The present embodiments relate generally to apparatus and methods for treating medical conditions, and more specifically, to stents and stent-grafts for use in body vessels to treat those medical conditions.
Stents may be inserted into an anatomical vessel or duct for various purposes. Stents may maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Other stents may be used for different procedures, for example, stents placed in or about a graft have been used to hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be either self-expanding or balloon-expandable, or they can have characteristics of both types of stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires and/or releasing diameter reducing ties. With self-expanding stents, the stents expand primarily based on their own expansive force without the need for further mechanical expansion. In a stent made of a shape-memory alloy such as nitinol, the shape-memory alloy may be employed to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its predeployment configuration.
When a stent-graft having at least one stent is deployed in a vessel, such as the aorta, and blood flows in a proximal to distal direction away from the heart, there is a possibility of “infolding” of graft material, particularly at the proximal end of the graft material. For example, if a stent-graft is deployed to treat an abdominal aortic aneurysm, blood flowing distally into the graft may pull the proximal edge of the graft in a radially inward direction, particularly if an optimal proximal seal is not achieved with the vessel wall. In this case, the graft material that becomes pulled inward may impede blood flow through the stent-graft lumen, or an endoleak may occur. Furthermore, if the proximal end of a stent-graft is deployed in a curved portion of a vessel, such as the aortic arch or thoracic aorta, it may be difficult to conform the proximal edge of the stent-graft to the curving vessel wall, which also may result in blood flow catching on the graft and potential endoleaks.
The present embodiments provide stents and stent-grafts for use in medical procedures.
In one embodiment, a stent may comprise a proximal segment comprising a zig-zag portion, which comprises a plurality of proximal and distal apices separated by a plurality of angled strut segments. The zig-zag portion may extend circumferentially around a full perimeter of the stent. A distal segment may comprise a connection strut, where the connection strut comprises a bent segment extending between adjacent distal apices of the zig-zag portion. The stent may comprise at least one diamond-shaped closed cell, which is bounded proximally by first and second angled strut segments of the zig-zag portion meeting at a first proximal apex of the zig-zag portion, and further bounded distally by the connection strut having the bent segment. At least one distal open region may be located distally beneath a second proximal apex of the zig-zag portion that is adjacent to the first proximal apex of the zig-zag portion.
In one example, in an expanded state, the at least one diamond-shaped closed cell may comprise an asymmetric shape, such that the first and second angled strut segments are different than a mirror image of the connection strut. In one embodiment, in an expanded state, a first axial length spanned between the proximal and distal apices of the zig-zag portion may be greater than a second axial length spanned by the connection strut when measured along a longitudinal axis of the stent.
In one example, at least one of the plurality of angled strut segments of the zig-zag portion may comprise a first thickness, which may be greater than a second thickness of the connection strut. Third and fourth angled strut segments of the zig-zag portion, which extend directly from the second proximal apex, may comprise thicknesses greater than the connection strut.
In one embodiment, the first and second angled strut segments associated with the diamond-shaped cells may be orientated at a first angle relative to a longitudinal axis of the stent in an expanded state, and third and fourth angled strut segments extending from the second proximal apex may be orientated at a second angle relative to the longitudinal axis of the stent in the expanded state. The first angle may be less than the second angle. The first angle may be between about 5 degrees and about 45 degrees, and the second angle may be between about 20 degrees and about 90 degrees.
In some embodiments, the connection strut may comprise one of a V-shape or a U-shape. In various embodiments, the stent may comprise alternating proximal apices having different features, where a first proximal apex comprises a bore sized to receive an imaging element, and a second proximal apex comprises at least one barb. In some embodiments, the stent may comprise at least one distal apex adapted to be coupled to a graft, the at least one distal apex comprising a suture bore, an imaging bore, and a barb.
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.
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.
In the present application, the term “proximal end” is used when referring to that end of a medical device closest to the heart after placement in the human body of the patient, and may also be referred to as the inflow end (the end that receives fluid first), and the term “distal end” is used when referring to that end opposite the proximal end, or the one farther from the heart after its placement, and may also be referred to as the outflow end (that end from which fluid exits).
Referring to
The stent 20 has a reduced diameter delivery state so that it may be advanced to a target location within a vessel or duct. The stent 20 also has an expanded deployed state to apply a radially outward force upon at least a portion of a vessel or duct, e.g., to maintain patency within a passageway, or to hold open the lumen of a graft. In the expanded state, fluid flow is allowed through a central lumen of the stent 20.
The stent 20 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 the stent 20 comprises a self-expanding material such as nitinol, the stent may be heat-set into the desired expanded state, whereby the stent 20 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, the stent 20 may be made from other metals and alloys that allow the stent 20 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, the stent 20 may comprise other materials such as stainless steel, cobalt-chrome alloys, amorphous metals, tantalum, platinum, gold and titanium. The stent 20 also may be made from non-metallic materials, such as thermoplastics and other polymers.
The stent 20 may be used alone or may be coupled to a graft, such as the graft 90 of
The proximal end 22 of the stent 20 may comprise multiple adjacent proximal apices 22a and 22b, while the distal end 24 of the stent 20 may comprise distal apices 82a separated by distal open regions 82b, as shown in
One or more pairs of adjacent, proximal apices 22a and 22b may comprise different features. For example, a first proximal apex 22a may comprise an end region 30 having a bore 31 formed therein, where the bore 31 is configured to receive an imaging element. A second, adjacent proximal apex 22b comprises an end region 40 having an integral barb 42 formed therein, as best seen in
The barbs 42 may be formed by laser cutting a desired barb shape into the end regions 40. A slit 41 therefore is formed into each end region 40 after the desired barb shape is formed, as best seen in
The stent 20 further generally comprises a proximal segment 50 and a distal segment 60, which are separated by a dividing line 59, as best seen in
Expansion of the stent 20 is at least partly provided by the angled strut segments 57, which may be substantially parallel to one another in a compressed state (not shown), but tend to bow outward away from one another in the expanded state shown in
The angled strut segments 57 meet with one another distally to form distal transition regions 58a and 58b, which are generally located at the dividing line 59, as best seen in
The distal segment 60, which is disposed distal to the dividing line 59, comprises at least one connection strut 62. In one embodiment, the connection strut 62 comprises a generally bent shape, and may comprise a V-shape, a U-shape, or the like, as depicted in
The first generally straight segment 63 of the connection strut 62 connects with one of the distal apices 54 of the zig-zag portion 52 at a first distal transition region 58a, as best seen in
In this manner, a plurality of diamond-shaped cells 70 are formed along the stent 20. Specifically, the diamond-shaped cells 70 are bounded on their four sides by first and second angled strut segments 57a and 57b of the zig-zag portion 52, together with the first and second generally straight segments 63 and 64 of the connection strut 62.
The upper vertex of each diamond-shaped cell 70 is located at a proximal apex 53 of the zig-zag portion 52 at alternating apices 22a of the broader stent 20. The lower vertex of each diamond-shaped cell 70 is located at the bent segment 65 of the connection strut 62, which is at distal apices 82a of the broader stent 20.
Notably, distal open regions 82b of the stent 20 are formed along the circumferential regions of the stent 20 coinciding with the alternating proximal apices 22b, which do not form diamond-shaped cells 70. Although third and fourth angled strut segments 57c and 57d extend from the second proximal apices 22b, the omission of the connection struts 62 in the areas beneath the second proximal apices 22b yields the distal open regions 82b, as shown in
In accordance with one aspect, the first and second angled strut segments 57a and 57b coinciding with the plurality of diamond-shaped cells 70 may comprise a first angle α1 relative to the longitudinal axis L of the stent 20, as shown in
In one example, the first angle α1 is between about 5 degrees and about 45 degrees when measured in the manner shown in
Advantageously, this variable angular orientation of the first and second angled strut segments 57a-57d yields a balanced behavior of the stent 20 overall, particularly when in the expanded state. Specifically, the distal open regions 82b of the zig-zag portion 52 (aligning with proximal apices 22b) would ordinarily be weaker in radial strength, while the closed design of the diamond-shaped cells 70 would ordinarily be stronger in radial strength, all other factors being considered equal. By providing a greater second angle α2 in the open areas of otherwise weaker radial strength, and a smaller first angle α1 in the closed areas of otherwise greater radial strength, a more balanced radial force behavior is achieved around the perimeter of the stent 20.
In accordance with another aspect, the thickness of struts of the stent 20 may vary in specific regions. In particular, some or all of the angled strut segments 57a-57d of the zig-zag portion 52 may comprise a first thickness t1, while one or all of the segments 63-65 along the length of the connection strut 62 may comprise a second thickness t2, when measured as shown in
Advantageously, the differing thicknesses t1 and t2 facilitate a balanced behavior of the stent 20 overall, particularly when in the expanded state. Specifically, the distal open regions 82b (aligning with proximal apices 22b) would ordinarily be weaker in radial strength, while the closed design of the diamond-shaped cells 70 would ordinarily be stronger in radial strength, all other factors being considered equal. By providing a greater thickness t1 in selected areas of otherwise weaker radial strength, and a smaller thickness t2 in selected areas of otherwise greater radial strength, a more balanced radial force behavior is achieved around the perimeter of the stent 20.
Notably, in this example, the angled strut segments 57c and 57d outside of the plurality of diamond-shaped cells 70 comprise the first thickness t1, while the angled strut segments 57a and 57b coinciding with the plurality of diamond-shaped cells 70 may comprise either the first thickness t1, the second thickness t2, or a third thickness that is different. Moreover, it is contemplated that the thickness may vary along the connection strut 62 itself, although it will be advantageous that at least a portion of the connection strut 62 comprises one or more areas of reduced thickness t2 relative to the first thickness t1.
As a related advantage, the areas with smaller thickness t2 take up less space in a compressed state, enabling a reduced overall delivery profile of the stent 20.
In accordance with yet another aspect, an axial length L1 spanned by the proximal segment 50 is greater than an axial length L2 spanned by the distal segment 60, when measured along the longitudinal axis L of the stent and with respect to the dividing line 59, as shown in
In contrast, it can be seen that the asymmetric design of the present embodiments shown in
As noted above, the stent 20 may be used alone, or may be coupled to the graft 90 as shown in
As one exemplary advantage, the stent 20 provides enhanced radial support to hold the proximal edge 94 of the graft 90 in an open configuration with a reduced risk of infolding, particularly due to an increased number of struts at or adjacent to the proximal edge 94. In the example of
As a further advantage, in the embodiment of
Therefore, the stent 20 may be suitable for a wider population, including those with smaller “landing zones” of healthy tissue, e.g., just beyond an aneurysm and prior to a branch vessel. It is expected that the required “landing zone” will be reduced by at least 50% when using the stent 20 at the proximal edge 94 of the graft 90, when compared to using separate sealing and attachment stents. Moreover, a stent-graft incorporating the stent 20 is expected to tolerate a more tortuous anatomy due to the reduced length using a single stent near the proximal edge 94, as compared to using separate sealing and attachment stents. As a related advantage, the reduced axial lengths of the connection struts 62, as part of the axially asymmetric diamond-shaped cells 70, help reduce the overall length of the stent 20.
Notably, an all diamond configuration of the stent 20 is not preferred in a tortuous anatomy or in a highly angulated vessel due to the lack of flexibility (and increased profile) of diamonds at every cell. The design of stent 20 is considerably more flexible than the all diamond configuration as the zig-zag portions 52 provide more flexible regions.
As depicted further in
Referring now to
Referring now to
In this example, alternating proximal apices 222a comprise end regions 230 having trigger wire bore 239. In this embodiment, the stent 220 may be delivered to a target site in a compressed state using a plurality of trigger wires, where a single trigger wire may be looped through a bore 239 of each first proximal apex 222a to restrain the stent 20 during delivery. In this embodiment, trigger wires are not coupled to the second proximal apices 22b, which comprise the barbs 42. By restraining selected ones of the proximal apices, such as each first proximal apex 222a, the adjacent second proximal apices 22b also may be indirectly pulled in a radially inward direction during delivery. The configuration of the stent 220 facilitates the indirect compression of the adjacent second proximal apices 22b. Advantageously, since only selected ones of the proximal apices are restrained during delivery, the number of trigger wires may be reduced.
Referring still to
The imaging bore 293 of the leg region 290 may be disposed between the suture bore 292 and the barb 294, as seen in
As will be appreciated, further alternative embodiments may comprise various combinations of suture holes for graft couplings, marker bores for imaging elements, trigger wire holes for receiving trigger wires, and barbs. Moreover, such components may be associated with either proximal and/or distal apices of the stents 20, 120 and 220 in a manner tailored for needs of a given procedure. In some embodiments, e.g., where the stent entirely overlaps with graft material, barbs may be omitted entirely.
Although the present embodiments have generally been described as having the zig-zag portion 52 being closer to the “proximal region” of the stent 20, and the connection strut 62 being closer to the “distal region,” this is for references purposes only to facilitate relative discussion of parts. The stent 20 may be placed in a bodily passageway such that the zig-zag portion 52 is at the inflow end while the connection strut 62 is at the outflow end (as generally explained in the exemplary embodiments herein), or may be disposed vice-versa such that the connection strut 62 is at the inflow end while the zig-zag portion is at an outflow end.
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.
This invention claims the benefit of priority of U.S. Provisional Application Ser. No. 62/808,608, entitled “Hybrid Stent Designs,” filed Feb. 21, 2019, the disclosure of which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
62808608 | Feb 2019 | US |