ENDOPROSTHESIS WITH PREDETERMINED CURVATURE FORMED BY TRI-TETHERS

[0001] An aneurysm is an abnormal dilation of a layer or layers of an arterial wall, usually caused by a structural defect due to hardening of the artery walls or other systemic defects such as aortic dissection due to high blood pressure. In the aorta leading into the heart, a thoracic aortic aneurysm (TAA) may occur when the arterial wall of the thoracic aorta is weakened due to the pressure of the blood being pumped by the heart. The TAA is typically presented as a large swelling or bulge under a chest X-ray or ultrasound. When left untreated, the aneurysm may rupture, usually causing rapid fatal hemorrhaging.

[0002] As is the case with abdominal aortic aneurysms, the widely accepted approach to treating an aneurysm in the thoracic aorta is surgical repair, involving replacing the aneurysmal segment with a prosthetic device. This surgery, as described above, is a major undertaking, with associated high risks and with significant mortality and morbidity.

[0003] One alternative to the surgical repair is to use an endovascular procedure, i.e., catheter directed, techniques for the treatment of aneurysms, specifically for TAA. This has been facilitated by the development of vascular stents, which can and have been used in conjunction with standard or thin-wall graft material in order to create a stent-graft or endograft. The potential advantages of less invasive treatments have included reduced surgical morbidity and mortality along with shorter hospital and intensive care unit stays.

[0004] One concern with the use of TAA is the prominence of endoleaks arising from a lack of apposition of a stent-graft to the aortic wall along the inside curve of the aorta. This is believed to be caused by a “bird-beak” (shown here in FIG. 7) in a radiologic image of the stent-graft in the aortic arch. In brief, the bird-beak is typically a triangulated wedge between the outside surface of the stent-graft and the inside surface of the aortic wall. The bird-beak is believed to lead endoleaks and the disruption of the normal fluid dynamics of the vasculature as described by F. Auricchio et al., “Patient-specific analysis of post-operative aortic hemodynamics: a focus on thoracic endovascular repair (TEVAR)” published Jan. 24, 2014.

[0005] Accordingly, I have devised an improved endoprosthesis that is believed to be heretofore not available in the prior art. My improvement is an endoprosthesis for repair of aneurysms. In particular, a thoracic endovascular implant is provided that includes a generally tubular graft, a plurality of stent hoops and at least one suture. The generally tubular graft extends along a longitudinal axis from a first opening to a second opening spaced apart along the longitudinal axis. The plurality of stent hoops is attached to the graft to define a stent graft. Each of the stent hoops has a sinusoidal configuration disposed about the longitudinal axis with apices spaced apart along the longitudinal axis. The apices of one stent hoop are spaced apart at a predetermined distance along the longitudinal axis from adjacent apices of another stent hoop. The at least one suture connects one apex of one stent hoop to two apices of another stent hoop to reduce the predetermined distance so that the stent-graft is generally linear in a constrained and compressed configuration and curved away from the longitudinal axis when in an uncompressed configuration in a blood vessel.

[0006] In yet another variation, an endovascular implant is provided that includes a generally tubular graft, a plurality of stent hoops and at least one suture. The generally tubular graft extends along a longitudinal axis from a first opening to a second opening spaced apart along the longitudinal axis. The plurality of stent hoops is attached to the graft to define a stent graft. Each of the stent hoops has a sinusoidal configuration disposed about the longitudinal axis with apices spaced apart along the longitudinal axis. The apices of one stent hoop are spaced apart at a predetermined distance along the longitudinal axis from adjacent apices of another stent hoop. The at least one suture connects one apex of one stent hoop to two apices of another stent hoop to reduce the predetermined distance so that in a compressed or crimped configuration (as inside a catheter sheath prior to delivery in a vessel), the stent-graft extends generally linearly as with the typical stent-graft. Yet in a released configuration (unconstrained in a catheter sheath) in a body vessel, the stent-graft is self-adjusting in-situ so as to curve away from the longitudinal axis to conform to the body vessel and reduce formation of a gap between one end of the stent-graft with an inner surface of the body vessel.

[0007] In addition to the embodiments described above, other features recited below can be utilized in conjunction therewith. For example, the at least one suture comprises three sutures in which each suture connects one apex of one stent hoop to two apices of another stent hoop; the one apex of one stent hoop is disposed between two apices of another stent hoop; the stent-graft is curved along a radius of about 3 centimeters. The radius of curvature defines an arcuate portion of a virtual circle, wherein the arcuate portion includes an angle of approximately 45 degrees; the generally tubular graft comprises a synthetic material selected from a group consisting of nylon, ePTFE, PTFE, Dacron and combinations thereof; the generally tubular graft comprises a generally constant inside diameter smaller than an outside diameter of the stent hoop; the generally tubular graft comprises at least one flared end; the plurality of stent hoops are disposed on the inside surface of the stent-graft; the predetermined distance comprises a distance selected from any value between about 1 mm to about 2 mm; another stent hoop configured with retention barbs is connected to a cranial end of the graft.

[0018] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention (wherein like numerals represent like elements).

[0019] The following detailed description should be read with reference to the drawings, in which like elements in different drawings are identically numbered. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

[0020] As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±50% of the recited value, e.g. “about 50%” may refer to the range of values from 51% to 99%. In addition, as used herein, the terms “patient,” “host,” “user,” and “subject” refer to any human or animal subject and are not intended to limit the systems or methods to human use, although use of the subject invention in a human patient represents a preferred embodiment. The uses of the terms “cranial” or “caudal” are in this application are used to indicate a relative position or direction with respect to the person receiving the implant. As applied to “cranial,” the term indicates a position or direction closer to the heart, while the term “caudal” indicates a position or direction further away from the heart of such a subject.

[0021] An endovascular implant 100 that can be used in a thoracic aortic aneurysm is shown in FIG. 1A. Implant 100 includes three components: a graft 200, stent hoops 300, and sutures 400. As shown in FIG. 1A, the implant 100 is in a constrained state such as in a delivery catheter prior to deployment. In this first state, the implant 100 has a small outer diameter while being constrained to a linear configuration. In the unconstrained (or expanded) state in which the implant 100 is unsupported, shown here in FIG. 4, the implant 100 takes on a curvilinear configuration, automatically (by virtue of this invention), in which a portion of the implant is linear and another portion is generally curved. Thus, the advantage of my invention is the ability to be constrained so as to conform to a linear configuration while in a catheter but yet when unconstrained, the implant 100 takes on a predetermined curvilinear configuration that mitigates or virtually the drawbacks of the formation of a “bird's beak” in the known TAA stent-graft shown in FIG. 8.

[0022] Referring back to FIG. 2, the graft 200 can be a generally tubular graft 200 that extends along a longitudinal axis L-L from a first opening 202 to a second opening 204 spaced apart along the longitudinal axis L-L. The graft 200 may be formed from a suitable synthetic material that is biocompatible with physiological fluids. In particular, the material of graft 200 is selected from a group primarily of nylon, ePTFE, PTFE, Dacron and combinations thereof. In one embodiment, the generally tubular graft 200 may have a generally constant inside diameter. Alternatively, the graft 200 may include at least one flared end portion 201 (FIG. 5) as part of implant 100′. Prior to attachment of the graft component to the stent hoops, crimps are formed between the stent positions by placing the graft material on a shaped mandrel and thermally forming indentations in the surface. In the exemplary embodiment illustrated in FIG. 2, the crimped grooves 140 are from about one millimeter (“mm”) to about two mm long and 0.5 mm deep. With these dimensions, the endovascular graft can bend and flex while maintaining an open lumen. Also, prior to attachment of the graft material to the stent hoops, the graft material is cut in a shape to conform to the shapes of the stent hoops. In one exemplary embodiment, the fabric for the graft material is a forty denier (denier is defined in grams of nine thousand meters of a filament or yarn), twenty-seven filament polyester yarn, having about seventy to one-hundred end yarns per cm per face and thirty-two to forty-six pick yarns per cm face. At this weave density, the graft material is relatively impermeable to blood flow through the wall, but is relatively thin, ranging from between approximately 0.08 to approximately 0.12 mm in wall thickness.

[0023] As shown diagrammatically in FIG. 2, the plurality of stent hoops 300 (designated as 300a-300f, from a caudal end to the cranial end) are attached to the graft 200 to define stent-graft 100 (including 100′ and 100″). The stent hoops 300 can be disposed on the outside surface of the graft 200. In the preferred embodiments, the stent hoops 300 are disposed on the inside surface of the graft 200 and attached with suture retainer 10 or adhesives. It is to be understood that retainer 10 (in the form of adhesive or sutures) is used in the remainder of the support hoops 300a-300e. Alternatively, the stent hoops can be captured between an inner tubular graft and an outer tubular graft, i.e., a sandwich arrangement. To ensure sufficient radial expansion force for support of the inner surface of body vessel, the stent hoop 300 may have an outside diameter greater than the inside diameter of the graft. At a distal end of the stent graft 100, a stent hoop 300 (or 302) to can act as an anchor by having a portion of the stent hoop attached to the graft 200. Where increased retention to a body vessel (e.g., in the thoracic artery) is desired, a stent hoop 302 with barbs or hooks 300b (FIG. 1C) can be provided. The configuration of stent hoop 302 allows for the hooks 302b to be retracted prior to delivery into the body vessel by virtue of the eyelets 300a. Details of the stent hoop 302 are provided in US Patent Publication No. 2011/0071614 filed on Sep. 24, 2009, which is hereby incorporated by reference.

[0024] Referring to FIGS. 1B and 1C, each of the stent hoops 300 (or a combination of stent hoops 300 and 302) may have a sinusoidal or zig-zag configuration (as indicated by the dashed line Z) disposed about the longitudinal axis L-L. The zig-zag configuration Z of each stent hoop provides for apices AP that are spaced apart along the longitudinal axis L-L. As shown in FIGS. 1B and 1C, the apices AP of each hoop (300 or 302) define two respective spaced apart circumferences 20a and 20b about the longitudinal axis L-L.

[0025] Referring back to FIG. 2, the circumference (20a or 20b) defined by the apices AP of one stent hoop 300 are then spaced apart to a circumference (20b or 20a) defined by the apices of another stent hoop 300 at a predetermined distance y along the longitudinal axis L-L. This separation distance y between each separate stent hoop 300 to adjacent stent hoop 300 can be seen for caudal stent hoops 300a and 300b at the bottom of FIG. 2. For stent hoops 300a and 300b, the hoops are not connected directly to each other but via the graft 100. However, for the remaining stent hoops 300c, 300d, 300e and 300f proximate the cranial end, at least one suture 400 is provided to connect one apex (AP1) of one stent hoop (300f) to two apices (e.g., AP2 and AP3) of another stent hoop (300e).

[0026] As can be seen in FIGS. 2 and 3, this additional connection reduces the predetermined distance y to a smaller magnitude (e.g., y1, y2, y3 . . . ) so that at least one stent hoop (and by virtue of the stent hoop being secured to the graft via retainer suture 10), the stent-graft 100 is pulled away from the longitudinal axis L-L. This allows the graft 100 (FIG. 4) to curve away from the longitudinal axis L-L. Depending on the distance y1, y2 or y3, the stent-graft 100 can conform closely to the body vessel and reduce the formation of a gap (i.e., the bird's beak shown in FIG. 8) between one end (202 or 2004) of the stent-graft 100 with the body vessel. In the preferred embodiment, there are three sutures 400 in which each suture connects one apex of one stent hoop to two apices of another stent hoop to define a “tri-tether” connection 500. That is, my tri-tether configuration ensures that one apex (AP1 of hoop 300f) is disposed between the two apices (AP2 and AP3 of hoop 300e) that are linked together with the suture 400, as shown here in FIGS. 2 and 3. The tri-tethers are preferably configured so that the middle apex AP1 of one stent hoop is aligned along an axis W-W that may be parallel to the longitudinal axis L-L with the respective apices AP1 of the other stent hoops 300e and 300f. It should be noted, however, that the implementation of the present invention is not limited to three sutures 400. Nor is one apex (e.g., AP1) of one stent hoop (e.g., 300f) is required to be disposed between two apices (e.g., AP2 and AP3) of the other stent hoop (e.g., 300e). Other configurations and orientations of the apices and the sutures are within the scope of the present invention such as, for example, the sutures 400 being located on the inner surface of the graft 200 or less than three tri-tether connections 500 being utilized.

[0027] It should be noted that the connector 400 is not required to connect to the respective apices such as that shown in FIG. 3 but can be connected at a location offset to the apices via a suitable retainer such as, for example, a hook or an eyelet and the like.

[0028] Depending on the number of sutures and the separation distance y1, y2, y3 . . . so on, different radii of curvature could be attained. For example, as shown in FIG. 4, stent-graft 100 is curved along a radius of curvature R of approximately ½ of a length L1 of the stent-graft 100 (i.e., R˜0.5L1). In particular, the radius of curvature R defines an arcuate portion of a virtual circle such that the arcuate portion includes an included angle θ of approximately 30 to 70 degrees as measured from normal stent hoop circumference 20b (e.g., stent-graft segment S5) to the end stent-graft segment (e.g., S1). In the exemplary configuration, the radius of curvature R provides for an included angle θ of about 45 degrees where included angle θ is the sum of the included angles θ₁, θ₂, θ₃, θ₄ and so on for each stent-graft segment (i.e., S1-S4) with respect to the adjacent segment stent-graft segment. One preferred embodiment may have a radius of about 3 cm but other values can be utilized by one skilled in the art when apprised of the principles of my invention. That is, the curvature R is not limited to about 3 cm as noted here. This is due to the variations in biological anatomies. Hence, the curvature R is dependent upon the specifics of the anatomy to which an embodiment of my invention will be utilized and therefore many different sizes can be designed and utilized other than the configuration described and illustrated here.

[0029] One of the many benefits of this design is that in the constrained or compressed configuration, there is no increase in the overall profile (or thickness when the stent-graft is viewed in a side cross-sectional view) of the implant. This and advantage is due to the combination of design features taught in this application that allow virtually no increase in the profile in the delivery stage but yet allow for a pre-configured curved once deployed in the blood vessel.

[0030] It is noted that while one curvilinear configuration is shown in FIGS. 1A-1C and 2-6, other curvilinear configurations can also be utilized within the scope of the present invention. For example, as shown in FIG. 6, an S-curved configuration can be utilized by implementing the tri-tether connection 500 at certain locations indicated on the stent-graft 100″ in FIG. 6 to achieve the desired curvature. It is noted that this embodiment can be used in tortuous vessels and therefore is not limited to uses in the aorta.

[0031] It is noted that in the application of the endoprosthesis for aneurysms, the suture 400 may be a non-bioresorbable material. In other applications, suture 400 may be formed from a bioresorbable material. Suitable biodegradable materials may include polymers such as polylactic acid (i.e., PLA), polyglycolic acid (i.e., PGA), polydioxanone (i.e., PDS), polyhydroxybutyrate (i.e., PHB), polyhydroxyvalerate (i.e., PHV), and copolymers or a combination of PHB and PHV (available commercially as Biopol®), polycaprolactone (available as Capronor®), polyanhydrides (aliphatic polyanhydrides in the back bone or side chains or aromatic polyanhydrides with benzene in the side chain), polyorthoesters, polyaminoacids (e.g., poly-L-lysine, polyglutamic acid), pseudo-polyaminoacids (e.g., with back bone of polyaminoacids altered), polycyanocrylates, or polyphosphazenes. As used herein, the term “bio-resorbable” includes a suitable biocompatible material, mixture of materials or partial components of materials being degraded into other generally non-toxic materials by an agent present in biological tissue (i.e., being bio-degradable via a suitable mechanism, such as, for example, hydrolysis) or being removed by cellular activity (i.e., bioresorption, bioabsorption, or bio-resorbable), by bulk or surface degradation (i.e., bioerosion such as, for example, by utilizing a water insoluble polymer that is soluble in water upon contact with biological tissue or fluid), or a combination of one or more of the bio-degradable, bio-erodable, or bio-resorbable material noted above. In yet other applications, the suture 400 may be a shape memory material such as shape memory metal or polymers.

[0032] The suture 10 or 400 can be infused or loaded with bioactive agents to aid in the healing response or to achieve a desired physiological response. For example, bio-active agents such as blood de-clotting agent (e.g., heparin, warfarin, etc.,) anti-proliferative/antimitotic agents including natural products such as vinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine), paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide), antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin and idarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin (mithramycin) and mitomycin, enzymes (L-asparaginase which systemically metabolizes L-asparagine and deprives cells which do not have the capacity to synthesize their own asparagine); antiplatelet agents such as G(GP) IIb/IIIa inhibitors and vitronectin receptor antagonists; anti-proliferative/antimitotic alkylating agents such as nitrogen mustards (mechlorethamine, cyclophosphamide and analogs, melphalan, chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine and thiotepa), alkyl sulfonates-busulfan, nirtosoureas (carmustine (BCNU) and analogs, streptozocin), trazenes-dacarbazinine (DTIC); anti-proliferative/antimitotic antimetabolites such as folic acid analogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine, and cytarabine), purine analogs and related inhibitors (mercaptopurine, thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine}); platinum coordination complexes (cisplatin, carboplatin), procarbazine, hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen); anti-coagulants (heparin, synthetic heparin salts and other inhibitors of thrombin); fibrinolytic agents (such as tissue plasminogen activator, streptokinase and urokinase), aspirin, dipyridamole, ticlopidine, clopidogrel, abciximab; antimigratory; antisecretory (breveldin); anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone, fludrocortisone, prednisone, prednisolone, 6α-methylprednisolone, triamcinolone, betamethasone, and dexamethasone), non-steroidal agents (salicylic acid derivatives i.e. aspirin; para-aminophenol derivatives i.e. acetominophen; indole and indene acetic acids (indomethacin, sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac, and ketorolac), arylpropionic acids (ibuprofen and derivatives), anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids (piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone), nabumetone, gold compounds (auranofin, aurothioglucose, gold sodium thiomalate); immunosuppressives: (cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenic agents: vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF); angiotensin receptor blockers; nitric oxide donors; anti-sense oligionucleotides and combinations thereof; cell cycle inhibitors, mTOR inhibitors, and growth factor receptor signal transduction kinase inhibitors; retenoids; cyclin/CDK inhibitors; HMG co-enzyme reductase inhibitors (statins); and protease inhibitors.

[0033] All of the stent hoops described herein are substantially tubular elements that may be formed utilizing any number of techniques and any number of materials. In the preferred exemplary embodiment, all of the stent hoops are formed from a nickel-titanium alloy (Nitinol), shape set laser cut tubing.

[0034] The graft material utilized to cover all of the stent hoops may be made from any number of suitable biocompatible materials, including woven, knitted, sutured, extruded, or cast materials forming polyester, polytetrafluoroethylene, silicones, urethanes, and ultra-light weight polyethylene, such as that commercially available under the trade designation SPECTRA™. The materials may be porous or nonporous. Exemplary materials include a woven polyester fabric made from DACRON™ or other suitable PET-type polymers.

[0035] As noted above, the graft material is attached to each of the stent hoops. The graft material may be attached to the stent hoops in any number of suitable ways. In the exemplary embodiment, the graft material is attached to the stent hoops by sutures.

[0036] Depending on the stent hoops location, different types of suture knots may be utilized for retainer suture 10. Details of various embodiments of the suture knots for suture 10 or suture 400 can be found in US Patent Application Publication No. US20110071614 filed on Sep. 24, 2009, which is hereby incorporated by reference as if set forth herein.

[0037] While the invention has been described in terms of particular variations and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the variations or figures described. In addition, where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the claims, it is the intent that this patent will cover those variations as well.