US 20080208318 A1
Blood vessels and other body lumens are stented using stent structures comprising a plurality of radially expansible rings where at least some of the rings comprise axially extending elements which interleave with axially extending elements on adjacent unconnected rings. The ring structures may be open cell structures or closed cell structures, and the axially extending elements will typically be formed as part of the open cell or closed cell structure.
1. A tubular prosthesis comprising:
a plurality of tubular rings radially expandable from a contracted configuration to an expanded configuration, each ring comprising a plurality of struts interconnected so as to form a circumferential series of closed cells,
wherein a pair of adjacent tubular rings each have an axially oriented curved end strut and wherein the pair of adjacent tubular rings are axially coupled together at a location by the merging of the apices of the axially oriented curved end struts.
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This application is a continuation of U.S. application Ser. No. 10/738,666 (Attorney Docket No. 021629-000510US) filed Dec. 16, 2003, which claims the priority benefit of U.S. Provisional Patent Application No. 60/440,839 (Attorney Docket No. 21629-000500US), filed Jan. 17, 2003, the full disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to apparatus and methods for delivering a plurality of separate luminal prostheses within a body lumen, such as a blood vessel.
Coronary artery disease is the leading cause of death and morbidity in the United States and Western society. In particular, atherosclerosis in the coronary arteries can cause myocardial infarction, commonly referred to as a heart attack, which can be immediately fatal or, even if survived, can cause damage to the heart which can incapacitate the patient.
While coronary artery bypass surgery can be an effective treatment for stenosed arteries resulting from atherosclerosis or other causes, it is a highly invasive procedure which is also expensive and which requires substantial hospital and recovery time. Percutaneous transluminal angioplasty, commonly referred to as balloon angioplasty, is less invasive, less traumatic, and significantly less expensive than bypass surgery. Heretofore, however, balloon angioplasty has not been considered as effective a treatment as bypass surgery. The effectiveness of balloon angioplasty, however, has improved significantly with the introduction of stenting, which involves the placement of a scaffold structure within an artery that has been treated by balloon angioplasty. The stent inhibits abrupt reclosure of the artery and has some benefit in inhibiting subsequent restenosis resulting from hyperplasia.
Presently available stents may be generally categorized as either “closed cell configurations” or “open cell configurations.” Closed cell configurations are characterized by ellipses, ovals, and polygonal structures, such as closed boxes, rhomboids, diamonds, and the like, which open in the circumferential direction and shorten in the axial direction as the stent is expanded. Open cell configurations include zigzag and serpentine structures which may be formed as a plurality of discreet rings or may be formed from a single continuous wire or other element. Closed cell stents are advantageous in that they provide better coverage of the blood vessel wall when the stent is deployed. This is particularly advantageous in tightly curved segments of the vasculature where even stent coverage in both the axial and circumferential directions on the outer wall of the vessel has been shown to reduce restenosis. Such even coverage is also an advantage in achieving uniform delivery from drug eluting stents. In contrast, open cell stent configurations are generally more flexible than the closed cell configurations. Such flexibility is advantageous in the tortuous regions of the vasculature where enhanced flexibility can provide better conformance to the vessel being treated. Better conformance can reduce the stress on the vessel wall, particularly at the stent ends, and lead to reduced restenosis.
For these reasons, it would be desirable to provide improved stents and stent structures. In particular, it would be desirable to provide stents and stent structures which combine the improved wall coverage of closed cell stent structures with the increased flexibility of open cell stent structures. It would be still further desirable if such improved stent structures allowed a physician to optimize the length of vessel being treated in accordance with the nature of the disease, allowed for the delivery of both very short and very long stent structures, and optionally permited delivery of stent structures at multiple contiguous and/or non-contiguous locations within a body lumen. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 6,200,337 and 5,870,381 describe stents having closed cell rings with overlapping portions connected by axial connecting members. U.S. Pat. No. 6,375,676 describes a stent having open cell rings with overlapping portions connected by axial connecting members. U.S. Patent Application Publication Nos. 2002/0188343 and 2002/0188347 describe expandable stents having interconnecting elements which interlock circumferentially adjacent bridges between axially adjacent stent segments. U.S. Pat. No. 4,580,568 describes the sequential placement of a plurality of zigzag ring stents where the stents may optionally be overlapped (
The present invention provides methods and apparatus for prosthesis placement, such as stenting of body lumens, typically blood vessels, and more typically coronary arteries. The methods and systems will also find significant use in the peripheral vasculature, the cerebral vasculature, and in other ducts, such as the biliary duct, the fallopian tubes, and the like. The terms “stent” and “stenting” are defined to include any of the wide variety of expandable prostheses and scaffolds which are designed to be intraluminally introduced to a treatment site and expanded in situ to apply a radially outward force against the inner wall of the body lumen at that site. The stents and prostheses of the present invention commonly comprise a closed or, less preferably, an open lattice structure, and are typically formed from a malleable or elastic metal. When formed from a malleable metal, such as stainless steel, gold, platinum, titanium, and super alloys, the stents will typically be expanded by a balloon which causes plastic deformation of the lattice so that it remains opened after deployment. When formed from an elastic metal, including super elastic metals such as nickel-titanium alloys, the lattice structures will usually be radially constrained when delivered and deployed by releasing the structures from such radial constraint so that they “self-expand” at the target site. When the stent or lattice structures are covered with a fabric or polymeric membrane covering, they are commonly referred to as grafts. Grafts may be used for the treatment of aneurysms or other conditions which require placement of a non-permeable or semi-permeable barrier at the treatment site. The terms “stent” and “stent structures” refer broadly to all radially expansible stents, grafts, and other scaffold-like structures which are intended for deployment within body lumens.
The stents and stent structures of the present invention may have any of a variety of common constructions, including closed cell constructions such as expansible ovals, ellipses, box structures, expandable diamond structures, expandable rhomboid structures, as well as other regular and irregular polygonal structures, etc. In addition, the closed cells may have complex slotted geometries, such as H-shaped slots, I-shaped slots, J-shaped slots, etc. Suitable open cell structures include zigzag structures, serpentine structures, and the like. Such conventional stent structures are well described in the patent and medical literature. Specific examples of suitable stent structures are described in the following U.S. Patents, the full disclosures of which are incorporated herein by reference: U.S. Pat. Nos. 6,315,794; 5,980,552; 5,836,964; 5,527,354; 5,421,955; 4,886,062; and 4,776,337. Preferred structures are described herein with reference to
According to one aspect of the present invention, stents will comprise a plurality of independent expansible rings each having a length of 1 mm or greater, usually 2 mm or greater, and sometimes of 3 mm or greater, usually being in the range from 1 mm to 10 mm, typically from 2 mm to 7 mm, more typically from 2 mm to 5 mm. The use of such short ring lengths is advantageous since the overall stent length will be a multiple of the ring length.
The methods and apparatus of the present invention will provide for the deployment of a plurality of stents or other prostheses from a common stent delivery catheter. Usually, the number of delivered stents will be in the range from 2 to 50, typically from 3 to 30, and most typically from 3 to 25. As more stents are placed on the delivery catheter, the individual stent length will often be somewhat less, although this is not necessarily the case in all instances. The multiple prostheses may be deployed individually or in groups of two or more at a single location or at multiple spaced-apart locations in the body lumen or lumens.
In another aspect of the present invention, stent structures will comprise a plurality of radially expansible rings, as generally described above, arranged along an axial line. Expansible rings are arranged adjacent to each other and will include axially extending elements which interleave or nest with similarly axially extending elements on adjacent rings. By “interleaved” it is meant that the axially extending elements on adjacent rings will interpenetrate with each other in an axial direction, at least prior to stent expansion and preferably even after stent expansion. Usually, the interpenetrating elements will not overlap, i.e., be positioned one over another in the radial direction, but it is possible that in some implementations there may be some overlapping prior to or even after expansion. The axial interpenetration will be at least 0.1 mm, usually being at least 1 mm, and often being in the range from 1 mm to 5 mm, and will of course depend on the axial length(s) of the adjacent ring(s). Expressed as a percentage, the axial length of the axially extending elements will usually be at least 5% of the axial length of the ring, usually being from 5% to 50%, and preferably being from 20% to 30%.
Preferably, the axially extending elements on adjacent rings will interleave without interlocking so as to permit axial separation between the adjacent rings prior to expansion of the rings. However, axially extending elements may, in some instances, also interpenetrate in a peripheral direction prior to expansion. Such peripheral interpenetration can provide axial interlocking of the axially adjacent expansible rings prior to expansion. It will usually be desirable or even necessary that the peripheral interpenetration be relieved during radial expansion of the stent structures so that the independent rings be released from each other when deployed. In other instances, however, a tether or other types of links may be provided to interconnect or otherwise restrain the rings even after expansion and deployment.
It is not necessary that all adjacent rings be unconnected, although at least two, and preferably three, four, five, eight, ten, or more adjacent rings will be unconnected. Thus, some (but fewer than all) of the adjacent rings of the stent structures may have ties or links therebetween, including flexible or non-flexible (deflectable) ties or links. The axially adjacent rings, however, will usually not be connected, although in some cases they may have easily separable or non-permanent connections as described in more detail below. Each expansible ring will preferably comprise expansible closed cell structures, as set forth above. Less preferably, the expansible rings may comprise expansible open cell structures, as set forth above. The lengths and diameters of the individual rings have been set forth generally above. The stent structure will typically comprise from 2 to 50 individual rings, usually from 3 to 30 individual rings, and often from 3 to 25 individual rings.
The spacing between adjacent rings may be uniform or non-uniform, preferably being uniform. In some cases, it is desirable that the edges of the adjacent rings be spaced-apart by a uniform distance in the axial direction, typically at least 0.1 mm, usually being from 0.1 mm to 0.5 mm, prior to stent expansion. In other situations, it will be preferred that the adjacent rings be in contact with each other at discreet points or along continuous sections of the edges. In some cases, the stent structures will be configured to shorten upon expansion to increase the spacing between rings. It is usually preferable that the edges of the adjacent rings not overlap, at least prior to deployment. Deployment of the stents, particularly in curved and tortuous luminal regions, may sometimes result in touching and overlapping of the stent rings.
The stent structures may be modified in a variety of ways which are used with other conventional stents. For example, some or all of the radially expansible rings may releasably carry a biologically active agent, such as an agent which inhibits hyperplasia. Exemplary anti-hyperplasia agents include anti-neoplastic drugs, such as paclitaxel, methotrexate, and batimastal; antibiotics such as doxycycline, tetracycline, rapamycin, everolimus and other analogs and derivatives of rapamycin, and actinomycin; amino suppressants such as dexamethasone and methyl prednisolone; nitric oxide sources such as nitroprussides; estrogen; estradiols; and the like.
In another aspect of the present invention, a stent deployment system comprises an elongate carrier having a central axis and including a plurality of radially expansible rings arranged over a surface thereof. At least some of the radially expansible rings will have the features and characteristics just described with respect to the present invention. The elongate carriers of the stent deployment systems will typically comprise a radially expansible balloon having an outer surface where the radially expansible rings are disposed over the outer surface of the balloon. In such cases, the balloon may comprise a single inflation chamber in which case all of the rings will be expanded simultaneously. Alternatively, the balloon may comprise a plurality of independently inflatable chambers so that individual expansible rings may be deployed separately from the other rings.
The elongated carrier of the stent deployment system may alternatively comprise a carrier tube having an inner surface which carries and constrains the radially expansible rings. In such cases, the expansible rings will usually be self-expanding, i.e., held in a radially constrained configuration by the carrier tube prior to release and expansion at a luminal target site. Usually, the carrier tube structures will further comprise a pusher tube arranged to axially advance the radially expansible rings from the carrier tube. The elongated carrier may still further comprise a balloon arranged to receive and expand individual rings as they advance from the carrier tube, in which case the carrier may be used for delivering the formable (balloon-expansible) stent structures. However, such a balloon may also be used with self-expanding stent structures to control or enhance expansion, to perform predilatation of a lesion prior to stent deployment, or to further expand the stent structures and dilate the vessel lumen after the structures have self-expanded.
In a further aspect of the present invention, multiple independent stent rings are arranged on a carrier by the following methods. An elongated carrier structure is provided and a plurality of radially expansible rings comprising axially extending elements are mounted on the carrier structure such that the axially extending elements on adjacent rings interleave or nest after they are mounted. The number of rings mounted on the carrier is selected to provide a desired overall stent length, and the number of rings is typically in the ranges set forth above, providing overall stent lengths in the range from 6 mm to 120 mm, usually from 9 mm to 100 mm, and typically from 12 mm to 50 mm. Other aspects of the individual radially expansible rings have been described above.
In yet another aspect of the present invention, methods for stenting a body lumen comprise delivering to the body lumen a stent structure having a plurality of radially expansible rings. The rings are as described above with respect to other aspects of the present invention, and at least some of the rings are expanded within the body lumen so that the axially extending elements open and axially move apart from each other as they radially expand. Preferably, the length of the axially extending elements and degree of radial expansion will be selected so that the elements remain interleaved even after being fully expanded within the body lumen. Such an interleaving structure enhances the continuity of lumenal wall coverage provided by the deployed stent structure. Target body lumens are typically blood vessels, more typically arteries, such as coronary arteries. The rings may be delivered simultaneously, typically using a single inflatable balloon, or sequentially, typically using a carrier tube, pusher tube and optionally deployment balloon. Methods may be used for delivering from 3 to 50 rings, usually from 3 to 30 rings, and typically from 3 to 25 rings, to cover a luminal length in the range from 6 mm to 120 mm, usually from 9 mm to 100 mm, and typically from 12 mm to 50 mm.
FIGS. 17A-I7C illustrate deployment of a closed cell stent structure according to the present invention with both a balloon having a single chamber (
The present invention provides apparatus, systems, and methods for preparing and delivering stent structures comprising a plurality of “separate” or “discreet” radially expansible ring segments. By “separate” or “discreet,” it is meant that the ring segments are unconnected (or easily disconnected) at the time they are delivered to a target body lumen. Usually, the ring segments will be closely packed to provide a relatively high degree of vessel wall coverage after they are expanded. By disconnecting the adjacent segments, however, such a tightly packed structure can retain a very high degree of flexibility permitting delivery and conformance in even highly torturous regions of the vasculature and other body lumens.
The ability to closely pack the expansible ring segments and achieve a high degree of vessel wall coverage is achieved at least partly because at least some of the axially adjacent rings comprise axially extending elements which interleave or nest with axially extending elements on an adjacent connected ring. Usually, the axially extending elements will be formed from a radially expansible portion of the ring, e.g., the element will be part of the closed cell structure or open cell structure as described in more detail hereinbelow. As these expansible sections will typically foreshorten as they are radially expanded, interleaving and nesting the segments on adjacent rings prior to expansion minimizes or preferably eliminates any gaps in coverage after the stent is expanded, as described in more detail below.
The stent structures of the present invention may be fabricated as either balloon-expansible or self-expanding stents according to methods well known in the art. Typical deformable materials suitable for fabricating balloon-expansible stent structures include 316L stainless steel, gold, platinum, cobalt chrome, platinum, and the like. Suitable resilient materials for self-expanding stents include nickel titanium alloys, various spring stainless steel alloys, Eligloy® alloy, and the like. It will also be possible to form the stent structures of the present invention from both natural and synthetic polymers. Natural polymers include collagen, gelatin, chitin, cellulose, and the like. Suitable synthetic polymers include polyglycolic acids (PGA), polylactic acids (PLA), poly ethylene glycols (PEG), polyamides, polyimides, polyesters, and the like. In some instances, it would be possible to form different radially expansible segments from different materials in order to achieve different properties.
The stent structures will comprise a plurality of the individual radially expansible ring segments with typical dimensions, numbers, and the like, described above in the summary. The plurality of ring segments will be arranged prior to delivery, in a manner suitable for delivery to and deployment within a target blood vessel or other body lumen. Usually, the plurality of radially expansible rings will be arranged along an axial line, typically defined by a deployment balloon, a delivery tube, or some combination thereof. The expansible ring segments will be arranged so that the axially extending elements on each of the segments is interleaved with corresponding axial extending elements on adjacent but unconnected ring segments. Referring now to
Of particular importance to the present invention,
The advantages of the present invention are particularly apparent in curved blood vessels BV, as illustrated in
A similar result can be achieved with a stent structure 20 comprising a plurality of open cell zigzag ring structures 22, shown in
Referring now to
Axial separation of the rings 32 of stent structure 30 can be inhibited by modifying the ring geometries in a variety of ways, such as shown in
Referring now to
Referring now to
Stent structures comprising multiple rings 50 are shown in their unexpanded and expanded configuration in
Ring structure 60 of
Ring structure 70 in
Ring structure 80 of
As illustrated thus far, the stent structures have generally maximized to vessel wall coverage achieved after expansion. While this will often be desired, in some instances it may be desired to lessen the amount of wall coverage. The stent structures shown in
Stent structure 96 (
Stent structures according to the present invention may be delivered in a variety of ways. As illustrated in
Referring now to
Referring now to
Referring now to
A further alternative stent structure according to the invention is illustrated in
Stent segment 201 is configured to interleave with an adjacent stent segment of similar construction. Upper and lower axial struts 206A, 206B and outer ends 208 form axial elements E that are received in the spaces S between each element E of the adjacent stent segment 201.
In a preferred embodiment, a spacing member 212 extends outwardly in the axial direction from a selected number of outer circumferential struts 209 and/or connecting struts 213. Spacing member 212 preferably itself forms a subcell 214 in its interior, but alternatively may be solid without any cell or opening therein. For those spacing members 212 attached to outer circumferential struts 209, subcell 214 preferably communicates with I-shaped cell 205. Spacing members 212 are configured to engage the curved outer ends 208 of an adjacent stent segment 201 so as to maintain appropriate spacing between adjacent stent segments. In one embodiment, spacing members 212 have outer ends 216 with two spaced-apart protrusions 218 that provide a cradle-like structure to index and stabilize the curved outer end 208 of the adjacent stent segment. Preferably, spacing members 212 have an axial length of at least about 10%, more preferably at least about 25%, of the long dimension L of I-shaped cells 205, so that the I-shaped cells 205 of adjacent stent segments are spaced apart at least that distance. This results in elements E interleaving a distance of at least about 10%, preferably at least about 25%, and more preferably at least about 50% of their axial length as measured from the circumferential connecting struts 213. Because spacing members 212 experience little or no axial shortening during expansion of stent segments 201, this minimum spacing between stent segments is maintained both in the unexpanded and expanded configurations.
As an additional feature, circumferential slots 204 provide a pathway through which vessel side branches can be accessed for catheter interventions. Should stent segment 201 be deployed at a location in which it covers the ostium of a side branch to which access is desired, a balloon dilatation catheter may be positioned through circumferential slot 204 and expanded. This deforms circumferential struts 209, 211 axially outward, thereby expanding circumferential slot 204 and further expanding upper and lower slots 207, as shown in phantom in
One of the differences between the embodiment of
In a preferred embodiment, stent segments 201′ retain some degree of interleaving in the expanded configuration, with outer ends 234 of elements E on adjacent stent segments being at least circumferentially aligned with each other, and preferably extending into spaces S of the adjacent stent segment a distance of at least about 1%, more preferably at least about 5%, and in some cases at least about 10% of the axial length of elements E as measured from circumferential connecting struts 242. In one exemplary embodiment, for a stent segment 201′ having an axial length of 4 mm and an unexpanded diameter of about 0.5-1.5 mm, elements E have an axial length of about 1 mm and are interleaved a distance Du of about 0.1-0.5 mm in the unexpanded configuration. Segments 201′ are expandable to a diameter of 2.5-3.5 mm and elements E are interleaved a distance De of about 0.01-0.1 mm in the expanded configuration.
It should also be noted that the embodiment of
As shown in
The stent structures of the invention are preferably radiopaque so as to be visible by means of fluoroscopy. Radiopaque markers and/or materials may be used in or on the stent structures. Markers of radiopaque materials may be applied to the exterior of the stents, e.g, by applying a metal such as gold, platinum, a radiopaque polymer, or other suitable coating or mark on all or a portion of the stents. Alternatively, the stent structures may include a radiopaque cladding or coating or may be composed of radiopaque materials such as MP35N (ASTM 562), L-605 cobalt chromium (ASTM F90), other suitable alloys containing radiopaque elements, or multilayered materials having radiopaque layers. As a further option, the stent structures may have a geometry conducive to fluoroscopic visualization, such as having struts of greater thickness, sections of higher density, or overlapping struts. Some of the possible materials that may be used in the stent segments, either alone or in combination, include (by ASTM number):
The preferred embodiments of the invention are described above in detail for the purpose of setting forth a complete disclosure and for the sake of explanation and clarity. Those skilled in the art will envision other modifications within the scope and sprit of the present disclosure.