Abstract:
Valve delivery catheter assemblies including components that limit trauma to the expanded prosthetic valve and body channels as the distal tip of the catheter is withdrawn through the expanded valve and thereafter from the body. In one embodiment, a catheter assembly according to the present invention includes a handle assembly, an introducer sheath, and a distal tip assembly. The handle assembly cap include a fixed main handle and two or more rotating handles that allow a user to control the distal tip assembly of the catheter. A valve retaining mechanism ears be included to assist in retaining the prosthetic valve prior to deployment. Each control knob on the handle assembly controls a portion of the components on the distal tip of the catheter by allowing for precise manipulation of various delivery shafts. Each delivery shaft extends from the handle assembly to respective positions towards the distal end of the catheter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit under 35 U.S.C. 119(e) to U.S. Provisional Patent Application 61/305,484, filed Feb. 17, 2010, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to heart valve delivery catheters and methods of delivering and implanting heart valves using delivery catheters. More specifically, the present invention relates to a delivery catheter with an improved handle design for controlling delivery of a heart valve via the catheter. 
       Background 
       [0003]    Recently, minimally invasive approaches have been developed to facilitate catheter-based implantation of valve prostheses on the beating heart, intending to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. For example, French Patent Application No. 99 14462 illustrates a technique and a device for the ablation of a deficient heart valve by percutaneous route, with a peripheral valvular approach. International Application (PCT) Nos. WO 93/01768 and WO 97/28807, as well as U.S. Pat. No. 5,814,097 to Sterman et al., U.S. Pat. No. 5,370,685 to Stevens, and U.S. Pat. No. 5,545,214 to Stevens illustrate techniques that are not very invasive as well as instruments for implementation of these techniques. 
         [0004]    U.S. Pat. No. 3,671,979 to Moulopoulos and U.S. Pat. No. 4,050,854 to Boretos describe catheter-mounted artificial heart valves for implantation in close proximity to a defective heart valve. Both of these prostheses are temporary in nature and require continued connection to the catheter for subsequent repositioning or removal of the valve prosthesis, or for subsequent valve activation. 
         [0005]    With regard to the positioning of a replacement heart valve, attaching a valve on a support with a structure in the form of a wire or network of wires, forming a frame, has been proposed. This frame can be contracted radially in such a way that it can be introduced into the body of the patient percutaneously by means of a catheter, and it can he deployed so as to be radially expanded once it is positioned at the desired target site. U.S. Pat. No. 3,657,744 to Ersek discloses a cylindrical, frame-supported, tri-leaflet tissue heart valve that can be delivered through a portion of the vasculature using an elongate tool. The frame is mounted onto the expansion toot prior to delivery to the target location where the frame and valve are expanded into place. 
         [0006]    Current techniques for delivering prosthetic heart valves via a catheter include a transpical approach for aortic valve replacement, typically involving the use of an introducer port, i.e., a large-bore overtube, of a trocar. A crimped, framed valve prosthesis reversibly coupled to a delivery catheter is transcatheterally advanced toward the native valve, where it is either forcefully deployed using a balloon catheter, or, alternatively, passively deployed using a self-expandable system. Accurate positioning of the replacement valve in the native annulus is critical to the success of the implantation. Although prior delivery catheter assemblies are sufficient to delivery a prosthetic valve to the native annulus, they do not provide a precise release mechanism for the valve such that error in placing the prosthetic valve in the native annulus is reduced. 
         [0007]    The present invention provides a delivery catheter with an improved handle design for controlling delivery of a heart valve via the catheter. Delivery catheters according to embodiments of the present invention can include two or more rotatable control knobs on the catheter handle. These control knobs allows for accurate manipulation of the distal tip of the catheter. Delivery catheters according to embodiments of the present invention can also allow for further adjustment of the delivery position of a prosthetic valve retained by the distal tip of the catheter after a portion of the prosthetic valve has been exposed to the body channel. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The catheter assemblies described herein seek to remedy one or more of the disadvantages of previous heart valve delivery catheters by providing catheters that allow for precise control of the release point of a prosthetic heart valve within the body. The catheter assemblies provided herein can also include components that limit trauma to the expanded prosthetic valve and body channels as the distal tip of the catheter is withdrawn through the expanded valve and thereafter from the body. In one embodiment, a catheter assembly according to the present invention includes a handle assembly, an introducer sheath, and a distal tip assembly. The handle assembly can include a fixed main handle and two or more rotating handles that allow a user to control the distal tip assembly of the catheter. The distal tip assemblies described herein can include a slotted tip for breaching the apex of the heart during a transapical delivery approach. Distal tip assemblies may also include two or more sleeves for retaining a prosthetic valve prior to deployment of the prosthetic valve. A valve retaining mechanism can be included to assist in retaining the prosthetic valve prior to deployment. Each control knob on the handle assembly controls a portion of the components on the distal tip of the catheter by allowing for precise manipulation of various delivery shafts. Each delivery shaft extends from the handle assembly to respective positions towards the distal end of the catheter. Preferably, rotating one of the control knobs causes a distal sleeve on the distal tip of the catheter to move in a distal direction, thereby at least partially releasing a prosthetic valve. Rotating a second one of the control knobs can cause a proximal sleeve on the distal tip of the catheter to move in a proximal direction, thereby fully releasing a self-expanding prosthetic valve at a desired location in the body. Once the valve is deployed, the catheter can be withdrawn from the body. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The accompanying figures, which are incorporated herein, form part of the specification and illustrate embodiments of heart valve delivery catheters end methods of delivering and implanting heart valves using delivery catheters. Together with the description, the figures further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the delivery catheters and methods of using delivery catheters described herein. In the drawings, like reference numbers indicate identical or functionally similar elements. 
           [0010]      FIG. 1  illustrates a closed catheter assembly in accordance with one embodiment presented herein. 
           [0011]      FIG. 2  illustrates the catheter assembly of  FIG. 1  in an open configuration. 
           [0012]      FIG. 3  is a depiction of the distal tip assembly and introducer of a catheter according to one embodiment of the present invention in a closed configuration. 
           [0013]      FIG. 4  illustrates the distal tip and introducer assemblies of a catheter in accordance with one embodiment presented herein in a partially open configuration. 
           [0014]      FIG. 5  illustrates a delivery catheter handle in accordance with one embodiment presented herein. 
           [0015]      FIG. 6  illustrates a simplified interior of a delivery catheter handle in accordance with one embodiment of the present invention. 
           [0016]      FIG. 7  illustrates a second simplified view of a portion of a delivery catheter handle in accordance with one embodiment of the present invention. 
           [0017]      FIG. 8  illustrates the distal tip assembly shown in  FIGS. 3 and 4  in one stage of delivery. 
           [0018]      FIG. 9  illustrates the distal tip assembly shown in  FIGS. 3 and 4  in a second stage of delivery. 
           [0019]      FIG. 10  illustrates the distal tip assembly shown in  FIGS. 3 and 4  in a third stage of delivery. 
           [0020]      FIG. 11  illustrates the distal tip assembly shown in  FIGS. 3 and 4  in one stage of withdrawal. 
           [0021]      FIG. 12  illustrates the distal tip assembly and introducer shown in  FIGS. 3 and 4  in a second stage of withdrawal. 
           [0022]      FIG. 13  is a flow diagram that is used as an aid to describe a method of implanting a prosthetic heart valve in a patient. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The following detailed description of heart valve delivery catheters and methods of delivering and implanting heart valves refers to the accompanying figures that illustrate exemplary embodiments. Other embodiments are possible. Modifications can be made to the embodiments described herein without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not meant to be limiting. Further, it would be apparent to one of skill in the art that the systems and methods described below can be implemented in many different embodiments of hardware. Any actual hardware described is not meant to be limiting. The operation and behavior of the systems and methods presented are described with the understanding that modifications and variations of the embodiments are possible given the level of detail presented. For example, while the description provided is directed to catheters for transapical delivery of a heart valve, the catheters and individual features of the catheters described herein should not be limited to transapical delivery of a heart valve. One of skill in the art would readily understand how to incorporate the features and structures described herein, into catheters intended for other purposes. For example, features of the catheters described herein can be incorporated into catheters intended for other types of transluminal heart valve delivery as well as catheters intended for thorascopic heart valve delivery. Features of the catheters described herein can also be incorporated into catheters designed for delivery of stems or valves to areas of the body other than the heart. 
         [0024]      FIG. 1  illustrates a catheter assembly  100  in accordance with one embodiment presented herein. Catheter assembly  100  is depicted in  FIG. 1  in a closed configuration. Catheter assembly  100  generally includes a handle assembly  102  located at the proximal end of the catheter, a distal tip assembly  104  located at the distal end of the catheter, and an introducer  116  slidably located along a outer delivery shaft  100  between the distal tip assembly  104  and the handle assembly  102 . 
         [0025]    Outer delivery shaft  106  is preferably a tubular flexible braided structure. Outer delivery snail  100  can be formed of braided material fabricated from materials such as, but not limited to, polyethylene naphthalate (PEN), polyester (PET), stainless steel, titanium, nitinol, cobalt, nickel alloy, polyamide, polyimide, or the like. In some embodiment, outer delivery shaft may contain reinforcing materials or structures. These structures can include an inner layer of polymer overlaid by a first reinforcing braid layer, overlaid by a coil reinforcement, finally overlaid with an outside layer of polymeric material. In another embodiment, the inner layer of polymeric material is overlaid by the coil reinforcements, which is overlaid by tile braided reinforcement, which is finally overlaid with the outside layer of a polymeric material. In other embodiments, the inner layer of polymeric material is overlaid by a braided layer, which is overlaid by the coil winding, which is overlaid by another layer of braid, which is in turn overlaid by an outer polymeric layer. Preferably, however, any reinforcing layer used allows outer delivery shaft  106  to retain a degree of flexibility. Other flexible materials can also be used to form outer delivery shaft  106  consistent with embodiments of the present invention. 
         [0026]    Handle assembly  102  includes a main handle  108 , a proximal control knob  110 , and a distal control knob  112 . Main handle  108 , a proximal control, knob  110 , and distal control knot  112  can be formed of any suitable material. For example, in some embodiments the handle and control knobs are formed of a polymer material. Other materials are possible, as would be understood in the art. A flushing port  114  can also be included on main handle  108 . Flushing port  114  can be used to de-air the catheter assembly. Also, the native annulus is exposed to the blood pressure in a patient&#39;s cardiovascular system during use of a heart valve delivery catheter. As a consequence, in the absence of any counter pressure in this annulus, blood can flow inside towards the proximal end of the catheter, where it may coagulate and cause thrombosis. Thus, flushing port  114  can also allow fluid to be introduced into the native annulus to prevent such complications. In some embodiments, flushing port  114  can also be used for site specific drug delivery or to introduce radiopaque fluid into the body. 
         [0027]    As will be described herein, proximal control knob  110 , and distal control knob  112  can be manipulated by a user in order to control operation of the distal tip assembly  104  of catheters described herein. A detailed description of the operation and structure of handle assembly  102  is provided below, particularly with reference to  FIGS. 5-10 . Distal tip assembly  104  includes a tip  122 , which is preferably slotted for the reasons described herein, a tip connector  124 , and a support arm sleeve  126 . A flushing tap  118  and a flushing tap lead  120  can be connected to an introducer  116 . Introducer  116  is preferably a tubular member that is slidably located over outer delivery shaft  100 . Introducer  316  may be formed of a variety of materials, for example, stainless steel or various polymer materials. A detailed description of the operation and structure of distal tip assembly  104  and introducer  116  is provided below, particularly with reference to  FIGS. 2-4  and  8 - 12 . Catheter  100  is configured to be advanced along a guide wire (not shown). Preferably, the catheter is advanced over a 0.035 inch guide wire. However, the dimensions of the catheter components can be adjusted for advancement over guide wires with larger or smaller diameters. 
         [0028]      FIG. 2  illustrates catheter assembly  100  in an open configuration. Catheter assembly  100  reaches the open configuration when introducer  116  is moved proximally along outer delivery shaft  106  to expose a valve retaining sleeve  204 , a valve retaining sleeve connector  208 , and semi-sphere  202  of distal tip assembly  104 . Valve retaining sleeve connector  208  secures valve retaining sleeve  204  to the distal end of the outer delivery shaft  106 . The outer delivery shaft  106  therefore extends from the interior of handle assembly  102  to sleeve connector  208 . Slotted tip  122  and semi-sphere  202  are positioned on and connected to the distal end of an intermediate delivery shaft  206 . Intermediate delivery shaft  206  extends from the interior of handle assembly  102  to slotted tip  122 , to which the distal end of intermediate delivery shaft  206  is attached. Intermediate delivery shaft  206  is encompassed by outer delivery shaft  106  from the interior of handle assembly  102  until the outer delivery shaft  106  ends at sleeve connector  208 . Semi-sphere  202  is attached to the proximal end of slotted tip  122 . In one embodiment, semi-sphere  202  can he attached directly to intermediate shaft  206 . Intermediate shaft  206  is preferably a tubular member. 
         [0029]    A guide wire shaft  504  (shown in  FIG. 5 ) is encompassed within intermediate shaft  206  and extends from the Inside of handle assembly  102  to the proximal end of slotted tip  122 . Thus, in one embodiment of the present invention, at least three shafts extend from the main handle, and the shafts are nested along at least a part of their lengths. Specifically, guide wire shaft  504  is encompassed by the intermediate delivery shaft  206  from a position inside of handle assembly  102  to the interior of slotted tip  122 , which is preferably hollow through at least a portion thereof. Intermediate delivery shaft  206  is connected to, and ends, at the proximal end of slotted tip  122 . In turn, intermediate delivery shaft  206  is encompassed by the outer delivery shaft  106  from a position inside of handle assembly  102  to the valve retaining sleeve connector  208 . Outer delivery shaft  106  is connected to, and ends, at the retaining sleeve connector  208 . Intermediate shaft  206  and guide wire shaft  504  can be constructed of various polymer materials, and may be braided structures using materials described above with reference to outer delivery shaft  106 . 
         [0030]      FIG. 3  is a depiction dm distal tip assembly  104  and introducer  116  of a catheter according to one embodiment of the present invention in a closed configuration. Introducer  116 , valve retaining sleeve  204 , support arm sleeve  126 , and tip connector  124  are rendered transparent in  FIG. 3  in order to Facilitate description of certain components. Tip connector  124  is slidably positioned over the proximal end of slotted tip  122 , as will be detailed below with reference to  FIG. 4 . The distal end of intermediate delivery shaft  206  is connected to slotted tip  122 . A simplified rendering of a prosthetic heart valve  304  is shown attached to a valve retainer  302 . Valve retainer  302  is also connected to intermediate delivery shaft  206 . Valve retainer  302  serves to retain prosthetic valve  304  in place during delivery to the desired location within a patient. Valve retainer  302  can be made from a polymer or metal material suitable for exposure to a patient&#39;s circulatory system. Prosthetic valve  304  preferably has a frame that is formed from a self-expanding material, for example, Nitinol. This material allows the structure to be contracted radially at a temperature different from that of the body of the patient and to regain its original expanded shape when its temperature approaches or reaches that of the body of the patient. The valve portion of prosthetic valve  304  can be made of biological tissue, such as bovine or porcine pericardium, or from synthetic materials. When in a closed configuration, at least a portion of prosthetic valve  304 , and valve retainer  302 , are encompassed by valve retaining sleeve  204 , and valve retaining sleeve  204  is in turn encompassed by introducer  116 . In this configuration, the distal end of introducer  116  abuts the proximal end of support arm sleeve  126 . 
         [0031]      FIG. 4  Illustrates the distal tip assembly  104  of a catheter in accordance with one embodiment presented herein in a partially open configuration. As shown in  FIG. 4 , tip connector  124  is affixed to the guide wire shaft  504  (not shown in  FIG. 4 ) via a connecting tin  404 . Connecting fin  404  is attached to the distal end of guide wire shaft  504 . An axial slot (not shown) in slotted tip  122  allows the connecting fin  404  to slide axially along slotted tip  122  when guide ware shaft  504  is moved in a distal direction. As noted above, slotted tip  122  is affixed to the distal end of intermediate delivery shaft  206 . The proximal end of intermediate delivery shaft  206  is preferably fixed in a stationary position inside handle assembly  102 . Thus, slotted tip  122  and semi-sphere  202 , which is preferably connected to slotted tip  122 , are held in a fixed position by intermediate delivery shaft  206  when guide wire shaft  504  is moved in an axial direction. In one embodiment, tip connector  124  is affixed to connecting fin  404  by over-molding the tip connector  124  around the connecting fin  404 . It is understood that tip connector  124  can be affixed to fin  404  by any one of several suitable methods, such as a tongue and groove assembly, gluing, etc. The distal cud of support arm sleeve  126  is connected to the proximal end of tip connector  124  so that the support arm sleeve  126  and tip connector  124  move together. In the configuration shown in  FIG. 4 , intermediate delivery shaft  206  has been advanced distally while outer delivery shaft  106  is retained in a fixed position. 
         [0032]      FIG. 5  illustrates a delivery catheter handle assembly  102  in accordance with one embodiment presented herein. Handle assembly  102  includes a main handle  108 , a rotatable proximal control knob  110 , and a rotatable distal control knob  112 . The handle sections of handle assembly  102  are preferably connected using O-rings (not shown). As seen in  FIG. 7 , knob pins  714  on the distal end of bundle assembly  102  locate distal control knob  112  on handle assembly  102 . A circular channel (not shown) is formed on the interior surface of distal control knob  112 , and the channel receives knob pins  714 , thereby preventing movement of distal control knob  112  in an axial direction while permitting rotation of distal control knob  112  around the longitudinal axis of handle assembly  102 . Knob pins  710  located under the proximal end of proximal control knob  110  locate proximal control knob  110  on handle assembly  102 . A circular channel (not shown) is formed on the interior surface of proximal control knob  110 , and the channel receives knob pins  716 , thereby preventing movement of proximal control knob  110  in an axial direction while permitting rotation of proximal control knob  110  around the longitudinal axis of handle assembly  102 . It is understood that the handle sections can be connected using other mechanisms that would allow movement of the sections relative to each other. Other structures can be used to secure control knobs  110  and  112  to handle assembly  102  to prevent axial movement thereof. For example, circular ridges can be provided in handle assembly in place of pins  714  and  716  in order to mate with the circular grooves formed on the interior surfaces of knobs  110  and  112 . A ratchet system can also be used to rotatably secure control knobs  110  and  112  to handle assembly  102 . Both proximal control knob  110  and distal control knob  112  are threaded on their interior surfaces, as shown in further detail in  FIG. 6 . The configuration of the handle assembly  102  allows a user to precisely control the movement of the guide wire shaft  504  and the outer delivery shaft  106 , and thereby manipulate the components of distal tip assembly  104 . As shown in  FIGS. 5-7  handle assembly  102  includes a distal guide wire shaft boss  616  configured to engage the inner threads  602  of the distal control knob  112 . Specifically, distal guide wire shaft boss  616  preferably has a tongue  617  that engages inner threads  602  of distal control knob  112 . Inner threads  602  are formed such that, as distal control knob  112  is rotated in a clockwise direction by a user, distal guide wire shaft boss  616  is forced in a distal direction, that is, towards the distal end of handle assembly  102 . Distal guide wire shaft boss  616  is connected to proximal guide wire shaft boss  608  by connecting bar  510 . Proximal guide wire shaft boss  608  is connected to guide wire shaft  504 . Therefore, in operation, clockwise rotation of distal control knob  112  moves distal guide wire shaft boss  616  towards the distal end of handle assembly  102 . Because distal guide wire shaft boss  616  is coupled to guide wire shaft  504  through connecting bar  510  and proximal guide wire shaft bass  608 , guide wire shaft  504  moves in a distal direction when distal guide wire shaft boss  616  moves in a distal direction. Distal guide wire shaft boss  616  and proximal guide wire shaft boss  608  can be affixed to connecting bar  510  using any suitable method of attachment, for example adhesive, friction fit, or both. Boss  616  and boss  608  can be clamped to connecting bar  510  and tightened using one or more tightening bolts (not shown). Although specific manners of connecting distal guide wire shaft boss  616  to guide wire shaft  504  is described above, it is understood that in other embodiments of the present invention, alternate mechanisms cam be used to ensure that rotation of distal control knob  112  results in axial movement of guide wire shaft  504 . 
         [0033]    Handle assembly  102  further includes an outer delivery shaft boss  612  configured to engage the inner threads  604  of the proximal control knob  110 . Specifically, outer delivery shaft boss  612  preferably has a tongue  618  that engages inner threads  604  of proximal control knob  110 . Outer delivery shaft boss  612  is connected to outer delivery shaft  106 . In operation, counter-clockwise rotation of proximal control knob  110  moves outer delivery shaft boss  612  towards the proximal end of handle assembly  102 . Because outer delivery shaft boss  612  is coupled to outer delivery shaft  106 , outer delivery shaft  106  moves in a proximal direction when proximal control knob  110  moves in a proximal direction. Proximal guide wire shaft boss  608  can be affixed to guide wire shaft  504  and outer delivery shaft boss  612  can be affixed to outer delivery shaft  106  using any suitable method of attachment, for example adhesive, friction fit, or both. Boss  608  may be clamped to guide wire shaft  504  and boss  612  may be clamped to outer delivery shaft  106 . Boss  608  and boss  612  can thereafter be tightened using one or more tightening bolts (not shown). Although specific manners of connecting outer delivery shaft boss  612  to outer delivery shaft  106  is described above, it is understood that in other embodiments of the present invention, alternate mechanisms can he used to ensure that rotation of other delivery shaft boss  612  results in axial movement of outer delivery shaft  106 . 
         [0034]    Handle assembly  102  also includes an intermediate delivery shaft  206 . Intermediate delivery shaft  206  is fixedly secured to the inside of main handle  108 , preferably by an O-ring. It is understood that intermediate delivery shaft  206  can be secured to main handle  108  by other methods, for example, by welding, bolting, over-molding, etc. Guide wire shaft  504  is encompassed by, but not affixed to, intermediate delivery shaft  200  such that guide wire shaft  504  is axially movable with respect to intermediate delivery shaft  206 . Intermediate delivery shaft  206  is encompassed by, but not affixed to, enter delivery shaft  100  such that outer delivery shaft  106  is axially movable with respect to intermediate delivery shaft  206 . The entire catheter assembly  100  can be placed over a pre-positioned guide wire (not shown) by sliding guide wire shaft  504  over the guide wire and out of guide wire port  512 . Guide wire port  512  can also be used as a supplemental flushing port. Handle assembly  102  further includes a flushing channel  502  located within main handle  108 . Flushing channel  502  is fluidly connected to the space between outer delivery shaft  106  and intermediate delivery shaft  206  and the space between intermediate delivery shaft  206  and guide wire shaft  504 . Flushing channel  502  is fluidly connected to flushing port  114 . In some embodiments, flushing channel  502  is fluidly connected to guide wire port  512  in addition to, or instead of, flushing port  114 . 
         [0035]    At the beginning of a procedure distal guide wire shaft boss  616  is positioned towards the distal end of handle assembly  102 , near distal control knob pins  714 , and outer delivery shaft boss  612  is positioned towards the proximal end of its movement area, near proximal control knob pins  716 . When bosses  610  and  612  are in these initial positions, distal tip assembly  104  is generally in the configuration shown in  FIG. 3 , although distal tip assembly  104  could be previously advanced out of introducer  116 . When in a closed configuration, heart valve  304  and valve retainer  302  are encompassed by valve retaining sleeve  204 , and valve retaining sleeve  204  is in turn encompassed by introducer  110 . In this configuration, the distal end of introducer  110  abets the proximal end of support arm sleeve  126 . Upon introduction into a body channel, distal tip assembly  104  is moved forward while introducer  116  is held at a fixed position, preferably at the apex of the heart after a minithoracotomy procedure, and distal tip assembly  104  is advanced until prosthetic valve  304  reaches a desired implant location, preferably the native valve annulus. 
         [0036]      FIGS. 8-10  illustrate distal tip assembly  104  in three stages of delivery. In  FIG. 8 , distal tip assembly has been advanced within the body such that prosthetic valve  304  is positioned and oriented approximately in the native valve location. Distal tip assembly  104  is shown in  FIG. 8  in a position that is reached after distal control knob  112  of handle assembly  102  has been rotated in a clockwise direction by a user in order to partially advance distal guide wire shaft boss  616 , and thereby guide wire shaft  504 . towards the distal end of handle assembly  102 . At the stage of delivery shown in  FIG. 8 , distal guide wire shaft boss  616 , and thereby guide wire shaft  504 , have not reached their maximum distal position. Advancing guide wire shaft  504  in a distal direction causes connecting fin  404 , tip connector  124 , and support arm sleeve  126  to advance in a distal direction over slotted tip  122 , and away from valve retaining sleeve  204 , which remains in its original position because proximal control knob  110  has remained in its original position. Slotted tip  122  is also held stationary during movement of tip connector  124  and support arm sleeve  126  because it is connected to intermediate delivery shaft  206 , which is anchored in handle assembly  102 . As shown in  FIG. 8 , valve prosthesis arms  802  are partially exposed, but the support arm sleeve  126  is covering the distal end of arms  802 . 
         [0037]    To achieve the configuration of distal tip assembly  104  shown in  FIG. 9 , distal control knob  112  of handle assembly  102  is further rotated in a clockwise direction in order to advance distal guide wire shaft boss  616 , and thereby guide wire shaft  504 , to their maximum distal location, that is, the location closest to distal control knob pins  714 . This distal movement of distal guide wire shaft boss  616  advances connecting fin  404 , tip connector  124 , and support arm sleeve  126  further distally, fully releasing valve prosthesis arms  802  from support arm sleeve  126 . The proximal portion of valve  304 , as well as valve retainer  302 , remain encompassed by valve retaining sleeve  204 . As a further result of advancing support arm sleeve  126  to its furthest distal location, semi-sphere  202  protrudes from the proximal end of support arm sleeve  126 . 
         [0038]    The clockwise and counterclockwise rotations of distal control know  112  and proximal control know  110  described above are merely exemplary. In embodiments of the present invention, the rotation of control knobs  110  and  112  can be reversed, and control knobs  110  and  112  can be rotated in the same direction. Inner threads  602  and  604  can be adjusted accordingly to ensure that grade wire shaft  504  and outer delivery shaft  100  move in the desired axial direction based on the rotational direction of control knobs  110  and  112 . 
         [0039]    To achieve the configuration of distal tip assembly  104  shown in  FIG. 10 , proximal control knob  110  of handle assembly  102  is rotated in a counterclockwise direction in order to move outer delivery shaft boss  612  in a proximal direction, thereby withdrawing outer delivery shaft  106 , valve retaining sleeve  204 , and valve retaining sleeve connector  208  in a proximal direction. As noted above, valve retainer  302  is fixed to intermediate delivery shaft  200 , and therefore does not experience axial movement when outer delivery shaft  106  or guide wire shaft  504  are manipulated. In this configuration, valve  304  is fully released from the inside of valve retaining sleeve  204 . The distal end of valve retaining sleeve  204  partially covers valve retainer  302 . Once released from valve retaining sleeve  204 , self-expanding-prosthetic valve  304  expands to its open position in the native annulus. 
         [0040]    After valve prosthesis  304  has been delivered to the native annulus, distal tip assembly  104  is prepared for removal from the body. As shown in  FIG. 11 , distal tip assembly  104  is withdrawn through the expanded valve prosthesis  304 . Semi-sphere  202  provides a smooth, non-snagging, surface to aid in withdrawing support arm sleeve through the expanded valve  304  without damaging the valve. Semi-sphere  202  also prevents injuries to body channels as the distal tip assembly  104  is withdrawn from the body. Other structures can be used in place of semi-sphere in embodiments of the present invention. For example, semi-sphere  202  can be replaced with a gently sloping cone or a semi-ellipsoid shape in order to prevent support arm sleeve and other components from snagging on prosthetic valve  304  as the catheter is removed from a patient&#39;s body. Semi-sphere  202  can be made from any semi-rigid polymer, metal, or other material suitable for exposure to a patient&#39;s circulatory system. 
         [0041]      FIG. 12  illustrates the distal tip assembly  104  and introducer  116  shown in  FIG. 3  in a second stage of withdrawal. In this stage, distal tip assembly  104  has been withdrawn to the apex of the heart. Semi-sphere  202 , valve retainer  302 , valve retaining sleeve  204 , and valve retaining sleeve connector  208  are encompassed by introducer  116 . The distal end of introducer  116  mates with semi-sphere  202  and abuts the proximal end of support arm sleeve  126 . Introducer  116  and distal tip assembly  104  are then removed from the body. 
         [0042]    A method of implanting a heart valve via a transapical approach using a catheter according to one embodiment of the present invention will be described with reference to  FIG. 13 . First, in step  1301 , a patient&#39;s chest and heart apex are prepped for an implantation procedure, preferably by minithoracotomy or a similar procedure. Various preparation procedures that provide access to the heart can also be used in embodiments of the present invention. For example, hemisternotomy or sternotomy can be used to gain access to the heart, although these procedures are less desirable because they are more invasive than minithoracotomy and cars resell in extended post-operative recovery times. In step  1302 , the user de-airs the catheter assembly  100  and places the catheter assembly  100  over a guide wire and advances the distal tip assembly  104  through the minithoracotomy and to the apex of the heart. Slotted tip  122  penetrates the apex of the heart to allow access to the interior of the heart. In step  1303 , the user positions introducer  116  across the apex of the heart, and advances the distal tip assembly  104  distally while holding the introducer stationary. In step  1304 , distal tip assembly  104  is advanced until the prosthetic valve  304  is correctly positioned and oriented in the native valvular annulus. 
         [0043]    Steps  1305  through  1307  release the prosthetic valve  304  from the distal tip assembly  104 . In step  1305 , the user rotates distal control knob  112  to move the support arm sleeve  126  distally to release the proximal end of valve prosthesis arms  802 . Note that the distal portion of valve prosthesis arms  802  are still contained within support arm sleeve  126 , which allows the user to retract the arms  802  if the prosthetic valve  304  is not correctly positioned. If the user is satisfied that Prosthetic valve  304  is properly positioned and oriented, the user further rotates the distal control knob  112  (step  1306 ) to advance support arm sleeve  126  further distally. This fully releases the valve prosthesis arms  802  from support arm sleeve  126 . Then, in step  1307 , the user retracts the valve retaining sleeve  204  by rotating the proximal control knob  110 , allowing the prosthetic valve  304  to fully expand in the native annulus. 
         [0044]    In steps  1308 - 1310 , the distal tip assembly  104  and introducer  116  are removed from the body. First, in step  1308 , semi-sphere  202 , support arm sleeve  126 , tip connector  124 , and slotted tip  122  are pulled back through the valve  304 . Semi-sphere  202  prevents the support arm sleeve  126  from snagging on and damaging valve  304 . In step  1300 , distal tip assembly  104  is withdrawn into introducer  116 , which encloses the device. The introducer  116  and distal tip assembly  104  are then withdrawn from the heart and from the body (stop  1310 ). The body can then be closed up in the conventional fashion (step  1311 ). 
         [0045]    Although the method described with reference to  FIG. 13  has been described with reference to a transapical approach, components and methods according to embodiments of the present invention can be used in conjunctions with catheters designed for alternate approaches. For example, distal tip assembly  104  and/or handle assembly  102 , or components thereof, can be used in catheters designed for delivery of a heart valve via a transfemoral approach. 
         [0046]    The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Other modifications and variations may be possible in light of the above teachings. The embodiments and examples were chosen and described in order to best explain the principles of the invention and its practical application and to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims he construed to include other alternative embodiments of the invention. 
       EXAMPLES 
       [0047]    The following paragraphs serve as examples of the above-described embodiments. 
       Example 1 
       [0048]    One embodiment provides a catheter for delivering an expandable prosthesis. The catheter comprises a handle assembly including a rotatable distal control knob and a rotatable proximal control knob. The catheter further comprises a distal tip assembly including a first sleeve and a second sleeve. A first elongate member extends from the handle assembly. The first elongate member has a proximal end and a distal end and the first sleeve is connected to the distal end of the first elongate member. A second elongate member also extends from the handle assembly. The second elongate member has a proximal end and a distal end and the second sleeve is connected to the distal end of the second elongate member. The rotatable distal control knob is connected to the first elongate member, and the catheter is configured so that rotation of the rotatable distal control knob moves the first sleeve in an axial direction. The rotatable proximal control knob is connected to the second elongate member, and the catheter is configured so that rotation of the rotatable proximal control knob moves the second sleeve in an axial direction. 
       Example 2 
       [0049]    Another embodiment provides a valve delivery system. The valve delivery system comprises a first elongate member comprising a flexible hollow shaft and a second elongate member comprising a hollow shaft. The valve delivery system further comprises a distal tip assembly having a first retaining sleeve attached to a distal end of the first elongate member and a second retaining sleeve attached to the distal end of the second elongate member. The distal tip assembly has a closed configuration and an open configuration, and when the distal tip assembly is in the closed configuration the first retaining sleeve is configured to retain at least a portion of the distal end of a prosthetic valve and the second retaining sleeve is configured to retain at least a portion of the proximal end of a prosthetic valve 
       Example 3 
       [0050]    Another embodiment provides a handle assembly for a delivery catheter having a distal end and a proximal end. The handle assembly comprises a first hollow elongate member partially housed within the handle assembly and a second hollow elongate member partially housed within the handle assembly. The second hollow elongate member is encompassed along at least a portion of its length by the first hollow elongate member, and the first and second hollow elongate members are axially movable with respect to one another. The handle assembly further comprises a first rotatable control knob, and rotation of the first rotatable control knob moves the first hollow elongate member in an axial direction. A second control knob is also included, and rotation of the rotatable proximal control knob moves the second hollow elongate member in an axial direction.