Vascular graft

Abstract: A vascular graft comprises a perforate tubular compressible frame having a fabric liner disposed over at least a portion of the frames lumen. The graft may be used in combination with a base structure to form a bifurcated graft in situ . The base structure compresses a compressible frame having a fabric liner which defines a pair of divergent legs. The base structure is positioned within the aorta so that one leg enters each iliac. The tubular grafts can then be introduced into each leg to form the bifurcated structure. A graft delivery catheter includes a controllably flared sheath which facilitates recapture of a partially deployed graft.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vascular graft. More particularly, the present invention relates to a low profile, compressible vascular graft structure for the treatment of abdominal and other aneurysms. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease and/or genetic predisposition which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aortic aneurysms occurring in the abdominal aorta, usually beginning below the renal arteries and often extending distally into one or both of the iliac arteries. Aortic aneurysms are most commonly treated in open surgical procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of a usually fatal ruptured abdominal aortic aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and require experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, however, patients being treated frequently are elderly and weakened from cardiovascular and other diseases, reducing the number of eligible patients. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 3% to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Additionally, even with successful surgery, recovery takes several weeks, and often requires a lengthy hospital stay. In order to overcome some or all of these drawbacks, endovascular graft placement for the treatment of aneurysms has been proposed. Although very promising, many of the proposed methods and apparatus suffer from other problems. Often times the proposed graft structures will have exposed anchors or frame which can be thrombogenic. It is also difficult to provide graft structures which remain sealed to the blood vessel lumen to prevent the leakage or bypass of blood into the weakened aneurysm, especially when subjected to external deforming forces which result from vessel expansion and contraction as the heart beats. Many vascular graft structures have difficulty in conforming to the internal arterial wall, particularly since the wall can have a highly non-uniform surface as a result of atherosclerosis and calcification and is expanding and contracting with the patient's heartbeat and blood flow. Additionally, many previous vascular graft structures are difficult to position and anchor within the target region of the vessel. For these reasons, it would be desirable if the graft structures were easy to place in the target region, displayed little or no thrombogenicity, provided a firm seal to the vascular wall to prevent leakage and blood bypass, and were able to conform to uniform and non-uniform blood vessel walls, even while the wall is expanding and contracting with the patient's heartbeat. 2. Description in the Background Art Vascular grafts and devices for their transluminal placement are described in U.S. Patent Nos. 5,219,355; 5,211,658, 5,104,399; 5,078,726; 4,820,298; 4,787,899; 4,617,932; 4,562,596; 4,577,631; and 4,140,126; and European Patent Publications 508 473; 466 518; and 461 791. Expandable and self-expanding vascular stents are described in U.S. Patent Nos. 5,147,370; 4,994,071; and 4,776,337; European patent Publications 575 719; 556 850; 540 290; 536 610; and 481 365; and German patent Publication DE 42 19 949. EP-A 0 556 850 against which the two-part form of claims 1 and 2 is delimited, describes a particular stent structure made of zig-zag wire that is connected at adjacent apices to form a continuous helix. The stent structure is compressible and self-expandable to a pre-compressed configuration and may be placed on the exterior or interior of a graft, to which it is fixed by hoop members. EP-A-0 540 290 discloses an expandable stent consisting of a plurality of radially expandable cylindrical elements, each made from a ribbon-like material and interconnected by at least one interconnective element. EP-A - 551179 discloses a bypass graft comprising separate tubular members cast into the expandable graft material. A flexible vascular stent structure having counter wound helical elements, some of which are separated at particular locations to enhance flexibility, is commercially available from Angiomed, Karlsruhe, Germany, as described in a brochure entitled Memotherm lliaca Stents. Catheters for placing vascular stents are described in U.S. Patent Nos. 5,192,297; 5,092,877; 5,089,005; 5,037,427; 4,969,890; and 4,886,062. Vascular grafts intended for open surgical implantation are described in U.S. Patent Nos. 5,236,447; 5,084,065; 4,842,575; 3,945,052; and 3,657,744; and PCT applications WO 88/00313 and WO 80/02641; and SU 1697787. Nickel titanium alloys and their use in medical devices are described in U.S. Patent Nos. 4,665,906 and 4,505,767. SUMMARY OF THE INVENTION The present invention comprises a vascular graft for the treatment of disease conditions, particularly aneurysms according to claim 1 or 2. In accordance with preferred embodiments the vascular grafts comprise a radially or laterally compressible, perforate tubular frame having a proximal end, a distal end, and an axial lumen between said ends. An interior liner, typically a fabric, polymeric sheet, membrane, or the like, covers all or most of the surface of the lumen of the tubular frame, extending from a near-proximal location to a near-distal location. The liner is attached to the frame at at least one end, as well as at a plurality of locations between said ends. Optionally, a second liner may be provided over at least a portion of the exterior of the frame to cover both sides of the frame. Such exterior coverage provides a circumferential seal against the inner wall of the blood vessel lumen in order to inhibit leakage of blood flow between the graft and the luminal wall into the aneurysm or stenosis which is being treated. The grafts of the present invention will find particular use in the treatment of vascular conditions, such as abdominal and other aneurysms, vascular stenoses, and other conditions which require creation of an artificial vessel lumen. For the treatment of vascular stenoses, the graft may serve as a stent to maintain vessel patency in a manner similar to that described in the above-described U.S. and foreign patent documents relating to stents. Other intraluminal uses of the present invention include stenting of the ureter, urethra, biliary tract, and the like, and may also be used for the creation of temporary or long term lumens, such as the formation of a fistula. Such graft structures provide a number of advantages over previously proposed designs, particularly for vascular uses. By covering the lumen of the tubular frame, thrombogenicity of the graft resulting from exposed frame elements is greatly reduced or eliminated. Such reduction of thrombogenicity is achieved while maintaining the benefits of having a frame structure extending over the graft. Such an external frame helps anchor the graft in place and maintain patency and evenness of the graft lumen, both of which are advantages over graft structures which are anchored and supported only at each end. The preferred vascular grafts of the present invention are also self-expanding and easy to place. The self-expanding nature of such a frame also counteracts external deforming forces that may result from the continuous physiologic expansion and contraction of the blood vessel lumen. Moreover, the lack of cleats, tines, or other penetrating elements on the graft allows the graft to more closely conform to the surrounding vessel wall and facilitates retrieval and/or repositioning of the graft, as will be described in more detail hereinafter. Additionally, a resilient tubular frame structure permits the graft to conform to even irregular regions of the blood vessel wall as the wall is expanding and contracting as a result of the pumping of the patient's heart. The tubular frame preferably comprises a plurality of radially compressible band or ring structures, each of which have a relaxed (i.e., non-compressed) diameter which is greater than the diameter of the blood vessel to be treated. Adjacent compressible band members are independent of each other. Independent band members will be held together by their attachment to the interior and/or exterior liner(s). Alternatively, the tubular frame may comprise a plurality of laterally compressible axial members, with adjacent axial members not being directly connected to each other. The axial members will usually comprise a multiplicity of repeating structural units, e.g., diamond-shaped elements, which are axially connected. The axial members will be attached to the inner liner, either by stitching or by capturing the axial members in pockets formed between the inner liner and an outer liner disposed over the frame. The pockets may be formed by attaching the inner and outer liners to each other along axial lines between adjacent axial members. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a vascular graft. Fig. 1 A is a side view of a first embodiment of a vascular graft constructed in accordance with the principles of the present invention. Fig. 1B is a side view of a second embodiment of a vascular graft constructed in accordance with the principles of the present invention. DESCRIPTION OF THE SPECIFIC EMBODIMENT The present invention provides a vascular graft for transluminal placement, particularly within the vascular system for treatment of aneurysms and other vascular conditions, but also in other body lumens, such as ureter, urethra, biliary tract, gastrointestinal tract, and the like, for the treatment of other conditions which benefit from the introduction of a reinforcing or protective structure in the lumen. The vascular graft can also find use in the creation of artificial lumens through solid tissue and structures. The vascular grafts will be placed endovascularly. As used herein, "endovascularly" will mean placement by percutaneous or cutdown transluminal procedures using a catheter over a guidewire under fluoroscopic guidance. The catheters and guidewires may be introduced through conventional access sites to the vascular system, such as through the brachial and subclavian arteries for access to the aorta and through the femoral arteries for access to the aorta or to peripheral and branch blood vessels. A vascular graft according to the present invention will comprise a radially compressible perforate tubular frame and an inner or interior liner attached within a central lumen defined by the frame and optionally a second or outer liner formed over the exterior of the frame. The radially compressible frame can take a variety of forms, usually comprising or consisting of a plurality of independent structural elements, such as rings, bands, helical elements, serpentine elements, axial struts, parallel bars, and the like, that can be compressed from a relaxed, large diameter configuration to a small diameter configuration to facilitate introduction, as discussed below. It is necessary, of course, that the liner(s) remain attached to the frame both in its radially compressed configuration and in its expanded, relaxed configuration. A preferred configuration for the tubular frame comprises a plurality of radially compressible band members, where adjacent band members are not directly connected to each other. Instead, the bands are connected only to the liner(s) which maintain the axial integrity of the graft. Preferably, the independent bands are stitched or sealed between interior and exterior liners, as will be described in more detail below. In an alternative configuration, the perforate tubular frame comprises a plurality of laterally compressible axial members which are attached directly, e.g ., by stitching, or indirectly, e.g., by lamination, to the inner liner. The axial members may be a multiplicity of repeating structural elements, such as diamonds. By positioning the axial members in pockets formed between an inner liner and an outer liner, the axial elements will be able to flex independently while providing the desired radial compressibility and self-expansion characteristics for the graft. The dimensions of the tubular graft will depend on the intended use. Typically, the graft will have a length in the range from about 50 mm to 500 mm, preferably from about 80 mm to 200 mm for vascular applications. The relaxed diameter will usually be in the range from about 4 mm to 45 mm, preferably being in the range from about 5 mm to 25 mm for vascular applications. The graft will be radially compressible to a diameter in the range from 3 mm to 9 mm, preferably from 4 mm to 6 mm for vascular applications. The liner(s) will be composed of conventional biological graft materials, such as polyesters, polytetrafluoroethylenes (PTFE's), polyurethanes, and the like, usually being in the form of woven fabrics, nonwoven fabrics, polymeric sheets, membranes, and the like. A presently preferred fabric liner material is a plain woven polyester, such as type 56 Dacron ® yarn (Dupont, Wilmington, Delaware), having a weight of 40 denier, woven at 27 filaments with 178 warp yarns per circumferential inch, and 78 yarns per inch in the fill direction. The liner will be attached to the interior lumen of the tubular frame and will cover most or all of the interior surface of the lumen. For example, the liner may be stitched or otherwise secured to the tubular frame along a plurality of circumferentially spaced-apart axial lines. Such attachment permits the liner to fold along a plurality of axial fold lines when the frame is radially compressed. The liner will further be able to open and conform to the luminal wall of the tubular frame as the frame expands. Alternatively, when inner and outer liners are used, the liners may be stitched, heat welded, or ultrasonically welded together to sandwich the tubular frame therebetween. In an exemplary embodiment where a plurality of independent band members are disposed between interior and exterior liners, the liners are secured together along circumferential lines between adjacent band members to form pockets for holding the band members. In a second exemplary embodiment where a plurality of independent axial members are disposed between interior and exterior liners, the liners are secured together along axial lines to form pockets for holding the axial members. The liner will preferably be circumferentially sealed against the tubular frame at at least one end, preferably at both ends in the case of straight (non-bifurcated) grafts. It is also preferred in some cases that the distal and proximal end of the perforate tubular frame be exposed, i.e., not covered by the liner material, typically over a length in the range from about 1 mm to 25 mm. Frame which is not covered by the liner permits blood perfusion through the perforations and into branch arteries such as the renal arteries in the case of abdominal aorta grafts, while providing additional area for anchoring the frame against the blood vessel lumen. In an exemplary embodiment, the liner will extend through the frame and over the exterior surface near either or both ends to provide a more effective seal against the adjacent blood vessel wall. The radially compressible perforate tubular frame will be composed of a resilient material, usually metal, often times a heat and/or shape memory alloy, such as nickel titanium alloys which are commercially available under the trade name Nitinol ® . The frames may also be composed of other highly elastic metals, such as MP-35 N, Elgiloy, 316 L stainless steel, and the like. In the case of Nitinol ® and other memory alloys, the phase transition between austenitic and martensitic states may occur between an introduction temperature, e.g., room temperature (approximately 22°C), and body temperature (37°C), to minimize stress on the unexpanded frame and enhance radial expansion of the frame from its radially compressed condition. Expansion can also be achieved based on the highly elastic nature of the alloy, rather than true shape recovery based on phase change. In some cases, it may be desirable to form a tubular frame having different elastic or other mechanical properties at different regions along its length. For example, it is possible to heat treat different regions of the tubular frame so that some regions possess elastic properties while others become malleable so that they may be deformed by external force. For example, by providing at least one malleable end portion and an elastic (radially compressible) middle portion, the graft can be firmly expanded and implanted by internal balloon expansion force (to anchor the end(s) in the inner wall of the blood vessel) while the middle will remain open due to the elastic nature of the tubular member. Malleable end portions are a particular advantage since they can be expanded with a sufficient force, and re-expanded if necessary, to assure a good seal with the blood vessel wall. Alternatively, the malleable ends could be formed from a different material than that of the middle portion of the tubular frame. The use of different materials would be particularly convenient when the frame is formed from a plurality of independent bands, where one or more band members at either or both ends could be formed of a malleable metal. Usually, such malleable end(s) will extend over a distance in the range from 5 mm to 50 mm, preferably from 5 mm to 20 mm. Malleable portions or segments can also be formed in other parts of the tubular frame. For example, some circumferentially spaced-apart segments of the tubular frame could be malleable while the remaining circumferential segments would be elastic. The frame would thus remain elastic but have an added malleability to permit expansion by applying an internal expansion force. Such a construction would be advantageous since it would allow the diameter of the graft or stent structure to be expanded if the initial diameter (which resulted entirely from elastic expansion) were not large enough for any reason. The proportion of elastic material to malleable material in the tubular frame can be selected to provide a desired balance between the extend of initial, elastic opening and the availability of additional, malleable opening. Such construction can be achieved by selective heat treatment of portions of a frame composed of a single alloy material, e.g. nickel titanium alloy, or by forming circumferential segments of the frame from different materials having different elastic/malleable properties. In particular, individual laterally compressible axial members 204 (as described in connection with Fig. 1 B) could be formed from materials having different elastic/malleable properties. Referring now to Fig. 1, an exemplary graft structure 10 will be described, which is similar in construction to the frame of a graft according to the invention, except that adjacent band members are connected to each other while according to the invention adjacent band or linear members are not directly connected to each other. The graft structure 10 includes a fabric liner 12 and a radially compressible perforate tubular frame 14. The frame is illustrated in its expanded (relaxed) configuration in each of these figures, but may be radially compressed by applying a radially inward compressive force, usually by placing the graft 10 in an outer sheath, as will be described in more detail hereinafter. The tubular frame 14 comprises a plurality of radially compressible band members 11, each of which comprises a zig-zag or Z-shaped element which forms a continuous circular ring. Each band member 11 will typically have a width w in the range from 2 mm to 15 mm, and the tubular frame will comprise from 1 to 30 individual band members. Adjacent band members 11 are preferably spaced-apart from each other by a short distance d and are joined by bridge elements 13. Flexibility is enhanced by providing only two diametrically opposed bridge elements 13 between each adjacent pair of band members 11. As will be described further with reference to Fig. 1A, flexibility can be further enhanced by leaving the band members connected only by the liner. Usually, the perforate tubular frame 14 will be left open at each end, e.g., at least a portion of the last band member 11 will remain uncovered by the liner 12. The liner 12 will be stitched or otherwise secured to the band members 11, preferably at the junctions or nodes when the element reverses direction to form the Z-pattern (although the stitching should not cross over between the band members in a way that would restrict flexibility). The liner 12 will usually pass outward from the inner lumen of the tubular frame 14 to the exterior of the frame through the gap between adjacent band members, as illustrated in Fig. 1. The portion of liner 12 on the exterior of the tubular frame 14 helps seal the end(s) of the graft 10 against the wall of the blood vessel or other body lumen in which it is disposed. The expansion is shown at 30°, but will frequently extend up to 60° or higher in use. A preferred method for forming the tubular frame 14 is as follows. A tube of the desired elastic material, such as nickel titanium alloy having a phase transformation temperature significantly below 37°C. preferably between 30°C and 32°C, is obtained. The tube will have dimensions roughly equal to the desired dimensions of the frame when radially compressed. The tube may be drawn, rolled, or otherwise treated to achieve the desired wall thickness, diameter, and the like. Suitable wall thicknesses are in the range of about 0.1 mm to 0.5 mm. A pattern of axial slots is then formed in the tube. The slots may be formed by electrical discharge machining (EDM), photochemical etching, laser cutting, machining or other conventional techniques. After the slots have been formed, the tube is mechanically expanded to its desired final (relaxed) diameter and heat treated at a suitable temperature to set the tube in the desired expanded state. Sharp edges are removed by conventional techniques, such as deburring, abrasive extrusion, or the like. The result of the expansion is the tubular frame illustrated in Fig. 1. Preferably, each end of the liner 12 will be circumferentially sealed at or near the distal and proximal ends of the tubular graft. As illustrated in Fig. 1A, this can be achieved by folding over the end of the liner 12 onto the external surface of the graft 10. Conveniently, this can be done through the gaps which are present between adjacent band members 14. Where the junctions 13 remain, the liner 12 can be carefully stitched onto the underlying surface of the frame, as shown at 18 in Fig. 1A. Other techniques for circumferentially sealing the liner include heat or ultrasonic welding of the liner, laminating an outer gasket, sewing an outer reinforcement member, or the like. Referring now to Fig. 1A, an exemplary embodiment 100 of a vascular graft constructed in accordance with the principles of the present invention will be described. The graft 100 comprises a perforate tubular frame 102 which includes a plurality of independent (non-connected) band members 104 separated from each other by gaps 106. The perforate tubular frame 102 is similar in construction to frame 14 of graft 10, except that adjacent band members 104 are not directly connected to each other. Band numbers 104 will be connected only by an inner liner 108 and an outer liner 110, where the inner and outer liners together encase or sandwich the otherwise free-floating band members 104. In order to secure the band members 104 in place, and secure the liners to the perforate tubular frame 102, the inner and outer liners are joined together along circumferential lines 112, preferably located in the gaps 106 between adjacent band members 104. The liners may be joined together by stitching, heat welding, ultrasonic welding, or the like. In the exemplary embodiment, the liners 108 and 110 are formed from polymeric sheet material and are joined together by ultrasonic welding. The band members 104 at each end of the graft 100 will have to be further secured to the liners 108 and 110. For example, they could be stitched, welded, or otherwise joined to the liners to hold them in place. The dimensions, materials, and other aspects of the graft 100 will be generally the same as those described previously for graft 10. Referring now to Fig. 1B, an alternative exemplary embodiment 200 of the vascular graft of the present invention is illustrated. The graft 200 comprises a perforate tubular frame 202 including a plurality of laterally compressible axial members 204. Each axial member 204 comprises a plurality of diamond-shaped structural elements which are connected to each other in a linear fashion. It will be appreciated that each diamond-shaped structural element is laterally compressible so that the frame 202 as a whole may be radially compressed from a reduced-diameter configuration to an expanded-diameter configuration. As illustrated in Fig. 1 B, the frame is in a partially compressed configuration. The axial members 202 will be captured between an inner liner 206 and an outer liner 208. The inner liner 206 and outer liner 208 will be secured to each other along a plurality of axial lines 210 disposed between adjacent axial members 204. In this way, each axial member 204 will be captured within a pocket formed between the inner liner 206 and outer liner 208. As with the other embodiment, the ends of the frame may extend beyond the liners to provide for improved anchoring and perfusion on either side of the graft.

Claims: A vascular graft comprising: a perforate self-expanding frame (102) having a proximal end, a distal end, and a lumen therebetween, and an inner liner (108) extending from a near-proximal location on the lumen to a near-distal location on the lumen, wherein the liner (108) covers the lumen of the tubular frame (102) over the entire distance from said near-proximal location to said near-distal location, characterized in that said frame (102) has a resilient tubular frame structure including a plurality of adjacent radially compressible band members (104) not directly connected to each other, and wherein the band members (104) comprising a zig-zag or Z-shaped element which forms a continuous circular ring are secured independently to the inner liner (108) which thereby maintains the axial integrity of the graft. A vascular graft comprising: a perforate self-expanding frame (202) having a proximal end, a distal end, and a lumen therebetween, and an inner liner (206) extending from a near-proximal location on the lumen to a near-distal location on the lumen, wherein the liner (206) covers the lumen of the tubular frame (202) over the entire distance from said near-proximal location to said near-distal location, characterized in that said frame (202) has a resilient tubular frame structure including a plurality of adjacent laterally compressible axial members (204) not directly connected to each other and being separated from each other by gaps (106), and wherein the axial members (204) comprise a multiplicity of repeating structural units, which are axially connected, whereby the axial members (204) are secured independently to the inner liner (206) which thereby maintains the radial integrity of the graft. A vascular graft as in claim 2, wherein the axial members (204) each comprise a plurality of diamond-shaped elements. A vascular graft as in one of the claims 1 to 3, wherein the liner (108, 206) is circumferentially sealed to the perforate tubular frame (102, 202) at at least one of said near-proximal and near-distal locations, and is spaced-inward from an end of the perforate tubular frame (102, 202) by a distance in the range from 1 mm to 20 mm, wherein at least one terminal portion of the perforate tubular frame (102, 202) remains uncovered. A vascular graft as in one of the claims 1 to 4, wherein the independent band members (104) or the axial members (204) are stitched to the liner (108, 206). A vascular graft as in one of the claims 1 to 5, wherein the band members (104) or the axial members (204) are secured to the inner liner (108, 206) by an outer liner (110, 208) sealed to the inner liner (108, 206).

Inventors: FOGERTY THOMAS J, FREISLINGER KIRSTEN, LENKER JAY A, FOGERTY, THOMAS J., FREISLINGER, KIRSTEN, LENKER, JAY A.
Applicants: CARDIOVASCULAR CONCEPTS INC, CARDIOVASCULAR CONCEPTS, INC.
Application year: 1995
Main classification: A61F2
IPC codes: A61F2