Endovascular Treatment of Resistant and Uncontrolled Hypertension

Beyond Conventional Control: Insights Into Drug-Resistant Hypertension

It is believed that 9-18% of patients with hypertension have resistant hypertension, a serious medical disease. The increased cardiovascular risk associated with this illness demands appropriate diagnosis and treatment. It is necessary to conduct an in-depth investigation of the various etiologies, indicators of risk, and multiple disorders of resistant hypertension. This is crucial in order to establish the diagnosis and make the best decisions regarding therapy. Treatment should also take lifestyle changes into account in addition to medicinal and interventional therapy. When there is a suspicion of resistant hypertension, examining the medications used to treat the hypertensive patient after ruling out pseudo hypertension, improper blood pressure monitoring and control, and the white-coat effect are necessary. Resistant hypertension, according to a specific definition, is a condition that cannot be treated with more than two antihypertensive drugs, including a diuretic. An effective multidrug therapy for the treatment of resistant hypertension includes angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, beta-blockers, diuretics, long-acting calcium channel blockers, and mineralocorticoid receptor antagonists. However, alternative, cutting-edge treatments, such as renal denervation or baroreflex activation, could develop a brand-new avenue for decreasing blood pressure. These new surgical interventions might prove out to be of immense importance in coming times. Secondary causes of resistant hypertension, such as obstructive sleep apnea, coronary artery diseases, nephropathy, or endocrinal diseases, must be checked out in order to make an accurate diagnosis of this illness. This review article briefly summarizes the epidemiology, risk factors, causes, pathogenesis, diagnosis, and treatment approaches that may help with the long-term management of resistant hypertension.

Renal Sympathetic Denervation Improves Outcomes in a Canine Myocardial Infarction Model

BACKGROUND Myocardial infarction (MI) is the main cause of heart failure (HF), and sympathetic nerve activity is associated with prognosis chronic heart failure. Renal sympathetic denervation (RDN) is noted for its powerful effect on the inhibition of sympathetic nerve activity. This study investigated the effect of RDN on heart failure in dogs after myocardial infarction. MATERIAL AND METHODS The experimental animals were randomized into 2 groups: the MI group (n=12) and the sham operation group (n=6). In the MI group we established an MI model by permanently ligating the left anterior descending branch. After 4 weeks, the MI dogs were randomly divided into 2 groups: the MI+RDN group (MI+renal sympathetic denervation, n=6) and the simple MI group (n=6). Animals in the MI+RDN group underwent both surgical and chemical renal denervation. RESULTS Compared with sham operation group, left ventricular fraction shortening (LVFS) and left ventricular ejection fraction (LVEF) were significantly reduced in the simple MI group, while the reduction was partly reversed in the MI+RDN group. RDN reduced sympathetic nerve activity and release of B-type natriuretic peptide (BNP) and Angiotensin II (AngII) in the MI+ RDN group but not in the simple MI group. CONCLUSIONS Canine renal sympathetic denervation prevents myocardial malignant remodeling by lowering the activity of the systemic sympathetic nerve and inhibiting renin-angiotensin-aldosterone system (RASS) activation, providing a new target and method for the treatment of heart failure.

Evaluation of later morphologic alterations in renal artery wall and renal nerves in response to catheter-based renal denervation in sheep: comparison of the single-point and multiple-point ablation catheters

This study evaluated the subacute morphologic alterations in renal artery wall and renal nerves in response to catheter-based renal denervation (RDN) in sheep and also compared the efficiency of single-point and multiple-point ablation catheters. Effect of each ablation catheter approved for the clinical use (Symplicity Flex(TM), Medtronic, Inc., or EnligHTN(TM), St. Jude Medical, INC.) was compared to intact contralateral renal artery in 12 sheep by histopathology and immunohistochemistry evaluation after a 10-day period post-RDN procedure. The safety was verified by extensive evaluation of kidney morphology. Vascular wall lesions and nerve injuries were more pronounced in those animals treated with multi-point EnligHTN catheter when compared with animals treated with single-point Symplicity Flex catheter. However, neither RDN procedure led to complete renal nerve ablation. Both systems, tested in the present study, provided only incomplete renal nerve ablation in sheep. Moreover, no appreciable progression of the nerve disintegration in subacute phase post-RDN procedure was observed. This study further supports the notion that the effectiveness remains fully dependent on anatomical inter-individual variability of the sympathetic nerve plexus accompanying the renal artery. Therefore, new systems providing deeper penetrance to targeted perivascular structure would be more efficient.

Comparison of two different radiofrequency ablation systems for renal artery denervation: Evaluation of short-term and long-term follow up

Objectives

To assess the clinical efficacy of renal artery denervation (RAD) in our center and to compare the efficacy of two different radiofrequency (RF) systems.

Background

Several systems are available for RF renal denervation. Whether there is a difference in clinical efficacy among various systems remains unknown.

Methods

Renal artery denervation was performed on 43 patients with resistant hypertension using either the single electrode Symplicity Flex (n = 20) or the multi‐electrode EnligHTN system (n = 23). Median post‐procedural follow‐up was 32.93 months. The primary outcome was post‐procedural change in office blood pressure (BP) within 1 year (short‐term follow‐up). Secondary outcomes were change in office BP between 1 and 4 years (long‐term follow‐up) and the difference in office BP reduction between the two systems at each follow‐up period.

Results

For the total cohort, mean baseline office BP (systolic/diastolic) was 174/94 mmHg. At follow‐up, mean changes in office BP from baseline were −19.70/−11.86 mmHg (P < 0.001) and −21.90/−13.94 mmHg (P < 0.001) for short‐term and long‐term follow‐up, respectively. The differences in office BP reduction between Symplicity and EnligHTN groups were 8.96/1.23 mmHg (P = 0.42 for systolic BP, P = 0.83 for diastolic BP) and 9.56/7.68 mmHg (P = 0.14 for systolic BP, P = 0.07 for diastolic BP) for short‐term and long‐term follow‐up, respectively.

Conclusions

In our cohort, there was a clinically significant office BP reduction after RAD, which persisted up to 4 years. No significant difference in office BP reduction between the two systems was found.

Renal denervation for resistant hypertension: yes

Sympathetic overactivity may have a role in triggering and maintaining resistant hypertension, and catheter-based renal denervation (RDN) has emerged as a promising treatment in refractory hypertension. Recently, the results of the Symplicity HTN-3, the first randomized, sham-controlled trial, failed to confirm the previously reported BP-lowering effects of RDN, although definitive conclusions cannot be drawn due to a number of study limitations. Consequently, although some centers halted their RDN programs, research continues and both the concept of denervation and treatment strategies are being redefined. A new generation of sham-controlled trials is currently underway with the aim of detecting which patients are expected to achieve the most beneficial effect from RDN. In this article, we examine the current data on RDN and discuss some insights and future opportunities.

Renal Denervation: A Novel Therapy at the Crossroads of Imaging, Intervention, and Innovation

Hypertension (HTN) is one of the most significant medical problems affecting society today. The estimated 76 million Americans with hypertension represent a significant public health problem, contributing to cardiac, vascular, renal, and neurovascular morbidity and mortality. HTN is the most common indication for lifelong pharmacologic treatment, mainly because of the incontrovertible reductions in cardiovascular events with blood pressure (BP) reduction and control. However, despite the availability and potency of multiple different antihypertensive drugs, up to half of American patients have BPs above the recommended target. Given the overwhelming evidence of both the cost to society of HTN and the benefits that are accrued from improved BP control, alternatives or adjuncts to current management options have been sought to aid in treatment of these patients. Over the past few years, a device-based approach involving modulation of the autonomic nervous system, termed renal denervation, has evolved to meet this challenge. With early trials showing startlingly good results, with few side effects, multiple devices were fast-tracked to clinical trials and hence to the market. However, larger trials have shone an unfavorable light on the field, with concerns about the short- and long-term effectiveness, diverting attention back to operational and procedural details. Despite this, image-guided manipulation of the sympathetic nervous system to treat HTN remains a fertile area of laboratory and clinical research.

Irreversible electroporation: evolution of a laboratory technique in interventional oncology

Electroporation involves applying electric field pulses to cells, leading to the alteration or destruction of cell membranes. Irreversible electroporation (IRE) creates permanent defects in cell membranes and induces cell death. By directly targeting IRE to tumors, percutaneous nonthermal ablation is possible. The history of IRE, evolution of concepts, theory, biological applications, and clinical data regarding its safety and efficacy are discussed.

Surgical, interventional, and device innovations in the management of hypertension

The prevalence of hypertension around the world has increased significantly with projections for an increasing major global burden of hypertension. Medication-resistant hypertension can be perplexing and frustrating. The existence of these difficult patients results in the need for additional approaches to treatment including surgery, percutaneous interventions, and device management. The sophistication of these techniques has progressed markedly and initial procedures such as classical sympathectomy and renal artery bypass are almost never performed. Newer techniques of angioplasty with stenting, renal artery denervation, and baroreflex activation therapy via electrical stimulation of the carotid baroreceptors are now in use with increasing evidence for significant benefit.

Renal denervation for resistant hypertension and beyond

Despite the availability of more than 125 approved antihypertensive medications, 36 million (48%) of 75 million people with hypertension, including 16 million treated with antihypertensive medications in the United States, do not achieve guideline blood pressure goals known to reduce cardiovascular morbidity and mortality and progression of kidney disease; 3% to 6% of these 75 million hypertensive individuals are estimated to have resistant hypertension. A major contributing factor for poor blood pressure control, besides inadequate diuretic therapy, is failure of antihypertensive agents to inhibit the sympathetic nervous system effectively. Consequently, alternative device-driven approaches have been developed. Recent technical advances targeting renal sympathetic nerves, that is, renal denervation therapy, are the focus of more invasive therapies to treat resistant hypertension. Encouraging results from the SYMPLICITY HTN-2 trial, regarding efficacy and safety of renal denervation therapy, were countered by disappointing efficacy results of SYMPLICITY HTN-3. Reasons for these divergent results and the future of the field are discussed.

Where and when device therapy may be useful in the management of drug-resistant hypertension

Device therapy for the treatment of uncontrolled and resistant hypertension has evolved significantly over the past several decades. Both renal artery disease and sympathetic hyperactivity have been linked to resistant hypertension. This manuscript will review the current evidence base supporting device therapy (e.g., renal artery revascularization, sympathetic nervous system modulation) for resistant hypertension.

MR-guided high-focused ultrasound for renal sympathetic denervation-a feasibility study in pigs

Background

Renal sympathetic denervation has recently gained clinical relevance for the treatment of therapy-resistant hypertension. Denervation is currently mainly performed using catheter-based transarterial radiofrequency ablation of periarterial sympathetic nerve fibers. Since this approach has numerous limitations, we conducted a study to evaluate the feasibility, safety, and efficacy of magnetic resonance-guided high-focused ultrasound (MRgHiFUS) for renal sympathetic denervation in pigs as an alternative to catheter-based ablation.

Methods

Renal periarterial MRgHiFUS was performed under general anesthesia in ten pigs. Blood pressure measurements and magnetic resonance imaging (MRI) of the kidneys, renal arteries, and surrounding structures were obtained immediately before and after the interventions and after 4 weeks. Histological examinations of periarterial tissues and determination of renal norepinephrine (NE) concentration were performed to assess treatment efficacy.

Results and discussion

In each pig, 9.8 ± 2.6 sonications with a mean energy deposition of 2,670 ± 486 J were performed. The procedure was well tolerated by all pigs. No major complications occurred. MRgHiFUS induced periarterial edema in three pigs, but only one pig showed corresponding histological changes. The NE level of the treated kidney was lower in five pigs (-8% to -38%) compared to the untreated side. Overall, there was no significant difference between the NE values of both kidneys in any of the treated pigs. Postinterventional MRI indicated absorption of ultrasound energy at the transverse process and fascia.

Conclusion

MRgHiFUS had some thermal periarterial effects but failed to induce renal denervation. Insufficient energy deposition is most likely attributable to a small acoustic window with beam path impediment in the porcine model. Since HiFUS treatment in humans is expected to be easier to perform due to better access to renal sympathetic nerves, further studies of this method are desirable to investigate the potential of MRgHiFUS as an alternative for patients not suitable for catheter-based renal sympathicolysis.

Renal denervation in patients with resistant hypertension: six-month results

INTRODUCTION

Increased activation of the sympathetic nervous system plays a central role in the pathophysiology of hypertension (HTN). Catheter-based renal denervation (RDN) was recently developed for the treatment of resistant HTN.

AIM

To assess the safety and efficacy of RDN for blood pressure (BP) reduction at six months in patients with resistant HTN.

METHODS

In this prospective registry of patients with essential resistant HTN who underwent RDN between July 2011 and May 2013, the efficacy of RDN was defined as ≥ 10 mm Hg reduction in office systolic blood pressure (SBP) six months after the intervention.

RESULTS

In a resistant HTN outpatient clinic, 177 consecutive patients were evaluated, of whom 34 underwent RDN (age 62.7 ± 7.6 years; 50.0% male). There were no vascular complications, either at the access site or in the renal arteries. Of the 22 patients with complete six-month follow-up, the response rate was 81.8% (n=18). The mean office SBP reduction was 22 mm Hg (174 ± 23 vs. 152 ± 22 mm Hg; p<0.001) and 9 mm Hg in diastolic BP (89 ± 16 vs. 80 ± 11 mm Hg; p=0.006). The number of antihypertensive drugs (5.5 ± 1.0 vs. 4.6 ± 1.1; p=0.010) and pharmacological classes (5.4 ± 0.7 vs. 4.6 ± 1.1; p=0.009) also decreased significantly. Of the 24-hour ambulatory BP monitoring and echocardiographic parameters analyzed, there were significant reductions in diastolic load (45 ± 29 vs. 27 ± 26%; p=0.049) and in left ventricular mass index (174 ± 56 vs. 158 ± 60 g/m(2); p=0.014).

CONCLUSION

In this cohort of patients with resistant HTN, RDN was safe and effective, with a significant BP reduction at six-month follow-up.

Novel strategies for treatment of resistant hypertension

Resistant hypertension, defined as blood pressure (BP) remaining above goal despite the use of 3 or more antihypertensive medications at maximally tolerated doses (one ideally being a diuretic) or BP that requires 4 or more agents to achieve control, occurs in a substantial proportion (>10%) of treated hypertensive patients. Refractory hypertension is a recently described subset of resistant hypertension that cannot be controlled with maximal medical therapy (⩾5 antihypertensive medications of different classes at maximal tolerated doses). Patients with resistant or refractory hypertension are at increased cardiovascular risk and comprise the target population for novel antihypertensive treatments. Device-based interventions, including carotid baroreceptor activation and renal denervation, reduce sympathetic nervous system activity and have effectively reduced BP in early clinical trials of resistant hypertension. Renal denervation interrupts afferent and efferent renal nerve signaling by delivering radiofrequency energy, other forms of energy, or norepinephrine-depleting pharmaceuticals through catheters in the renal arteries. Renal denervation has the advantage of not requiring general anesthesia, surgical intervention, or device implantation and has been evaluated extensively in observational proof-of-principle studies and larger randomized controlled trials. It has been shown to be safe and effective in reducing clinic BP, indices of sympathetic nervous system activity, and a variety of hypertension-related comorbidities. These include impaired glucose metabolism/insulin resistance, end-stage renal disease, obstructive sleep apnea, cardiac hypertrophy, heart failure, and cardiac arrhythmias. This article reviews the strengths, limitations, and future applications of novel device-based treatment, particularly renal denervation, for resistant hypertension and its comorbidities.

Percutaneous renal sympathetic denervation: 2013 and beyond

Systemic hypertension affects almost a quarter of Canadian adults. Although most can achieve adequate blood pressure control using a combination of medical and lifestyle interventions, many have resistant hypertension and are unable to reach their target. Percutaneous renal sympathetic denervation has been developed to address a crucial mechanism in the pathophysiology of hypertension: renal sympathetic overactivity. In 2009, the first-in-man experience with renal denervation was published. Several studies followed, including the randomized Symplicity HTN-2 trial of 106 patients: 6-month mean blood pressure reduction was 32/12 mm Hg in those who underwent renal denervation, vs a change of +1/0 Hg in those who did not. However, all the evidence to date suffers from the same drawbacks: studies are small, and follow-up is short and largely incomplete. The future of renal denervation will be determined by 3 factors. First, there will be more and better evidence. Symplicity HTN-3 has randomized 530 patients to renal denervation vs a sham procedure; 24-hour ambulatory blood pressure monitoring will be assessed in all participants. Other quality trials will follow, including ones that will assess clinical end points. Second, other indications for this treatment will be investigated. Sympathetic overactivity is implicated in many other conditions, including heart failure and arrhythmia; sympathetic denervation might benefit these patients as well. Third, myriad devices, using different methods to achieve renal denervation, are being developed. The first renal denervation system was approved for clinical use in Canada in March 2012. Until more data are available, patients undergoing this procedure should be carefully screened and, ideally, enrolled in research protocols.

Renal sympathetic denervation for resistant hypertension treatment : current perspectives

The authors review the concept of resistant hypertension and the involvement of the sympathetic nervous system in hypertension as a rational basis for the technique of renal sympathetic denervation (RSD) performed percutaneously. This revision is the result of an active search for scientific articles with the term "renal denervation" in the Medline and PubMed databases. The techniques and devices used in the procedure are presented, as well as clinical outcomes at six, 12 and 24 months after the intervention with the Symplicity catheter. Significant decreases and progressively higher reductions of systolic and diastolic blood pressure were observed after RSD. The complication rate was minimal. New devices for RSD and its ongoing clinical studies are cited. In conclusion, the RSD presents itself as an effective and safe approach to resistant hypertension. Results from ongoing studies and longer follow-up of these patients are expected to confirm the initial results and put into perspective the expansion of the procedure use in hypertension approach.