Use of the VENOVO™ and Sinus Obliquus™ venous stents in the treatment of non-thrombotic or post-thrombotic iliac vein lesions – Short-term results from a multi-centre Asian cohort

Abstract

Objectives

Deep venous stenting with intravascular ultrasound (IVUS) guidance is gaining favour as the treatment modality of choice for symptomatic ilio-femoral venous occlusive disease. The aim was to determine the short-term patency and symptomatic relief gained using the Bard Venovo™ and Optimed Sinus Obliquus™ stents in the endovascular treatment of non-thrombotic iliac vein lesions (NIVL) and post-thrombotic venous obstruction (PTO) from two Asian tertiary vascular centres.

Methods

Sixty patients (males = 21/60 (35.0%); median age 67 years (interquartile range 54–77)) who underwent IVUS interrogation and ilio-femoral stenting (June 2018–May 2019) in two Asian centres were prospectively followed. Clinical improvement was determined by the revised Venous Clinical Severity Score (rVCSS), pain using the Visual Analogue Scale (VAS) and ulcer healing rate. Patency rates were evaluated using Duplex ultrasound and computer tomography venogram.

Results

Seventy-one legs were interrogated and stented; 11/60 (18.3%) patients had a bilateral procedure. Indications for surgery were PTO (n = 11/71 (15.5%)) and NIVL (n = 60/71 (84.5%)). Twenty-seven of 71 (38.0%) patients had CEAP 6 disease. The median follow-up was 283 (interquartile range 211–370) days. Technical and procedural success was both 100%. Twenty-one of 71 (29.6%) legs had a combination of Venovo™ and Sinus Obliquus™ stents inserted for concurrent ilio-caval and iliac lesions. There were no major post-operative complications. Six-month primary, assisted primary and secondary patency rates were 94.1, 97.1 and 100%, respectively. There were no stent fractures. Mean rVCSS and VAS improved from 12.26 (±3.31) to 4.33 (±2.78) and 6.97 (±1.38) to 2.03 (±1.65), respectively, at three months (p < 0.01). Complete ulcer healing was seen in 27/27 (100%) patients at three months.

Conclusion

Use of Venovo™ and Sinus Obliquus™ stents for symptomatic ilio-femoral venous disease showed excellent six-month primary patency rate with no stent fractures. There were significant clinical improvement and low-device-related complications. Longer follow-up is awaited to see how these dedicated venous stents perform.

Keywords

Deep vein stenting venovo venous stent vascular patency post-thrombotic syndrome non-thrombotic iliac vein lesion May–Thurner syndrome

Introduction

Post-thrombotic venous obstruction (PTO) and non-thrombotic iliac vein lesions (NIVL) can cause symptomatic chronic iliofemoral venous obstruction (IFVO).¹ PTO is the most common complication of deep vein thrombosis (DVT), despite timely and optimal anticoagulant therapy, occurring in 20–40% of patients within the first two years.² NIVL includes May–Thurner Syndrome (MTS), a condition where the left common iliac vein is compressed between the right common iliac artery and the fifth lumbar vertebrae.³ The prevalence of NIVL is widespread in the asymptomatic general population and may play a permissive role in the development of chronic venous disease.⁴

Percutaneous deep venous stenting guided by intravascular ultrasound (IVUS) imaging is presently the method of choice in the treatment of IFVO.⁵ It is safe and effective, with high technical success, few complications and high patency rates.^6–8 Arterial stents were originally adapted for use in the venous system but were too rigid and had inadequate radial force. This led to lower patency rates and higher rates of in-stent compression.^9,10 Older, non-dedicated venous stents such as the Wallstent™ (Boston Scientific, Marlborough, USA) showed reasonable outcomes, but has two critical shortcomings – low radial force at its ends and significant foreshortening during the stent post-dilatation process.¹¹ They under-expand in the ilio-caval venous system, and their final positioning is difficult to predict especially at the ilio-caval junction.¹²

Dedicated venous stents were developed with favourable features for the venous system – more flexibility, higher radial forces and adequate sizes and diameters.¹³ Existing studies have shown favourable short-term outcomes for Sinus Obliquus™ (Optimed, Ettlingen, Germany),¹⁴ Zilver Vena™ (Cook, Bjæverskov, Denmark)¹⁵ and Vici Venous™ (Boston Scientific, Marlborough, USA)¹⁶ stents. There are few studies analysing the Venovo™ stent (BD Medical, Arizona, USA). Existing studies include data from the Arnsberg Venous Registry⁹ and the ongoing VERNACULAR trial.¹⁷ Both studies captured a vastly Caucasian demographic from the United States, Europe, Australia and New Zealand. There are currently no reported studies investigating the efficacy of Venovo™ and Sinus Obliquus™ stents in treating IFVO in Asians, who are reported to have different truncal vein diameters, reflux patterns and symptomology.¹⁸

Our centres have stopped deploying the Wallstent™ for the last three years for the aforementioned reasons. Currently, combination therapy using the Venovo™ and Sinus Obliquus™ stents has been favoured by the senior author (TYT).¹⁹ The aim of this study was to evaluate the short-term patency rates and symptomatic relief gained from using the Venovo™ and Sinus Obliquus™ venous stents in the endovascular treatment of NIVL or PTO from two Asian centres in Singapore and Taiwan.

Materials and methods

Patients and study design

This was a two-centre (Singapore General Hospital, Singapore (PI = TYT) and Tainan An-nan Municipal Hospital, Taiwan (PI = JWHT)) prospective study of 60 patients (71 legs) with symptomatic PTO or NIVL, who underwent IVUS-guided ilio-femoral stenting from June 2018 to May 2019. Symptomatic patients of Clinical, Etiology, Anatomy and Pathophysiology (CEAP) classification²⁰ (three disease status and above) were included. They were offered IVUS and stenting after secondary causes of lower limb swelling (cardiac, renal, hepatic) were excluded. Patient demographics, co-morbidities, procedural, angiographic and follow-up data were recorded. Informed consent to collect, analyse and publish anonymized patient data was obtained. The local Institutional Review Boards of the two centres approved this study (CIRB number: 2018/3150).

Pre-operatively, patients had a contrast-enhanced computed tomography venogram (CTV) or magnetic resonance venogram (MRV) to look for iliac vein compression and (more importantly) to rule out intra-abdominal masses causing extrinsic venous compression. Patients underwent Duplex ultrasonography (DUS) to identify concomitant superficial and deep venous reflux.

In Singapore, stent patency rates were determined using DUS at Day 1 and at 3-, 6- and 12-months after intervention. In Taiwan, CTV was used at 6- and 12-months post-procedure. Clinical improvement was determined by the revised Venous Clinical Severity Score (rVCSS)²¹ and pain score using the visual analogue scale (VAS) pre and post-procedure (three months). Ulcer healing outcomes were also documented. All venous ulcers had four-layer compression applied until complete wound healing occurred.

Procedure and post-operative care

The procedure was performed with the patient under general anaesthesia or deep sedation in the supine position. The ipsilateral femoral vein in the mid-thigh was accessed in an antegrade fashion using an 18-gauge needle with an aspiration 5 ml syringe. A 5 French (Fr) vascular access sheath (GLIDESHEATH™, Terumo Medical, Tokyo, Japan) was inserted. To identify the presence of stenosis of iliac veins and collateral draining veins, digital subtraction venograms were performed to image from the common femoral vein (CFV) up to the distal inferior vena cava (IVC), in at least two orthogonal planes. A combination of 4 Fr Bernstein catheter (Tempo™, Cordis, USA) and a 0.35” hydrophilic-angled guidewire (Glide wire™, Terumo Medical, Tokyo, Japan) was used to cross the ilio-femoral segment under fluoroscopy. The hydrophilic guidewire was exchanged for a 0.35” stiff guidewire (HI-TORQUE Supracore™, Abbott Medical, USA), and the access sheath was upsized to a 10 Fr (GLIDESHEATH™, Terumo Medical, Tokyo, Japan) to allow IVUS interrogation and stenting. The IVUS catheter (Volcano™, Philips Healthcare, Eindhoven, Netherlands) was introduced over the guidewire into the distal IVC under fluoroscopy guidance. A preliminary pull back scanning run was performed, with and without the wire, to get an overview of the ilio-femoral lesions. Cross-sectional areas of the distal IVC, common iliac vein (CIV), external iliac vein (EIV) and CFV were measured using the IVUS catheter.

During the procedure, full anticoagulation with unfractionated heparin was given, targeting an activated clotting time of 250–300 s. Pre-dilatation was mandatorily performed using an appropriately sized balloon (usually 16/18 × 40/60 mm Atlas Gold™ balloon (BD Medical, Arizona, USA) for CIV and 14 mm × 40/60 mm balloon for EIV/CFV), and this was judged using the IVUS catheter to measure the normal-sized segment vein diameter.

Using combined IVUS and fluoroscopic guidance, stents were deployed across the affected segment, stenting from normal to normal venous zones, with generous stent overlap (>2 cm), with no spot stenting allowed. We performed routine post-dilatation of the stents with the appropriate-sized balloons at recommended burst pressure to achieve complete expansion of the stent. Venogram and IVUS were performed post-stenting to confirm the adequacy of treatment, blood flow and to rule out potential complications, such as stent under-expansion, migration and acute thrombosis. The access sheath and wires were removed, and hemostasis was achieved with manual compression for 10 min, without requiring any compression dressing or closure device. Figure 1 shows an example of a complex Venovo™ intervention for a PTS patient whereby we had to deploy the stents from the neck as the mid femoral vein was very diseased.

Figure 1.

Forty-one-year-old Indian male with severe PTS affecting the right leg: (a) venography showing long iliac vein occlusion from right CFV to IVC; (b) bidirectional approach taken from mid-thigh SFV and internal jugular vein, showing re-entry from below; (c) IVUS imaging was performed from above and pre-dilatation of iliac vein occlusion from below; (d) stenting was performed from the neck using a 10 Fr sheath, for Venovo™ stent deployment from the iliac bifurcation down to the SFV. Dog boning and disease within the right CFV is shown; (e) final stenting using 16 mm (CIV), 14 mm (EIV) and 12 mm (CFV/SFV); (f) stenting was done from the neck because the SFV was very diseased and tracking of balloons was difficult. Decision not to use a large sheath from the thigh was made; (g, h) IVUS imaging showing disease within the CFV and SFV, respectively; (i,j) post-stenting IVUS showing excellent lumen gain within the CIV and SFV, respectively; (k) final venogram run was fast with no lighting up of collaterals.

Post-operatively, patients were placed in intermittent pneumatic compression (Flowpac, Huntleigh Healthcare, Cardiff, UK). Therapeutic low-molecular-weight heparin (enoxaparin) was administered the same evening, followed by conversion to either warfarin (target international normalized ratio 2.0–2.5) or a direct oral anticoagulant (DOAC; i.e. Rivaroxaban (Bayer AG, Leverkusen, Germany) 20 mg/day).

Outcome definitions

Technical success was defined as successful deployment of stents to their intended locations. Procedural success was defined as technical success with at least one indicator of hemodynamic or clinical success. Primary patency rate was defined as the percentage of patients with uninterrupted stent patency. Assisted primary patency rate was defined as the percentage of patients with stent patency, irrespective of reintervention for a significantly narrowed (>50%) but still patent stent. Secondary patency rate was defined as the percentage of patients with stent patency after primary procedural and technical success, irrespective of interval therapies after a complete obstruction.

Statistical analysis

Continuous numeric variables were reported as mean and standard deviation for parametric distribution and median (interquartile range (IQR)) for non-parametric distribution. Categorical variables were reported as absolute number and percent, unless stated otherwise. Continuous numeric data were compared using the Student t test or Mann–Whitney U test for parametric and non-parametric data, respectively. Categorical data were compared using the Chi-square or Fisher exact tests. Statistical significance was assumed at p < 0.05. Kaplan–Meier survival estimation was used to calculate the stent patency rates. The statistical analyses were performed using SPSS statistical software version 25.0 (IBM Corp, Armonk, NY, USA).

Results

Baseline demographics

Sixty patients with a median age of 67 (IQR 54–77) years were followed-up over a median duration of 283 (IQR 211–370) days. Twenty-one of 60 (35.0%) were male; 11/60 (18.3%) had bilateral disease operated on at the same sitting. The mean body mass index (BMI) was 28.80 kg/m² ( $±$ 6.65), and 19/60 (31.7%) were diabetic. Table 1 summarizes the baseline demographics.

Table 1.

Baseline demographics.

Baseline demographics	N = 60 patients (%) (IQR) (SD)
Age (years)	67 (54–77)
Male	21/60 (35.0%)
Bilateral venous disease	11/60 (18.3%)
BMI	28.80 (±6.65)
Diabetes mellitus	19/60 (31.7%)
Hypertension	35/60 (58.3%)
Hyperlipidemia	21/60 (35.0%)
Peripheral vascular disease	6/60 (10.0%)
Obstructive sleep apnea	2/60 (3.3%)
Coagulation disorder	5/60 (8.3%)
History of smoking	9/60 (15.0%)

Lesion characteristics

Seventy-one limbs were analysed (left = 44/71 (62.0%)). Majority of lesions were NIVLs (60/71 (84.5%)), and 36/71 (50.7%) had MTS. Twenty-seven of 71 (38.0%) patients presented with CEAP 6 disease. Thrombi was found in 4/71 (5.6%) limbs, and 1/71 (1.4%) had complete venous occlusion. Table 2 summarizes the lesion characteristics.

Table 2.

Lesion characteristics.

Lesion characteristics	N = 71 limbs (%)
Left limb	44/71 (62.0%)
NIVL	60/71 (84.5%)
MTS	36/71 (50.7%)
Presence of varicose veins	37/71 (52.1%)
Pre-op. CTV showing compression	14/44 (31.8%)
Deep venous reflux on DUS	39/67 (58.2%)
Previous superficial venous ablation	30/71 (42.3%)
Concomitant superficial venous ablation	7/71 (9.9%)
Previous trauma/surgery	26/71 (36.6%)
CEAP classification
CEAP 3	19/71 (26.8%)
CEAP 4a	7/71 (9.9%)
CEAP 4b	14/71 (19.7%)
CEAP 5	4/71 (5.6%)
CEAP 6	27/71 (38.0%)
Presence of thrombus	4/71 (5.6%)
Presence of occlusion	1/71 (1.4%)

Procedural characteristics and complications

Ninety-four stents were placed in 71 limbs (Venovo™ = 73/94 (77.7%), Sinus Obliquus™ = 21/94 (22.3%)). A median of one stent (IQR 1–2) was placed per limb, and 21/71 (29.6%) limbs had iliocaval lesions, which required a combination of Sinus Obliquus™ and Venovo™ stents. Two of 71 (2.8%) limbs had two Venovo™ stents inserted. The average diameter and length of Venovo™ stents deployed were 15.84 (±1.58) mm and 78.65 (±19.11) mm, respectively. Pre-dilation was performed in all procedures. All procedures achieved technical and procedural success. Rivaroxaban was the post-operative anticoagulant of choice in the majority of procedures (49/71 (69.0%)). There were no major post-operative complications. Table 3 summarizes the post-operative anticoagulation of choice and complications.

Table 3.

Post-operative anticoagulation of choice and complications.

Post-operative anticoagulation of choice	N = 71 limbs (%)
Xarelto	46/71 (64.9%)
Warfarin	5/71 (7.0%)
Clopidogrel	16/71 (22.5%)
Clopidogrel + Xarelto	3/71 (4.2%)
Apixaban	1/71 (1.4%)
Post-operative complications	N = 71 limbs (%) (IQR)
Post-operative length of stay	1.5 (1–2)
Post-operative complication rate	7/71 (9.9%)
In-stent thrombosis	4/71 (5.6%)
Atelectasis	1/71 (1.4%)
Asymptomatic bradycardia	1/71 (1.4%)
Cellulitis	1/71 (1.4%)

Patency and stent integrity

Overall, primary patency rates were 94.7% (36/38), 94.6% (35/37), 94.1% (64/68) and 85.2% (23/27) immediately post-intervention, 3, 6 and 12 months, respectively. Four of 71 (5.6%) limbs developed in-stent thrombosis (PTO = 2/4 (50%); underlying coagulopathy = 1/4 (25%)). Two of four (50.0%) of patients with in-stent thrombosis underwent percutaneous transluminal angioplasty and catheter-directed thrombolysis. One of four (25.0%) had the thrombosed stent relined and extended distally. One of four (25.0%) had a spontaneous resolution of the thrombus. The two NIVL patients had distal disease not appreciated on the initial IVUS, and these cases were both extended with a further Venovo™ stent with no subsequent issues. Six months’ primary assisted- and secondary patency rates were 97.1% (66/68) and 100% (68/68), respectively. Figure 2 shows the Kaplan–Meier curves for the cumulative patency rates for PTO and NIVL. There were no stent migrations or stent fractures.

Figure 2.

Kaplan–Meier curves for stent patency rates in PTO versus NIVL patients.

Clinical outcomes

At three-month post-procedure, the mean rVCSS and VAS pain score improved from 12.26 (±3.31) to 4.33 (±2.78) (p < 0.01) and 6.97 (±1.38) to 2.03 (±1.65) (p < 0.01), respectively. All patients experienced a decrease in rVCSS and VAS. Sixty of 71 (84.5%) limbs had at least one CEAP score improvement and 27/27 (100%) venous ulcers healed completely, at three-month post-procedure.

Discussion

Venovo™ is a novel venous stent intended for treatment of IFVO. It comprises a self-expanding electro-polished nitinol stent (nickel-titanium alloy) with six markers located on each end, with an open-cell stent design. The flared ends have a diameter 3 mm larger than the stent body to ensure adequate wall apposition after inflation.⁹ The stents are pre-mounted on and delivered using an over-the-wire delivery tri-axial wheel system, allowing for precise placement. Stent diameters range from 10 to 20 mm (2 mm increments). Stent lengths range from 40 to 160 mm (20 mm increments).

A combination of Sinus Obliquus™ and Venovo™ stents were deployed in 21/71 (29.6%) limbs, all of which had lesions at the origin of the CIV. Fifteen of 21 (71.4%) of these limbs had MTS. Combination therapy using Venovo™ and Sinus Obliquus™ stents is useful for deep vein work involving the ilio-caval bifurcation. Sinus Obliquus™ stents were preferred for proximal iliac lesions. The superior radial force of its proximal closed-cell segment (24.2 N/cm) resists circumferential compression which can occur anywhere along the course of the iliac vein.^19,22,23 Overextension of the CIV stent into the IVC is a risk factor for contralateral DVT after iliac vein stent placement (‘jailing phenomenon’).²⁴ The oblique design at the proximal end prevents jailing of the contralateral iliac vein. The ‘kissing balloon’ technique was used for bilateral CIV lesions involving the origin to leave an uninterrupted outflow from both iliac veins into the inferior vena cava⁵ (Figure 3). The senior author (TYT) favours extending the stenting zone using Venovo™ stents. Venovo™ stents are stable during deployment and have higher radial resistive forces (16.5 N/cm), relative to the distal open-cell segment of the Sinus Obliquus™ stent (15.9 N/cm).^19,22

Figure 3.

Kissing stenting with Venovo™ stents (18 mm stents).

Our study revealed a high percentage of patients with NIVL (84.5%), as compared to data from the Arnsberg registry (37.0%)⁹ and the VERNACULAR trial (45.3%).¹⁷ This is likely due to a local referral pathway issue. In Singapore, PTO patients are initially managed by hematologists. Only patients with severe refractory venous disease despite medical therapy (external compression stockings, venoactive drugs and exercise) are referred to vascular surgeons for evaluation.¹⁹

Our study revealed excellent short-term patency rates, with few re-interventions. Our 6-month primary patency result (94.1%) is similar to existing data from the Arnsberg venous registry (97.0%). Improvement in clinical outcomes was also significant and expedient.⁹ The ongoing VERNACULAR trial revealed promising primary patency rates of 88.3% (vs. 85.2% in our study) and 83.0% at 12 and 24 months post-procedure, with no stent fractures.¹⁷ This shows a sustained benefit in deploying Venovo™ venous stents for IFVO.

Stenting past the inguinal ligament is a current concern and is associated with in-stent restenosis and stent fractures.^25–27 Black et al.²⁸ reported three cases of stent fractures, all of which occurred at the inguinal ligament. However, stenting past the inguinal ligament is often necessary to ensure sufficient inflow and disease coverage.²⁹ Covering the entire obstructive lesion with stent is vital for long-term patency, even if it involves crossing the inguinal ligament.^26,29 In our study, there were no stent migration or stent fractures, despite five procedures requiring stenting across the inguinal ligament. No stent fractures were reported in the VERNACULAR trial and data from the Arnsberg registry.^9,17 Venovo™ stents are ideal at the inguinal ligament due to their high chronic outward force and great radial resistive force.²² Its open-cell stent design provides sufficient stent flexibility to accommodate movement at the hip joint without stent tapering.³⁰

Both Venovo™ and Vici Venous™ stents recently received the United States Food and Drug Administration (FDA) approval for the treatment of IFVO. The VIRTUS trial on Vici Venous™ stents revealed similar 12-month primary patency rates of 84.0% and excellent clinical outcomes at six-month post-procedure. Ten of 281 (3.6%) Vici Venous™ stents showed signs of stent fracture at one year.³¹ The Vici Venous™ stent is a laser-cut, closed-cell nitinol, self-expanding stent. It is more rigid than open-cell design stents but shows sufficient flexibility for physiological angles.²⁸ Relative to Venovo™ stents, Vici Venous™ stents were reported to have lower maximal radial resistive forces and chronic outward forces, but higher crush resistance. Its high scaffold thickness-to-strut ratio provides significant crush resistance and maintains durability.²²

Despite deep vein stenting gaining popularity in treating IFVO, there are few recommendations for periprocedural antithrombotic therapy.³² Traditionally, Vitamin K antagonists (VKA) were commonly used. Recently, DOACs gained popularity due to its wide therapeutic window, low incidence of major bleeding and convenience.³³ At our centres, the majority of patients received rivaroxaban (46/71 (64.9%)). Our anticoagulation regime in Singapore is consistent with the consensus statement published by Milinis et al.³⁴ Patients with recurrent DVT or thrombophilia receive lifelong anticoagulation. Anticoagulation is stopped after six months and switched to aspirin for NIVL patients, if DUS is satisfactory. In Taiwan, PTO patients were prescribed warfarin. NIVL patients received either rivaroxaban, clopidogrel or both. Tosenovsky showed excellent one-year stent patency rates for NIVL patients with just antiplatelet therapy.³⁵ Langwieser³⁶ found that a combination of Rivaroxaban and Clopidogrel in patients after iliofemoral deep vein stenting was safe and effective. Post-stenting anticoagulation remains a complex and controversial issue. Continued evaluation is required to produce a set of international guidelines.³²

Limitations

This was a single-arm study (albeit multi-centre), with different follow-up modalities of stent patency. The duration of follow-up was also short, lacking long-term outcomes, which are awaited for this venous stent worldwide. The post-operative follow-up and anticoagulation regime were not standardized between the two centres.

Conclusion

Deep vein stenting of symptomatic IFVO with Venovo™ and Sinus Obliquus™ stents is associated with low device-related complication rates and excellent short-term patency rates. Sinus Obliquus™ stents were particularly useful for proximal iliac lesions. Few reinterventions were required. Clinical outcomes were significantly improved at three months post-intervention. Ulcer healing rates were expedient. Continued evaluation of the safety and efficacy of deep vein stenting using the novel Venovo™ venous stent is required.

Footnotes

Acknowledgements

This article was an oral presentation at the 2020 Annual Winter Vascular and Endovascular Surgery Society (VESS) Meeting, Colorado, USA, 30 January–1 February 2020.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: TYT has previously received investigator-initiated grants from Bard BD for unrelated research projects.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

The Institutional Review Board of Singapore approved this study (Centralised Institutional Review Board [CIRB] number: 2018/3150).

Guarantor

TYT.

Contributorship

TYT conceived the study and revised the paper for intellectual content. MHHL, KD, CJQY, QWSL and HYY were involved in data collection, data analysis and drafting of the manuscript. TTC revised the paper for intellectual content. JWHT coordinated efforts from the Taiwan centre. All authors reviewed and edited the manuscript and approved the final version of the manuscript.

ORCID iDs

Tjun Y Tang

Mervin HH Lim

Shaun QW Lee

References

Neglén

Thrasher

Raju

Venous outflow obstruction: an underestimated contributor to chronic venous disease. J Vasc Surg 2003; 38: 879–885.

Kahn

Partsch

Vedantham

, et al. on behalf of the Subcommittee on Control of Anticoagulation of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis. Definition of post-thrombotic syndrome of the leg for use in clinical investigations: a recommendation for standardization. J Thromb Haemost 2009; 7: 879–883.

Liddell

Evans

NS.

May-Thurner syndrome vascular medicine (London, England). Vasc Med 2018; 23: 493–496.

Raju

Neglen

High prevalence of nonthrombotic iliac vein lesions in chronic venous disease: a permissive role in pathogenicity. J Vasc Surg 2006; 44: 136–143.

Neglen

Darcey

Olivier

, et al. Bilateral stenting at the iliocaval confluence. J Vasc Surg 2010; 51: 1457–1466.

Neglen

Berry

Raju

Endovascular surgery in the treatment of chronic primary and post-thrombotic iliac vein obstruction. Eur J Vasc Endovasc Surg 2000; 20: 560–571.

Wen-da

Yue-Xin

Stenting for chronic obstructive venous disease: a current comprehensive meta-analysis and systematic review. Phlebology 2016; 31: 376–389.

Razavi

Jaff

Miller

LE.

Safety and effectiveness of stent placement for iliofemoral venous outflow obstruction: systematic review and meta-analysis. Circ Cardiovasc Interv 2015; 8: e002772.

Lichtenberg

MKW

de Graaf

Stahlhoff

, et al. Venovo venous stent in the treatment of non-thrombotic or post-thrombotic iliac vein lesions – short-term results from the Arnsberg venous registry. VASA 2019; 48: 175–180.

10.

Jalaie

Arnoldussen

Barbati

, et al. What predicts outcome after recanalization of chronic venous obstruction: hemodynamic factors, stent geometry, patient selection, anticoagulation or other factors? Phlebology 2014; 29: 97–103.

11.

Gagne

Kucher

, et al. Long-term clinical outcomes and technical factors with the wallstent for treatment of chronic iliofemoral venous obstruction. J Vasc Surg Venous Lymphat Disord 2019; 7: 45–55.

12.

Mandel

Ostrozhynskyy

Hingorani

, et al. Underexpansion of wallstents((R)) in the treatment of nonthrombotic iliac vein lesions. Ann Vasc Surg 2018; 52: 163–167.

13.

van Vuuren

Doganci

Wittens

Patency rates and clinical outcomes in a cohort of 200 patients treated with a dedicated venous stent. J Vasc Surg Venous Lymphat Disord 2018; 6: 321–329.

14.

Lichtenberg

de Graaf

Stahlhoff

, et al. Patency rates, safety and clinical results of the sinus-Obliquus venous stent in the treatment of chronic ilio-femoral venous outflow obstruction – data from the arnsberg venous registry. VASA Zeitschrift Gefasskrank 2019; 48: 270–275.

15.

O'Sullivan

GJ.

Iliofemoral venous stenting extending into the femoral region: initial clinical experience with the purpose-designed zilver vena stent. J Cardiovasc Surg 2013; 54: 255–261.

16.

Razavi

Marston

Black

, et al. The initial report on 1-year outcomes of the feasibility study of the VENITI VICI VENOUS STENT in symptomatic iliofemoral venous obstruction. J Vasc Surg Venous Lymph Disord 2018; 6: 192–200.

17.

BARD® The VENOVO™ Venous Stent Study for Treatment of Iliofemoral Occlusive Disease. Available from: https://ClinicalTrials.gov/show/NCT02655887 (2016, accessed 11 March 2020).

18.

Lee

QWS

Gigson

Chan

, et al. A comparison between Caucasian and Asian superficial venous anatomy and reflux patterns – implications for potential precision endovenous ablation therapy. Phlebology 2020; 35: 39–45.

19.

Tang

Goh

Damodharan

, et al. RE: “long-term follow-up of stenting across the ilio-caval confluence in patients with iliac venous lesions”: the value of using IVUS and a dedicated oblique venous stent for deep vein work involving the ilio-caval bifurcation. J Thromb Thrombol 2019; 47: 328–330.

20.

Rutherford

Padberg

Jr Comerota

, et al. Venous severity scoring: an adjunct to venous outcome assessment. J Vasc Surg 2000; 31: 1307–1312.

21.

Vasquez

Munschauer

CE.

Venous clinical severity score and quality-of-life assessment tools: application to vein practice. Phlebology 2008; 23: 259–275.

22.

Dabir

Feisst

Thomas

, et al. Physical properties of venous stents: an experimental comparison. Cardiovasc Interv Radiol 2018; 41: 942–950.

23.

Stuck

Kunz

Baumgartner

, et al. Patency and clinical outcomes of a dedicated, self-expanding, hybrid oblique stent used in the treatment of common iliac vein compression. J Endovasc Ther 2017; 24: 159–166.

24.

Lee

Park

K-M

, et al. Contralateral deep vein thrombosis after iliac vein stent placement in patients with May-Thurner syndrome. J Vasc Interv Radiol 2018; 29: 774–780.

25.

Jiang

, et al. Technical details and clinical outcomes of transpopliteal venous stent placement for postthrombotic chronic total occlusion of the iliofemoral vein. J Vasc Interv Radiol 2014; 25: 925–932.

26.

Rosales

Sandbaek

Jorgensen

JJ.

Stenting for chronic post-thrombotic vena cava and iliofemoral venous occlusions: mid-term patency and clinical outcome. Eur J Vasc Endovasc Surg 2010; 40: 234–240.

27.

Neglén

Raju

In-stent recurrent stenosis in stents placed in the lower extremity venous outflow tract. J Vasc Surg 2004; 39: 181–187.

28.

Black

Gwozdz

Karunanithy

, et al. Two year outcome after chronic iliac vein occlusion recanalisation using the vici venous stent((R)). Eur J Vasc Endovasc Surg 2018; 56: 710–718.

29.

Neglen

Tackett

Jr Raju

Venous stenting across the inguinal ligament. J Vasc Surg 2008; 48: 1255–1261.

30.

van Vuuren

de Wolf

Wittens

CH.

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

Phlebology 2019; 34: 459–465.

31.

Razavi

Black

Gagne

, et al.; VIRTUS Investigators. Pivotal study of endovenous stent placement for symptomatic iliofemoral venous obstruction. Circ Cardiovasc Interv 2019; 12: e008268.

32.

Yap HY, Loa J, Tosenovsky PJ, et al. Use of anticoagulation therapy post deep venous stenting for post-thrombotic disease and non-thrombotic iliac vein lesions - Any consensus? Phlebology, 2020; 35: 545–547.

33.

Mekaj

Duci

, et al. New oral anticoagulants: their advantages and disadvantages compared with vitamin K antagonists in the prevention and treatment of patients with thromboembolic events. Ther Clin Risk Manag 2015; 11: 967–977.

34.

Milinis

Thapar

Shalhoub

, et al. Antithrombotic therapy following venous stenting: international delphi consensus. Eur J Vasc Endovasc Surg 2018; 55: 537–544.

35.

Tosenovsky

One-year results of iliocaval stenting. Ann Vasc Surg 2019; 59: 208–216.

36.

Langwieser

Bernlochner

Wustrow

, et al. Combination of factor Xa inhibition and antiplatelet therapy after stenting in patients with iliofemoral post-thrombotic venous obstruction. Phlebology 2016; 31: 430–437.