Blood pressure response to renal nerve stimulation in patients undergoing renal denervation: a feasibility study

Differences in the effectiveness and safety of different renal denervation devices

Renal denervation (RDN) is a minimally invasive, endovascular catheter-based procedure using radiofrequency, ultrasound, or alcohol-mediated ablation to treat resistant hypertension. RDN gained popularity in 2009 when it was shown to have an antihypertensive effect. However, concerns about the efficacy of RDN were raised in the HTN-3 trial published in 2014, and the development of several RDN devices was then discontinued. In the process, new randomized controlled trials were conducted after the development of some of the RDN devices, the quality assurance of the procedure, changes in ablation points, and improvements in study design. In November 2023, the U.S. Food and Drug Administration approved a radiofrequency RDN device and an ultrasound RDN device. The results of a randomized controlled trial of an alcohol-mediated RDN device have been published, and future trends are being watched closely. In this mini-review, we summarize the differences in the antihypertensive effect and safety of the different RDN devices and the endpoints of the procedure in order to contribute to the further development of RDN devices Currently available renal denervation device. A multielectrode radiofrequency ablation (Spyral), (B) ultrasound denervation (Paraise), and (C) alcohol-mediated perivascular denervation (Peregrine). ASBP ambulatory systolic blood pressure, ADBP ambulatory diastolic blood pressure, OSBP office systolic blood pressure, ODBP office diastolic blood pressure. Analysis according to types of renal denervation device (radiofrequency, ultrasound, or alcohol-mediated device). P values for interaction were 0.578 (ambulatory SBP), 0.499 (ambulatory diastolic BP), 0.853 (office SBP), and 0.870 (office diastolic BP).

Current problems in renal denervation and a hope to break the stage

Renal denervation (RDN) is currently confronted with the considerable heterogeneity of different post-procedural blood pressure responses. The challenges predominantly arise from not only the lack of selection of appropriate responders but also the absence of detection for the successful endpoints of intervention. In this paper, we summarize the significant characteristics of potentially appropriate hypertensive patients and propose a hopeful way to improve the accuracy of RDN, that is, the application of three-dimensional reconstruction technology combined with electrical renal nerve stimulation to guide the radiofrequency catheter ablation, which may promote the development of selective and accurate RDN in real-world clinical practice. This paper focuses on two current critical concerns of renal denervation (RDN): appropriate patient selection and the improvement in the accuracy of selective RDN. A hopeful way of accurate RDN may be the combination of 3D electroanatomic mapping systems for the renal artery with modified renal nerve stimulation (RNS) techniques and technology for appropriate hypertensive candidates.

Renal Denervation as a Complementary Treatment Option for Uncontrolled Arterial Hypertension: A Situation Assessment

Uncontrolled arterial hypertension is a major global health issue. Catheter-based renal denervation has shown to lower blood pressure in sham-controlled trials and represents a device-based, complementary treatment option for hypertension. In this situation assessment, the authors, who are practicing experts in hypertension, nephrology, general practice and cardiology in the Republic of Ireland, discuss the current evidence base for the BP-lowering efficacy and safety of catheter-based renal denervation with different modalities. Although important questions remain regarding the identification of responders, and long-term efficacy and safety of the intervention, renal denervation has the potential to provide much-needed help to address hypertension and its adverse consequences. The therapeutic approach needs to be multidisciplinary and personalised to take into account the perspective of patients and healthcare professionals in a shared decision-making process.

Advances in Renal Denervation in the Treatment of Hypertension

Hypertension significantly increases the risk of cardiovascular events and it is associated with high rates of disability and mortality. Hypertension is a common cause of cardiovascular and cerebrovascular accidents, which severely affect patients’ quality of life and lifespan. Current treatment strategies for hypertension are based primarily on medication and lifestyle interventions. The renal sympathetic nervous system plays an important role in the pathogenesis of hypertension, and catheter-based renal denervation (RDN) has provided a new concept for the treatment of hypertension. In recent years, studies on RDN have been performed worldwide. This article reviews the latest preclinical research and clinical evidence for RDN.

Renal nerve stimulation identifies renal innervation and optimizes the strategy for renal denervation in canine

BACKGROUND

Renal denervation (RDN) was still performed without any intra-procedural method for nerve mapping. Whether renal nerve stimulation (RNS) is an efficient way to identify renal autonomic innervation and optimize the strategy for RDN remain to be worthy for further exploration.

METHODS

The characteristics of renal autonomic innervation at the sites with different blood pressure (BP) responses to RNS were explored. Then, dogs anatomically eligible for RDN were randomly assigned into elevated BP response ablation group, reduced BP response ablation group, and RNS-control group. The postoperative outcomes were measured at baseline and after 4 weeks follow-up.

RESULTS

The proportion of afferent sensory nerve was higher at elevated BP response sites (ERS) than reduced BP response sites (RRS) and non-response sites (NRS) (P = 0.012 and P = 0.004). Conversely, the proportion of parasympathetic nerve at RRS was the highest (RRS vs. ERS, P = 0.017; RRS vs. NRS, P = 0.023). More importantly, there was a significant correlation between systolic blood pressure changes and the area ratios of afferent sensory and parasympathetic nerve (R = 0.859; P < 0.001). In addition, ablation at BP-elevation sites can result in a significant decrease in BP and plasma norepinephrine (NE) after 4 weeks (P = 0.002; P = 0.008), while ablation at BP-reduction sites can lead to significant increases in BP and plasma NE (P = 0.016; P = 0.033).

CONCLUSIONS

RNS is an effective method to identify renal autonomic innervation. It could not only help to identify optimal target sites, but also avoid ablation of sympathetic-inhibitory areas during RDN.

The intrarenal blood pressure modulation system is differentially altered after renal denervation guided by different intensities of blood pressure responses

The aim of this study was to investigate alterations in the intrarenal blood pressure (BP) regulation system after renal denervation (RDN) guided by renal nerve stimulation (RNS). Twenty-one dogs were randomized to receive RDN at strong (SRA group, n = 7) or weak (WRA group, n = 7) BP-elevation response sites identified by RNS or underwent RNS only (RNS-control, RSC, n = 7). After 4 weeks of follow-up, renal sympathetic components, the main components of renin-angiotensin system (RAS) and the major transporters involved in sodium and water reabsorption were assessed by immunohistochemical analysis. Compared with RSC treatment, RDN therapy significantly reduced renal norepinephrine and tyrosine hydroxylase levels, decreased the renin content and inhibited the onsite generation of angiotensinogen. Moreover, the expression of exciting axis components, including angiotensin-converting enzyme (ACE), angiotensin II and angiotensin II type-1 receptor, was downregulated, while protective axis components for the cardiovascular system, including ACE2 and Mas receptors, were upregulated in both WRA and SRA groups. Moreover, RDN reduced the abundance of aquaporin-1 and aquaporin-2 in kidneys. Although RDN had a minimal effect on overall NKCC2 expression, its activation (p-NKCC2) and directional enrichment in the apical membrane (mNKCC2) were dramatically blunted. All these changes were more obvious in the SRA group than WRA group. Selective RDN guided by RNS effectively reduced systemic BP by affecting the renal neurohormone system, as well as the sodium and water transporter system, and these effects at sites with a strong BP response were more superior.

The role of renal nerve stimulation in percutaneous renal denervation for hypertension: A mini-review

Recent trials have demonstrated the efficacy and safety of percutaneous renal sympathetic denervation (RDN) for blood pressure (BP)-lowering in patients with uncontrolled hypertension. Nevertheless, major challenges exist, such as the wide variation of BP-lowering responses following RDN (from strong response to no response) and lack of feasible and reproducible peri-procedural predictors for patient response. Both animal and human studies have demonstrated different patterns of BP responses following renal nerve stimulation (RNS), possibly related to varied regional proportions of sympathetic and parasympathetic nerve tissues along the renal arteries. Animal studies of RNS have shown that rapid electrical stimulation of the renal arteries caused renal artery vasoconstriction and increased norepinephrine secretion with a concomitant increase in BP, and the responses were attenuated after RDN. Moreover, selective RDN at sites with strong RNS-induced BP increases led to a more efficient BP-lowering effect. In human, when RNS was performed before and after RDN, blunted changes in RNS-induced BP responses were noted after RDN. The systolic BP response induced by RNS before RDN and blunted systolic BP response to RNS after RDN, at the site with maximal RNS-induced systolic BP response before RDN, both correlated with the 24-h ambulatory BP reductions 3-12 months following RDN. In summary, RNS-induced BP changes, before and after RDN, could be used to assess the immediate effect of RDN and predict BP reductions months following RDN. More comprehensive, large-scale and long term trials are needed to verify these findings.

Present Evidence of Determinants to Predict the Efficacy of Renal Denervation

Sympathetic overactivation is one of the main contributors to development and progress of hypertension. Renal denervation (RDN) has been evidenced by series of clinical trials for its efficacy and safety to treat overactivated sympathetic nervous system induced diseases. However, the results were inconsistent and not all patients benefited from RDN. Appropriate patient selection and intraoperative factors to improve the efficacy of RDN need to be solved urgently. Over the decade, research studies on the correlations between indicators and the antihypertensive effects have been conducted and made a fairly well progress. Herein, we comprehensively reviewed the research studies on how to make RDN more predictable or improve the efficacy of RDN and summarized these potential indicators or devices which might be applied in clinical settings.

Renal nerve stimulation: complete versus incomplete renal sympathetic denervation

PURPOSE

Blood pressure (BP) reduction after renal sympathetic denervation (RDN) is highly variable. Renal nerve stimulation (RNS) can localize sympathetic nerves. The RNS trial aimed to investigate the medium-term BP-lowering effects of the use of RNS during RDN, and explore if RNS can check the completeness of the denervation.

MATERIAL AND METHODS

Forty-four treatment-resistant hypertensive patients were included in the prospective, single-center RNS trial. The primary study endpoint was change in 24-h BP at 6- to 12-month follow-up after RDN. The secondary study endpoints were the acute procedural RNS-induced BP response before and after RDN; number of antihypertensive drugs at follow-up; and the correlation between the RNS-induced BP increase before versus after RDN (delta [Δ] RNS-induced BP).

RESULTS

Before RDN, the RNS-induced systolic BP rise was 43(±21) mmHg, and decreased to 9(±12) mmHg after RDN (p < 0.001). Mean 24-h systolic/diastolic BP decreased from 147(±12)/82(±11) mmHg at baseline to 135(±11)/76(±10) mmHg (p < 0.001/<0.001) at follow-up (10 [6-12] months), with 1 antihypertensive drug less compared to baseline. The Δ RNS-induced BP and the 24-h BP decrease at follow-up were correlated for systolic (R = 0.44, p = 0.004) and diastolic (R = 0.48, p = 0.003) BP. Patients with ≤0 mmHg residual RNS-induced BP response after RDN had a significant lower mean 24-h systolic BP at follow-up compared to the patients with >0 mmHg residual RNS-induced BP response (126 ± 4 mmHg versus 135 ± 10 mmHg, p = 0.04). 83% of the patients with ≤0 mmHg residual RNS-induced BP response had normal 24-h BP at follow-up, compared to 33% in the patients with >0 mmHg residual RNS-induced BP response (p = 0.023).

CONCLUSION

The use of RNS during RDN leads to clinically significant and sustained lowering of 24-h BP with fewer antihypertensive drugs at follow-up. RNS-induced BP changes were correlated with 24-h BP changes at follow-up. Moreover, patients with complete denervation had significant lower BP compared to the patients with incomplete denervation.

Mapping Renal Innervations by Renal Nerve Stimulation and Characterizations of Blood Pressure Response Patterns

Increased sympathetic nervous activity is one of main contributors to pathogenesis and progression of hypertension. Renal denervation (RDN) has been demonstrated as a potential therapy for treatment of hypertension; however, lack of indicators of intra-/post-procedure results in inconsistent clinical outcomes. Renal nerve stimulation (RNS), a simple and promising method, could evoke elevated blood pressure as an intraoperative indicator for RDN. But related researches on patterns of blood pressure responses to RNS are still incomplete. To investigate and categorize the phenotypes of blood pressure response to RNS and heart rate alteration before and after RNS, 24 Chinese Kunming dogs were used to perform RNS from bifurcation to ostium of renal arteries after angiography, and a total of 483 stimulated sites were complete. We identified five different patterns of blood pressure response to RNS in 483 stimulated sites, (1) continuous ascending and finally keeping steady above baseline (26.9%), (2) declining and then rising over baseline (11.8%), (3) declining and then rising but below baseline (14.5%), (4) fluctuating in the vicinity of baseline (39.5%), and (5) continuous declining and finally keeping steady below baseline (7.2%), and found no difference in RR intervals among five blood pressure responses before and after renal nerve stimulation. Renal nerve stimulation could elicit different patterns of blood pressure response, which could potentially assist in distinguishing sympathetic-excitatory sites and sympathetic-inhibitory sites from mixed nerve components, which might help to improve the efficacy of RDN.

Metabolic effects two years after renal denervation in insulin resistant hypertensive patients. The Re-Shape CV-risk study

BACKGROUND & AIMS

Denervation of renal sympathetic nerves (RDN) is an invasive endovascular procedure introduced as an antihypertensive treatment with a potential beneficial effect on insulin resistance (IR). We have previously demonstrated a reduction in blood pressure (BP) six months after RDN, but severe hepatic and peripheral IR, assessed by glucose tracer and two step hyperinsulinemic-euglycemic clamp (HEC), did not improve. The aim of the current study was to evaluate IR and adipokines profiles in relation to BP and arterial stiffness changes two years after RDN.

METHODS

In 20 non-diabetic patients with true treatment-resistant hypertension, ambulatory and office BP were measured after witnessed intake of medications prior to, six and 24 months after RDN. Arterial stiffness index (AASI) was calculated from ambulatory BP. Insulin sensitivity (IS) was assessed using an oral glucose tolerance test (OGTT), the Homeostasis Model Assessment (HOMA-IR), HOMA-Adiponectin Model Assessment (HOMA-AD), the Quantitative Insulin Sensitivity Check Index (QUICKI), the Triglyceride and Glucose Index (TyG) and the Leptin-to-Adiponectin Ratio (LAR). These surrogate indices of IS were compared with tracer/HEC measurements to identify which best correlated in this group of patients.

RESULTS

All measured metabolic variables and IS surrogate indices remained essentially unchanged two years after RDN apart from a significant increase in HOMA-AD. OGTT peak at 30 min correlated best with reduction in endogenous glucose release (EGR) during low insulin HEC (r = -0.6, p = 0.01), whereas HOMA-IR correlated best with whole-body glucose disposal (WGD) (r = -0.6, p = 0.01) and glucose infusion rate (r = -0.6, p = 0.01) during high insulin HEC. BP response was unrelated to IS prior to RDN. Nocturnal systolic BP and arterial stiffness before RDN correlated positively with a progression in hepatic IR at six-month follow-up.

CONCLUSION

IR, adiponectin and leptin did not improve two years after RDN. There was no correlation between baseline IS and BP response. Our study does not support the notion of a beneficial metabolic effect of RDN in patients with treatment resistant hypertension.

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.

Quantitative analysis of renal arterial variations affecting the eligibility of catheter-based renal denervation using multi-detector computed tomography angiography

Catheter-based renal denervation (RDN) was introduced to treat resistant hypertension. However, the reduction in blood pressure after the RDN was modest. Catheter-based RDN was performed only at main renal arteries, except for accessory and branch arteries due to the diameter being too small for the catheter to approach. Here, we retrospectively analyzed the anatomy of diverse renal arteries via 64-channel multi-detector computed tomography angiograms of 314 consecutive donors who underwent living donor nephrectomy from January 2012 to July 2017. Occurrence rates of one or more accessory renal arteries in donors were 25.3% and 19.4% on the left and right sides, respectively. Early branching rates before 25 mm from the aorta to the right and left renal arteries were 13.7% and 10.5%, respectively. Overall, 63.1% and 78.3% of donors had no accessory artery bilaterally and no branched renal artery, respectively. As a result, 47.1% had only main renal arteries without an accessory artery and early-branching artery. Approximately half of the donors had multiple small renal arteries bilaterally, for which catheter-based denervation may not be suitable. Thus, preoperative computed tomography angiography requires careful attention to patient selection, and there is a need for improved methods for denervation at various renal arteries.

Renal Denervation in Asia: Consensus Statement of the Asia Renal Denervation Consortium

The Asia Renal Denervation Consortium consensus conference of Asian physicians actively performing renal denervation (RDN) was recently convened to share up-to-date information and regional perspectives, with the goal of consensus on RDN in Asia. First- and second-generation trials of RDN have demonstrated the efficacy and safety of this treatment modality for lowering blood pressure in patients with resistant hypertension. Considering the ethnic differences of the hypertension profile and demographics of cardiovascular disease demonstrated in the SYMPLICITY HTN (Renal Denervation in Patients With Uncontrolled Hypertension)-Japan study and Global SYMPLICITY registry data from Korea and Taiwan, RDN might be an effective hypertension management strategy in Asia. Patient preference for device-based therapy should be considered as part of a shared patient-physician decision process. A practical population for RDN treatment could consist of Asian patients with uncontrolled essential hypertension, including resistant hypertension. Opportunities to refine the procedure, expand the therapy to other sympathetically mediated diseases, and explore the specific effects on nocturnal and morning hypertension offer a promising future for RDN. Based on available evidence, RDN should not be considered a therapy of last resort but as an initial therapy option that may be applied alone or as a complementary therapy to antihypertensive medication.

Renal denervation: Alternative treatment options for hypertension?

Hypertension affects millions of Americans and has adverse long-term consequences increasing morbidity and mortality. Resistant hypertension (RH) continues to be difficult to treat with medications alone which may be associated with significant side effects. Alternate therapies have been evaluated for treating RH and renal denervation has been investigated extensively. We review the data from renal denervation trials and other novel technologies which are not FDA approved to date.

Selective Renal Denervation Guided by Renal Nerve Stimulation in Canine

Renal nerve stimulation (RNS) can result in substantial blood pressure (BP) elevation, and the change was significantly blunted when repeated stimulation after ablation. However, whether RNS could provide a meaningful renal nerve mapping for identification of optimal ablation targets in renal denervation (RDN) is not fully clear. Here, we compared the antihypertensive effects of selective RDN guided by two different BP responses to RNS and explored the nerve innervations at these sites in Kunming dogs. Our data indicated that ablation at strong-response sites showed a more systolic BP-lowering effect than at weak-response sites ( P =0.002), as well as lower levels of tyrosine hydroxylase and norepinephrine in kidney and a greater reduction in plasma norepinephrine ( P =0.004 for tyrosine hydroxylase, P =0.002 for both renal and plasma norepinephrine). Strong-response sites showed a greater total area and mean number of renal nerves than weak-response sites ( P =0.012 for total area and P <0.001 for mean number). Systolic BP-elevation response to RNS before RDN and blunted systolic BP-elevation to RNS after RDN were correlated with systolic BP changes at 4 weeks follow-up ( R =0.649; P =0.012 and R =0.643; P =0.013). Changes of plasma norepinephrine and renal norepinephrine levels at 4 weeks were also correlated with systolic BP changes at 4 weeks ( R =0.837, P <0.001 and R =0.927, P <0.001). These data suggest that selective RDN at sites with strong BP-elevation response to RNS could lead to a more efficient RDN. RNS is an effective method to identify the nerve-enriched area during RDN procedure and improve the efficacy of RDN.

Neuromodulation for the Treatment of Heart Rhythm Disorders

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Derangement of autonomic nervous signaling is an important contributor to cardiac arrhythmogenesis.

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Modulation of autonomic nervous signaling holds significant promise for the prevention and treatment of cardiac arrhythmias.

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Further clinical investigation is necessary to establish the efficacy and safety of autonomic modulatory therapies in reducing cardiac arrhythmias.

There is an increasing recognition of the importance of interactions between the heart and the autonomic nervous system in the pathophysiology of arrhythmias. These interactions play a role in both the initiation and maintenance of arrhythmias and are important in both atrial and ventricular arrhythmia. Given the importance of the autonomic nervous system in the pathophysiology of arrhythmias, there has been notable effort in the field to improve existing therapies and pioneer additional interventions directed at cardiac-autonomic targets. The interventions are targeted to multiple and different anatomic targets across the neurocardiac axis. The purpose of this review is to provide an overview of the rationale for neuromodulation in the treatment of arrhythmias and to review the specific treatments under evaluation and development for the treatment of both atrial fibrillation and ventricular arrhythmias.

Electrical stimulation-based renal nerve mapping exacerbates ventricular arrhythmias during acute myocardial ischaemia

OBJECTIVE

Blood pressure elevation in response to transient renal nerve stimulation (RNS) has been used to determine the ablation target and endpoint of renal denervation. This study aimed to evaluate the safety of transient RNS in canines with normal or ischaemic hearts.

METHODS

In ten normal (Group 1) and six healed myocardial infarction (HMI) (Group 2) canines, a large-tip catheter was inserted into the left or right renal artery to perform transient RNS. The left stellate ganglion neural activity (LSGNA) and ventricular electrophysiological parameters were measured at baseline and during transient RNS. In another 20 acute myocardial infarction (AMI) canines, RNS (Group 3, n = 10) or sham RNS (Group 4, n = 10) was intermittently (1 min ON and 4 min OFF) performed for 1 h following AMI induction. The LSGNA and AMI-induced ventricular arrhythmias were analysed.

RESULTS

In normal and HMI canines, although transient RNS significantly increased the LSGNA and facilitated the action potential duration (APD) alternans, it did not induce any ventricular arrhythmias and did not change the ventricular effective refractory period, APD or maximum slope of the APD restitution curve. In AMI canines, transient RNS significantly exacerbated LSG activation and promoted the incidence of ventricular arrhythmias.

CONCLUSION

Transient RNS did not increase the risk of ventricular arrhythmias in normal or HMI hearts, but it significantly promoted the occurrence of ventricular arrhythmias in AMI hearts. Therefore, electrical stimulation-based renal nerve mapping may be unsafe in AMI patients and in patients with a high risk for malignant ventricular arrhythmias.

Is renal denervation still a treatment option in cardiovascular disease?

The role of renal sympathetic denervation (RDN) has been the topic of ongoing debate ever since the impressive initial results. The rationale of RDN is strong and supported by non-clinical studies, which lies in uncoupling the autonomic nervous crosstalk between the kidneys and the central nervous system. Since we know that cardiovascular diseases, such as hypertension, atrial, ventricular arrhythmias and heart failure (HF) are related to sympathetic (over)activity, modulation of the renal nerve activity appears to be a reasonable and attractive therapeutic target in these patients. This review will focus on the existing evidence and potential future perspectives for RDN as treatment option in cardiovascular disease.

Blood pressure response to renal denervation is correlated with baseline blood pressure variability: a patient-level meta-analysis

BACKGROUND

Sympathetic tone is one of the main determinants of blood pressure (BP) variability and treatment-resistant hypertension. The aim of our study was to assess changes in BP variability after renal denervation (RDN). In addition, on an exploratory basis, we investigated whether baseline BP variability predicted the BP changes after RDN.

METHODS

We analyzed 24-h BP recordings obtained at baseline and 6 months after RDN in 167 treatment-resistant hypertension patients (40% women; age, 56.7 years; mean 24-h BP, 152/90 mmHg) recruited at 11 expert centers. BP variability was assessed by weighted SD [SD over time weighted for the time interval between consecutive readings (SDiw)], average real variability (ARV), coefficient of variation, and variability independent of the mean (VIM).

RESULTS

Mean office and 24-h BP fell by 15.4/6.6 and 5.5/3.7 mmHg, respectively (P < 0.001). In multivariable-adjusted analyses, systolic/diastolic SDiw and VIM for 24-h SBP/DBP decreased by 1.18/0.63 mmHg (P ≤ 0.01) and 0.86/0.42 mmHg (P ≤ 0.05), respectively, whereas no significant changes in ARV or coefficient of variation occurred. Furthermore, baseline SDiw (P = 0.0006), ARV (P = 0.01), and VIM (P = 0.04) predicted the decrease in 24-h DBP but not 24-h SBP after RDN.

CONCLUSION

RDN was associated with a decrease in BP variability independent of the BP level, suggesting that responders may derive benefits from the reduction in BP variability as well. Furthermore, baseline DBP variability estimates significantly correlated with mean DBP decrease after RDN. If confirmed in younger patients with less arterial damage, in the absence of the confounding effect of drugs and drug adherence, baseline BP variability may prove a good predictor of BP response to RDN.

Electrical stimulation of renal nerves for modulating urine glucose excretion in rats

BACKGROUND

The role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion.

METHODS

We performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1-50 kHz) or low frequencies (2-5 Hz), with intravenous administration of a glucose bolus shortly into the 25-40-min stimulation period. Urine samples were collected at 5-10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (α = 0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (α = 0.005).

RESULTS

For kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+ 24.5%; n = 9) than 1 kHz (- 5.9%; n = 6) and 50 kHz (+ 2.3%; n = 14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (- 40.4%; n = 6) than 2 Hz (- 27.2%; n = 5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant (p < 0.005). Similar outcomes were observed for urine flow rate, which may suggest an associated response. No trends or statistical significance were observed for urine glucose concentrations.

CONCLUSION

To our knowledge, this is the first study to investigate electrical stimulation of renal nerves to modulate urine glucose excretion. Our experimental results show that stimulation of renal nerves may modulate urine glucose excretion, however, this response may be associated with urine flow rate. Future work is needed to examine the underlying mechanisms and identify approaches for enhancing regulation of glucose excretion.

Selective vs. Global Renal Denervation: a Case for Less Is More

PURPOSE OF REVIEW

Review the renal nerve anatomy and physiology basics and explore the concept of global vs. selective renal denervation (RDN) to uncover some of the fundamental limitations of non-targeted renal nerve ablation and the potential superiority of selective RDN.

RECENT FINDINGS

Recent trials testing the efficacy of RDN showed mixed results. Initial investigations targeted global RDN as a therapeutic goal. The repeat observation of heterogeneous response to RDN including non-responders with lack of a BP reduction, or even more unsettling, BP elevations after RDN has raised concern for the detrimental effects of unselective global RDN. Subsequent studies have suggested the presence of a heterogeneous fiber population and the potential utility of renal nerve stimulation to identify sympatho-stimulatory fibers or "hot spots." The recognition that RDN can produce heterogeneous afferent sympathetic effects both change therapeutic goals and revitalize the potential of therapeutic RDN to provide significant clinical benefits. Renal nerve stimulation has emerged as potential tool to identify sympatho-stimulatory fibers, avoid sympatho-inhibitory fibers, and thus guide selective RDN.

Renal Nerve Stimulation as Procedural End Point for Renal Sympathetic Denervation

PURPOSE OF REVIEW

Renal sympathetic denervation (RDN) as treatment option for hypertension has a strong rationale; however, variable effects on blood pressure (BP) have been reported ranging from non-response to marked reductions in BP. The absence of a procedural end point for RDN is one of the potential factors associated with the variable response. Studies have suggested the use of renal nerve stimulation (RNS) to adequately address this issue. This review aims to provide an overview of the clinical and experimental data available regarding the effects of RNS in the setting of RDN.

RECENT FINDINGS

Animal studies have shown that high-frequency electrical stimulation of the sympathetic nerves in the adventitia of the renal arteries elicits an increase in BP and leads to an increased norepinephrine spillover as a marker of increased sympathetic activity and these effects of stimulation were attenuated or blunted after RDN. In a human feasibility study using RNS both before and after RDN, similar BP responses were observed. Moreover, in patients with resistant hypertension, RNS-induced changes in BP appeared to be correlated with 24-h BP response after RDN. These data suggest that RNS is a useful tool to identify renal sympathetic nerve fibers in patients with treatment-resistant hypertension undergoing RDN, and to predict the likely effectiveness of RDN treatments. In acute procedural settings both in animal and human models, RNS elicits increase in BP and HR before RDN and these effects are blunted after RDN. Up to now, there is preliminary evidence that the RNS-induced BP changes predict 24-h ABPM outcome at follow-up in patients with resistant hypertension. Of note, studies are small sized and results of large trials comparing conventional RDN to RNS-guided RDN are warranted.

Treatment of atrial fibrillation in patients with enhanced sympathetic tone by pulmonary vein isolation or pulmonary vein isolation and renal artery denervation: clinical background and study design : The ASAF trial: ablation of sympathetic atrial fibrillation

BACKGROUND

Hypertension is an important, modifiable risk factor for the development of atrial fibrillation (AF). Even after pulmonary vein isolation (PVI), 20-40% experience recurrent AF. Animal studies have shown that renal denervation (RDN) reduces AF inducibility. One clinical study with important limitations suggested that RDN additional to PVI could reduce recurrent AF.

OBJECTIVE

The goal of this multicenter randomized controlled study is to investigate whether RDN added to PVI reduces AF recurrence.

METHODS

The main end point is the time until first AF recurrence according to EHRA guidelines after a blanking period of 3 months. Assuming a 12-month accrual period and 12 months of follow-up, a power of 0.80, a two-sided alpha of 0.05 and an expected drop-out of 10% per group, 69 patients per group are required. We plan to randomize a total of 138 hypertensive patients with AF and signs of sympathetic overdrive in a 1:1 fashion. Patients should use at least two antihypertensive drugs. Sympathetic overdrive includes obesity, exercise-induced excessive blood pressure (BP) increase, significant white coat hypertension, hospital admission or fever induced AF, tachycardia induced AF and diabetes mellitus. The interventional group will undergo PVI + RDN and the control group will undergo PVI.

RESULTS

Patients will have follow-up for 1 year, and continuous loop monitoring is advocated.

CONCLUSION

This randomized, controlled study will elucidate if RDN on top of PVI reduces AF recurrence.

Renal Denervation: Paradise Lost? Paradise Regained?

Renal denervation is a relatively recent concept whose initial promising results suffered a setback following the SYMPLICITY 3 trial, which did not show a significant blood pressure-lowering effect in comparison to sham. In this review article, we begin with the history including the physiological basis behind the concept of renal denervation. Furthermore, we review the literature in support of renal denervation, including the recently published SPYRAL HTN-OFF MED, which demonstrated significant blood pressure reduction in the absence of antihypertensive medication. We further touch upon the potential pitfalls and possible future directions of renal denervation.

Predictive factors for successful renal denervation: should we use them in clinical trials?

Renal denervation (RDN) is facing various challenges to its initial claimed value in hypertension treatment. Major concerns are the choice of the patients and the technical efficacy of the RDN. Different factors have been described as predicting the capacity of RDN to decrease blood pressure. These factors are related to the patients, the procedure and the tools to confirm successful neural ablation. Their use in future trials should help to improve RDN trials understanding and outcomes. This review summarizes the different predictive factors available and their potential benefits in patient selection and in procedure guidance.

Changes in renal artery dimensions are associated with clinical response to radiofrequency renal denervation: a series of studies using quantitative angiography and intravascular ultrasound

OBJECTIVE

Renal denervation (RDN) can cause focal (notches) and global (spasms) changes in renal artery dimensions. We quantified these changes and related them to renal norepinephrin tissue content in animals and to blood pressure (BP) changes in patients.

METHODS

We measured renal artery dimensions pre-RDN and post-RDN, utilizing quantitative renal angiography (QRA) in a porcine model and in a retrospective patient cohort, and intravascular ultrasound (IVUS) in a prospective patient cohort. Focal and global measurements were minimum and mean diameter/area/volume with QRA, minimum lumen/vessel/wall area and volume with IVUS. BP was assessed with 24-h ambulatory monitoring, norepinephrin content with liquid chromatography.

RESULTS

In 36 pigs treated unilaterally with RDN, norepinephrin content of the treated right kidney was 48.2% of the untreated left kidney. QRA measurements following RDN were associated with norepinephrin content only of the (treated) right kidney. In the human QRA study (n = 43 patients), mean 24-h BP fell by 8/4 and 12/6 mmHg at 1 and 12 months, respectively. More pronounced changes in QRA measurements were associated with a more pronounced BP drop. In multiple regression models, the change in minimum diameter was independently associated with BP changes at 12 months. In the prospective IVUS study (n = 17 patients), a larger decrease in minimum lumen/vessel area and larger increase of wall area/volume were associated with a larger BP drop.

CONCLUSION

Focal and global changes in renal arteries following RDN can be quantified, using QRA or IVUS, and may serve as markers of a successful procedure.

Procedural Reassessment of Radiofrequency Renal Denervation in Resistant Hypertensive Patients

INTRODUCTION

Recent anatomical and clinical studies have led to the hypothesis that in several cases of failure of response to renal denervation (RDN), the procedure has not been technically correct.

AIM

To perform procedural reassessment in patients with true resistant hypertension who underwent RDN.

METHODS

We retrospectively reassessed the procedural technique of RDN in 10 true resistant hypertensive patients, comparing the sites of renal ablations with the knowledge of animal and human post mortem evidences. Procedural ablation technique was assessed in terms of number of ablations for each renal artery and site of ablation (quadrant and distance from renal ostium) by using the radiologic images of each RDN and the number of radiofrequency ablation attempts documented in the reports of each denervation session.

RESULTS

10 patients were studied, 9 denervated with Simplicity monoelectrode catheter, 1 with multielectrode balloon technique. Responders to the procedure underwent more ablations and particularly at least a quadrant ablation in one of the kidney arteries, >2 ablations in Dorsal plus Ventral quadrants and in 67% of then >10 ablations were done in superior inferior and ventral quadrants.

CONCLUSION

This study confirms the importance of a well knowledge of renal artery anatomy and underlines the relevance of the choice of ablation sites in order to obtain a successful RDN procedure.

Renal vascular calcification and response to renal nerve denervation in resistant hypertension

Renal sympathetic nerve denervation (RDN) is accepted as a treatment option for patients with resistant hypertension. However, results on decline in ambulatory blood pressure (BP) measurement (ABPM) are conflicting. The high rate of nonresponders may be related to increased systemic vascular stiffness rather than sympathetic overdrive. A single center, prospective registry including 26 patients with treatment resistant hypertension who underwent RDN at the Isala Hospital in the Netherlands. Renal perivascular calcium scores were obtained from noncontrast computed tomography scans. Patients were divided into 3 groups based on their calcium scores (group I: low 0-50, group II: intermediate 50-1000, and group III: high >1000). The primary end point was change in 24-hour ABPM at 6 months follow-up post-RDN compared to baseline. Seven patients had low calcium scores (group I), 13 patients intermediate (group II), and 6 patients had high calcium scores (group III). The groups differed significantly at baseline in age and baseline diastolic 24-hour ABPM. At 6-month follow-up, no difference in 24-hour systolic ABPM response was observed between the 3 groups; a systolic ABPM decline of respectively -9 ± 12, -6 ± 12, -12 ± 10 mm Hg was found. Also the decline in diastolic ambulatory and office systolic and diastolic BP was not significantly different between the 3 groups at follow-up. Our preliminary data showed that the extent of renal perivascular calcification is not associated with the ABPM response to RDN in patients with resistant hypertension.

Renal Nerve Stimulation–Induced Blood Pressure Changes Predict Ambulatory Blood Pressure Response After Renal Denervation

Blood pressure (BP) response to renal denervation (RDN) is highly variable and its effectiveness debated. A procedural end point for RDN may improve consistency of response. The objective of the current analysis was to look for the association between renal nerve stimulation (RNS)–induced BP increase before and after RDN and changes in ambulatory BP monitoring (ABPM) after RDN. Fourteen patients with drug-resistant hypertension referred for RDN were included. RNS was performed under general anesthesia at 4 sites in the right and left renal arteries, both before and immediately after RDN. RNS-induced BP changes were monitored and correlated to changes in ambulatory BP at a follow-up of 3 to 6 months after RDN. RNS resulted in a systolic BP increase of 50±27 mm Hg before RDN and systolic BP increase of 13±16 mm Hg after RDN ( P <0.001). Average systolic ABPM was 153±11 mm Hg before RDN and decreased to 137±10 mm Hg at 3- to 6-month follow-up ( P =0.003). Changes in RNS-induced BP increase before versus immediately after RDN and changes in ABPM before versus 3 to 6 months after RDN were correlated, both for systolic BP ( R =0.77, P =0.001) and diastolic BP ( R =0.79, P =0.001). RNS-induced maximum BP increase before RDN had a correlation of R =0.61 ( P =0.020) for systolic and R =0.71 ( P =0.004) for diastolic ABPM changes. RNS-induced BP changes before versus after RDN were correlated with changes in 24-hour ABPM 3 to 6 months after RDN. RNS should be tested as an acute end point to assess the efficacy of RDN and predict BP response to RDN.

Renal denervation in the era of HTN-3. Comprehensive review and glimpse into the future

The pathophysiological role of sympathetic overactivity in conditions such as hypertension has been well documented. Catheter-based renal denervation (RDN) is a minimally invasive percutaneous procedure which aims to disrupt sympathetic nerve afferent and efferent activity through the application of radiofrequency energy directly within the renal artery wall. This technique has emerged as a very promising treatment with dramatic effects on refractory hypertension but also in other conditions in which a sympathetic influence is present. Several studies have evaluated the safety and efficacy of this procedure, presently surrounded by controversy since the recent outcome of Symplicity HTN-3, the first randomized, sham-control trial, which failed to confirm RDN previous reported benefits on BP and cardiovascular risk lowering. Consequently, although some centers halted their RDN programs, research continues and both the concept of denervation and treatment strategies are being redefined to identify patients who can drive the most benefit from this technology. In the United States, the Food and Drug Administration (FDA) has appropriately mandated that RDN remains an investigative procedure and a new generation of sham-controlled trials are ongoing and aimed to assess not only its efficacy against pharmacotherapy but also trials in drug free patients with the objective of demonstrating once and for all whether the procedure actually does lower BP in comparison to a placebo arm. In this article, we present an overview of the sympathetic nervous system and its role in hypertension, examine the current data on RDN, and share some insights and future expectations.

Persistent Increase in Blood Pressure After Renal Nerve Stimulation in Accessory Renal Arteries After Sympathetic Renal Denervation

Blood pressure response to renal denervation is highly variable, and the proportion of responders is disappointing. This may be partly because of accessory renal arteries too small for denervation, causing incomplete ablation. Renal nerve stimulation before and after renal denervation is a promising approach to assess completeness of renal denervation and may predict blood pressure response to renal denervation. The objective of the current study was to assess renal nerve stimulation–induced blood pressure increase before and after renal sympathetic denervation in main and accessory renal arteries of anaesthetized patients with drug-resistant hypertension. The study included 21 patients. Nine patients had at least 1 accessory renal artery in which renal denervation was not feasible. Renal nerve stimulation was performed in the main arteries of all patients and in accessory renal arteries of 6 of 9 patients with accessory arteries, both before and after renal sympathetic denervation. Renal nerve stimulation before renal denervation elicited a substantial increase in systolic blood pressure, both in main (25.6±2.9 mm Hg; P <0.001) and accessory (24.3±7.4 mm Hg; P =0.047) renal arteries. After renal denervation, renal nerve stimulation–induced systolic blood pressure increase was blunted in the main renal arteries (Δ systolic blood pressure, 8.6±3.7 mm Hg; P =0.020), but not in the nondenervated renal accessory renal arteries (Δ systolic blood pressure, 27.1±7.6 mm Hg; P =0.917). This residual source of renal sympathetic tone may result in persistent hypertension after ablation and partly account for the large response variability.