Blood pressure and autonomic responses to electrical stimulation of the renal arterial nerves before and after ablation of the renal artery

Efficacy and safety of sympathetic mapping and ablation of renal nerves for the treatment of hypertension (SMART): 6-month follow-up of a randomised, controlled trial

Background

Previous trials of renal denervation (RDN) have been designed to investigate reduction of blood pressure (BP) as the primary efficacy endpoint using non-selective RDN without intraoperatively verified RDN success. It is an unmet clinical need to map renal nerves, selectively denervate renal sympathetic nerves, provide readouts for the interventionalists and avoid futile RDN. We aimed to examine the safety and efficacy of renal nerve mapping/selective renal denervation (msRDN) in patients with uncontrolled hypertension (HTN) and determine whether antihypertensive drug burden is reduced while office systolic BP (OSBP) is controlled to target level (＜140 mmHg).

Methods

We conducted a randomized, prospective, multicenter, single-blinded, sham-controlled trial. The study combined two efficacy endpoints at 6 months as primary outcomes: The control rate of patients with OSBP ＜140 mmHg (non-inferior outcome) and change in the composite index of antihypertensive drugs (Drug Index) in the treatment versus Sham group (superior outcome). This design avoids confounding from excess drug-taking in the Sham group. Antihypertensive drug burden was assessed by a composite index constructed as: Class N (number of classes of antihypertensive drugs) × (sum of doses). 15 hospitals in China participated in the study and 220 patients were enrolled in a 1:1 ratio (msRDN vs Sham). The key inclusion criteria included: age (18-65 years old), history of essential HTN (at least 6 months), heart rate (≥70 bpm), OSBP (≥150 mmHg and ≤180 mmHg), ambulatory BP monitoring (ABPM, 24-h SBP ≥130 mmHg or daytime SBP ≥135 mmHg or nighttime SBP ≥120 mmHg), renal artery stenosis (＜50%) and renal function (eGFR ＞45 mL/min/1.73 m2). The catheter with both stimulation and ablation functions was inserted in the distal renal main artery. The RDN site (hot spot) was selected if SBP increased (≥5 mmHg) by intra-renal artery (RA) electrical stimulation; an adequate RDN was confirmed by repeated electronic stimulation if no increase in BP otherwise, a 2nd ablation was performed at the same site. At sites where there was decreased SBP (≥5 mmHg, cold spot) or no BP response (neutral spot) to stimulation, no ablation was performed. The mapping, ablation and confirmation procedure was repeated until the entire renal main artery had been tested then either treated or avoided. After msRDN, patients had to follow a predefined, vigorous drug titration regimen in order to achieve target OSBP (＜140 mmHg). Drug adherence was monitored by liquid chromatography-tandem mass spectrometry analysis using urine. This study is registered with ClinicalTrials.gov (NCT02761811) and 5-year follow-up is ongoing.

Findings

Between July 8, 2016 and February 23, 2022, 611 patients were consented, 220 patients were enrolled in the study who received standardized antihypertensive drug treatments (at least two drugs) for at least 28 days, presented OSBP ≥150 mmHg and ≤180 mmHg and met all inclusion and exclusion criteria. In left RA and right RA, mapped sites were 8.2 (3.0) and 8.0 (2.7), hot/ablated sites were 3.7 (1.4) and 4.0 (1.6), cold spots were 2.4 (2.6) and 2.0 (2.2), neutral spots were 2.0 (2.1) and 2.0 (2.1), respectively. Hot, cold and neutral spots was 48.0%, 27.5% and 24.4% of total mapped sites, respectively. At 6 M, the Control Rate of OSBP was comparable between msRDN and Sham group (95.4% vs 92.8%, p = 0.429), achieved non-inferiority margin -10% (2.69%; 95% CI -4.11%, 9.83%, p ＜ 0.001 for non-inferiority); the change in Drug Index was significantly lower in msRDN group compared to Sham group (4.37 (6.65) vs 7.61 (10.31), p = 0.010) and superior to Sham group (-3.25; 95% CI -5.56, -0.94, p = 0.003), indicating msRDN patients need significantly fewer drugs to control OSBP ＜140 mmHg. 24-hour ambulatory SBP decreased from 146.8 (13.9) mmHg by 10.8 (14.1) mmHg, and from 149.8 (12.8) mmHg by 10.0 (14.0) mmHg in msRDN and Sham groups, respectively (p < 0.001 from Baseline; p > 0.05 between groups). Safety profiles were comparable between msRDN and Sham groups, demonstrating the safety and efficacy of renal mapping/selective RDN to treat uncontrolled HTN.

Interpretation

The msRDN therapy achieved the goals of reducing the drug burden of HTN patients and controlling OSBP <140 mmHg, with only approximately four targeted ablations per renal main artery, much lower than in previous trials.

Funding

SyMap Medical (Suzhou), LTD, Suzhou, China.

Renal denervation ameliorated salt-induced hypertension by improving cardiac work, cardiac enzyme and oxidative balance in Sprague-Dawley rats

Background

Hypertension is associated with cardiovascular dysfunction, dysregulation of the antioxidant system and alteration of the level of some enzymes in the metabolic pathway. The possible modulatory effect of acute renal denervation (ARD) on cardiovascular function and the antioxidant system is still a subject of intense debate. This study sought to ascertain the ameliorative effects of ARD on cardiovascular parameters, antioxidant system, creatine kinase and lactate dehydrogenase levels.

Methods

Thirty-six Sprague-Dawley rats (5-6 weeks old) were divided into 6 groups of 6 animals each consisting of Normal Salt, High Salt, Normal Salt + Sham Denervation, High Salt + Sham Denervation, Normal Salt + Renal Denervation and High Salt + Renal Denervation. Induction of hypertension with 8 % salt in the diet lasted for 8 weeks. Renal or Sham denervation was thereafter done on selected groups. At the end of the experimental period, cardiovascular parameters, plasma antioxidant status, plasma creatine kinase (CK) and lactate dehydrogenase (LDH) levels were assessed. Significance level was set at p < 0.05.

Results

Salt-loading significantly increased systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial blood pressure (MABP), rate pressure product (RPP) while reducing superoxide dismutase (SOD), reduced glutathione (GSH) and catalase (CAT). Acute renal denervation significantly (p < 0.0001) reduced SBP, DBP, MABP, RPP, LDH and norepinephrine level while increasing SOD, GSH and CAT. ARD did not significantly alter CK level.

Conclusion

Acute renal denervation, by reducing sympathetic activity, ameliorates cardiovascular and antioxidant functions as well as reduces LDH level without significantly altering CK level in salt-induced hypertension.

Twenty-Four-Month Blood Pressure Results After Renal Denervation Using Endovascular Ultrasound

BACKGROUND Renal denervation has proven its efficacy to lower blood pressure in comparison to sham treatment in recent randomized clinical trials. Although there is a large body of evidence for the durability and safety of radiofrequency-based renal denervation, there are a paucity of data for endovascular ultrasound-based renal denervation (uRDN). We aimed to assess the long-term efficacy and safety of uRDN in a single-center cohort of patients. METHODS AND RESULTS Data from 2 previous studies on uRDN were pooled. Ambulatory 24-hour blood pressure measurements were taken before as well as 3, 6, 12, and 24 months after treatment with uRDN. A total of 130 patients (mean age 63±9 years, 24% women) underwent uRDN. After 3, 6, 12, and 24 months, systolic mean 24-hour ambulatory blood pressure values were reduced by 10±12, 10±14, 8±15, and 10±15 mm Hg, respectively, when compared with baseline (P<0.001). Corresponding diastolic values were reduced by 6±8, 6±8, 5±9, and 6±9 mm Hg, respectively (P<0.001). Periprocedural adverse events occurred in 16 patients, and all recovered without sequelae. CONCLUSIONS In this single-center study, uRDN effectively lowered blood pressure up to 24 months after treatment.

Rationale and Design of Sympathetic Mapping/Ablation of Renal Nerves Trial (SMART) for the Treatment of Hypertension: a Prospective, Multicenter, Single-Blind, Randomized and Sham Procedure-Controlled Study

Renal denervation (RDN) is proposed as a durable and patient compliance independent treatment for hypertension. However, 20-30% non-responder after RDN treatment weakened the therapeutic effect, which may be due to blind ablation. The renal nerve mapping/selective ablation system developed by SyMap Medical Ltd (Suzhou), China, has the function of mapping renal sympathetic/parasympathetic nerve sites and selectively removing renal sympathetic nerves and is expected to meet the urgent unmet clinical need of targeted RDN. The "Sympathetic Mapping/Ablation of Renal Nerves Trial" (SMART) is a prospective, multicenter, randomized, single-blinded, sham procedure-controlled trial, to evaluate the safety and efficacy of targeted renal sympathetic denervation in patients with essential and uncontrolled hypertension. The study is the first clinical registry trial using a targeted RDN for the treatment of uncontrolled hypertension; the dual-endpoint design can answer the question of how many antihypertensive drugs can be reduced in patients after RDN. The trial is registered on clinicaltrials.gov NCT02761811.

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.

Intravascular Ultrasound Can Be Used to Locate Nerves, but not Confirm Ablation, During Renal Sympathetic Denervation

Background

No methods exist for confirming nerve ablation in catheter-based renal sympathetic denervation (RDN).

Methods

We investigated the feasibility of using intravascular ultrasound (IVUS) to locate nerves and observe nerve integrity changes during RDN in a pig. To confirm our observations, we used post-RDN histological sections matched anatomically to the IVUS images.

Results

IVUS revealed multiple hypoechoic structures along the renal artery, whose locations matched those of nerves in the histological sections. Nerves clustered near the junction between the renal artery and vein. Histology confirmed necrosis of nerve bundles at RDN ablation sites, but no changes in echogenicity were observed using IVUS.

Conclusions

Although IVUS cannot currently be used to confirm ablation during RDN, it clearly reveals some clusters of renal sympathetic nerves. It remains to be demonstrated how IVUS can guide RDN devices and potentially improve ablation success.

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.

Predictors of blood pressure response to ultrasound renal denervation in the RADIANCE-HTN SOLO study

The blood pressure (BP) lowering response to renal denervation (RDN) remains variable with about one-third of patients not responding to ultrasound or radiofrequency RDN. Identification of predictors of the BP response to RDN is needed to optimize patient selection for this therapy. This is a post-hoc analysis of the RADIANCE-HTN SOLO study. BP response to RDN was measured by the change in daytime ambulatory systolic blood pressure (dASBP) at 2 months post procedure. Univariate regression was used initially to assess potential predictors of outcome followed by multivariate regression analysis. In the univariate analysis, predictors of response to RDN were higher baseline daytime ambulatory diastolic blood pressure (dADBP), the use of antihypertensive medications at screening, and presence of orthostatic hypertension (OHTN) whilst the presence of untreated accessory arteries was a negative predictor of response. Multivariate analysis determined that dADBP and use of antihypertensive medications were predictors of response to RDN with a trend for OHTN to predict response. Obese females also appeared to be better responders to RDN in an interaction model. RDN is more effective in patients with elevated baseline dADBP and those with OHTN, suggesting increased peripheral vascular resistance secondary to heightened sympathetic tone. These assessments are easy to perform in clinical setting and may help in phenotyping patients who will respond better to RDN.

Renal arteries denervation with second generation systems: a remedy for resistant hypertension?

Initial studies on renal denervation (RDN) for the treatment of non-controlled arterial hypertension (HTN) through radiofrequency ablation of renal arteries demonstrated that RDN is an effective therapeutic strategy to reduce arterial blood pressure (BP). Nonetheless, the first randomized study, SYMPLICITY-HTN-3, failed to demonstrate a clear benefit for RND over the control group. Technologic evolution, with the introduction of new second generation multi-electrode devices, allowed deep energy delivery along the full circumference of the vessel. Two recent randomized studies involving patients assuming (SPYRAL HTN-ON MED) or not (SPYRAL HTN-OFF MED) antihypertensive pharmacologic treatment, demonstrated the efficacy and safety of RDN using second generation systems for radiofrequency ablation. Another recent randomized study demonstrated that RDN with ultrasounds (RADIANCE-HTN SOLO) of the main renal arteries led to a significant BP reduction compared to the control group. These studies have once again raised the interest of the scientific community towards attempting to define the appropriate role of RDN in the treatment of hypertension. Nonetheless, larger and longer clinical trials will be necessary to draw further conclusions.

Extended Renal Artery Denervation Is Associated with Artery Wall Lesions and Acute Systemic and Pulmonary Hemodynamic Changes: A Sham-Controlled Experimental Study

Objectives

We sought to assess acute changes in systemic and pulmonary hemodynamics and microscopic artery lesions following extended renal artery denervation (RDN).

Background

RDN has been proposed to reduce sympathetic nervous system hyperactivation. Although the effects of RDN on systemic circulation and overall sympathetic activity have been studied, data on the impact of RDN on pulmonary hemodynamics is lacking.

Methods

The study comprised 13 normotensive Landrace pigs. After randomization, 7 animals were allocated to the group of bilateral RDN and 6 animals to the group of a sham procedure (SHAM). Hemodynamic measures, cannulation, and balloon-based occlusion of the renal arteries were performed in both groups. In the RDN group, radiofrequency ablation was performed in all available arteries and their segments. An autopsy study of the renal arteries was carried out in both groups.

Results

The analysis was performed on 12 pigs (6 in either group) since pulmonary thromboembolism occurred in one case. A statistically significant drop in the mean diastolic pulmonary artery pressure (PAP) was detected in the RDN group when compared with the SHAM group (change by 13.0 ± 4.4 and 10.0 ± 3.0 mmHg, correspondingly; P = 0.04). In 5 out of 6 pigs in the RDN group, a significant decrease in systemic systolic blood pressure was found, when compared with baseline (98.8 ± 17.8 vs. 90.2 ± 12.6 mmHg, P = 0.04), and a lower mean pulmonary vascular resistance (PVR) (291.0 ± 77.4 vs. 228.5 ± 63.8 dyn∗sec∗cm⁻⁵, P = 0.03) after ablation was found. Artery dissections were found in both groups, with prevalence in animals after RDN.

Conclusions

Extensive RDN leads to a rapid and significant decrease in PAP. In the majority of cases, RDN is associated with an acute lowering of systolic blood pressure and PVR. Extended RDN is associated with artery wall lesions and thrombus formation underdiagnosed by angiography.

Renal denervation as a synergistic tool for the treatment of polymorphic ventricular ectopic beats: A case report

INTRODUCTION

Ventricular ectopic beats (VEBs) are very common and often occur in hypertensive or obese individuals, as well as in patients presenting with either sleep apnea or structural cardiac disease. Sympathetic overactivity plays a crucial role in the development, continuation, and exacerbation of ventricular arrhythmias. Recent studies have reported the relevance of sympathetic activation in patients with ventricular arrhythmias and suggested a potential role for catheter-based renal denervation (RDN) in reducing the arrhythmic burden.

PATIENT CONCERNS

We describe a 38-year-old female symptomatic patient that at the time of presentation was complaining of fatigue in response to minor and medium efforts and not tolerating any physical activity, and episodes of tachycardia associated with dyspnoea, pre-syncope, and syncope.

DIAGNOSIS

She had a high incidence of polymorphic VEBs on 24-hour-Holter monitoring who also presented with left ventricular (LV) hypertrophy for which she was treated with bisoprolol 10 mg/d. The 24-hour-Holter on bisoprolol at baseline showed sinus rhythm with an average heart rate of 92 bpm. There were 44,743 isolated VEBs. A total of 2538 nonsustained ventricular tachycardia events were registered. Her cardiac magnetic resonance imaging showed an increase in LV diastolic diameter and impairment of the right ventricle.

INTERVENTIONS

The patient underwent endocardial ablation of the right ventricular outflow tract and the LV free lateral wall, and concomitantly underwent bilateral RDN.

OUTCOMES

Three months post-procedure, her 24-hour-Holter off medication demonstrated an average heart rate 72 bpm and a substantially reduced number of 2823 isolated monomorphic VEBs. Thus far, 18-months follow-up, she has been asymptomatic and doing physical exercises.

CONCLUSION

In our current patient, we used RDN as a synergistic method to attenuate the sympathetic overactivity, which is narrowly linked to VEBs appearance. Our case report highlighted that RDN may become a potential adjuvant treatment for VEBs in the future.

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.

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.

Enhanced arrhythmogenic potential induced by renal autonomic nerve stimulation: Role of renal artery catheter ablation

BACKGROUND

Renal artery catheter ablation has been reported as a possible therapeutic option for drug-refractory ventricular arrhythmias (VAs) associated with structural heart diseases.

OBJECTIVE

To further clarify its therapeutic background, we examined the relationship between electrical nerve stimulation (ENS)-induced blood pressure (BP) elevation and occurrence of VAs by using an acute canine model of renal artery ablation.

METHODS

Using a decapolar electrode catheter, ENS was successively applied from the distal, mid, and proximal segments of the renal artery in 8 beagles. The same ENS was repeated after accomplishment of radiofrequency ablation at the ostial site of the renal artery by using an irrigation catheter.

RESULTS

Before ablation, ENS increased BP from 140 ± 11/77 ± 11 to 167 ± 20/98 ± 16 mm Hg and heart rate from 100 ± 21 to 131±33 beats/min as well as induced VAs in 20 of the 45 ENS applications. Occurrence of VAs was associated with a greater magnitude of sympathetic nerve augmentation, and VAs were more frequently observed by ENS at the distal (67%) rather than mid/proximal segments of the renal artery (33%). Renal artery ablation was accomplished without any angiographic stenosis, and ENS-induced BP elevation, heart rate acceleration, and VAs occurrence were attenuated not only at the close segment (proximal) but also at the remote segments (mid/distal) of the renal artery.

CONCLUSION

The renal autonomic nerves are considered as one of the therapeutic targets for suppression of frequent VAs because its activation has arrhythmogenic potential and induces premature ventricular beats.

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.

Synergy of pulmonary vein isolation and catheter renal denervation in atrial fibrillation complicated with uncontrolled hypertension: Mapping the renal sympathetic nerve and pulmonary vein (the pulmonary vein isolation plus renal denervation strategy)?

INTRODUCTION

Disturbance of sympathetic and vagal nervous system participates in the pathogenesis of hypertension and atrial fibrillation (AF). Renal denervation (RDN) can modulate autonomic nervous activity and reduce blood pressure (BP) in hypertensive patients. We aimed to evaluate the effect of RDN combined with pulmonary vein isolation (PVI) in patients with AF and hypertension.

METHODS

Clinical trials including randomized data comparing PVI plus RDN vs PVI alone were enrolled. Primary outcome was incidence of AF recurrence after procedure.

RESULTS

A total of 387 patients, of them 252 were randomized and were enrolled. Mean age was 57 ± 10 years, 71% were male, and mean left ventricular ejection fraction was 57.4% ± 6.9%. Follow-up for randomized data was 12 months. Overall comparison for primary outcome showed that PVI + RDN was associated with significantly lower AF recurrence as compared with PVI alone (35.8% vs 55.4%, P < 0.0001). This advantageous effect was consistently maintained among randomized patients (37.3% vs 61.9%, odds ratio = 0.37, P = 0.0001), and among patients with implanted devices for detection of AF recurrence (38.9% vs 61.6%, P = 0.007). Post-hoc sensitivity and regression analysis demonstrated very good stability of this primary result. Pooled Kaplan-Meier analysis further showed that PVI + RDN was associated with significantly higher freedom from AF recurrence as compared with PVI alone (log-rank test, P = 0.001). Besides, RDN resulted in significant BP reduction without additionally increasing the risk of adverse events.

CONCLUSIONS

RDN may provide synergetic effects with PVI to reduce the burden of AF and improve BP control in patients with AF and uncontrolled hypertension.

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.

Reduction of Blood Pressure Following After Renal Artery Adventitia Stripping During Total Nephroureterectomy: Potential Effect of Renal Sympathetic Denervation

Case series

Patients: Male, 85 • Male, 89

Final Diagnosis: Essential hypertension

Symptoms: High blood pressure

Medication: Anti-hypertensive agents

Clinical Procedure: Operation

Specialty: Cardiology and Hypertension

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.

Resistant hypertension: Renal denervation or intensified medical treatment?

Resistant hypertension (RH) can be diagnosed if blood pressure (BP) is not controlled with the combination of three antihypertensive drugs, including a diuretic, all at effective doses. Patients affected by this condition exhibit a marked increase in the risk of cardiovascular and renal morbid and fatal events. They also exhibit an increased activity of the sympathetic nervous system which is likely to importantly contribute at the renal and other vascular levels to the hypertensive state. Almost 10years ago renal denervation (RDN) by radiofrequency thermal energy delivery to the walls of the renal arteries was proposed for the treatment of RH. Several uncontrolled studies initially reported that this procedure substantially reduced the elevated BP values but this conclusion has not been supported by a recent randomized control trial, which has almost marginalized this therapeutic approach. A revival, however, is under way because of recent positive findings and technical improvement that hold promise to make renal denervation more complete. The antihypertensive efficacy and overall validity of RDN will have to be tested against drug treatment of RH. Several studies indicate that an excess of aldosterone production contributes to RH and recent evidence documents indisputably that anti-aldosterone agents such as spironolactone can effectively control BP in many RH patients, although with some side effects that require close patients' monitoring. At present, it is advisable to treat RH with the addition of an anti-aldosterone agent. If BP control is not achieved or serious side effects become manifest RDN may then be considered.

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.

Cardiac autonomic innervation

The autonomic nervous system plays a key role in regulating changes in the cardiovascular system and its adaptation to various human body functions. The sympathetic arm of the autonomic nervous system is associated with the fight and flight response, while the parasympathetic division is responsible for the restorative effects on heart rate, blood pressure, and contractility. Disorders involving these two divisions can lead to, and are seen as, a manifestation of most common cardiovascular disorders. Over the last few decades, extensive research has been performed establishing imaging techniques to quantify the autonomic dysfunction associated with various cardiovascular disorders. Additionally, several techniques have been tested with variable success in modulating the cardiac autonomic nervous system as treatment for these disorders. In this review, we summarize basic anatomy, physiology, and pathophysiology of the cardiac autonomic nervous system including adrenergic receptors. We have also discussed several imaging modalities available to aid in diagnosis of cardiac autonomic dysfunction and autonomic modulation techniques, including pharmacologic and device-based therapies, that have been or are being tested currently.

Renal Afferents

Purpose of Review

The etiology of hypertension, a critical public health issue affecting one in three US adults, involves the integration of the actions of multiple organ systems, including the renal sympathetic nerves. The renal sympathetic nerves, which are comprised of both afferent (sensory input) and efferent (sympathetic outflow) arms, have emerged as a major potential therapeutic target to treat hypertension and disease states exhibiting excess renal sympathetic activity.

Recent Findings

This review highlights recent advances in both clinical and basic science that have provided new insight into the distribution, function, and reinnervation of the renal sympathetic nerves, with a focus on the renal afferent nerves, in hypertension and hypertension-evoked disease states including salt-sensitive hypertension, obesity-induced hypertension, and chronic kidney disease.

Summary

Increased understanding of the differential role of the renal afferent versus efferent nerves in the pathophysiology of hypertension has the potential to identify novel targets and refine therapeutic interventions designed to treat hypertension.

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.

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.

Twenty-Four-Hour Blood Pressure Monitoring to Predict and Assess Impact of Renal Denervation: The DENERHTN Study (Renal Denervation for Hypertension)

The DENERHTN trial (Renal Denervation for Hypertension) confirmed the blood pressure (BP) lowering efficacy of renal denervation added to a standardized stepped-care antihypertensive treatment for resistant hypertension at 6 months. We report here the effect of denervation on 24-hour BP and its variability and look for parameters that predicted the BP response. Patients with resistant hypertension were randomly assigned to denervation plus stepped-care treatment or treatment alone (control). Average and standard deviation of 24-hour, daytime, and nighttime BP and the smoothness index were calculated on recordings performed at randomization and 6 months. Responders were defined as a 6-month 24-hour systolic BP reduction ≥20 mm Hg. Analyses were performed on the per-protocol population. The significantly greater BP reduction in the denervation group was associated with a higher smoothness index (P=0.02). Variability of 24-hour, daytime, and nighttime BP did not change significantly from baseline to 6 months in both groups. The number of responders was greater in the denervation (20/44, 44.5%) than in the control group (11/53, 20.8%; P=0.01). In the discriminant analysis, baseline average nighttime systolic BP and standard deviation were significant predictors of the systolic BP response in the denervation group only, allowing adequate responder classification of 70% of the patients. Our results show that denervation lowers ambulatory BP homogeneously over 24 hours in patients with resistant hypertension and suggest that nighttime systolic BP and variability are predictors of the BP response to denervation.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01570777.

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.

Integration of renal sensory afferents at the level of the paraventricular nucleus dictating sympathetic outflow

The sympathetic nervous system has been identified as a major contributor to the pathophysiology of chronic heart failure (CHF) and other diseases such as hypertension and diabetes, both in experimental animal models and patients. The kidneys have a dense afferent sensory innervation positioning it to be the origin of multimodal input to the central nervous system. Afferent renal nerve (ARN) signals are centrally integrated, and their activation results in a general increase in sympathetic tone, which is directed toward the kidneys as well as other peripheral organs innervated by the sympathetic nerves. In the central nervous system, stimulation of ARN increases the neuronal discharge frequency and neuronal activity in the paraventricular nucleus (PVN) of the hypothalamus. The activity of the neurons in the PVN is attenuated during iontophoretic application of glutamate receptor blocker, AP5. An enhanced afferent renal input to the PVN may be critically involved in dictating sympathoexcitation in CHF. Furthermore, renal denervation abrogates the enhanced neuronal activity within the PVN in rats with CHF, thereby possibly contributing to the reduction in sympathetic tone. Renal denervation also restores the decreased endogenous levels of neuronal nitric oxide synthase (nNOS) in the PVN of rats with CHF. Overall, these data demonstrate that sensory information originating in the kidney excites pre-autonomic sympathetic neurons within the PVN and this "renal-PVN afferent pathway" may contribute to elevated sympathetic nerve activity in hyper-sympathetic disease conditions such as CHF and hypertension.