Abstract:
Medical device delivery systems, and related methods and components, are disclosed. In some embodiments, an implantable medical endoprosthesis delivery system includes a catheter, a sheath at least partially surrounding the catheter, and a tip coupled to a distal end portion of the catheter. The tip can cooperate with a distal end surface of the sheath to form a gap therebetween so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of and claims priority to U.S. application Ser. No. 10/753,715, filed on Jan. 8, 2004. 
     
    
     TECHNICAL FIELD  
       [0002]     The invention relates to medical device delivery systems, and related methods and components.  
       BACKGROUND  
       [0003]     Systems are known for delivering medical devices, such as stents, into a body lumen. Often, such systems include a proximal portion that remains outside the body during use and a distal portion that is disposed within the body during use. The proximal portion typically includes a handle that is held by an operator of the system (e.g., a physician) during use, and the distal portion can include an outer tube surrounding an inner tube with a stent positioned therebetween. Generally, the operator of the system positions the distal portion within the lumen at a desired location (e.g., so that the stent is adjacent an occlusion). The operator can then retract the outer tube to allow the stent to engage the occlusion/lumen wall. Thereafter, the operator removes the distal portion of the system from the lumen. In many instances, a system can be designed to be flushed (e.g., with a saline solution) prior to delivery to a targeted site within the body. Such flushing can, for example, enhance the lubricity and/or deliverability of a system.  
       SUMMARY  
       [0004]     The invention relates to medical device delivery systems, and related methods and components.  
         [0005]     In one aspect, the invention features an implantable medical endoprosthesis delivery system. The system includes a catheter and a sheath that at least partially surrounds the catheter. The sheath has a proximal end, a distal end, and at least one orifice between the proximal and distal ends of the sheath. The catheter and the sheath are configured so that an implantable medical endoprosthesis can be disposed therebetween. The at least one orifice in the sheath is between the distal end of the sheath and a location in the sheath adjacent a proximal end of the implantable medical endoprosthesis.  
         [0006]     In another aspect, the invention features a method of implanting an endoprosthesis in a lumen of a subject. The method includes disposing a system in the lumen of the subject. The system includes a catheter, a sheath that at least partially surrounds the catheter, and an implantable medical endoprosthesis between the catheter and the sheath. The sheath has a proximal end, a distal end, and at least one orifice between the proximal and distal ends of the sheath. The at least one orifice in the sheath is between the distal end of the sheath and a location in the sheath adjacent a proximal end of the implantable medical endoprosthesis. The method also includes at least partially retracting the sheath.  
         [0007]     In a further aspect, the invention features an implantable medical endoprosthesis delivery system. The system includes a catheter and a sheath that at least partially surrounds the catheter. The sheath has a proximal end, a distal end, and at least one orifice that is at most about 100 millimeters from the distal end of the sheath. The catheter and the sheath are configured so that an implantable medical endoprosthesis can be disposed therebetween.  
         [0008]     In one aspect, the invention features a method of implanting an endoprosthesis in a lumen of a subject. The method includes disposing a system in the lumen of the subject. The system includes a catheter, a sheath at least partially surrounding the catheter, and an implantable medical endoprosthesis between the catheter and the sheath. The sheath has a proximal end, a distal end, and at least one orifice that is at most about 100 millimeters from the distal end of the sheath. The method also includes at least partially retracting the sheath.  
         [0009]     In another aspect, the invention features an implantable medical endoprosthesis delivery system. The system includes a catheter, a sheath and a tip. The sheath has a distal end with a shaped surface, and the sheath at least partially surrounds the catheter. The catheter and the sheath are configured so that an implantable medical endoprosthesis can be disposed therebetween. The tip is coupled to the distal end of the catheter, and the tip has a surface in partial contact with the shaped surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0010]     In a further aspect, the invention features a method of implanting an endoprosthesis in a lumen of a subject. The method includes disposing a system in the lumen of the subject. The system includes a catheter, a sheath and a tip. The sheath has a distal end with a shaped surface, and the sheath at least partially surrounds the catheter. The system also includes an implantable medical endoprosthesis between the catheter and the sheath. The tip is coupled to the distal end of the catheter, and the tip has a surface in partial contact with the shaped surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath. The method further includes at least partially retracting the sheath.  
         [0011]     In one aspect, the invention features an implantable medical endoprosthesis delivery system. The system includes a catheter, a sheath and a tip. The sheath at least partially surrounds the catheter. The catheter and the sheath are configured so that an implantable medical endoprosthesis can be disposed therebetween. The tip is coupled to the distal end of the catheter, and the tip has a shaped surface in partial contact with the surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0012]     In another aspect, the invention features a method of implanting an endoprosthesis in a lumen of a subject. The method includes disposing a system in the lumen of the subject. The system includes a catheter, a sheath and a tip. The sheath at least partially surrounds the catheter.  
         [0013]     An implantable medical endoprosthesis is disposed between the catheter and the sheath. The tip is coupled to the distal end of the catheter, and the tip has a shaped surface in partial contact with the surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath. The method further includes at least partially retracting the sheath.  
         [0014]     In a further aspect, the invention features an implantable medical endoprosthesis delivery system. The system includes a catheter, a sheath and a tip. The sheath has a distal end with a surface, and the sheath at least partially surrounds the catheter so that an implantable medical endoprosthesis can be disposed therebetween. The tip is coupled to the distal end of the catheter. At least one slot of material is disposed between the surface of the tip and the surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0015]     In one aspect, the invention features a method of implanting an endoprosthesis in a lumen of a subject. The method includes disposing a system in the lumen of the subject. The system includes a catheter and a sheath. An implantable medical endoprosthesis is disposed between the catheter and the sheath. The system also includes a tip that is coupled to the distal end of the catheter. The system further includes at least one slot of material that is disposed between the surface of the tip and the surface of the distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath. The method further includes at least partially retracting the sheath.  
         [0016]     In another aspect, the invention features a method that includes passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath through an orifice in the sheath. The system includes the sheath and a catheter that is at least partially surrounded by the sheath, so that an implantable medical endoprosthesis can be disposed between the catheter and the sheath in a location. The orifice is between a distal end of a sheath and a location in the sheath that is adjacent a proximal end of the location for the implantable medical endoprosthesis.  
         [0017]     In a further aspect, the invention features a method that includes passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath through an orifice in the sheath. The system includes the sheath and a catheter that is at least partially surrounded by the sheath so that an implantable medical endoprosthesis can be disposed between the catheter and the sheath. The orifice in the sheath is at most about 100 millimeters from the distal end of the sheath.  
         [0018]     In one aspect, the invention features a method that includes passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath. The system includes the sheath, a catheter at least partially surrounded by the sheath so that an implantable medical endoprosthesis can be disposed between the catheter and the sheath, and a tip coupled to a distal end of the catheter. The tip has a surface that is in partial contact with a shaped surface of a distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0019]     In another aspect, the invention features a method that includes passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath. The system includes the sheath, a catheter at least partially surrounded by the sheath so that an implantable medical endoprosthesis can be disposed between the catheter and the sheath, and a tip coupled to a distal end of the catheter. The tip has a shaped surface that is in partial contact with a surface of a distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0020]     In a further aspect, the invention features a method that includes passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath. The system includes the sheath, and a catheter at least partially surrounded by the sheath so that an implantable medical endoprosthesis can be disposed between the catheter and the sheath. The system also includes a tip that is coupled to a distal end of the catheter and that has a surface. The system filter includes at least one slot of material that is disposed between the surface of the tip and a surface of a distal end of the sheath so that there is fluid communication between an interior region of the sheath and an exterior region of the sheath.  
         [0021]     In one aspect, the invention features a guide catheter that has a proximal end, a distal end, and at least one orifice between the proximal and distal ends of the guide catheter. The at least one orifice is at most about 100 millimeters from the distal end of the guide catheter.  
         [0022]     Embodiments can include one or more of the following features. The system can be configured so that, when the implantable medical endoprosthesis is disposed between the catheter and the sheath, the system can deliver the implantable medical endoprosthesis into a lumen of a subject.  
         [0023]     In some embodiments, a sheath can include a plurality of orifices, with at least some of the orifices being between the distal end of the sheath and the location in the sheath adjacent the proximal end of the implantable medical endoprosthesis.  
         [0024]     The implantable medical endoprosthesis can be, for example, a stent, a stent-graft or a vena cava filter.  
         [0025]     In some embodiments, the implantable medical endoprosthesis can have at least one strut with a maximum dimension that is greater than the maximum dimension of the at least one orifice.  
         [0026]     In certain embodiments, the-maximum dimension of the at least one orifice is about 0.02 inch or less (e.g., about 0.01 inch or less).  
         [0027]     A sheath can include multiple layers. One or more of the layers can be a support material (e.g., a mesh, a wire, a braided material). The implantable medical endoprosthesis can have at least one strut with a maximum dimension that is smaller than a maximum dimension of the at least one orifice in the sheath.  
         [0028]     The system can further include the implantable medical endoprosthesis between the catheter and the sheath.  
         [0029]     The implantable medical endoprosthesis can be a self-expanding implantable medical endoprosthesis. The implantable medical endoprosthesis can expand as the sheath is at least partially retracted.  
         [0030]     The implantable medical endoprosthesis can be a balloon expandable implantable medical endoprosthesis. The catheter can include an inflatable member, and the method can further include, after at least partially retracting the sheath, inflating the inflatable member to expand the implantable medical endoprosthesis. The system can further include a tip coupled to a distal end of the catheter.  
         [0031]     The at least one orifice can be at most about 100 millimeters from the distal end of the sheath, and/or the at least one orifice can be at least about one millimeter from the distal end of the sheath. The system can include a plurality of orifices, and at least some of the orifices can be at most about 100 millimeters from the distal end of the sheath.  
         [0032]     A shaped surface can be, for example, a scalloped surface or a serrated surface.  
         [0033]     In some embodiments, the system includes a plurality of slots of material.  
         [0034]     The at least one slot of material can be integral with the tip.  
         [0035]     The at least one slot of material can extend outwardly from the tip.  
         [0036]     The at least one slot of material can be integral with the sheath.  
         [0037]     The at least one slot of material can extend inwardly from the sheath.  
         [0038]     A portion of the sheath can surround (e.g., can be line fit to) a portion of the at least one slot of material.  
         [0039]     Passing a fluid from an interior of a sheath of an implantable medical endoprosthesis delivery system to an exterior of the sheath (e.g., through an orifice in the sheath) can remove substantially all gas from the interior of the sheath.  
         [0040]     Embodiments can include one or more of the following advantages.  
         [0041]     In certain embodiments, a system can be lubricated and/or purged (e.g., using a saline solution) prior to use without undesired separation of the sheath from the tip. For example, in some embodiments, a system can be lubricated and/or purged (e.g., using a saline solution) without the sheath flaring outwardly.  
         [0042]     In some embodiments, a system can be efficiently and/or effectively flushed (e.g., to lubricate the system). For example, in certain embodiments, a system can be thoroughly flushed using a relatively low number of flushing cycles.  
         [0043]     In certain embodiments, a system can exhibit enhanced medical device deployment performance. For example, by being properly lubricated, the sheath can be retracted in a relatively uniform manner, resulting in relatively high control over the positioning of the medical device (e.g., within the lumen of the subject).  
         [0044]     In certain embodiments, the systems can be flushed (e.g., prior to use in vivo) to purge or aspirate the systems of substantially all gas (e.g., air pockets and/or air bubbles). Features and advantages of the invention are in the description, drawings, and claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0045]      FIG. 1A  is a perspective view of an embodiment of a stent delivery system.  
         [0046]      FIG. 1B  is a cross-sectional view of the stent delivery system of  FIG. 1A .  
         [0047]      FIG. 1C  is an illustration of an embodiment of a method of flushing the stent delivery system of  FIGS. 1A and 1B .  
         [0048]      FIG. 2  is a perspective view of an embodiment of a stent delivery system.  
         [0049]      FIG. 3  is a perspective view of an embodiment of a stent delivery system.  
         [0050]      FIG. 4  is a cross-sectional view of an embodiment of a stent delivery system.  
         [0051]      FIG. 5A  is a perspective view of an embodiment of a stent delivery system.  
         [0052]      FIG. 5B  is an exploded view of the stent delivery system of  FIG. 5A .  
         [0053]      FIG. 5C  is a cross-sectional view of a component of the stent delivery system of  FIG. 5B , taken along line  5 C- 5 C.  
         [0054]      FIG. 5D  is a cross-sectional view of the stent delivery system of  FIG. 5A , taken along line  5 D- 5 D.  
         [0055]      FIG. 5E  is a cross-sectional view of the stent delivery system of  FIG. 5D , taken along line  5 E- 5 E.  
         [0056]      FIG. 5F  is a cross-sectional view of the stent delivery system of  FIG. 5D , taken along line  5 F- 5 F.  
         [0057]      FIG. 5G  is an illustration of an embodiment of a method of flushing the stent delivery system shown in  FIG. 5F .  
         [0058]      FIG. 5H  is an illustration of an embodiment of a method of flushing the stent delivery system shown in  FIG. 5E .  
         [0059]      FIG. 6A  is a perspective view of an embodiment of stent delivery system.  
         [0060]      FIG. 6B  is an exploded view of the stent delivery system of  FIG. 6A .  
         [0061]      FIG. 6C  is a side view of a distal tip of the stent delivery system of  FIGS. 6A and 6B .  
         [0062]      FIG. 6D  is a side view of the stent delivery system of  FIGS. 6A and 6B .  
         [0063]      FIG. 6E  is a side view of the stent delivery system of  FIGS. 6A and 6B .  
         [0064]      FIG. 7A  is a side view of an embodiment of a stent delivery system.  
         [0065]      FIG. 7B  is an exploded view of the stent delivery system of  FIG. 7A .  
         [0066]      FIG. 7C  is an illustration of an embodiment of a method of flushing the stent delivery system of  FIGS. 7A and 7B .  
         [0067]      FIG. 8A  is a side view of an embodiment of a stent delivery system.  
         [0068]      FIG. 8B  is an exploded view of the stent delivery system of  FIG. 8A .  
         [0069]      FIG. 8C  is an illustration of an embodiment of a method of flushing the stent delivery system of  FIGS. 8A and 8B . 
     
    
     DETAILED DESCRIPTION  
       [0070]     In general, the delivery systems are designed to provide fluid communication between the interior and exterior regions of the sheath, particularly toward the distal region of the sheath. It is believed that such systems can reduce the likelihood that the sheath will undergo undesired separation from the tip during flushing of the system. For example, allowing fluid communication between the interior and exterior regions of the sheath can reduce gas build up in the interior region of the sheath during flushing. Certain embodiments of the systems are disclosed below.  
         [0071]     In some embodiments, fluid communication between the interior and exterior regions of the sheath is provided by one or more holes in the sheath. For example,  FIGS. 1A and 1B  show a stent delivery system  10  that includes a distal tip  12 , a catheter  20  and a sheath  22  having holes  30  and  32 . Sheath  22  surrounds catheter  20  so that a stent  26  (shown in  FIG. 1C ) can be disposed in a space  24  between catheter  20  and sheath  22 . Distal tip  12  includes a head portion  16  and a proximal portion  18 . Head portion  16  includes a ledge  17  that is in contact with a distal end  36  of sheath  22 . As shown in  FIG. 1C , when system  10  is flushed with a fluid (e.g., a saline solution), the fluid (depicted as arrows) travels through space  24  and exits system  10  through holes  30  and  32 .  
         [0072]     In general, holes  30  and  32  are positioned toward distal end  36  of sheath  22 . In some embodiments, holes  30  and  32  are located between distal end  36  of sheath  22  and a location  19  in sheath  22  that is adjacent a proximal end  27  of stent  26 . In certain embodiments, holes  30  and  32  are located at least about one millimeter (e.g., at least about two millimeters, at least about five millimeters, at least about 10 millimeters, at least about 15 millimeters, at least about 20 millimeters) from distal end  36  of sheath  22 , and/or at most about 100 millimeters (e.g., at most about 90 millimeters, at most about 80 millimeters, at most about 70 millimeters, at most about 60 millimeters) from distal end  36  of sheath  22 .  
         [0073]     Generally, holes  30  and  32  can be dimensioned as desired. In certain embodiments, holes  30  and/or  32  have a maximum dimension (e.g., a diameter) of at most about 0.05 inch (e.g., at most about 0.03 inch, at most about 0.02 inch, at most about 0.01 inch, at most about 0.005 inch). In some embodiments, holes  30  and/or  32  are dimensioned to a component (e.g., a strut) of stent  26  from protruding through the holes  30  and  32 . In such embodiments, holes  30  and  32  can have, for example, a maximum dimension that is smaller than a maximum dimension of the component (e.g., the strut) of stent  26 . As an example, a coronary stent delivery system (e.g., having struts with dimensions of 0.004 inch×0.004 inch) can include a sheath that has one or more holes with a maximum dimension of, for example, 0.003 inch (e.g., one or more square holes with dimensions of 0.003 inch×0.003 inch). As another example, a peripheral stent delivery system (e.g., having struts with dimensions of 0.008 inch×0.008 inch) can include a sheath that has, one or more holes with a maximum dimension of, for example, 0.007 inch (e.g., one or more square holes with dimensions of 0.007 inch×0.007 inch).  
         [0074]     In some embodiments, a sheath can have one or more holes that are partially covered by a strip of material across the hole(s). For example,  FIG. 2  shows a sheath  52  with an opening  50  (e.g., a hole) having a strip of material  54  across hole  50 . Typically, strip  54  is attached (e.g., adhesive-bonded) to a wall  56  of sheath  52 . Strip  54  can be formed of the same material as sheath  50  or a different material from sheath  50 . Examples of materials from which strip  54  can be formed include polymers (e.g., PEBAX, Hytrel, Arnitel, Nylon) and/or metals (e.g., stainless steel, platinum, gold, tantalum). In certain embodiments the strip of material can be integral with (e.g., formed of the same material as) the sheath. For example,  FIG. 3  shows a sheath  60  with an opening  62  is partially covered by a strip of material  64  that is integrally formed with a wall  66  of sheath  60 . In embodiments in which a hole in a sheath is partially covered by a strip of material, the hole can have a maximum dimension (e.g., a maximum diameter) of at least about 0.020 inch (e.g., at least about 0.025 inch, at least about 0.030 inch) and/or at most about 0.060 inch (e.g., at most about 0.050 inch, at most about 0.040 inch).  
         [0075]     In certain embodiments, the sheath can include multiple layers of material. In such embodiments, one or more of the layers can be formed of an open support material (e.g., a mesh, a wire, a braided, material). Typically, the support material is covered by one or more of the other layers of material.  FIG. 4  shows a stent delivery system  500  with a sheath  502  that includes an outer layer (e.g., a PEBAX layer)  504 , a middle layer (e.g., a metal braided layer)  506 , and an inner layer (e.g., a PTFE layer)  508 . Sheath  502  includes holes  510  and  512  that extend in layers  504  and  508  but not in layer  506 . Because of the open nature of layer  506 , there is fluid communication between an interior region  514  of sheath  502  and an exterior region  516  of sheath  502  via holes  510  and  512 .  
         [0076]     In general, a hole can be formed in a sheath by any of a number of different methods. Such methods include, for example, mechanical drilling, punching, cutting, and laser drilling/ablation, and chemical etching.  
         [0077]     In some embodiments, fluid communication between the interior and exterior regions of the sheath is provided by disposing slots of material between the distal end of the sheath and the distal tip. For example,  FIGS. 5A-5F  show a stent delivery system  110  that includes a distal tip  112 , a catheter  120 , and a sheath  122  that partially surrounds catheter  120  so that an implantable medical endoprosthesis (e.g., a stent) can be disposed in a space  124  between catheter  120  and sheath  122 . System  110  also includes a distal tip  112  with a head portion  116  that is integral with a proximal portion  118 . Slots of material  130 ,  132 ,  134 , and  136  are attached to sheath  122  and disposed between sheath  122  and portion  118  of distal tip  112 . The outer diameter of portion  118  is about the same as distance “d” so that the slots and portion  118  form a line fit. Outlets  151  are located at a distal end  150  of sheath  122  where slots  130 ,  132 ,  134 , and  136  are not present. As shown in  FIGS. 5G and 5H  (which correspond to the views of  FIGS. 5F and 5E , respectively), a flushing fluid (depicted as arrows) can travel through space  124  between catheter  120  and sheath  122 , and exit sheath  122  via openings  151  . The line fit between the slots and portion  118  can prevent distal end  150  of sheath  122  from extending outwardly during flushing.  
         [0078]     In some embodiments, the slots of material can be attached to the distal tip of a stent delivery system. For example,  FIGS. 6A-6E  show a stent delivery system  160  that includes a distal tip  162 , a catheter  166 , and a sheath  164  that partially surrounds catheter  166  so that an implantable medical endoprosthesis (e.g., a stent) can be disposed in a space  180  between catheter  166  and sheath  164 . System  160  also includes a distal tip  162  with a head portion  168  that is integral with a proximal portion  170 . Slots of material  172 ,  174 ,  176 , and  178  are attached to portion  170 . Outlets  161  are located at a distal end  165  of sheath  164  where slots  172 ,  174 ,  176 , and  178  are not present. The slots and portion  170  are line fit, which can prevent distal end  165  of sheath  164  from extending outwardly during flushing.  
         [0079]     In general, the dimensions of a slot of material can be selected as desired. In some embodiments, a slot of material can have a length “L” (shown in  FIG. 6C ) of at least about 0.050 inch (e.g., at least about 0.060 inch, at least about 0.070 inch) and/or at most about 0.100 inch (e.g., at most about 0.090 inch, at most about 0.080 inch). In certain embodiments, a slot of material can have a thickness “T” (shown in  FIG. 6C ) of at least about 0.015 inch (e.g., at least about 0.01  0  inch, at least about 0.005 inch) and/or at most about 0.020 inch (e.g., at most about 0.017 inch, at most about 0.015 inch).  
         [0080]     The slots of material can be formed of, for example, a polymer, a metal, or a combination of these materials. Examples of polymers include PEBAX, Arnitel, Hytrel, and combinations of these materials. In some embodiments, one or more polymers can include a filler (e.g., a radiopaque material). Examples of metals include stainless steel, platinum, gold, tantalum, and MP35N (a nickel-cobalt-chromium-molybdenum alloy). In some embodiments, the slots of material can be formed of the same material as the distal tip and/or the sheath.  
         [0081]     Generally, a slot of material can be attached to a tip or sheath using any desired method. Examples of methods include adhesive bonding and/or heat bonding (e.g., using laser heating, using RF heating). In some embodiments, a slot of material can be integrally formed (e.g., extruded or molded) with the sheath or distal tip.  
         [0082]     In certain embodiments, fluid communication between the interior and exterior regions of the sheath is provided by shaping a surface of the tip and/or the surface of the distal end of the sheath. For example,  FIGS. 7A-7C  show a stent delivery system  200  that includes a distal tip  204 , a catheter  207 , and a sheath  209  that partially surrounds catheter  207  so that an implantable medical endoprosthesis (e.g., a stent) can be disposed in a space  202  between catheter  207  and sheath  209 . Distal tip  204  has a head portion  203  and a proximal portion  205 . Head portion  203  has a scalloped (shaped) surface  206  so that, when system  200  is assembled, portions of surface  206  contact a surface  208  of a distal end  211  of sheath  209 , defining gaps  210  between surface  208  and the portions of surface  206  that do not contact surface  208 . As shown in  FIG. 7C , when a flushing fluid (depicted as arrows) travels through space  202 , the fluid can travel from space  202  to the exterior of sheath  209  via gaps  210 . The presence of gaps  210  can prevent distal end  211  of sheath.  209  from extending outwardly during flushing.  
         [0083]     While a system has been shown in which a surface of the tip has a scalloped shape, surfaces with other shapes can also be used. For example, the surface of the tip can be a serrated surface, a wavy surface, a pronged surface, or a surface having other types of protrusions (e.g., square protrusions, elliptical protrusions).  
         [0084]     In some embodiments, the surface of the distal end of the sheath, rather than a surface of the tip, can be shaped. For example,  FIGS. 8A and 8B . show a stent delivery system  300  that includes a distal tip  304 , a catheter  309 , and a sheath  308  that partially surrounds catheter  309  so that an implantable medical endoprosthesis (e.g., a stent) can be disposed in a space  302  between catheter  309  and sheath  308 . Sheath  308  has a distal end  311  with a serrated (shaped) surface  310  so that, when system  300  is assembled, portions of surface  310  contact a surface  306  of tip  304 , defining gaps  312  between surface  306  and the portions of surface  310  that do not contact surface  306 . As shown in  FIG. 8C , when a flushing fluid (depicted as arrows) travels through space  302 , the fluid can travel from space  302  to the exterior of sheath  308  via gaps  310 . The presence of gaps  310  can prevent distal end  311  of sheath  209  from extending outwardly during flushing.  
         [0085]     The surface of a tip and/or a sheath can generally be formed using any desired method. Examples of methods include cutting, heating, and laser-drilling a non-shaped (flat) surface. In some embodiments, a shaped surface can be molded and/or extruded as part of a sheath and/or distal tip. In certain embodiments, a protrusion can be attached to a non-shaped (flat) surface to provide a shaped surface.  
         [0086]     The distal tip in stent delivery system is typically formed of a polymer. Alternatively or additionally, the sheath in a stent delivery system can be made of, for example, a polymer. Examples of polymers include the PEBAX family of polymers, silicones, thermoplastic polymers, thermoset polyrmers, Hytrel, Arnitel, PEEK (polyetheretherketone), and HDPE (high density polyethylene).  
         [0087]     The catheter in a stent delivery system can be made of, for example, PEBAX, Hytrel, Arnitel, PEEK, and/or HDPE.  
         [0088]     While certain embodiments have been described, the invention is not so limited.  
         [0089]     As an example, while embodiments have been described in which a sheath includes two holes, in some embodiments, a sheath can include more or fewer than two holes. For example, a sheath can include one hole or three or more holes (e.g., four holes, five holes, six holes, seven holes, eight holes, nine holes, ten holes).  
         [0090]     As another example, while embodiments have been described in which the holes in a sheath have had the same shape and/or size, in certain embodiments, at least some of the holes can have different shapes and/or sizes from each other.  
         [0091]     As a further example, while embodiments have been described in which the holes in a sheath are all substantially the same distance from the distal end of the sheath, in some embodiments, at least some of the holes can be located at different distances from the distal end of the sheath.  
         [0092]     As another example, while embodiments have been described in which the holes in the sheath are circular, in certain embodiments, at least some of the holes in a sheath can be noncircular (e.g., rectangular, square, triangular, elliptical).  
         [0093]     As an additional example, in some embodiments, a hole in a sheath can be partially covered by multiple (e.g., two, three, four, five) strips of material.  
         [0094]     As a further example, while rectangular slots have been described, slots of other shapes (e.g., cubic, cylindrical, spherical) can also be used.  
         [0095]     As a farther example, while systems have been described that include four slots of material, in some embodiments, the number of slots can be greater than four or less than four. For example, a system can include one slot, two slots, three slots, five slots, six slots, seven slots, eight slots, nine slots, ten slots. In embodiments in which a stent delivery system includes multiple slots of material, the slots can all have the same size and/or shape, or can have different sizes and/or shapes.  
         [0096]     As an additional example, both the surface of the distal end of the sheath and a surface of the distal tip can be shaped.  
         [0097]     As another example, while systems have been described for delivering stents, in some embodiments, the systems can be used to deliver different implantable medical endoprostheses. In some embodiments, the system can be a stent-graft delivery system, In certain embodiments, the system can be a vena cava filter delivery system.  
         [0098]     As described above, in some embodiments, the sheath can include one layer of material or three layers of material. However, in certain embodiments, the sheath can include a different number of layers of material (e.g., two layers of material, four layers of material, five layers of material). In embodiments in which the sheath is multilayered, the layers can be the same as, or different from, each other. In some cases, one or more of the layers in a sheath can be a support (e.g., mesh, wire, braided material) layer. In embodiments in which the sheath is multilayered, one or more of the holes can extend through the support material.  
         [0099]     As a further example, embodiments have been described in which the sheath of an implantable medical endoprostheses delivery system has one or more holes located therein, other embodiments are possible. As an example, a guide catheter (e.g., a guide catheter having the above-described multiple layer arrangement) can have one or more orifices located therein. The holes can be positioned toward the distal end of the guide catheter as described above.  
         [0100]     Other embodiments are in the claims.