Translational medicine: the antihypertensive effect of renal denervation

Integrative Blood Pressure Response to Upright Tilt Post Renal Denervation

BACKGROUND

Whether renal denervation (RDN) in patients with resistant hypertension normalizes blood pressure (BP) regulation in response to routine cardiovascular stimuli such as upright posture is unknown. We conducted an integrative study of BP regulation in patients with resistant hypertension who had received RDN to characterize autonomic circulatory control.

METHODS

Twelve patients (60 ± 9 [SD] years, n = 10 males) who participated in the Symplicity HTN-3 trial were studied and compared to 2 age-matched normotensive (Norm) and hypertensive (unmedicated, HTN) control groups. BP, heart rate (HR), cardiac output (Qc), muscle sympathetic nerve activity (MSNA), and neurohormonal variables were measured supine, and 30° (5 minutes) and 60° (20 minutes) head-up-tilt (HUT). Total peripheral resistance (TPR) was calculated from mean arterial pressure and Qc.

RESULTS

Despite treatment with RDN and 4.8 (range, 3-7) antihypertensive medications, the RDN had significantly higher supine systolic BP compared to Norm and HTN (149 ± 15 vs. 118 ± 6, 108 ± 8 mm Hg, P < 0.001). When supine, RDN had higher HR, TPR, MSNA, plasma norepinephrine, and effective arterial elastance compared to Norm. Plasma norepinephrine, Qc, and HR were also higher in the RDN vs. HTN. During HUT, BP remained higher in the RDN, due to increases in Qc, plasma norepinephrine, and aldosterone.

CONCLUSION

We provide evidence of a possible mechanism by which BP remains elevated post RDN, with the observation of increased Qc and arterial stiffness, as well as plasma norepinephrine and aldosterone levels at approximately 2 years post treatment. These findings may be the consequence of incomplete ablation of sympathetic renal nerves or be related to other factors.

Improvement in health-related quality of life after renal sympathetic denervation in real-world hypertensive patients: 12-month outcomes in the Global SYMPLICITY Registry

Renal denervation has been shown to reduce blood pressure in patients with uncontrolled hypertension, but less is known about its impact on quality of life. This analysis evaluated 12-month blood pressure and quality of life outcomes in 934 patients from the Global SYMPLICITY Registry who completed the EuroQoL five-dimensions three-level questionnaire (EQ-5D-3L). At baseline, 32% of patients reported anxiety/depression and 48% reported pain/discomfort. At 12 months (n=496), office and 24-hour ambulatory systolic blood pressure were reduced by 13.9±26.6 and 7.7±19.3 mm Hg, respectively, and 8% (P<.001) more patients reported no problems in anxiety/depression. Furthermore, numerically more patients reported no problems in pain/discomfort (4%, P=.08). Perceived health-related quality of life (visual analog scale) improved from baseline to 12 months (68±18 vs 73±17, P<.001), and the improvement was largest among patients with severe anxiety/depression at baseline (50±24 vs 64±22, P=.005 [n=32]). In this analysis, renal denervation was associated with a significant improvement in health-related quality of life, particularly anxiety/depression.

Interventional procedures and future drug therapy for hypertension

Hypertension management poses a major challenge to clinicians globally once non-drug (lifestyle) measures have failed to control blood pressure (BP). Although drug treatment strategies to lower BP are well described, poor control rates of hypertension, even in the first world, suggest that more needs to be done to surmount the problem. A major issue is non-adherence to antihypertensive drugs, which is caused in part by drug intolerance due to side effects. More effective antihypertensive drugs are therefore required which have excellent tolerability and safety profiles in addition to being efficacious. For those patients who either do not tolerate or wish to take medication for hypertension or in whom BP control is not attained despite multiple antihypertensives, a novel class of interventional procedures to manage hypertension has emerged. While most of these target various aspects of the sympathetic nervous system regulation of BP, an additional procedure is now available, which addresses mechanical aspects of the circulation. Most of these new devices are supported by early and encouraging evidence for both safety and efficacy, although it is clear that more rigorous randomized controlled trial data will be essential before any of the technologies can be adopted as a standard of care.

Urinary Sodium Concentration Is an Independent Predictor of All-Cause and Cardiovascular Mortality in a Type 2 Diabetes Cohort Population

OBJECTIVE

Sodium intake is associated with cardiovascular outcomes. However, no study has specifically reported an association between cardiovascular mortality and urinary sodium concentration (UNa). We examined the association of UNa with mortality in a cohort of type 2 diabetes (T2D) patients.

METHODS

Patients were followed for all-cause death and cardiovascular death. Baseline UNa was measured from second morning spot urinary sample. We used Cox proportional hazard models to identify independent predictors of mortality. Improvement in prediction of mortality by the addition of UNa to a model including known risk factors was assessed by the relative integrated discrimination improvement (rIDI) index.

RESULTS

Participants (n = 1,439) were followed for a median of 5.7 years, during which 254 cardiovascular deaths and 429 all-cause deaths were recorded. UNa independently predicted all-cause and cardiovascular mortality. An increase of one standard deviation of UNa was associated with a decrease of 21% of all-cause mortality and 22% of cardiovascular mortality. UNa improved all-cause and cardiovascular mortality prediction beyond identified risk factors (rIDI = 2.8%, P = 0.04 and rIDI = 4.6%, P = 0.02, resp.).

CONCLUSIONS

In T2D, UNa was an independent predictor of mortality (low concentration is associated with increased risk) and improved modestly its prediction in addition to traditional risk factors.

Effect of renal denervation on kidney function in patients with chronic kidney disease

AIMS

Renal denervation (RDN) can reduce blood pressure (BP) and slow the decline of renal function in chronic kidney disease (CKD) up to one year. Whether this effect is maintained beyond 12months and whether the magnitude of BP reduction affects estimated glomerular filtration rate (eGFR) is unknown.

METHODS AND RESULTS

We examined eGFR in 46 CKD patients (baseline eGFR ≤60mL/min/1.73m²) on a yearly basis from 60months before to 3, 6, 12 and 24months after RDN. Ambulatory BP was measured before and after RDN. Linear mixed models analysis demonstrated a significant progressive decline in eGFR from months 60 to 12months (-15.47±1.98mL/min/1.73m², P<0.0001) and from 12months to baseline prior to RDN (-3.41±1.64mL/min/1.73m², P=0.038). Compared to baseline, RDN was associated with improved eGFR at 3months (+3.73±1.64mL/min/1.73m², P=0.02) and no significant changes at 6 (+2.54±1.66mL/min/1.73m², P=0.13), 12 (+1.78±1.64mL/min/1.73m², P=0.28), and 24 (-0.24±2.24mL/min/1.73m², P=0.91) months post procedure were observed. RDN significantly reduced daytime SBP from baseline to 24months post procedure (148±19 vs 136±17mmHg, P=0.03) for the entire cohort. Changes in SBP were unrelated to the eGFR changes at 6 (r=0.033, P=0.84), 12 (r=0.01, P=0.93) and 24months (r=-0.42, P=0.17) follow-up.

CONCLUSION

RDN can slow further deterioration of renal function irrespective of BP lowering effects in CKD. RDN-induced inhibition of sympathetic outflow to the renal vascular bed may account for improved eGFR via alterations of intrarenal and glomerular hemodynamics.

Oxidative Stress and Hypertensive Diseases

It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.

Anti-Inflammatory Effects and Prediction of Blood Pressure Response by Baseline Inflammatory State in Catheter-Based Renal Denervation

This retrospective analysis aimed to examine off-target effects on inflammatory and renal function parameters in n=78 subsequent patients treated with renal denervation (RDN) for resistant hypertension. Ambulatory and office blood pressure (ABP/OBP), serum creatinine, glomerular filtration rate (GFR), cystatin C, C-reactive protein (CRP), interleukin-6 (IL-6), and white blood cell count (WBC) were assessed before, 6 and 12 months after RDN. ABP was significantly reduced by -8.2/-3.8 mm Hg (P=.002/.021) at 1 year after RDN, while an initial OBP reduction was not sustained during follow-up. IL-6 levels significantly decreased by -0.5 pg/mL (P=.042) and by -1.7 pg/mL (P<.001) at 6 and 12 months, baseline IL-6 levels possibly predicting ABP response to RDN (r=-0.295; P=.020). Concurrently, leukocyte count was reduced by -0.5 × 103 /μL (P=.017) and -0.8 × 103 /μL (P<.001), respectively. Serum creatinine and GFR remained unchanged, but we observed a significant increase in cystatin C by 0.04 mg/L (P=.026) and 0.14 mg/L (P<.001) at 6 and 12 months after the intervention.

Resting Afferent Renal Nerve Discharge and Renal Inflammation: Elucidating the Role of Afferent and Efferent Renal Nerves in Deoxycorticosterone Acetate Salt Hypertension

Renal sympathetic denervation (RDNx) has emerged as a novel therapy for hypertension; however, the therapeutic mechanisms remain unclear. Efferent renal sympathetic nerve activity has recently been implicated in trafficking renal inflammatory immune cells and inflammatory chemokine and cytokine release. Several of these inflammatory mediators are known to activate or sensitize afferent nerves. This study aimed to elucidate the roles of efferent and afferent renal nerves in renal inflammation and hypertension in the deoxycorticosterone acetate (DOCA) salt rat model. Uninephrectomized male Sprague-Dawley rats (275-300 g) underwent afferent-selective RDNx (n=10), total RDNx (n=10), or Sham (n=10) and were instrumented for the measurement of mean arterial pressure and heart rate by radiotelemetry. Rats received 100-mg DOCA (SC) and 0.9% saline for 21 days. Resting afferent renal nerve activity in DOCA and vehicle animals was measured after the treatment protocol. Renal tissue inflammation was assessed by renal cytokine content and T-cell infiltration and activation. Resting afferent renal nerve activity, expressed as a percent of peak afferent nerve activity, was substantially increased in DOCA than in vehicle (35.8±4.4 versus 15.3±2.8 %Amax). The DOCA-Sham hypertension (132±12 mm Hg) was attenuated by ≈50% in both total RDNx (111±8 mm Hg) and afferent-selective RDNx (117±5 mm Hg) groups. Renal inflammation induced by DOCA salt was attenuated by total RDNx and unaffected by afferent-selective RDNx. These data suggest that afferent renal nerve activity may mediate the hypertensive response to DOCA salt, but inflammation may be mediated primarily by efferent renal sympathetic nerve activity. Also, resting afferent renal nerve activity is elevated in DOCA salt rats, which may highlight a crucial neural mechanism in the development and maintenance of hypertension.

What we need to know about renal nerve ablation for treatment of hypertension and other states of sympathetic overactivity

Renal nerves are key players in the regulation of kidney function and blood pressure control. Targeting the neurogenic mechanisms underlying hypertension and cardiac and renal disease has been attempted by means of surgical and pharmacologic approaches and most recently by catheter-based interventions aimed at disrupting renal sympathetic nerve traffic. The recent developments in the area and the relevant questions that need to be addressed to advance the field further are briefly reviewed in this article.

Invasive aortic pulse wave velocity as a marker for arterial stiffness predicts outcome of renal sympathetic denervation

AIMS

A recurrent finding of trials on renal sympathetic denervation is a certain percentage of non-responders. The aim of this study was to examine the influence of arterial stiffness to predict response.

METHODS AND RESULTS

Eighty-eight patients were included in the study. Arterial stiffness was measured by invasive pulse wave velocity. Antihypertensive medication had to be unchanged during follow-up. Ambulatory blood pressure measurement (ABPM) was used to record blood pressure before and six months after denervation. Fifty-eight patients without changes in medication were included in the final analysis. Responders (n=37; blood pressure reduction -12.8±6.4 mmHg) had a significantly lower pulse wave velocity (14.4±4.4 m/s versus 17.7±4.5 m/s; p=0.009) compared to non-responders (n=21; blood pressure reduction +3.0±4.5 mmHg; p<0.001 for comparison with responders). In multivariate analysis, invasive pulse wave velocity was the only significant predictor of blood pressure reduction after denervation (odds ratio 1.15, 95% confidence interval [CI] 1.014-1.327; p=0.03). Patients with increased stiffness were older (p=0.001), had a higher prevalence of diabetes (p=0.008), more often had isolated systolic hypertension (p=0.007), and had a higher invasive pulse pressure (p<0.001).

CONCLUSIONS

Patients with lower pulse wave velocity showed a significantly better response to denervation. These findings emphasise that pulse wave velocity might be used as a selection criterion for renal denervation.

Clinical neurocardiology defining the value of neuroscience-based cardiovascular therapeutics

The autonomic nervous system regulates all aspects of normal cardiac function, and is recognized to play a critical role in the pathophysiology of many cardiovascular diseases. As such, the value of neuroscience-based cardiovascular therapeutics is increasingly evident. This White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology, pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.

Renal Sympathetic Denervation: Hibernation or Resurrection?

The most current versions of renal sympathetic denervation have been invented as minimally invasive approaches for the management of drug-resistant hypertension. The anatomy, physiology and pathophysiology of renal sympathetic innervation provide a strong background supporting an important role of the renal nerves in the regulation of blood pressure (BP) and volume. In addition, historical data with surgical sympathectomy and experimental data with surgical renal denervation indicate a beneficial effect on BP levels. Early clinical studies with transcatheter radiofrequency ablation demonstrated impressive BP reduction, accompanied by beneficial effects in target organ damage and other disease conditions characterized by sympathetic overactivity. However, the failure of the SYMPLICITY 3 trial to meet its primary efficacy end point raised a lot of concerns and put the field of renal denervation into hibernation. This review aims to translate basic research into clinical practice by presenting the anatomical and physiological basis for renal sympathetic denervation, critically discussing the past and present knowledge in this field, where we stand now, and also speculating about the future of the intervention and potential directions for research.

Blood Pressure: Return of the Sympathetics?

This brief review highlights new ideas about the role of the sympathetic nervous system in human blood pressure regulation. We emphasize how this role varies with age and sex and use our findings to raise questions about the sympathetic nervous system and hypertension in humans. We also focus on three additional areas, including (1) novel ideas about the carotid body and sympathoexcitation as it relates to hypertension, (2) clinical trials of renal denervation that attempted to treat hypertension by reducing ongoing sympathoexcitation, and (3) new ideas about resistant hypertension and cerebral blood flow. We further highlight that success of device-based therapy to modulate the sympathetic nervous system relies heavily on patient selection. Furthermore, data suggest that the majority of patients respond to anti-hypertensive therapy and the major cause of "resistant" hypertension is poor patient adherence. While the enthusiasm for device therapy or perhaps even "precision medicine" is high, it is likely that by far the most benefit to the most patients will occur via better screening, more aggressive therapy, and the development of strategies that improve patient adherence to medication regimens and lifestyle changes.

Renal denervation in hypertensive patients not on blood pressure lowering drugs

Introduction

Studies on the blood pressure lowering effect of renal denervation (RDN) in resistant hypertensive patients have produced conflicting results. Change in medication usage during the studies may be responsible for this inconsistency. To eliminate the effect of medication usage on blood pressure we focused on unmedicated hypertensive patients who underwent RDN.

Methods and results

Our study reports on a cohort of patients, who were not on blood pressure lowering drugs at baseline and during follow-up, from eight tertiary centers. Data of patients were used when they were treated with RDN and had a baseline office systolic blood pressure (SBP) ≥140 mmHg and/or 24-h ambulatory SBP ≥130 mmHg. Our primary outcome was defined as change in office and 24-h SBP at 12 months after RDN, compared to baseline. Fifty-three patients were included. There were three different reasons for not using blood pressure lowering drugs: (1) documented intolerance or allergic reaction (57 %); (2) temporary cessation of medication for study purposes (28 %); and (3) reluctance to take antihypertensive drugs (15 %). Mean change in 24-h SBP was −5.7 mmHg [95 % confidence interval (CI) −11.0 to −0.4; p = 0.04]. Mean change in office SBP was −13.1 mmHg (95 % CI −20.4 to −5.7; p = 0.001). No changes were observed in other variables, such as eGFR, body–mass-index and urinary sodium excretion.

Conclusion

This explorative study in hypertensive patients, who are not on blood pressure lowering drugs, suggests that at least in some patients RDN lowers blood pressure.

Electronic supplementary material

The online version of this article (doi:10.1007/s00392-016-0984-y) contains supplementary material, which is available to authorized users.

The blood pressure-lowering effect of renal denervation is inversely related to kidney function

OBJECTIVES

In renal denervation (RDN), a wide range in the blood pressure (BP)-lowering effect has been reported. On the basis of the current knowledge of pathophysiology, we hypothesized that the BP-lowering effect of RDN would be inversely related to kidney function. Second, we investigated whether direct and indirect variables of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS) would be related as well.

METHODS

Sixty-seven patients from a prospective cohort of patients treated with RDN with completed 6 months follow-up were included. Data collected during routine standardized work-up before RDN were used: 24-h urine excretion of creatinine, albumin, sodium and catecholamines, plasma creatinine, renin activity and aldosterone, ambulatory BP-monitoring and a captopril challenge test. When considered well tolerated, antihypertensive drugs were stopped before these investigations.

RESULTS

The BP-lowering was inversely related to estimated glomerular filtration rate (eGFR) in patients who stopped antihypertensive drugs prior to testing (ß: 0.46, P = 0.013). There was a positive relation between SBP at baseline and the BP-lowering effect of RDN (ß:-0.55 mmHg per mmHg, P < 0.001). Parameters related to the rennin-angiotensin system (aldosterone, captopril test) and the sympathetic nervous system (dipping pattern and catecholamines in urine) positively related to the BP-lowering effect of RDN.

CONCLUSION

The present explorative study shows an inverse relation between the BP-lowering effect of RDN and eGFR. Second, we found relations between variables of the RAAS and SNS with the BP-lowering effect of RDN. The data complement current concepts on pathophysiology of sympathetic hyperactivity and hypertension and may give some insight in the wide range of the effect of RDN.

New insights into sodium transport regulation in the distal nephron: Role of G-protein coupled receptors

The renal handling of Na⁺ balance is a major determinant of the blood pressure (BP) level. The inability of the kidney to excrete the daily load of Na⁺ represents the primary cause of chronic hypertension. Among the different segments that constitute the nephron, those present in the distal part (i.e., the cortical thick ascending limb, the distal convoluted tubule, the connecting and collecting tubules) play a central role in the fine-tuning of renal Na⁺ excretion and are the target of many different regulatory processes that modulate Na⁺ retention more or less efficiently. G-protein coupled receptors (GPCRs) are crucially involved in this regulation and could represent efficient pharmacological targets to control BP levels. In this review, we describe both classical and novel GPCR-dependent regulatory systems that have been shown to modulate renal Na⁺ absorption in the distal nephron. In addition to the multiplicity of the GPCR that regulate Na⁺ excretion, this review also highlights the complexity of these different pathways, and the connections between them.

Complex reinnervation pattern after unilateral renal denervation in rats

Renal denervation (DNX) is a treatment for resistant arterial hypertension. Efferent sympathetic nerves regrow, but reinnervation by renal afferent nerves has only recently been shown in the renal pelvis of rats after unilateral DNX. We examined intrarenal perivascular afferent and sympathetic efferent nerves after unilateral surgical DNX. Tyrosine hydroxylase (TH), CGRP, and smooth muscle actin were identified in kidney sections from 12 Sprague-Dawley rats, to distinguish afferents, efferents, and vasculature. DNX kidneys and nondenervated kidneys were examined 1, 4, and 12 wk after DNX. Tissue levels of CGRP and norepinephrine (NE) were measured with ELISA and mass spectrometry, respectively. DNX decreased TH and CGRP labeling by 90% and 95%, respectively (P < 0.05) within 1 wk. After 12 wk TH and CGRP labeling returned to baseline with a shift toward afferent innervation (P < 0.05). Nondenervated kidneys showed a doubling of both labels within 12 wk (P < 0.05). CGRP content decreased by 72% [3.2 ± 0.3 vs. 0.9 ± 0.2 ng/gkidney; P < 0.05] and NA by 78% [1.1 ± 0.1 vs. 0.2 ± 0.1 pmol/mgkidney; P < 0.05] 1 wk after DNX. After 12 wk, CGRP, but not NE, content in DNX kidneys was fully recovered, with no changes in the nondenervated kidneys. The use of phenol in the DNX procedure did not influence this result. We found morphological reinnervation and transmitter recovery of afferents within 12 wk after DNX. Despite morphological evidence of sympathetic regrowth, NE content did not fully recover. These results suggest a long-term net surplus of afferent influence on the DNX kidney may be contributing to the blood pressure lowering effect of DNX.

Does sympathetic overactivation feature all hypertensives? Differences of sympathovagal balance according to night/day blood pressure ratio in patients with essential hypertension

When evaluating the 'night/day BP ratio', both hypertensives and normotensives can be arbitrarily classified into four groups: extreme dippers (ratio ⩽0.8), dippers (0.8<ratio ⩽0.9), mild dippers (0.9<ratio⩽1.0) and reverse dippers (ratio ⩾1.0). Reverse and mild dipper hypertensives have poorer prognoses compared with the physiological dipper profile, but the prognostic relevance of the extreme dipper profile remains uncertain. The evaluation of heart rate variability (HRV), obtained by 24-h Holter ECG monitoring, is the most frequently used noninvasive form of assessment of the activity of the autonomic nervous system. Reverse and mild dipper hypertensives have reduced HRV, indicating an overactivation of the sympathetic nervous system (SNS); however, the HRV behavior in extreme dippers is still controversial. The goal of this study was to compare HRV indexes of extreme vs. reverse dipper essential hypertensives measured on the basis of time domains. We enrolled 125 hypertensive subjects, divided in 4 quartiles according to day/night blood pressure (BP) ratios. The upper and lower quartiles (31 subjects per quartile) were compared; 30 normotensive subjects were enrolled as a control group. Time domain HRV parameters of the three groups revealed a higher degree of sympathetic activation in the lower quartile (reverse dipper) vs. the upper quartile (extreme) and normotensive controls. HRV parameters related to parasympathetic tone did not show any significant variations among the three groups. Contrary to common belief, not all hypertensives have SNS overactivation.

Renal denervation therapy for hypertension: pathways for moving development forward

This scientific statement provides a summary of presentations and discussions at a cardiovascular Think Tank co-sponsored by the American Society of Hypertension (ASH), the United States Food and Drug Administration (FDA), and the National Heart, Lung, and Blood Institute (NHLBI) held in North Bethesda, Maryland, on June 26, 2014. Studies of device therapies for the treatment of hypertension are requested by regulators to evaluate their safety and efficacy during their development programs. Think Tank participants thought that important considerations in undertaking such studies were: (1) Preclinical assessment: how likely it is that both efficacy and safety data indicating benefit in humans will be obtained, and/or whether a plausible mechanism of action for efficacy can be identified; (2) Early human trial(s): the ability to determine that the device has an acceptable benefit-to-risk balance for its use in the intended patient population and without the influence of drug therapy during a short-term follow-up period; and (3) Pivotal Phase III trial(s): the ability to prove the effectiveness of the device in a broad population in which the trial can be made as non-confounded as possible while still allowing for the determination for benefits when added to antihypertensive therapies.

The rise, fall, and possible resurrection of renal denervation

Renal denervation has a chequered history. Dramatic reductions in blood pressure after denervation of the renal arteries were observed in early trials, but later trials in which denervation was tested against a sham procedure produced neutral results. Although a sound pathophysiological basis exists for interruption of the renal sympathetic nervous system as a treatment for hypertension, trial data to date are insufficient to support renal denervation as an established clinical therapy. In this Perspectives article, we summarize the currently available trial data, device development, and trials in progress, and provide recommendations for future trial design.

Renal denervation: Not as easy as it looks

Renal sympathetic denervation with intravascular radiofrequency catheters in hypertensive patients is less effective than anticipated, owing to radio frequency energy being applied to a part of the renal artery where the nerves are at the greatest distance from the aortic lumen and to distortion of energy distribution and temperature gradients by regional tissue anatomical variations (Tzafriri et al., this issue).

Drug resistant hypertension – no simple way out

Hypertension poses growing challenge for health policy-makers and doctors worldwide. Recently published results of Symplicity-III trial (HTN-3), the first blinded, randomized, multicenter study on the efficacy of renal denervation for the treatment of resistant hypertension did not show a significant reduction of BP in patients with resistant hypertension 6 months after renal-artery denervation, as compared with controls. In this paper we review clinical and experimental studies on renal denervation. In order to identify causes of inconsistent results in renal denervation studies we look at basic science support for renal denervation and at designs of clinical trials.

Retrospective morphometric study of the suitability of renal arteries for renal denervation according to the Symplicity HTN2 trial criteria

OBJECTIVE

The aim of this study was to describe the renal arteries of humans in vivo, as precisely as possible, and to formulate an expected value for the exclusion of renal denervation due to the anatomical situation based on the criteria of the Symplicity HTN trials.

DESIGN AND SETTING

In a retrospective cohort study, the renal arteries of 126 patients (57 women, 69 men, mean age 60 ± 17.2 years (CI 57.7 to 63.6)) were segmented semiautomatically from high-contrast CT angiographies.

RESULTS

Among the 300 renal arteries, there were three arteries with fibromuscular dysplasia and one with ostial renal artery stenosis. The first left renal artery was shorter than the right (34 ± 11.4 mm (CI 32 to 36) vs 45.9 ± 15 mm (CI 43.2 to 48.6); p<0.0001), but had a slightly larger diameter (5.2 ± 1.4 mm (CI 4.9 to 5.4) vs 4.9 ± 1.2 mm (CI 4.6 to 5.1); p>0.05). The first left renal arteries were 1.1 ± 0.4 mm (CI 0.9 to 1.3), and the first right renal arteries were 0.3 ± 0.6 mm (CI 0.1 to 0.5) thinner in women than in men (p<0.05). Ostial funnels were up to 14 mm long. The cross-sections were elliptical, more pronounced on the right side (p<0.05). In 23 cases (18.3%), the main artery was shorter than 2 cm; in 43 cases (34.1%), the diameter was not >4 mm. Some 46% of the patients, or 58.7% when variants and diseases were taken into consideration, were theoretically not suitable for denervation.

CONCLUSIONS

Based on these precise measurements, the anatomical situation as a reason for ruling out denervation appears to be significantly more common than previously suspected. Since this can be the cause of the failure of treatment in some cases, further development of catheters or direct percutaneous approaches may improve success rates.

The SPYRAL HTN Global Clinical Trial Program: Rationale and design for studies of renal denervation in the absence (SPYRAL HTN OFF-MED) and presence (SPYRAL HTN ON-MED) of antihypertensive medications

Renal sympathetic activation plays a key role in the pathogenesis of hypertension, as demonstrated by high renal norepinephrine spillover into plasma of patients with essential hypertension. Renal denervation has demonstrated a significant reduction in blood pressure in unblinded studies of hypertensive patients. The SYMPLICITY HTN-3 trial, the first prospective, masked, randomized study of renal denervation versus sham control, failed its primary efficacy end point and raised important questions around potentially confounding factors, such as drug changes and adherence, study population, and procedural methods. The SPYRAL HTN Global Clinical Trial Program is designed to address limitations associated with predicate studies and provide insight into the impact of pharmacotherapy on renal denervation efficacy. The 2 initial trials of the program focus on the effect of renal denervation using the Symplicity Spyral multielectrode renal denervation catheter in hypertensive patients in the absence (SPYRAL HTN OFF-MED) and presence (SPYRAL HTN ON-MED) of antihypertensive medications. The SPYRAL HTN ON-MED study requires patients to be treated with a consistent triple therapy antihypertensive regimen, whereas the SPYRAL HTN OFF-MED study includes a 3- to 4-week drug washout period followed by a 3-month efficacy and safety end point in the absence of antihypertensive medications. The studies will randomize patients with combined systolic-diastolic hypertension to renal denervation or sham procedure. Both studies allow renal denervation treatments in renal artery branches and accessories. These studies will inform the design of the second pivotal phase of the program, which will more definitively analyze the antihypertensive effect of renal denervation.

Prevalence and predictors of asymmetric hypertensive heart disease: insights from cardiac and aortic function with cardiovascular magnetic resonance

AIMS

We sought to determine the prevalence of asymmetric hypertensive heart disease (HHD) overlapping morphologically with hypertrophic cardiomyopathy (HCM) and to determine predictors of this pattern of hypertensive remodelling.

METHODS AND RESULTS

One hundred and fifty hypertensive patients underwent 1.5 T cardiovascular magnetic resonance imaging. Twenty-one patients were excluded due to concomitant cardiac pathology that may confound the hypertrophic response, e.g. myocardial infarction, moderate-severe valvular disease, or other cardiomyopathy. Asymmetric HHD was defined as a segmental wall thickness of ≥15 mm and >1.5-fold the opposing wall in ≥1 myocardial segments, measured from short-axis cine stack at end-diastole. Ambulatory blood pressure, myocardial replacement fibrosis, aortic distensibility and aortoseptal angle were investigated as predictors of asymmetric HHD by multivariate logistic regression. Out of 129 hypertensive subjects (age: 51 ± 15 years, 50% male, systolic blood pressure: 170 ± 30 mmHg, diastolic blood pressure: 97 ± 16 mmHg), asymmetric HHD occurred in 21%. Where present, maximal end-diastolic wall thickness (EDWT) was 17.8 ± 1.9 mm and located exclusively in the basal or mid septum. In asymmetric HHD, aortoseptal angle (114 ± 10° vs. 125 ± 9° vs. 123 ± 12°, P < 0.05, respectively) was significantly reduced compared to concentric left ventricular hypertrophy (LVH) and compared to no LVH, respectively. Aortic distensibility in asymmetric HHD (1.01 ± 0.60 vs. 1.83 ± 1.65 mm²/mmHg × 10³, P < 0.05, respectively) was significantly reduced compared to subjects with no LVH. Age (odds ratio [95th confidence interval]: 1.10 [1.02-1.18], P < 0.05) and indexed LV mass (1.09 [0.98-1.28], P < 0.0001) were significant, independent predictors of asymmetric HDD.

CONCLUSIONS

Asymmetric HHD morphologically overlapping with HCM, according to the current ESC guidelines, is common. Postulating a diagnosis of HCM on the basis of EDWT of ≥15 mm should be made with caution in the presence of arterial hypertension particular in male subjects with elevated LV mass.

Renal denervation for the management of resistant hypertension

Renal sympathetic denervation (RSD) as a therapy for patients with resistant hypertension has attracted great interest. The majority of studies in this field have demonstrated impressive reductions in blood pressure (BP). However, these trials were not randomized or sham-controlled and hence, the findings may have been overinflated due to trial biases. SYMPLICITY HTN-3 was the first randomized controlled trial to use a blinded sham-control and ambulatory BP monitoring. A surprise to many was that this study was neutral. Possible reasons for this neutrality include the fact that RSD may not be effective at lowering BP in man, RSD was not performed adequately due to limited operator experience, patients’ adherence with their anti-hypertensive drugs may have changed during the trial period, and perhaps the intervention only works in certain subgroups that are yet to be identified. Future studies seeking to demonstrate efficacy of RSD should be designed as randomized blinded sham-controlled trials. The efficacy of RSD is in doubt, but many feel that its safety has been established through the thousands of patients in whom the procedure has been performed. Over 90% of these data, however, are for the Symplicity™ system and rarely extend beyond 12 months of follow-up. Long-term safety cannot be assumed with RSD and nor should it be assumed that if one catheter system is safe then all are. We hope that in the near future, with the benefit of well-designed clinical trials, the role of renal denervation in the management of hypertension will be established.

Renal denervation mitigates cardiac remodeling and renal damage in Dahl rats: a comparison with β-receptor blockade

Chronic activation of the sympathetic nervous system (SNS) contributes to cardiac remodeling and the transition to heart failure (HF). Renal sympathetic denervation (RDN) may ameliorate this damage by improving renal function and sympathetic cardioregulation in hypertensive HF patients with renal injury. The efficacy may be comparable to that of chronic β-blocker treatment. Dahl salt-sensitive hypertensive rats were subjected to RDN in the hypertrophic stage. Another group of Dahl rats were subjected to sham operations and treated chronically with vehicle (CONT) or β-blocker bisoprolol (BISO). Neither RDN nor BISO altered the blood pressure; however, BISO significantly reduced the heart rate (HR). Both RDN and BISO significantly prolonged survival (22.2 and 22.4 weeks, respectively) compared with CONT (18.3 weeks). Echocardiography revealed reduced left ventricular (LV) hypertrophy and improved LV function, and histological analysis demonstrated the amelioration of LV myocyte hypertrophy and fibrosis in the RDN and BISO rats at the HF stage. Tyrosine hydroxylase and β1-adrenergic receptor (ADR) expression levels in the LV myocardium significantly increased only in the RDN rats, whereas the α1b-, α1d- and α2c-ADR expression levels increased only in the BISO rats. In both groups, renal damage and dysfunction were also reduced, and this reduction was accompanied by the suppression of endothelin-1, renin and angiotensin-converting enzyme mRNAs. RDN ameliorated the progression of both myocardial and renal damage in the hypertensive rats independent of blood pressure changes. The overall effects were similar to those of β-receptor blockade with favorable effects on HR and α-ADR expression. These findings may be associated with the restoration of the myocardial SNS and renal protection.

Brain Gαi 2 -subunit proteins and the prevention of salt sensitive hypertension

To counter the development of salt-sensitive hypertension, multiple brain G-protein-coupled receptor (GPCR) systems are activated to facilitate sympathoinhibition, sodium homeostasis, and normotension. Currently there is a paucity of knowledge regarding the role of down-stream GPCR-activated Gα-subunit proteins in these critically important physiological regulatory responses required for long-term blood pressure regulation. We have determined that brain Gαi₂-proteins mediate natriuretic and sympathoinhibitory responses produced by acute pharmacological (exogenous central nociceptin/orphanin FQ receptor (NOP) and α₂-adrenoceptor activation) and physiological challenges to sodium homeostasis (intravenous volume expansion and 1 M sodium load) in conscious Sprague–Dawley rats. We have demonstrated that in salt-resistant rat phenotypes, high dietary salt intake evokes site-specific up-regulation of hypothalamic paraventricular nucleus (PVN) Gαi₂-proteins. Further, we established that PVN Gαi₂ protein up-regulation prevents the development of renal nerve-dependent sympathetically mediated salt-sensitive hypertension in Sprague–Dawley and Dahl salt-resistant rats. Additionally, failure to up-regulate PVN Gαi₂ proteins during high salt-intake contributes to the pathophysiology of Dahl salt-sensitive (DSS) hypertension. Collectively, our data demonstrate that brain, and likely PVN specific, Gαi₂ protein pathways represent a central molecular pathway mediating sympathoinhibitory renal-nerve dependent responses evoked to maintain sodium homeostasis and a salt-resistant phenotype. Further, impairment of this endogenous “anti-hypertensive” mechanism contributes to the pathophysiology of salt-sensitive hypertension.

The future of renal denervation in resistant hypertension

Resistant hypertension, defined as inadequate blood pressure control despite three or more antihypertensive medications at maximally tolerated doses, is strongly linked to increased cardiovascular morbidity and mortality. Increased renal afferent and efferent sympathetic activity carried by nerves which arborize the adventitia of the renal arteries, appears to be central to the pathobiology of resistant hypertension. Historical experience indicates that surgical denervation and/or sympathectomy often dramatically reduced blood pressure in patients with malignant hypertension. Catheter-based radio-frequency renal denervation was developed in the past decade as a percutaneous adaptation of surgical denervation. Percutaneous renal denervation using a variety of systems has demonstrated to date, in non-randomized and unblinded studies, dramatic reductions in office-based blood pressure, but more modest impact on ambulatory blood pressure. The only single, appropriately powered, blinded, sham-controlled study of renal denervation conducted to date, however, failed to meet its primary endpoint, casting doubt on the value of the therapy. Ancillary benefits of renal denervation have been described in such conditions as diabetes mellitus, heart failure, and sleep apnea but require further study. While renal denervation is already widely available outside of the USA for commercial use, its utility in resistant hypertension must be vetted by further rigorous investigation before its use can be routinely recommended.

Renal Denervation Prevents Immune Cell Activation and Renal Inflammation in Angiotensin II-Induced Hypertension

RATIONALE

Inflammation and adaptive immunity play a crucial role in the development of hypertension. Angiotensin II and probably other hypertensive stimuli activate the central nervous system and promote T-cell activation and end-organ damage in peripheral tissues.

OBJECTIVE

To determine if renal sympathetic nerves mediate renal inflammation and T-cell activation in hypertension.

METHODS AND RESULTS

Bilateral renal denervation using phenol application to the renal arteries reduced renal norepinephrine levels and blunted angiotensin II-induced hypertension. Bilateral renal denervation also reduced inflammation, as reflected by decreased accumulation of total leukocytes, T cells, and both CD4+ and CD8+ T cells in the kidney. This was associated with a marked reduction in renal fibrosis, albuminuria, and nephrinuria. Unilateral renal denervation, which partly attenuated blood pressure, only reduced inflammation in the denervated kidney, suggesting that this effect is pressure independent. Angiotensin II also increased immunogenic isoketal-protein adducts in renal dendritic cells (DCs) and increased surface expression of costimulation markers and production of interleukin (IL)-1α, IL-1β, and IL-6 from splenic DCs. Norepinephrine also dose dependently stimulated isoketal formation in cultured DCs. Adoptive transfer of splenic DCs from angiotensin II-treated mice primed T-cell activation and hypertension in recipient mice. Renal denervation prevented these effects of hypertension on DCs. In contrast to these beneficial effects of ablating all renal nerves, renal afferent disruption with capsaicin had no effect on blood pressure or renal inflammation.

CONCLUSIONS

Renal sympathetic nerves contribute to DC activation, subsequent T-cell infiltration and end-organ damage in the kidney in the development of hypertension.

Frequency of renal artery stenosis after renal denervation in patients with resistant arterial hypertension

Catheter-based ablation of nerves in the adventitia of renal arteries (renal artery denervation [RAD]) using radiofrequency energy can reduce blood pressure (BP) in patients with resistant arterial hypertension (RAH). Occurrence of renal artery stenosis after RAD is still an important concern. We systematically investigated the renal artery anatomy using magnetic resonance imaging (MRI) or computed tomography (CT) angiography in a consecutive series of patients 6 months after RAD. Patients with RAH were treated by RAD after exclusion of secondary causes of hypertension. RAH was defined by a mean systolic office BP >160 mm Hg. Renal artery imaging was performed 6 months after RAD by MRI angiography. In case of any contraindication for MRI, a CT angiography was performed. The primary end point was the incidence of significant renal artery stenosis (≥70% lumen diameter reduction). RAD was performed in 76 patients, and evaluation of renal artery anatomy by MRI (n = 66; 87%) or CT angiography (n = 10; 13%) was performed in all patients 6 months after RAD. We found no renal artery stenosis but 2 cases of new nonsignificant stenosis (50% TO 69% lumen diameter reduction). In responders, mean systolic office BP reduction was -30 mm Hg (p <0.001) and mean systolic 24-hour BP reduction was -18 mm Hg (p <0.001). In conclusion, the incidence of significant renal artery stenosis 6 months after RAD seems to be very low. However, late-onset development of nonsignificant renal artery narrowing cannot be excluded in some patients and should be anticipated in the case of RAH relapse or worsening of renal function after successful RAD.

Influence of pseudo-resistance on the effect of renal denervation on 24-hour ambulatory blood pressure levels

BACKGROUND

Renal denervation (RDN) is a promising treatment option in addition to medical antihypertensive treatment in patients suffering from resistant hypertension. Despite the growing interest in RDN, the negative result of the Symplicity HTN-3 trial led to a debate on the efficacy of RDN.

METHODS

We systematically investigated the effects of RDN, evaluated by 24-hr ambulatory blood pressure measurements (ABPM), in a consecutive series of patients with resistant hypertension, which was defined by a mean office systolic blood pressure (SBP) >160 mm Hg (>150 mm Hg in patients with diabetes). Patients with a mean 24-hr SBP of less than 130 mm Hg at baseline were classified as pseudo-resistant, while all other patients were classified as true-resistant. After six months, we analyzed the response rates in true-resistant and in pseudo-resistant patients, respectively, by the means of 24-hr ABPM. Thereby, patients with a reduction of more than 5 mm Hg in 24-hr SBP were classified as responders.

RESULTS

RDN was performed in 106 patients. By 24-hr ABPM, 20 patients (18.9%) were classified as pseudo-resistant patients. In this cohort, we only found two responders (response rate 10%) six months after RDN. By contrast, in true-resistant patients, the response rate was almost 60% and the mean BP reduction was -18.6/-9 mm Hg in 24-hr ABPM.

CONCLUSIONS

We found a significant BP reduction in almost 60% of patients with true-resistant hypertension, but only in 10% in patients with pseudo-resistant hypertension. According to our results, patient selection seems to be crucial for acceptable response rates after RDN.

The Renin-Angiotensin and Renal Dopaminergic Systems Interact in Normotensive Humans

The renin-angiotensin-aldosterone (RAAS) and renal dopaminergic systems interact to maintain sodium balance. High NaCl intake increases renal synthesis of dopamine and dopaminergic receptor activity, decreasing epithelial sodium transport, whereas sodium deficit activates the RAAS, increasing epithelial sodium transport. We tested the hypothesis that attenuation of the natriuretic effect of dopamine D1-like receptors during salt restriction results in part from increased RAAS activity in seven salt-resistant normotensive adults using a double-blind placebo-controlled balanced crossover design. All subjects attained sodium balance on low (50 mmol Na(+)/day) and high (300 mmol Na(+)/day) NaCl diets, administered 4 weeks apart. Sodium, potassium, lithium, para-aminohippurate, and creatinine clearances were measured before, during, and after a 3-hour infusion of fenoldopam, a D1-like receptor agonist, with and without pretreatment with enalapril, an angiotensin converting enzyme inhibitor. On the high NaCl diet, fenoldopam-induced natriuresis was associated with the inhibition of renal proximal and distal tubule sodium transport. On the low NaCl diet, fenoldopam decreased renal distal tubule sodium transport but did not cause natriuresis. The addition of enalapril to fenoldopam restored the natriuretic effect of fenoldopam and its inhibitory effect on proximal tubule sodium transport. Thus, on a high NaCl diet fenoldopam causes natriuresis by inhibiting renal proximal and distal tubule transport, but on a low NaCl diet the increased RAAS activity prevents the D1-like receptor from inhibiting renal proximal tubule sodium transport, neutralizing the natriuretic effect of fenoldopam. These results demonstrate an interaction between the renin-angiotensin and renal dopaminergic systems in humans and highlight the influence of dietary NaCl on these interactions.

The sympathetic/parasympathetic imbalance in heart failure with reduced ejection fraction

Cardiovascular autonomic imbalance, a cardinal phenotype of human heart failure, has adverse implications for symptoms during wakefulness and sleep; for cardiac, renal, and immune function; for exercise capacity; and for lifespan and mode of death. The objectives of this Clinical Review are to summarize current knowledge concerning mechanisms for disturbed parasympathetic and sympathetic circulatory control in heart failure with reduced ejection fraction and its clinical and prognostic implications; to demonstrate the patient-specific nature of abnormalities underlying this common phenotype; and to illustrate how such variation provides opportunities to improve or restore normal sympathetic/parasympathetic balance through personalized drug or device therapy.

SYMPLICITY HTN-Japan - First Randomized Controlled Trial of Catheter-Based Renal Denervation in Asian Patients -

BACKGROUND

SYMPLICITY HTN-Japan is a prospective, randomized, controlled trial comparing renal artery denervation (RDN) with standard pharmacotherapy for treatment of resistant hypertension (systolic blood pressure [SBP] ≥160 mmHg on ≥3 anti-hypertensive drugs including a diuretic for ≥6 weeks). When SYMPLICITY HTN-3 failed to meet the primary efficacy endpoint, the HTN-Japan enrollment was discontinued before completion. METHODS AND RESULTS: The 6-month change in office and 24-h ambulatory SBP were compared between RDN (n=22) and control (n=19) subjects. Mean baseline office SBP was 181.0±18.0 mmHg and 178.7±17.8 mmHg for the RDN and control groups, respectively. The 6-month office SBP change was -16.6±18.5 mmHg for RDN subjects (P<0.001) and -7.9±21.0 mmHg for control subjects (P=0.117); the difference between the 6-month change in RDN and control subjects was -8.64 (95% CI: -21.12 to 3.84, P=0.169). Mean 24-h SBP was 164.7±18.3 (RDN group) and 163.3±17.2 mmHg (control group). The 24-h 6-month SBP change for the RDN group was -7.52±11.98 mmHg (P=0.008) and -1.38±10.2 mmHg (P=0.563) for control subjects; the between-group difference in SBP change was -6.15 (95% CI: -13.23 to 0.94, P=0.087). No major adverse events were reported.

CONCLUSIONS

SYMPLICITY HTN-Japan, the first randomized controlled trial of RDN in an Asian population, was underpowered for the primary endpoint analysis and did not demonstrate a significant difference in 6-month BP change between RDN and control subjects.