Abstract:
Embodiments of the present disclosure provide a delivery apparatus for delivering a prosthetic heart valve to a native valve site via the human vasculature. The delivery apparatus is particularly well-suited for advancing a prosthetic valve through the aorta (i.e., in a retrograde approach) for replacing a stenotic aortic valve.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 60/843,470, filed Sep. 8, 2006, which is incorporated herein by reference. 
     
     FIELD 
       [0002]    The present application concerns embodiments of a system for delivering a prosthetic valve to a heart via the patient&#39;s vasculature. 
       BACKGROUND 
       [0003]    Endovascular delivery catheters are used to implant prosthetic devices, such as a prosthetic valve, at locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. The usefulness of delivery catheters is largely limited by the ability of the catheter to successfully navigate through small vessels and around tight bends in the vasculature, such as around the aortic arch. 
         [0004]    Known delivery apparatuses include a balloon catheter having an inflatable balloon that mounts a prosthetic valve in a crimped state and a retractable cover that extends over the valve to protect the interior walls of the vasculature as the valve is advanced to the implantation site. Various techniques have been employed to adjust the curvature of a section of the delivery apparatus to help “steer” the valve through bends in the vasculature. The balloon catheter may also include a tapered tip portion mounted distal to the balloon to facilitate tracking through the vasculature. The tip portion, however, increases the length of the relatively stiff, non-steerable section of the apparatus. Unfortunately, due to the relatively long stiff section, successful delivery of a prosthetic valve through tortuous vasculature, such as required for retrograde delivery of a prosthetic aortic heart valve, has proven to be difficult. 
         [0005]    A known technique for adjusting the curvature of a delivery apparatus employs a pull wire having a distal end fixedly secured to the steerable section and a proximal end operatively connected to a rotatable adjustment knob located outside the body. Rotation of the adjustment applies a pulling force on the pull wire, which in turn causes the steerable section to bend. The rotation of the adjustment knob produces less than 1:1 movement of the pull wire; that is, rotation of the knob does not produce equal movement of the steerable section. To facilitate steering, it would be desirable to provide an adjustment mechanism that can produce substantially 1:1 movement of the steerable section. 
         [0006]    It is also known to use an introducer sheath for safely introducing a delivery apparatus into the patient&#39;s vasculature (e.g., the femoral artery). An introducer sheath has an elongated sleeve that is inserted into the vasculature and a seal housing that contains one or more sealing valves that allow a delivery apparatus to be placed in fluid communication with the vasculature with minimal blood loss. A conventional introducer sheath typically requires a tubular loader to be inserted through the seals in the sheath housing to provide an unobstructed path through the seal housing for a valve mounted on a balloon catheter. A conventional loader extends from the proximal end of the introducer sheath, and therefore decreases the available working length of the delivery apparatus that can be inserted through the sheath and into the body. 
         [0007]    Accordingly, there remains a need in the art for improved endovascular systems for implanting valves and other prosthetic devices. 
       SUMMARY 
       [0008]    Certain embodiments of the present disclosure provide a heart valve delivery apparatus for delivery of a prosthetic heart valve to a native valve site via the human vasculature. The delivery apparatus is particularly suited for advancing a prosthetic valve through the aorta (i.e., in a retrograde approach) for replacing a stenotic native aortic valve. 
         [0009]    The delivery apparatus in particular embodiments includes a balloon catheter having an inflatable balloon which mounts a crimped valve for delivery through the patient&#39;s vasculature. The delivery apparatus can include a guide, or flex, catheter having a shaft that extends over the shaft of the balloon catheter. The guide catheter shaft has a steerable section, the curvature of which can be adjusted by the operator to facilitate navigation of the delivery apparatus around bends in the vasculature. The delivery apparatus also can include a nose catheter having a shaft that extends through the balloon catheter shaft and a nose piece located distally of the valve. The nose piece desirably has a tapered outer surface and is made of a flexible material to provide atraumatic tracking through the arteries and a stenotic native valve. The nose piece desirably has an internal bore that is dimensioned to receive at least a distal end portion of the deflated balloon during delivery of the valve. 
         [0010]    By inserting a portion of the balloon into the nose piece, the length of the non-steerable section of the delivery apparatus can be reduced (e.g., by about 1.5 to 2.0 cm in some examples), which greatly enhances the ability of the delivery apparatus to track through the aortic arch with little or no contact between the end of the delivery apparatus and the inner walls of the aorta. Once the delivery apparatus has been advanced to the implantation site, the nose catheter can be moved distally relative to the balloon catheter to withdraw the balloon from the nose piece so as not to interfere with inflating the balloon. 
         [0011]    The guide catheter shaft can be provided with a cover at its distal end to cover a portion of the balloon and/or the valve that is not already covered by the nose piece. In particular embodiments, the cover extends over the remaining portion of the balloon and the valve that is not covered by the nose piece. In this manner, the entire outer surface of the valve and the balloon are shielded by the nose piece and the cover. Consequently, an introducer sheath need not be used to introduce the delivery apparatus into the patient&#39;s vasculature. Unlike an introducer sheath, the cover need only be in contact with the femoral and iliac arteries for only a short period of time, and thus minimizes the possibility of trauma to these vessels. Further, by eliminating the introducer sheath, the maximum diameter of the system can be reduced, and therefore it is less occlusive to the femoral artery. 
         [0012]    In one variation of the delivery apparatus, the nose piece has an internal bore dimensioned to receive the entire valve and substantially the entire balloon during delivery of the valve. Thus, in this embodiment, the cover attached to the end of the guide catheter need not be provided. In another variation, the cover of the guide catheter extends completely over the valve and the balloon, and the nose catheter is not provided. The cover can be an expandable mesh basket that can collapse around the valve and the balloon to provide a smooth tracking profile. The mesh basket can be expanded by the operator, such as by pulling one or more pull wires, which dilates a distal opening in the mesh basket permitting the balloon and the valve to be advanced from the basket for deployment. 
         [0013]    As noted above, the guide catheter desirably has a steerable section that can be deflected or bent by the operator to assist in tracking the delivery apparatus around bends in the vasculature. In certain embodiments, the guide catheter can be provided with a manually operated adjustment mechanism that produces substantially 1:1 movement of the steerable section. To such ends, the adjustment mechanism can include a pivotable lever that is operatively coupled to the steerable section via a pull wire extending through a lumen in the guide catheter shaft. Pivoting the lever operates a pulley, which retracts the pull wire, producing substantially 1:1 movement of the steerable section. Pivoting the lever in the opposite direction releases tension in the pull wire, and the resiliency of the steerable section causes the steerable section to return to its normal, non-deflected shape. 
         [0014]    In cases where an introducer sheath is used to assist in inserting the delivery apparatus into the patient&#39;s vasculature, the introducer sheath can be provided with an integrated loader tube that extends into the seal housing of the sheath. The loader tube is connected to an end piece coupled to the distal end of the seal housing. The end piece is moveable along the length of the seal housing between a first, extended position where the loader tube is spaced from the sealing valves in the seal housing and a second, retracted position where the loader tube extends through the sealing valves to provide an unobstructed pathway for a valve mounted on a balloon catheter. Because the loader tube does not extend behind the end piece, the loader tube does not decrease the available working length of the delivery apparatus that can be inserted through the sheath and into the vasculature. 
         [0015]    In one representative embodiment, an apparatus for delivering a prosthetic valve through the vasculature of a patient comprises a balloon catheter, a guide catheter, and a nose catheter configured to move longitudinally relative to each other. The balloon catheter comprises an elongated shaft and a balloon connected to a distal end portion of the shaft, the balloon being adapted to carry the valve in a crimped state and being inflatable to deploy the valve at an implantation site in the patient&#39;s body. The guide catheter comprises an elongated shaft extending over the balloon catheter shaft, the shaft of the guide catheter comprising a steerable section. The guide catheter further comprises an adjustment mechanism operatively coupled to the steerable section. The adjustment mechanism is configured to adjust the curvature of the steerable section and the portion of the balloon catheter shaft extending through the steerable section. The nose catheter comprises an elongated shaft extending through the balloon catheter shaft and a nose piece connected to a distal end of the nose catheter shaft. The nose piece has an internal bore adapted to receive at least a distal end portion of the balloon in a deflated state during delivery of the valve. 
         [0016]    In another representative embodiment, a method of implanting a prosthetic valve at an implantation site in a patient&#39;s body comprises placing the valve on an inflatable balloon of a balloon catheter of a delivery apparatus and inserting at least a distal end portion of the balloon in a nose piece of a nose catheter of the delivery apparatus. The balloon catheter and the nose catheter are then inserted into the body and advanced through the patient&#39;s vasculature. At or near the implantation site, the nose catheter is moved distally relative to the balloon catheter to uncover the portion of the balloon inside the nose piece, and thereafter the valve can be deployed at the implantation site by inflating the balloon. 
         [0017]    In another representative embodiment, a method of implanting a prosthetic valve at an implantation site in a patient&#39;s body comprises placing the valve in a crimped state on the distal end portion of an elongated delivery apparatus and advancing the delivery apparatus through the patient&#39;s vasculature. Subsequent to the act of advancing the delivery apparatus, the crimped valve is moved onto an inflatable balloon on the distal end portion of the delivery apparatus and then deployed at the implantation site by inflating the balloon. 
         [0018]    In yet another representative embodiment, an apparatus for delivering a prosthetic valve through the vasculature of a patient comprises a balloon catheter and a nose catheter. The balloon catheter comprises an elongated shaft, a balloon connected to a distal end portion of the shaft, and a tapered wedge connected to the distal end portion adjacent the balloon. The nose catheter comprises an elongated shaft extending through the shaft of the balloon catheter, the balloon, and the wedge. The nose catheter further includes a nose piece connected to a distal end of the nose catheter shaft. The valve can be mounted in a crimped state between the nose piece and the wedge. The nose piece can be retracted proximally to push the valve over the wedge and onto the balloon, with the wedge partially expanding the valve before it is placed on the balloon. 
         [0019]    In another representative embodiment, a guide catheter for an endovascular delivery apparatus comprises an elongated shaft having a steerable section, a handle comprising a pivotable lever, and a pull wire. The pull wire has a proximal end portion coupled to the lever and a distal end portion fixedly secured to the steerable section such that pivoting movement of the lever applies a pulling force on the pull wire to cause the steerable section to bend. 
         [0020]    In another representative embodiment, an endovascular delivery apparatus comprises a balloon catheter comprising an elongated shaft and a balloon connected to a distal end portion of the shaft. A guide catheter comprises an elongated shaft comprising an inner polymeric tubular liner having a lumen sized to permit insertion of the balloon and the balloon catheter shaft therethrough. The shaft further comprises a braided metal layer surrounding the tubular liner, and an outer polymeric layer surrounding the braided metal layer. 
         [0021]    In another representative embodiment, a method for making a catheter comprises forming an inner tubular layer from a polymeric material, the inner tubular layer having a lumen dimensioned to allow a balloon of a balloon catheter to pass therethrough, forming a tubular pull wire conduit from a polymeric material, placing the conduit and the inner tubular layer side-by-side in a parallel relationship relative to each other, forming a braided metal layer around the conduit and the inner tubular layer, and forming an outer polymeric layer around the braided metal layer. 
         [0022]    In another representative embodiment, an introducer sheath comprises an elongated tubular sleeve having a lumen and adapted to be inserted into a patient&#39;s vasculature, a seal housing comprising an inner bore in communication with the lumen of the sleeve and one or more sealing valves housed in the bore, and an end piece coupled to the sealing housing opposite the sleeve. The end piece comprises a loader tube extending into the bore and is moveable along a length of the seal housing to move the loader tube from a first position spaced from the one or more sealing valves to a second position wherein the loader tube extends through the sealing valves. 
         [0023]    The foregoing and other features and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is side view of an endovascular delivery apparatus for implanting a prosthetic valve, according to one embodiment. 
           [0025]      FIG. 2A  is side view of the balloon catheter of the delivery apparatus of  FIG. 1 , shown partially in section. 
           [0026]      FIG. 2B  is an enlarged, cross-sectional view of the balloon catheter shown in  FIG. 2A , taken along the length of the catheter. 
           [0027]      FIG. 3A  is a cross-sectional view of the guide catheter of the delivery apparatus of  FIG. 1 , taken along a plane extending along the length of the guide catheter. 
           [0028]      FIG. 3B  is a cross-sectional view of the guide catheter, taken along a plane that is perpendicular to the plane defining the cross-section view shown in  FIG. 3A . 
           [0029]      FIG. 4A  is a cross-sectional view of the nose catheter of the delivery apparatus shown in  FIG. 1 , taken along the length of the nose catheter. 
           [0030]      FIG. 4B  is an enlarged, cross-sectional view of the nose catheter. 
           [0031]      FIGS. 5A and 5B  are cross-sectional and perspective views, respectively, of a slide nut used in the handle portion of the guide catheter. 
           [0032]      FIGS. 6A and 6B  are perspective and side views, respectively, of an inner sleeve used in the handle portion of the guide catheter. 
           [0033]      FIG. 7A  is a cross-sectional view of a guide catheter, according to one embodiment, taken along the length thereof. 
           [0034]      FIG. 7B  is a transverse cross-sectional view of the guide catheter shown in  FIG. 7A . 
           [0035]      FIG. 7C  is an enlarged, longitudinal cross-sectional view of the distal end portion of the guide catheter shown in  FIG. 7A . 
           [0036]      FIGS. 8A-8C  are cross-sectional views of the distal end portion of the delivery apparatus of  FIG. 1 , illustrating the operation of the same for implanting a prosthetic valve. 
           [0037]      FIG. 9  is side view of an endovascular delivery apparatus for implanting a prosthetic valve, according to another embodiment. 
           [0038]      FIG. 10A  is a side view of the introducer sheath of the deliver apparatus shown in  FIG. 9 . 
           [0039]      FIG. 10B  is a side view of the introducer sheath of  FIG. 10A  shown partially in section. 
           [0040]      FIG. 10C  is an end view of the introducer sheath of  FIG. 10A . 
           [0041]      FIG. 11  is a perspective view of an alternative embodiment of a guide catheter. 
           [0042]      FIG. 12  is a top plan view of the guide catheter of  FIG. 11 . 
           [0043]      FIG. 13  is a side elevation view of the guide catheter of  FIG. 11 . 
           [0044]      FIG. 14  is a perspective, exploded view of the guide catheter of  FIG. 11 . 
           [0045]      FIG. 15  is a partial, cross-sectional view of the guide catheter of  FIG. 11 . 
           [0046]      FIGS. 16A and 16B  are perspective views of a pulley used in the guide catheter of  FIG. 11 . 
           [0047]      FIG. 17  is a perspective view of a lever portion used in the guide catheter of  FIG. 11 . 
           [0048]      FIGS. 18A and 18B  are partial, cross-sectional views of the guide catheter of  FIG. 11  illustrating the operation of an adjustable lever for adjusting the curvature of the guide catheter. 
           [0049]      FIG. 19A  is a perspective view of the distal end portion of alternative embodiment of a nose catheter. 
           [0050]      FIGS. 19B and 19C  are cross-sectional views illustrating the operation of the nose catheter shown in  FIG. 19A . 
           [0051]      FIG. 20A  is a side elevation view of the distal end portion of a delivery apparatus, according to another embodiment. 
           [0052]      FIG. 20B  is a transverse cross-sectional view of the guide catheter of the delivery apparatus of  FIG. 20A . 
           [0053]      FIGS. 21A-21C  are cross-sectional views of an alternative embodiment of a delivery apparatus, illustrating the operation of the same for implanting a prosthetic valve. 
           [0054]      FIGS. 22A and 22B  are cross-sectional views of the distal end portion of another embodiment of a delivery apparatus. 
           [0055]      FIG. 23A  shows a cross-sectional view of another embodiment of an introducer sheath and an exemplary delivery apparatus that can be introduced into a patient&#39;s vasculature via the sheath. 
           [0056]      FIG. 23B  is a cross-sectional view of the introducer sheath of  FIG. 23A  after insertion of the delivery apparatus into the sheath. 
           [0057]      FIGS. 24A-24B  are cross-sectional views of another embodiment of a delivery apparatus. 
           [0058]      FIGS. 25A-25E  schematically illustrate another embodiment of a delivery apparatus. 
           [0059]      FIGS. 26A-26E  schematically illustrate another embodiment of an introducer sheath. 
       
    
    
     DETAILED DESCRIPTION 
       [0060]      FIG. 1  shows a delivery apparatus  10  adapted to deliver a prosthetic heart valve  12  (e.g., a prosthetic aortic valve) to a heart, according to one embodiment. The apparatus  10  generally includes a steerable guide catheter  14  (also referred to as a flex catheter), a balloon catheter  16  extending through the guide catheter  14 , and a nose catheter  18  extending through the balloon catheter  16 . The guide catheter  14 , the balloon catheter  16 , and the nose catheter  18  in the illustrated embodiment are adapted to slide longitudinally relative to each other to facilitate delivery and positioning of the valve  12  at an implantation site in a patient&#39;s body, as described in detail below. 
         [0061]    The guide catheter  14  includes a handle portion  20  and an elongated guide tube, or shaft,  22  extending from the handle portion  20 . The balloon catheter  16  includes a proximal portion  24  adjacent the handle portion  20  and an elongated shaft  26  that extends from the proximal portion  24  and through the handle portion  20  and the guide tube  22 . An inflatable balloon  28  is mounted at the distal end of the balloon catheter. The valve  12  is shown mounted on the balloon  28  in a crimped state having a reduced diameter for delivery to the heart via the patient&#39;s vasculature. 
         [0062]    The nose catheter  18  includes an elongated shaft  30  that extends through the proximal portion  24 , the shaft  26 , and the balloon  28  of the balloon catheter. The nose catheter  18  further includes a nose piece  32  mounted at the distal end of the shaft  30  and adapted to receive a distal end portion of the balloon when the apparatus  10  is used to advance the valve through the patient&#39;s vasculature to the implantation site. 
         [0063]    As can be seen in  FIGS. 2A and 2B , the balloon catheter  16  in the illustrated configuration further includes an inner shaft  34  ( FIG. 2B ) that extends from the proximal portion  24  and coaxially through the outer shaft  26  and the balloon  28 . The balloon  28  can be supported on a distal end portion of the inner shaft  34  that extends outwardly from the outer shaft  26  with a proximal end portion  36  of the balloon secured to the distal end of the outer shaft  26  (e.g., with a suitable adhesive). The outer diameter of the inner shaft  34  is sized such that an annular space is defined between the inner and outer shafts along the entire length of the outer shaft. The proximal portion  24  of the balloon catheter can be formed with a fluid passageway  38  that is fluidly connectable to a fluid source (e.g., a water source) for inflating the balloon. The fluid passageway  38  is in fluid communication with the annular space between the inner shaft  34  and the outer shaft  26  such that fluid from the fluid source can flow through the fluid passageway  38 , through the space between the shafts, and into the balloon  28  to inflate the same and deploy the valve  12 . 
         [0064]    The proximal portion  24  also defines an inner lumen  40  that is in communication with a lumen  42  of the inner shaft  34 . The lumens  40 ,  42  in the illustrated embodiment are sized to receive the shaft  30  of the nose catheter. The balloon catheter  16  also can include a coupler  44  connected to the proximal portion  24  and a tube  46  extending from the coupler. The tube  46  defines an internal passage which fluidly communicates with the lumen  40 . The balloon catheter  16  also can include a slide support  48  connected to the proximal end of the coupler  44 . The slide support  48  supports and cooperates with an adjustment ring  50  (FIGS.  1  and  4 A- 4 B) of the nose catheter  18  to allow the nose catheter to be maintained at selected longitudinal positions relative to the balloon catheter  16 , as described in greater detail below. 
         [0065]    As shown in  FIG. 2A , the outer surface of the outer shaft  26  can include one or more annular grooves or notches  52   a ,  52   b ,  52   c  spaced apart from each other along the proximal end portion of the shaft  26 . The grooves cooperate with a locking mechanism  84  of the guide catheter  14  ( FIGS. 3A-3B ) to allow the guide catheter  14  to be maintained at selected longitudinal positions relative to the balloon catheter  16 , as described in greater detail below. 
         [0066]    The inner shaft  34  and the outer shaft  26  of the balloon catheter can be formed from any of various suitable materials, such as nylon, braided stainless steel wires, or a polyether block amide (commercially available as Pebax®). The shafts  26 ,  34  can have longitudinal sections formed from different materials in order to vary the flexibility of the shafts along their lengths. The inner shaft  34  can have an inner liner or layer formed of Teflon® to minimize sliding friction with the nose catheter shaft  30 . 
         [0067]    The guide catheter  14  is shown in greater detail in  FIGS. 3A and 3B . As discussed above, the guide catheter  14  includes a handle portion  20  and an elongated guide tubes or shaft,  22  extending distally therefrom. The guide tube  22  defines a lumen  54  sized to receive the outer shaft  26  of the balloon catheter and allow the balloon catheter to slide longitudinally relative to the guide catheter. The distal end portion of the guide tube  22  comprises a steerable section  56 , the curvature of which can be adjusted by the operator to assist in guiding the apparatus through the patient&#39;s vasculature, and in particular, the aortic arch. 
         [0068]    The guide catheter desirably includes a cover, or shroud,  23  secured to the distal end of the guide tube  22 . The cover  23  in particular embodiments is sized and shaped to receive the valve  12  crimped around the balloon and to abut against the proximal end surface of the nose piece  32 , which is adapted to cover a distal end portion of the balloon  28  (as shown in  FIG. 8A ). Thus, when the apparatus is advanced to the deployment site, the valve  12  and the balloon  28  can be completely enclosed within the cover  23  and the nose piece  32 . 
         [0069]    As further shown in  FIGS. 3A and 3B , the handle portion  20  includes a main body, or housing,  58  formed with a central lumen  60  that receives the proximal end portion of the guide tube  22 . The handle portion  20  can include a side arm  62  defining an internal passage which fluidly communicates with the lumen  60 . A stopcock  63  can be mounted on the upper end of the side arm  62 . 
         [0070]    The handle portion  20  is operatively connected to the steerable section  56  and functions as an adjustment to permit operator adjustment of the curvature of the steerable section  56  via manual adjustment of the handle portion. In the illustrated embodiment, for example, the handle portion  20  includes an inner sleeve  64  that surrounds a portion of the guide tube  22  inside the handle body  58 . A threaded slide nut  68  is disposed on and slidable relative to the sleeve  64 . The slide nut  68  is formed with external threads that mate with internal threads of an adjustment knob  70 . 
         [0071]    As best shown in  FIGS. 5A and 5B , the slide nut  68  is formed with two slots  76  formed on the inner surface of the nut and extending the length thereof. As best shown in  FIGS. 6A and 6B , the sleeve  64  is also formed with longitudinally extending slots  78  that are aligned with the slots  76  of the slide nut  68  when the slide nut is placed on the sleeve. Disposed in each slot  78  is a respective elongated nut guide  66   a ,  66   b  ( FIG. 3B ), which can be in the form of an elongated rod or pin. The nut guides  66   a ,  66   b  extend radially into respective slots  76  in the slide nut  68  to prevent rotation of the slide nut  68  relative to the sleeve  64 . By virtue of this arrangement, rotation of the adjustment knob  70  (either clockwise or counterclockwise) causes the slide nut  68  to move longitudinally relative to the sleeve  64  in the directions indicated by double-headed arrow  72 . 
         [0072]    One or more pull wires  74  connect the adjustment knob  70  to the steerable section  56  to produce movement of the steerable section upon rotation of the adjustment knob. In certain embodiments, the proximal end portion of the pull wire  74  can extend into and can be secured to a retaining pin  80  ( FIG. 3A ), such as by crimping the pin  80  to the pull wire. The pin  80  is disposed in a slot  82  in the slide nut  68  (as best shown in  FIG. 5A ). The pull wire  74  extends from pin  80 , through a slot  98  in the slide nut, a slot  100  in the sleeve  64 , and into and through a pull wire lumen in the shaft  22  ( FIG. 3A ). The distal end portion of the pull wire  74  is secured to the distal end portion of the steerable section  56 . 
         [0073]    The pin  80 , which retains the proximal end of the pull wire  74 , is captured in the slot  82  in the slide nut  68 . Hence, when the adjustment knob  70  is rotated to move the slide nut  68  in the proximal direction (toward the proximal portion  24  of the balloon catheter), the pull wire  74  also is moved in the proximal direction. The pull wire pulls the distal end of the steerable section  56  back toward the handle portion, thereby bending the steerable section and reducing its radius of curvature. The friction between the adjustment knob  70  and the slide nut  68  is sufficient to hold the pull wire taut, thus preserving the shape of the bend in the steerable section if the operator releases the adjustment knob  70 . When the adjustment knob  70  is rotated in the opposite direction to move the slide nut  68  in the distal directions tension in the pull wire is released. The resiliency of the steerable section  56  causes the steerable to return its normal, non-deflected shape as tension on the pull wire is decreased. Because the pull wire  74  is not fixed to the slide nut  68 , movement of the slide nut in the distal direction does not push on the end of the pull wire, causing it to buckle. Instead, the pin  80  is allowed to float within slot  82  of the slide nut  68  when the knob  70  is adjusted to reduce tension in the pull wire, preventing buckling of the pull wire. 
         [0074]    In particular embodiments, the steerable section  56  in its non-deflected shape is slightly curved and in its fully curved position, the steerable section generally conforms to the shape of the aortic arch. In other embodiments, the steerable section can be substantially straight in its non-deflected position. 
         [0075]    The handle portion  20  can also include a locking mechanism  84  that is configured to retain the balloon catheter  16  at selected longitudinal positions relative to the guide catheter  14 . The locking mechanism  84  in the illustrated configuration comprises a push button  86  having an aperture  88  through which the outer shaft  26  of the balloon catheter extends. As best shown in  FIG. 3A , the button  86  has a distal end portion  90  that is partially received in an internal slot  92 . A coil spring  94  disposed in the slot  92  bears against and resiliently urges the distal end portion  90  toward the shaft  26 . The distal end portion  90  can be formed with a small projection  96  that can nest within any of grooves  52   a ,  52   b ,  52   c  on the shaft  26  ( FIG. 2A ). When one of the grooves is aligned with the projection  96 , the spring  94  urges the projection into the groove to retain the shaft  26  at that longitudinal position relative to the guide catheter (as depicted in  FIG. 3A ). Since the grooves in the illustrated embodiment extend circumferentially completely around the shaft  26 , the balloon catheter can be rotated relative to the guide catheter when the longitudinal position of the balloon catheter is locked in place by the button  86 . The position of the balloon catheter can be released by pressing inwardly on the button  86  against the bias of the spring  94  to remove the projection  96  from the corresponding groove on the shaft  26 . 
         [0076]    The handle portion  20  can have other configurations that are adapted to adjust the curvature of the steerable section  56 . One such alternative handle configuration is shown co-pending U.S. patent application Ser. No. 11/152,288 (published under Publication No. US2007/0005131), which is incorporated herein by reference. Another embodiment of the handle portion is described below and shown in  FIGS. 11-15 . 
         [0077]      FIGS. 7A and 7B  show the guide catheter shaft  22  constructed in accordance with one specific embodiment. The shaft  22  in the illustrated embodiment comprises a tubular inner liner  104  made of a low-friction polymeric material, such as PTFE. The liner  104  is sized to allow a deflated balloon  28  and the balloon catheter shaft  26  to be inserted therethrough. A smaller conduit, or liner  106 , which extends along the outside of the inner liner  104 , defines a lumen through which the pull wire  74  extends. An outer layer  108  surrounds the liners  104 ,  106  and imparts the desired flexibility and stiffness to the shaft  22 . 
         [0078]    The outer layer  108  in the illustrated embodiment comprises a braided layer formed from braided metal wire  110  wound around the liner  104  and the conduit  106 , and a polymeric material  112  surrounding and encapsulating the braided metal wire layer. In particular embodiments, the shaft can be formed by forming the liners  104 ,  106 , placing the liners side-by-side in a parallel relationship relative to each other, wrapping the metal wire around the liners to form the braided layer, placing a polymeric sleeve over the braided layer, and reflowing the sleeve to form a uniform laminate layer  108  surrounding the liners. In certain embodiments, the polymeric material  112  comprises any suitable material, but desirably comprises a thermoplastic elastomer, such as Pebax®. The braided metal layer can be constructed from stainless steel wire. 
         [0079]    As best shown in  FIG. 7A , the shaft  22  desirably comprises a relatively stiff section  114  extending from the proximal end  116  of the shaft to the proximal end  118  of the steerable section  56 . In particular embodiments, the length of the steerable section  56  comprises about ¼ of the overall length of the shaft  22 . In a working embodiment, the overall length of the shaft  22  is about 45 inches (including the steerable section) and the length of the steerable section is about 11.7 inches, although the overall length of the shaft and/or the length of the steerable section can be varied depending on the particular application. 
         [0080]    The steerable section  56  of the shaft desirably is formed from a relatively soft durometer material  112  to allow the steerable section to bend upon adjustment of the adjustment knob  70 , as described above. The stiff section  114  desirably is formed from a relatively stiffer polymeric material  112  that resists bending when the pull wire is tensioned by the adjustment knob  70 . The stiff section  114  desirably exhibits sufficient rigidity to allow the operator to push the apparatus  10  through a potentially constricting body vessel. In particular embodiments, the polymeric material  112  of the steerable section comprises 55D Pebax® and the polymeric material  112  of the remaining section  114  of the shaft comprises 72D Pebax®, which is stiffer than 55D Pebax®. 
         [0081]    In alternative embodiments, the metal braided layer in the steerable section  56  can be replaced with a metal coil (e.g., a stainless steel coil) disposed on the inner liner  104  to enhance the flexibility of the steerable section. Thus, in this alternative embodiment, the braided metal layer extends along the stiff section  114  and the metal coil extends along the steerable section  56 . In another embodiment, the metal braided layer in the steerable section  56  can be replaced with a stainless steel hypotube that is formed with laser-cut, circumferentially extending openings, such as disclosed in co-pending U.S. patent application Ser. No. 11/152,288. 
         [0082]    As shown in  FIG. 7C , the distal end of the shaft  22  can include a flared, or enlarged, end portion  116 . The outer diameter D of the end portion  116  is equal to or about the same as the outer diameter of the crimped valve  12  supported on the balloon  28 . Accordingly, when the valve  12  is advanced through an introducer sheath, the end portion  116  pushes against the crimped valve  12 , rather than the balloon  28 . This minimizes inadvertent movement between the balloon catheter and the valve, which can cause the position of the valve on the balloon to move. In particular embodiments, the shaft  22  has an outer diameter of about 16 F to about 18 F and the end portion  116  has an outer diameter D of about 22 F. The enlarged end portion  116  can be made of any of various suitable materials. For example, the end portion  116  can be molded from Pebax® (e.g., 55D Pebax®) and reflowed on the end portion of the steerable section  56 . 
         [0083]    As mentioned above, the distal end of the pull wire  74  is secured at the distal end of the steerable section  56 . As best shown in  FIG. 7C , this can be achieved by securing the distal end portion of the pull wire  74  to a metal ring  118  embedded in the outer layer  108  of the shaft, such as by welding the pull wire to the metal ring. 
         [0084]    Although not shown in  FIGS. 7A-7C , the guide catheter shaft  22  can include a cover  23  for covering the valve  12  and the balloon  28  (or a portion thereof) during delivery of the valve. As explained below, the use of an introducer sheath can be optional if the valve is covered upon insertion into the patient&#39;s vasculature. 
         [0085]    Referring to  FIGS. 4A and 4B , and as discussed briefly above, the nose catheter  18  includes an adjustment ring  50  at its proximal end and a nose piece  32  at its distal end, and an elongated shaft  30  extending therebetween. The shaft  30  desirably is formed with a lumen  120  extending the length of the shaft for receiving a guide wire  140  ( FIG. 8A ) so that the apparatus  10  can be advanced over the guide wire after it is inserted into the delivery path in the body. As shown in  FIGS. 4A and 4B , the nose piece  32  desirably is formed with an opening or cavity  122  sized and shaped to receive at least a distal end portion of the balloon  28 . 
         [0086]    As best shown in  FIG. 4A , the adjustment ring  50  is disposed on and slidable relative to the slide support  48  of the balloon catheter, which function as a locking or retaining mechanism for retaining the nose catheter at selective longitudinal positions relative to the balloon catheter. Explaining further, the shaft  30  extends through and is fixedly secured to a shaft support  124  disposed within the side support  48 . The adjustment ring  50  is secured to the shaft support  124  by screws  126 , which extend through elongated slots  128   a ,  128   b  in the slide support  48 . Slots  128   a ,  128   b  extend longitudinally along the length of the slide support  48 . Hence, when the adjustment ring  50  is slid longitudinally along the length of the slide support  48  (in the directions indicated by double-headed arrow  130 ), the shaft support  124  and the shaft  30  are caused to move in the same direction so as to adjust the longitudinal position of the nose catheter relative to the balloon catheter. 
         [0087]    The slot  128   a  is formed with circumferentially extending notches  132   a - 132   d  and the slot  128   b  is formed with similar circumferentially extending notches  134   a - 134   d  opposite the notches  132   a - 132   d . Thus, for each notch  132   a - 132   d , there is a corresponding, diametrically opposed notch  134   a - 134   d  extending from slot  128   b . To retain the longitudinal position of the nose catheter relative to the balloon catheter, the adjustment ring  50  is moved to align the screws  126  with a pair of diametrically opposed notches and then rotated slightly to position the screws  126  in the notches. For example,  FIG. 4A  shows the screws  126  positioned in notches  132   b  and  134   b . The notches restrict movement of the screws  126 , and therefore the shaft support  124  and the shaft  30 , in the distal and proximal directions. 
         [0088]    In the illustrated embodiment, each slot  128   a ,  128   b  is formed with four notches. When the screws  126  are positioned in notches  132   c ,  134   c  or in notches  132   d ,  134   d , the nose piece  32  is retained at a position covering a distal end portion of the balloon  28  and abutting the cover  23  of the guide catheter  14  such that the balloon  28  and the valve  12  are completely enclosed by the cover  23  and the nose piece  32  ( FIG. 8A ). When the screws  126  are positioned in notches  132   b ,  134   b , the nose piece  32  is retained at a position spaced distally a first distance from the balloon  28  so that the valve can be deployed by inflating the balloon without inference from the nose piece ( FIG. 8C ). When the screws are positioned in notches  132   a ,  134   a , the nose piece is retained at a position spaced distally a second distance, greater than the first distance, from the balloon  28 . In this position, the balloon  28  can be refolded inside the cover  23  (after valve deployment) without interference from the nose piece. 
         [0089]    The valve  12  can take a variety of different forms. In particular embodiments, the valve generally comprises an expandable stent portion that supports a valve structure. The stent portion desirably has sufficient radial strength to hold the valve at the treatment site and resist recoil of the stenotic native valve leaflets. Additional details regarding balloon expandable valve embodiments can be found in U.S. Pat. Nos. 6,730,118 and 6,893,460, each entitled IMPLANTABLE PROSTHETIC VALVE, which are incorporated by reference herein. It will also be appreciated that the delivery system may be used with self-expanding prosthetic valves. For example, when using a self-expanding valve, a pusher may be used to assist in ejecting the self-expanding valve from a delivery sleeve that maintains the valve in its compressed state. 
         [0090]    When the valve  12  is used to replace the native aortic valve (or a previously implanted, failing prosthetic aortic valve), the valve  12  can be implanted in a retrograde approach where the valve, mounted on the balloon in a crimped state, is introduced into the body via the femoral artery and advanced through the aortic arch to the heart. In use, a guide wire  140  ( FIG. 8A ) can be used to assist in advancing the delivery device  10  through the patient&#39;s vasculature. The guide wire  140  can be placed in the body vessel through a dilator (not shown), which expands the inner diameter of the body vessel for introducing the delivery device. Dilator diameters range between, for example, 12 and 22 French. 
         [0091]    As noted above, and as shown in  FIG. 8A , the valve  12  can be positioned inside the cover  23  with the nose piece  32  covering the distal end portion of the balloon  28  and abutting the distal end of the cover  23 . The adjustment ring  50  of the nose catheter can be locked in place to retain nose piece  32  against the cover  23  during delivery. In this position, the nose catheter desirably is placed in slight tension with the nose piece  32  held tightly against the cover  32  to inhibit separation of the nose piece from the cover while tracking the device through the vasculature and during removal of the delivery apparatus from the body. 
         [0092]    Advantageously, because the valve  12  in the illustrated embodiment can be completely covered by the cover  23 , an introducer sheath is not needed to introduce the valve into the body vessel. An introducer sheath having a diameter of about 22 to 24 French typically is used in a retrograde procedure. In contrast, the cover  23  desirably has an outer diameter that is less than the outer diameter of the introducer sheath, and in particular embodiments, the outer diameter of the cover  23  is in the range of about 0.260 inch to about 0.360 inch, with about 0.330 inch being a specific example. By reducing the overall diameter of the device, it is less occlusive to the femoral artery and the patient&#39;s leg can remain well perfused during the procedure. Further, because the cover  23 , which represents the largest diameter of the delivery device, need only be in contact with the femoral and iliac arteries for only a very short period of time, trauma to these vessels can be minimized. 
         [0093]    Although less desirable, in other embodiments the cover  23  can be shorter in length so that less of the outer surface of the valve and the balloon is covered by the cover  23  during delivery. For example, the cover  23  can be dimensioned to extend over only a proximal end portion of the balloon or a proximal end portion of the valve. 
         [0094]    As the delivery apparatus  10  is advanced over the guide wire  140  and through the aortic arch, the guide catheter  14  is used to “steer” the apparatus away from the inner surface of the aorta. The tapered distal end portion of the nose piece  32  assists in tracking through the femoral and iliac arteries, as well as provides atraumatic tracking through over the aortic arch and smooth crossing of the native aortic valve. In prior delivery systems, it is known to fix a nose piece at the distal end of the balloon catheter, which increases the length of the portion of the device that cannot be curved by operation of a guide catheter. In contrast, the nose piece  32  in the illustrated embodiment is mounted on separate nose catheter  18  that can be moved relative to the valve  12 . The nose piece  32  therefore can be mounted over the distal end portion of the balloon during delivery in order to minimize the length of the nonsteerable section at the distal end of the delivery device. This allows for easier tracking through the aortic arch with little or no contact between the end of the delivery device and the inner walls of the aorta. In particular embodiments, the length L ( FIG. 8A ) of the non-steerable section at the end of the delivery device is about 6 cm or less. 
         [0095]    Using conventional fluoroscopy, the operator can track the positions of marker bands  142  ( FIGS. 2A and 2B ) on the guide wire shaft  34  in order to position the valve at the implantation site. After the valve  12  is advanced into the aortic annulus, the nose catheter can be moved distally relative to the balloon catheter to advance the nose piece  32  distally away from the balloon  28  ( FIG. 8B ) and the guide catheter can be moved proximally relative to the balloon catheter to expose the valve  12  from the cover  23  ( FIG. 8C ). As explained above, the longitudinal positions of the nose catheter and the guide catheter can be fixed relative to the balloon catheter while the operator adjusts the position of and then deploys the valve  12 . Inflation of the balloon  28  is effective to expand the valve  12  to engage the native valve leaflets. The balloon  28  can then be deflated and retracted back into the cover  23  and the nose piece  32  can be pulled back over the distal end portion of the balloon. The entire delivery apparatus can then withdrawn back over the guide wire  140  and removed from the body, after which the guide wire can be removed from the body. 
         [0096]      FIG. 9  shows an alternative embodiment of the delivery apparatus  10 . In this embodiment, the guide catheter  14  is not provided with a cover  23  (as previously illustrated in  FIGS. 3A and 3B ) and instead an introducer sheath  150  can be used to introduce the delivery apparatus into the body. As best shown in  FIGS. 10A and 10B , the introducer sheath  150  in the illustrated embodiment includes an introducer housing  152  and an introducer sleeve  154  extending from the housing  152 . The housing  152  houses a sealing valve  166 . In use, the sleeve  154  is inserted into a body vessel (e.g., the femoral artery) while the housing  152  remains outside the body. The delivery apparatus  10  is inserted through a proximal opening  168  in the housing, the sealing valve  166 , the sleeve  154  and into the body vessel. The sealing valve  166  sealingly engages the outer surface of the guide catheter shaft  22  to minimize blood loss. In certain embodiments, the sleeve  154  can be coated with a hydrophilic coating and extends into the body vessel about 9 inches, just past the iliac bifurcation and into the abdominal aorta of the patient. 
         [0097]    The sleeve  154  can have a tapered section  156  that tapers from a first diameter at a proximal end  158  to a second, smaller diameter at a distal end  160 . A reduced diameter distal end portion  162  extends from the tapered portion  156  to the distal end of the sleeve  154 . The tapered portion  156  provides for a smoother transition between the outer surface of the sleeve  154  and the outer surface of the guide shaft  22  of the guide catheter  14 . The tapered portion  156  also allows for variable placement of the sleeve  154  in the patient&#39;s vasculature to help minimize complete occlusion of the femoral artery. 
         [0098]      FIGS. 11-15  show an alternative embodiment of a handle portion, indicated at  200 , that can be used in the guide catheter  14  ( FIGS. 1 and 3A ), in lieu of handle portion  20 . The handle portion  200  in the illustrated embodiment includes a main housing  202  and an adjustment lever  204  pivotably connected to the housing  202 . The lever  204  can be pivoted distally and proximally (as indicated by double-headed arrow  206  in  FIG. 13 ) to adjust the curvature of the shaft  22 , as further described below. 
         [0099]    As best shown in  FIG. 14 , the housing  202  can be formed from first and second housing portions  208 ,  210  that can be secured to each other using a suitable adhesive, mechanical fasteners, a snap fit connection, or other suitable techniques. Disposed within the housing  202  is a seal housing  212  that has a central bore  226  extending therethrough. The distal end portion of the bore  226  can form an enlarged portion that receives the proximal end portion  214  of the shaft  22 . The shaft  22  extends from the seal housing  212  through the main housing  202  and out of a nose piece  228  connected to the distal end of the main body  202 . An end piece  216  can be connected to the proximal end of the seal housing  212  with a seal  218  captured between these two components. As best shown in  FIG. 15 , the end piece  216  can be formed with a stepped bore shaped to receive the seal  218  and an end portion of the seal housing  212 . The seal  218  can be made of a suitable elastomer, such as silicon. The shaft  26  of the balloon catheter  16  extends through the end piece  216 , a central opening in the seal  218 , the seal housing  212 , and the guide catheter shaft  22 . The seal housing  212  can be formed with a flush port  220  that is in fluid communication with the central bore  226 . The flush port  220  receives one end of a flexible tube  222 . The opposite end of the tube  222  can be connected to a stopcock  224  ( FIG. 11 ). 
         [0100]    As shown in  FIG. 14 , the lever  204  in the illustrated configuration comprises first and second lever portions  230 ,  232 , respectively, mounted on opposite sides of the main housing  202 . The inner surface of each lever portion can be formed with an annular groove  274  adapted to receive a respective O-ring  234 . The lever portion  230  can be coupled to a pulley  236  mounted in the housing to produce rotation of the pulley upon pivoting movement of the lever portion. For example, the lever portion  230  can be formed with a projection  238  that extends through the housing portion  208  and into a complementary shaped recess  240  ( FIG. 16A ) in the pulley  236 . The projection  236  can be formed with fiats on its outer surface that engage corresponding flats in the recess  240  to produce rotation of the pulley when the lever is activated. The pulley  236  can also be formed with a non-circular recess or opening  242  that is shaped to receive one end portion of a shaft  244  ( FIG. 14 ). The opposite end of the shaft  244  extends through the second housing portion  210  and into a complementary shaped recess or opening  246  of the lever portion  232  ( FIG. 17 ). In the illustrated configuration, the end portions of the shaft  244  and the corresponding openings  242  and  246  are hexagonal to inhibit relative rotation between the shaft  244 , the pulley  236 , and the lever portion  232 , although various other non-circular shapes can be used. Alternatively, the end portions of the shaft and the openings  242 ,  246  can be circular if the shaft is otherwise fixed against rotation relative to the pulley and the lever portion. 
         [0101]    Upper and lower cross-bars  248 ,  250 , respectively, are connected to and extend between respective upper and lower ears of the first and second lever portions  230 ,  232 . Screws  252  extending through the ears of the lever portions  230 ,  232  and tightened into the cross-bars  248 ,  250  can be used to secure the components of the lever  204  to the main body  202 . A screw  254  can extend through the lever portion  230 , the housing portion  208 , and into a threaded opening in the shaft  244 . An adjustment knob  266  can be fixedly secured to a screw  268 , which can extend through the lever portion  232 , the housing portion  210 , and into a threaded opening in the opposite end of the shaft  244 . The screw  268  can be fixedly secured to the adjustment knob, for example, by adhesively securing the head of the screw within a recess (not shown) on the inner surface of the adjustment knob. Consequently, the adjustment knob  266  can be manually rotated to loosen or tighten the screw into the shaft  244  to adjust the rotational friction of the pulley  236 . 
         [0102]    Referring again to  FIG. 15 , a pull wire  74  extends through a pull wire lumen in the shaft  22  and extends from the shaft inside of the main housing  202 . A flexible tension member  256 , such as a piece of string, is tied off or otherwise connected to at one thereof to the end of the pull wire  74 . The tension member  256  extends around a cross-member  258 , partially around the outer circumference of the pulley  236 , through a radially extending opening  260  in the pulley and is tied off or otherwise connected to the shaft  244  adjacent the center of the pulley  236 . As shown in  FIGS. 16A and 16B , the pulley  236  can be formed with an annular groove or recess  262  adapted to receive the tension member  256 . 
         [0103]    Explaining the operation of the handle portion  200 ,  FIG. 18A  shows the adjustment lever  204  in a forward-most position. In this position, the steerable section  56  of the shaft  22  is in its normal, non-deflected state (e.g., straight, such as shown in  FIG. 1 , or slightly curved). As the lever  204  is pivoted rearwardly, in the direction of arrow  264 , the pulley  236  is rotated clockwise in the illustrated embodiment, causing the tension member to wind around the pulley and pull the pull wire  74  rearwardly. The pull wire  74 , in turn, pulls on the distal end of the shaft to adjust the curvature of the steerable section  56 , in the manner previously described.  FIG. 18B  shows the lever  204  in a rearward-most position corresponding to the fully curved position of the steerable section of the shaft  22 . 
         [0104]    The rotational friction of the pulley  236  is sufficient to hold the pull wire taut, thus preserving the shape of the bend in the steerable section if the operator releases the adjustment lever  204 . When the lever  204  is pivoted back toward the forward-most position ( FIG. 18A ), tension in the pull wire is released. The resiliency of the steerable section  56  causes the steerable section to return to its normal, non-deflected shape as tension on the pull wire is released. Because the tension member  256  in the illustrated embodiment does not apply a pushing force to the pull wire, movement of the lever  204  toward the forward-most position does not cause buckling of the pull wire. Further, as noted above, the adjustment knob  266  can be adjusted by the operator to vary the rotational friction of the pulley  236 . The rotational friction desirably is adjusted such that if the guide catheter is pulled back inadvertently while in the patient&#39;s vasculature, the pulley can rotate toward the forward-most position under a forward pulling force of the pull wire (as indicated by arrow  270  in  FIG. 18B ) to allow the steerable section to straighten out as it is pulled through the vasculature, minimizing trauma to the vasculature walls. 
         [0105]    Advantageously, the adjustment lever  204  in the illustrated embodiment provides a substantially 1:1 deflection of the steerable section in response to movement of the lever; that is, rotation of the lever  204  causes a substantially 1:1 movement of the pull wire and therefore the steerable section  56 . In this manner, the adjustment lever  204  provides the operator tactile feedback of the curvature of the steerable section to facilitate tracking through the vasculature. In addition, the lever is ergonomically positioned for maintaining the proper orientation of the guide catheter during use. Another advantage of the illustrated handle portion  200  is that the proximal portion  24  of the balloon catheter  16  ( FIG. 2B ) or a portion thereof can seat within the end piece  216  to minimize the working length of the balloon catheter. 
         [0106]      FIGS. 19A and 19B  illustrate an alternative nose catheter  300 , according to one embodiment, that can used with the delivery apparatus  10  ( FIG. 1 ), in lieu of the nose catheter  18 . The nose catheter  300  in the illustrated configuration includes a nose piece or valve cover  302  connected to a nose catheter shaft  304 . The valve cover  302  is adapted to cover the balloon  28  and a valve  12  mounted on the balloon. Thus, in this embodiment, the guide catheter  14  need not have a cover  23  ( FIG. 8A ) to cover the valve during delivery. The shaft  304  is fixedly secured at its distal end to the distal end of the cover  302  and extends through the balloon  28  and the balloon catheter shaft  26 . The shaft  304  can have a lumen to receive a guide wire  140 . The shaft  304  can move longitudinally relative to the balloon catheter and the guide catheter, much like the nose catheter  18  previously described. 
         [0107]    As best shown in  FIG. 19A , the cover  302  has a proximal end portion  306  formed with a plurality of slits defining triangular flaps  308 . The flaps  308  can flex radially outwardly from each other to form an opening large enough to allow passage of the balloon  28  and the valve  12  when it is desired to deploy the valve. The proximal end portion  306  can be tapered as shown to facilitate retraction of the cover  302  back into an introducer sheath. The tapered shape of the end portion  306  also provides an atraumatic surface to minimize trauma to the vasculature walls when the delivery apparatus is withdrawn from the body. The cover also can have a tapered distal end portion  310  to assist in tracking through the femoral and iliac arteries, as well as provide atraumatic tracking through the aortic arch and smooth crossing of the native aortic valve. 
         [0108]    The cover  302  desirably is made from a flexible material, such as nylon, Pebax®, or PET and can have a wall thickness in the range of about 0.0015 inch to about 0.015 inch. By making the cover  302  sufficiently flexible, the only relatively stiff, non-flexible section along the portion of the delivery apparatus advanced through the patient&#39;s vasculature is the section of the balloon covered by the valve. This greatly enhances the ability of the delivery apparatus to follow the path of the guide wire  140  as it is advanced through tortuous body vessels. 
         [0109]    In use, the delivery apparatus is advanced over the guide wire  140  until the valve is positioned at or near the deployment location. The nose catheter  300  is then advanced distally relative to the balloon catheter  16  to uncover the balloon and the valve  12 , as illustrated in  FIG. 19C . As the cover  302  is advanced distally, the balloon and the valve can pass through the proximal opening formed by flaps  308 . Once the valve  12  is exposed, the balloon  28  can be inflated to deploy the valve. 
         [0110]      FIG. 20A  shows a modification of the guide catheter  14  where the valve cover  23  is replaced with an expandable mesh basket or cover  400  connected to the distal end of the guide catheter shaft  22 . The cover  400  is sized and shaped to cover the valve  12  and the balloon  28 . Thus, in this embodiment, a nose catheter (e.g., nose catheter  18 ) need not be used. The cover  400  can have a braided mesh construction formed from metal wire (e.g., Nitinol or stainless steel wires). 
         [0111]    One or more ribbon wires  402  are connected to the distal end  404  of the cover  400  and extend through respective lumens in the guide catheter shaft  22  along the length thereof ( FIG. 20B ). The wires  402  can be, for example, 0.003 inch×0.020 inch Nitinol ribbon wire. The wires  402  are connected at their proximal ends to a handle portion of the guide catheter that allows the operator to apply pushing or pulling forces to the wires. Pushing the wires  402  forward, in the direction of arrow  406 , causes the cover to collapse over the balloon  28  and the valve  12  to provide a smooth tracking profile. Pulling the wires  402  rearward, in the direction of arrow  408 , causes the cover to expand and allows the balloon and valve to be advanced outwardly through an opening at the distal end  404  of the cover  400 . 
         [0112]    In use, the cover  400  is placed in a collapsed state covering the valve and the balloon for delivery through the patient&#39;s vasculature to the deployment site. The wires  402  are then pulled in the proximal direction (as indicted by arrow  408 ) to expand the cover  400 . The guide catheter can then be pulled in the proximal direction to advance the balloon and the valve from the distal end of the cover. Alternatively, the balloon catheter  16  can be advanced distally relative to the guide catheter  14  to advance the balloon and the valve from the cover  400 . 
         [0113]      FIGS. 21A-21C  show an alternative embodiment of a delivery apparatus, indicated at  500 . The delivery apparatus  500  allows a valve  12  to be mounted on a balloon  28  of a balloon catheter inside a body vessel. The balloon catheter can have a construction similar to the balloon catheter shown in  FIGS. 2A and 2B  except that in the embodiment of  FIGS. 21A-21B , the balloon catheter shaft  26  has a distal end portion  504  that extends distally from the balloon  28  and an annular tapered wedge  502  is disposed on the distal end portion  504  adjacent the balloon. The tapered wedge  502  functions to expand the valve to facilitate positioning the same on the balloon inside the body, as further described below. The wedge  502  desirably is made from a low-friction material, such as nylon, to allow the valve to easily slide over the wedge and onto the balloon. 
         [0114]    The delivery apparatus includes a nose catheter comprising a shaft  506  and a nose piece  508  connected to the distal end of the shaft  506 . The nose catheter shaft  506  can have a guide wire lumen to receive a guide wire  140  so that the apparatus can be advanced over the guide wire with the guide wire passing through the lumen. The delivery apparatus  500  can further include a guide catheter comprising a guide catheter shaft  22  and an elongated cover  510  extending from the distal end of the shaft  22 . The nose catheter, balloon catheter, and guide catheter are moveable longitudinally relative to each other and can have locking mechanisms at the proximal end of the apparatus for retaining the catheters at selected longitudinal positions relative to each other, as described in detail above. 
         [0115]    As shown in  FIG. 21A , the valve  12  is initially mounted in a crimped state on the nose catheter shaft  506  between the nose piece  508  and the tapered wedge  502 , rather than on the balloon prior to inserting the delivery apparatus into the body. The valve is crimped onto the nose catheter shaft such that that valve can still move along the shaft when it is desired to place the valve on the balloon  28 . The nose piece  508  can be formed with a stepped bore comprising a first bore portion  512  and a second, enlarged bore portion  514  at the proximal end of the nose piece. The stepped bore can be formed with an annular shoulder  516  extending between the first and second bore portions and adapted to engage the distal end of the valve  12  when the valve is inserted into the second portion  514 . The nose piece  508  can have an outer surface that tapers in a direction toward the distal end of the nose piece  508  to provide atraumatic tracking through tortuous vasculature. The cover  510  which can be optional, is adapted to extend over and cover the balloon  28 , the wedge  502 , and at least a proximal end portion of the valve  12  when the valve is positioned on the nose catheter shaft for delivery. In the illustrated embodiment, the distal end of the cover  510  can be positioned to abut the proximal end of the nose piece  508  so as to completely enclose the valve during delivery. In alternative embodiments, the cover  510  can be shorter in length so that less of the outer surface of the valve or the balloon is covered during delivery. 
         [0116]    The nose piece  508 , when moved proximally relative to the balloon catheter (in the direction indicated by arrow  518 ), pushes the valve  12  over the wedge  502  and onto the balloon  28 . As the valve passes over the wedge, the valve expands slightly to facilitate positioning the same on the balloon. The balloon catheter shaft  26  can have radiopaque markers  520  ( FIG. 21A ) to assist the operator in aligning the valve at the proper location on the balloon. The nose piece can have an outer layer  522  formed from a relatively soft and flexible material and an inner layer  524  formed from a relatively harder material. The inner layer  524  in the illustrated embodiment forms the shoulder  516  and the inner surface of the first bore portion  512 . In this manner, the nose piece exhibits sufficient rigidity to push the valve  12  over the wedge and onto the balloon and provides a soft outer surface to minimize trauma to the body vessels. For example, the outer layer  522  can be made of 55D Pebax® and the inner layer can be made of 72D Pebax®, which is stiffer than 55D Pebax®. 
         [0117]    The section of the delivery apparatus mounting the valve typically defines the maximum outer diameter of the apparatus inserted into the body. By mounting the valve  12  on the nose catheter shaft rather than on the balloon prior to insertion into the body, the valve  12  can be crimped to a smaller diameter than if the valve is mounted on the balloon. Accordingly, the maximum outer diameter of the delivery apparatus can be reduced for insertion into and through the vasculature. As noted above, by reducing the maximum diameter of the delivery apparatus, it is less occlusive to the femoral artery and therefore the patient&#39;s leg can remain well perfused during the procedure. In certain embodiments, the maximum outer diameter of the cover  510  and the nose piece  508  (at its proximal end) is about 0.223 inch, which is the maximum diameter of the portion of the delivery apparatus that is inserted into the body. The wedge  502  can have a diameter at its proximal end of about 0.120 inch and the guide catheter shaft  22  can have an outer diameter of about 0.184 inch. 
         [0118]    Explaining now the operation of the delivery apparatus  500 , according to one embodiment, the valve  12  is initially mounted on the nose catheter shaft and inserted into the nose piece  508  and the cover  510 . After a guide wire  140  is inserted into the body, the proximal end of the wire extending from the body can be inserted into the distal end of the guide wire lumen and the delivery apparatus  500  can be inserted into a body vessel (e.g., the femoral artery) and advanced through the body (as depicted in  FIG. 21A ). Alternatively, an introducer sheath can be inserted first into the body vessel, for example if a cover  510  is not provided to cover the valve  12 . Subsequent to inserting the introducer sheath, the delivery apparatus can be inserted through the introducer sheath and into the body vessel. 
         [0119]    When the distal end of the delivery apparatus is advanced to a location that is convenient to slide the valve  12  onto the balloon, the guide catheter is retracted proximally relative to the balloon catheter to advance the valve and the balloon from the cover  510 . For example, if implanting a prosthetic valve within the native aortic valve, the valve and the balloon can be advanced into the ascending aorta or into the left ventricle where the valve can then be moved onto the balloon. In any case, as shown in  FIG. 21B , the nose catheter can be retracted proximally to advance the valve over the wedge  502  and onto the balloon  28 . Markers  520  ( FIG. 21A ) can be used to center the valve on the balloon. After mounting the valve on the balloon, the nose catheter can be advanced distally so as not to interfere with inflation of the balloon, as shown in  FIG. 21C . The valve can then be positioned at the implantation site (e.g., within the native aortic valve) and deployed by inflating the balloon. 
         [0120]      FIGS. 22A and 22B  show a modification of the delivery apparatus  10  ( FIGS. 1-8 ). In the embodiment of  FIGS. 22A and 22B , the cover  23  has a generally tubular shape but is provided in a rolled up state on the distal end portion of the guide catheter shaft  22 . After the valve  12  is mounted on the balloon  28 , the cover can be unrolled over the valve  12  for insertion into and through the patient&#39;s vasculature. The operation of the deliver apparatus shown in  FIGS. 22A and 22B  is otherwise identical to the operation of the delivery apparatus  10  described above with reference to  FIGS. 8A-8C . 
         [0121]      FIGS. 23A and 23B  show an embodiment of an improved introducer sheath, indicated at  600 , that can be used to facilitate insertion of a delivery apparatus into a body vessel. The introducer sheath  600  is particularly suited for use with a delivery apparatus that is used to implant a prosthetic valve, such as the embodiments of delivery apparatus described herein. The introducer sheath  600  also can be used to introduce other types of delivery apparatus for placing various types of intraluminal devices (e.g., stents, stented grafts, etc.) into many types of vascular and nonvascular body lumens (e.g., veins, arteries, esophagus, ducts of the biliary tree, intestine, urethra, fallopian tube, other endocrine or exocrine ducts, etc.). The example illustrated in  FIG. 23A  shows the distal end portion of a delivery apparatus used to implant a prosthetic valve  12 . The delivery apparatus comprises a balloon catheter and a guide catheter. The balloon catheter comprises a shaft  26  and a balloon  28  mounted on the distal end portion of the shaft. The guide catheter comprises a shaft  22  extending over the balloon catheter shaft  26 . The remaining portions of the balloon catheter and the guide catheter can be constructed according to the embodiment shown in  FIGS. 1-8 . 
         [0122]    A conventional introducer sheath typically requires a tubular loader to be inserted through the seals in the sheath housing to provide an unobstructed path for a valve mounted on a balloon catheter. The loader extends from the proximal end of the introducer sheath, thereby increasing its working length, and decreasing the available working length of a delivery apparatus that can be inserted into the body. The introducer sheath  600  includes a integrated loader tube housed in the sheath housing to reduce the working length of the sheathe and therefore increase the available working length of a delivery apparatus that can be inserted into the body. 
         [0123]    For example, the illustrated sheath  600  includes a seal housing  602  and a tubular sleeve  604  extending distally from the housing. The seal housing  602  houses one or more sealing valves, such as a cross-slit valve  606 , a disc valve  608 , and a hemostatic valve  610  as shown in the illustrated embodiment. The valves desirably are fabricated from a resilient biocompatible material, such as polyisoprene, although similar biocompatible materials also can be used. The valves  606 ,  608 ,  610  are further shown and described in U.S. Pat. No. 6,379,372, which is incorporated herein by reference. A spacer  612  can be interposed between the disc valve  608  and the cross-slit valve  606 . 
         [0124]    Coupled to the proximal end of the seal housing is an end piece  614  adapted to move longitudinally along the length of the seal housing. In the illustrated embodiment, the end piece has a tubular body formed with internal threads  616  that engage external threads  618  formed on the outer surface of the seal housing  602 . Thus, rotation of the end piece  614  moves the same inwardly and outwardly relative to the seal housing. The end piece  614  has a central opening  620  and an elongated loader tube  622  fixedly secured to the proximal end portion of the end piece and extending distally therefrom. The opening  620  and the loader tube  622  are dimensioned to permit passage of the valve  12  (or other prosthesis) mounted on the delivery apparatus. The end piece  614  also houses a seal  624  having a central opening aligned with the opening  620 . The seal  624  sealingly engages the outer surface of the delivery apparatus when it is inserted into the introducer sheath  600 . 
         [0125]    As noted above, the end piece  614  can be adjusted inwardly and outwardly relative to the seal housing  602 . Adjusting the end piece  614  from the extended position shown in  FIG. 23A  to the retracted position shown in  FIG. 23B  moves the loader tube  622  through the seals  606 ,  608 ,  610  to provide an unobstructed path for the valve  12  to pass through the introducer sheath. Because the loader tube does not extend behind the end piece, as in a conventional introducer sheath, the loader tube does not decrease the available working length of the delivery apparatus that can be inserted into the vasculature. 
         [0126]    In use, the introducer sheath  600  in the extended position shown in  FIG. 23A  can be placed on a previously inserted guide wire  140  and advanced thereon until the sleeve  604  extends into a body vessel a desired distance. The delivery apparatus can then be inserted through the opening  620  to position the valve  12  in the loader tube  622  with the seal  624  forming a fluid tight seal around the guide catheter shaft  22 . Subsequently, the end piece  614  is rotated to slide the loader tube  622  through the valves  606 ,  608 ,  610  ( FIG. 23B ), thus placing the delivery apparatus in communication with the lumen of the sleeve  604  and the body vessel in which the sleeve is inserted. Advantageously, this approach simplifies the loading process and reduces the number of steps and parts required to load the valve into the sheath. 
         [0127]    In an alternative embodiment of the introducer sheath  600 , the seal housing  602  can have internal threads that engage external threads on the end piece  614 . The end piece can be rotated to adjust the position of the loader tube  622  as previously described. In addition, the pitch of the threads on the seal housing and the end piece can be varied to vary the amount of rotational movement required to extend the loader through the sealing valves. In another embodiment, the end piece  614  can be slidingly positionable along the length of the seal housing by pushing and pulling the end piece without rotating the same. 
         [0128]      FIGS. 24A and 24B  show another embodiment of a nose catheter, indicated at  700 , that can be used in the delivery apparatus  10  ( FIG. 1 ). The nose catheter  700  includes a nose piece  702  and a nose catheter shaft  704 . The nose piece  702  has a distal end  706  connected to the nose catheter shaft  704  and a proximal end connected to the distal end of a balloon catheter shaft  26 . The nose piece  702  comprises a balloon or similar structure formed from a thin, flexible material, such as nylon or PET, capable of assuming an inverted shape covering a valve  12  and a balloon  28  or portions thereof when the nose piece  702  is urged against the balloon  28 . For example, the nose piece  702  can have a structure similar to the balloon  28 . 
         [0129]    The nose catheter shaft  704  is slidable relative to the balloon catheter shaft  26 , although the proximal end of the nose piece  702  is connected to the balloon catheter shaft. Hence, as the nose catheter shaft  704  is moved proximally relative to the balloon catheter shaft  26  (in the direction of arrow  710 ) from a first, extended position ( FIG. 24B ) toward a second, retracted position ( FIG. 24A ), the nose piece  702  is urged against the distal end of the balloon catheter shaft  26 , causing the nose piece  702  to assume an inverted position covering a portion of the outer surface of the balloon  28  and the valve  12 . Similarly, it can be seen that moving the balloon catheter shaft distally relative to the nose catheter shaft from the extended position shown in  FIG. 24B  also is effective to cause the nose piece to assume an inverted position over the balloon and the valve. 
         [0130]    In use, the nose piece  702  is initially placed in the inverted position shown in  FIG. 24A  to provide a smooth tracking profile during delivery of the valve through the patient&#39;s vasculature. At or near the implantation site, the nose catheter shaft  704  is moved distally relative to the balloon catheter shaft  20  (in the direction of arrow  712 ) to uncover the valve  12  and the balloon  28  for subsequent deployment of the valve. Desirably, although not necessarily, the nose piece  702  can be partially inflated so that it can more readily assume the inverted position shown in  FIG. 24A . In this regard, the lumen of the nose catheter shaft  704  can be fluidly connected to a fluid source for partially inflating the nose piece  702 , similar to the way the balloon catheter shaft is used to deliver a fluid to the balloon  28 . 
         [0131]      FIG. 25A  shows the distal end portion of a modification of the delivery apparatus  10 . The delivery apparatus in this embodiment includes a stepped balloon  800  mounted on the distal end portion of the balloon catheter shaft  26  and inner shaft  34 . As shown in  FIG. 25B , the illustrated balloon  800  includes a first slender portion  802 , a first conical portion  804 , a main cylindrical portion  806 , a second conical portion  808 , a second cylindrical portion  810 , a third conical portion  812 , and a second slender portion  814 . A valve  12  ( FIG. 25A ) can be mounted in a crimped state on the main cylindrical portion  806 . The stepped balloon  800  is further described in detail in co-pending U.S. application Ser. No. 11/252,657 (the &#39;657 application) (published as U.S. Patent Application Publication No. 2007/0088431), which is incorporated herein by reference. 
         [0132]    As shown in  FIG. 25A , the delivery apparatus includes a guide catheter comprising a guide catheter shaft  22  having an enlarged end portion  816  that abuts the proximal end of the valve  12 . The guide catheter further includes a retractable cover  818  that extends over and covers the valve  12 . The cover  818  is operable to slide longitudinally relative to the valve and the distal end of the guide catheter shaft  22  to uncover the valve for deployment inside a body vessel. Portions  802 ,  804  of the balloon  800  extend from the distal end of the cover  818  and can be partially inflated to provide a transition member between the distal end of the balloon catheter and the cover  818 , thereby facilitating tracking through the patient&#39;s vasculature, much like nose piece  32  ( FIG. 1 ). The end of the balloon extending from the cover  818  also can be used as a dilator to dilate stenotic leaflets of a native heart valve or other portions of the patient&#39;s vasculature prior to deploying the valve at the desired implantation site, as further described in the &#39;657 application. 
         [0133]    As further shown in  FIG. 25A , the cover  818  in the illustrated embodiment has a cylindrical distal end portion  820  that extends over the valve  12  and a plurality of circumferentially spaced fingers  822  extending proximally from the proximal end of the cylindrical distal end portion  820 . The proximal end portion of each finger  822  is connected to a pull wire  826  that extends through a respective lumen in the guide catheter shaft  22 . As shown in  FIG. 25C , each pull wire  826  extends distally from a respective lumen  828 , through an opening  830  in the proximal end portion  824  of a respective finger  822 , and back into the lumen  828 . The guide catheter can further include a flexible outer cover  838  extending over the portions of the pull wires  826  extending from the shaft  22  to prevent the wires from contacting the inner walls of the vasculature. The cover  838  can be fixedly secured to the outer surface of the shaft  22 , such as with a suitable adhesive. Alternatively, the cover  838  can be adapted to slide longitudinally relative to the shaft  22 . 
         [0134]    The cover  818  in the illustrated example has four fingers  822 , each of which is connected to a pull wire  826  that extends through a respective lumen  828 . As shown in  FIG. 25D , the lumens  828  can be equally spaced around a central lumen  54  of the shaft  22 . The shaft  22  also can include another lumen for receiving a pull wire  74  for adjusting the curvature of the guide catheter, as described above. The pull wires  826  extend the length of the guide catheter shaft  22  and are operatively connected to an adjustment mechanism at the proximal end of the shaft to permit manual adjustment of the pull wires  826 , and therefore the cover  818 . 
         [0135]      FIG. 25E  is a schematic illustration of a handle portion  832  connected to the proximal end of the guide catheter shaft. The handle potion  832  can have a construction similar to the handle portion  20  (described above and shown in  FIGS. 3A-3B ) except that the former can include an additional adjustment mechanism  834  connected to the pull wires  826 . The adjustment mechanism  834  can be moved fore and aft (in the directions of double-headed arrow  836 ) by the operator to move the pull wires  826 . The pull wires  826  desirably exhibit sufficient rigidity to apply a pushing force to the cover  818  in the distal direction without buckling. The pull wires can be, for example, 0.006 inch×0.012 inch Nitinol ribbon wire. In this manner, the cover  818  can be retracted in the proximal direction relative to the valve, and if necessary, moved in the distal direction, such as to retrieve the valve back into the cover  818 , by operation of the adjustment mechanism  834 . Further details of an adjustment mechanism that can be used to produce movement of the pull wires in the distal and proximal directions is described in detail in the &#39;657 application. 
         [0136]    When the valve is advanced to the implantation site inside the body, the cover  818  is retracted by operation of the adjustment mechanism to uncover the valve. As the cover  818  is retracted (relative to the shaft  22  and the outer cover  838 ), the distal end of the shaft end portion  816  abuts against the valve to prevent inadvertent movement of valve&#39;s position on the balloon  800 . Thereafter, the balloon catheter can be advanced distally relative to the guide catheter to advance the balloon  800  a sufficient distance from the cover  838  and the shaft end portion  816  to permit full inflation of the balloon for deploying the valve  12 . The valve  12  can be a balloon-expandable valve that is deployed by the balloon, or alternatively, the valve  12  can be a self-expanding valve that radially expands when advanced from the cover  818 . In the latter case, the balloon  800  can be used to further expand the valve to ensure tight engagement with the orifice of the native valve. 
         [0137]    In an alternative embodiment, the shaft distal end portion  816  can be configured to provide a releasable attachment to the valve  12 , such as described in detail in the &#39;657 application. In this manner, the guide catheter can be moved fore and aft to adjust the position of the valve in the body vessel as the valve is being deployed. Prior to deployment (or after partial deployment, or expansion, of the valve), control of valve positioning can be achieved by the operator pushing, pulling, or twisting the guide catheter. Once the operator is satisfied with the position of the valve, the valve can be fully deployed and the valve is detached from the distal end of the guide catheter shaft. 
         [0138]      FIGS. 25A-25E  illustrate another embodiment of an introducer sheath, indicated at  900 , that can be used to facilitate the introduction of a delivery apparatus into a blood vessel. The introducer sheath  900  has an expandable, elongated sleeve  902  that can be radially expanded from a first diameter ( FIG. 25A ) to a second, larger diameter ( FIG. 25B ) to facilitate insertion of the largest portion the delivery apparatus (the portion on which the valve or other prosthetic device is mounted). The sheath  900  further includes a handle portion  904  connected to the proximal end of the sleeve  902 . The sleeve  902  includes an inner layer  906  and an outer layer  908 . The inner layer  906  can be a braided polymeric layer made from a suitable material such as, peek, nylon, or polypropylene. The outer layer  908  can be formed from urethane or another suitable material. The outer surface of the outer layer  908  can be provided with a hydrophilic coating. The handle portion  904  can house one or more sealing valves configured to sealingly engage the outer surface of a delivery apparatus inserted through the sheath, as previously described. 
         [0139]    As shown in  FIG. 25C , the sleeve  902  can be formed with a main lumen  910  sized to permit passage of a delivery apparatus and one or more inner conduits  912  defining side lumens spaced around the main lumen  910 . Extending through each side lumen is a respective pull wire  914 . The proximal end of each pull wire  914  is connected to an adjustment mechanism  916  on the handle portion  904 . The distal end of each pull wire  914  is fixedly secured to the distal end portion of the sleeve  902 . For example, as shown in  FIG. 25D , each pull wire  914  can extend outwardly from the distal end of a respective lumen and can be welded to the inner layer  906  adjacent the distal end of the sleeve. 
         [0140]    The adjustment mechanism  916  is configured to permit manual adjustment of the diameter of the sleeve  902  between a first diameter ( FIG. 25A ) and a second, larger diameter ( FIG. 25B ). In the illustrated embodiment, for example, the adjustment mechanism can move longitudinally relative to the handle portion  904 , in the directions indicated by double-headed arrow  918 . Moving the adjustment mechanism in the proximal direction (away from the sleeve  902 ) is effective to pull the pull wires  914  in the same direction, which causes the sleeve  902  to radially expand and to shorten in length. Moving the adjustment mechanism  914  in the distal direction (toward the sleeve) releases tension on the pull wires  914  to permit the sleeve  902  to radially contract and elongate under its own resiliency. In particular embodiments, the sleeve  902  has an outer diameter of about 18 F in its contracted state and can expand to an outer diameter of about 28 F. 
         [0141]    In use, the sleeve  902  can be inserted into a blood vessel as previously described. As a delivery apparatus (e.g., delivery apparatus  10 ) is inserted through the sleeve  902 , the sleeve  902  can be radially expanded to allow a prosthetic valve (e.g., valve  12 ) or other prosthetic device mounted on the delivery apparatus to easily pass through the sleeve  902 . Once the prosthetic valve is inserted into the blood vessel, the sleeve  902  can be reduced in diameter to minimize occlusion of the vessel. 
         [0142]    In an alternative embodiment, as depicted in  FIG. 25E , the inner layer  906  can be a laser cut tube rather than a braided layer. The tube can be formed with a plurality of longitudinally extending cuts or slits  920  that allow the tube to radially expand and contract. 
         [0143]    The various embodiments of the delivery apparatus disclosed herein can be used for implanting prosthetic devices other than prosthetic heart valves into the body. For example, the delivery apparatus can be used to deliver and deploy various types of intraluminal devices (e.g., stents, stented grafts, etc.) into many types of vascular and non-vascular body lumens (e.g., veins, arteries, esophagus, ducts of the biliary tree, intestine, urethra, fallopian tube, other endocrine or exocrine ducts, etc.). In one specific example, the delivery apparatus can be used to implant a balloon-expandable stent into a coronary artery (or other blood vessels) to maintain the patency of the vessel lumen. 
         [0144]    In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.