Abstract
Background/Purpose
We update the pre-clinical and early clinical results using a novel endovascular approach, to perform chemical renal denervation, via peri-adventitial injection of micro-doses of dehydrated alcohol (ethanol–EtOH).
Methods/Materials
A novel, three-needle delivery device (Peregrine™) was used to denervate the renal arteries of adult swine (n = 17) and in a first-in-man feasibility study (n = 18). In the pre-clinical testing EtOH was infused bilaterally with one infusion per renal artery into to the perivascular space, using EtOH doses of 0.3 ml/artery (n = 8), and 0.6 ml/artery (n = 9), and with saline sham control (0.4 ml/artery n = 3). Renal parenchymal norepinephrine (NE) concentration (performed blindly), and safety were the primary endpoints. Data from the first-in-man study (n = 18) to evaluate device performance, safety and peri-procedural pain are reported.
Results
In the pre-clinical testing renal function was unchanged at 3-month follow-up. Angiography at 90 days (n = 34 arteries) demonstrated normal appearing renal arteries, unchanged from baseline, and without stenosis or other abnormalities. The reductions in mean renal parenchymal NE reductions at 3 months were 68% and 88% at doses of 0.3 and 0.6 ml, respectively (p < 0.001 vs. controls). In the first-in-man study, there was 100% device success, no complications, a mean treatment time of 4.3 ± 3 minutes/artery, and minimal or no patient discomfort during treatment. Angiography at 6-months showed no evidence of renal artery stenosis, and evidence of a reduction of blood pressure from baseline.
Conclusion
Perivascular RDN using micro-doses of alcohol is a promising alternative to energy-based systems to achieve dose-dependent, predictable, safe and essentially painless renal denervation. Further clinical evaluation is warranted.
Summary
(For annotated table of contents) This paper describes the preclinical results, in a porcine model, and the early first-in-man results, using the Peregrine™ chemical renal denervation catheter to perform renal sympathetic denervation using micro-doses of alcohol.
1
Introduction
In the 1930s–1950s surgical renal sympathectomy was used to treat severe hypertension . More recently, catheter-based renal sympathetic denervation has been performed using a point-by-point, mono-polar radiofrequency (RF) ablation catheter from the lumen of the renal artery to treat patients . This technique has been shown to disrupt renal sympathetic nerve activity , resulting in significant and sustained reduction in office-based blood pressure in patients with severe and medically resistant hypertension .
Despite this early success, the concept of renal sympathetic nerve denervation (RDN) as a means to treat resistant hypertension has been challenged by the recent negative efficacy results from the Symplicity HTN-3 trial . However, before dismissing renal denervation, it is important to understand that there are significant issues with radiofrequency, point-by-point ablation that may limit efficacy and the ability to predictably achieve adequate levels of renal sympathetic nerve denervation. These shortcomings include pain, limited nerve ablation depth , a risk of stenosis and intimal thrombus formation related to medial thermal injury , as well as inconsistent and unpredictable circumferential denervation. Second generation, energy-based, multi-electrode radiofrequency and ultrasound ablation concepts may decrease pain burden and procedure time, but may not resolve the inherent limitations related to thermal injury to the media, depth and adequacy of denervation, and pain .
In this context, catheter-based chemical neurolysis, with the selective infusion of a potent neurolytic agent, such as alcohol, into the perivascular (adventitial) space, has the potential to minimize intimal and medial vessel injury while providing circumferential, deep and consistent renal sympathetic denervation. The encouraging short-term results using alcohol for renal denervation in a porcine model were recently reported .
The longer-term preclinical studies, presented in this paper, demonstrate that alcohol delivered locally and precisely to the adventitial and peri-adventitial space produces a sustained, profound and predictable reduction in renal parenchymal norepinephrine levels, with histopathological evidence of circumferential, and deep (typically 7–12 mm deep to the intima) sympathetic nerve injury, and with sparing of the normal constituents of the renal artery wall. The early results from the first in man clinical study, presented here demonstrate safety, ease of use, lack of pain, and the feasibility of this approach.
2
Materials and methods
2.1
Preclinical studies
A novel, three needle-based delivery device, (Peregrine System™, Ablative Solutions, Inc., Kalamazoo, MI) was introduced via the femoral artery into renal arteries of adult swine using fluoroscopic guidance. This drug infusion catheter is an endovascular delivery catheter that contains three distal needles housed within individual guide tubes, which are contained within body of the catheter. The catheter has a steerable, radio-opaque 2 cm fixed, floppy guide-wire at its distal end to minimize renal artery trauma and allow steer ability, when needed, into appropriate branch vessels ( Fig. 1 ).
This study was conducted under the general principles of Good Laboratory Practice (GLP) regulations as set forth in 21 CFR 58. The protocol for this study was reviewed and approved by the IACUC of the test facility, which is accredited by AALAC and licensed by the USDA. Animals were pre-medicated with 325 mg of aspirin and 75 mg of clopidogrel by mouth once daily for 2 days before the procedure.
After the animals were prepared for sterile surgery, one femoral artery was accessed using the Seldinger technique, and a 7 French introducer was placed. Intravenous heparin was given to all animals to achieve an ACT of > 250 sec. In all cases the right and left renal arteries of the pig were engaged using a 7 French RDC-1 guiding catheter. Prior to infusion of either ethanol or saline injections, angiography of each renal artery was performed using iohexol contrast diluted by 25% with normal saline.
The Peregrine™ injection catheter is intended to be used under fluoroscopic guidance by a single-operator using standard endovascular techniques and to allow safe and reproducible fluid injection into the adventitial and peri-adventitial space of a target vessel ( Fig. 2 ). The 0.008” needles that reside within the distal tip of the catheter’s guide tubes are advanced to a depth of 3.5 ± 0.25 mm deep to the intima (i.e., beyond the tip of the guide tube) and at 120° separation, one needle to the others. The specialized handle, allows advancement of the three guiding tubes, followed by simultaneous advancement of the three injection needles into the adventitial space. These tiny needles are made radiopaque, so that they can be easily seen under fluoroscopy. The needles are the equivalent of a ~ 30 gauge needle so that they can be safely advanced through the renal arterial wall without causing bleeding, even after heparin administration . The alcohol (ethanol) is delivered through a luer-lock connector at the proximal end of the handle, resulting in the infusion of the alcohol through the tips of the three needles of the Peregrine™ catheter, and directly into the perivascular, adventitial and peri-adventitial space. This creates a reproducible, deep and circumferential delivery of alcohol to the perivascular space ( Fig. 3 ).
In both the pre-clinical and clinical studies, the successful deployment of the tubes and needles are confirmed by fluoroscopy ( Figs. 1 and 2 ). The radio-opacity of the guide tube tips and of the needles allows visual confirmation of the exact placement of the needle tips and prevents the potential for injection into the lumen. In the porcine study the EtOH or saline (sham) fluid was then administered, using a 1.0 ml luer-lock syringe attached to the proximal injection lumen at the handle of the catheter. The infusion is performed over 1–2 minutes.
Two volumes of EtOH were used in this study: 0.3 ml/artery (n = 8 pigs/16 arteries) and 0.6 ml/artery (n = 9 pigs/18 arteries). A procedural control group was also studied using the infusion of 0.4 ml of saline/artery (n = 3). This was a “sham” arm to control for nonspecific effects that might be caused by mechanical injury from either the guide tubes or the needles, and/or any non-specific effects of fluid delivery. Once the treatment agent was infused, the dead space of the catheter was flushed with a very small volume of normal saline (0.1 ml) to clear the dead space and ensure delivery of the agent. After treatment of the first renal artery the device was removed from the animal, inspected and flushed. The contra-lateral renal artery was then engaged, and the same fluid infusion sequence was performed in the contralateral renal artery. After the treatment of the second renal artery, the animals were recovered and housed for restudy and sacrifice at 3-months post-intervention. The animals were treated with aspirin 162 mg/day for seven days after intervention.
Histopathology was used to evaluate circumferential spread of alcohol by having the pathologist evaluate and document the location (in terms of circumference and depth) of any noted neuritis and neurolysis. The pathologists were blinded as to the treatment (control, alcohol or naïve).
The efficacy of denervation was assessed by measurement of renal parenchymal norepinephrine (NE) levels (analyzed by HPLC, with electrochemical detection), as well as histopathologic evaluation of the peri-renal nerves at the end of the three-month sacrifice period. Safety was evaluated by serial blood tests for renal function, 45 and 90-day angiographic studies, and histopathologic evaluation of the renal artery and kidney. At the end of the study period the animals were anesthetized, and angiography of the treated right and left renal arteries was performed to evaluate vessel patency and to look for any luminal narrowing, or other abnormalities as compared to baseline angiography. Evaluation of the angiograms was conducted in a blinded fashion by the angiographic core lab.
After angiographic follow-up a necropsy was performed. The renal arteries and kidneys were harvested for histopathological evaluation. Gross pathology to examine the status of the renal arteries was performed to look for renal artery abnormalities such as aneurysms, perforations, dissections, hematoma, etc., as well as inspection of the surrounding tissues for any abnormalities. The renal arteries were cannulated, flushed and perfused with formalin while in-situ. The renal arteries and the kidneys were harvested, retaining the peri-adventitial tissue around the artery. The renal artery tissue was embedded in paraffin using standard techniques. Each renal artery was evaluated in at three locations; proximal, mid and distal. Tissue was stained with H&E and Movat‟s pentachrome. Microscopic evaluation was conducted in a blinded fashion.
Prior to euthanasia of each animal, the kidneys were isolated, and four samples were obtained from random locations at each of the proximal, mid and distal regions of each kidney for a total of 12 samples/kidney. The tissue samples were weighed, placed in cryovials and flashed frozen by immersion into dry ice. The frozen samples were then stored at − 70 o C. They were sent in dry ice to an independent laboratory for (blinded) measurement of renal parenchymal norepinephrine levels.
Renal norepinephrine concentrations in the treated animals from this study were also compared to values from naïve control animals of the same age and species (n = 8) with renal tissue sampling performed in an identical fashion to the treated animals.
2.2
First-in-Man Study
The protocol for this study was approved by the local ethics committee (Republic of Paraguay) and conducted in accordance with local regulations and statutes. Patients were enrolled in the study only after giving written informed consent. This was a pilot study performed in patients with refractory or “resistant” hypertension, using the same definition of refractory hypertension, as defined in the Symplicity studies . Patients were enrolled after careful screening and a 4-week run in period to measure serial office-based BP. All study patients were treated with maximally tolerated doses of at least three anti-hypertensive medications.
Eighteen patients were enrolled in the study and underwent bilateral renal artery denervation using the Peregrine™ device with a dose of 0.3 ml/artery. Only modest conscious sedation was used such that pain scores could be assessed during the alcohol infusions. Pain was assessed using a standard numeric pain rating scale (0 = no pain; 10 = severe pain) scoring system using verbal interaction with the patient in real-time at the time of start of the infusion and then repeated every 60 seconds after the infusion, until the complete resolution of pain (0/10).
Patient safety was assessed by serial measurement of BUN, Cr, and eGFR and by follow-up bilateral renal angiography at 6-month follow-up. Office-based BP was measured prior to intervention (× 2) and then at one-month, 3 months and at 6-months after denervation. Medication compliance was challenging in this study due to the demographics of this patient population studied, and a language barrier.
For statistical analysis, between-group comparisons were made using a Wilcoxon rank-sum test, performed in R (Version 2.14.1, Vienna, Austria). Data are shown in graphs as mean ± SD. A p value of < 0.05 was considered significant.
2
Materials and methods
2.1
Preclinical studies
A novel, three needle-based delivery device, (Peregrine System™, Ablative Solutions, Inc., Kalamazoo, MI) was introduced via the femoral artery into renal arteries of adult swine using fluoroscopic guidance. This drug infusion catheter is an endovascular delivery catheter that contains three distal needles housed within individual guide tubes, which are contained within body of the catheter. The catheter has a steerable, radio-opaque 2 cm fixed, floppy guide-wire at its distal end to minimize renal artery trauma and allow steer ability, when needed, into appropriate branch vessels ( Fig. 1 ).
This study was conducted under the general principles of Good Laboratory Practice (GLP) regulations as set forth in 21 CFR 58. The protocol for this study was reviewed and approved by the IACUC of the test facility, which is accredited by AALAC and licensed by the USDA. Animals were pre-medicated with 325 mg of aspirin and 75 mg of clopidogrel by mouth once daily for 2 days before the procedure.
After the animals were prepared for sterile surgery, one femoral artery was accessed using the Seldinger technique, and a 7 French introducer was placed. Intravenous heparin was given to all animals to achieve an ACT of > 250 sec. In all cases the right and left renal arteries of the pig were engaged using a 7 French RDC-1 guiding catheter. Prior to infusion of either ethanol or saline injections, angiography of each renal artery was performed using iohexol contrast diluted by 25% with normal saline.
The Peregrine™ injection catheter is intended to be used under fluoroscopic guidance by a single-operator using standard endovascular techniques and to allow safe and reproducible fluid injection into the adventitial and peri-adventitial space of a target vessel ( Fig. 2 ). The 0.008” needles that reside within the distal tip of the catheter’s guide tubes are advanced to a depth of 3.5 ± 0.25 mm deep to the intima (i.e., beyond the tip of the guide tube) and at 120° separation, one needle to the others. The specialized handle, allows advancement of the three guiding tubes, followed by simultaneous advancement of the three injection needles into the adventitial space. These tiny needles are made radiopaque, so that they can be easily seen under fluoroscopy. The needles are the equivalent of a ~ 30 gauge needle so that they can be safely advanced through the renal arterial wall without causing bleeding, even after heparin administration . The alcohol (ethanol) is delivered through a luer-lock connector at the proximal end of the handle, resulting in the infusion of the alcohol through the tips of the three needles of the Peregrine™ catheter, and directly into the perivascular, adventitial and peri-adventitial space. This creates a reproducible, deep and circumferential delivery of alcohol to the perivascular space ( Fig. 3 ).
