Abstract:
A catheter for use in an endoluminal delivery assembly includes a device holding region or element on which there is provided a plurality of flexible fingers extending outwardly therefrom. The fingers act to maintain a device to be deployed in the correct position on the catheter and act to resist deformation of the device during deployment.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an introducer or deployment assembly for deploying implants and other prostheses within a patient, and in particular to the catheter or cannula which carries the implant or other prosthesis. 
       BACKGROUND OF THE INVENTION 
       [0002]    A typical endoluminal introducer or deployment system includes an inner catheter or cannula, which may also be arranged as a pusher and/or dilator (hereinafter referred to as an inner catheter or catheter element) and a sheath covering the inner catheter. An implant or prosthesis is carried on the inner catheter and is fixed thereto by means of the covering sheath and with or without one or more restraining wires or any of a number of other known retention systems. 
         [0003]    The implant or prosthesis might be a stent, a stent graft, a vena cava filter, an occlusion device or any other implantable device of such a nature. 
         [0004]    Once the distal end of the catheter has been positioned inside a patient, typically at the site of the patient&#39;s vasculature to be treated, the device is released and deployed in the desired position. The deployment operation involves retracting the covering sheath so as to expose the device to be implanted, which device is then deployed, either by self-expansion or by means of an expansion device such as an inflatable balloon. In the case where the device is also held by restraining wires, these are withdrawn, typically after retraction of the sheath. Restraining wires may or may not be used in such apparatus, generally in dependence upon the nature of the device to be deployed, size restrictions and the particular medical application or intervention procedure. 
         [0005]    The step of retracting the covering sheath from the inner catheter has been known to compress or otherwise deform the device to be implanted. This can affect the positioning of the device at the deployment site and can in some circumstances damage the device itself. These problems can be experienced particularly in the case of delicate implants such as some stents. 
         [0006]    Various systems have been proposed to deal with this problem. For example, US Patent Publication No. 2004/0106977 discloses in some embodiments the provision of one or more bands of an adhesive on the outer surface of the inner catheter, which is intended to hold a stent until its deployment, and in other embodiments ridges or stepped walls on the outer surface of the inner catheter which engage struts of the stent to prevent longitudinal movement thereof along the inner catheter as the covering sheath is retracted. 
         [0007]    A problem with providing adhesive on the inner catheter is that this is another material to which a patient is exposed, even if only temporarily. It also requires a constant compressive force on the device held on the inner catheter for the glue to perform its function fully. The pressure required to compress the stent reliably into the adhesive layer results in there being a higher friction between the sheath and the stent, which provides an undesirable compromise in such devices. 
         [0008]    The mechanical holding function provided by ridges or stepped walls on the inner catheter can be significantly better at holding the device firmly on the inner catheter during the deployment operation. However, there are risks that the ridges on the outer surface of the inner catheter can snag on the device once this has been deployed or on the inner surfaces of the patient&#39;s vasculature as it is retracted from within the patient. This can cause movement or damage to the implanted device or irritation or damage to the patient&#39;s vasculature or organs. The risks are increased where the device to be implanted is small and/or particularly delicate and when the device is implanted in or near a tortuous part of a patient&#39;s vasculature. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention seeks to provide an improved deployment assembly and an improved inner catheter or cannula. 
         [0010]    According to an aspect of the present invention, there is provided a catheter element for an introducer designed to carry a medical device to be implanted in a patient, which medical device includes a structure with one or more interstices therein; the catheter element including an elongate device support region on which a device can be located and at least one flexible member arranged on at least a portion of said support region, said flexible member extending radially outwardly from said support region and being partially deformable by a said medical device carried on the catheter element so as to be at least partially locatable in the interstice or interstices of the medical device. 
         [0011]    The device support element is typically a portion of the catheter designed to hold the device to be implanted. 
         [0012]    The flexible fingers, which are preferably of a fibrous or filamentary type, are able to engage with the device being carried so as to provide support to the device in the longitudinal direction of the catheter, particularly upon the removal of a covering sheath. The flexible nature of the fingers prevents or substantially eliminates the risk of damage to the device or to the patient during withdrawal of the catheter once the device has been deployed. In particular, even with fingers which are substantially evenly flexible throughout their length, the tips of the fingers will be able to deflect more than their bases, with the result that if they come into contact with the deployed device or the walls of the patient&#39;s vasculature or organ, they will brush against these without causing damage. 
         [0013]    It is to be understood that the term catheter element as used herein is intended to encompass all forms of device for carrying such implants and prostheses endoluminally in a patient, including inner catheters, cannulae and devices acting as pushers and/or dilators. 
         [0014]    The fingers may be substantially flat, they may be substantially round or oval in cross-section or may have any other suitable cross-sectional shape. 
         [0015]    In some embodiments, the fingers extend substantially perpendicularly to the longitudinal axis of the device support region. In other embodiments, the fingers extend at an angle to the transverse direction. A preferred embodiment has fingers which extend towards a distal end of the catheter, for example at 45° or at any angle between 20° to 80°, more preferably 30° to 60°. 
         [0016]    It is envisaged that there could be a variety of different sets of fingers, arranged at different angles to one another. 
         [0017]    Preferably, the fingers extend in a radial direction of the device support region. 
         [0018]    The fingers may be substantially straight but they could be curved. Again, the catheter could be provided with a mixture or straight curved fingers. 
         [0019]    In some embodiments, at least some of the fingers have hooked ends. 
         [0020]    Preferably, the fingers are formed from the same material as the elongate element. This allows the fingers to be moulded with the device support region. 
         [0021]    In another embodiment, the fingers are formed from a material different from the device support region and the catheter. 
         [0022]    The length of the fingers will be dependent upon the particular dimensions of the catheter and of the device to be held thereby. In the preferred embodiment, the fingers are arranged on the device support region in sets. They may be grouped radially around the device support region or they may be grouped longitudinally along the device support region. In a particular embodiment, the fingers are grouped both in the radial and in the longitudinal direction. 
         [0023]    According to another aspect of the present invention, there is provided an introducer system including a catheter element as specified herein, a sheath and a device to be deployed in a patient. 
         [0024]    Preferably, the device is a stent, a stent graft, a vena cava filter or an occlusion device. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0025]    Embodiments of the present invention are described below, by way only, with reference to the accompanying drawings, in which: 
           [0026]      FIG. 1  is a side elevational view of an example of known stent delivery device which can be modified to include a catheter element according to the teachings herein; 
           [0027]      FIGS. 2 and 3  show the stent delivery device of  FIG. 1  during deployment of a stent; 
           [0028]      FIG. 4  is a side elevational view of the distal end of an embodiment of a catheter; 
           [0029]      FIG. 5  is a view of the catheter of  FIG. 4  from its distal end; 
           [0030]      FIG. 6  is a side elevational view of another embodiment of a catheter having hooked fingers; 
           [0031]      FIG. 7  is a side elevational view of an embodiment of a catheter having fingers at an angle of between 20° to 80° relative to the longitudinal direction of the catheter; 
           [0032]      FIG. 8  is a side elevational view of another embodiment of a catheter having a plurality of sets of fingers arranged in the longitudinal direction of the catheter; 
           [0033]      FIG. 9  is a view of another embodiment of a catheter having a plurality of sets of fingers arranged in the radial direction of the catheter; 
           [0034]      FIG. 10  is a side elevational view of another embodiment of a catheter having curved fingers; 
           [0035]      FIG. 11  is an elevational view in cross-section of the embodiment of a catheter of  FIG. 4  with a stent located thereon; and 
           [0036]      FIG. 12  is a perspective view of another embodiment of a catheter. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    It is to be understood that the Figures are schematic and do not show the various components in their actual scale. In many instances, the Figures show scaled up components to assist the reader. 
         [0038]    In this description, when referring to an introducer or deployment assembly, the term distal is used to refer to an end of a component which in use is furthest from the surgeon during the medical procedure, including within a patient. The term proximal is used to refer to an end of a component closest to the surgeon and in practice in or adjacent an external manipulation part of the deployment of treatment apparatus. 
         [0039]    On the other hand, when referring to an implant such as a stent or stent graft, the term proximal refers to a location which in use is closest to the patient&#39;s heart, in the case of a vascular implant, and the term distal refers to a location furthest from the patient&#39;s heart. 
         [0040]    The example of delivery system shown in  FIGS. 1 to 3  is the applicant&#39;s delivery system for its Zilver™ stent and in particular for its Zilver biliary stent. 
         [0041]    The delivery assembly  10  shown in  FIG. 1  includes a tubular handle  12 , conventionally made of a plastics material, and a hub  14 , also made of a plastics material. A safety lock  16  is removably fitted into a portion of the handle  12 , for purposes to be described below. 
         [0042]    An introducer catheter  18 , made of any of the conventional or otherwise suitable catheter materials known in the art, extends from and is attached to the handle  12 , in this example by a threaded nut  15 . Housed within the introducer catheter  18  is an inner catheter  36  (visible in  FIG. 3 ) which carries stent  30  and which is provided at its distal end with a flexible dilator tip  20 . The inner catheter  36  has a bore passing therethrough for the introduction of a guide wire  34 , shown in  FIGS. 2 and 3 . 
         [0043]    The handle  12  is provided with a side arm flushing port  22 , of conventional form, for flushing the space inside the introducer catheter  18 . 
         [0044]    The hub  14  is fixed to a metal cannula  24  which is itself attached to the inner catheter  36 . 
         [0045]    The introducer system  10  is provided with radiopaque markers  26 . In this example, the proximal marker  26  is located on the introducer catheter  18 , while the distal marker  26  is provided on the inner catheter  36 , as will be apparent from  FIG. 3 . 
         [0046]    The hub  14  is provided with an inner support stylet  28  operable to receive and support a guide wire  34 , which guide wire  34  passes through the inner stylet  28 , the hub  14 , the metal cannula  24 , the inner catheter  26  and out of distal end of the introducer tip  20 . 
         [0047]    The distal end of the inner catheter  36 , adjacent the dilator tip  20 , supports a stent  30 , in this example a Zilver™ biliary stent obtainable from the applicant. The introducer catheter  18  overlies and acts as a holding sheath for the stent  30 . This stent  30  is provided, in this example, with its own radiopaque markers  32 , in a form known in the art. 
         [0048]    The safety lock  16  acts to lock the metal cannula in an extended position relative to the handle  12 , as shown in  FIG. 1 , and thus to lock the introducer catheter over the inner catheter  36 , until the time of deployment. 
         [0049]    Referring now to  FIGS. 2 and 3 , a stent is deployed, in this case in a biliary tract of a patient, by first introducing a guide wire  34  through an access catheter (not shown) across the distal segment of the target lesion  40  of the biliary tract. Once the guide wire  34  is in place, the introducer catheter  18  is fed over the guide wire  34  until the distal end of the introducer catheter is over the target lesion  40 . During this process the introducer catheter is flushed with saline solution through the side arm flushing port  22 . 
         [0050]    Once the introducer catheter  18  has been located at the deployment site, the stent  30  held by the device  10  is ready to be deployed. This position of the introducer assembly  10  is shown in  FIG. 2 , with the two fluorescent markers  26  appearing either side of the target lesion site  40 . 
         [0051]    In order to deploy the stent  30 , the safety lock  16  is removed, which allows the handle  12  to be slid over the metal cannula  24 . In other words, once the safety lock  16  has been removed, the handle  12  can be pulled back whilst holding the hub  14  steady. This action of pulling back the handle  12  retracts the introducer catheter  18  from the inner catheter  36  with the result that the stent  30  is exposed and allowed to expand gradually as the introducer catheter  18  moves backwards relative to the inner catheter  36 .  FIG. 3  shows the introducer catheter  18  fully withdrawn and the stent  30  fully deployed at the target lesion  40 . 
         [0052]    Once the stent  30  has been deployed, the delivery assembly can be withdrawn by pulling the handle  12  and the hub  14  together in a withdrawal direction, that is out of the patient. This procedure is known in the art in particular in connection with deployment of the applicant&#39;s Zilver™ stent. 
         [0053]    As has been explained above, in some instances, it is possible that friction can develop between the introducer catheter  18  and the stent  30  with the result that the stent  30  can in some instances become deformed as the introducer catheter  18  is withdrawn, typically by compression of the stent. 
         [0054]      FIG. 4  shows in side elevation the distal end of an embodiment of catheter  100  for use in the assembly of  FIG. 1 . The catheter  100  is of a structure substantially similar to conventional inner catheters or cannulae, including those arranged with pushers and/or dilators and other elements used to deploy devices intraluminally and within organs of a patient. 
         [0055]    In the embodiment of  FIG. 4 , the device holding region or element  102  of the catheter  100 , that is the region on which the device to be implanted is fitted for deployment, is provided with a plurality of flexible fingers  104  extending outwardly from the holding region  102  of the catheter  100 . 
         [0056]    The holding region  102  is typically a portion of the catheter  100  designed to hold the device to be implanted and may, for example, have a smaller outer diameter than the remainder of the catheter  100  and may be provided with a shoulder at its proximal end for applying a pushing pressure to the device carried thereby. 
         [0057]    The flexible fingers  104  are able to engage with a device being carried on the catheter  100  so as to provide support to the device in the longitudinal direction of the catheter. This is described in more detail below in connection with  FIG. 11 . 
         [0058]    The fingers  104  are preferably substantially uniform throughout their length but it is envisaged that in some embodiments these may have varying flexibilities, for example to become more flexible towards their tips  106 . This may be achieved by tapering the thickness or diameter of the fingers  104  towards their tips  106  although it is envisaged that this could also be achieved by use of different materials within each finger. 
         [0059]    The fingers  104  may be substantially flat, they may be substantially round or oval in cross-section or may have any other suitable shape. 
         [0060]    It is preferred that the array of fingers  102  extends for at least the length of the holding region. In some embodiments, the array of fingers  104  might extend for only a portion of the holding region  102 . In fact, in some applications it is not necessary for the fingers  104  to extend over the full length of a device to be carried on the holding element  102 . 
         [0061]      FIG. 6  shows an embodiment of catheter  200  in which at least some of the fingers  204  have hooked ends  206 . These can have the function of hooking over the strut of a stent located on the holding region such as to hold the stent better on the catheter  200 . This can reduce the force required to be applied by the sheath to compress the stent, particularly in the case where restraining wires are not used, and thus reduce the friction between the sheath and the stent. 
         [0062]    It is preferred that the hooked fingers  204  provide a restraining force which is not sufficient to hold the device in a compressed state on the catheter  200 , thus allowing the device to expand normally once the sheath is withdrawn. 
         [0063]      FIGS. 4 and 5  in particular show the fingers  104  extending substantially perpendicularly from longitudinal axis of the holding region  102  of the catheter  100 . In some embodiments, some or all of the fingers  102  could extend at another angle.  FIG. 7  shows an embodiment of catheter  300  in which the fingers  304  extend outwardly and towards the distal end  308  of the catheter  300 . This angle may be, for example, 45° or 60° or any angle between 20° to 80°, more preferably 30° to 60°. 
         [0064]    It is envisaged that there could be a variety of different sets of fingers  304 , set at different angles to one another. 
         [0065]    The fingers  104  are shown in  FIGS. 4 and 5  to be substantially evenly spaced along and around the holding region  102 . However, other embodiments are envisaged.  FIG. 8 , for example, depicts an embodiment of catheter  400  having a plurality of sets  404  of fingers which are spaced from one another in the longitudinal direction of the catheter  400 .  FIG. 9  shows an end view of an embodiment of catheter  500  having a plurality of sets  504  of fingers which are spaced from one another in the radial direction of the catheter  500 . It is also envisaged that the fingers may be grouped both in the radial and in the longitudinal direction. 
         [0066]    The fingers  104  may be substantially straight, as shown in  FIGS. 4 and 5 , but they could equally be curved as shown in  FIG. 10 , preferably in a direction towards the distal end  608  of the catheter  600 . In some embodiments, the catheter  600  could be provided with a mixture or straight curved fingers. Equally, in some embodiments there could be fingers which curve away from the distal end  608 . 
         [0067]    In another embodiment, the fingers may be arranged in one or more helixes around the elongate element  102 . 
         [0068]    The fingers may be formed from the same material as the elongate element  102 , and in practice as the catheter  100 . This allows the fingers to be moulded with the catheter. 
         [0069]    It is also envisaged that the fingers could be are formed from a material different from the elongate element and the catheter, such as of a fibrous material such as metal, metal alloy, Nitinol, nylon. In this case, the fingers could be embedded, welded or adhered onto the holding portion of the catheter. 
         [0070]    The length of the fingers will be dependent upon the particular dimensions of the catheter and of the device to be held thereby. In some embodiments, the fingers will be of a length to touch the inner surface of the outer sheath. They may also be longer than this. 
         [0071]    The fingers need not be the same length as one another. They could, for example, decrease in length from one end of the element  102  to the other or could decrease in length towards or away from its centre. 
         [0072]      FIGS. 4 and 5  show a plurality of rows of fingers  104  extending along the elongate element  102 , in particular eight rows. In other embodiments a different number of rows may be provided, including just two located diametrically opposite one another. 
         [0073]      FIG. 11  shows a cross-sectional view of the embodiment of catheter  100  of  FIGS. 4 and 5  with a stent  110  thereon. The stent  110  is formed of a plurality of interconnected struts  112  which sit between adjacent fingers  104  of the catheter  100 . The fingers  104  have the effect of providing resistance to longitudinal movement of the stent  110  when the sheath  114  is retracted during the deployment operation and in many embodiments also resistance against twisting of the stent  110  in a radial direction, caused for example by twisting or bending of the catheter  100  or the sheath  114  during withdrawal of the sheath  114 . 
         [0074]    Given the flexible nature of the fingers  104 , as a stent is being compressed onto the catheter  100  during the assembly process, the fingers  104  will tend to deflect out of their way, in a manner shown in  FIG. 11 . 
         [0075]    Furthermore, flexible nature of the fingers prevents or substantially eliminates the risk of damage to the stent or to the patient during withdrawal of the catheter once the stent has been deployed. In particular, even with fingers which are substantially evenly flexible throughout their length, the tips  106  of the fingers will be able to deflect more than their bases, with the result that if they come into contact with the deployed device or the walls of the patient&#39;s vasculature or organ, they will brush against these without causing damage. 
         [0076]    Although  FIG. 11  shows a stent  110  carried on the catheter  100 , any other device could likewise be carried, including for example a stent graft, a vena cava filter or an occlusion device. 
         [0077]    In another embodiment, in place of fingers  104 , there may be provided one or more discs on the elongate member  102 , as shown in  FIG. 12 . The discs  700  are made from a flexible material such as silicon, nylon or any other suitable biocompatible material. The discs  700  extend annually around the elongate carrier element  102  at spaced intervals. The discs are sufficiently thin to be able to fold when a stent is compressed onto the elongate carrier  102 , such that parts of the discs  700  not directly under a stent strut are not completely compressed and extend into spaces between the stent struts to hold the stent on the elongate carrier  102 . 
         [0078]    In an alternative embodiment, the discs could instead be in the form of an annular connector for fixing to the elongate carrier, with formed integrally thereon a series of fingers extending annularly from the annular connector so as to fan out from the connector. 
         [0079]    Thus, in the described embodiments, the flexible member, that is the fibres, fingers of disks, are able to flex in such a manner as to extend into the interstices of the medical device so as to hold this in position longitudinally on the carrier. 
         [0080]    It will be appreciated that the various features of the fingers disclosed herein, including but not limited to the features of curvature, hooked ends, flexibilities and placement in sets may be combined with one another as desired by the skilled person and not restricted to the particular embodiments in which they are described. 
         [0081]    The skilled person will also appreciate that there are many methods available in the art for producing such catheter structures with fingers or discs thereon, including for example moulding, adhesion, welding and the like. It is therefore not necessary to describe any such methods in detail herein. 
         [0082]    Moreover, although the preferred embodiments have been described in relation to the applicant&#39;s Zilver™ stent and delivery system, the teachings herein are applicable to all other catheter or cannula based delivery systems suitable for delivering stents, stent-grafts, filters, occlusion devices and other implants.