US20130123899A1 - Vascular Prosthesis and Methods of Use - Google Patents

Abstract

An implantable vascular prosthesis is provided for use in a wide range of applications wherein at least first and second helical sections having alternating directions of rotation are coupled to one another. The alternating helical section includes a first and second helical portions each having a flange and having adjacent ends joined directly to one another to define an apex. Each helical portion has a widened flange portion adjacent to the apex, the widened flange portions extending into a space between the helical portions. The prosthesis is configured to conform to a vessel wall without substantially remodeling the vessel, and permits accurate deployment in a vessel without shifting or foreshortening.

Description

RELATED APPLICATIONS
• This application is a divisional of U.S. application Ser. No. 11/716,472; filed on 9 Mar. 2007 (NOCO 1013-1).
FIELD OF THE INVENTION
• The present invention relates to an implantable vascular prosthesis configured for use in a wide range of applications, and more specifically, to a prosthesis having an alternating helical section.
BACKGROUND OF THE INVENTION
• Today there are a wide range of intravascular prostheses on the market for use in the treatment of aneurysms, stenoses, and other vascular irregularities. Balloon expandable and self-expanding stents are well known for restoring patency in a stenosed vessel, e.g., after an angioplasty procedure, and the use of coils and stents are known techniques for treating aneurysms.
• Previously-known self-expanding stents generally are retained in a contracted delivery configuration using an outer sheath, then self-expand when the sheath is retracted. Such stents commonly have several drawbacks, for example, the stents may experience large length changes during expansion (referred to as “foreshortening” or “jumping”) and may shift within the vessel prior to engaging the vessel wall, resulting in improper placement. Another disadvantage is that after the stent is deployed it can experience longitudinal movement within the vessel (also referred to as “migration”), which can be attributed to repetitive longitudinal loading and unloading of the stent.
• Additionally, repetitive loading and unloading of a stent have also been known to cause fatigue induced strut failure, which may contribute to restenosis and subsequent vessel narrowing and/or occlusion. Additionally, many self-expanding stents have relatively large delivery profiles because the configuration of their struts limits further compression of the stent. Accordingly, such stents may not be suitable for use in smaller vessels, such as cerebral vessels and coronary arteries.
• For example, PCT Publication WO 00/62711 to Rivelli describes a stent comprising a helical mesh coil having a plurality of turns and including a lattice having a multiplicity of pores. The lattice is tapered along its length. In operation, the plurality of turns are wound into a reduced diameter helical shape, and then constrained within a delivery sheath. The delivery sheath is retracted to expose the distal portion of the stent and anchor the distal end of the stent. As the delivery sheath is further retracted, subsequent individual turns of the stent unwind to conform to the diameter of the vessel wall.
• The stent described in the foregoing publication has several drawbacks. For example, due to friction between the turns and the sheath, the individual turns of the stent may “bunch up,” or overlap with one another, when the delivery sheath is retracted. In addition, once the sheath is fully retracted, the turns may shift within the vessel prior to engaging the vessel wall, resulting in improper placement of the stent. Moreover, because the distal portion of the stent may provide insufficient engagement with the vessel wall during subsequent retraction of the remainder of the sheath, ambiguity concerning accuracy of the stent placement may arise.
• In another example, U.S. Pat. No. 5,603,722 to Phan et al. describes a stent formed of expandable strip-like segments. The strip-like segments are joined along side regions in a ladder-like fashion along offsetting side regions. A shortcoming of such a stent is that the junctions between adjacent segments are not provided with a means of addressing longitudinal loading. As a result, such a stent is susceptible to strut fracture.
• In another example, U.S. Pat. No. 5,607,445 to Summers describes a balloon expandable stent. In one embodiment, the stent is constructed from a single wire that is configured so that each half of the wire is zig-zagged and curved to generally form a half-cylinder. The zig-zags of each half-cylinder are intermeshed so that they combine to form a cylindrical stent. The stent described in the foregoing publication has several drawbacks. The stent does not allow for longitudinal loading. As a result, applying a longitudinal load will cause the bends to move radially inward which will bias them into the vessel flow. Additionally, the stent design may be susceptible to fracture with repetitive loading and unloading.
• In yet another example, U.S. Pat. No. 5,707,387 to Wijay describes a stent constructed from a plurality of bands, where each band is composed of a solid wire-like material formed into a closed, substantially rectangular shape. Each band is circumferentially offset from the adjacent band and adjacent bands are connected by one or more cross-tie members. This stent also has several drawbacks. The rectangular cell design does not allow for longitudinal loading because the cells are not flexible. Therefore, under a longitudinal load the apex will move out of plane and will be biased into the vessel (i.e., into the vessel flow). Secondly the stent may be susceptible to fracture with repetitive loading and unloading because of the rigid cells.
• When utilizing stents in interventional procedures, it may be advantageous to deliver therapeutic agents to a vessel wall via the surface of the stent. Drug eluting stents have many advantages, such as controlled delivery of therapeutic agents over an extended period of time without the need for intervention, and reduced rates of restenosis after angioplasty procedures. Typically, the drug is disposed in the matrix of a bioabsorbable polymer coated on an exterior surface of the struts of the stents, and then gradually released into a vessel wall. The quantity of the therapeutic agent provided by the stent generally is limited by the surface area of the struts. Increasing the surface area of the struts may enhance drug delivery capability, but may compromise the overall delivery profile of the stent. There therefore exists a need for a prosthesis having a reduced delivery profile and enhanced drug delivery capabilities. This would be especially beneficial if other attributes such as radial strength and flexibility are not compromised.
• In view of the drawbacks of previously known devices, it would be desirable to provide apparatus and methods for an implantable vascular prosthesis comprising a plurality of helical portions joined together, wherein the prosthesis is configured to be used in a wide range of applications including maintaining patency in a vessel and delivering drugs to a vessel.
• It also would be desirable to provide apparatus and methods for a vascular prosthesis that is flexible enough to conform to a natural shape of a vessel without substantially remodeling the vessel.
• It further would be desirable to provide apparatus and methods for a vascular prosthesis having one or more radially expanding anchors that allow for additional control over the deployment of the vascular prosthesis at a desired location within a vessel.
• It still further would be desirable to provide apparatus and methods for a vascular prosthesis that has a surface area that may be selected to facilitate in-vivo delivery of therapeutic agents without adversely impacting the mechanical properties (e.g., radial strength, flexibility, etc.) of the prosthesis.
• It additionally would be desirable to provide apparatus and methods for a vascular prosthesis that has a strut configuration that allows for repetitive longitudinal loading and unloading of the prosthesis.
• It further would be desirable to provide apparatus and methods for a vascular prosthesis that has a structure having the ability to absorb or distribute loads.
• It yet further would be desirable to provide apparatus and methods for a vascular prosthesis that has a small delivery configuration to allow the prosthesis to be used in smaller vessels.
SUMMARY OF THE INVENTION
• In view of the foregoing, it is an object of the present invention to provide apparatus and methods for an implantable vascular prosthesis comprising a plurality of helical stent portions having alternating directions of rotation joined together, wherein the prosthesis is configured to be used in a wide range of applications including, but not limited to, maintaining patency in a vessel and delivering drugs to a vessel.
• It is a further object of the present invention to provide apparatus and methods for a vascular prosthesis that is flexible enough to conform to a natural shape of a vessel without substantially remodeling the vessel.
• It is another object of the present invention to provide apparatus and methods for a vascular prosthesis having at least one alternating helical section that allows for controlled deployment of the vascular prosthesis at a desired location within a vessel.
• It is another object of the present invention to provide apparatus and methods for a vascular prosthesis having a strut configuration that dampens the stresses associated with repetitive longitudinal loading and unloading, torsional loads, buckling and bending.
• It is another object of the present invention to provide apparatus and methods for a vascular prosthesis having independent cells that absorb and/or distribute loads applied to the prosthesis.
• It is a further object of the present invention to provide apparatus and methods for a vascular prosthesis that has a surface area that facilitates in-vivo delivery of therapeutic agents.
• It is a further object of the present invention to provide apparatus and methods for a vascular prosthesis that has a small delivery configuration to allow the prosthesis to be used in smaller vessels.
• These and other objects of the present invention are accomplished by providing a vascular prosthesis comprising a plurality of helical portions having alternating directions of rotation that are joined together. The prosthesis is configured to engage a vessel wall and adapt to a natural curvature of the vessel. The vascular prosthesis may be used in a wide range of applications.
• In a preferred embodiment, the vascular prosthesis comprises a shape memory material, such as Nitinol, and includes an alternating helical section. As used in this specification, an “alternating helical section” is formed of two or more helical portions that are joined together and have at least one change in direction of rotation of the helices.
• Prostheses of the present invention are delivered to a target vessel in a contracted state, constrained within an outer sheath, in which radially inwardly directed compressive forces are applied by the outer sheath to the anchor section(s). In the contracted state, the helical section is wound down to a reduced diameter configuration, so that adjacent turns preferably partially overlap. As an alternative, the helical section may be configured so that there is no overlap if desired. As a still further alternative, the helical section may be compressed radially to a reduced diameter configuration in addition to or in lieu of winding.
• In a preferred method of operation of a prosthesis the alternating helical section is provided in its contracted state within an outer sheath and the prosthesis is fluoroscopically advanced into a selected vessel using techniques that are known in the art. The alternating helical section then is positioned adjacent a target region of a vessel, such as a stenosed region. The outer sheath then is retracted proximally to cause the first helical portion(s) of the alternating helical section to self-deploy and engage the vessel wall at the target region. Advantageously, by overlapping portions of the alternating helical section, the alternating helical section will expand in a controlled manner. This technique ensures that the prosthesis will not shift within the vessel during deployment.
• The vascular prosthesis of the present invention is flexible enough to conform to the shape of a vessel without substantially remodeling the vessel.
• Additionally, the mesh configuration of the alternating helical section preferably conforms to the vasculature of the target region since each of the plurality of turns is free to assume a curved configuration substantially independently of one another. Also, because the alternating helical section of the vascular prosthesis has a ribbon-like helical structure, it may be rolled down to a contracted state with a more accurate reduced delivery profile, compared to slotted-tube stents. This feature makes the stent of the present invention especially useful for treating defects in smaller vessels, such as cerebral arteries.
• In accordance with another aspect of the present invention, the plurality of turns of the alternating helical section may comprise a substantially increased surface area relative to conventional stents that have a plurality of interconnected struts. The increased surface area of the turns is particularly advantageous for localized drug delivery. The turns may be coated with a drug-laden polymer coating or, alternatively, one or more dimples or through-holes may be disposed in a lateral surface of the turns to elute drugs over an extended period of time.
• Methods of using the vascular prosthesis of the present invention, for example, in the treatment of the peripheral vasculature, also are provided.
BRIEF DESCRIPTION OF THE DRAWINGS
• Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which:
• FIG. 1 is a schematic representation of a vascular prosthesis of the present invention in a deployed state;
• FIG. 2 is a schematic representation of the vascular prosthesis of the present invention in a contracted state;
• FIG. 3 is a side view of a vascular prosthesis of the present invention;
• FIG. 4 is a schematic representation of the vascular prosthesis ofFIG. 3 shown in a flattened configuration;
• FIG. 5 is an enlarged side view of a vascular prosthesis of the present invention in a deployed state;
• FIG. 6 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 7 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 8 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 9 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 10 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 11 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 12 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 13 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 14 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIG. 15 is an enlarged side view of a portion of an embodiment of a vascular prosthesis of the present invention;
• FIGS. 16A and 16B are side views of an apex portion of a vascular prosthesis according to the present invention;
• FIG. 17 is a side view of another embodiment of a vascular prosthesis of the present invention;
• FIG. 18 is a side view of another embodiment of a vascular prosthesis of the present invention;
• FIG. 19 is a side view of another embodiment of a vascular prosthesis of the present invention;
• FIG. 20 is a cross-sectional view of a delivery system suitable for use in delivering the vascular prosthesis ofFIGS. 3; and
• FIGS. 21A-21D are side sectional views illustrating use of the vascular prosthesis in the treatment of an aneurysm;
• FIG. 22 is a side view of a vascular prosthesis of the present invention that includes distal and proximal anchors;
• FIG. 23 is a schematic representation of the vascular prosthesis ofFIG. 22 shown in a flattened configuration;
• FIG. 24 is a side view of another embodiment of a vascular prosthesis of the present invention; and
• FIG. 25 is a side view of another embodiment of a vascular prosthesis of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• The vascular prosthesis, according to the present invention, has an alternating helix configuration that provides a more accurate reduced delivery profile than previously known devices. Additionally, the prosthesis is configured to conform to a vessel wall without substantially remodeling the vessel, to provide improved compression resistance, deployment accuracy, migration resistance and load dampening characteristics.
• Referring now toFIGS. 1 and 2, a schematic representation of a vascular prosthesis constructed in accordance with principles of the present invention is described. Vascular prosthesis (“stent”)20 illustratively comprises alternatinghelical section21 capable of assuming contracted and deployed states. InFIG. 1, alternatinghelical section21 is depicted in the deployed state.
• Alternatinghelical section21 is constructed from two or more helical portions having at least one change in the direction of rotation of the helices, and being joined at apex portions where the directions of rotation of adjacent helices change. In particular, first (i.e., proximal-most)helical portion24ahas a generally clockwise rotation about longitudinal axis X ofprosthesis20.Helical portion26aadjoins the distal end ofhelical portion24aat apex28aand has a generally counter-clockwise rotation about longitudinal axis X.Helical portion24badjoins the distal end ofhelical portion26aatapex28b, and in turn is coupled to the proximal end ofhelical portion26batapex28c.As a result of the alternating direction of rotation of the adjoininghelical portions24a,26a,24band26bofvascular prosthesis20 includes threeapices28a,28band28cthat are oriented such that they point in alternating directions about the circumference ofvascular prosthesis20, generally in a plane that is normal to longitudinal axis X ofvascular prosthesis20. Preferably, each helical portion includes at least one full helical turn between adjacent apices. However, each helical portion may include more or less turns between adjacent apices, for example a helical portion may include 0.5-2.0 helical turns between adjacent apices.
• The terminal ends of the alternating helical section may have any desired configuration. For example, as shown inFIG. 1, the terminal ends, or tails, of alternatinghelical section21 cut along a plane that is perpendicular to the longitudinal axis ofvascular prosthesis20. Alternatively, the terminal ends may be cut along any plane, such as for example parallel to the longitudinal axis. The terminal ends may end in a pointed or rounded tip or they may be truncated. As a further alternative, the width of the ribbon or mesh that forms the terminal helical portions may be varied. For example, the width of the ribbon of the terminal helical portion may taper so that it has the largest width adjacent the nearest apex and the smallest width near the terminal end. These features may be selected to provide a desired transitional flexibility at the ends of the alternating helical portion. That transitional flexibility may be used to assure that the curvature of a vessel remains smooth near the end of the stent.
• A significant advantage of alternatinghelical section21 as compared to other vascular prosthesis structures, is that the apices of the alternating helical section provide additional anchoring force at discrete locations along the length of the alternating helical section. That anchoring force may be used to increase the radial force applied by the vascular prosthesis to a vessel wall as well as providing additional migration resistance. That anchoring force may be increased if desired by flaring out the ends and/or apices of the alternating helical section. Those portions may be flared outward by applying expansion and heat treatment so that those portions have a larger expanded diameter than the remainder of alternatinghelical section21. Additionally, the alternating helical configuration also allows the wall thickness of the device to be reduced because the design provides increased radial strength.
• Flanges29 are included at each apex28. Eachflange29 is configured so that a portion of acorresponding apex28 may overlap a portion offlange29 in both the contracted and deployed states. Overlap ofapex28 and a correspondingflange29 provides reinforcement atapex28 to increase the radial strength (i.e., resistance to radial compression) of the alternating helical section at the apex. Additionally, the flange provides improved metal coverage because it may be used to reduce or eliminate a gap between an apex and the corresponding flange when the stent is in a deployed configuration. The flange allows the stent to be configured so that there is overlap at a small diameter and a controlled gap at a large diameter without requiring side-to-side overlap throughout the alternating helical section.
• In the illustrated embodiment, eachhelical portion24,26 includesflange29adjacent apex28, which is a widening of the adjacenthelical portions24,26 so that the gap therebetween is reduced. For example, in an embodiment apices28aand28cremain radially inward offlanges29 whileapex28bremains radially outward offlanges29 throughout use. It should be appreciated however that the stent may be configured so that at the largest expanded diameter there is a gap between an apex and the corresponding flange.
• Alternatinghelical section21 preferably is formed from a solid tubular member comprised of a shape memory material, such as nickel-titanium alloy (commonly known in the art as Nitinol). However, it should be appreciated that alternatinghelical section21 may be constructed from any suitable material recognized in the art. The solid tubular member then is laser cut, using techniques that are known in the art, to define a specific pattern or geometry in the deployed configuration. Preferably, alternatinghelical section21 is cut from the tube so thathelical portions24a,26a,24b,26bare integrally formed as a single monolithic body. However, it should be appreciated that separate helical portions may be mechanically coupled, such as by welding, soldering or installing mechanical fasteners to construct alternatinghelical section21. An appropriate expansion and heat treatment then may be applied to alternatinghelical section21 ofvascular prosthesis20 so that the device may be configured to self-deploy from a contracted, delivery configuration to the deployed configuration.
• Referring now toFIG. 2,vascular prosthesis20 is shown in the contracted, delivery configuration, wherein alternatinghelical section21 is in the contracted, reduced diameter state. Alternatinghelical section21, however, is placed in the contracted state by windinghelical portions24,26 about longitudinal axis X. InFIG. 2,apices28aand28cmay be temporarily engaged to the inner shaft of a delivery catheter, and the shaft is rotated while apex28band the distal and proximal ends of alternatinghelical section21 are held stationary.
• Consequently,apices28aand28care tightly wound onto the shaft of the delivery catheter and the remainder of eachhelical portion24,26 is wound against the shaft so that each turn of eachportion24,26 overlaps an adjacent turn. For example, in some embodiments, approximately ⅔ of a layer is overlapped by the next layer. As a result, apex28band the distal and proximal ends of alternatinghelical section21 are located furthest radially outward on the rolled alternatinghelical section21. The overlap of the turns ofhelical portions24,26 are indicated by dashed lines inFIG. 2. The overlapping turns andflanges29 of alternatinghelical section21 thus secureapices28aand28cwhenvascular prosthesis20 is disposed within a delivery system.
• Referring now toFIGS. 3 and 4, an embodiment ofvascular prosthesis20, constructed in accordance with principles of the present invention, is described. It should be appreciated thatFIG. 4 is a schematic view ofvascular prosthesis20 as it would appear if it were flattened. The components ofvascular prosthesis20 are identical to those depicted inFIGS. 1 and 2 and identical reference numbers are employed in the following description.
• Alternatinghelical section21 preferably comprises a helical mesh configuration including two or morehelical portions27.Helical portions27 may include multiplicity ofopenings53,54,56 of different shapes and sizes. The shape, size and orientation of any particular opening is selected to provide a desired response to longitudinal loads and also may be dependent upon the location of the openings within the mesh structure. The shape, size and orientation of the opening may also be selected to provide desired deployment, unwrapping, radial force and surface area coverage characteristics.
• As shown inFIG. 4, alternatinghelical section21 includes diamond-shapedopenings53 of generally equal size through the majority of eachhelical portion24,26.
• A wide variety of openings may be employed atapices28a,28band28c, where the helical portions adjoin adjacent helical portions andflanges29. The openings may have any shape and/or size desired. Some designs include diamond, polygon, circles, ellipses, elongated diamonds, etc. In addition, the openings ofapices28 andflanges29 need not be symmetric with respect to a centerline ofapex28. It should be appreciated that the size, shape and orientation of any of the openings may be selected so that in the deployed state some struts may bow radially outward or inward so that they interlock with adjacent overlapping openings.
• InFIG. 4, each apex includes plurality ofopenings54 and onetip opening56 that forms a tip of the respective apex, which may be triangular as shown.Openings54 are defined bystruts55 that extend between adjacenthelical portions24,26.
• Referring toFIG. 5, the interaction betweenapices28 andflanges29 will be described in greater detail.Flanges29 are formed by widenedhelical portions24,26 adjacent to apices28. In particular,helical portions24,26 are widened so that the gap between twoadjacent portions24,26 is reduced. As shown by dashed lines, in the deployed state a tip portion of each apex28 overlaps flange29 in the deployed state. In the present embodiment, it is preferred to maintain the two lateral apices,28a,28c,radially inward andflanges29 assure that they remain in that position. It will be appreciated thatflanges29 of adjacenthelical portions24,26 may be joined if desired to provide additional overlap betweenflange29 andapex28.
• Referring toFIGS. 6-15, exemplary embodiments offlange29 will be described. In one embodiment, shown inFIG. 6, flange is constructed fromadditional struts60 that extend from each of adjacenthelical portions24,26 into the space between the helical portions.Struts60 form a plurality ofopenings61 that are generally irregularly shaped. However, it will be appreciated that struts60 may be configured so thatopenings61 have any desired shape. As shown inFIG. 7,openings61 may be enlarged by removingstruts60.FIGS. 8-15 illustrate various other possible configurations offlange29. In some embodiments, such as those shown inFIGS. 8 and 15, the flange may include a wavy edge. In others, such as those shown inFIGS. 9-14, the flange may include a smooth edge. It should be appreciated, upon inspection of the exemplary embodiments illustrated inFIGS. 6-15 that any shaped cells may be utilized to form flanges with desired characteristics.
• The number of and configuration of struts may be tailored as desired to provide various characteristics. For example, includingstruts60 that are parallel to the longitudinal axis of the vascular prosthesis may increase longitudinal rigidity and the strength ofhelical portions24,26 near flanges. Additionally, includingstruts60 oriented circumferentially about vascular prosthesis may increase radial stiffness ofapex28 of the vascular prosthesis. The flexibility is tailored to improve radial force applied by and/or fatigue strength of the prosthesis or to aid deployment. Additionally, the strut configuration throughouthelical portions24,26 may also be tailored to provide such characteristics as will be discussed in greater detail below.
• Referring toFIGS. 16A and 16B, an alternative strut configuration for the apices of the vascular prosthesis is described.Apex28′ is constructed withstruts55 that form plurality ofcells59 definingelongate openings58.Elongate openings58 allowcells59 to be compressed in response to longitudinal loads (shown by arrows F) placed onvascular prosthesis20.
• In addition, tip aperture51, or eyelet, is included inapex28′. Apertures51 are provided so that apex28′ may be easily coupled to a delivery device, as will be described in greater detail below. As shown, aperture51 is generally elliptical, but it should be appreciated that the shape of aperture51 will generally correspond to the structure of the intended delivery device.
• Elongate openings58 each generally have major axis B corresponding to the longest distance across opening58 and minor axis C corresponding to the shortest distance acrossopening58. Referring toFIG. 16B, a portion of apex28′ ofFIG. 16A is shown withcells59 compressed under the influence of longitudinal forceF. Elongate openings58 are oriented so that major axis B of eachopening58 is parallel withcenter line57 ofapex28′ and minor axis C of eachopening58 is perpendicular tocenter line57. During compression minor axis C is reduced while major axis B remains generally unchanged. As a result, the longitudinal load may be dampened by compression of the mesh structure ofvascular prosthesis20.
• Elongate openings58 preferably are shaped to reduce stress concentration. In the present embodiment,elongate openings58 are generally diamond-shaped withrounded corners49 at the junctions ofadjacent struts55. It should be appreciated that elongate openings may be any elongate shape. The size, shape and orientation ofcells59 on either side ofcenter line57 are shown generally identical. With such a configuration, dampening occurs equally from both sides ofcenter line57 when a longitudinal load is applied. However, it should be appreciated that the dampening characteristics ofvascular prosthesis20 may be tailored by including cells having different size, shape and/or orientation on either or both sides ofcenter line57. Furthermore, it should be appreciated that the apices included throughoutvascular prosthesis20 need not be identical and may be configured to provide differing dampening characteristics throughoutvascular prosthesis20.
• Referring toFIG. 17, another embodiment ofvascular prosthesis70 will be described.Vascular prosthesis70 generally includes alternatinghelical section71. Alternatinghelical section71 includes a plurality ofhelical portions74,76 that have alternating directions of rotation and are joined byapices78. The edges ofhelical portions74,76 are wavy, which may be provided so that a relative sliding of the portions of alternatinghelical section81 may provide a ratchet effect so that the overlapping portions may be incrementally and temporarily interlocked during deployment. Aflange79 is included on each helical portion adjacent to apices78. As described previously,flanges79 are widened portions ofhelical portions74,76 that are used to maintain a desired amount of metal coverage and may be used to retain apices in their respective radial position throughout a portion of use ofvascular prosthesis70. For example, whenvascular prosthesis70 is in a contracted state,apices78 are either located radially outward or inward of correspondingflanges79.Flanges79 are configured so that when vascular prosthesis is transitioned to a deployed state, each apex78 remains in the same radial relationship withcorresponding flange79. It will be appreciated that althoughvascular prosthesis70 is illustrated havingflanges79 with configurations generally corresponding to those ofFIG. 6, any flange configuration may be incorporated.
• Referring toFIG. 18, another embodiment ofvascular prosthesis80 will be described.Vascular prosthesis80 generally includes alternatinghelical section81. Alternatinghelical section81 includes a plurality ofhelical portions84,86 that have alternating directions of rotation and are joined byapices88. In addition, the edges ofhelical portions84,86 are straight rather than wavy, which may be provided so that relative sliding of portions of alternatinghelical section81 may be simplified during deployment. Moreover, the tip or tail portion of each of the helical portions on the proximal and distal ends of alternatinghelical portion81 have been truncated. Aflange89 also is included on each helical portion adjacent to apices88. As described previously,flanges89 are widened portions ofhelical portions84,86 that retain apices in their respective radial position throughout use ofvascular prosthesis80. It will be appreciated that althoughvascular prosthesis80 is illustrated havingflanges89 with configurations generally corresponding to those ofFIG. 6, any flange configuration may be incorporated.
• In yet another embodiment, shown inFIG. 19, alternatinghelical section91 includeshelical portions94,96 that are formed withelongated openings93 that extend substantially the entire length of the respective helical portion. The struts that formopenings93 have a greater thicknessadjacent apices98 than the thickness at locations spaced betweenapices98. Such graduated thickness may be used to control radial strength of the stent or so that the radial forces exerted by vascular prosthesis during expansion and compression are uniform at different locations around the circumference of the vascular prosthesis. For example, the radial force exerted byapices98 may be altered so that it is approximately equal to the force exerted by the remainder of each helical portion of alternatinghelical section91 by altering the thickness of the struts. As shown, the struts nearapex98 have a greater thickness to reduce the flexibility of the vascular prosthesis nearapex98.
• As will be apparent to one skilled in the art, the configuration of the alternating helical sections depicted herein is merely for illustrative purposes. Any combination of covered portions and openings of any shape and size may be provided along the helical portions, as desired to provide a desired amount of metal coverage. Alternatively, one or more helical portions may be completely solid, such that the openings are omitted entirely from that portion.
• As will be apparent to those skilled in the art, a combination of solid regions and openings may be provided along the length of the alternating helical section, for example, to selectively increase surface area and drug delivery capabilities along the alternating helical section, or to influence flow dynamics within a vessel.
• It will be appreciated that different drug delivery modalities may be used in conjunction with the vascular prosthesis of the present invention. For example, vascular prosthesis may include one or more dimples and/or through holes that may have a therapeutic agent disposed therein. As a further alternative, a therapeutic agent may be incorporated into the any of the openings previously described above. As a still further alternative, a therapeutic agent may be disposed in the matrix of a bioabsorbable polymer coated on any portion of the vascular prosthesis, and the drug may be gradually released into a localized region of a vessel wall.
• One or more of the helical portions also may be selectively coated with an elastomeric polymer, such as polyurethane. The elastomeric polymer may partially or fully cover the selected portions. For example, the elastomeric polymer may be disposed on a portion of the circumference of the alternating helical section, e.g., to reduce blood flow into a sac of the aneurysm. As a further alternative, the entire alternating helical section may be covered so that the device may be used as a stent graft. In such an embodiment, ePTFE and DACRON are examples of materials that may be used to cover the alternating helical section. It should also be appreciated that covering material may be included within the openings of the mesh structure so that it fills the openings without increasing the overall diameter of the struts. Additionally, a therapeutic agent may be disposed on the elastomeric polymer to increase the working surface area of the alternating helical section. Alternatively, the therapeutic agent may be disposed directly on the alternating helical section, either with or without the use of a elastomeric polymer.
• The therapeutic agent may include, for example, antiplatelet drugs, anticoagulant drugs, antiproliferative drugs, agents used for purposes of providing gene therapy to a target region, or any other agent, and may be tailored for a particular application. Radiopaque markers (not shown) also may be selectively disposed on any portion of vascular prosthesis including in the vicinity of the therapeutic agents to facilitate alignment of the therapeutic agents with a target site of a vessel wall. Advantageously, higher doses of such agents may be provided using the vascular prosthesis of the present invention, relative to previously known coils or stents having interconnected struts, due to the increased surface area associated with the alternating helical section.
• In operation, the overlap of portions of the alternating helical section when it is in the contracted state and the number of helical portions, causes alternatinghelical section101 to deploy in a unique sequence, as will be described in greater detail below with reference toFIGS. 21A-21D. Advantageously, the order of deployment of the portions of alternatinghelical section101 alleviates drawbacks associated with the prior art such as the tendency of the turns of the helical section to jump or shift during deployment and also results in the location of deployment being more easily controlled. Another benefit is that deployment of discrete segments may be more easily controlled. Additionally, the alternating helical section may be balloon expandable. In particular, the structure allows a user to post dilate discrete sections with a balloon. For example, a user may expand a selected portion of the device adjacent a specific apex.
• InFIG. 20, adelivery system100 suitable for use in delivering a vascular prosthesis of the present invention is described.Delivery system100 comprisescatheter body102,outer sheath104, and a lumen dimensioned for the passage ofguidewire108.Catheter body102 preferably includesdistal marker111 and stop110 located adjacent the distal end of alternatinghelical section101 andproximal stop112 located adjacent the proximal end of alternatinghelical section101.
• Distal stop110 may comprise a raised ledge oncatheter body102 so that the distal end of alternatinghelical section101 bears on the ledge to prevent relative movement between alternatinghelical section101 andcatheter body102 in the distal direction. Alternatively,distal stop110 may comprise a plurality of raised pins or knobs that prevent relative motion between alternatinghelical section101 andcatheter body102 parallel to the longitudinal axis.Proximal stop112 also may comprise a raised ledge, pins or knobs oncatheter body102, and both distal andproximal stops110 and112 may be radiopaque, so as to be visible under a fluoroscope and provide a radiopaque marker. It should be appreciated that any portion of the delivery device or vascular prosthesis may include one or more radiopaque markers.
• Vascular prosthesis109 is collapsed ontocatheter body102 by winding alternatinghelical section101 aroundcatheter body102. In order to wind alternatinghelical section101 oncatheter body102,apices103aand103cmay be temporarily coupled tocatheter body102 and the remainder of alternatinghelical section101 is wound aroundcatheter body102 until it is collapsed as shown inFIG. 20.
• After alternatinghelical section101 is wound oncatheter body102,outer sheath104 is advanced distally overcatheter body102 to capture alternatinghelical section101 betweencatheter body102 andouter sheath104.
• Referring toFIG. 21A, in operation, guidewire108 is percutaneously and transluminally advanced through a patient's vasculature, using techniques that are known in the art.Guidewire108 is advanced until a distal end of guidewire68 is positioned distal of aneurysm A, which is situated in vesselV. Delivery system100, havingvascular prosthesis109 contracted therein, then is advanced overguidewire108 through the central lumen ofcatheter body102.Delivery system100 preferably is advanced under fluoroscopic guidance untildistal marker111 is situated distally to aneurysm A and alternatinghelical section101 and apex103bare situated adjacent to the aneurysm.
• Once alternatinghelical section101 is located adjacent to aneurysm A,outer sheath104 is refracted proximally to cause alternating helical sections to deploy untilouter sheath104 is retracted toproximal stop112.
• Referring toFIGS. 21B and 21C, after the distal end of alternatinghelical section101 is secured distal of aneurysm A,outer sheath104 is further retracted proximally to allow alternatinghelical section101 to continue to expand and deploy to its predetermined deployed shape. During proximal retraction ofouter sheath104, the stent rotates within the artery, or may be manually rotated through rotation of the delivery system, to enable alternatinghelical section101 to unwind. Because central portions of the alternating helical section are over-wrapped, rotation ofcatheter body102 is not required for the alternating helical section to expand.
• Asouter sheath104 is further refracted, the turns of alternatinghelical section101 unwinds and engages and conforms to an inner wall of vessel V in a controlled manner. Helical portion116bexpands asouter sheath104 is moved proximal of the distal end of alternatinghelical section101. Helical portion116bis not able to expand until the distal end ofouter sheath104 is moved proximal of apex103bbecause alternatinghelical section101 is wound so that apex103bis located radially outward (i.e., outer-wrapped) and overlaps the adjacent helical portions. After the distal end ofouter sheath104 is moved proximal of apex103b, helical portions114band116aare allowed to expand. For example, inner-wrapped apices, such asapices103aand103c, are constrained by the adjacent helical portions114 and116 and as a result those apices remain constrained until sufficient exposure of the stent occurs to release the helical portions, thereby creating a controlled release of the stent. Finally, aftersheath104 is moved proximal of the proximal end of alternatinghelical section101,helical portion114ais able to expand, as illustrated inFIG. 21C.
• Proximal movement ofouter sheath104 may be halted once the distal edge ofouter sheath104 is substantially aligned withproximal stop112 to allow alternatinghelical section101 to expand. It will be appreciated that because of the sequence of deployment of alternatinghelical section101, the location of the deployed alternatinghelical section101 may be easily controlled and the problems encountered in previous systems (e.g., stent jumping) may be avoided.
• Whenvascular prosthesis109 is fully deployed,delivery system100 is proximally refracted overguidewire108 and withdrawn from the patient's vessel, and guidewire108 is removed. After removal ofdelivery system100 and guidewire108,vascular prosthesis109 remains deployed, as shown inFIG. 21D.
• In the present invention, the partial overlap of portions of alternatinghelical section101 reduce the surface area that is available to frictionally engage an inner surface ofouter sheath104. Furthermore, the sequence of deployment of the alternating helices included in alternatinghelical section101 also assures that the prosthesis remains properly located during deployment. Advantageously, the helical portions of the alternating helical section will be accurately deployed within vessel V, with substantially no proximal or distal shifting or foreshortening of the prosthesis with respect to the vessel as the outer sheath of the delivery device is refracted.
• It should be appreciated that the furthest proximal and the furthest distal helical portions may be configured so that the proximal and distal tips of the alternating helical section are either inner-wrapped or outer-wrapped as desired. As shown inFIGS. 21A-D both tips may be outer-wrapped. As a further alternative, one tip may be inner-wrapped. It will be appreciated that inner-wrapped portions of the alternating helical section generally require expansion of complimentary portions of the alternating helical section before the entire prosthesis is capable of expansion.
• Referring toFIGS. 22 and 23, another embodiment ofvascular prosthesis20 is shown, which includes optional distal andproximal anchor sections22,23.Distal anchor section22 preferably is a tubular mesh structure that is coupled to a distal end of alternatinghelical section21. In particular,distal anchor section22 includes a pair of concentrically aligned zig-zag rings30 that are spaced from one another and coupled by struts32.Struts32 extend betweencorresponding apices34 ofrings30 and are oriented parallel to a longitudinal axis ofvascular prosthesis20.Apices34 may comprise one or more radiopaque markers33 such as a radiopaque marker band or coating. As a result, rings30 and struts32 combine to define a plurality ofopenings36 shaped as parallelograms, thereby forming a tubular mesh. The tubular mesh preferably is formed by laser cutting a solid tube.
• Distal anchor section22 preferably is formed from a solid tubular member comprising a shape memory material, such as nickel-titanium alloy, which is laser cut, using techniques that are known in the art, to a desired deployed configuration. Preferably,distal anchor section22 is cut from the tube so that rings30 and struts32 are formed as a single monolithic body. However, it should be appreciated thatdistal anchor section22 may be constructed fromseparate rings30 and struts that are mechanically coupled in a secondary operation, such as by welding, soldering or employing a mechanical fastener, such as a rivet. An appropriate heat treatment then may be applied so thatdistal anchor section22 may be configured to self-deploy radially outward from a contracted, delivery configuration to a deployed configuration in conjunction with alternatinghelical section21, described above. Alternatively,distal anchor section22 may be configured to be balloon expandable.
• Proximal anchor section23 also preferably has a tubular mesh construction.Proximal anchor section23 includes pair of concentrically aligned zig-zag rings40 that are spaced from one another and coupled by struts42.Struts42 extend between correspondingapices44.Apices44 may comprise one or more radiopaque markers43 such as a radiopaque marker, band or coating.Rings40 are oriented parallel to longitudinal axis X ofvascular prosthesis20.Rings40 and struts42 combine to define a plurality ofopenings46 shaped as parallelograms. Similar todistal anchor section22, the tubular mesh structure ofproximal anchor section23 preferably is formed by laser cutting a solid tube.Proximal anchor section23 may be constructed in the same manner described above with respect todistal anchor section22. Alternatively,proximal anchor section23 also may be constructed to be balloon expandable.
• Moreover,distal anchor section22 andproximal anchor section23 may have different constructions. Althoughdistal anchor section22 andproximal anchor section23 as described above are identical, they alternatively may have different zig-zag or cell structures or deployment modes (e.g., self-expanding at the distal end and balloon expandable at the proximal end). For example,anchor sections22,23 may be constructed as a single zig-zag ring. As a further alternative,anchor sections22,23 may be configured so thatopenings36,46 have shapes other than parallelograms, e.g.,openings36,46 may be shaped as diamonds or any other polygonal shape, circles or ellipses. Furthermore, althoughanchor sections22,23 are illustrated as includingstruts32,42 extending between each set of corresponding apices, struts32,42 may extend between fewer sets of corresponding apices. For example, struts may extend between relatively few apices. In addition, the distance between the zig-zag rings ofanchor sections22,23 may also be selected to provide an anchor section of any desired length.
• Furthermore, the outer edges ofanchor sections22,23 may be biased so that the proximal-most edge ofanchor section23 and the distal-most edge ofanchor section22 expand further radially outward than with respect to longitudinal axis X than the remainder of the anchor section. This configuration may be useful to increase radial outward force upon a patient's vessel and thus improve anchoring ofvascular prosthesis20 within the vessel. Such a biased configuration may be established by heat-treating a shape memory material using techniques that are known in the art.
• Distal anchor section22 is coupled to the distal end of alternatinghelical section21 atjunction48. Similarly,proximal anchor section23 is coupled to the proximal end of alternatinghelical section21 atjunction50. Preferably,junctions48,50 are formed from a strut of alternatinghelical section21 that extends from that section and is coupled to a portion of the adjacent zig-zag rings30,40 of therespective anchor section22,23.
• Junctions48,50 may comprise one or moreradiopaque markers52 such as a radiopaque marker band or coating.Radiopaque marker52 facilitates positioning ofjunctions48,50 at a desired longitudinal position within a patient's vessel, and further facilitates alignment ofvascular prosthesis20 at a desired axial orientation within the vessel. For example,radiopaque markers52 may be used to orient alternatinghelical section21 so that a desired lateral surface of alternatinghelical section21 deploys to overlay the diseased vessel segment.
• It will be apparent to those skilled in the art thatjunctions48,50 may comprise other strut arrangements to connectdistal anchor section22 andproximal anchor section23 to alternatinghelical section21. For example, more than one strut may extend from alternatinghelical section21 to arespective anchor22,23.
• In one preferred embodiment, alternatinghelical section21,distal anchor section22 andproximal anchor section23 are integrally formed as a single monolithic body, such as by laser cutting all three components from a single tube. In such a construction ofvascular prosthesis20, the struts extending from alternatinghelical section21 that formjunctions48,50 also may form struts32,42 of therespective anchor section22,23. Alternatively,anchor sections22,23 may be manufactured separately from alternatinghelical section21 and mechanically coupled in a subsequent process, such as by soldering, welding, installing mechanical fasteners (e.g., rivets) or other means, as will be apparent to one skilled in the art.
• Referring toFIG. 24, another embodiment of the vascular prosthesis will be described. The present embodiment illustrates a version ofvascular prosthesis70, described above that includesdistal anchor72 andproximal anchor73. Distal andproximal anchors72,73 are similar in construction to those described with respect toFIGS. 22 and 23. Alternatinghelical section71 is similar in construction to that described with respect toFIG. 17 and will not be further described.
• Referring toFIG. 25, another embodiment of the vascular prosthesis will be described. The present embodiment illustrates a version ofvascular prosthesis80, described above, that includesdistal anchor82 andproximal anchor83. Distal andproximal anchors82,83 are similar in construction to those described with respect toFIGS. 22 and 23 but include zig-zag rings that are slightly offset to define diamond-shaped openings and fewer struts between the rings are employed. Alternatinghelical section81 is similar in construction to that described with respect toFIG. 18 and will not be further described.
• A further advantage over the above-mentioned publications is that the configuration of the alternating helical section provides dampening characteristics for longitudinal, torsional and buckling forces applied to the vascular prosthesis.
• Although a method of treating diseased vessels has been described, it will be apparent from the method described herein that the vascular prosthesis may be used in a variety of procedures. For example, vascular prosthesis also may be used in general stenting procedures, for example, to maintain patency in a vessel after a carotid angioplasty procedure, or may be used as an intravascular drug delivery device, or may be used in other applications apparent to those skilled in the art.
• In accordance with another aspect of the present invention, the vascular prosthesis of the present invention is configured to be flexible enough to substantially conform to the shape of vessel V without causing the vessel to remodel. In particular, the alternating direction of rotation of the helical portions of the alternating helical section allow for increased flexibility of the prosthesis.
• While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.

Claims (2)

1. A method of deploying a vascular prosthesis, comprising:

advancing a guidewire to a diseased vessel segment;

advancing a delivery system having a vascular prosthesis loaded therein over the guidewire to the diseased vessel segment, the vascular prosthesis including an alternating helical section, the alternating helical section comprising a first helical portion including a flange and a second helical portion including a flange, the first and second helical portions having adjacent ends joined directly to one another to define an apex, each of the first and second helical portions comprising a widened flange portion adjacent to the apex, the widened flange portions extending into a space between the first and second helical portions, the first helical portion having a direction of rotation opposite to that of the second helical portion, and the vascular prosthesis being wound onto a catheter body of the delivery system when the vascular prosthesis is in a contracted configuration;

retracting an outer sheath of the delivery system proximally to expose the alternating helical section, the alternating helical section expanding to a deployed configuration;

overlapping a portion of the apex by the widened flange portions during at least a portion of a treatment range between the radially contracted and expanded states; and

retracting the delivery system from the vessel.

2. The method of deploying a vascular prosthesis ofclaim 1, wherein the vascular prosthesis further comprises an anchor section coupled to an end of the alternating helical section, the method further comprising retracting the outer sheath proximally to allow the anchor section to expand to a deployed configuration prior to retracting the delivery system from the vessel.

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