Peregrine system infusion catheter for neurolytic renal denervation in hypertension: an overview of its safety and efficacy

INTRODUCTION

Resistant hypertension (HTN), despite the tremendous advances in pharmacotherapy, is a major global problem. Transcatheter renal denervation (RDN) could be a pertinent strategy for resistant HTN and patients with poor pharmacotherapy adherence. Nonetheless, the adoption of energy-based RDN in clinical practice is slow and alternative approaches are needed.

AREAS COVERED

The review focuses on the assessment of the Peregrine System Infusion Catheters. The system is designed for chemically mediated transcatheter RDN by the infusion publications on the Peregrine system. The theoretical assumptions for chemically mediated RDN, design of the system, data from preclinical and clinical studies, and further perspectives are discussed.

EXPERT OPINION

Peregrine System Infusion Catheters are the only catheter on the market designed for chemically mediated RDN by the infusion of the neurolytic agent. Chemical neurolysis more efficiently destroys nerves around the renal artery in comparison to energy-based catheters, due to deeper tissue penetration and circumferential distribution resulting in a wider range of effective nerve injury. Chemically mediated RDN by the infusion of the neurolytic agent (alcohol) has an excellent safety profile as confirmed in initial clinical trials which also suggested high efficacy. Currently, there is an ongoing phase III sham-control study. Other possible applications of this technology include clinical settings like heart failure or atrial fibrillation.

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.

Long-Term Results up to 12 Months After Catheter-Based Alcohol-Mediated Renal Denervation for Treatment of Resistant Hypertension

Supplemental Digital Content is available in the text.

Background:

Primary results of this prospective, open-label, multicenter trial suggested that alcohol-mediated renal denervation with perivascular injection of dehydrated alcohol using the Peregrine System Infusion Catheter safely reduces blood pressure (BP) in patients with resistant hypertension. To date, maintenance of the BP-lowering effect beyond 6 months using this novel technology has not been reported. This article describes the final, 12-month follow-up data on the safety and efficacy of alcohol-mediated renal denervation in these patients.

Methods:

Forty-five patients with resistant hypertension on a stable regimen of on average 5.1±1.5 antihypertensive medications underwent successful bilateral renal denervation using the Peregrine Catheter with alcohol as the neurolytic agent (0.6 mL per renal artery). Apart from 2 vascular access pseudoaneurysms (both without sequelae), no major procedural complications occurred.

Results:

At 12 months post-procedure, mean 24-hour ambulatory systolic and diastolic BP were reduced by 10 mm Hg (95% CI, −16 to −5) and 7 mm Hg (−10 to −3), respectively (P<0.001). Office systolic/diastolic BP was reduced by 20/10 mm Hg (−27, −13/−14, −6; <0.001). Compared with baseline, the number of antihypertensive medications was reduced in 21% of patients, while it was increased in 19%. From baseline to 12 months, serum creatinine, urea, cystatin C, and spot urine albumin levels remained unchanged. The change in estimated glomerular filtration rates (−3.9±10.3 mL/minute per 1.73 m² [95% CI, −7.1 to −0.75]; P=0.02) was within the expected range. There were no cases of renal artery stenosis up to 12-month follow-up.

Conclusions:

Catheter-based chemical renal denervation with dehydrated alcohol using the Peregrine Catheter seems to safely reduce BP at follow-up of up to 12 months. Further randomized and sham controlled studies are underway to further validate these findings.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02570113.

Blood pressure lowering with alcohol-mediated renal denervation using the Peregrine infusion Catheter is independent of injection site location

OBJECTIVES

The current analysis utilized core laboratory angiographic data from a prospective, single-arm, open-label, multi-center feasibility study to ascertain whether the location of alcohol infusion within main renal arteries during renal denervation (RDN) had an impact on the BP-lowering effect at 6 months.

BACKGROUND

The influence of the location of alcohol infusion during RDN, within the main renal artery (proximal, middle, or distal), on the magnitude of the blood pressure (BP) lowering is unstudied.

METHODS

The Peregrine Catheter was used to perform alcohol-mediated RDN with an infusion of 0.6 mL of alcohol per artery as the neurolytic agent in 90 main arteries and four accessory arteries of 45 patients with hypertension.

RESULTS

No relationship between the site of alcohol infusion and change from baseline in both office systolic and 24-hour systolic ambulatory BP (ABP) at 6 months was observed. When analyzed at the artery level, the least squares (LS) mean changes ± SEM from baseline to 6 months post-procedure in 24-hour systolic ABP when analyzed by renal arterial location were -11.9 ± 2.4 mmHg (distal), -10 ± 1.6 mmHg (middle), and -10.6 ± 1.3 mmHg (proximal) (all p < 0.0001 for change from baseline within groups). The results were similar for office systolic BP. There was no difference between treated locations (proximal is reference).

CONCLUSION

In this post-hoc analysis, the location of alcohol infusion within the main renal artery using the Peregrine system, with alcohol as the neurolytic agent for chemical RDN, did not affect the magnitude of BP changes at 6 months.

Catheter-based alcohol-mediated renal denervation for the treatment of uncontrolled hypertension: design of two sham-controlled, randomized, blinded trials in the absence (TARGET BP OFF-MED) and presence (TARGET BP I) of antihypertensive medications

BACKGROUND

Arterial hypertension is a common and life-threatening condition and poses a large global health burden. Device-based treatments have been developed as adjunctive or alternative therapy, to be used with or without antihypertensive medication for treating uncontrolled hypertension. The safety and feasibility of chemical renal denervation (RDN) using the Peregrine Catheter and alcohol were demonstrated in a first-in-man and open-label clinical trials, prompting the initiation of the ongoing TARGET BP OFF-MED and TARGET BP I trials.

DESIGN

The TARGET BP trials are randomized, blinded, sham-controlled trials designed to assess the safety and efficacy of alcohol-mediated RDN for the treatment of uncontrolled hypertension in the absence of antihypertensive medications (TARGET BP OFF-MED) or in addition to prescribed antihypertensive medications (TARGET BP I). Subjects with confirmed uncontrolled hypertension and suitable renal artery anatomy are randomized (1:1) to receive either RDN using the Peregrine Kit with alcohol (0.6 mL per renal artery) infused through the Peregrine Catheter or diagnostic renal angiography only (sham procedure). TARGET BP OFF-MED completed enrollment and randomized 96 subjects. TARGET BP I will randomize approximately 300 subjects and will transition to an open-label safety cohort of approximately 300 subjects receiving RDN once the primary efficacy endpoint of the Randomized Controlled Trial (RCT) cohort has been met. Primary endpoints are change in mean 24-hour ambulatory systolic blood pressure from baseline to 8 weeks (TARGET BP OFF-MED) and 3 months (TARGET BP I) post-procedure.

CONCLUSION

The TARGET BP trials are the first large-scale, international, randomized trials aimed to investigate the safety and BP lowering efficacy of a novel RDN method, with perivascular alcohol delivery using the Peregrine Kit.

Evaluating the thermal performance of a balloon-based renal sympathetic denervation system with array electrodes: a finite element study

Renal denervation transmits radiofrequency (RF) energy through an electrode to treat resistant hypertension (RH), applying ablation in the renal artery. Several experimental studies have shown that this treatment has been used effectively to treat RH. The aim of this paper is to investigate the effect of ablation parameters (i.e., electrode length, applied voltage, ablation time, and blood flow) on the temperature distribution using a balloon-based array electrodes system. A simplified three-dimensional model including four electrodes and a balloon was established. The balloon diameter was 3 mm and placed in a 5 mm diameter renal artery for forming intra-arterial occlusion. Four electrodes were mounted on the balloon and distributed in the same plane to mimic circumferential RF ablation. Computer simulations were conducted to investigate the thermal performances of the device by setting different electrode configurations, treatment protocols, and physiological factors. The thermal performances including the thermal distribution, maximum lesion depth, length, and area were analyzed. The lesion shape of the array RF electrodes was approximately a sphere with a 100% circumference coverage rate of the renal artery. The lesion depth and length increase with each factor except for blood velocity. Increasing the electrode length from 2 to 4 mm or 2 to 6 mm, the lesion depth increases by 1.15 mm and 0.54 mm at 60 s. The corresponding lesion length increases by 2.65 mm and 2.34 mm, respectively. The range of effective lesion depth is 1.90-4.90 mm, at a voltage of 15-30 V. But the peak temperature at the arterial outer wall exceeded 100 °C when the voltage is above 25 V. In tissue, the degree of thermal injury in the 2 mm area reached 100%, but in blood was not more than 5%. There was no significant difference at different flow conditions because the difference value in lesion depth was not exceeded 0.5 mm. The results showed that the balloon-based four electrodes system is expected to overcome the difficulty of incomplete ablation. In clinical application, 2 mm-electrode is recommended to avoid long wall damage as much as possible and control the voltage below 25 V. This treatment has little thermal injury on the blood, which means it may avoid coagulation formation. Moreover, the application of this device does not need to consider the difference in individual blood velocity.

Microdissection of the Human Renal Nervous System

Despite the use of renal denervation to treat hypertension, the anatomy of the renal nervous system remains poorly understood. We performed a detailed quantitative analysis of the human renal nervous system anatomy with the goal of optimizing renal denervation procedural safety and efficacy. Sixty kidneys from 30 human cadavers were systematically microdissected to quantify anatomic variations in renal nerve patterns. Contrary to current clinical perception, not all renal innervation followed the main renal artery. A significant portion of the renal nerves (late arriving nerves) frequently reached the kidney (73% of the right kidney and 53% of the left kidney) bypassing the main renal artery. The ratio of the main renal artery length/aorta-renal hilar distance proved to be a useful variable to identify the presence/absence of these late arriving nerves (odds ratio, 0.001 (95% CI, 0.00002–0.0692; P : 0.001) with a cutoff of 0.75 (sensitivity: 0.68, specificity: 0.83, area under ROC curve at threshold: 0.76). When present, polar arteries were also highly associated with the presence of late arriving nerve. Finally, the perivascular space around the proximal main renal artery was frequently occupied by fused ganglia from the solar plexus (right kidney: 53%, left kidney: 83%) and/or by the lumbar sympathetic chain (right kidney: 63%, left kidney: 60%). Both carried innervation to the kidneys but importantly also to other abdominal and pelvic organs, which can be accidentally denervated if the proximal renal artery is targeted for ablation. These novel anatomic insights may help guide future procedural treatment recommendations to increase the likelihood of safely reaching and destroying targeted nerves during renal denervation procedures.

Effects of different ablation points of renal denervation on the efficacy of resistant hypertension

Objective

To explore the blood pressure response to different ablation points of renal denervation (RDN) in patients with resistant hypertension

Methods

A total of 42 cases with resistant hypertension treated by RDN in our center from 2013 to 2015 were retrospectively analyzed. The patients were divided into two groups according to the different ablation points of RDN: the standard treatment group (spiral ablation from near to proximal, with less than 8 points per artery) and the intensive treatment group (from near to far by spiral ablation, with at least 8 points per artery), with 21 patients in each group. The ablation parameters, including points, impedance, actual wattage, and actual temperature, were recorded intraoperatively. Renal angiography was performed again after RDN. Ambulatory blood pressure (ABP) images were taken for all patients at the baseline and 6 months after operation.

Results

The mean 24-h blood pressure of the standard treatment group was lower than that of the baseline (24-h systolic blood pressure decreased by 7.4 ± 10.6 mmHg and 24-h diastolic blood pressure decreased by 4.6  ± 6.1 mmHg), and the mean 24-h blood pressure decreased significantly from baseline to 6 months in the intensive treatment group (24–h systolic blood pressure decreased by 27.4 ±  11.4 mmHg, P < 0.0001; 24–h diastolic blood pressure decreased by 10.9 ±  9.6 mmHg, P = 0.005). There was a positive correlation between the decrease of systolic/diastolic 24-hour mean and the number of ablation points used in the procedure. The mean value of systolic and diastolic blood pressure was positively correlated with ablation points at 24-hour (R² = 0.777 and 0.633 respectively, P < 0.01). There were no adverse events in either group after the operation and during the follow-up.

Conclusions

RDN could significantly reduce BP in patients with resistant hypertension. Our study showed that the antihypertensive effect appeared to be positively correlated with the number of ablation points.

Alcohol-Mediated Renal Sympathetic Neurolysis for the Treatment of Hypertension: The Peregrine™ Infusion Catheter

Renal sympathetic denervation using conventional non-irrigated radiofrequency catheters has potential technical shortcomings, including limited penetration depth and incomplete circumferential nerve damage, potentially impacting therapeutic efficacy. Against this background, second generation multi-electrode, radiofrequency and ultrasound renal denervation systems have been developed to provide more consistent circumferential nerve ablation. Irrigated catheters may allow deeper penetration while minimizing arterial injury. In this context, catheter-based chemical denervation, with selective infusion of alcohol, a potent neurolytic agent, into the perivascular space, may minimize endothelial, intimal and medial injury while providing circumferential neurolysis. Animal studies demonstrate pronounced renal norepinephrine level reductions and consistent renal nerve injury after perivascular alcohol infusion using the Peregrine Catheter. Early clinical studies demonstrated significant blood pressure reductions and a reasonable safety profile. Randomized sham-controlled trials (NCT03503773, NCT02910414) are underway to examine whether the aforementioned theoretical advantages of alcohol-medicated denervation with the Peregrine System™ Kit translate into clinical benefits.

Laparoscopic Renal Denervation System for Treating Resistant Hypertension: Overcoming Limitations of Catheter-Based Approaches

GOAL

In a pivotal clinical trial, the percutaneous catheter-based renal denervation system developed to treat resistant hypertension did not show effectiveness in reducing blood pressure because of its fundamental limitation to ablate deeper nerves present around the renal artery.

METHODS

We propose a new renal denervation strategy called laparoscopicdenervation system (LDS) based-on laparoscopy procedure to ablate the renal nerves completely but inhibit the thermal arterial damage.The system has flexible electrodes to bend around the arterial wall to ablate nervesThe simulation study using validated in-silico models evaluated the heat distributionon the outer arterial wall,and an acute animal study (swine model) was conducted to demonstrate the feasibility of LDS in vivo.

RESULTS

The simulation studyconfirmedthat LDS could localize the heat distributionbetween the electrode and the outer arterial wall. In the animal study, we could maximize nerve denervation by the localizing ablation energy within the renal nerves and achieve nerve denaturationand decrease in neural density by 20.78% (P < 0.001), while maintaining a constant tip temperature of 65 °C for the duration of 70 s treatment. The study confirmed intact lumen artery through histological analysis and acute reduction in systolic blood pressure by 9.55 mmHg (p < 0.001) Conclusion: The LDS presented here has potential to effectively and safely ablate the renal nerves, independent of anatomical variation and nerve distribution, to control hypertension in real clinical conditions.

SIGNIFICANCE

LDS approach is innovative, inventive, and presents a novel technique totreat hypertension.

Accurate Depth of Radiofrequency-Induced Lesions in Renal Sympathetic Denervation Based on a Fine Histological Sectioning Approach in a Porcine Model

Background—

Ablation lesion depth caused by radiofrequency-based renal denervation (RDN) was limited to <4 mm in previous animal studies, suggesting that radiofrequency-RDN cannot ablate a substantial percentage of renal sympathetic nerves. We aimed to define the true lesion depth achieved with radiofrequency-RDN using a fine sectioning method and to investigate biophysical parameters that could predict lesion depth.

Methods and Results—

Radiofrequency was delivered to 87 sites in 14 renal arteries from 9 farm pigs at various ablation settings: 2, 4, 6, and 9 W for 60 seconds and 6 W for 120 seconds. Electric impedance and electrode temperature were recorded during ablation. At 7 days, 2470 histological sections were obtained from the treated arteries. Maximum lesion depth increased at 2 to 6 W, peaking at 6.53 (95% confidence interval, 4.27–8.78) mm under the 6 W/60 s condition. It was not augmented by greater power (9 W) or longer duration (120 seconds). There were statistically significant tendencies at 6 and 9 W, with higher injury scores in the media, nerves, arterioles, and fat. Maximum lesion depth was positively correlated with impedance reduction and peak electrode temperature (Pearson correlation coefficients were 0.59 and 0.53, respectively).

Conclusions—

Lesion depth was 6.5 mm for radiofrequency-RDN at 6 W/60 s. The impedance reduction and peak electrode temperature during ablation were closely associated with lesion depth. Hence, these biophysical parameters could provide prompt feedback during radiofrequency-RDN procedures in the clinical setting.

Renal Artery Branch Denervation: Evaluation of Lesion Characteristics Using a Thermochromic Liquid Crystal Phantom Model

BACKGROUND

Lately, combined main vessel and branch ablation has been recommended during radiofrequency (RF) renal artery denervation. Utilising a validated renal artery phantom model, we aimed (1) to determine thermal injury extent (lesion depth, width and circumferential coverage) and electrode-tissue interface temperature for branch renal artery ablation, and (2) to compare the extent of thermal injury for branch versus main vessel ablation using the same RF System.

METHODS

We employed a gel based renal artery phantom model simulating variable vessel diameter and flow, which incorporated a temperature sensitive thermochromic-liquid-crystal (TLC) film for assessing RF ablation thermodynamics. Ablations in a branch renal artery model (n = 32) were performed using Symplicity Spyral (Medtronic, Minneapolis, MN, USA). Lesion dimensions defined by the 51 °C isotherm, circumferential injury coverage, and electrode-tissue interface temperature were measured for all ablations at 60 seconds.

RESULTS

Lesion dimensions were 2.13 ± 0.13 mm and 4.13 ± 0.18 mm for depth and width, respectively, involving 23% of the vessel circumference. Maximum electrode-tissue interface temperature was 68.31 ± 2.29 °C. No significant difference in lesion depth between branch and main vessel ablations was found (Δ = 0.02 mm, p = 0.60). However, lesions were wider in the branch (Δ=0.49 mm, p < 0.001) with a larger circumferential coverage compared to main vessel (arc angle of 82.02±3.27° versus 54.90±4.36°, respectively).

CONCLUSIONS

In the phantom model, branch ablations were of similar depth but had larger width and circumferential coverage compared to main vessel ablations. Concerning safety, no overheating at the electrode-tissue interface was observed.

Anatomic Conformation of Renal Sympathetic Nerve Fibers in Living Human Tissues

Renal denervation using radiofrequency catheter ablation is known to eliminate the renal sympathetic nerve and to lower blood pressure in patients with resistant hypertension. We sought to investigate the detailed anatomic conformation of the peri-renal arterial sympathetic nerve fibers with living human specimens. Peri-renal arterial tissue was harvested from patients undergoing elective radical or simple nephrectomy. Digital images of each section from the distal arterial bifurcation to the proximal margin were obtained and analyzed after immunohistochemical staining with anti-tyrosine hydroxylase antibodies. A total of 3,075 nerve fibers were identified from 84 sections of peri-renal arterial tissue from 28 patients (mean age 62.5 ± 10.2 years, male 68%). Overall, 16% of nerve fibers were located at distances greater than 3 mm from the endoluminal surface of the renal artery. The median distance from the arterial lumen to the nerve fibers of the proximal, middle, and distal renal arterial segments was 1.51 mm, 1.48 mm, and 1.52 mm, respectively. The median diameter of the nerve fibers was 65 μm, and there was no significant difference between the segments. A substantial proportion of the sympathetic nerve fibers were located deeper in the peri-arterial soft tissue than in the lesion depth created by the conventional catheter-based renal sympathetic denervation system.

Renal Denervation by Transaortic Periarterial Ethanol Injection: An Experimental Study in Porcines

AIMS

To evaluate the feasibility, safety and efficacy of renal sympathetic denervation via endoluminal transaortic periarterial ethanol injection.

METHODS AND RESULTS

In 11 normotensive pigs transaortic puncture was performed with a 90-cm 21G needle with subsequent unilateral ethanol injection to the periarterial space. Needle placement was achieved using a 7F steerable sheath fluoroscopically positioned slightly above the renal artery origin. Blood pressure measurements and abdominal CT scans were performed immediately pre- and postintervention and 4 weeks later. After euthanasia norepinephrine concentration of both kidneys (RTNEC) was determined and renal arteries and surrounding tissues histologically examined to assess induced nerve fibre degeneration.

RESULTS

All but one procedure were technically successful. One major complication with accidental ethanol injection into the renal artery and subsequent infarction occurred. One pig died from no intervention-related cardiac arrest. The 4-week follow-up was uneventful in the remaining 10 animals. RTNEC was significantly lower on the treated side in eight of ten pigs (mean decrease 36.6%) with correlating histopathological signs of nerve degeneration.

CONCLUSIONS

Renal sympathicolysis by transaortic periarterial ethanol injection was feasible and effective in a porcine model. This approach may be an alternative to catheter-based RFA or other methods of renal denervation.

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.

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.