Nitinol stent-assisted maturation of the dysfunctional cannulation zone in the immature arteriovenous fistula.

INTRODUCTION: The native arteriovenous fistula may remain immature despite adequate arterial inflow after formation. This may occur when the puncturable vein segment (cannulation zone) is too small to be reliably punctured, occluded or too deep under the skin for needle access. We performed stenting (stent-assisted maturation) of arteriovenous fistulas with an immature cannulation zone, allowing for a large subcutaneous channel which could then be immediately punctured for dialysis. METHODS: We performed a retrospective review of 49 patients (mean age was 58.7 ± 16.09 (12-83) years, mean arteriovenous fistula age of 162.6 ± 27.28 days) with end-stage renal failure who underwent balloon dilatation and bare-metal stent implantation (1.6 ± 0.67 (1-3) stents, median diameter and length of 8 (5-14) mm and 80 (40-150) mm, respectively) through their cannulation zone (forced maturation). Radiocephalic (35 arteriovenous fistulas), brachiocephalic (10 arteriovenous fistulas) and autogenous loop arteriovenous fistulas (4 arteriovenous fistulas) were included with 30 patients (61.2%) having an inadequate cannulation zone venous diameter, 9 patients (18.4%) having an absent cannulation zone and 10 patients (20.4%) having a patent cannulation zone deeper than 1 cm which was not reliably puncturable. The study was conducted over 9 years (January 2008-December 2016) with implantation of the SMART® stent and Absolute Pro® stent in 61.2% and 38.8%, respectively. Long-term outcomes including primary useable segmental and access circuit patency as well as assisted primary access circuit patency, rate of re-intervention, technical success and complications were analysed. RESULTS: At 6 months, 12 months and 4 years, respectively, cannulation zone primary patency was 84.4%, 74.4% and 56.1% and access circuit primary patency was 62.2%, 45.3% and 23.2%; however, assisted primary access circuit patency was 95.6%, 91.1% and 83.8%, achieved with an endovascular re-intervention rate of 0.53 procedures/year with only four thrombosed circuits occurring. DISCUSSION: Forced maturation using nitinol stents allows for long-term haemodialysis access with a low rate of re-intervention.

Renal Artery Denervation in Resistant Hypertension: The Good, The Bad and The Future.

Early studies of renal artery denervation (RAD) demonstrated efficacy in treating resistant hypertension patients with significant reduction in office blood pressure (BP). This resulted in a growing enthusiasm in the field and a rapid evolution of technology with expanding procedural indications. However, the first randomised sham-controlled trial, Symplicity HTN-3, failed to demonstrate a significant difference in BP reduction between the RAD and the sham control arm, which subsequently led to a major reduction in the clinical application of this procedure. Additionally, the results generated further interest into understanding the mechanism and factors affecting procedural success and identifying the limitations within the field. Many lessons were learned from Symplicity HTN-3 trial, and with recent evidence emerging for RAD in hypertension treatment, the field continues to be refined.

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.

Use of Paclitaxel Eluting Stents in Arteriovenous Fistulas: A Pilot Study.

PURPOSE: We report short-term patency outcomes of a proof of concept study conducted to determine the efficacy of drug-eluting stent (DES) for the treatment of arteriovenous fistula (AVF) stenosis in hemodialysis patients. MATERIALS AND METHODS: This is a single-center, retrospective observational study involving 10 patients with AVF dysfunction treated with DESs between January 2017 and December 2017. The primary outcome was AVF patency confirmed by sonographic and clinical assessment at 1 month and 6 to 9 months after treatment. RESULTS: A total of 12 DESs were deployed in 10 patients with dysfunctional AVF (radiocephalic: 7, brachiocephalic: 3). During the early follow up (mean: 28.6 days), primary access circuit and DES patency was 100%, with an average volume flow rate of 886.4 mL/min. Nine patients were available for short-term follow up (mean: 202.4 days; 1 unrelated death), with a mean volume flow rate of 1,048.9 mL/min. The primary DES patency was 7/9 (77.8%), and 3 patients required angioplasty at other parts of the circuit (primary access circuit patency: 4/9 [44.4%]). The assisted primary access circuit patency was 77.8%. In 2 patients, the ultrasound revealed that the DESs were thrombosed without any antecedent stenosis; they were salvaged with angioplasty. Both patients previously underwent 2 DESs implanted and recently stopped dual antiplatelet therapy. B-mode sonographic assessment at all timepoints showed minimal intimal ingrowth on the stent struts. CONCLUSION: This study demonstrates acceptable short-term patency for DESs in the treatment of AVF stenosis. Dual antiplatelet therapy is probably mandatory in the short term.

Comparison of two different radiofrequency ablation systems for renal artery denervation: Evaluation of short-term and long-term follow up.

OBJECTIVES: To assess the clinical efficacy of renal artery denervation (RAD) in our center and to compare the efficacy of two different radiofrequency (RF) systems. BACKGROUND: Several systems are available for RF renal denervation. Whether there is a difference in clinical efficacy among various systems remains unknown. METHODS: Renal artery denervation was performed on 43 patients with resistant hypertension using either the single electrode Symplicity Flex (n = 20) or the multi-electrode EnligHTN system (n = 23). Median post-procedural follow-up was 32.93 months. The primary outcome was post-procedural change in office blood pressure (BP) within 1 year (short-term follow-up). Secondary outcomes were change in office BP between 1 and 4 years (long-term follow-up) and the difference in office BP reduction between the two systems at each follow-up period. RESULTS: For the total cohort, mean baseline office BP (systolic/diastolic) was 174/94 mmHg. At follow-up, mean changes in office BP from baseline were -19.70/-11.86 mmHg (P < 0.001) and -21.90/-13.94 mmHg (P < 0.001) for short-term and long-term follow-up, respectively. The differences in office BP reduction between Symplicity and EnligHTN groups were 8.96/1.23 mmHg (P = 0.42 for systolic BP, P = 0.83 for diastolic BP) and 9.56/7.68 mmHg (P = 0.14 for systolic BP, P = 0.07 for diastolic BP) for short-term and long-term follow-up, respectively. CONCLUSIONS: In our cohort, there was a clinically significant office BP reduction after RAD, which persisted up to 4 years. No significant difference in office BP reduction between the two systems was found.

Juxta-anastomotic stenting with aggressive angioplasty will salvage the native radiocephalic fistula for dialysis.

OBJECTIVE: This study describes our technique of aggressive angioplasty with juxta-anastomotic stenting (JXAS) in the autogenous arteriovenous fistula and reviews our outcomes with this technique in its mature form. METHODS: We developed a JXAS technique during the last 7 years. Since 2006, we have placed 135 JXASs. The study period reviews 68 consecutive JXASs placed from 2008 to 2012 using the mature technique. We retrospectively analyzed the prospectively collected data. Thirty-three fistulas received JXAS for failure to mature, and 35 were mature but inadequately dialyzing fistulas (problem fistulas). The JXAS technique involves (1) treating the JXA segment as a unit, (2) aggressive angioplasty with rupture of stenoses, and (3) placement of an uncovered nitinol stent. RESULTS: Technical success was 97%. Of the fistulas that had failed to mature, 75% were brought to maturity by 6 months and 88% by 12 months. Adequate dialysis was achieved in all 35 problem fistulas immediately postoperatively. Assisted fistula patency was 90% at 2 years and 80% at 4 years. CONCLUSIONS: JXAS is an effective technique for maturing and maintaining the wrist radiocephalic arteriovenous fistula.

Evaluation of lesion and thermodynamic characteristics of Symplicity and EnligHTN renal denervation systems in a phantom renal artery model.

AIMS: Radiofrequency renal artery denervation has been used effectively to treat resistant hypertension. However, comparison of lesion and thermodynamic characteristics for different systems has not been previously described. We aimed to assess spatiotemporal lesion growth and ablation characteristics of Symplicity and EnligHTN systems. METHODS AND RESULTS: A total of 39 ablations were performed in a phantom renal artery model using Symplicity (n=17) and EnligHTN (n=22) systems. The phantom model consisted of a hollowed gel block surrounding a thermochromic liquid crystal (TLC) film, exhibiting temperature sensitivity of 50-78°C. Flow was simulated using 37°C normal saline with impedance equal to blood. Radiofrequency ablations with each system were delivered with direct electrode tip contact to the TLC. Lesion size was interpreted from the TLC as the maximum dimensions of the 51°C isotherm. Mean lesion depth was 3.82 mm±0.04 versus 3.44 mm±0.03 (p<0.001) for Symplicity and EnligHTN, respectively. Mean width was 7.17 mm±0.08 versus 6.23 mm±0.07 (p<0.001), respectively. With EnligHTN, steady state temperature was achieved 20 sec earlier, and was 15°C higher than Symplicity. CONCLUSIONS: In this phantom model, Symplicity formed larger lesions compared to EnligHTN with lower catheter-tip temperature. The clinical significance of our findings needs to be explored further.

Novel use of NavX three-dimensional mapping to guide renal artery denervation.

AIMS: Renal artery denervation (RAD) is an effective treatment for resistant hypertension. The Navigation and Visualisation Technology (NavX) system creates three-dimensional (3-D) anatomical maps to guide catheter position and identify ablation sites. This first-in-human study assessed the utility of NavX 3-D mapping for RAD. METHODS AND RESULTS: Consecutive patients who underwent RAD using fluoroscopy alone (control group, n=8) were compared to NavX-guided RAD (NavX group, n=10). Where NavX was utilised, orthogonally located skin patches were applied to the torso for acquisition of 3-D geometry of each renal artery. Baseline clinical characteristics and renal artery anatomy were similar between groups. Median contrast dose was significantly higher in the control versus NavX group (123 ml versus 78 ml, p=0.016). Median radiation dose was significantly higher in the control versus NavX group (166 Gy cm² versus 43 Gy cm², p=0.034). Mean changes in systolic and diastolic BP at three-month follow-up were -22/-9 mmHg and -23/-11 mmHg in the control and NavX group, respectively (p=0.99). CONCLUSIONS: Use of NavX mapping as compared to standard renal artery denervation was found to correlate with a significant reduction in contrast load and radiation exposure. This study demonstrates both the feasibility and potential benefits of NavX 3-D mapping to guide renal artery denervation.

Use of inferior vena cava filters in a tertiary referral centre in Australia.

INTRODUCTION: To investigate the use of inferior vena cava (IVC) filters in a tertiary referral centre, looking at indication, types of filters and, with temporary/optional filters, removal rates. METHODS: Data was collected from a prospective database of all IVC filters inserted from January 2003 to January 2007. Patients' records and radiological imaging were all reviewed. RESULTS: 66 patients (40 males) had IVC filters inserted during the study period. The median age of the male patients was 57.5 (21-79) years, and females 56 (24-81). There were 49 (74.2%) temporary/optional filters and 17 (25.8%) permanent filters. The most common indication for filter was a contraindication to anticoagulation for both permanent (64.7%) and temporary/optional filters (77.6%). In the temporary/optional filter group, 38 of 49 (77.6%) patients had documented venous thromboembolism, while in the permanent filter group, this was 14 of 17 (82.4%). Of the optional filters, 22 of 49 (45.8%) have been removed. CONCLUSION: More than half (54.2%) of temporary/optional filters were not removed and with potential for long-term complications. A protocol has now being instituted for vascular surgeons to authorize the insertion of filters and to then be responsible for ensuring their removal.

Prevalence of carotid stent fractures in a single-center experience.

PURPOSE: To assess the prevalence of carotid stent fractures and quantify any associated restenosis or clinical events in a single-center experience. METHODS: Seventy-eight consecutive patients were recorded in a prospective database between 2003 and 2007. Nearly two thirds (51, 65%) were available for follow-up, which included magnified multiplanar radiography and selective duplex ultrasonographic studies to evaluate fracture and restenosis in 53 self-expanding stents (49 open-cell and 4 closed-cell designs). The images were assessed independently by 2 vascular radiologists blinded to the patients' clinical data. RESULTS: There was 1 (1.9%) stent fracture with no associated adverse events or restenosis. Six (11%) stents had an irregular "fish-scale" appearance that was easily confused for fracture and seen only in the open-cell stents. CONCLUSION: Stent fractures do occur in the carotid artery; however, they are rare and, in our experience, have no clinical sequelae. Radiological assessment should be incorporated into clinical and ultrasound surveillance protocols.

A novel hybrid device for avoiding redo surgery in synchronous iliac and femoral peri-anastomotic pseudo-aneurysms.

Synchronous peri-anastomotic pseudo-aneurysms were discovered in a 65-year-old man 26 years after an aorto-bi-iliac bypass and 11 years after an ileo-femoral bypass. He was a poor surgical candidate owing to his obesity, hostile abdomen, and multiple medical comorbidities. Therefore, a novel hybrid device was designed that was part stent graft with the addition of two 6-mm Dacron limbs for anastomosis onto the superficial femoral and profunda femoris arteries. An unexpected type 2 endoleak developed through the internal iliac artery, which was thought to be occluded. This was successfully treated with a direct injection of bovine thrombin. This was an excellent outcome, and the patient made an uneventful recovery.