Abstract:
A stent is provided with arms for positioning the stent between two passageways. The stent may also be a stent-graft with a transition between a covered portion and an uncovered portion that is positioned relative to the junction between the two passageways. The arms are self-expanding and are biased outward from the tubular wall of the stent structure. The arms engage the wall of the first passageway around the junction to the second passageway to position a portion of the stent in the first passageway and another portion of the stent in the second passageway.

Description:
[0001]    This application claims priority to U.S. Provisional Application No. 61/755,719, filed Jan. 23, 2013, which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to medical devices and more particularly to a stent. 
         [0003]    One type of intraluminal medical procedure that uses a stent-graft is the TIPS procedure. TIPS refers to a transjugular intrahepatic portalsystemic shunt that is used to treat portal hypertension that typically occurs due to chronic liver problems, such as cirrhosis. Cirrhosis of the liver may occur due to alcohol abuse or hepatitis B and C, and results in scarring of the liver tissues which reduces blood flow through the liver. Because of the reduced blood flow through the liver, blood pressure can build in the portal vein system, which can cause a number of problematic symptoms. 
         [0004]    In order to relieve pressure in the portal vein system, a TIPS procedure involves placing a shunt in the liver between a portal vein and an hepatic vein. As a result, blood flowing through the shunt effectively bypasses the obstructed liver tissues. While this treatment does not cure the underlying liver problems that cause portal hypertension, it does diminish the side effects caused by portal hypertension and can improve a patient&#39;s quality of life and possibly extend a patient&#39;s life until a liver transplant can be performed. 
         [0005]    In a conventional TIPS procedure, access to the patient&#39;s venous system is usually gained at the neck into the internal jugular vein. A catheter and needle are then threaded through the venous system to the inferior vena cava and an hepatic vein. From the hepatic vein, the physician penetrates through the tissues of the liver with the needle until the needle intersects a portal vein. A balloon is typically used to inflate the passageway created between the hepatic and portal veins, and a stent-graft is implanted into the passageway to maintain fluid communication between the portal vein and the hepatic vein. 
         [0006]    Stent-grafts used in TIPS procedures typically have an uncovered portion and a covered portion that are designed, respectively, to allow blood flow through the stent wall and isolate blood flow within the lumen of the stent. For example, it is usually desirable to place the stent-graft so that a portion of the distal end of the stent-graft extends into the portal vein. This portion of the stent-graft is preferably uncovered so that blood can access the inner lumen of the stent and pass through the passageway of the shunt, but also so that blood can flow past the shunt and through the liver tissues to utilize any remaining liver function that may exist. However, the proximal portion of the stent-graft that extends through the shunt passageway is preferably covered to seal the blood flow within the lumen of the stent. This is important because the surrounding liver tissues would quickly stenos and close the shunt if a non-covered stent were used, and also because the shunt will typically intersect bile ducts between the portal and hepatic vein which would cause blood flow through the stent to quickly clot if the blood were exposed to the bile ducts. 
         [0007]    In order to ensure that the stent-graft in a TIPS procedure performs successfully, it is important that the transition between the uncovered portion and the covered portion be accurately located at the junction between the portal vein and the shunt. For example, if the uncovered portion is positioned partially within the shunt, the opening of the shunt could stenos and obstruct blood flow into the shunt. Also, the portion of the shunt that is exposed through the uncovered portion of the stent can cause blood clotting. Conversely, if the covered portion of the stent is located within the portal vein, the covered portion can block blood flow into the lumen of the stent and past the stent-graft into the liver. 
         [0008]    Accordingly the inventor believes it would be desirable to provide a stent with arms for positioning the stent at a junction between two passageways. 
       SUMMARY 
       [0009]    A stent is described for positioning the stent relative to a junction between first and second passageways. The stent has arms that engage the wall of the first passageway at the junction so that part of the stent is located in the first passageway and part of the stent is located in the second passageway. The arms may be located adjacent a transition between an uncovered portion and a covered portion of a stent-graft. Thus, the arms may be used to position the transition between the covered and uncovered portions relative to the junction between the first and second passageways. The inventions herein may also include any other aspect described below in the written description, the claims, or in the attached drawings and any combination thereof. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The invention may be more fully understood by reading the following description in conjunction with the drawings, in which: 
           [0011]      FIG. 1  is a partial cross-sectional view of a stent-graft implanted in a patient&#39;s liver; 
           [0012]      FIG. 2  is a side view of one embodiment of the stent-graft; 
           [0013]      FIG. 3  is a partial cross-sectional view of the stent-graft being implanted, showing the restraining sheath withdrawn from self-expanding arms; 
           [0014]      FIG. 4  is a partial cross-sectional view of the stent-graft being implanted, showing the stent-graft pulled into the shunt and the shunt opening compressing the arms; 
           [0015]      FIG. 5  is a side view of another embodiment of the stent-graft; 
           [0016]      FIG. 6  is a partial cross-sectional view of the stent-graft implanted, showing the wall of the portal vein contacting the inner surfaces of the arms; 
           [0017]      FIG. 7  is a partial plan view of the stent-graft, showing one arrangement for the transition between the covered portion and the uncovered portion of the stent-graft; 
           [0018]      FIG. 8  is a partial plan view of the stent-graft, showing another arrangement for the transition between the covered portion and the uncovered portion of the stent-graft; 
           [0019]      FIG. 9A  is a partial plan view of the stent-graft, showing another arrangement for the transition between the covered portion and the uncovered portion of the stent-graft; 
           [0020]      FIG. 9B  is a partial plan view of the stent-graft, showing another arrangement for the transition between the covered portion and the uncovered portion of the stent-graft. 
           [0021]      FIG. 10  is a partial plan view of the stent-graft, showing another arrangement for the transition between the covered portion and the uncovered portion of the stent-graft; 
           [0022]      FIG. 11  is a partial plan view of the stent-graft, showing another arrangement for the transition between the covered portion and the uncovered portion of the stent-graft; and 
           [0023]      FIG. 12  is a partial plan view of a stent without a graft covering. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring now to the figures, and particularly to  FIG. 1 , a stent-graft  10  is shown implanted within a patient&#39;s liver  22  following a typical TIPS procedure. As shown, the distal portion  16  of the stent-graft  10  extends into a portal vein  24 , while the proximal portion  18  extends through a shunt  28  formed between the portal vein  24  and an hepatic vein  26  and within a portion of the hepatic vein  26 . Preferably, the entire length of the distal portion  16  extending into the portal vein  24  is uncovered by the graft  14 . On the other hand, the majority of the length of the proximal portion  18  extending from the junction  30  between the shunt  28  and the portal vein  24  is preferably covered by the graft  14 . Even more preferably, the entire proximal portion  18  from the transition  32  adjacent the junction  30  between the shunt  28  and the portal vein  24  to the proximal end of the stent  12  is covered by the graft  14 . The graft  14  may be made of any suitable graft material, and may be, for example, Thoralon or electrospun PTFE. It is understood that the graft  14  covering  18  may cover the outside of the stent  12 , the inside of the stent  12 , or the stent wall may be embedded within the covering  18 . In a TIPS procedure where it is desirable to seal the liver  22  tissue surrounding the shunt  28 , the graft layer  14  is preferably generally impermeable. Because the distal portion  16  is uncovered by the graft  14 , blood is able to pass through the wall of the stent structure  12  to enter the lumen of the stent  12  and may also pass entirely through the stent structure  12  in order to flow through portions of liver  22  downstream from the shunt  28 . By contrast, the graft  14  along the proximal portion  18  isolates the fluid passing through the lumen of the stent structure  12  to direct blood flow toward the hepatic vein  26 . Thus, the shunted liver tissue is restricted from stenosing and closing the shunt and intersecting bile ducts are blocked so that blood flowing through the stent is not exposed to the bile ducts. 
         [0025]    As shown in  FIGS. 2 and 5 , the stent-graft  10  may be provided with one or more arms  28  adjacent the transition  32  between the distal, uncovered portion  16  and the proximal, covered portion  18 . Preferably, the stent-graft  10  has at least two arms  20 , and more preferably three to five arms  20 , equally spaced around the circumference of the stent structure  12 . The arms  20  are preferably self-expanding so that the free end  34  of each arm  20  naturally flares outward from the wall of the stent structure  12  when there is no inward restraining force applied to the arms  20 . 
         [0026]    As shown in the embodiments of  FIGS. 2-4 , the free ends  34  of the arms  28  may extend toward the distal end of the stent-graft  10 . Thus, the end  36  of each arm  20  that is connected to the stent structure  12  is closer to the proximal end, and the free end  34  of each arm  20  is closer to the distal end. The stent-graft  10  may be deployed as shown in  FIGS. 3-4 . Because the arms  20  are self-expanding, it is desirable to have an outer restraining sheath  38  that initially covers the arms  20  to press the arms  20  against the wall of the stent structure  12 . As shown in  FIG. 3 , the arms  20  are initially located within the portal vein  24 . Once the arms  20  are located in the portal vein  24 , the restraining sheath  38  is withdrawn to a position proximal from the arms  20  to allow the arms  20  to expand outward from the wall of the stent structure  12 . Where the stent structure  12  is also self-expanding, the distal portion  16  will self-expand as the restraining sheath  38  is withdrawn from the distal portion  16  and the arms  20 . The delivery system may also be provided with an inner catheter  40  with a stop at the proximal end of the stent-graft  10  to prevent the stent-graft  10  from moving proximally with the restraining sheath  38  as the sheath  38  is withdrawn. A guidewire  42  may also pass through the lumen of the stent-graft  10  or the inner catheter  40 . 
         [0027]    As shown in  FIG. 4 , after the restraining sheath  38  has been partially withdrawn to allow the arms  20  to expand, the restraining sheath  38 , stent-graft  10 , and inner catheter  40  may be pulled together proximally into the shunt  28 . When the arms  20  contact the junction  30  between the shunt  28  and the portal vein  24 , the arms  28  engage the wall of the portal vein  24  at the opening  30  of the shunt  28 . As the stent-graft  10  continues to move proximally, the opening  30  of the shunt  28  will begin to compress the arms  20  inward toward the wall of the stent-graft  10 . As shown in  FIG. 7 , the free end  34  of each arm  20  is preferably provided with a radiopaque marker  44  that increases X-ray visibility of the free ends  34  of the arms  20 . Thus, when the junction  30  between the shunt  28  and the portal vein  24  begins to compress the arms  20 , the physician will be able to visually see the radial movement of the free ends  34  of the arms  20 . As a result, this provides an indication to the physician that the transition  32  between the covered and uncovered portions  18 ,  16  of the stent-graft  10  is positioned adjacent the junction  30  between the shunt  28  and the portal vein  24 . Once the stent-graft  10  is positioned as desired, the restraining sheath  38  may be fully withdrawn from the stent-graft  10  to implant the proximal portion  18  within the shunt  28 . Because the shunt-portal vein junction  30  collapses the arms  28  toward the stent-graft  10  in the same manner that the arms  20  are collapsed prior to deployment, the arms  20  primarily provide a visual cue to the physician of the position of the covered and uncovered portions  18 ,  16 . In other words, the arms  20  in  FIGS. 2-4  provide minimal resistance to proximal movement through the opening  30  of the shunt  28 . Thus, for example, in  FIGS. 8 and 9 , the transitions  32  between the distal and proximal portions  16 ,  18  can be placed close to the free ends  34  of the arms  20  so that the arms  20  are almost fully collapsed by the shunt-portal vein junction  30  when the transition  32  between the distal and proximal portions  16 ,  18  is positioned at the junction  30 . 
         [0028]    As shown in  FIGS. 5-6 , the free ends  34  of the arms  20  may alternately extend toward the proximal end of the stent-graft  10 . Thus, the end  36  of each arm  20  that is connected to the stent structure  12  is closer to the distal end, and the free end  34  of each arm  20  is closer to the proximal end. The stent-graft  10  may be deployed similar to the method described above. However, in the embodiment of  FIGS. 5-6 , the arms  20  will provide more of a tactile cue to the position of the stent-graft  10  than the embodiment of  FIGS. 2-4 . That is, because the wall of the portal vein  24  engages the inside of the arms  20 , the arms  20  flare further out as the arms  20  are pulled against the junction  30 . Thus, the arms  20  provide significant resistance to proximal movement through the opening  30  of the shunt  28 . Where the free ends  34  of the arms  28  have radiopaque markers  44 , the physician may be able to see some radial outward movement of the free ends  34  of the arms  20 , and a lack of proximal movement of the arms  20  in response to proximal movement of the stent-graft  10 . However, tactile feedback may provide a more distinguishable indication that the arms  20  are located at the shunt opening  30 . 
         [0029]    As shown in  FIG. 7 , the stent structure  12  includes a series of zig-zag rings  46  made up of struts  48  connected together by bends  50 . The zig-zag rings  46  may be interconnected by longitudinal connecting members  52 . In  FIG. 7 , the stent structure  12  is shown in the collapsed configuration. As those of skill in the art will understand, when the stent structure  12  is expanded to the expanded configuration, the struts  48  will expand away from each other and will be angled with respect to the longitudinal axis of the stent  12 .  FIG. 7  represents only a partial view of the preferred stent  12  for a TIPS procedure, as the preferred stent  12  will be both longer and wider around the circumference. However, the full stent structure  12  can be envisioned by extending and repeating the pattern illustrated in  FIG. 7 . As those of skill in the art will recognize,  FIG. 7  shows the stent structure  12  in a laid-out plan view, but in practice the stent structure  12  will have a tubular wall defined by the zig-zag rings  46  and an inner lumen extending lengthwise therethrough. Preferably, the entire stent structure  12  is integral, including the arms  20 . Thus, the arms  20  need not be separately attached to the stent structure  12  by welding, bonding, etc. Although it is possible for the stent structure  12  to be balloon-expandable while the arms  20  are self-expanding, it is preferable for the stent structure  12  and the arms  20  to both be self-expanding. 
         [0030]    Although the described stent-graft  10  may be used to treat a number of medical conditions, the preferred embodiment of a stent-graft  10  for a TIPS procedure will typically require a distal, uncovered portion  16  from the transition  32  to the distal end about 1 cm to about 4 cm long, and a proximal, covered portion  18  from the transition  32  to the proximal end about 3 cm to about 12 cm long. More desirably, the distal, uncovered portion  16  from the transition  32  to the distal end may be about 2 cm long, and the proximal, covered portion  18  from the transition  32  to the proximal end may be about 4 cm long. The diameter of the stent-graft  10  in the expanded diameter is also preferably about 0.6 cm to about 1.5 cm, and more preferably, about 0.8 cm to about 1.2 cm, and most preferably, about 1 cm. 
         [0031]    As shown  FIG. 7 , one end  36  of each of the arms  20  may be connected to one side of one of the zig-zag rings  46 A, and the free end  34  may extend to the opposing side of the zig-zag ring  46 A. More preferably, the free end  34  extends past the opposing side of the zig-zag ring  46 A. Unlike the other zig-zag rings  46 , the adjacent zig-zag ring  46 B along the opposing side may be spaced  54  farther away than the other zig-zag rings  46  to allow the free end  34  to be positioned in the extra space  54  between the rings  46 A,  46 B. This may be accomplished by orienting the ring  46 A that the arm  20  is connected to and the adjacent ring  46 B so that the outsides of two adjacent bends  50  face each other. A connector  56  about the length of the space  54  may then connect the bends  50  together. The free end  34  of the arm  20  may also have an enlarged eyelet  44  with an opening  58  through which a radiopaque material like gold or platinum can be pressed into. Thus, as noted above, the free end  34  of each of the arms  20  may have a radiopaque marker  44 , which as shown in  FIG. 7  may be located in the extra space  54  between the adjacent rings  46 A,  46 B. In order to further enhance visualization of the stent-graft  10 , the distal and proximal ends of the stent structure  12  may also be provided with radiopaque markers  60  as shown in  FIGS. 2 and 5 . 
         [0032]    As shown in  FIGS. 7-11 , the graft  14  may be positioned on the stent structure  12  in various ways depending on the characteristics of the arms  20  and the graft  14  and the desired location of the transition  32  between the covered and uncovered portions  18 ,  16 . In  FIG. 7-9  the free ends  34  of the arms  20  extend toward the distal end, while in  FIGS. 10-11  the free ends  34  of the arms  20  extend toward the proximal end. 
         [0033]    In  FIG. 7 , the transition  32  between the covered and uncovered portions  18 ,  16  may be located adjacent the end  36  of the arm  20  connected to the stent structure  12 . Thus, the arm  20  and the free end  34  extending away from the connected end  36  are uncovered by the graft  14 . This arrangement may be desirable where the graft  14  would be expected to exert an undesirable restraining force on the arm  20  if it was covered by the graft layer  14 . Since the ring  46 A that the arm  20  is attached to is uncovered, this embodiment may also be preferred where the physician is expected to stop proximal movement of the stent-graft  10  during placement when the arms  20  just begin but do not completely collapse. That is, in this arrangement, it may be preferable for only the proximal side of the uncovered ring  46 A and the arm  20  to be positioned within the shunt opening  30 . Alternatively, this arrangement could be used where it is acceptable for a short uncovered portion to be located in the shunt opening  30 . 
         [0034]    In  FIG. 8 , the transition  32  between the covered and uncovered portions  18 ,  16  may be located adjacent the side of the zig-zag ring  46 A that is opposite from the end  36  of the arm  20  connected to the stent structure  12 . Thus, the ring  46 A that the arm  20  is connected to and the arm  20  itself are covered by the graft  14 . However, if the free end  34  extends past the transition  32 , the free end  34  may not be covered as shown in  FIG. 8 . This arrangement may be desirable where the graft  14  is not expected to exert an excessive restraining force on the arm  20 . This arrangement may also be preferred where the physician is expected to pull the stent-graft  10  into the shunt  28  until the free ends  34  of the arms  20  are collapsed close to the wall of the stent structure  12  by the shunt opening  30 . Further, this arrangement may be useful where it is desired to maximize graft  14  coverage around the shunt opening  30 . 
         [0035]    In  FIGS. 9A-9B , the transition  32  between the covered and uncovered portions  18 ,  16  may be located adjacent the side of the zig-zag ring  46 A that is opposite from the end  36  of the arm  20  connected to the stent structure  12  like  FIG. 8 . However, unlike  FIG. 8 , the arm  20  is separated from the graft  14  along the covered portion  18 . For example, in  FIG. 9A , this may be accomplished by masking off the arm  20  during the graft  14  coating process or by other known methods so that the arm  20  is uncovered along the covered portion  18 . Alternatively, in  FIG. 9B , the arm  20  may be covered by the graft  14  along the covered portion  18 , but the graft  14  may be split with a razor or other cutting instrument along the sides of the arm  20 . The arrangements of  FIGS. 9A-9B  may be desirable where the graft  14  would be expected to exert an undesirable restraining force on the arm  20  if it was covered by the graft  14  layer. Other than the separated arms  20 , the arrangements of  FIGS. 9A-9B  could be used in a similar manner as the arrangement of  FIG. 8 . 
         [0036]    In  FIG. 10 , the transition  32  between the covered and uncovered portions  18 ,  16  may be located adjacent the free end  34  of the arm  20  without covering the free end  34 . This arrangement may be preferred where it is desired to have the arm  20  uncovered by the graft  14 , and it is not expected that the uncovered ring  46 A will substantially enter the shunt opening  30  or it is acceptable for the uncovered ring  46 A to be located in the shunt opening  30 . 
         [0037]    In  FIG. 11 , the transition  32  between the covered and uncovered portions  18 ,  16  may be located adjacent the end  36  of the arm  20  connected to the stent structure  20 . However, it is preferred that the free end  34  of the arm  20 , and more preferably, the entire arm  20  be uncovered by the graft  14 . Although it is possible that at least part of the arm  20  could be covered by the graft  14 , as described above, in this arrangement the wall of the portal vein  24  at the junction  30  of the shunt  28  must be able to engage the inside surface of the free end  34  of the arm  20 . Thus, a graft  14  covering that prevented the portal vein  24  wall from contacting the inside surface of the free end  34  of the arm  20  would be undesirable in the arrangements of both  FIGS. 10 and 11  where the arms  20  extend toward the proximal end. 
         [0038]    While the preferred embodiment of the device as described above is a stent-graft  12 , the arms  20  may also be used with a stent  12  that is not covered by a graft  14  or a stent  12  that is fully covered by a graft  14 . For example, as shown in  FIG. 12 , the stent  12  may have a structure as described above but without a graft  14  covering the stent  12 . As shown, the arm  20  extends through the zig-zag ring  46 A to which it is connected, and the free end  34  extends past the zig-zag ring  46 A. Unlike the other zig-zag rings  46  that are spaced closer together, the zig-zag rings  46 A,  46 B at the free end  34  of the arm  20  are spaced farther apart to accommodate the portion of the free end  34  that extends past the zig-zag ring  46 A. Also, the free end  34  may have an enlarged portion  72  that is wider than the width of the portion of the arm  20  that extends through the zig-zag ring  46 A and the widths of the struts  48  that form the zig-zag ring  46 A. Although the enlarged portion  72  is shown solid in  FIG. 12 , the enlarged portion  72  may also have an opening for a radiopaque marker as described above. 
         [0039]    While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein. Furthermore, the advantages described above are not necessarily the only advantages of the invention, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the invention.