Abstract:
In a particular embodiment, the present disclosure provides a delivery apparatus for delivering a medical device. The delivery apparatus includes an elongated component with an engagement portion and a disengagement portion. Rotating the elongated component in a first rotational direction moves the travelling component along the engagement portion in a first axial direction. When the travelling component is located within the disengagement portion, continued rotation of the elongated component in the first rotational direction does not cause further movement of the travelling component in the first axial direction. A biasing member is located proximate the disengagement portion and urges the travelling component to reengage the engagement potion. The delivery apparatus can reduce or prevent damage to the delivery apparatus, or a patient with whom the delivery apparatus is used, by reducing or eliminating torque transfer from the travelling component to an end of the elongated component.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of, and incorporates by reference, U.S. Provisional Patent Application Ser. No. 62/254,124, filed Nov. 11, 2015. 
     
    
     FIELD 
       [0002]    The present disclosure relates generally to moving a travelling component axially along an elongated component upon rotation of the elongated component. Particular implementations relate to elongated components having a disengagement portion for receiving the travelling component and, when so received, continued rotation of the elongated component in a first rotational direction does not result in further axial movement of the travelling component in a first axial direction. 
       BACKGROUND 
       [0003]    Prosthetic cardiac valves have been used for many years to treat cardiac valvular disorders. The native heart valves (such as the aortic, pulmonary, and mitral valves) serve critical functions in assuring the forward flow of an adequate supply of blood through the cardiovascular system. These heart valves can be rendered less effective by congenital, inflammatory, or infectious conditions. Such damage to the valves can result in serious cardiovascular compromise or death. For many years, the definitive treatment for such disorders was the surgical repair or replacement of the valve during open heart surgery, but such surgeries are prone to many complications. More recently a transvascular technique has been developed for introducing and implanting a prosthetic heart valve using a flexible catheter in a manner that is less invasive than open heart surgery. 
         [0004]    In this technique, a prosthetic valve is mounted in a crimped state on the end portion of a flexible catheter and advanced through a blood vessel of the patient until the prosthetic valve reaches the implantation site. The prosthetic valve at the catheter tip is then expanded to its functional size at the site of the defective native valve, such as by inflating a balloon on which the prosthetic valve is mounted. Alternatively, the prosthetic valve can have a resilient, self-expanding stent or frame that expands the prosthetic valve to its functional size when it is advanced from a delivery sheath at the distal end of the catheter. 
         [0005]    Balloon-expandable prosthetic valves typically are preferred for replacing calcified native valves because the catheter balloon can apply sufficient expanding force to anchor the frame of the prosthetic valve to the surrounding calcified tissue. On the other hand, self-expanding prosthetic valves sometimes are preferred for replacing a defective, non-stenotic (non-calcified) native valve, although they also can be used to replace stenotic valves. 
         [0006]    Because the catheter must be directed through a patient&#39;s vasculature, it typically is beneficial for the operator to be able to precisely control the operation of the catheter, including mechanisms that allow the catheter to be bent to assist in navigating the vasculature, and mechanisms that control deployment of the prosthetic valve. 
       SUMMARY 
       [0007]    In various aspects, the present disclosure provides a clutch mechanism that causes a travelling component to engage an elongated component. A travelling component is a component that moves axially along the elongated component in first and second directions when the elongated components is rotated, respectively, in first or second directions. When the travelling component is engaged with the elongated component, rotation of the elongated component in the first rotational direction causes the travelling component to move axially along the elongated component in a first axial direction. When the travelling component is disengaged from the elongated component, continued rotation of the elongated component in the first rotational direction does not cause further axial movement of the travelling component in the first axial direction. When the elongated component is rotated in the second rotational direction, the clutch mechanism facilitates reengagement of the travelling component with the elongated component such that rotation of the elongated component in first and second directions again results in axial movement of the travelling component in, respectively, first or second axial directions. 
         [0008]    Certain embodiments of the present disclosure incorporate a clutch mechanism in a delivery apparatus for a medical device. The delivery apparatus can include an elongated, first component having an engagement portion having threads or grooves and a disengagement portion lacking the threads or grooves. The delivery apparatus can further include a travelling component coaxially disposed relative to the first elongated component. The travelling component can include threads or grooves for engaging the threads or grooves of the first elongated component. In specific examples, the travelling component is a threaded nut, ring, or sleeve. The disengagement portion, in some implementations, has a length that is equal to or greater than the length of a threaded or grooved portion of the travelling component, such as a length that is at least the length of the travelling component. 
         [0009]    In particular implementations, the delivery apparatus includes a biasing member located proximate the disengagement portion of the first elongated component. The biasing member, in a more particular implementation, is a spring. In further implementations, the biasing member, such as the spring, is selected to provide audible or tactile feedback to a user when the biasing member is sufficiently compressed by the travelling component, such as when the traveling component is located in the disengagement portion. 
         [0010]    The first elongated component is configured to be rotatable relative to the traveling component such that rotation of the first elongated component in a first rotational direction causes the travelling component to move axially along the threads or grooves of the engagement portion in a first axial direction. When the travelling component moves into the disengagement portion, it disengages from the threads or grooves of the engagement portion. Further rotation of the first elongated component in the first rotational direction does not cause further axial movement of the travelling component in the first axial direction. When present, the biasing member biases the traveling component against the threads or grooves of the engagement potion such that, upon reversing the rotational direction of the first elongated component, the travelling component is urged by the biasing member to reengage the engagement portion. 
         [0011]    By allowing the travelling component to disengage from the first elongated component, continued rotation of the first elongated component does not continue to axially move the travelling component along the length of the first elongated component, where it could abut and apply undue stress to components located at an end of the first elongated component. Similarly, the ability of the travelling component to disengage from the first elongated shaft can help prevent the travelling component from causing the delivery apparatus to twist, as it might if the torque from the travelling component were transmitted to components at an end of the first elongated component. 
         [0012]    In particular implementations, the engagement portion and the disengagement portion are formed on an inner surface of the first elongated component. In some examples, the delivery apparatus includes a pull wire coupled to the travelling component. The pull wire may be further coupled to a distal end portion of a shaft of the delivery apparatus. Axial movement of the travelling component along the first elongated component causes the distal end portion of the shaft to deflect or return to a pre-deflected position, depending on the direction of axial movement. 
         [0013]    In another implementation, the engagement portion and the disengagement portion are formed on an outer surface of the first elongated component. The delivery apparatus, in some examples, includes a delivery sheath configured to receive and retain a prosthetic valve in a compressed delivery state. The sheath is coupled to the travelling component. Rotation of the first elongated component causes the delivery sheath to advance or retract relative to the prosthetic valve when the travelling component is located on the engagement portion, depending on the direction of rotation. 
         [0014]    In another aspect, the disengagement portion is a first disengagement portion located at a first end of the first elongated component and the first elongated component includes a second disengagement portion located at a second end of the first elongated component. In a particular implementation, the biasing member is a first biasing member located at the first end of the first elongated component and the delivery apparatus includes a second biasing member located at the second end of first elongated component. 
         [0015]    In other embodiments, the present disclosure provides a method that includes inserting the distal end of an elongated delivery apparatus into the vasculature of a patient. The elongated delivery apparatus can include an elongated component having an engagement portion that includes threads or grooves and a disengagement portion lacking the threads or grooves. The elongated component is rotated in a first rotational direction to move a travelling component axially along the engagement portion of the elongated component in a first axial direction. The travelling component is axially moved into the disengagement portion of the elongated component. Continued rotation of the elongated component in the first rotational direction does not cause the travelling component to continue to move axially in the first axial direction. When the rotational direction of the elongated component is reversed, the travelling component reengages the engagement portion of the elongated component and moves axially along the elongated component in a second axial direction. In a particular example, when in the disengagement portion, the travelling component is biased, such as by compressing a spring, to facilitate reengagement of the travelling component with the engagement portion of the elongated component. 
         [0016]    In one implementation, rotating the elongated component causes deflection of a portion of a distal end of the elongated delivery apparatus. For example, the travelling component may pull a pull wire coupled to a distal portion of the travelling component. In another implementation, the elongated delivery apparatus includes a delivery sheath containing a prosthetic valve in a radially compressed state. Rotating the elongated component causes the delivery sheath to move relative to the prosthetic valve. 
         [0017]    In further implementations, the method includes providing tactile or audible feedback to a user when the travelling component is moved within the disengagement portion of the elongated component. In a particular example, the tactile or audible feedback is provided by a biasing member, such as a spring selected to have a suitable spring constant. 
         [0018]    There are additional features and advantages of the various embodiments of the present disclosure. They will become evident from the following disclosure. 
         [0019]    In this regard, it is to be understood that this is a summary of the various embodiments described herein. Any given embodiment of the present disclosure need not provide all features noted above, nor must it solve all problems or address all issues in the prior art noted above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Various embodiments are shown and described in connection with the following drawings in which: 
           [0021]      FIG. 1  is a perspective view of a prosthetic valve that can be used to replace the native aortic valve of the heart, according to one embodiment. 
           [0022]      FIG. 2  is a perspective view of a portion of the prosthetic valve of  FIG. 1  illustrating the connection of two leaflets to the support frame of the prosthetic valve. 
           [0023]      FIG. 3  is side elevation view of the support frame of the prosthetic valve of  FIG. 1 . 
           [0024]      FIG. 4  is a perspective view of the support frame of the prosthetic valve of  FIG. 1 . 
           [0025]      FIG. 5A  is a cross-sectional view of the heart showing the prosthetic valve of  FIG. 1  implanted within the aortic annulus. 
           [0026]      FIG. 5B  is an enlarged view of  FIG. 5A  illustrating the prosthetic valve implanted within the aortic annulus, shown with the leaflet structure of the prosthetic valve removed for clarity. 
           [0027]      FIG. 6  is a perspective view of the leaflet structure of the prosthetic valve of  FIG. 1  shown prior to being secured to the support frame. 
           [0028]      FIG. 7  is a cross-sectional view of the prosthetic valve of  FIG. 1 . 
           [0029]      FIG. 8  is a cross-sectional view of an embodiment of a delivery apparatus that can be used to deliver and implant a prosthetic valve, such as the prosthetic valve shown in  FIG. 1 . 
           [0030]      FIGS. 8A-8C  are enlarged cross-sectional views of sections of  FIG. 8 . 
           [0031]      FIG. 9  is an exploded view of the delivery apparatus of  FIG. 8 . 
           [0032]      FIG. 10  is a side view of the guide catheter of the delivery apparatus of  FIG. 8 . 
           [0033]      FIG. 11  is a perspective, exploded view of the proximal end portion of the guide catheter of  FIG. 10 . 
           [0034]      FIG. 12  is a perspective, exploded view of the distal end portion of the guide catheter of  FIG. 10 . 
           [0035]      FIG. 13  is a side view of the torque shaft catheter of the delivery apparatus of  FIG. 8 . 
           [0036]      FIG. 14  is an enlarged side view of the rotatable screw of the torque shaft catheter of  FIG. 13 . 
           [0037]      FIG. 15  is an enlarged perspective view of a coupling member that may be disposed at the end of the torque shaft of  FIG. 13 . 
           [0038]      FIG. 16  is an enlarged perspective view of the threaded nut used in the torque shaft catheter of  FIG. 13 . 
           [0039]      FIG. 17  is an enlarged side view of the distal end portion of the nose cone catheter of the delivery apparatus of  FIG. 8 . 
           [0040]      FIG. 17A  is an enlarged, cross-sectional view of the nose cone of the nose cone catheter shown  FIG. 17 . 
           [0041]      FIG. 17B  is an enlarged cross-sectional view of the distal end portion of the delivery apparatus of  FIG. 8  showing the stent of a prosthetic valve retained in a compressed state within a delivery sheath. 
           [0042]      FIG. 18  is an enlarged side view of the distal end portion of the delivery apparatus of  FIG. 8  showing the delivery sheath in a delivery position covering a prosthetic valve in a compressed state for delivery into a patient. 
           [0043]      FIG. 19  is an enlarged cross-sectional view of a section of the distal end portion of the delivery apparatus of  FIG. 8  showing the valve-retaining mechanism securing the stent of a prosthetic valve to the delivery apparatus. 
           [0044]      FIG. 20  is an enlarged cross-sectional view similar to  FIG. 19 , showing the inner fork of the valve-retaining mechanism in a release position for releasing the prosthetic valve from the delivery apparatus. 
           [0045]      FIGS. 21 and 22  are enlarged side views of a distal end portion of the delivery apparatus of  FIG. 8 , illustrating the operation of the torque shaft for deploying a prosthetic valve from a delivery sheath. 
           [0046]      FIGS. 23-26  are various views of an embodiment of a motorized delivery apparatus that can be used to operate the torque shaft of the delivery apparatus shown in  FIG. 8 . 
           [0047]      FIG. 27  is a perspective view of an alternative motor that can be used to operate the torque shaft of the delivery apparatus shown in  FIG. 8 . 
           [0048]      FIG. 28A  is an enlarged view of a distal segment of the guide catheter shaft of  FIG. 10 . 
           [0049]      FIG. 28B  shows the cut pattern for forming the portion of the shaft shown in  FIG. 28A , such as by laser cutting a metal tube. 
           [0050]      FIG. 29A  is an enlarged view of a distal segment of a guide catheter shaft, according to another embodiment. 
           [0051]      FIG. 29B  shows the cut pattern for forming the shaft of  FIG. 29A , such as by laser cutting a metal tube. 
           [0052]      FIGS. 30A-30C  are enlarged, cross-sectional views of an alternative implementation of a flex control mechanism useable in the guide catheter of  FIG. 11 . 
           [0053]      FIG. 31A  is a side view of an alternative implementation of a torque shaft catheter useable in the delivery apparatus of  FIG. 8 . 
           [0054]      FIGS. 31B and 31C  are cross-sectional views of the torque shaft catheter of  FIG. 31A . 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    Referring first to  FIG. 1 , there is shown a prosthetic aortic heart valve  10 , according to one embodiment. The prosthetic valve  10  includes an expandable frame member, or stent,  12  that supports a flexible leaflet section  14 . The prosthetic valve  10  is radially compressible to a compressed state for delivery through the body to a deployment site and expandable to its functional size shown in  FIG. 1  at the deployment site. In certain embodiments, the prosthetic valve  10  is self-expanding; that is, the prosthetic valve can radially expand to its functional size when advanced from the distal end of a delivery sheath. Apparatuses particularly suited for percutaneous delivery and implantation of a self-expanding prosthetic valve are described in detail below. In other embodiments, the prosthetic valve can be a balloon-expandable prosthetic valve that can be adapted to be mounted in a compressed state on the balloon of a delivery catheter. The prosthetic valve can be expanded to its functional size at a deployment site by inflating the balloon, as known in the art. 
         [0056]    The illustrated prosthetic valve  10  is adapted to be deployed in the native aortic annulus, although it also can be used to replace the other native valves of the heart. Moreover, the prosthetic valve  10  can be adapted to replace other valves within the body, such venous valves. 
         [0057]      FIGS. 3 and 4  show the stent  12  without the leaflet section  14  for purposes of illustration. As shown, the stent  12  can be formed from a plurality of longitudinally extending, generally sinusoidal shaped frame members, or struts,  16 . The struts  16  are formed with alternating bends and are welded or otherwise secured to each other at nodes  18  formed from the vertices of adjacent bends so as to form a mesh structure. The struts  16  can be made of a suitable shape memory material, such as the nickel titanium alloy known as Nitinol, that allows the prosthetic valve to be compressed to a reduced diameter for delivery in a delivery apparatus (such as described below) and then causes the prosthetic valve to expand to its functional size inside the patient&#39;s body when deployed from the delivery apparatus. If the prosthetic valve is a balloon-expandable prosthetic valve that is adapted to be crimped onto an inflatable balloon of a delivery apparatus and expanded to its functional size by inflation of the balloon, the stent  12  can be made of a suitable ductile material, such as stainless steel. 
         [0058]    The stent  12  has an inflow end  26  and an outflow end  27 . The mesh structure formed by the struts  16  comprises a generally cylindrical “upper” or outflow end portion  20 , an outwardly bowed or distended intermediate section  22 , and an inwardly bowed “lower” or inflow end portion  24 . The intermediate section  22  desirably is sized and shaped to extend into the Valsalva sinuses in the root of the aorta to assist in anchoring the prosthetic valve in place once implanted. As shown, the mesh structure desirably has a curved shape along its entire length that gradually increases in diameter from the outflow end portion  20  to the intermediate section  22 , then gradually decreases in diameter from the intermediate section  22  to a location on the inflow end portion  24 , and then gradually increases in diameter to form a flared portion terminating at the inflow end  26 . 
         [0059]    When the prosthetic valve is in its expanded state, the intermediate section  22  has a diameter D 1 , the inflow end portion  24  has a minimum diameter D 2 , the inflow end  26  has a diameter D 3 , and the outflow end portion  20  has a diameter D 4 , where D 2  is less than D 1  and D 3 , and D 4  is less than D 2 . In addition, D 1  and D 3  desirably are greater than the diameter of the native annulus in which the prosthetic valve is to be implanted. In this manner, the overall shape of the stent  12  assists in retaining the prosthetic valve at the implantation site. More specifically, and referring to  FIGS. 5A and 5B , the prosthetic valve  10  can be implanted within a native valve (the aortic valve in the illustrated example) such that the lower section  24  is positioned within the aortic annulus  28 , the intermediate section  24  extends above the aortic annulus into the Valsalva&#39;s sinuses  56 , and the lower flared end  26  extends below the aortic annulus. The prosthetic valve  10  is retained within the native valve by the radial outward force of the lower section  24  against the surrounding tissue of the aortic annulus  28  as well as the geometry of the stent. Specifically, the intermediate section  24  and the flared lower end  26  extend radially outwardly beyond the aortic annulus  28  to better resist against axial dislodgement of the prosthetic valve in the upstream and downstream directions (toward and away from the aorta). Depending on the condition of the native leaflets  58 , the prosthetic valve  10  typically is deployed within the native annulus  28  with the native leaflets  58  folded upwardly and compressed between the outer surface of the stent  12  and the walls of the Valsalva sinuses, as depicted in  FIG. 5B . In some cases, it may be desirable to excise the leaflets  58  prior to implanting the prosthetic valve  10 . 
         [0060]    Known prosthetic valves having a self-expanding frame typically have additional anchoring devices or frame portions that extend into and become fixed to non-diseased areas of the vasculature. Because the shape of the stent  12  assists in retaining the prosthetic valve, additional anchoring devices are not required and the overall length L of the stent can be minimized to prevent the stent upper portion  20  from extending into the non-diseased area of the aorta, or to at least minimize the extent to which the upper portion  20  extends into the non-diseased area of the aorta. Avoiding the non-diseased area of the patient&#39;s vasculature helps avoid complications if future intervention is required. For example, the prosthetic valve can be more easily removed from the patient because the stent is primarily anchored to the diseased part of the native valve. Furthermore, a shorter prosthetic valve is more easily navigated around the aortic arch. 
         [0061]    In particular embodiments, for a prosthetic valve intended for use in a 22-mm to 24-mm annulus, the diameter D 1  is about 28 mm to about 32 mm, with 30 mm being a specific example; the diameter D 2  is about 24 mm to about 28 mm, with 26 mm being a specific example; the diameter D 3  is about 28 mm to about 32 mm, with 30 mm being a specific example; and the diameter D 4  is about 24 mm to about 28 mm, with 26 mm being a specific example. The length L in particular embodiments is about 20 mm to about 24 mm, with 22 mm being a specific example. 
         [0062]    Referring again to  FIG. 1 , the stent  12  can have a plurality of angularly spaced retaining arms, or projections, in the form of posts  30  (three in the illustrated embodiment) that extend from the stent upper portion  20 . Each retaining arm  30  has a respective aperture  32  that is sized to receive prongs of a valve-retaining mechanism that can be used to form a releasable connection between the prosthetic valve and a delivery apparatus (described below). In alternative embodiments, the retaining arms  30  need not be provided if a valve-retaining mechanism is not used. 
         [0063]    As best shown in  FIGS. 6 and 7 , the leaflet assembly  14  in the illustrated embodiment comprises three leaflets  34   a ,  34   b ,  34   c  made of a flexible material. Each leaflet has an inflow end portion  60  and an outflow end portion  62 . The leaflets can comprise any suitable biological material (e.g., pericardial tissue, such as bovine or equine pericadium), bio-compatible synthetic materials, or other such materials, such as those described in U.S. Pat. No. 6,730,118, which is incorporated herein by reference. The leaflet assembly  14  can include an annular reinforcing skirt  42  that is secured to the outer surfaces of the inflow end portions of the leaflets  34   a ,  34   b ,  34   c  at a suture line  44  adjacent the inflow end of the prosthetic valve. The inflow end portion of the leaflet assembly  14  can be secured to the stent  12  by suturing the skirt  42  to struts  16  of the lower section  24  of the stent (best shown in  FIG. 1 ). As shown in  FIG. 7 , the leaflet assembly  14  can further include an inner reinforcing strip  46  that is secured to the inner surfaces of the inflow end portions  60  of the leaflets. 
         [0064]    Referring to  FIGS. 1 and 2 , the outflow end portion of the leaflet assembly  14  can be secured to the upper portion of the stent  12  at three angularly spaced commissure attachments of the leaflets  34   a ,  34   b ,  34   c . As best shown in  FIG. 2 , each commissure attachment can be formed by wrapping a reinforcing section  36  around adjacent upper edge portions  38  of a pair of leaflets at the commissure formed by the two leaflets and securing the reinforcing section  36  to the edge portions  38  with sutures  48 . The sandwiched layers of the reinforcing material and leaflets can then be secured to the struts  16  of the stent  12  with sutures  50  adjacent the outflow end of the stent. The leaflets therefore desirably extend the entire length or substantially the entire length of the stent from the inflow end  26  to the outflow end  27 . The reinforcing sections  36  reinforce the attachment of the leaflets to the stent so as to minimize stress concentrations at the suture lines and avoid “needle holes” on the portions of the leaflets that flex during use. The reinforcing sections  36 , the skirt  42 , and the inner reinforcing strip  46  desirably are made of a bio-compatible synthetic material, such as polytetrafluoroethylene (PTFE), or a woven fabric material, such as woven polyester (e.g., polyethylene terephtalate (PET)). 
         [0065]      FIG. 7  shows the operation of the prosthetic valve  10 . During diastole, the leaflets  34   a ,  34   b ,  34   c  collapse to effectively close the prosthetic valve. As shown, the curved shape of the intermediate section  22  of the stent  12  defines a space between the intermediate section and the leaflets that mimics the Valsalva sinuses. Thus, when the leaflets close, backflow entering the “sinuses” creates a turbulent flow of blood along the upper surfaces of the leaflets, as indicated by arrows  52 . This turbulence assists in washing the leaflets and the skirt  42  to minimize clot formation. 
         [0066]    The prosthetic valve  10  can be implanted in a retrograde approach where the prosthetic valve, mounted in a crimped state at the distal end of a delivery apparatus, is introduced into the body via the femoral artery and advanced through the aortic arch to the heart, as further described in U.S. Patent Publication No. 2008/0065011, which is incorporated herein by reference. 
         [0067]      FIGS. 8 and 9  show a delivery apparatus  100 , according to one embodiment, that can be used to deliver a self-expanding prosthetic valve, such as prosthetic valve  10  described above, through a patient&#39;s vasculature. The delivery apparatus  100  comprises a first, outermost or main catheter  102  (shown alone in  FIG. 10 ) having an elongated shaft  104 , the distal end of which is coupled to a delivery sheath  106  ( FIG. 18 ; also referred to as a delivery cylinder). The proximal end of the main catheter  102  is connected to a handle of the delivery apparatus. 
         [0068]      FIGS. 23-26  show an embodiment of a handle mechanism having an electric motor for operating the delivery apparatus. The handle mechanism is described in detail below. During delivery of a prosthetic valve, the handle can be used by a surgeon to advance and retract the delivery apparatus through the patient&#39;s vasculature. Although not required, the main catheter  102  can comprise a guide catheter that is configured to allow a surgeon to guide or control the amount of bending or flexing of a distal portion of the shaft  104  as it is advanced through the patient&#39;s vasculature, such as further described below. Another embodiment of a guide catheter is disclosed in U.S. Patent Publication No. 2008/0065011, which is incorporated herein by reference. 
         [0069]    As best shown in  FIG. 9 , the delivery apparatus  100  also includes a second, intermediate catheter  108  (also referred to herein as a torque shaft catheter) having an elongated shaft  110  (also referred to herein as a torque shaft) and an elongated screw  112  connected to the distal end of the shaft  110 . The shaft  110  of the intermediate catheter  108  extends coaxially through the shaft  104  of the main catheter  102 . The delivery apparatus  100  can also include a third, nose-cone catheter  118  having an elongated shaft  120  and a nose piece, or nose cone,  122  secured to the distal end portion of the shaft  120 . The nose piece  122  can have a tapered outer surface as shown for atraumatic tracking through the patient&#39;s vasculature. 
         [0070]    The shaft  120  of the nose-cone catheter  118  extends through the prosthetic valve  10  (not shown in  FIGS. 8-9 ) and the shaft  110  of the intermediate catheter  108 . In the illustrated configuration, the innermost shaft  120  is configured to be moveable axially and rotatably relative to the shafts  104 ,  110 , and the torque shaft  110  is configured to be rotatable relative to the shafts  104 ,  120  to effect valve deployment and release of the prosthetic valve from the delivery apparatus, as described in detail below. Additionally, the innermost shaft  120  can have a lumen for receiving a guide wire so that the delivery apparatus can be advanced over the guide wire inside the patient&#39;s vasculature. 
         [0071]    As best shown in  FIG. 10 , the outer catheter  102  can comprise a flex control mechanism  168  at a proximal end thereof to control the amount the bending or flexing of a distal portion of the outer shaft  104  as it is advanced through the patient&#39;s vasculature, such as further described below. The outer shaft  104  can comprise a proximal segment  166  that extends from the flex control mechanism  168  and a distal segment  126  that comprises a slotted metal tube that increases the flexibility of the outer shaft at this location. The distal end portion of the distal segment  126  can comprises an outer fork  130  of a valve-retaining mechanism  114  ( FIG. 8 ) that is configured to releasably secure a prosthetic valve  10  to the delivery apparatus  100  during valve delivery, as described in detail below. 
         [0072]      FIG. 28A  is an enlarged view of a portion of the distal segment  126  of the outer shaft  104 .  FIG. 28B  shows the cut pattern that can be used to form the distal segment  126  by laser cutting the pattern in a metal tube. The distal segment  126  comprises a plurality of interconnected circular bands or links  160  forming a slotted metal tube. A pull wire  162  can be positioned inside the distal segment  126  and can extend from a location  164  of the distal segment  126  ( FIGS. 10 and 12 ) to the flex control mechanism. The distal end of the pull wire  162  can be secured to the inner surface of the distal segment  126  at location  164 , such as by welding. The proximal end of the pull wire  162  can be operatively connected to the flex control mechanism  168 , which is configured to apply and release tension to the pull wire in order to control bending of the shaft, as further described below. The links  160  of the shaft and the gaps between adjacent links are shaped to allow bending of the shaft upon application of light pulling force on the pull wire  162 . In the illustrated embodiment, as best shown in  FIG. 12 , the distal segment  126  is secured to a proximal segment  166  having a different construction (e.g., one or more layers of polymeric tubing). In the illustrated embodiment, the proximal segment  166  extends from the flex control mechanism  168  to the distal segment  126  and therefore makes up the majority of the length of the outer shaft  104 . In alternative embodiments, the entire length or substantially the entire length of the outer shaft  104  can be formed from a slotted metal tube comprising one or more sections of interconnected links  160 . In any case, the use of a main shaft having such a construction can allow the delivery apparatus to be highly steerable, especially when use in combination with a torque shaft having the construction shown in  FIGS. 13 and 14  (described below). 
         [0073]    The width of the links  160  can be varied to vary the flexibility of the distal segment along its length. For example, the links within the distal end portion of the slotted tube can be relatively narrower to increase the flexibility of the shaft at that location while the links within the proximal end portion of the slotted tube can be relatively wider so that the shaft is relatively less flexible at that location. 
         [0074]      FIG. 29A  shows an alternative embodiment of a distal segment, indicated at  126 ′, which can be formed, for example, by laser cutting a metal tube. The segment  126 ′ can comprise the distal segment of an outer shaft of a delivery apparatus (as shown in  FIG. 12 ) or substantially the entire length of an outer shaft can have the construction shown in  FIG. 29A .  FIG. 29B  shows the cut pattern for forming the segment  126 ′. In another embodiment, a delivery apparatus can include a composite outer shaft comprising a laser-cut metal tube laminated with a polymeric outer layer that is fused within the gaps in the metal layer. In one example, a composite shaft can comprise a laser cut metal tube having the cut pattern of  FIGS. 29A and 29B  and a polymeric outer layer fused in the gaps between the links  160  of the metal tube. In another example, a composite shaft can comprise a laser cut metal tube having the cut pattern of  FIGS. 28A and 28B  and a polymeric outer layer fused in the gaps between the links  160  of the metal tube. A composite shaft also can include a polymeric inner layer fused in the gaps between the links  160  of the metal tube. 
         [0075]    Referring to  FIGS. 8A and 11 , the flex control mechanism  168  can comprise a rotatable housing, or handle portion,  186  that houses a slide nut  188  mounted on a rail  190 . The slide nut  188  is prevented from rotating within the housing by one or more rods  192 , each of which is partially disposed in a corresponding recess within the rail  190  and a slot or recess on the inside of the nut  188 . The proximal end of the pull wire  162  is secured to the nut  188 . The nut  188  has external threads that engage internal threads of the housing  186 . Thus, rotating the housing  186  causes the nut  188  to move axially within the housing in the proximal or distal direction, depending on the direction of rotation of the housing. Rotating the housing in a first direction (e.g., clockwise), causes the nut  188  to travel in the proximal direction, which applies tension to the pull wire  162 , which causes the distal end of the delivery apparatus to bend or flex. Rotating the housing  186  in a second direction (e.g., counterclockwise), causes the nut  188  to travel in the distal direction, which relieves tension in the pull wire  162  and allows the distal end of the delivery apparatus to flex back to its pre-flexed configuration under its own resiliency. 
         [0076]      FIGS. 30A-30C  illustrate an alternative implementation of a flex control mechanism  300 , which includes a clutch mechanism that permits a travelling component, such as the slide nut  188 , to engage and disengage from the threads of an elongated component, such as a handle portion, or housing,  304 . With reference to  FIG. 30A , the housing  304  includes an engagement portion  308  located along a proximal end portion  310  of the housing  304 . The engagement portion  308  includes threads or grooves  314  for engaging the threads or grooves  316  of the slide nut  188  (as best shown in  FIG. 30C ). The housing  304  further includes a disengagement portion  320  located along the distal end portion  322  of the housing  304 . The disengagement portion  320  lacks the threads or grooves of the engagement portion  308 , such as having a smooth annular surface. In other implementations, the disengagement portion  320  may have a different configuration, provided that the slide nut  188  does not move axially with respect to the housing  304  by further rotation of the housing  304  when all of the threads  316  of the nut  188  disengage from the threads  314  of the engagement portion  308  and are received in the disengagement portion  320 . 
         [0077]    The rail  190  desirably extends the entire, or substantially the entire, combined length of the engagement portion  308  and the disengagement portion  320 , such that the nut  188  is supported on the rail  190  as the nut  188  is moved axially between the engagement portion  308  and the disengagement portion  320 , as further described below. One or more rods  192  (not shown in  FIG. 30A-30C , but analogous to the rods  192  of  FIG. 11 ) also desirably extend the entire, or substantially the entire, combined length of the engagement portion  308  and the disengagement portion  320 , so that the nut  188  remains engaged with the one or more rods  192  as the nut  188  is moved axially between the engagement portion  308  and the disengagement portion  320 . 
         [0078]    In at least certain implementations, the size of the disengagement portion  320  is at least about as large, such as being as large or larger than, the threaded portion of the slide nut  188 . For example, the disengagement portion  320  may have a diameter and length greater than at least the threaded portion of the slide nut  188 , or otherwise be sized to receive all, or at least the threaded portion, of the slide nut  188 . The disengagement portion  320  may have a different size, in other examples, provided that the slide nut  188  does not move axially with respect to the housing  304  by further rotation of the housing  304  when all of the threads  316  of the slide nut  188  disengage from the threads  314  of the engagement portion  308  and are received within the disengagement portion  320 . 
         [0079]    Thus, when the slide nut  188  is positioned in the engagement portion  308 , rotation of the housing  304  causes the slide nut  188  to move axially to adjust the tension in a pull wire (not shown in  FIGS. 30A-30C , but analogous to the pull wire  162  of  FIG. 11 , as described above). When the housing  304  is rotated to move the slide nut  188  distally in the direction of arrow  324 , the threads  316  of the slide nut  188  eventually disengage from threads  314  of the housing  304 . When all of the threads  316  of the slide nut  188  disengage from the threads  314  of the housing  304  and are received in the disengagement portion  320  ( FIG. 30C ), further rotation of the housing  304  does not cause the slide nut  188  to move axially in the distal direction. 
         [0080]    In this manner, the flex control mechanism  300  can allow a user to rotate the housing  304  without causing the slide nut  188  to abut and exert undue pressure against the distal end of the housing  304 , or components thereof, such as a ring or bushing  328  disposed at the distal end of the housing  304 , as may happen if the threads or grooves  314  of the housing  304  extended further towards the distal end  322  of the housing  304 . 
         [0081]    In particular examples, the housing  304  includes a biasing device  332  configured to promote re-engagement of the threads  316  of the slide nut  188  with the threads  314  of the housing  304 . In this manner, the biasing device  332  and the disengagement portion  320  of the housing  304  function as a clutch mechanism that engages and disengages the slide nut  188  from the threads  314  of the housing  304 . The biasing device  332  may be, for example, a spring, a spring washer (such as a Belleville washer), or a resilient material, including an elastomer, such as rubber, or a foam. As shown in  FIG. 30A , the biasing device  332  in the illustrated embodiment can be located within the disengagement portion  320  and has one end that abuts the ring  328  and an opposite end that abuts the slide nut  188 . The biasing device  332  is configured to exert an axial, proximally directed force against the slide nut  188  when the slide nut  188  is moved into contact with the biasing device  332 . For example, the biasing device  332  may be selected such that it exerts a desired amount of force against the slide nut  188 . When the biasing device  332  is a spring, the spring may be selected to have a sufficiently large spring constant to exert the desired amount of axial force. 
         [0082]    The biasing device  332  may be selected based on additional properties, in further examples. The biasing device  332  may be selected, for example, to provide tactile or audible feedback to a user when the biasing device  332  reaches a particular level of compression, such as being fully compressed. The tactile or audible feedback may be provided, for example, by selecting a spring with an appropriate spring constant. 
         [0083]      FIG. 30B  illustrates the slide nut  188  having been moved into contact with the biasing device  332 . As shown in  FIG. 30C , continued rotation of the housing  304  causes the slide nut  188  to enter the disengagement portion  320  and to compress the biasing device  332 . The biasing device  332  exerts an axial, proximally-directed force against the slide nut  188 . As discussed above, when the entire threaded portion of the slide nut  188  is received with the disengagement portion  320 , further rotation of the housing  304  does not cause distal axial movement of the slide nut  188 . However, if the direction of rotational movement of the housing  304  is reversed, the biasing device  332  will urge the threads  316  of the slide nut  188  into reengagement with the threads  314  of the housing  304 , and cause the slide nut  188  to move proximally along the engagement section  308 . 
         [0084]    Although  FIGS. 30A-30C  illustrate a disengagement portion  320  and biasing device  332  at the distal end  322  of the housing  304 , it should be appreciated that the flex control mechanism  300  may have other configurations. For example, the housing  304  may include a disengagement portion, and optionally a biasing device, at the proximal end  310  of the housing  304 , in place of, or in addition to, the disengagement portion  320  and biasing device  332  located at the distal end  322  of the housing  304 . 
         [0085]    As best shown in  FIG. 13 , the torque shaft catheter  108  includes an annular projection in the form of a ring  128  (also referred to as an anchoring disc) mounted on the distal end portion of the torque shaft  110  adjacent the screw  112 . The ring  128  is secured to the outer surface of the torque shaft  110  such that it cannot move axially or rotationally relative to the torque shaft. The inner surface of the outer shaft  104  is formed with a feature, such as a slot or recess, that receives the ring  128  in such a manner that the ring and the corresponding feature on the inner surface of the outer shaft  104  allow the torque shaft  110  to rotate relative to the outer shaft  104 , but prevent the torque shaft from moving axially relative to the outer shaft. The corresponding feature on the outer shaft  104  that receives the ring  128  can be inwardly extending tab portions formed in the distal segment  126 , such as shown at  164  in  FIG. 12 . In the illustrated embodiment (as best shown in  FIG. 14 ), the ring  128  is an integral part of the screw  112  (i.e., the screw  112  and the ring  128  are portions of single component). Alternatively, the screw  112  and the ring  128  are separately formed components but are both fixedly secured to the distal end of the torque shaft  110 . 
         [0086]    The torque shaft  110  desirably is configured to be rotatable relative to the delivery sheath  106  to effect incremental and controlled advancement of the prosthetic valve  10  from the delivery sheath  106 . To such ends, and according to one embodiment, the delivery apparatus  100  can include a sheath retaining ring in the form of a threaded nut  150  mounted on the external threads of the screw  112 . As best shown in  FIG. 16 , the nut  150  includes internal threads  152  that engage the external threads of the screw  112  and axially extending legs  154 . Each leg  154  has a raised distal end portion that extends into and/or forms a snap fit connection with openings  172  in the proximal end of the sheath  106  (as best shown in  FIG. 18 ) so as to secure the sheath  106  to the nut  150 . As illustrated in  FIGS. 17B and 18 , the sheath  106  extends over the prosthetic valve  10  and retains the prosthetic valve in a radially compressed state until the sheath  106  is retracted by the user to deploy the prosthetic valve. 
         [0087]    As best shown in  FIGS. 21 and 22 , the outer fork  130  ( FIG. 10 ) of the valve-retaining mechanism comprises a plurality of prongs  134 , each of which extends through a region defined between two adjacent legs  154  of the nut so as to prevent rotation of the nut  150  relative to the screw  112  upon rotation of the screw. As such, rotation of the torque shaft  110  (and thus the screw  112 ) causes corresponding axial movement of the nut  150 . The connection between the nut  150  and the sheath  106  is configured such that axial movement of the nut along the screw  112  (in the distal or proximal direction) causes the sheath  106  to move axially in the same direction relative to the screw and the valve-retaining mechanism. 
         [0088]      FIG. 21  shows the nut  150  in a distal position wherein the sheath  106  (not shown in  FIG. 21 ) extends over and retains the prosthetic valve  10  in a compressed state for delivery. Movement of the nut  150  from the distal position ( FIG. 21 ) to a proximal position ( FIG. 22 ) causes the sheath  106  to move in the proximal direction, thereby deploying the prosthetic valve  10  from the sheath  106 . Rotation of the torque shaft  110  to effect axial movement of the sheath  106  can be accomplished with a motorized mechanism (such as shown in  FIGS. 23-26  and described below) or by manually turning a crank or wheel. 
         [0089]      FIGS. 31A-31C  illustrate an alternative implementation  400  of a torque shaft catheter (generally similar to the torque shaft catheter  108  of  FIG. 13 ), which in this implementation includes a clutch mechanism that allows a travelling component, such as the nut  150 , to engage and disengage from an elongated component, such as a screw  410 . 
         [0090]    The torque shaft  404  in this embodiment includes an engagement portion  408  corresponding to a screw  410 , and thus includes threads or grooves  412  for engaging the mating threads or grooves  152  on the nut  150  (as best shown in  FIG. 16 ). When the nut  150  is positioned on the screw  410 , rotation of the torque shaft  404  causes the nut  150  to move axially along the screw  410 , thereby moving the sheath  106 , as discussed above. 
         [0091]    The torque shaft  404  further includes a disengagement portion  416 . The disengagement portion  416  lacks threads or grooves, such as having a smooth annular surface. In further implementations, the disengagement portion  416  has a different configuration, provided that the nut  150  does not move axially with respect to the torque shaft  404  by further rotation of the torque shaft when all of the threads  152  of the nut  150  disengage from the threads  412  of the screw  410 . 
         [0092]    In at least certain implementations, the size of the disengagement portion  416  is at least about as large, such as being as large or larger than, the threaded portion of the nut  150 . For example, the disengagement portion  416  may have a length greater than at least the threaded portion of the nut  150 , or otherwise be sized to receive all, or at least the threaded portion, of the nut  150 . In the embodiment of  FIGS. 31A-31C , the threads  152  are only on a proximal portion of the nut  150  (the portion of the nut between the proximal ends of the legs  154  and the proximal end of the nut) and not on the legs. As such, the disengagement portion  416  has an axial length at least greater than the length of the proximal portion of the nut  150 . 
         [0093]    In other implementations, the disengagement portion  416  may have a different size and/or shape, provided that the nut  150  does not move axially with respect to the torque shaft  404  by further rotation of the torque shaft  404  when all of the threads  152  of the nut  150  disengage from the threads  412  of the screw  410 . For example, if the legs  154  of the nut  150  are threaded, the size of the disengagement portion  416  may be correspondingly increased. 
         [0094]    When the torque shaft  404  is rotated to move the nut  150  and the sheath  106  proximally in the direction of arrow  420 , the threads  152  of the nut  150  eventually disengage from the threads  412  of the screw  410 . When all of the threads  152  of the nut  150  disengage from the threads  412  of the screw  410  ( FIG. 31C ), further rotation of the torque shaft  404  does not cause the nut  150  to move axially in the proximal direction. In this manner, the torque shaft catheter  400  can allow a user to freely rotate the torque shaft  404  without causing the nut  150  to abut and exert undue pressure against the annular projection  128  once the nut  150  reaches the end of the screw  410 , thereby avoiding torque build-up and undesirable stress on the components of the delivery apparatus. 
         [0095]    In particular examples, the torque shaft catheter  400  includes a biasing device  426  configured to promote re-engagement of the threads  152  of the nut  150  with the threads  412  of the screw  410 . In this manner, the biasing device  426  and the disengagement portion  416  of the torque shaft  404  function as a clutch mechanism that engages and disengages the nut  150  from the screw  410 . The biasing device  426  may be, in various implementations, a spring, a spring washer (such as a Belleville washer), or a resilient material, including elastomers, such as rubber, or foam. 
         [0096]    As shown in  FIG. 31A , the biasing device  426  in the illustrated embodiment is co-axially disposed on the torque shaft  404 , within the disengagement portion  416 , and has one end that abuts the annular projection  128  and an opposite end that abuts the nut  150 . The biasing device  426  is configured to exert an axial, distally directed, force against the nut  150  when the nut is moved into contact with the biasing device. For example, the biasing device  426  may be selected such that it exerts a desired amount of force against the nut  150 . When the biasing device  426  is a spring, the spring may be selected to have a sufficiently large spring constant to exert the desired amount of axial force. 
         [0097]    The biasing device  426  may be selected based on additional properties, in further examples. The biasing device  426  may be selected, in some examples, to provide tactile or audible feedback to a user when the biasing device  426  reaches a particular level of compression, such as being fully compressed. The tactile or audible feedback may be provided by, for example, selecting a spring with an appropriate spring constant, such that the spring vibrates sufficiently to be felt by a user, or emits a noise audible to a user, when compressed. 
         [0098]      FIG. 31B  illustrates the nut  150  having been rotated into contact with the biasing device  426 . As shown in  FIG. 31C , further rotation of the torque shaft  404  causes the nut  150  to enter the disengagement portion  416 , and to compress the biasing device  426 . The biasing device  426  exerts an axial, distally directed force against the nut  150 . As discussed above, when the entire threaded portion of the nut  150  is received within the disengagement portion  416 , further rotation of the torque shaft  404  does not cause axial movement of the nut  150 . However, if the direction of rotation of the torque shaft  404  is reversed, the biasing device  426  will urge the threads of the nut  150  into reengagement with the threads  412  of the screw  410 , and cause the nut  1  to move distally along the screw. 
         [0099]    Although  FIGS. 31A-31C  illustrate a disengagement portion  416  and biasing device  426  adjacent the proximal end of the screw  410 , it should be appreciated that the torque shaft catheter  400  may have other configurations. For example, the torque shaft catheter  400  may include a disengagement portion, and optionally a biasing device, adjacent the distal end of the screw  410 , in place of, or in addition to, the disengagement portion  416  and biasing device  426  adjacent the proximal end of the screw  410 . 
         [0100]      FIG. 17  shows an enlarged view of the nose cone  122  secured to the distal end of the innermost shaft  120 . The nose cone  122  in the illustrated embodiment includes a proximal end portion  174  that is sized to fit inside the distal end of the sheath  106 . An intermediate section  176  of the nose cone is positioned immediately adjacent the end of the sheath  106  in use and is formed with a plurality of longitudinal grooves, or recessed portions,  178 . The diameter of the intermediate section  176  at its proximal end  180  desirably is slightly larger than the outer diameter of the sheath  106 . 
         [0101]    The proximal end  180  can be held in close contact with the distal end of the sheath  106  to protect surrounding tissue from coming into contact with the metal edge of the sheath. The grooves  178  allow the intermediate section  176  to be compressed radially as the delivery apparatus is advanced through an introducer sheath. This allows the nose cone  122  to be slightly oversized relative to the inner diameter of the introducer sheath.  FIG. 17B  shows a cross-section of the nose cone  122  and the sheath  106  in a delivery position, with the prosthetic valve retained in a compressed delivery state inside the sheath  106  (for purposes of illustration, only the stent  12  of the prosthetic valve is shown). As shown, the proximal end  180  of the intermediate section  176  can abut the distal end of the sheath  106  and a tapered proximal surface  182  of the nose cone can extend within a distal portion of the stent  12 . 
         [0102]    As noted above, the delivery apparatus  100  can include a valve-retaining mechanism  114  ( FIG. 8B ) for releasably retaining a stent  12  of a prosthetic valve. The valve-retaining mechanism  114  can include a first valve-securement component in the form of an outer fork  130  (as best shown in  FIG. 12 ) (also referred to as an “outer trident” or “release trident”), and a second valve-securement component in the form of an inner fork  132  (as best shown in  FIG. 17 ) (also referred to as an “inner trident” or “locking trident”). The outer fork  130  cooperates with the inner fork  132  to form a releasable connection with the retaining arms  30  of the stent  12 . 
         [0103]    The proximal end of the outer fork  130  is connected to the distal segment  126  of the outer shaft  104 , and the distal end of the outer fork is releasably connected to the stent  12 . In the illustrated embodiment, the outer fork  130  and the distal segment  126  can be integrally formed as a single component (e.g., the outer fork and the distal segment can be laser cut or otherwise machined from a single piece of metal tubing), although these components can be separately formed and subsequently connected to each other. The inner fork  132  can be mounted on the nose catheter shaft  120  (as best shown in  FIG. 17 ). The inner fork  132  connects the stent to the distal end portion of the nose catheter shaft  120 . The nose catheter shaft  120  can be moved axially relative to the outer shaft  104  to release the prosthetic valve from the valve-retaining mechanism, as further described below. 
         [0104]    As best shown in  FIG. 12 , the outer fork  130  includes a plurality of angularly-spaced prongs  134  (three in the illustrated embodiment) corresponding to the retaining arms  30  of the stent  12 , which prongs extend from the distal end of distal segment  126 . The distal end portion of each prong  134  includes a respective opening  140 . As best shown in  FIG. 17 , the inner fork  132  includes a plurality of angularly-spaced prongs  136  (three in the illustrated embodiment) corresponding to the retaining arms  30  of the stent  12 , which prongs extend from a base portion  138  at the proximal end of the inner fork. The base portion  138  of the inner fork is fixedly secured to the nose catheter shaft  120  (e.g., with a suitable adhesive) to prevent axial and rotational movement of the inner fork relative to the nose catheter shaft  120 . 
         [0105]    Each prong  134  of the outer fork  130  cooperates with a corresponding prong  136  of the inner fork  132  to form a releasable connection with a retaining arm  30  of the stent  12 . In the illustrated embodiment, for example, the distal end portion of each prong  134  is formed with an opening  140 . When the prosthetic valve  10  is secured to the delivery apparatus (as best shown in  FIG. 19 ), each retaining arm  30  of the stent  12  extends inwardly through an opening  140  of a prong  134  of the outer fork  130  and a prong  136  of the inner fork  132  is inserted through the opening  32  of the retaining arm  30  so as to retain the retaining arm from backing out of the opening  140 . 
         [0106]      FIG. 19  shows the prosthetic valve  10  secured to the delivery apparatus by the inner  132  and outer  130  forks before the prosthetic valve is loaded into the sheath  106 . Retracting the inner prongs  136  proximally (in the direction of arrow  184  in  FIG. 20 ) to remove the inner prongs from the openings  32  is effective to release the prosthetic valve  10  from the retaining mechanism. When the inner fork  132  is moved to a proximal position ( FIG. 20 ), the retaining arms  30  of the stent  12  can move radially outwardly from the openings  140  in the outer fork  130  under the resiliency of the stent. In this manner, the valve-retaining mechanism  114  forms a releasable connection with the prosthetic valve that is secure enough to retain the prosthetic valve relative to the delivery apparatus to allow the user to fine tune or adjust the position of the prosthetic valve after it is deployed from the delivery sheath. When the prosthetic valve is positioned at the desired implantation site, the connection between the prosthetic valve and the retaining mechanism can be released by retracting the nose catheter shaft  120  relative to the outer shaft  104  (which retracts the inner fork  132  relative to the outer fork  130 ). 
         [0107]    Techniques for compressing and loading the prosthetic valve  10  into the sheath  106  are described below. Once the prosthetic valve  10  is loaded in the delivery sheath  106 , the delivery apparatus  100  can be inserted into the patient&#39;s body for delivery of the prosthetic valve. In one approach, the prosthetic valve can be delivered in a retrograde procedure where a delivery apparatus is inserted into a femoral artery and advanced through the patient&#39;s vasculature to the heart. Prior to insertion of the delivery apparatus, an introducer sheath can be inserted into the femoral artery followed by a guide wire, which is advanced through the patient&#39;s vasculature through the aorta and into the left ventricle. The delivery apparatus  100  can then be inserted through the introducer sheath and advanced over the guide wire until the distal end portion of the delivery apparatus containing the prosthetic valve  10  is advanced to a location adjacent to or within the native aortic valve. 
         [0108]    Thereafter, the prosthetic valve  10  can be deployed from the delivery apparatus  100  by rotating the torque shaft  110  relative to the outer shaft  104 . As described below, the proximal end of the torque shaft  110  can be operatively connected to a manually rotatable handle portion or a motorized mechanism that allows the surgeon to effect rotation of the torque shaft  110  relative to the outer shaft  104 . Rotation of the torque shaft  110  and the screw  112  causes the nut  150  and the sheath  106  to move in the proximal direction toward the outer shaft ( FIG. 22 ), which deploys the prosthetic valve from the sheath. 
         [0109]    Rotation of the torque shaft  110  causes the sheath  106  to move relative to the prosthetic valve in a precise and controlled manner as the prosthetic valve advances from the open distal end of the delivery sheath and begins to expand. Hence, unlike known delivery apparatuses, as the prosthetic valve  10  begins to advance from the delivery sheath  106  and expand, the prosthetic valve is held against uncontrolled movement from the sheath caused by the expansion force of the prosthetic valve against the distal end of the sheath. In addition, as the sheath  106  is retracted, the prosthetic valve  10  is retained in a stationary position relative to the ends of the inner shaft  120  and the outer shaft  104  by virtue of the valve-retaining mechanism  114 . As such, the prosthetic valve  10  can be held stationary relative to the target location in the body as the sheath  106  is retracted. Moreover, after the prosthetic valve  10  is partially advanced from the sheath  106 , it may be desirable to retract the prosthetic valve back into the sheath, for example, to reposition the prosthetic valve or to withdraw the prosthetic valve entirely from the body. The partially deployed prosthetic valve  10  can be retracted back into the sheath  106  by reversing the rotation of the torque shaft, which causes the sheath to advance back over the prosthetic valve in the distal direction. 
         [0110]    In known delivery devices, the surgeon must apply push-pull forces to the shaft and/or the sheath to unsheathe the prosthetic valve. It is therefore difficult to transmit forces to the distal end of the device without distorting the shaft (e.g., compressing or stretching the shaft axially), which in turn causes uncontrolled movement of the prosthetic valve during the unsheathing process. To mitigate this effect, the shaft and/or sheath can be made more rigid, which is undesirable because the device becomes harder to steer through the vasculature. In contrast, the manner of unsheathing the prosthetic valve described above eliminates the application of push-pull forces on the shaft, as required in known devices, so that relatively high and accurate forces can be applied to the distal end of the shaft without compromising the flexibility of the device. In certain embodiments, as much as 20 lbs. of force can be transmitted to the end of the torque shaft without adversely affecting the unsheathing process. In contrast, prior art devices utilizing push-pull mechanisms typically cannot exceed about 5 lbs. of force during the unsheathing process. 
         [0111]    After the prosthetic valve  10  is advanced from the delivery sheath  106  and expands to its functional size, the prosthetic valve remains connected to the delivery apparatus via the retaining mechanism  114 . Consequently, after the prosthetic valve  10  is advanced from the delivery sheath  106 , the surgeon can reposition the prosthetic valve relative to the desired implantation position in the native valve, such as by moving the delivery apparatus in the proximal and distal directions or side to side, or rotating the delivery apparatus, which causes corresponding movement of the prosthetic valve. The retaining mechanism  114  desirably provides a connection between the prosthetic valve  10  and the delivery apparatus that is secure and rigid enough to retain the position of the prosthetic valve relative to the delivery apparatus against the flow of the blood as the position of the prosthetic valve is adjusted relative to the desired implantation position in the native valve. 
         [0112]    Once the surgeon positions the prosthetic valve  10  at the desired implantation position in the native valve, the connection between the prosthetic valve and the delivery apparatus can be released by retracting the innermost shaft  120  in the proximal direction relative to the outer shaft  104 , which is effective to retract the inner fork  132  to withdraw its prongs  136  from the openings  32  in the retaining arms  30  of the prosthetic valve ( FIG. 20 ). Slightly retracting of the outer shaft  104  allows the outer fork  130  to back off the retaining arms  30  of the prosthetic valve  10 , which slide outwardly through openings  140  in the outer fork to completely disconnect the prosthetic valve from the retaining mechanism  114 . Thereafter, the delivery apparatus can be withdrawn from the body, leaving the prosthetic aortic valve  10  implanted within the native valve (such as shown in  FIGS. 5A and 5B ). 
         [0113]    The delivery apparatus  100  has at its distal end a semi-rigid segment comprised of relatively rigid components used to transform rotation of the torque shaft into axial movement of the sheath. In particular, this semi-rigid segment in the illustrated embodiment is comprised of the prosthetic valve and the screw  112 . An advantage of the delivery apparatus  100  is that the overall length of the semi-rigid segment is minimized because the nut  150  is used rather than internal threads on the outer shaft to affect translation of the sheath  106 . The reduced length of the semi-rigid segment increases the overall flexibility along the distal end portion of the delivery catheter. Moreover, the length and location of the semi-rigid segment remains constant because the torque shaft does not translate axially relative to the outer shaft. As such, the curved shape of the delivery catheter can be maintained during valve deployment, which improves the stability of the deployment. A further benefit of the delivery apparatus  100  is that the ring  128  prevents the transfer of axial loads (compression and tension) to the section of the torque shaft  110  that is distal to the ring. 
         [0114]    In an alternative embodiment, the delivery apparatus can be adapted to deliver a balloon-expandable prosthetic valve  10 . As described above, the valve retaining mechanism  114  can be used to secure the prosthetic valve to the end of the delivery apparatus. Since the stent  12  of the prosthetic valve  10  is not self-expanding, the sheath  106  can be optional. The retaining mechanism  114  enhances the pushability of the delivery apparatus and prosthetic valve assembly through an introducer sheath. 
         [0115]      FIGS. 23-26  illustrate the proximal end portion of the delivery apparatus  100 , according to one embodiment. The delivery apparatus  100  can comprise a handle  202  that is configured to be releasably connectable to the proximal end portion of a catheter assembly  204  comprising catheters  102 ,  108 ,  118 . It may be desirable to disconnect the handle  202  from the catheter assembly  204  for various reasons. For example, disconnecting the handle  202  can allow another device to be slid over the catheter assembly  204 , such as a valve-retrieval device or a device to assist in steering the catheter assembly. It should be noted that any of the features of the handle  202  and the catheter assembly  204  can be implemented in any of the embodiments of the delivery apparatuses disclosed herein. 
         [0116]      FIGS. 23 and 24  show the proximal end portion of the catheter assembly  204  partially inserted into a distal opening of the handle  202 . The proximal end portion of the main shaft  104  is formed with an annular groove  212  (as best shown in  FIG. 24 ) that cooperates with a holding mechanism, or latch mechanism,  214  inside the handle  202 . When the proximal end portion of the catheter assembly  204  is fully inserted into the handle  202 , as shown in  FIGS. 25 and 26 , an engaging portion  216  of the holding mechanism  214  extends at least partially into the groove  212 . 
         [0117]    One side of the holding mechanism  214  is connected to a button  218  that extends through the housing of the handle  202 . The opposite side of the holding mechanism  214  is contacted by a spring  220  that biases the holding mechanism to a position engaging the main shaft  104  at the groove  212 . The engagement of the holding mechanism  214  within the groove  212  prevents axial separation of the catheter assembly  204  from the handle  202 . The catheter assembly  204  can be released from the handle  202  by depressing button  218 , which moves the holding mechanism  214  from locking engagement with the main shaft  104 . Furthermore, the main shaft  104  can be formed with a flat surface portion within the groove  212 . The flat surface portion is positioned against a corresponding flat surface portion of the engaging portion  216 . This engagement holds the main shaft  104  stationary relative to the torque shaft  110  as the torque shaft is rotated during valve deployment. 
         [0118]    The proximal end portion of the torque shaft  110  can have a driven nut  222  ( FIG. 26 ) that is slidably received in a drive cylinder  224  ( FIG. 25 ) mounted inside the handle  202 . The nut  222  can be secured to the proximal end of the torque shaft  100  by securing the driven nut over a coupling member  170  ( FIG. 15 ).  FIG. 26  is a perspective view of the inside of the handle  202  with the drive cylinder  224  and other components removed to show the driven nut  222  and other components positioned within the drive cylinder. The drive cylinder  224  has a through opening (or lumen) extending the length of the cylinder that is shaped to correspond to the flats of the nut  222  such that rotation of the drive cylinder is effective to rotate the nut and the torque shaft  110 . The drive cylinder  224  can have an enlarged distal end portion  236  that can house one or more seals (e.g., O-rings  246 ) that form a seal with the outer surface of the main shaft  104  ( FIG. 25 ). The handle  202  can also house a fitting  238  that has a flush port in communication with the lumen of the torque shaft  110  and/or the lumen of the main shaft  104 . 
         [0119]    The drive cylinder  224  is operatively connected to an electric motor  226  through gears  228  and  230 . The handle  202  can also house a battery compartment  232  that contains batteries for powering the motor  226 . Rotation of the motor  226  in one direction causes the torque shaft  110  to rotate, which in turn causes the sheath  106  to retract and uncover a prosthetic valve  10  at the distal end of the catheter assembly. Rotation of the motor  226  in the opposite direction causes the torque shaft  110  to rotate in an opposite direction, which causes the sheath  106  to move back over the prosthetic valve  10 . An operator button  234  on the handle  202  allows a user to activate the motor  226 , which can be rotated in either direction to un-sheath a prosthetic valve  10  or retrieve an expanded or partially expanded prosthetic valve. 
         [0120]    As described above, the distal end portion of the nose catheter shaft  120  can be secured to an inner fork  132  that is moved relative to an outer fork  130  to release a prosthetic valve  10  secured to the end of the delivery apparatus. Movement of the shaft  120  relative to the main shaft  104  (which secures the outer fork  130 ) can be effected by a proximal end portion  240  of the handle  202  that is slidable relative to the main housing  244 . The end portion  240  is operatively connected to the shaft  120  such that movement of the end portion  240  is effective to translate the shaft  120  axially relative to the main shaft  104  (causing a prosthetic valve  10  to be released from the inner  132  and outer  130  forks). 
         [0121]    The end portion  240  can have flexible side panels  242  on opposite sides of the handle  202  that are normally biased outwardly in a locked position to retain the end portion relative to the main housing  244 . During deployment of the prosthetic valve  10 , the user can depress the side panels  242 , which disengage from corresponding features in the housing  244  and allow the end portion  240  to be pulled proximally relative to the main housing, which causes corresponding axial movement of the shaft  120  relative to the main shaft. Proximal movement of the shaft  120  causes the prongs  136  of the inner fork  132  to disengage from the apertures  32  in the stent  12 , which in turn allows the retaining arms  30  of the stent to deflect radially outwardly from the openings  140  in the prongs  134  of the outer fork  130 , thereby releasing the prosthetic valve. 
         [0122]      FIG. 27  shows an alternative embodiment of a motor, indicated at  400 , that can be used to drive a torque shaft (e.g., torque shaft  110 ). In this embodiment, a catheter assembly can be connected directly to one end of a shaft  402  of the motor, without gearing. The shaft  402  includes a lumen that allows for passage of an innermost shaft (e.g., shaft  120 ) of the catheter assembly, a guide wire, and/or fluids for flushing the lumens of the catheter assembly. 
         [0123]    Alternatively, the power source for rotating the torque shaft  110  can be a hydraulic power source (e.g., hydraulic pump) or pneumatic (air-operated) power source that is configured to rotate the torque shaft. In another embodiment, the handle  202  can have a manually movable lever or wheel that is operable to rotate the torque shaft  110 . 
         [0124]    In another embodiment, a power source (e.g., an electric, hydraulic, or pneumatic power source) can be operatively connected to a shaft, which is turn is connected to a prosthetic valve  10 . The power source is configured to reciprocate the shaft longitudinally in the distal direction relative to a valve sheath in a precise and controlled manner in order to advance the prosthetic valve from the sheath. Alternatively, the power source can be operatively connected to the sheath in order to reciprocate the sheath longitudinally in the proximal direction relative to the prosthetic valve to deploy the prosthetic valve from the sheath. 
       General Considerations 
       [0125]    For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, devices, and systems should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods, devices, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved. 
         [0126]    Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
         [0127]    Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. As used herein, the terms “a”, “an” and “at least one” encompass one or more of the specified element. That is, if two of a particular element are present, one of these elements is also present and thus “an” element is present. The terms “a plurality of” and “plural” mean two or more of the specified element. 
         [0128]    As used herein, the term “and/or” used between the last two of a list of elements means any one or more of the listed elements. For example, the phrase “A, B, and/or C” means “A,” “B,” “C,” “A and B,” “A and C,” “B and C” or “A, B and C.” 
         [0129]    As used herein, the term “coupled” generally means physically coupled or linked and does not exclude the presence of intermediate elements between the coupled items absent specific contrary language. 
         [0130]    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. Accordingly, 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.