Anatomic assessment of sympathetic peri-arterial renal nerves in man

BACKGROUND

Although renal sympathetic denervation therapy has shown promising results in patients with resistant hypertension, the human anatomy of peri-arterial renal nerves is poorly understood.

OBJECTIVES

The aim of our study was to investigate the anatomic distribution of peri-arterial sympathetic nerves around human renal arteries.

METHODS

Bilateral renal arteries were collected from human autopsy subjects, and peri-arterial renal nerve anatomy was examined by using morphometric software. The ratio of afferent to efferent nerve fibers was investigated by dual immunofluorescence staining using antibodies targeted for anti-tyrosine hydroxylase and anti-calcitonin gene-related peptide.

RESULTS

A total of 10,329 nerves were identified from 20 (12 hypertensive and 8 nonhypertensive) patients. The mean individual number of nerves in the proximal and middle segments was similar (39.6 ± 16.7 per section and 39.9 ± 1 3.9 per section), whereas the distal segment showed fewer nerves (33.6 ± 13.1 per section) (p = 0.01). Mean subject-specific nerve distance to arterial lumen was greatest in proximal segments (3.40 ± 0.78 mm), followed by middle segments (3.10 ± 0.69 mm), and least in distal segments (2.60 ± 0.77 mm) (p < 0.001). The mean number of nerves in the ventral region (11.0 ± 3.5 per section) was greater compared with the dorsal region (6.2 ± 3.0 per section) (p < 0.001). Efferent nerve fibers were predominant (tyrosine hydroxylase/calcitonin gene-related peptide ratio 25.1 ± 33.4; p < 0.0001). Nerve anatomy in hypertensive patients was not considerably different compared with nonhypertensive patients.

CONCLUSIONS

The density of peri-arterial renal sympathetic nerve fibers is lower in distal segments and dorsal locations. There is a clear predominance of efferent nerve fibers, with decreasing prevalence of afferent nerves from proximal to distal peri-arterial and renal parenchyma. Understanding these anatomic patterns is important for refinement of renal denervation procedures.

Treating resistant hypertension with new devices

Arterial hypertension is a frequent, chronic disease, which is one of the main risk factor for cardiovascular and renal diseases such as heart failure, chronic kidney disease, hypertensive heart disease, stroke as well as cardiac arrhythmias. In the clinical setting it remains challenging to accomplish the thresholds of guideline blood pressure (BP) levels now defined as office based BP to be below <140 mmHg. Patients on three or more antihypertensive drugs, with systolic BP values above ≥160 mmHg (≥150 mmHg for patients with type 2 diabetes) are classified as having resistant hypertension. In the past six years the development of interventional sympathetic renal artery denervation (RDN) opened a new treatment option targeting the afferent and efferent sympathetic nerves of the kidney to reduce BP. A large variety of devices are available on the market. Newly developed devices try to focus on new strategies such as ultrasound or irrigated catheters, which might reduce the post-procedural complications and increase the success rate. The first generation SymplicityTM device (Medtronic, Palo Alto, CA, USA) was shown to be safe, with side effects rarely occurring. Clinical trials demonstrate that this procedure is successful in about 70% of patients. However current data from Simplicity HTN-3 with 25% african-americans and a massive BP-lowering effect in the control "sham" group was not able to find a significant effect in the overall patient cohort. Possibly devices which allow to safely destroy sympathetic renal innervation more efficiently might allow for a higher responder rate. Irrigated RDN and ultrasound devices could deliver more energy to deeper tissue levels. This article provides an overview of currently available data on devices.

Renal denervation for resistant hypertension: acute results and long-term follow-up

INTRODUCTION

Renal sympathetic hyperactivity is vital for the maintenance and progression of essential hypertension. Catheter-based renal denervation is an evolving concept with favourable results regarding the control of hypertension; however, clinical experience is still limited.

METHODS

We enrolled 15 patients with resistant hypertension who underwent percutaneous, catheter-based radiofrequency treatment for renal artery denervation. Patients were followed up for 4 to 13 months.

RESULTS

Baseline mean blood pressure was 169/96 mmHg (SD 9/11), and patients were receiving a mean 3.9 ± 0.8 antihypertensive medications. Blood pressure values were reduced to 136/79 mmHg (SD 10/7), and antihypertensive medications to 2.9 ± 0.8 at 6.9 ± 3.4 months after the procedure. All procedures were uneventful and technically easy. The only drawbacks of the procedure are pain that the patient may feel during energy delivery, and the inability to obtain a sustained impedance reduction that allows completion of radiofrequency current delivery at some sites in the renal artery.

CONCLUSIONS

Renal denervation facilitates control of resistant hypertension with reduction of medication, and appears to be a safe and technically easy procedure to accomplish.

A controlled trial of renal denervation for resistant hypertension

BACKGROUND

Prior unblinded studies have suggested that catheter-based renal-artery denervation reduces blood pressure in patients with resistant hypertension.

METHODS

We designed a prospective, single-blind, randomized, sham-controlled trial. Patients with severe resistant hypertension were randomly assigned in a 2:1 ratio to undergo renal denervation or a sham procedure. Before randomization, patients were receiving a stable antihypertensive regimen involving maximally tolerated doses of at least three drugs, including a diuretic. The primary efficacy end point was the change in office systolic blood pressure at 6 months; a secondary efficacy end point was the change in mean 24-hour ambulatory systolic blood pressure. The primary safety end point was a composite of death, end-stage renal disease, embolic events resulting in end-organ damage, renovascular complications, or hypertensive crisis at 1 month or new renal-artery stenosis of more than 70% at 6 months.

RESULTS

A total of 535 patients underwent randomization. The mean (±SD) change in systolic blood pressure at 6 months was -14.13±23.93 mm Hg in the denervation group as compared with -11.74±25.94 mm Hg in the sham-procedure group (P<0.001 for both comparisons of the change from baseline), for a difference of -2.39 mm Hg (95% confidence interval [CI], -6.89 to 2.12; P=0.26 for superiority with a margin of 5 mm Hg). The change in 24-hour ambulatory systolic blood pressure was -6.75±15.11 mm Hg in the denervation group and -4.79±17.25 mm Hg in the sham-procedure group, for a difference of -1.96 mm Hg (95% CI, -4.97 to 1.06; P=0.98 for superiority with a margin of 2 mm Hg). There were no significant differences in safety between the two groups.

CONCLUSIONS

This blinded trial did not show a significant reduction of systolic blood pressure in patients with resistant hypertension 6 months after renal-artery denervation as compared with a sham control. (Funded by Medtronic; SYMPLICITY HTN-3 ClinicalTrials.gov number, NCT01418261.).

Renal denervation using an irrigated catheter in patients with resistant hypertension: a promising strategy?

Background

Systemic hypertension is an important public health problem and a significant cause of cardiovascular mortality. Its high prevalence and the low rates of blood pressure control have resulted in the search for alternative therapeutic strategies. Percutaneous renal sympathetic denervation emerged as a perspective in the treatment of patients with resistant hypertension.

Objective

To evaluate the feasibility and safety of renal denervation using an irrigated catheter.

Methods

Ten patients with resistant hypertension underwent the procedure. The primary endpoint was safety, as assessed by periprocedural adverse events, renal function and renal vascular abnormalities at 6 months. The secondary endpoints were changes in blood pressure levels (office and ambulatory monitoring) and in the number of antihypertensive drugs at 6 months.

Results

The mean age was 47.3 (± 12) years, and 90% of patients were women. In the first case, renal artery dissection occurred as a result of trauma due to the long sheath; no further cases were observed after technical adjustments, thus showing an effect of the learning curve. No cases of thrombosis/renal infarction or death were reported. Elevation of serum creatinine levels was not observed during follow-up. At 6 months, one case of significant renal artery stenosis with no clinical consequences was diagnosed. Renal denervation reduced office blood pressure levels by 14.6/6.6 mmHg, on average (p = 0.4 both for systolic and diastolic blood pressure). Blood pressure levels on ambulatory monitoring decreased by 28/17.6 mmHg (p = 0.02 and p = 0.07 for systolic and diastolic blood pressure, respectively). A mean reduction of 2.1 antihypertensive drugs was observed.

Conclusion

Renal denervation is feasible and safe in the treatment of resistant systemic arterial hypertension. Larger studies are required to confirm our findings.

Percutaneous renal denervation and the second generation EnligHTN System

Hypertension remains a major public health burden despite the plethora of therapeutic agents available for this disorder, compelling innovation of alternate therapies including interventional approaches where necessary. The kidney is a major player in the pathophysiology of this disease with increased sympathetic activity being the key factor in the initiation and maintenance of drug resistant hypertension in many patients. Thus renal denervation targeted at decreasing sympathetic drive is becoming the apparent choice in carefully selected patients with resistant hypertension who have exhausted all medical options. The Symplicity and EnligHTN trials using first and second generation catheters respectively have demonstrated that renal sympathetic denervation results in significant blood pressure reduction. The initial renal denervation catheter used in the Symplicity trial was a single electrode system. Refinement of this process has led to the EnligHTN catheter's design. This is a multielectrode self-expanding nitinol basket that allows the positioning of the thermal injury pattern to be pre-specified and in theory lead to better positioning of the lesions. We present a review of the premise behind renal artery denervation, discuss the data and early technologies focusing on the characteristics and utility of the first multielectrode renal denervation device, the EnligHTN renal denervation catheter.

[Renal sympathetic denervation in treatment-resistant hypertension]

BACKGROUND

Renal denervation (RDN) has been introduced as a potential new treatment for patients with treatment-resistant hypertension, defined as a blood pressure above 140/90 mm Hg despite treatment with at least three antihypertensive drugs. We present an overview of this type of treatment, describe the method and discuss its possible future uses.

METHOD

The review is based on a discretionary selection of relevant articles from our archive, our own experience and a literature search in PubMed.

RESULTS

The use of RDN for treatment-resistant hypertension is based on a single randomised study with a total of 104 patients, in which the intervention group experienced a fall in blood pressure of 32/12 mm Hg, while blood pressure in the control group remained unchanged. More than 16,000 patients, particularly in Germany, have been treated on this basis. In the USA, data from a larger randomised study (n = 530) that includes sham surgery are awaited before any decision is made on whether to approve the method for use.

INTERPRETATION

Before RDN can become recommended treatment in Norway, more evidence is required that the method lowers blood pressure, and that this reduces morbidity and mortality.

[The first experience with the use of catheter denervation of renal arteries in patients with refractory hypertension]

The prevalence of refractory arterial hypertension in Russia is estimated at 15%. We report the first experience with surgical treatment of this pathology. The method is based on the reduction of activity of the sympathetic nervous system by selective breaking of connections between of neurons with the help of interventional intravascular radiowave ablation. Renal endovascular sympathetic denervation allows to more effectively control AP and optimize antihypertensive therapy but does not ensure recovery from AH.

[Renal denervation a treatment for resistant hypertension: a French experience]

Arterial hypertension is the largest single contributor to global mortality, and is poorly controlled in approximately 50% of patients despite lifestyle and pharmacologic interventions. Randomized clinical trials have demonstrated that catheter-based renal sympathetic denervation reduces blood pressure (BP) in patients with resistant hypertension. We sought to evaluate the efficacy of this novel therapy in "Real World" clinical practice. Consecutive patients with treatment-resistant primary hypertension, as defined as home BP>160 mmHg despite treatment with ≥3 antihypertensive drugs, were selected for denervation following renal artery screening. Ambulatory and home BP monitoring was performed in all patients prior to and following percutaneous renal sympathetic denervation. In total, 35 patients were selected for catheter-based renal sympathetic denervation. The mean age was 63.6 ± 11.7 years, 37.1% were women, 37.1% were diabetic, and 11.4% had renal impairment (GFR<45 mL/min). The basal BP (home or ambulatory) was 179.1 ± 20.75/99.66 ± 19.76 mmHg, despite an average of 4.91 ± 0.98 medications per patient. Successful bilateral sympathetic denervation was performed in 33/35 patients (1 renal artery stenosis on angiography [not ablated], 1 patient with renal artery spasm [unilateral denervation]), with an average 5.9 ± 1.6 ablations per renal artery. No procedural complications occurred. At 6 months, blood pressure was 15.5 ± 22.37/87.76 ± 13.97 mmHg (P<0.01). At 2 years follow-up, systolic blood pressure (ABPM or Home BP) was 143.8 ± 15.30 mmHg (P<0.0001) and diastolic 83.42 ± 12.80 mmHg (P=0.0004). There were no adverse events during follow-up, and no deterioration in renal function was observed. Catheter-based renal denervation is safe and efficacious treatment, which results in significant reductions in blood pressure in patients with treatment-resistant hypertension, stable at 2 years follow-up. These results are applicable to real-world patient populations.

[Renal denervation 2013]

Arterial hypertension is a worldwide serious clinical problem. It affects 30- 40% of the adult population. Resistant hypertension is defined as systolic blood pressure that remains 140mmHg while in the doctors surgery and/ or as average systolic blood pressure during a 24- hour monitoring of an outpatient 130mmHg after a combination of three antihypertensive agents (including a diuretic) has been administered in the maximum tolerated dose amounts. Renal denervation is an invasive method of catheter radio frequency ablation of sympathetic nerves located in the walls of renal arteries. The results of the Symplicity HTN 1 and HTN 2 trials proved that renal denervation can safely decrease blood pressure in patients with resistant hypertension. Further research is necessary in order to verify these data, to clarify the questions which remained unanswered and to evaluate future applications of renal denervation. Current experience and recommendations are included, as well as an overview of existing denervation devices and devices which are in development.

Chemical denervation of the renal artery with vincristine for the treatment of resistant arterial hypertension: first-in-man application

Renal artery denervation has recently emerged as a novel therapy for patients with resistant hypertension. Clinical results from renal sympathetic denervation support the safety and efficacy of this method over a period of 18 months. However, several limitations have been reported. Previous studies have shown that chemical denervation by vincristine is safe and effective in an experimental model. We describe the first-in-man application of chemical denervation with vincristine in a 74-year-old male patient with resistant arterial hypertension.

Safety and efficacy of a multi-electrode renal sympathetic denervation system in resistant hypertension: the EnligHTN I trial

AIMS

Catheter-based renal artery sympathetic denervation has emerged as a novel therapy for treatment of patients with drug-resistant hypertension. Initial studies were performed using a single electrode radiofrequency catheter, but recent advances in catheter design have allowed the development of multi-electrode systems that can deliver lesions with a pre-determined pattern. This study was designed to evaluate the safety and efficacy of the EnligHTN(™) multi-electrode system.

METHODS AND RESULTS

We conducted the first-in-human, prospective, multi-centre, non-randomized study in 46 patients (67% male, mean age 60 years, and mean baseline office blood pressure 176/96 mmHg) with drug-resistant hypertension. The primary efficacy objective was change in office blood pressure from baseline to 6 months. Safety measures included all adverse events with a focus on the renal artery and other vascular complications and changes in renal function. Renal artery denervation, using the EnligHTN system significantly reduced the office blood pressure from baseline to 1, 3, and 6 months by -28/10, -27/10 and -26/10 mmHg, respectively (P < 0.0001). No acute renal artery injury or other serious vascular complications occurred. Small, non-clinically relevant, changes in average estimated glomerular filtration rate were reported from baseline (87 ± 19 mL/min/1.73 m2) to 6 months post-procedure (82 ± 20 mL/min/1.73 m2).

CONCLUSION

Renal sympathetic denervation, using the EnligHTN multi-electrode catheter results in a rapid and significant office blood pressure reduction that was sustained through 6 months. The EnligHTN system delivers a promising therapy for the treatment of drug-resistant hypertension.

[Comparison of efficacy between continuous positive airway pressure and renal artery sympathetic denervation by radiofrequency ablation in obstructive sleep apnea syndrome patients with hypertension]

OBJECTIVE

To compare the efficacy of renal arterial sympathetic denervation (RSD) and continuous positive airway pressure (CPAP) in patients with coexisting moderate-to-severe obstructive sleep apnea syndrome (OSAS) and hypertension.

METHODS

Retrospective analysis was conducted for patients with coexisting moderate to severe OSAS and hypertension for the efficacy of RSD (RSD group, n = 15) and CPAP (CPAP group, n = 16). Comparison was made for polysomnographic parameters and 24 hours ambulatory blood pressure (Bp) between two groups.

RESULTS

There was no significant difference in age, gender, body mass index, nocturnal apnea hypopnea index (AHI), mean and minimal pulse oxygen saturation (mean SpO2 and mini SpO2) between two groups. Compared with those at pre-treatment, the following changes were observed at Day 30 post-treatment: in RSD group, the nocturnal AHI and T90 statistically decreased (27 ± 14 vs 32 ± 12, 8.7% ± 7.8% vs 13.8% ± 13.1%, all P < 0.05) with a significant increase in mean SpO2 (94.3% ± 2.2% vs 93.9% ± 2.0%, P < 0.05) while mini SpO2 showed no significant difference (80.1% ± 6.2% vs 79.5% ± 4.7%, P > 0.05); in CPAP group during treatment, nocturnal AHI and the ratio of duration SpO2 < 90% to total sleep time (T90) were all significantly reduced (5 ± 3 vs 35 ± 12, 1.5% ± 1.2% vs 12.9% ± 6.3%, all P < 0.05) while mean SpO2 and mini SpO2 became significantly elevated (95.6% ± 1.4% vs 93.6% ± 1.7%, 89.2% ± 2.7% vs 79.1% ± 4.0%, all P < 0.05). Compared with RSD group, there was a significantly lower AHI (P = 0.000) but higher mean SpO2 and mini SpO2 (all P < 0.05) at Day 30 in CPAP group. At Day 30 in RSD and CPAP groups, the mean systolic blood pressure (MSBp) were (122 ± 9) and (130 ± 12) mm Hg (1 mm Hg = 0.133 kPa) respectively while the mean diastolic blood pressure (MDBp) (80 ± 8) and (83 ± 7) mm Hg respectively. All these were significantly lower than those at pre-treatment with MSBp (134 ± 20) mm Hg and MDBp (88 ± 14) mm Hg in RSD group and MSBp (136 ± 14) mm Hg and MDBp (87 ± 7) mm Hg in CPAP group. The extent of decrease in MSBp post-treatment was more remarkable in RSD group than that in CPAP group (P < 0.05).

CONCLUSIONS

In moderate-to-severe OSAS patients with hypertension, both RSD and CPAP may improve sleep respiratory parameters and blood pressure to varying degrees. There is a more significant improvement of nocturnal AHI and SpO2 in CPAP group and more lower MSBp in RSD group.

Irrigated radiofrequency ablation catheter and electro-anatomical mapping with computerized tomography integration for renal artery sympathetic denervation

Despite over 6 decades of progress in the development of pharmacological therapy for hypertension, severe drug-resistant hypertension remains a major problem. Endovascular radiofrequency ablation of the proximal renal arteries has been reported to decrease renal artery sympathetic activity and improve long-term hypertensive control. Existing "approved" catheters for this procedure are solid tip, non-irrigated, and often difficult to steer. The existing technique uses angiography and lends itself to increased risk of renal scarring and possible stenosis. We describe a patient with multi-drug resistant hypertension who underwent catheter ablation of the bilateral renal arteries, using for the first time, an open irrigated cardiac ablation catheter with both electro-anatomical guidance and computerized tomography anatomical integration. We used "off-label" irrigated catheters, which are less prone to overheating and char formation at the catheter-surface interface, thereby decreasing the possibility of distal embolization to the renal parenchyma. The integration of electro-anatomical mapping into this procedure allowed us to avoid inadvertent circumferential ablation of the artery using electro-anatomical mapping may lower the risk of subsequent renal artery stenosis.

Catheter-based renal denervation for treatment of resistant hypertension

INTRODUCTION

Activation of renal sympathetic nerves is associated with the development of hypertension. Catheter-based renal sympathetic denervation with radiofrequency energy ablation is a new promising treatment option for resistant hypertension. We here report the first Danish experiences and results with this technique.

MATERIAL AND METHODS

Nine patients with resistant hypertension and a day-time 24-hour ambulatory blood pressure (BP) of 152/89 mmHg ± 10/10 (standard deviation) mmHg despite treatment with 5.4 ± 1.4 anti-hypertensive drugs underwent catheter-based renal sympathetic denervation with the Symplicity catheter.

RESULTS

No periprocedural complications or adverse events during follow-up were observed. Seven patients received complete ablation and two patients only partial ablation. Five patients responded to the treatment with a reduction in day-time 24-hour ambulatory BP from 158/94 ± 13/9 mmHg to 139/82 ± 10/8 mmHg (p < 0.05) at the one month follow-up and a reduction in the number of anti-hypertensive drugs from 5.4 ± 1.6 to 3.4 ± 0.9 (p < 0.05). BP in the remaining four patients was not significantly changed and antihypertensive therapy was not changed.

CONCLUSION

Catheter-based renal sympathetic denervation is a feasible and in several cases also effective treatment option for patients with resistant hypertension. Adequately designed controlled trials are needed to assess the long-term safety and the full potential of this treatment.

[Frequency of hypertension resistant to treatment and indication for renal denervation]

OBJECTIVE

To evaluate in hypertensive patients followed in a specialized hypertension unit, the prevalence of subjects uncontrolled despite triple therapy including a diuretic. The aim is to estimate the percentage of hypertensive patients with an indication to renal denervation.

METHOD

From a database of computerized medical records of a unit specialized in hypertension, it was extracted 144 consecutive cases of subjects treated and followed for at least 1year and having had a home pressure monitoring (HPM) on treatment, and if necessary a work-up for a secondary hypertension. The blood pressure (BP) was evaluated in office by automated method (after 2 and 8minutes) and with HPM (average of three measurements in the morning and evening for three consecutive days).

RESULTS

The population has the following characteristics: age 62 with 26% over 70years, treated dyslipidemia (39%), treated diabetes (11%), adrenal hypertension treated medically (14%), severe renal failure (3%). The means of treatment are: a monotherapy (33%), bitherapy (35%), triple therapy (17%), quadritherapy (7%), pentatherapy or more (1%), spironolactone (45%), thiazide diuretics (49%). The uncontrolled hypertension was observed in 26% if the BP is evaluated with HPM, in 52% if the BP is evaluated at the office after 2minutes of rest and 7% if the BP is evaluated after 8minutes of rest (P<0.01). In patients treated with at least a tritherapy in association with a diuretic, an uncontrolled hypertension was observed in 5% if the BP is evaluated with HPM. Failure to control for the SBP is the cause of 80% of resistant hypertension.

CONCLUSION

The frequency of resistant hypertension is 5% of hypertensive patients followed in a specialized hypertension unit when guidelines are applied in the case of uncontrolled hypertension. These results indicate that the indication for renal denervation affects only a small percentage of patients treated for hypertension.

[Endovascular radiofrequency denervation of renal arteries as an innovation method of treatment of refractory arterial hypertension. First experience in Russia]

Excessive activation of the sympathetic nervous system forms the basis of pathogenesis of essential arterial hypertension (AH). The present work was aimed at evaluating efficacy and safety of endovascular radiofrequency denervation of renal arteries in patients with AH refractory AH based on the initial first experience in with using this methodology in the Russian Federation. The interventions were carried out on December 14-15th, 2011 in the first five patients presenting with AH refractory to antihypertensive therapy consisting of three and more drugs in therapeutic doses, one of which was a diuretic. The selection criteria were systolic arterial pressure (SAP) ≥160 mm Hg or ≥150 mm Hg in the presence of type 2 diabetes mellitus. The obligatory conditions for selection were the preserved renal function [glomerular filtration rate (GFR) ≥45 ml/min] and the absence of the secondary form of AH. The procedure of denervation was performed in the conditions of roentgen-operating room using special Medtronic Ardian Simplicity Catheter System™. In all cases we managed to perform bilateral denervation of renal arteries with the radiofrequency effect in not less than 4 zones of each of vessels. Efficacy of each of the effect was registered with due regard for reaching certain temperature and values of impedance. The interventions were not accompanied by the development of any complications either in the area of manipulations or the site of puncture. Neither were there any complications from the side of the cardiovascular or excretory systems of the body. Diurnal monitoring of AP (DMAP) registered a significant decrease in SAP averagely from 174±12 to 145±10 mm Hg three days after the intervention. A persistent antihypertensive effect was confirmed by the DMAP findings one month after denervation - the SAP level averagely amounted to 131±6 mm Hg. Endovascular radiofrequency denervation of renal arteries is a safe and efficient method of treatment of AH resistant to multicomponent antihypertensive therapy.

[Renal denervation a new treatment option in resistant arterial hypertension]

Resistant hypertension is defined as blood pressure that remains above therapeutic goal despite the use of 3 antihypertensive drugs including a diuretic. After exclusion of secondary causes and medical in compliance, the estimated prevalence of resistant arterial hypertension ranges from 4% to 19% in hypertensive patients. Treatment requires a multimodal therapeutic approach. Hyperactivation of the sympathetic nervous system plays a key role in the genesis of hypertension. Targeting renal sympathetic nerves, percutaneous catheter-based renal denervation is a new therapeutic option for the treatment of resistant arterial hypertension in selected drug resistant patients.

Renal nerves in the maintenance of hypertension: a potential therapeutic target

Renal sympathetic efferent and afferent nerves, which lie within and immediately adjacent to the wall of the renal arteries, contribute to the maintenance of hypertension. Because the causative factors of hypertension change over time, denervation of both efferent and afferent renal nerves should result in long-term attenuation of hypertension. The importance of the renal nerves in hypertensive patients can now be defined with the novel development of percutaneous, minimally invasive renal denervation from within the renal artery using radiofrequency energy as a therapeutic strategy. Studies thus far show that catheter-based renal denervation in patients with resistant essential hypertension lowers systolic blood pressure 27 mm Hg by 12 months, with the estimated glomerular filtration rate remaining stable. The decrease in arterial pressure after renal denervation is associated with decreased peripheral sympathetic nervous system activity, suggesting that the kidney is a source of significant central sympathetic outflow via afferent renal nerve activity.

New developments in the treatment of severe drug resistant hypertension

The purpose of this paper is to review the state-of-the-art of renal denervation system technology for treatment of drug resistant hypertension. We describe an investigational device that is currently tested in an on-going clinical trial. The denervation device uses the RF thermal ablation catheter attached to the RF generator. The RF catheter is inserted into the renal artery and positioned in the vicinity of the efferent and afferent parasympathetic innervations. Renal denervation is a minimally invasive, localized procedure and the procedural and recovery times are very short. The entire procedure lasts about 40 min. In early clinical trials, the systolic blood pressure in 87% of patients who underwent the denervation procedure resulted in an average blood pressure drop of greater than 10 mm Hg. The procedure has no systematic side effects, and appears to be beneficial in the management of hypertension in patients refractory to pharmacological therapy.

Catheter-based renal sympathetic denervation for resistant hypertension: a multicentre safety and proof-of-principle cohort study

BACKGROUND

Renal sympathetic hyperactivity is associated with hypertension and its progression, chronic kidney disease, and heart failure. We did a proof-of-principle trial of therapeutic renal sympathetic denervation in patients with resistant hypertension (ie, systolic blood pressure >/=160 mm Hg on three or more antihypertensive medications, including a diuretic) to assess safety and blood-pressure reduction effectiveness.

METHODS

We enrolled 50 patients at five Australian and European centres; 5 patients were excluded for anatomical reasons (mainly on the basis of dual renal artery systems). Patients received percutaneous radiofrequency catheter-based treatment between June, 2007, and November, 2008, with subsequent follow-up to 1 year. We assessed the effectiveness of renal sympathetic denervation with renal noradrenaline spillover in a subgroup of patients. Primary endpoints were office blood pressure and safety data before and at 1, 3, 6, 9, and 12 months after procedure. Renal angiography was done before, immediately after, and 14-30 days after procedure, and magnetic resonance angiogram 6 months after procedure. We assessed blood-pressure lowering effectiveness by repeated measures ANOVA. This study is registered in Australia and Europe with ClinicalTrials.gov, numbers NCT 00483808 and NCT 00664638.

FINDINGS

In treated patients, baseline mean office blood pressure was 177/101 mm Hg (SD 20/15), (mean 4.7 antihypertensive medications); estimated glomerular filtration rate was 81 mL/min/1.73m(2) (SD 23); and mean reduction in renal noradrenaline spillover was 47% (95% CI 28-65%). Office blood pressures after procedure were reduced by -14/-10, -21/-10, -22/-11, -24/-11, and -27/-17 mm Hg at 1, 3, 6, 9, and 12 months, respectively. In the five non-treated patients, mean rise in office blood pressure was +3/-2, +2/+3, +14/+9, and +26/+17 mm Hg at 1, 3, 6, and 9 months, respectively. One intraprocedural renal artery dissection occurred before radiofrequency energy delivery, without further sequelae. There were no other renovascular complications.

INTERPRETATION

Catheter-based renal denervation causes substantial and sustained blood-pressure reduction, without serious adverse events, in patients with resistant hypertension. Prospective randomised clinical trials are needed to investigate the usefulness of this procedure in the management of this condition.

Influence of cardiopulmonary reflex on the sympathetic activity during myocardial infarction

The time-course of changes in renal sympathetic nerve activity (RSNA), arterial and cardiopulmonary baroreflexes sensitivities was evaluated in conscious rats eight hours (8 h) and ten days (10 day) after myocardial infarction (MI), induced by coronary artery ligation. RSNA was recorded by a platinum electrode implanted in left renal nerve. Arterial and cardiopulmonary baroreflexes sensitivities were evaluated by changes in blood pressure and serotonin administration, respectively. Both 8 h and 10 day groups presented hypotension (103+/-4 vs. 102+/-2 vs. 115+/-4 mm Hg), but only 8 h showed tachycardia (422+/-22 vs. 378+/-11 vs. 384+/-9 bpm) when compared to Control rats. RSNA was depressed 8 h after MI and increased in 10 day group (12+/-2 vs. 39+/-8 vs. 22+/-2 mV/cycle). Although arterial baroreflex control of heart rate was similar in all groups, the arterial baroreflex control of RSNA in 8 h group was impaired during reductions (-0.35+/-0.10 vs. -1.66+/-0.23 vs. -0.09+/-0.14 mV/cycle/mm Hg) or increases (-0.77+/-0.17 vs. -1.63+/-0.58 vs. -1.66+/-0.17 mV/cycle/mm Hg) in blood pressure when compared to Control animals. Moreover, cardiopulmonary baroreflex bradycardic response was increased in 8 h rats and normalized in 10 day group. The results suggest that the increased cardiopulmonary baroreflex sensitivity in 8 h may contribute to the reduction in the tonic level of RSNA as well as in the impairment of the baroreflex control of RSNA in the presence of hypotension.

Interaction of transthoracic ultrasound and intravenous microbubbles with cardiac mechanoreceptors

The purpose of this study was to examine the effect of transthoracic ultrasound (TTU) and intravenous microbubbles (MB) on cardiac mechanoreceptors. In 16 rabbits (eight normal and eight chronic heart failure), renal sympathetic nerve activity (RSNA), heart rate and mean arterial pressure were examined before, during and after 1 MHz TTU at different peak negative pressures (0.12 to 0.43 MPa) and duty cycles in the presence and absence of perfluorocarbon MB. TTU applications were for 10 s, and the overall duration of MB infusion was approximately 60 s for each setting. TTU without MB had no effect on any parameter. During the microbubble infusion, however, TTU at higher peak negative pressures (> or =0.27 MPa) and 100% duty cycle resulted in a consistent decrease in RSNA(-41 +/- 41% p < 0.001). This was accompanied by brief reflex reductions in mean arterial pressure and heart rate. The changes in RSNA induced by TTU and MB in all rabbits were abolished by vagotomy. TTU, in the presence of MB, stimulates mechanoreceptors in the heart reflexively to reduce RSNA.

Ultrastructural anatomy of the renal nerves in rats

The innervation within mammalian kidneys (intrinsic innervation) has been extensively described in the literature, particularly for rats. In contrast, there is still a lack of detailed description of the morphology of the extrinsic renal nerves leading to the kidney. The aim of the present study was to describe, in detail, the morphology of the renal nerves in rats. Left renal nerves were evaluated in 6 normal adult Wistar rats. After nerve recordings, in order to ascertain that the nerves studied were the extrinsic renal nerves, rats were killed and the nerves prepared for transmission electron microscopy. Morphometry was carried out with the aid of computer software. The total numbers of myelinated and unmyelinated fibers were 22+/-6 and 1246+/-110, respectively, with a ratio of unmyelinated/myelinated fiber of 109+/-26. The diameters of myelinated fibers showed an unimodal distribution with a peak at 3.0 microm but more than 17% of the fibers showed diameters larger than 5 microm. Unmyelinated fiber distribution was unimodal, with peak between 0.5 and 0.7 microm. The present study adds new information on the morphology of renal nerves in rats and provides morphological basis for further studies involving the structural basis of altered renal responses in conditions such as hypertension, ageing, diabetes and peripheral neuropathies.

Frequency response characteristic of sympathetic mediated low-frequency blood pressure fluctuations in conscious rats

A quantitative relationship between power densities of blood pressure (PBP) and sympathetic nerve activity (PSNA) in a low-frequency range (LF, 0.016-0.85 Hz), expressed as PSNA=PBPxax10bx(frequency) was proposed in pentobarbital-anesthetized rats. For evaluating the general applicability of this equation, the quantitative relationship of power density ratio Hf=PBP/PSNA across frequency was tested in a conscious state. Wistar rats were chronically instrumented with a femoral artery catheter and recording electrode around the renal sympathetic nerve. The blood pressure and renal sympathetic nerve activity were monitored both under pentobarbital anesthesia and in a conscious state. Linear regression analysis of the relationship between the frequency and logarithmic magnitude of the power density ratio in the LF range revealed excellent fit in both conditions (r=-0.96+/-0.01 and -0.93+/-0.01 for anesthetized and conscious rats, respectively). Comparing the regression lines, rats under pentobarbital anesthesia had significantly larger values for the y-intercept and slope compared to rats in a conscious state (y-intercepts: 0.80+/-0.09>0.53+/-0.08; slopes: -2.86+/-0.26>-1.62+/-0.21). Our results demonstrate that it is also feasible to use the weighted PBP in LF as a quantitative index of sympathetic variability in conscious rats, but the evaluation of possible complications controlling the regression parameters is called for.

Modulation of sympathetic neurotransmission by neuropeptide Y Y2 receptors in rats and guinea pigs

We have investigated the effect of the Y2 receptor agonist (Y2 agonist; N-acetyl [Leu28,31] NPY 24-36), on contractions evoked by transmural electrical stimulation of sympathetic nerves of isolated arteries from a range of vascular beds in rats and guinea pigs. Contractions evoked by transmural stimulation of the rat renal, mesenteric and femoral arteries were significantly attenuated in the presence of the Y2 agonist. In these arteries, contractions were significantly inhibited in the presence of an alpha-adrenoceptor antagonist (76-97%). So we conclude that these responses were primarily mediated by noradrenaline and that the Y2 agonist attenuates the release of noradrenaline via presynaptic Y2 receptors. Contractions of the rat carotid artery were not attenuated by the Y2 agonist but were completely abolished in the presence of an alpha-adrenoceptor antagonist suggesting that in this artery the Y2 agonist has no effect on release of noradrenaline. In the guinea pig, carotid arteries contractions evoked by transmural nerve stimulation were attenuated in the presence of the Y2 agonist and inhibited by an alpha-adrenoceptor antagonist 75-87% suggesting that the Y2 agonist attenuates the release of noradrenaline via presynaptic Y2 receptors in this vessel. In the guinea pig femoral artery contractions evoked by transmural stimulation were not modified in the presence of the Y2 agonist but were completely abolished in the presence of an alpha-adrenoceptor antagonist. This suggests that the Y2 agonist does not modify noradrenaline release in this vessel. Contractions of the guinea pig mesenteric artery were significantly potentiated by the Y2 agonist, possibly by potentiation of neuropeptide Y (NPY) at the Y1 receptor. The Y1 antagonist inhibited more than 70 % of the response, indicating that the majority of the contraction was mediated by NPY. The current study demonstrates heterogeneity of neurotransmitter substances in sympathetic nerves supplying vascular beds within and across species and in subsequent functional response.

Vasopressin receptor antagonists: pharmacological tools and potential therapeutic agents

The present survey deals with the development and applications of non-peptidergic vasopressin receptor antagonists. The existence of at least three vasopressin receptors (V(1), V(2) and V(3) respectively) is firmly established. V(1)-receptors play a relevant role in the regulation of vascular tone, whereas V(2)-receptors are known to mediate the antidiuretic activity of vasopressin at the level of the renal collecting ducts. The V(3)-receptor appears to be involved in the release of the adreno-corticotropic hormone. Vasopressin receptor antagonists which are peptides have been known for several decades, more recently, both V(1)- and V(2)-receptor blockers which are non-peptidergic have been introduced, as well as agents with affinity for both V(1)- and V(2)-receptor subtypes. A survey of these non-peptidergic antagonists is presented here. Such compounds are useful as pharmacological tools, and they can also be thought of as therapeutic agents as therapeutic agents in cardiovascular and renal diseases. Selective V(1)- and V(2)-receptor antagonists were used to study the interaction between vasopressin receptors and sympathetic neurones. Depending on the experimental model used this interaction can occur at either the pre- or postsynaptic sites. In both cases predominantly V(1)-receptors are involved. A brief survey is given of the potential use of V-receptor antagonists in the drug therapy of syndrome of inappropriate antidiuretic hormone secretion and other water retaining disorders, congestive heart failure and certain forms of hypertension (in particular in the Negroid hypertensive patients).

Neurogenic constrictor response of isolated small renal arteries in rats after 2-week simulated microgravity

The study was aimed at investigation of the effects of 2-week tail suspension upon the constrictor responses of isolated small renal arteries in rats. 1st-2nd-order branches of renal artery were perfused with saline under the constant flow conditions. Constrictor responses to electrical stimulation of periarterial nerves, noradrenaline and serotonin were investigated. In post-suspension rats as compared to controls the response to nerve stimulation was slightly reduced during 15-Hz stimulation, but similar at smaller frequencies. Thus, simulated microgravity has no prominent effect of neurogenic responses of renal vessels, in agreement with non-changed density of periarterial adrenergic nerve plexus. Along with that, in post-suspension rats impairment of prejunctional sympathetic mechanisms might be compensated by augmented sensitivity of vascular smooth muscle to vasoconstrictors.

Selective increase in renal arcuate innervation density and neurogenic constriction in chronic angiotensin II-infused rats

This study investigated the effects of angiotensin II "slow pressor" hypertension on structure and function of nerves supplying the renal vasculature. Low-dose angiotensin II (10 ng/kg per minute, initially sub-pressor) or saline vehicle was infused intravenously for 21 days in rats, and the effects were compared in renal and mesenteric arteries. Mean arterial pressure averaged 12+/-2 mm Hg higher than in vehicle-infused rats at 21 days. Using electron microscopy, the innervation density of renal arcuate, but not mesenteric arteries of equivalent size, was significantly higher in angiotensin II-infused than in vehicle-infused rats. Functional testing on a pressure myograph revealed that constrictions evoked by nerve stimulation in arcuate arteries were 2.3+/-0.7-fold greater in vessels from angiotensin II-infused compared with vehicle-infused rats (P<0.0001), whereas there was no significant difference in nerve-induced constrictions in mesenteric arteries. Sensitivity to and maximum amplitude of constrictions evoked by phenylephrine were not different in renal or mesenteric arteries between groups, suggesting that the increased neurally evoked constriction in renal arcuate arteries was not caused by postsynaptic changes. Endothelium-dependent vasorelaxation and the vessel wall physical properties were not different between the two groups in either artery. Thus, angiotensin II infusion appeared to evoke renal-specific increases in vessel innervation and increased vasoconstriction to nerve stimulation. These changes appear early and occur before changes in renal endothelial function are apparent. Thus, "slow pressor" angiotensin II hypertension is associated with increased renal innervation, compatible with a pathogenetic role.

Dynamic interactions between arterial pressure and sympathetic nerve activity: role of arterial baroreceptors

The role of arterial baroreceptors in controlling arterial pressure (AP) variability through changes in sympathetic nerve activity was examined in conscious rats. AP and renal sympathetic nerve activity (RSNA) were measured continuously during 1-h periods in freely behaving rats that had been subjected to sinoaortic baroreceptor denervation (SAD) or a sham operation 2 wk before study (n = 10 in each group). Fast Fourier transform analysis revealed that chronic SAD did not alter high-frequency (0.75-5 Hz) respiratory-related oscillations of mean AP (MAP) and RSNA, decreased by approximately 50% spectral power of both variables in the midfrequency band (MF, 0.27-0.74 Hz) containing the so-called Mayer waves, and induced an eightfold increase in MAP power without altering RSNA power in the low-frequency band (0.005-0.27 Hz). In both groups of rats, coherence between RSNA and MAP was maximal in the MF band and was usually weak at lower frequencies. In SAD rats, the transfer function from RSNA to MAP showed the characteristics of a second-order low-pass filter containing a fixed time delay ( approximately 0.5 s). These results indicate that arterial baroreceptors are not involved in production of respiratory-related oscillations of RSNA but play a major role in the genesis of synchronous oscillations of MAP and RSNA at the frequency of Mayer waves. The weak coupling between slow fluctuations of RSNA and MAP in sham-operated and SAD rats points to the interference of noise sources unrelated to RSNA affecting MAP and of noise sources unrelated to MAP affecting RSNA.

Vasodilator reactivity to calcitonin gene-related peptide is increased in mesenteric arteries of rats during early pregnancy

The objective of the present study was to determine the effect of early pregnancy on the sensitivity to, and endogenous production of calcitonin gene-related peptide (CGRP). Contractile responses of arteries of 10-day pregnant and nonpregnant rats were studied in myographs. During contractions induced by 40 mmol/l K(+), exogenous CGRP elicited an approximately 30% stronger relaxation in mesenteric arteries in pregnancy, an effect not seen in renal and uterine arteries. Capsaicin treatment during K(+)-induced contractions caused a persistent potentiation of the contractile response in mesenteric arteries, indicating that K(+) stimulates the endogenous release of CGRP. This potentiation was similar in the pregnant and nonpregnant state (+81 +/- 23% and +82 +/- 23%, respectively), suggesting no effect of pregnancy on the endogenous CGRP release. The latter was paralleled by comparable CGRP content in the arteries of both groups, indicating similar tissue CGRP availability. The results of this study support the concept that early pregnancy is associated with a rise in the vascular sensitivity to CGRP in selected areas of the vascular bed without concomitant increase in the vascular CGRP production and release.

Effect of renal nerve stimulation on responsiveness of the rat renal vasculature

When the renal nerves are stimulated with sinusoidal stimuli over the frequency range 0.04-0.8 Hz, low (< or =0.4 Hz)- but not high (> or =0.4 Hz)-frequency oscillations appear in renal blood flow (RBF) and are proposed to increase responsiveness of the renal vasculature to stimuli. This hypothesis was tested in anesthetized rats in which RBF responses to intrarenal injection of norepinephrine and angiotensin and to reductions in renal arterial pressure (RAP) were determined during conventional rectangular pulse and sinusoidal renal nerve stimulation. Conventional rectangular pulse renal nerve stimulation decreased RBF at 2 Hz but not at 0.2 or 1.0 Hz. Sinusoidal renal nerve stimulation elicited low-frequency oscillations (< or =0.4 Hz) in RBF only when the basal carrier signal frequency produced renal vasoconstriction, i.e., at 5 Hz but not at 1 Hz. Regardless of whether renal vasoconstriction occurred, neither conventional rectangular pulse nor sinusoidal renal nerve stimulation altered renal vasoconstrictor responses to norepinephrine and angiotensin. The RBF response to reduction in RAP was altered by both conventional rectangular pulse and sinusoidal renal nerve stimulation only when renal vasoconstriction occurred: the decrease in RBF during reduced RAP was greater. Sinusoidal renal nerve stimulation with a renal vasoconstrictor carrier frequency results in a decrease in RBF with superimposed low-frequency oscillations. However, these low-frequency RBF oscillations do not alter renal vascular responsiveness to vasoconstrictor stimuli.