Abstract:
An endovascular prosthesis includes a tubular body and a flexible springy mobile external coupling. The tubular body includes a graft material and stents coupled thereto with a forms a lumen therethrough. The mobile external coupling extends outwardly from the tubular body. The mobile external coupling includes a graft material and is generally frustoconically shaped. The mobile external coupling includes a base coupled to the tubular body, a top spaced from the tubular body, and a coupling lumen disposed between the base and the top, wherein the coupling lumen is in flow communication with the body lumen. A helically shaped stent may be coupled to the coupling graft material to make it flexible and springy.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to endoluminal medical devices and procedures, and more particularly to an endoluminal prosthesis or graft having a mobile external coupling for connecting a main graft to a branch vessel graft. 
     BACKGROUND 
     Aneurysms and/or dissections may occur in blood vessels, and most typically occur in the aorta and peripheral arteries. Depending on the region of the aorta involved, the aneurysm may extend into areas having vessel bifurcations or segments of the aorta from which smaller “branch” arteries extend. Various types of aortic aneurysms may be classified on the basis of the region of aneurysmal involvement. For example, thoracic aortic aneurysms include aneurysms present in the ascending thoracic aorta, the aortic arch, and branch arteries that emanate therefrom, such as subclavian arteries, and also include aneurysms present in the descending thoracic aorta and branch arteries that emanate therefrom, such as thoracic intercostal arteries and/or the suprarenal abdominal aorta and branch arteries that emanate therefrom, such as renal, superior mesenteric, celiac and/or intercostal arteries. Lastly, abdominal aortic aneurysms include aneurysms present in the aorta below the diaphragm, e.g., pararenal aorta and the branch arteries that emanate therefrom, such as the renal arteries. 
     The thoracic aorta has numerous arterial branches. The arch of the aorta has three major branches extending therefrom, all of which arise from the convex upper surface of the arch and ascend through the superior thoracic aperture to the root of the neck. The brachiocephalic artery originates anterior to the trachea. The brachiocephalic artery divides into two branches, the right subclavian artery (which supplies blood to the right arm) and the right common carotid artery (which supplies blood to the right side of the head and neck). The left common carotid artery arises from the arch of the aorta just to the left of the origin of the brachiocephalic artery. The left common carotid artery supplies blood to the left side of the head and neck. The third branch arising from the aortic arch, the left subclavian artery, originates behind and just to the left of the origin of the left common carotid artery and supplies blood to the left arm. 
     For patients with thoracic aneurysms of the aortic arch, surgery to replace the aorta may be performed where the aorta is replaced with a fabric substitute in an operation that uses a heart-lung machine. In such a case, the aneurysmal portion of the aorta is removed or opened and a substitute lumen is sewn across the aneurysmal portion. Such surgery is highly invasive, requires an extended recovery period and, therefore, cannot be performed on individuals in fragile health or with other contraindicative factors. 
     Alternatively, the aneurysmal region of the aorta can be bypassed by use of a tubular exclusion device, e.g., by a stent-graft placed inside the vessel spanning the aneurysmal portion of the vessel, to seal off the aneurysmal portion from further exposure to blood flowing through the aorta. A stent-graft can be implanted without a chest incision, using specialized catheters that are introduced through arteries, usually through incisions in the groin region of the patient. The use of stent-grafts to internally bypass, within the aorta or flow lumen, the aneurysmal site, is also not without issues. In particular, where a stent-graft is used in a thoracic location, care must be taken so that critical branch arteries are not covered or occluded by the stent-graft yet the stent-graft must seal against the aorta wall and provide a flow conduit for blood to flow past the aneurysmal site. Where the aneurysm is located immediately adjacent to the branch arteries, there is a need to deploy the stent-graft in a location which partially or fully extends across the location of the origin of the branch arteries from the aorta to ensure sealing of the stent-graft to the artery wall. 
     To accommodate side branches, main vessel stent-grafts having a fenestration or opening in a side wall thereof may be utilized. The main vessel stent graft is positioned to align the fenestration with the ostium of the branch vessel after deployment. In use, a proximal end of the stent-graft, having one or more side openings, is prepositioned and securely anchored in place so that the fenestrations or openings are oriented and deployed in the main vessel to avoid blocking or restricting blood flow into the side branches. Fenestrations by themselves do not form or include discrete conduit(s) through which blood can be channeled into the adjacent side branch artery. As a result, blood leakage is prone to occur into the space between the outer surface of the aortic graft and the surrounding aortic wall between the edges of the graft surrounding the fenestrations and the adjacent vessel wall. Similar blood leakage can result from post-implantation migration or movement of the stent-graft causing misalignment of the fenestration(s) and the branch artery(ies), which may also result in impaired flow into the branch artery(ies). 
     In some cases, the main vessel stent graft is supplemented by another stent-graft, often referred to as a branch stent-graft. The branch graft is deployed through the fenestration into the branch vessel to provide a conduit for blood flow into the branch vessel. The branch stent-graft is preferably sealingly connected to the main graft in situ to prevent undesired leakage. This connection between the branch graft and main graft may be difficult to create effectively in situ and is a site for potential leakage. 
     In some instances, branch graft extensions (stent-grafts) are incorporated into the main stent-graft. Such branch graft extensions are folded or collapsed against the main stent-graft for delivery and require complicated procedures, requiring multiple sleeves and guidewires, to direct the branch extension into the branch vessel and subsequently expand. Further, in some instances, such branch stent-grafts tend to return to their folded or collapsed configuration, and thus do not provide an unobstructed flow path to the branch vessel. 
     Thus, there remains a need in the art for improvements for directing flow from a main vessel, such as the aorta, into corresponding branch vessels, such as branch vessels of the aortic arch. 
     SUMMARY OF THE INVENTION 
     An embodiment of an endovascular prosthesis includes a tubular body and a mobile external coupling. The tubular body includes a graft material and stents coupled thereto, a forms a lumen therethrough. The mobile external coupling extends outwardly from the tubular body. The mobile external coupling includes a graft material and is generally frustoconically shaped. The mobile external coupling includes a base coupled to the tubular body, a top spaced from the tubular body, and a coupling lumen disposed between the base and the top, wherein the coupling lumen is in flow communication with the body lumen. A helically shaped stent may be coupled to the coupling graft material. The configuration of the mobile external coupling provides flexibility for coupling the prosthesis to a branch vessel prosthesis. 
     In a method for delivering and deploying the endovascular prosthesis a main prosthesis is delivered in a compressed configuration to a target location in a main vessel such that the mobile external coupling is generally aligned with a branch vessel. A sleeve is retracted to expose the mobile external coupling. Minor adjustments to the location of the mobile external coupling to better align it with the branch vessel may be necessary. The tubular body is deployed such that it expands from the compressed configuration to an expanded configuration. A branch vessel prosthesis may be delivered in a compressed configuration to the branch vessel. The branch vessel prosthesis may be deployed such that the branch vessel prosthesis radially expands to an expanded configuration and an outside surface of a portion of the branch vessel prosthesis is in contact with an inner surface of a portion of the mobile external coupling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of embodiments according to the invention will be apparent from the following description as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the described embodiments herein. The drawings are not to scale. 
         FIG. 1  is a schematic side view of an endoluminal stent-graft according to an embodiment hereof. 
         FIG. 2  is a schematic close up illustration of a portion of the stent-graft of  FIG. 1 . 
         FIG. 3  is a schematic illustration of a stent portion of the mobile external coupling of the stent-graft of  FIG. 1 . 
         FIG. 4  is a schematic illustration of a stent-graft delivery device. 
         FIG. 5  is a schematic perspective view of the tip of the stent-graft delivery device of  FIG. 4 . 
         FIG. 6  is a schematic illustration of a portion of the stent-graft and a portion of the stent-graft delivery device. 
         FIGS. 7 and 8  are schematic illustrations of the stent-graft delivery device of  FIG. 4  as the sheath is retracted. 
         FIGS. 9-14  are schematic illustrations of progressive steps of a method for delivering and deploying the stent-graft of  FIG. 1  and a branch stent-graft to a target location. 
         FIG. 15  is a schematic side view of a stent-graft in accordance with another embodiment hereof. 
     
    
    
     DETAILED DESCRIPTION 
     Specific embodiments are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. Unless otherwise indicated, for the delivery system the terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” and “distally” are positions distant from or in a direction away from the clinician, and “proximal” and “proximally” are positions near or in a direction toward the clinician. For the stent graft device proximal is the portion nearer the heart by way of blood flow path while distal is the portion of the stent graft further from the heart by way of blood flow path. 
     With reference to  FIGS. 1-3 , a stent-graft  100  is configured for placement in a vessel such as the aorta. Stent-graft  100  includes graft material  102  coupled to stents  104 . Graft material  102  may be coupled to stents  104  using stitching  110  or other means known to those of skill in the art. In the embodiment shown in  FIGS. 1-3  stents  104  are coupled to an outside surface of graft material  102 . However, stents  104  may alternatively be coupled to an inside surface of graft material  102 . Graft material  102  may be any suitable graft material, for example and not limited to, woven polyester, DACRON material, expanded polytetrafluoroethylene, polyurethane, silicone, or other suitable materials. Stents  104  may be any conventional stent material or configuration. As shown, stents  104  are preferably made from a shape memory material, such as thermally treated stainless steel or nickel-titanium alloy (nitinol), and are formed into a zig-zag configuration. Stent-graft  100  includes a proximal end  106 , a distal end  108 , and a body  107  therebetween. Proximal stent  112  and distal stent  114  may extend outside of the graft material  102 , as shown, and may also be generally described as anchor stents or crown stents in the art. Body  107  has a lumen  116  disposed therethrough. Stent-graft  100  further includes a mobile external coupling  120 , described in detail below. Except for the mobile external coupling  120 , stent graft- 100  may be similar to the Medtronic, Inc.&#39;s VALIANT® thoracic stent-graft, or other known stent-grafts. 
     Mobile external coupling  120  is disposed on an outside surface of stent-graft  100  at an opening in graft material  102 . Mobile external coupling  120  is generally frustoconically shaped. Mobile external coupling  120  includes graft material  128  coupled to a helical stent  122 . Graft material  128  is preferably the same type of graft material as graft material  102  of the body  107  and is preferably a continuation of graft material  102 , although graft material  128  can be a separate piece of graft material attached to graft material  102 . Mobile external coupling  120  and stent  122  include a base  124  and a top  126 . Although mobile external coupling  120  is described as generally frustoconical in shape, base  124  is preferably generally elliptical rather than circular. Base  124  may have, for example and not by way of limitation, a long axis of approximately 20-30 mm and a short axis of approximately 15-20 mm. Further, the height of mobile external coupling  120  may be approximately 10-15 mm. Further, the diameter of the top  126  of mobile external coupling may be approximately 6-9 mm if it is to be used at the junction of the aorta and left common carotid artery or the junction of the aorta and left subclavian artery. If the mobile external coupling  120  is to be used at the junction of the aorta and the brachiocephalic artery, the diameter of the top  126  may be approximately 8-12 mm. 
     Stent  122  of mobile external coupling  120  is generally helical and configured to create frustoconically shaped outline such that bottom  124  has a larger diameter than top  124 , as shown schematically in  FIG. 3 . Stent  122  is coupled to graft material  128  using stitches (e.g.,  110 ) or other similar coupling means. Stent  122  is preferably made from shape memory material such a nitinol. Stent  122  may be made from the same material as main body stents  104  or may be made from different material. For example, stents  104  may be balloon expandable and stent  122  may be self-expanding. Preferably, stents  104  and stent  122  are made from shape memory materials such as nitinol and are self-expanding. 
     Mobile external coupling  120  allows for significant flexibility in aligning stent-graft  100  with a branch vessel because the top of the mobile external coupling  120  can move. This mobility is due to the shape of mobile external coupling  120  and can be further improved by utilizing some excess graft material  128  when forming mobile external coupling  120 . Thus, if stent-graft  100  is not perfectly aligned with a branch vessel, the top  126  of mobile external coupling  120  can be moved or shifted such that mobile external coupling  120  will extend into the branch vessel. Further, due to the force stored in the shape memory helical stent  122 , mobile external coupling  120  pops out from body  107  of stent-graft  100  when released from a sleeve during delivery to a target site. This prevents bunching or collapse of the mobile external coupling  120  when released from the delivery system. 
       FIGS. 4-8  show an example of a delivery system that can be used to delivery stent-graft  100  to the target location within a vessel.  FIG. 4  is a schematic partial cross-sectional view of a stent-graft delivery system  200  with stent-graft  100  disposed therein. Stent-graft delivery system  200  includes a tapered tip  202  that is flexible and able to provide trackability in tight and tortuous vessels. Other tip shapes such as bullet-shaped tips could also be used. The tip  202  includes a lumen  204  disposed therethrough for accommodating a first guidewire  220 . 
     The tapered tip  202  includes a tapered outer surface  216  that gradually decreases in diameter in a distal direction. More particularly, tapered outer surface  216  has a first diameter at a proximal end and gradually decreases in diameter distally, i.e., in the direction away from the operator. Tapered outer surface  216  further includes a groove  218 , as best seen in  FIG. 5 , for accommodating a second guidewire  222 . A shoulder  212  reduces the diameter of a proximal portion of tip  202  to provide a sleeve landing surface  226 . Shoulder  212  is generally annular and perpendicular to a longitudinal axis of stent-graft delivery system  200 . 
     A first or outer sleeve  210  of stent-graft delivery system  200  extends over the outer cylindrical surface of sleeve landing surface  220  and abuts against shoulder  212  when the stent-graft delivery system  200  is in a pre-deployment configuration, as shown in  FIG. 4 . A second or inner sleeve  214  is disposed within outer sleeve  210 . Inner sleeve  214  includes an opening through which mobile external coupling  120  extends, as described in more detail below. 
     Stent-graft delivery system  200  also includes an inner tube  205  that is coupled to a tip lumen  204  such that first guidewire  220  may extend the length of delivery system  200 . Delivery system  200  may also include an outer tube  206  surrounding inner tube  205 . A stop  208  is located at a distal end of stent-graft  100  when stent-graft  100  is loaded onto the delivery system  200 . Stop  208  prevents longitudinal movement of stent-graft  100  as outer and inner sleeves  210 ,  214  are retracted or otherwise removed to release stent-graft  100 . Stent-graft  100  is disposed within outer and inner sleeves  210 ,  214  in a compressed or delivery configuration wherein the diameter of stent-graft  100  is reduced such that it can be inserted through the vasculature. 
     Second guidewire  222  extends through stent-graft delivery system  200 , through lumen  116  of stent-graft  100 , through lumen  130  of mobile external coupling  120 , between inner sleeve  214  and outer sleeve  210 , and out a distal end of outer sleeve  210  through groove  218  of tip  202 . A tube  224  may be provided to guide second guidewire  222  along this path and tube  224  may extend proximally to the proximal portion of delivery system  200 . In the delivery or compressed configuration, mobile external coupling  120  may be folded proximally as shown schematically in  FIGS. 4 and 6 . 
     Outer sleeve  210  is a hollow tube and defines a lumen therein within which outer tube  206 , inner tube  204 , inner sleeve  214 , and stent-graft  100  are disposed in the delivery configuration. Outer sleeve  210  is moved proximally, i.e. retracted, relative to outer tube  206  to release or deploy mobile external coupling  120 .  FIG. 7  shows outer sleeve  210  retracted and mobile external coupling  120  extended (deployed). After outer sleeve  210  is retracted, inner sleeve  214  is removed by, for example, a pull wire or other method known to those skilled in the art. A conventionally retracted inner sleeve  214  is not desirable because it would interfere with mobile external coupling  120 . However, a pull string (not shown) to create a longitudinal slit to split inner sleeve  214  prior to retracting it may be used. Alternatively, a weakened (frangible) area (line) in inner sleeve  214  distal to mobile external coupling  120  may be utilized such that retracting inner sleeve  214  would cause the weakened area to split around mobile external coupling  120 . Other means to accommodate mobile external coupling  120  when retracting inner sleeve  214  may be utilized, as would be apparent to those skilled in the art. Retracting inner sleeve  214  allows stent-graft  100  to deploy from its compressed configuration to its deployed or expanded configuration, as shown schematically in  FIG. 8 . 
     The stent-graft delivery system  200  described herein is only an example of a delivery system that can be used to delivery and deploy stent-graft  100  and many other delivery systems known to those skilled in the art could be utilized. For example, stent-graft  100  could be mounted onto a balloon to be expanded when at the target site. Other stent-graft-delivery systems, for example and not by way of limitation, the delivery systems described in U.S. Published Patent Application Publication Nos. 2008/0114442 and 2008/0262590 and U.S. Pat. No. 7,264,632, each of which is incorporated herein by reference in its entirety, may be utilized to deliver and deploy stent graft  100 . 
       FIGS. 9-14  schematically show a method of delivering stent-graft  100  to a target site in a main vessel and a method of delivering a branch stent-graft to branch vessel. In the example described herein, the stent-graft  100  is delivered and deployed into the aorta  300 . Portions of the aorta  300  include the ascending aorta  302 , the aortic arch  304 , and the descending aorta  306 . Branching from the aortic arch are the brachiocephalic trunk  308 , the left common carotid artery  314 , and the left subclavian artery  316 . The brachiocephalic trunk branches into the right subclavian artery  310  and the right common carotid artery  312 . An aneurysm  318  in the area of the aortic arch  304  can be difficult to bypass or exclude with a stent-graft because blood flow to the branch arteries must be maintained. 
     In the embodiment shown in  FIGS. 9-14 , the aneurysm is sufficiently close to brachiocephalic trunk  308  that the stent-graft must extend between the brachiocephalic trunk  308  and the heart. In such a case and with a stent-graft  100  with only a single mobile external coupling  120 , the mobile external coupling  120  is designed so as to be deployed into the brachiocephalic trunk  308  to perfuse the brachiocephalic trunk  308 . Prior to the procedure for inserting stent-graft  100 , a by-pass procedure installing bypass grafts or vessels (not shown) is performed to connect the right common carotid artery  312  to the left common carotid artery  314  and the left common carotid artery to the left subclavian artery  316 . Such a procedure may be performed one to two weeks prior to insertion of the stent-graft, and presents significantly less complications and risk than a surgical solution to repair an aneurysm  318  in the aortic arch. In this manner, maintaining perfusion to the brachiocephalic trunk  308 , and hence the right common carotid artery  312 , maintains perfusion to the left common carotid artery  314  and the left subclavian artery  314 . Thus, the openings (or ostia) to these branch vessels directly from the aortic arch may be blocked by stent-graft  100 . In the alternative, multiple mobile external couplings  120  may be provided in stent-graft  100 . Further, if the aneurysm only affects the left common carotid artery  314  and the left subclavian artery  316 , only one by-pass between the left common carotid artery  314  and the left subclavian artery needs to be performed, and then a stent-graft with a single mobile external coupling  120  can be utilized to perfuse the left common carotid artery  314 . Alternatively, in such a situation, a stent-graft with two mobile external couplings may be provided, one for each of the branch vessels noted. Accordingly, while the embodiment of stent-graft  100  in the method described below includes a single mobile external coupling  120  and the mobile external coupling is deployed in the brachiocephalic trunk  308 , those skilled in the art would recognize that multiple mobile external coupling can be used and the mobile external coupling(s) may be deployed in other branch arteries. 
       FIG. 9  shows the first guidewire  220  advanced from the descending aorta  306 , through the aortic arch  304 , and into the ascending aorta  302  and second guidewire  222  advanced from the descending aorta  306 , through the aortic arch  304 , and into brachiocephalic trunk  308 . Guidewires  200 ,  222  are typically inserted into the femoral artery and routed up through the abdominal aorta, and into the thoracic aorta, as is known in the art. 
       FIG. 10  shows stent-graft delivery system  200 , with stent-graft  100  compressed therein, advanced over guidewires  220 ,  222  to the target location in the aortic arch  304 . The location of the stent-graft delivery system  200  and/or the stent-graft  100  may be verified radiographically and delivery system  200  and/or stent-graft  100  may include radiopaque markers as known in the art. 
     After stent-graft delivery system  200  is in the proper location with the mobile external coupling  120  of the stent graft  100  approximately aligned with the opening into the branch vessel, outer sleeve  210  is retracted proximally to release mobile external coupling  120 , as shown in  FIG. 11 . Mobile external coupling  120  provides a positive outward force due to helical stent  122  that reduces the possibility of the mobile external coupling collapsing against body  107  after deployment. Delivery system  200  may then be moved to better align mobile external coupling with the branch artery, in this case, the brachiocephalic trunk  308 . Further, due to the configuration of mobile external coupling  120 , even if it is not perfectly aligned with brachiocephalic trunk  308 , the top of the mobile external coupling  120  may move as it contacts and is being moved closers and closer and into the opening of the branch vessel to properly align it with brachiocephalic trunk  308  without having to move the entire stent-graft  100 . As well, tension on branch guide wire  222  can be created by pulling either end of the wire. This tension will urge the distal end of the MEC distally away from the main graft and into the lumen of the branch vessel. 
     Once mobile external coupling  120  is deployed and in position in the brachiocephalic trunk  308 , inner sleeve  214  may be retracted as explained above with respect to  FIG. 8 , thereby deploying the main body of the stent graft  100 , as shown in  FIG. 12 . Once mobile external coupling  120  and stent-graft  100  are deployed, delivery system  200  may be removed. Second guidewire  222  may remain in place in brachiocephalic trunk  308  or may be replaced by another guidewire. A branch stent-graft delivery system  404  is advanced over second guidewire  222  and into brachiocephalic trunk  308 , as shown in  FIG. 13 . Branch stent-graft delivery system includes a tip  402  and a sleeve (not shown), and contains therein a branch stent-graft  400 . Branch stent-graft delivery system  404  and branch stent-graft  400  may be conventional. Branch stent-graft delivery system  404  is advanced into brachiocephalic trunk  308  such that a proximal portion  406  of branch stent-graft  400  remains inside of mobile external coupling  120 . The sleeve constraining branch stent-graft  400  is then retracted proximally, thereby releasing branch stent-graft  400  from delivery system  404 . The delivery system  404  is then withdrawn, as shown in  FIG. 14 . Because proximal portion  406  of branch stent-graft  400  is disposed within mobile external coupling  120  when branch stent-graft  400  is expanded, proximal portion  406  neck (narrows) at the top  126  of mobile external coupling  120  to conform with an inside surface of mobile external coupling  120 . 
       FIG. 15  shows an alternative embodiment of a stent-graft  100 ′. Stent graft  100 ′ is similar to stent-graft  100  shown in  FIG. 1  and the same reference numerals have been used to identify the same parts. However, mobile external coupling  120 ′ shown in  FIG. 15  does not include a helical stent disposed therein. Mobile external coupling  120 ′ includes a graft material  128 ′, a base  124 ′ coupled to body  107 , and a top  126 ′. Top  126 ′ includes a stent ring (not shown but similar to top  126  of helical stent  122  shown in  FIG. 3 ). Mobile external coupling  120 ′ is generally frustoconically shaped, although base  124 ′ may be generally elliptical as described above with respect to mobile external coupling  120 . The dimensions described above with respect to stent-graft  100  are similarly applicable to stent-graft  100 ′ and the delivery system and method described above may be similarly used with respect to stent-graft  100 ′. 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.