Patent Publication Number: US-2021177594-A1

Title: Medical Device Delivery System and Methods of Delivering a Medical Device

Description:
BACKGROUND 
     Field 
     Certain embodiments of the present invention are related to medical device delivery systems and methods of delivering a medical device. 
     Background Art 
     Existing medical device delivery systems, such as those for use in percutaneous medical procedures, can allow a medical device to be delivered through a patient&#39;s vascular to a delivery site where it can be implanted within a patient. In some procedures a medical device in the form of a valve prosthesis can be compacted and loaded onto a delivery device for advancement through a patient&#39;s vasculature in a transfemoral, transapical, and/or transatrial procedure. There is a continuous need for improved delivery systems for use in percutaneous and other delivery techniques. 
     BRIEF SUMMARY 
     In some embodiments, a medical device delivery system can include a dilator including a tip having a taper in a distal direction, a coupler, and a flap that radially protrudes from the tip. The flap can be configured to bend against a body lumen to cover at least a portion of the delivery system when the dilator is tracked through the body lumen. 
     In some embodiments, a medical device delivery system can include a dilator including a tip having a lumen and a coupler having a lumen. The coupler can be configured to securely connect to the tip such that the lumen of the tip is aligned with the lumen of the coupler to allow a guide wire to pass therethrough. Methods for loading a medical device into a delivery catheter are also disclosed. 
     In some embodiments, a method of loading a medical device into a delivery catheter can include securing a coupler to a delivery catheter shaft, the shaft having a lumen for receiving the medical device, crimping the medical device to a diameter permitting the medical device to be loaded into the shaft lumen, loading the medical device into the shaft lumen, and securing a dilator tip to the coupler after the medical device is loaded into the shaft lumen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying figures, which are incorporated herein, form part of the specification and illustrate embodiments of percutaneous medical procedure systems and related methods. Together with the description, the figures further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make, use, and implant the valve prosthesis described herein. 
         FIG. 1  illustrates a front view of a medical device that can be used in one or more of the systems described herein. 
         FIG. 2  illustrates a delivery system in accordance with one embodiment. 
         FIGS. 3 a - c  and 4 a - c    illustrate the delivery system of  FIG. 2  in various states. 
         FIG. 5  illustrates a cross-sectional view of a portion of the delivery system of  FIG. 2 . 
         FIG. 6  illustrates a cross-sectional view of a portion of the delivery system of  FIG. 2  in a body lumen. 
         FIG. 7  illustrates a front perspective view of a dilator in accordance with one embodiment. 
         FIG. 8  illustrates a side view of the dilator of  FIG. 7 . 
         FIG. 9  illustrates an exploded view of the dilator of  FIG. 7 . 
         FIG. 10  illustrates a cross-sectional view of a dilator in accordance with one embodiment in a first state. 
         FIG. 11  illustrates a cross-sectional view of the dilator of  FIG. 10  in a second state. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying figures which illustrate several embodiments. Other embodiments are possible. Modifications can be made to the embodiments described herein without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not meant to be limiting. 
       FIG. 1  illustrates a medical device  10  that can be used in one or more of the systems described herein. In some embodiments, medical device  10  can be in the form of a prosthetic heart valve including a frame  12  attached to a valve body  14 . In some embodiments, valve body  14  can be formed, for example, from one or more of biocompatible synthetic materials, synthetic polymers, autograft tissue, homograft tissue, xenograft tissue, or one or more other suitable materials. In some embodiments, valve body  14  can be formed, for example, from bovine, porcine, equine, ovine, and/or other suitable animal tissues. In some embodiments, valve body  14  can be formed, for example, from heart valve tissue, pericardium, and/or other suitable tissue. In some embodiments, valve body  14  can comprise one or more valve leaflets, such as for example, a tri-leaflet bovine pericardium valve, a bi-leaflet valve, or another suitable valve. 
     A suitable medical device  10  is not limited to prosthetic heart valves. In some embodiments, medical device  10  can be a device configured to be transported via a delivery catheter. In some embodiments, medical device  10  can be an expandable device, such as, for example, a percutaneously delivered device configured to be compacted and loaded onto a delivery catheter for advancement through a natural or artificial body lumen, such as for example through a patient&#39;s vasculature. In some embodiments, medical device  10  is not expandable. In some embodiments, medical device  10  is not designed to be implanted within the patient&#39;s body. In some embodiments, medical device  10  can be an embolic filter. In some embodiments, medical device  10  can be a tool that can be used, for example, to retrieve an item from inside a patient. 
       FIG. 2  illustrates a delivery system  16  in accordance with one embodiment of the present invention. In some embodiments, system  16  can be used in one or more percutaneous delivery procedures. For example, in some percutaneous procedures, a valve prosthesis can be compacted and loaded onto a delivery device, such as for example a catheter, for advancement through a patient&#39;s vasculature. In some embodiments, system  16  can be configured for use in illiofemoral, apical, radial, direct aortic, and subclavian/axillary entry locations. System  16  can be configured to allow access from multiple locations per procedure (e.g. bilateral femoral access). In some embodiments, system  16  can be configured to deliver medical device  10  through an artery or vein, a femoral artery, a femoral vein, a jugular vein, a subclavian artery, an axillary artery, an aorta, an atrium, and/or a ventricle. System  16  can be configured to deliver medical device  10  via a transfemoral, transapical, transseptal, transatrial, transventrical, or transaortic procedure. In some embodiments, one or more components or portion of components of system  16  can be configured to flex to facilitate the traversal of system  16  through a body lumen during a delivery procedure. In some embodiments, one or more components of system  16  or portions thereof can include a curved outer surface and/or shape to facilitate movement through a curved body lumen. 
     As described above, in some embodiments, system  16  can be configured for use in a transfemoral delivery procedure. In one example of such a procedure, a delivery device including a prosthetic heart valve can be advanced in a retrograde manner through a patient&#39;s femoral artery and into the patient&#39;s descending aorta. A catheter can then be advanced under fluoroscopic guidance over the simulated aortic arch, through the ascending aorta, into the left ventricle, and mid-way across the defective aortic valve. Once positioning of the catheter is confirmed, the valve prosthesis can be deployed within the valve annulus. The valve prosthesis can then expand against the simulated annulus. In some embodiments, as the valve prosthesis is expanded, it can trap leaflets against the annulus, which can retain the native valve in a permanently open state. 
     As described above, in some embodiments, system  16  can be configured for use in a transapical delivery procedure. In one example of such a procedure, a trocar or overtube can be inserted into a patient&#39;s left ventricle through an incision created in the apex of the patient&#39;s heart. A dilator can be used to aid in the insertion of the trocar. In this approach, the native valve (for example, the mitral valve) can be approached downstream relative to blood flow. The trocar can be retracted sufficiently to release the self-expanding valve prosthesis. The dilator can be presented between the leaflets. The trocar can be rotated and adjusted to align the valve prosthesis in a desired alignment. The dilator can be advanced into the left atrium to begin disengaging the proximal section of the valve prosthesis from the dilator. 
     In some embodiments, system  16  can be configured for use in a transatrial delivery procedure. In one example of such a procedure, a dilator and trocar can be inserted through an incision made in the wall of the left atrium of the heart. The dilator and trocar can then be advanced through the native valve and into the left ventricle of the heart. The dilator can then be withdrawn from the trocar. A guide wire can be advanced through the trocar to the point where the valve prosthesis comes to the end of the trocar. The valve prosthesis can be advanced sufficiently to release a self-expanding valve prosthesis from the trocar. The trocar can be rotated and adjusted to align the valve prosthesis in a desired alignment. The trocar can be withdrawn completely from the heart such that the valve prosthesis self-expands into position and can assume the function of the native valve. 
     The few example procedures described above are not intended to be exhaustive. It is understood that not every act need be performed and additional acts can be included as would be apparent to one of ordinary skill in the art. In addition, the acts can be reordered as desired. Other medical devices and delivery techniques can be used with any of the parts described herein. It is further understood that the above delivery routes are merely exemplary and that other suitable delivery routes can be employed. The terms “delivery” and “delivery system” as used herein is intended to refer broadly to positioning a medical device at a desired location and related systems. Such terms do not necessitate a system that actually deposits a medical device at a site, such as for example a device that can be used to implant a prosthetic heart valve. The term “delivery system” can cover, for example, a system that temporarily positions a medical device at a desired location. For example, the delivery system can be used to position an embolic filter at a desired location within a patient&#39;s vascular for a period of time before removing the embolic filter. 
     The delivery system  16  of  FIG. 2  can include a handle  17 , one or more retractable sheaths  19  and  21 , a hub  23 , an introducer  25 , a capsule  27 , and a dilator  18 . In some embodiments, dilator  18  can be configured to dilate a tube, cavity, and/or opening in the body to facilitate introduction of system  16  for a delivery procedure. In some embodiments, dilator  18  can be configured to facilitate removal of system  16  following delivery of medical device  10 . 
     In some embodiments, dilator  18  can be connected to handle  17  via one or more inner shafts (see, for example, shaft  29  described below with respect to  FIG. 5 ). In some embodiments, one or more of handle  17 , retractable sheaths  19  and  21 , hub  23 , introducer  25 , and capsule  27  can be slidably disposed over one or more of the inner shafts. In some embodiments, capsule  27  can be configured to releasably engage with dilator  18 . In some embodiments, a distal edge  33  of capsule  27  can abut a proximal end of dilator  18 . 
     In some embodiments, capsule  27  can be configured to house medical device  10  for delivery via system  16 . Capsule  27  can include a lumen (shown for example in  FIG. 5 ) that is configured to receive the entirety of medical device  10  or a portion thereof. In some embodiments, capsule  27  can be in the form of a tube or another suitable shape. In some embodiments, capsule  27  can be in the form of a sheath. In some embodiments, a portion of capsule  27  can be tapered. For example, in some embodiments, one or both of a proximal and distal end portions of capsule  27  can be tapered. 
     In some embodiments, capsule  27  can be configured to move relative to medical device  10  to partially or fully release medical device  10  for delivery by system  16 . In some embodiments, system  16  is configured to move capsule  27  relative to medical device  10  by moving capsule  27  from a first position to a second position while medical device  10  is relatively stationary. For example, in some embodiments, capsule  27  can be configured to move in a proximal direction relative to medical device  10  (towards handle  17 ) to partially or fully expose medical device  10  to allow for delivery medical device  10 . In some embodiments, system  16  is configured to move capsule  27  relative to medical device  10  by moving medical device  10  from a first position to a second position while capsule  27  is relatively stationary. For example. In some embodiments, medical device  10  can be pushed relative to capsule  27  in a distal direction to partially or fully expose medical device  10  for delivery in system  16 . 
     In some embodiments, movement of capsule  27  can be automatically or manually actuated. In some embodiments, handle  17  can include a control knob  37  configured to retract capsule  27 . In some embodiments, movement of capsule  27  can be controlled by a user, such as by rotating control knob  37  on handle  17  or via another suitable actuator. In some embodiments, one or more portions of system  16  can include a flushing port  39 , which in some embodiments can be configured to maintain hemostasis during a medical procedure. Flushing port  39  can be connected to handle  17 , or another suitable portion of system  16 . In some embodiments, one or more portions of system  16 , such as for example an exterior of capsule  27  can be coated with a biocompatible lubricant. 
     In some embodiments, hub  23  can include an integrated hemostasis control feature. Hub  23  can be connected to introducer  25  and can be configured to move introducer  25  by sliding hub  23  distally towards dilator  18 . In some embodiments, hub  23  can include a feature, such as for example a spring-loaded button, that can be configured to avoid accidental movement of hub  23  during a procedure. 
     In some embodiments, introducer  25  can be in the form of a flexible sheath. In some embodiments, introducer  25  can be used to push capsule  27  against dilator  18  after medical device  10  has been delivered. In some embodiments, introducer  25  can be configured to cover the exposed edges of capsule  27 , which in some embodiments can facilitate retraction through the deployed prosthesis. In some embodiments, once medical device  10  is released and expands against a body lumen, a user can slide hub  23  in a distal direction. System  16  can be configured such that distal movement of hub  23  will move introducer  25  in a distal direction. In some embodiments, system  16  is configured such that distal movement of introducer  25  will thereby slide capsule  27  to engage a proximal end of dilator  18 . 
     As described above, in some embodiments, system  16  can be configured for use in a percutaneous delivery procedure including a medical device that is compacted and loaded into system  16  for advancement through a patient&#39;s vasculature.  FIGS. 3 a - c  and 4 a - c    illustrate various stages of one example of a delivery procedure. In particular,  FIG. 3 a    illustrates delivery system  16  with medical device  10  fully housed within capsule  27 .  FIG. 3 b    illustrates sheath  19  and capsule  27  partially retracted to expose a portion of medical device  10 .  FIG. 3 c    illustrates sheath  19  and capsule  27  further retracted to further expose medical device  10 .  FIG. 4 a    illustrates sheath  19  and capsule  27  completely retracted to fully expose medical device  10 .  FIGS. 4 b    and  4 C illustrate stages of capsule  27  being returned to dilator  18  after delivery of medical device  10 . In particular,  FIG. 4 b    illustrates delivery system  16  with capsule  27  partially returned to dilator  18 .  FIG. 4 c    illustrates delivery system  16  with capsule  27  engaged with dilator  18  with system  16  ready to be retracted from the body lumen. In some embodiments, capsule  27  does not engage with dilator  18  before system  16  is retracted from the body lumen. 
       FIG. 5  illustrates a cross-sectional view of a medical device delivery system  16  in accordance with one embodiment. As described above, delivery system  16  can include medical device  10 , dilator  18 , and capsule  27 . System  16  can further include a shaft  29  and a guide wire  22 . Dilator  18  and shaft  29  can include respective lumens  24  and  43  formed therein for receiving guide wire  22  such that dilator  18  and shaft  29  are slidably disposed relative to guide wire  22 . In some embodiments, medical device  10  can be crimped around shaft  29 . 
     In some conditions, an edge  33  of capsule  27  can align with dilator  18  such that it allows for a substantially continuous surface with dilator  18 . However, in other conditions, such as while traversing a body lumen, a gap can be created between dilator  18  and edge  33  of capsule  27 . In some embodiments, such a gap can be formed as a result of capsule  27  “fish mouthing”, which can occur when a portion of edge  33  is bent in a shape resembling an open fish mouth. In some cases, a gap between dilator  18  and capsule  27  can undesirably scrape an inside of a body lumen. In some cases, a gap between dilator  18  and capsule  27  can cause damage to one or more of capsule  27 , dilator  18 , medical device  10 , or another component of system  16 . 
     In order to avoid complications relating to fish mouthing, or for other advantages, delivery system  16  can be configured to cover a gap formed between capsule  27  and dilator  18  or between other components of system  16 . For example, in some embodiments, dilator  18  can include flaps  32  that are configured to cover edge  33  of capsule  27  as system  16  traverses through a body lumen. In some embodiments, flaps  32  can be configured to prevent catching or snagging of the system during implantation or removal of the medical device. For example, in some embodiments, a proximal end of dilator  18  can cover an opening formed by a lumen of capsule  27 . In some embodiments, flaps  32  can flex down over a portion of dilator  18  to keep a smooth transition between dilator  18  and capsule  27 . In some embodiments, flaps  32  can be configured so that when medical device  10  traverses through a body lumen, one of flaps  32  can be on the outside curvature of medical device  10 . 
     In some embodiments, flaps  32  can reduce or eliminate certain effects when recrossing a native valve, such as a native aortic valve, after resheathing. For example, when some dilators recross a native valve, a distal edge of the dilator or another component can flare out. In some cases, the flared dilator can make it difficult for a physician to cross through a native valve. In some embodiments, flaps  32  can flex down over a portion of dilator  18 . In some embodiments, this can provide a smooth transition between dilator  18  and capsule  27 , which in some cases can facilitate tracking through a native valve. 
     In some embodiments, dilator  18  can be assembled such that flaps  32  protrude from dilator  18  at an angle of approximately 90 degrees from axial direction  64 . In some embodiments, flaps  32  protrude from dilator  18  at an angle greater than or less than 90 degrees, such as for example approximately 30 degrees, approximately 45 degrees, approximately 120 degrees, or approximately 150 degrees. In some embodiments, one of flaps  32  can protrude at a first angle, such as for example, approximately 90 degrees, and another of flaps  32  can protrude at a second and different angle, such as for example, approximately 30 degrees. In some embodiments, flaps  32  can be made of a thin film of polymer. In some embodiments, flaps  32  can be configured so that they are flexible enough to bend towards first portion  28  and/or second portion  30  of dilator  18  when system  16  is tracked through a body lumen. In some embodiments, flaps  32  can be stiff enough so that flaps  32  straighten back out to be perpendicular to axial direction  64  when flaps  32  are no longer pressed towards first portion  28  or second portion  30 . 
     In some embodiments, flaps  32  are configured to bend so that flaps  32  are substantially parallel to capsule  27 . As shown for example in  FIG. 9 , flaps  32  can be configured to bend towards and over capsule  27  when delivery system  16  is moved relative to a body lumen in a first direction, such as axial direction  64 . In some embodiments, this direction can correspond to a direction that dilator  18  moves when medical device  10  is being delivered to a delivery site. 
     In some embodiments, flaps  32  can additionally be configured to bend towards first portion  28  when delivery system  16  is moved in a direction opposite to the first direction. In some embodiments, the direction opposite to the first direction can correspond to a direction in which dilator  18  moves when delivery system  16  is being retracted from a patient. In some embodiments, an ability of flaps  32  to bend towards first portion  28  can facilitate removing dilator  18  from a body lumen. In some embodiments, flaps  32  can bend towards second portion  30  when dilator  18  is moved towards a delivery site and then be inverted to bend towards first portion  28  when dilator  18  is being retracted. In some embodiments, flaps  32  are configured to only bend in one direction. 
       FIG. 6  illustrates a cross-sectional view of delivery system  16  bent within a body lumen  31 . As shown therein, as dilator  18  bends relative to capsule  27 , flap  32  covers edge  33  of capsule  27 . 
       FIGS. 7-9  illustrate various views of dilator  18  in accordance with one embodiment. In particular,  FIG. 7  illustrates a front perspective view of dilator  18 ,  FIG. 8  illustrates a side view of dilator  18 , and  FIG. 9  illustrates an exploded view of dilator  18 . In some embodiments, dilator  18  can include a dilator body  35  having a first portion  28  and second portion  30 . Dilator  18  can further include one or more flaps  32 . In some embodiments, first portion  28  is a distal portion of dilator  18  and second portion  30  is a proximal portion of dilator  18 . In some embodiments, first portion  28  and second portion  30  can be two or more pieces attached together. In some embodiments, first portion  28  and second portion  30  can be a monolithic piece of material. In some embodiments, flaps  32  can be ends of a monolithic piece of material. In some embodiments, first portion  28  and second portion  30  abut at a junction  34 . In some embodiments, first portion  28  and second portion  30  can be removably attached. In some embodiments, first portion  28  and/or second portion  30  can include respective tapered outer surfaces. In some embodiments, an outer surface of first portion  28  can be configured to induce dilation in a body lumen or another site in a patient. 
     In some embodiments, first portion  28  can include a lumen configured to allow guide wire  22  to pass therethrough. In some embodiments, second portion  30  can include a lumen configured to allow guide wire  22  to pass therethrough. In some embodiments, the lumen of first portion  28  and the lumen of second portion  30  can be configured to align to form a single lumen  24  that can allow guide wire  22  to pass through both first portion  28  and second portion  30 . In some embodiments, only one of first portion  28  and second portion  30  includes a lumen. 
     In some embodiments, such as for example the embodiment shown in  FIG. 9 , flaps  32  can be the ends of a single piece  46  of flap material that protrudes from dilator  18  on either side of axis  48  of dilator  18 . In some embodiments, piece  46  can be sandwiched between first portion  28  and second portion  30  of dilator  18 . In some embodiments, piece  46  can be hourglass shaped, as shown for example in  FIG. 9 . In some embodiments, a central portion  50  of piece  46  can be narrower than flaps  32  such that flaps  32  include flared distal ends. In some embodiments, central portion  50  can be equal to or wider than flaps  32 . In some embodiments, a narrower portion of piece  46  can facilitate the bending of flaps  32  around first portion  28  and/or second portion  30 . In some embodiments, piece  46  can be substantially rectangular, circular, elliptical, or a suitable non-geometric shape. In some embodiments, piece  46  can include an opening  52  that corresponds to lumen  24  of dilator  18 . 
     In embodiments including multiple flaps  32 , flaps  32  can be formed from separate pieces of flap material. For example, in some embodiments, a left flap can be attached to a left side of dilator  18  and a right flap can be attached to a right side of dilator  18 . 
     In some embodiments, dilator  18  includes only a single flap  32 . In some embodiments, dilator  18  includes more than two flaps. For example, in some embodiments, piece  46  can be X-shaped, with four flaps protruding from an outer surface of dilator  18 . In some embodiments, flaps  32  can include an end  54  that can be substantially flat, shown for example in  FIG. 9 . In some embodiments, end  54  can be rounded, or another desired shape. 
     As further shown in  FIG. 9 , in some embodiments, one or both of first portion  28  and second portion  30  can include one or more extensions  56  and  58  which can correspond to one or more openings  60 ,  62  for securing flaps  32 . In some embodiments, first portion  28  and second portion  30  are two pieces that are sandwiched around flaps  32  and bonded together. In some embodiments, first portion  28  and second portion  30  are molded around flaps  32  as one piece. In some embodiments, dilator  18  can include recesses where flaps  32  protrude to ensure that when first portion  28  is inserted through an introducer, flaps  32  can fold down within the recess so that dilator  18  can achieve a desired diameter, such as for example 19 Fr or another suitable diameter. 
       FIGS. 10-11  illustrate a dilator  66  in accordance with one embodiment. In particular,  FIG. 10  illustrates a perspective cross-sectional view of dilator  66  in a first state and  FIG. 11  illustrates a side cross-sectional view of dilator  66  in a second state. Dilator  66  can be used, for example, in delivery system  16 . In some embodiments, dilator  66  can be used for another delivery system. Dilator  66  can include a tip  68  and a coupler  70 . In some embodiments, both tip  68  and coupler  70  include respective lumens  72  and  74  formed therein. In some embodiments, lumens  72  and  74  can be configured to align to allow a guide wire to pass therethrough. In some embodiments, tip  68  includes an arm  86  that can flex to securely receive coupler  70 . In some embodiments, tip  68  can include an outer surface  90  that is tapered. In some embodiments, tip  68  includes a cavity  88  configured to receive coupler  70 . In some embodiments, cavity  88  can be configured to partially receive coupler  70 . In some embodiments, cavity  88  can be configured to receive the entirety of coupler  70 . 
     In  FIG. 10 , coupler  70  is shown disengaged from tip  68 . However, as shown for example in  FIG. 11 , tip  68  and coupler  70  can be joined together to restrain movement between coupler  70  and dilator  66 . For example, in some embodiments, tip  68  and coupler  70  can be joined via threads  76  and  78 . In some embodiments, tip  68  and coupler  70  can include a collet  80  having a stepped surface  82  corresponding to an end surface  84  of coupler  70  to prevent removal of coupler  70  from tip  68 . In some embodiments, collet  80  can include an angled surface  96  which can be configured to facilitate insertion of coupler  70  into cavity  88  of tip  68 . In some embodiments coupler  70  includes an angled surface  98  which can be configured to facilitate insertion of coupler  70  into cavity  88  of tip  68 . As shown for example in  FIG. 11 , coupler  70  can be joined to tip  68  via both threads  76  and collet  80 . In some embodiments, coupler  70  can be bonded to tip  68  via adhesives or another suitable bonding technique. In some embodiments, coupler  70  can be attached to tip  68  via a clip. In some embodiments, coupler  70  can be attached to tip  68  via a ratchet-style connection. In some embodiments, coupler  70  can be over-moulded onto a shaft or another piece within system  16 . Cavity  88  can include a stepped surface  92  configured to abut an end surface  94  of coupler  70  when coupler  70  can be received within cavity  88 . In some embodiments, tip  68  is securely coupled to coupler  70  such that tip  68  cannot fall off or be dislodged during delivery of dilator  66 . 
     In some embodiments, a method of loading a medical device, such as medical device  10  into a delivery catheter can include securing coupler  70  to a delivery catheter shaft, the shaft having a lumen for receiving medical device  10 . The method can further include crimping medical device  10  to a diameter that permits medical device  10  to be loaded into the shaft lumen. The method can further include loading medical device  10  into the shaft lumen. The method can further include securing dilator tip  68  to coupler  70  after medical device  10  is loaded into the shaft lumen. In some embodiments, tip  68  is secured to coupler  70  by threading dilator tip  68  onto coupler  70 , such as via threads  76  and  78 . In some embodiments, tip  68  is secured to coupler  70  via a snap fit between the tip  68  and the coupler  70 , such as via arm  86  and collet  80 . In some embodiments, coupler  70  is secured to the delivery catheter shaft via a press fit. In some embodiments, coupler  70  is secured to the delivery catheter shaft via adhesive or another suitable fastening means. 
     As described above, in some embodiments, tip  68  can be configured to attach to coupler  70  after a medical device, such as a valve prosthesis has been inserted into a system. In some embodiments, allowing tip  68  to attach to coupler  70  after a medical device has been loaded can increase the options for insertion of the device into the system. In some embodiments, such a configuration can allow tip  68  to be easily and securely attached to the system after loading of the device. In some embodiments, such a configuration can allow for variation in tip design for varying anatomy. 
     The choice of materials for the various valve prostheses described herein can be informed by the requirements of mechanical properties, temperature sensitivity, biocompatibility, moldability properties, or other factors apparent to a person having ordinary skill in the art. For example, one more of the parts (or a portion of one of the parts) can be made from suitable plastics, such as a suitable thermoplastic, suitable metals, and/or other suitable materials. One or more components or portions of components can be made of the same or similar material as any other component. One or more components or portions of components can be configured such that they are more flexible than another component or portion of component. In some embodiments, one or more components can include radiopaque materials. 
     In some embodiments, one or more components can include additional and/or embedded structure configured to provide increased mechanical strength while allowing for increased flexibility. In some embodiments, one or more components, such as for example capsule  27  or introducer  25 , can include a metal laser cut tube, a wound coil, braid, or other suitable structure for increasing mechanical strength. 
     In some embodiments, one or more components can be entirely or partially constructed using a single material or a composite material and/or a multi-layer material. In some embodiments, one or more of the components can include a material with a low coefficient of friction. In some embodiments, such a material can, for example, assist in loading system  16 , delivering medical device  10  and/or withdrawing system  16  from a body lumen. In some embodiments, one or more components can include a multi-layer design, including for example one or more layers can be made entirely or partially of polymer. In some embodiments, one or more layers can be made entirely or partially of high-density polyethylene (HDPE). In some embodiments, one or more layers can be made entirely or partially of polytetrafluoroethylene (PTFE). 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Other modifications and variations can be possible in light of the above teachings. The embodiments and examples were chosen and described in order to best explain the principles of the invention and its practical application and to thereby enable others skilled in the art to best utilize the invention in various embodiments with modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention.