Vagus nerve stimulation: a proven therapy for treatment of epilepsy strives to improve efficacy and expand applications

Effects of non-invasive vagus nerve stimulation on clinical symptoms and molecular biomarkers in Parkinson's disease

Non-invasive vagus nerve stimulation (nVNS) is an established neurostimulation therapy used in the treatment of epilepsy, migraine and cluster headache. In this randomized, double-blind, sham-controlled trial we explored the role of nVNS in the treatment of gait and other motor symptoms in Parkinson's disease (PD) patients. In a subgroup of patients, we measured selected neurotrophins, inflammatory markers and markers of oxidative stress in serum. Thirty-three PD patients with freezing of gait (FOG) were randomized to either active nVNS or sham nVNS. After baseline assessments, patients were instructed to deliver six 2  min stimulations (12  min/day) of the active nVNS/sham nVNS device for 1  month at home. Patients were then re-assessed. After a one-month washout period, they were allocated to the alternate treatment arm and the same process was followed. Significant improvements in key gait parameters (speed, stance time and step length) were observed with active nVNS. While serum tumor necrosis factor- α decreased, glutathione and brain-derived neurotrophic factor levels increased significantly (p < 0.05) after active nVNS treatment. Here we present the first evidence of the efficacy and safety of nVNS in the treatment of gait in PD patients, and propose that nVNS can be used as an adjunctive therapy in the management of PD patients, especially those suffering from FOG. Clinical trial registration: identifier ISRCTN14797144.

Vagus Nerve Stimulation in Early Stage of Acute Myocardial Infarction Prevent Ventricular Arrhythmias and Cardiac Remodeling

Aims: To evaluate whether low level left vagus nerve stimulation (LLVNS) in early stage of myocardial infarction (MI) could effectively prevent ventricular arrhythmias (VAs) and protect cardiac function, and explore the underlying mechanisms.

Methods and Results: After undergoing implantable cardioverter defibrillators (ICD) and left cervical vagal stimulators implantation and MI creation, 16 dogs were randomly divided into three groups: the MI (n = 6), MI+LLVNS (n = 5), and sham operation (n = 5) groups. LLVNS was performed for 3 weeks. VAs, the left ventricular function, the density of the nerve fibers in the infarction area and gene expression profiles were analyzed. Compared with the MI group, dogs in the MI+LLVNS group had a lower VAs incidence (p < 0.05) and better left ventricular function. LLVNS significantly inhibited excessive sympathetic nerve sprouting with the evidences of decreased density of TH, GAP43 and NF positive nerves (p < 0.05). The gene expression profiling found a total of 206 genes differentially expressed between MI+LLVNS and MI dogs, mainly involved in cardiac tissue remodeling, cardiac neural remodeling, immune response and apoptosis. These genes, including 55 up-regulated genes and 151 down-regulated genes, showed more protective expressions under LLVNS.

Conclusions: This study suggests that LLVNS was delivered without altering heart rate, contributing to reduced incidences of VAs and improved left ventricular function. The potential mechanisms included suppressing cardiac neuronal sprouting, inhibiting excessive sympathetic nerve sprouting and subduing pro-inflammatory responses by regulating gene expressions from a canine experimental study.

Study protocol for a pivotal randomised study assessing vagus nerve stimulation during rehabilitation for improved upper limb motor function after stroke

BACKGROUND

Vagus nerve stimulation (VNS) paired with a motor task improves motor outcome in rat stroke models. It is hypothesised that VNS delivered during rehabilitation will improve upper limb function compared to control rehabilitation therapy. Two pilot clinical studies demonstrated acceptable safety and feasibility of VNS paired with rehabilitation for improved upper limb function after stroke. Participants who received rehabilitation paired with VNS demonstrated clinically meaningful improvements in motor function that exceed gains seen among controls who received similar rehabilitation without VNS. These preliminary data support a larger pivotal trial.

METHODS

VNS-REHAB (VNS-Rehabilitation) is a pivotal, multi-site, double-blinded, randomised trial designed to evaluate safety and efficacy of VNS paired with upper limb rehabilitation after ischaemic stroke. The study will include up to 120 participants with upper limb weakness due to stroke nine months to 10 years prior. All participants will be implanted with a VNS device and randomised to receive either Active (0.8 mA) or Control VNS (0.0 mA) paired with upper limb rehabilitation. All participants receive 18 sessions of in-clinic therapy for six weeks, followed by a home-based therapy for three months. The rehabilitation therapy involves progressive, functionally based and intensive practice of hand and arm tasks. VNS is delivered during each movement repetition. After blinded follow-up is completed, the Active vagus nerve stimulation group continues with home-based Active VNS and the Control group receive six weeks of in-clinic therapy with Active VNS followed by home-based Active VNS. The primary efficacy endpoint will be the difference in Fugl-Meyer assessment-upper extremity scores between the Active VNS and Control VNS groups at the end of six weeks of in-clinic therapy. Additional secondary endpoints will also be measured. Safety will be assessed with analysis of adverse events and device complications during study participation.

DISCUSSION

This pivotal trial will determine whether VNS paired with rehabilitation is a safe and effective treatment for improving arm function after stroke.Trial Registration: ClinicalTrials.gov, NCT03131960. Registered on 27 April 2017.

Cervical vagal nerve stimulation activates the stellate ganglion in ambulatory dogs

Background and Objectives

Recent studies showed that, in addition to parasympathetic nerves, cervical vagal nerves contained significant sympathetic nerves. We hypothesized that cervical vagal nerve stimulation (VNS) may capture the sympathetic nerves within the vagal nerve and activate the stellate ganglion.

Materials and Methods

We recorded left stellate ganglion nerve activity (SGNA), left thoracic vagal nerve activity (VNA), and subcutaneous electrocardiogram in seven dogs during left cervical VNS with 30 seconds on-time and 30 seconds off time. We then compared the SGNA between VNS on and off times.

Results

Cervical VNS at moderate (0.75 mA) output induced large SGNA, elevated heart rate (HR), and reduced HR variability, suggesting sympathetic activation. Further increase of the VNS output to >1.5 mA increased SGNA but did not significantly increase the HR, suggesting simultaneous sympathetic and parasympathetic activation. The differences of integrated SGNA and integrated VNA between VNS on and off times (ΔSGNA) increased progressively from 5.2 mV-s {95% confidence interval (CI): 1.25-9.06, p=0.018, n=7} at 1.0 mA to 13.7 mV-s (CI: 5.97-21.43, p=0.005, n=7) at 1.5 mA. The difference in HR (ΔHR, bpm) between on and off times was 5.8 bpm (CI: 0.28-11.29, p=0.042, n=7) at 1.0 mA and 5.3 bpm (CI 1.92 to 12.61, p=0.122, n=7) at 1.5 mA.

Conclusion

Intermittent cervical VNS may selectively capture the sympathetic components of the vagal nerve and excite the stellate ganglion at moderate output. Increasing the output may result in simultaneously sympathetic and parasympathetic capture.

Role of the autonomic nervous system in atrial fibrillation: pathophysiology and therapy

Autonomic nervous system activation can induce significant and heterogeneous changes of atrial electrophysiology and induce atrial tachyarrhythmias, including atrial tachycardia and atrial fibrillation (AF). The importance of the autonomic nervous system in atrial arrhythmogenesis is also supported by circadian variation in the incidence of symptomatic AF in humans. Methods that reduce autonomic innervation or outflow have been shown to reduce the incidence of spontaneous or induced atrial arrhythmias, suggesting that neuromodulation may be helpful in controlling AF. In this review, we focus on the relationship between the autonomic nervous system and the pathophysiology of AF and the potential benefit and limitations of neuromodulation in the management of this arrhythmia. We conclude that autonomic nerve activity plays an important role in the initiation and maintenance of AF, and modulating autonomic nerve function may contribute to AF control. Potential therapeutic applications include ganglionated plexus ablation, renal sympathetic denervation, cervical vagal nerve stimulation, baroreflex stimulation, cutaneous stimulation, novel drug approaches, and biological therapies. Although the role of the autonomic nervous system has long been recognized, new science and new technologies promise exciting prospects for the future.

Low-amplitude, left vagus nerve stimulation significantly attenuates ventricular dysfunction and infarct size through prevention of mitochondrial dysfunction during acute ischemia-reperfusion injury

BACKGROUND

Right cervical vagus nerve stimulation (VNS) provides cardioprotective effects against acute ischemia-reperfusion injury in small animals. However, inconsistent findings have been reported.

OBJECTIVE

To determine whether low-amplitude, left cervical VNS applied either intermittently or continuously imparts cardioprotection against acute ischemia-reperfusion injury.

METHODS

Thirty-two isoflurane-anesthetized swine (25-30 kg) were randomized into 4 groups: control (sham operated, no VNS), continuous-VNS (C-VNS; 3.5 mA, 20 Hz), intermittent-VNS (I-VNS; continuously recurring cycles of 21-second ON, 30-second OFF), and I-VNS + atropine (1 mg/kg). Left cervical VNS was applied immediately after left anterior descending artery occlusion (60 minutes) and continued until the end of reperfusion (120 minutes). The ischemic and nonischemic myocardium was harvested for cardiac mitochondrial function assessment.

RESULTS

VNS significantly reduced infarct size, improved ventricular function, decreased ventricular fibrillation episodes, and attenuated cardiac mitochondrial reactive oxygen species production, depolarization, and swelling, compared with the control group. However, I-VNS produced the most profound cardioprotective effects, particularly infarct size reduction and decreased ventricular fibrillation episodes, compared to both I-VNS + atropine and C-VNS. These beneficial effects of VNS were abolished by atropine.

CONCLUSIONS

During ischemia-reperfusion injury, both C-VNS and I-VNS provide significant cardioprotective effects compared with I-VNS + atropine. These beneficial effects were abolished by muscarinic blockade, suggesting the importance of muscarinic receptor modulation during VNS. The protective effects of VNS could be due to its protection of mitochondrial function during ischemia-reperfusion.

Continuous low-level vagus nerve stimulation reduces stellate ganglion nerve activity and paroxysmal atrial tachyarrhythmias in ambulatory canines

BACKGROUND

We hypothesize that left-sided low-level vagus nerve stimulation (LL-VNS) can suppress sympathetic outflow and reduce atrial tachyarrhythmias in ambulatory dogs.

METHODS AND RESULTS

We implanted a neurostimulator in 12 dogs to stimulate the left cervical vagus nerve and a radiotransmitter for continuous recording of left stellate ganglion nerve activity, vagal nerve activities, and ECGs. Group 1 dogs (N=6) underwent 1 week of continuous LL-VNS. Group 2 dogs (N=6) underwent intermittent rapid atrial pacing followed by active or sham LL-VNS on alternate weeks. Integrated stellate ganglion nerve activity was significantly reduced during LL-VNS (7.8 mV/s; 95% confidence interval [CI] 6.94 to 8.66 versus 9.4 mV/s [95% CI, 8.5 to 10.3] at baseline; P=0.033) in group 1. The reduction was most apparent at 8 am, along with a significantly reduced heart rate (P=0.008). Left-sided low-level vagus nerve stimulation did not change vagal nerve activity. The density of tyrosine hydroxylase-positive nerves in the left stellate ganglion 1 week after cessation of LL-VNS were 99 684 μm(2)/mm(2) (95% CI, 28 850 to 170 517) in LL-VNS dogs and 186 561 μm(2)/mm(2) (95% CI, 154 956 to 218 166; P=0.008) in normal dogs. In group 2, the frequencies of paroxysmal atrial fibrillation and tachycardia during active LL-VNS were 1.4/d (95% CI, 0.5 to 5.1) and 8.0/d (95% CI, 5.3 to 12.0), respectively, significantly lower than during sham stimulation (9.2/d [95% CI, 5.3 to 13.1]; P=0.001 and 22.0/d [95% CI, 19.1 to 25.5], P<0.001, respectively).

CONCLUSIONS

Left-sided low-level vagus nerve stimulation suppresses stellate ganglion nerve activities and reduces the incidences of paroxysmal atrial tachyarrhythmias in ambulatory dogs. Significant neural remodeling of the left stellate ganglion is evident 1 week after cessation of continuous LL-VNS.