Safety of catheter-based radiofrequency renal denervation on branch renal arteries in a porcine model

Emerging topics on renal denervation in hypertension: anatomical and functional aspects of renal nerves

Inappropriate sympathetic activation is closely associated with the development and progression of hypertension. Renal denervation (RDN) is a neuromodulation therapy performed using an intraarterial catheter in patients with hypertension. Recent randomized sham-operated controlled trials have shown that RDN has significant antihypertensive effects that last for at least 3 years. Based on this evidence, RDN is nearly ready for general clinical application. On the other hand, there are remaining issues to be addressed, including elucidation of the precise antihypertensive mechanisms of RDN, the appropriate endpoint of RDN during the procedure, and the association between reinnervation after RDN and the long-term effects of RDN. This mini review focuses on studies implicating anatomy of the renal nerves, which consist of afferent or efferent and sympathetic or parasympathetic nerves, the response of blood pressure to renal nerve stimulation, and reinnervation of renal nerves after RDN. A comprehensive understanding of the anatomical and functional aspects of the renal nerves and the antihypertensive mechanisms of RDN, including its long-term effects, will enhance our ability to incorporate RDN into strategies to treat hypertension in clinical practice. This mini review focuses on studies implicating anatomy of the renal nerves, which consist of afferent or efferent and sympathetic or parasympathetic nerves, the response of blood pressure to renal nerve stimulation, and reinnervation of renal nerves after renal denervation. Whether the ablation site is sympathetic dominant or parasympathetic dominant, and afferent dominant or efferent dominant, would in turn determine the final output of renal denervation. BP: blood pressure.

Computational Modeling of Catheter-based Radiofrequency Renal Denervation with Patient-specific Model

Renal sympathetic denervation (RDN) is an effective approach for uncontrolled hypertension. Although several studies have compared the ablation characteristics at various locations, there is no direct comparative study on the effect of ablation in main and branch renal artery (RAs) and different electrode materials. The study aims to investigate the effect of different electrode materials (copper, gold, and platinum) and positions (proximal, middle, or distal site) on ablation. A 3D patient-specific renal artery model and a unipolar model (470 kHz) were constructed to mimic RDN. Two therapeutic strategies, including main (site 1 and 2) and branch (site 3) ablations were simulated with three electrode materials. The finite element method was used to calculate the coupled electric-thermal-flow field. Maximum lesion depth, width, area, and lesion angle were analyzed. The results showed that the difference in lesion width and depth was no mere than 0.5 mm, and the maximum difference value in lesion area is 0.683 mm² among three electrode materials. The lesion angle of proximal site 1 versus middle site 2 was 58.39 ° and 52.23 °, but the difference between distal site 3 and site 1, or site 2 was 29.19 ° and 35.35 ° respectively. There is no significant difference in the use of the three electrode materials, and ablation at the distal site of the artery is more effective.Clinical Relevance-This provides a reference for the selection of RF electrode materials and ablation locations.

Comparison of ablation characteristics of three different radiofrequency applicators in renal sympathetic denervation

OBJECTIVE

Renal sympathetic denervation (RDN) is an alternative treatment for resistant hypertension (RH). This study aims to compare ablation effects using three radiofrequency applicators (i.e., balloon-based four electrodes, spiral and monopolar devices).

METHODS

An idealized three-dimensional model of the renal artery was established using COMSOL Multiphysics to mimic radiofrequency ablation (RFA). Radiofrequency (RF) energy was delivered to the tissue at the same simulation settings, i.e., 4, 6, and 8 W for 60 s, using the three abovementioned RF applicators. The temperature distribution in the tissue was calculated using the coupled electrical-thermal-fluid finite element method. Lesion borders were defined using 50 °C isotherms. The maximum lesion depth, width, area, and circumferential coverage rate were compared among the three applicators at a blood flow of 0.4 m/s. Monopolar RF ablations in a renal artery phantom model were performed to validate the reliability of the simulation method.

RESULTS

The balloon-based system yields greater lesion depths and widths compared with spiral and monopolar denervation under the same power. The range of maximum lesion depth is 1.58-3.11 mm for balloon-based RDN, 0.90-1.81 mm for spiral RDN and 1.12-2.38 mm for monopolar RDN, at a power of 4-8 W. The corresponding ranges of maximum lesion width are 2.22-5.73, 1.48-3.54, and 1.93-5.31 mm, respectively, and the circumferential coverage rates of the renal artery are 41.43%-91.99%, 31.71%-66.23%, and 9.55%-23.06%, respectively. The average velocity after balloon-based, spiral, and monopolar RDN increases by 3, 5, and 1 cm/s, respectively. The validation of the computer model offered prediction errors are <5% in terms of temperature at different locations (i.e., 2, 4, and 8 mm).

CONCLUSIONS

In terms of lesion size, balloon-based RDN appears to be the best option for the treatment of RH. However, the change in flow velocity in the arterial flow field suggests that its hemodynamic changes must be prioritized for investigating its safety. Although spiral catheter ablation yields the smallest lesion size and a significant change in flow velocity in the flow field, its coverage rate is larger than that of monopolar RDN; compared with balloon-based RDN, it did not obstruct most of the blood flow.

Renal Denervation by Noninvasive Stereotactic Radiotherapy Induces Persistent Reduction of Sympathetic Activity in a Hypertensive Swine Model

Background

We have previously reported the feasibility of noninvasive stereotactic body radiotherapy (SBRT) as a novel approach for renal denervation.

Methods and Results

Herein, from a translational point of view, we assessed the antihypertensive effect and chronological evolution of SBRT‐induced renal nerve injury within 6 months in a hypertensive swine model. Hypertension was induced in swine by subcutaneous implantation of deoxycorticosterone acetate pellets in combination with a high‐salt diet. A single dose of 25 Gy with SBRT was delivered for renal denervation in 9 swine within 3.4±1.0 minutes. Blood pressure levels at baseline and 1 and 6 months post‐SBRT were comparable to control (n=5), whereas renal norepinephrine was significantly lower at 6 months (P<0.05). Abdominal computed tomography, performed before euthanasia and renal function assessment, remained normal. Standard semiquantitative histological assessment showed that compared with control (1.4±0.4), renal nerve injury was greater at 1 month post‐SBRT (2.3±0.3) and peaked at 6 months post‐SBRT (3.2±0.8) (P<0.05), along with a higher proportion of active caspase‐3–positive nerves (P<0.05). Moreover, SBRT resulted in continuous dysfunction of renal sympathetic nerves and low level of nerve regeneration in 6 months by immunohistochemistry analysis.

Conclusions

SBRT delivering 25 Gy for renal denervation was safe and related to sustained reduction of sympathetic activity by aggravating nerve damage and inhibiting nerve regeneration up to 6 months; however, its translation to clinical trial should be cautious because of the negative blood pressure response in the deoxycorticosterone acetate–salt hypertensive swine model.

Combined renal and common hepatic artery denervation as a novel approach to reduce cardiometabolic risk: technical approach, feasibility and safety in a pre-clinical model

Background

Cardiovascular and metabolic regulation is governed by neurohumoral signalling in relevant organs such as kidney, liver, pancreas, duodenum, adipose tissue, and skeletal muscle. Combined targeting of relevant neural outflows may provide a unique therapeutic opportunity for cardiometabolic disease.

Objectives

We aimed to investigate the feasibility, safety, and performance of a novel device-based approach for multi-organ denervation in a swine model over 30 and 90 days of follow-up.

Methods

Five Yorkshire cross pigs underwent combined percutaneous denervation in the renal arteries and the common hepatic artery (CHA) with the iRF Denervation System. Control animals (n = 3) were also studied. Specific energy doses were administered in the renal arteries and CHA. Blood was collected at 30 and 90 days. All animals had a pre-terminal procedure angiography. Tissue samples were collected for norepinephrine (NEPI) bioanalysis. Histopathological evaluation of collateral structures and tissues near the treatment sites was performed to assess treatment safety.

Results

All animals entered and exited the study in good health. No stenosis or vessel abnormalities were present. No significant changes in serum chemistry occurred. NEPI concentrations were significantly reduced in the liver (− 88%, p = 0.005), kidneys (− 78%, p < 0.001), pancreas (− 78%, p = 0.018) and duodenum (− 95%, p = 0.028) following multi-organ denervation treatment compared to control animals. Histologic findings were consistent with favourable tissue responses at 90 days follow-up.

Conclusions

Significant and sustained denervation of the treated organs was achieved at 90 days without major safety events. Our findings demonstrate the feasibility of multi-organ denervation using a novel iRF Denervation System in a single procedure.

Safety of catheter-based radiofrequency renal denervation on branch renal arteries in a porcine model

OBJECTIVES

We aimed to investigate the safety of radiofrequency (RF)-renal denervation (RDN) on branch renal arteries (RAs) in a porcine model.

BACKGROUND

The efficacy of RF-RDN was enhanced by treatment of the branch RA, in addition to the main RA. However, there are concerns regarding the safety of RF-RDN on branch RA because of their smaller diameter and proximity to the kidney.

METHODS

RF was delivered to 24 RA from 12 swine. A total of 8 RA from 4 swine were untreated. Treated RA were examined by angiography and histopathology at 7, 30, and 90 days. Serum creatinine concentration, biophysical parameters during RF delivery, and renal norepinephrine concentration were also assessed.

RESULTS

Angiography revealed minimal late lumen loss and diameter stenosis in the main and branch RA at any time point. There was no change in serum creatinine after RF-RDN. Histopathologically, no augmentation of medial damage or neointimal formation was found in branch RA compared with main RA. No or minimal damage to surrounding tissues including the kidneys, ureters, lymph nodes, and muscles was observed at any time point in both the main and branch RA. Equivalent electrode temperature in the main and branch RA was achieved by automatic adjustment of output power by the generator. The renal norepinephrine concentration was significantly lower in the treated group compared with the untreated group.

CONCLUSIONS

RF-RDN on branch RA was safe in a porcine model, with stenosis-free healing of treated arteries and negligible kidney damage at 7, 30, and 90 days.