Patent Publication Number: US-2010114300-A1

Title: Medical device with leak path

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/291,636, filed on Dec. 1, 2005 and which claims priority to U.S. Provisional Application Ser. No. 60/522,998, filed on Dec. 1, 2004. Each of these related applications is hereby incorporated by reference into this disclosure in its entirety. 
    
    
     FIELD 
     The application for patent relates to medical devices. Exemplary embodiments described herein relate to valves that can be implanted in a body vessel or other suitable locations within the body of an animal, such as a human. 
     BACKGROUND 
     Many vessels in animal bodies transport fluids from one bodily location to another. Frequently, fluid flows in a unidirectional manner along the length of the vessel. Varying fluid pressures over time, however, can introduce a reverse flow direction in the vessel. In some vessels, such as mammalian veins, natural valves are positioned along the length of the vessel and act as one-way check valves that open to permit the flow of fluid in the desired direction and close to prevent fluid flow in a reverse direction, i.e., retrograde flow. The valves can change from an open position in response to a variety of circumstances, including changes in the cross-sectional shape of the vessel and the fluid pressure within the vessel. 
     While natural valves may function for an extended time, some may lose effectiveness, which can lead to physical manifestations and pathology. For example, venous valves are susceptible to becoming insufficient due to one or more of a variety of factors. Over time, the vessel wall may stretch, affecting the ability of the valve members to close. Furthermore, the valve members may become damaged, such as by formation of thrombus and scar tissue, which may also affect the ability of the valve members to close. Once valves are damaged, venous valve insufficiency may be present, which can lead to discomfort and possibly ulcers in the legs and ankles. 
     Current treatments for venous valve insufficiency include the use of compression stockings that are placed around the leg of a patient in an effort to force the vessel walls radially inward to restore valve function. Surgical techniques are also employed in which valves can be bypassed, eliminated, or replaced with autologous sections of veins having competent valves. 
     Minimally invasive techniques and instruments for placement of intraluminal medical devices have developed over recent years. A wide variety of treatment devices that utilize minimally invasive technology has been developed and includes stents, stent grafts, occlusion devices, infusion catheters and the like. Minimally invasive intravascular devices have especially become popular with the introduction of coronary stents to the U.S. market in the early 1990s. Coronary and peripheral stents have been proven to provide a superior means of maintaining vessel patency, and have become widely accepted in the medical community. Furthermore, the use of stents has been extended to treat aneurysms and to provide occlusion devices, among other uses. Recently, valves that are implantable by minimally invasive techniques have been developed. Frequently, a valve member is attached to a support frame and provides a valve function to the device. For example, the valve member can be in the form of a leaflet that is attached to a support frame and movable between first and second positions. In a first position, the valve is open and allows fluid flow to proceed through a vessel in a first direction, and in a second position the valve is closed to prevent fluid flow in a second, opposite direction. Examples of this type of valve are described in commonly owned U.S. Pat. No. 6,508,833 to Pavcnik for a MULTIPLE-SIDED INTRALUMINAL MEDICAL DEVICE, United States Patent Application Publication No. 2001/0039450 to Pavcnik for an IMPLANTABLE VASCULAR DEVICE, and U.S. patent application Ser. No. 10/642,372, filed on Aug. 15, 2003, each of which is hereby incorporated by reference in its entirety. In other examples of valve medical devices, a tube that terminates in valve members is attached to one or more support frames to form a valve. The valve members open to permit fluid flow in a first direction in response to fluid pressure on one side of the valve members, and close to prevent fluid flow in a second, opposite direction in response to fluid pressure on opposite sides of the valve members. An example of this configuration is provided in U.S. Pat. No. 6,494,909 to Greenhalgh for AN ENDOVASCULAR VALVE, which is hereby incorporated by reference in its entirety. 
     Natural valves can be somewhat ‘leaky,’ allowing a relatively small quantity of fluid to flow in a reverse direction, i.e., retrograde flow, when the valve is in a closed position. It is believed that this leakiness is beneficial for several reasons. For example, it is believed that a small amount of retrograde flow limits the pooling of blood around the natural valve during periods of low pressure, which can reduce the formation of thrombus adjacent the valve members and, therefore, increase the effective lifetime of the valve. 
     Prior art valve devices, however, do not permit a controlled amount of retrograde flow. Indeed, most prior art valves have been designed to prevent leakage as much as possible. Accordingly, there is a need for valve devices that permit a controlled amount of retrograde flow. 
     SUMMARY OF EXEMPLARY EMBODIMENTS 
     Medical devices comprising a valve for regulating fluid flow through a body vessel are described. The valves can be used in a variety of locations, including venous and cardiac applications, and include a leak path through which a controlled amount of retrograde flow can pass. 
     An implantable medical device according to one exemplary embodiment comprises a support frame having radially compressed and radially expanded configurations and a means for forming a leak path between the support frame and an interior wall of said body vessel. A valve member is attached to the support frame and is moveable between a first position that permits said fluid flow in a first direction and a second position that substantially prevents said fluid flow in a second direction. Any suitable means for forming a leak path can be used, including one or more channels, one or more projections, one or more contours, such as a series of scallops, and one or more support wings. 
     An implantable medical device according to another exemplary embodiment comprises a support frame having radially compressed and radially expanded configurations. A portion of the support frame defines a channel that forms a leak path with a portion of a body vessel and allows passage of a controlled amount of fluid flow. A valve member is attached to the support frame and is moveable between first and second positions to selectively allow fluid flow through a valve orifice. 
     Additional understanding of the invention can be obtained with review of the description of exemplary embodiments of the invention, appearing below, and the appended drawings that illustrate exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a medical device according to a first exemplary embodiment. 
         FIG. 2  is a perspective view of a body vessel containing the medical device illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged sectional view of the area highlighted in  FIG. 2 . 
         FIG. 4  is a perspective view of a medical device according to a second exemplary embodiment. 
         FIG. 5  is a perspective view of a body vessel containing the medical device illustrated in  FIG. 4 . 
         FIG. 6  is an enlarged sectional view of the area highlighted in  FIG. 5 . 
         FIG. 7  is a perspective view of a medical device according to an alternate embodiment. 
         FIG. 8  is a perspective view of a medical device according to an alternate embodiment. 
         FIG. 9  is a perspective view of a medical device according to a third exemplary embodiment. 
         FIG. 10  is a sectional view of a body vessel containing the medical device illustrated in  FIG. 9 . 
         FIG. 11  is a perspective view of a medical device according to a fourth exemplary embodiment. 
         FIG. 12  is a sectional view of a body vessel containing the medical device illustrated in  FIG. 11 . 
         FIG. 13  is a perspective view of a medical device according to a fifth exemplary embodiment. 
         FIG. 14  is a sectional view of a body vessel containing the medical device illustrated in  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following provides a detailed description of exemplary embodiments. The description is not intended to limit the scope of the invention, or its protection, in any manner, but rather serves to enable those skilled in the art to practice the invention. 
     Medical devices that can be used in a variety of applications are provided. For example, medical devices according to exemplary embodiments comprise valves that can be used to regulate fluid flow through a body vessel. The valves can be implanted in a body vessel, or in any other suitable environment, to regulate the flow of fluid. Valves according to the invention can also be implanted in ducts, canals, and other passageways in the body, as well as cavities and other suitable locations. Valves according to exemplary embodiments of the invention can be implanted in the vessels of the vasculature, such as veins, to regulate the flow of blood through the vessels. Valves according to the invention can also be implanted in the vessels of the heart, including the aorta, as a heart valve. 
     As used herein, the term “implanted,” and grammatically related terms, refers to the positioning of an item in a particular environment, either temporarily, semi-permanently, or permanently. The term does not require a permanent fixation of an item in a particular position. 
       FIGS. 1 through 3  illustrate a first exemplary embodiment. The medical device according to this embodiment is a valve  110  for regulating fluid flow through a vessel. In this embodiment, the valve  110  includes two valve members  112 ,  114  that are attached to a support frame  116  that defines a series of scallops  118 . As best illustrated in  FIG. 3 , a leak path  120  is formed between each scallop  118  of the support frame  116  and an interior wall  182  of the body vessel  180  in which the valve  110  is implanted. The leak path  120  provides a path through which fluid can flow without encountering the valve orifice  122  defined by the valve members  112 ,  114 . 
     The valve members  112 ,  114  comprise a section of material. The valve members  112 ,  114  can be formed of any suitable material, and need only be biocompatible or be able to be made biocompatible and be able to perform as described herein. The valve members  112 ,  114  advantageously can be formed of a flexible material. Examples of suitable materials for the valve members  112 ,  114  include natural materials, synthetic materials, and combinations of natural and synthetic materials. Examples of suitable natural materials include extracellular matrix (ECM) materials, such as small intestine submucosa (SIS), and other bioremodellable materials, such as bovine pericardium. Other examples of ECM materials that can be used in the medical devices of the invention include stomach submucosa, liver basement membrane, urinary bladder submucosa, tissue mucosa, and dura mater. Examples of suitable synthetic materials include polymeric materials, such as expanded polytetrafluoroethylene and polyurethane. ECM materials are particularly well-suited materials for use in the valve members  112 ,  114  at least because of their abilities to remodel and to provide a scaffold onto which cellular in-growth can occur, eventually allowing the material to remodel into a structure of host cells. 
     The valve members  112 ,  114  can be attached to the support frame  116  in any suitable manner. As illustrated in  FIG. 1 , sutures  124  or other attachment members can be used to attach the valve members  112 ,  114  to the support frame  116 . Alternatively, the valve members  112 ,  114  can be attached to the support frame  116  by other means for attaching, such as adhesives, heat sealing, tissue welding, weaving, cross-linking, or other suitable means for attaching. The specific means for attaching chosen will depend at least upon the materials used in the valve members  112 ,  114  and the support frame  116 . 
     Free edges  126 ,  128  of the valve members  112 ,  114  cooperatively define a valve orifice  122 . The valve members  112 ,  114  are moveable between first and second positions. In the first position, the orifice  122  is open and allows fluid flow through the valve  110  in a first direction, represented by arrow  170 . In the second position, the free edges  126 ,  128  of the valve members  112 ,  114  come together to close the orifice  122  and substantially prevent fluid flow through the valve  110  in a second, opposite direction, represented by arrow  172 . 
     The leak path  120  permits a controlled amount of fluid flow through the valve  110 . This controlled fluid flow can pass through the leak path  120  when the valve orifice  122  is in the open and/or closed position. It is expected, however, that fluid will flow through the leak path  120  more readily when the orifice  122  is closed because, in this configuration, the leak path  120  is the only path through which fluid can flow through the valve  110 . As a result, the leak path  120  is expected to provide a path for retrograde flow to flow across the valve  110 . 
     The support frame  116  can comprise any suitable support frame. A wide variety of support frames are known in the medical technology arts, and any suitable support frame can be utilized. The specific support frame chosen will depend on several considerations, including the nature of the valve member, the nature of the point of treatment at which the medical device will be implanted, and the medical condition for which the medical device is being used. The support frame  116  need only provide a surface to which the valve member can be attached and provide the structure needed to form the leak path  120 . 
     The support frame  116  advantageously has radially compressed and radially expanded configurations. Such a support frame  116  can be implanted at a point of treatment within a body vessel by minimally invasive techniques, such as via delivery and deployment with an intravascular catheter. The support frame  116  can optionally provide additional function to the medical device  110 . For example, the support frame  116  can provide a stenting function, i.e., exert a radially outward force on the interior wall  182  of the vessel  180  in which the medical device  110  is implanted. By including a support frame  116  that exerts such a force, a medical device according to the invention can provide both a stenting and a valving function at a point of treatment within a body vessel. 
     The support frame  116  can be self-expandable or balloon expandable. The structural characteristics of both of these types of support frames are known in the art, and are not detailed herein. Each type of support frame has advantages and, for any given application, one type may be more desirable the other based on a variety of considerations. For example, in the peripheral vasculature, vessels are generally more compliant and typically experience dramatic changes in their cross-sectional shape during routine activity. Medical devices for implantation in the peripheral vasculature should retain a degree of flexibility to accommodate these changes of the vasculature. Accordingly, medical devices according to the invention intended for implantation in the peripheral vasculature, such as venous valves, advantageously include a self-expandable support frame. These support frames, as known in the art, are generally more flexible than balloon-expandable support frames following deployment. 
     The support frame  116  can be formed of any suitable material and need only be biocompatible or able to be made biocompatible. The support frame  116  is advantageously made from a resilient material, preferably metal wire formed from stainless steel or a superelastic alloy, such as nitinol. While round wire is depicted in  FIG. 1 , other types, such as flat, square, triangular, D-shaped, and delta-shaped wire, may be used to form the support frame  116 . Other examples of suitable materials include, without limitation, stainless steel, nickel titanium (NiTi) alloys, e.g., nitinol, other shape memory and/or superelastic materials, polymers, and composite materials. Also, resorbable and bioremodellable materials can be used, including the resorbable and bioremodellable materials described herein. 
     As used herein, the term “resorbable” refers to the ability of a material to be absorbed into a tissue and/or body fluid upon contact with the tissue and/or body fluid. The contact can be prolonged, and can be intermittent in nature. A number of resorbable materials are known in the art, and any suitable resorbable material can be used. Examples of suitable types of resorbable materials include resorbable homopolymers, copolymers, or blends of resorbable polymers. Specific examples of suitable resorbable materials include poly-alpha hydroxy acids such as polylactic acid, polylactide, polyglycolic acid (PGA), and polyglycolide; trimethylene carbonate; polycaprolactone; poly-beta hydroxy acids such as polyhydroxybutyrate and polyhydroxyvalerate; and other polymers such as polyphosphazenes, polyorganophosphazines, polyanhydrides, polyesteramides, polyorthoesters, polyethylene oxide, polyester-ethers (e.g., polydioxanone) and polyamino acids (e.g., poly-L-glutamic acid or poly-L-lysine). There are also a number of naturally derived resorbable polymers that may be suitable, including modified polysaccharides, such as cellulose, chitin, and dextran, and modified proteins, such as fibrin and casein. 
     As described above, the support frame  116  defines a series of scallops  118  for formation of the leak paths  120 . Any suitable size, configuration, and number of scallops  118  can be used, and the specific size, configuration, and number used in a medical device according to a particular embodiment of the invention will depend on several considerations, including the desired quantity of fluid flow through the leak paths  120 . In the illustrated embodiment, the scallops  118  are defined by a portion of the support frame  116  that has a substantially sinusoidal configuration. 
       FIGS. 4 through 6  illustrate a medical device  210  according to a second embodiment of the invention. The device  210  of this embodiment is similar to the device illustrated in  FIGS. 1 through 3 , except as described below. Accordingly, the device  210  comprises a valve and includes two valve members  212 ,  214  that are attached to a support frame  216 . Free edges  218 ,  220  of the valve members  212 ,  214  cooperatively define a valve orifice  222 . The valve members  212 ,  214  are moveable between first and second positions. In the first position, the orifice  222  is open and allows fluid flow through the valve  210  in a first direction, represented by arrow  270 . In the second position, the free edges  218 ,  220  of the valve members  212 ,  214  come together to close the orifice  222  and substantially prevent fluid flow through the valve  210  in a second, opposite direction, represented by arrow  272 . 
     In this embodiment, the support frame  216  defines a projection  224 . As best illustrated in  FIGS. 5 and 6 , the projection  224  spaces an interior wall  282  of a body vessel  280  from the support frame  216  when the valve  210  is positioned within a lumen of the body vessel  280 . As a result, a leak path  226  is formed. The leak path  226  permits a controlled amount of fluid flow through the valve  210 , including retrograde flow  272 . 
     The projection  224  can have any suitable shape and configuration, and can be positioned at any suitable location on the support frame  216 . As best illustrated in  FIGS. 4 and 5 , the projection  224  can be generally rectangular in shape and be positioned across a midpoint of a length of a linear portion of the support frame  216 , such as a strut. The rectangular shape of the projection  224  allows for an extended interface area between the valve  210  and the interior wall  282  of the body vessel  280 , which may facilitate anchoring of the valve  210  in the body vessel  280 . 
       FIGS. 7 and 8  illustrate alternative projections. In the embodiment illustrated in  FIG. 7 , the valve  210 ′ includes a projection  224 ′ that has a curvilinear surface  230 ′. This embodiment may be advantageous because the curvilinear surface  230 ′ substantially eliminates edges of the projection  224 ′ that interact with the vessel wall  282 . 
     In the embodiment illustrated in  FIG. 8 , the valve  210 ″ includes a projection  224 ″ that has a substantially triangular shape. This embodiment may be advantageous because the substantially triangular shape may enhance anchoring of the valve  210 ″ in a body vessel by providing a point  232 ″ that can function as a barb that interacts with a wall of the body vessel. The specific shape, configuration, and position of the projection in a medical device according to a particular embodiment of the invention will depend on several considerations, including the type of body vessel in which the medical device will be implanted. 
       FIGS. 9 and 10  illustrate a medical device  310  according to a third exemplary embodiment of the invention. The device  310  of this embodiment is similar to the device illustrated in  FIGS. 1 through 3 , except as described below. Accordingly, the device  310  comprises a valve and includes two valve members  312 ,  314  that are attached to a support frame  316 . Free edges  318 ,  320  of the valve members  312 ,  314  cooperatively define a valve orifice  322 . The valve members  312 ,  314  are moveable between first and second positions. In the first position, the orifice  322  is open and allows fluid flow through the valve  310  in a first direction. In the second position, the free edges  318 ,  320  of the valve members  312 ,  314  come together to close the orifice  322  and substantially prevent fluid flow through the valve  310  in a second, opposite direction. 
     In this embodiment of the invention, a portion of the support frame  316  defines a channel  324  that permits a controlled amount of fluid flow through the valve  310 , including retrograde flow. The channel  324  cooperates with an interior wall  382  of a body vessel  380  to form a leak path. 
     Any suitable configuration can be used for the channel  324 . Further, more than one channel can be included. The specific configuration and number chosen for any particular medical device according to the invention will depend on several considerations, including the type of support frame used and the quantity of flow needed to pass through a leak path. 
     In the embodiment illustrated in  FIGS. 9 and 10 , two struts  390 ,  392  of the support frame  316  include a channel  324 . In this configuration, leak paths are provided on one side of the valve orifice  322  and not on the opposite side. This may be advantageous as it is expected to create an unequal distribution of retrograde flow at the valve orifice  322 , which may facilitate a prevention of pooling of fluid in or around the valve  310 . It is understood, however, that more or fewer channels in more or fewer struts, or other portions of a support frame, can be used without departing from the scope of the invention. 
       FIG. 10  illustrates the valve  310  disposed within a body vessel  380 . In the illustrated embodiment, the channel  324  of the support frame  316  has a substantially ovoid cross-sectional shape. An ovoid shape is considered advantageous because it provides a relatively large void region through which fluid can flow. Any suitable cross-sectional shape can be used in the channel  324 , however, and the specific cross-sectional shape used in a medical device according to a particular embodiment of the invention will depend on several considerations, including the desired quantity of fluid flow through the leak paths formed by the channel. 
     To facilitate fluid flow through the channel  324 , it may be advantageous to include a coating on the portions of the support frame  316  that define the channel  324 . Any suitable coating can be used and should be chosen to facilitate, rather than hinder, fluid flow. Examples of suitable coatings include non-thrombogenic and thromboresistant coatings, such as heparin and suitable heparin-containing compounds and mixtures. Of course, any coating having desirable properties can be used. 
     In this embodiment, the valve members  312 ,  314  are attached to the support frame  316  in a manner that does not significantly obstruct fluid flow through the channel  324 . As illustrated in  FIGS. 9 and 10 , the valve members  312 ,  314  can be attached to the support frame  316  without sutures. Suture alternatives such as adhesives, heat sealing, tissue welding, weaving, cross-linking, or any other suitable means for attaching the valve members  312 ,  314  to the support frame  316  can be used. The specific means for attaching chosen will also depend upon the materials used in the valve members  312 ,  314  and the support frame  316 . 
       FIGS. 11 and 12  illustrate a medical device  410  according to a fourth exemplary embodiment. In this embodiment, the medical device  410  is a valve for regulating fluid flow through a body vessel. The valve includes first  412  and second  414  support frames. The first support frame  412  is a wire frame member and the second support frame  414  is a solid circumferential member, although any suitable support frame can be used for each of the support frames  412 ,  414 . The second support frame  414  is disposed within the first support frame  412  at an end portion  416 . A tubular graft member  418  is disposed on an external side  420  of the first support frame  412  and inverted into a space between the first  412  and second  414  support frames. 
     A first end  422  of the graft member  418  terminates in a valve orifice  424  that is supported by first  426  and second  428  upstanding arms formed by the second support frame  414 . The valve orifice  424  opens and closes to permit and substantially prevent fluid flow through the valve  410  in first and second directions, respectively. 
     A second end  430  of the graft member  418  is attached to a circumferential support member  432  of the first support frame  412 . The circumferential support member  432  defines a series of undulations  434 . The second end  430  of the graft member  418  is attached to the circumferential support member  432  to substantially follow the series of undulations  434 . As illustrated in  FIG. 12 , this configuration forms a series of leak paths  436  between the graft member  418  and an interior wall  482  of a body vessel  480  when the valve  410  is implanted in a body vessel  480 . The leak paths  436  permit a controlled amount of fluid flow through the body vessel  480  at the location of the valve  410  without encountering the valve orifice  424 . 
     The circumferential support member  432  can have any suitable configuration, and the illustrated configuration is exemplary in nature. The circumferential support member  432  need only provide a configuration that facilitates formation of one or more leak paths between the graft member  418  and the interior vessel wall  482 . 
     The graft member  418  can also include additional features that facilitate the passage of fluid flow that does not encounter the valve orifice  424 , such as slits  438 . 
     The graft member  418  is a flexible member and can be formed of any suitable material, including all materials described above for the valve members in other embodiments. 
       FIGS. 13 and 14  illustrate a medical device  510  according to a fifth exemplary embodiment. The medical device  510  according to this embodiment is similar to the embodiment illustrated in  FIGS. 11 and 12 , except as described below. Accordingly, the medical device  510  comprises a valve that includes first  512  and second  514  support frames, a tubular graft member  518  that forms a valve orifice  524  at one end  522  and is attached to the first support frame  512  at a second end  530 . 
     In this embodiment, first  550  and second  552  spacing wings are disposed on the first support frame  512 . As illustrated in  FIG. 14 , the spacing wings  550 ,  552  space the graft member  518  from an interior wall  582  of a body vessel  580  to form a series of leak paths  536  that permit a controlled amount of fluid flow through the body vessel  580  at the location of the valve  510  without encountering the valve orifice  524 . 
     In the illustrated embodiment, the spacing wings  550 ,  552  are integrally formed by the wire member of the first support frame  512 . The wings  550 ,  552  can, however, comprise separately attached members or have any other suitable configuration. Also, while the illustrated embodiment includes two spacing wings  550 ,  552 , any suitable number of spacing wings can be used. The number chosen for a medical device according to a particular embodiment of the invention will depend on several considerations, including the quantity of fluid flow desired to pass through the body vessel without encountering the valve orifice  524 . 
     In the tubular valve embodiments illustrated in  FIGS. 11 through 14 , it is understood that a single support frame and that the second support frame is an optional element. Also, the a substantially tubular graft member could be used instead of a tubular graft member. For example, two or more graft members could be arranged on the support frame to substantially create a tubular formation, despite their separate and distinct nature. 
     The leak path in any embodiment can enable flow from any suitable location or locations along a length of the medical device. The location(s) chosen for a medical device according to a particular embodiment will depend on several considerations, including the environment in which the medical device is intended to be placed. For example, venous valves that include one or more valve members that form pockets with the vessel wall may benefit from a leak path that enables retrograde flow from the pocket region of the device. Adaptations, such as the scallops illustrated in  FIGS. 1 through 3  and the projections illustrated in  FIGS. 4 through 8 , can be positioned in the appropriate location to enable flow from the desired location. As another example, valve devices may also benefit from flow enabled from another location along the length of the device, such as a top or proximal region.  FIGS. 9 and 10  illustrate an exemplary medical device in which retrograde flow is enabled from a location at the proximal end of the device. This structure can be used in conjunction with additional structure that enables flow from another location along the length of the device, such as a space between portions of the support frame at the distal end, as best illustrated in  FIG. 9 . Also, as best illustrated in  FIGS. 11 through 14 , a leak path can be used in conjunction with other flow-enabling features, such as openings and slits in valve members. 
     The inclusion of a leak path in medical devices in which a flexible material is used in the valve-forming element, such as the valve members illustrated in  FIGS. 1 through 9  and the graft member illustrated in  FIGS. 11 through 14 , is particularly advantageous because the flexible material is likely to move intermittently and/or irregularly when the device is placed in a body vessel. This movement may create areas in which fluid is largely excluded from flushing action of normal flow, which could lead to stagnation and, in the case of blood vessels, thrombus formation. The leak paths can be positioned to provide a draining effect from such areas. 
     The foregoing detailed description provides exemplary embodiments of and includes the best mode for practicing the invention. These embodiments are intended only to serve as examples of the invention, and not to limit the scope of the invention, or its protection, in any manner.