Use of Polyvinyl Alcohol Sponge Cubes for Vagal Nerve Stimulation: A Suggestion for the Wrapping Step. Technical Note and Step-by-Step Operative Technique

A pilot study on the programming protocol of vagus nerve stimulation in children with drug-resistant epilepsy: High pulse amplitude or high duty cycle

OBJECTIVE

To compare the efficacy and safety of vagus nerve stimulation using different modes in patients with drug-resistant epilepsy (DRE).

METHODS

Children with DRE who underwent vagus nerve stimulator implantation between March 2019 and December 2022 were prospectively enrolled at the Peking University First Hospital. Ninety-four children were randomly divided into the high pulse amplitude [pulse amplitude was gradually increased to maximum tolerance value (≤2.8 mA) and duty cycle was maintained at 10%] and high duty cycle groups [pulse amplitude was maintained at 1.5 mA and duty cycle was subsequently increased to maximum tolerance value (≤37%)]. At the 55-week follow-up, the responder rate, seizure-free rate, and adverse effects were compared between the two groups.

RESULTS

Ninety-four children with DRE were included (47 patients each in the high pulse amplitude group and the high duty cycle group). For epileptic seizures, the responder rate of the high pulse amplitude group was 53.2% (25/47), while that of the high duty cycle group was 38.3% (18/47). High pulse amplitude had a higher responder rate of focal seizures (60.7% in the high pulse amplitude group vs. 29.2% in the high duty cycle group; chi-squared test, p = 0.023). Among children with a ≥ 75% reduction in epileptic spasms, the high duty cycle group had a higher responder rate than the high pulse amplitude group (54.5% vs. 16.7%; Fisher's exact test, p = 0.022). In addition, in the high duty cycle group, the responder rate in children with epileptic spasms was higher than that in children without epileptic spasms (59.1% vs. 20.0%; chi-square test, p = 0.011). Among children with implantation age <6 years, the responder rate of the high pulse amplitude group was higher (chi-square test, p = 0.024). The incidence of adverse effects in the two groups was not statistically different.

SIGNIFICANCE

The overall responder rates in the two modes were similar. The high pulse amplitude mode may be more effective for focal seizures, whereas the high duty cycle mode may be more effective for epileptic spasms. Patients aged <6 years with DRE and VNS implantation may require a higher pulse amplitude to achieve better efficacy.

PLAIN LANGUAGE SUMMARY

This study compared the anti-seizure efficacy of two different vagus nerve stimulation (VNS) treatments. We found that the overall efficacy of the two treatments was similar. The high pulse amplitude mode may be more effective for focal seizures, whereas the high duty cycle mode may be more effective for epileptic spasms. Patients aged <6 years with drug-resistant epilepsy (DRE) and VNS treatment may require a higher pulse amplitude to achieve better efficacy.

Vagus nerve stimulation lead durability: Insights from an extensive monocentric single-operator adult series

BACKGROUND

Vagus nerve stimulation (VNS) is an established surgical option for neuromodulation. Lead failure is a significant complication mainly reported in children.

METHODS

We conducted a retrospective review of all VNS-related surgeries for refractory epilepsy in adults performed by a single experienced surgeon at a French national referral center from November 2011 to March 2023. We analyzed lead survival using Kaplan-Meier estimators and calculated failure rates.

RESULTS

The study included 267 patients (144 females, mean age 36.56 years) with a mean follow-up of 4.32 years. Of 235 leads implanted, accumulating 1355 device years, four lead failures (1.74%) were identified. The cumulative 5-year and 10-year lead survival probabilities were 98.14% (95% CI: 96.06%-100%) and 97.33% (95% CI: 94.75%-100%), respectively. The lead failure rate was 0.00295 events per device-year. All lead failures were associated with abnormally high impedance (>10,000 ohms).

CONCLUSIONS

This study characterizes technical VNS lead durability, with a failure rate comparable to other neuromodulation devices. Lead longevity is influenced by technical specifications, surgical techniques, and patient-related factors. To optimize lead durability, surgeons should consider the latest technical developments, adhere to best practices, and provide proper patient counseling. Future research should focus on refining lead design and implantation techniques to further improve long-term outcomes.

Right-sided vagus nerve stimulation for drug-resistant epilepsy: A systematic review of the literature and perspectives

BACKGROUND

Right-sided vagus nerve stimulation (RS-VNS) is indicated when the procedure was deemed not technically feasible or too risky on the indicated left side.

OBJECTIVE

The present study aims to systematically review the literature on RS-VNS, assessing its effectiveness and safety.

METHODS

A systematic review following PRISMA guidelines was conducted: Pubmed/MEDLINE, The Cochrane Library, Scopus, Embase and Web of science databases were searched from inception to August 13th,2023. Gray literature was searched in two libraries. Eligible studies included all studies reporting, at least, one single case of RS-VNS in patients for the treatment of drug-resistant epilepsy.

RESULTS

Out of 2333 initial results, 415 studies were screened by abstract. Only four were included in the final analysis comprising seven patients with RS-VNS for a drug-resistant epilepsy. One patient experienced nocturnal asymptomatic bradycardia whereas the other six patients did not display any cardiac symptom. RS-VNS was discontinued in one case due to exercise-induced airway disease exacerbation. Decrease of epileptic seizure frequency after RS-VNS ranged from 25 % to 100 % in six cases. In the remaining case, VNS effectiveness was unclear. In one case, RS-VNS was more efficient than left-sided VNS (69 % vs 50 %, respectively) whereas in another case, RS-VNS was less efficient (50 % vs 95 %, respectively).

CONCLUSION

Literature on the present topic is limited. In six out of seven patients, RS-VNS for drug-resistant epilepsy displayed reasonable effectiveness with a low complication rate. Further research, including prospective studies, is necessary to assess safety and effectiveness of RS-VNS for drug-resistant epilepsy patients.

Vagus nerve stimulation allows to cease maintenance electroconvulsive therapy in treatment-resistant depression: a retrospective monocentric case series

Context

The use of vagus nerve stimulation (VNS) to reduce or stop electroconvulsive therapy (ECT) in treatment-resistant depression seems promising. The aim of this study was to investigate the efficacy of VNS on the reduction of ECT sessions and mood stabilization.

Methods

We conducted a monocentric retrospective case series of patients who suffered from treatment-resistant depression, treated with ECT and referred to our center for VNS. We investigated the number and the frequency of ECT sessions before and after VNS implantation. Secondary criteria consisted in the Montgomery Åsberg Depression Rating Scale (MADRS) score, number of medical treatments, dosage of the main treatment and length of hospital stays before and after VNS. Additionally, we sent an anonymous survey to psychiatrists and other physicians in our institution to investigate their knowledge and perception of VNS therapy to treat treatment-resistant depression.

Results

Seven patients benefited from VNS: six (86%) were female (mean age of 51.7 +/- 16.0 years at surgery), and five (71%) suffered from bipolar depression (three type I and two type II). All patients were followed up at least 2 years post-implantation (range: 27-68 months). Prior to VNS, six patients were treated by maintenance ECT. After VNS, three (43%) patients did not require maintenance ECT anymore, and three (43%) patients required less frequent ECT session with a mean 14.7 +/- 9.8 weeks between sessions after VNS vs. 2.9 +/- 0.8 weeks before VNS. At last follow-up, 4 (57%) patients had stopped ECT. Five (71%) patients implanted with VNS were good responders (50% decrease relative to baseline MADRS). According to the survey, psychiatrists had a significantly better perception and knowledge of ECT, but a worse perception and knowledge of VNS compared to other physicians.

Conclusion

VNS is a good option for treatment-resistant depression requiring maintenance ECT dependence. Larger on-going studies will help broaden the implanted patients while strengthening psychiatrists' knowledge on this therapy.

Training and teaching of vagus nerve stimulation surgery: Worldwide survey and future perspectives

OBJECTIVE

Vagus nerve stimulation (VNS) therapy has been used for more than two decades to treat drug resistant epilepsy and depression and most recently received FDA approval for stroke rehabilitation. Expanding indications will renew the interest in the technique and increase the number of surgeons to be trained. The aim of this study was to survey surgeons with substantial expertise on optimal teaching and training approaches.

METHODS

Anonymous forms comprising 16 questions were sent by e-mail to surgeons with substantial expertise. Statistical analyses were used to compare the answers of the most experienced surgeons (>5 years) with the less experienced ones (<5 years).

RESULTS

Fully-completed forms were collected from 57 experts from 20 countries. The placement of the helical coils was deemed to be the most difficult step by 36 (63.2%) experts, and the use of optical magnification during this step was deemed necessary by 39 (68.4%) experts. Vocal cord palsy should be largely avoidable with proper surgical technique according to 44 (77.2%) experts. The teaching tool considered the most useful was mentoring (38, 66.7%). The future of VNS surgery teaching was deemed to be in anatomical workshops (29, 50.9%) and surgical simulation (26, 45.6%). Overall, answers did not vary significantly according to experience.

CONCLUSIONS

VNS surgery should be mastered by actively participating in dedicated practical training courses and by individual mentoring during actual surgery, which is still the best way to learn. This study highlights the need for a formal training course and possible specific accreditation.

Latest Views on the Mechanisms of Action of Surgically Implanted Cervical Vagal Nerve Stimulation in Epilepsy

BACKGROUND

Vagus nerve stimulation (VNS) is approved as an adjunctive treatment for drug-resistant epilepsy. Although there is a substantial amount of literature aiming at unraveling the mechanisms of action of VNS in epilepsy, it is still unclear how the cascade of events triggered by VNS leads to its antiepileptic effect.

OBJECTIVE

In this review, we integrated available peer-reviewed data on the effects of VNS in clinical and experimental research to identify those that are putatively responsible for its therapeutic effect. The topic of transcutaneous VNS will not be covered owing to the current lack of data supporting the differences and commonalities of its mechanisms of action in relation to invasive VNS.

SUMMARY OF THE MAIN FINDINGS

There is compelling evidence that the effect is obtained through the stimulation of large-diameter afferent myelinated fibers that project to the solitary tract nucleus, then to the parabrachial nucleus, which in turn alters the activity of the limbic system, thalamus, and cortex. VNS-induced catecholamine release from the locus coeruleus in the brainstem plays a pivotal role. Functional imaging studies tend to point toward a common vagal network that comes into play, made up of the amygdalo-hippocampal regions, left thalamus, and insular cortex.

CONCLUSIONS

Even though some crucial pieces are missing, neurochemical, molecular, cellular, and electrophysiological changes occur within the vagal afferent network at three main levels (the brainstem, the limbic system [amygdala and hippocampus], and the cortex). At this final level, VNS notably alters functional connectivity, which is known to be abnormally high within the epileptic zone and was shown to be significantly decreased by VNS in responders. The effect of crucial VNS parameters such as frequency or current amplitude on functional connectivity metrics is of utmost importance and requires further investigation.

Polyvinyl Alcohol Sponges to Facilitate Cerebral Bypass Surgery: Technical Note

OBJECTIVE

The standard way of isolating bypass vessels from surrounding structures during cerebral bypass surgery has been to use a rubber dam or neurosurgical patty. Here, the use of polyvinyl alcohol (PVA) sponges is described as a possible upgrade from these traditional bypass dams.

METHODS

PVA sponges were used to isolate bypass arteries from surrounding tissues during microvascular anastomosis in 25 patients undergoing bypass surgery at our institution.

RESULTS

There were no adverse events related to the use of PVA for microvascular anastomosis. PVA sponges offered some specific advantages when compared with rubber and cottonoid dams.

CONCLUSIONS

Although preliminary, our experience using PVA sponges during microvascular anastomosis suggests some of their properties can facilitate cerebral bypass surgery.

VNS implantation in a NF1 patient: massive nerve hypertrophy discovered intra-operatively preventing successful electrode placement. Case report

For the vast majority of surgeons, no specific investigation is necessary before vagal nerve stimulation (VNS) implantation. We report our intraoperative unexpected finding of a massively enlarged vagus nerve in a patient with neurofibromatosis type 1 (NF1). The nerve hypertrophy prevented wrapping the coils of the helical electrode. The patient had no signs of vagus nerve dysfunction preoperatively (no hoarseness or dysphonia). This exceptional mishap is undoubtedly related to NF1-associated peripheral nerve sheath tumors. Even though it is not advisable to routinely perform any imaging prior to VNS, in such specific context, preoperative imaging work-up, especially cervical ultrasound, might be judicious to rule out any asymptomatic enlarged left vagus nerve.

Flat electrode contacts for vagus nerve stimulation

The majority of available systems for vagus nerve stimulation use helical stimulation electrodes, which cover the majority of the circumference of the nerve and produce largely uniform current density within the nerve. Flat stimulation electrodes that contact only one side of the nerve may provide advantages, including ease of fabrication. However, it is possible that the flat configuration will yield inefficient fiber recruitment due to a less uniform current distribution within the nerve. Here we tested the hypothesis that flat electrodes will require higher current amplitude to activate all large-diameter fibers throughout the whole cross-section of a nerve than circumferential designs. Computational modeling and in vivo experiments were performed to evaluate fiber recruitment in different nerves and different species using a variety of electrode designs. Initial results demonstrated similar fiber recruitment in the rat vagus and sciatic nerves with a standard circumferential cuff electrode and a cuff electrode modified to approximate a flat configuration. Follow up experiments comparing true flat electrodes to circumferential electrodes on the rabbit sciatic nerve confirmed that fiber recruitment was equivalent between the two designs. These findings demonstrate that flat electrodes represent a viable design for nerve stimulation that may provide advantages over the current circumferential designs for applications in which the goal is uniform activation of all fascicles within the nerve.