Renal Denervation Update From the International Sympathetic Nervous System Summit

The current status of renal denervation for the treatment of arterial hypertension

Despite the availability of safe and effective antihypertensive drugs, blood pressure (BP) control to guideline-recommended target values is poor. Several device-based therapies have been introduced to lower BP. The most extensively investigated approach is catheter-based renal sympathetic denervation (RDN), which aims to interrupt the activity of afferent and efferent renal sympathetic nerves by applying radiofrequency energy, ultrasound energy, or injection of alcohol in the perivascular space. The second generation of placebo-controlled trials have provided solid evidence for the BP-lowering efficacy of radiofrequency- and ultrasound-based RDN in patients with and without concomitant pharmacological therapy. In addition, the safety profile of RDN appears to be excellent in all registries and clinical trials. However, there remain unsolved issues to be addressed. This review summarizes the rationale as well as the current evidence and discusses open questions and possible future indications of catheter-based RDN.

Function of Renal Nerves in Kidney Physiology and Pathophysiology

Renal sympathetic (efferent) nerves play an important role in the regulation of renal function, including glomerular filtration, sodium reabsorption, and renin release. The kidney is also innervated by sensory (afferent) nerves that relay information to the brain to modulate sympathetic outflow. Hypertension and other cardiometabolic diseases are linked to overactivity of renal sympathetic and sensory nerves, but our mechanistic understanding of these relationships is limited. Clinical trials of catheter-based renal nerve ablation to treat hypertension have yielded promising results. Therefore, a greater understanding of how renal nerves control the kidney under physiological and pathophysiological conditions is needed. In this review, we provide an overview of the current knowledge of the anatomy of efferent and afferent renal nerves and their functions in normal and pathophysiological conditions. We also suggest further avenues of research for development of novel therapies targeting the renal nerves.

A Systematic Review of Randomized Controlled Trials Comparing Renal Sympathetic Denervation Versus Sham Procedure for the Management of Uncontrolled Hypertension

ABSTRACT

The efficacy of renal sympathetic denervation (RSD) in the treatment of uncontrolled hypertension (HTN) remains uncertain. A systematic review of randomized controlled trials was performed to evaluate the efficacy and safety of RSD for resistant HTN. PubMed, EMBASE, MEDLINE, Cochrane, Directory of Open Access Journals, CINAHL, and Google Scholar were searched from January 01, 2001, through July 30, 2020. Randomized controlled trials comparing RSD with the sham procedure for uncontrolled HTN were selected. The primary efficacy outcome was the reduction in ambulatory systolic blood pressure. We used random-effects models. Nine prospective clinical trials met the inclusion criteria. The ReSet and Symplicity HTN-3 Trial showed no significant changes because of discrepancies in complete circumferential ablation during RSD. The Relief study, The Radiance HTN solo, and the SPYRAL HTN OFF medical trials showed a significant reduction in systolic blood pressure in the group that had undergone the intervention compared with the sham group attributed to rigorous trial design. In conclusion, our systematic review suggests that efficacy of RSD seems to be superior to sham-controlled interventions provided circumferential denervation is performed. However, difference in efficacy is marginal.

Renal Denervation and Celiac Ganglionectomy Decrease Mean Arterial Pressure Similarly in Genetically Hypertensive Schlager (BPH/2J) Mice

Supplemental Digital Content is available in the text.

Renal denervation (RDNX) lowers mean arterial pressure (MAP) in patients with resistant hypertension. Less well studied is the effect of celiac ganglionectomy (CGX), a procedure which involves the removal of the nerves innervating the splanchnic vascular bed. We hypothesized that RDNX and CGX would both lower MAP in genetically hypertensive Schlager (BPH/2J) mice through a reduction in sympathetic tone. Telemeters were implanted into the femoral artery in mice to monitor MAP before and after RDNX (n=5), CGX (n=6), or SHAM (n=6). MAP, systolic blood pressure, diastolic blood pressure, and heart rate were recorded for 14 days postoperatively. The MAP response to hexamethonium (10 mg/kg, IP) was measured on control day 3 and postoperative day 10 as a measure of global neurogenic pressor activity. The efficacy of denervation was assessed by measurement of tissue norepinephrine. Control MAP was similar among the 3 groups before surgical treatments (≈130 mm Hg). On postoperative day 14, MAP was significantly lower in RDNX (−11±2 mm Hg) and CGX (−11±1 mm Hg) groups compared with their predenervation values. This was not the case in SHAM mice (−5±3 mm Hg). The depressor response to hexamethonium in the RDNX group was significantly smaller on postoperative day 10 (−10±5 mm Hg) compared with baseline control (−25±10 mm Hg). This was not the case in mice in the SHAM (day 10; −28±5 mm Hg) or CGX (day 10; −34±7 mm Hg) group. In conclusion, both renal and splanchnic nerves contribute to hypertension in BPH/2J mice, but likely through different mechanisms.

Impact of anesthesia, sex, and circadian cycle on renal afferent nerve sensitivity

Elevated renal afferent nerve (ARNA) activity or dysfunctional reno-renal reflexes via altered ARNA sensitivity contribute to hypertension and chronic kidney disease. These nerves contain mechano- and chemosensitive fibers that respond to ischemia, changes in intrarenal pressures, and chemokines. Most studies have utilized various anesthetized preparations and exclusively male animals to characterize ARNA responses. Therefore, this study assessed the impact of anesthesia, sex, and circadian period on ARNA responses and sensitivity. Multifiber ARNA recordings were performed in male and female Sprague-Dawley rats (250-400 g) and compared across decerebrate versus Inactin, isoflurane, and urethane anesthesia groups. Intrarenal artery infusion of capsaicin (0.1-50.0 μM, 0.05 mL) produced concentration-dependent increases in ARNA; however, the ARNA sensitivity was significantly greater in decerebrate versus Inactin, isoflurane, and urethane groups. Increases in renal pelvic pressure (0-30 mmHg, 30 s) produced pressure-dependent increases in ARNA; however, ARNA sensitivity was again greater in decerebrate and Inactin groups versus isoflurane and urethane. Acute renal artery occlusion (30 s) increased ARNA, but responses did not differ across groups. Analysis of ARNA responses to increased pelvic pressure between male and female rats revealed significant sex differences only in isoflurane and urethane groups. ARNA responses to intrarenal capsaicin infusion were significantly blunted at nighttime versus daytime; however, ARNA responses to increased pelvic pressure or renal artery occlusion were not different between daytime and nighttime. These results demonstrate that ARNA sensitivity is greatest in decerebrate and Inactin-anesthetized groups but was not consistently influenced by sex.NEW & NOTEWORTHY We determined the impact of anesthesia, sex, and circadian cycle on renal afferent nerve (ARNA) sensitivity to chemical and mechanical stimuli. ARNA sensitivity to renal capsaicin infusion was greatest in decerebrate > Inactin > urethane or isoflurane groups. Elevated renal pelvic pressure significantly increased ARNA; decerebrate and Inactin groups exhibited the greatest ARNA sensitivity. Sex differences in renal afferent responses were not consistently observed. Circadian cycle altered chemosensory but not mechanosensory responses.

Ambulatory Blood Pressure Monitoring to Predict Response to Renal Denervation: A Post Hoc Analysis of the RADIANCE-HTN SOLO Study

Renal denervation (RDN) is effective in lowering blood pressure (BP) in patients with hypertension. The issue remains how to best identify potential responders. Ambulatory BP monitoring may be useful. Baseline nighttime systolic BP (SBP) ≥136 mm Hg and its variability (SD) ≥12 mm Hg in DENER-HTN trial or 24-hour heart rate ≥73.5 bpm in SPYRAL HTN-OFF MED Trial were shown to predict the BP response to RDN. We applied these criteria to the patients with hypertension in the sham-controlled RADIANCE-HTN SOLO trial to predict the BP response to ultrasound RDN at 2 months while patients were maintained off medications. BP responders were defined as: clinical with 24-hour SBP <130 mm Hg (RDN: 22/64 versus sham: 7/58); meaningful with 24-hour SBP reduction ≥10 mm Hg (RDN: 24/64, sham: 7/58); and extreme with 24-hour SBP reduction above mean+2 SD of the SBP decrease in the sham group, that is, ≥16.5 mm Hg (RDN: 10/64 versus sham: 2/58). The predictive criteria reported above were tested for sensitivity, specificity, and positive and negative predictive values. The predictive value varied according to the definition of response, with the clinical definition being strongly influenced by regression to the mean. Baseline nighttime SBP and its variability, especially when combined, offered good specificity (>90% irrespective of definition) but low sensitivity (from 9.1% to 30% depending on the definition) to predict responders; the heart rate criterion had insufficient predictive value. This analysis suggests the potential role of nighttime SBP and its variability to predict BP response to RDN in patients with hypertension. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02649426.

Comprehensive Assessment of Human Accessory Renal Artery Periarterial Renal Sympathetic Nerve Distribution

OBJECTIVES

The aim of this study was to understand the anatomy of periarterial nerve distribution in human accessory renal arteries (ARAs).

BACKGROUND

Renal denervation is a promising technique for blood pressure control. Despite the high prevalence of ARAs, the anatomic distribution of periarterial nerves around ARAs remains unknown.

METHODS

Kidneys with surrounding tissues were collected from human autopsy subjects, and histological evaluation was performed using morphometric software. An ARA was defined as an artery arising from the aorta above or below the dominant renal artery (DRA) or an artery that bifurcated within 20 mm of the takeoff of the DRA from the aorta. The DRA was defined as an artery that perfused >50% of the kidney.

RESULTS

A total of 7,287 nerves from 14 ARAs and 9 DRAs were evaluated. The number of nerves was smaller in the ARA than DRA (median: 30 [interquartile range: 17.5 to 48.5] vs. 49 [interquartile range: 36 to 76]; p < 0.0001). In both ARAs and DRAs, the distance from the arterial lumen to nerve was shortest in the distal, followed by the middle and proximal segments. On the basis of the post-mortem angiography, ARAs were divided into large (≥3 mm diameter) and small (<3 mm) groups. The number of nerves was greatest in the DRA, followed by the large and small ARA groups (53 [41 to 97], 38 [25 to 53], and 24.5 [10.5 to 36.3], respectively; p = 0.001).

CONCLUSIONS

ARAs showed a smaller number of nerves than DRAs, but these results were dependent on the size of the ARA. Ablation, especially in large ARAs, may allow more complete denervation with the potential to further reduce blood pressure.

The randomised Oslo study of renal denervation vs. Antihypertensive drug adjustments: efficacy and safety through 7 years of follow-up

PURPOSE

The blood pressure (BP) lowering effect of renal sympathetic denervation (RDN) in treatment-resistant hypertension shows variation amongst the existing randomised studies. The long-term efficacy and safety of RDN require further investigation. For the first time, we report BP changes and safety up to 7 years after RDN, compared to drug adjustment in the randomised Oslo RDN study.

MATERIALS AND METHODS

Patients with treatment-resistant hypertension, defined as daytime systolic ambulatory BP ≥135 mmHg after witnessed intake of ≥3 antihypertensive drugs including a diuretic, were randomised to either RDN (n = 9) or drug adjustment (n = 10). The initial primary endpoint was the change in office BP after 6 months. The RDN group had their drugs adjusted after 1 year using the same principles as the Drug Adjustment group. Both groups returned for long-term follow-up after 3 and 7 years.

RESULTS

The decrease in office BP and ambulatory BP (ABPM) after 6 months did not persist, but gradually increased in both groups. From 6 months to 7 years follow-up, mean daytime systolic ABPM increased from 142 ± 10 to 145 ± 15 mmHg in the RDN group, and from 133 ± 11 to 137 ± 13 mmHg in the Drug Adjustment group, with the difference between them decreasing. In a mixed factor model, a significantly different variance was found between the groups in daytime systolic ABPM (p = .04) and diastolic ABPM (p = .01) as well as office diastolic BP (p<.01), but not in office systolic BP (p = .18). At long-term follow-up we unveiled no anatomical- or functional renal impairment in either group.

CONCLUSIONS

BP changes up to 7 years show a tendency towards a smaller difference in BPs between the RDN and drug adjustment patients. Our data support RDN as a safe procedure, but it remains non-superior to intensive drug adjustment 7 years after the intervention.

Resistant Hypertension: Where are We Now and Where Do We Go from Here?

Resistant hypertension is an important subtype of hypertension that leads to an increased risk of cerebrovascular, cardiovascular, and kidney disease. The revised guidelines from the American College of Cardiology and American Heart Association now define resistant hypertension as blood pressure that remains above goal despite use of three maximally titrated anti-hypertensive medications including a diuretic or as a hypertensive patient who requires 4 or more agents for adequate BP control. These agents typically include a calcium-channel blocker, a renin-angiotensin system inhibitor, and a diuretic at maximal or maximally tolerated doses. As recognition of resistant hypertension increases, it is important to distinguish pseudo-resistant or apparent hypertension from true resistant hypertension. Etiologies of apparent resistant hypertension include measurement error and medication non-adherence. The prevalence of true resistant hypertension is likely much lower than reported in the literature when accounting for patients with apparent resistant hypertension. Evaluation of patients with true resistant hypertension includes screening for causes of secondary hypertension and interfering medications. Successful management of resistant hypertension includes lifestyle modification and optimization of medical therapy, often including the use of mineralocorticoid receptor antagonists. Looking ahead at developments in hypertension management, a slew of new device-based therapies are under active development. Of these, renal denervation is the closest to routine clinical application. Further study is needed before these devices can be recommended in the routine treatment of resistant hypertension.

Effect of combined renal denervation and pulmonary vein isolation in atrial fibrillation recurrence in hypertensive patients: A meta-analysis

BACKGROUND

Atrial Fibrillation (AF) is the most common cardiac arrhythmia and hypertension is the most common risk factor associated with AF. The addition of renal sympathetic nerve denervation (RSDN) to pulmonary vein isolation (PVI) in AF patients with hypertension has been reported to improve clinical outcomes.

METHODS

A systematic search was performed for studies on patients with AF and hypertension that compared RSDN with PVI versus PVI-alone. Risk ratio (RR) for categorical variables and mean difference (MD) for continuous variables with 95% confidence intervals were used.

RESULTS

Seven studies with a total of 734 patients were included. A total of 340 patients were in the RSDN + PVI group (46.32%) and 394 (53.67%) in the PVI group. A total of 608 patients had paroxysmal AF (83%) while 126 patients had persistent AF (17%). At 12 months follow-up, RSDN + PVI decreased the overall risk of AF recurrence in hypertensive patients with RR 0.60 [95% CI 0.50-0.72, P < .00001]. A subgroup analysis performed in patients with drug-resistant hypertension showed a similar reduction in AF recurrence with RR 0.61 [95% CI: 0.47-0.79, P = .0002). Procedure duration MD + 28.05 min [95% CI: 18.88-37.23, P < .00001] and fluoroscopy duration MD + 5.59 min [95% CI: 3.31-8.19, P < .00001] were significantly longer with the RSDN + PVI group. There was no significant difference in complications between the two groups.

CONCLUSION

The addition of RSDN to PVI in patients with AF and hypertension appears safe and decreases AF recurrence. Similar results were observed in patients with drug-resistant hypertension. Larger trials are needed to confirm these results.

Efficacy and safety of renal denervation in addition to pulmonary vein isolation for atrial fibrillation and hypertension-Systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

This systematic review and meta-analysis aimed to assess the latest evidence on the use of renal denervation (RDN) + pulmonary vein isolation (PVI) compared to PVI alone for treating atrial fibrillation (AF) with hypertension.

METHODS

A systematic literature search from several electronic databases was performed up until January 2020. The primary outcome was AF recurrence defined as AF/atrial flutter (AFL)/atrial tachycardia (AT) ≥30 seconds at 12-month follow-up and the secondary outcome was procedure-related complications.

RESULTS

There were 568 subjects from five studies. AF recurrence was 90/280 (32.1%) in the RDN + PVI group and 142/274 (51.8%) in the PVI group. RDN + PVI was associated with a lower incidence of AF recurrence (RR 0.62 [0.51, 076], P < .001; I 2: 0%). Pooled analysis of HR showed that RDN + PVI was associated with reduced AF recurrence (HR 0.51 [0.38, 0.70], P < .001; I 2: 0%). Complications were 7/241 (2.9%) in the RDN + PVI group and 8/237 (3.4%) in the PVI group. The rate of complications between the groups was similar (RR 0.87 [0.33, 2.29], P = .77; I 2: 0%). In the subgroup analysis of paroxysmal AF, RDN + PVI was shown to reduce AF recurrence (RR 0.64 [0.49, 0.82], P < .001; I 2: 0% and HR 0.56 [0.38, 0.82], P = .003; I 2: 0%) compared to PVI alone. RDN + PVI has a moderate certainty of evidence in the reducing AF recurrence with an absolute reduction of 197 fewer per 1000 (from 254 fewer to 124 fewer).

CONCLUSION

RDN in addition to PVI, is associated with reduced 12-month AF recurrence and similar procedure-related complications compared to PVI alone.

α 2-Adrenoceptors: Challenges and Opportunities-Enlightenment from the Kidney

It was indeed a Don Quixote-like pursuit of the mechanism of essential hypertension when we serendipitously discovered α₂-adrenoceptors (α₂-ARs) in skin-lightening experiments in the frog. Now α₂-ARs lurk on the horizon involving hypertension causality, renal denervation for hypertension, injury from falling in the elderly and prazosin's mechanism of action in anxiety states such as posttraumatic stress disorder (PTSD). Our goal here is to focus on this horizon and bring into clear view the role of α₂-AR-mediated mechanisms in these seemingly unrelated conditions. Our narrative begins with an explanation of how experiments in isolated perfused kidneys led to the discovery of a sodium-retaining process, a fundamental mechanism of hypertension, mediated by α₂-ARs. In this model system and in the setting of furosemide-induced sodium excretion, α₂-AR activation inhibited adenylate cyclase, suppressed cAMP formation, and caused sodium retention. Further investigations led to the realization that renal α₂-AR expression in hypertensive animals is elevated, thus supporting a key role for kidney α₂-ARs in the pathophysiology of essential hypertension. Subsequent studies clarified the molecular pathways by which α₂-ARs activate prohypertensive biochemical systems. While investigating the role of α₁-adrenoceptors (α₁-ARs) versus α₂-ARs in renal sympathetic neurotransmission, we noted an astonishing result: in the kidney α₁-ARs suppress the postjunctional expression of α₂-ARs. Here, we describe how this finding relates to a broader understanding of the role of α₂-ARs in diverse disease states. Because of the capacity for qualitative and quantitative monitoring of α₂-AR-induced regulatory mechanisms in the kidney, we looked to the kidney and found enlightenment.

Report of the National Heart, Lung, and Blood Institute Working Group on Hypertension: Barriers to Translation

The National Heart, Lung, and Blood Institute convened a multidisciplinary working group of hypertension researchers on December 6 to 7, 2018, in Bethesda, MD, to share current scientific knowledge in hypertension and to identify barriers to translation of basic into clinical science/trials and implementation of clinical science into clinical care of patients with hypertension. The goals of the working group were (1) to provide an overview of recent discoveries that may be ready for testing in preclinical and clinical studies; (2) to identify gaps in knowledge that impede translation; (3) to highlight the most promising scientific areas in which to pursue translation; (4) to identify key challenges and barriers for moving basic science discoveries into translation, clinical studies, and trials; and (5) to identify roadblocks for effective dissemination and implementation of basic and clinical science in real-world settings. The working group addressed issues that were responsive to many of the objectives of the National Heart, Lung, and Blood Institute Strategic Vision. The working group identified major barriers and opportunities for translating research to improved control of hypertension. This review summarizes the discussion and recommendations of the working group.

Sympathetic Nervous System Contributions to Hypertension: Updates and Therapeutic Relevance

The sympathetic nervous system plays a pivotal role in the long-term regulation of arterial blood pressure through the ability of the central nervous system to integrate neurohumoral signals and differentially regulate sympathetic neural input to specific end organs. Part 1 of this review will discuss neural mechanisms of salt-sensitive hypertension, obesity-induced hypertension, and the ability of prior experiences to sensitize autonomic networks. Part 2 of this review focuses on new therapeutic advances to treat resistant hypertension including renal denervation and carotid baroactivation. Both advances lower arterial blood pressure by reducing sympathetic outflow. We discuss potential mechanisms and areas of future investigation to target the sympathetic nervous system.

Sympathetic Nerve Traffic and Arterial Baroreflex Function in Apparent Drug-Resistant Hypertension

True drug-resistant hypertension (RHT) is characterized by a marked neuroadrenergic activation and reflex alterations compared with the nonresistant hypertensive state. It is unknown however, whether this behavior is specific for the RHT state or is also shared by apparent RHT (ARHT). In 38 middle-age patients with RHT, 44 treated essential controlled hypertensives (HT) and 32 ARHT; we evaluated sphygmomanometric, beat-to-beat (Finapres) and 24-hour (Spacelabs) blood pressure, heart rate and muscle sympathetic nerve traffic (microneurography). Measurements included plasma aldosterone, plasma norepinephrine, homeostasis model assessment index, and spontaneous baroreflex-muscle sympathetic nerve traffic sensitivity. All the various above-mentioned blood pressure values were significantly greater in both RHT and ARHT as compared with HT, while 24-hour blood pressure was significantly lower in ARHT as compared with RHT. In ARHT, muscle sympathetic nerve traffic was significantly lower than RHT (74.8±5.2 versus 89.2±4.8 bursts/100 hb, P<0.01) and similar to HT (69.7±4.8 bursts/100 hb, P=NS). RHT showed, at variance from the other 2 groups, greater plasma aldosterone and homeostasis model assessment index values and an impaired baroreflex function. In RHT, but not in ARHT and HT, muscle sympathetic nerve traffic was significantly and inversely related to baroreflex function (r=-0.40, P<0.02) and directly to plasma aldosterone and homeostasis model assessment index values (r=0.34-0.36, P<0.05). Plasma norepinephrine and heart rate values were not significantly different in the 3 groups. These data provide evidence that the marked sympathetic activation and baroreflex dysfunction detected in RHT is not present in ARHT, which displays a sympathetic and baroreflex profile superimposable to that seen in HT. These differences in the neurogenic function may have important clinical and therapeutic implications.