Ethics Board of the University Health Network (No. 14-8196).

Results

We recruited a total of 123 patients. The results presented here include 110 patients who completed the study, 48 of whom were in the first group, and 62 in the second group. The statistical analysis used was as follows: Group 1: Simple linear regression analysis and the linear discriminate analysis were preformed. It was found that for patients without the InterStim^® implant with a combined CPT/CPD of 800 and above, the Neurometer^® could predict the test screening results with an accuracy of 71%. Group 2: Same analysis and tests were conducted for patients with the InterStim^® implant, and the results showed that if the patient had a combined CPT/CPD of 600 and above, the Neurometer^® could predict the patients satisfaction or dissatisfaction with an accuracy of 72%.

Conclusion

Neurometer^® may play a role in predicting test trial positive responders and patient satisfaction after the placement of InterStim^® implant.

Comparison of Active Stimulating Electrodes of Sacral Neuromodulation

OBJECTIVE

The goal of this study was to compare the motor response to sacral neuromodulation (SNM) with different pairs of stimulating electrodes in anesthetized and awake sheep.

MATERIALS AND METHODS

Similar to SNM clinical use in humans, the InterStim^® quadripolar tined lead was implanted adjacent to the S3 nerve root in sheep and bipolar stimulation was configured with one electrode negative and one electrode positive on the four contacts (0 most distal to device, 1, 2, and 3 most proximal).

RESULTS

Electrode 3-cathode and electrode 0-anode (3-/0+) stimulation had the lowest visual response threshold (0.46 ± 0.14V, anesthetized, 0.56 ± 0.21V, conscious), representing the most sensitive stimulation. Stimulation on electrode 0 (0-/1+) had the highest response threshold among tested electrodes (2.70 ± 0.23V, anesthetized, 3.38 ± 0.96V, conscious). The order according to response threshold from low to high was 3 < 2 < 1 < 0. The triggered response by 3-/0+ stimulation solely occurred in the perineum, tail, or bellows. In contrast, the 0-/1+ stimulation frequently evoked response in gluteal and thigh regions. The electromyographic activities from the anus were sensitive to low intensities of stimulation on electrode 3 (e.g., 3-/0+, 3-/2+).

CONCLUSIONS

Objective motor responses to SNM as a functional indicator for optimal lead placement may be used to demonstrate that the contact which is most proximal to the foramen (electrode 3) is an optimal electrode to trigger an "on-target" response to lower intensity stimulation. Data from this preclinical work suggest that there are several principles that may be referenced to simplify and expedite the programming process in clinical practice.

Evaluation of Pulse-Width of Spinal Nerve Stimulation in a Rat Model of Bladder Micturition Reflex

OBJECTIVES

The spinal nerve stimulation (SNS) evoked motor threshold (T_mot ) response across different pulse-widths (PWs) was first explored and a subset of selected stimulation PWs were further assessed with respect to bladder reflex contraction (BRC).

MATERIALS AND METHODS

In anesthetized female rats, wire electrodes were placed under each of the L6 spinal nerves to produce bilateral SNS. The relationship of T_mot response with PW was analyzed using a monoexponential nonlinear regression. A cannula was placed into the bladder via the urethra to ensure an isovolumetric bladder. Saline infusion induced BRC.

RESULTS

The chronaxie of the T_mot -PW curve was 0.04 ms. The stimulation charges/energies (current × PW) associated with shorter PWs of 0.02, 0.03, and 0.06 ms were significantly lower than those with longer PW (e.g., >0.15 ms). SNS (T_mot , 10 Hz) at selected PWs from 0.03 to 0.21 ms inhibited the frequency of BRCs. There were no significantly different attenuations among tested PWs. SNS of PWs of 0.03, 0.06, and 0.09 ms decreased bladder contraction frequency from 103 ± 3%, 100 ± 4%, and 103 ± 4% of controls, to 52 ± 16% (n = 8, p = 0.02, paired t-test), 56 ± 15% (n = 11, p = 0.02) and 40 ± 19% (n = 10, p = 0.01), respectively.

CONCLUSIONS

Effective PWs to produce bladder inhibitory effects in the rat appear much shorter than 0.21 ms typically used with sacral neuromodulation in practice. Potential battery savings manifested by shorter PW while maintaining equivalent efficacy would provide more efficient therapy delivery and increased longevity of the stimulator.

Postoperative issues of sacral nerve stimulation for fecal incontinence and constipation: a systematic literature review and treatment guideline

BACKGROUND

There is a lack of knowledge on the incidence and management of suboptimal therapeutic effect and the complications associated with sacral nerve stimulation for fecal incontinence and constipation.

OBJECTIVE

This study aimed to review current literature on postoperative issues and to propose a treatment algorithm.

DATA SOURCE

PubMed, MEDLINE, and EMBASE were searched using the keywords "sacral nerve stimulation," "sacral neuromodulation," "fecal incontinence," and "constipation" for English-language articles published from January 1980 to August 2010. A further search was conducted on a wider literature using the keywords "complication," "adverse effect," "treatment failure," "equipment failure," "infection," "foreign-body migration," "reoperation," "pain," and "algorithm."

STUDY SELECTION

Four hundred sixty-one titles were identified, and after a title and abstract review, 135 were subjected to full article review; 89 were finally included in this review. Five articles were added by manual search and consensus.

RESULTS

Forty-eight studies were identified as cohort studies reporting on postoperative issues, including 1661 patients who underwent percutaneous nerve evaluation and 1600 patients who proceeded to sacral nerve stimulation therapy. Pooled data showed that the most common problem during percutaneous nerve evaluation was lead displacement (5.3%). The incidence of suboptimal outcome, pain, and infection after implantation was 12.1%, 13.0%, and 3.9%.

LIMITATIONS

There was significant underreporting of untoward events, because 60% of the studies did not report complications during percutaneous nerve evaluation, and suboptimal outcome after implantation was not disclosed in 44% of the studies.

CONCLUSIONS

The incidence of untoward events associated with sacral nerve stimulation appears to be low. However, there is a significant underreporting of the incidence. Using the information from the structured and systematic literature review, we formulated a clinically relevant guideline for reporting and managing postoperative issues. The guideline can provide a framework for clinical practice.

Sacral nerve stimulation for faecal incontinence: results from a single centre over a 10-year period

AIM

Sacral nerve stimulation (SNS) is considered a first-line surgical treatment option for faecal incontinence. There is little information on long-term results. The results of SNS for faecal incontinence performed at a single centre over a 10-year period are reported.

METHOD

A cohort analysis of consecutive patients treated with SNS for faecal incontinence over a 10-year period was carried out. Data were collected prospectively using bowel habit diaries and St Mark's and Cleveland Clinic incontinence scores. Treatment success was defined as a >50% reduction in episodes of faecal incontinence compared with baseline.

RESULTS

Temporary SNS was performed in 118 patients, and 91 (77%) were considered suitable for chronic stimulation. The median period of follow up was 22 (1-138) months. Seventy patients were followed for 1 year with success in 63 (90%). Of 18 patients followed for 5 years, 15 (83%) reported continued success, 11 (61%) maintained full efficacy, 4 (22%) reported some loss, and 3 (17%) reported complete loss. Three patients with a 10-year follow up had no loss in efficacy. Overall, complete loss of efficacy was observed in 14 (16%) patients at a median of 11.5 months following implantation. A further 5 (6%) patients showed deterioration with time. In 9 (47%), no reason for the deterioration in symptoms could be identified.

CONCLUSIONS

SNS can be effective for up to 10 years. Some patients experience deterioration in symptoms over time. The reasons for this are often not evident.

Sacral nerve stimulation for faecal incontinence: optimizing outcome and managing complications

AIM

A knowledge of the principles of neurostimulation is essential to achieve optimal efficacy and minimize adverse effects. The aim of this article was to review the current evidence regarding device programming in the management of patients having sacral nerve stimulation (SNS) for faecal incontinence.

METHOD

A Medline search was performed including the keywords and/or MeSH headings of sacral nerve stimulation, neuromodulation, artificial pacemaker, faecal incontinence, programming, adverse effects and complications. Further studies were identified by cross-referencing from relevant articles and by appraisal of recent peer-reviewed conference abstracts and proceedings.

RESULTS

Neurostimulator programming is an important component of SNS. Efficacy can be improved or restored with reprogramming. Adverse stimulation is often reversible, and nonstimulation-related complications are correctable. A total loss of efficacy can be explained in over one-half of patients.

CONCLUSION

An improved outcome of SNS can be achieved by selecting the best possible stimulation parameters individualized to each patient. Further research into the optimal settings is needed.

Neuromodulation and the role of electrodiagnostic techniques

Electrodiagnostic techniques have been utilized in surgery since the early 1960s. These techniques have been primarily used in neurosurgery; however, with the introduction of neuromodulation for voiding dysfunction, these techniques have now found their way into the field of female pelvic medicine. This article will review techniques applicable to evaluate pelvic floor function as it relates to neuromodulation. It will also review the literature describing how these techniques are used to help determine appropriate candidates as well as improve surgical outcomes. A PubMed search was conducted using the terms neuromodulation, Interstim, electrodiagnosis, electrodiagnostic techniques, electromyography with limits to the pelvic floor, and voiding dysfunction. Eight articles and three abstracts were found that directly related to the use of electrodiagnostic techniques as they apply to neuromodulation. Electrodiagnostic techniques may play a role in helping predict appropriate candidates for neuromodulation as well as improve surgical outcomes.

Sacral nerve stimulation in faecal incontinence: position statement based on a collective experience

OBJECTIVE

Since the first paper published by Matzel et al., in 1995, on the efficacy of sacral nerve stimulation (SNS) in patients with faecal incontinence, the indications, the contraindications, the stimulation technique and follow up of implanted patients have changed. The aim of this article was to provide a consensus opinion on the management of patients with faecal incontinence treated with SNS.

METHOD

Recommendations were based on a critical review of the literature when available and on expert opinions in areas with insufficient evidence.

RESULTS

We have reviewed the indications and contraindications, proposed an algorithm for patient management showing the place of SNS. The temporary test technique, the implantation technique, the patient follow up and the approach in case of treatment failure were discussed.

CONCLUSION

We hope not only to provide a guide on patient management to clinical practitioners interested in SNS but also to harmonize our practices.

Improving the efficacy of sacral nerve stimulation for faecal incontinence by alteration of stimulation parameters

Background

Sacral nerve stimulation (SNS) is an effective treatment for faecal incontinence, but only standard stimulation parameters have been used. This study assessed the clinical impact of altering the parameters.

Methods

Twelve patients with partially improved faecal incontinence following SNS underwent acute testing to select optimal stimulation parameters; rectal compliance was used as a surrogate marker. Parameters tested were: stimulation off; frequency 14 (standard), 31 or 6·9 Hz; and pulse duration 210 (standard), 450 or 90 µs. Patients completed a 2-week bowel diary, St Mark's continence score (SMCS) and Rockwood faecal incontinence quality-of-life (FIQL) score before testing using standard settings, and after testing using optimized settings.

Results

Optimal settings, determined by greatest increase in rectal compliance, were shorter pulse width in five patients and higher frequency in seven. Optimized stimulation resulted in a decrease in mean episodes of incontinence from 2·3 to 1·2 per week (P = 0·031), soiling from 3·3 to 1·7 days per week (P = 0·016), faecal urgency from 31 to 18 per cent of all evacuations (P = 0·055) and SMCS from 12·3 to 8·7 (P = 0·008); the FIQL coping/behaviour score improved (P = 0·008).

Conclusion

With a shorter pulse width and higher frequency, clinical efficacy in patients undergoing SNS for faecal incontinence can be improved.