Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/95—Instruments specially adapted for placement or removal of stents or stent-grafts
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/95—Instruments specially adapted for placement or removal of stents or stent-grafts
  • A61F2/962—Instruments specially adapted for placement or removal of stents or stent-grafts having an outer sleeve
  • A61F2/97—Instruments specially adapted for placement or removal of stents or stent-grafts having an outer sleeve the outer sleeve being splittable
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/95—Instruments specially adapted for placement or removal of stents or stent-grafts
  • A61F2/9522—Means for mounting a stent or stent-graft onto or into a placement instrument

Definitions

• This invention relates to a method of loading a self- expanding stent into a delivery sheath that is part of a catheter for transluminal delivery of the stent to a stenting location in the body of a patient, with the stent being deployed at that location by removal from the stent of the constraint on its radial expansion that is provided up to that point by the sheath.
• Stent designers are succeeding in creating ever more sophisticated stents and stent grafts, for location in ever more sites in the body. There is consequently pressure on designers of stent delivery systems, to come up with designs for catheters that will reach ever more demanding requirements to convey such stents to the desired locations in the body.
• a stent diameter is in units of "French".
• One French is one third of a millimetre.
• a stent delivery system with a passing diameter of "6 French” has an outside diameter of 2mm.
• a reduction of diameter from, say, 6 French to 5 French is a powerful technical advantage, and a great challenge for designers of stents and stent delivery systems.
• Measures that are capable of delivering even the tiniest reduction of the passing diameter of a stent delivery catheter might still be of considerable interest to such designers, provided the catheter is still as flexible, pushable and capable of reliable operations as a fatter catheter.
• One way to release a stent from the constraint of a sheath is to run a slitter down the length of the sheath that surrounds the stent. See, for example, WO 01/08599, WO 93/17636 and WO 98/20812.
• a far more commonly used method is to pull the sheath proximally, relative to the stent, to release the stent progressively, starting at its distal end. See, for example, US-A-5833694 Poncet .
• pulling on the sheath from its proximal end will impose tensile stresses on the sheath material, in the length direction of the sheath.
• the sheath must therefore be physically strong enough, not only to resist the radially outward spring force that is coming from the self -expanding stent constrained within the sheath, but also the stresses to which the sheath is subject during the time that it is being pulled proximally, to release the stent.
• a force that tends to stretch a tube will also tend to reduce the diameter of that tube.
• a simple example is the toy called the "Chinese finger" that is in the form of a braided tube. The child slips it over his finger and then pulls the free end of the tube, causing the braiding to neck down, and grip tightly the finger within the lumen of the braided tube.
• the wall thickness of the sheath makes a contribution to the totality of the passing profile of the stent delivery system, at least at the distal end of the catheter delivery system, in the "capsule" that contains the stent to be delivered by that system, for any such capsule is liable to be that portion of the length of the catheter that exhibits the greatest passing diameter. It is normally possible to devise a catheter delivery system in which the length of the catheter, the shaft, between the proximal end of the catheter held in the hand of the operator, and the distal end that exhibits the capsule containing the stent, will be of smaller passing diameter.
• a method of loading a self -expanding stent into a delivery sheath comprising the steps of: i) compressing the stent to a relatively small diameter ii) providing a loading sheath with an inner diameter dl iii) with the stent exhibiting an outside diameter of d2, where d2 ⁇ dl , providing relative translational movement between the stent and the sheath, whereby the stent is accommodated within the lumen of the loading sheath; iv) advancing the loading sheath, containing the stent, into the lumen of the delivery sheath; and v) deploying the stent into the lumen of the delivery sheath, by withdrawing the loading sheath while restraining the stent from axial movement out of the lumen of the delivery sheath.
• apparatus for installing a self -expanding stent in a sheath of a stent delivery catheter, the apparatus comprising a loading sheath with a lumen for containing the self -expanding stent, the apparatus deploying the stent into the delivery sheath by advancing into the lumen of the delivery sheath the loading sheath containing the stent, and then withdrawing from the lumen of the delivery sheath the loading sheath but not the stent.
• a self -expanding stent within the lumen of a delivery sheath of a stent delivery system, the delivery sheath being formed of polymeric material that has been cold drawn with the stent in situ, within the lumen of the sheath.
• the delivery sheath is subject to a lengthwise strain, after the stent has been installed in the lumen of the sheath, to draw down the inner diameter of the delivery sheath to a diameter d3 , which is less than diameter dl .
• the sheath is one which can be parted along a line extending axially the full length of the stent, to allow the stent to push the material of the longitudinally parted sheath of the way, during the radial expansion of the stent that occurs as the stent deploys into a bodily lumen.
• the sheath is made of polyethyleneterephthalate ⁇ PET ⁇ and typically has a wall thickness of 30 ⁇ m prior to any drawing down of the diameter after placement of the stent in the lumen of the sheath.
• any such strain initiation zone somewhere between the opposite ends of the stent, such as midway along the length of the stent.
• the form of any such strain initiation zone could be a portion of the sheath that exhibits a reduced wall thickness .
• a tool that extends along the lumen of the stent and supports the stent matrix from within that lumen.
• designers have the option of leaving the tool in place, within the lumen of the stent, for making a contribution to the construction and operation of the delivery system for the stent or, in the alternative, removing the tool from the lumen of the stent, once the stent has been installed in the delivery sheath, and using for stent support during deployment of the stent some other component within the construction of the delivery system.
• an optional feature of the method of the present invention is the step of introducing into the lumen of the stent, as part of the process of installing the stent in the delivery sheath, a component of the delivery system that will deliver the stent to the stenting site within the body.
• the sheath is of remarkably small wall thickness and so amenable to being cold-drawn in a simple manual operation in which the sheath is gripped in the hands of a skilled person.
• the left and right hands can simply be pulled apart from each other, simply to stretch the sheath in the portion of its length surrounding the stent.
• such procedures are not ideally suited to meet rigorous quality control procedures. It is therefore envisaged that the manually- achieved cold drawing step will, in real production, be replaced by a rigorously specified mechanical step so that the stretching process is performed always in the same way, for every delivery system produced.
• first and second sheath grippers one at each end of the sheath, beyond the respective end of the stent within the sheath, such grippers likely gripping the sheath all around the circumference of the sheath, probably with a high enough friction grip to hold the sheath ends securely, possibly with grip surfaces of silicone rubber material, with the first and second sheath grippers moving apart from each other in a controlled fashion, with sensors to provide control engineering feedback so that the sheath is always cold-drawn in the same manner.
• Sheath delivery systems with a distal end capsule having an outside diameter of 6 French, or even less, are well within the contemplation of the inventors of the present invention.
• Fig. 1 is a longitudinal axial section through a device for loading a stent into a delivery sheath
• Fig. 2 shows the device of Fig. 1, but with the stent partially loaded in the sheath;
• Fig. 3 is a flow diagram of method steps for installing a stent or stent graft within a sheath, in accordance with the present invention.
• Fig.l shows a crimped covered stent 10 ready for deploying from a loading sheath into a delivery sheath 12, by advancing the stent 10, in a loading tool 14 into the lumen 16 of the sheath 12, in the direction of arrow P.
• the stent 10 is a radially self-expanding nickel titanium alloy stent covered in an ePTFE film. This covered stent is constrained by a loading sheath 18 in a radially compact disposition.
• the stent is installed in the loading sheath 18 by a "crimping" procedure known per se in which a j ig (not shown) compresses the stent radially inwardly, down to its compact disposition, whereupon the stent 10 and the loading sheath 18 are moved relative to each other axially (usually by holding the sheath 18 stationary and translating the stent 10 into the lumen of the sheath 18) .
• a shaft 24 carrying a sequence of rings standing proud of the cylindrical surface of the shaft, or a spiral thread 22 running along the shaft.
• the covered stent is crimped down onto the shaft, whereupon the shaft can push the stent along its axis, supporting the stent all the way along the length of the stent, within its lumen.
• Annex A see Annex A, at the end of this description.
• the stent 10 is then "deployed" into the lumen 16 of the delivery sheath 12.
• the confining sheath 18 is pulled proximally by a pulling tube 26 contiguous with the proximal end 28 of the loading sheath 18.
• the delivery sheath 12 is of rather thin-walled PET tubular material. It is gripped at its proximal end 30 by an annular gripper chuck 32 and gripped at its distal end 34 by a similar annular gripping chuck 36, so that the two chucks 32 and 36 hold the opposite ends 30 and 34 of the delivery sheath 12 at a desired distance apart, while the stent is deployed into the sheath lumen 16.
• the full radially outwardly directed stenting force from the stent 10 is carried by the delivery sheath 12, and the lumen 46 of the stent is big enough for simple proximal withdrawal from that lumen of the tubular element 24 of the loading machine.
• the stent 10 is now radially confined within the delivery sheath 12 and can be regarded as a precursor for a "capsule" for placement at the distal end of a catheter delivery system for the stent.
• Fig. 3 identifies further steps of the manufacturing process.
• the sequence of steps in Fig. 3 is identified by references A to I and we have the following comments on these process steps.
• Step A is the step of providing the stent or stent graft of choice.
• a bare stent is one without any covering.
• a stent graft is a covered bare stent and the covering is typically of expanded polytetrafluoroethylene (ePTFE) but other covering materials are known to those skilled in the art.
• ePTFE expanded polytetrafluoroethylene
• Step B is the step of installing in the lumen of the chosen stent an inner catheter tool and the one preferred by the present Applicant is that described in its earlier publication WO 2004/096091 which goes by the acronym "ALFSR".
• Step C is the step of crimping the stent to bring the outside diameter of the chosen stent down to one that is small enough for loading the crimped stent into the chosen loading sheath 18.
• step D the crimped stent is translated axially into the lumen of the loading sheath 18.
• the loading sheath carrying the stent is translated (as explained in Figs. 1 and 2) into the lumen 16 of the delivery sheath 12 and the loading sheath 18 is withdrawn in order to deploy the stent into the delivery sheath.
• the delivery sheath 12 is conveniently a PET tube having a length about three times that of the stent, with a pre-thinned zone in the PET tube located midway along the length of the stent in the lumen of the PET tube.
• the inner catheter loading tool can be removed, step F, from the lumen of the deployed stent.
• step G any desired component of the catheter delivery system which is to be located in the lumen of the stent can now be introduced into that lumen.
• the delivery sheath can now be cold-drawn, lengthwise, to impose substantial strain on the material of the delivery sheath.
• This strain will have the effect of reducing the wall thickness of the delivery sheath, and generating hoop stresses within the delivery sheath being cold-drawn, which hoop stresses will tend to compress the stent inside the lumen of the delivery sheath, and therefore marginally reduce its diameter.
• the Fig. block diagram carries notes in relation to this step H of the process. These notes teach to use a soft sticky material to grip the delivery sheath for achieving the cold-drawing strain.
• the stent -bearing capsule is ready for combining with other components of the catheter system that is to deliver the stent to the site of stenting in the body of a patient.
• Applicant has an earlier-dated patent application, GB- 0720327.6 which described a sheath splitting system. Annex A to this description follows immediately below, and provides the reader with an enabling description of one way to provide a splitting system for the sheath delivery catheter system described above.
• Readers will understand that the illustrated embodiments are non-limiting. Readers have enough background technical knowledge to modify the specific teachings above so as to conform to their own perceptions of good design and conformity with their own stent products or other requirements of the market.
• Annex A (comprising 29 sheets of text corresponding to the description and claims of Annex A, the associated drawings of which are incorporated as Figures IA to 7A of this application) , followed in turn by the claims in which the present invention is defined.
• Annex A forms part of and is incorporated into the present description, and its pages are correspondingly numbered in sequence with the present specification.
• This invention relates to a delivery system for a self- expanding device for placement in a bodily lumen, the system comprising a sheath that confines the device to a radially compact delivery disposition until the device is to be released into the lumen.
• the invention relates to a catheter delivery system for introducing and placing an endoprosthesis in a human or animal body.
• the catheter delivery system comprises a region in which to receive the endoprosthesis, an elongate sheath to surround the endoprosthesis in the region and a device for splitting the sheath along its length, to release the endoprosthesis from the region.
• Catheter delivery systems are commonly used to introduce self-expanding endoprostheses in human or animal bodies and to advance them to the clogged or narrowed area.
• the elongate endoprosthesis is held in a radially compressed state by a surrounding sheath to facilitate a smooth delivery.
• the endoprosthesis I Annex A 13 When the endoprosthesis I Annex A 13 has been placed in the destined area, it is expanded by- withdrawing or opening up the sheath.
• a catheter delivery system where the endoprosthesis is expanded by cutting open the sheath is disclosed in FR 2688688.
• three cutting wires are arranged equidistantly around the periphery of the endoprosthesis. Each wire runs from a proximal end of the catheter to a distal end, with the wire placed between the radially compressed endoprosthesis and the sheath in the region where the endoprosthesis is received, leaves the sheath at its distal end and runs back to the proximal catheter end along the outside of the sheath, so as to form a loop around the sheath wall.
• Both parts of the wires, in- and outside the sheath, are guided parallel to one another and the overall six proximal wire ends are attached to a handle at the proximal end of the catheter.
• the sheath is opened by pulling the handle so that the distal ends of the three wire loops move proximal Iy and cut through the wall of the sheath.
• a catheter delivery system that uses only one cutting wire is disclosed in WO-A-01/08S99.
• the wire consists of an inner pull element, running within the sheath, an outer pull element, running outside the sheath, and a separating element, located between the distal ends of the two pull elements at the distal end of the sheath.
• both pull elements are simultaneously pulled in a proximal direction, so that the separating element moves along the endoprosthesis towards the proximal catheter end and cuts through the sheath wall.
• the profile of the distal catheter end, comprising the endoprosthesis to be deployed has to be strongly reduced, in order to facilitate accurate placement of the endoprosthesis and thus sheaths with thin walls have to be used.
• the friction generated by the abluminal surface of the expanded endoprosthesis and the luminal surface of the vessel may cause either the sheath to tear, inhibiting its complete removal, or the endoprosthesis to move proximally with the sheath being pulled away from the axial position in the bodily lumen where it ought to be.
• a main objective of the invention is to provide a catheter delivery system, where the sheath surrounding the endoprosthesis can be easily and reliably removed.
• the invention aims to provide a I Annex A 15 catheter delivery system with a simplified sheath splitting mechanism that reduces the risk of damage to the body tissue when the sheath is cut open.
• the invention provides a catheter delivery system for introducing and placing an elongate endoprosthesis in a human or animal body.
• the catheter delivery system has a proximal end and a distal end and comprises an elongate region at the distal end, in which to receive the endoprosthesis, an elongate sheath to surround the endoprosthesis in the region, and a device for splitting the sheath along its length, to release the endoprosthesis from the region where the endoprosthesis is received.
• the device for splitting the sheath comprises a first pull element with a proximal end at the proximal end of the delivery system and a distal end, comprising a splitting section for splitting the sheath.
• the first pull element extends to a distal end of the sheath at a distal end of the delivery system and can be pulled along the length of the sheath from the proximal end of the catheter delivery system.
• the catheter delivery system comprises a second pull element that pulls the distal end of the sheath proximally during the movement of the first pull element along the length of the sheath.
• the endoprosthesis expands from a radially compressed state to a radially expanded state in the region where the sheath has already been split.
• the second pull element pulls the distal sheath end towards the proximal end of the catheter delivery system, thereby removing [ Annex A 16 the sheath from the region where the endoprosthesis has expanded. Once the sheath is fully split, it can be completely removed from the distal end of the catheter delivery system, using the second pull element, and subsequently taken out of the patient's body.
• the force exerted by the second pull element onto the sheath during the sheath removal process acts on the distal sheath end, so that stretching of the sheath along the pull direction (which may occur when the sheath is pulled from its proximal end ⁇ is avoided. Furthermore, when the sheath is starting to be removed, the endoprosthesis has only partly expanded. Thus, the area where the sheath is pushed against the vessel wall by the expanded endoprosthesis is smaller than for the case of a fully expanded endoprosthesis. This leads to a reduction of the frictional forces that have to be overcome in order to move the sheath.
• the force required to pull out the sheath is reduced, simplifying the removal process, and the sheath is exposed to a significantly lower level of stress. This is particularly important for the case of thin-walled sheaths, used for deployment of small endoprostheses in narrow blood vessels etc., that may easily stretch or tear, rendering a complete removal impossible or causing undesired movement of the endoprosthesis.
• the first pull element is a wire.
• the pull element can be made with small lateral dimensions, so as to keep a reduced profile of the distal catheter delivery system end and sufficiently stable to avoid deformation or breakage when a pulling force is applied.
• the wire may have a round radial cross section or may be flattened along a circumferential direction of the endoprosthesis such as to have a ribbon-like shape. In the latter case, lateral movement of the wire along the periphery of the endoprosthesis during the pulling process is reduced and ( Annex A 17 the wire is guided on the abluminal endoprosthesis surface.
• the splitting section may be attached to the distal end of the wire or may be formed as an integral part thereof.
• the distal wire end may have a cross section that differs from that of the rest of its length, and that is particularly suited to split the sheath.
• the distal wire end may stand up in a radial direction of the endoprosthesis or form a hooked portion, so as to reliably catch and split the sheath.
• the second pull element is a wire.
• the radial wire cross section may be round or ribbon- like, whereby the latter configuration allows for a guided movement of the wire along the length of the endoprosthesis.
• the second pull element has a hooked portion at its distal end and the distal end of the sheath is received within the hooked portion.
• the distal sheath end can be securely attached to the distal end of the second pull element, without the need for any additional means of attachment that may increase the profile of the distal catheter delivery system end.
• the distal end of the second pull element may be bent backwards, so as to form a hooked portion and the distal sheath end may be clamped within said portion, rendering the fabrication process cheap and simple .
• the distal end of the sheath is provided with a slit to receive the splitting section.
• a slit causes a reduction of the pulling force that is required to split the sheath at its distal end and j Annex A 18 thereby helps to prevent the formation of ripples in the sheath when the splitting section is moved towards the proximal end of the catheter delivery system.
• movement of the splitting section along the periphery of the sheath at the beginning of the splitting process is avoided, so that the sheath can be cut along a well-defined direction.
• the sheath is at least partially covered with a hydrophilic coating.
• a hydrophilic coating effects a reduction of the frictional forces between sheath and luminal vessel surface, reducing the force required to remove the sheath.
• the second pull element runs between the endoprosthesis and the sheath in the region where the endoprosthesis is received.
• the second pull element can be prevented from moving across the body tissue of the inner vessel wall during the sheath removal process, avoiding possible damage to the patient's body or entanglement of the pull element.
• the pull element is securely guided between sheath and endoprosthesis when the sheath is removed.
• first pull element and the second pull element are provided at positions that are substantially opposite each other on the circumference of the endoprosthesis.
• This arrangement allows for a maximum separation distance between the two pull elements and thus helps to avoid possible entanglement of the two components.
• the force applied to the sheath is evenly distributed between the two parts of the split sheath portion that lie on opposite sides of the cut in a circumferential direction of the endoprosthesis.
• a smooth and Annex A 19 uniform sheath removal can be achieved.
• a slit for receiving the splitting section may be placed opposite the position where the distal sheath end is secured to the second pull element.
• the first pull element and the second pull element are coupled to each other by a coupling mechanism in such a way that, when the first pull element is pulled from its proximal end, also the second pull element is pulled via the coupling mechanism.
• the coupling mechanism may be formed in a way that it ensures opposite positions of the two pull elements on the circumference of the endoprosthesis, as described above.
• the coupling mechanism could be a ring-shaped object, with the two pull elements attached on opposite sides on its circumference .
• both the distal end of the first pull element and the distal end of the second pull element move towards the proximal end of the catheter delivery system, with the distal end of the second pull element lagging behind the distal end of the first pull element by a predetermined distance, so that first the separating section starts separating the sheath and then the distal end of the sheath is pulled towards the proximal end of the catheter delivery system by the second pull element.
• I Annex A 20 achieved, for example, by making the second pull element longer than the actual distance between the position where it is secured to the distal sheath end and the position where it is attached to the coupling mechanism.
• This excess length is compensated for by arranging the second pull element in a wavy or undulating structure close to its proximal end.
• the pulling force is transmitted to the second pull element via the coupling mechanism.
• the proximal end of the second pull element moves in the same direction, thereby straightening said wavy structure.
• the distal sheath end is pulled towards the proximal catheter delivery system end.
• the lag between the splitting section and the distal sheath end is defined by the excess length of the second pull element, and can thus be easily adjusted in the fabrication process.
• the splitting section starts splitting the sheath before the distal sheath end is pulled out, towards the proximal end of the catheter delivery system.
• the lag between the two components defines the length along which the sheath is split before it is starting to be removed and thus also substantially sets the length over which the endprosthesis expands prior to the sheath removal process.
• the lag should be set large enough to warrant that the sheath splitting process is initiated before the sheath removal process, yet small enough to ensure that a sufficiently small of the endprosthesis has expanded, to allow smooth removal of the sheath.
• a lag of a few millimetres is chosen, for example 5 mm.
• the endoprosthesis comprises a stent.
• the invention allows for the use of very thin-walled sheaths, avoiding any complications in the sheath removal process, and is thus particularly useful for delivering endoprostheses with a small radial diameter, such as vascular stents.
• the distal end profile of the catheter delivery system can be reduced to ensure precise positioning of the stent in the patient's body and once in its desired place, the stent can be controllably expanded.
• the endoprosthesis comprises a self -expansible stent.
• the stent expansion and sheath removal process can be controlled and coordinated by adjusting the lag between splitting section and distal sheath end, as described above.
• the catheter delivery system of the invention offers a significant improvement over the traditional method of stent delivery, where the sheath is withdrawn from its proximal end. This procedure may cause thin-walled sheaths to stretch or tear, thereby limiting the minimum sheath wall thickness and thus also the minimum achievable distal end profile of the catheter delivery system. Nevertheless, the invention may be useful even with prostheses that are not self-expanding, such as the well-known balloon-expandable stents.
• the stent has an elongate shape, can be in a radially expanded and in a radially compressed state, and has a radial diameter of 6 French or less when it is in the radially compressed state and a radial diameter of 4 mm or more when it is in the radially expanded state.
• the catheter delivery system Annex A 22 of the invention allows for a significant reduction in radial stent diameter, thus considerably extending the range of use of the apparatus.
• the sheath is made from PET.
• PET is known for its low compliance.
• a balloon of PET behaves like a paper bag.
• low compliance polymers are likely to be more useful in the present invention than higher compliance polymers like polyethylene.
• PET sheaths are cheap and easy to manufacture .
• the endoprosthesis can be easily loaded into such a PET sheath, simply by placing the endoprosthesis inside the sheath and cold drawing the sheath in such a way as to axially strain it sequentially, preferably from the distal to the proximal end of the sheath. In this way, the sheath is stretched in its axial direction and the radial sheath diameter is adjusted by controlling this stretching process.
• the invention provides another catheter delivery system for introducing and placing an elongate endoprosthesis in a human or animal body.
• the catheter delivery system has a proximal end and a distal end and comprises an elongate region at the distal end, in which to receive the endoprosthesis, an elongate sheath to surround the endoprosthesis in the region, and a device for splitting the sheath along its length, to release the endoprosthesis from the region where the endoprosthesis is received.
• the device for splitting the sheath comprises a pull element with a proximal end at the proximal end of the delivery system and a distal end, comprising a splitting section for splitting the sheath.
• the pull element extends to a distal end of the I Annex A 23 sheath at a distal end of the delivery system and can be pulled along the length of the sheath from the proximal end of the catheter delivery system.
• the pull element In the region where the endoprosthesis is received, the pull element is devoid of any structure outside the sheath and the distal end of the pull element is distal of a distal end of the endoprosthesis at a distal end of the catheter delivery system. In this way, it can be prevented that the pull element moves across the body tissue of the inner vessel wall during the sheath splitting process, thereby avoiding possible damage to the patient's body or entanglement of the pull element. If the pull element is retained between sheath and endoprosthesis, it is securely guided during the sheath splitting process.
• the splitting section may be attached to the pull element at its distal end or may form an integral part thereof.
• the splitting section could comprise a sharp edge, like a blade, to cut the sheath when moved along its length.
• the splitting section may include a blunt component or portion instead that has the shape of, for example, a ball, a wedge or a "humpback".
• the blunt component or portion has a larger thickness in the radial direction of the delivery system than the rest of the pull element.
• This latter embodiment is particularly useful when the sheath is provided with a slit to receive the splitting section, reducing the force necessary to initiate the sheath splitting process.
• the splitting location is defined by the position of the slit and no sharp edges are present that might carry a risk of damage to the vessel wall tissue.
• only one pull element has to be pulled in order to split the sheath.
• Use of only one pull element is particularly advantageous in combination also with the first aspect of the invention, namely the splitting device aspect. In this case, only one pull element has to be pulled in order to split the sheath and reliably remove it from the region of the endoprosthesis.
• the present invention can also be embodied in devices which exhibit more than one pull element, distributed around the circumference of the sheath. More than four such pull elements around the circumference, however, is not preferred.
• Figure IA shows an axial cross section of a catheter delivery system according to a preferred embodiment in an initial position
• Figure 2A shows an axial cross section of a catheter delivery system according to a preferred embodiment in a first intermediate position, where the sheath cutting process has started;
• Figure 3A shows an axial cross section of a catheter delivery system according to a preferred embodiment in a second intermediate position, where the sheath removal process has started.
• Figure IA shows an axial cross section of a catheter delivery system 10 according to a preferred embodiment in an initial position before expansion of the endoprosthesis.
• the delivery system 10 has a proximal I Annex A 25 end 11 and a distal end 13, comprising an elongate region 16 where a vascular self -expansible stent 12 is received.
• the stent 12 is surrounded and held in its radially compressed state by a sheath 14 made of PET.
• the delivery system 10 comprises a first 18 and a second 20 pull element that both consist of a metallic wire and run between the stent 12 and the sheath 14 in the region 16 where the stent 12 is received.
• the wires of both pull elements 18, 20 are flattened along a circumferential direction of the stent 12, so as to have a ribbon-like shape.
• the first pull element 18 has a splitting section 22 at its distal end that is formed by a wire portion standing up in a radial direction of the delivery system 10 and a handle 30 attached to its proximal end for pulling the pull element 18 in a direction towards the proximal end 11 of the delivery system 10.
• the second pull element 20 has a hooked portion 24 at its distal end that is clamped onto the distal end of the sheath 14, so as to provide a secure attachment .
• the second pull element 20 is attached to a metallic ring 28 that is itself attached to the first pull element 18 and serves as a coupling mechanism.
• the two pull elements 18, 20 are arranged opposite each other on the circumference of the stent 12 and secured in this configuration by the coupling mechanism 28. Close to the coupling mechanism 28, the second pull element 20 has an undulating portion 26.
• the first pull element 18 is pulled towards the proximal end 11 of the delivery system 10, using the handle 30. This causes the splitting section 22 to move along the length of the stent 12 in the same direction, thereby splitting the sheath 14 along its length as is shown in Fig. 2A.
• FIG. 1 shows an axial cross section of the catheter delivery system 10 of Fig. IA in a first intermediate position, where the second pull element 20 has been fully straightened and the undulating portion 26 has disappeared. However, the hooked portion 24 of the second pull element 20 is still in its initial position.
• the sheath 14 has been partially split and the stent 12 has started expanding in the split region 32, but the sheath 14 removal process has not started yet .
• the hooked portion 24 starts pulling the sheath 14 proximally from its distal end as can be seen in Fig. 3A, showing the catheter delivery system 10 of Figs. IA and 2A in a second intermediate position.
• the present embodiment represents an example for a combination of the two aspects of the invention and illustrates the advantages of such a configuration: sheath splitting and removal can be performed reliably and quickly in one work step, simply by pulling a single pull element 18; the danger of damage to body tissue due to moving elements is minimised; entanglement of different pull elements is avoided; and the distal end profile of the catheter delivery system 10 can be reduced, allowing accurate placement and controlled deployment even of very small endoprostheses .
• WO2004/066809 which suggests to use a deployment line that is integral with a pull back sheath, to release an endoluminal device from inside the sheath.
• the present invention provides a delivery system as identified above, which includes an elongate pull element to be pulled proximally from its proximal end, which pull element is arranged radially inside the sheath for pulling preferentially on a pull zone on the circumference of the distal end of the sheath, thereby to tear the sheath progressively along a tear line running the length of the sheath, starting at the distal end of the sheath, to release the device from the confining effect of the sheath, progressively, beginning at the distal end of the device.
• the present invention represents another step long the path of design of delivery systems for devices such as self- expanding stents and stent grafts, at a location within the body that is difficult to reach, and challenging in terms of the small dimensions of the stenting location.
• a sheath that confines the self -expanding stent radially, until the moment when it is to be released into the bodily lumen, should be strong enough to confine the stent, but with a wall thickness as thin as can be achieved, for maximum flexibility and maximum capability to advance to the site of delivery through narrow and tortuous bodily lumens.
• T h e inventive concept of releasing the stent by pulling the sheath proximally while tearing the sheath progressively, along a tear line that begins at the distal end of the sheath, fits with the concept of progressive release of a self-expanding stent commencing a £ j_£ S istal end.
• the idea of using a pull element to pull proximally the distal end of the sheath, during the progressive release of the stent fits with the idea of pulling the sheath back proximally, away from its I Annex A 28 location between the stent and the bodily lumen to be stented, before the stent has fully expanded radially and pressed itself into the tissue wall of the lumen, thereby facilitating proximal withdrawal from the stenting location of the stent delivery system, including the sheath that has been torn by the pull element .
• a stent release mechanism that works by tearing and pulling a sheath offers the potential to deploy stents and stent grafts that are axially longer than conventional. Indeed, one envisages deploying with the present invention stents and stent grafts having lengths of up to around 300 mm (or even longer) .
• a preferred material for making the sheath is polyethylene phthalate-PET- that is cold-drawn over the prosthesis mounted in a catheter delivery system.
• PET sheath can be sequentially axially stretched by the cold-drawing process, starting from the distal end of the self -expanding device and moving through to the proximal end of the device, to control the radial shrink diameter and final profile.
• the distal tip of the sheath is drawn down to an outside diameter that is substantially smaller than the outside diameter of the sheath where it embraces the self -expanding device, in order that the sheath shall itself define the outside of an atraumatic tip section for the delivery system as such.
• the embodiment that is for the time being preferred has a single line of weakness in the wall thickness of the sheath, that extends lengthwise along the sheath, starting from a tear initiation point on the circumference of the distal end of the sheath and running to the proximal end of the sheath, the line of the line of weakness being near to the pull zone at the distal end of the sheath.
• pulling on the elongate pull element will impose tearing forces on the sheath at the tear initiation point of the line of weakness near to the pull zone, initiating a tearing of the sheath along the line of weakness, that progresses as the pull element is pulled and withdrawn proximally.
• each line of weakness is conveniently provided as a line of perforations through the wall thickness of the sheath and, preferably, each line of weakness terminates, at its tear initiation point, in a slit.
• the pull element will be contiguous with the sheath, monolithic with the sheath, but not cold-drawn in the same way as the sheath.
• a pull element could be a band of the sheath material that has a width of as little as around 1 mm, band widths preferred for the time being are widths that take up at least 50% of the circumference of the sheath, so that pulling on the pull element directly pulls proximally into the annulus between the sheath and the self -expanding device an arc of the circumference of the sheath that is more than half of the circumference.
• An important application of the present invention is in catheter delivery systems for self -expanding stents of nickel -titanium shape memory alloy, as well as for stent grafts and other covered stents based on such alloys.
• it is conventional to provide a pusher that abuts the stent and is effective to resist proximal movement of the stent during the period that the sheath surrounding the stent is being withdrawn proximally.
• the shaft of the catheter of the delivery system exhibits a push element and a pull element.
• the pull element running along the shaft is functional to pull the radially confining sheath proximally to release the stent.
• the push element is capable of enduring a compressive stress along its length, that provides to the pusher that is abutting the I Annex A 31 stent the necessary pushing force to restrain the stent from moving proximal Iy with the retreating sheath.
• the state of the art in such delivery systems is replete with examples of systems that use a wire as the pull element and a tubular member such as a stainless steel hypo tube as the pushing element that delivers the pushing force to the pusher that is abutting the stent.
• a connection is needed, between the pull wire that runs the length of the catheter shaft, and the elongate pull element of the present invention, that pulls the sheath proximally to release the stent.
• connection it may be convenient to provide this connection in the form of a complete or partial ring to which the pull wire is brazed or welded, or otherwise fixed, thereby to extend proximally from the ring, while the elongate pull element a band of PET sheath material in preferred embodiments of the present invention) is bonded in some other way to the connector ring.
• the connector ring could be provided as two components that snap- fit together, captivating the pull element between the two ring components when they snap together.
• Stenting delivery systems are usually provided with rings that serve as radiopaque markers, so that the progress of the delivery system, and the progress of progressive stent release into the bodily lumen, can be monitored radioscopically .
• the connector ring that connects the elongate pull element to a pull wire running the length of the shaft of the catheter is an element that lends itself to formulation as a radiopaque marker element.
• the connector ring being located close to the proximal end of the stent during the delivery phase, and moving proximally away from the stent pusher during deployment of the stent .
• the growing gap between the stent pusher and the connector ring serves as an indication of progress of stent release into the bodily lumen.
• Fig. 4A is a diametral longitudinal section through the distal end of a stent delivery system
• Fig. 5A is a section that is the same as Fig. 4, but shows only the sheath and elongate pull element of Fig. 4, for improved clarity;
• Fig. 6A is a view from the side, of the distal end of the sheath and pull element of Fig. 5;
• Fig. 7A is a section corresponding to that of Fig. 4, but showing the system part way through the process of stent release.
• a self -expanding nickel -titanium shape memory alloy stent 10 is confined within a sheath 12 in a catheter device 14 which constitutes a transluminal delivery system for the stent 10, that has a tapered atraumatic distal tip 16.
• the catheter has a shaft 18 that defines a bore 20 for a guidewire along which the catheter delivery system may be advanced until its distal end zone carrying the zone 10 is in the desired site of stenting.
• a distal tip element 22 Carried on the shaft 18 at its distal end zone is a distal tip element 22 that receives an inwardly tapered end portion 24 of the sheath 12 surrounding the stent .
• a pusher annulus 26 At the proximal end of the stent 10 is a pusher annulus 26 that is also a I Annex A 33 radiopaque marker and is fixed to the outside surface of the catheter shaft element 18.
• a line of weakness 34 that is created by a line of elongate perforations 36, co-linear and spaced from each other to provide a line of weakness running all the way from the tearing initiation site 32 to the proximal end annulus of the sheath 12.
• the residual material 38 in the gaps between the slits 36 is sufficient to maintain the hoop stresses and integrity of the sheath 12 until the moment when it is desired to release the stent by tearing down the line of weakness by rupturing the sequence of material bridges 38 between adjacent slits 36.
• a pull element 40 which is shown in Fig. 6A extending distally away from the end annulus 30 of the sheath 12 but which is in actual use of the device folded inside the open end 42 of the sheath 12 so that it lies sandwiched between the stent 10 and the inside surface 44 of the sheath 12, running the full length of the stent 10 and extending further, proximally, beyond the pusher annulus 26.
• I Annex A 34 indicated by reference 46 is a coating of hydrophilic material on the major surfaces of the sheath 12.
• the structure of the catheter proximal of the pushing annulus 26 is the structure of the catheter proximal of the pushing annulus 26.
• the catheter shaft might be of the "over the wire” variety or of the “rapid exchange” variety, depending on the length of the guidewire lumen.
• a pushing member (conveniently a tube) to convey the endwise compressive stress to the pusher 26.
• a pull element (conveniently a pull wire) to deliver to the pull element 40 the necessary tensile stress to tear the sheath.
• connection between the pull wire running the length of the catheter shaft, and the pull element 40 that extends from proximal of the pusher annulus 26 to the distal end of the sheath 12, is an annular element that slides on the shaft 18 and conveniently serves as a radiopaque marker of the progress of the pulling element 40 as it progresses proximally release of the stent.
• the pull element might extend proximally the full length of the catheter. Proximal of the stent, it could be twirled into a strand with a helical trace on its cylindrical surface, that extends along a pull wire lumen in the catheter shaft.
• Fig. 7A we can observe the stent release process with a "snapshot" of the process in progress, with a distal portion 50 of the stent 10 already released from the radially confining effect of the sheath 12, as the pull element 40 moves proximally relative to the stent 10 lying radially inside it and the sheath 12 laying radially outside it.
• This proximal progress of the pull element 40 draws into the annulus between the untorn sheath 12 and the stent 10 the distal -most portion of the sheath 12, that has already been parted along the line of weakness 34, thereby releasing hoop stresses in the distal-most portion of the sheath 12 and I Annex A 35 allowing it to relax distally outwardly, even as it finds itself being pulled proximally into the annulus between the untorn sheath 12 and the stent 10.
• This distal -most portion of the sheath is indicated by reference 52 in Fig. 7A. We can already see in Fig.
• this distal portion of the sheath is remarkably compliant and amenable to the creasing and folding that is going to occur when a full 360° circumference is pulled proximally by a pull element 40 that extends around only a portion of that circumference adjacent to the line of weakness where the sheath is progressively rupturing from its distal end to its proximal end.
• the entire length of the stent will have expanded radially into position in the bodily lumen to be stented, and any portion of the sheath 12 that lies sandwiched between the stent and the bodily lumen will be only at the zone of the stent closest to its proximal end and will therefore be relatively easily withdrawn from between the stent and the bodily lumen, as soon as the stent delivery system as a whole is pulled proximally away from the deployed stent.
• the idea of providing a pull element between two parallel lines of weakness, so that the arc of sheath material between the two lines of weakness is pulled proximally by the pull element, but not the arc on the other side of the diameter of the sheath is an intermediate embodiment between the previously proposed "cheesewire” system in which the full circumference of the sheath continues to lie between the expanded stent and the wall of the bodily lumen, and the "single line of weakness" embodiment shown in the present drawings, in which the full circumference of the sheath is pulled proximally with the pull element 40.
• the pull element 40 is a band that extends around a substantial part of the circumference of the sheath, for example, halfway around the circumference of the sheath.
• proximal withdrawal of half the sheath material will leave for withdrawal after stent deployment sheath material amounting to only half of the circumference, instead of the prior art full circumference. This is worthwhile progress, especially with lengthy devices to be placed in the lumen.
• the presently preferred material for the sheath is PET, this does not exclude other materials.
• Materials [ Annex A 37 selection is part of the routine duties of the person skilled in the art when seeking to optimise stent delivery systems.
• the "best mode" of realising the present invention involves using a sheath of PET, cold drawn (that is to say, drawn at a temperature of 50°C or less) and with a wall thickness after cold drawing ⁇ and with the stent or stent graft inside the PET tube lumen) of 0.035 mm (or even less) .
• Al. Delivery system for a self -expanding device for placement in a bodily lumen comprising a sheath that confines the device to a radially compact delivery disposition until the device is to be released into the lumen, the system being characterised by: an elongate pull element to be pulled proximally from its proximal end, which pull element is arranged radially inside the sheath for pulling preferentially on a pull zone on the circumference of the distal end of the sheath, thereby to tear the sheath progressively along a tear line running the length of the sheath, starting at the distal end of the sheath, to release the device from the confining effect of the sheath, progressively, beginning at the distal end of the device .
• the sheath has a wall thickness and at least one line of weakness in the wall thickness that extends lengthwise, along the sheath, the line starting at a tear initiation point on the circumference of the distal end of the sheath, near the pull zone.
• a sheath for a system for delivering a self -expanding device to a bodily lumen, the sheath serving to confine the device radially, until the device is to be freed of the confining effect of the sheath, for release of the device into the lumen characterised in that the sheath comprises a uniaxial Iy drawn PET tube that has been cold drawn along its longitudinal axis.

Landscapes

• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Cardiology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Transplantation (AREA)
• Heart & Thoracic Surgery (AREA)
• Vascular Medicine (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Media Introduction/Drainage Providing Device (AREA)
• Prostheses (AREA)
• Surgical Instruments (AREA)

Priority Applications (5)

Applications Claiming Priority (6)

Publications (1)

Family

ID=40875073

Family Applications (1)

Country Status (6)

Cited By (10)

Families Citing this family (7)

Citations (2)

Family Cites Families (123)

• 2009
  • 2009-05-08 CN CN2009801164256A patent/CN102014806B/zh active Active
  • 2009-05-08 JP JP2011507936A patent/JP5480887B2/ja active Active
  • 2009-05-08 EP EP09742152.3A patent/EP2278943B1/en active Active
  • 2009-05-08 WO PCT/EP2009/055592 patent/WO2009135934A1/en not_active Ceased
  • 2009-05-08 US US12/991,112 patent/US9687370B2/en active Active
  • 2009-05-08 CA CA2720466A patent/CA2720466A1/en not_active Abandoned

Patent Citations (2)

Also Published As

Similar Documents

Legal Events