Endoscopic venous valve transplantation with a valve-stent device

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.

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.

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

Lower extremity chronic deep venous insufficiency (CDVI) is common and remains a major health problem worldwide. Selected patients benefited from direct deep vein valve surgical repair or valve transplantation. A major limitation of this approach is that most of the patients are not candidates for these procedures due to obstructions or residual thrombus throughout the vein. The past 15 years have witnessed experimental efforts at catheter-based management of CDVI. This review describes the initial designs and experimental evolution of a mechanical and bioprosthetic venous valve that can be implanted by using a transcatheter technique. These valves consisted of single, double, or triple cusp leaflets made of synthetic or biological materials attached to a carrier or frame. All described devices for percutaneous transcatheter valve placement rely on some form of a vascular stent for valve attachment.

Percutaneous autologous venous valve transplantation: Short-term feasibility study in an ovine model

BACKGROUND

Limited experience with bioprosthetic venous valve percutaneously inserted into femoral veins in 15 patients has been promising in short-term results only to show disappointing long-term results. Percutaneous autogenous venous valve (PAVV) transplantation was explored in an ovine model as a possible alternative treatment.

METHODS

PAVV consisted of a vein segment containing a valve that was attached to a stent template. The stent templates (n = 9) were designed and hand made in our research laboratory. They consist of two stainless steel square stents 13 or 15 mm in diameter to fit the ovine jugular veins (JV), which ranges from 10 to 15 mm in diameter. A valve-containing segment of JV was harvested and attached with sutures and barbs inside the stent template (n = 9). The valve devices were then manually folded and front loaded inside the 4 cm chamber of the 13F delivery sheath and delivered into the contralateral JV by femoral vein approach. Transplanted PAVVs were studied by immediate and 3 months venograms. Animals were euthanized at 3 months, and jugular veins harvested to perform angioscopic evaluations in vitro.

RESULTS

PAVV transplantation was successful in all nine animals. Good valve function with no reflux was observed on immediate and 3 months venograms in eight valves. The transplanted maximal JV diameter ranged from 10.2 mm to 15.4 mm (mean 13.1 +/- 1.5 mm). Venoscopic examination revealed intact, flexible, nonthickened valve leaflets in eight specimens. One PAVV exhibited normal function of one leaflet only; the other cusp was accidentally cut during the transplantation procedure. All transplanted autologous valves were free of thrombus and incorporated into the vein wall of the host vessel.

CONCLUSION

This study demonstrated that autogenous valve transplants remained patent and competent without long-term anticoagulation for up to 3 months. The percutaneous autogenous venous valve may provide in future minimally invasive treatment for patients with chronic deep venous insufficiency, but long-term studies need to be done to document its continued patency and function.

Percutaneous stent-mounted valve for treatment of aortic or pulmonary valve disease

The objective of this study was to develop a prosthetic cardiac valve designed for percutaneous transcatheter implantation. Percutaneous catheter-based therapies play a limited role in the management of cardiac valve disease. Surgical implantation of prosthetic valves usually requires thoracotomy and cardiopulmonary bypass. The stent-valve is constructed of a rolled sheet of heat-treated nitinol. Although malleable when cooled, once released from a restraining sheath at body temperature the stent unrolls, becomes rigid, and assumes its predetermined cylindrical conformation. A ratcheting lock-out mechanism prevents recoil and external protrusions facilitate anchoring. Valve leaflets are constructed of bovine pericardium. The feasibility of catheter implantation, prosthetic valve function, and survival were investigated in an animal model. In vitro and pulse duplicator testing documented valve durability. Endovascular delivery of the prototype stent-valve to the aortic or pulmonary position was feasible. Accurate positioning was required to ensure exclusion of the native valve leaflets and, in the case of the aortic valve, to avoid compromise of the coronary ostia or mitral apparatus. Oversizing of the stent in relation to the valve annulus was desirable to facilitate anchoring and prevent paravalvular insufficiency. Stent-valve implantation proved feasible and compatible with survival in an animal model. Transcatheter implantation of prosthetic valves is possible. Further evolution of this technology will involve lower-profile devices with design features that facilitate vascular delivery, visualization, positioning, deployment, and valvular function.

Planning endovascular vein valve implantation: significance of vein size variability

OBJECTIVE

Endovascular placement of prosthetic valves is currently in clinical trials as treatment for lower extremity venous hypertension caused by valvular insufficiency. Femoropopliteal vein sizing is a critical factor in treatment planning. A wide diameter range could influence selection of an endoprosthesis. Quantitative data describing intrasubject vein diameter variation are scant. We measured vein diameters with ultrasound imaging to assess minimum-maximum diameter range under forced conditions of venoconstriction and venodilatation.

METHODS

Diameter of the common femoral vein (CFV), proximal femoral vein (PFV), mid-femoral vein (MFV), and distal femoral vein (DFV) in the thigh and the popliteal vein (PV) was measured in the morning under conditions of minimal venodilation and in the afternoon under conditions of stressed venodilatation that included activities of daily living and a 5-minute treadmill walk. Measurements were obtained twice on two different days in both extremities in 20 subjects with CEAP clinical classification C(0) (n = 10), C(3) (n = 7), C(4) (n = 1), or C(5) (n = 2).

RESULTS

Average vein diameter increased, from 11.2 +/- 2.5 (SD) mm to 14.5 +/- 2.3 mm at the CFV, from 6.9 +/- 1.8 mm to 9.4 +/- 1.9 mm at the PFV, from 6.9 +/- 1.6 mm to 9.0 +/- 1.8 mm at the MFV, from 7.3 +/- 1.7 mm to 9.1 +/- 1.5 mm at the DFV, and from 8.4 +/- 1.4 mm to 9.7 +/- 1.8 mm at the PV (P <.001 for all differences). Maximum diameter change was 8.2 mm at the CFV, 7.0 mm at the PFV, 6.6 mm at the MFV, 6.0 mm at the DFV, and 5.1 mm at the PV. Dilatation of 4 mm or greater occurred in 43% of CFV, 15% of PFV, 11% of MFV, 3% of DFV, and 1% of PV. Minimum vein diameter was found at PFV in 41%, MFV in 34%, and DFV in 23% of morning measurements and at PFV in 21%, MFV in 38%, DFV in 28%, and PV in 16% of afternoon measurements.

CONCLUSIONS

Femoropopliteal veins demonstrated a wide range of diameters, and significant diameter changes were detected in all vein segments. Variations in vein diameter must be evaluated in candidates for endovascular venous valve prostheses. Such devices must adapt to a wide range in vein diameter.

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.

Percutaneous deployment of a valved bovine jugular vein in the swine venous system: a potential treatment for venous insufficiency

PURPOSE

To develop a system for potential use in the treatment of chronic venous insufficiency by using percutaneous techniques.

MATERIALS AND METHODS

A segment of a glutaraldehyde-fixed bovine external jugular vein with valves was trimmed and sutured to a nitinol stent. Animals were premedicated and anesthetized (n = 11). Venography of the right external jugular vein, inferior vena cava (IVC), and common iliac vein was performed. Deployment was accomplished via a sheath (12-24 F) with use of fluoroscopic guidance. Eleven bioprostheses were deployed in 11 animals. Bioprostheses were deployed in the IVC (n = 3) or right external iliac vein (n = 6). Animals were killed immediately after deployment (n = 7) at 1 week (n = 1) or at 2 weeks (n = 2). One animal was found dead in the cage. At necropsy, each bioprosthesis (n = 4) was explanted and histopathologic analysis was performed.

RESULTS

Deployments of the bioprostheses were successful in nine of 11 swine. Two deployments were unsuccessful (one accidental deployment in the right renal vein, one deployment in the IVC caused rupture of the vein). Postdeployment venography (n = 9) confirmed no reflux (in the recumbent position of the swine) of the valve leaflets and patency of the vein inferior to the level of the bioprostheses. in the first group of animals (n = 5), valve leaflets were normal and competent. In the survival animal group (n = 4), the bioprostheses remained patent without evidence of thrombus formation by ascending and descending venography. Gross inspection of the explanted bioprostheses (n = 4) demonstrated grossly normal valves that fully occluded the lumen. Complications included hemarthrosis (n = 1), death (n = 1), and bioprosthesis thrombosis immediately after deployment (n = 1). Histopathologic analysis showed endothelial cells covering the luminal surfaces. The wall of the bioprostheses had granulomatous response and foreign body reaction. Bacterial contamination was noted in one bioprosthesis.

CONCLUSIONS

Deployment of a glutaraldehyde-fixed bovine vein sutured to a self-expanding nitinol stent in the swine iliac vein or IVC 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.