Intermittent electrical stimulation of the right cervical vagus nerve in salt-sensitive hypertensive rats: effects on blood pressure, arrhythmias, and ventricular electrophysiology

Efficacy and safety of transcutaneous auricular vagus nerve stimulation for frequent premature ventricular complexes: rationale and design of the TASC-V trial

BACKGROUND

Premature Ventricular Complexes (PVCs) are very common in clinical practice, with frequent PVCs (more than 30 beats per hour) or polymorphic PVCs significantly increasing the risk of mortality. Previous studies have shown that vagus nerve stimulation improves ventricular arrhythmias. Stimulation of the auricular distribution of the vagus nerve has proven to be a simple, safe, and effective method to activate the vagus nerve. Transcutaneous au ricular vagus nerve stimulation (taVNS) has shown promise in both clinical and experimental setting for PVCs; however, high-quality clinical studies are lacking, resulting in insufficient evidence of efficacy.

METHODS

The study is a prospective, randomized, parallel-controlled trial with a 1:1 ratio between the two groups. Patients will be randomized to either the treatment group (taVNS) or the control group (Sham-taVNS) with a 6-week treatment and a subsequent 12-week follow-up period. The primary outcome is the proportion of patients with a ≥ 50% reduction in the number of PVCs monitored by 24-hour Holter. Secondary outcomes include the proportion of patients with a ≥ 75% reduction in PVCs, as well as the changes in premature ventricular beats, total heartbeats, and supraventricular premature beats recorded by 24-hour Holter. Additional assessments compared score changes in PVCs-related symptoms, as well as the score change of self-rating anxiety scale (SAS), self-rating depression scale (SDS), and 36-item short form health survey (SF-36).

DISCUSSION

The TASC-V trial will help to reveal the efficacy and safety of taVNS for frequent PVCs, offering new clinical evidence for the clinical practice.

TRIAL REGISTRATION

Clinicaltrials.gov: NCT04415203 (Registration Date: May 30, 2020).

Vagus nerve stimulation for the treatment of epilepsy: things to note on the protocols, the effects and the mechanisms of action

Epilepsy is a chronic brain disorder that is characterized by repetitive un-triggered seizures that occur severally within 24 h or more. Non-pharmacological methods for the management of epilepsy were discussed. The non-pharmacological methods include the vagus nerve stimulation (VNS) which is subdivided into invasive and non-invasive techniques. For the non-invasive techniques, the auricular VNS, stimulation of the cervical branch of vagus nerve in the neck, manual massage of the neck, and respiratory vagal nerve stimulation were discussed. Similarly, the stimulation parameters used and the mechanisms of actions through which VNS improves seizures were also discussed. Use of VNS to reduce seizure frequency has come a long way. However, considering the cost and side effects of the invasive method, non-invasive techniques should be given a renewed attention. In particular, respiratory vagal nerve stimulation should be considered. In doing this, the patients should for instance carry out slow-deep breathing exercise 6 to 8 times every 3 h during the waking hours. Slow-deep breathing can be carried out by the patients on their own; therefore this can serve as a form of self-management.HIGHLIGHTSEpilepsy can interfere with the patients' ability to carry out their daily activities and ultimately affect their quality of life.Medications are used to manage epilepsy; but they often have their serious side effects.Vagus nerve stimulation (VNS) is gaining ground especially in the management of refractory epilepsy.The VNS is administered through either the invasive or the non-invasive methodsThe invasive method of VNS like the medication has potential side effects, and can be costly.The non-invasive method includes auricular VNS, stimulation of the neck muscles and skin and respiratory vagal nerve stimulation via slow-deep breathing exercises.The respiratory vagal nerve stimulation via slow-deep breathing exercises seems easy to administer even by the patients themselves.Consequently, it is our opinion that patients with epilepsy be made to carry out slow-deep breathing exercise 6-8 times every 3 h during the waking hours.

Subdiaphragmatic vagal nerve stimulation attenuates the development of hypertension and alters nucleus of the solitary tract transcriptional networks in the spontaneously hypertensive rat

Augmented vagal signaling may be therapeutic in hypertension. Most studies to date have used stimulation of the cervical vagal branches. Here, we investigated the effects of chronic intermittent electric stimulation of the ventral subdiaphragmatic vagal nerve branch (sdVNS) on long-term blood pressure, immune markers, and gut microbiota in the spontaneously hypertensive rat (SHR), a rodent model of hypertension characterized by vagal dysfunction, gut dysbiosis, and low-grade inflammation. We evaluated the effects of sdVNS on transcriptional networks in the nucleus of the solitary tract (NTS), a major cardioregulatory brain region with direct gut vagal projections. Male juvenile SHRs were implanted with radiotelemetry transmitters and vagal nerve cuffs for chronic intermittent electric sdVNS, applied three times per day for 7 consecutive weeks followed by 1 wk of no stimulation. Blood pressure was measured once a week using telemetry in the sdVNS group as well as age-matched sham-stimulated SHR controls. At the endpoint, colonic and circulating inflammatory markers, corticosterone, and circulating catecholamines were investigated. Bacterial 16 s sequencing measured gut bacterial abundance and composition. RNA sequencing evaluated the effects of sdVNS on transcriptional networks in the NTS. SHRs that received sdVNS exhibited attenuated development of hypertension compared with sham animals. No changes in peripheral inflammatory markers, corticosterone, or catecholamines and no major differences in gut bacterial diversity and composition were observed following sdVNS, apart from decreased abundance of Defluviitaleaceale bacterium detected in sdVNS SHRs compared with sham animals. RNA sequencing revealed significant sdVNS-dependent modulation of select NTS transcriptional networks, including catecholaminergic and corticosteroid networks.NEW & NOTEWORTHY We show that stimulation of the ventral subdiaphragmatic vagal nerve branch may be a promising potential approach to treating hypertension. The data are especially encouraging given that rodents received only 30 min per day of intermittent stimulation therapy and in view of the potential of long-term blood pressure effects that are not stimulus-locked.

The Changes of Cardiovascular Neurotransmitter Levels under Low-Intensity Focused Ultrasound Stimulation of the Vagus Nerve

BACKGROUND

Our previous study has shown that stimulation of the vagus nerve with low-intensity focused ultrasound could modulate blood pressure (BP), but the underlying mechanisms remain unclear. This study investigated the changes of cardiovascular neurotransmitter levels to indirectly evaluate the responses of the autonomic nervous system and renin-angiotensin system under low-intensity focused ultrasound stimulation (FUS) of the vagus nerve.

METHODS

Cardiovascular neurotransmitter levels of epinephrine (EPI), norepinephrine (NE), and angiotensin II (ANGII) were measured and compared before and after the FUS in seven spontaneously hypertensive rats; and were also measured and compared between a target stimulation group (FUS, n = 6) and non-target stimulation group (Control, n = 5) after stimulation to exclude the influence of potential confounding factors.

RESULTS

The t-test results showed that the levels of EPI, NE, and ANGII were significantly decreased (P < 0.05) after stimulation compared to before stimulation. Additionally, the levels of NE and EPI were significantly lower (P < 0.05) in the FUS group than in the Control group after stimulation, indicating that the activities of the sympathetic nervous system and renin-angiotensin system of the vagus nerve might be inhibited by FUS of the vagus nerve.

CONCLUSION

These findings reveal the mechanism of BP lowing in response to FUS of the vagus nerve.Clinical Relevance-This study revealed the mechanism of BP lowering in response to focused ultrasound stimulation of the vagus nerve through analyzing the changes of cardiovascular neurotransmitter levels.

Effects on heart rate from direct current block of the stimulated rat vagus nerve

Objective.Although electrical vagus nerve stimulation has been shown to augment parasympathetic control of the heart, the effects of electrical conduction block have been less rigorously characterized. Previous experiments have demonstrated that direct current (DC) nerve block can be applied safely and effectively in the autonomic system, but additional information about the system dynamics need to be characterized to successfully deploy DC nerve block to clinical practice.Approach.The dynamics of the heart rate (HR) from DC nerve block of the vagus nerve were measured by stimulating the vagus nerve to lower the HR, and then applying DC block to restore normal rate. DC block achieved rapid, complete block, as well as partial block at lower amplitudes.Main Results. Complete block was also achieved using lower amplitudes, but with a slower induction time. The time for DC to induce complete block was significantly predicted by the amplitude; specifically, the amplitude expressed as a percentage of the current required for a rapid, 60 s induction time. Recovery times after the cessation of DC block could occur both instantly, and after a significant delay. Both blocking duration and injected charge were significant in predicting the delay in recovery to normal conduction.Significance. While these data show that broad features such as induction and recovery can be described well by the DC parameters, more precise features of the HR, such as the exact path of the induction and recoveries, are still undefined. These findings show promise for control of the cardiac autonomic nervous system, with potential to expand to the sympathetic inputs as well.

Autonomic modulation by low-intensity focused ultrasound stimulation of the vagus nerve

Objective.Our previous study has shown that low-intensity focused ultrasound stimulation (FUS) of the vagus nerve could modulate blood pressure (BP), but its underlying mechanisms remain unclear. We hypothesized that low-intensity FUS of the vagus nerve would regulate autonomic function and thus BP.Approach.17 anesthetized spontaneously hypertensive rats were treated with low-intensity FUS of the left vagus nerve for 15 min each trial. Continuous BP, heart rate, respiration rate (RR), and core body temperature were simultaneously recorded to evaluate the effects on BP and other physiological parameters. Heart rate variability (HRV), systolic BP variability, and baroreflex sensitivity were computed to evaluate the autonomic modulation function. A Control-sham group without stimulation and another Control-FUS group with non-target stimulation were also examined to exclude the influence of potential confounding factors on autonomic modulation.Main results.A prolonged significant decrease in BP, pulse pressure, RR, the normalized low-frequency power of HRV, and the low-to-high frequency power ratio of HRV were found after the low-intensity FUS of the left vagus nerve in comparison with the baseline and those of the control groups, demonstrating that activities of the sympathetic nervous system were inhibited. The prolonged significant increase of the normalized high-frequency power of HRV suggested the activation of parasympathetic activity.Significance.Low-intensity FUS of the left vagus nerve effectively improved the autonomic function by activating parasympathetic efferent and inhibiting sympathetic efferent, which contributes to BP reduction. The findings shed light on the hypotensive mechanism underlying FUS.

Multimodal imaging shows fibrosis architecture and action potential dispersion are predictors of arrhythmic risk in spontaneous hypertensive rats

Hypertensive heart disease (HHD) increases risk of ventricular tachycardia (VT) and ventricular fibrillation (VF). The roles of structural vs. electrophysiological remodelling and age vs. disease progression are not fully understood. This cross-sectional study of cardiac alterations through HHD investigates mechanistic contributions to VT/VF risk. Risk was electrically assessed in Langendorff-perfused, spontaneously hypertensive rat hearts at 6, 12 and 18 months, and paced optical membrane voltage maps were acquired from the left ventricular (LV) free wall epicardium. Distributions of LV patchy fibrosis and 3D cellular architecture in representative anterior LV mid-wall regions were quantified from macroscopic and microscopic fluorescence images of optically cleared tissue. Imaging showed increased fibrosis from 6 months, particularly in the inner LV free wall. Myocyte cross-section increased at 12 months, while inter-myocyte connections reduced markedly with fibrosis. Conduction velocity decreased from 12 months, especially transverse to the myofibre direction, with rate-dependent anisotropy at 12 and 18 months, but not earlier. Action potential duration (APD) increased when clustered by age, as did APD dispersion at 12 and 18 months. Among 10 structural, functional and age variables, the most reliably linked were VT/VF risk, general LV fibrosis, a measure quantifying patchy fibrosis, and non-age clustered APD dispersion. VT/VF risk related to a quantified measure of patchy fibrosis, but age did not factor strongly. The findings are consistent with the notion that VT/VF risk is associated with rate-dependent repolarization heterogeneity caused by structural remodelling and reduced lateral electrical coupling between LV myocytes, providing a substrate for heterogeneous intramural activation as HHD progresses. KEY POINTS: There is heightened arrhythmic risk with progression of hypertensive heart disease. Risk is related to increasing left ventricular fibrosis, but the nature of this relationship has not been quantified. This study is a novel systematic characterization of changes in active electrical properties and fibrotic remodelling during progression of hypertensive heart disease in a well-established animal disease model. Arrhythmic risk is predicted by several left ventricular measures, in particular fibrosis quantity and structure, and epicardial action potential duration dispersion. Age alone is not a good predictor of risk. An improved understanding of links between arrhythmic risk and fibrotic architectures in progressive hypertensive heart disease aids better interpretation of late gadolinium-enhanced cardiac magnetic resonance imaging and electrical mapping signals.

An ASIC System for Closed-Loop Blood Pressure Modulation through Right Cervical Vagus Nerve Stimulation

OBJECTIVE

Heart disease is the leading cause of death worldwide. Hypertension is an important precursor and the most common risk factor to heart failure. While some patients can control their high blood pressure with pharmaceuticals, many suffer from resistant hypertension, where antihypertensive medications do not achieve the desired outcome. Electrical stimulation is an emerging therapy to modulate blood pressure and integrating it with closed-loop feedback can improve blood pressure control.

METHODS

We design and fabricate two application-specific integrated circuits (ASICs) for stimulation and pressure sensing using TSMC's 180 nm MS RF G process. We create a closed-loop system by integrating the ASICs with a microscale pressure sensor and a custom-built Python script and test the full system in six Long Evans rats using vagus nerve stimulation.

RESULTS

After calibration and benchtop verification, we prove the functionality of the system in lowering, and maintaining a desired blood pressure in vivo. The system effectively monitors pressure and stimulates when that pressure exceeds the user-determined threshold.

CONCLUSION

By combining this stimulation therapy with a pressure sensor, we present a novel closed-loop, electroceutical system that has the potential to monitor and modulate blood pressure.

SIGNIFICANCE

We present a drug-free, potentially side-effect-free electroceutical therapeutic for managing resistant hypertension.

Therapeutic targeting of inflammation in hypertension: from novel mechanisms to translational perspective

Both animal models and human observational and genetic studies have shown that immune and inflammatory mechanisms play a key role in hypertension and its complications. We review the effects of immunomodulatory interventions on blood pressure, target organ damage, and cardiovascular risk in humans. In experimental and small clinical studies, both non-specific immunomodulatory approaches, such as mycophenolate mofetil and methotrexate, and medications targeting T and B lymphocytes, such as tacrolimus, cyclosporine, everolimus, and rituximab, lower blood pressure and reduce organ damage. Mechanistically targeted immune interventions include isolevuglandin scavengers to prevent neo-antigen formation, co-stimulation blockade (abatacept, belatacept), and anti-cytokine therapies (e.g. secukinumab, tocilizumab, canakinumab, TNF-α inhibitors). In many studies, trial designs have been complicated by a lack of blood pressure-related endpoints, inclusion of largely normotensive study populations, polypharmacy, and established comorbidities. Among a wide range of interventions reviewed, TNF-α inhibitors have provided the most robust evidence of blood pressure lowering. Treatment of periodontitis also appears to deliver non-pharmacological anti-hypertensive effects. Evidence of immunomodulatory drugs influencing hypertension-mediated organ damage are also discussed. The reviewed animal models, observational studies, and trial data in humans, support the therapeutic potential of immune-targeted therapies in blood pressure lowering and in hypertension-mediated organ damage. Targeted studies are now needed to address their effects on blood pressure in hypertensive individuals.

Effects of transcutaneous auricular vagus nerve stimulation on cardiovascular autonomic control in health and disease

Autonomic nervous system (ANS) dysfunction is a well-known feature of cardiovascular diseases (CVDs). Studies on heart rate variability (HRV), a non-invasive method useful in investigating the status of cardiovascular autonomic control, have shown that a predominance of sympathetic modulation not only contributes to the progression of CVDs but has a pivotal role in their onset. Current therapies focus more on inhibition of sympathetic activity, but the presence of drug-resistant conditions and the invasiveness of some surgical procedures are an obstacle to complete therapeutic success. On the other hand, targeting the parasympathetic branch of the autonomic nervous system through invasive vagus nerve stimulation (VNS) has shown interesting results as alternative therapeutic approach for CVDs. However, the invasiveness and cost of the surgical procedure limit the clinical applicability of VNS and hinder the research on the physiological pathway involved. Transcutaneous stimulation of the auricular branch of the vagus nerve (tVNS) seems to represent an important non-invasive alternative with effects comparable to those of VNS with surgical implant. Thus, in the present narrative review, we illustrate the main studies on tVNS performed in healthy subjects and in three key examples of CVDs, namely heart failure, hypertension and atrial fibrillation, highlighting the neuromodulatory effects of this technique.

Benefits of pharmacological and electrical cholinergic stimulation in hypertension and heart failure

Systemic arterial hypertension and heart failure are cardiovascular diseases that affect millions of individuals worldwide. They are characterized by a change in the autonomic nervous system balance, highlighted by an increase in sympathetic activity associated with a decrease in parasympathetic activity. Most therapeutic approaches seek to treat these diseases by medications that attenuate sympathetic activity. However, there is a growing number of studies demonstrating that the improvement of parasympathetic function, by means of pharmacological or electrical stimulation, can be an effective tool for the treatment of these cardiovascular diseases. Therefore, this review aims to describe the advances reported by experimental and clinical studies that addressed the potential of cholinergic stimulation to prevent autonomic and cardiovascular imbalance in hypertension and heart failure. Overall, the published data reviewed demonstrate that the use of central or peripheral acetylcholinesterase inhibitors is efficient to improve the autonomic imbalance and hemodynamic changes observed in heart failure and hypertension. Of note, the baroreflex and the vagus nerve activation have been shown to be safe and effective approaches to be used as an alternative treatment for these cardiovascular diseases. In conclusion, pharmacological and electrical stimulation of the parasympathetic nervous system has the potential to be used as a therapeutic tool for the treatment of hypertension and heart failure, deserving to be more explored in the clinical setting.

Bioelectronic medicine for the autonomic nervous system: clinical applications and perspectives

Bioelectronic medicine (BM) is an emerging new approach for developing novel neuromodulation therapies for pathologies that have been previously treated with pharmacological approaches. In this review, we will focus on the neuromodulation of autonomic nervous system (ANS) activity with implantable devices, a field of BM that has already demonstrated the ability to treat a variety of conditions, from inflammation to metabolic and cognitive disorders. Recent discoveries about immune responses to ANS stimulation are the laying foundation for a new field holding great potential for medical advancement and therapies and involving an increasing number of research groups around the world, with funding from international public agencies and private investors. Here, we summarize the current achievements and future perspectives for clinical applications of neural decoding and stimulation of the ANS. First, we present the main clinical results achieved so far by different BM approaches and discuss the challenges encountered in fully exploiting the potential of neuromodulatory strategies. Then, we present current preclinical studies aimed at overcoming the present limitations by looking for optimal anatomical targets, developing novel neural interface technology, and conceiving more efficient signal processing strategies. Finally, we explore the prospects for translating these advancements into clinical practice.

Vagus nerve stimulation ameliorates L-NAME-induced preeclampsia-like symptoms in rats through inhibition of the inflammatory response

Background

Preeclampsia is characterized by an excessive inflammatory response. Recent studies have shown that vagus nerve stimulation (VNS) has anti-inflammatory properties in vivo. This study aims to investigate whether VNS is safe for use during pregnancy and to explore the therapeutic potential and underlying mechanisms of VNS in PE.

Methods

Pregnant Sprague-Dawley rats were randomly chosen to receive N-nitro-L-arginine methyl ester (L-NAME)-containing water (preeclampsia-like mouse model) or saline (normal pregnancy control) daily at gestational days 14.5–20.5. VNS and the α7nAChR antagonist methyllycaconitine citrate (MLA, 1 mg/kg/d) were given daily at the same time.

Results

VNS decreased the high systolic blood pressure and urinary protein observed in the PE rats. In addition, VNS mitigated abnormal pregnancy outcomes. Moreover, VNS alleviated the inflammatory response by decreasing the levels of inflammatory cytokines. VNS significantly increased the expression of α7nAChR and attenuated the activation of NF-κB p65 in the placenta.

Discussion

Our findings indicate that maternal VNS treatment is safe during pregnancy and has a protective effect in a pregnant rat model of preeclampsia induced by L-NAME.

Non-invasive Auricular Vagus Nerve Stimulation as a Potential Treatment for Covid19-Originated Acute Respiratory Distress Syndrome

Background: Covid-19 is an infectious disease caused by an invasion of the alveolar epithelial cells by coronavirus 19. The most severe outcome of the disease is the Acute Respiratory Distress Syndrome (ARDS) combined with hypoxemia and cardiovascular damage. ARDS and co-morbidities are associated with inflammatory cytokine storms, sympathetic hyperactivity, and respiratory dysfunction. Hypothesis: In the present paper, we present and justify a novel potential treatment for Covid19-originated ARDS and associated co-morbidities, based on the non-invasive stimulation of the auricular branch of the vagus nerve. Methods: Auricular vagus nerve stimulation activates the parasympathetic system including anti-inflammatory pathways (the cholinergic anti-inflammatory pathway and the hypothalamic pituitary adrenal axis) while regulating the abnormal sympatho-vagal balance and improving respiratory control. Results: Along the paper (1) we expose the role of the parasympathetic system and the vagus nerve in the control of inflammatory processes (2) we formulate our physiological and methodological hypotheses (3) we provide a large body of clinical and preclinical data that support the favorable effects of auricular vagus nerve stimulation in inflammation, sympatho-vagal balance as well as in respiratory and cardiac ailments, and (4) we list the (few) possible collateral effects of the treatment. Finally, we discuss auricular vagus nerve stimulation protective potential, especially in the elderly and co-morbid population with already reduced parasympathetic response. Conclusions: Auricular vagus nerve stimulation is a safe clinical procedure and it could be either an effective treatment for ARDS originated by Covid-19 and similar viruses or a supplementary treatment to actual ARDS therapeutic approaches.

Non-invasive Low-level Tragus Stimulation in Cardiovascular Diseases

Low-level tragus stimulation (LLTS) is a non-invasive approach of transcutaneous vagus nerve stimulation. LLTS has applications in diseases of multiple systems, including epilepsy, depression, headache and potentially several cardiovascular diseases. LLTS has shown promising results in suppressing AF, alleviating post-MI ventricular arrhythmias and ischaemia-reperfusion injury along with improving diastolic parameters in heart failure with preserved left ventricular ejection fraction (HFpEF). Preliminary pilot clinical studies in patients with paroxysmal AF, HFpEF, heart failure with reduced ejection fraction and acute MI have demonstrated promising results. The beneficial effects are likely secondary to favourable alteration of the sympathovagal imbalance. On-going exploratory work focused on underlying mechanisms of LLTS in cardiovascular disease states and larger scale clinical trials will shed more light on the non-invasive modulation of the neuro-immune axis.

Vagus Nerve Stimulation and the Cardiovascular System

The vagus nerve plays an important role in maintaining physiological homeostasis, which includes reflex pathways that regulate cardiac function. The link between vagus nerve activity and the high-frequency component of heart rate variability (HRV) has been well established, correlating with vagal tone. Recently, vagus nerve stimulation (VNS) has been investigated as a therapeutic for a multitude of diseases, such as treatment-resistant epilepsy, rheumatoid arthritis, Crohn's disease, and asthma. Because of the vagus nerve's innervation of the heart, VNS has been identified as a potential therapy for cardiovascular disorders, such as cardiac arrest, acute myocardial infarction, and stroke. Here, we review the current state of preclinical and clinical studies, as well as the potential application of VNS in relation to the cardiovascular system.

Ventricular Arrhythmias Underlie Sudden Death in Rats With Heart Failure and Preserved Ejection Fraction

BACKGROUND

Heart failure (HF) with preserved ejection fraction (HFpEF) is increasingly common clinically, now rivaling or exceeding HF with reduced ejection fraction . Sudden death is the leading mode of exodus in patients with HFpEF, but the underlying causes are largely unknown. Using ambulatory recordings in a rat model, we test the hypothesis that ventricular arrhythmias (VA) underlie sudden death in HFpEF.

METHODS

Dahl salt-sensitive rats (7 weeks of age) were fed a high-salt diet to induce HFpEF (n=13) or a normal-salt diet (controls, n=9). Transthoracic echocardiography was performed to check systolic and diastolic function at 14 to 18 weeks of age. Telemetric electrocardiographic recordings were analyzed for QT interval duration, burden of premature ventricular contractions, spontaneous VA, and heart rate variability. Survival was monitored twice daily.

RESULTS

High-salt-fed rats with clear diastolic dysfunction, preserved ejection fraction, and HF signs were diagnosed with HFpEF at 14 to 15 weeks of age. QT and QTc intervals were prolonged in HFpEF rats compared with controls. Heart rate variability was reduced in HFpEF rats compared with controls. Spontaneous VA were more prevalent in HFpEF rats (6/13=46.1% versus 0/9=0% in controls; P<0.05), and sudden death was observed in 4 of 13 HFpEF rats. Three of the 4 sudden deaths were associated with VA as the terminal rhythm.

CONCLUSIONS

In this rat model with phenotypically verified HFpEF, sudden death was common and generally associated with VA. Further clinical studies are warranted to determine whether these insights translate to sudden death in HFpEF patients.

Current Directions in the Auricular Vagus Nerve Stimulation I - A Physiological Perspective

Electrical stimulation of the auricular vagus nerve (aVNS) is an emerging technology in the field of bioelectronic medicine with applications in therapy. Modulation of the afferent vagus nerve affects a large number of physiological processes and bodily states associated with information transfer between the brain and body. These include disease mitigating effects and sustainable therapeutic applications ranging from chronic pain diseases, neurodegenerative and metabolic ailments to inflammatory and cardiovascular diseases. Given the current evidence from experimental research in animal and clinical studies we discuss basic aVNS mechanisms and their potential clinical effects. Collectively, we provide a focused review on the physiological role of the vagus nerve and formulate a biology-driven rationale for aVNS. For the first time, two international workshops on aVNS have been held in Warsaw and Vienna in 2017 within the framework of EU COST Action "European network for innovative uses of EMFs in biomedical applications (BM1309)." Both workshops focused critically on the driving physiological mechanisms of aVNS, its experimental and clinical studies in animals and humans, in silico aVNS studies, technological advancements, and regulatory barriers. The results of the workshops are covered in two reviews, covering physiological and engineering aspects. The present review summarizes on physiological aspects - a discussion of engineering aspects is provided by our accompanying article (Kaniusas et al., 2019). Both reviews build a reasonable bridge from the rationale of aVNS as a therapeutic tool to current research lines, all of them being highly relevant for the promising aVNS technology to reach the patient.

The role of low-level vagus nerve stimulation in cardiac therapy

Introduction: Cardiovascular diseases are accompanied by autonomic nervous system (ANS) imbalance which is characterized by decreased vagal tone. Preclinical and clinical studies have revealed that increasing vagal activity via vagus nerve stimulation (VNS) could protect the heart. Based on these studies, VNS has emerged as a potential non-pharmaceutical treatment strategy. Although it's still difficult to find the optimal stimulus parameters, however, in arrhythmia model, it is reported that low-level VNS (LL-VNS) exacts paradoxical effects from the high-level VNS. Thus, the concept of LL-VNS is introduced. Areas covered: Animal and human studies have discussed the safety and efficacy of VNS and LL-VNS, and this review will discuss the research data in cardiovascular diseases, including atrial arrhythmia, ventricular arrhythmia, ischemia/reperfusion injury, heart failure, and hypertension. Expert opinion: In this regard, various clinical studies have been performed to verify the safety and efficacy of VNS. It is shown that VNS is well-tolerated and safe, but the results of its efficacy are conflicting, which may well block the translational process of VNS. The appearance of LL-VNS brings new idea and inspiration, suggesting an important role of subthreshold stimulation. A better understanding of the LL-VNS will contribute to translational research of VNS.

Chronic Low-Level Vagus Nerve Stimulation Improves Long-Term Survival in Salt-Sensitive Hypertensive Rats

Chronic hypertension (HTN) affects more than 1 billion people worldwide, and is associated with an increased risk of cardiovascular disease. Despite decades of promising research, effective treatment of HTN remains challenging. This work investigates vagus nerve stimulation (VNS) as a novel, device-based therapy for HTN treatment, and specifically evaluates its effects on long-term survival and HTN-associated adverse effects. HTN was induced in Dahl salt-sensitive rats using a high-salt diet, and the rats were randomly divided into two groups: VNS (n = 9) and Sham (n = 8), which were implanted with functional or non-functional VNS stimulators, respectively. Acute and chronic effects of VNS therapy were evaluated through continuous monitoring of blood pressure (BP) and ECG via telemetry devices. Autonomic tone was quantified using heart rate (HR), HR variability (HRV) and baroreflex sensitivity (BRS) analysis. Structural cardiac changes were quantified through gross morphology and histology studies. VNS significantly improved the long-term survival of hypertensive rats, increasing median event-free survival by 78% in comparison to Sham rats. Acutely, VNS improved autonomic balance by significantly increasing HRV during stimulation, which may lead to beneficial chronic effects of VNS therapy. Chronic VNS therapy slowed the progression of HTN through an attenuation of SBP and by preserving HRV. Finally, VNS significantly altered cardiac structure, increasing heart weight, but did not alter the amount of fibrosis in the hypertensive hearts. These results suggest that VNS has the potential to improve outcomes in subjects with severe HTN.

Low-level transcutaneous vagus nerve stimulation attenuates cardiac remodelling in a rat model of heart failure with preserved ejection fraction

NEW FINDINGS

What is the central question of this study? What is the effect of chronic intermittent low-level transcutaneous vagus nerve stimulation on cardiac inflammation, fibrosis and diastolic dysfunction in a rat model of heart failure with preserved ejection fraction? What is the main finding and its importance? In salt-sensitive rats fed with high salt diet, low-level transcutaneous vagus nerve stimulation significantly attenuated blood pressure elevation, ameliorated diastolic function, and attenuated left ventricular inflammation and fibrosis compared to the sham group. Further studies to examine the efficacy of this novel treatment in humans are warranted.

ABSTRACT

Inflammation and fibrosis play a central role in the development of heart failure with preserved ejection fraction (HFpEF). We previously showed that low-level, transcutaneous stimulation of the vagus nerve at the tragus (LLTS) is anti-inflammatory. We investigated the effect of chronic intermittent LLTS on cardiac inflammation, fibrosis and diastolic dysfunction in a rat model of HFpEF. Dahl salt-sensitive (DS) rats were randomized in three groups: low salt (LS, 0.3% NaCl; n = 12; control group without stimulation) and high salt (HS, 4% NaCl) with either active (n = 18) or sham (n = 18) LLTS at 7 weeks of age. After 6 weeks of diet (baseline), sham or active LLTS (20 Hz, 2 mA, 0.2 ms) was implemented for 30 min daily for 4 weeks. Echocardiography was performed at baseline and 4 weeks after treatment (endpoint). At endpoint, left ventricle (LV) histology and gene expression were examined. After 6 weeks of diets, HS rats developed hypertension and LV hypertrophy compared to LS rats. At endpoint, LLTS significantly attenuated blood pressure elevation, prevented the deterioration of diastolic function and improved LV circumferential strain, compared to the HS sham group. LV inflammatory cell infiltration and fibrosis were attenuated in the HS active compared to the HS sham group. Pro-inflammatory and pro-fibrotic genes (tumour necrosis factor, osteopontin, interleukin (IL)-11, IL-18 and IL-23A) were differentially altered in the two groups. Chronic intermittent LLTS ameliorates diastolic dysfunction, and attenuates cardiac inflammation and fibrosis in a rat model of HFpEF, suggesting that LLTS may be used clinically as a novel non-invasive neuromodulation therapy in HFpEF.

Modified Sequence Method to Assess Baroreflex Sensitivity in Rats

Baroreceptors respond to fluctuations in blood pressure (BP) by modifying physiology in order to maintain a homeostatic set point. Baroreflex sensitivity (BRS) is used to quantify baroreceptor function and is a useful metric for tracking cardiovascular disease state and treatment effects. Pathological conditions such as hypertension (HTN) alter baroreflex function and reduce BRS. Traditionally, the sequence method is used to measure BRS, in which the linear slope of concomitant changes in BP and RR intervals are assessed. However, in rats, a high respiratory rate reduces the reliability of the sequence method. Here, we present a modified sequence method that captures BRS at lower frequencies and decreases the variability of the BRS estimate. This method was demonstrated using ECG and BP data from two groups of HTN rats: Sham rats and rats treated with vagus nerve stimulation. The modified sequence method resulted in lower BRS estimates than the traditional sequence technique when applied to the same data sets. Additionally, the modified sequence method resulted in lower BRS estimate variability.

Acute cardiovascular and hemodynamic effects of vagus nerve stimulation in conscious hypertensive rats

Hypertension (HTN) affects over 1 billion people worldwide, with a significant number who are unable to control their blood pressure (BP) with conventional therapies. Recently, novel device-based therapies targeting the autonomic nervous system have been evaluated for treating HTN, including vagus nerve stimulation (VNS). Numerous studies have indicated the beneficial effects of chronic VNS in various models of HTN, however the acute effects of VNS on physiological responses have not been widely investigated. To better understand the acute effects of VNS, this study evaluates cardiovascular and hemodynamic responses from conscious hypertensive rats implanted with VNS stimulators and physiological telemeters for simultaneous monitoring of BP and heart rate (HR) as therapy is applied. We demonstrated that there are no acute changes in mean BP, HR and contractility measures as a result of VNS stimulation. However, there were significant increases in both HR variability and BP variability during VNS, which returned to baseline levels immediately at the cessation of therapy. The small acute changes observed during intermittent VNS could be additive, leading to beneficial chronic changes in BP and HR control, and may help in furthering the understanding of beneficial effects demonstrated in chronic use of VNS therapy.

The influences of the M2R-GIRK4-RGS6 dependent parasympathetic pathway on electrophysiological properties of the mouse heart

A large body of work has established the prominent roles of the atrial M₂R-I_KACh signaling pathway, and the negative regulatory protein RGS6, in modulating critical aspects of parasympathetic influence on cardiac function, including pace-making, heart rate (HR) variability (HRV), and atrial arrhythmogenesis. Despite increasing evidence of its innervation of the ventricles, and the expression of M₂R, I_KACh channel subunits, and RGS6 in ventricle, the effects of parasympathetic modulation on ventricular electrophysiology are less clear. The main objective of our study was to investigate the contribution of M₂R-I_KACh signaling pathway elements in murine ventricular electrophysiology, using in-vivo ECG measurements, isolated whole-heart optical mapping and constitutive knockout mice lacking I_KACh (Girk4^–/–) or RGS6 (Rgs6^-/-). Consistent with previous findings, mice lacking GIRK4 exhibited diminished HR and HRV responses to the cholinergic agonist carbachol (CCh), and resistance to CCh-induced arrhythmic episodes. In line with its role as a negative regulator of atrial M₂R-I_KACh signaling, loss of RGS6 correlated with a mild resting bradycardia, enhanced HR and HRV responses to CCh, and increased propensity for arrhythmic episodes. Interestingly, ventricles from mice lacking GIRK4 or RGS6 both exhibited increased action potential duration (APD) at baseline, and APD was prolonged by CCh across all genotypes. Similarly, CCh significantly increased the slope of APD restitution in all genotypes. There was no impact of genotype or CCh on either conduction velocity or heterogeneity. Our data suggests that altered parasympathetic signaling through the M₂R-I_KACh pathway can affect ventricular electrophysiological properties distinct from its influence on atrial physiology.

Stochastic vagus nerve stimulation affects acute heart rate dynamics in rats

Vagus nerve stimulation (VNS) is an approved therapy for treatment of epilepsy and depression. While also shown to be promising in several preclinical and clinical studies to treat cardiovascular diseases, optimal therapeutic stimulation paradigms are still under investigation. Traditionally, parameters such as frequency, current, and duty cycle are used to adjust the efficacy of VNS therapy. This study explored the effect of novel stochastic VNS (S-VNS) on acute heart rate (HR) dynamics. The effect of S-VNS was evaluated in Sprague Dawley rats by comparing the acute HR and HR variability (HRV) responses to standard, periodic VNS (P-VNS) across different frequencies (FREQs, 10-30 Hz). Our results demonstrate that both S-VNS and P-VNS produced negative chronotropic effects in a FREQ-dependent manner with S-VNS inducing a significantly smaller drop in HR at 10 Hz and 20 Hz compared to P-VNS (p<0.05). S-VNS demonstrated a FREQ-dependent drop in the SD1/SD2 ratio, a measure of HRV, which was absent in P-VNS, suggesting that S-VNS may acutely modulate the nonlinear relationship between short- and long-term HRV. In conclusion, S-VNS is a novel stimulation procedure that may provide different physiological outcomes from standard P-VNS, as indicated by our analysis of HR dynamics. Our study provides a rationale for further detailed investigations into the therapeutic potential of S-VNS as a novel neuromodulation technique.

Toward Bioelectronic Medicine-Neuromodulation of Small Peripheral Nerves Using Flexible Neural Clip

Neural modulation technology and the capability to affect organ function have spawned the new field of bioelectronic medicine. Therapeutic interventions depend on wireless bioelectronic neural interfaces that can conformally and easily attach to small (few hundred micrometers) nerves located deep in the body without neural damage. Besides size, factors like flexibility and compliance to attach and adapt to visceral nerves associated moving organs are of paramount importance and have not been previously addressed. This study proposes a novel flexible neural clip (FNC) that can be used to interface with a variety of different peripheral nerves. To illustrate the flexibility of the design, this study stimulates the pelvic nerve, the vagus nerve, and branches of the sciatic nerve and evaluates the feasibility of the design in modulating the function of each of these nerves. It is found that this FNC allows fine-tuning of physiological processes such as micturition, heart rate, and muscle contractions. Furthermore, this study also tests the ability of wirelessly powered FNC to enable remote modulation of visceral pelvic nerves located deep in the body. These results show that the FNC can be used with a range of different nerves, providing one of the critical pieces in the field of bioelectronics medicines.

Device-based Therapy for Hypertension

Hypertension continues to be a major contributor to global morbidity and mortality, fuelled by an abundance of patients with uncontrolled blood pressure despite the multitude of pharmacological options available. This may occur as a consequence of true resistant hypertension, through an inability to tolerate current pharmacological therapies, or non-adherence to antihypertensive medication. In recent years, there has been a rapid expansion of device-based therapies proposed as novel non-pharmacological approaches to treating resistant hypertension. In this review, we discuss seven novel devices—renal nerve denervation, baroreflex activation therapy, carotid body ablation, central iliac arteriovenous anastomosis, deep brain stimulation, median nerve stimulation, and vagal nerve stimulation. We highlight how the devices differ, the varying degrees of evidence available to date and upcoming trials. This review also considers the possible factors that may enable appropriate device selection for different hypertension phenotypes.

Vagus nerve stimulation: a new promising therapeutic tool in inflammatory bowel disease

Inflammatory bowel disease (IBD), that is Crohn's disease (CD) and ulcerative colitis, affects about 1.5 million persons in the USA and 2.2 million in Europe. The pathophysiology of IBD involves immunological, genetic and environmental factors. The treatment is medico-surgical but suspensive. Anti-TNFα agents have revolutionized the treatment of IBD but have side effects. In addition, a non-negligible percentage of patients with IBD stop or take episodically their treatment. Consequently, a nondrug therapy targeting TNFα through a physiological pathway, devoid of major side effects and with a good cost-effectiveness ratio, would be of interest. The vagus nerve has dual anti-inflammatory properties through its afferent (i.e. hypothalamic-pituitary-adrenal axis) and efferent (i.e. the anti-TNFα effect of the cholinergic anti-inflammatory pathway) fibres. We have shown that there is an inverse relationship between vagal tone and plasma TNFα level in patients with CD, and have reported, for the first time, that chronic vagus nerve stimulation has anti-inflammatory properties in a rat model of colitis and in a pilot study performed in seven patients with moderate CD. Two of these patients failed to improve after 3 months of vagus nerve stimulation but five were in deep remission (clinical, biological and endoscopic) at 6 months of follow-up and vagal tone was restored. No major side effects were observed. Thus, vagus nerve stimulation provides a new therapeutic option in the treatment of CD.

Vagus nerve stimulation: state of the art of stimulation and recording strategies to address autonomic function neuromodulation

OBJECTIVE

Neural signals along the vagus nerve (VN) drive many somatic and autonomic functions. The clinical interest of VN stimulation (VNS) is thus potentially huge and has already been demonstrated in epilepsy. However, side effects are often elicited, in addition to the targeted neuromodulation.

APPROACH

This review examines the state of the art of VNS applied to two emerging modulations of autonomic function: heart failure and obesity, especially morbid obesity.

MAIN RESULTS

We report that VNS may benefit from improved stimulation delivery using very advanced technologies. However, most of the results from fundamental animal studies still need to be demonstrated in humans.

Chronic cyclic vagus nerve stimulation has beneficial electrophysiological effects on healthy hearts in the absence of autonomic imbalance

Cardiovascular disease degrades the regulatory function of the autonomic nervous system. Cyclic vagus nerve stimulation (VNS) is an already FDA-approved therapy for drug-resistant epilepsy and depression, and has been shown to normalize autonomic function and improve objective measures of heart function and subjective measures of heart failure symptoms. However, it remains unclear whether VNS may induce negative effects in patients with potentially healthy hearts where VNS can be used for epileptic patients. Hence, this study aims to investigate the effects of VNS on the hearts of healthy rats with normal autonomic balance. Sprague-Dawley rats were implanted with stimulators and randomized to either Sham or VNS groups. Rats in VNS group received 10 weeks of chronic intermittent VNS via stimulation of the right cervical vagus nerve. Echocardiography was performed at Baseline (prior to VNS), Week 2, and Week 9. After 10 weeks, high-resolution optical mapping was performed in ex vivo perfused hearts to evaluate the electrophysiological remodeling that occurs in the heart as a result of the VNS therapy. Chronic VNS modified the electrophysiological properties of healthy rat hearts by reducing the action potential duration at 50% (APD50) and 80% (APD80) repolarization. Chronic VNS also affected the restitution properties of the heart at the APD50 level and increased myocardial conduction velocity (CV). VNS did not induce any significant changes to ventricular ejection fraction (EF) and spatial dispersion of APD, thus indicating that VNS did not negatively affect cardiac function. VNS also reduced the susceptibility to ventricular arrhythmias (ventricular fibrillation [VF] and ventricular tachycardia [VT]) during ex vivo programmed electrical stimulation. In summary, chronic application of cyclic VNS induces changes to the electrophysiological properties of healthy rat hearts. The observed decrease in APD and increase in CV suggest that the beneficial effects of VNS do not require the presence of existing autonomic imbalance.