Aortic and venous valve for percutaneous insertion

Stabilizing interventional instruments in the cardiovascular system: A classification of mechanisms

Positioning and stabilizing a catheter at the required location inside a vessel or the heart is a complicated task in interventional cardiology. In this review we provide a structured classification of catheter stabilization mechanisms to systematically assess their challenges during cardiac interventions. Commercially available, patented, and experimental prototypes of catheters were classified with respect to their stabilizing mechanisms. Subsequently, the classification was used to define requirements for future cardiac catheters and persisting challenges in catheter stabilization. The classification showed that there are two main stabilization mechanisms: surface-based and volume-based. Surface-based mechanisms apply attachment through surface anchoring, while volume-based mechanisms make use of locking through shape or force against the vessel or cardiac wall. The classification provides insight into existing catheter stabilization mechanisms and can possibly be used as a tool for future design of catheter stabilization mechanisms to keep the catheter at a specific location during an intervention. Additionally, insight into the requirements and challenges for catheter stabilization inside the heart and vasculature can lead to the development of more dedicated systems in the future, allowing for intervention- and patient-specific instrument manipulation.

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.

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.

Percutaneous therapy for deep vein reflux

At present, there are no widely accepted surgical or percutaneous treatment options for chronic venous insufficiency of the deep venous system. The small intestinal submucosa square stent bicuspid venous valve (BVV) has shown the most promising results of artificial venous valves developed to date. In experimental long-term studies in sheep jugular veins, 88% of implanted valves exhibited good function; 12% had decreased function related to valve tilting, of which only 4% had partial thrombosis. BVVs were also placed in three patients and have remained patent without thrombosis or other complications since 2002. At present, 3 years after BVV placement, symptoms in two patients are decreased. Proper sizing and proper placement of the valves were critical to their function. To eliminate occasional tilting of the original BVV, a second-generation BVV has been developed and tested.

Second-generation percutaneous bioprosthetic valve: a short-term study in sheep

OBJECTIVES

To eliminate occasional tilting of the original bioprosthetic venous valve (BVV) a second-generation BVV has been developed. This study was performed to evaluate deployment, stability, and short-term function of the second-generation BVV in an animal model.

METHODS

A second-generation percutaneously placed BVV consisting of a square stent and lyophilized small intestinal submucosa attached to a second square stent (DS BVV) or Z-stent (ZS BVV) were tested. DS BVVs (n = 32) were constructed with a nitinol (n = 28) or stainless steel double stent (n = 4), and ZS BVVs (n = 16) were made of nitinol (n = 8) or stainless steel (n = 4). BVVs were implanted percutaneously through a femoral vein approach into the jugular vein in 24 female sheep with an over-the-wire 13F or 10F delivery system. All BVVs were placed across the natural valve of the proximal jugular vein. Deployment, stability, and function of BVVs were studied at immediate venography with contrast medium injections peripheral and central to the BVVs. Animals underwent follow-up venography and were sacrificed at 6 weeks (n = 24). Gross pathologic examination was performed.

RESULTS

Jugular vein diameter ranged from 9.8 to 14.4 mm (mean, 12.1 +/- 1.2 mm) in 24 sheep. The 10-mm to 12-mm valve was deployed in 27 jugular veins, and the 12-mm to 14-mm valve was deployed in 21 jugular veins. No tilting was seen at placement of 48 BVVs into the jugular veins, and all valves exhibited good function on immediate venograms. Angiographic competency for the nitinol and stainless steel ZS BVV (100%) was similar to that for the nitinol DS BVV (92.3%; P = .488) but was significantly better than for the stainless steel DS BVV at 6 weeks (50%; P = .03). Dysfunction of 4 valves was caused by either nitinol DS BVV oversizing (n = 2) or intimal hyperplasia with the stainless steel DS BVV (n = 2).

CONCLUSION

Placement without tilting appears essential for proper valve function. The second-generation BVV enables placement without tilting. Exact matching of valve size with vein diameter is necessary for good valve function.

CLINICAL RELEVANCE

At present there are no widely accepted surgical or percutaneous treatment options for deep chronic venous insufficiency. A manufactured, percutaneously implantable, nonimmunogenic and nonthrombogenic bioprosthetic venous valve that remains patent and competent over time is an attractive alternative to direct venous valve reconstruction or transplantation. our results and the potential for effective treatment with bioprosthetic venous valves warrants clinical research in carefully selected patients and may lead to an effective, minimally invasive treatment for deep chronic venous invasive treatment for deep chronic venous insufficiency.

Percutaneous bioprosthetic venous valve: a long-term study in sheep

A long-term evaluation of a new percutaneously placed bioprosthetic, bicuspid venous valve (BVV) consisting of a square stent and small intestinal submucosa (SIS) covering was performed in 12 sheep. Of 26 BVVs placed into the jugular veins, 25 exhibited good valve function on immediate venography and 22 on venograms obtained before the sheep were killed. Gross and histologic examination results demonstrated incorporation of remodeled and endothelialized SIS BVVs into the vein wall. Slight to moderate leaflet thickening was found mostly at their bases. Percutaneously placed SIS BVV is a promising one-way, competent valve that resists venous back-pressure while allowing forward flow.