Caliber-targeted reinterventional overdilation of iliac vein Wallstents

Indications, technical aspects, and outcomes of stent placement in chronic iliofemoral venous obstruction

BACKGROUND

Iliofemoral venous stent placement (IVS) has evolved to a well-established endovascular treatment modality for chronic iliofemoral venous obstruction (CIVO). Dedicated venous stents gained approval from the US Food and Drug Administration in 2019 and solidified IVS as a defined intervention with clear indications, contraindications, risks, benefits, and procedural management principles. This review focuses on the indications, technical aspects and outcomes of stenting for CIVO. Other aspects pertaining to IVS are covered in other articles that are a part of this series.

METHODS

This study conducted a literature search limited to English articles. Three search strategies were used, and references were managed in Covidence software. Four investigators screened and evaluated articles independently, excluding meta-analyses, clinical trial protocols, and nonrelevant studies. Eligible studies, focused on clinical outcomes and stent patencies, underwent thorough review.

RESULTS

The literature search yielded 1704 studies, with 147 meeting eligibility criteria after screening and evaluation. Exclusions were based on duplicates, irrelevant content, and noniliac vein stent placement.

CONCLUSIONS

Successful IVS for CIVO relies on meticulous patient selection, consistent use of intravascular ultrasound examination during procedures and attention to the technical details of IVS.

Endovascular mechanical thrombectomy of iliofemoral venous stent occlusion with the novel RevCore thrombectomy system: case reports and literature review

Venous in-stent restenosis is not completely understood, and the currently available treatment is usually unsatisfactory. We describe the cases of two patients treated with the RevCore thrombectomy system (Inari Medical), designed for venous in-stent thrombosis. Case 1 involves a 62-year-old woman with post-thrombotic syndrome from iliac vein stent placement 15 years earlier. Case 2 describes a 30-year-old woman with post-thrombotic syndrome from recurrent iliac vein stent occlusion, despite therapeutic anticoagulation. Both patients had previous recanalization attempts at outside facilities that were unsuccessful. The RevCore system was safe and feasible in these initial cases, and more studies are warranted.

Mechanical thrombectomy of venous in-stent thrombosis with the novel RevCore thrombectomy system: A report of 2 cases

In-stent thrombosis (IST) is a common venous stent complication. Acute IST warranting intervention can generally be treated with catheter-directed thrombolysis or aspiration thrombectomy. However, thrombosed stents often have chronic-appearing components that pose a significant treatment challenge as the thrombus firmly adheres to the stent and vessel wall and becomes resistant to thrombolytics and aspiration thrombectomy. Alternate treatment options such as venoplasty, stent relining, and medical management do not remove existing IST but rather remodel the lumen with limited long-term efficacy. This report details 2 cases of chronic-appearing IST successfully debulked with the novel RevCore Thrombectomy System. RevCore, designed to mechanically liberate acute to chronic IST via an expandable nitinol coring element, achieved substantial luminal gain and sustained patency in both patients.

Novel venous balloon for compliance measurement and stent sizing in a post-thrombotic swine model

Objective: Real-time accurate venous lesion characterization is needed during endovenous interventions for stent deployment. The goal of this study is to validate a novel device for venoplasty sizing and compliance measurements. Methods: A compliance measuring sizing balloon (CMSB) uses real-time electrical conductance measurements based on Ohm's Law to measure the venous size and compliance in conjunction with pressure measurement. The sizing accuracy and repeatability of the CMSB system were performed with phantoms on the bench and in a swine model with an induced post thrombotic (PT) stenosis in the common femoral vein of swine. Results: The accuracy and repeatability of the CMSB system were validated with phantom bench studies of known dimensions in the range of venous diameters. In 9 swine (6 experimental and 3 control animals), the luminal cross-sectional areas (CSA) increased heterogeneously along the PT stenosis when the CMSB system was inflated by stepwise pressures. The PT stenosis showed lower compliance compared to the non-PT vein segments (5 mm2 vs. 10 mm2 and 13 mm2 at a pressure change of 40 cm H2O). Compliance had no statistical difference between venous hypertension (VHT) and Control. Compliance at PT stenosis, however, was significantly smaller than that at Control and VHT (p < 0.05, ANOVA). Conclusion: The CMSB system provides accurate, repeatable, real-time measurements of CSA and compliance for assessment of venous lesions to guide interventions. These findings provide the impetus for future first-in-human studies.

Conduit design with expanding diameter for enhanced flow

Conduits are commonly used for treating lesions in arteries and veins. The conventional stents are cylindrical in shape, which increases flow resistance with length. This study presents a design of stents and conduits where the conduit caliber expands gradually to reduce resistance while avoiding flow separation. Inflow was provided from a header tank at two different pressures (i.e., 10 and 25 mm Hg pressure) into a cylindrical or expanding conduit. The initial conduit calibers were 2-, 3-, 4-, and 5-mm and 160-, 310-, and 620-mm lengths in each case. The flow rates of expanding caliber conduits (at a rate of r4-6/cm where r is the initial conduit radius) were compared to traditional cylindrical conduits of constant radius. The expanded caliber yields a significantly increased flow of 16-55% for R4/L expansion, 9-44% for R5/L expansion, and 1-28% for R6/L expansion. Simulated flow models using computational fluid dynamics (CFD) were used to validate and expand the experimental findings. Flow separation was detected for certain simulations by flow pathlines and wall shear stress (WSS) calculations. The results showed that a caliber expansion rate of r6/cm is the optimal rate of expansion for most potential applications with minimum flow separation, lower resistance, and increased flow.

Intravascular ultrasound guidance for lower extremity arterial and venous interventions

This review details the utility of intravascular ultrasound (IVUS) for the management of peripheral artery and venous disease. The purpose of this document is to provide an update in the use of IVUS in peripheral arterial and venous pathology and demonstrate the use of IVUS as a practical diagnostic imaging procedure to evaluate and treat peripheral vascular disorders. IVUS, a diagnostic tool that relies on sound waves to produce precise images of the vessel being evaluated, was originally introduced to the medical community for the purposes of peripheral artery imaging, though it was quickly adapted for coronary interventions with positive outcomes. The utility of IVUS includes vessel measurement, pre- and post-procedural planning, treatment optimisation, and detection of thrombus, dissection or calcium severity. While angiography remains the standard imaging approach during peripheral intervention, multiple observational studies and small prospective trials have shown that in comparison, IVUS provides more accurate imaging detail, which may improve procedural outcomes. IVUS can also address limitations of angiography, including the need to administer contrast medium and eliminate the ambiguity associated with other forms of imaging. This review provides contemporary examples of where IVUS is being used during peripheral intervention as well as representative imaging to serve as a resource for the practising clinician.

An overview of in-stent restenosis in iliofemoral venous stents

BACKGROUND

Although endovenous stents have been associated with overall low morbidity, they can require reinterventions to correct stent malfunction due to in-stent restenosis (ISR). ISR has often occurred iliofemoral venous stents but has not been well described. It has been reported to develop in >70% of patients who have undergone iliofemoral venous stenting. We sought to provide an overview of ISR in iliofemoral venous stents, including the pathologic, diagnostic, and management considerations and the identification of several areas of potential research in the future.

METHODS

A search of reported English-language studies was performed in PubMed and the Cochrane Library. "In-stent restenosis," "vein," "venous," "iliac," and "iliofemoral" were used as keywords. The pertinent reports included in the present review had addressed the pathology, diagnosis, and current management options for ISR.

RESULTS

ISR refers to the narrowing of the luminal caliber of the stent owing to the development of stenosis inside the stent itself. ISR should be differentiated from stent compression. Two main types of ISR have been described: soft and hard lesions. These lesions respond differently to angioplasty. Stent inflow and shear stress are important factors in the development of ISR. The treatment options available at present include balloon angioplasty (hyperdilation or isodilation), laser ablation, atherectomy, and Z-stent placement.

CONCLUSIONS

Reintervention for ISR should be determined by the presence of residual or recurrent symptoms and not simply by a numeric value obtained from an imaging study. Overall stent occlusion due to ISR is rare, and no role exists for prophylactic angioplasty to treat asymptomatic ISR. The current treatment options for ISR are mostly durable and effective. However, more research is needed on methods to prevent the development of ISR. The role of antiplatelet and anticoagulant agents in the prevention of ISR requires further investigation, with particular attention to unique subset of patients (after thrombosis vs nonthrombotic iliac vein lesions). For high-risk, post-thrombotic patients, anticoagulation can be considered to prevent ISR. The role of triple therapy (anticoagulation and dual antiplatelet therapy) in the prevention of ISR remains unclear.

Iliofemoral venous stenting in patients with central neuromuscular disorders

BACKGROUND

Leg swelling in patients with various central neuromuscular disorders is a common clinical scenario and can lead to significant morbidity. The aim of the present study was to evaluate a subset of patients with central neuromuscular disorders who had undergone iliofemoral venous stenting at a specialty venous clinic at a tertiary care hospital.

METHODS

From January 2000 to December 2020, the medical records of all patients with a known central neuromuscular disorder who had undergone iliofemoral venous stenting for chronic iliofemoral venous obstruction were retrospectively analyzed.

RESULTS

A total of 42 patients (45 limbs) with central neuromuscular disorders had undergone iliofemoral stenting after failure of a trial of conservative therapy. The central neuromuscular disorders included Parkinson disease (n = 20 limbs), multiple sclerosis (n = 15 limbs), and other neuromuscular conditions (n = 10 limbs). The mean age of the sample was 59 ± 14 years. The ratio of post-thrombotic to nonthrombotic iliac vein lesions was 3:1. Most of the patients had had CEAP (clinical, etiologic, anatomic, pathophysiologic) class ≥C4 (64.4%); 25 limbs had a history of venous thromboembolism (56%). A trend was seen toward improvement in all clinical parameters measured (venous clinical severity score, visual analog scale for pain score, and edema grade) after stenting. An ulcer healing rate of ≤90% was noted after stenting. Of the 45 limbs, 24 had required some form of reintervention (53%) after initial stent placement.

CONCLUSIONS

Venous intervention in the form of endovenous stenting was associated with improvement in the clinical parameters for patients with central neuromuscular disorders. However, these patients should be counseled regarding the relatively higher rate of reinterventions that might be required to correct residual or recurrent symptoms.

Dimensional disparity between duplex and intravascular ultrasound in the assessment of iliac vein stenosis

Minimum iliac vein caliber necessary to maintain normal peripheral venous pressure can be derived by the Poiseuille equation. Duplex was compared to intravascular ultrasound (IVUS) in the assessment of iliac vein stenosis in this single center retrospective study. Parallel IVUS and duplex caliber data for common iliac vein (CIV) and external iliac vein (EIV) in 382 limbs were separately compared. One or both segments were stenotic by IVUS criteria in 213 limbs. Neither segment was stenotic by IVUS in 22 limbs. Bland-Altman analyses and Passing-Bablok linear regressions were used. Duplex calibers were dimensionally smaller than corresponding IVUS images of CIV and EIV segments in Bland-Altman comparison by a mean of 54 mm² and 34 mm², respectively. Passing-Bablok regression suggested the difference was due to a systematic bias and not proportional. Duplex yields a smaller cross-sectional image of CIV and EIV compared to IVUS. Duplex is not a reliable diagnostic test for iliac vein stenosis.

Role of laser ablation in recalcitrant instent restenosis post iliofemoral venous stenting

Instent restenosis (ISR) represents the most common reason for recurrent symptoms requiring reintervention in patients who have undergone venous stenting for chronic iliofemoral venous obstruction. Treatment of ISR requires stent angioplasty typically using angioplasty balloons equal to or larger than the rated diameter of the stent. At times this does not yield the required result, and in these patients, utilization of a laser catheter supported by an angled sheath is helpful to ablate the ISR or make it more amenable to repeat balloon angioplasty. The authors report their experience with this technique for 18 patients with recurrent symptoms impacting quality of life as a result of recalcitrant ISR in this retrospective review of contemporaneously entered electronic medical record data. 12 (67%) limbs underwent laser ablation only, while 6 (33%) limbs underwent additional angioplasty post laser ablation. Post intervention for ISR, at 12 months, the venous clinical severity score improved from 5 to 3.5 (P = .0005) and the VAS pain score went from 7 to 5 (P = .0005). At 10 months, primary patency was 87% and primary assisted patency was 100%. There were no stent occlusions. Laser ablation of recalcitrant instent restenosis in patients presenting with recurrent chronic iliac venous obstruction post iliofemoral venous stenting is a safe and effective option. Corroboration from larger studies is warranted.

Experimental analysis of aspect ratio in iliac vein stenosis

BACKGROUND

Veins are thin-walled tubes. Their lumen is roughly circular with an aspect ratio close to 1:1 under physiologic pressures. When they collapse owing to decreased internal pressure or external compression, the aspect ratio changes. The vertical diameter is usually diminished more than the transverse, with a considerable decrease in the lumen area. The recent emergence of stent correction of many venous compression syndromes, particularly iliac vein stenosis, has brought attention to the importance of the aspect ratio, quite apart from an overall decrease in caliber. The iliac vein pressure is influenced not only by stenosis, but also intra-abdominal pressure, right atrial pressure, and collaterals. We investigated the impact of aspect ratio in an experimental model incorporating these factors.

METHODS

Inflow was provided from a header tank at 25 mm Hg pressure into a Penrose tubing enclosed in a polyethylene cylinder pressurized (Starling pressure) to simulate intra-abdominal pressures of 5 and 10 mm Hg. The Penrose drained into an outflow tank with a pressure of 7 mm Hg, simulating right atrial pressure. Stenosis was simulated with a series of three-dimensional, printed plastic nozzles with caliber areas of 50, 100, and 200 mm² and varying in aspect ratios of 1:1 to 1:4. The flow and pressure in this system was monitored with the use of overflow collaterals in some experiments.

RESULTS

Free flow from the header tank through the Penrose (zero Starling pressure) with a 200 mm² circle nozzle into the outflow tank with zero pressure resulted in flow pressure of approximately 1.5 mm Hg. Using nozzles of a smaller caliber or an increased aspect ratio resulted in an increase of flow pressures of up to approximately 3.7 mm Hg. Flow into an outflow tank of 7 mm Hg simulating right atrial pressure further increased flow pressures by approximately 7 mm Hg. The addition of Starling pressures of 5 and 10 mm Hg simulating abdominal pressure increased flow pressure even further to the 10 to 17 mm Hg range. When the Starling pressure was dominant, the additional contribution of nozzle caliber stenosis or aspect ratio reduction to the overall flow pressure ranged from 2 to 6 mm Hg. Collateral overflow varied inversely with collateral resistance. Some experiments yielded an anomalous flow/pressure phenomena known to occur in collapsible tube flows.

CONCLUSIONS

A decrease in the caliber or the aspect ratio of iliac vein stenosis was among several other factors that generate peripheral venous hypertension in an experimental model. Increased intra-abdominal pressure is a major influence that amplifies the pressure effects of aspect ratio or caliber reduction.

Catheter Interventions for Acute Deep Venous Thrombosis: Who, When and How

Deep venous thrombosis (DVT) is common and can be a source of morbidity by way of pulmonary embolism and post-thrombotic syndrome. Recent trials have demonstrated both early and late symptomatic benefit in venous thrombolysis and early recanalisation of the iliocaval system of selected patients. Based on the emerging evidence, national societies have published guidelines that recommend early thrombus removal in iliofemoral DVT in patients with low bleeding risk and good life expectancy. In light of these recommendations, endovenous thrombolysis and/or thrombectomy have become more popular among vein specialists. As more venous technology becomes available, surgeons and interventionalists should take pause and ensure their patient selection and treatment algorithms parallel that of existing and emerging evidence. This article summarises current evidence, technology, and the approach used at a high-volume academic centre in treating iliofemoral DVT.

Diagnostic yield of intravascular ultrasound in patients with clinical signs and symptoms of lower extremity venous disease

BACKGROUND

Intravascular ultrasound (IVUS) examination has a higher sensitivity compared with venography in the assessment of obstructive venous disease. However, at most venous centers, both modalities continue to be used concomitantly. This study evaluated the diagnostic clinical yield of IVUS examination as a singular intraoperative investigative modality in patients in whom clinical signs and symptoms of venous disease were severe enough to merit such an examination and in whom a venogram was not performed simultaneously.

METHODS

From January, 2013, to December, 2018, there were 31 limbs (29 patients) who only had IVUS planimetry without concomitant venogram. Clinical parameters such as pain, swelling and Venous Clinical Severity Score were measured preoperatively and postoperatively. The degree of stenosis noted on intraoperative IVUS was compared with the preoperative duplex. Incidence of complications, technical success, and clinical yield of IVUS examination were noted.

RESULTS

The etiology of venous lesion was post thrombotic in the majority of patients (74%). All patients (100%) were either in Clinical, Etiologic, Anatomic, and Pathologic class C3 or higher. In all patients (100%) taken to the operating room, IVUS examination identified stenosis in at least one of the following three veins: common iliac vein, external iliac vein, and common femoral vein. Intervention was in the form of angioplasty with endovenous stenting. There was significant improvement in pain, swelling and Venous Clinical Severity Score after the intervention.

CONCLUSIONS

IVUS is an effective diagnostic tool that displays high quality, real-time cross-sectional anatomy during venous interventions. When used as the sole intraoperative diagnostic modality, it seems to have a high clinical yield in patients in whom signs and symptoms of venous disease are severe enough to merit intervention.