US20120116496A1 - Stent structures for use with valve replacements - Google Patents

Abstract

The present embodiments provide a medical device for implantation in a patient comprising a stent and a valve. The stent comprises a proximal region comprising a cylindrical shape having a first outer diameter in an expanded state, and a distal region comprising a cylindrical shape having a second outer diameter in the expanded state. The second outer diameter is greater than the first outer diameter. A proximal region of the valve is at least partially positioned within the proximal region of the stent, and the distal region of the valve is at least partially positioned within one of tapered and distal regions of the stent. When implanted, the proximal region of the stent and the proximal region of the valve are aligned with a native valve, and the distal region of the valve is distally spaced-apart from the native valve.

Description

PRIORITY CLAIM
• This invention claims the benefit of priority of U.S. Provisional Application Ser. No. 61/410,540, entitled “Stent Structures For Use With Valve Replacements,” filed Nov. 5, 2010, the disclosure of which is hereby incorporated by reference in its entirety.
BACKGROUND
• The present embodiments relate to implantable medical devices, and more particularly to an implantable medical device for the repair of a damaged endoluminal valve, such as an aortic valve.
• The aortic valve functions as a one-way valve between the heart and the rest of the body. Blood is pumped from the left ventricle of the heart, through the aortic valve, and into the aorta, which in turn supplies blood to the body. Between heart contractions the aortic valve closes, preventing blood from flowing backwards into the heart.
• Damage to the aortic valve can occur from a congenital defect, the natural aging process, and from infection or scarring. Over time, calcium may build up around the aortic valve causing the valve not to open and close properly. Certain types of damage may cause the valve to “leak,” resulting in “aortic insufficiency” or “aortic regurgitation.” Aortic regurgitation causes extra workload for the heart, and can ultimately result in weakening of the heart muscle and eventual heart failure.
• After the aortic valve becomes sufficiently damaged, the valve may need to be replaced to prevent heart failure and death. One current approach involves the use of a balloon-expandable stent to place an artificial valve at the site of the defective aortic valve. Another current approach involves the positioning of an artificial valve at the site of the aortic valve using a self-expanding stent. The normal aortic valve functions well because it is suspended from above through its attachment to the walls of the coronary sinus in between the coronary orifices, and it has leaflets of the perfect size and shape to fill the space in the annulus. However, these features may be difficult to replicate with an artificial valve. The size of the implantation site depends on the unpredictable effects of the balloon dilation of a heavily calcified native valve and its annulus. Poor valve function with a persistent gradient or regurgitation through the valve may result. In addition, different radial force considerations may be needed at the different locations for the prosthesis to optimally interact with a patient's anatomy. Still further, it is important to reduce or prevent in-folding or “prolapse” of an artificial valve after implantation, particularly during diastolic pressures.
SUMMARY
• The present embodiments provide a medical device for implantation in a patient. The medical device comprises a stent and a valve. The stent comprises a proximal region comprising a cylindrical shape having a first outer diameter when the stent is in an expanded state, and a distal region comprising a cylindrical shape having a second outer diameter when the stent is in the expanded state. The second outer diameter is greater than the first outer diameter.
• In one embodiment, a plurality of closed cells are disposed around the perimeter of the proximal region of the stent, and another plurality of closed cells are disposed around the perimeter of the distal region of the stent. An overall length of each of the closed cells of the proximal region of the stent is less than an overall length of each of the closed cells of the distal region of the stent when the stent is in the expanded state.
• In one embodiment, the stent further comprises a tapered region disposed between the proximal and distal regions. The tapered region transitions the stent from the first diameter to the second diameter. The tapered region further comprises a plurality of closed cells. An overall length of each of the closed cells of the tapered region is greater than the overall length of each of the closed cells of the proximal region and less than the overall length of each of the closed cells of the distal region when the stent is in the expanded state.
• A proximal region of the valve is at least partially positioned within the proximal region of the stent, and the distal region of the valve is at least partially positioned within one of the tapered and distal regions of the stent. When implanted, the proximal region of the stent and the proximal region of the valve are aligned with a native valve, and the distal region of the valve is distally spaced-apart from the native valve.
• Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be within the scope of the invention, and be encompassed by the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.
• FIGS. 1-2 are, respectively, side and perspective views of an exemplary stent to structure in an expanded state.
• FIG. 3 is a side view illustrating the stent structure ofFIGS. 1-2 in a compressed state.
• FIG. 4 is a side view of an exemplary integral barb of the stent structure ofFIGS. 1-2.
• FIGS. 5-6 are perspective views of an exemplary aortic valve when no forces are imposed upon the valve.
• FIG. 7 is a perspective view the aortic valve ofFIGS. 5-6 during systole.
• FIGS. 8-9 are side views illustrating a technique for coupling the aortic valve ofFIGS. 5-7 to the stent structure ofFIGS. 1-3.
• FIG. 10 is a schematic showing the aortic prosthesis ofFIG. 9 disposed within a patient's anatomy.
• FIGS. 11-12 are, respectively, perspective views of an aortic valve comprising suspension ties when no forces are imposed and during diastole.
• FIG. 13 is a side view illustrating coupling of the aortic valve ofFIGS. 11-12 to the stent structure ofFIGS. 1-3.
• FIGS. 14-16 are, respectively, perspective views illustrating an aortic valve comprising reinforcement strips when no forces are imposed, during systole and during diastole.
• FIGS. 17-19 illustrate aortic valves comprising one or more alternative reinforcement strips.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• In the present application, the term “proximal” refers to a direction that is generally closest to the heart during a medical procedure, while the term “distal” refers to a direction that is furthest from the heart during a medical procedure.
• Referring now toFIGS. 1-2, a first embodiment of astent structure20, which may be used in conjunction with an aortic valve prosthesis, is shown and described. Thestent structure20 may be used in conjunction with anaortic valve120 to form a completedaortic valve prosthesis10 as shown inFIG. 9 below.
• Thestent structure20 has a collapsed delivery state and an expanded deployed state, and generally comprises aproximal region30, atapered region50, and adistal region70, as shown inFIGS. 1-2. A pattern of thestent structure20, depicted in a flattened and collapsed state, is shown inFIG. 3.
• Thestent structure20 may be manufactured from a continuous cylinder into which a pattern may be cut by a laser or by chemical etching to produce slits in the wall of the cylinder. The resulting structure may then be heat set to give it a desired final configuration. As shown inFIGS. 1-2, the final configuration may include a shape having a series of multiple closed cells.
• Theproximal region30 of thestent structure20 comprises a generally cylindrical shape having an expanded outer diameter d₁. Theproximal region30 is configured to be disposed at least partially within the aortic sinus, as shown inFIG. 10 below. By contrast, thedistal region70 of thestent structure20 comprises a generally cylindrical shape having an expanded outer diameter d₂, and is configured to be disposed at least partially within the ascending aorta. Thetapered region50 generally bridges the change from diameter d₁to diameter d₂.
• Theproximal region30 of thestent structure20 may comprise multiple adjacentproximal apices31. Eachproximal apex31 may comprise anend region32 having anintegral barb33 formed therein, as shown inFIG. 4. Thebarb33 may be formed by laser cutting a desired barb shape into theend regions32. A slit34 therefore is formed into eachend region32 after the desired barb shape is formed, as shown inFIG. 4. Once the desired barb shape is cut, a main body of thebarb33 may be bent in a radially outward direction with respect to theend region32. The angle may comprise any acute angle, or alternatively may be substantially orthogonal or obtuse. If desired, thebarb33 may be sharpened, for example, by grinding the tip of the barb, to facilitate engagement at a target tissue site.
• Referring still toFIGS. 1-2, theproximal region30 of thestent structure20 further may comprise a plurality ofclosed cells35 formed by multiple angled strut segments. In one example, fourangled strut segments36,37,38 and39 form oneclosed cell35, as shown inFIG. 1. In this example, a firstproximal apex31 extends distally and splits into first and secondangled strut segments36 and37, respectively, which are joined to one another at ajunction41. Further, third and fourthangled strut segments38 and39 are joined at thejunction41 and extend distally therefrom, as shown inFIG. 1. In a compressed state, the angled strut segments36-39 of thecell35 may be compressed such that they are substantially parallel to one another.
• The first and secondangled strut segments36 and37 each generally comprise a length L₁, and each are generally disposed at an angle α₁relative to a longitudinal axis L of thestent structure20, as shown inFIG. 1. The third and fourthangled strut segments38 and39 each generally comprise a length L₂and each are generally disposed at an angle α₂relative to the longitudinal axis L, as shown inFIG. 1. Theclosed cell35 comprises a total length L₃, representing the combined lengths L₁and L₂, as shown inFIG. 1.
• In this example, the length L₁of the first and secondangled strut segments36 and37 is greater than the length L₂of the third and fourthangled strut segments38 and39. In one embodiment, the length L₁may be about 1.5 to about 4.0 times greater than the length L₂.
• Moreover, a cross-sectional area of the first and secondangled strut segments36 and37 may be greater than a cross-sectional area of the third and fourthangled strut segments38 and39. In one embodiment, the cross-sectional area of the first and secondangled strut segments36 and37 is about 4 times greater than the cross-sectional area of the third and fourthangled strut segments38 and39. The increased cross-sectional area of the first and secondangled strut segments36 and37 causes these segments to primarily provide the radial force within theclosed cells35, while the third and fourthangled strut segments38 and39 are mainly intended for connecting adjacentclosed cells35 and55a,instead of providing significant radial force.
• Further, in this example, the angle α₂of the third and fourthangled strut segments38 and39 is greater than the angle α₁of the first and secondangled strut segments36 and37. Since the first and secondangled strut segments36 and37 are primarily providing the radial force, the angle α₁is selected to achieve the desired radial force, while as noted above, the third and fourthangled strut segments38 and39 are mainly intended for connecting adjacentclosed cells35 and55a,and therefore yield a different angle α₂for this different primary purpose. In one embodiment, the angle α₂may be about 1.2 to 4.0 times greater than the angle α₁.
• Overall, given the relative lengths and angle configurations described above, eachclosed cell35 comprises a generally spade-shaped configuration, as shown inFIGS. 1-2. As will be apparent, however, the relative lengths and angles may be greater or less than depicted and/or provided in the exemplary dimensions disclosed herein.
• The pattern of angled strut segments36-39 may be repeated around the circumference of theproximal region30 of thestent structure20. In this manner, thestent structure20 may be formed into a continuous, generally cylindrical shape. In one example, tenproximal apices31 and tenclosed cells35 are disposed around the circumference of theproximal region30, although greater or fewer proximal apices and closed cells may be provided to vary the diameter and/or radial force characteristics of the stent.
• Theproximal region30 may be flared slightly relative to the longitudinal axis L. In one example, a proximal end of each apex31 may be bowed outward relative to a distal end of thesame apex31. Such a flaring may facilitate engagement with the aortic sinus when implanted.
• Referring still toFIGS. 1-2, the taperedregion50 also comprises a plurality of closed cells. In this example, four differentclosed cells55a,55b,55cand55dare provided along the length of the taperedregion50. Each of the closed cells55a-55dmay comprise a slightly different shape, as shown inFIGS. 1-2. In this example, ten of each series of closed cells55a-55dare disposed around the circumference of the taperedregion50, and the diameter of the taperedregion50 increases from the outer diameter d₁to the outer diameter d₂.
• In one example, fourangled strut segments56,57,58 and59 form oneclosed cell55b,as shown inFIG. 1. The first and secondangled strut segments56 and57 each generally comprise a length L₄and each are generally disposed at an angle relative to the longitudinal axis L that may be about the same as, or slightly greater or less than, the angle α₁. The third and fourthangled strut segments58 and59 each generally comprise a length L₅and each are generally disposed at an angle relative to the longitudinal axis L that may be about the same as, or slightly greater or less than, the angle α₂. Theclosed cell55bcomprises a total length L₆, representing the combined lengths L₄and L₅, as shown inFIG. 1.
• In this example, the length L₄of the first and secondangled strut segments56 and57 is greater than the length L₅of the third and fourthangled strut segments58 and59. In one embodiment, the length L₄may be about 1.1 to about 4 times greater than the length L₅.
• Further, in this example, the total length L₆of theclosed cell55bof the taperedregion50 is greater than the total length L₃of theclosed cell35 of theproximal region30, as shown inFIG. 1. Moreover, in one example, the length of one or more individual struts of the taperedregion50, e.g., first and secondangled strut segments56 and57 having length L₄, may be longer than the total length L₃of theclosed cell35 of theproximal region30.
• Thedistal region70 similarly comprises a plurality of closed cells. In this example, two differentclosed cells75aand75bare provided along the length of thedistal region70. Theclosed cells75aand75bmay comprise a different shape relative to one another, as shown inFIGS. 1-2. In this example, ten of each series ofclosed cells75aand75bare disposed around the circumference of thedistal region70 to form the overall outer diameter d₂.
• In one example, the most distalclosed cell75bcomprises fourangled strut segments76,77,78 and79, as shown inFIG. 1. The first and secondangled strut segments76 and77 each generally comprise a length L₇and each are generally disposed at an angle relative to the longitudinal axis L that may be about the same as, or slightly greater or less than, the angle α₁. The third and fourthangled strut segments78 and79 each generally comprise a length L₉and each are generally disposed at an angle relative to the longitudinal axis L that may be about the same as, or slightly greater or less than, the angle α₂.
• Further, abarbed region80 having abarb83 is disposed between the angled strut segments, as shown inFIG. 1. Thebarb83 of thebarbed region80 may be formed integrally in the same manner as thebarb33 of theproximal region30, as shown inFIG. 4, but preferably faces in a proximal direction. Thebarbed region80 is generally parallel to the longitudinal axis L of thestent structure20 and comprises a length L₈. Thecell55bcomprises a total length L₁₀, representing the combined lengths L₇, L₈and L₉, as shown inFIG. 1.
• In this example, the length L₇of the first and secondangled strut segments76 and77 is greater than the length L₉of the third and fourthangled strut segments78 and79. In one embodiment, the length L₇may be about 1.1 to about 4.0 times greater than the length L₉.
• Further, in this example, the total length L₁₀of theclosed cell75bof thedistal region70 is greater than the total length L₆of theclosed cell55bof the taperedregion50, which in turn is greater than the total length L₃of theclosed cell35 of theproximal region30, as shown inFIG. 1. Therefore, the lengths of individual closed cells increase along the stent structure from aproximal end22 to adistal end24 of thestent structure20.
• Advantageously, since the lengths of individual closed cells generally increase along to thestent structure20 from theproximal end22 to thedistal end24, the forces imposed by thestent structure20 along different regions may be varied for a patient's anatomy. Radial force and stiffness are a function of the individual cell lengths. Therefore, in the example of an aortic valve replacement, a relatively short length L₃of theclosed cell35 of theproximal region30 yields a relatively high radial force imposed upon the aortic sinus to allow for an enhanced and rigid attachment at this location. Conversely, a relatively long length L₁₀of theclosed cell75bof thedistal region70 yields a relatively low radial force imposed upon the ascending aorta, thereby facilitating a flexible contour at thedistal region70 that does not adversely impact the ascendingaorta105.
• Additionally, radial force and stiffness are a function of the strut angles. In the example ofFIGS. 1-2, the individual struts36 and37 of theproximal region30 may have a shallower strut angle relative to the individual struts76 and77 of thedistal region70, i.e., the individual struts36 and37 may be more perpendicular to the longitudinal axis L of the device. Therefore, the angles of the individual struts36 and37 may contribute to a higher radial force at theproximal region30 relative to the individual struts76 and77 of thedistal region70.
• Further, an increased strut width may be provided at theproximal region30 to promote a higher radial force relative to the strut width at thedistal region70. In sum, thestent structure20 has different radial force properties at its proximal anddistal regions30 and70 that beneficially interact with their associated regions into which they are implanted, e.g., the aortic sinus and the ascending aorta, respectively.
• In one embodiment, the lengths of individual cells may always increase relative to one another moving in a proximal to distal direction, i.e., each closed cell has an overall length that is greater than a length of every other closed cell that is disposed proximally thereof. In other embodiments, adjacent cells may comprise about the same length, or a proximal cell may comprise a lesser length than an adjacent distal cell. Therefore, while the lengths of individual angled strut segments generally increase in a proximal to distal direction, it is possible that some of the individual angled strut segments of a more distal region may be smaller than a more proximally oriented region.
• Expansion of thestent structure20 is at least partly provided by the angled strut segments, which may be substantially parallel to one another in a compressed state ofFIG. 3, but may tend to bow outward away from one another in the expanded state shown inFIGS. 1-2. Thestent structure20 may be formed from any suitable material, and formed from a laser-cut cannula. Thestent structure20 has a reduced diameter delivery state so that it may be advanced to a target location within a vessel or duct. Further, the struts of the stent may comprise a substantially flat wire profile or may comprise a rounded profile. As best seen inFIGS. 1-2, the struts of the stent generally comprise a flat wire profile in this example.
• Thestent structure20 may be manufactured from a super-elastic material. Solely by way of example, the super-elastic material may comprise a shape-memory alloy, such as a nickel titanium alloy (nitinol). If thestent structure20 comprises a self-expanding material such as nitinol, the stent may be heat-set into the desired expanded state, whereby thestent structure20 can assume a relaxed configuration in which it assumes the preconfigured first expanded inner diameter upon application of a certain cold or hot medium. Alternatively, thestent structure20 may be made from other metals and alloys that allow thestent structure20 to return to its original, expanded configuration upon deployment, without inducing a permanent strain on the material due to compression. Solely by way of example, thestent structure20 may comprise other materials such as stainless steel, cobalt-chrome alloys, amorphous metals, tantalum, platinum, gold and titanium. Thestent structure20 also may be made from non-metallic materials, such as thermoplastics and other polymers.
• It is noted that some foreshortening of thestent structure20 may occur during expansion of the stent from the collapsed configuration ofFIG. 3 to the expanded deployed state ofFIGS. 1-2. Since theproximal region30 of thestent structure20 is deployed first, it is expected that such foreshortening is not problematic since a precise landing area of thedistal region70 within the ascending aorta is generally not needed, so long as solid contact is achieved.
• Moreover, in order to reduce migration of the stent structure when implanted at a target site, it is preferred that thebarbs33 of theproximal region30 are oriented in a distally-facing direction, whereas thebarbs83 of thedistal region70 are oriented in a proximally-facing direction. However, additional or fewer barbs may be disposed at various locations along thestent structure20 and may be oriented in the same or different directions. Moreover, integral and/or externally attached barbs may be used.
• Referring now toFIGS. 5-7, a first embodiment of anaortic valve120, which may be used in conjunction with thestent structure20 to form an aortic prosthesis, is shown and described. Theaortic valve120 generally comprises proximal anddistal regions130 and170, respectively, and atapered region150 disposed therebetween. Theaortic valve120 comprises a delivery state in which it may be compressed for percutaneous implantation along with thestent structure20, and further comprises different states during systole and diastole. Generally, antegrade flow opens theaortic valve120 while retrograde flow closes theaortic valve120. In the phase of systole for theaortic valve120, depicted inFIG. 7, blood may flow through the opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120. In the phase of diastole for theaortic valve120, opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120 are generally adjacent to one another to inhibit blood flow back through the valve.
• Theproximal region130 generally comprises a cylindrical body having an outer diameter that is approximately equal to, or just less than, an expanded inner diameter of theproximal region30 of thestent structure20. In one method of manufacture, shown inFIGS. 8-9 and described below, theaortic valve120 is disposed generally within thestent structure20 such that theproximal region130 is at least partially aligned with theproximal region30 of thestent structure20.
• The taperedregion150 of theaortic valve120 may comprise two opposingflat surfaces152 and154, as shown inFIGS. 5-6. The opposingflat surfaces152 and154 generally each comprise aproximal portion156 in the form of a curved area that reduces the diameter of theproximal region130, and adistal portion157 in the form of a wide flat panel that transitions into thedistal region170, as shown inFIGS. 5-6.
• Thedistal region170 of theaortic valve120 may comprise a generally rectangular profile from an end view, i.e., looking at the device from a distal to proximal direction. Thedistal region170 comprises the opposingflat surfaces172 and174 noted above, which are separated by narrowerflat sides175aand175b,as shown inFIGS. 5-6. The opposingflat surfaces152 and154 of the taperedregion150 generally transition into the opposingflat surfaces172 and174 of thedistal region170, respectively. The opposingflat surfaces152 and154 of the taperedregion150 are angled relative to both theproximal region130 and thedistal region170, as shown inFIGS. 5-6.
• Theaortic valve120 may comprise a biocompatible graft material is preferably non-porous so that it does not leak under physiologic forces. The graft material may be formed of Thoralon® (Thoratec® Corporation, Pleasanton, Calif.), Dacron® (VASCUTEK® Ltd., Renfrewshire, Scotland, UK), a composite thereof, or another suitable material. Preferably, the graft material is formed without seams. The tubular graft can be made of any other at least substantially biocompatible material including such fabrics as other polyester fabrics, polytetrafluoroethylene (PTFE), expanded PTFE, and other synthetic materials. Naturally occurring biomaterials are also highly desirable, particularly a derived collagen material known as extracellular matrix. An element of elasticity may be incorporated as a property of the fabric or by subsequent treatments such as crimping.
• Referring toFIGS. 8-9, in one method of manufacture, theaortic valve120 is disposed generally within thestent structure20 such that theproximal region130 of theaortic valve120 is at least partially aligned with theproximal region30 of thestent structure20. Aproximal attachment portion132 of theaortic valve120 having a length x is disposed proximal to theproximal apices31 of thestent structure20, as shown inFIG. 8, then theproximal attachment portion132 is folded externally over theproximal apices31, as shown inFIG. 9. Theproximal attachment portion132 then may be sutured or otherwise attached to theproximal apices31 and/or any of the angled strut segments36-39, thereby securing a portion of theaortic valve120 to thestent structure20 to form a completeaortic prosthesis10, as depicted inFIG. 9. Thebarbs33 of thestent structure20 may protrude through the fabric of theproximal attachment portion132 for engagement with targeted tissue.
• When theaortic valve120 is coupled to thestent structure20 as shown inFIGS. 8-9, thedistal region170 of theaortic valve120 may extend within the taperedregion50 and/or thedistal region70 of thestent structure20, and may be generally centrally disposed therein, although the exact positioning ofdistal region170 of theaortic valve120 relative to thestent structure20 may be varied as needed. Moreover, one or more reinforcement members, described generally inFIGS. 11-19 below, may be coupled to theaortic valve120 and/or thestent structure20 to enhance structural integrity and/or functionality of theaortic prosthesis10.
• Advantageously, thedistal region170 of theaortic valve120 is disposed within the taperedregion50 and/or thedistal region70 of thestent structure20, which are positioned in the proximal ascending thoracic aorta above (distal to) the annulus and above the native aortic valve. Previous valves are designed to occupy the aortic annulus; however, the unpredictable shape and diameter of the aortic annulus makes the valve unpredictable in shape and diameter, leading to asymmetric replacement valve movement, leakage and reduced durability. In short, by moving thedistal region170 of theaortic valve120 to a distally spaced-apart location relative to the native aortic valve, i.e., the unpredictable shape and diameter of the aortic annulus have less impact upon the spaced-apartdistal region170 of theaortic valve120, and therefore thedistal region170 is less subject to asymmetric valve movement and leakage, and may have increased durability.
• The shape and dimensions of the proximal andtapered regions130 and150 can vary without significantly affecting flow or valve function at thedistal region170. While thedistal region170 of thevalve120 is shown having a generally rectangular shape, a tricuspid-shaped distal region of the valve may be provided, in which case the taperedregion150 may be omitted or altered to accommodate such a tricuspid-shaped distal region.
• Referring now toFIG. 10, a partial cut-away view of aheart102 and anaorta104 are shown. Theheart102 may comprise anaortic valve106 that does not seal properly. This defect of theaortic valve106 allows blood to flow from theaorta104 back into the left ventricle, leading to a disorder known as aortic regurgitation. Also shown inFIG. 10 are abrachiocephalic trunk112, a left commoncarotid artery114, and a leftsubclavian artery116. A portion of theaorta104 referred to herein as an ascendingaorta105 is shown located between theaortic valve106 and thebrachiocephalic trunk112. A patient'scoronary arteries117 and118 are located distal to theaortic valve106.
• Theaortic prosthesis10 is introduced into a patient's vascular system, delivered, and deployed using a deployment device, or introducer. The deployment device delivers and deploys theaortic prosthesis10 within the aorta at a location to replace theaortic valve106, as shown inFIG. 10. The deployment device may be configured and sized for endoluminal delivery and deployment through a femoral cut-down. Theaortic prosthesis10, with thestent structure20 in a radially collapsed state, may be inserted into a delivery catheter using conventional methods. In addition to a delivery catheter, various other components may need to be provided in order to obtain a delivery and deployment system that is optimally suited for its intended purpose. These include and are not limited to various outer sheaths, pushers, trigger wires, stoppers, wire guides, and the like. For example, the Zenith® Thoracic Aortic Aneurysm Endovascular Graft uses a delivery system that is commercially available from
• Cook Inc., Bloomington, Ind., and may be suitable for delivering and deploying an aortic prosthesis in accordance with the present embodiments.
• In one aspect, a trigger wire release mechanism is provided for releasing a retained end of thestent structure20 of theaortic prosthesis10. Preferably, the trigger wire arrangement includes at least one trigger wire extending from a release mechanism through the deployment device, and the trigger wire is engaged with selected locations of thestent structure20. Individual control of the deployment of various regions of thestent structure20 enables better control of the deployment of theaortic prosthesis10 as a whole.
• While thestent structure20 is generally described as a self-expanding framework herein, it will be appreciated that a balloon-expandable framework may be employed to accomplish the same functionality. If a balloon-expandable stent structure is employed, then a suitable balloon catheter is employed to deliver the aortic prosthesis as generally outlined above. Optionally, after deployment of a self-expandingstent structure20, a relatively short balloon expandable stent may be delivered and deployed inside of theproximal region30 of thestent structure20 to provided added fixation at the location of the aortic sinus.
• Upon deployment, theaortic prosthesis10 is positioned as generally shown inFIG. 10. Advantageously, as noted above, since the lengths of individual cells generally increase along thestent structure20 from theproximal end22 to thedistal end24, a relatively high radial force is imposed by theclosed cells35 of theproximal region30 upon theaortic sinus106 to allow for an enhanced and rigid attachment at this location. Conversely, a relatively low radial force is imposed by theclosed cells75aand75bof thedistal region70 upon the ascendingaorta105, thereby facilitating a flexible contour at the distal region that does not adversely impact the ascendingaorta105.
• When theaortic prosthesis10 is implanted, sufficient flow into thecoronary arteries117 and118 is maintained during retrograde flow. In particular, after blood flows through thedistal region170 of theaortic valve120, blood is allowed to flow adjacent to the outside of the taperedcentral region150 of theaortic valve120 and into thecoronary arteries117 and118, i.e., through the open individual cells of thestent structure20.
• Further, if thebarbs33 are disposed at theproximal region30, thebarbs33 promote a secure engagement with theaortic sinus106. Similarly, thebarbs83 at thedistal region70 promote a secure engagement with the ascendingaorta105. In the event barbs are omitted, the proximal anddistal regions30 and70 may be configured so that the radial forces exerted upon thecoronary sinus105 and the ascendingaorta105, respectively, are enough to hold thestent structure20 in place.
• The shape, size, and dimensions of each of the members of theaortic prosthesis10 may vary. The size of a preferred prosthetic device is determined primarily by the diameter of the vessel lumen (preferably for a healthy valve/lumen combination) at the intended implant site, as well as the desired length of the overall stent and valve device. Thus, an initial assessment of the location of the natural aortic valve in the patient is determinative of several aspects of the prosthetic design. For example, the location of the natural aortic valve in the patient will determine the dimensions of thestent structure20 and theaortic valve120, the type of valve material selected, and the size of deployment vehicle.
• After implantation, theaortic valve120 replaces the function of the recipient's native damaged or poorly performing aortic valve. Theaortic valve120 allows blood flow when the pressure on the proximal side of theaortic valve120 is greater than pressure on the distal side of the valve. Thus, theartificial valve120 regulates the unidirectional flow of fluid from the heart into the aorta.
• Referring now toFIGS. 11-19, various reinforcement members are described that may be coupled to theaortic valve120 and/or thestent structure20 to enhance structural integrity and/or functionality of theaortic prosthesis10. The normal, native aortic valve is suspended from above through its attachment to the walls of the coronary sinus, and suspended aortic valves resist the forces created by diastolic pressure on closed leaflets through attachment to downstream support. The various reinforcement members ofFIGS. 11-19 are intended to reinforce theaortic valve120, and in particular, prevent in-folding or “prolapse” of the valve during diastole.
• InFIGS. 11-13, a first embodiment of reinforcement members comprises a plurality of suspension ties180a-180dthat are coupled between thetapered region150 of theaortic valve120 and the taperedregion50 of thestent structure20. In the phase of systole for theaortic valve120, blood may flow through the opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120, and the suspension ties180a-180dare relatively slack allowing for normal opening of theaortic valve120. In the phase of diastole for theaortic valve120, opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120 are generally adjacent to one another to inhibit blood flow back through the valve, while the suspension ties180a-180dbecome more taut and prevent prolapse of theaortic valve120 when retrograde flow is imposed upon the exterior surfaces of the valve, as depicted in the finite element analysis simulation ofFIG. 12. In effect, the suspension ties180a-180dadvantageously provide a safety mechanism by which prolapse is avoided during retrograde flow.
• In the example ofFIGS. 11-13, the suspension ties180a-180dmay be molded into theaortic valve120 in the manner that fiber reinforcements are molded into a graft structure, and further may be coupled to one or more struts of thestent structure20 usingsutures198 or another suitable coupling member that does not impede expansion of thestent structure20. While first ends of the suspension ties180a-180dare shown coupled to the taperedregion150 of theaortic valve120, they may alternatively, or additionally, be coupled to another location, such as thedistal region170. Similarly, while second ends of the suspension ties180a-180dare shown coupled to the taperedregion50 of thestent structure20, they may alternatively, or additionally, be coupled to another location, such as thedistal region70. While four exemplary suspension ties180a-180dare shown, greater or fewer suspension ties may be used, and their positioning may be varied as noted above, to achieve the desired functionality and reduce potential prolapse of theaortic valve120.
• The angles α₃of the suspension ties180a-180drelative to the longitudinal axis L, as shown inFIG. 13, may be between about 40-80 degrees when relatively slack. However, it will be appreciated the angles α₃may be greater or less than what is depicted inFIG. 13.
• In one example, the suspension ties180a-180dcomprise a thickness of between about 0.002-0.02 inches, and are molded into a Thoralon® or Dacron® coating. Other materials may be used, so long as the suspension ties180a-180dare non-thrombogenic, or coated with a non-thrombogenic material.
• Advantageously, in the case where the tapered ordistal regions150 and170 of theaortic valve120 are supported from above through attachment to thestent structure20 at a location in the ascending thoracic aorta, theaortic valve120 can therefore be as long as necessary for optimal valve function, even if it is of a simple bicuspid design. In other words, the length of theaortic valve120 can be varied such that thedistal region170 of theaortic valve120 is positioned at the desired location within the ascending thoracic aorta spaced-apart from the native aortic annulus.
• Referring now toFIGS. 14-19, alternative embodiments of reinforcement members are shown and described that comprise one or more reinforcement strips. InFIGS. 14-16, afirst reinforcement strip185agenerally extends between a portion of theproximal region130, through one opposingflat surface152 of the taperedregion150, and to one opposingflat surface172 of thedistal region170, as shown inFIGS. 14-16. Asecond reinforcement strip185bis disposed about 90 degrees apart from thefirst reinforcement strip185a,and generally extends between a portion of theproximal region130 towards one of the narrowerflat sides175a.Athird reinforcement strip185cis disposed about 90 degrees apart from thefirst reinforcement strip185a,and generally extends between a portion of theproximal region130, through one opposingflat surface154 of the taperedregion150, and to one opposingflat surface174 of thedistal region170. A fourth reinforcement strip is obscured inFIGS. 14-16 but may be disposed about 90 degrees apart from thesecond reinforcement strip185band is a mirror image thereof.
• In the phase of systole for theaortic valve120, shown inFIG. 15, blood may flow through the opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120, and the reinforcement strips185a-185care relatively flat allowing for normal opening of theaortic valve120. In the phase of diastole for theaortic valve120, shown inFIG. 16, opposingflat surfaces172 and174 at thedistal end170 of theaortic valve120 are generally adjacent to one another to inhibit blood flow back through the valve, while the reinforcement strips185a-185dmay become bowed radially inward along the taperedregion150 to prevent prolapse of theaortic valve120 when retrograde flow is imposed upon the exterior surfaces of the valve. In one example, the reinforcement strips185a-185cmay snap between the states depicted inFIGS. 15-16 during systole and diastole, respectively, when the associated pressures are imposed upon theaortic valve120. In effect, the reinforcement strips185a-185cadvantageously provide a safety mechanism by which prolapse is avoided during retrograde flow.
• In one example, the reinforcement strips185a-185cofFIGS. 14-16 comprise stainless steel or nitinol, though any suitable material to perform such functions may be used. The reinforcement strips may comprise a thickness of about 0.002 to about 0.010 inches and may be molded into the material of theaortic valve120, or coupled externally thereto.
• InFIGS. 17-19, various alternative reinforcement strips are depicted. InFIG. 17, at least oneelliptical reinforcement strip190 is coupled to a portion of theproximal region130 of theaortic valve120 and extends distally into the taperedregion150, positioned generally between the opposingflat surfaces152 and154 of the taperedregion150. InFIG. 18, a firstelliptical reinforcement strip191 is coupled entirely to theflat surface152 of the taperedregion150, while a secondlongitudinal reinforcement strip192 extends between theproximal region130 and taperedregion150 and is positioned generally between the opposingflat surfaces152 and154 of the taperedregion150. InFIG. 19, a diamond-shapedreinforcement strip193 is coupled between theproximal region130 and theflat surface152 of the taperedregion150. Like the reinforcement strips185a-185cofFIGS. 14-16, the reinforcement strips190-193 ofFIGS. 17-19 may snap between two states during systole and diastole. In each of the embodiments ofFIGS. 17-19, the reinforcement strips190-193 advantageously provide a safety mechanism by which prolapse is avoided during retrograde flow. While various exemplary reinforcement strip shapes and locations are shown inFIGS. 14-19, the shapes and locations of the reinforcement strips may be varied, and greater or fewer strips may be used, without departing from the spirit of the present embodiments.
• In still further embodiments, thestent structure20 shown herein may be used in connection with different aortic valves, beside theaortic valve120. Solely by way of example, and without limitation, various artificial valve designs may have two or three membranes, and may be arranged in various shapes including slots and flaps that mimic the natural functionality of an anatomical valve. Conversely, theaortic valve120 shown herein may be used in conjunction with different stent structures.
• While various embodiments of the invention have been described, the invention is not to be restricted except in light of the attached claims and their equivalents. Moreover, the advantages described herein are not necessarily the only advantages of the invention and it is not necessarily expected that every embodiment of the invention will achieve all of the advantages described.

Claims (20)

1. A medical device for implantation in a patient, the medical device comprising:

a stent comprising:

a proximal region comprising a cylindrical shape having a first outer diameter when the stent is in an expanded state;

a distal region comprising a cylindrical shape having a second outer diameter when the stent is in the expanded state, where the second outer diameter is greater than the first outer diameter;

a tapered region disposed between the proximal and distal regions, where the tapered region transitions the stent from the first diameter to the second diameter; and

a valve coupled to at least a portion of the stent, the valve having proximal and distal regions, where the proximal region of the valve is at least partially positioned within the proximal region of the stent and the distal region of the valve is at least partially positioned within one of the tapered and distal regions of the stent.

2. The medical device ofclaim 1 where, when implanted, the proximal region of the stent and the proximal region of the valve are aligned with a native valve, and the distal region of the valve is distally spaced-apart from the native valve.

3. The medical device ofclaim 1 further comprising a plurality of closed cells disposed around the perimeter of the proximal region of the stent, and another plurality of closed cells disposed around the perimeter of the distal region of the stent.

4. The medical device ofclaim 3 where the tapered region further comprises a plurality of closed cells, where an overall length of each of the closed cells of the tapered region is greater than an overall length of each of the closed cells of the proximal region of the stent and less than an overall length of each of the closed cells of the distal region of the sent when the stent is in the expanded state.

5. The medical device ofclaim 3 where the plurality of closed cells of the proximal region of the stent comprise a higher radial force relative to the plurality of closed cells of the distal region of the stent when the stent is in the expanded state.

6. The medical device ofclaim 3 where at least one of the closed cells of the distal region of the stent comprises four angled strut segments, and where two of the angled strut segments comprise a greater length relative to the other two angled strut segments within the closed cell.

7. The medical device ofclaim 1 where the proximal region of the valve comprises a cylindrical body, and the distal region of the valve has a generally rectangular shape comprising opposing flat surfaces that are separated by narrower flat sides, where the opposing flat surfaces at the distal end of the valve allow fluid flow therethrough during antegrade flow and are generally adjacent to one another to inhibit blood flow through the valve during retrograde flow.

8. The medical device ofclaim 1 where the proximal region of the stent comprises a plurality of proximal apices, where at least one of the proximal apices has an end region having an integral barb formed therein, where the plurality of closed cells of the proximal region are disposed distal to the plurality of proximal apices.

9. A medical device for implantation in a patient, the medical device comprising:

a stent having proximal and distal regions, and further comprising delivery and expanded states;

a plurality of closed cells disposed at various locations between the proximal and distal regions of the stent,

where each closed cell has an overall length, when the stent is in the expanded state, that is greater than a length of every other closed cell that is disposed proximally thereof; and

a valve coupled to at least the proximal region of the stent.

10. The medical device ofclaim 9, where the stent comprises at least three longitudinal regions in which a plurality of closed cells are disposed around a perimeter of the stent, where the first longitudinal region is disposed proximal to the second longitudinal region, and the second longitudinal region is disposed proximal to the third longitudinal region,

where an overall length of each of the closed cells of the first longitudinal region is less than an overall length of each of the closed cells of the second longitudinal region, and where the overall length of each of the closed cells of the second longitudinal region is less than an overall length of each of the closed cells of the third longitudinal region.

11. The medical device ofclaim 9 where a plurality of closed cells disposed around a perimeter of the proximal region of the stent comprise a higher radial force relative to a plurality of closed cells disposed around a perimeter of the distal region of the stent.

12. The medical device ofclaim 9 where at least one of the closed cells comprises four angled strut segments, and where two of the angled strut segments comprise a greater length relative to the other two angled strut segments within the closed cell.

13. The medical device ofclaim 9 where at least one of the closed cells comprises four angled strut segments, and where two of the angled strut segments comprise a first width, which is greater than a second width of the other two angled strut segments within the closed cell.

14. The medical device ofclaim 9 where the proximal region of the stent comprises a cylindrical shape having a first outer diameter when the stent is in the expanded state, and where the distal region of the stent comprises a cylindrical shape having a second outer diameter when the stent is in the expanded state, where the second outer diameter is greater than the first outer diameter, the stent further comprising:

a tapered region disposed between the proximal and distal regions, where the tapered region transitions the stent from the first outer diameter to the second outer diameter.

15. A medical device for implantation in a patient, the medical device comprising:

a stent comprising:

a proximal region comprising a cylindrical shape having a first outer diameter when the stent is in an expanded state;

a distal region comprising a cylindrical shape having a second outer diameter when the stent is in the expanded state, where the second outer diameter is greater than the first outer diameter;

a tapered region disposed between the proximal and distal regions, where the tapered region transitions the stent from the first diameter to the second diameter; and

a valve having proximal and distal regions, where the proximal region of the valve is positioned at least partially within the proximal region of the stent, and where at least a portion of the valve is mechanically coupled to one of the tapered and distal regions of the stent.

16. The medical device ofclaim 15 where an overall length of each of a plurality of closed cells of the proximal region of the stent is less than an overall length of each of a plurality of closed cells of the distal region of the stent when the stent is in the expanded state.

17. The medical device ofclaim 16 where the tapered region of the stent further comprises plurality of closed cells, where an overall length of each of the closed cells of the tapered region is greater than the overall length of each of the closed cells of the proximal region of the stent and less than an overall length of each of the closed cells of the distal region of the stent.

18. The medical device ofclaim 16 where at least one of the closed cells of the proximal region of the stent comprises four angled strut segments, and where two of the angled strut segments comprise a greater length relative to the other two angled strut segments within the closed cell.

19. The medical device ofclaim 16 where at least one of the closed cells of the proximal region of the stent comprises four angled strut segments, where two of the angled strut segments comprise a first width, which is greater than a second width of the other two angled strut segments within the closed cell.

20. The medical device ofclaim 15 where the proximal region of the stent comprises a plurality of proximal apices, where at least one of the proximal apices has an end region having an integral barb formed therein, where the plurality of closed cells of the proximal region of the stent are disposed distal to the plurality of proximal apices.

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