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Editor's Choice – Clinical Efficacy of Venastent - A Novel Iliac Vein Stent for Non-Thrombotic Iliac Vein Lesions: A Multi-Centre Randomised Controlled Trial

Open AccessPublished:April 09, 2022DOI:https://doi.org/10.1016/j.ejvs.2022.04.005

      Objective

      To determine the efficacy of Venastent - a novel iliac vein stent for non-thrombotic iliac vein lesions (NIVLs).

      Methods

      From October 2018 to January 2021, 256 NIVL patients were recruited at 19 Chinese hospitals. A randomised controlled trial was conducted to compare the efficacy of the new iliac vein stent-Venastent (Tianhong China) with Zilver stent (Cook USA). All patients were allocated randomly to two groups: the experimental group patients used Venastent, while the control group received the Zilver stent. The trial was registered in Chinese Clinical Trial Registry (ChiCTR2200057851).

      Results

      A total of 123 patients in the experimental group and 122 patients in the control group had a full set of data collected (p = ns). The technical success rate was 100% (n = 245/245). The patency rate was 100% (n = 123/123) in the experimental group and 98.4% (n = 120/122) in control group one year after operation (p = ns). The lower extremity swelling remission rate was 79.1% (n = 87/110) in the experimental group and 78.4% (n = 91/116) in the control group (p = ns). The lower extremity pain relief rate was 68.8% (n = 50/80) in the experimental group and 77.2% (n = 71/92) in the control group (p = ns). The ulcer healing rate was 90% (n = 18/20) in the experimental group and 87% (n = 20/23) in the control group (p = ns). There was no difference in stent re-stenosis or clinical remission between the two groups.

      Conclusion

      The new iliac vein stent, Venastent, had a comparable high patency rate and safety profile as the Zilver stent (Cook) in NIVLs patients. Venastent significantly reduced symptoms of chronic venous disease.

      Keywords

      The new iliac stent provided a relatively easy to handle, safe, and effective endovascular treatment for non-thrombotic iliac vein lesions.

      Introduction

      Non-thrombotic iliac vein lesions (NIVLs) most frequently result from extrinsic compression of various segments of the common or external iliac vein. They typically result from compression of the left common iliac vein (CIV) between the right common iliac artery (CIA) and the vertebra, which induces chronic venous disease (CVD) or pelvic venous disease.
      • Harbin M.M.
      • Lutsey P.L.
      May-Thurner syndrome: History of understanding and need for defining population prevalence.
      The signs and symptoms of NIVLs include lower limb swelling, varicose veins, pain, and chronic pelvic pain.
      • Santoshi R.K.N.
      • Lakhanpal S.
      • Satwah V.
      • Lakhanpal G.
      • Malone M.
      • Pappas P.J.
      Iliac vein stenosis is an underdiagnosed cause of pelvic venous insufficiency.
      ,
      • Esposito A.
      • Charisis N.
      • Kantarovsky A.
      • Uhl J.F.
      • Labropoulos N.
      A comprehensive review of the pathophysiology and clinical importance of iliac vein obstruction.
      Endovascular therapy is currently a common treatment for symptomatic patients with NIVLs.
      • De Maeseneer M.G.
      • Kakkos S.K.
      • Aherne T.
      • Baekgaard N.
      • Black S.
      • Blomgren L.
      • et al.
      European Society for Vascular Surgery (ESVS) 2022 clinical practice guidelines on the management of chronic venous disease of the lower limbs.
      ,
      • Razavi M.K.
      • Jaff M.R.
      • Miller L.E.
      Safety and effectiveness of stent placement for iliofemoral venous outflow obstruction.
      The primary goal is to relieve obstruction, restore normal haemodynamics, and reduce the incidence of deep vein thrombosis (DVT).
      • Seager Mj
      • Busuttil A.
      • Dharmarajah B.
      • Davies A.H.
      Editor's Choice-- A systematic review of endovenous stenting in chronic venous disease secondary to iliac vein obstruction.
      At present, most of the stents used in NIVLs are atypical stents designed for arterial disease, including Wallstent (Boston Scientific), E-luminexx (Bard), and Gianturco (Cook).
      • Jayaraj A.
      • Noel C.
      • Kuykendall R.
      • Raju S.
      Long-term outcomes following use of a composite Wallstent-Z stent approach to iliofemoral venous stenting.
      • Erben Y.
      • Bjarnason H.
      • Oladottir G.L.
      • Mcbane R.D.
      • Gloviczki P.
      Endovascular recanalization for nonmalignant obstruction of the inferior vena cava.
      • Ruihua W.
      • Xin W.
      • Guang L.
      • Kaichuang Y.
      • Jinbao Q.
      • Minyi Y.
      • et al.
      Technique and clinical outcomes of combined stent placement for postthrombotic chronic total occlusions of the iliofemoral veins.
      To investigate long term patency and the remission of CVD after stent implanting for NIVLs, a randomised controlled trial (RCT) was conducted to compare the efficacy and safety of a new iliac vein stent, Venastent, with the Zilver stent (Cook company) for NIVLs. Clinical, Etiological, Anatomical, and Pathophysiological (CEAP) classification and revised Venous Clinical Severity Score (r-VCSS) were used to evaluate venous function.
      • Raju S.
      • Neglen P.
      High prevalence of nonthrombotic iliac vein lesions in chronic venous disease: a permissive role in pathogenicity.
      • Neglen P.
      • Thrasher T.L.
      • Raju S.
      Venous outflow obstruction: An underestimated contributor to chronic venous disease.
      • Williams Z.F.
      • Dillavou E.D.
      A systematic review of venous stents for iliac and venacaval occlusive disease.

      Materials and methods

      From December 2018 to January 2021, 256 NIVL patients at the 19 participating centres were recruited. Participants were randomly allocated to an experimental group and a control group. The experimental group was implanted with Venastent (Tianhong company China), while the control group was implanted with the Zilver stent (Cook company USA).

      Pre-operative evaluation

      Prior to inclusion, the clinical features for the injured limb and duplex ultrasound (DUS) were evaluated by a doctor for the preliminary screening. All subjects were scanned by multiplanar venography to calculate the baseline stenosis rate during operation. The diameter of the most stenotic site was measured, and the normal diameter of the site was simulated by QAngio XA version 7.3 software (Medis medical imaging systems BV).
      • Kołtowski A.
      • Zaleska M.
      • Maksym J.
      • Tomaniak M.
      • Soliński M.
      • Puchta D.
      • et al.
      Quantitative flow ratio derived from diagnostic coronary angiography in assessment of patients with intermediate coronary stenosis: a wire-free fractional flow reserve study.
      The stenosis rate was then obtained by comparing the two. If the patient met the inclusion criteria, the next step was performed immediately.

      Patient inclusion and randomisation

      The inclusion criteria were as follows: 1) aged 18 – 75 years, 2) stenosis of iliac vein ≥ 50% (confirmed by venography during operation) and, 3) clinical feature class of CEAP ≥ C3. Patients understood the experimental characteristics and aims of this study and consented to undergo endovascular treatment with the Venastent or Zilver stent. The exclusion criteria were as follows: 1) iliac vein stenosis caused by pelvic tumour compression, 2) previous radiotherapy, 3) post-thrombotic syndrome (medical history and DUS examination), 4) patients with previous interventional surgery in target iliac vein, 5) iliac vein stenosis after catheterisation, thrombolysis or thrombectomy due to DVT within six months, 6) contraindication for the use of contrast agent or anticoagulant drugs, 7) severe abnormal blood coagulation, 8) severe hepatic and/or renal insufficiency, 9) life expectancy < 12 months, 10) iliac vein size not applicable to vein stent (normal iliac vein diameter around the stenosis lesion < 6 mm), 11) history of allergy to materials (nickel titanium and tantalum), and 12) gestational lactation. Patients meeting the inclusion criteria were randomly assigned to one of the groups using computer generated random numbers immediately before stent placement. The central telephone randomisation system was used for allocation concealment (the experimenter contacted the third party researcher by telephone for computer extraction of random numbers). The trial was conducted in a single blind manner to patients, and data analysts were blinded to prevent bias (Fig. 1). The clinical practice was carried out in accordance with the requirements of the Helsinki Declaration and relevant national regulations. The experiment was approved by the ethics committee of the Drum Tower Hospital affiliated with Nanjing University (20180530/2018-155-02/2018.09.05), and all patients enrolled in the study signed informed consent.
      Figure 1
      Figure 1Consort flow diagram representing recruitment, randomisation, and follow up of patients with non-thrombotic iliac vein lesions between December 2018 and January 2021. Stent mismatch occurred in one patient randomised to the experimental group. All lesions included in the control group were stented. DSA = digital subtraction angiongraphy; CTV = computed tomography venography.

      Stent design and operative procedure

      The new stent, Venastent, is specifically designed for the iliac vein and is a self expanding bare stent system made with nickel titanium alloy and a conveying system. The structure of Venastent has introduced some new designs to improve the patency rate and intra-operative manipulation. 1) The head of the stent is designed with a large mesh corolla, which extends into the contralateral canal wall, so as to avoid stent displacement, and the large mesh ensures outflow of the contralateral iliac vessels. 2) Continuous compression by the overlying artery or the presence of intraluminal plaques requires strong radial forces to overcome collapse and maintain long term patency. The Venastent body below the corolla adopts a closed loop design to ensure radial forces that maintain an adequate lumen. Meanwhile, the end of the stent is designed with an open loop to ensure flexibility and vascular adhesion. At both ends of the scaffold and the corolla junction, three tantalum markers are inlaid to improve the Xray visibility of the scaffold. Stent diameters include 10 mm, 12 mm, 14 mm, and 16 mm. Stent lengths are available in 60 mm, 80 mm, and 100 mm. The stent is conveyed through a 0.035 guide wire and 8 F or 10 F vascular sheath (Fig. 2). Operating requirements include an 8 F or 10 F vascular sheath, a guide wire, puncture needle, balloon catheter, angiography catheter, contrast agent, and digital subtraction angiography (DSA) machine.
      Figure 2
      Figure 2(A) The venous iliac stent, Venastent, has a large mesh corolla at the head, ensuring blood flow from the contralateral iliac vessels. The proximal half of the stent adopts a closed loop design to ensure radial force, whilst the distal half of the stent is designed with an open loop to ensure flexibility and vascular adhesion. (B and C) Digital subtraction angiography (DSA) representing the left iliac vein before stent implantation. (D and E) Intra-operative DSA after stent implantation. (F and G) Post-operative DSA 12 months after stent implantation. The yellow area represents the stenosis area and the orange line represents the simulated normal vein diameter.
      After local anaesthesia in the groin, the common femoral vein was punctured, the guide wire was inserted, and the vascular sheath and angiography catheter were passed to the stenotic vein. Anteroposterior and lateral radiography were performed to document the iliac vein stenosis. The appropriate balloon catheter was inserted over the guide wire to pre-dilate the stenosis. The delivery system was then inserted into the CIV until both the proximal and distal ends of the marker covered the lesion segment. The operator held the handle in position and then pushed a button distally along the handle to withdraw the sheath. When the outer sheath retreated to the proximal mark, stent release was complete, and the stent expanded naturally. Anteroposterior and lateral angiography were performed to determine whether the CIV lesion had expanded after stent release. If necessary, the balloon catheter was inflated in the stent for further expansion.
      Venastent was tested and approved by the Shenzhen testing centre of medical devices (ZY20180132) and has been patented in China (ZL201610267898.8), the United States (US 10,695,201 B2), and Europe (PCT/CN2016089590); animal test were also completed.
      • Wang K.
      • Feng H.Q.
      • Tian R.
      • Na R.
      • Wang Y.G.
      • Mao Y.J.
      Performance test and experimental study of special stent for treatment of iliac vein stenosis.

      Post-operative care

      All patients received the oral anticoagulant rivaroxaban (20 mg once a day) for three months after intervention. After the procedure, patients were hospitalised for two – three days. A routine blood examination, as well as liver, kidney and coagulation function were performed on the first post-operative day.

      Follow up examinations

      Computed tomography venography (CTV) or venography was performed to calculate the in stent re-stenosis rate 12 months after intervention. Pain, lower limb swelling, and ulcer were evaluated using the r-VCSS and limb swelling was measured by comparing with the contralateral limb.
      • Vasquez M.A.
      • Munschauer C.E.
      Revised venous clinical severity score: a facile measurement of outcomes in venous disease.
      ,
      • Marston W.A.
      • Vasquez M.A.
      • Lurie F.
      • Wakefield T.W.
      • Rabe E.
      • Shortell C.K.
      • et al.
      Multicenter assessment of the repeatability and reproducibility of the revised Venous Clinical Severity Score (rVCSS).
      R-VCSS were scored by physicians at three and 12 months post-operatively at outpatient follow up.

      Primary and secondary outcome

      The primary outcome was stent patency at 12 months post-operatively. The stenosis rate was detected by venography or CTV and a stenosis rate > 50% was defined as in stent re-stenosis. Secondary evaluation indices included: minimum lumen diameter, technical success rate, adverse events, r-VCSS, and degree of stenosis 12 months after intervention.

      Statistical analysis

      All statistical analyses were performed using SPSS 22.0 (SPSS, Chicago, IL, USA). Continuous data are presented as mean ± standard deviation and categorical data as counts and percentages. Student's t test and the Chi square test were employed to compare continuous and categorical data, respectively. All statistical tests that were performed were two tailed. A two tailed p value < .05 was considered statistically significant. The sample size calculation is in Supplementary materials.

      Results

      Demographics

      There were 256 patients who met the inclusion criteria and were randomly allocated to experimental and control groups (Fig. 1). Baseline characteristics of age, gender, body mass index, CEAP, r-VCSS, degree of iliac vein stenosis, diameter at narrowest point before operation, and length of venous stenosis were documented; no difference between the two groups in baseline characteristics was found (Table 1).
      Table 1Demographic and lesion characteristics of 245 patients with non-thrombotic iliac vein lesions randomised to treatment with Venastent or Zilver stent, and with complete 12 months of follow up
      CharacteristicsExperimental group (n = 123)Control group (n = 122)p value
      Age – y58.4 ± 9.957.5 ± 9.5.48
      Gender.12
       Male48 (39.1)60 (49.2)
       Female75 (60.9)62 (50.8)
      BMI – kg/m225.4 ± 3.825.3 ± 3.3.83
      CEAP clinical classification.46
       327 (22)32 (26.2)
       476 (61.8)64 (52.5)
       59 (7.3)14 (11.5)
       611 (8.9)12 (9.8)
      r-VCSS score7.6 ± 3.98.6 ± 4.8.072
      Degree of iliac vein stenosis – %69.3 ± 11.767.8 ± 11.5.30
      Diameter at narrowest point before operation – mm4.39 ± 24.54 ± 1.9.55
      Length of vein stenosis – mm45.1 ± 17.944.7 ± 17.8.85
      Data are presented as mean ± standard deviation or n (%).
      BMI = body mass index; CEAP = Clinical, Etiology, Anatomical, and Pathophysiological classification; r-VCSS = revised venous clinical severity score.

      Peri-operative outcomes

      Mean procedural time was 46.4 ± 21.2 minutes in the experimental group and 42.7 ± 16.7 minutes in control group. There was no statistical difference between the two groups in length of procedure. Stent mismatch was present in one experimental case. After balloon pre-dilation, the diameter of iliac vein expanded to 17 mm, while the maximum diameter of Venastent was 16 mm, so there was no suitable stent to match. All other stents were successfully delivered, and the lesion sites were all covered. All CIVs were pre-dilated with a balloon, and 185 cases underwent post-dilation after stent release (96 cases in the experimental group and 89 cases in the control group). In 156 cases, the cranial end of the stent was inserted into the inferior vena cava (IVC), ending above the CIV confluence (88 cases in the experimental group and 68 cases in the control group (71.5% vs. 55.7%; p = .010).
      Peri-operative adverse events included hypertension (systolic pressure ≥ 140 mmHg or diastolic pressure ≥ 90 mmHg) in 10 cases (experimental group four cases, control group six cases), liver function damage (transaminase increases) in 16 cases (experimental group nine cases, control groups seven cases), back pain in 20 cases (experimental group 14 cases, control groups six cases), and post-operative fever in three cases (experimental group three cases). Overall, there was no statistical difference between the two groups in operation time or complication rate.

      Post-operative outcome

      A total of 245 patients had follow up data one year after intervention and 10 cases did not (four cases in the experimental group, six cases in the control group, Fig. 1). The mortality rate over the follow up period was 0.8% (n = 1/123) in the experimental group and 0% (n = 0/122) in control group. The primary outcome showed that follow up stent patency was 100% (123/123) in the experimental group and 98.4% (120/122) in the control group. The minimum lumen diameter and degree of stenosis 12 months after intervention and r-VCSS between the two groups are listed in Table 2. There was no statistically significant difference in primary and secondary outcome between the two groups.
      Table 2Patency rate and clinical remission 12 months after stent implantation in 245 patients with non-thrombotic iliac vein lesions randomised to treatment with Venastent or Zilver stent
      CharacteristicsExperimental group (n = 123)Control group (n = 122)p value
      Degree of iliac vein stenosis – %20.7 ± 9.822.1 ± 11.2.32
      Patients per stenosis degree.25
       ≤10%20 (16)20 (16.4)
       11–20%40 (32.5)27 (22.1)
       21–30%36 (29.3)49 (40.2)
       31–40%23 (18.7)22 (18)
       41–50%4 (3.3)2 (1.6)
       >50%0 (0)2 (1.6)
      r-VCSS score
       3 mo after operation4.6 ± 2.75.1 ± 3.3.23
       12 mo after operation3.2 ± 2.33.6 ± 3.30
      Lower extremity swelling remission rate87/110 (79.1)91/116 (78.4).99
      Lower extremity pain remission rate55/80 (68.8)71/92 (77.2).23
      Lower extremity ulcer healing rate10/11 (91)10/12 (83).99
      Data are presented as mean ± standard deviation or n (%)
      r-VCSS = revised venous clinical severity score
      Eleven major adverse events were noted in the follow up period. One of them was a stent related event in the control group that developed a pulmonary embolism and DVT of ipsilateral lower limb. Eleven months after surgery, the patient presented swelling of the left lower limb with chest tightness. DUS suggested femoral vein thrombosis distal to the iliac vein stent, and pulmonary artery CTA suggested pulmonary embolism. Angiography showed that the thrombus was absorbed 48 hours after thrombolytic therapy. Seven cases developed haemorrhage related to oral anticoagulants (experimental group five cases, control group two cases), including two cases of haemoptysis, three cases of gastrointestinal bleeding, and two cases of soft tissue bleeding. Three patients had a hypertension related cerebral infarction (experimental group two cases, control group one case). There was no contralateral lower limb swelling during the follow up period. According to CTV or venography 12 months post-operatively, there was no stent thrombosis or venous collateral compensation in either group. Lower extremity swelling remission, pain remission, and ulcer healing rate are listed in Table 2, and there was no statistically significant difference between the two groups (Table 2).

      Discussion

      This RCT was designed to investigate the patency and efficacy of Venastent in the treatment of NIVLs compared with the Zilver stent. The results show that the one year patency rate of Venastent for NIVLs was 100%, compared with 98.4% for the Zilver stent. Venastent has the same efficacy as the Zilver stent in patency rate and CVD remission.
      The treatment of iliac vein stenosis usually involves arterial stents such as Wallstent. These stents have significant shortcomings when adapted for the iliac vein.
      • Wang W.D.
      • Zhao Y.
      • Chen Y.X.
      Stenting for chronic obstructive venous disease: A current comprehensive meta-analysis and systematic review.
      For example, Wallstent collapses with relatively weak radial force at the ends (compared with the stent body) and cannot maintain an adequate lumen in the presence of dense fibrotic lesions in the central CIV. The stent may be compressed and cause stent collapse or caudal stent migration.
      • Raju S.
      • Tackett P.
      • Neglen P.
      Reinterventions for nonocclusive iliofemoral venous stent malfunctions.
      A cumulative rate of contralateral DVT at five years in 755 patients treated with Wallstent extending into the IVC by 3 – 5 cm of up to 2.1% (16/755) has been reported.
      • Murphy E.H.
      • Johns B.
      • Varney E.
      • Buck W.
      • Jayaraj A.
      • Raju S.
      Deep venous thrombosis associated with caval extension of iliac stents.
      The reason for this is the varying pathophysiology of arterial stenosis and venous obstructions. Arterial stenosis is mostly caused by atherosclerosis; therefore, the treatment goal is to restore peripheral perfusion, so arterial revascularisation is performed without recreating the normal anatomical size of the vessel.
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      • Berrett T.B.
      • Chowdhury M.M.
      • Coughlin P.A.
      Site and burden of lower limb atherosclerosis predicts long-term mortality in a cohort of patients with peripheral arterial disease.
      On the other hand, venous stenosis related to external compression, mural fibrosis, intraluminal webs,
      • Cockett F.B.
      • Thomas M.L.
      The iliac compression syndrome.
      and minor residual stenosis may contribute to elevated peripheral venous pressures and residual symptoms. Therefore, pre-balloon and post-balloon dilatation as well as large diameter stents are needed to maintain normal venous lumen size.
      • Shamimi-Noori S.M.
      • Clark T.
      Venous stents: current status and future directions.
      ,
      • Kocaaslan C.
      • Bademci M.S.
      • Bayraktar F.A.
      • Oztekin A.
      • Aydin E.
      • Tayfur K.
      Treatment strategies of iliac vein stenosis.
      Current stents for the arterial system are often quite rigid.
      • Sebastian T.
      • Gnanapiragasam S.
      • Spirk D.
      • Engelberger R.P.
      • Moeri L.
      • Lodigiani C.
      • et al.
      Self-expandable nitinol stents for the treatment of nonmalignant deep venous obstruction.
      Venastent has unique features and differences from arterial stents. It includes a positioning area and support area. The positioning area has 4 – 10 corolla monomers with several markers, which improve positioning accuracy without affecting contralateral blood flow. The support area is divided into two parts, a central support area and a terminal support area. The radial force of the central support area ensures appropriate diameter sizing to decrease peripheral venous hypertension, and the flexibility of the terminal support area enables the stent to adapt to the shape of the vein and move with changing pelvic geometry without kinking or significant decreases in cross sectional area. The Zilver stent is one of the most commonly used venous stents on the market, due to its high patency in chronic iliofemoral obstruction;
      • Salem A.M.
      • Abdelazeem A.H.
      • Fakhr M.E.
      Long-term outcome of dedicated venous stents in management of chronic iliofemoral obstruction.
      therefore, the patency and efficacy of Venastent was compared with the Zilver stent in NIVLs.
      During the intervention, stent positioning was accurate and the lesion site was completely covered. All stents completely extended and did not show any shrinkage after post-dilation. No stent migration or stent thrombosis was observed during follow up. It has been found with Venastent that 1) intravenous high pressure injection angiography is important to improve imaging quality and accurately display lesions and the contralateral iliac vein. 2) Pre-balloon dilatation is very important for NIVLs, and adequate pre-dilatation is recommended. As elastic retraction is obvious in the venous system, it is more appropriate to choose a stent with a diameter that is oversized by 20% and use post-dilatation if necessary. 3) The true length of a lesion often exceeds the range shown by venography, and the stent should cover a longer area of lesion. 4) The length of iliac vein stent implantation into the IVC remains controversial. Insufficient stent length into the IVC leads to an inability to support the lesion. Conversely, if the stent enters too far into the IVC, the risk of contralateral DVT increases. The large mesh design at the tip of Venastent reduces interference with contralateral iliac vein blood flow, and it is therefore proposed to extend the stent into the IVC to completely cover the stenosed segment.
      Common adverse events during the peri-operative period include back pain, liver function damage, hypertension, and fever. Some patients complained of back pain without obvious abdominal discomfort, which was associated with vein tension caused by oversized stents. Typically, a 20% – 30% oversized stent is chosen, and the symptoms spontaneously disappear in most patients after two weeks. Sixteen patients displayed mildly raised transaminase, the reason for which was unclear. The patients who suffered from hypertension after the operation had a history of hypertension and blood pressure that was not effectively controlled before the intervention, and the pain induced by pre-dilation was also a trigger. During the follow up period, one case of pulmonary embolism was associated with DVT after vein stent implantation. Seven patients developed major post-operative bleeding complications, which can be reduced by regular checking of blood coagulation function and timely withdrawal of oral anticoagulants.
      • Arendt V.A.
      • Mabud T.S.
      • Kuo W.T.
      • Jeon G.S.
      • An X.
      • Cohn D.M.
      • et al.
      Comparison of anticoagulation regimens following stent placement for nonthrombotic lower extremity venous disease.
      ,
      • Zhang X.
      • Huang J.
      • Peng Z.
      • Lu X.
      • Yang X.
      • Ye K.
      Comparing safety and efficacy of rivaroxaban with warfarin for patients after successful stent placement for chronic iliofemoral occlusion: a retrospective single institution study.
      The adverse events of stroke were related to underlying diseases such as carotid artery stenosis or atrial fibrillation.
      • Noubiap J.J.
      • Kamtchum-Tatuene J.
      • Fitzgerald J.L.
      • Sanders P.
      Stroke risk associated with carotid and aortic atherosclerosis in patients with atrial fibrillation: A systematic review.
      The present study has some limitations. First, the follow up time was one year, and a longer term follow up at three and five years is planned to evaluate the long term efficacy of Venastent in future research. Second, medical management was not included as another control group to compare stent implantion with medical management in NIVLs. Third, as intravascular ultrasound is not yet in widespread use in China, intravascular ultrasound was not chosen, and three dimensional venography or CTV was used to detect vascular stenosis.
      • Saleem T.
      • Raju S.
      Comparison of intravascular ultrasound and multidimensional contrast imaging modalities for characterization of chronic occlusive iliofemoral venous disease: A systematic review.

      Conclusion

      Venastent is as efficient as the Zilver stent and provides a safe and effective endovascular treatment for NIVLs.

      Conflict of interest

      None.

      Funding

      The Fundamental Research Funds for the Central Universities ( WK9110000187 ).

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:

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