Patent Publication Number: US-11026823-B2

Title: Method and apparatus for controlling the deployment of a stent

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. non-provisional application Ser. No. 14/123,650, filed Dec. 3, 2013, entitled METHOD AND APPARATUS FOR CONTROLLING THE DEPLOYMENT OF A STENT, which is a U.S. national stage application of PCT international patent application No. PCT/GB2012/051235, filed Jun. 1, 2012, entitled METHOD AND APPARATUS FOR CONTROLLING THE DEPLOYMENT OF A STENT, which claims the benefit of United Kingdom patent application No. 1109305.1, filed Jun. 3, 2011, entitled METHOD AND APPARATUS FOR CONTROLLING THE DEPLOYMENT OF A STENT, which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the deployment of a stent element, and in particular to the deployment of a stent element to stabilise a tubular prosthesis. 
     BACKGROUND TO THE INVENTION 
     Artificial prostheses consisting of a tubular conduit having an open lumen are well-known and are used in medicine to replace diseased or damaged natural body lumens, such as, for example, blood vessels or other hollow organs for example bile ducts, sections of intestine or the like. The most common use of such artificial prostheses is to replace diseased or damaged blood vessels. 
     A number of vascular disorders can be treated by use of an artificial prosthesis. One relatively common vascular disorder is an aneurysm. Aneurysm occurs when a section of natural blood vessel wall, typically of the aortic artery, dilates and balloons outwardly. Whilst small aneurysms cause little or no symptoms, larger aneurysms pose significant danger to a patient. Rupture of an aortic aneurysm can occur without warning and is usually fatal, so significant emphasis is placed on early diagnosis and treatment. With an increasing ageing population, the incidence of aneurysm continues to rise in western societies. 
     Provided that an aneurysm is diagnosed prior to rupture, surgical treatment to repair the affected vessel wall is effective. Surgical treatment of aneurysm involves the replacement or reinforcement of the aneurismal section of aorta with a synthetic graft or prosthesis under general anaesthesia allowing the patient&#39;s abdomen or thorax to be opened (see Parodi et al., Annals of Vascular Surgery (1991) 5:491-499). The patient will then have a normal life expectancy. 
     Surgical repair of aneurysm is however a major and invasive undertaking and there has been much effort in developing less invasive methods. Currently, aneurysm repair generally involves the delivery by catheter of a fabric or ePTFE graft which is retained at the required location by deployment of metallic stent elements. The ability to deliver the graft/stent device by catheter reduces the surgical intervention to a small cut-down to expose the femoral artery and, in suitable circumstances, the device can be deployed percutaneously. Catheter delivery is beneficial since the reduced invasive nature of the procedure allows utilisation of a local anaesthetic and leads to reduced mortality and morbidity, as well as decreased recovery time. For example, endovascular repair is typically used for repair of infra-renal abdominal aortic aneurysms where the graft is placed below the renal arteries. Many different types of devices useful for endovascular repair are now available, for example a resiliently engaging endovascular element described in U.S. Pat. No. 6,635,080 (Vascutek) or a tubular fabric liner having a radially expandable supporting frame and a radiopaque marker element stitched to the liner as disclosed in U.S. Pat. No. 6,203,568 (Medtronic). 
     However, whilst the endovascular repair of aneurysms is now accepted as the method of choice, the technique has significant limitations and is not suitable for all patients. 
     As mentioned above, other vascular disorders are treatable by use of a vascular prosthesis. Examples include (but not limited to) occlusions, stenosis, vascular damage due to accident or trauma, and the like. Vascular prostheses are also used in by-pass techniques. 
     Endovascular techniques involve the delivery of a prosthesis by catheter. Since the internal lumen of the catheter defines the maximum dimensions of the prosthesis to be inserted, much effort has been expended in the design of prostheses which can be packaged in a minimal volume, and are easy to deploy once positioned at the required location. 
     One successful type of prosthesis is a stent graft comprising a conduit formed of a flexible sleeve attached to a rigid support or stent. The sleeve will typically be made of a fabric (usually a knitted or woven fabric) of ePTFE, PTFE, polyester (for example DACRON), polyethylene or polypropylene and may optionally be coated to reduce friction; discourage clotting or to deliver a pharmaceutical agent. The fabric will generally be porous on at least one surface to enable cell ingrowth. 
     The stent may be self-expandable and formed of a shape memory material, such as nitinol (a nickel-titanium alloy). 
     The stent grafts are inserted using a delivery catheter and, once correctly located at the site requiring treatment, are deployed by the withdrawal of a delivery sheath of the delivery catheter. The self-expandable stents are deployed by expanding radially upon release from the delivery sheath. Once deployed, the stents hold the graft in location by contact with the inner wall of the blood vessel. 
     One suitable stent design is a series of ring stent elements formed from discrete rings of a shape memory material, such as nitinol, attached to the fabric sleeve at spaced intervals. Such a design fulfils the requirements for minimal volume when packaged and, once delivered, readily expands to maintain the patency of the fabric lumen. However, stent grafts having such ring stent elements have the disadvantage that the rings are not readily capable of being contracted again and so do not allow adjustment of the position of the stent graft once deployed. 
     It is an object of the present invention to over come one or more of the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a delivery apparatus for controlling the deployment of a stent, the apparatus comprising:
         a delivery shaft adapted to carry a tubular prosthesis thereon and having a proximal end for insertion into a lumen and a distal end remote from the proximal end;   a retractable sleeve adapted to contain a tubular prosthesis carried on the delivery shaft;   a control handle adjacent the distal end of the delivery shaft;   at least one stent peak control wire extending from the proximal end of the delivery shaft to the control handle;   a peak controller at the control handle adapted to control the position of the stent peak control wire.       

     The term “wire” as used in this specification includes metallic and non-metallic wire, thread and filament. 
     The apparatus may comprise two or more stent peak control wires extending from the proximal end of the delivery shaft to the control handle, and the peak controller may be adapted to control the position of the two or more stent peak control wires. 
     The apparatus may further comprise:
         at least one stent valley control wire extending from the proximal end of the delivery shaft to the control handle; and   a valley controller at the control handle adapted to control the position of the stent valley control wire.       

     The apparatus may comprise two stent valley control wires extending from the proximal end of the delivery shaft to the control handle, and the apparatus may include two valley controllers at the control handle, each valley controller being adapted to control the position of a respective stent valley control wire. 
     The delivery shaft may include a plurality of longitudinal passages, each control wire extending through a respective longitudinal passage. 
     The apparatus may include one or more tow wires provided at the proximal end of the delivery shaft adapted for connection to a proximal end of a tubular prosthesis carried on the delivery shaft. The apparatus may include one or more back tether wires provided between the proximal end of the delivery shaft and the control handle adapted for connection to a distal end of a tubular prosthesis carried on the delivery shaft. 
     The control handle may include a manifold having a plurality of apertures, each control wire extending through a respective aperture. The manifold may include a plurality of haemostasis valves switchable between open and closed positions. 
     The peak controller may comprise a rotatable collar. The rotatable collar may be mounted for rotation about a longitudinal axis of the control handle. The peak controller may include a winder which rotates with the collar and on which are wound the stent peak control wires. 
     Each valley controller may comprise a slider. Each valley controller may include an actuating surface and a ratchet adapted to allow the slider to move when the actuating surface is depressed and to hold the slider in an engaged position when the actuating surface is released. The sliders may be mounted for longitudinal sliding movement. Each slider may include a wire connector to which is connected the respective stent valley control wire. 
     Preferably the delivery shaft includes a plurality of peak apertures adjacent the proximal end thereof, each stent peak control wire extending through one of said plurality of peak apertures. Preferably the delivery shaft includes a plurality of valley apertures adjacent the proximal end thereof, each stent valley control wire extending through one of said plurality of valley apertures. Preferably the valley apertures are arranged between the peak apertures and the distal end. 
     The control wires may be looped wires which extend from the control handle to the proximal end of the delivery shaft and back to the control handle. 
     The apparatus may include a plurality of release wires extending from the control handle along the delivery shaft and having a proximal end at or near the proximal end of the delivery shaft and a distal end at the control handle. The proximal end of each release wire is adapted to be connected to a respective connection between a tubular prosthesis carried on the delivery shaft and one of the stent peak control wires, the stent valley control wires, the tow wires and the back tether wires. The distal end of each release wire may be connected to a release clip mounted on the control handle. The release clip may be removed from the control handle and pulled with its corresponding release wire or wires away from the apparatus, thereby releasing the respective connection between a tubular prosthesis carried on the delivery shaft and one of the stent peak control wires, the stent valley control wires, the tow wires and the back tether wires. 
     According to a second aspect of the present invention there is provided a method of deploying a ring stent, the method comprising the steps of:
         providing a tubular prosthesis including a ring stent thereon on a delivery shaft, the delivery shaft having a proximal end for insertion into a lumen and a distal end remote from the proximal end, and having two stent peak control wires extending from the proximal end to the distal end;   attaching the first ends of two stent peak control wires to first and second diametrically opposed peak connection points on the tubular prosthesis adjacent the ring stent;   attaching the second ends of the two stent peak control wires to a peak controller provided at a control handle adjacent the distal end of the delivery shaft;   holding the two stent peak control wires under tension such that the peak connection points are held by the stent peak control wires in a folded arrangement towards the delivery shaft; and   operating the peak controller to permit movement of the stent peak control wires along the delivery shaft such that the peak connection points are urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent adopts a partially deployed position.       

     The peak connection points may be on the ring stent. 
     The delivery shaft may include two stent valley control wires extending from the proximal end to the distal end, and the method may comprise the further steps of:
         attaching the first ends of the two stent valley control wires to first and second diametrically opposed valley connection points on the tubular prosthesis adjacent the ring stent, the valley connection points being provided midway between the peak connection points;   attaching the second ends of the two stent valley control wires to first and second valley controllers respectively provided at the control handle;   holding the two valley peak control wires under tension such that the valley connection points are held by the stent valley control wires in a folded arrangement towards the delivery shaft; and   selectively operating one of the first and second valley controllers to permit movement of the stent valley control wires along the delivery shaft such that the first or second valley connection point is urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent is rotated in the partially deployed position.       

     The valley connection points may be on the ring stent or may be on a valley line between two adjacent ring stents on the tubular prosthesis. 
     The method may include the further step of selectively operating the other of the first and second valley controllers to permit movement of the stent valley control wires along the delivery shaft such that both the first and second valley connection points are urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent adopts a fully deployed position. 
     The method may include the further step of selectively operating one or more of the peak controller and first and second valley controllers to pull at least some of the control wires along the delivery shaft such that one or more of the connection points adjacent the ring stent are moved towards the delivery shaft against the resilience of the ring stent to permit the ring stent to be moved in position. 
     The control wires may be looped wires which extend from the control handle to the peak or valley connection points and back to the control handle. The peak or valley connection points may be eyelets through which the looped wires are threaded. 
     The step of operating the peak controller may include rotating a rotatable collar to wind or unwind the stent peak control wires on a winder. 
     The step of operating the first or second valley controller may include moving a slider which includes a wire connector to which is connected the respective stent valley control wire. 
     According to a third aspect of the present invention there is provided a method of causing the rotation of a ring stent in a lumen, the method comprising the steps of:
         providing a tubular prosthesis including a ring stent thereon on a delivery shaft, the delivery shaft having a proximal end for insertion into a lumen and a distal end remote from the proximal end, and having two stent valley control wires extending from the proximal end to the distal end;   attaching the first ends of two stent valley control wires to first and second diametrically opposed valley connection points on the tubular prosthesis adjacent the ring stent;   attaching the second ends of the two stent valley control wires to first and second valley controllers respectively provided at a control handle adjacent the distal end of the delivery shaft;   holding the two stent valley control wires under tension such that the valley connection points are held by the stent valley control wires in a folded arrangement towards the delivery shaft; and   selectively operating one of the first and second valley controllers to permit movement of the stent valley control wires along the delivery shaft such that the first or second valley connection point is urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent is rotated.       

     The valley connection points may be on the ring stent or may be on a valley line between two adjacent ring stents on the tubular prosthesis. 
     The method may include the further step of selectively operating the other of the first and second valley controllers to permit movement of the stent valley control wires along the delivery shaft such that both the first and second valley connection points are urged by the resilience of the ring stent to move away from the delivery shaft by a respective selected amount and the ring stent adopts a selected rotational position. 
     The delivery shaft may include two stent peak control wires extending from the proximal end to the distal end, and the method may comprise the further steps of:
         attaching the first ends of the two stent peak control wires to first and second diametrically opposed peak connection points on the tubular prosthesis adjacent the ring stent, the peak connection points being provided midway between the valley connection points;   attaching the second ends of the two stent peak control wires to a peak controller provided at a control handle adjacent the distal end of the delivery shaft;   holding the two stent peak control wires under tension such that the peak connection points are held by the stent peak control wires in a folded arrangement towards the delivery shaft; and   operating the peak controller to permit movement of the stent peak control wires along the delivery shaft such that the peak connection points are urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent adopts a fully deployed position.       

     The peak connection points may be on the ring stent. 
     The method may include the further step of selectively operating one or more of the peak controller and first and second valley controllers to pull at least some of the control wires along the delivery shaft such that one or more of the connection points adjacent the ring stent are moved towards the delivery shaft against the resilience of the ring stent to permit the ring stent to be moved in position. 
     The control wires may be looped wires which extend from the control handle to the peak or valley connection points and back to the control handle. The peak or valley connection points may be eyelets through which the looped wires are threaded. 
     The step of operating the peak controller may include rotating a rotatable collar to wind or unwind the stent peak control wires on a winder. 
     The step of operating the first or second valley controller may include moving a slider which includes a wire connector to which is connected the respective stent valley control wire. 
     According to a fourth aspect of the present invention there is provided a stent system comprising a tubular prosthesis including a resilient ring stent at a first end thereof, and an apparatus for controlling the deployment of the ring stent, the apparatus comprising:
         a delivery shaft carrying the tubular prosthesis thereon and having a proximal end for insertion into a lumen and a distal end remote from the proximal end, the ring stent being adjacent the proximal end;   a retractable sleeve adapted to contain the tubular prosthesis carried on the delivery shaft;   a control handle adjacent the distal end of the delivery shaft;   a first stent peak control wire extending from the proximal end of the delivery shaft to the control handle; and   a peak controller at the control handle adapted to control the position of the first stent peak control wire;   wherein the stent peak control wire is connected to a first peak connection point on the tubular prosthesis adjacent the ring stent.       

     The apparatus may further include a second stent peak control wire extending from the proximal end of the delivery shaft to the control handle, wherein the peak controller is adapted to control the position of the second stent peak control wire, and wherein the second stent peak control wire is connected to a second peak connection point on the tubular prosthesis adjacent the ring stent diametrically opposed to the first peak connection point. 
     The peak connection points may be on the ring stent. 
     The apparatus may further include a first stent valley control wire extending from the proximal end of the delivery shaft to the control handle, and a first valley controller adapted to control the position of the first stent valley control wire, wherein the first stent valley control wire is connected to a first valley connection point on the tubular prosthesis adjacent the ring stent interposed between the first and second peak connection points. 
     The apparatus may further include a second stent valley control wire extending from the proximal end of the delivery shaft to the control handle, and a second valley controller adapted to control the position of the second stent valley control wire, wherein the second stent valley control wire is connected to a second valley connection point on the tubular prosthesis adjacent the ring stent diametrically opposed to the first valley connection point. 
     The valley connection points may be on the ring stent or may be on a valley line between two adjacent ring stents on the tubular prosthesis. 
     Preferably the apparatus is an apparatus according to the first aspect of the invention. 
     The ring stent may have the shape of the perimeter of a saddle. The first and second peak connection points may be provided at peaks of the saddle. The first and second valley connection points may be provided at valleys of the saddle. Preferably the distance between the valley connection points and the control handle is less than the distance between the peak connection points and the control handle. 
     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. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will now be further described by reference to the following figures, in which: 
         FIG. 1  is a schematic illustration of a delivery shaft and stent graft of a delivery apparatus of the invention; 
         FIGS. 2 and 3  are a top view and a side view respectively of the stent graft of  FIG. 1 ; 
         FIGS. 4 and 5  are a top view and a side view respectively of the apparatus of  FIG. 1 ; 
         FIG. 6  is a schematic illustration of an operator operating the apparatus of  FIG. 1 ; 
         FIG. 7  is a schematic illustration of a thoracic arch during a first stage of a method of deployment of a ring stent according to the invention; 
         FIG. 8  is a side view of the handle of the delivery apparatus during a second stage of a method of deployment of a ring stent according to the invention; 
         FIG. 9  is a schematic illustration of a thoracic arch during the second stage of a method of deployment of a ring stent according to the invention; 
         FIG. 10  is a schematic illustration of a thoracic arch during a third stage of a method of deployment of a ring stent according to the invention; 
         FIG. 11  is a side view of the handle of the delivery apparatus during a fourth stage of a method of deployment of a ring stent according to the invention; 
         FIG. 12  is a view of the handle of the delivery apparatus during a fifth stage of a method of deployment of a ring stent according to the invention; 
         FIG. 13  is a schematic illustration of a thoracic arch during the fourth and fifth stages of a method of deployment of a ring stent according to the invention; 
         FIG. 14  is a view of the handle of the delivery apparatus during a sixth stage of a method of deployment of a ring stent according to the invention; 
         FIG. 15  is a partial sectional view through the control handle of the delivery apparatus of  FIG. 1 ; 
         FIGS. 16 and 17  are a partial top view and a partial side view respectively of the delivery apparatus of  FIG. 1 ; 
         FIG. 18  is a partial isometric view of the control handle of the delivery apparatus of  FIG. 1 ; 
         FIG. 19  is a partial top view of the control handle of the delivery apparatus of  FIG. 1  with the control wires installed; 
         FIG. 20  is a partial isometric view of the control handle of the delivery apparatus of  FIG. 1  with the control wires installed; 
         FIG. 21  is a schematic partial view of the proximal end of the delivery shaft of the delivery apparatus of  FIG. 1  with the control wires installed; and 
         FIG. 22  is a schematic view of the stent graft on the delivery shaft of the delivery apparatus of  FIG. 1  with the control wires installed. 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Referring to  FIG. 1 , there is shown a delivery apparatus  10  used to deliver a tubular prosthesis, for example a stent graft  20 , to the thoracic arch. The delivery apparatus  10  includes a delivery shaft  30  having a central passage  31  adapted to travel on a guide wire  32  provided in the thoracic arch, so that the shaft  30  can be extended within the body of a patient to the correct location. Such guide wires are known in the art and are not described further. 
     The stent graft is shown in more detail in  FIGS. 2 and 3 . The stent graft includes a first ring stent  22 , a second ring stent  24  and a number of other ring stents  26 . The ring stents  22 ,  24 ,  26  are attached to a sleeve  28  of the stent graft  20 . The sleeve  28  is a flexible tubular conduit having the ring stents  22 ,  24 ,  26  attached thereto to maintain the patency of the sleeve lumen after deployment. The sleeve  28  is a woven or knitted flexible fabric which is generally impervious to fluid such as blood. Suitable materials include polyester, such as Dacron. The sleeve  28  may be coated to reduce blood clotting, to reduce friction or to deliver a medicament. The stent graft  20  shown in  FIGS. 1 to 3  in the expanded or deployed configuration. 
     The ring stents  22 ,  24 ,  26  are typically formed from a resilient alloy material suitable for medical use, such as nitinol, and are generally saddle shaped. The first ring stent  22  has two diametrically opposed ring stent peaks  40 A,  42 A and two diametrically opposed ring stent valleys  44 A,  46 A. The ring stent  22  can fold about its peaks  40 A,  42 A and valleys  44 A,  46 A to adopt a compact folded configuration, but the resilience of the ring stent urges it towards the expanded position shown in  FIGS. 1 to 3 . Similarly the second ring stent  24  has two diametrically opposed ring stent peaks  40 B,  42 B and two diametrically opposed ring stent valleys  44 B,  46 B, and can fold in the same way about its peaks and valleys. The folding of at least some of the peaks and valleys of the first and second ring stents  22 ,  24  can be selectively controlled by control wires, as is described below. The remaining stents are also capable of folding about their peaks and valleys so that they can adopt a compact folded configuration when held in a retractable sleeve  36 , but their peaks and valleys are not selectively foldable. 
     Adjacent to the ring stent peaks  40 ,  42  of the first and second ring stents  22 ,  24  are provided hooks  48  which engage with the lumen in which the stent graft  20  is deployed when the ring stent peaks  40 ,  42  expand away from the delivery shaft  30 . Also adjacent to the ring stent peaks  40 ,  42  of the first and second ring stents  22 ,  24  are provided connection loops  146 , which serve as stent peak connection points, and through which stent peak control wires  50 ,  52 ,  54 ,  56  are connected, as described below. Further connection loops  148  are provided adjacent to the ring stent valleys  44 ,  46  of the first ring stent  22 . The loops  148  serve as stent valley connection points for the connection of stent valley control wires  70 ,  72 , as described below. Instead of providing stent valley connection points at the first ring stent  22 , as illustrated in  FIGS. 1 to 3 , they may be provided at the second ring stent  24 , or at both the first and second ring stents  22 ,  24 , or at both the first and third ring stents  22 ,  24 , or on the fabric of the sleeve  28  on the valley line between the first and second ring stents  22 ,  24 . The control wires may be of any suitable material and in a preferred embodiment are of Ultra High Molecular Weight Polyethylene. 
     The delivery apparatus  10  is shown in  FIGS. 4 to 6 . The delivery apparatus  10  comprises a delivery shaft  30  having a proximal end  33  and a distal end  34 . Surrounding the delivery shaft is a retractable sleeve  36  which can be retracted using a retraction wheel  120  or a manual slider  122 , which serve to retract the retractable sleeve  36  inside the shaft  124  of the apparatus. The retraction mechanism, including the retraction wheel  120  and manual slider  122 , does not form part of the present invention, and is described in more detail in the applicant&#39;s UK patent application GB1109316.8 filed 3 Jun. 2011. 
     At the distal end of the shaft  124  is a grip portion  126 , which the operator holds in one hand  128  while operating the retraction wheel  120  with the other hand  129  to retract the sleeve  36 . Beyond the grip portion  126  is the control handle  38  which is used to control the deployment and position of the first and/or second ring stents  22 ,  24 . The control handle  38  includes a rotary collar  58  which serves as a peak controller and two sliders  74 ,  76  which serve as valley controllers. 
     The use of the delivery apparatus  10  to deploy a ring stent  22  of a stent graft  20  in the thoracic arch  100  will now be described with reference to  FIGS. 7 to 13 , which show the thorax and apparatus schematically as well as images of the sort produced by a suitable medical imaging device. Although the invention is described with reference to the thoracic arch, it is to be understood that the apparatus and method of the invention may be used in any location in a lumen  100  where control of the angle and position of a ring stent is required, and the invention is not limited to use with the thorax. 
     A guide wire  32  is located to guide the delivery apparatus  10 . An intended landing zone  102  for the ring stent  22  at the end of the stent graft  20  is identified. Preferably the intended landing zone is perpendicular to the vessel wall  104 ,  106  on both the inner and outer aspects of the thoracic arch. The delivery shaft  30 , on which the stent graft  20  is held by the retractable sleeve  36 , is slowly advanced along the guide wire  32  until the ring stent  22 , which is in its folded state within the retractable sleeve  36 , is at the intended landing zone, as shown in  FIG. 7 . 
     The retraction wheel  120  is then slowly rotated, as shown in  FIG. 8 , to retract the sleeve  36  to the position shown in  FIG. 9 . The first ring stent  22  is prevented from unfolding by the stent peak control wires  50 ,  52  which hold the ring stent peaks  40 A,  42 A towards the delivery shaft  30 . However the ring stents  26  which are not restrained by control wires are free to expand as the sleeve  36  is retracted so that the stent graft  20  adopts a tapered balloon shape. At this stage some longitudinal movement or rotation of the apparatus  10  and delivery shaft  30  is possible to ensure correct orientation and positioning of the ring stent peaks  40 ,  42  and valleys  44 ,  46 , since the hooks  48  which engage with the internal surface of the lumen  100  must be orientated correctly. Once the required position and orientation have been achieved, the stent graft  20  can be unsheathed from the sleeve  36  more rapidly by sliding the manual slider  122 , until the stent graft  20  is fully unsheathed as shown in  FIG. 10 . The release wire  140  associated with the retractable sleeve can then be removed. 
     The position of the proximal ring stent  22  can now be adjusted to ensure that the ring stent  22  is positioned perpendicular to the lumen  100 . The positions of the ring stent valleys  44 ,  46  are optimised by opening the valleys so that they are positioned perpendicular to the lumen wall  104 ,  106 . The first ring stent valley  44  can be opened and collapsed by moving the corresponding first valley controller slider  74  forwards in the direction of arrow  134 , as shown in  FIG. 11 , and backwards respectively. Similarly the second ring stent valley  46  can be opened and collapsed by moving the corresponding second valley controller slider  76  forwards in the direction of arrow  136 , as shown in  FIG. 11 , and backwards respectively. 
     Movement of the sliders  74 ,  76  results in movement of the corresponding stent valley control wires  70 ,  72  which extend from the control handle  38  along longitudinal passages  90  in the delivery shaft  30  and out of the delivery shaft  30  through apertures  132  to connection points  148  on the first and second ring stent valleys  44 ,  46  respectively. Each valley  44 ,  46  can be opened and closed independently of the other by moving the corresponding slider  74 ,  76 . The resilience of the ring stent  22  urges the valleys  44 ,  46  towards the open position, but the sliders  74 ,  76  are provided with a ratchet  80 , seen in  FIGS. 15 and 18 , so that they can only be moved when the operator releases the slider  74 ,  76  from the ratchet  80  by pressing on the actuator surface  78  of the slider  74 ,  76 . 
     Once the valley positions are optimised, the peaks  40 ,  42  of the ring stent  22  can be opened so that the proximal portion of the stent graft  20  is engaged with the vessel wall  104 ,  106 . The peaks  40 ,  42  are opened by depressing one or more buttons or tabs  59  on the peak controller rotary collar  58  and turning it in a clockwise direction in the direction of arrow  67  about the longitudinal axis  66  of the control handle, as shown in  FIG. 12 . Rotation of the collar  58  results in rotation of a peak controller winder  68  which permits movement of corresponding stent peak control wires  50 ,  52  which extend from the control handle  38  along longitudinal passages  90  in the delivery shaft  30  and out of the delivery shaft  30  through apertures  130  to connection points  146  on the first and second ring stent peaks  40 A,  42 A respectively, to permit the peaks to move way from the delivery shaft  30  under the resilience of the ring stent  22 . Instead of only the peaks  40 A,  42 A of the first ring stent  22  being controllable, the peaks  40 B,  42 B of the second ring stent  24  or other ring stents  26  may also be connected by associated stent peak control wires  54 ,  56  coupled in the same way to the peak control winder  68 , so that on rotation of the collar  58 , the peaks  40 B,  42 B of the second ring stent  24  also move way from the delivery shaft  30  under the resilience of the ring stent  22 . 
     The resilience of the ring stents  22 ,  24  urges the peaks  40 ,  42  towards the open position, but the button  59  prevents rotation of the collar  58  unless the button  59  is depressed, by means of a ratchet (not shown) so that the peaks  40 ,  42  can only be moved when the operator depresses the button  59 . 
     Once the peaks  40 ,  42  are fully opened the position of the ring stent  22  and stent graft  20  can be checked. If the position needs further adjustment, the peaks  40 ,  42  are retracted again to the collapsed position on the delivery shaft  30  by rotating the peak controller  58  in an anti-clockwise direction opposite to that of arrow  67 , and then the valleys  44 ,  46  are similarly retracted by moving the sliders in the direction opposite to that of arrows  134 ,  136 . The valleys and peaks can then be realigned to achieve a more accurate position. As before, once the valley positions are satisfactory, the peaks are opened to allow the stent graft  20  to engage with the vessel walls  104 ,  106  by means of the hooks  48 . The release wires  140 , whose proximal ends  96  hold the proximal end  92  of the stent graft  20  on the delivery shaft  30 , and the looped back tether wires  98 , which hold the distal end  94  of the stent graft  20  on the delivery shaft  30 , can then be removed, prior to re-sheathing with the retractable sleeve  36  and removal of the delivery apparatus from the lumen  100 . The proximal end  96  of each release wire  140  is associated with a connection  146 ,  148  between the stent graft  20  and one of the stent peak control wires  50 ,  52 , the stent valley control wires  70 ,  72 , and the tow or back tether wires  98 , so that pulling the release wire  140  causes the connection  146 ,  148  to be broken. Such release wires  140  are known, for example in EP-A-910309, and are not described further. In the described embodiment the release wires travel through the proximal end  33  of delivery shaft  30  to assist in providing stability during the removal of the release wires. The distal ends  144  of the release wires  140  may each be secured to a release clip  154  mounted at the distal end of the control handle  38 . The release wires  140  associated with the stent peak control wires  50 ,  52  and the stent valley control wires  70 ,  72  are also removed by pulling the corresponding release clip  154  distally along the longitudinal axis  66  of the control handle, as shown in  FIG. 14 . 
     The interior of the control handle is shown more clearly in  FIGS. 15 to 18  with the handle access cover removed and with the control wires omitted for clarity. The control wires  50 ,  52 ,  54 ,  56 ,  70 ,  72  pass from the proximal end  33  of the delivery shaft  30  through one or more longitudinal passages in the delivery shaft  30  to the distal end  34  where they enter the shaft  124  of the control handle  38  through a central passage  127 . The control wires  50 ,  52 ,  54 ,  56 ,  70 ,  72  then pass through a manifold  60  having a discrete tube aperture  62  for each control wire. This provides a smooth and continuous passage for each control wire from the connection point  146 ,  148  at the stent graft  20  to the peak controller  58  or valley controllers  74 ,  76 . The manifold  60  enables feeder wires (not shown) to pass freely for loading the control wires when assembling the apparatus. Integral haemostasis valves are provided in a haemostasis switching plate  64  adjacent to the manifold  60  to allow flushing of the system with saline prior to use. The haemostasis valves also provide a controlled restriction to prevent excessive blood loss while maintaining control of the stent graft  20  by the apparatus. The manifold apertures may comprise passages which diverge from the connection with central passage  127  to the distal side of the haemostasis switching plate  64 , to enable the control wires to be distributed and loaded onto the peak controller  58  or valley controllers  74 ,  76 . 
     The valley controllers  74 ,  76  each include an actuating surface  78  which must be depressed to disengage the slider  74 ,  76  from the ratchet  80  to allow the slider to be moved. Once pressure is removed from the actuating surface  78 , the slider  74 ,  76  becomes engaged again with the ratchet  80  and further movement of the slider  74 ,  76  is prevented. The valley controllers  74 ,  76  each include a connector  82  to which the corresponding stent valley control wire  70 ,  72  is connected. 
     The peak controller  58  includes a winder  68  (omitted in  FIG. 15  but shown in  FIGS. 16 to 20 ) which is mounted for rotation on a winder spindle  69 . The rotary collar  58  is omitted for clarity in  FIGS. 15 to 20 . A ratchet plate (not shown) is mounted on the winder spindle  69  and provides bearing and ratchet interfaces to the winder  68 . 
     The connection of the control wires  50 ,  52 ,  54 ,  56 ,  70 ,  72  is shown in  FIGS. 19 to 22 . Each wire may comprise a looped wire, having two strands, but is referred to in this specification as a single wire. At the distal end the stent valley control wires  70 ,  72  pass out of the manifold apertures  62  in the control handle  38  and are connected to the slider wire connectors  82 . At the proximal end the stent valley control wires  70 ,  72  pass out of the valley apertures  132  in the delivery shaft  38  and are connected to the connection points  148  on the ring stent valleys  44 ,  46 . In the illustrated example of  FIG. 22  the stent valley control wires  70 ,  72  are connected to the connection points  148  on the valleys  44 B,  46 B on the second ring stent  24 , but they could instead be connected to the valleys  44 A,  46 A on the first or third ring stent  22 ,  24 , or to the valleys of two ring stents  22 ,  24 ,  26 , or to the sleeve  28  between the ring stents  22 ,  24 ,  26 . 
     At the distal end the stent peak control wires  50 ,  52 ,  54 ,  56  pass out of the manifold apertures  62  in the control handle  38 , pass through apertures  160  and are connected to connection points on the peak controller winder  68 . In the illustrated example the connection points are anchor pins or fixing clamps  162  which enable adjustment of the control wires to achieve the correct length. At the proximal end the stent peak control wires  50 ,  52 ,  54 ,  56  pass out of the peak apertures  130  in the delivery shaft  38  and are connected to the connection points  146  on the ring stent peaks  40 A,  42 A,  40 B,  42 B. In the illustrated example the stent peak control wires are connected to the connection points  146  on the peaks of the both the first and second ring stents  22 ,  24 , but they could instead be connected to the peaks on the first ring stent  22  only, or the peaks of the second ring stent  24  only. 
     The apparatus and method of the invention allow the controlled rotation and orientation of a ring stent  22 ,  24  in a lumen  100  by selectively operating one of the first and second valley controllers  74 ,  76  to permit movement of the stent valley control wires  70 ,  72  along the delivery shaft  30  such that the first or second diametrically opposed valley connection point  148  on the ring stent  22 ,  24  is urged by the resilience of the ring stent to move away from the delivery shaft  30 , thereby rotating the ring stent. The movement is reversible so that the valley connection point  148  can also be moved towards the delivery shaft  30  to a folded or contracted position. During assembly of the apparatus the stent graft  20  adopts its expanded position shown in  FIG. 22 , but prior to sheathing the two stent valley control wires  70 ,  72  are tensioned such that the valley connection points  148  are held by the stent valley control wires  70 ,  72  in a folded arrangement towards the delivery shaft. In addition the two stent peak control wires  50 ,  52 ,  54 ,  56  are tensioned such that the peak connection points  146  are also held in a folded arrangement towards the delivery shaft. 
     The apparatus and method of the invention allow the controlled deployment of a ring stent  22 ,  24  in a lumen  100  by operating the peak controller  58  to permit movement of the stent peak control wires  50 ,  52 ,  54 ,  56  along the delivery shaft such that the peak connection points  146  on one or more proximal ring stents  22 ,  24  are urged by the resilience of the ring stent to move away from the delivery shaft and the ring stent adopts a fully deployed position. The movement is reversible so that the peak connection point  146  can also be moved towards the delivery shaft  30  to a folded or contracted position if the ring stent requires repositioning. 
     The peak and valley connection points  146 ,  148  may be eyelets through which the looped control wires are threaded. 
     All documents referred to in this specification are herein incorporated by reference. Various modifications and variations to the described embodiments of the inventions will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes of carrying out the invention which are obvious to those skilled in the art are intended to be covered by the present invention.