Venous valvular insufficiency: Influence of a single venous valve (native and experimental)

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.

Tissue engineered bovine saphenous vein extracellular matrix scaffolds produced via antigen removal achieve high in vivo patency rates

Diseases of small diameter blood vessels encompass the largest portion of cardiovascular diseases, with over 4.2 million people undergoing autologous vascular grafting every year. However, approximately one third of patients are ineligible for autologous vascular grafting due to lack of suitable donor vasculature. Acellular extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissue have potential to serve as ideal biomaterials for production of off-the-shelf vascular grafts capable of eliminating the need for autologous vessel harvest. A modified antigen removal (AR) tissue process, employing aminosulfabetaine-16 (ASB-16) was used to create off-the-shelf small diameter (< 3 mm) vascular graft from bovine saphenous vein ECM scaffolds with significantly reduced antigenic content, while retaining native vascular ECM protein structure and function. Elimination of native tissue antigen content conferred graft-specific adaptive immune avoidance, while retention of native ECM protein macromolecular structure resulted in pro-regenerative cellular infiltration, ECM turnover and innate immune self-recognition in a rabbit subpannicular model. Finally, retention of the delicate vascular basement membrane protein integrity conferred endothelial cell repopulation and 100% patency rate in a rabbit jugular interposition model, comparable only to Autograft implants. Alternatively, the lack of these important basement membrane proteins in otherwise identical scaffolds yielded a patency rate of only 20%. We conclude that acellular antigen removed bovine saphenous vein ECM scaffolds have potential to serve as ideal off-the-shelf small diameter vascular scaffolds with high in vivo patency rates due to their low antigen content, retained native tissue basement membrane integrity and preserved native ECM structure, composition and functional properties. STATEMENT OF SIGNIFICANCE: The use of autologous vessels for the treatment of small diameter vascular diseases is common practice. However, the use of autologous tissue poses significant complications due to tissue harvest and limited availability. Developing an alternative vessel for use for the treatment of small diameter vessel diseases can potentially increase the success rate of autologous vascular grafting by eliminating complications related to the use of autologous vessel and increased availability. This manuscript demonstrates the potential of non-antigenic extracellular matrix (ECM) scaffolds derived from xenogeneic vascular tissue as off-the-shelf vascular grafts for the treatment of small diameter vascular diseases.

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.

Antigen removal process preserves function of small diameter venous valved conduits, whereas SDS-decellularization results in significant valvular insufficiency

Chronic venous disease (CVD) is the most common reported chronic condition in the United States, affecting more than 25 million Americans. Regardless of its high occurrence, current therapeutic options are far from ideal due to their palliative nature. For best treatment outcomes, challenging cases of chronic venous insufficiency (CVI) are treated by repair or replacement of venous valves. Regrettably, the success of venous valve transplant is dependent on the availability of autologous venous valves and hindered by the possibility of donor site complications and increased patient morbidity. Therefore, the use of alternative tissue sources to provide off-the-shelf venous valve replacements has potential to be extremely beneficial to the field of CVI. This manuscript demonstrates the capability of producing off-the-shelf fully functional venous valved extracellular matrix (ECM) scaffold conduits from bovine saphenous vein (SV), using an antigen removal (AR) method. AR ECM scaffolds maintained native SV structure-function relationships and associated venous valves function. Conversely, SDS decellularization caused significant changes to the collagen and elastin macromolecular structures, resulting in collagen fibril merging, elimination of fibril crimp, amalgaming collagen fibers and fragmentation of the inner elastic lamina. ECM changes induced by SDS decellularization resulted in significant venous valve dysfunction. Venous valved conduits generated using the AR approach have potential to serve as off-the-shelf venous valve replacements for CVI. STATEMENT OF SIGNIFICANCE: Retention of the structure and composition of extracellular matrix (ECM) proteins within xenogeneic scaffolds for tissue engineering is of crucial importance, due to the undeniable effect ECM proteins can impose on repopulating cells and function of the resultant biomaterial. This manuscript demonstrates that alteration or elimination of ECM proteins via commonly utilized decellularization approach results in complete disruption of venous valve function. Conversely, retention of the delicate ECM structure and composition of native venous tissue, using an antigen removal tissue processing method, results in preservation of native venous valve function.

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.

A percutaneous approach to deep venous valve insufficiency with a new self-expanding venous frame valve

PURPOSE

To ascertain if a percutaneously delivered venous valve bioprosthesis (PVVB) can be implanted in the porcine venous system and function without complications.

METHODS

The PVVB is a glutaraldehyde-preserved, valve-bearing venous xenograft sutured inside a memory-coded nitinol frame (diameter 10, 12, or 14 mm). In 10 50-kg pigs, the external jugular vein was exposed, and a 16-F introducer sheath was positioned in the common iliac vein. One PVVB was inserted and deployed in each iliac vein under fluoroscopic control. After PVVB implantation, all animals were randomly given either vitamin K antagonists (1-2 mg/d) (group I) or a combination of aspirin (150 mg/d) and clopidogrel (75 mg/d) (group II), which were shown in a preliminary pilot study to be the most effective anticoagulation regimens in the pig model. Ascending and descending completion phlebograms were performed. PVVBs were evaluated with phlebography at 4 weeks to assess patency and competence; all PVVBs were explanted and processed for histological analysis.

RESULTS

In 8 animals, the PVVB was successfully deployed in both the left and right iliac veins. In 2 pigs, only 1 PVVB was inserted due to vascular anomalies. Completion phlebography demonstrated 18 patent and competent valves. At 2 weeks, bleeding complications occurred in 3 group I pigs; all 5 animals were terminated to prevent further complications. Of the 8 valves in this group, 7 were patent (3 competent) by phlebography; 1 PVVB had migrated due to known undersizing of the stent frame. At 4 weeks, group II (5 pigs, 10 valves) analysis revealed 5 patent (3 competent) valves; no bleeding complications occurred in this group. Histology showed thrombosis as the cause of occlusion in all 5 non-patent valves from group II.

CONCLUSIONS

Deployment of a glutaraldehyde-fixed bovine vein sutured to a self-expanding nitinol stent in the porcine iliac vein is technically feasible. Development of a venous bioprosthesis that can be placed percutaneously may have important clinical applications as an endovascular treatment for chronic venous insufficiency when it is due to valvular incompetence.

Tissue-engineered bioprosthetic venous valve: a long-term study in sheep

OBJECTIVE

to develop a graft bearing an immunologically tolerated tissue-engineered venous valve (TE graft) that will be incorporated into a native vessel, and restore normal valve function for the treatment of chronic venous insufficiency.

METHODS

twenty-four TE grafts were grown using decellularised allogeneic ovine veins as donor matrix, which was subsequently repopulated with the future recipient's myofibroblasts (MFB) and endothelial cells (EC). TE grafts were implanted into the external jugular vein. Animals were sacrificed at 1, 6, and 12 weeks (n=4, each). Autografts served as controls (1 week, n=4; 6 weeks, n=4). Specimen for histology and immunohistochemistry were taken.

RESULTS

the matrix was successfully repopulated with MFB and EC (n=8). Patency on venography in the TE graft-group was44,44, and 34 at 1, 6, and 12 weeks, and44 (44) in autografts at 1 (6) weeks, respectively. Except for 2 TE grafts after 12 weeks, valves were competent (duplex ultrasound). Patent TE grafts were merely distinguishable from autografts with minor inflammatory reactions. Reflux was caused by neo-intima formation related to the basis of the TE graft.

CONCLUSION

acellularisation and consecutive in vitro autogeneic re-seeding of valved venous conduits can lead to immunologically acceptable, patent, and competent implants in sheep.

Animal models for the study of lower extremity chronic venous disease: lessons learned and future needs

The purpose of this review is to define animal models of chronic venous disease and to demonstrate how animal studies can impact our understanding and treatment of this disorder. To this end an extensive literature search was conducted highlighting potential animal models of chronic lower extremity venous disease. Scientific investigations using animals to study particular aspects of this disease are also reviewed. This review was conducted by members of the Committee on Research of the American Venous Forum to help provide direction for future venous research endeavors. Useful models of chronic venous occlusive disease involve controlled ligation of a major lower limb vein and multiple tributaries. Such a model can provide sustained venous hypertension and studies using this model have confirmed that an isodiametric graft can provide early hemodynamic relief. Models of primary, postphlebitic, and isolated chronic deep venous insufficiency are available for study. Valve repair or transplantation can positively impact the insufficiency observed in these models. Investigations into valve substitutes have generally been disappointing or are undergoing early evaluation. In conclusion, animal models for the study of some aspects of chronic venous disease do exist and have already affected our clinical approach to patients. The scientific study of basic pathophysiology, diagnostics, end-organ response, and long-term surgical treatments of this disorder in well-controlled animal experiments have not been conducted.

Experimental repair of venous valvular insufficiency using a cryopreserved venous valve allograft aided by a distal arteriovenous fistula

PURPOSE

To evaluate the patency and hemodynamic impact of a cryopreserved allograft venous valve transplanted to the superficial femoral vein (SFV) of a canine insufficiency model aided by a distal arteriovenous fistula (dAVF).

METHODS

Eight greyhounds had intravenous hemodynamic parameters measured (venous filling time [VFT], 90% of venous refilling time [VRT90], and simulated ambulatory venous pressure [AVP]) before (T0) and after complete hindlimb venous valvulotomy (T1) to produce venous insufficiency. Simultaneously, a valve-containing vein segment was harvested from the opposite SFV or external jugular vein (n = 1) and cryopreserved. Three weeks later a blood type-matched cryopreserved valve was transplanted to the insufficient SFV aided by a low-flow (n = 4) or high-flow (n = 4) dAVF. The fistula was ligated in 3 to 6 weeks, and venous indexes (T2) were obtained 3 weeks later. Analysis of variances compared the venous indexes at T0, T1, and T2 for statistical significance. Gross and histologic inspection assessed valve integrity.

RESULTS

Two valves aided by a low-flow dAVF exhibited thrombosis and scarring. The hemodynamics of the six remaining valves demonstrated normalization of the VRT90, an AVP consistent with insufficiency, and a VFT between normal and total venous insufficiency. The patent valves were normal on gross examination and by histologic examination with signs of normal external healing.

CONCLUSIONS

A cryopreserved venous valve allograft transplanted to the SFV of an incompetent hindlimb partially corrects venous hemodynamics. A high-flow arteriovenous fistula most consistently preserves transplant patency.

Valve transplantation to the canine popliteal vein: the utility of a distal arteriovenous fistula and the hemodynamic result of a single functional valve

PURPOSE

The objectives were to transplant a venous valve into the popliteal vein of a canine insufficiency model that would maintain long-term function and then to measure the hemodynamic benefit of such a valve.

METHODS

Indexes of venous valvular function, including venous filling time, 90% of venous refilling time, and simulated ambulatory venous pressure, were measured in 11 greyhounds before intervention (Control) and after hind limb venous valvulotomy, which produces chronic venous insufficiency. Three weeks later a valve-containing segment of external jugular vein was transplanted to the popliteal vein with (n = 6) or without (n = 5) a distal arteriovenous fistula. The fistula was ligated in 4 to 6 weeks. Repeat venous indexes were obtained an average of 2 weeks after the last operative intervention. Gross anatomic inspection +/- duplex scanning performed before the animals were killed were used to distinguished normal from damaged valves.

RESULTS

Four of five simple valve transplants demonstrated scarring and/or thrombosis and the average venous filling time, ambulatory venous pressure, and 90% of venous refilling time were consistent with chronic venous insufficiency and/or obstruction. One fistula failed in the six valve distal arteriovenous fistula transplants, and that valve was incompetent. Analysis of the remaining five functional valves demonstrated venous filling time consistent with chronic venous insufficiency, normalization of ambulatory venous pressure, and 90% of venous refilling time between normal, and chronic venous insufficiency. These valves appeared normal.

CONCLUSIONS

Popliteal vein valve transplant anatomy is preserved by an adjunctive distal arteriovenous fistula, and a competent valve transplant improves postexercise venous hemodynamics to approach those of a normal limb.

Details of a canine venous insufficiency model

Continued study of a chronic deep venous insufficiency (CDVI) model allows optimal comparison with the human condition. This study evaluates the model's long-term stability, its lack of observed clinical effect, and a simulated exercise study as a physiologic estimate of normal hindlimb walking. The time to maximal ankle venous pressure after standing (VFT), and to 90% of the venous refilling time after electrical stimulation, quadripedal, or hindlimb walking (VRT90), and the minimal pressure after exercise (AVP) were measured up to 10 months after CDVI model creation. The animals' intravenous resting pressure was obtained after standing stationary on all four limbs. Analysis of variance was used to determine statistical significance where indicated. VFT, AVP, and VRT90 measurements demonstrated values consistent with CDVI in animals studied up to 10 months after model creation and were statistically different from control limb values (p < or = .002, n = 8). Animals studied during quadripedal walking showed no difference in resting pressure, AVP, and VRT90 between model and control limbs (n = 5). There was no statistical difference in AVP or VRT90 measured under conditions of stimulated exercise or bipedal walking; and both conditions produced hemodynamic changes consistent with CDVI (n = 5). This animal model is a reliable long-term CDVI hemodynamic model. The normal venous hemodynamics recorded during quadripedic walking may explain the lack of clinical sequelae observed in this model. Lastly, the method of simulated exercise used in this study is a reliable test that reflects physiologic measurements obtained during bipedal walking.

Venous valve repair: early results in fifty-two cases

PURPOSE

Chronic deep venous insufficiency, usually secondary to the postthrombotic syndrome, is due to primary valve failure in approximately 15% of cases. In these cases surgical repair of the valvular mechanism may be indicated.

METHODS

Fifty-two limbs in 42 patients were treated with superficial femoral vein valvuloplasty after appropriate investigation. Adjunctive operations on the superficial or perforating veins were performed on 49 limbs during the same hospital admission.

RESULTS

Of the 27 patients who have completed one year of follow-up, 85% are free of reflux on duplex scanning and 68% have had normalization of venous refilling times. Of 11 limbs with venous ulceration followed up for more than 1 year, only one has had a recurrent ulcer (9%). In patients without ulceration the procedure has been successful in alleviating symptoms of venous insufficiency.

CONCLUSIONS

We conclude that the procedure, in conjunction with appropriate superficial venous operation, is effective in selected patients with deep vein reflux whose conditions remain uncontrolled by conservative measures. At 1 year, 85% of valvuloplasties in this series remained competent.