Renal denervation for the management of resistant hypertension

The denervation or activation of renal sympathetic nerve and renal blood flow

The denervation or activation of the sympathetic nerve in the kidney can affect renal hemodynamics. The sympathetic nervous system regulates the physiological functions of the kidneys. Stimulation of sympathetic efferent nerves affects various parameters related to renal hemodynamics, including sodium excretion, renin secretion, and renal blood flow (RBF). Hence, renal sympathetic fibers may also play an essential role in regulating systemic vascular resistance and controlling blood pressure. In the absence of renal nerves, the hemodynamics response to stimuli is negligible or absent. The effect of renal sympathetic denervation on RBF is dependent on several factors such as interspecies differences, the basic level of nerve activity in the vessels or local density of adrenergic receptor in the vascular bed. The role of renal denervation has been investigated therapeutically in hypertension and related disorders. Hence, the dynamic impact of renal nerves on RBF enables using RBF dynamic criteria as a marker for renal denervation therapy.

The Potential Role of Renal Denervation in the Management of Heart Failure

Sympathetic nervous system activation in patients with heart failure is one of the main pathophysiologic mechanisms associated with the worse outcomes. Pharmacotherapies targeting neurohormonal activation have been at the center of heart failure management. Despite the advancement of therapies and the available treatments, heart failure continues to have an overall poor prognosis. Renal denervation was originally developed to lower systemic blood pressure in patients with poorly controlled hypertension, by modulating sympathetic outflow. However, more recently, multiple studies have investigated the effect of renal denervation in heart failure patients with both preserved (HFpEF) and reduced ejection fractions (HFrEF). This paper provides an overview of the potential effect of renal denervation in altering the various pathophysiologic, sympathetically mediated pathways that contribute to heart failure, and reviews the literature that supports its future use in those patients.

Technical advance in silico and in vitro development of a new bipolar radiofrequency ablation device for renal denervation

Background

Renal denervation with radiofrequency ablation has become an accepted treatment for drug-resistant hypertension. However, there is a continuing need to develop new catheters for high-accuracy, targeted ablation. We therefore developed a radiofrequency bipolar electrode for controlled, targeted ablation through Joule heating induction between 60 and 100 °C. The bipolar design can easily be assembled into a basket catheter for deployment inside the renal artery.

Methods

Finite element modeling was used to determine the optimum catheter design to deliver a minimum ablation zone of 4 mm (W) × 10 mm (L) × 4 mm (H) within 60 s with a 500 kHz, 60 Vp-p signal, and 3 W maximum. The in silico model was validated with in vitro experiments using a thermochromic phantom tissue prepared with polyacrylamide gel and a thermochromic ink additive that permanently changes from pink to magenta when heated over 60 °C.

Results

The in vitro ablation zone closely matched the size and shape of the simulated area. The new electrode design directs the current density towards the artery walls and tissue, reducing unwanted blood temperature increases by focusing energy on the ablation zone. In contrast, the basket catheter design does not block renal flow during renal denervation.

Conclusions

This computational model of radiofrequency ablation can be used to estimate renal artery ablation zones for highly targeted renal denervation in patients with resistant hypertension. Furthermore, this innovative catheter has short ablation times and is one of the lowest power requirements of existing designs to perform the ablation.

Paradise™ Ultrasound Renal Denervation System for the treatment of hypertension

Catheter-based renal denervation is a novel treatment approach for patients with hypertension and initial unblinded trials have shown promising results. The Paradise™ Ultrasound Renal Denervation System (ReCor Medical, CA, USA) is an ultrasound-based catheter with a distal balloon that acts as a coolant to protect the renal arterial wall. This device received CE-mark in 2012. Randomized, sham-controlled trials and postmarket studies have shown promising efficacy and safety results. Currently, three additional ongoing randomized, sham-controlled trials are underway in the USA, Europe, Japan and Korea, and the results will be pivotal in device approval in some of these countries. These studies with larger numbers of patients and longer duration of follow-up are needed to further confirm the safety and efficacy of this device.

Renal Artery Denervation for Hypertension

PURPOSE OF REVIEW

Hypertension (HTN) has a growing impact, already affecting over 1 billion people. An estimated 2-16% of those with HTN have resistant HTN. The sympathetic nervous system (SNS) is a recognized contributor to the pathophysiology of resistant HTN. Current hypertensive pharmacotherapy has not fully targeted the SNS; therefore, the SNS has become a prominent research therapeutic target. This review summarizes the evidence and rationale behind renal denervation (RDN) therapy and the technology available.

RECENT FINDINGS

Prior to the SYMPLICITY HTN-3 clinical trial, trials found RDN to be an effective procedure to control resistant hypertension. The failure of SYMPLICITY HTN-3 to meet its primary efficacy endpoint sparked further studies to address potential shortcomings. The subsequent SPYRAL program trials demonstrated efficacy of RDN therapy in a controlled manner; however, they were not adequately powered. Ongoing research is examining new, innovative RDN technology as well as defining appropriate patients to target for treatment. The data currently available for RDN in HTN and other states of SNS activation suffer from potential biases and limitations, highlighting the need for continued exploration. Contemporary studies are more promising and hypothesis-generating. Future trials and continued device innovation will be crucial for understanding the clinical applications of RDN therapy.

Exercise as a tool for hypertension and resistant hypertension management: current insights

Although there has been an observed progress in the treatment of hypertension, its prevalence remains elevated and constitutes a leading cause of cardiovascular disease development. Resistant hypertension is a challenge for clinicians, as the available treatment options have reduced success. Physical activity and exercise training play an important role in the management of blood pressure. The importance of physical activity and exercise training as part of a comprehensive lifestyle intervention is acknowledged by several professional organizations in their recommendations/guidelines for the management of arterial hypertension. Aerobic exercise, dynamic resistance exercise, and concurrent training - the combination of dynamic resistance and aerobic exercise training in the same exercise session or on separate days - has been demonstrated to reduce blood pressure and help in the management of hypertension. The present review draws attention to the importance of exercise training in the management of blood pressure in both hypertension and resistant hypertension individuals.

The autonomic nervous system as a therapeutic target in heart failure: a scientific position statement from the Translational Research Committee of the Heart Failure Association of the European Society of Cardiology

Despite improvements in medical therapy and device-based treatment, heart failure (HF) continues to impose enormous burdens on patients and health care systems worldwide. Alterations in autonomic nervous system (ANS) activity contribute to cardiac disease progression, and the recent development of invasive techniques and electrical stimulation devices has opened new avenues for specific targeting of the sympathetic and parasympathetic branches of the ANS. The Heart Failure Association of the European Society of Cardiology recently organized an expert workshop which brought together clinicians, trialists and basic scientists to discuss the ANS as a therapeutic target in HF. The questions addressed were: (i) What are the abnormalities of ANS in HF patients? (ii) What methods are available to measure autonomic dysfunction? (iii) What therapeutic interventions are available to target the ANS in patients with HF, and what are their specific strengths and weaknesses? (iv) What have we learned from previous ANS trials? (v) How should we proceed in the future?

Device-based Therapy for Hypertension

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

Effects of renal denervation on vascular remodelling in patients with heart failure and preserved ejection fraction: A randomised control trial

OBJECTIVE

To assess the effect of renal denervation (RDT) on micro- and macro-vascular function in patients with heart failure with preserved ejection fraction (HFpEF).

DESIGN

A prospective, randomised, open-controlled trial with blinded end-point analysis.

SETTING

A single-centre London teaching hospital.

PARTICIPANTS

Twenty-five patients with HFpEF who were recruited into the RDT-PEF trial.

MAIN OUTCOME MEASURES

Macro-vascular: 24-h ambulatory pulse pressure, aorta distensibilty (from cardiac magnetic resonance imaging (CMR), aorta pulse wave velocity (CMR), augmentation index (peripheral tonometry) and renal artery blood flow indices (renal MR). Micro-vascular: endothelial function (peripheral tonometry) and urine microalbuminuria.

RESULTS

At baseline, 15 patients were normotensive, 9 were hypertensive and 1 was hypotensive. RDT did not lower any of the blood pressure indices. Though there was evidence of abnormal vascular function at rest, RDT did not affect these at 3 or 12 months follow-up.

CONCLUSIONS

RDT did not improve markers of macro- and micro-vascular function.