Percutaneous management of chronic deep venous reflux: review of experimental work and early clinical experience with bioprosthetic valve

Systematic review and meta-analysis of deep venous reflux correction in chronic venous insufficiency

OBJECTIVE

The aim of this study was to investigate the technical feasibility, operative techniques, safety, and efficacy outcomes of procedures aimed at correcting deep venous reflux, in patients with chronic venous insufficiency.

METHODS

We performed systematic literature searches in PubMed, Embase, and Web of Science from databases' inception to February 2022. We included systematic reviews, randomized controlled trials, and observational studies describing surgical procedures to treat patients with deep reflux due to primary and secondary incompetence, post-thrombotic syndrome (PTS). Proportion meta-analyses were performed for all the efficacy and safety outcomes.

RESULTS

We included 57 studies in the quantitative synthesis: three randomized controlled trials including 252 patients and 54 case series including 4004 patients. Studies included a median of 38 patients, with a mean age of 51 years; 52% of them were males. Forty percent of studies included 2291 patients with primary incompetence, 29% of studies included 595 patients with PTS, and 31% of studies included 1118 patients with both diseases. As for primary incompetence, pooled estimates for all procedures showed an 89% (95% confidence interval [CI], 82%-94%) of ulcer healing, 10% (95% CI, 4%-18%) ulcer recurrence, 98% (95% CI, 93%-100%) valve patency, 84% (95% CI, 78%-90%) valve competence, 0.05% (1/1904 patients) pulmonary embolism, 1% (95% CI, 0%-3%) wound infections, 5% (95% CI, 1%-9%) hematoma, 2% (95% CI, 0%-6%) lymphocele, 2% (95% CI, 1%-4%) thrombosis, 85% (95% CI, 74%-94%) pain improvement, 89% (95% CI, 65%-100%) edema improvement, and 85% (95% CI, 73%-93%) lipodermatosclerosis improvement. Patients with PTS showed less favorable outcomes: 82% (95% CI, 71%-91%) of ulcer healing, 18% (95% CI, 5%-36%) ulcer recurrence, 88% (95% CI, 78%-96%) valve patency, 78% (95% CI, 66%-88%) valve competence, no pulmonary embolism, 6% (95% CI, 0%-22%) wound infections, 6% (95% CI, 3%-10%) hematoma, 5% (95% CI, 1%-12%) lymphocele, 7% (95% CI, 1%-16%) thrombosis, 79% (95% CI, 59%-94%) pain improvement, 75% (95% CI, 61%-88%) edema improvement, and 64% (95% CI, 9%-100%) lipodermatosclerosis improvement.

CONCLUSIONS

The number of studies included in each meta-analysis are limited, and knowing how this element can affect the statistical power, as well as the absence of comparative control groups, it is not possible to draw definitive conclusions. Nevertheless, deep venous reconstructive surgery for reflux may increase the probability of clinical improvement in patients affected by chronic venous insufficiency. Outcomes appear to be satisfactory even if possible adjunctive procedures may be required over the course of the patient's lifetime. Consequently, a strict follow-up protocol is required to maintain outcomes. Further studies are required to evaluate deep venous reconstructive surgery for reflux particularly as to how it compares with the more recently introduced endovenous approaches.

Biohybrid elastin-like venous valve with potential for in situ tissue engineering

Chronic venous insufficiency (CVI) is a leading vascular disease whose clinical manifestations include varicose veins, edemas, venous ulcers, and venous hypertension, among others. Therapies targeting this medical issue are scarce, and so far, no single venous valve prosthesis is clinically available. Herein, we have designed a bi-leaflet transcatheter venous valve that consists of (i) elastin-like recombinamers, (ii) a textile mesh reinforcement, and (iii) a bioabsorbable magnesium stent structure. Mechanical characterization of the resulting biohybrid elastin-like venous valves (EVV) showed an anisotropic behavior equivalent to the native bovine saphenous vein valves and mechanical strength suitable for vascular implantation. The EVV also featured minimal hemolysis and platelet adhesion, besides actively supporting endothelialization in vitro, thus setting the basis for its application as an in situ tissue engineering implant. In addition, the hydrodynamic testing in a pulsatile bioreactor demonstrated excellent hemodynamic valve performance, with minimal regurgitation (<10%) and pressure drop (<5 mmHg). No stagnation points were detected and an in vitro simulated transcatheter delivery showed the ability of the venous valve to withstand the implantation procedure. These results present a promising concept of a biohybrid transcatheter venous valve as an off-the-shelf implant, with great potential to provide clinical solutions for CVI treatment.

Glutaraldehyde fixation of venous valve tissue: A benchmark for alternative fixation methods

Objective

Bioprosthetic venous valves have yet to achieve long-term patency due to issues with calcification following implantation that is influenced by current xenograft fixation methods, most notably glutaraldehyde. The goal of this study was to investigate the effects of glutaraldehyde fixation on the functional properties of venous tissue to establish a benchmark for the evaluation of alternative fixation methods.

Methods

The degree of crosslinking was evaluated by determining shrink temperature and the stability of tissue with pronase and collagenase digestion.

Results

Glutaraldehyde fixation of venous tissue was confirmed by a significant difference in the shrink temperature between fresh and glutaraldehyde treated samples. Significant differences in the amount of tissue remaining following digestion were observed for venous versus cardiac tissue.

Conclusions

This study demonstrates the importance of tissue-specific evaluation in the development of alternative xenograft fixation methods to improve outcomes with bioprosthetic venous valves.

Safety and feasibility report on nonimplantable endovenous valve formation for the treatment of deep vein reflux

OBJECTIVE

Definitive treatment techniques for symptomatic deep venous reflux have been relegated to complex and invasive open surgery which is rarely performed today. The BlueLeaf System provides an endovenous method for the formation of deep venous valves without an implant, avoiding the complications associated with permanent foreign materials. The system has the adaptability to form valves within the femoral and popliteal veins at multiple levels in a single procedure. The aim was to determine the midterm safety and efficacy of this novel device in an early feasibility study.

METHODS

Feasibility of endovenous deep venous valve formation was assessed in patients with chronic venous insufficiency (Clinical, Etiologic, Anatomic, Pathophysiologic [CEAP] 4-6). Follow-up was completed through 1 year, assessing vein patency and reflux time (RT) with duplex ultrasound examination. Venous clinical improvement was evaluated using the revised Venous Clinical Severity Scale.

RESULTS

Of the 14 patients, 13 (93%) had successful formation of at least one monocuspid valve, with a mean number of 1.4 valves (range, 0-3 valves) per patient. There were no device-related serious adverse events during the index procedure. There were no deep venous thromboses reported at any time point, including 10 patients through the 1-year follow-up. In patients with at least one valve formed, site reported duplex ultrasound examination measured the average RT in the popliteal vein below valve formations, was 3.0 ± 1.0 seconds at baseline, 3.9 ± 3.1 seconds at 30 days, and 3.6 ± 2.1 seconds at 360 days. The revised Venous Clinical Severity Scale improved in all 13 successfully treated patients, decreasing from 15.0 ± 6.0 at baseline to 11.6 ± 5.5 at 30 days, 10.7 ± 5.3 at 210 days, and 9.4 ± 5.0 at 360 days (P = .0002; baseline to 360 days). Among the five patients with an ulcer who reached the 360-day follow-up visit, all (100%) healed at least one ulcer. Two patients (40%) healed all ulcers and three patients (60%) had a decrease in ulcers number but remained at C6 at 360 days. The five patients with a total of nine active ulcers at baseline had four active ulcers at 360 days.

CONCLUSIONS

The BlueLeaf System holds promise as a minimally invasive means to safely form fully autogenous deep venous valves. Reconstructed deep veins remained patent, without deep venous thrombosis and symptomatic improvement was consistently observed; however, a decrease in the RT was not. Incremental device design improvements have been undertaken to improve valve function. The results of these iterations await further clinical evaluation.

Advances in Engineering Venous Valves: The Pursuit of a Definite Solution for Chronic Venous Disease

Native venous valves enable proper return of blood to the heart. Under pathological conditions (e.g., chronic venous insufficiency), venous valves malfunction and fail to prevent backward flow. Clinically, this can result in painful swelling, varicose veins, edema, and skin ulcerations leading to a chronic wound situation. Surgical correction of venous valves has proven to drastically reduce these symptoms. However, the absence of intact leaflets in many patients limits the applicability of this strategy. In this context, the development of venous valve replacements represents an appealing approach. Despite acceptable results in animal models, no venous valve has succeeded in clinical trials, and so far no single prosthetic venous valve is commercially available. This calls for advanced materials and fabrication approaches to develop clinically relevant venous valves able to restore natural flow conditions in the venous circulation. In this study, we critically discuss the approaches attempted in the last years, and we highlight the potential of tissue engineering to offer new avenues for valve fabrication. Impact statement Venous valves prosthesis offer the potential to restore normal venous flow, and to improve the prospect of patients that suffer from chronic venous disease. Current venous valve replacements are associated with poor outcomes. A deeper understanding of the approaches attempted so far is essential to establish the next steps toward valve development, and importantly, tissue engineering constitutes a unique toolbox to advance in this quest.

[Reconstructive surgery of deep veins in post-thrombotic disease: possibilities and perspectives]

This article is a review of the literature related to the possibilities and perspectives of reconstructive operations on deep veins for post-thrombotic disease (with the data retrieved from such databases as the PubMed, Scopus, Medline and EMBASE). The most optimal variants of performing reconstructive operations on deep veins are described, accompanied and followed by analysing their outcomes with the discussion of approaches to determining the indications for these interventions. Also considered are the perspectives of bettering the results of reconstructive operations at the expense of modernizing the technologies of diagnosis and surgical treatment.

Performance changes of venous valves following tissue treatment with novel in vitro system

OBJECTIVES

The purpose of this study is to test venous valve performance and identify differences between native tissue and replacement devices developed with traditional tissue treatment methods using a new in vitro model with synchronized hemodynamic parameters and high-speed valve image acquisition.

METHODS

An in vitro model mimicking the venous circulation to test valve performance was developed using hydrostatic pressure driven flow. Fresh and glutaraldehyde-treated vein segments were placed in the setup and opening/closing of the valves was captured by a high-speed camera. Hemodynamic data were obtained using synchronized hardware and virtual instrumentation.

RESULTS

Geometric orifice area and opening/closing time of the valves was evaluated at the same hemodynamic conditions. A reduction in geometric orifice area of 27.2  ± 14.8% (p < 0.05) was observed following glutaraldehyde fixation. No significant difference in opening/closing time following chemical fixation was observed.

CONCLUSIONS

The developed in vitro model was shown to be an effective method for measuring the performance of venous valves. The observed decrease in geometric orifice area following glutaraldehyde treatment indicates a decrease in flow through the valve, demonstrating the consequences of traditional tissue treatment methods.

Search for an Optimal Design of a Bioprosthetic Venous Valve: In silico and in vitro Studies

OBJECTIVE/BACKGROUND

Valve incompetence is a progressive disease of the venous system that may eventually lead to venous hypertension, pain, and ulcers. There is a need for a venous valve prosthesis to replace incompetent valves. Computational and experimental investigations on venous valve design and associated haemodynamics will undoubtedly advance prosthesis design and treatments. Here, the objective is to investigate the effect of venous valve on the fluid and solid mechanics. The hypothesis is that there exists a valve geometry that maximises leaflet shear stress (LSS) but minimises leaflet intramural stress (LIS; i.e., minimise stress ratio = LIS/LSS).

METHODS

To address the hypothesis, fully dynamic fluid-structure interaction (FSI) models were developed. The entire cycle of valve opening and closure was simulated. The flow validation experiments were conducted using a stented venous valve prosthesis and a pulse duplicator flow loop.

RESULTS

Agreement between the output of FSI simulations and output of pulse duplicator was confirmed. The maximum flow rates were within 6% difference, and the total flow during the cycle was within 10% difference. The simulated high stress ratio region at the leaflet base (five times the leaflet average) predicted the disease location of the vast majority of explanted venous valves reported in clinical literature. The study found that the reduced valve height and leaflet dome shape resulted in optimal performance to provide the lowest stress ratio.

CONCLUSION

This study proposes an effective design of venous prostheses and elaborates on the correlations of venous valve with clinical observations.

Human Femoral Vein Diameter and Topography of Valves and Tributaries: A Post Mortem Analysis

The femoral vein (FV) is a clinically important vessel. Failure of its valves can lead to chronic venous insufficiency (CVI) with severe manifestations such as painful ulcers. Although they are crucial for identifying suitable implant sites for therapeutic valves, studies on the topography of FV tributaries and valves are rare. Moreover, the femoral vein diameter (FVD) must be known to assess the morphometric requirements for valve implants. To reassess the anatomical requirements for valve implants, 155 FVs from 82 human corpses were examined. FVDs and tributary and valve topographies were assessed using a laboratory straightedge. The FVD increased from 6 mm in the distal femoropopliteal vein to 11 mm in the iliofemoral vein proximal to the saphenofemoral junction (SFJ). Diameters were significantly bigger in males than females. Height correlated positively with FVD. Distal to the SFJ, within a distance of 38 cm, one to eight valves were present. Up to two valves were present within 10 cm proximal to the SFJ. Individual tributary and valve topography must be considered to ensure appropriate design and successful implantation of a venous valve for CVI therapy in the FV. A suitable implant site would be proximal to the SFJ via an infrainguinal transfemoral access. Clin. Anat. 31:1065-1076, 2018. © 2018 Wiley Periodicals, Inc.

Tissue Engineering of Vein Valves Based on Decellularized Natural Matrices

Valvular repair or transplantation, designed to restore the venous valve function of the legs, has been proposed as treatment in chronic venous insufficiency. Available grafts or surgeries have provided limited durability so far. Generating venous valve substitutes by means of tissue engineering could be a solution. We generated decellularized jugular ovine vein conduits containing valves (oVVC) after reseeding with ovine endothelial cells differentiated from peripheral blood-derived endothelial cells (oPBEC), cultivated in vitro corresponding to the circulatory situation in the lower leg at rest and under exertion. oVVC were decellularized by detergent treatment. GFP-labeled oPBEC were seeded onto the luminal side of the decellularized oVVC and cultivated under static-rotational conditions for 6 h (group I) and 12 h (group II), respectively. Reseeded matrices of group I were exposed to continuous low flow conditions (“leg at rest”). The tissues of group II were exposed to a gradually increasing flow (“leg under effort”). After 5 days, the grafts of group I revealed a uniform luminal endothelial cell coverage of the examined areas of the venous walls and adjacent venous valve leaflets. In group II, the cell coverage on luminal areas of the venous wall parts was found to be nearly complete. The endothelial cell coverage of adjacent venous valve leaflets was revealed to be less dense and confluent. Endothelial cells cultured on acellular vein tissues of both groups were distinctly orientated uniformly in the flow direction, clearly creating a stable and flow-orientated layer. Thus, an endothelium could successfully be reestablished on the luminal surface of a decellularized venous valve by seeding peripheral blood endothelial cells and culturing under different conditions.

Proof-of-Concept Evaluation of the SailValve Self-Expanding Deep Venous Valve System in a Porcine Model

Purpose: To evaluate the SailValve, a new self-expanding deep venous valve concept based on a single polytetrafluoroethylene cusp floating up and down in the bloodstream like a sail, acting as a flow regulator and allowing minimal reflux to reduce thrombogenicity. Methods: Both iliac veins of 5 pigs were implanted with SailValve devices; the first animal was an acute pilot experiment to show the feasibility of accurately positioning the SailValve via a femoral access. The other 4 animals were followed for 2 weeks (n=2) or 4 weeks (n=2) under a chronic implantation protocol. Patency and valve function were evaluated directly in all animals using ascending and descending phlebography after device placement and at termination in the chronic implant animals. For reasons of clinical relevance, a regimen of clopidogrel and calcium carbasalate was administered. Histological analysis was performed according to a predefined protocol by an independent pathologist. Results: Deployment was technically feasible in all 10 iliac veins, and all were patent directly after placement. No perioperative or postoperative complications occurred. Ascending phlebograms in the follow-up animals confirmed the patency of all valves after 2 or 4 weeks. Descending phlebograms showed full function in 5 of 8 valves. Limited reflux was seen in 1 valve (4-week group), and the function in the remaining 2 valves (2-week group) was insufficient because of malpositioning. No macroscopic thrombosis was noted on histology. Histology in the follow-up groups revealed a progressive inflammatory reaction to the valves. Conclusion: This animal study shows the potential of the SailValve concept with sufficient valve function after adequate positioning and no (thrombogenic) occlusions after short-term follow-up. Future research is essential to optimize valve material and long-term patency.

Bioactive Anti-Thrombotic Modification of Decellularized Matrix for Vascular Applications

The decellularized matrix derived from porcine small intestinal submucosa (SIS) is a widely used biomaterial being investigated for numerous applications. Currently, thrombus deposition and neointimal hyperplasia have limited the use of SIS in some vascular applications. To limit these detrimental processes, this work applies bioactive, endothelial-inspired properties to the material. SIS is modified with the endothelial cell membrane protein thrombomodulin and the glycosaminoglycan heparin to facilitate protein C activation and anticoagulant activity, respectively. Modifying SIS with thrombomodulin alone enables robust activated protein C (APC) generation, and thrombomodulin activity is maintained after prolonged exposure to fluid shear and blood plasma. Heparin-modified SIS has a potent anticoagulant activity. When both modifications are applied sequentially, SIS modified first with thrombomodulin then with heparin retains the full activity of each individual modification. Tubular SIS devices are connected to a baboon arteriovenous shunt to quantify thrombus deposition on these materials. After being exposed to flowing whole blood for 60 min, SIS devices modified first with thrombomodulin then with heparin have significantly less platelet accumulation compared to unmodified SIS devices. These studies demonstrate that modifying SIS with thrombomodulin and heparin confers APC generation and anticoagulant activity that results in reduced thrombogenesis.

Valve reconstructions

The history of venous valve reconstruction extends back to 1968 when Robert L Kistner performed the first internal valve plasty to treat deep venous axial reflux. Throughout the past 50 years other techniques of reconstructive deep venous surgery (RDVS) were developed, not only to repair but also to replace venous valves. And the fact that several surgeons and centers have undertaken RDVS in the treatment of chronic venous insufficiency (CVI) reporting outcomes, has added knowledge to define more clearly the role of this kind of specialized surgery. Patients who may benefit from RDVS are among those where conventional treatment with compression stockings combined with superficial surgery has failed. Ulcer-healing rates of up to 70% have been reported after RDVS and ulcer-free periods of up to 36 months have been generated. But during five-year follow-up, freedom from ulceration period and clinical improvement rates were reduced significantly. This raises then the issue and challenge of durability of RDVS since the average age of patients who can benefit from it is about 50 years.

Contemporary management of acute and chronic deep venous thrombosis

INTRODUCTION

This review aims to provide an update on the management of deep vein thrombosis (DVT).

SOURCES OF DATA

A systematic search of PubMed, Google Scholar and Cochrane databases was carried out.

AREAS OF AGREEMENT

Direct oral anticoagulants (DOACs) are as effective and easier to use than vitamin K antagonists for the treatment of DVT. Catheter-directed thrombolysis can reduce post thrombotic syndrome in patients with iliofemoral DVT. Compression bandaging can help heal a venous ulcer.

AREAS OF CONTROVERSY

Compression hosiery to prevent post thrombotic syndrome. Long-term evidence to show clinical benefit of using endovenous therapies to restore deep vein patency.

GROWING POINTS

Developing imaging methods to identify patients who would benefit from venous thrombolysis. The evolution of dedicated venous stents.

AREAS TIMELY FOR DEVELOPING RESEARCH

Understanding the mechanisms that lead to stent occlusion and investigation into the appropriate treatments that could prevent in-stent thrombosis is required.

Open surgical treatment for postthrombotic syndrome

The postthrombotic syndrome counts as a frequent long-term complication after deep vein thrombosis with approximately 20%–50% of affected patients after deep vein thrombosis. The earliest that diagnosis of postthrombotic syndrome can be made is 6 months after deep vein thrombosis. Most patients suffer from swelling and chronic pain. In all, 5%–10% of patients may even develop venous ulcers. The complex etiology consists of limited venous drainage because of chronic occlusions and secondary insufficiencies of venous valves inducing non-physiological venous reflux. Conservative management, first of all compression therapy, is of crucial importance in treatment of postthrombotic syndrome. Endovascular and open surgical techniques can additionally be used in a small subgroup of patients. Although rarely performed, this article illuminates the open surgical techniques in treatment of postthrombotic syndrome such as venous bypass surgery, valve repair and varicose vein surgery.

In vivo assessment of two endothelialization approaches on bioprosthetic valves for the treatment of chronic deep venous insufficiency

Chronic deep venous insufficiency is a debilitating disease with limited therapeutic interventions. A bioprosthetic venous valve could not only replace a diseased valve, but has the potential to fully integrate into the patient with a minimally invasive procedure. Previous work with valves constructed from small intestinal submucosa (SIS) showed improvements in patients' symptoms in clinical studies; however, substantial thickening of the implanted valve leaflets also occurred. As endothelial cells are key regulators of vascular homeostasis, their presence on the SIS valves may reduce the observed thickening. This work tested an off-the-shelf approach to capture circulating endothelial cells in vivo using biotinylated antikinase insert domain receptor antibodies in a suspended leaflet ovine model. The antibodies on SIS were oriented to promote cell capture and showed positive binding to endothelial cells in vitro; however, no differences were observed in leaflet thickness in vivo between antibody-modified and unmodified SIS. In an alternative approach, valves were pre-seeded with autologous endothelial cells and tested in vivo. Nearly all the implanted pre-seeded valves were patent and functioning; however, no statistical difference was observed in valve thickness with cell pre-seeding. Additional cell capture schemes or surface modifications should be examined to find an optimal method for encouraging SIS valve endothelialization to improve long-term valve function in vivo. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1610-1621, 2016.

Successful tissue engineering of competent allogeneic venous valves

OBJECTIVE

The purpose of this study was to evaluate whether tissue-engineered human allogeneic vein valves have a normal closure time (competency) and tolerate reflux pressure in vitro.

METHODS

Fifteen human allogeneic femoral vein segments containing valves were harvested from cadavers. Valve closure time and resistance to reflux pressure (100 mm Hg) were assessed in an in vitro model to verify competency of the vein valves. The segments were tissue engineered using the technology of decellularization (DC) and recellularization (RC). The decellularized and recellularized vein segments were characterized biochemically, immunohistochemically, and biomechanically.

RESULTS

Four of 15 veins with valves were found to be incompetent immediately after harvest. In total, 2 of 4 segments with incompetent valves and 10 of 11 segments with competent valves were further decellularized using detergents and DNAse. DC resulted in significant decrease in host DNA compared with controls. DC scaffolds, however, retained major extracellular matrix proteins and mechanical integrity. RC resulted in successful repopulation of the lumen and valves of the scaffold with endothelial and smooth muscle cells. Valve mechanical parameters were similar to the native tissue even after DC. Eight of 10 veins with competent valves remained competent even after DC and RC, whereas the two incompetent valves remained incompetent even after DC and RC. The valve closure time to reflux pressure of the tissue-engineered veins was <0.5 second.

CONCLUSIONS

Tissue-engineered veins with valves provide a valid template for future preclinical studies and eventual clinical applications. This technique may enable replacement of diseased incompetent or damaged deep veins to treat axial reflux and thus reduce ambulatory venous hypertension.

Crosslinking decreases the hemocompatibility of decellularized, porcine small intestinal submucosa

Decellularized tissues have been widely used as scaffolds for biomedical applications due to their presentation of adhesion peptide sequences and growth factors, which facilitate integration with surrounding tissue. One of the most commonly used decellularized tissues is derived from porcine small intestinal submucosa (SIS). In some applications, SIS is crosslinked to modulate the mechanical properties or degradation rate of the scaffold. Despite the widespread use of SIS, there has been no mechanistic characterization of blood reactions with SIS, or how crosslinking affects these reactions. Therefore, we characterized the effect of SIS and carbodiimide-crosslinked SIS (cSIS) on plasma coagulation, including targeted assessments of the intrinsic and extrinsic coagulation pathways, and thrombus formation using flowing whole blood. SIS inhibited plasma coagulation initiated by recalcification, as well as low concentrations of thrombin or tissue factor. SIS prolonged the activated partial thromboplastin time by 14.3 ± 1.54s, indicating inhibition of the intrinsic coagulation pathway. Carbodiimide crosslinking abrogated all anticoagulant effects of SIS, as did heparinase I and III treatment, suggesting that heparin and heparan sulfate are predominantly responsible for SIS anticoagulant effects. Inhibiting contact activation of the intrinsic pathway prevented cSIS-mediated coagulation. When tubular SIS devices were connected to a nonhuman primate arteriovenous shunt loop, which enables whole blood to flow across devices without the use of anticoagulants, SIS demonstrated remarkably limited platelet accumulation and fibrinogen incorporation, while cSIS initiated significantly higher platelet and fibrinogen accumulation. These results demonstrate that SIS is a thromboresistant material and crosslinking markedly reduces the hemocompatibility of SIS.

Living-engineered valves for transcatheter venous valve repair

BACKGROUND

Chronic venous insufficiency (CVI) represents a major global health problem with increasing prevalence and morbidity. CVI is due to an incompetence of the venous valves, which causes venous reflux and distal venous hypertension. Several studies have focused on the replacement of diseased venous valves using xeno- and allogenic transplants, so far with moderate success due to immunologic and thromboembolic complications. Autologous cell-derived tissue-engineered venous valves (TEVVs) based on fully biodegradable scaffolds could overcome these limitations by providing non-immunogenic, non-thrombogenic constructs with remodeling and growth potential.

METHODS

Tri- and bicuspid venous valves (n=27) based on polyglycolic acid-poly-4-hydroxybutyrate composite scaffolds, integrated into self-expandable nitinol stents, were engineered from autologous ovine bone-marrow-derived mesenchymal stem cells (BM-MSCs) and endothelialized. After in vitro conditioning in a (flow) pulse duplicator system, the TEVVs were crimped (n=18) and experimentally delivered (n=7). The effects of crimping on the tissue-engineered constructs were investigated using histology, immunohistochemistry, scanning electron microscopy, grating interferometry (GI), and planar fluorescence reflectance imaging.

RESULTS

The generated TEVVs showed layered tissue formation with increasing collagen and glycosaminoglycan levels dependent on the duration of in vitro conditioning. After crimping no effects were found on the MSC level in scanning electron microscopy analysis, GI, histology, and extracellular matrix analysis. However, substantial endothelial cell loss was detected after the crimping procedure, which could be reduced by increasing the static conditioning phase.

CONCLUSIONS

Autologous living small-diameter TEVVs can be successfully fabricated from ovine BM-MSCs using a (flow) pulse duplicator conditioning approach. These constructs hold the potential to overcome the limitations of currently used non-autologous replacement materials and may open new therapeutic concepts for the treatment of CVI in the future.

Reconstructive surgery for deep vein reflux

DVR is defined as a reflux affecting the deep venous system. DVR essentially arises from two etiologies, primary deep valve incompetence (PDVI) and posthrombotic syndrome (PTS), knowing that axial reflux is correlated with severe chronic venous insufficiency. DVR correction aims at reducing the increased ambulatory venous pressure, which results from reflux in deep veins in orthodynamic conditions.

The results of DVR surgery are not easy to assess, as it is mostly combined with surgery for superficial venous system and/or perforators insufficiency.

In cases of primary insufficiency, valvuloplasty, the operation of choice, is credited at 5 years follow-up with a 70 % success rate in terms of clinical outcome and improved hemodynamic performance. In PTS, a meta-analysis of transpositions and transplants at more than 5 years estimates successful clinical outcome and improved hemodynamic performance at approximately 50 %. The Maleti neovalve construction technique has achieved by far better results.

Indications for DVR surgery are based on clinical, hemodynamic and imaging data. Etiology is a decisive factor in the choice of the technique.

Endovenous valve transfer for chronic deep venous insufficiency

OBJECTIVES

The aims of the study were to test the safety and efficacy of a custom-made endovenous valve transfer stent, and delivery system in animals and humans.

METHODS

The internal jugular veins of 16 sheep, weighing 45-55 kg, were used. A segment of vein with venous valve was enclosed circumferentially with a barbed stent. This segment from the internal jugular vein was introduced and deployed remotely into the contralateral internal jugular vein. Harvesting occurred acutely (one sheep) and at 1, 3, and 6 months postoperatively (five sheep per group). Operative competence testing, histological and scanning electron microscopic (SEM) examinations were performed. Four males with recalcitrant ulcers (mean age of 22 years) had axillary veins transferred from the popliteal vein and were followed for a mean of 3.8 years.

RESULTS

At harvest, all the transferred valves were competent, with no evidence of thrombosis, tilting, endoleak, or migration with normal macroscopic and SEM findings. Although only 50% of the ulcers completely healed in humans, the remainder were improved, with all valves being competent and patent.

CONCLUSIONS

Endovenous valve transfer with a custom-made circumferential stent produces near perfect results in sheep and encouraging results in a small pilot study.

Percutaneous venous valve designs for treatment of deep venous insufficiency

At present, no widely accepted surgical options exist for treating chronic deep venous insufficiency (CDVI). Experimental efforts to improve catheter-based management for CDVI have shown disappointing results, hindering application of these techniques in the clinical arena. A review of the literature focusing on technical aspects of valve stent design was conducted. Eight experimental studies were scrutinized to derive data on (1) stent design and configuration; (2) valve design, composition, and configuration; (3) delivery system; (4) functional outcome; and (5) histology to provide a basis for the design of a new prosthetic venous valve. The analysis of available experimental data found that all prosthetic valve designs currently under development/testing rely on some type of a stent to act as a carrier or frame for valve attachment. Most valve models reviewed were for the most part implanted safely and accurately, with good short-term patency and competency. The most commonly reported adverse event was thrombosis, which limited durability. It is assumed that valve configuration determines long-term results after repair. Hence, the newly proposed valve design consisted of 2 stent rings without barbs to fix the valve in the host vein. Because a little reflux might actually benefit the patency of the valve, the valve cusp in the new design forms a billowing "sail" that does not completely open or close, which also prevents the valve cusp from sticking to the wall. This technology remains of great interest to the interventionist and all physicians who are involved in the care for patients with advanced chronic venous disease. Valve design remains a challenge, but promising new valve substitutes such as the one outlined here are under evaluation.

Retention of an autologous endothelial layer on a bioprosthetic valve for the treatment of chronic deep venous insufficiency

PURPOSE

Percutaneous transcatheter implantation of porcine small intestinal submucosa (SIS) bioprosthetic valves has been reported as a treatment for chronic deep venous insufficiency (CDVI). Endothelial progenitor outgrowth cells (EOCs), isolated from whole ovine blood, were evaluated as a source of in vitro autologous seeding for SIS endothelialization. Retention of the EOC monolayer was evaluated to test the feasibility of delivering an endothelialized SIS valve.

MATERIALS AND METHODS

Twenty bioprosthetic venous valves were constructed from SIS sutured onto collapsible square stent frames and were seeded with ovine EOCs in vitro. Retention of the endothelial monolayer through valve loading and delivery (three valves), in vitro flow (three valves), and ex vivo flow (four valves) was evaluated with immunofluorescent staining and histologic analysis compared with paired unmanipulated control valves. In the ex vivo shunt loop, venous blood was pulled from an implanted dialysis catheter, through the valve, and returned to the sheep.

RESULTS

Immunofluorescent staining of EOCs on the valves after in vitro seeding revealed a confluent monolayer (95.6% ± 2.3% confluent) on each side of the valve. When examined by immunofluorescent staining, the endothelial monolayer remained intact after loading and delivery (97.1% ± 1.7%) and when subjected to flow in the in vitro loop (96.0% ± 3.0%). Histologic analysis of the valves subjected to the ex vivo shunt loop revealed retention of the endothelial monolayer.

CONCLUSIONS

Endothelial monolayers seeded on SIS were retained under loading and delivery, in vitro flow, and ex vivo flow. EOCs are a promising cell source for autologous endothelialization of bioprosthetic valves for the treatment of CDVI.

Venous leg ulcerations: a treatment update

OPINION STATEMENT

Selecting the appropriate treatment for venous leg ulcerations is essential for optimal wound healing and patient quality of life. Compression therapy remains the mainstay of treatment for these wounds. Compression methods should be carefully selected and tailored for compatibility with patients' daily life. Pain management should not be neglected. When response to compression therapy is limited, adjuvant therapy such as medication, débridement, or surgical procedures should be considered on an individual basis.