WO2016123676A1

WO2016123676A1 - Aortic stent graft, delivery system and method

Info

Publication number: WO2016123676A1
Application number: PCT/AU2016/050070
Authority: WO
Inventors: Michael Wilson; Michael VALLELY; James Wood
Original assignee: State Of The Heart Innovations Pty Ltd
Priority date: 2015-02-05
Filing date: 2016-02-05
Publication date: 2016-08-11

Abstract

Embodiments of the present invention provide an aortic stent graft configured for placement in the aortic arch and a delivery system to enable endovascular delivery of the aortic stent graft. The configuration of the aortic arch presents particular problems for endovascular repair. The aortic stent graft comprises a tubular main graft body, and three tubular graft branches. The tubular main graft body is configured to extend from within a portion of the ascending aorta to within a portion the descending aorta. The three tubular graft branches extend from the tubular main graft body to align with and extend into three aortic branch vessels extending from the aortic arch. The aortic stent graft and delivery system allows positioning of the tubular main body in the aortic arch and each one of the three tubular graft branches into one aortic branch vessel via an endovascular procedure, with the stent graft delivered via a trans-apical route, anterograde, via a left lateral thoracotomy, through the left ventricle of the heart.

Description

AORTIC STENT GRAFT, DELIVERY SYSTEM AND METHOD

Field of the invention

The field of the present invention is endovascular surgery and stents for deployment in endovascular surgery. A particular application for embodiments of the invention is for endovascular repair of aortic arch aneurysms.

Background of the invention

An aortic arch aneurysm is an enlargement of the aorta and associated weakness in the wall of the aorta in the arch of the aorta proximal arterial branches for the innominate artery (which branches into the right subclavian artery and right carotid artery), left carotid artery and left subclavian artery.

Rupture of an aortic arch aneurysm is fatal. Current surgery to prevent ruptures of aortic arch aneurysms requires cardiopulmonary bypass and deep hypothermic circulatory arrest. Such surgery is associated with a 10% risk of death and a 20% risk of neurological injury.

Other options for aortic arch repair that have been tried include open repair requiring sternotomy, where a vertical inline incision is made along the sternum, after which the sternum itself is divided, or "cracked", to expose the aortic arch for the surgeon to perform the repair procedure. Open surgery, de-branching of aortic arch branch vessels and then retrograde deployment of a stent has also been tried. Open surgery carries 17% risk of death and 12% risk of stroke. The outcomes form such surgeries are not always satisfactory. Patient rehabilitation after such surgeries is typically extensive. Further, some patients may not be well enough for open surgery to be a satisfactory risk.

To avoid open surgical procedures to treat aneurysms techniques for endovascular surgery have been developed. Aneurysms elsewhere in the aorta can be repaired with a self-fixing synthetic stent grafts delivered through an endovascular route. This significantly reduces the risks of open surgery. Endovascular repair of abdominal aortic aneurysms is now the routine. However, endovascular thoracic aortic aneurysm repair is limited to aneurysms distal to the left subclavian artery (LSCA). The stents used for such aneurysm repair cannot reliably be deployed in the aortic arch for a least the following reasons.

• Configuration of the arch makes it difficult to locate the endovascular graft securely. • An arch graft would occlude the arteries to the brain and upper body.

• Difficulty securing the stent in the ascending aorta proximal the coronary arteries and aortic valve.

• Risks associated with stent delivery in a diseased aorta causing

embolization and stroke.

• Risks associated with stent delivery causing damage to femoral vessels and compromising circulation.

Despite these problems some attempts have been made to repair aortic arch aneurysms using endovascular techniques. One technique to attempt endovascular repair of aortic arch aneurysms is retrograde deployment of a stent then fenestration of orifices of arch branch vessels. This approach is unsatisfactory because deployment of the stent causes blocking of the arch branch vessels until fenestration to make openings in the stent wall at the orifices of the branch vessels. Thus, blocking blood flow to the vital organs (including the brain) served by these vessels.

Another technique to attempt endovascular repair of aortic arch aneurysms is anterograde deployment of a stent into the aortic arch and placement of Chimney, Periscope or Snorkel (CHIMPS) grafts to branch vessels. However, this approach has been complicated by kinking of the grafts and perigraft endoleaks.

There is a need for new techniques and devices to enable endovascular repair of aortic arch aneurysms.

Summary of the invention

According to one aspect of the present invention there is provided an aortic stent graft configured for placement in the aortic arch, the stent graft comprising:

a tubular main graft body having an ascending aorta end and a descending thoracic aorta end; and

three tubular graft branches extending from the tubular main graft body between the ascending aorta end and descending thoracic aorta end;

the main graft body being configured to, in a deployed position, have a diameter corresponding to the internal diameter of the aorta and a length to allow the main graft body to extend from within a portion of the ascending aorta to within a portion the descending aorta;

the three tubular graft branches being configured to, in a deployed position, align with and extend into three aortic branch vessels extending from the aortic arch; the tubular main graft body and tubular graft branches being formed from a flexible biocompatible material with self-expanding support mechanism to be flexible in a pre-deployment position where the tubular main body and tubular graft branches are in a collapsed state to allow positioning of the tubular main body in the aortic arch and each one of the three tubular graft branch into one aortic branch vessel via an endovascular procedure, and expansion to a deployed position to engage walls of the aortic arch and branch vessels.

The three tubular graft branches are spaced apart and configured to deploy into the innominate artery (IA), left common carotid artery (LCCA) and left subclavian artery (LSCA) respectively.

The tubular main body can be configured to extend, in the deployed position, from above the sinotubular junction of the aorta to the descending thoracic aorta beyond the LSCA. For example, in an embodiment, in the deployed position, the tubular main body is configured to expand to a diameter of 30 to 35mm, and a first tubular graft branch for deployment into the IA is configured to expand to a diameter of 10m and second and third graft branches for deployment into the LCA and LSCA respectively are configured to expand to a diameter of 8mm.

In an embodiment the tubular graft branch for deployment into the innominate artery (IA) and the tubular graft branch for deployment into the left common carotid artery (LCCA) are closely adjacent to conform to an aortic arch anatomy where the IA and LCCA share a common origin.

In an embodiment of the aortic stent graft the self-expanding support mechanism is provided by a memory metal alloy skeleton. For example, the memory metal alloy can be a nickel titanium alloy.

In an embodiment the flexible biocompatible material is a polyester material. For example, the flexible biocompatible material can be polyethylene terephthalate.

The aortic stent graft can further comprise a fixative at a base of each of the tubular main graft body and the three tubular graft branches to aid fixation and sealing the graft against the vessel wall. For example, the fixative can be a biocompatible adhesive.

According to another aspect of the present invention there is provided a delivery system for an aortic stent graft as described above, the delivery system comprising:

a protective sheath holding each of the tubular main graft body and the three tubular graft branches in a collapsed position for delivery into the aortic arch;

a main guide wire extending through the protective sheath and engaged with the tubular main graft body and manipulate to guide the tubular main body into the aortic arch extending into the descending aorta; and

three branch guide wires, each one of the three branch guide wires extending through the protective sheath and engaged with one respective tubular graft branch to guide the respective tubular graft branch into a respective aortic branch vessel.

In an embodiment of the delivery system each of the main and branch guide wires extend through the main tubular graft body and respective tubular graft branches to engage at the distal end thereof to allow independent guidance of each tubular branch graft into position in each aortic branch vessel in a collapsed state permitting blood flow past the aortic stent graft through all aortic branch vessels during positioning of each of the main tubular graft body and three tubular branch grafts.

In an embodiment each of the guide wires is engaged with the distal end of the respective main tubular graft body and tubular graft branches via a tip structure, the tip structure being configured to hold the respective tubular graft in a collapsed state until disengagement of the guide wire. In an embodiment the tip structure is cone shaped.

In an embodiment the four guide wires all extend through the main tubular body of the aortic stent graft from the ascending aorta end toward the descending thoracic aorta end to allow anterograde delivery of the aortic stent graft via a patient's left ventricle. The three branch guide wires can be configured to direct each of the three tubular branch grafts with blood flow into the respective aortic branch vessels.

The protective sheath can be configured to be withdrawn in a direction away from the descending thoracic aorta end toward the ascending aorta end, and on disengagement of the guide wires and withdrawal of the protective sheath past the ascending to allow expansion of the aortic stent graft, blood flow through the aortic stent graft from the ascending aorta end encourages expansion and engagement with the vessel walls. The delivery system can further comprise one or more retaining threads releasably engaged with the tubular main body at the ascending aorta end to retain the tubular main body in position against blood flow during positioning and expansion of the aortic stent graft.

According to another aspect of the invention there is provided a method of aortic arch aneurysm repair using an aortic stent graft and a delivery system as described above, the method comprising the steps of:

delivering the aortic stent graft in the collapsed position covered by the protective sheath to the aortic arch of a patient via a left lateral thoracotomy, through the left ventricle; partially withdrawing the protective sheath toward the ascending aorta end to allow positioning of the three tubular branch grafts into respective aortic arch branch vessels;

manipulating each of the three branch guide wires to guide each respective tubular branch graft with blood flow into a respective aortic branch vessel; and

withdrawing the guide wires and protective sheath to allow expansion of the aortic stent graft with blood flow.

Brief description of the drawings

An embodiment, incorporating all aspects of the invention, will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is an illustrative example of a stent graft according to an embodiment of the present invention in a deployed configuration;

Figure 2 is an illustrative example of a stent graft according to an embodiment of the present invention configured for deployment;

Figure 3 is an illustrative example of a configuration of guide wires used to aid

positioning the main stent body and stent branches within the aortic arch and branch vessels;

Figure 4 is an illustrative example of a guide wires passing through the stent graft of an embodiment of the present invention;

Figure 5 illustrates a first intermediate stage of a method of deploying a stent graft in accordance with an embodiment of the present invention;

Figure 6 illustrates a second intermediate stage of a method of deploying a stent graft in accordance with an embodiment of the present invention;

Figure 7 illustrates a third intermediate stage of a method of deploying a stent graft in accordance with an embodiment of the present invention;

Figure 8 illustrates the most common anatomy of a human aortic arch;

Figure 9 illustrates an example of a tip structure and guide wire for a stent graft

tubular according to an embodiment of the invention.

Definitions

Aneurysm - an enlargement of the aorta and associated weakness in the wall of the aorta that can lead to rupture of the wall of the aorta.

Anterograde - with the direction of blood flow.

Aortic Arch - part of the aorta forming a curve between the ascending aorta and descending thoracic aorta, from which the branch vessels for the innominate artery (IA), left common carotid artery (LCCA) and left subclavian artery (LSCA) arise.

Embolization - passage of an intravascular mass within the bloodstream.

Endovascular surgery - a form of minimally invasive surgery designed to access many regions of the body via major blood vessels.

Fenestration - openings in the wall of a structure, naturally occurring or created

surgically.

Retrograde - against the direction of blood flow.

Detailed description

Embodiments of the present invention provide an aortic stent graft configured for placement in the aortic arch and a delivery system to enable endovascular delivery of the aortic stent graft. The configuration of the aortic arch presents particular problems for endovascular repair. The branch vessels for the innominate artery (IA), left common carotid artery (LCCA) and left subclavian artery (LSCA) are located close together in the aortic arch. The IA branches separately into the right subclavian artery (RSCA) and the right common carotid artery (RCCA) above the aortic arch. Aortic stent grafts in accordance with embodiments of the present invention are configured for deployment into the aortic arch and branch vessels for aneurysm repair in this region.

An aortic stent graft in accordance with an embodiment of the present invention is illustrated in Figure 1. The aortic stent graft 100 comprises a tubular main graft body 1 10, and three tubular graft branches 120, 130, 140. The tubular main graft body 1 10 is configured to, in a deployed position, have a diameter corresponding to the internal diameter of the aorta. The tubular main graft body 110 has an ascending aorta end 150 and a descending thoracic aorta end 160 and is long enough to allow the main graft body to extend 1 10 from within a portion of the ascending aorta to within a portion the descending aorta. The three tubular graft branches 120, 130, 140 extend from the tubular main graft body and are configured to, in a deployed position, align with and extend into three aortic branch vessels extending from the aortic arch.

In the embodiment shown, the three tubular graft branches are configured as an IA branch 120 to deploy into the innominate artery (IA), an LCCA branch 130 to deploy into the left common carotid artery (LCCA) and an LSCA branch 140 to deploy into the left subclavian artery (LSCA). IN a deployed position the tubular main body 1 10 is configured to extend from above the sinotubular junction of the aorta to the descending thoracic aorta beyond the LSCA. Thus, the aortic stent graft can support vessel walls through the whole of the aortic arch topography.

The aortic stent graft 100 is formed from a flexible biocompatible material with a self-expanding support mechanism. The material allows the aortic stent graft to be flexible in a pre-deployment position, where the tubular main body 110 and tubular graft branches 120, 130, 140 are in a collapsed state. This allows positioning of the tubular main body 1 10 in the aortic arch and each one of the three tubular graft branches 120, 130, 140 into one aortic branch vessel via an endovascular procedure. The self-expanding support mechanism causes expansion to a deployed position to engage walls of the aortic arch and branch vessels. The self-expanding support system can be formed from memory shape material. For example, the aortic stent graft may be formed from a polyester material with a memory metal alloy skeleton. The aortic stent graft can also have a fixative at a base of each of the tubular main graft body and the three tubular graft branches to aid fixation and sealing the graft against the vessel wall.

Embodiments of the present invention also provide a delivery system for deployment of the aortic stent graft. The delivery system comprises a protective sheath holding each of the tubular main graft body and the three tubular graft branches in a collapsed position for delivery into the aortic arch, and four guide wires. A main guide wire extends through the protective sheath and engages with the tubular main graft body and is manipulate to guide the tubular main body into the aortic arch. Three branch guide wires, one for each tubular graft branch extend through the protective sheath and engage with one respective tubular graft branch to guide the respective tubular graft branch into a respective aortic branch vessel.

An embodiment of the delivery system will be described with reference to Figures 2, 3 and 4. Figure 2, shows an illustrative example of an aortic stent graft 100 in a collapsed position within a protective sheath 200. Figure 3 shows an example of the four guide wires 210, 220, 230, 240 entering the tubular main graft body at the ascending aorta end 150. Each guide wire extends through to the end of the respective tubular graft branch. The main guide wire 210 extends through the tubular main graft body 1 10 from the ascending aorta end 150 to the descending thoracic aorta end 160. A first branch guide wire 220 extends through the tubular main graft body 1 10 from the ascending aorta end 150 and through the I A branch 120. A second branch guide wire 230 extends through the tubular main graft body 110 from the ascending aorta end 150 and through the LCA branch 130. A third branch guide wire 240 extends through the tubular main graft body 110 from the ascending aorta end 150 and through the LSCA branch 140.

Figure 4 shows an example (not to scale) of the four guide wires extending through the main stent graft body to the tips of each of the tips of the tubulars. For delivery into the aortic arch of the patient the stent is covered by the protective sheath. Once in the aortic arch the sheath can be partially withdrawn and the individual tubular positioned in their respective vessels while still in a collapsed state. It should be appreciated that blood can flow through all vessels past the stent graft while it is in the collapsed state during positioning. The guide wires are fixed in such a way that they can be released and retracted form the branch graft once the branch graft is positioned. The graft can then be allowed to expand to engage the vessel walls. This expansion and engagement can be aided by blood flow through the expanding tubular graft branches.

Guide wires extending through the tubular branches of the stent graft is a preferred embodiment for the delivery system and this is in line with current practice for stent graft placement. However, alternative arrangements are envisaged. For example, guide wires for one or more of the tubular graft branches may extend along the outside of the tubular main graft body and engage with the outside of the tubular graft branch.

An example of an aortic stent graft, delivery system and method of deliver will now be discussed with reference to Figures 5, 6 and 7. In this example, the

endovascular aortic arch graft takes the form of a woven polyester tube graft supported by a nickel titanium memory shape alloy (for example, nitinol) skeleton that will expand when pressurized at body temperature and maintain its expanded form. The tubular main graft body 1 10 will have three tubular graft branches 120, 130, 140 from the convex surface. The descending thoracic aorta end of the tubular main graft body 160 extends around 50-60mm beyond the last branch 140. The length of the main tubular body is configured such that when deployed the ascending aorta end 150 will lie around 15-20mm above the sinotubular junction of the aorta, and the main tubular body 1 10 will extend to the descending thoracic aorta beyond the LSCA. The overall length of a preferred embodiment of the graft will be around 300-350mm. When deployed the main body of the graft will expand to 30-35mm, corresponding to the internal diameter of the aorta. The tubular graft branches 120, 130, 140 will be 10, 8 and 8mm respectively corresponding to the internal diameters of the IA, LCCA and LSCA. The tubular graft branches are configured to extend from the tubular main graft body at positions corresponding to the openings of the IA, LCCA and LSCA

respectively.

In this embodiment the branched aortic stent graft will be delivered by an endovascular route. It will be delivered via a trans-apical route, anterograde, via a left lateral thoracotomy, through the left ventricle of the heart. This avoids the need to access the femoral vessels and reduces the chance of injury. For this procedure the graft will be provided in a collapsed state in a delivery system as described above with all 4 wires preloaded and covered by a protective sheath.

The main body of the graft will accommodate 4 guide wires that will be used to direct the graft and its branches into position in the corresponding branches of the aortic arch and finally the descending thoracic aorta. For a preferred embodiment the guide wires will be 0.035 inch diameter nitinol guide wires with hydrophilic coating. Each branch of the graft will have a closed tip with a mechanism to engage the guide wire. The wire will be used to direct the graft branch into the corresponding aortic arch branch. The tip mechanism allows the guide wire to be released and removed after the branch graft is correctly positioned and deployed allowing blood flow through the graft.

The guide wires 210, 220, 230, 240 extend through the tubular main graft body 1 10 from the ascending aorta end 150 through the respective branches, these being the descending thoracic aorta end 160 of the main body for the main guide wire 210, the I A branch 120 for the I A guide wire 220, the LCCA branch 130 for the LCCA guide wire 230 and the LSCA branch 140 for the LSCA guide wire 240. These graft branches will eventually be guided into the arch branches (IA, LCCA LSCA and Descending Thoracic Aorta) by the wire. In a preferred embodiment the entire delivery mechanism, with the graft in its collapsed state, preloaded with the guide wires and the entire graft covered with a protective sheath, has an external diameter of around 10- 12mm. In one embodiment the diameter is 11.33mm (34Fr), this is a size of sheath that has been has been successfully passed across the apex of the heart, for example, as used for deployment of transcatheter aortic valves. It should be appreciated that the diameter of the protective sheath may vary depending on the embodiment and any diameter sufficient to retain the collapsed stent and be successfully deployed through the apex of the heart. Improvements in sheathing materials and technologies may enable the external diameter of the protective sheath to be reduced.

A first stage of the deployment procedure is illustrated in Figure 5. The left ventricle 510 will be approached through a mini left antero-lateral thoracotomy and the device passed through a purse string suture in the muscle. The graft within the protective sheath 200 will be passed through the left ventricle 510 through the aortic valve 520 under radiological control with the heart beating in sinus rhythm. The graft and delivery wires will be delivered through the apex, across the aortic valve and sinotubular junction and positioned in a collapsed state in the ascending aorta proximal to the IA, under X-ray guidance.

Once across the aortic valve 520 and into the ascending aorta 530 the sheath 200 will be withdrawn to just before the first branch 120, as shown in Figure 6. Thus, allowing the branches 120, 130, 140 of the graft to be directed under radiological control using the internal wires to their respective positions in the branches 540, 550, 560 of the aortic arch, and the distal end 160 of the main body 110 to be directed into position in the descending thoracic aorta 570. At this point the graft remains collapsed lying freely in the flow of blood around the arch.

The wires are then used to guide each branch graft 120, 130, 140, 160 into its respective branch one each to IA 540, LCCA 550, LSCA 560 and descending thoracic aorta 570. Each finger-like branch graft remains sealed at the tip and blood continues to flow past it in its collapsed state. It should be appreciated that as the graft branches are being manipulated into position with the flow of blood from the heart through the vessels, the blood flow may assist positioning of the branch grafts into the vessels.

The guide wires are fixed in a way that they can be released, to allow expansion of the branch graft, and allow the guide wire to be retracted from the branch graft, once the graft is positioned.

The graft remains in a collapsed state and blood can freely flow past it in to all the vessels of the arch during positioning. Once the graft is correctly positioned, the sheath will then be withdrawn to expose the proximal portion 150 of the graft which, now free from the constraints of the sheath, to allow the graft to expand. Expansion of the graft is aided by the blood flow, expanding as it is pressurized by the flow of blood from the contracting ventricle. An example illustrating expanding of the graft is shown in Figure 7, where similar to a windsock, each branch of the graft will fill and deploy in its respective position. The graft deploys using the pressure of anterograde blood flow, becomes filled with blood at left ventricle (LV) pressures and fills like a windsock, deploying into each of the branches as positioned previously.

When the position is judged as satisfactory by radiological assessment the guiding wire will be withdrawn from each graft branch sequentially allowing the branch to become open and unobstructed for flow to occur through it.

In some embodiments, before withdrawing the guiding wire, the graft can be fixed to the respective branches by an internal stent placed using the guiding wire. An example of a suitable style of internal stent is, an expandable stent such as those used in the stunting of atherosclerotic plaques in leg arteries or coronary arteries. Such stents have a tubular, lattice structure and can be assembled from a range of metals, including nitinol, stainless steel, and cobalt chromium. The internal stent will be chosen to have a diameter (expanded) depending on the diameter of the individual vessel. The internal stent can be expanded by a balloon, and the stent remains in the graft. Such stents are associated with blocking with blood clots, attempts have been made to prevent this by adding a clot prevention agent to the internal stent. For example, the internal stent may be coated with anti-thrombotics or made to slowly elute antithrombotics to reduce risks of blocking due to blood clots. Examples of suitable stents include: first-generation sirolimus-eluting stents, bare-metal (cobalt-chromium) stents, or a second-generation everolimus-eluting stents.

In an embodiment the tubular main graft body can have retaining threads 710, 720 attached at the proximal end 150 to aid retaining the graft in the correct position in in the aorta as it is deployed and begins to experience a force pushing it distally as a result of an increase resistance offered to blood flow, for example as the sheath is removed and the graft allowed to expand. These threads can be released and removed one the graft has fully expanded and is retained in position by engagement with the vessel wall.

In an embodiment at the base of each branch graft and the most proximal portion of the main body of the graft is a sealing means that provides active sealing and fixation of the graft against the vessel wall, to reduce the incidence of endoleaks.

For example, this sealing means may be a fixative in the form of a biocompatible coating or mechanical fixing mechanism. In an embodiment at the base of each graft branch and the main body of the graft will be a coating to form a sealing mechanism when pressurized against the wall of the vessel. For example, the coating may be an adhesive released during deployment of the sent to secure the sent to the vessel wall.

Alternatively the stent skeleton structure may be configured to mechanically grip the vessel wall to secure the stent in place. Another suitable sealing means is a polymer coating which becomes swollen on exposure to blood to effect sealing between the graft and the vessel wall. A balloon can be passed into the ascending aorta end section of the graft and expanded such that the sealing means is activated and the graft fills with blood. If the sealing mechanism is not successful, further balloon dilatation of the graft underlying the sealing mechanism can be performed aiming to prevent endoleaks.

Once all branches are deployed all the wires are removed and completion angiography will be carried out to check for position and leaks.

The above example of an embodiment of an aortic arch stent graft and its deployment system enables a trans-apical, anterograde endovascular aortic arch repair procedure. It is believed by the inventors that anterograde delivery of the stent graft can be advantageous compared with retrograde delivery. Retrograde delivery of a stent graft retrograde in a diseased aorta can cause embolization increasing the risk of stroke. In addition the necessity of cannulating the femoral vessels to allow the passage of a large caliber retrograde delivery system carries increased risk of damage to the femoral vessels so compromising the circulation to the lower limbs. The trans- apical route of delivery has been successfully used in the delivery of Transcatheter

Aortic Valve Implantation (TAVI) and embodiments of the present invention now enable this procedure to be used for aortic arch aneurysm repair.

Embodiments of the present invention may also be utilized for endovascular repair of the ascending aorta. For example, it can be difficult to secure conventional tubular stent grafts proximally on zone 0 (shown in Figure 8) of the ascending aorta due to proximity of coronary arteries and aortic valve. Embodiments of the aortic stent graft described above may offer improved patient outcomes.

Although, a procedure for advantageous anterograde delivery of the aortic arch stent graft has been described, other methods of deployment of the aortic arch stent graft are also considered within the scope of the present invention. For example, retrograde delivery may be necessary for some patients, or ascending aortic delivery with hemisternotomy and an access graft sutured to the aortic wall. If the apex of the heart is unsuitable for cannulation the graft can be delivered via the side branch of a graft to the ascending aorta. This graft to the ascending aorta could be placed via a hemisternotomy prior to graft deployment, reducing the need for deep hypothermic circulatory arrest and full sternotomy.

For retrograde delivery the delivery system is modified such that the guide wires extend through the tubular main graft body 1 10 from the descending thoracic aorta end 160 toward the ascending aorta end 150, with each of the branch guide wires extending through the tubular graft branches 120, 130, 140 and the main guide wire extending to the ascending aorta end of the main tubular graft body. This embodiment may require stiffer guide wires than an embodiment for anterograde deployment, in particular for the main guide wire due to the requirement for positioning against the direction of blood flow in the aortic arch. Deploying the graft will require removal of the sheath 200 from the ascending aorta end 150 to just before the LSCA branch graft 140 and manipulation of the graft into position in the ascending aorta and branch vessels. Once all the branches are in position the sheath can be withdrawn and the ascending aorta end of the tubular main graft body opened to allow expansion of the stent graft and blood flow through to encourage expansion and sealing in each of the branch vessels via a windsock effect as described above. In this embodiment the aortic stent graft may be provided with a sealing means that assists opening and fixing of the ascending aorta end 150 against the vessel wall, for example a

mechanical fixing means incorporated with the memory shape skeleton for the stent.

It should be appreciated that different configurations for the delivery system are envisaged within the scope of the present invention.

In a preferred embodiment, the wires are initially fixed to the apex of each branch of the graft by way of a collapsible nose cone that will give form and an ability to direct the tip into each arch branch. The cone tip will seal the branch graft until it is detached, so there will be no flow through it until the positioning wire is removed at which point there will be pressure to expand the correctly positioned graft. An example of a sealing mechanism is illustrated in Figure 9. In this embodiment the tip of the tubular 910 is closed with a sealing tip 920 allowing the guide wire 930 to pass through whilst still maintaining a seal. The guide wire 930 is inserted into the stent graft to engage with the tip 930. In the embodiment illustrated the guide wire 930 extends through the seal 920. In this way the graft can be "backloaded" in a collapsed state onto the wires prior placement of the wires. After correctly positioning the tubular 910, and deployed the wires 930 can be removed breaking the seal 920 and allowing flow of blood through the graft tubular 910.

In a preferred embodiment the material of the graft would be polyester with a self-expanding support system. For example, the graft may be formed of polyethylene terephthalate, also known by the trade mark Dacron, however any suitable

biocompatible material may be used. The material of the stent graft may also be woven. The self-expanding support mechanism can be provided using a memory shape polymer or metal alloy. For example, a memory shape skeleton attached to the material of the graft. In a preferred embodiment a memory shape metal alloy skeleton can be formed using a nickel titanium alloy having memory shape properties, for example the alloy known as nitinol. However, any biocompatible memory shape material may be used.

It should be appreciated that embodiments of the stent graft can have different spacing between the branch vessels to correspond to variants of patients' aortic arch anatomy. The distance between the branch tubulars can vary between embodiments of the invention to accommodate different individual's anatomies. The size of the main and branch graft tubulars can also vary between embodiments as well as the spacing between the branch grafts. It should be appreciated that stent grafts may be manufactured in one or more sizes, configured to be suitable for the most commonly occurring aortic arch anatomy, as shown in Figure 8, to treat a majority of patients. Embodiments of the sent graft can also be configured to have the branches for the IA and LCCA closely adjacent, suitable for deployment in the most commonly occurring bovine aortic arch variant, where the IA shares a common origin with the LCCA (occurring in -15% of the population and more common in individuals of African descent). Embodiments for such variants may have variations in the self-expanding support structure to allow the stent graft to conform to the variation in aortic arch anatomy when deployed. Such embodiments may also be suitable for use in some patient having a less common bovine aortic arch anatomy variant where the LCCA branches from the IA but not sharing a common origin (occurring in -9% of the population). For example, if the LCCA branching is sufficiently close to the opening of the IA, flexibility in the stent may also allow it to conform to this branching and provide sufficient support to the aortic arch to effect repair. A patient's particular aortic arch anatomy variant may be determined using pre-operative imaging and the correct stent graft embodiment chosen. Stent grafts could also be custom prepared to suit other variations in individual patient aortic arch anatomy. For example, a stent graft with only two branches may be required for some patients.

It is envisaged that embodiments of this invention may provide an entirely endovascular option for aortic arch repair surgery. There will be no requirement for open surgery, cardiopulmonary bypass or deep hypothermic circulatory arrest, reducing the complications of death and neurological injury associated with these. However, embodiments could also be used as part of a hybrid procedure allowing less invasive replacement of the aortic root to take place after the arch graft has been deployed. It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Claims

1. An aortic stent graft configured for placement in the aortic arch, the stent graft comprising:

2. The aortic stent graft as claimed in claim 1 , wherein the three tubular graft branches are spaced apart and configured to deploy into the innominate artery (IA), left common carotid artery (LCCA) and left subclavian artery (LSCA) respectively.

3. The aortic stent graft as claimed in claim 1 or claim 2, wherein the tubular main body is configured to extend, in the deployed position, from above the sinotubular junction of the aorta to the descending thoracic aorta beyond the LSCA.

4. The aortic stent graft as claimed in claim 2 or claim 3, wherein, in the deployed position, the tubular main body is configured to expand to a diameter of 30 to 35mm, and a first tubular graft branch for deployment into the IA is configured to expand to a diameter of 10m and second and third graft branches for deployment into the LCA and LSCA respectively are configured to expand to a diameter of 8mm.

5. The aortic stent graft as claimed in claim 1 wherein the tubular graft branch for deployment into the innominate artery (IA) and the tubular graft branch for deployment into the left common carotid artery (LCCA) are closely adjacent to conform to an aortic arch anatomy where the IA and LCCA share a common origin.

6. The aortic stent graft as claimed in any one or the preceding claims wherein the self-expanding support mechanism is provided by a memory metal alloy skeleton.

7. The aortic stent graft as claimed in claim 6 wherein the memory metal alloy is a nickel titanium alloy.

8. The aortic stent graft as claimed in any one of the preceding claims wherein the flexible biocompatible material is a polyester material.

9. The aortic stent graft as claimed in claim 8 wherein the flexible biocompatible material polyethylene terephthalate.

10. The aortic stent graft as claimed in any one of the preceding claims further comprising a fixative at a base of each of the tubular main graft body and the three tubular graft branches to aid fixation and sealing the graft against the vessel wall.

1 1. The aortic stent graft as claimed in claim 9 wherein the fixative is a

biocompatible adhesive.

12. A delivery system for an aortic stent graft as claimed in any one of the preceding claims, the delivery system comprising:

13. The delivery system as claimed in claim 12, wherein each of the main and branch guide wires extend through the main tubular graft body and respective tubular graft branches to engage at the distal end thereof to allow independent guidance of

5 each tubular branch graft into position in each aortic branch vessel in a collapsed state permitting blood flow past the aortic stent graft through all aortic branch vessels during positioning of each of the main tubular graft body and three tubular branch grafts.

14. The delivery system as claimed in claim 13 wherein each of the guide wires is0 engaged with the distal end of the respective main tubular graft body and tubular graft branches via a tip structure, the tip structure being configured to hold the respective tubular graft in a collapsed state until disengagement of the guide wire.

15. The delivery system as claimed in claim 14 wherein the tip structure is cone5 shaped.

16. The delivery system as claimed in any one of claims 12 to 15, wherein the four guide wires all extend through the main tubular body of the aortic stent graft from the ascending aorta end toward the descending thoracic aorta end to allow anterograde o delivery of the aortic stent graft via a patient's left ventricle.

17. The delivery system as claimed in claim 16 wherein the three branch guide wires are configured to direct each of the three tubular branch grafts with blood flow into the respective aortic branch vessels.

5

18. The delivery system as claimed in claim 17 wherein the protective sheath is configured to be withdrawn in a direction away from the descending thoracic aorta end toward the ascending aorta end, and on disengagement of the guide wires and withdrawal of the protective sheath past the ascending to allow expansion of the aortic 0 stent graft, blood flow through the aortic stent graft from the ascending aorta end

encourages expansion and engagement with the vessel walls.

19. The delivery system as claimed in claim 18 further comprising one or more retaining threads releasably engaged with the tubular main body at the ascending5 aorta end to retain the tubular main body in position against blood flow during positioning and expansion of the aortic stent graft.

20. A method of aortic arch aneurysm repair using an aortic stent graft as claimed in any one of claims 1 to 11 and a delivery system as claimed in claim 15, the method comprising the steps of:

delivering the aortic stent graft in the collapsed position covered by the protective sheath to the aortic arch of a patient via a left lateral thoracotomy, through the left ventricle;

partially withdrawing the protective sheath toward the ascending aorta end to allow positioning of the three tubular branch grafts into respective aortic arch branch vessels;