In human pathology, the proper functioning of both cardiac and venous valves is of paramount importance. Disorders of cardiac valves cause significant morbidity and mortality. These disorders affect persons of all ages and can result from congenital or degenerative conditions, as well as from the sequelae of infections. Stenosis and insufficiency of the aortic or mitral valves have a greater incidence than stenosis and insufficiency of the tricuspid and pulmonary valves. Venous insufficiency is believed to contribute to various maladies, including edema, varicose veins, aching leg pain while standing, lipodermatosclerosis, and ulcerations. Venous insufficiency is essentially caused by venous hypertension and chronic venous stasis due to valvular incompetence both of an idiopathic nature and of a secondary nature following past illnesses of the venous systems.
A prosthetic cardiac or venous valve may regulate the direction of the pulsating blood flow so as to limit the occurrence of blood stasis in the region about the valve. By maintaining the direction of blood flow therethrough, a prosthetic cardia, aortic, or venous valve may alleviate the maladies resulting from valve disorders or venous insufficiency. A prosthetic valve should therefore permit blood flow in the proper predetermined direction to limit or prevent backflow of the blood in a reverse direction.
The art has seen several attempts for providing a prosthetic valve to alleviate the consequences of cardiac valve disorders and of venous insufficiency. These attempts generally fall into two categories, biologic valves and mechanical valves. Biologic valves are comprised of a stent supporting a number of circumferential leaflets made of a flexible material. If the material is biologic in nature, it may be either a xenograft, that is, harvested from a non-human cadaver, or an allograft, that is, harvested from a human cadaver. For example, it is known in the art to apply a pericardium biological tissue layer covering, for providing the valve leaflets, to a stent which provides structural annular integrity to the prosthesis. Non-biologic material such as polyurethane has also been used. The second category of prosthetic valves, mechanical valves, usually comprise a rigid annulus supporting up to three rigid leaflets. The annulus and leaflets are frequently formed in pyrolitic carbon, a particularly hard and wear resistant form of carbon. The annulus is captured within a sewing ring so that the valve may be attached to tissue at the location of the replaced valve. Unfortunately, surgically positioning these implants typically requires suturing or sewing the device into the blood vessel, increasing the risk of thrombosis due to the resulting suturing or anastomoses of the body vessel.
These attempts typically provide a valve structure having a relatively rigid tubular body structure which supports a flexible valve leaf structure. That is, any structural rigidity imparted to the tubular body structure is separated from the valve leaf structure. For example, U.S. Pat. No. 4,759,759 discloses a prosthetic valve having a solid stent member having a diametrically-opposed upstanding posts and a substantially cylindrical flexible cover. The two portions of the cover extending between the upstanding stent posts may be collapsed against each other in sealing registry over a fluid passageway defined by the stent. The stent, being a solid member, limits the radial collapsing thereof for endoscopic delivery within a body lumen. The cover, being unsupported by the stent within the fluid passageway of the valve, must itself provide sufficient strength and resiliency to optimally regulate fluid flow. Alternatively, U.S. Pat. No. 5,855,691 discloses a prosthetic valve having a radially expandable covered stent which defines an elongate fluid passageway therethrough. A flexible valve is disposed within the fluid passageway to regulate fluid flow therethrough. The valve is formed of a flexible and compressible material formed into a disc with at least three radial incisions to form deflectable leaflets. While the stent circumferentially supports the valve body, the leaflets are not supported by any other structure within the fluid passageway. There is therefore a need in the art for a unitary prosthetic valve construction which provides structural reinforcement to both the tubular body portion of the valve and to the valve leafs supported thereon.