Ablation of the sphenopalatine ganglion does not attenuate the infarct reducing effect of vagus nerve stimulation

Assessment of safety and feasibility of non-invasive vagus nerve stimulation for treatment of acute stroke

BACKGROUND

Non-invasive vagus nerve stimulation (nVNS) using a hand-held stimulator placed on the neck is an FDA-approved treatment for primary headache disorders. The safety of nVNS is unknown in stroke patients.

OBJECTIVE

To assess the safety and feasibility of nVNS for the acute treatment of stroke.

METHODS

TR-VENUS (clinicaltrials.gov identifier NCT03733431) was a randomized, sham-controlled, open-label, multicenter trial conducted in patients with acute ischemic stroke (IS) or intracerebral hemorrhage (ICH). Patients were randomly assigned to standard-dose nVNS, high-dose nVNS, or sham stimulation. The primary endpoint was a composite safety outcome defined as bradycardia or reduction in mean arterial blood pressure during treatment or progression of neurological or death within 24 h of treatment. The feasibility endpoints were the proportion of eligible subjects receiving nVNS within 6 h of symptom onset and the proportion completing all pre-specified treatment doses. Efficacy assessments included infarct growth from baseline to 24 h after treatment.

RESULTS

Sixty-nine patients (61 IS, 8 ICH) completed the study. The composite safety outcome was achieved in 32.0% in sham and 47.7% in nVNS group (p = 0.203). Treatment was initiated in all but two randomized patients. All dosed subjects received 100% of prespecified stimulations. A non-significant reduction in infarct growth was observed in the high-dose nVNS group (184.2% in sham vs. 63.3% in high-dose nVNS; p = 0.109).

CONCLUSIONS

The results of this study suggest that nVNS may be safe and feasible in the setting of acute stroke. These findings support further development of nVNS as a potential treatment for acute ischemic stroke.

Ultrasound-Guided Suprazygomatic Nerve Blocks to the Pterygopalatine Fossa: A Safe Procedure

OBJECTIVES

Large-scale procedural safety data on pterygopalatine fossa nerve blocks (PPFBs) performed via a suprazygomatic, ultrasound-guided approach are lacking, leading to hesitancy surrounding this technique. The aim of this study was to characterize the safety of PPFB.

METHODS

This retrospective chart review examined the records of adults who received an ultrasound-guided PPFB between January 1, 2016, and August 30, 2020, at the University of Florida. Indications included surgical procedures and nonsurgical pain. Clinical data describing PPFB were extracted from medical records. Descriptive statistics were calculated for all variables, and quantitative variables were analyzed with the paired t test to detect differences between before and after the procedure.

RESULTS

A total of 833 distinct PPFBs were performed on 411 subjects (59% female, mean age 48.5 years). Minor oozing from the injection site was the only reported side effect, in a single subject. Although systolic blood pressure, heart rate, and oxygen saturation were significantly different before and after the procedure (132.3 vs 136.4 mm Hg, P < 0.0001; 78.2 vs 80.8, P = 0.0003; and 97.8% vs 96.3%, P < 0.0001; respectively), mean arterial pressure and diastolic blood pressure were not significantly different (96.2 vs 97.1 mm Hg, P = 0.1545, and 78.2 vs 77.4 mm Hg, P = 0.1314, respectively). Similar results were found within subgroups, including subgroups by sex, race, and indication for PPFB.

DISCUSSION

We have not identified clinically significant adverse effects from PPFB performed with an ultrasound-guided suprazygomatic approach in a large cohort in the hospital setting. PPFBs are a safe and well-tolerated pain management strategy; however, prospective multicenter studies are needed.

The Potential Role of Neuromodulation in Subarachnoid Hemorrhage

OBJECTIVES

Aneurysmal subarachnoid hemorrhage (SAH) continues to be a difficult cerebrovascular disease with limited pharmacologic treatment options. Cerebral vasospasm (CV) and delayed cerebral ischemia (DCI) are leading causes of morbidity and mortality after SAH. Despite the advances in the understanding of its pathophysiology and tremendous efforts to date, nimodipine is currently the sole Food and Drug Administration-approved treatment for patients with SAH, with benefits that are marginal at best. The neuromodulation therapies are promising, especially those that target CV and DCI to improve functional outcomes. The aim of this review is therefore to summarize the available evidence for each type of neuromodulation for CV and DCI, with a special focus on its pathophysiological mechanisms, in addition to their clinical utility and drawbacks, which we hope will lead to future translational therapy options after SAH.

MATERIALS AND METHODS

We conducted a comprehensive review of preclinical and clinical studies demonstrating the use of neuromodulation for SAH. The literature search was performed using PubMed, Embase, and ClinicalTrials.gov. A total of 21 articles published from 1992 to 2021 and eight clinical trials were chosen.

RESULTS

The studies reviewed provide a compelling demonstration that neuromodulation is a potentially useful strategy to target multiple mechanisms of DCI and thus to potentially improve functional outcomes from SAH. There are several types of neuromodulation that have been tested to treat CV and DCI, including the trigeminal/vagus/facial nerve stimulation, sphenopalatine ganglion and spinal cord stimulation, transcranial direct electrical stimulation, transcutaneous electrical neurostimulation, and electroacupuncture. Most of them are in the preclinical or early phases of clinical application; however, they show promising results.

CONCLUSIONS

DCI has a complex pathogenesis, making the unique anatomical distribution and pleiotropic capabilities of various types of neuromodulation a promising field of study. We may be at the cusp of a breakthrough in the use of these techniques for the treatment of this stubbornly difficult disease.

Stimulating the Facial Nerve to Treat Ischemic Stroke: A Systematic Review

Acute ischemic stroke (AIS) is a common devastating disease that has increased yearly in absolute number of cases since 1990. While mechanical thrombectomy and tissue plasminogen activator (tPA) have proven to be effective treatments, their window-of-efficacy time is very short, leaving many patients with no viable treatment option. Over recent years there has been a growing interest in stimulating the facial nerves or ganglions to treat AIS. Pre-clinical studies have consistently demonstrated an increase in collateral blood flow (CBF) following ganglion stimulation, with positive indications in infarct size and neurological scores. Extensive human trials have focused on trans-oral electrical stimulation of the sphenopalatine ganglion, but have suffered from operational limitations and non-significant clinical findings. Regardless, the potential of ganglion stimulation to treat AIS or elongate the window-of-efficacy for current stroke treatments remains extremely promising. This review aims to summarize results from recent trial publications, highlight current innovations, and discuss future directions for the field. Importantly, this review comes after the release of four important clinical trials that were published in mid 2019.

Facial nerve stimulation as a future treatment for ischemic stroke

Stimulation of the autonomic parasympathetic fibers of the facial nerve system (hereafter simply “facial nerve”) rapidly dilates the cerebral arteries and increases cerebral blood flow whether that stimulation is delivered at the facial nerve trunk or at distal points such as the sphenopalatine ganglion. Facial nerve stimulation thus could be used as an emergency treatment of conditions of brain ischemia such as ischemic stroke. A rich history of scientific research has examined this property of the facial nerve, and various means of activating the facial nerve can be employed including noninvasive means. Herein, we review the anatomical and physiological research behind facial nerve stimulation and the facial nerve stimulation devices that are in development for the treatment of ischemic stroke.

Transcutaneous Cervical Vagus Nerve Stimulation Ameliorates Acute Ischemic Injury in Rats

BACKGROUND

Direct stimulation of the vagus nerve in the neck via surgically implanted electrodes is protective in animal models of stroke. We sought to determine the safety and efficacy of a non-invasive cervical VNS (nVNS) method using surface electrodes applied to the skin overlying the vagus nerve in the neck in a model of middle cerebral artery occlusion (MCAO).

METHODS

nVNS was initiated variable times after MCAO in rats (n = 33). Control animals received sham stimulation (n = 33). Infarct volume and functional outcome were assessed on day 7. Brains were processed by immunohistochemistry for microglial activation and cytokine levels. The ability of nVNS to activate the nucleus tractus solitarius (NTS) was assessed using c-Fos immunohistochemistry.

RESULTS

Infarct volume was 43.15 ± 3.36 percent of the contralateral hemisphere (PCH) in control and 28.75 ± 4.22 PCH in nVNS-treated animals (p < 0.05). The effect of nVNS on infarct size was consistent when stimulation was initiated up to 4 hours after MCAO. There was no difference in heart rate and blood pressure between control and nVNS-treated animals. The number of c-Fos positive cells was 32.4 ± 10.6 and 6.2 ± 6.3 in the ipsilateral NTS (p < 0.05) and 30.4 ± 11.2 and 5.8 ± 4.3 in the contralateral NTS (p < 0.05) in nVNS-treated and control animals, respectively. nVNS reduced the number of Iba-1, CD68, and TNF-α positive cells and increased the number of HMGB1 positive cells.

CONCLUSIONS

nVNS inhibits ischemia-induced immune activation and reduces the extent of tissue injury and functional deficit in rats without causing cardiac or hemodynamic adverse effects when initiated up to 4 hours after MCAO.

Vagus Nerve Stimulation During Rehabilitative Training Improves Forelimb Recovery After Chronic Ischemic Stroke in Rats

BACKGROUND AND OBJECTIVE

Stroke is a leading cause of long-term disability. Currently, there are no consistently effective rehabilitative treatments for chronic stroke patients. Our recent studies demonstrate that vagus nerve stimulation (VNS) paired with rehabilitative training improves recovery of function in multiple models of stroke. Here, we evaluated the ability of VNS paired with rehabilitative training to improve recovery of forelimb strength when initiated many weeks after a cortical and subcortical ischemic lesion in subjects with stable, chronic motor deficits.

METHODS

Rats were trained to perform an automated, quantitative measure of voluntary forelimb strength. Once proficient, rats received injections of endothelin-1 to cause a unilateral cortical and subcortical ischemic lesion. Then, 6 weeks after the lesion, rats underwent rehabilitative training paired with VNS (Paired VNS; n = 10), rehabilitative training with equivalent VNS delivered 2 hours after daily rehabilitative training (Delayed VNS; n = 10), or rehabilitative training without VNS (Rehab, n = 9).

RESULTS

VNS paired with rehabilitative training significantly improved recovery of forelimb function compared with control groups. The Paired VNS group displayed an 86% recovery of strength, the Rehab group exhibited 47% recovery, and the Delayed VNS group exhibited 42% recovery. Improvement in forelimb function was sustained in the Paired VNS group after the cessation of stimulation, potentially indicating lasting benefits. No differences in intensity of rehabilitative training, lesion size, or MAP-2 expression were observed between groups.

CONCLUSION

VNS paired with rehabilitative training confers significantly greater recovery of forelimb function after chronic ischemic stroke in rats.

Electrical stimulation of the vagus nerve protects against cerebral ischemic injury through an anti-infammatory mechanism

Vagus nerve stimulation exerts protective effects against ischemic brain injury; however, the underlying mechanisms remain unclear. In this study, a rat model of focal cerebral ischemia was established using the occlusion method, and the right vagus nerve was given electrical stimulation (constant current of 0.5 mA; pulse width, 0.5 ms; frequency, 20 Hz; duration, 30 seconds; every 5 minutes for a total of 60 minutes) 30 minutes, 12 hours, and 1, 2, 3, 7 and 14 days after surgery. Electrical stimulation of the vagus nerve substantially reduced infarct volume, improved neurological function, and decreased the expression levels of tumor necrosis factor-α and interleukin-6 in rats with focal cerebral ischemia. The experimental findings indicate that the neuroprotective effect of vagus nerve stimulation following cerebral ischemia may be associated with the inhibition of tumor necrosis factor-α and interleukin-6 expression.

Electrical stimulation of the vagus nerve dermatome in the external ear is protective in rat cerebral ischemia

BACKGROUND

Although cervical vagus nerve stimulation is effective for reducing infarct volume in rats, it is not feasible for acute human stroke as it requires surgical incision of the neck. We hypothesized that stimulation of the dermatome in the external ear innervated by the vagus nerve (auricular vagus nerve stimulation; aVNS) reduces infarct volume after transient focal ischemia in rats.

METHODS

Animals were randomized to active aVNS or sham stimulation. For aVNS, electrical stimulation of the left cavum concha (1 h duration) using percutaneous needles was initiated 30 min after induction of ischemia. Behavioral and tissue outcome were measured 24 h after induction of ischemia. In a separate experimental dataset, c-Fos immunohistochemistry was performed to identify the brain regions activated after the stimulation.

RESULTS

Stimulation of the left cavum concha resulted in bilateral c-Fos staining in the nuclei tractus solitarii and the loci coerulei in all animals. There was no c-Fos staining in any part of the brainstem in sham control animals. The mean infarct volume (SD) as calculated by indirect method was 44.20 ± 7.58% in controls and 31.65 ± 9.67% in treated animals (P < 0.0001). The effect of aVNS on tissue outcome was associated with better neurological scores at 24 h after ischemia (P < 0.0001).

CONCLUSIONS

Electric stimulation of the vagus nerve dermatome in the external ear activates brainstem afferent vagal nuclei and reduces infarct volume in rats. This finding has potential to facilitate the development of treatments that leverage the brain's endogenous neuroprotective pathways at the setting of acute ischemic stroke.

Vagus nerve stimulation in ischemic stroke: old wine in a new bottle

Vagus nerve stimulation (VNS) is currently Food and Drug Administration-approved for treatment of both medically refractory partial-onset seizures and severe, recurrent refractory depression, which has failed to respond to medical interventions. Because of its ability to regulate mechanisms well-studied in neuroscience, such as norepinephrine and serotonin release, the vagus nerve may play an important role in regulating cerebral blood flow, edema, inflammation, glutamate excitotoxicity, and neurotrophic processes. There is strong evidence that these same processes are important in stroke pathophysiology. We reviewed the literature for the role of VNS in improving ischemic stroke outcomes by performing a systematic search for publications in Medline (1966–2014) with keywords “VNS AND stroke” in subject headings and key words with no language restrictions. Of the 73 publications retrieved, we identified 7 studies from 3 different research groups that met our final inclusion criteria of research studies addressing the role of VNS in ischemic stroke. Results from these studies suggest that VNS has promising efficacy in reducing stroke volume and attenuating neurological deficits in ischemic stroke models. Given the lack of success in Phase III trials for stroke neuroprotection, it is important to develop new therapies targeting different neuroprotective pathways. Further studies of the possible role of VNS, through normally physiologically active mechanisms, in ischemic stroke therapeutics should be conducted in both animal models and clinical studies. In addition, recent advent of a non-invasive, transcutaneous VNS could provide the potential for easier clinical translation.

CIR-Myo News: Proceedings of the 2014 Spring Padua Muscle Days: Terme Euganee and Padova (Italy), April 3-5, 2014

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