Acute effect of sacral neuromodulation for treatment of detrusor overactivity on urodynamic parameters

Pathways and parameters of sacral neuromodulation in rats

The stimulation paradigm for sacral neuromodulation has remained largely unchanged since its inception. We sought to determine, in rats, whether stimulation-induced increases in bladder capacity correlated with the proportion of sensory pudendal (PudS) neurons at each stimulated location (L6, S1). If supported, this finding could guide the choice of stimulation side (left/right) and level (S2, S3, S4) in humans. Unexpectedly, we observed that acute stimulation at clinically relevant (low) amplitudes [1-1.5 × motor threshold (Tm)], did not increase bladder capacity, regardless of stimulus location (L6 or S1). More importantly for the ability to test our hypothesis, there was little anatomic variation, and S1 infrequently contributed nerve fibers to the PudS nerve. During mapping studies we noticed that large increases in PudS nerve activation occurred at amplitudes exceeding 2Tm. Thus, additional cystometric studies were conducted, this time with stimulation of the L6-S1 trunk, to examine further the relationship between stimulation amplitude and cystometric parameters. Stimulation at 1Tm to 6Tm evoked increases in bladder capacity and decreases in voiding efficiency that mirrored those produced by PudS nerve stimulation. Many animal studies involving electrical stimulation of nerves of the lower urinary tract use stimulation amplitudes that exceed those used clinically (∼1Tm). Our results confirm that high amplitudes generate immediate changes in cystometric parameters; however, the relationship to low-amplitude chronic stimulation in humans remains unclear. Additional studies are needed to understand changes that occur with chronic stimulation, how these changes relate to therapeutic outcomes, and the contribution of specific nerve fibers to these changes.NEW & NOTEWORTHY Acute low-amplitude electrical stimulation of sacral nerve (sacral neuromodulation) did not increase bladder capacity in anesthetized CD, obese-prone, or obese-resistant rats. Increasing stimulation amplitude correlated with increases in bladder capacity and pudendal sensory nerve recruitment. It is unclear how the high-amplitude acute stimulation that is commonly used in animal experiments to generate immediate effects compares mechanistically to the chronic low-amplitude stimulation used clinically.

Transcutaneous Electrical Stimulation of the Abdomen, Ear, and Tibial Nerve Modulates Bladder Contraction in a Rat Detrusor Overactivity Model: A Pilot Study

PURPOSE

The global prevalence of overactive bladder (OAB) is estimated at 11.8%. Despite existing treatment options such as sacral neuromodulation, a substantial number of patients remain untreated. One potential alternative is noninvasive transcutaneous electrical stimulation. This form of stimulation does not necessitate the implantation of an electrode, thereby eliminating the need for highly skilled surgeons, expensive implantable devices, or regular hospital visits. We hypothesized that alternative neural pathways can impact bladder contraction.

METHODS

In this pilot study, we conducted transcutaneous electrical stimulation of the abdominal wall (T6-L1), the ear (vagus nerve), and the ankle (tibial nerve) of 3 anesthetized female Sprague-Dawley rats. Stimulation was administered within a range of 20 Hz to 20 kHz, and its impact on intravesical pressure was measured. We focused on 3 primary outcomes related to intravesical pressure: (1) the pressure change from the onset of a contraction to its peak, (2) the average duration of contraction, and (3) the number of contractions within a specified timeframe. These measurements were taken while the bladder was filled with either saline or acetic acid (serving as a model for OAB).

RESULTS

Transcutaneous stimulation of the abdominal wall, ear, and ankle at a frequency of 20 Hz decreased the number of bladder contractions during infusion with acetic acid. As revealed by a comparison of various stimulation frequencies of the tibial nerve during bladder infusion with acetic acid, the duration of contraction was significantly shorter during stimulation at 1 kHz and 3 kHz relative to stimulation at 20 Hz (P = 0.025 and P = 0.044, respectively).

CONCLUSION

The application of transcutaneous electrical stimulation to the abdominal wall, ear, and tibial nerve could provide less invasive and more cost-effective treatment options for OAB relative to percutaneous tibial nerve stimulation and sacral neuromodulation. A follow-up study involving a larger sample size is recommended.

Safety of Magnetic Resonance Imaging in patients under Sacral Neuromodulation with an InterStim Neuromodulator

OBJECTIVE

To retrospectively investigate the safety of magnetic resonance imaging (MRI) in patients under sacral neuromodulation (InterStim II).

METHODS

Data of patients who received a sacral neuromodulator at the urological department of a Swiss center of tertiary care from 2007 to 2018 and subsequently received at least 1 MRI with implanted device were retrospectively analyzed. Patient characteristics, data on implantation, MRI characteristics and complications potentially related to the MRI were analyzed. In addition, patient interviews were performed to verify the data gathered from patient records.

RESULTS

A total of 55 consecutive patients with a median age of 48 years (range 16 - 80 years) and a total of 191 MRIs (median 3, range 1 - 13) were included to the study. The majority of MRIs (92%) were performed with 1.5 Tesla. The majority of the 1.5 Tesla (58%) as well as 3 Tesla (56%) MRIs assessed body regions other than the head. Complication possibly related to the MRI were only found in 2 (1%) MRI scans in two patients who reported on transient electrifying pain and heat sensation at the implantation site of the neuromodulator during MRI.

CONCLUSION

MRI scans in patients with an implanted InterStim II sacral neuromodulator and with the device being turned off seem to be safe, even if they involve body regions other than the head, at least with 1.5 Tesla.

Acute effect of sacral neuromodulation for treatment of detrusor overactivity on urodynamic parameters

Aim

The aim of this study is to evaluate the acute effects of sacral neuromodulation (SNM) on various urodynamic parameters.

Methods

Patients with overactive bladder and detrusor overactivity (DO) who were planned for percutaneous nerve evaluation (PNE) were included. Directly after the PNE, a urodynamic study (UDS) was performed. The stimulation was turned off during the first UDS (UDS 1), and during the second filling cycle, stimulation was turned on (UDS 2). The UDS was followed by a test phase of 1 week and the bladder diaries were evaluated during an outpatient clinic visit. Primary outcome measures were the differences in UDS parameter values with SNM off and on.

Results

Ten female patients were included in the study and completed the study protocol. Eight patients showed ≥50% improvement of symptoms following a test phase. There were no differences between UDS 1 and UDS 2 in the UDS parameters; bladder volume at first sensation, bladder volume at first DO, highest DO pressure, bladder capacity, maximum flow rate, and pressure at maximum flow rate.

Discussion

None of the aforementioned urodynamic parameters was influenced by acute SNM in patients who responded to SNM. To the best of our knowledge, this is the first study investigating the acute effects of SNM on bladder function.