Low profile device for the treatment of vascular abnormalities

A low profile stent graft for treatment of vascular abnormalities such as aneurysms. The endoskeleton of the stent graft has first and second self-expandable stents. The stents are spaced apart and connected together by at least one, and preferably three, flexible strut members. A tubular graft is placed around the endoskeleton while the stents are in a partially compressed state, and attached to the stents. A bifurcated configuration is disclosed that can be employed where the stent graft is to be used for repair of an aneurysm of the abdominal aorta.

BACKGROUND OF THE INVENTION
 This invention relates to a low profile device for treatment of vascular
 abnormalities, such as the repair of aneurysms.
 In the past, treatment of aneurysms involved an open surgical procedure
 which exposed the affected lumen and bypassing the aneurysm with an
 artificial tubular graft.
 More recently stent grafts have been employed as a minimally invasive
 alternative to traditional graft bypass surgery. There are a number of
 stent graft designs that have been tried. Current designs are limited to
 use with patients having large vessels because of the large size of the
 delivery systems. Such large sizes require surgical exposure of the
 vascular system and in smaller patients, often females, such stent grafts
 are simply too large to use at all. In addition, such larger stent graft
 designs can be difficult to position and may cause damage to the blood
 vessels.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a stent graft design
 that has a low cross sectional profile that can be delivered
 percutaneously and used in patients with small and tortuous vessels.
 It is a further object to provide a stent graft that is highly flexible.
 It is a still further object to provide a stent graft that is simple and
 inexpensive to construct.
 These and other objects are achieved by providing a stent graft that has a
 minimal metallic endoskeleton that holds the graft material in place until
 secondary deployment of additional stents. Such a minimal metallic
 endoskeleton allows the delivery system to have a lower cross-sectional
 profile than conventional stent grafts.
 The endoskeleton of the stent graft of this invention has a first self
 expandable metallic stent located at the distal end thereof and a second
 self expandable metallic stent located at the proximal end thereof. At
 least one flexible longitudinal strut member extends between and is
 connected to the first and second stents. The strut member can have a
 fixed length or can be a compound strut comprised of two or more strut
 sections that are fastened together in a manner that allows a sliding
 motion between the strut sections so that the compound strut can be
 elongated by applying traction to the proximal stent.
 The endoskeleton of the stent graft of this invention may be bifurcated for
 use with aneurysms of the abdominal aorta.
 The endoskeleton of the stent graft of this invention is inserted into a
 tube of a graft material and the tube attached to the first and second
 stents. In the case of the bifurcated system, the graft material is also
 connected to the third contralateral stent.

DESCRIPTION OF PREFERRED EMBODIMENTS
 The endoskeleton 10 of the straight tubular form of stent graft 30 is
 illustrated in FIG. 1.
 Endoskeleton 10 is comprised of a first stent 12 and a second stent 14.
 Stents 12 and 14 are identical in construction, each being a cylindrical
 spring assembly made from a single piece of fine gauge stainless steel
 spring wire or nitinol having a diameter of about 0.4 to 0.5 mm that is
 bent into a sinusoidal configuration comprised of a plurality of arms 16
 and outer and inner elbows 18 and 19, respectively, as best seen in FIG.
 2. Elbows 18 and 19 are illustrated as being simple arches, but other
 elbow configurations, such as a recurved arch or aperatured arch may be
 used.
 Struts 20, 21, and 22 extend between first and second stents 12 and 14, as
 shown. Struts 20-22 are constructed of fine gauge stainless steel spring
 wire or nitinol having a diameter of about 0.3 to 0.6 mm. Struts 20-22 are
 attached to stents 12 and 14 in any suitable manner, such as soldering to
 outer elbows 18 at solder joint 24; they may, alternatively be attached by
 bending, or cut from a single piece of metal. The struts are substantially
 evenly spaced apart around cylindrical stents 12 and 14.
 Although three struts are preferred, a single strut may be used. More than
 three struts may also be used, but the number used should not be such that
 the flexibility of the stent graft is compromised.
 A straight tubular stent graft 30 is formed by compressing stents 12 and 14
 and inserting endoskeleton 10 into elongated cylindrical graft tube 31, as
 best seen in FIG. 3. The graft tube 31 is attached to stents 12 and 14 by
 sutures 32 passed through graft 31 and outer elbows 18.
 Graft tube 31 may be formed of any conventional graft material which is
 known to be substantially biologically inert, non-biodegradable, and
 durable. A suitable such graft material is polytetrafluoroethylene
 ("PTFE") sold under the trademark "IMPRA" by Bard of Tempe, Arizona. The
 diameter of the graft tube 31 can be between about 6 and about 40 mm in
 diameter and between about 1.5 and about 400 mm in length.
 The endoskeleton 40 of a bifurcated form of stent graft 60 of this
 invention is illustrated in FIG. 4. Endoskeleton 40 is comprised of a
 first stent 42 and a second stent 44 having struts 46, 47, and 48
 extending therebetween and attached thereto in the same manner as for the
 straight tubular form 10 discussed above. Stents 42 and 44 are cylindrical
 spring assemblies of the same configuration and material as discussed
 above, except that stent 42 has approximately twice the diameter of stent
 44. Stent 50 is attached to stent 42 by means of a single strut 52.
 Bifurcated stent graft 60 is formed by positioning a partially compressed
 bifurcated endoskeleton 40 inside a bifurcated tubular graft 61 as shown
 in FIG. 5. Graft 61 is formed of the same material as graft 31.
 Stent 44 is located inside, and adjacent the end of, channel 62 and sewn to
 graft 61 by sutures 63, only two of which are shown. Stent 44 is in a
 partially compressed state so that an outward force is applied to the
 inner side of channel 62.
 Stent 50 is located inside, and adjacent the end of, channel 64 and sewn to
 graft 61 by sutures 65, only two of which are shown. Stent 50 is in a
 partially compressed state so that an outward force is applied to the
 inner side of channel 64.
 Stent 42 extends outwardly from the end of channel 66 and is sewn to graft
 61 by sutures 67, only two of which are shown. Being in a partially
 compressed state at its inner end, stent 42 exerts an outward force on the
 inner side of channel 66.
 Stent 42 is not covered by graft material 61 to allow placement of the
 stent graft 60 across critical branch vessels without causing occlusion,
 the blood flowing through the open structure of the uncovered stent. This
 is especially true in the abdominal aorta where the renal arteries are
 just above the level of the aneurysms. An uncovered stent 42 can be placed
 safely across the origins of the renal arteries and still allow a fixation
 site for the stent graft 60.
 Graft material 61 is configured to wrap around stent 50 and is sewn along
 stitch line 68 to form channel 64. There is no communication between
 channel 62 and channel 64 along the stitch line 68, but both channels 62
 and 64 communicate with channel 66.
 Bifurcated stent graft 60 is used to repair aneurysms of the abdominal
 aorta which typically occur where the aorta branches into smaller (iliac)
 arteries. Bifurcated stent graft 60 can be used in conjunction with the
 straight tubular stent graft 30 described above by inserting straight
 tubular stent graft 30 into channel 64 of bifurcated stent graft 60 and
 sewing it into place. The end of bifurcated stent graft 60 containing
 channel 66 is located in the aorta with channel 50 (extended by insertion
 of a stent graft 30) and channel 62 being located in the adjacent iliac
 arteries.
 A variation of the endoskeleton of bifurcated stent graft 60 is shown in
 FIGS. 6 and 7. In this variation, single strut 52 of FIG. 4 is replaced by
 a two component strut comprised of fixed strut 152 and sliding strut 252.
 Fixed strut 152 is attached to stint 142 and sliding strut 252 is attached
 to stint 150, the reference numbers of the components in FIGS. 6 and 7
 common to those in FIG. 4 being the same but increased by 100 or, in the
 case of the sliding strut, by 200.
 Sliding strut 252 has a ring 254 attached at its outer end. Ring 254 fits
 over fixed strut 142 in sliding relationship. In FIG. 6 sliding strut 252
 is shown in its unextended (collapsed) configuration. In FIG. 7 sliding
 strut 252 is shown in its extended configuration. Cap 154 attached to the
 outer end of fixed strut 152 prevents passage of ring 254 thereover.
 FIG. 8 illustrates the bifurcated configuration employing the sliding strut
 configuration illustrated in FIGS. 6 and 7. In other respects, the
 bifurcated configuration of FIG. 8 is the same as the bifurcated
 configuration illustrated in FIG. 5, and identical components of the FIG.
 8 configuration have the same reference numbers as those used in FIG. 5,
 but increased by 100.
 In FIG. 8, the sliding strut 152/252 (not shown) is in the collapsed
 configuration shown in FIG. 6. That portion of graft 161 covering sliding
 strut 152/252 and stent 150 is collapsed, accordion style, since it must
 have a length long enough to accompany stent 150 (to which it is attached
 by sutures 165) as strut portion 252 is extended.
 The endoskeletons of both the straight stent graft 30 and bifurcated stent
 graft 60 are easily compressed into a small diameter endoprosthesis
 package for percutaneous delivery to the required aneurysm repair site
 since a minimum number of stents are employed (two in straight stent graft
 30 and three in stent graft 60). For example, straight stent graft 30 can
 be collapsed to a diameter of about 3.3 mm and bifurcated stent graft 60
 can be collapsed to a diameter of about 4.0 mm.
 The stent grafts 30 and 60 of the invention are introduced through a
 conventional sheath with a hemostatic valve. The sheath and taper dilator
 is initially positioned over an intravascular guide wire. The tapered
 dilator is removed and the stent graft is advanced through the sheath with
 a blunt pushing device. The distal tip of the sheath is demarcated with a
 radiopaque marker.
 After stent graft 30 or stent graft 60 is secured in place in the artery of
 a patient, additional (secondary) stents can be inserted inside the graft
 tube along the length thereof.