Stent for intraluminal grafts and device and methods for delivering and assembling same

0001The present invention relates to intraluminal stents and grafts, particularly for repairing defects in arteries and other lumens within the body. More particularly, the present invention relates to a device and method for delivering and assembling same <i>in situ</i> for repairing defective body lumens, and particularly abdominal aortic aneurysms.

0002An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta as it passes through the abdomen. The aorta is the main artery of the body, supplying blood to all organs and parts of the body except the lungs. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen, and finally divides into the two iliac arteries which supply blood to the pelvis and lower extremities.

0003The aneurysm ordinarily occurs in the portion of the aorta below the kidneys. When left untreated, the aneurysm will eventually cause the sac to rupture with ensuing fatal hemorrhaging in a very short time. The repair of abdominal aortic aneurysms has typically required major abdominal surgery in which the diseased and aneurysmal segment of the aorta is removed and replaced with a prosthetic device, such as a synthetic graft.

0004As with all major surgeries, there are many disadvantages to the foregoing surgical technique, the foremost of which is the high mortality and morbidity rate associated with surgical intervention of this magnitude. Other disadvantages of conventional surgical repair include the extensive recovery period associated with such surgery; difficulties in suturing the graft to the aorta; the loss of the existing thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients, particularly older patients exhibiting co-morbid conditions; and the problems associated with performing the surgical procedure on an emergency basis after the aneurysm has already ruptured.

0005In view of the foregoing disadvantages of conventional surgical repair techniques, techniques have been developed for repairing abdominal aortic aneurysms by intraluminally delivering an aortic graft to the aneurysm site through the use of a catheter based delivery system, and securing the graft within the aorta using an expandable stent. Since the first documented clinical application of this technique was reported by Parodi et al. in the Annals of Vascular Surgery, volume 5, pages 491-499 (1991), the technique has gained more widespread recognition and is being used more commonly. As vascular surgeons have become more experienced with this endovascular technique, however, certain problems have been encountered. One problem has been the difficult nature of the procedure. Particularly complex is the step of transferring one leg of the graft from one iliac artery to the other, which requires the careful manipulation of numerous catheters and guide wires. Another problem has been the kinking and/or twisting of the graft both during and after the graft has been implanted. Another is fully deploying the stent and graft so that the graft is substantially smooth after being deployed.

0006There therefore exists a need for a better stent graft system and an implantation method which will overcome the foregoing deficiencies of the prior art. More particularly, there exists a need for a stent and graft system which will more accurately accommodate the widely varying arterial sizes in patients, as well as preventing the graft from kinking. There also exists a need for a method for delivering and implanting the stent and graft which avoids the complex procedure for implanting prior art stent graft systems.

0007A stent graft device is disclosed for use with a insertion catheter wherein the device has an expandable stent with various portions of the stent and graft being secured together. Secured to the stent graft is a band or bands and release wire for maintaining and releasing the stent graft from a compressed state. The device also has a holding means for retaining the graft smooth and in a set position when deployed from the insertion catheter as well as means to hold the front portion of the graft from folding back upon itself during deployment from the insertion catheter.

0008A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description, in which reference is made to the accompanying drawings in which: <ul id="ul0001" list-style="none" compact="compact"><li>FIGURE 1 is a perspective view of a main body of a stent graft for a modular system in accordance with the present invention;</li><li>FIGURE 2 is a perspective view of the stent graft of the modular system of FIGURE 1, partially broken away to reveal the stent structures in the interior thereof in one embodiment of the present invention;</li><li>FIGURES 3 is a highly schematic partial cross-sectional views of an abdominal aortic aneurysm showing a catheter and guidewire inserted therein as is known in the prior art;</li><li>FIGURE 4 is a side view showing the locating magnetic tip in accordance with the present invention;</li><li>FIGURE 5 is a side view of the forks and fork wire in accordance with the present invention;</li><li>FIGURE 6 is a side view of the stent graft partially deployed from the sheath in accordance with the present invention;</li><li>FIGURE 7 is a side view of the graft with a compression band and release wire attached in accordance with the present invention;</li><li>FIGURE 8 is a side view of the main stent and smaller end connecting stents in accordance with the present invention;</li><li>FIGURE 9 is a side view of a ring assembly of the individual ring stent components in accordance with the present invention;</li><li>FIGURE 9a is a prior art system for pushing the stent graft from the sheath in accordance with the present invention;</li><li>FIGURE 10 is a side view of a stent ring in its expanded position in accordance with the present invention;</li><li>FIGURE 11 is a side view of a stent ring in its compacted position in accordance with the present invention;</li><li>FIGURE 12 is a side view of two ring sections connected at the tangent point of a cell of the ring in accordance with the present invention;</li><li>FIGURE 13 is a side view of two ring section connected by heat shrink in accordance with the present invention;</li><li>FIGURE 14 is a side view of the inserted magnetic guide wire tip adhered to the fork wire in accordance with the present invention;</li><li>FIGURE 15 is a side view of the introducer catheter being inserted over the positioned guide wire in accordance with the present invention;</li><li>FIGURE 16 is perspective view of the stent of the referred to co-pending application showing the connection points between the cells of the ring and the rings; and</li><li>FIGURE 17 is a side view of the individual components of the main graft with one of the legs cut away to show the support stent in accordance with the present invention.</li></ul>

0009In the detailed description which follows, the features of the present invention will be described in connection with the repair of an abdominal aortic aneurysm. A typical abdominal aortic aneurysm is illustrated in FIGURE 3, in which the wall of the aorta 200 is weakened and forms a bulge 202 in the region between the renal arteries 204 and the point at which the aorta 200 branches into the right iliac artery 206 and left iliac artery 208. It will be appreciated, however, that the various features of the present invention may be readily utilized to repair defects in any body lumen which branches into two or more lumens. Indeed, the features of the present invention may be utilized to repair a variety of defects in a body lumen even where the lumen does not have branches associated with it.

0010Referring to FIGURE 17, there is illustrated one embodiment of portions of a modular system 100 for forming a bifurcated stent graft 305 system, it being understood that the term stent graft refers to the combination of a stent 154 and graft, be it graft 112, 114 or 116 or any other combination of a stent and graft, in accordance with one aspect of the present invention. As used herein, the term "modular" refers to the fact that system 100 includes a number of individual components which may be separately delivered by intraluminal techniques to the aneurysm site and then interconnected with one another <i>in situ</i> to form the bifurcated stent graft 305. Each of the components of modular system 100 may be a fully supported structure as shown in FIGURE 2, or main graft 112 may only be supported by stent 154 at its proximal circumference 600 as shown in FIGURE 1, to provide sufficient strength to permit the in situ construction of the bifurcated graft. In accordance with one embodiment hereof, see FIGURE 17, modular system 100 includes, but is not limited to, a main graft 112, first and second leg grafts 114 and 116 respectively, all of which are fabricated as separate components and may be assembled in preselected size combinations depending upon the arterial morphology presented by the patient. Accordingly, each of the various components is preferably provided in a range of sizes sufficient to accommodate the arterial morphology which the surgeon is likely to face in the vast majority of patients.

0011Main graft 112, as shown in FIGURE 1, preferably includes a proximal body portion 111 which contains a stent 154 at least at its proximal circumference 600. The body portion 111 bifurcates to form two separate distal non-communicating channels, 112a and 113 for insertion of legs 114 and 116, see FIGURE 17. As used herein, the term "proximal" refers to the end of a component which is upstream or closest to the heart, and the term "distal" refers to the end of a component which is downstream or farthest away from the heart. Main graft 112 may be provided in a number of lengths.

0012Each leg graft 114 and 116, see FIGURE 17, consists of a flexible outer layer 152 which is fully supported internally along substantially its entire length by an expandable stent 154 which assumes a generally cylindrical or tapered configuration in the expanded condition, depending upon the configuration it is given when initially formed. This provides the graft legs 114 and 116 with sufficient structural strength to permit either of them to be inserted in situ within either channel 112a and 113, whichever is appropriate, notwithstanding that said channels 112a and 113 may or may not be fully supported by stent 154. In any of the grafts 112, 114 and 116, stent 154 may protrude beyond the proximal ends 110a, 114a or 116a thereof. The proximal end of any individual cell 360 of rings 309, see FIGURE 9, may include one or more barbs 156, see FIGURE 1 for anchoring graft 112 to the inside wall of aorta 200 and thereby assist in holding modular assembly 100 in place after it is deployed. The barbs 156 in legs 114 and 116, if used, assist in holding said legs 114 and 116 in place within main graft 112.

0013Outer layer 152 is preferably formed from a biocompatible material having sufficient strength to withstand the surgical implantation procedure described more fully below and to withstand the blood-flow and other biomechanical forces which will be exerted on modular system 100. Such materials may include, for example, polyester materials, such as DACRON, polytetrafluoroethylene, expanded polytetrafluoroethylene, polyester materials coated with polytetrafluoroethylene, polyurethane, expanded polyurethane and silicone. Outer layers 152 formed from woven materials are preferred. To reduce the bulk and facilitate the intraluminal delivery of grafts 110, 114 and 116, outer layer 152 preferably has a thickness of about 0.1 mm which is about one-third the thickness of conventional graft materials. It will be appreciated, of course, that the present invention can be practiced with many different materials and well as many different thicknesses.

0014Stents, such as stent 154, may be formed from a wire or the like of a low shape-memory material which has been bent back and forth in a curved pattern in the longitudinal direction of the graft and then wrapped in a circumferential direction transverse to the longitudinal direction to form one or more loops of a predetermined circumference. As used herein, the term "low shape-memory material" refers to a material that, once deformed from an initial shape to a subsequent shape, will tend to maintain the subsequent shape and not return to the initial shape. Such materials preferably include biocompatible metals, including, for example, stainless steel, titanium, tantalum, gold, platinum, copper and the like, as well as alloys of these metals. Biocompatible low shape-memory plastics may also be used to form stents. Alternatively, stents may be formed from a high shape-memory plastic or alloy, such as nitinol, which automatically transforms from one shape to another shape as its temperature passes through a critical point.

0015A stent of the above type is disclosed in commonly assigned U.S. Patent Application Serial No. 08/353,066 entitled "High Hoop Strength Intraluminal Stent".

0016However, in the above application as in other such applications as shown in FIGURE 9a, the stent is being pushed out of the applicator 699, by the pusher 700 being held in a fixed position and the outer sheath 301 being pulled back. This causes the disadvantage of compressing the stent graft 305 from behind which causes the stent graft 305, while inside sheath 301, to increase in diameter and thereby increases the force to be overcome in removing the stent graft 305 from the sheath 301. Therefore, unlike prior stents and the stent disclosed in the previously cited co-pending patent application, stent 154 used with grafts 112, 114 and 116 of the present invention has atraumatic forks 300 as shown in FIGURE 5 to allow stent 154 to be pulled from the sheath 301 as opposed to pushed. While forks 300 are shown in a "V" type configuration, they may be formed in any type of configuration, known in the art, that would cooperate with eyes 304, see FIGURE 8, to have the net effect of pulling the stent graft 305 out of sheath 301. After stent 154, with a graft secured to it leaves outer sheath 301, see FIGURE 6, and the stent 154 and graft fully deploy and expand to cling to the arterial wall, forks 300, no longer being needed to retain the front portion of the stent graft 305 in place, can be retracted without displacement of the stent graft 305, since the clinging force to the arterial wall of stent 154 is much higher than the sliding force of the retracting forks 300 moving over the internal portion of the stent graft 305.

0017To allow forks 300 to pull graft 112, 114 or 116 and stent 154 from sheath 301, the proximal portion of stent 154 which is first deployed from sheath 301, contains eyes 304, see FIGURE 8, into which the forks 300 are inserted so that the compressed stent graft 305, see FIGURES 6 and 7, is activated, forks 300 being inserted into eyes 304, see FIGURE 8, to retain stent 154, when any of grafts 112, 114 or 116 are attached, in a set position, within the lumen being repaired, as outer sheath 301 is retracted from that set position within the lumen being repaired. Once fully deployed from outer sheath 301, graft 112, 114 or 116 and stent 154, still being constrained at their front portion by band 302 or at other locations, not shown, by one or more additional bands 302 or by securing means known in the art, can be easily positioned by the user within the artery, since at the front portion of graft 112, 114 or 116 and stent 154 is maintained at a smaller diameter than the inside of the artery by band 302. Once properly positioned by the user, release wire 303 is activated releasing band 302. To facilitate the releasing of band 302, band 302 may be perforated prior to being place over any of grafts 112, 114 or 116, but it does not have to be, since there are many ways in the art to release band 302 by wire 303. The release of band 302 allows stent 154 to expand and thereby expand the graft to which it is attached until a tight seal is formed between the attached graft and the inside of the artery or the inside of the graft to which it is being joined. It is at this point that forks 300 are retracted and slid through the interior of stent 154 causing a slight force to be applied toward the outer sheath 301. This can be done without disturbing the positioning of the stent 154 or the graft to which it is attached, since the clinging force to the arterial wall of the stent 154 is much higher than the sliding force of the retracting forks 300. In this manner, the graft material 152 is straightened by the retraction of outer sheath 301, since the forks 300, while still being in place, hold the fabric 152 of the graft in place while the movement of outer sheath 301 over the outer portion of the stent graft 305. In addition, further smoothing of the stent graft 305 is accomplished by the movement of forks 300, once released, over the internal portion of the stent graft 305.

0018As shown in FIGURE 8, stent 154 has a boundary ring set 306, which may be of the same configuration as the make up of rings 309 of stent 154, but of smaller dimension. This boundary ring set 306 supports graft 112, 114 or 116 in those areas of graft between the tip portions 307 of stent 154 thereby preventing the graft from flapping back upon itself.

0019As shown in co-pending application serial no. 08/353,066 that stent is interconnected as shown in FIGURE 16, by both its tip portions 307 and its tangent portions 308. Compacting a stent, when constructed in the heretofore mentioned manner, for the purpose of inserting it into sheath 301 expands the length of such a stent proportionately with the number of stent rings 309, see FIGURE 9. As shown in FIGURES 10 and 11, length expanded is less than length contracted and total elongation is equivalent to the number of rings times "L" contracted. This cumulative elongation of each ring elongates to a point that makes it more difficult to position within the artery due to its expanded length and shortening upon deployment. However, if stent 154 is connected only at points A as shown in FIGURE 12, or at points A and B as shown in FIGURE 13 which maintains each ring 309 of stent 154 a certain distance apart, it reduces the cumulative elongation during packing and deployment, which eases targeting the stent graft 305.

0020Connecting the rings 309 of stent 154 may be accomplished in various ways as is known in the art, however, as shown in FIGURE 9, a preferred way is to laser weld points tangent points A and B of each cell 360 of each ring 309 with a connecting wire 900, preferably of the same material as the sent 154. An alternative to this is to heat shrink the connection by wrapping wire 900 with a heat shrinkable material so that rings 309 are secured at points A and b when heat is applied to the heat shrinkable material as is shown in FIGURE 13. A further alternative is to cut the form as shown in FIGURE 9 as a whole unit and subsequently secure the joining members by welding, bonding or other known method.

0021As shown in FIGURE 4, the wire 312 attached to forks 300 is preferably a drawn wire of magnetic steel. The individual wires 312 and forks 300 that are used in any procedure may be of different sizes in order for the user to easily identify the individual wires 312 and forks 300 being used in the procedure. To further distinguish the individual wires, they may be color coated at their distal ends.

0022When the bifurcated stent graft 305 is to be used, in order to aide in positioning the different legs 114 and 116 which are usually overdimentioned to ensure proper fit within the distal ends 112a and 113 of main graft 112, as shown in FIGURE 17 all the components parts of the total stent graft 305 system may have electrically dense materials 903 or other detectable materials at key points so that the user can establish the location of each part of the stent graft 305 during the positioning process. To further aide in positioning of legs 114 and 116 of the stent graft 305, a magnetic tip 310, as shown in FIGURE 4, preferably of Nd-Fe-B material, is attached to the flexible end 311 of a guide wire 605, see FIGURE 14. Under fluoroscopic guidance, when guide wire 605 is inserted into the contralateral femoral artery, notwithstanding which artery is first used to deploy a leg of the stent graft 305, guide wire 605 is moved until magnetic tip 310 comes into contact with the wire base 950 of fork 300, it being understood that in this procedure at least one fork 300 is not retracted so that it may be used as a guide, see FIGURE 4. Once magnetic tip 310 is in contact with the wire base 950 of fork 300, magnetic tip 310 is advanced up said wire 950 until it is in position inside bifurcated stent graft 305 body 112 at which time fork wire 300 may be removed, see FIGURE 14. The introducer catheter 313, see FIGURE 15, is then inserted over guidewire 605 until it makes contact with the flexible end 311 of guidewire 605 thereby assuring that either leg 114 or 116 is properly located in either channel 112a or 113 of main graft 112.

0023Although the invention herein has been described with reference to a particular embodiment, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention