Transluminally implantable venous valve

Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Including valve

Reexamination Certificate

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Reexamination Certificate

active

06299637

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to the replacement of incompetent venous valves, and, more particularly, to minimally invasive methods and devices for transluminally implanting prosthetic venous valves.
The human venous system of the lower limbs includes the superficial venous system and the deep venous system with perforating veins connecting the two systems. The superficial system includes the great saphenous vein and the small saphenous vein. The deep venous system includes the anterior and posterior tribial veins which unite to form the popliteal vein which in turn becomes the femoral vein when joined by the small saphenous vein. The venous systems contain a plurality of valves for directing blood flow (generally superiorly) to the heart.
Venous valves are usually bicuspid valves, with each cusp forming a sack or reservoir for blood which, under pressure, forces the free edges of the cusps together to prevent retrograde flow of the blood and allow only antegrade flow to the heart. When an incompetent valve attempts to close in response to a pressure gradient across the valve, the cusps do not seal properly and retrograde flow of blood occurs.
There are two chronic venous diseases in which incompetence of venous valves is thought to be an important factor in the pathophysiology. These are chronic venous insufficiency and varicose veins.
Chronic venous insufficiency is essentially caused by venous hypertension and chronic venous stasis due to valvular incompetence both of a primitive nature (or primary or essential or idiopathic) and of a secondary nature following past illnesses of the venous system (generally speaking, deep venous thrombosis or phlebitis).
As the veins dilate due to increased pressure, the valves in the veins become less able to withstand the weight of the blood above them. This causes the veins to dilate further and the valves in the veins to fail. As they fail, the effective height of the column of blood above the feet and ankles grows taller, with an increase in the pressure exerted on the tissues of the ankle and foot. When the weight of that column reaches a critical point because of enough dilation and valve failures, the patient begins to have ulceration of the ankle which start deep and eventually come to the surface. These ulcerations are very difficult to heal because the weight of blood causing them still exists, with the tendency to enlarge the ulcer, and because they are deep, often to the bone. Chronic venous insufficiency thus consists of hypertension of the lower limb in the deep, perforating and often superficial veins with associated pigmentation, pain, swelling and ulceration.
Existing treatments for chronic venous insufficiency are less than ideal. The only therapies currently available include elevation of the legs for twenty minutes every two hours, elastic support hose to compress the veins externally and surgical repair or replacement of the valves by grafting veins from the patient's arm into the leg. These methods are variably effective. Moreover, surgery has associated complications with morbidity and mortality risk and is usually very expensive. Similarly, the palliative therapies require major lifestyle changes for the patient with potentially suboptimal long term patient compliance. Also, without repairing the valves, even if the ulcers are healed, the ulcers will recur unless the patient continues to elevate the legs and to use support hose continuously.
The varicose vein condition consists of dilatation and tortuosity of the superficial veins of the lower limb and resulting cosmetic impairment, pain and ulceration. Primary varicose veins are the result of primary incompetence of the venous valves of the superficial venous system. Secondary varicose veins occur as the result of deep venous hypertension which has damaged the valves of the perforating veins, as well as the deep venous valves.
The initial defect in primary varicose veins often involves localized incompetence of a venous valve thus allowing reflux of blood from the deep venous system to the superficial venous system. This incompetence is traditionally thought to arise at the saphenofemoral junction but may also start at the perforators. Thus, gross saphenofemoral valvular dysfunction may be present in even mild varicose veins with competent distal veins. Even in the presence of incompetent perforation, occlusion of the saphenofemoral junction usually normalizes venous pressure.
The initial defect in secondary varicose veins is often incompetence of a venous valve secondary to hypertension in the deep venous system. Since this increased pressure is manifested in the deep and perforating veins, correction of one site of incompetence could clearly be insufficient as other sites of incompetence will be prone to develop. However, repair of the deep vein valves would correct the deep venous hypertension and could potentially correct the secondary valve failure. Apart from the initial defect, the pathophysiology is similar to that of varicose veins.
Effective treatment of venous valvular incompetence remains elusive. Some methods of valvular reconstructive surgery may allow the recovery of valvular function in certain cases. However, the use of reconstructive surgery is limited by the delicate nature, and, in many cases, the irreversible damage of the valvular structure.
While bioprosthetic heart valves are known, bioprosthetic venous valves are not readily available. The major deterrent in constructing venous valves is the need to provide a valve which remains normally open, but closes under slight backflow. Another deterrent in constructing such valves is the need to provide proper valve leaflet and sinus geometry as the valve opens and closes. Prosthetic heart valves, and the current methods of preparing them, are generally not suitable as venous valve replacements. Prosthetic heart valves are usually made from porcine valves, which have a geometry unsuitable as a replacement for venous valves. These types of valves are also generally larger than venous valves, and include valve leaflets generally thicker and stiffer than the leaflets of venous valves. The thicker heart valve leaflets require a greater opening pressure, which can enhance the likelihood of venous stasis and thrombus formation, and makes such valves unsuitable for the venous system.
Thus, there remains a need for an implantable valve and related support structure and deployment system for replacing incompetent venous valves. Preferably the prosthetic valve is transluminally implantable, minimally thrombogenic, and meets the flow requirements unique to the venous system.
SUMMARY OF THE INVENTION
There is provided in accordance with one aspect of the present invention, a method of implanting a prosthetic vascular valve. The method comprises the steps of providing a prosthetic vascular valve having at least one leaflet therein. The leaflet has a minor axis extending substantially perpendicular to a longitudinal axis of the vessel, and a major axis extending perpendicular to the minor axis. The leaflet is compressed along its minor axis, to a reduced cross sectional profile and positioned within the vessel. The leaflet is thereafter permitted to self expand along its minor axis, within the vessel. Preferably, the leaflet is pivotably attached to a self expandable tubular support structure, for retaining the leaflet in a pivotable orientation within the vessel.
In accordance with another aspect of the present invention, there is provided a self expandable prosthetic venous valve. The valve comprises a tubular wire support, expandable from a first, reduced diameter to second, enlarged diameter. The tubular wire support has a flow path extending therethrough, for permitting venous blood flow.
At least on leaflet is pivotably positioned in the flow path, for permitting flow in a forward direction and resisting flow in a reverse direction. The leaflet comprises a major axis which is perpendicular to and longer than a minor axis, and the leaflet is compressible and

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