Grafts with suture connectors

A graft for use in vascular anastomosis is provided. The graft includes a cylindrical metal braided frame and suture retention structures at the ends of the braided frame which provide suture sites for anastomosis.

BACKGROUND OF THE INVENTION
 This invention relates to grafts for use in the repair, replacement or
 supplement of a medical patient's natural body organ structures or
 tissues. More particularly, this invention relates to a graft with a
 suture connector for use in vascular anastomosis (the surgical connection
 of vessels).
 An example of the possible uses of the invention is a minimally invasive
 cardiac bypass procedure. This and other examples are considered in detail
 in David S. Goldsteen et al., U.S. patent application Ser. No. 08/745,618,
 filed Nov. 7, 1996, which is incorporated herein by reference.
 Vascular anastomosis is a delicate and time-consuming procedure.
 Conventional anastomosis using a graft requires placement of fine sutures
 circumferentially around the vessel at the anastomosis (vessel attachment)
 site.
 Conventional anastomosis using graft suturing, as shown in FIG. 1a, may
 have certain limitations. First, the anastomosis created may be
 non-compliant (i.e., the graft may not readily expand or contract
 radially). This may produce a compliance mis-match between the graft and
 the native vessel. As the native vessel expands or contracts under
 hemodynamic pressure, the suture site tends to remain more nearly rigid,
 producing high stress which may eventually result in tissue and/or graft
 deterioration, as shown for the graft in FIG. 1b. Second, the selection of
 materials for grafts is necessarily limited to those materials of
 sufficient tensile strength in order to withstand suturing. For example, a
 well-known bio-compatible and bio-stable material such as silicone has not
 been used to its full potential in grafts because of its limited
 mechanical ability to retain sutures.
 In view of the foregoing, it is an object of the present invention to
 provide a graft which is compliant at the anastomosis site.
 It is also an object of the present invention to provide a graft which is
 formed from a material which is bio-compatible and bio-stable.
 SUMMARY OF THE INVENTION
 These and other objects are accomplished by providing a graft for use in
 vascular anastomosis comprising a generally cylindrical metal braided
 frame and suture retention structures at distal ends of the braided frame
 which provide suture sites for anastomosis.

DETAILED DESCRIPTION OF THE INVENTION
 As has been mentioned, conventional anastomosis using graft suturing, as
 shown in FIG. 1a, may have the disadvantage that the anastomosis created
 may be relatively non-compliant (i.e., graft 1 can not expand or contract
 radially). Native vessel 20 is shown in its "rest" state as indicated by
 reference numeral 20 and in its "expanded" state as indicated by reference
 numeral 25. (Of course, native vessel 20 can also contract but this
 "contracted" state is not shown in FIG. 1a, for clarity.) This expansion
 and contraction may produce a compliance mis-match between graft 1 and the
 native vessel 20. As native vessel 20 expands or contracts under
 hemodynamic pressure, suture site 10 remains rigid, producing high stress
 and, eventually, tissue and graft damage as suture thread 15 pulls through
 material 12 (e.g., woven polyester or non-woven PTFE (Teflon)) of graft 1,
 as shown in FIG. 1b. Second, the material selected for graft 1 is
 necessarily limited to those materials of tensile strength sufficient to
 withstand suturing. For example, a well-known bio-compatible and
 bio-stable material such as silicone has not been used in grafts because
 of its limited mechanical ability to retain sutures.
 FIG. 2a shows graft 1 for use in vascular anastomosis according to the
 present invention. Graft 1 includes cylindrical metal braided frame 30
 (preferably formed from a compliant material such as a nickel titanium
 alloy), and suture retention structures at distal ends of the frame which
 provide suture sites 10 for anastomosis. The suture retention structures
 are preferably metal loops 40 coupled to distal ends of braided frame 30.
 Metal loops 40 of the suture retention structures can be coupled to distal
 ends of braided frame 30 such that the openings of metal loops 40 are at
 any angle to the central axis of the frame. For example, metal loops 40 of
 the suture retention structures can be coupled to distal ends of braided
 frame 30 such that the openings of metal loops 40 are substantially
 perpendicular to the central axis of the frame. As shown in FIG. 2b, such
 an arrangement facilitates expanding the diameter ED the mouth of graft 1
 (e.g., from an un-expanded diameter D of 4 mm to an expanded diameter ED
 of 5 mm) to provide optimal anastomosis. Alternatively, metal loops 40 of
 the suture retention structures can be coupled to distal ends of braided
 frame 30 such that the openings of metal loops 40 are substantially
 parallel to the central axis of the frame.
 Metal braided frame 30 preferably includes welds 50 at distal ends to
 prevent unraveling. As shown in FIG. 3a, welded ends 50 of frame 30 can
 serve as suture retention structures for coupling to native vessel 20. For
 example, given a 36 strand, 4 mm graft, suture spacing would be 0.028
 inches (18 sutures). Other possible strand sizes include 8, 16, 32, 64 and
 72, each with corresponding graft sizes and suture spacing. FIG. 3b shows
 an expanded view of a single braid loop with welded end 50 and the
 direction of the principal force acting on that welded end.
 The suture retention structures can also include suture rings 60, as shown
 in FIG. 4, which are radially offset from frame 30. Suture rings 60 can be
 made of metal, polyester or resilient polymer, for example, and are
 coupled to distal ends of frame 30. Suture rings 60 are preferably
 constructed as disclosed in commonly assigned Berg et al. U.S. patent
 application Ser. No. 09/016,721, filed Jan. 30, 1998, incorporated herein
 by reference. The advantage of using suture rings 60 is that they help to
 absorb the stress of the forces acting on anastomosis site 10, allowing
 any covering (for example, polymer) to be essentially stress free. Thus
 the covering is no longer limited by mechanical suture strength.
 Suture retention structures can also include polymer caps 80 fused to
 distal ends of frame 30. FIGS. 5a and 5b show graft 1 for use in vascular
 anastomosis according to the present invention including a polymer cap,
 before (reference numeral 70) and after (reference numeral 80) fusing,
 respectively. To minimize added rigidity, polymer caps 80 are kept
 relatively short.
 In order to provide radiopacity to anastomosis site 10, the suture
 retention structures can be plated. Plating provides a visual marker if
 future access to the site is needed.
 The graft 1, including the suture retention structures, can also be coated
 with a bio-compatible and bio-stable material such as silicone.
 Thus, it is seen that a graft is provided in which is compliant at the
 anastomosis site. In addition, the graft can be formed from a material
 which is bio-compatible and bio-stable. One skilled in the art will
 appreciate that the present invention can be practiced by other than the
 described embodiments, which are presented for purposes of illustration
 and not of limitation, and the present invention is limited only by the
 claims which follow.