Restoration of normal sympathetic neural function in heart failure following baroreflex activation therapy: final 43-month study report

Baroreflex activation therapy for heart failure with reduced ejection fraction: A comprehensive systematic review and meta-analysis

Background

In recent years, baroreflex activation therapy (BAT) has been utilized to treat heart failure with reduced ejection fraction (HFrEF). However, the supporting literature on its efficacy and safety is still limited. This investigation elucidates the effects of BAT in HFrEF patients to provide a reference for future clinical applications.

Methods

This investigation follows Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) 2020 guidelines. Relevant investigations on the use of BAT in HFrEF patients were searched and selected from 5 databases, including Web of Science, MEDLINE, PubMed, Embase, and Cochrane Library, from inception to December 2022. The methodological quality of eligible articles was assessed via the Cochrane risk of bias tool, and for meta-analysis, RevMan (5.3) was used.

Results

Randomized controlled trials comprising 343 participants were selected for the meta-analysis, which revealed that in HFrEF patients, BAT enhanced the levels of LVEF (MD: 2.97, 95 % CI: 0.53 to 5.41), MLHFQ (MD: -14.81, 95 % CI: -19.57 to -10.06) and 6MWT (MD: 68.18, 95 % CI: 51.62 to 84.74), whereas reduced the levels of LVEDV (MD: -15.79, 95 % CI: -32.96 to 1.37) and DBP (MD: -2.43, 95 % CI: -4.18 to -0.68).

Conclusion

It was concluded that BAT is an efficient treatment option for HFrEF patients. However, to validate this investigation, further randomized clinical trials with multiple centers and large sample sizes are needed.

Neural control of the circulation during exercise in heart failure with reduced and preserved ejection fraction

Patients with heart failure with reduced (HFrEF) and preserved ejection fraction (HFpEF) exhibit severe exercise intolerance that may be due, in part, to inappropriate cardiovascular and hemodynamic adjustments to exercise. Several neural mechanisms and locally released vasoactive substances work in concert through complex interactions to ensure proper adjustments to meet the metabolic demands of the contracting skeletal muscle. Specifically, accumulating evidence suggests that disease-related alterations in neural mechanisms (e.g., central command, exercise pressor reflex, arterial baroreflex, and cardiopulmonary baroreflex) contribute to heightened sympathetic activation and impaired ability to attenuate sympathetic vasoconstrictor responsiveness that may contribute to reduced skeletal muscle blood flow and severe exercise intolerance in patients with HFrEF. In contrast, little is known regarding these important aspects of physiology in patients with HFpEF, though emerging data reveal heightened sympathetic activation and attenuated skeletal muscle blood flow during exercise in this patient population that may be attributable to dysregulated neural control of the circulation. The overall goal of this review is to provide a brief overview of the current understanding of disease-related alterations in the integrative neural cardiovascular responses to exercise in both HFrEF and HFpEF phenotypes, with a focus on sympathetic nervous system regulation during exercise.

Efficacy and safety of baroreflex activation therapy for heart failure with reduced ejection fraction: systematic review

Baroreflex activation therapy (BAT) is a possible adjuvant treatment for patients with heart failure with reduced ejection fraction (HFrEF) who remain symptomatic despite optimal medical therapy and may be an alternative therapy in patients with contraindications or drug intolerance. Our aim was to evaluate the efficacy and safety of BAT in patients with HFrEF. The protocol for this study was registered with PROSPERO (CRD42022349175). Searches were conducted using MEDLINE, preMedLine (via PubMed), EMBASE, Cochrane Library, Web of Science, Trip Medical Database, WHO International Clinical Trials Registry, and ClinicalTrials.gov. We included randomized controlled trials that compared the effects of BAT with pharmacological treatment. We assessed the risk of bias of each study using the Cochrane RoB2 tool and the certainty of the results using the GRADE approach. We performed a meta-analysis of treatment effects using a fixed-effects or random-effects model, depending on the heterogeneity observed. Two studies were included in the meta-analysis (HOPE4HF and BeAT-HF). The results showed that BAT led to statistically significant improvements in New York Heart Association functional class (relative risk 2.13; 95% confidence interval [CI, 1.65 to 2.76]), quality of life (difference in means -16.97; 95% CI [-21.87 to -12.07]), 6 min walk test (difference in means 56.54; 95% CI [55.67 to 57.41]) and N-terminal probrain natriuretic peptide (difference in means -120.02; 95% CI [-193.58 to -46.45]). The system- and procedure-related complication event-free rate varied from 85.9% to 97%. The results show that BAT is safe and improves functional class, quality of life and congestion in selected patients with HFrEF. Further studies and long-term follow-up are needed to assess efficacy in reducing cardiovascular events and mortality.

A Methodological Perspective on the Function and Assessment of Peripheral Chemoreceptors in Heart Failure: A Review of Data from Clinical Trials

Augmented peripheral chemoreceptor sensitivity (PChS) is a common feature of many sympathetically mediated diseases, among others, and it is an important mechanism of the pathophysiology of heart failure (HF). It is related not only to the greater severity of symptoms, especially to dyspnea and lower exercise tolerance but also to a greater prevalence of complications and poor prognosis. The causes, mechanisms, and impact of the enhanced activity of peripheral chemoreceptors (PChR) in the HF population are subject to intense research. Several methodologies have been established and utilized to assess the PChR function. Each of them presents certain advantages and limitations. Furthermore, numerous factors could influence and modulate the response from PChR in studied subjects. Nevertheless, even with the impressive number of studies conducted in this field, there are still some gaps in knowledge that require further research. We performed a review of all clinical trials in HF human patients, in which the function of PChR was evaluated. This review provides an extensive synthesis of studies evaluating PChR function in the HF human population, including methods used, factors potentially influencing the results, and predictors of increased PChS.

Modeling the physiological roles of the heart and kidney in heart failure with preserved ejection fraction during baroreflex activation therapy

Heart failure (HF) is a leading cause of death and is increasing in prevalence. Unfortunately, therapies that have been efficacious in patients with HF with reduced ejection fraction (HFrEF) have not convincingly shown a reduction in cardiovascular mortality in patients with HF with preserved ejection fraction (HFpEF). It is thought that high sympathetic nerve activity (SNA) in the heart plays a role in HF progression. Clinical trials demonstrate that baroreflex activation therapy reduces left ventricular (LV) mass and blood pressure (BP) in patients with HFpEF and hypertension; however, the mechanisms are unclear. In the present study, we used HumMod, a large physiology model to simulate HFpEF and predict the time-dependent changes in systemic and cardiac hemodynamics, SNA, and cardiac stresses during baroreflex activation. The baseline HFpEF model was associated with elevations in systolic BP, diastolic dysfunction, and LV hypertrophy and stiffness similar to clinical HFpEF. Simulating 12 mo of baroreflex activation resulted in reduced systolic BP (-25 mmHg) and LV mass (-15%) similar to clinical evidence. Baroreflex activation also resulted in sustained decreases in cardiac and renal SNA (-22%) and improvement in LV β1-adrenergic function. However, the baroreflex-induced reductions in BP and improvements in cardiac stresses, mass, and function were mostly attenuated when renal SNA was clamped at baseline levels. These simulations suggest that the suppression of renal SNA could be a primary determinant of the cardioprotective effects from baroreflex activation in HFpEF.NEW & NOTEWORTHY Treatments that are efficacious in patients with HFrEF have not shown a significant impact on cardiovascular mortality in patients with HFpEF. We believe these simulations offer novel insight into the important roles of the cardiac and renal nerves in HFpEF and the potential mechanisms of how baroreflex activation alleviates HFpEF disease progression.

Novel Therapeutic Devices in Heart Failure

Heart failure (HF) constitutes a significant clinical problem and is associated with a sizeable burden for the healthcare system. Numerous novel techniques, including device interventions, are investigated to improve clinical outcome. A review of the most notable currently studied devices targeting pathophysiological processes in HF was performed. Interventions regarding autonomic nervous system imbalance, i.e., baroreflex activation therapy; vagus, splanchnic and cardiopulmonary nerves modulation; respiratory disturbances, i.e., phrenic nerve stimulation and synchronized diaphragmatic therapy; decongestion management, i.e., the Reprieve system, transcatheter renal venous decongestion system, Doraya, preCardia, WhiteSwell and Aquapass, are presented. Each segment is divided into subsections: potential pathophysiological target, existing evidence and weaknesses or unexplained issues. Novel therapeutic devices represent great potential in HF therapy management; however, further evidence is necessary to fully evaluate their utility.

Nonpharmacologic Treatment for Heart Failure: A Review of Implantable Carotid Baroreceptor Stimulators As a Therapeutic Option

There has been significant interest in research for the development of device-based therapy as a treatment option of heart failure (HF), whether it is with reduced or preserved ejection fraction. This is due to the high morbidity and mortality rate in patients with HF despite recent advances in pharmacologic treatment. Following the success of cardiac resynchronization therapy, baroreceptor activation therapy has emerged as another novel device-based treatment for HF. The Barostim neo was developed by CVRx Minneapolis, MN for the treatment of mild to severe HF. The device works by electrically activating the baroreceptor reflex with the goal to restore the maladaptive autonomic imbalance that is seen in patients with HF. Preliminary clinical investigations have given promising results with an encouraging safety profile. Baroreceptor activation therapy as a treatment option is still investigational at this time; however, several trials in different patient populations have already shown benefit with a very good safety profile. In this review, we will summarize the current state of technology and the available literature of the use of baroreceptor activation therapy in patients with different comorbidities, with a focus on this device-based therapy in patients with HF.

CENTRAL AND PERIPHERAL SYMPATHETIC ACTIVATION IN HEART FAILURE

The sympathetic nervous system overdrive occurring in heart failure has been reported since more than half a century. Refinements in the methodological approaches to assess human sympathetic neural function have allowed during recent years to better define various aspects related to the neuroadrenergic alteration. These include 1) the different participation of the individual regional sympathetic cardiovascular districts at the process, 2) the role of the central nervous system in determining the neuroadrenergic overdrive, 3) the involvement of baroreflex, cardiopulmonary reflex and chemoreflex mechanisms in the phoenomenon, which is also closely linked to inflammation and the immune reaction, 4) the relationships with the severity of the disease, its ischaemic or idiopathic nature and the preserved or reduced left ventricular ejection fraction and 5) the adverse functional and structural impact of the sympathetic activation on cardiovascular organs, such as the brain, the heart and the kidneys. Information have been also gained on the active role exerted by the sympathetic activation on the disease outcome and its potential relevance as target of the therapeutic interventions based on non-pharmacological, pharmacological and invasive approaches, including the renal denervation, the splanchnic sympathetic nerve ablation and the carotid baroreflex stimulation. The still undefined aspects of the neurogenic alterations and the unmet goals of the therapeutic approach having the sympathetic activation as a target of the intervention will be finally mentioned.

Sympathoinhibitory effect of sacubitril-valsartan in heart failure with reduced ejection fraction: A pilot study

Chronic sympathetic nervous system (SNS) overactivity, characteristic of heart failure (HF) with reduced ejection fraction (HFrEF), is associated with poor prognosis and contributes to increased mortality risk. Sacubitril-valsartan is a recently approved, first-in-class, angiotensin receptor neprilysin inhibitor (ARNI) drug that markedly reduces the risks of death from cardiovascular causes and hospitalization for HF in patients with HFrEF, but the physiological mechanisms underlying these benefits are not fully understood. This single-arm, open-label, prospective study sought to test the hypothesis that short-term treatment with sacubitril-valsartan reduces SNS activity, measured directly via muscle sympathetic nerve activity (MSNA), in patients with HFrEF. MSNA, heart rate (HR), and arterial blood pressure (BP) were assessed in stable Class II and III patients with HFrEF (n = 9, 69 ± 8 yrs.; 28.6 ± 3.6 kg/m²) on contemporary, guideline-directed medical treatment who were subsequently started on sacubitril-valsartan. These measurements were repeated after two months of treatment with sacubitril-valsartan. Sacubitril-valsartan reduced MSNA burst frequency (baseline: 43 ± 10 bursts/min; 2-month: 36 ± 10 bursts/min, p = 0.05) and burst incidence (baseline: 68 ± 16 bursts/100 heartbeats; 2-month: 55 ± 16 bursts/100 heartbeats, p = 0.02), while HR and BP were unchanged following of treatment (p > 0.05). These preliminary findings provide new evidence regarding the ability of sacubitril-valsartan to rapidly reduce SNS activity in patients with HFrEF, suggesting the presence of a novel sympathoinhibitory effect of this new drug class.

Autonomic cardiovascular alterations as therapeutic targets in chronic kidney disease

Purpose

The present paper will review the impact of different therapeutic interventions on the autonomic dysfunction characterizing chronic renal failure.

Methods

We reviewed the results of the studies carried out in the last few years examining the effects of standard pharmacologic treatment, hemodialysis, kidney transplantation, renal nerve ablation and carotid baroreceptor stimulation on parasympathetic and sympathetic control of the cardiovascular system in patients with renal failure.

Results

Drugs acting on the renin–angiotensin system as well as central sympatholytic agents have been documented to improve autonomic cardiovascular control. This has also been shown for hemodialysis, although with more heterogeneous results related to the type of dialytic procedure adopted. Kidney transplantation, in contrast, particularly when performed together with the surgical removal of the native diseased kidneys, has been shown to cause profound sympathoinhibitory effects. Finally, a small amount of promising data are available on the potential favorable autonomic effects (particularly the sympathetic ones) of renal nerve ablation and carotid baroreceptor stimulation in chronic kidney disease.

Conclusions

Further studies are needed to clarify several aspects of the autonomic responses to therapeutic interventions in chronic renal disease. These include (1) the potential to normalize sympathetic activity in uremic patients by the various therapeutic approaches and (2) the definition of the degree of sympathetic deactivation to be achieved during treatment.

CORP: Standardizing methodology for assessing spontaneous baroreflex control of muscle sympathetic nerve activity in humans

The use of spontaneous bursts of muscle sympathetic nerve activity (MSNA) to assess arterial baroreflex control of sympathetic nerve activity has seen increased utility in studies of both health and disease. However, methods used for analyzing spontaneous MSNA baroreflex sensitivity are highly variable across published studies. Therefore, we sought to comprehensively examine methods of producing linear regression slopes to quantify spontaneous MSNA baroreflex sensitivity in a large cohort of subjects (n = 150) to support a standardized procedure for analysis that would allow for consistent and comparable results across laboratories. The primary results demonstrated that 1) consistency of linear regression slopes was considerably improved when the correlation coefficient was above -0.70, which is more stringent compared with commonly reported criterion of -0.50, 2) longer recording durations increased the percentage of linear regressions producing correlation coefficients above -0.70 (1 min = 15%, 2 min = 28%, 5 min = 53%, 10 min = 67%, P < 0.001) and reaching statistical significance (1 min = 40%, 2 min = 69%, 5 min = 78%, 10 min = 89%, P < 0.001), 3) correlation coefficients were improved with 3-mmHg versus 1-mmHg and 2-mmHg diastolic blood pressure (BP) bin size, and 4) linear regression slopes were reduced when the acquired BP signal was not properly aligned with the cardiac cycle triggering the burst of MSNA. In summary, these results support the use of baseline recording durations of 10 min, a correlation coefficient above -0.70 for reliable linear regressions, 3-mmHg bin size, and importance of properly time-aligning MSNA and diastolic BP. Together, these findings provide best practices for determining spontaneous MSNA baroreflex sensitivity under resting conditions for improved rigor and reproducibility of results.

Reappraisal on pharmacological and mechanical treatments of heart failure

Heart failure (HF) is a highly frequent disorder with considerable morbidity, hospitalization, and mortality; thus, it invariably places pressure on clinical and public health systems in the modern world. There have been notable advances in the definition, diagnosis, and treatment of HF, and newly developed agents and devices have been widely adopted in clinical practice. Here, this review first summarizes the current emerging therapeutic agents, including pharmacotherapy, device-based therapy, and the treatment of some common comorbidities, to improve the prognosis of HF patients. Then, we discuss and point out the commonalities and areas for improvement in current clinical studies of HF. Finally, we highlight the gaps in HF research. We are looking forward to a bright future with reduced morbidity and mortality from HF.

Endovascular baroreflex amplification for resistant hypertension: what you need to know

Endovascular baroreflex amplification is an alternative treatment strategy for patients with resistant hypertension. In endovascular baroreflex, the carotid baroreflex is activated by a MobiusHD^® device (MD) which has been implanted in the internal carotid artery. This review will discuss the MD technology and mechanism of action and promising results in the first-in-human prospective study involving the use of the MD in patients with resistant hypertension.

Baroreflex Activation Therapy for Resistant Hypertension and Heart Failure

Hypertension and heart failure are important contributors to global morbidity and mortality. Despite therapeutic lifestyle and pharmacological measures, a significant proportion of people with hypertension do not reach treatment targets. Patients with resistant or poorly controlled hypertension are at significantly increased risk of cardiovascular events, including heart failure. Since dysfunction of the sympathetic nervous system appears to play a key role in the development and progression of both hypertension and heart failure, these patients may benefit from treatment modalities aimed at reducing sympathetic function. The purpose of this paper is to provide an overview of baroreflex activation therapy as a potential treatment strategy in patients with resistant hypertension or heart failure.

Sex differences in baroreflex function in health and disease

This brief review summarizes the current knowledge on sex differences in baroreflex function, with a major focus on studies in humans. It has been demonstrated that healthy women have blunted cardiovagal baroreflx sensitivity during a rapid (i.e., within seconds) hypertensive stimulus, but baroreflex sensitivity is similar between the sexes during a hypotensive stimulus. Normal aging decreases cardiovagal baroreflex sensitivity and the rate of decline is similar in men and women. Cardiovagal baroreflex sensitivity is reduced in pathological conditions such as hypertension and type II diabetes, and the reduction is greater in female patients than male patients. There is no clear sex difference in sympathetic baroreflex sensitivity among young individuals, however, with women of more advanced age, sympathetic baroreflex sensitivity decreases, which appears to be associated with greater arterial stiffness compared with similarly aged men. The blunted sympathetic baroreflex sensitivity in older women may predispose them to an increased prevalence of hypertension and cardiovascular disease.

Clinical Implications of Baroreflex Sensitivity in Type 2 Diabetes

The evaluation of baroreflex sensitivity (BRS), which maintains systemic circulatory homeostasis, is an established tool to assess cardiovascular autonomic neuropathy in type 2 diabetes mellitus (T2DM). As BRS plays an important function in blood pressure regulation, reduced BRS leads to an increase in blood pressure variability, which further leads to reduced BRS. This sequence of events becomes a vicious cycle. The major risk factors for reduced BRS are T2DM and essential hypertension, but many other risk factors have been reported to influence BRS. In recent years, reports have indicated that glycemic variability (GV), such as short- and long-term GV that are considered important risk factors for macrovascular and microvascular complications, is involved in reductions in BRS independently of blood glucose levels. In this review, we discuss reduced BRS in T2DM, its features, and the potential for its reversal.

Role of the heart in blood pressure lowering during chronic baroreflex activation: insight from an in silico analysis

Electrical stimulation of the baroreflex chronically suppresses sympathetic activity and arterial pressure and is currently being evaluated for the treatment of resistant hypertension. The antihypertensive effects of baroreflex activation are often attributed to renal sympathoinhibition. However, baroreflex activation also decreases heart rate, and robust blood pressure lowering occurs even after renal denervation. Because controlling renal sympathetic nerve activity (RSNA) and cardiac autonomic activity cannot be achieved experimentally, we used an established mathematical model of human physiology (HumMod) to provide mechanistic insights into their relative and combined contributions to the cardiovascular responses during baroreflex activation. Three-week responses to baroreflex activation closely mimicked experimental observations in dogs including decreases in blood pressure, heart rate, and plasma norepinephrine and increases in plasma atrial natriuretic peptide (ANP), providing validation of the model. Simulations showed that baroreflex-induced alterations in cardiac sympathetic and parasympathetic activity lead to a sustained depression of cardiac function and increased secretion of ANP. Increased ANP and suppression of RSNA both enhanced renal excretory function and accounted for most of the chronic blood pressure lowering during baroreflex activation. However, when suppression of RSNA was blocked, the blood pressure response to baroreflex activation was not appreciably impaired due to inordinate fluid accumulation and further increases in atrial pressure and ANP secretion. These simulations provide a mechanistic understanding of experimental and clinical observations showing that baroreflex activation effectively lowers blood pressure in subjects with previous renal denervation. NEW & NOTEWORTHY Both experimental and clinical studies have shown that the presence of renal nerves is not an obligate requirement for sustained reductions in blood pressure during chronic electrical stimulation of the carotid baroreflex. Simulations using HumMod, a mathematical model of integrative human physiology, indicated that both increased secretion of atrial natriuretic peptide and suppressed renal sympathetic nerve activity play key roles in mediating long-term reductions in blood pressure during chronic baroreflex activation.

Fifty years of microneurography: learning the language of the peripheral sympathetic nervous system in humans

As a primary component of homeostasis, the sympathetic nervous system enables rapid adjustments to stress through its ability to communicate messages among organs and cause targeted and graded end organ responses. Key in this communication model is the pattern of neural signals emanating from the central to peripheral components of the sympathetic nervous system. But what is the communication strategy employed in peripheral sympathetic nerve activity (SNA)? Can we develop and interpret the system of coding in SNA that improves our understanding of the neural control of the circulation? In 1968, Hagbarth and Vallbo (Hagbarth KE, Vallbo AB. Acta Physiol Scand 74: 96-108, 1968) reported the first use of microneurographic methods to record sympathetic discharges in peripheral nerves of conscious humans, allowing quantification of SNA at rest and sympathetic responsiveness to physiological stressors in health and disease. This technique also has enabled a growing investigation into the coding patterns within, and cardiovascular outcomes associated with, postganglionic SNA. This review outlines how results obtained by microneurographic means have improved our understanding of SNA outflow patterns at the action potential level, focusing on SNA directed toward skeletal muscle in conscious humans.

Oxidative Stress in the Rostral Ventrolateral Medulla Contributes To Cardiovascular Regulation in Preeclampsia

Background: It has been demonstrated that preeclampsia, a pregnancy-specific hypertension disorder, is characterized by high blood pressure (BP) and sympathetic overactivity. Increased reactive oxygen species (ROS) in the rostral ventrolateral medulla (RVLM), a key region for controlling sympathetic tone, has been reported to contribute to high level of BP and sympathetic outflow. The aim of the present study was to determine the role of the RVLM ROS in mediating the preeclampsia-associated cardiovascular dysfunction.

Methods: The animal model of preeclampsia was produced by administration of desoxycorticosterone acetate (DOCA) to pregnant rats.

Results: Compared with normal pregnant rats without DOCA treatment (NP), the protein concentration and norepinephrine excretion in 24-h urine, as well as BP in pregnant rats with DOCA treatment (PDS) were significantly increased. The levels of superoxide anion and the protein expression of NADPH oxidase subtype (NOX4) in the RVLM were significantly increased in PDS than in NP groups. Furthermore, microinjection of the superoxide dismutase (SOD) mimic Tempol (5 nmol) into the RVLM significantly decreased BP, heart rate, and renal sympathetic never activity in PDS but not in NP group.

Conclusion: The present data suggest that high BP and sympathetic overactivity in preeclampsia rats is associated with increased oxidative stress in the RVLM via upregulation of NOX4 expression.