Introducer for deploying a stent graft in a curved lumen

An introducer (10) includes release wires (42′) that constrain at least one stent (4′) while the remainder of a stent graft (18) is expanded during deployment. By allowing the constrained stent (4′) to expand after an adjacent stent (4), the constrained stent (4′) overlaps with the interior of the adjacent stent (4) where the stent graft (18) is deployed within a curved body lumen (70).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of United Kingdom patent application number, 0820066.9, filed Oct. 31, 2008. This application is related to United Kingdom patent application number 0820061.0, filed Oct. 31, 2008.

TECHNICAL FIELD

The present invention relates to an introducer for deploying a stent graft within a curved lumen.

BACKGROUND OF THE INVENTION

Stent grafts are used to replace or repair vessels of the body such as the arteries. A stent graft is usually formed from a tubular body of a biocompatible graft with one or more stents mounted into or onto the tubular body to provide support therefor. The stents may be balloon expandable stents or self-expanding stents.

Endovascular methods have been proposed for treatment of an aneurysm of the aorta particularly where the aneurysm is adjacent the aorta bifurcation. However, when an aneurysm occurs higher up in the aorta, in the region of the descending aorta adjacent the thoracic arch or in the ascending aorta, endovascular techniques for treating these aneurysms are somewhat more difficult because of the tight curvature of the thoracic arch, the occurrence of major arteries in the region and the proximity to the heart. Placement of a substantially cylindrical prosthesis in such a curved region can cause problems.

Stent grafts are typically deployed using endovascular techniques on an introduction device in which the stent graft is retained in a radially contracted condition by a sheath. Upon withdrawal of the sheath and release of any retention arrangement where provided, for example in cases in which the stent graft has self-expanding stents, the stent graft can expand under the action of the self-expanding stents towards the vessel walls to redefine the blood flow path. The introduction device is withdrawn after deployment.

Currently, stent grafts are deployed in curved lumens by causing these to follow the curvature imparted to the introducer. However, this can result in the stent graft not sitting properly in the blood vessel and in the lumen of the prosthesis being closed off or reduced in diameter. Kinks can also occur along the length of the prosthesis and these can cause problems with restriction of flow in the lumen.

Furthermore, when deploying a stent graft that is substantially cylindrical in a curved aorta there is a danger that the proximal end of the stent graft, that is, the end nearest the heart, will not lie flat against the walls of the aorta (i.e., is not positioned perpendicularly to the wall of the vessel) and blood can flow underneath the edge of the graft, particularly on the inner side of the curve of the thoracic arch and cause the stent graft to buckle and close off thereby causing serious problems.

In general this application relates to the placement of prostheses in the aorta in the region known as the thoracic arch where the aorta leaves the heart and curves over in approximately a semi-circle to the descending aorta and then into the abdominal aorta and then into the lower limbs via the iliac arteries. The invention is, however, not so restricted and can relate to placement of prostheses within or in place of lumens in any portion of a human or animal body, though it is particularly relevant to curved lumens, particularly tightly curved lumens.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved introducer for deploying a stent graft within a curved lumen.

According to a first aspect of the present invention, there is provided an introducer for deploying a stent graft in a curved lumen, the introducer including: a carrier for a stent graft including a plurality of stents; a release mechanism including a constraining mechanism operable to maintain at least a portion of at least one stent of the stent graft in a radially constrained configuration during deployment whilst allowing at least a portion of the stent graft to expand, wherein the portion of the constrainable stent is radially constrained substantially entirely therearound; the release mechanism operable to enable the constrained stent to expand so as to overlap with the interior of at least a portion of an adjacent stent in the expanded portion of the stent graft.

The introducer enables a substantially cylindrical stent graft to be deployed in a curved lumen without the need to match the curve of the stent graft to the lumen either prior to, or during, deployment. Furthermore, the stent graft can be accommodated within a curved lumen without the stents bunching together and creating gaps that might cause blood leakage.

In a preferred embodiment, the constrainable stent is not the most proximal stent of the stent graft or the most distal stent of the stent graft. This assists in enabling the ends of the stent graft to be securely anchored within the vessel.

The constraining mechanism may include a release wire for co-operating with a wire-receiving mechanism provided on the constrainable stent.

More than one stent may be maintained in a constrained configuration during deployment whilst at least a portion of the stent graft expands.

According to another aspect of the present invention, there is provided a stent graft for deployment within a curved lumen by means of the above-described introducer, the stent graft including a plurality of stents, the stent graft including a mechanism for allowing at least a portion of at least one stent to be radially constrained during deployment whilst a portion of the stent graft is expanded, wherein the portion of the constrainable stent is radially constrained substantially entirely therearound.

The stent graft is typically substantially cylindrical prior to deployment, but is able to be securely located within a curved lumen, irrespective of the extent of the curvature of the lumen and without the need to match curvature of the stent graft with the curvature of the lumen either prior to, or during, deployment.

Preferably, the mechanism is not provided at the most proximal stent of the stent graft or at the most distal stent of the stent graft. This facilitates secure anchoring of the stent graft within the lumen.

The mechanism may include at least one wire-receiver for co-operating with a release wire of the introducer. The wire-receiver may be a loop of material, such as a loop of thread.

In an embodiment, the mechanism may be provided at only one end of the constrainable stent, for example, it may be provided only at the proximal end of the constrainable stent. In another embodiment, the mechanism may be provided at both the proximal end and the distal end of the constrainable stent.

The stent graft may include more than one constrainable stent. In an embodiment, it may include at least one constrainable stent in which the mechanism is provided only at one of its ends, and at least one constrainable stent in which the mechanism is provided at both its proximal end and its distal end.

DETAILED DESCRIPTION

It is to be understood that the Figures are schematic and do not show the various components in their actual scale. In many instances, the Figures show scaled up components to assist the reader.

In this description, when referring to a deployment assembly, the term distal is used to refer to an end of a component which in use is furthest from the surgeon during the medical procedure, including within a patient. The term proximal is used to refer to an end of a component closest to the surgeon and in practice in or adjacent an external manipulation part of the deployment or treatment apparatus.

On the other hand, when referring to an implant such as a stent or stent graft, the term proximal refers to a location which in use is closest to the patient's heart, in the case of a vascular implant, and the term distal refers to a location furthest from the patient's heart.

Referring toFIGS. 1 and 2, an implant deployment device10includes an external manipulation section12, a proximal attachment region14and a distal attachment region16. The proximal attachment region14and the distal attachment region16secure the two ends of the implant18. During the medical procedure to deploy the implant18, the proximal and distal attachment regions14and16will travel through the patient's vasculature, in this example, to a desired deployment site. The external manipulation section12at the proximal end of the implant deployment device10, which is operated by a surgeon to manipulate the introducer, remains outside of the patient throughout the procedure.

The distal attachment region16of the implant deployment device10includes a dilator tip20, which is typically provided with a bore22therein for receiving a guide wire (not shown) of conventional type. The longitudinal bore22also provides a channel for the introduction of medical reagents. For example, it may be desirable to supply a contrast agent to allow angiography to be performed during placement and deployment phases of the medical procedure.

An inner catheter or cannula24, conventionally made from a flexible thin walled metal tube, is fastened to the dilator tip20. The inner catheter24is flexible so that the implant deployment device10can be advanced along a relatively tortuous vessel, such as a femoral artery, and so that the distal end of the implant deployment device10can be longitudinally and rotationally manipulated. The inner catheter24carries a stent18or other device to be implanted in the patient. The catheter24extends through the implant deployment device10to the manipulation section12, terminating at a connection device26, in conventional manner.

The connection device26is designed to accept a syringe to facilitate the introduction of reagents into the inner catheter24and for this purpose is typically provided with a threaded luer lock connection.

Where provided, a pusher sheath or rod30(hereinafter referred to as a pusher member), typically made from a plastics material, is mounted coaxial with and radially outside of the inner catheter24. The pusher member30is “thick walled”, that is the thickness of its wall is preferably several times greater than that of the guide wire catheter24. In some instances, the pusher member30and the inner catheter24are the same component, possibly having different outer diameters at the location at which the stent18is to be carried.

A sheath32extends coaxially over and radially outside of the pusher member30. The pusher member30and the sheath32extend distally to the manipulation region12.

The implant18, which may be a stent, a stent graft or any other implant or prosthesis deliverable by the implant deployment device10, is retained in a compressed condition by the sheath32. The sheath32extends proximally to a sheath manipulator and haemostatic sealing unit34of the external manipulation section12. The haemostatic sealing unit34includes a haemostatic seal (not shown) and a side tube36held to the unit34by a conventional luer lock38.

The sheath manipulator and haemostatic sealing unit34also includes a clamping collar (not shown) that clamps the sheath32to the haemostatic seal and a silicone seal ring (not shown) that forms a haemostatic seal around the pusher member30. The side tube38facilitates the introduction of medical fluids between the pusher member30and the sheath32. Saline solution is typically used.

During assembly of the implant deployment device10, the sheath32is advanced over the proximal end of the dilator tip20of the proximal attachment region16while the implant18is held in a compressed state by an external force. A suitable distal attachment (retention) section (not visible in this view) is coupled to the pusher member30and retains a distal end40of the prosthesis18during the procedure. The distal end of the prosthesis18may be provided with a loop of material (not shown) through which a distal restraining wire42extends. The distal restraining wire also extends through an aperture (not shown inFIGS. 1 and 2) in the proximal attachment section40into an annular region44between the inner catheter24and the pusher member30. The distal restraining wire42extends through the annular space44to the manipulation region12and exits the annular space44at a distal wire release mechanism46.

A proximal portion of the external manipulation section12includes at least one restraining wire actuation section50mounted on a body48, in turn mounted onto the pusher member30. The inner catheter24passes through the body48. The distal wire release mechanism46and the proximal wire release mechanism50are mounted for slidable movement on the body48.

Clamping screws52prevent inadvertent early release of the prosthesis18. A haemostatic seal (not shown) is included so that the release wires can extend out through the body48without unnecessary blood loss during the medical procedure.

A proximal portion of the external manipulation section12includes a pin vice54mounted onto the proximal end of the body48. The pin vice54has a screw cap56. When screwed in, vice jaws (not shown) of the pin vice54clamp against or engage the inner catheter24. When the vice jaws are engaged, the inner catheter24can only move with the body48and hence it can only move with the pusher member30. With the screw cap56tightened, the entire assembly can be moved together as one piece.

Once the implant deployment device10is in the desired deployment position, the sheath32is withdrawn and the proximal and distal wire release mechanisms50,46are released to allow the prosthesis18to expand.

For some procedures, the sheath32may be left in place after expansion of the implant18. The pusher member30and inner catheter24may be withdrawn and replaced by a further component, using the sheath32as a guide.

FIG. 3illustrates a prior art stent graft18′ for deployment within a curved body lumen. The stent graft18′ comprises a graft material tube1which is substantially cylindrical. The graft material tube1has a proximal end2and a distal end3. The graft1has a number of self expanding zig-zag or well-known Gianturco Z-stents4positioned at intervals along the length of the tube and providing the force necessary to open the graft1out to the walls of the aorta when deployed. The stents5and6at the distal end3and proximal end2respectively are inside the graft1and the other intermediate stents4are on the outside of the graft1.

The stent graft18′ includes a length reduction arrangement comprising an elastic material8such as a silicone rubber or similar material which is fastened at9at the proximal end2of the prosthesis18′ and joined at11near the distal end3of the prosthesis18′. The length reduction arrangement can also comprise a shape memory metal such as Nitinol, a nickel titanium alloy, which is heat set in a curved configuration.

Upon deployment, the ends of the graft18′ are released from a deployment device and the elastic material8takes up its shortened rest position so that the points9and11move closer together which causes the graft to form a curved shape. The curved stent graft18′ can then sit within a body lumen having the same curve.

FIGS. 4 and 5illustrate a stent graft18in accordance with an embodiment of the present invention. The stent graft18is formed from a tubular piece of biocompatible graft material1having, in this example, six Z-stents4,4′,5,6disposed along its length. In this embodiment the stents5,6found at the distal end3and the proximal end2of the tubular piece of graft material1are located on the inside of the tube1, whereas the intermediate stents4,4′ are located on the outside of the tube1.

In this embodiment, one of the stents4′ is provided, at substantially equally spaced locations therearound, with loops of, in this embodiment, suture material140. The loops of suture material140are able to engage with a release wire42′ of an introducer10′ for deployment of the stent graft18. The purpose of this is described below.

For deployment of the stent graft18illustrated inFIGS. 4 and 5, the stent graft18is loaded in a radially compressed condition onto an inner catheter24of a deployment device10′ such as that shown inFIG. 6. The introducer10′ illustrated inFIG. 6is similar to that shown inFIGS. 1 and 2. However, the introducer10′ shown inFIG. 6includes a release mechanism including trigger wires42′ able to engage with the suture loops140of the stent graft18. The compressed stent graft18is then covered by the sheath32in a conventional manner for deployment.

The stent graft18is delivered to the site of deployment, which in this example is within a curved body lumen (such as the thoracic arch). Once the implant deployment device10is in the desired deployment position, the sheath32is withdrawn and the stent graft18is allowed to expand (seeFIG. 7). However, the engagement between the release wires42and the suture loops140retains a single stent4′ in a constrained configuration. The constrained stent4′ is typically constrained by over 50% of its expanded configuration, and may be constrained by up to 70 or 80%. This will depend upon the spacing between the stents. In practice it will be kept in its fully constrained condition, whereby it is constrained around the catheter24of the implant deployment device10. In an embodiment, however, the constrained stent4′ may expand partially prior to release of the constraining mechanism. In a preferred embodiment the partial expansion comprises the constrained stent4′ expanding to no more than 50% of its fully deployed diameter.

Next, the release wires42′ are released from the suture loops140to allow the constrained stent4′ to expand.

Once the constrained stent4′ has expanded, the pusher member30and inner catheter24may be withdrawn leaving the expanded stent graft18in place (seeFIG. 8).

FIGS. 7 and 8illustrate the improved positioning effect of this deployment process.FIG. 7shows the stent graft18partially expanded after withdrawal of the sheath32. Only the constrained stent4′ remains in its compressed state by means of the release wires42′ and the suture loops140. The stent graft18is located such that the constrained stent4′ is positioned at the tightest part of the bend of the curved body vessel70. As such, the stents4,5,6, which are allowed to expand as soon as the sheath32is withdrawn, engage against the walls of the body vessel70effectively because the vessel is not too curved at the location where the stents4,5,6of the expanded portion are located. It can be seen fromFIG. 7, however, that the stent4located immediately proximally of the constrained4′ and the stent4located immediately distally of the constrained stent4′ are positioned such that they are closer together on the inside part of the curved body lumen70than they are towards the outside of the curve. This results from the constrained stent4′ drawing the graft material1and the adjacent stents4towards it. As a result, the adjacent stents4are able to locate within the vessel70closer together on the inside of the curve than they would have if the stent4′ between them had not been constrained whilst they expand. Consequently, when the constrained stent4′ is allowed to expand it overlaps80with its adjacent stents4on the inside of the curve of the curved body vessel70. This is because the gap between the adjacent stents4is less than the length of the constrained stent4′. Because the stents4adjacent to the constrained stent4′ were allowed to expand first, these properly engage the wall of the vessel70, and the expanded constrained stent4′ engages with the interior of the adjacent stents4providing an area of overlap80.

A second embodiment is illustrated inFIGS. 9 and 10. The difference between the embodiment ofFIGS. 9 and 10and that ofFIGS. 7 and 8is that the constrained stent is constrained only at its proximal end so that it forms a “cone-shape” prior to release, but after expansion of the remainder of the stent graft18. Again, when the constrained stent4′ is allowed to expand by removal of the release wire42from the suture loops140, the constrained stent4′ expands such that it overlaps with the interior of the stent4immediately proximal to the constrained stent4′. As shown inFIG. 10, the result is a single region of overlap80between the constrained stent4′ and its immediately proximal stent4.

Constraining only the proximal end of the constrained stent4′ can provide a positioning of the stent graft18that maximises blood flow through the stent graft18after deployment.

In a third embodiment, more than one constrained stent4′ is provided with suture loops140. In such an embodiment, each constrained stent4′ may include suture loops140at both its proximal ends and distal ends (c.f.FIG. 7), or, as illustrated inFIG. 11, (and in particular, where two adjacent constrained stents4′ are provided) each constrained stent4′ is provided with suture loops only at one end, in this example, the proximal ends. As illustrated inFIG. 12this arrangement leads to a plurality of regions of overlap80with constrained stents4′ overlapping with the interior of an immediately proximal stent4,6.

An advantage of the above-described embodiments is that a substantially straight stent graft18can be deployed in a curved vessel. The stents4adjacent the constrained stent expand first and are properly anchored within the vessel. As the constrained stent4′ expands during a second stage of deployment, the stent graft18can be used in any type of vessel, whether straight, having only a slight bend, or having a sharp bend. Proper curvature of the stent graft18within the vessel is therefore obtained. In addition, the curve of the stent graft18does not have to be matched to the curve of the vessel prior to deployment. Furthermore, the surgeon or clinician does not have to ensure that the stent graft is deployed in a particular orientation to match the curve of the vessel as is the case with prior art prostheses. Constraining a stent4′ creates a neck portion, which imparts increased flexibility to the stent graft18. This assists in enabling the stent graft18to conform to the curvature of a vessel70irrespective of the extent of the curvature of the vessel.

Of course, the skilled person will appreciate that the different types of constrained stent4′ may be combined within a single stent graft18where appropriate. Furthermore, the constrained stent4′ may be located at any point along the stent graft18, depending on the particular requirements. For example, the constrained stent4′ may be at the proximal end, in the middle, or in any one or more of the stents along the stent graft18. In another modification, it is envisaged that every stent of the stent graft18could be constrained, preferably only at one end, which would preferably be at the proximal end of each stent4′. In an embodiment, the constrained stent4′ is not the stent6at the proximal end2of the stent graft18. This is because the stent6at the proximal end2of the stent graft18can be useful for anchoring and positioning of the stent graft18.

In another modification, the release wire42′ may be the same as the wire42that holds the proximal end of the stent graft to the distal end of the introducer.

In another modification, the suture loops140of different constrained stents140can co-operate with different release wires42′. This enables greater control over the deployment process where desired by allowing different constrained stents4′ to be released in a particular desired order.

The suture loops140could be provided on the graft material1instead of on the stent4′. The suture loops140could additionally or alternatively be provided to co-operate with release wires42inside the tubular graft1instead of outside.

In another example of a restraining mechanism illustrated inFIG. 13, a thread of suture material130having loops132at each end may be provided around the stent4′ of the stent graft18, and which, when pulled tight, constrains the stent4′. The loops132at each end of the thread of suture material130overlap one another and a release wire42′ is threaded therethrough, thereby maintaining an overlap of the loops132and maintaining the stent4′ in its constrained configuration. Withdrawal of the release wire42′ allows the loops132at each end of the thread of suture material130to separate and the constrained stent4′ to expand. In the example illustrated inFIG. 13the inner catheter24is provided with an aperture134through which the suture material132extends in order to engage with the release wire42′. Other suitable arrangements may be envisaged.

The term thread as used herein is intended to include any filamentary material which can perform the stated function and could, for example, be of conventional suture material, a multi-filamentary structure formed of yarns for example and of a natural or synthetic material such as cotton, other biocompatible material or a polymer material such as polyester, or a mono-filamentary structure of a natural material, other biocompatible material, a metal such as gold or an alloy such as Nitinol.

The features of the various embodiments described above and their modifications may be substituted for or combined with one another as desired. It is also to be understood that the various features of the dependent claims appended hereto may be used with one another in any desired combination of those claims.