GB2516928A

GB2516928A - Prosthesis Device

Info

Publication number: GB2516928A
Application number: GB201314123A
Authority: GB
Inventors: David Stevenson
Original assignee: Vascutek Ltd
Current assignee: Vascutek Ltd
Priority date: 2013-08-07
Filing date: 2013-08-07
Publication date: 2015-02-11
Also published as: GB201314123D0

Abstract

A partially covered stent prosthesis 10 for isolating an aneurysm or dissection occurring in the region of the aortic arch comprises a first stent member 11 located at a proximal end of the prosthesis, a second stent member 13h located at a distal end, a third stent member 13a located intermediate the first and second stent members 11, 13h and a graft sleeve 20 attached to the stent members and defining a conduit. A portion 20A of the sleeve 20 is attached around the full perimeter of stent members 11, 12a-d, 13a in a proximal portion to form a fully enclosed conduit, for location over the site of a dissection tear (30, Fig. 4), but is attached around less than the full perimeter of stent members 13b-h in a distal portion to form a partially enclosed conduit having a radial opening extending to the distal end of the prosthesis for alignment with the intersection of the major branch vessels of the aorta.

Description

PROSTHESIS DEVICE

The present invention relates to a prosthesis for treatment of aortic aneurysms and particularly, though not exclusively, to a partially covered stent device for treatment of aortic dissections occurring in the region of the aortic arch.

An aortic dissection is a form of aneurysm in which a tear in the internal wall of the aorta allows blood to penetrate the tunica intima layer and enter the tunica media. High pressures within the aorta can lead to tissue damage propagating along-the Length of the aorta from the site of the tear to form a fake lumen extending distaily (away from the heart-] and/or proximally (towards the heart). An aortic dissection can be a medical emergency.

Endovascular repair of an aortic dissection is a recognised alternative to highly invasive surgical techniques. It involves the insertion of a catheter carrying a fabric covered stent-graft prosthesis through a surgical opening in the femoral artery. The catheter is guided through a patient's arteries until the stent-graft is correctly positioned relative to the aortic dissection to be isolated. The stent-graft expands upon deployment from the catheter to form a continuous conduit isolating any entry tears and thus restoring normal blood flow through the true lumen.

In order to promote expansion of the true lumen it is often desirable to extend the coverage of a fabric-covered stent-graft along a significant distance distal to any entry tears. However, since aortic dissections commonly originate in the ascending aorta and propagate distally to, or even beyond, the aortic arch, it is necessary to adapt the stent-graft to facilitate branch perfusion in the arch region. It is already known to employ bare metal stents to facilitate branch perfusion at the aortic arch. However, long length bare metal stents -such as the Zenith® Dissection stent sold by Cook Incorporated -may be ineffective in isolating entry tears and may promote erosion of the arterial wall proximate their apices.

Attempts have been made to overcome problems associated with bare metal stents by employing fenestrated fabric-covered stent-grafts. Difficulties associated with deploying a graft within the aortic arch are well recognised. In such circumstances endovascular repair is only possible using bespoke grafts having appropriate branch extensions and/or fenestrations to match the individual branch anatomy of a patient Whilst such grafts can be obtained commercially -e.g. the Zenith® stent-graft soW by Cook Incorporated -meticulous design of such grafts relies on accurate pre-operative imaging data. The use of bespoke grafts is therefore expensive and requires significant pre-planning. Although elective procedures are common) the use of bespoke grafts will normally be precluded for emergency situations. For fenestrated designs, significant technical difficulties can arise in aligning fenestrations with the muhipe branch vessels and scope for adjustment during deployment is at best very limited. Furthermore, the manipulation required within the aortic arch during deployment of bespoke grafts is known to increase the risk of emboli and stroke.

The present invention seeks to provide an alternative stent-graft which overcomes, or at least ameliorates, one or more shortcomings associated with the aforementioned

prior art devices.

According to the present invention, there is provided a prosthesis for isolating an aneurysm or dissection proximate the aortic arch, comprising: (i) a first stent member located along a 1ongitudina axis of the prosthesis at its proxima' end; (ii) a second stent member located along the longitudinal axis of the prosthesis at its distal end; (iii) a third stent member located intermediate the first and second stent members; and (iv) a graft material attached to the first, second and third stent members and defining a conduit therebetween; wherein a proxima' portion of the prosthesis is delimited along the longitudina' axis by the proximal end and the third stent member, and a distal portion of the prosthesis is delimited along the longitudinal axis by the distal end and the third stent member; and wherein the graft material is attached around the full perimeter of stent members in the proximal portion to form a fully enclosed conduit extending to the proximal end of the prosthesis but is attached around less than the full perimeter of stent members in the distal portion to form a partially enclosed conduit having a radial opening extending to the distal end of the prosthesis.

Optionally, the first stent member defines the limit of the prosthesis along the longitudinal axis at its proximal end.

Optionally, the second stent member defines the limit of the prosthesis along the longitudinal axis at its distal end.

Optionally, each stent member is formed from a continuous loop.

Optionally, each stent member is arranged so as to have radial symmetry about the longitudinal axis of the prosthesis.

Optionally, at least one stent member in the proximal portion is a saddle-shaped stent member.

Preferably, at least four stent members in the proximal portion are a saddle-shaped stent members.

Optionally, the inner circumference of each saddle-shaped stent member in the proximal portion is greater than the outer circumference of the graft material.

Optionally, the graft material extends around the full inner circumference of stent members in the proximal portion to form a fully enclosed cylindrical conduit.

Optionally, at least one stent member in the distal portion is a ring-shaped stent member.

Optionally, all stent members in the distal portion are ring-shaped stent members.

Optionally, the inner circumference of each ring-shaped stent member in the distal portion is substantially identical to the outer circumference of the graft material.

Optionally, the graft material extends around less than the full inner circumference of stent members in the distal portion to form a partially enclosed conduit Optionally, the graft material extends between 160 degrees and 320 degrees around the inner circumference of stent members in the distal portion.

More preferably, the graft material extends between 180 degrees and 300 degrees around the inner circumference of stent members in the distal portion.

Preferred or alternative features of each aspect or embodiment of the invention apply mutatis mutandis to each other aspect or embodiment of the invention, unless the context demands otherwise.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic perspective view of a stent graft of the present invention; Fig. 2 is a schematic side view of a stent graft of the present invention; Fig. 3 is a schematic underside view of a stent graft of the present invention; and Fig. 4 is a schematic side sectional view of the aortic arch with the stent graft of the present invention located therein isolating a dissection tear.

Referring to the drawings, Figs. 1 to 3 show a prosthesis 10 according to the present invention in a deployed configuration. The prosthesis 10 is approximately 220 mm in length and comprises a sleeve 20 surrounding a central longitudinal axis X. The material of the sleeve 20 is preferably selected so as be biocompatible and substantially impervious to blood. It may optionally be coated to reduce friction,

S

discourage clotting, or to deliver a pharmaceutical agent The sleeve 20 may optionally be coated internally or externally prior to attachment of the stent elements. The sleeve 20 will usually be a knitted or woven fabric of ePTFE, PTFE or polyester, e.g. polyethylene or polypropylene. Although the sleeve 20 is shown with a constant radius relative to the longitudinal axis X, it could also be formed with a taper.

Two groups of stents are attached onto the external surface of sleeve 20, for example by sewing with a suture material. Although this is typically the most convenient means of manufacture, it is also possible for some or all of the stent elements to be attached internally) within the lumen of sleeve 20.

The first stent group includes a single annular ring stent 11 defining a longitudinal limit of the prosthesis 10 at its proximal end. The ring stent 11 is formed from multiple windings of a resilient material such as PEEK or nitinol wire formed into a continuous closed circular ring.

Adjacent to the first stent and also forming part of the first stent group are four separate stents 12a-d spaced along the longitudinal axis X each formed from multiple windings of PEEK or of nitinol wire formed into a continuous closed loop.

Each stent 12 is significantly over-sized relative to the diameter of the sleeve 20 and is distorted into a saddle shape. By "saddle shaped" it is to be understood that a circular ring stent is formed of a material which is sufficiently resilient as to be distorted so that a first pair of diametrically opposed points on the circumference of the ring are displaced in one axial direction whilst a second pair of diametrically opposed points, centrally located on the circumference between the first pair, are displaced in the opposing axial direction to form a symmetrical saddle shape. For convenience, the first pair of points can be described as "peaks", and the second pair of points can be described as "valleys".

The peak and valleys of all stents 12a-d within the first stent group are respectively aligned in the direction of longitudinal axis X. The saddle height of each stent 12 can be the same or different. In the illustrated embodiment the saddle height is the same for each stent 12. In a non-limiting example, the ratio of sleeve diameter to saddle-shaped ring diameter falls within the range oft 1.05 -to -1: 1.3. Having regard to Figs. 2 and 3, stents 12a-d are regularly spaced along the sleeve 20 at approximately 20mm intervals and attached so that the peak of each stent 12a-d of the first stent group is also circumferentially aligned with the valley of the immediately neighbouring stent. Thus) the peak 12A of one stent 12 is aligned with the valley 12B of its neighbouring stent 12. This arrangement increases the axial and torsional stiffness of the portion of the prosthesis covered by stents 12a-d as described in the applicant's application No. PCT/GB2012/051234 which is incorporated herein by reference.

The second stent group is located adjacent the first stent group distally of stent lid approximately 35-40% of the way along the length of the stent graft prosthesis 10.

It comprises eight regularly spaced annular ring stents 13a-h regularly spaced along the longitudinal axis X at approximately 20mm intervals, the last of which 13h defines a longitudinal limit of the prosthesis 10 at its distal end, i.e. at the opposite end of the prosthesis 10 relative to ring stent 11. The ring stents 13a-h are each formed from multiple windings of a resilient material such as PEEK or nitinol wire formed into a continuous closed circular ring.

The proximal portion of the prosthesis 10 delimited in the longitudinal direction of axis X by the single ring stents 11, Ha is provided with a sleeve portion 20A which extends around the full inner circumference of all stents 11, 12a-d, 13a of the first stent group thus forming when deployed) a fully enclosed cylindrical conduit of constant radius relative to the longitudina' axis X. The term circumference is intended to include both the linear distance around the inside of a closed circular stent and the linear distance around the inside of a saddle shaped stent. Whilst four separate stents 12a-d are illustrated, it will be appreciated by a person of ordinary skill in the art that this number may vary depending upon the overall required length and/or stiffness requirements for this part of the prosthesis 10.

The distal portion of the prosthesis 10 delimited in the longitudinal direction of axis X by ring stent 13a and ring stent 13h is provided with a sleeve portion 20B which extends partially around the inner circumference of stents 13b-h of the second stent group thus forming, when deployed, a partially enclosed conduit. In the non-limiting example illustrated in Figs. 1 to 3, the sleeve portion 20B extends around just over 180 degrees of the inner circumference of stents 13b-h so as to form a semi-cylindrical and hence semi-enclosed conduit. Therefore each stent 13b-h is left exposed around approximately 50% of its circumference thus providing an opening in the radial direction relative to longitudinal axis X. Whilst eight separate stents 13a-h are illustrated, it will be appreciated by a person of ordinary skill in the art that this number may vary depending upon the overall required length and/or stiffness requirements for this part of the prosthesis 10.

Similarly, whilst sleeve portion ZOB extends approximately 180-200 degrees around the inner circumference of stents 13b-h in the illustrated example, it will be appreciated by a person of ordinary skill in the art that the extent of circumferential coverage may vary depending upon the particular requirements for this part of the prosthesis 10. For example, in certain circumstances it is envisaged that a sleeve portion which extends around approximately 300 degrees of the inner circumference of stents 13b-h maybe more appropriate.

Ring stent 13a is located at the region of transition between the fully and partially enclosed conduit portions. The transition may be abrupt or there may be a graduated change in the degree of enclosure over the longitudinal distance between ring stents 13a, 13b. The full and partial sleeve portions 20A, 2DB may be provided as a single integral piece of material, or from two or more separate pieces of material. In one example (not shown), the diameter of the prosthesis 10 may change at the region of transition between the fully and partially enclosed conduit portions. In a non-limiting example, the proximal portion of the prosthesis 10 corresponding to sleeve portion 20A may have a relatively larger diameter (e.g. 38mm) than the distal portion of the prosthesis 10 corresponding to sleeve portion

B

20B (e.g. 32mm]. Such an arrangement may find particular application in cases of chronic aortic dissection where the true lumen is not expected to open.

The ring stents 11, 13a-h of the first and second stent groups have an inner circumference which is substantially identical to -and preferably is identical to -the outer circumference of the sleeve portions 20A, 20B. By Tsubstantially identical toT' it is to be understood that the circumference is equal to or up to 5% greater than the outer circumference of the sleeve portion; but preferably is equal to or up to 2% greater than the outer circumference of the sleeve portion; and most preferably equal to or up to 1% greater than the outer circumference of the sleeve portion.

The advantages associated with the aforementioned technical features can be more readily understood with reference to Fig. 4 which shows a sectional view of the aortic arch into which the prosthesis 10 of the present invention has been inserted and deployed in order to isolate a dissection tear 30 occurring in the ascending aorta.

The prosthesis 10 has been deployed such that ring stent 11 which defines the longitudinal limit of the prosthesis 10 at its proximal end and ring stent 13a are respectively located upstream and downstream of the site of a dissection tear 30.

Accordingly, the proximal portion of the prosthesis 10 delimited in the longitudinal direction of axis X by those single ring stents 11, 13a serves to provide a fully enclosed lumen which bypasses the site of a dissection tear 30. The aforementioned arrangement of the saddle-shaped stents 12a-d spaced between ring stents 11, 13a increases the axial and torsional stiffness of this fully enclosed conduit portion of the prosthesis 10 in order to provide appropriate sealing performance and wall apposition.

The distal portion of the prosthesis 10 delimited in the longitudinal direction of axis X by ring stents 13a and 13h presents a radial opening relative to longitudinal axis X which is aligned with the intersection of the major branch vessels of the aorta (i.e. the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery]. The length and circumferential extent of the radial opening is selected to allow appropriate blood perfusion to the branch vessels according to their varying diameters and locations, and without the need for excessive pre-operative planning or manipulation during positioning and deployment By providing a different stent architecture at the proximal and distal portions the axial forces applied to the vessel wall can be controlled over the length of the prosthesis 10. In particular, each saddle-shaped stents 12a-d is significantly oversized relative to both the sleeve portion 20A to which they are connected and the true lumen. Conversely, each circular ring stent 13a-h is only marginally oversized relative to both the sleeve portion 2DB to which they are connected and the true lumen. The consequent differential in the force applied to the vessel wall at the proximal and distal portions of the prosthesis 10 is particularly advantageous since it ensures good sealing performance and wall apposition (proximally] over the site of a dissection tear 30 whilst reducing trauma against the vessel wall (distally) at the more sensitive region proximate the branch vessels 40. In particular, the absence of any longitudinally extending stent elements at the distal portion, and the inherent inability of the distal portion to expand beyond a chosen diameter, eliminates or minimises the extent of any trauma to the surrounding vessel walls.

Modifications and improvements may be made to the foregoing without departing from the scope of the invention as defined by the accompanying claims. For example, the stent members 12a-d of the second stent group may have one or more stents which has a different saddle shape or spacing relative to one or more of the other stents. Although, each stent is described above as being attached to the graft sleeve portions by sewing, any other suitable means of attachment such as adhesive or heat bonding could alternatively be employed.

Claims

CLAIMS1. A prosthesis for isolating an aneurysm or dissection proximate the aortic arch, comprising: (i) a first stent member located along a longitudinal axis of the prosthesis at its proximal end; (ii] a second stent member located along the longitudinal axis of the prosthesis at its distal end; (iii) a third stent member located intermediate the first and second stent members; and (iv) a graft material attached to the first, second and third stent members and defining a conduit therebetween; wherein a proximal portion of the prosthesis is delimited along the longitudinal axis by the proximal end and the third stent member, and a distal portion of ftc prosthesis is delimited along the longitudinal axis by the distal end and the third stent member; and wherein the graft material is attached around the full perimeter of stent members in the proximal portion to form a fully endosed conduit extending to the proximal end of the prosthesis but is attached around less than the full perimeter of stent members in the distal portion to form a partially enclosed conduit having a radial opening extending to the distal end of the prosthesis.
2. A prosthesis according to claim 1, wherein the first stent member defines the limit of the prosthesis along the longitudinal axis at its proximal end.
3. A prosthesis according to claim 1 or 2, wherein the second stent member defines the limit of the prosthesis along the longitudinal axis at its distal end.
4. A prosthesis according to any preceding claim) wherein each stent member is formed from a continuous loop.
5. A prosthesis according to any preceding claim, wherein each stent member is arranged so as to have radial symmetry about the longitudinal axis of the prosthesis.
6. A prosthesis according to any preceding claim, wherein at least: one stent member in the proximal portion is a saddle-shaped stent member.
7. A prosthesis according to claim 6, wherein at least four stent members in the proximal portion are saddle-shaped stent members.
8. A prosthesis according to claim 6 or 7, wherein the inner circumference of each saddle-shaped stent member in the proximal portion is greater than the outer circumference of the graft material.
9. A prosthesis according to any of claims 4 to 8, wherein the graft material extends around the full inner circumference of stent members in the proximal portion to form a fully enclosed cylindrical conduit
10. A prosthesis according to any preceding claim, wherein at least one stent member in the distal portion is a ring-shaped stent member.
11. A prosthesis according to claim 10, wherein all stent members in the distal portion are ring-shaped stent members.
12. A prosthesis according to claim 10 or 11, wherein the inner circumference of each ring-shaped stent member in the distal portion is substantially identical to the outer circumference of the graft material.
13. A prosthesis according to any of claims 4, 5, 10, 11 and 12, wherein the graft material extends around less than the full inner circumference of stent members in the distal portion to form a partially enclosed conduit
14. A prosthesis according to claim 13, wherein the graft material extends between 160 degrees and 320 degrees around the inner circumference of stent members in the distal portion.
15. A prosthesis according to claim 13, wherein the graft material extends between 180 degrees and 300 degrees around the inner circumference of stent members in the distal portion.