Acute Device-Based Blood Pressure Reduction: Electrical Activation of the Carotid Baroreflex in Patients Undergoing Elective Carotid Surgery

Home-Based Remote Rehabilitation Leads to Superior Outcomes for Older Women With Knee Osteoarthritis: A Randomized Controlled Trial

OBJECTIVES

To examine the effects of a home-based lower-extremity strengthening exercise program in community-dwelling older women with knee osteoarthritis.

DESIGN

Randomized controlled trial.

SETTING AND PARTICIPANTS

Women aged ≥60 years with knee osteoarthritis and Kellgren-Lawrence grade 1 or 2 on anteroposterior/lateral radiographs of both knee joints.

METHODS

Patients (n = 36) were randomly divided into experimental (EG) and control (CG) groups. The EG performed home-based remote rehabilitation lower-extremity strengthening exercises for 8 weeks, whereas the CG received no intervention. Assessment was performed at baseline and week 8. The primary outcome was the five-times sit-to-stand test (FTSST) result. Secondary outcomes included timed up-and-go (TUG) test results, knee extensor and flexor strength, quadriceps (rectus femoris) muscle activity, skeletal muscle index, blood pressure (BP), visual analog scale (VAS) scores, C-reactive protein level, and erythrocyte sedimentation rate.

RESULTS

A statistically significant difference in the FTSST times was observed between the groups after 8 weeks of intervention (EG: 7.95 ± 1.08 seconds, CG: 10.01 ± 2.03 seconds, P < .001). In the EG, the TUG test score decreased by 0.75 ± 0.80 seconds (P = .002), right and left knee flexor strength increased by 4.69 ± 6.05 kg (P = .007) and 3.98 ± 6.98 kg (P = .038), respectively, and the right knee extensor root mean square (RMS) ratio increased by 1.24 ± 0.39 (P = .027). Additionally, systolic and diastolic BP decreased by 9.50 ± 10.75 mm Hg (P = .005) and 4.25 ± 4.91 mm Hg (P = .003), respectively. In the CG, the VAS scores decreased by 9.10 ± 13.68 mm (P = .022).

CONCLUSIONS AND IMPLICATIONS

The home-based exercise program using a remote rehabilitation medical device was effective in improving lower extremity strength and function in community-dwelling older women with knee osteoarthritis. This finding suggests that the remote rehabilitation medical device may be used as an alternative to exercise interventions for patients with knee osteoarthritis.

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.

Perioperative baseline -blockers: An independent protective factor for post-carotid endarterectomy hypertension

OBJECTIVE

Post-carotid endarterectomy hypertension is a well-recognized phenomenon closely related to surgical complications. This study aimed to determine whether different kinds of perioperative antihypertensive drugs had a protective effect on post-carotid endarterectomy hypertension and influence on intraoperative hemodynamics.

METHOD

We retrospectively investigated 102 carotid stenosis patients who underwent conventional endarterectomy with a perioperative baseline antihypertensive regimen. Post-carotid endarterectomy hypertension was defined as a postoperative peak systolic blood pressure ≥160 mmHg and/or a requirement for any additional antihypertensive therapies. We compared the clinical characteristics and types of baseline perioperative antihypertensive drugs between patients with and without post-carotid endarterectomy hypertension and then determined the significant independent effect of antihypertensive drugs on post-carotid endarterectomy hypertension through multivariate regression and detected their influence on intraoperative hypertension (induction-related systolic blood pressure and vasodilators consumption) and hemodynamic depression (intra-arterial systolic blood pressure ≤100 mmHg and/or heart rate ≤50 beats/min). We also investigated adverse events such as stroke, death, myocardial infarction, and cerebral hyperperfusion syndrome during the postoperative hospitalization.

RESULTS

A total of 52/102 (51.0%) patients were defined as having post-carotid endarterectomy hypertension during the first three days postoperative, including eight patients with a postoperative systolic blood pressure that exceeded 160 mmHg at least once, 31 patients requiring postoperative antihypertensive treatment in addition to their baseline regimen, and 13 patients with both. The incidence of stroke/death/myocardial infarction and cerebral hyperperfusion syndrome after conventional endarterectomy during hospitalization were both 1.9%. A significantly increased risk of composite postoperative complications (including cerebral hyperperfusion syndrome, hyperperfusion-related symptoms, transient ischemic attacks, stroke, death, and cardiac complications) was observed in patients with post-carotid endarterectomy hypertension than without (15.4% versus 2.0%, p = 0.032). Patients free of post-carotid endarterectomy hypertension had a higher incidence of perioperative baseline β-blocker use than patients who suffered from post-carotid endarterectomy hypertension (46.0% versus 21%, p = 0.008). In multivariate analysis, β-blocker use was a significant independent protective factor for post-carotid endarterectomy hypertension (OR = 0.356, 95% CI: 0.146-0.886, p = 0.028). Patients taking β-blockers had a lower postoperative peak systolic blood pressure than the β-blocker-naïve population (137.1 ± 12.1 mmHg versus 145.0 ± 11.2 mmHg, p = 0.008), but the postoperative mean systolic blood pressure showed no intergroup difference. However, the incidence of hemodynamic depression during conventional endarterectomy was higher in patients with perioperative β-blocker use than in those without (44.1% versus 25.0%, p = 0.050). The difference in intraoperative hemodynamic depression became more prominent between the β-blocker and non-β-blocker groups (81.8% versus 33.3%, p = 0.014) for whose preoperative baseline heart rate was equal to or lower than 70 beats/min.

CONCLUSION

The perioperative use of β-blockers is a protective factor for post-carotid endarterectomy hypertension and contributes to stabilizing the postoperative peak systolic blood pressure three days after conventional endarterectomy. However, β-blockers might also lead to intraoperative hemodynamic depression, especially for patients with a low baseline heart rate.

Renal denervation: Alternative treatment options for hypertension?

Hypertension affects millions of Americans and has adverse long-term consequences increasing morbidity and mortality. Resistant hypertension (RH) continues to be difficult to treat with medications alone which may be associated with significant side effects. Alternate therapies have been evaluated for treating RH and renal denervation has been investigated extensively. We review the data from renal denervation trials and other novel technologies which are not FDA approved to date.

Sustained Reduction of Blood Pressure With Baroreceptor Activation Therapy: Results of the 6-Year Open Follow-Up

Baroreflex activation therapy is a novel technique for treating patients with resistant hypertension. Although short-term studies have demonstrated that it lowers blood pressure, long-term results have not yet been reported. The aim of the present study is to assess the long-term efficacy and safety of baroreflex activation therapy. Long-term follow-up data were analyzed from all patients who had been included in 1 of the 3 trials that focused on treatment-resistant hypertensive patients. Altogether, 383 patients were available for analysis: 143 of these had completed 5 years of follow-up and 48 patients had completed 6 years of follow-up. In the entire cohort, office systolic blood pressure fell from 179±24 mm Hg to 144±28 mm Hg (P<0.0001), whereas office diastolic pressure dropped from 103±16 mm Hg to 85±18 mm Hg (P<0.0001). Heart rate fell from 74±15 beats per minute to 71±13 beats per minute (P<0.02). The effect of baroreflex activation therapy is greater than average in patients with signs of heart failure and less than average in patients with isolated systolic hypertension. In ≈25% of patients, it was possible to reduce the number of medications from a median of 6 to a median of 3. Temporary side effects, related to either the surgical procedure or the cardiovascular instability, do occur, but they do not require specific measures and resolve over time.After a follow-up of 6 years, baroreflex activation therapy maintains its efficacy for persistent reduction of office blood pressure in patients with resistant hypertension without major safety issues.

Carotid baroreceptor stimulation blood pressure response mapped in patients undergoing carotid endarterectomy (C-Map study)

OBJECTIVE

Continuous stimulation of the carotid baroreceptors has been shown to evoke a sustained systolic blood pressure (SBP) reduction in hypertensive subjects. This study conducted a detailed mapping of the SBP and heart rate response to electrical stimulus at different locations in the carotid sinus region in patients undergoing a carotid endarterectomy (CEA).

METHODS

The Carotid Sinus Autonomic Response Mapping (C-Map) Study is a multicenter, prospective, non-randomized, acute feasibility study conducted in 10 hypertensive subjects undergoing CEA. Electrode pairs were placed in multiple locations in the region of the carotid sinus for acute stimulation, and the tests were repeated after plaque removal and vessel repair.

RESULTS

The configuration that elicited the largest pressure reduction in 8 of 10 patients was with the electrodes arranged longitudinally along the medial (in relation to the bifurcation) wall of the internal carotid artery (ICA) near the bifurcation (11.2±8.1mmHg, p<0.05). There was no difference in average maximum response pre vs. post plaque removal. Spontaneous baroreflex sensitivity increased from 6.0±3.2ms/mmHg pre-CEA to 8.2±5.4ms/mmHg post-CEA (p=0.040).

CONCLUSIONS

Endarterectomy surgery did not affect maximal acute stimulation response but improved baroreflex sensitivity acutely. Acute extravascular baroreceptor stimulation (BRS) mapping demonstrated that blood pressure reductions are dependent on electrode location and orientation. In most subjects, the largest SBP reductions were elicited in the region of the medial wall of the ICA. This area can be targeted for future BRS lead design and implant.

Vagal modulation of hypertension

Resistant hypertension despite compliance with pharmacologic therapies continues to hamper optimal blood pressure control. Vagal modulation via direct stimulation of the body's parasympathetic nervous system is proving a promising therapeutic modality to help patients achieve their blood pressure goals. In this article, we review some of the key concepts of different vagal modulations for resistant hypertension including baroreflex activation therapy, renal sympathetic denervation, and direct vagal nerve stimulation.

Carotid Baroreceptor Stimulation in Resistant Hypertension and Heart Failure

A significant number of hypertensive subjects fail to achieve adequate blood pressure control despite adherence to maximal doses of several antihypertensive drugs. In the same way although medical and device therapies continue to improve the clinical course of heart failure patients, morbidity, mortality and healthcare costs remain high. Electrical stimulation of the carotid sinus is a new interesting approach for the treatment of resistant hypertension and heart failure. The purpose of this paper is to overview the argument starting from physiological background and evaluating the clinical results obtained with this approach in these pathophysiological conditions.

Drug therapy for the patient with resistant hypertension

ABSTRACT 

Resistant hypertension is associated with high morbidity and mortality. Resistant hypertension is defined as blood pressure above targets despite treatment with at least three antihypertensive drugs in adequate dose and combination. Nonadherence is a frequent cause of uncontrolled hypertension and can be improved by providing fixed dose (of two or three agents) single pill combination. Triple combination of the most widely used antihypertensive agents (renin–angiotensin–aldosterone system antagonists, calcium channel blockers and diuretics) is a safe and effective therapy. Fourth line therapy is the use of an aldosterone antagonist. Renal denervation and baroreceptor stimulation can be considered in patients who remained uncontrolled despite optimal medical therapy.

The sympathetic nervous system as a target for the treatment of hypertension and cardiometabolic diseases

The regulation of blood pressure by the sympathetic nervous system is reviewed with an emphasis on the role of the sympathetic nervous system in the development and maintenance of hypertension. Evidence from patients and animal models is summarized. Because it is clear that there is a neural contribution to many types of human hypertension and other cardiometabolic diseases, the case is presented for a renewed emphasis on the development of sympatholytic approaches for the treatment of hypertension and other conditions associated with hyperactivity of the sympathetic nervous system.

Novel and nonpharmacologic approaches to cardio-protection in hypertension

Hypertension has wide (30-45 %) prevalence in the general population and is related to important increases in overall cardiovascular morbidity and mortality. Despite lifestyle modifications and optimal medical therapy (three drugs, one being diuretic), about 5-20 % of hypertensives are affected by resistant hypertension. Chronic high blood pressure has adverse effects on the heart and other organs such as the kidneys and vasculature. Renal sympathetic denervation and baroreceptor stimulation are invasive approaches initially investigated to treat resistant hypertension. Their pleiotropic effects appear promising in cardiovascular remodeling, heart failure and arrhythmias and could potentially affect cardiovascular morbidity and mortality.

Endothelial and neuronal nitric oxide synthases variably modulate the oestrogen-mediated control of blood pressure and cardiovascular autonomic control

1. We have shown previously that long-term oestrogen (E2) replacement lowers blood pressure (BP) and improves cardiovascular autonomic control in ovariectomized (OVX) rats. In the present study, we investigated whether constitutive and/or inducible (i) nitric oxide synthase (NOS) modulate these E2 effects. 2. We evaluated changes in BP, myocardial contractility index (dP/dtmax ) and power spectral indices of haemodynamic variability following selective inhibition of endothelial (e) NOS with N(5)-(1-iminoethyl)-L-ornithine (L-NIO), neuronal (n) NOS with N(ω)-propyl-L-arginine (NPLA) or iNOS with 1400W in telemetered OVX rats treated for 16 weeks with (OVXE2) or without (control; OVXC) E2. 3. The OVXE2 rats exhibited: (i) reduced BP and increased dP/dtmax ; (ii) cardiac parasympathetic dominance, as reflected by the reduced low-frequency (LF; 0.25-0.75 Hz)/high-frequency (HF; 0.75-3 Hz) ratio of interbeat intervals (IBI(LF/HF)); and (iii) reduced LF oscillations of systolic BP, suggesting a reduced vasomotor sympathetic tone. Inhibition of eNOS (L-NIO; 20 mg/kg, i.p.) elicited a shorter-lived pressor response in OVXE2 than OVXC, rats along with reductions in dP/dtmax and increases in the spectral index of spontaneous baroreflex sensitivity (index α). Treatment with 1 mg/kg, i.p., NPLA reduced BP and increased the IBI(LF/HF) ratio in OVXE2 but not OVXC rats. The iNOS inhibitor 1400W (5 mg/kg, i.p.) caused no haemodynamic changes in OVXC or OVXE2 rats. 4. Overall, constitutive NOS isoforms exert restraining tonic modulatory BP effects that encompass eNOS-mediated reductions and nNOS-mediated elevations in BP in OVXE2 rats. Baroreflex facilitation and dP/dtmax reductions may account for the shorter pressor action of L-NIO in E2-treated, compared with untreated, OVX rats.

Baroreflex activation: from mechanisms to therapy for cardiovascular disease

Recent technical advances have led to the development of a medical device that can reliably activate the carotid baroreflex with an acceptable degree of safety. Because activation of the sympathetic nervous system plays an important role in the pathogenesis of hypertension and heart failure, the unique ability of this device to chronically suppress central sympathetic outflow in a controlled manner suggests potential value in the treatment of these conditions. This notion is supported by both clinical and experimental animal studies, and the major aim of this article is to elucidate the physiological mechanisms that account for the favorable effects of baroreflex activation therapy in patients with resistant hypertension and heart failure. Illumination of the neurohormonal, renal, and cardiac actions of baroreflex activation is likely to provide the means for better identification of those patients that are most likely to respond favorably to this device-based therapy.

Baroreflex activation therapy for patients with drug-resistant hypertension

Uncontrolled or resistant hypertension is still a major problem facing many physicians daily in the clinic. Several new therapies are being developed to help those patients whose blood pressure does not respond sufficiently to regular antihypertensive medication. One of these promising therapies is electrical activation of the carotid sinus baroreflex. In this overview, the authors predominantly summarize the background, efficacy and safety of this promising treatment with its latest achievements in patients with resistant hypertension. The authors also discuss certain issues that need further clarification before this therapy can be added to the common treatment guidelines of hypertension.

The baroreceptor as a therapeutic target for heart failure

Sympathoactivation is a prominent feature of heart failure (HF). Its role in cardiac remodeling and arrhythmogenesis is well-recognized today, although incomplete understanding of autonomic mechanisms was a barrier to development of contemporary medical therapies. Despite widespread availability of drugs and devices, mortality and morbidity in HF remain unacceptably high. Recognition of an additional phenotype, HF with preserved ejection fraction (EF), poses additional challenges. New treatment options are required. Electrical modulation of the central nervous system with baroreflex activation therapy offers a new approach. Activation of this afferent pathway induces the central nervous system to rebalance autonomic modulation of the cardiovascular system. Results in animal models of HF demonstrating increased survival and beneficial cardiac remodeling recently led to a clinical feasibility study in HF with reduced EF wherein the clinical course of patients dramatically improved. Results in resistant hypertension patients further suggest potential for benefit in HF with preserved EF.

Clinical end points in baroreflex activation therapy: what do we need to know?

Many studies have shown that the sympathetic nervous system plays an important part in blood pressure regulation. One of its components is the baroreceptor reflex, which buffers sudden and also potentially chronic changes in blood pressure. The carotid baroreceptors have become a new target in the treatment of hypertensive patients in whom optimal antihypertensive medication fails to normalize the pressure. By electrically stimulating the baroreceptor area, it is now possible to substantially reduce blood pressure in such patients and the effect is well maintained over a prolonged period of time. The hypotensive response is associated with a fall in muscle sympathetic nerve activity, which lends support to the view that baropacing suppresses overall sympathetic outflow from the brain. The procedure appears to be safe and well tolerated. Nevertheless, the authors still need definite proof from prognostic trials that baropacing is superior to intensified medical treatment.

Device therapy of resistant hypertension

It is well known that hypertension is an independent cardiovascular risk factor. Treatment of hypertension frequently includes administration of three or more drugs. Resistant hypertension is defined when blood pressure remains above target value despite full doses (the patient’s maximum tolerated dose) of antihypertensive medication consisting of at least three different classes of drugs including a diuretic. Pharmacological treatment of hypertension is often unsuccessful despite the increasing number of drug combinations. Uncontrolled hypertension, however, increases the cardiovascular risk. Device treatment of resistant hypertension is currently testing two major fields. One of them the stimulation of baroreceptors in the carotid sinus and the other is radiofrequency ablation of sympathetic nerve fibers around renal arteries to reduce blood pressure in drug resistant hypertension. Orv. Hetil., 2013, 154, 203–208.

Electrical carotid sinus stimulation in treatment resistant arterial hypertension

Treatment resistant arterial hypertension is commonly defined as blood pressure that remains above goal in spite of the concurrent use of three antihypertensive agents of different classes. The sympathetic nervous system promotes arterial hypertension and cardiovascular as well as renal damage, thus, providing a logical treatment target in these patients. Recent physiological studies suggest that baroreflex mechanisms contribute to long-term control of sympathetic activity and blood pressure providing an impetus for the development of electrical carotid sinus stimulators. The concept behind electrical stimulation of baroreceptors or baroreflex afferent nerves is that the stimulus is sensed by the brain as blood pressure increase. Then, baroreflex efferent structures are adjusted to counteract the perceived blood pressure increase. Electrical stimulators directly activating afferent baroreflex nerves were developed years earlier but failed for technical reasons. Recently, a novel implantable device was developed that produces an electrical field stimulation of the carotid sinus wall. Carefully conducted experiments in dogs provided important insight in mechanisms mediating the depressor response to electrical carotid sinus stimulation. Moreover, these studies showed that the treatment success may depend on the underlying pathophysiology of the hypertension. Clinical studies suggest that electrical carotid sinus stimulation attenuates sympathetic activation of vasculature, heart, and kidney while augmenting cardiac vagal regulation, thus lowering blood pressure. Yet, not all patients respond to treatment. Additional clinical trials are required. Patients equipped with an electrical carotid sinus stimulator provide a unique opportunity gaining insight in human baroreflex physiology.

Baroreflex activation therapy for the treatment of drug-resistant hypertension: new developments

In the past few years, novel accomplishments have been obtained in carotid baroreflex activation therapy (BAT) for the treatment of resistant hypertension. In addition, this field is still evolving with promising results in the reduction of blood pressure and heart rate. This overview addresses the latest developments in BAT for the treatment of drug-resistant hypertension. Although not totally understood considering the working mechanisms of BAT, it appeared to be possible to achieve at least as much efficacy of single-sided as bilateral stimulation. Therefore unlike the first-generation Rheos system, the second-generation Barostim neo operates by unilateral baroreflex activation, using a completely different carotid electrode. Also significant improvements in several cardiac parameters have been shown by BAT in hypertensive patients, which set the basis for further research to evaluate BAT as a therapy for systolic heart failure. Yet important uncertainties need to be clarified to guarantee beneficial effects; hence not all participants seem to respond to BAT.

Fluid Structure Interaction With Contact Surface Methodology for Evaluation of Endovascular Carotid Implants for Drug-Resistant Hypertension Treatment

Drug-resistant hypertensive patients may be treated by mechanical stimulation of stretch-sensitive baroreceptors located in the sinus of carotid arteries. To evaluate the efficacy of endovascular devices to stretch the carotid sinus such that the induced strain might trigger baroreceptors to increase action potential firing rate and thereby reduce systemic blood pressure, numerical simulations were conducted of devices deployed in subject-specific carotid models. Two models were chosen—a typical physiologic carotid and a diminutive atypical physiologic model representing a clinically worst case scenario—to evaluate the effects of device deployment in normal and extreme cases, respectively. Based on the anatomical dimensions of the carotids, two different device sizes were chosen out of five total device sizes available. A fluid structure interaction (FSI) simulation methodology with contact surface between the device and the arterial wall was implemented for resolving the stresses and strains induced by device deployment. Results indicate that device deployment in the carotid sinus of the physiologic model induces an increase of 2.5% and 7.5% in circumferential and longitudinal wall stretch, respectively, and a maximum of 54% increase in von Mises arterial stress at the sinus wall baroreceptor region. The second device, deployed in the diminutive carotid model, induces an increase of 6% in both circumferential and longitudinal stretch and a 50% maximum increase in von Mises stress at the sinus wall baroreceptor region. Device deployment has a minimal effect on blood-flow patterns, indicating that it does not adversely affect carotid bifurcation hemodynamics in the physiologic model. In the smaller carotid model, deployment of the device lowers wall shear stress at sinus by 16% while accelerating flow entering the external carotid artery branch. Our FSI simulations of carotid arteries with deployed device show that the device induces localized increase in wall stretch at the sinus, suggesting that this will activate baroreceptors and subsequently may control hypertension in drug-resistant hypertensive patients, with no consequential deleterious effects on the carotid sinus hemodynamics.

Carotid baroreflex activation: past, present, and future

Electrical activation of the carotid baroreceptor system is an attractive therapy for the treatment of resistant hypertension. In the past, several attempts were made to directly activate the baroreceptor system in humans, but the method had to be restricted to a few selected patients. Adverse effects, the need for better electrical devices and better surgical techniques, and the lack of knowledge about long-term effects has greatly hampered developments in this area for many years. Recently, a new and promising device was evaluated in a multicenter feasibility trial, which showed a clinically and statistically significant reduction in office systolic blood pressure (>20 mm Hg). This reduction could be sustained for at least 2 years with an acceptable safety profile. In the future, this new device may stimulate further application of electrical activation of the carotid baroreflex in treatment-resistant hypertension.

Carotid baroreceptor stimulation for the treatment of resistant hypertension

Interventional activation of the carotid baroreflex has been an appealing idea for the management of resistant hypertension for several decades, yet its clinical application remained elusive and a goal for the future. It is only recently that the profound understanding of the complex anatomy and pathophysiology of the circuit, combined with the accumulation of relevant experimental and clinical data both in animals and in humans, has allowed the development of a more effective and well-promising approach. Indeed, current data support a sustained over a transient reduction of blood pressure through the resetting of baroreceptors, and technical deficits have been minimized with a subsequent recession of adverse events. In addition, clinical outcomes from the application of a new implantable device (Rheos) that induces carotid baroreceptor stimulation point towards a safe and effective blood pressure reduction, but longer experience is needed before its integration in the everyday clinical practice. While accumulating evidence indicates that carotid baroreceptor stimulation exerts its benefits beyond blood pressure reduction, further research is necessary to assess the spectrum of beneficial effects and evaluate potential hazards, before the extraction of secure conclusions.

Novel procedure- and device-based strategies in the management of systemic hypertension

Despite the considerable advances in the treatment of hypertension that have been made over the past few decades, adequate management and control of this condition remains poor, and efforts are ongoing to develop new strategies to improve related outcomes. Novel therapeutic approaches to the management of systemic hypertension fall into two major categories: (i) those that seek to improve blood pressure-lowering efficacy using new therapeutic strategies in addition to standard non-pharmacological and pharmacological approaches and (ii) novel ways to optimize and improve the efficacy and utility of existing therapies. Novel procedure- and device-based strategies to control hypertension include renal sympathetic denervation and baroreflex sensitization. These two techniques will be the focus of the present review.

Novel baroreflex activation therapy in resistant hypertension: results of a European multi-center feasibility study

OBJECTIVES

This study assessed the safety and efficacy of a novel implantable device therapy in resistant hypertension patients.

BACKGROUND

Despite the availability of potent antihypertensive drugs, a substantial proportion of patients remain hypertensive. A new implantable device (Rheos system, CVRx, Inc., Minneapolis, Minnesota) that activates the carotid baroreflex may help these patients.

METHODS

Forty-five subjects with systolic blood pressure ≥160 mm Hg or diastolic ≥90 mm Hg despite at least 3 antihypertensive drugs were enrolled in a prospective, nonrandomized feasibility study to assess whether Rheos therapy could safely lower blood pressure. Subjects were followed up for as long as 2 years. An external programmer was used to optimize and individualize efficacy.

RESULTS

Baseline mean blood pressure was 179/105 mm Hg and heart rate was 80 beats/min, with a median of 5 antihypertensive drugs. After 3 months of device therapy, mean blood pressure was reduced by 21/12 mm Hg. This result was sustained in 17 subjects who completed 2 years of follow-up, with a mean reduction of 33/22 mm Hg. The device exhibited a favorable safety profile.

CONCLUSIONS

The Rheos device sustainably reduces blood pressure in resistant hypertensive subjects with multiple comorbidities receiving numerous medications. This unique therapy offers a safe individualized treatment option for these high-risk subjects. This novel approach holds promise for patients with resistant hypertension and is currently under evaluation in a prospective, placebo-controlled clinical trial.

Carotid baroreceptor stimulation, sympathetic activity, baroreflex function, and blood pressure in hypertensive patients

In animals, electric field stimulation of carotid baroreceptors elicits a depressor response through sympathetic inhibition. We tested the hypothesis that the stimulation acutely reduces sympathetic vasomotor tone and blood pressure in patients with drug treatment-resistant arterial hypertension. Furthermore, we tested whether the stimulation impairs the physiological baroreflex regulation. We studied 7 men and 5 women (ages 43 to 69 years) with treatment-resistant arterial hypertension. A bilateral electric baroreflex stimulator at the level of the carotid sinus (Rheos) was implanted > or =1 month before the study. We measured intra-arterial blood pressure, heart rate, muscle sympathetic nerve activity (microneurography), cardiac baroreflex sensitivity (cross-spectral analysis and sequence method), sympathetic baroreflex sensitivity (threshold technique), plasma renin, and norepinephrine concentrations. Measurements were performed under resting conditions, with and without electric baroreflex stimulation, for > or =6 minutes during the same experiment. Intra-arterial blood pressure was 193+/-9/94+/-5 mm Hg on medications. Acute electric baroreflex stimulation decreased systolic blood pressure by 32+/-10 mm Hg (range: +7 to -108 mm Hg; P=0.01). The depressor response was correlated with a muscle sympathetic nerve activity reduction (r(2)=0.42; P<0.05). In responders, muscle sympathetic nerve activity decreased sharply when electric stimulation started. Then, muscle sympathetic nerve activity increased but remained below the baseline level throughout the stimulation period. Heart rate decreased 4.5+/-1.5 bpm with stimulation (P<0.05). Plasma renin concentration decreased 20+/-8% (P<0.05). Electric field stimulation of carotid sinus baroreflex afferents acutely decreased arterial blood pressure in hypertensive patients, without negative effects on physiological baroreflex regulation. The depressor response was mediated through sympathetic inhibition.

Acute and chronic electrical activation of baroreceptor afferents in awake and anesthetized subjects

Electrical stimulation of baroreceptor afferents was used in the 1960's in several species, including human beings, for the treatment of refractory hypertension. This approach bypasses the site of baroreceptor mechanosensory transduction. Chronic electrical stimulation of arterial baroreceptors, particularly of the carotid sinus nerve (Hering's nerve), was proposed as an ultimate effort to treat refractory hypertension and angina pectoris due to the limited nature of pharmacological therapy available at that time. Nevertheless, this approach was abandoned in the early 1970's due to technical limitations of implantable devices and to the development of better-tolerated antihypertensive medications. More recently, our laboratory developed the technique of electrical stimulation of the aortic depressor nerve in conscious rats, enabling access to hemodynamic responses without the undesirable effect of anesthesia. In addition, electrical stimulation of the aortic depressor nerve allows assessment of the hemodynamic responses and the sympathovagal balance of the heart in hypertensive rats, which exhibit a well-known decrease in baroreflex sensitivity, usually attributed to baroreceptor ending dysfunction. Recently, there has been renewed interest in using electrical stimulation of the carotid sinus, but not the carotid sinus nerve, to lower blood pressure in conscious hypertensive dogs as well as in hypertensive patients. Notably, previous undesirable technical outcomes associated with electrical stimulation of the carotid sinus nerve observed in the 1960's and 1970's have been overcome. Furthermore, promising data have been recently reported from clinical trials that evaluated the efficacy of carotid sinus stimulation in hypertensive patients with drug resistant hypertension.

Effects of chronic baroreceptor stimulation on the autonomic cardiovascular regulation in patients with drug-resistant arterial hypertension

In patients with drug-resistant hypertension, chronic electric stimulation of the carotid baroreflex is an investigational therapy for blood pressure reduction. We hypothesized that changes in cardiac autonomic regulation can be demonstrated in response to chronic baroreceptor stimulation, and we analyzed the correlation with blood pressure changes. Twenty-one patients with drug-resistant hypertension were prospectively included in a substudy of the Device Based Therapy in Hypertension Trial. Heart rate variability and heart rate turbulence were analyzed using 24-hour ECG. Recordings were obtained 1 month after device implantation with the stimulator off and after 3 months of chronic electric stimulation (stimulator on). Chronic baroreceptor stimulation decreased office blood pressure from 185+/-31/109+/-24 mm Hg to 154+/-23/95+/-16 mm Hg (P<0.0001/P=0.002). Mean heart rate decreased from 81+/-11 to 76+/-10 beats per minute(-1) (P=0.001). Heart rate variability frequency-domain parameters assessed using fast Fourier transformation (FFT; ratio of low frequency:high frequency: 2.78 versus 2.24 for off versus on; P<0.001) were significantly changed during stimulation of the carotid baroreceptor, and heart rate turbulence onset was significantly decreased (turbulence onset: -0.002 versus -0.015 for off versus on; P=0.004). In conclusion, chronic baroreceptor stimulation causes sustained changes in heart rate variability and heart rate turbulence that are consistent with inhibition of sympathetic activity and increase of parasympathetic activity in patients with drug-resistant systemic hypertension; these changes correlate with blood pressure reduction. Whether the autonomic modulation has favorable cardiovascular effects beyond blood pressure control should be investigated in further studies.

Carotid baroreceptor stimulation as a therapeutic target in hypertension and other cardiovascular conditions

BACKGROUND

The role of the carotid baroreflex in blood pressure regulation has been known for a long time but its effects were thought to be short lived. Recent data indicate that stimulation of carotid baroreceptors may lower blood pressure not only for short periods of time, but also in the long run.

OBJECTIVE/METHODS

Recent advances in technology permitted the development of a new device (Rheos) that addresses problems with older devices. Several questions remain to be addressed before Rheos can be used widely, and several potential clinical applications remain to be clarified. This review examines these issues and comprehensively describes this therapeutic approach.

RESULTS/CONCLUSIONS

The carotid baroreceptor reflex is probably not completely in control of blood pressure. Baroreflexes are one of many control systems acting in concert.