In vivo evaluation of safety and performance of a nitinol venous stent in an ovine iliac venous model

In vivo evaluation of safety and performance of a tapered nitinol venous stent with inclined proximal end in an ovine iliac venous model

A tapered stent with inclined proximal end is designed for fitting the iliac anatomically. The aim of the present study was to evaluate the safety and performance of the new stent in ovine left iliac veins. The experiment was performed in 30 adult sheep, and one nitinol-based VENA-BT® iliac venous stent (KYD stent) was implanted into each animal's left common iliac vein. Follow-up in all sheep consisted of angiographic, macroscopic, and microscopic examinations at Day 0 (< 24 h), Day 30, Day 90, Day 180 and Day 360 post-stenting (six animals per each time-point). 30 healthy ~ 50 kg sheep were included in this study and randomly divided into five groups according to the follow-up timepoint. All stents were implanted successfully into the left ovine common iliac vein. No significant migration occurred at follow-up. There is no statistically significant difference between the groups (p > 0.05), indicating no serious lumen loss occurred during the follow-up period. Common iliac venous pressure was further measured and the results further indicated the lumen patency at follow-up. Histological examinations indicated that no vessel injury and wall rupture, stent damage, and luminal thrombus occurred. There was moderate inflammatory cell infiltration around the stent in Day-0 and Day-30 groups with the average inflammation score of 2.278 and 2.167, respectively. The inflammatory reaction was significantly reduced in Day-90, Day-180 and Day-360 groups and the average inflammation scores were 0.9444 (p < 0.001, Day-90 vs Day-0), 1.167 (p < 0.001, Day-180 vs Day-0) and 0.667 (p < 0.001, Day-90 vs Day-0), respectively. The microscopic examinations found that the stents were well covered by endothelial cells in all follow-up time points. The results suggested that the KYD stent is feasible and safe in animal model. Future clinical studies may be required to further evaluate its safety and efficacy.

No More Venous Ulcers-What More Can We Do?

Venous leg ulcers (VLUs) are the most severe complication caused by the progression of chronic venous insufficiency. They account for approximately 70-90% of all chronic leg ulcers (CLUs). A total of 1% of the Western population will suffer at some time in their lives from a VLU. Furthermore, most CLUs are VLUs, defined as chronic leg wounds that show no tendency to heal after three months of appropriate treatment or are still not fully healed at 12 months. The essential feature of VLUs is their recurrence. VLUs also significantly impact quality of life and could cause social isolation and depression. They also have a significant avoidable economic burden. It is estimated that the treatment of venous ulceration accounts for around 3% of the total expenditure on healthcare. A VLU-free world is a highly desirable aim but could be challenging to achieve with the current knowledge of the pathophysiology and diagnostic and therapeutical protocols. To decrease the incidence of VLUs, the long-term goal must be to identify high-risk patients at an early stage of chronic venous disease and initiate appropriate preventive measures. This review discusses the epidemiology, socioeconomic burden, pathophysiology, diagnosis, modes of conservative and invasive treatment, and prevention of VLUs.

Angioscopic evaluation after venous stents

BACKGROUND

Venous stenting is increasingly used to manage femoro-ilio-caval venous outflow obstruction/stenosis due to post-thrombotic syndrome. Although the safety, efficacy, and long-term patency of venous stents have been reported, re-interventions due to stent occlusion and in-stent restenosis (ISR) have also been reported. The mechanism of ISR and the in-stent neointimal growth after venous stenting remains unclear. We performed angioscopy to evaluate intraluminal details after venous stenting, allowing real-time direct visualization of the vessel lumen.

METHODS

Ten angioscopic procedures in four patients with post-thrombotic syndrome were performed. All evaluated vessels were stented iliac veins, and their native pathology was chronic post-thrombotic occlusion. Nine procedures in three patients underwent serial evaluation of the neointimal changes after stent implantation to study the natural time course of neointimal proliferation/coverage over the stent. The serial follow-up angioscopic evaluations were performed at the end of the venous stent deployment procedure, and at 6 months, 12 months, and 24 months. One procedure was performed 1 month after the stent implantation to evaluate ISR, which was observed at the first month of routine stent surveillance. A 5.7F angioscope was used to visualize the target veins. Continuous irrigation was used to displace blood and clear the visual field.

RESULTS

At 6 months after stent implantation, stent struts were covered by a thin neointima in two of the three patients. The struts were partially covered in one patient, but there was little neointimal growth overall. Neointimal coverage increased over time, and at 12 months stent struts in 2 patients were almost completely covered. There was no significant change between the 12 and 24 months after stent implantation. In the ISR case, angioscopy demonstrated an overgrown thickened neointima, and the stent struts were fully embedded and invisible in the entire stented area. No thrombus and no webs or trabeculae were found in the area evaluated as an ISR lesion.

CONCLUSIONS

At 6 months after stent placement, the stent struts were almost covered by a neointima. The stent struts were completely covered 1 year after stent implantation. Neointimal coverage was unchanged from the 1-year follow-up to the 2-year follow-up, suggesting that neointimal proliferation proceeded gradually with subsequent neointimal remodeling up to 1 year. The cause of ISR might be the overgrown thickened neointima rather than the formation of thrombosis.

Ovine Iliac Vein Model for Endovascular Thrombectomy of Acute Deep Venous Thrombosis

An ovine iliac vein thrombosis model was devised to test a wall-contacting rotational thrombectomy device. Thrombosis was successfully induced in 9 sheep with an average clot length of 31 mm ± 12 and >60% vessel occlusion on angiography. The thrombus was subsequently removed, maintaining normal intraoperative pulmonary arterial pressure (5.9 mm Hg ± 3.6) and complete distal reperfusion after thrombectomy. Additionally, the sheep were without signs of vascular trauma or embolic complications on gross necropsy and histopathologic analysis. The findings from this study support the use of an ovine iliac deep vein thrombosis model for testing of a lower extremity thrombectomy device.

Immediate postprocedure anticoagulation with factor Xa inhibitors of venous stents for nonthrombotic venous lesions does not increase stent patency

BACKGROUND

Many clinicians will prescribe anticoagulation therapy for patients after iliac vein stenting to prevent early or late stent thrombosis. At present, it is unknown whether therapeutic anticoagulation has any effect on stent patency. Thus, we assessed the role of short-term anticoagulation on iliac vein stent patency in patients with nonthrombotic iliac vein lesions (NIVLs).

METHODS

We performed a retrospective medical record review of all iliac vein stents placed for NIVLs at the Center for Vascular Medicine from January 2018 to December 2019. We compared the stent patency in the two groups. The anticoagulation (AC) group had received rivaroxaban or apixaban postoperatively for a minimum of 90 days and were compared with a group that had received no postoperative anticoagulation (NAC). Stent patency was assessed using transabdominal ultrasound at 3, 6, 12, 18, 24, and 30 months. At the discretion of the treating physician, the patients who demonstrated thrombus layering on surveillance ultrasound scanning continued rivaroxaban or apixaban until thrombus resolution was observed. The demographics and stent location, diameter, and length were assessed. Stent patency was analyzed using life table analyses. Differences in stent patency were analyzed using GraphPad Prism, version 8, statistical software (GraphPad Software Inc, La Jolla, Calif) and the log-rank (Mantel-Cox) test.

RESULTS

The number of patients and stents in each group were as follows: AC group, 299 patients and 308 stents; and NAC group, 77 patients and 90 stents. The average age was 52.24 ± 13.44 years and 55.63 ± 14.49 years in the AC and NAC groups, respectively (P ≤ .065). Women constituted 76% of the patients in the AC group and 72% in the NAC group. The average stent diameter and length for the AC group was 20 ± 2 mm and 77 ± 13 mm and for the NAC group was 19 ± 2 mm and 82 ± 9 mm, respectively. The stents had been placed in the right common iliac vein, bilaterally, or left common iliac vein territory in 15%, 3%, and 82% in the AC group and 18%, 2%, and 80% in the NAC group, respectively. The cumulative stent patency at 30 months was 98.7% and 94.6% for the NAC and AC groups, respectively (P ≤ .83). All the stents placed were Wallstents (Boston Scientific, Marlborough, Mass). A total of eight insertion site thromboses occurred that did not affect stent patency: five in the AC group (1.6%) and three in the NAC group (4.5%; P = .15). In addition, 19 patients demonstrated evidence of thrombus layering, with 6 receiving extended anticoagulation.

CONCLUSIONS

Our data indicate that perioperative stent thrombosis in patients with NIVLs is uncommon. Thus, anticoagulation for perioperative stent thrombosis prophylaxis is not necessary. Anticoagulation should only be used for patients with insertion site thromboses and should be considered if thrombus layering is observed on surveillance scanning.

Early thrombosis after iliac stenting for venous outflow occlusion is related to disease severity and type of anticoagulation

BACKGROUND

Stenting of the iliac venous system is often performed for symptomatic obstruction, with high patency rates reported. However, patients with post-thrombotic disease and those with more extensive obstruction have experienced poorer outcomes, including a higher rate of early post-stent thrombosis. In the present study, we examined the outcomes of patients with complete venous outflow occlusion. We focused on the variables associated with early post-stenting thrombosis to identify opportunities to reduce its incidence.

METHODS

From 2010 to 2020, the patients who had undergone stenting for chronic obstruction of the common femoral vein, iliac veins, and/or inferior vena cava were retrospectively reviewed. The pre- and intraoperative imaging studies were examined to identify those who had had total occlusion of one venous outflow segment (type III disease) or multiple venous outflow segments (type IV disease). The patient characteristics and procedural and post-stent variables were recorded. The post-procedure follow-up visits and imaging studies were reviewed to determine stent patency and thrombotic complications. Key variables were studied to determine their association with early stent reocclusion.

RESULTS

A total of 106 patients were identified, including 43 with type III (40.6%) and 63 with type IV (59.4%) disease. The mean patient age was 49.8 ± 13.7 years, and the mean stented length was 177.3 ± 63 mm. Stainless steel Wallstents were used solely in 44% of the cases, with a variety of nitinol stents used in the remainder. Femoral vein inflow was minimally diseased in 50% of the cases, moderately diseased in 26%, and severely diseased or occluded in 24%. Antiplatelet medications were prescribed after intervention for 52.8% and anticoagulation medication for 95.3% of the patients. Occlusion of the stented segment occurred within 3 months in 25.5%. Primary patency was 74.5% at 3 months, 63.9% at 12 months, and 58.5% at 3 years. Secondary patency was 93.4% at 3 months and 76.1% at 3 and 5 years. Univariate analysis of variables related to early stent thrombosis identified the presence of a hypercoagulable state, type IV obstruction, and the type of anticoagulation used after stenting were associated with early stent thrombosis. On multivariate analysis, each of these variables was independently associated with early stent thrombosis. The presence of type IV obstruction (odds ratio [OR], 4.596; 95% confidence interval [CI], 1.424-18.109) or a hypercoagulable state (OR, 3.835; 95% CI, 1.207-12.871) was associated with significantly greater odds of reocclusion than was class III obstruction and no hypercoagulable state. Treatment with low-molecular-weight heparin for >10 days was associated with significantly lower odds (OR, 0.012; 95% CI, 0.001-0.130) of reocclusion.

CONCLUSIONS

Patients who require recanalization of a completely occluded venous outflow tract before stenting have a high rate of early reocclusion. Patients with more extensive occlusion and a hypercoagulable state have greater odds of reocclusion. Treatment with low-molecular-weight heparin for >10 days reduced the odds of early reocclusion.

Effect of Stent Strut Interval on Neointima Formation After Venous Stenting in an Ovine Model

OBJECTIVE

The impact of stent design on venous patency is not well studied. The purpose of this study was to investigate the effect of stent material burden on endothelial coverage of stented venous segments, which may contribute to vessel healing and patency.

METHODS

Segmented self expanding bare nitinol stents (18 × 50 mm) comprising 5 mm long attached metallic rings separated by 2, 5, or 8 mm gaps were implanted in the inferior vena cava (IVC) of 10 sheep. These stents were designed and manufactured for the purposes of this study. At six, 12, and 24 weeks after implantation the animals were euthanised and the stented vessels harvested for histomorphometric analysis. Three sections from the metallic part as well as the gaps between the struts were reviewed for quantification of endothelialisation after six, 12, and 24 weeks. The intimal thickness over and between the stent struts was measured. The endothelialisation score (graded from 1 for complete luminal endothelialisation to 5 for absence of endothelial cells) was determined.

RESULTS

All stents were successfully deployed and all 10 sheep survived until the time of harvesting. Macroscopic inspection after 24 weeks showed only partial endothelialisation over stents with 2 mm and 5 mm skipped segments, whereas the stents with 8 mm skipped segments were totally incorporated into the vein wall. After 24 weeks, the mean (SD) neointimal thicknesses over stent struts with 2 mm, 5 mm, and 8 mm skipped segments were 254.0 (51.6), 182.2 (98.1), and 194.6 (101.1) μm, respectively. Comparison of endothelialisation scores of stents over time showed statistically significantly better endothelialisation over stents with 8 mm gaps after 12 and 24 weeks.

CONCLUSION

Stent designs providing structural support to veins with larger gaps between the scaffold material appear to lead to faster and more complete endothelialisation as well as a thinner intimal layer.

Relevance of flexibility versus radial force in rigid versus more flexible venous stents?

Introduction

Deep venous stenting has gained increasing interest. More flexible venous stents are thought to gain superior clinical outcomes. This research evaluated the patency and clinical outcomes between more rigid stents and more flexible stents.

Material and methods

The Venous Clinical Severity Score, Villalta, complication rates and patency rates were evaluated. The more rigid stents included the Sinus XL, the Veniti VICI and the Sinus Obliquus. The flexible group included the Zilver Vena or the Sinus Venous stents.

Results

Differences in Venous Clinical Severity Score (p = 0.09) and Villalta score were found (p = 0.28). Tapering (0 versus 5, p = 0.03) and bad alignment were found (0 versus 5, p = 0.03). The rigid stents showed patency rates of 80, 86 and 92% compared to 88, 96 and 98% in the flexible group.

Conclusion

Dedicated venous stents show good patency outcomes and clinical results. Tapering and bad alignment between connecting stents are more frequently seen in more rigid stents.

A novel endovenous scaffold for the treatment of chronic venous obstruction in a porcine model: Histological and ultrastructural assessment

OBJECTIVE

To investigate the biological effects of a novel endovenous scaffold in a porcine model.

METHODS

Petalo is a compliant venous scaffold implanted into the internal jugular veins of 12 healthy pigs. The pigs were sacrificed at one, two, three, and six months, respectively. Microscopic investigations were performed at two blinded laboratories.

RESULTS

Neo-intima formation progressively covering up the stent metallic bars was observed. The inflammatory response of the venous wall showed a peak after three months by the implant, followed by marked reduction after six months. The device induced a significant ( p < 0.01) increase of the thickness respect to the control regions, but was comparable in sections obtained after three and six months.

CONCLUSIONS

The implant of Petalo compliant venous scaffold in the venous wall of this porcine model is characterized by neointima formation and by an inflammatory reaction which tends to decrease after six months. Our data point against the induction of smooth muscle cells proliferation and migration as confirmed by electronic transmission microscopy analyses.

Preliminary report of a new type of braided vein stent in animals

Background

Iliofemoral vein stenosis or occlusion is a common cause of severe chronic venous insufficiency. Endovascular venous stenting has become a preferred treatment because it is minimally invasive and has a high safety profile. Despite the wide application of the wallstent, it is not specifically designed for veins. There are currently few studies on braided stents in the field of veins. We designed a novel braided vein stent, which has higher radial resistive force and more optimized looped ends structure compared with the wallstent. The purpose of this study was to evaluate the safety and performance of the stent in animals, providing a reference for further clinical trials.

Methods

The Wallstent is used as a control group. The novel stent and the Wallstent were implanted in the iliac vein of sheep. After 30 days and 90 days, vascular injury, thrombus, neointima coverage, and luminal stenosis were evaluated through venous angiography, endoscopic observation of stent specimen and histopathology. Imaging, histology, and integration data were analyzed by t-test for comparisons between the groups.

Results

Two groups of stents were successfully implanted. Follow-up observation showed that there was no thrombosis or obstruction >50% occurred in any group and no significant differences in patency, vascular injury, or intimal hyperplasia compared with the Wallstent.

Conclusion

The novel stent significantly increases the radial resistive force and does not increase vascular injury, thrombus and stent stenosis during 30-day and 90-day follow-up. The next step is to further validate the effectiveness of the stent through long-term animal observation and human clinical trials.

A systematic review on management of nutcracker syndrome

OBJECTIVE

Although nutcracker syndrome (NS) is rare, patients presenting with symptoms or signs and anatomic compression of the left renal vein (LRV) can be considered for intervention. Open, laparoscopic, and endovascular techniques have been developed to decrease the venous outflow obstruction of the LRV. The paucity of data regarding the management of this uncommon disease process poses a challenge for adequate recommendations of the best treatment modality. Herein, we aim to present a systematic review for the management of NS.

METHODS

We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement standards to systematically search the electronic databases of MEDLINE from October 1982 to July 2017 for articles about the management of NS. Included were studies in English, Spanish, and German in all age groups.

RESULTS

The literature search provided 249 references. After abstract and full review screening for inclusion, 17 references were analyzed. Eight (47%) described the open surgical approach. The LRV transposition was the most commonly reported technique, followed by renal autotransplantation. Seven (41.11%) described the endovascular technique of stent implantation, and two (11.7%) described the minimally invasive laparoscopic extravascular stent implantation.

CONCLUSIONS

NS is a rare entity. Multiple techniques have been developed for the treatment of this condition. However, the rarity of this syndrome, the paucity of data, and the short-term follow-up of the existing evidence are the disadvantages that prevent recommendations for the best treatment strategy. Up to now, open surgical intervention, specifically LRV transposition, has been considered by some experts the mainstay for treatment of NS. The endovascular approach is gaining strength as more evidence has become available. However, the long-term patency and durability of this approach remain to be elucidated. Therefore, careful selection of patients is necessary in recommending this technique.