United States Patent [19]
`Porter
`
`[54] SELF-EXPANDING PROSTHESIS HAVING
`STABLE AXIAL LENGTH
`[75] Inventor:
`Christopher H. Porter, Woodenville,
`Wash.
`[73] Assigneez' Schneider (USA) Inc., Minneapolis,
`Minn.
`[21] Appl. No.: 544,923
`[22] Filed:
`Jun. 28, 1990
`[51] Int. Cl.5 .............................................. .. A61F 2/04
`[52] U.S. C1. .................................... .. 623/12; 606/151;
`606/198
`[58] Field of Search ....................... .. 623/1, 11, 12, 13;
`604/96, 104; 606/151, 153, 155, 158, 191, 198
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`3,868,956 3/1975 Al?di et a1. .
`4,553,545 11/1985 Maass et a1. ...................... .. 604/104
`4,572,186 2/1986 Gould et a1. .
`604/104
`4,649,922 3/1987 Wiktor ....... ..
`623/1
`4,655,771 4/1987 Wallsten ............................... .. 623/1
`4,681,110 7/1987 Wiktor .
`4,699,611 10/1987 Bowden ............................ .. 604/105
`4,732,152 3/1988 Wallsten et a1. .
`4,733,665 3/1988 Palmaz .................................. .. 623/1
`4,793,348 12/1988 Palmaz .
`4,800,882 l/1989 Gianturco ........................... .. 623/13
`
`4,830,003 5/1989 Wolff et a1. . . . . . .
`
`. . . . . . .. 623/1
`
`604/271
`4,848,343 7/1989 Wallsten et al. .
`623/1
`4,856,516 8/1989 Hillstead ........ ..
`4,886,062 12/1989 Wiktor .................................. .. 623/1
`
`OTHER PUBLICATIONS
`Interventional Radiology, “Self-Expanding Metallic
`Stents for Small Vessels: An Experimental Evaluation”,
`Duprat et al, pp. 469-472, vol. 162, Feb. 1987.
`“Self-Expanding’Endovascular Prosthesis: An Experi
`mental Study”, Radiology, 1987 (Sep.), pp. 709-714,
`Rousseau et al.
`
`[11]
`[451
`
`Patent Number:
`Date of Patent:
`
`5,064,435
`Nov.v 12, 1991
`
`“When Hope is All In Vein”, Sweden Now, Mar., 1988.
`“Transluminally-_Placed Coilspring Endarterial Tube
`Grafts", Charles T. Dotter, MD, pp. 239-332, Investiga
`tive Radiology, Sep.-Oct. 1969, vol. 4.
`Technical Developments and Instrumentation, “Tram
`sluminal Expandable Nitinol Coil Stent Grafting: Pre
`liminary Report”, Dotter et al, pp. 259-260, Radiology
`147, Apr. 1983.
`“Atherosclerotic Rabbit Aortas: Expandable lntralu
`minal Grafting”, Radiology, 1986 (Sep.), pp. 723-726,
`Palmaz et al.
`Primary Examiner—Randy Citrin Shay
`Attorney, Agent, or Firm——l-Iaugen and Nikolai
`[57]
`ABSTRACT
`A body implantable stent consists of two or more gener
`ally tubular, coaxial and slidably connected stent seg
`ments. Each of the stent segments is of open weave
`construction, formed of multiple braided, helically
`wound strands of resilient material. The stent is elasti
`cally deformed to a reduced radius when deployed.
`Whenreleased after positioning, the stent self-expands
`radially into contact with a tissue wall segment de?ning
`a blood vessel or other body cavity. As each stent seg
`ment expands radially, it contracts in the axial direction.
`To preserve a consistent length of the stent in spite of
`axial contraction of the segments, the axially outward
`and non-overlapping portions of the stent can be de
`signed for secure ?xation to the tissue wall segment, for
`example as radially outward flares. Accordingly, axial
`contraction occurs as a reduction in the length of the
`medial regions where adjacent stent segments overlap.
`Alternative approaches to maintain axial length include
`the addition of reinforcing ?laments near the stent op
`posite ends to increase the restoring force, the provision
`of ?xation hooks at opposite ends of the stent, and se
`curing an elongate, axially directed, flexible and inex
`tensible wire to the opposite ends of the stent.
`
`26 Claims, 2 Drawing Sheets
`
`40
`
`00 ...¢ no
`
`00
`
`W.L. Gore & Associates, Inc.
`Exhibit 1023-1
`
`

`
`US. Patent
`
`Nov. 12, 1991
`
`Sheet 1 of 2
`
`5,064,435
`
`FIG.2
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`W.L. Gore & Associates, Inc.
`Exhibit 1023-2
`
`

`
`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 2 of 2
`
`5,064,435
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`W.L. Gore & Assogizltes, Inc.
`Exhibit 1023-3
`
`
`
`W.L. Gore & Associates, Inc.
`Exhibit 1023-3
`
`

`
`1
`
`-.
`
`5,064,435
`
`SELF-EXPANDING PROSTHESIS HAVING
`STABLE AXIAL LENGTH
`
`5
`
`' 2
`case, the spring preferably is elastic, with a memory
`favoring the radially expanded con?guration.
`A self-expanding stent or prosthesis often is preferred
`over a plastically deformed device. Resilient stents can
`be deployed without dilatation balloons or other stent
`expanding means. A self-expanding stent can be prese
`lected in accordance with the diameter of the blood
`vessel or other ?xation site. While deployment requires
`skill in positioning the prosthesis, the added skill of
`properly dilating the balloon to plastically expand a
`prosthesis to a selected diameter is not required. Also,
`the self¢expanding device remains at least slightly com
`pressed after ?xation, and thus has a restoring force
`which facilitates acute ?xation. By contrast, the plasti
`cally expanded stent must rely on the restoring force of
`deformed tissue, or on hooks, barbs or other indepen
`dent ?xation means.
`Further advantages arise from constructing the pros
`thesis of multiple, braided and helically wound strands
`or ?laments as in the aforementioned Wallsten patent.
`The ?laments themselves have a restoring force which
`causes the ?laments to bear against tissue walls of the
`body cavity in which the stent is ?xed, thus maintaining
`the cavity open. At the same time there is suf?cient
`space between adjacent ?laments to promote embed
`ding of the stent into the tissue, and ?brotic growth to
`enhance long-term ?xation. A further advantage of this
`construction is that it enables a substantial radial con
`traction of the prosthesis during deployment, for exam
`ple to as little as about one-fourth of the normal diame
`ter (the diameter in the relaxed state, i.e. when subject
`to no external forces). This facilitates deployment of the
`prosthesis through narrow vessels or other constrictions
`on the way to the point of ?xation.
`At the same time, a substantial axial elongation ac
`companies the radial contraction. There is a substantial
`axial contraction or shortening as the stent self expands,
`once free of its radial constraint. Thus, there is a rubbing
`or scraping action axially along tissue as the radially
`expanding stent also axially shortens. Should tissue at
`the ?xation area further yield to radial prosthesis expan
`sion in the longer term, such expansion causes further
`axial shortening and wiping action, and presents further
`risk of injury to tissue. A further drawback is that a stent
`during its ?xation may radially expand more than ex
`pected, retaining less than the intended or minimum
`necessary axial length. Likewise, a plastically deform
`able stent may require more than the anticipated radial
`expansion and axial shortening.
`Therefore, it is an object of the present invention to
`provide a prosthesis of open weave, helical and braided
`construction capable of _ substantially maintaining its
`axial length as it radially self-expands.
`Another object is to provide a radially expanding
`tubular stent comprised of at least two stent segments,
`with an area of overlap of the sections variable in axial
`length to maintain a consistent axial separation between
`non-overlapping ends of the stent.
`Yet another object is to provide a stent with a medial
`portion variable in axial length, in combination with
`means at the opposite end portions of the stent for ?xing
`the stent to bodily tissue, such that the bodily tissue
`maintains a substantially constant axial separation of the
`two end portions during any radial expansion or con
`traction of the stent.
`
`BACKGROUND OF THE INVENTION
`The present invention relates to body implantable
`devices, and more particularly to prostheses and grafts
`intended for long-term or permanent ?xation in body
`cavities.
`'
`A wide variety of patient treatment and diagnostic
`procedures involve the use of devices inserted into the
`body of the patient, with some of these devices being
`permanently implanted. Among these devices are pros- .
`theses or grafts for transluminal implantation, for exam
`ple as disclosed in U.S. Pat. No. 4,655,771 (Wallsten).
`The prosthesis described in Wallsten is a ?exible tubular
`braided structure formed of helically wound thread
`elements. Gripping members at opposite ends of the
`prosthesis initially secure it to a catheter, with the proxi
`mal gripping member being movable distally to give the
`prosthesis the shape of a balloon. In deployment, the
`gripping members and catheter are removed, leaving
`the prosthesis to assume a substantially cylindrical
`shape as it slightly expands and substantially conforms
`25
`to a blood vessel wall or other tissue. Another prosthe
`sis is disclosed in U.S. Pat. No. 4,681,110 (Wiktor). A
`?exible tubular liner, constructed of braided strands of a
`?exible plastic, is insertable into the aorta, whereupon it
`self-expands against an aneurysm to direct blood ?ow
`30
`past the aneurysm. The braided stents of Wallsten and
`Wiktor axially contract as they radially expand.
`Another elastic stent is shown in U.S. Pat. No.
`4,830,003 (Wolff et al). The stent includes a series of
`generally longitudinal wires welded together in pairs,
`with the wires in each pair then bent into a “V” shape.
`Like the braided stents, this stent shortens axially as it
`radially expands.
`Prostheses also have been constructed of plastically
`deformable materials. U.S. Pat. No. 4,733,665 (Palmaz)
`discloses intraluminal vascular grafts radially expanded
`using angioplasty balloons. The grafts are wire mesh
`tubes, and axially shorten as they radially expand. U.S.
`Pat. No. 4,800,882 (Gianturco) features a stent formed
`of wire, including a plurality of serpentine bends to
`form opposed loops. A balloon is in?ated to radially
`expand the stent, without substantial axial shortening.
`Yet another approach to prosthesis design is shown in
`U.S. Pat. No. 3,868,956 (Al?di et al). Al?di et al dis
`closes a strainer or screen with a plurality of generally
`longitudinal wires, bound together by a cylindrical
`sleeve. The wires are deformable into a longitudinal,
`straight-line con?guration for implantation. Once im
`planted, the device is heated. Due to the recovery prop
`erty of the metal forming the wires (e.g. nitinol alloy),
`heating causes the wires to ?are radially outward at the
`opposite ends, thus to secure the device at the desired
`location.
`A stent including means for maintaining a constant
`axial length in spite of radial expansion or contraction, is
`disclosed in U.S. Pat. No. 4,553,545 (Maass et al). as a
`prosthesis in the form of a helical coil spring. In one
`embodiment, a constant axial length of the spring is
`_maintained, with opposite ends of the spring rotated
`relative to one another to change the spring pitch and
`radius. An alternative approach involves maintaining a
`constant pitch over a given section of a spring, by pro
`viding spring material to a “constant length” section
`from a more compressed section of the Spring. In each
`
`45
`
`20
`
`35
`
`55
`
`65
`
`W.L. Gore & Associates, Inc.
`Exhibit 1023-4
`
`

`
`3
`‘SUMMARY OF THE INVENTION
`To achieve these and other objects, there is provided
`a body implantable device, including coaxial ?rst and
`second open weave stent segments slidably engaged to
`form a stent. The stent segments are engaged along
`respective concentric ?rst and second axially inward
`portions overlapping one another to form a medial re
`gion of the stent. Further, the stent segments include
`opposite non-overlapping ?rst and second axially out
`ward regions with respective and opposite ?rst and
`second ends of the stent. The stent segments, at least
`along the axially inward portions, have a predetermined
`?rst diameter and a predetermined ?rst axial length.
`The stent segments are radially compressible to a sec
`ond diameter less than the ?rst diameter and to a second
`axial length longer than the ?rst axial length, to facili
`tate an axial insertion of the stent into a body cavity for
`delivery to a selected location along the body cavity
`and subsequent ?xation of the stent to a cavity wall
`segment de?ning the body cavity. During its ?xation,
`the stent radially expands. The ?rst and second axially
`inward portions slide relative to one another to reduce
`the axial length of the medial region during the radial
`expansion. Thus the stent maintains a substantially con
`stant axial length during radial expansion.
`A preferred approach uses means for ?xing the out
`ward ends of a self-expanding stent, e.g. respective ?rst
`and second flared outer end portions along the axially
`outward regions of the stent. The ?rst and second ends
`have diameters greater than the ?rst diameter when the
`stent is in the relaxed state, and when compressed tend
`to have a greater restoring force against the cavity wall
`segment, as compared to the remainder of the stent. The
`end diameters should be greater than the medial region
`diameter by ?ve percent or more, ensuring a substantial
`difference in restoring force for a relatively constant
`diameter of the cavity along the tissue wall segment.
`Alternatively, the outer end portion of each stent
`segment can have the same diameter as the medial re
`gion, but be composed of larger diameter ?laments,
`added windings of ?laments or otherwise have in
`creased stiffness or resistance to radial contraction as
`compared to the medial region Yet another alternative
`is to provide ?xation elements, for example hooks, at
`the opposite ends of the stent.
`In combination with positive ?xation of the stent
`ends, a substantial medial overlapping region is pro
`vided when the stent segments are in a radially com
`pressed or delivery con?guration. For example, the
`overlapping region may comprise three-fourths or more
`of the axial length of the compressed stent. Then, upon
`deployment of the stent, both stent segments radially
`expand and axially shorten. With the outer ends of the
`stent ?xed, the axial shortening occurs only along the
`medial region, substantially shortening the region of
`overlap but maintaining the desired axial separation of
`the opposite stent ends.
`An open weave of braided, helically wound strands
`or ?laments is the preferred structure of the tubular
`stent. The open weave structure enables substantial
`self-expansion in the stent, for example to a ?xation
`diameter at least three times the diameter during deliv
`ery. This of course results in a substantial corresponding
`axial shortening in each of the stent segments, but due to
`the overlapping medial region of the stent, the overall
`axial length remains virtually constant.
`
`4
`A pliable catheter is a suitable apparatus for delivery
`and deployment of the stent. More particularly, a pli
`able sheath can surround at least the distal end portion
`of the catheter and extend beyond the distal tip to sur
`round the stent segments as well, maintaining them in a
`radially compressed delivery con?guration. The cathe
`ter can be provided with a lumen, through which a
`guide wire may be inserted to facilitate travel of the
`catheter and compressed stent through blood vessels or
`other body cavities to the ?xation area. Once the cathe
`ter is inserted properly to position the stent at the de
`sired ?xation point, the outer sheath is withdrawn prox
`imally, with the stent abutting the catheter and thus
`secured against proximal travel with the sheath. The
`distal portion of the stent self-expands ?rst, and in ex
`panding against tissue, secures the stent segment against
`proximal travel. With one end of the stent constrained
`by tissue and the opposite end constrained by a station
`ary catheter, the axial length of the stent remains sub
`stantially constant. Axial shortening of the stent seg
`ments, which accompanies their radial expansion, tends
`to diminish the length of the medial region and leave the
`overall axial length unaffected.
`Following ?xation, further yielding of the tissue seg
`ment can result in further radial expansion of the stent.
`However, with the opposite ends of the stent secure,
`any axial shortening of the stent segments again affects
`only the medial overlapping region. Thus, the advan
`tages of the open weave construction are retained, with
`out an undesirable shortening of the stent as it radially
`self-expands.
`
`IN THE DRAWINGS
`For a further understanding of the above and other
`features and advantages, reference is made to the fol
`lowing detailed description and the drawings, in which:
`FIG. 1 is a side elevation of a body implantable de
`vice constructed in accordance with the present inven
`tiOn;
`FIG. 2 is a side sectional view of a catheter and
`sheath retaining the implantable device in a radially
`compressed condition;
`FIG. 3 is an end view of the device, catheter and
`sheath;
`FIG. 4 is a side sectional view showing deployment
`of the device within a body cavity;
`FIG. 5 is a side view of the device ?xated within the
`cavity;
`FIG. 6 is a side elevation of an alternative embodi
`ment device in the relaxed or fully radially expanded
`condition;
`FIG. 7 is a side elevation showing yet another alter
`native device in the expanded or relaxed condition;
`FIG. 8 is a side elevation illustrating a further alterna
`tive device in a radially compressed state;
`FIG. 9 is a side elevation of the device of FIG. 8 in
`the expanded condition;
`FIG. 10 is a side elevation showing yet another alter
`native device, in a radially compressed condition;
`FIG. 11 is a side elevation of the device of FIG. 10 in
`the radially expanded condition;
`FIG. 12 is a side elevation of another alternative
`device, in a radially expanded condition;
`FIG. 13 is a side elevation of a further alternative
`device, in a radially expanded condition;
`FIG. 14 is a side elevation of another alternative
`device, in a radially expanded condition; and
`
`5,064,435
`
`45
`
`60
`
`65
`
`W.L. Gore & Associates, Inc.
`Exhibit 1023-5
`
`

`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`Turning now to the drawings, there is shown in FIG.
`1 a body implantable prosthesis or stent 16. Stent 16 has
`an open mesh or weave construction, formed of heli
`cally wound and braided strands or ?laments 18 of a
`resilient material, for example a body compatible stain
`less steel or an elastomer, e.g. polypropylene, polyure
`thane, polysulfone or a polyester.
`Stent 16 includes coaxial proximal and distal stent
`segments 20 and 22. A medial region 24 is formed by the
`overlapping of respective axially inward portions of
`stent segments 20 and 22. Axially outward, non-over
`lapping portions of the stent segments are indicated at
`30 and 32, respectively. At opposite ends of the stent are
`?ared ends 34 and 36, each having a greater radius than
`the nominal radius over the majority of the stent length.
`As is later explained, ?ared ends 34 and 36 provide a
`?xation feature useful to maintain a constant overall
`axial length in stent 16, even while stent segments 20
`and 22 radially self-expand and axially contract during
`
`25
`
`35
`
`40
`
`5,064,435
`5
`6
`FIG. 15 is a side elevation of yet another alternative
`nary bypass operations, acute closure and recurrence of
`device, in a radially expanded condition.
`stenosis are signi?cant problems in up to about thirty
`percent of constricted or blocked passages opened by
`balloon angioplasty. The ?xation of stent 16 within a
`blood vessel along a previously occluded region tends
`to keep this region permanently open.
`'
`Fixation of stent 16, within a blood vessel 46 having
`a tissue wall segment 48, begins with intravascular in
`sertion of the stent, catheter and sheath in the delivery
`con?guration shown in FIGS. 2 and 3. The reduced
`radius facilitates insertion of this assembly through
`blood vessel 46 until stent 16 reaches a predetermined
`?xation location along the blood vessel. Once the
`proper positioning of the stent is con?rmed, e.g.
`through use of one or more radiopaque markings on the
`stent, sheath or catheter, sheath 38 is moved proximally
`with respect to catheter 40.
`With distal tip 42 abutting stent 16, the catheter pre
`vents the stent from traveling proximally with sheath 38
`as the sheath is withdrawn. Thus, as seen from FIG. 4,
`stent 16 becomes free of sheath 38 over an increasing
`distal portion of its axial length. As each of stent seg
`ments 20 and 22 becomes free, it radially self-expands
`until contacting tissue wall segment 48, then undergoes
`slightly further radial expansion until the tendency to
`radially expand is counterbalanced by the restoring
`force exerted radially inward by the tissue wall seg
`ment. At the equilibrium condition, shown in FIG. 5,
`stent is not fully radially expanded to the relaxed con?g
`uration shown in FIG. 1, and thus applies a restoring
`force which tends to maintain the stent at the ?xation
`position within vessel 46.
`A salient feature of the present invention is the con
`centric and slidable mounting of stent segments 20 and
`22 in combination with the ?xation provided by flared
`ends 34 and 36. During initial withdrawal of sheath 38,
`the distal flared end 36 is the ?rst to encounter tissue
`wall segment 48. Due to its larger nominal (relaxed
`state) diameter, ?ared end 36 tends to radially expand
`somewhat more than the remainder of axially outward
`portion 32 of this segment, and applies comparatively
`greater restoring force in the radially outward direction
`against the tissue wall segment. Accordingly, the axial
`shortening of distal stent segment 22 which accompa
`nies radial expansion, e.g. from a length of 100 mm
`when delivered to a ?xation length of 50 mm, occurs
`almost entirely by travel of axially inward portion 28,
`distally or rightwardly as viewed in FIG. 4. The slid
`able engagement of segments 20 and 22 permits such
`distal travel while proximal segment 20 remains sub~
`stantially ?xed relative to catheter 40.
`As sheath 38 is further withdrawn, proximal segment
`20 likewise radially expands and axially shortens As
`illustrated in FIG. 4, much of axially outward portion
`30 of segment 20 remains radially compressed within
`sheath 38, and thus is held ?xed with respect to the
`catheter. Consequently, the axial contraction of proxi
`mal stent segment 20 during radial expansion occurs
`almost entirely by virtue of proximal travel of its axially
`inward portion. This of course involves further sliding
`of the stent segments relative to one another, and fur
`ther reduces the axial length of medial overlapping
`region 24.
`As seen from FIGS. 2 and 5, the total axial length of
`stent 16, designated “L", is substantially the same
`whether the stent is in the deployment state, or the
`radially expanded to equilibrium or ?xation. Proximal
`stent segment 20 and distal stent segment 22 are each
`
`?xation.
`'
`In FIG. 1, stent 16 is shown in its relaxed condition,
`with no external forces applied to radially contract the
`stent. Stent 16 is self-expanding in the sense that when
`not subject to external forces, it assumes a diameter
`much larger than the diameter illustrated in FIGS. 2
`and 3. In these ?gures, the stent is elastically deformed
`and maintained in a radially reduced con?guration by a
`pliable, dielectric sheath 38 surrounding the stent.
`An elongate and pliable catheter 40, of which just the
`distal end region is shown in FIG. 2, includes a distal tip
`42 which abuts the proximal end of the stent. The proxi
`mal portion of sheath 38 surrounds the distal end region
`of the catheter. Catheter 40 has a central lumen 44 open
`to tip 42 and running the length of the catheter, to per
`mit delivery of a drug, in liquid form, to the catheter
`distal tip from a supply at the proximal end of the cathe
`ter. Lumen 44 further enables the use of a guide wire
`(not shown) which can be intravenously inserted, by its
`distal end to the desired point of ?xation for stent 16.
`With the guide wire in place, catheter 40, stent 16 and
`sheath 38 are positioned to surround the proximal end
`of the guide wire with the guide wire contained within
`lumen 44. Then, the catheter, sheath and stent are
`moved distally or advanced, directed by the guide wire
`to the ?xation location, whereupon the guide wire can
`be withdrawn.
`,
`Sheath 38 preferably isconstructed of silicone rubber
`or other suitable biocompatible material, and surrounds
`the stent and catheter at least along the catheter distal
`end region‘, or along the full length of the catheter if
`desired. Sheath 38 preferably is thin to facilitate intra
`vascular insertion of the catheter, sheath and stent, yet
`is sufficiently thick to maintain stent 16 in a reduced
`radius or delivery con?guration against the restoring
`force of strands 18. The outside diameter of the assem
`bly including the catheter, stent and sheath is approxi
`mately 2.3 millimeters.
`Stent 16 is particularly well suited for use as a pros
`thesis or graft in a blood vessel or other body cavity.
`One advantageous use of the stent occurs in connection
`with percutaneous transluminal coronary angioplasty
`(PTCA) procedures. While such procedures afford
`signi?cantly reduced cost and risk as compared to coro
`
`45
`
`55
`
`65
`
`W.L. Gore & Associates, Inc.
`Exhibit 1023-6
`
`

`
`5
`
`5
`
`5,064,435
`7
`8
`substantially shorter in equilibrium. However, virtually
`body tissue. with axial contraction occurring as substan
`all of the reduction in axial length is re?ected in the
`tial reduction in the length of medial region 58.
`substantially reduced length of medial overlapping re
`FIG. 7 illustrates yet another approach to preserving
`gion 24, which accounts for more than three-fourths of
`the axial length of the stent, in this case, a plurality of
`the total stent length in FIG. 2, and only about one-?fth
`?xation hooks 70 at the opposite ends of a stent 72 hav
`of the overall stent length in FIG. 5.
`ing a slidably interconnected and coaxial proximal and
`Eventually, ?xation of stent 16 becomes permanent
`distal stent segments 74 and 76. Fixation hooks 70 pres
`by virtue of the embedding of strands 18 into tissue wall
`ent some risk of injury and thus are more limited in their
`segment 48, and ?brotic growth of tissue between and
`application than the ?xation alternatives previously
`around strands to anchor the stent. This type of ?xation
`discussed. Nonetheless, hooks 70 provide a positive and
`occurs over a period of weeks, and in the intervening
`immediate ?xation of stent 72 within a cavity at the
`opposite stent ends. Subsequent radial expansion and
`time, tissue wall segment 48 may yield to allow further
`radial expansion of a stent,-and further axial shortening
`axial contraction of stent segments 74 and 76 serves to
`reduce the length of a medial region 78, preserving the
`of stent segments 20 and 22. The axial length “L” re
`overall length of the stent.
`mains substantially constant nonetheless, "as this further
`axial contraction is again re?ected in a further shorten
`FIGS. 8 and 9 illustrate a further embodiment stent or
`ing of the medial overlapping region. Axial contraction
`prosthesis 80 including a proximal segment 82, a distal
`segment 84 and a center segment 86 slidably engaged
`occurs along the medial region, since flared ends 34 and
`with the proximal and distal segments. All three seg
`36 continue to exert a comparatively greater restoring
`ments of prosthesis 80 have the previously described
`force against the tissue, thus more securely anchoring
`open mesh or weave construction of braided ?laments.
`the ends as compared to the central portions of the
`Stent 80 thus includes two overlapping regions interme
`stent. Thus, the overall length of the stent is maintained
`diate its proximal and distal ends 88 and 90, namely a
`not only during and immediately after ?xation, but in
`proximal intermediate region 92 and a distal intermedi
`the interim until ?brosis permanently secures the stent.
`ate region 94. While center segment 86 is shown with a
`FIG. 6 shows an alternative embodiment stent 52,
`smaller radius than the other segments for convenience
`again with concentric and slidably connected proximal
`of illustration, all segments preferably have substan
`and distal stent segments as indicated at 54 and 56. Axi
`tially the same radius.
`ally inward portions of the stent segments overlap to
`FIG. 9 illustrates stent 80 in the relaxed or radially
`form a medial region 58. Stent 52 has an open mesh or
`expanded state. Each of segments 82, 84 and 86 has a
`weave construction, formed of helically wound and
`reduced axial dimension as well as a larger radius.
`braided ?laments 60.
`Nonetheless, the axial distance between proximal end 88
`Stent 52, illustrated in its relaxed or unstressed state,
`and distal end 90 remains about the same, with virtually
`does not include radially outward flares at its opposite
`all of the axial contraction re?ected in the substantially
`ends. In lieu of ?ared ends, each of stent segments 54
`35
`reduced axial dimensions of intermediate overlapping
`and 56 includes at its axially outward end a plurality of
`regions 92 and 94.
`reinforcing strands 62 connected to the braided ?la
`Prosthesis 80 can be deployed in the manner de
`ments 60, thus to create respective proximal and distal
`scribed above in connection with other embodiments.
`reinforced end regions 64 and 66. The reinforcing
`Following the desired positioning of the prosthesis
`strands 62 can, but need not, be of the same construction
`within a blood vessel or other body cavity, a surround
`as the base ?laments. In either event, the reinforcement
`ing sheath is withdrawn slidably or folded back from a
`strands lend further elastic resistance to radial compres
`surrounding relation to the prosthesis, permitting it to
`sion, such that a given elastic radial compression of
`radially self-expand into contact with a tissue wall seg
`stent 52 requires a greater force at reinforced end re
`ment forming the cavity (not shown). Of course, the
`gions 64 and 66 as compared to the force required be
`diameter of the cavity should be less than the normal or
`tween these regions.
`radially expanded diameter of the prosthesis. Prosthesis
`Stent 52 can be deployed in the manner described
`80 does not utilize any special end ?xation structure
`above in connection with stent 16. Following proper
`such as the earlier described hooks, reinforced ends or
`positioning of the stent within a blood vessel or other
`?ared ends. Rather, the prosthesis is positioned by vir
`body cavity, a surrounding sheath similar to sheath 38 is
`tue of the self-expansion and restoring force of the seg
`withdrawn proximally from its surrounding relation
`ments, to maintain their relative positions, particularly
`with stent 52, allowing the stent to radially self-expand
`during their deployment and release from a sheath or
`into contact with the tissue forming the cavity. Again,
`the like, but also after ?xation. It should be noted that
`stent 52 is selected to have a nominal diameter (in the
`this approach is suitable for the two-segment stents
`relaxed state) greater than the diameter of the body
`earlier described, although some type of end ?xation
`cavity, so that base ?laments 60 and reinforcement
`means facilitates maintaining a constant axial length of
`strands 62 engage the tissue before full expansion, and
`the stent. If desired, a ?xation structure can be provided
`are contained short of full expansion by body tissue, for
`at ends 88 and 90.
`an equilibrium of the restoring force in the stent and the
`FIGS. 10 and 11 illustrate yet another embodiment
`oppositely directed restoring force in the body tissue.
`stent 96 including proximal and distal segments 98 and
`With the stent in equilibrium (as shown in FIG. 5 in
`100, slidably engaged and overlapping along a medial
`connection with stent 16), reinforced end regions 64 and
`region 102. A strand or wire 104 runs parallel to stent 96
`66 may or may not ?are slightly radially outward from
`and is secured at points 106 and 108 near proximal and
`the remainder of the stent. In either event, the restoring
`distal ends 110 and 112, respectively. Wire 104 is suf?
`force at the reinforced end r