Abstract:
The catheter apparatus may be used to assist in creating a fistula between two adjacent blood vessels. The apparatus includes a catheter for inserting into a first blood vessel which lies adjacent to a second blood vessel, the catheter having a plurality of openings through which a physician may navigate a piercing tool. The physician maneuvers the tip of the catheter to a position within the first blood vessel adjacent to a portion of the first blood vessel wall in which the physician intends to create an opening. The physician may then rotate the piercing tool within the catheter and extend the piercing tool through one opening at a time, without rotating the catheter, until the physician chooses an opening that is properly aimed at the second blood vessel. Such a configuration allows for a wide arc of potential firing space.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of application Ser. No. 11/340,324, filed Jan. 25, 2006, the disclosure of which is incorporated by reference. This application also claims the benefit of Provisional Application Ser. No. 60/887,277, filed on Jan. 30, 2007, the disclosure of which is incorporated by reference. 
     
    
     BACKGROUND  
       [0002]     This disclosure relates generally to a catheter system for connecting adjacent blood vessels, e.g, an artery and an adjacent vein to adapt the vein for arterial blood flow. More particularly the invention concerns a system of two catheters with mating, magnetic tips for creating openings in the artery wall and vein wall to form a fistula connecting the blood vessels. Further, the disclosure relates to a ratchetable catheter having a wide arc of potential space through which a piercing tool may be fired from a first blood vessel to a second blood vessel.  
         [0003]     A catheter apparatus and method for arterializing a section of a vein to bypass a clogged artery are shown in U.S. Pat. No. 6,464,665, which is hereby incorporated by reference. The method is used to bypass a stenosis in the artery that obstructs blood flow in a portion of the artery. If the obstructed portion of the artery can be bypassed, blood flow will be restored downstream from the stenosis. A vein running alongside the artery in the obstructed portion of the artery can be used for the bypass.  
         [0004]     The catheter apparatus includes one catheter for inserting into the artery and another catheter for inserting into the adjacent vein. The physician maneuvers the tips of both catheters to coincident positions within each blood vessel adjacent one end of the obstructed portion of the artery. The physician then creates an opening from the inside of one blood vessel through the vessel wall and then through the wall of the other blood vessel.  
         [0005]     An issue arises in co-locating the openings in the two blood vessels and holding the vessel walls in place to ensure that a channel will be created between the vessels so that blood will flow from one vessel to the other. A further issue arises in aiming and maintaining the position of the catheters inside the vessels. In particular, veins often have diameters much larger than arteries, making hitting a smaller artery from a larger vein difficult. Additionally, larger veins often allow a catheter too much freedom of movement inside the vein.  
       SUMMARY OF THE INVENTION  
       [0006]     The disclosed system and method provides for creating paired, co-located openings and a consequent fistula between an artery and an adjacent vein to bypass an arterial blockage. The system includes a piercing tool on a first catheter that mates with a receptor on a second catheter to create the co-located openings at one side of the blockage. Magnets incorporated in either or both catheters may be used to draw the piercing tool into the receptor. The piercing tool and receptor typically are provided with complementary, mating contours to draw the piercing tool sufficiently into the receptor to ensure completion of the openings. The openings may be expanded by balloon angioplasty and a stent is typically then installed to interconnect the openings to ensure a fistula is established between the vessels. The process may be repeated at the other side of the arterial blockage to complete the bypass.  
         [0007]     Another aspect of the disclosure provides for a plurality of openings that may be used to assist in creating a fistula between two adjacent blood vessels. The apparatus includes a catheter for inserting into a first blood vessel which lies adjacent to a second blood vessel, the catheter having a plurality of openings through which a physician may navigate a piercing tool. The physician maneuvers the tip of the catheter to a position within the first blood vessel adjacent to a portion of the first blood vessel wall in which the physician intends to create an opening. The physician may then rotate the piercing tool within the catheter and extend the piercing tool through one opening at a time, without rotating the catheter, until the physician chooses an opening that is properly aimed at the second blood vessel. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a partial cross-sectional view showing an obstructed artery, including the obstruction and the area adjacent both ends of the obstruction, and a vein alongside the artery.  
         [0009]      FIG. 2  is a cross-sectional view of an embodiment of the present invention in the blood vessels of  FIG. 1  with a first catheter with a distal end inserted into the artery and a second catheter with a distal end inserted into the vein, the catheters carrying at their distal ends mating tips, i.e., a piercing tool on the first catheter and a receptor on the second catheter.  
         [0010]      FIG. 3  is a cross-sectional view of the vein, artery, and two catheters, as in  FIG. 2  with the tips of the catheters mated to create a pair of co-located openings in the walls of the vein and artery for connection of a fistula between the artery and the vein.  
         [0011]      FIG. 4  is a cross-sectional view of the vein and artery with a balloon inserted through both openings.  
         [0012]      FIG. 5  is a cross-sectional view of the vein and artery with a stent installed through the openings between the vein and artery to maintain a fistula therebetween.  
         [0013]      FIG. 6  is a cross-sectional view of a first catheter inserted in the artery and a second catheter inserted in the vein at the other end of the obstruction depicted in  FIGS. 1-4 , the catheters including mating tips shown in a joined position to create a second pair of co-located openings through the vein and artery walls.  
         [0014]      FIG. 7  is a cross-sectional view of the vein and artery with a balloon inserted through the second pair of openings between the vein and the artery.  
         [0015]      FIG. 8  is a cross-sectional view of the vein and artery with a second stent installed through the second pair of openings between the vein and artery to maintain a fistula therebetween.  
         [0016]      FIG. 9  is a close-up perspective view of the mating tips of the first and second catheters, showing the receptor, which includes a proximal end, a distal opening, and a channel providing a guide surface, and the piercing tool, which includes a needle and a plug encompassing the catheter adjacent the base of the needle, and showing the contours of the plug, needle, and receptor channel that provide for mating between the tips.  
         [0017]      FIG. 10  is a piercing tool for use in a second embodiment of the present invention that includes a base and a needle that is offset from the base by an angle.  
         [0018]      FIG. 11  illustrates the use of the piercing tool of  FIG. 10  in conjunction with a double-balloon catheter to create openings in a vein and an artery.  
         [0019]      FIG. 12  illustrates the use of the piercing tool of  FIGS. 2, 3 ,  6 , and  9  in conjunction with a double-balloon catheter to create openings in a vein and an artery.  
         [0020]      FIG. 13  is a cross-sectional view of another aspect of the present disclosure having a plurality of openings.  
         [0021]      FIG. 14  is a cross-sectional view of an embodiment similar to that shown in  FIG. 13  having a plurality of openings and a resizable portion.  
         [0022]      FIG. 15  is a cross-sectional view of the embodiment of  FIG. 13  inside the lumen of a first vessel and aimed at a second vessel.  
         [0023]      FIG. 16  is a cross-sectional view of two vessels with an embodiment of the present disclosure having an expandable balloon support in an expanded state, with a piercing tool extending from an opening of the catheter, through walls of the first and second vessels, and into the lumen of the second vessel.  
         [0024]      FIG. 17  is a cross-sectional view of the two vessels and an embodiment of this disclosure with pivotable members stabilizing it inside the lumen of the first vessel, where a physician has twice attempted unsuccessfully to traverse from the first vessel to the second vessel, and has succeeded in a third attempt.  
         [0025]      FIG. 18  is a cross-sectional view of the two vessels and an embodiment of this disclosure with an expandable stent stabilizing it inside the lumen of the first vessel, where a physician has twice attempted unsuccessfully to traverse from the first vessel to the second vessel, and has succeeded in a third attempt.  
         [0026]      FIG. 19  shows one possible arrangement of the plurality of openings on the catheter.  
         [0027]      FIG. 20  shows another possible arrangement of the plurality of openings on the catheter. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     As shown in  FIG. 1 , an artery  30 , formed by an artery wall  32 , has a blood flow, indicated by arrow A, that is partially or totally blocked by an obstruction or occlusion  34 , typically formed by plaque. A vein  36  roughly similar in dimension to artery  30  lies alongside and generally parallel to artery  30 . Vein  36 , formed by a vein wall  38 , includes, in the area proximal to occlusion  34 , a portion  40  in close proximity to artery  30  that the physician has selected as a venous site for creating a fistula between artery  30  and vein  36 . The normal blood flow through vein  36  would be in the direction indicated by arrow B.  
         [0029]     An embodiment of the invented system, indicated generally at  42  in  FIG. 2 , is a catheter apparatus that includes a first catheter  62  and a second catheter  44 . In  FIG. 2 , the first catheter is in the artery and the second catheter is in the vein, but this can be reversed. Similarly, the first catheter in the artery is shown upstream from occlusion  34 , but this may alternatively be reversed to begin the procedure downstream from the occlusion and proceeding afterwards to the upstream side.  
         [0030]     Second catheter  44  may include at least one lumen  58  which runs generally parallel to a longitudinal axis LV of catheter  44 . A wire  46  may be inserted through lumen  58 . Typically, wire  46  has an outer diameter of 0.035-inches, but any suitable dimension may be used. Wire  46  may be controllable by the physician in position relative to catheter  44 . Wire  46  may be a guidewire for catheter  44 , or a separate guidewire may be used, with other lumens in catheter  44  providing the channel for the separate guidewire.  
         [0031]     As shown in  FIG. 2 , first catheter  62  of catheter apparatus  42  includes a distal end  67  that the physician may insert into artery  30  for positioning adjacent arterial fistula site  54 . First catheter  62  may include one or more lumens running generally parallel to a longitudinal axis of catheter  62 . First catheter  62  may be guided along a guidewire or may itself be a guidewire, typically with an outer diameter of 0.035-inches, although any suitable dimension may be used. First catheter  62  preferably is hollow.  
         [0032]     A piercing tool  77  that includes a sharp needle  78  may be selectively deployed, as shown in  FIGS. 2 and 3 , or withdrawn into the lumen of catheter  62 . Needle  78  is preferably withdrawn while catheter  44  is maneuvered to the fistula site so as not to cause trauma to the blood vessel wall.  
         [0033]     As best seen in  FIG. 9 , needle  78  may be disposed at the distal end of a wire  178  disposed in the lumen of catheter  62 . The physician can control the positioning of wire  178  and needle  78  relative to catheter  62 . Guidewire  46  may include a receptor  150 , such as substantially cup-shaped socket  152 . Receptor  150  includes a distal opening  154 , preferably circular, and a proximal end  156 . Receptor  150  includes a channel  158  leading from opening  154  toward proximal end  156 . Channel  158  preferably narrows in a direction from opening  154  toward proximal end  156 . Channel  158  is defined by an inner surface  160  that provides a guide surface for needle  78  that directs the needle toward proximal end  156  of receptor  150 . Channel  158  may be substantially conical, or have such other shape as tends to mate with, and guide piercing tool  77  into receptor  150 .  
         [0034]     Piercing tool  77  on catheter  62  preferably includes a plug  162  provided with an outer contour that narrows from a proximal end  164  toward a distal end  166 . Plug  162  preferably mates with channel  158  in receptor  150 . Plug  162  preferably encompasses catheter  62  adjacent the distal end of the catheter. As seen in  FIGS. 2, 3 , and  9 , the piercing tool and the receptor have a complementary configuration that supports their mating together.  
         [0035]     Typically, piercing tool  77  will include a magnet with one pole oriented toward the distal end of the tool, while receptor  150  will include a magnet with the opposite pole oriented toward the distal end of the receptor which will draw the needle into the receptor. For example, the magnets may be annular rings or donuts and formed of a strong permanent magnet material suitable for the intended use.  
         [0036]     A typical arrangement, shown in  FIG. 9 , is that plug  162  includes a first magnet  168  generally in a donut shape and having a north pole N positioned distally with respect to a south pole S. Typically magnet  168  is spaced from the distal end of plug  162 . A second magnet  170  may be disposed on, or form an integral part of receptor  152 , preferably adjacent distal opening  154  of socket  152 . Second magnet  170  may be arranged with a south pole S distal of a north pole N to attract magnet  168  when the tips of the two catheters are in proximity, e.g., with each catheter in an adjacent blood vessel. Alternatively or in addition, one or more magnets may be arranged in various locations on plug  162  and/or needle  78  and on or in receptor  150 , e.g., adjacent proximal end  156 , with the poles arranged to draw piercing tool  77  into receptor  150 .  
         [0037]     As shown in  FIGS. 3 and 4 , after creating openings  80 ,  82  with a tool such as needle  78 , the physician withdraws catheter  62  from the fistula site, leaving wire  178  in place, and a balloon  92  may be inserted over wire  178  and through openings  80 ,  82  and inflated to enlarge the openings. Balloon  92  may include radiopaque markers and may be inflated with a solution containing a radiopaque dye or contrast to allow the physician to radiographically monitor and adjust the position of the balloon before, during, and after inflation.  
         [0038]     As shown in  FIG. 5 , a device for maintaining an open, leak-free connection between openings  80  and  82 , such as stent  100 , is inserted through the openings. Stent  100  includes a frame  102  having two open ends  104  and  106  that preferably create leak-free couplings to the inside of artery  30  and vein  36 . With openings  80 ,  82  connected to form a fistula, vein  36  is arterialized, and blood flows from artery  30  into vein  36  in the direction indicated by arrows A and BA.  
         [0039]     Stent  100  is typically a short, covered stent, such as the Hemobahn stent made by WL Gore &amp; Associates.  
         [0040]     As shown in  FIGS. 6, 7 , and  8  a second pair of co-located openings may be created, and a stented fistula established therebetween, using essentially the same catheter system and method as described for  FIGS. 1-5  and  9 .  FIG. 6  illustrates that the first catheter with the piercing tool preferably is inserted into the artery and the openings created from the artery into the vein. Alternatively, the openings may be created from the vein into the artery.  
         [0041]     An alternative embodiment for the piercing tool in shown in  FIG. 10 . This tool  77   a  may be used with a metal guidewire  62   a  that preferably includes a lumen  58   a.  An inner wire  178   a  may be inserted in lumen  58   a,  providing a base for a needle  78   a.  The coupling between the needle and base incorporates a curvature such that the needle is nominally offset from the base by an angle OA, typically between about 30-degrees and about 90-degrees. Inner wire  178   a  is typically made of a sufficiently rigid material, such as nitinol and/or stainless steel, as to maintain the offset angle as the needle is used to pierce blood vessels. Guidewire  62   a  is preferably formed of a sufficiently rigid material such that when needle  78   a  is retracted into lumen  58   a,  the curvature between the needle and the base is overcome and the needle temporarily aligns with the base in a non-traumatic configuration. Inner wire  178   a  may have an outer diameter of 0.010, 0.014, 0.018, or 0.021-inches, or such other dimension as is suited to the particular application.  
         [0042]     As shown in  FIG. 11 , piercing tool  77   a  may be inserted in artery  30 , typically while withdrawn into the catheter  62   a  while maneuvering to the fistula site. Piercing tool  77   a  may be used in conjunction with a catheter having two balloons  124  and  126  that are inserted in vein  36 . In such case, the catheter tips are maneuvered to opposing sides of the proposed fistula site and balloons  124  and  126  are inflated to press the vein wall against the artery wall. Also, fluid may be injected into the sealed-off area to further press the two blood vessel walls together. Then piercing tool  77   a  is deployed and maneuvered through the artery and then the vein wall to create openings for forming the fistula as for the embodiments described above.  
         [0043]      FIG. 11  depicts the piercing tool and the balloon catheter in different vessels. Alternatively, piercing tool  77   a  may be inserted in the same blood vessel with the balloon catheter. In such an embodiment, the balloons are preferably independently inflatable, and typically the distal balloon  124  is inflated first to stop blood flow. Then, piercing tool  77   a  is maneuvered to the fistula site in a manner similar to that for the previously described embodiment, typically with the piercing tool withdrawn into the guidewire to the non-traumatic configuration.  
         [0044]     With the piercing tool at the fistula site, the proximal balloon  126  is inflated to seal off the fistula site and also to press the vein against the artery. Then, piercing tool  77   a  is deployed at the end of guidewire  62   a  and maneuvered by the physician to create the openings from one blood vessel, through both walls, to the other blood vessel.  
         [0045]     In either case, piercing tool  77   a  may be used to create multiple pairs of co-located openings which are then stented to arterialize a portion of the vein to bypass a blockage using a similar method as described above for the embodiment of  FIGS. 1-9 .  
         [0046]     As shown in  FIG. 12 , the double balloon catheter may also be used in conjunction with the catheters  44  and  62  that include the mating tips. In this embodiment, the double balloon catheter helps to control blood flow at the planned fistula site and to press the blood vessel walls together to assist in the mating of the tips. The fistula creation otherwise proceeds in a similar manner as for the embodiment of  FIGS. 1-9 .  
         [0047]      FIG. 13  depicts another aspect of the disclosure directed towards a catheter  230  having an outer surface  232 , a distal end  234 , a first lumen  236  (not shown), and a plurality of openings  240 .  
         [0048]      FIG. 14  shows a alternative catheter  230  according to the present disclosure, the catheter  230  having the same features of the catheter in  FIG. 13 , except this catheter  230  has a resizable portion  250  disposed on its outer surface, and an arc of its surface  252  which is unobstructed by the resizable portion  250 .  
         [0049]      FIG. 15  shows a first vessel  210 , formed by a vessel wall  212  and having a first diameter  214 , with a first portion  216  intended for an opening or a fistula. A second vessel  220  lies alongside and generally parallel to first vessel  210 . Second vessel  220 , formed by a second vessel wall  222  and having a second diameter  224 , includes a second portion  226 , in the second vessel wall  222  in close proximity to the first portion  216  of the first vessel wall  212 , that a physician may select as a site for creating a fistula between first vessel  210  and second vessel  220 . In this particular example, the first diameter  214  is substantially similar to the second diameter  224 . However, as seen in  FIGS. 16-18 , the first diameter  214  may also be substantially larger than the second diameter  224 , which would typically be the case if the first vessel  210  is a vein, and the second vessel  220  is an artery. A catheter system of the present disclosure may be used in any of the above scenarios.  
         [0050]     A catheter  230  similar to the one depicted in  FIG. 13  is seen inside the lumen of the first vessel  210  in  FIG. 15 . The plurality of openings  240  are seen pointed generally towards the second vessel  220 .  
         [0051]      FIG. 16  shows a view where the first diameter  214  is greater than the second diameter  224 . In this figure a piecing tool  244  is seen extending from one of the openings  240  in the catheter  230 , through the first vessel wall  212  at the portion intended for a fistula  216 , through the second vessel wall  222  at the second portion intended for fistula  226 , and into the lumen of the second vessel  220 . Also shown is a resizable portion  250  disposed on the outer surface  232  of the catheter  230 , which will be described in greater detail below.  
         [0052]     While the openings  240  are shown in the figures as comprising three openings, it should be understood that any number of openings may be disposed in the outer surface  232  or on the distal end  234  of the catheter  230 . Further, while the openings  240  are shown generally defining an arc which subtends an angle less than 360° of the catheter  230  circumference, it is possible that the openings  240  may define any arc on the catheter  230 , including the entire circumference of the catheter  230 . In the preferred embodiment, the angle subtended by the arc created by the openings  240  is between 0° and 180°.  
         [0053]      FIGS. 17 and 18  show similar views. In both figures, the physician has made first and second unsuccessful attempts (denoted ‘A’ and ‘B’) to create a fistula between the first vessel  210  and the second vessel  220  using a piercing tool  244 , followed by a successful attempt in which the piercing tool  244  has pierced the first vessel wall  212  and the second vessel wall  222  and has extended into the lumen of the second vessel  220 .  
         [0054]     The piercing tool  244  may be rotated within the catheter  230  without rotating the catheter  230 . In this arrangement, a physician may fire the piercing tool  244  through any of the openings  240 , giving the physician a wide arc of potential space through which the piercing tool  244  may be fired. Such an arc enables the physician to avoid rotating the catheter  230  any more than necessary, minimizing possible damage to the first vessel  210 .  
         [0055]     The piercing tool  244  may be selectively deployed, as shown in  FIGS. 16-20 , or withdrawn into the first lumen of catheter  230 . The piercing tool  244  is preferably withdrawn while catheter  230  is maneuvered to the fistula site so as not to cause trauma to the blood vessel wall. The piercing tool  244  may come in numerous varieties, including but not limited to the instruments recited in U.S. Pat. No. 6,464,665, as well as the catheter systems described above.  
         [0056]      FIGS. 19 and 20  depict alternative embodiments of how the piercing tool  244  may be extended. As depicted in  FIG. 19 , the openings  240  may be disposed on the outer surface  232  of the catheter  230  on a side portion of the catheter. In this embodiment, the piercing tool  244  may exit the catheter  230  at an angle θ to the longitudinal pole of the catheter  230 . θ may be any angle between 0° and 90°.  
         [0057]     In  FIG. 20 , the piercing tool  244  may extend from any one of the plurality of openings  240  which are disposed on the distal end  234  of the catheter  230 . In this embodiment, the piercing tool  244  may exit the catheter  230  at any angle from perpendicular to the longitudinal axis of the catheter  230  to substantially parallel to the longitudinal axis.  
         [0058]     The resizable portion  250  may surround any portion of the outer surface  232  of the catheter. In an exemplary embodiment, the resizable portion  250  may surround less than the whole arc of the surface  232 . The arc (or arcs) of the surface not surrounded by the resizable portion  250 , hereafter known as the free arc(s)  252 , may provide an unobstructed pathway for a piercing tool  244  to traverse. Thus, free arc  252  must be large enough to accommodate a piercing tool  244  extending from any of the plurality of openings  240 , as seen best in  FIGS. 16 and 18 .  
         [0059]     The resizable portion  250  may have a nominal configuration and an active configuration. In the nominal configuration, the resizable portion may have a nominal diameter  254  (seen in  FIGS. 14 and 20 ). In the active configuration the resizable portion  250  may have an active diameter  256 , which may be greater than the nominal diameter  254  (seen in  FIGS. 14 and 20 ).  
         [0060]     The resizable portion  250  may be completely or partially radiopaque, so that a physician can view and adjust the position of the free arc  252 , and hence control the direction which the piercing tool  244  will fire. In one embodiment, the resizable portion  250  is independently rotatable within a vessel. As seen best in  FIGS. 16 and 18 , the resizable portion  250  is aligned so that the free arc  252  faces the portion intended for the fistula  216  and the second vessel  220 .  
         [0061]     The resizable portion  250  is shown in the active configuration having an active diameter  256  in  FIG. 16 . The active diameter  256  may be substantially equal to the first diameter  214  of the first vessel  210 . It should be understood that having an active diameter  256  substantially equal to the first diameter of the first vessel will cause the resizable portion  250  to stabilize the catheter  230  within the first vessel  210 .  
         [0062]     Some embodiments of the resizable portion  250  may hold the catheter  230  in the center of the first vessel  210 . Other embodiments may hold the catheter  230  against a site intended for an opening  216  of a vessel wall  212 , or somewhat spaced from such a site  216 .  
         [0063]     In one embodiment of the disclosure, depicted in  FIGS. 14, 16  and  20 , the resizable portion  250  is a balloon  260  having a nominal configuration and an active configuration. In such an embodiment, catheter  230  may include a second lumen  238  used to inflate the balloon  260 .  
         [0064]     In the nominal configuration (seen in  FIG. 14 ), the balloon  260  is deflated with a nominal diameter  254  which is less than the first diameter  214  (seen in  FIGS. 15-18 ) of the first vessel  210 . In the active configuration, the balloon  260  may be inflated to an active diameter  256 . The active diameter  256  may be of any size greater than the nominal diameter  254  that will hold the catheter  230  stable in the first vessel  210  by causing the balloon surface  262  to contact the wall  212  of the vessel  210 , including but not limited to equal to the diameter  214  of the vessel  210 , slightly larger than the diameter  214  of vessel  210 , or even slightly smaller than the diameter  214  of the first vessel  210 .  
         [0065]     Balloon  260  may include radiopaque markers and/or may be inflated with a solution containing a radiopaque dye or contrast to allow the physician to radiographically monitor and adjust the position of the balloon  260  before, during, and after inflation.  
         [0066]     In another embodiment, depicted in  FIG. 17 , catheter  230  has a resizable portion  250  comprising a plurality of retractable members  270 . Each retractable member  272  has a proximal end  274  pivotally coupled to the outer surface  232  and a free distal end  276 . In the nominal configuration, each retractable member  272  is retracted so that the distal end  276  is in close proximity with the outer surface  232 , allowing for easy movement of the catheter  230  through the first vessel  210 . In the active configuration, each retractable member  272  is extended so that the distal end  276  is extended away from the outer surface  232  and abutting the first vessel wall  212 .  
         [0067]     In some embodiments, some retractable members  270  may be longer than others, as shown in  FIG. 17 . In particular, all the retractable members  270  disposed on a particular portion of the outer surface  232  may be longer or shorter than the retractable members  270  disposed on a different portion of the outer surface. Such differences in length cause the catheter  230  to be held in a position that is offset from the center of the first vessel  210 .  
         [0068]     In another embodiment, depicted in  FIG. 18 , catheter  230  has a resizable portion  250  comprising an expandable stent  280  made of stent cells  282  and having an outer surface  284 . The stent  280  may be constructed out of any suitable material. In one embodiment, the stent  280  may be metallic. In another embodiment, the stent  280  is at least partially comprised of self-expanding nitinol.  
         [0069]     In the nominal configuration, the stent  280  is retracted to a diameter  254  which is less than the first diameter of the first vessel  210 , allowing for easy movement of the catheter  230  through the first vessel  210 . In the active configuration, the  280  stent is expanded to a diameter  256  substantially equal to the first diameter  214  of the first vessel  210  so that the outer surface  284  of the stent abuts the first vessel wall  212 . The diameter  256  in the active configuration may be of any size that will hold the catheter  230  stable in the vessel  210  by causing the outer stent surface  284  to abut the first wall  212  of the vessel  210 , including but not limited to equal to the first diameter  214  of the vessel  210 , slightly larger than the first diameter  214 , or even slightly smaller than the first diameter  214 .  
         [0070]     It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed disclosures and are novel and non-obvious. Disclosures embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different disclosure or directed to the same disclosure, whether different, broader, narrower or equal in scope to the original claims, are also included within the subject matter of the disclosures of the present disclosure.