A Percutaneous Approach to Deep Venous Valve Insufficiency With a New Self-Expanding Venous Frame Valve

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.

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.

Evaluation of prosthetic venous valves, fabricated by electrospinning, for percutaneous treatment of chronic venous insufficiency

Chronic venous insufficiency (CVI) remains a major health problem worldwide. Direct venous valve surgical repair and venous segment transplantation are clinical options; however, they are highly invasive procedures. The objectives of this study were to fabricate prosthetic venous valves (PVVs) by electrospinning, for percutaneous treatment of CVI, and evaluate their hydrodynamic characteristics in vitro at the same locations and under the same flow conditions. The PVVs consisted of polyurethane fiber scaffolds attached to a cobalt-chromium stent. PVVs with two different valve-leaflet configurations were compared: biomimetic PVV (bPVV) and open PVV (oPVV). A balloon catheter was used to implant the devices in a poly(vinyl chloride) tube and the column outlet was set at a height of 100 cm above the test valve to simulate the elevation of the heart above a distal vein valve while standing; 50 wt% glycerin solution was used as the test fluid. The devices were evaluated for antegrade flow, effect of ankle flexion, and stagnation zones around the valve leaflets. During sudden hydrostatic backpressure, little leakage and constant peripheral pressure were observed for the devices; under forward pulsatile pressure of 0-4 mmHg, to simulate the effect of breathing, the oPVV had a higher flow rate than the bPVV. With regard to the effect of ankle flexion, the oPVV was functionless. Moreover, the stagnation zone around the oPVV valve leaflets was larger than that around the bPVV valve leaflets. These results suggest that the bPVV would be clinically suitable for percutaneous treatment of CVI.

In Vitro Evaluation of a New Autologous Valve-Stent for Deep Venous Incompetence

PURPOSE

To report the results of in vitro hydrostatic bench testing of a new vein-stent combination to correct deep venous incompetence.

METHODS

Twelve valves were constructed from a modified Palmaz stent encased in a segment of great saphenous vein harvested from patients during routine varicose vein surgery. An in vitro flow circuit was set up to evaluate opening and closing pressures (in cm H(2)O), and the valve was subsequently subjected to repetitive cycles of increasing prograde flow and reflux pressures. Duplex scanning was used to evaluate valve closure time and detect any possible reflux.

RESULTS

The valve mechanism required only 1 to 3 cm H(2)O for opening and 2 to 4 cm H(2)O for closing. Prograde flow of up to 1000 mL/min passed easily through this valve, which remained competent with reflux pressures up to 180 cm H(2)O. Mean valve closure time was 0.15+/-0.07 seconds. Unligated side branches or damage from dissection impaired the competence of 3 valves.

CONCLUSION

This new vein-stent valve functions as a normal deep vein valve, requiring only minimal pressures for opening and closing. It allows high flow passage and still remains competent at high reflux pressures. This valve may provide a minimally invasive solution for the correction of deep venous incompetence using autologous material. Further in vivo evaluation will be mandatory.

Significance of spatial orientation of percutaneously placed bioprosthetic venous valves in an ovine model

PURPOSE

To investigate two spatial orientations of a percutaneously placed bicuspid second-generation bioprosthetic venous valve (SG-BVV) in the jugular vein (JV).

MATERIALS AND METHODS

Twelve SG-BVVs, consisting of small intestinal submucosa attached to a nitinol frame were placed across a natural valve (NV) in the distal JV in six sheep. Six SG-BVVs were oriented as NV leaflets (group A) and the other six SG-BVVs were rotated 90 degrees to NV leaflets (group B). SG-BVV function was studied by venography performed immediately after placement and at 5 weeks after placement. Animals were killed at 5 weeks, and gross examinations were performed.

RESULTS

Desired valve orientation after deployment was seen in all SG-BVVs. In group A, all valves exhibited good valve function on immediate and 5-week venography. At gross examination, leaflets were attached mostly at the valve base and free cusp areas were similar in both cusps with a mean of 154.8 mm2 +/- 45.6 for one cusp and 142 mm2 +/- 53.4 for the other cusp (P = .188). In group B, all valves showed good function on immediate venography and in five valves prior to killing. Valve attachment to the vein wall in this group involved a longer segment of leaflets and their free areas were smaller with a wide variety of cusp sizes. Mean free leaflet areas of opposing cusps measured 106.3 mm2 +/- 36.5 and 66.1 mm2 +/- 34.6, respectively (P = .025). Difference in leaflet areas between group A and group B was significant (P = .019).

CONCLUSION

Proper spatial orientation of the SG-BVV at deployment is important for valve function and should have the same orientation as the NV.