Endovascular prosthesis accommodating torsional and longitudinal displacements and methods of use

A prosthesis is provided comprising a plurality of telescoping tubular members that are deployed and assembled in vivo to define a lumen through a diseased portion of a vascular system. The individual tubular members are capable of accommodating torsional and longitudinal displacements caused by relative motion of the healthy portions on either side of the diseased portion of vessel.

FIELD OF THE INVENTION
 The field of the invention relates to prostheses for repairing occlusive
 and aneurysmal vascular disease, and more particularly, an endovascular
 prosthesis capable of accommodating torsional and longitudinal
 displacements between its ends.
 BACKGROUND OF THE INVENTION
 The recent introduction of endoluminal graft prostheses, such as stents and
 stent-graft systems, for the treatment of arterial and venous defects,
 such as aneurysms, hold the promise of reduced procedural morbidity and
 mortality compared to previously known surgical alternatives.
 For example, U.S. Pat. No. 5,078,726 to Kreamer describes a stent graft
 system wherein a graft is affixed to intact portions of a vessel above and
 below an aneurysm using coiled sheet stents. Likewise, U.S. Pat. No.
 5,219,355 to Parodi et al. shows a graft affixed to intact portions of a
 vessel wall above and below an aneurysm using balloon-expandable stents.
 U.S. Pat. No. 5,275,622 to Lazarus also shows a graft affixed at its upper
 and lower ends using self-expanding sinusoidal rings.
 One drawback encountered with systems such as those described in the
 foregoing patents is that relative movement of the upper and lower
 fixation devices after initial deployment of the stents may result in
 twisting of the graft material. Such torsional displacements between the
 ends of the graft may cause a reduction in the flow area of the graft
 and/or the creation of stagnation zones that promote clotting within the
 lumen of the graft.
 In addition, excluding an aneurysm from the flow path and subsequent
 clotting of the blood contained within the aneurysmal cavity may result in
 foreshortening of the vessel, thereby causing longitudinal movement of the
 graft fixation devices towards one another. Such longitudinal
 displacements may in turn cause buckling: the graft may bow outward, sag,
 kink, or crumple, again promoting stagnation zones and thrombus formation
 within the lumen of the graft.
 Moreover, because the structure of the human vascular tree varies from
 patient to patient, each procedure is a unique experience. For example, an
 aneurysm existing in a straight vessel segment may be excluded with a
 tubular graft, whereas an aneurysm occurring at, abutting or including a
 vessel bifurcation may require the use of a custom prosthesis.
 Repair of an aneurysm located adjacent to a bifurcated vessel presents
 further technical difficulties, including the inability to easily enter
 both vessel branches because of vessel size, vessel tortuosity, device
 size, or limited device flexibility. There may also be an inability to
 adequately expand the device and create fluid seals at the ends of the
 aneurysm. If a custom device does not fit, surgical intervention also may
 be necessary to remove the device, thereby exposing the patient to
 additional risk. These problems are compounded where the diseased area of
 a vessel may change in length, size, and shape after the prosthesis has
 been deployed.
 In view of the foregoing, it would be desirable to provide a vascular
 prosthesis that may be readily adapted to vessels of various sizes,
 including bifurcated vessels.
 It further would be desirable to provide a vascular prosthesis that can
 accommodate changes in the size and shape of the vessel after the
 prosthesis has been deployed.
 It also would be desirable to provide a vascular prosthesis that can
 accommodate torsional and longitudinal displacements between the fixation
 devices that affix the vascular prosthesis to intact portions of the
 vessel wall, without twisting or kinking of the prosthesis.
 SUMMARY OF THE INVENTION
 In view of the foregoing, it is an object of the present invention to
 provide a vascular prosthesis that may be readily adapted to vessels of
 various sizes, including bifurcated vessels.
 It is another object of this invention to provide a vascular prosthesis
 that can accommodate changes in the size and shape of the vessel after the
 prosthesis has been deployed.
 It is a further object of the present invention to provide a vascular
 prosthesis that can accommodate torsional and longitudinal displacements
 between the fixation devices that affix the vascular prosthesis to intact
 portions of the vessel wall, without twisting or kinking of the
 prosthesis.
 These and other objects of the invention are accomplished by providing a
 vascular prosthesis having first and second interconnecting members. One
 end of each of the first and second members is fixed to an intact portion
 of vessel wall on either side of a vascular defect to be excluded. In
 accordance with the principles of the present invention, the other ends of
 the first and second members are interconnected so that one end telescopes
 and rotates within the other end. The first and second members of the
 graft of the present invention therefore define a custom, self-adjusting
 member, assembled in vivo, that spans a diseased section of a vascular
 system.
 The prosthesis of the present invention also facilitates repair of complex
 vascular structures, such as bifurcated vessels. Changes in the size and
 shape of the damaged section may be readily accommodated without buckling
 or twisting of the graft. In addition, the prosthesis may comprise a
 semipermeable material that relieves pressure build up in the aneurysm
 cavity, and promotes clot formation in the aneurysm cavity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The present invention provides an endovascular prosthesis capable of
 accommodating torsional and longitudinal displacements between its ends.
 The two portions of the prosthesis define a custom, self-adjusting device
 that may be assembled in vivo to span a diseased section of a vessel. The
 prosthesis is especially well suited for repairing complex vascular
 structures, such as bifurcated vessels. Changes in the size and shape of
 the damaged section are accommodated without twisting, kinking or buckling
 of the prosthesis.
 Referring to FIG. 1, a previously known prosthesis 10 is described that
 spans a vascular defect, illustratively an aneurysm. Prosthesis 10 may
 comprise any of the stent-graft combinations described hereinabove.
 Prosthesis 10 comprises graft 11 having end 12 affixed by stent 13 to
 portion V.sub.1 of the vessel, and end 14 affixed by stent 15 to portion
 V.sub.2 of the vessel. Prosthesis 10 includes central lumen 16 that
 conducts blood from portion V.sub.1 of the vessel to portion V.sub.2,
 while excluding vascular defect VD.
 Vascular defect VD may be, for example, a localized, pathological, blood
 filled dilation of vessel V caused by a disease or weakening of the vessel
 wall to form aneurysm A. Though vascular defect VD is illustratively
 described herein as an aneurysm, the defect may also be an obstruction,
 stenosis, dissection, clot, weakened vessel wall or the like without
 departing from the scope of the present invention.
 As a consequence of deployment of prosthesis 10, vessel V is subjected to a
 twisting moment T that creates a relative torsional displacement of ends
 12 and 14 of the prosthesis, for example, by clotting of the blood
 excluded within the aneurysm or return of the vessel portions V.sub.1 and
 V.sub.2 to an original state before the development of vascular defect VD.
 This torsional displacement may lead to twisting of the material
 constituting graft 11, and result in reduced flow area of central lumen 16
 (shown in dotted line in FIG. 1). In addition, the helical folds of
 material in graft 11 accompanying twisting of graft 11 may create
 stagnation zones within central lumen 16 that promote clot and thrombus
 formation within lumen 16 of prosthesis 10. Accordingly, central lumen 16
 may become a site that spawns emboli, or may even completely occlude. It
 is an object of the present invention to remedy this defect in previously
 known stent-graft systems.
 Referring now also to FIG. 2, problems associated with longitudinal
 foreshortening of previously known stent-graft systems are also described.
 Prosthesis 20 comprises graft 21 having end 22 affixed by stent 23 to
 vessel portion V.sub.1 and end 24 affixed by stent 25 to vessel portion
 V.sub.2. Prosthesis 20 includes central lumen 26 that channels blood
 between vessel portions V.sub.1 and V.sub.2, while excluding vascular
 defect VD, illustratively aneurysm A.
 It is contemplated that after successful exclusion of aneurysm A, clotting
 of the blood captured within the aneurysm may result in shortening of the
 diseased length of vessel V between vessel portions V.sub.1 and V.sub.2,
 thereby applying a compressive axial load to graft 21 of prosthesis 20.
 This compressive axial load may in turn cause longitudinal movement of
 ends 22 and 24 of prosthesis 20 towards one another. Such longitudinal
 displacement is expected to cause buckling of graft 21 (shown in dotted
 line in FIG. 2), resulting in sagging or crumpling of the graft material
 in a such a way that central lumen 26 of the prosthesis is narrowed.
 Narrowing of central lumen 26 also may promote the development of
 stagnation zones and thrombus formation sites within central lumen 26 of
 prosthesis 20. Alternatively, an axial tensile load may be applied to
 opposite ends 22 and 24 of prosthesis 20, also resulting in reduction of
 the flow area within central lumen 26. It is also an object of the present
 invention to address this drawback of previously known stent-graft
 systems.
 Referring now to FIGS. 3A and 3B, the steps of assembling in vivo an
 endovascular prosthesis 30, constructed in accordance with the principles
 of the present invention, is described. Prosthesis 30 comprises
 interconnecting tubular members 31 and 32 disposed within vascular defect
 VD, illustratively aneurysm A. Tubular member 31 has end 33 affixed to
 vessel portion V.sub.1 and free end 34. Tubular member 32 has end 35
 affixed to vessel portion V.sub.2 and free end 36. In accordance with the
 present invention, free ends 34 and 36 of tubular members 31 and 32,
 respectively, are interconnected in an overlapping, telescoping manner
 within aneurysm A to provide a structurally rigid prosthesis that replaces
 the weakened walls of the vessel.
 Tubular members 31 and 32, which may comprise a polymer covered plastically
 deformable alloy or metal structure, are expanded to engage the interior
 wall of non-diseased vessel portions V.sub.1 and V.sub.2 and preferably
 may be customized to fit the diameter of vessel V. Free ends 34 and 36 are
 interconnected so that the may move longitudinally relative to one another
 and rotate relative to one another. Prosthesis 30 therefore may be
 customized to accommodate the length of the aneurysm by varying the extent
 to which tubular members 31 and 32 overlap one another. Since the length
 and radial orientation of tubular members 31 and 32 may be determined upon
 deployment within the vessel, prosthesis 30 may be customized in vivo to
 vascular defects of varying sizes and shapes.
 As described hereinabove, one problem associated with repairing a diseased
 area of a vessel with a fixed-length prosthesis is that the diseased blood
 vessel may shrink or expand in length, or otherwise change in shape. The
 change in size or shape of the diseased vessel may cause the prosthesis to
 become kinked or twisted, thereby narrowing or blocking the lumen through
 the diseased area formed by the prosthesis. Because tubular members 31 and
 32 of prosthesis 30 may move axially and radially with respect to each
 other once deployed, prosthesis 30 can accommodate changes in the size and
 shape of the vessel.
 More specifically, in FIG. 3A, vascular defect VD may be a localized
 pathological, blood filled dilation of blood vessel V caused by a disease
 or weakening of the blood vessel wall to form aneurysm A. Tubular member
 32 is introduced into vessel portion V.sub.2 (illustratively, the
 descending aorta) transluminally along guide wire 100 via a femoral
 artery, as is per se known. Tubular member 32 then is expanded so that end
 35 engages healthy vessel portion V.sub.2 and free end 36 extending within
 aneurysm A as shown in FIG. 3A. Thus, tubular member 32 is secured in
 place only by its attachment to vessel portion V.sub.2.
 Assembly of prosthesis 30 is now completed by introducing tubular member 31
 into vessel V along guide wire 100, so that free end 34 is disposed within
 free end 36 of tubular member 32. Tubular member 31 is then expanded, so
 that end 33 engages vessel portion V.sub.1 and the interconnected tubular
 members 31 and 32 exclude aneurysm A from the blood flow path. Free end 34
 of tubular member 31, which is overlapped by, and thus interconnected with
 free end 36 of tubular member 32, permits rotational and longitudinal
 motion between the tubular members, while minimizing blood passing through
 the overlap region into aneurysm A. Prosthesis 30 thus forms a continuous
 lumen through aneurysm A.
 The length of prosthesis 30 is determined by the length of free end 34 of
 tubular member 31 that overlaps free end 36 of tubular member 32.
 Prosthesis 30 may therefore be customized in vivo to fit within vessel
 defects of various sizes. Once tubular members 31 and 32 have been
 deployed, they may move radially and axially with respect to each other to
 accommodate torsional or longitudinal movement of vessel portions V.sub.1
 and V.sub.2. For example, tubular member 31 may rotate without causing
 free end 36 of tubular member 32 to rotate. In addition, tubular member 31
 may telescope within tubular member 32 if vascular defect VD shrinks in
 length. Thus, if vascular defect VD changes in size or shape, prosthesis
 30 can adapt without becoming kinked or twisted, as is believed to occur
 with prostheses 10 and 20 of FIGS. 1 and 2.
 Preferably, tubular members 31 and 32 comprise a semi-permeable or
 impermeable material, such as a nickel-titaniums alloy ("nitinol"),
 stainless steel, or polymeric mesh, that provides a structural framework
 for prosthesis 30, while providing sufficient flexibility to allow the
 placement of the device within a vascular defect. In the preferred
 embodiment shown in FIGS. 3A and 3B, tubular members 31 and 32 comprise a
 mesh having a plurality of longitudinal members interconnected by
 serpentine members inclined at an angle with respect to the longitudinal
 members, such as described in U.S. Pat. Nos. 5,314,444 and 5,758,562,
 which are incorporated herein by reference.
 Referring now to FIG. 4, an alternative embodiment of a prosthesis of the
 present invention is described. Prosthesis 40 is similar in construction
 to prosthesis 30 of FIG. 3, but in addition includes a resilient seal that
 couples the free ends of the tubular members together.
 In particular, prosthesis 40 comprises interconnected tubular members 41
 and 42. Tubular member 41 includes end 43 adapted to expand to engage a
 healthy vessel portion, such as vessel portion V.sub.1 in FIG. 3, and free
 end 44. Tubular member 42 includes end 45 adapted to expand to engage a
 healthy vessel portion, such as vessel portion V.sub.2 in FIG. 3, and free
 end 46, which overlaps free end 44 of tubular member 41 when the
 prosthesis is fully assembled.
 In the embodiment of FIG. 4, tubular member 41 further includes resilient
 seal 47 affixed to either the exterior surface of free end 44 or the
 interior surface of free end 46. Resilient seal 47 Preferably comprises an
 annular cylindrical gasket of soft material such as
 polytetrafluoroethylene ("PTFE") or biocompatible closed-cell foam. Seal
 47 is designed to reduce bypass flow of blood through the overlapping free
 ends into the vascular defect VD, while reducing friction between
 overlapping ends 44 and 46 to facilitate the movement and rotation of
 tubular members 41 and 42 with respect to each other.
 With respect to FIG. 5, a further alternative embodiment is described.
 Prosthesis 50 comprises tubular member 51 having tissue-engaging end 53
 and free end 54, and tubular member 52 having tissue-engaging end 55 and
 free end 56. Free end 56 overlaps free end 54 of tubular member 51 when
 the prosthesis assembled. Rings 57 and 58 prevent tubular members 51 and
 52 from coming apart once deployed in the diseased vessel. Tubular member
 51 has ring 57 attached to free end 54, while tubular member 52 has 58
 attached to free end 56. Rings 57 and 58 are expandable along with tubular
 members 51 and 52 when the tubular members are deployed in the vessel.
 Specifically, ring 57 is placed inside tubular member 52 when tubular
 member 51 is positioned inside the vessel to sealingly engage the interior
 wall of tubular member 52. When tubular member 51 moves proximally (to the
 left in FIG. 5), ring 57 engages ring 58 to prevent further proximal
 movement. Thus, rings 57 and 58 prevent tubular members 51 and 52 from
 becoming separated. In addition, rings 57 and 58 allow tubular members 51
 and 52 to move axially and radially with respect to each other without
 compromising the prosthesis or the vessel.
 The principles of the present invention also may be applied to grafts for
 use in bifurcated vessels, for example, so that a second tubular member
 may span a vessel bifurcation. With respect to FIG. 6, prosthesis 60 is
 described comprises three telescoping portions 61, 62 and 63 that are
 assembled in vivo. Tubular member 61 has a tissue-engaging end (not shown)
 adapted to engage a healthy vessel portion, as in FIG. 3, and free end 65.
 Tubular member 62 includes trunk end 66 that telescopes within free end 65
 of tubular 25 member 61, branch 67 and joining region 68. Tubular member
 63 includes tissue-engaging end 69 and free end 70. When fully assembled,
 trunk end 66 of tubular member 62 is overlappingly interconnected with
 free end 65 of tubular member 61, and free end 70 of tubular member 63 is
 overlappingly interconnected with joining region 68 of tubular member 62.
 In accordance with the principles of the present invention, tubular members
 61, 62 and 63 are axially and radially movable with respect to each other.
 If either of the branches of the vessel move with respect to each other or
 the trunk of the vessel, tubular members 61, 62 and 63 can move and rotate
 with respect to each to accommodate the changes in relative orientation of
 the vessels, without buckling or twisting of one or both legs of
 prosthesis 60. The prosthesis of FIG. may be especially advantageous in
 implementing bifurcated grafts, such as that described in U.S. Pat. No.
 5,961,548 to Shmulewitz, which is incorporated herein by reference.
 Tubular members 61-63 preferably comprise balloon expandable metal or metal
 alloy structures, such as described in the above-incorporated patents, and
 are covered with an impermeable or semi-permeable biocompatible membrane.
 Alternatively, tubular members 61-63 may comprise membrane covered
 self-expanding structures or thermally-expanded metal alloy structures.
 Tubular members 61-63 may incorporate any of the sealing mechanisms
 described hereinabove, such as resilient seal 47 of the embodiment of FIG.
 4 or the rings of the embodiment of FIG. 5.
 While preferred illustrative embodiments of the present 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. Although, the present invention has been described
 with respect to vascular defects, the present invention also may be used
 to reline an organ. The foregoing references to a vessel should therefore
 be understood to include organs. In is intended in the appended claims to
 cover all such changes and modifications which fall within the true spirit
 and scope of the invention.