Patent Publication Number: US-2022211484-A1

Title: Stent-graft prosthesis with pressure relief channels

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to stent-graft prostheses having pressure relief channels. 
     BACKGROUND OF THE INVENTION 
     Stent-graft prostheses are prostheses for percutaneous implantation in blood vessels or other similar organs of the living body. These stent-graft prostheses typically include one or more radially compressible stents that can be expanded within the body vessel at a diameter slightly larger than the body vessel, and a graft material interior or exterior of the stent. When the stent-graft prosthesis is radially expanded in situ, the one or more stents anchor the tubular graft material to the wall of a blood vessel or anatomical conduit. Thus, stent-graft prostheses are typically held in place by mechanical engagement and friction due to the opposition forces provided by the radially expanded stents against the vessel wall. When the one or more stents are expanded, the graft material is anchored on the interior wall of the body vessel. Thus, the graft material is held in place by the friction between the one or more stents and the body vessel. 
     Stent-graft prostheses are often utilized for treating aneurysms, dissections and transections. In an example, an aneurysm may result from weak, thinned blood vessel walls that “balloon” or expand due to aging, disease and/or blood pressure in the vessel. These aneurysmal blood vessels have a potential to rupture, causing internal bleeding and potentially life threatening conditions. When the stent-graft prosthesis is implanted within an aneurysmal blood vessel, with the stent-graft prosthesis extending proximal and distal of the aneurysm, the stent-graft prosthesis acts as a bypass lumen that permits blood to flow through the graft material instead of the expanded section of the aneurysm. Stent-graft prostheses, therefore, isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall and reducing the chance of vessel rupture. 
     Stent-graft prostheses may have an open-web configuration or a closed-web configuration. In an open-web configuration, the end of the frame (stent(s)) of the stent-graft prosthesis extends beyond a corresponding end of the graft material, and thus has a portion that is not covered by the graft material. The uncovered portion generally permits blood flow through the stent-graft prosthesis during implantation. The uncovered portion of the open-web configuration further provides a convenient location for coupling to a tip-capture mechanism of a delivery catheter. However, with the uncovered portion of the frame gathered tightly by the tip-capture mechanism, flow through the uncovered portion is not always ideal. In the closed-web configuration, the end of the frame (stent(s)) of the stent-graft prosthesis is covered or lined by the graft material. Thus, the closed-web configuration has no exposed stents and is intended to reduce potential trauma between the stent-graft prosthesis and the vessel. For example, stent-graft prostheses having a closed-web configuration may be selected to treat aneurysms, dissections or vessel transections due to the delicate condition of the vessel tissue. A closed-web configuration stent-graft prosthesis thus is less traumatic to sensitive tissues and disease states. A closed-web configuration stent-graft prosthesis offers convenience by preserving the structural integrity of fragile blood vessel tissues. 
     For implantation within a blood vessel, the stent-graft prosthesis is deployed through a minimally invasive intraluminal delivery procedure. More particularly, a body lumen or vasculature is accessed percutaneously at a convenient entry point, such as a femoral artery, and the stent-graft prosthesis is routed through the vasculature to the desired treatment location. For example, a self-expanding stent-graft prosthesis may be compressed and disposed within a distal end of an outer shaft or sheath component of a delivery catheter as part of a delivery system. A proximal or upstream end of the stent-graft prosthesis is removably coupled to a tip capture mechanism of an inner shaft or member. The delivery system is then maneuvered, typically tracked through a body lumen until a distal end of the delivery system and the stent-graft prosthesis are positioned at the intended treatment site. The outer sheath of the delivery system is withdrawn. The tip capture mechanism prevents the stent-graft prosthesis from being withdrawn with the outer sheath, and further prevents the proximal or upstream end of the stent-graft prosthesis from fully expanding. As the outer sheath is withdrawn, the stent-graft prosthesis is released from the confines thereof and a distal portion of the stent-graft prosthesis radially expands to contact and substantially conforms to a portion of the surrounding interior of the body lumen, e.g., the blood vessel wall. When the stent-graft prosthesis is in the desired positon, the tip capture mechanism is actuated. As the tip capture mechanism is actuated, the proximal or upstream end of the stent-graft prosthesis radially expands to transition the stent-graft prosthesis to a radially expanded configuration. 
     However, when the stent-graft prosthesis is partially expanded against the vessel wall, but the proximal (upstream) end of the stent-graft prosthesis is captured by the tip capture mechanism, there is nowhere for the blood to flow past the stent-graft prosthesis. Thus, pulsatile blood pressure against the proximal or upstream end of the stent-graft prosthesis may cause the stent-graft prosthesis to move during deployment, thereby presenting challenges in accurately positioning and deploying the stent-graft prosthesis. Further, blood does not flow to vessels downstream of the stent-graft prosthesis, thereby risking injury due to ischemia. Further, in some methods in which the upstream end of the stent-graft prosthesis is deployed first and the downstream end of the stent-graft prosthesis remains captured by the delivery system, blood flow entering the stent-graft prosthesis at the upstream end cannot escape the stent-graft prosthesis, thereby depriving blood flow distal of the stent-graft prosthesis. 
     Accordingly, there is a need for stent-graft prostheses providing blood flow during deployment thereof for improved positioning and deployment accuracy, and to maintain blood flow to vessels distal of the stent-graft prosthesis. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments hereof relate to a stent-graft prosthesis for implantation within a body vessel. The stent-graft prosthesis includes a graft material, a frame, and a channel. The graft material includes a first end, a second end, and a graft lumen extending between the first and the second end. The frame is coupled to the graft material. The channel of the stent-graft prosthesis is configured for relieving pressure associated with pulsatile blood flow during implantation of the stent-graft prosthesis within a body vessel. The channel of the stent-graft prosthesis permits blood to flow from an upstream side of the stent-graft prosthesis to a downstream side of the stent-graft prosthesis when the stent-graft prosthesis is in a partially expanded configuration in the body vessel. 
     Embodiments hereof also relate to a stent-graft prosthesis for implantation within a body vessel. The stent-graft prosthesis includes a graft material, a frame, and a channel. The graft material includes a first end, a second end, and a graft lumen extending between the first and the second end. The frame is coupled to the graft material. The channel of the stent-graft prosthesis is configured to relieve pressure associated with pulsatile blood flow during implantation of the stent-graft prosthesis within a body vessel. The channel of the stent-graft prosthesis permits blood to flow from an upstream side of the stent-graft prosthesis to a downstream side of the stent-graft prosthesis when the stent-graft prosthesis is in a partially expanded configuration in the body vessel. The channel includes a channel lumen extending from a channel entrance to a channel exit. The channel lumen is a portion of the graft lumen. The channel entrance is disposed through the graft material and is configured to permit blood flow to the channel lumen when the stent-graft prosthesis is in the partially expanded configuration. The channel exit is disposed through the graft material distal of the channel entrance and is configured to permit blood flow from the channel lumen when the stent-graft prosthesis is in the partially expanded configuration. 
     Embodiments hereof further relate to a stent-graft prosthesis for implantation within a body vessel. The stent-graft prosthesis includes a graft material, a frame, and a channel. The graft material includes a first end, a second end, and a graft lumen extending between the first and the second end. The frame is coupled to the graft material. The frame includes at least one body stent. The channel of the stent-graft prosthesis is configured to relieve pressure associated with pulsatile blood flow during implantation of the stent-graft prosthesis within a body vessel. The channel is defined between the outer surface of the graft material and an adjacent first segment of the at least one body stent to which the graft material is not attached in the radially expanded state when the stent-graft prosthesis is in the partially expanded configuration. The channel of the stent-graft prosthesis is configured to permit blood to flow from an upstream side of the stent-graft prosthesis to a downstream side of the stent-graft prosthesis when the stent-graft prosthesis is in a partially expanded configuration in the body vessel. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of the invention 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 invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  depicts a side view of a stent-graft prosthesis having channels for relieving pulsatile blood pressure according to an embodiment hereof, wherein the stent-graft prosthesis is in a radially expanded configuration. 
         FIG. 2  depicts a perspective view of a first end of the stent-graft prosthesis of  FIG. 1 , wherein the stent-graft prosthesis is in the radially expanded configuration. 
         FIG. 3  depicts a perspective view of a second end of the stent-graft prosthesis of  FIG. 1 , wherein the stent-graft prosthesis is in the radially expanded configuration. 
         FIG. 4  depicts a perspective view of the stent-graft prosthesis of  FIG. 1 , wherein the stent-graft prosthesis is in a partially expanded configuration. 
         FIG. 5  depicts a view of the stent-graft prosthesis of  FIG. 1  from the first end, showing a plurality of channel entrances. 
         FIG. 6  depicts a side view of the stent-graft prosthesis of  FIG. 1 , wherein the stent-graft prosthesis is in the radially expanded configuration and a plurality of channel exits is shown. 
         FIG. 7  depicts a perspective view of a valve assembly of the channel entrance or the channel of the stent-graft prosthesis of  FIG. 1 , wherein the valve assembly is in an open state. 
         FIG. 8  depicts a perspective view of the valve assembly of  FIG. 7 , wherein the valve assembly is in a closed state. 
         FIG. 9  depicts a side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is disposed on a distal portion of a delivery system in a radially compressed configuration. 
         FIG. 10  depicts a side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is disposed on a distal portion of a delivery system and is in the partially expanded configuration. 
         FIG. 11  depicts another side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is in the partially expanded configuration. 
         FIG. 11A  depicts a side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is in a partially expanded configuration with the proximal or upstream end radially compressed and the distal or downstream end radially expanded. 
         FIG. 11B  depicts a side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is in a partially expanded configuration with the proximal or upstream end radially expanded and the distal or downstream end radially compressed. 
         FIG. 12  depicts a side view of the stent-graft prosthesis of  FIG. 1  in situ, wherein the stent-graft prosthesis is in the radially expanded configuration and the valve assemblies are in the closed state. 
         FIG. 13  depicts a side view of a stent-graft prosthesis having at least one channel for relieving pulsatile blood pressure according to another embodiment hereof, wherein the stent-graft prosthesis is in a radially expanded configuration. 
         FIG. 14  depicts a side view of a body stent of the stent-graft prosthesis of  FIG. 13 , wherein the body stent has been cut and laid flat for illustrative purposes. 
         FIG. 15  depicts a perspective view of the stent-graft prosthesis of  FIG. 13 , wherein the stent-graft prosthesis is in a partially expanded configuration. 
         FIG. 16  depicts a cross-sectional view of the stent-graft prosthesis taken along line  16 - 16  of  FIG. 15 . 
         FIG. 17  depicts a side view of the stent-graft prosthesis of  FIG. 13  in situ, wherein the stent-graft prosthesis is disposed on a distal portion of a delivery system and is in a radially compressed configuration. 
         FIG. 18A  depicts a side view of the stent-graft prosthesis of  FIG. 13  in situ, wherein the stent-graft prosthesis is disposed at the distal portion of the delivery system and is in a partially expanded configuration. 
         FIG. 18B  depicts a side view of the stent-graft prosthesis of  FIG. 13  in situ in a partially expanded configuration with the outer sheath retracted more than in  FIG. 18A . 
         FIG. 18C  depicts a partial cross-sectional view of a distal portion of the stent-graft prosthesis 
         FIG. 19  depicts a side view of the stent-graft prosthesis of  FIG. 13  in situ, wherein the stent-graft prosthesis is in a radially expanded configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal”, when used in the following description to refer to a catheter and/or other system components hereof are with respect to a position or direction relative to the treating clinician. Thus, “distal” and “distally” refer to positions distant from or in a direction away from the treating clinician, and the terms “proximal” and “proximally” refer to positions near or in a direction toward the treating clinician. The terms “distal” and “proximal”, when used in the following description to refer to a native vessel or a device to be implanted into a native vessel, such as a stent-graft prosthesis, are with reference to the direction of blood flow. Thus, “distal” and “distally” refer to positions in a downstream direction with respect to the direction of blood flow and the terms “proximal” and “proximally” refer to positions in an upstream direction with respect to the direction of blood flow. 
     In addition, the term “self-expanding” is used in the following description with reference to one or more stent structures of the stent-graft prosthesis, and is intended to convey that the structures are shaped or formed from a material that can be provided with a mechanical memory to return the structure from a radially compressed or collapsed configuration to a radially expanded configuration. Non-exhaustive exemplary self-expanding materials include stainless steel, a pseudo-elastic metal such as a nickel titanium alloy (e.g. NITINOL), various polymers, or a so-called super alloy, which may have a base metal of nickel, cobalt, chromium, or other metal. Mechanical memory may be imparted to a wire or stent structure by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy (e.g. NITINOL). 
     The following detailed description is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of the treatment of blood vessels such as the aorta, the invention may also be used in any other body passageways where it is deemed useful, non-limiting examples of which include coronary arteries, carotid arteries, and renal arteries. Therefore, the term body vessel, or vessel, is used to apply to the body passageways as a whole. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
     A stent-graft prosthesis in accordance with embodiments hereof includes at least one channel configured to relieve pulsatile blood pressure at a first, proximal or upstream end of the stent-graft prosthesis when the stent-graft prosthesis is in a partially expanded configuration. As will be explained in more detail below, the stent-graft prosthesis includes at least one channel configured to permit blood flow from upstream of the stent-graft prosthesis to downstream of the stent-graft prosthesis as the stent-graft prosthesis is transitioning from a radially compressed configuration for delivery to a radially expanded configuration when deployed. 
       FIGS. 1-12  illustrate a stent-graft prosthesis  100  according to an embodiment hereof. As shown in  FIG. 1 , the stent-graft prosthesis  100  includes a graft material  102 , a frame  104 , and channels  106 . The stent-graft prosthesis  100  has a radially compressed configuration for delivery, a radially expanded configuration when deployed, and a partially expanded configuration when transitioning between the radially compressed and the radially expanded configurations. When the stent-graft prosthesis  100  is in the radially expanded configuration at a desired treatment location, the stent-graft prosthesis  100  is configured to bypass a vessel abnormality such as an aneurysm within a body vessel. While described herein as configured to bypass an aneurysm, such as an abdominal aortic aneurysm, this is by way of example and not limitation, and the stent-graft prosthesis  100  may be configured to support/bypass other vessel abnormalities such as, but not limited to dissections and transections. 
     The graft material  102  is of a generally tubular shape having a central longitudinal axis L A , a first end or edge  110 , a second end or edge  112 , and a graft lumen  114  extending from the first end  110  to the second end  112 . The graft material  102  has a longitudinal length  116 , which may vary based upon the application. The graft material  102  further includes an inner surface  118  and an outer surface  120 . The first end  110  of the graft material  102  may be referred to as a proximal or an upstream end or edge of the graft material  102 . In the embodiment shown, the first end  110  of the graft material is also a first, proximal or upstream end or edge  111  of the stent-graft prosthesis  100 . The second end  112  of the graft material  102  may be referred to as a distal or a downstream end or edge of the graft material  102 . In the embodiment shown, the second end  112  of the graft material  102  is also a second, distal, or downstream end or edge  113  of the stent-graft prosthesis  100 . For a stent-graft prosthesis for an abdominal aortic aneurysm delivered from the femoral artery, the proximal or upstream end  111  of the stent-graft prosthesis  100  is the end that is coupled to a tip capture mechanism of a delivery system. The graft material  102  may be formed from any suitable graft material, for example and not way of limitation, the graft material  102  may be formed from a low-porosity woven or knit polyester, DACRON material, expanded polytetrafluoroethylene, polyurethane, silicone, or other suitable materials. In another embodiment, the graft material could also be a natural material such as pericardium or another membranous tissue such as intestinal submucosa. 
     In the embodiment of  FIGS. 1-12 , the frame  104  of the stent-graft prosthesis  100  includes a sealing or seal stent  122  and at least one body stent  124 . The frame  104  is configured to support the graft material  102 . The seal stent  122  and each of the body stents  124  of the frame  104  are coupled to the graft material  102 . In the embodiment illustrated in  FIG. 1 , the stent-graft prosthesis  100  is shown in the radially expanded configuration and includes one (1) seal stent  122  adjacent to the first end  110 , and six (6) body stents  124 A,  124 B,  124 C,  124 D,  124 E, and  124 F axially or longitudinally spaced between the first end  110  and the second end  112  of the graft material  102 . Although shown with six (6) body stents  124 , it will be understood that the stent-graft prosthesis  100  may include a greater or smaller number of body stents  124  depending upon the desired length  116  of the stent-graft prosthesis  100  and/or the intended application. The seal stent  122  and each of the body stents  124  are self-expanding and each includes a radially compressed state, a partially expanded state, and a radially expanded state. Accordingly, the seal stent  122  and each of the body stents  124  are constructed from self-expanding materials as described previously. The seal stent  122  and each of the body stents  124  may be sinusoidal patterned rings including a plurality of crowns or bends  126  and a plurality of struts or straight segments  128  with each crown  126  being formed between a pair of adjacent struts  128 . While the seal stent  122  and the body stents  124  are shown in  FIG. 1  as having a similar sinusoidal pattern, it will be understood that the seal stent  122  and the body stents  124  may have different patterns or configurations. The seal stent  122  and the body stents  124  are coupled to the graft material  102  by stitches, sutures, or other suitable methods. In the embodiment of  FIG. 1 , the seal stent  122  and the body stents  124  are coupled to the outer surface  120  of the graft material  102 . However, the seal stent  122  and the body stents  124  may each alternatively be coupled to the inner surface  118  of the graft material  102 . When the stent-graft prosthesis  100  is used for treating an aneurysm, the seal stent  122  is configured with sufficient radial spring force and flexibility to conformingly engage the stent-graft prosthesis  100  with the body lumen inner wall, to avoid excessive leakage, and to prevent pressurization of the aneurysm, i.e., to provide a leak-resistant seal. 
     As briefly explained above, in the embodiment of  FIG. 1 , the proximal end  111  of the stent-graft prosthesis  100  has a closed-web configuration in which the endmost crowns  126  of the seal stent  122  are covered or lined by the graft material  102 , as best viewed in  FIG. 2 . Thus, the endmost crowns  126  of the seal stent  122  do not extend past or beyond the first end  110  of the graft material  102 . As utilized herein, “endmost” crowns are the crowns, peaks, or apexes of a stent that are most proximate to an end or edge of the graft material  102  in the direction of the end or edge, such as the first end  110 . As best viewed in  FIG. 3 , the stent-graft prosthesis  100  further includes a closed-web configuration at the distal end  113 , with the endmost crowns  126  of the body stent  124 F also covered or lined by the material graft  102 , i.e., they do not extend outside of or beyond the second end  112  of the graft material  102 . In other embodiments hereof (not shown), the endmost crowns of the seal stent  122  and/or the body stent  124 F may extend beyond the first end  110  and the second end  112 , respectively, of the graft  102  in an open-web configuration. 
     The plurality of channels  106  are configured to permit blood flow from an upstream side of the stent-graft prosthesis  100  to a downstream side of the stent-graft prosthesis  100  when the stent-graft prosthesis  100  is in the partially expanded configuration. Accordingly, when the stent-graft  100  is in the partially expanded configuration, the channels  106  are configured to relieve pressure associated with pulsatile blood flow on the stent-graft prosthesis  100  during implantation within a body vessel. The partially expanded configuration, as used herein, means that a portion or portions of the stent-graft prosthesis  100  are in a radially compressed state, portions of the stent-graft prosthesis are in a partially expanded state, and at least a portion of the stent-graft prosthesis is in a radially expanded state, as will be described below. 
     As best shown in  FIGS. 4-6 , there are seven (7) channels  106  including seven (7) channel entrances  130  (hereafter referred to as “channel entrances”  130 ), twenty-one (21) channel exits  132  (hereafter referred to as “channel exits”  132 ) and a channel lumen  134 . The channel lumen  134  extends within and is a portion of the graft lumen  114 , extending from the channel entrances  130  to the channel exits  132 . The channel lumen  134  may also be thought of as seven (7) channel lumens  134  as the channel entrances  130  are aligned with the channel exits  132 , as explained in more detail below. 
     In the embodiment of  FIGS. 1-12 , the channel entrances  130  are disposed through the graft material  102  and in fluid communication with the channel lumen  134 . Each channel entrance  130  is an opening or aperture extending from the outer surface  120  through the inner surface  118  (not visible in  FIG. 4 ) of the graft material  102 . When the stent-graft prosthesis  100  is in the partially expanded configuration, the channel entrances  130  are configured to permit blood flow from outside the graft-material  102  to the channel lumen  134 . Each channel exit  132  is disposed through the graft material  102  and in fluid communication with the channel lumen  134 . Each channel exit  132  is an opening or aperture extending from the inner surface  118  (not visible in  FIG. 4 ) through the outer surface  120  of the graft material  102 , and extending to outside the graft material  102 . The channel exits  132  are configured to permit blood flow from the channel lumen  134  to outside the graft material  102  when the stent-graft prosthesis  100  is in the partially expanded configuration. Thus, when the stent-graft prosthesis  100  is in the partially expanded configuration, the channels  106  permit blood flow from an upstream side of the stent-graft prosthesis  100 , through the channel lumen  134 , to a downstream side of the stent-graft prosthesis  100 . While the stent-graft prosthesis  100  is shown with seven (7) channels  106  including seven (7) channel entrances  130  and twenty-one (21) channel exits  132 , this is by way of example and not limitation, and there may be more or fewer channels  106 , channel entrances  130  and channel exits  132 . The shape of the channel entrances  130  may be different than the shape of the channel exits  132  to facilitate the difference in the natural taper of the stent-graft prosthesis  100  in the partially expanded configuration, as described below. 
     In the embodiment of  FIGS. 1-12 , each channel entrance  130  includes three (3) corresponding channel exits  132  that are circumferentially aligned with and longitudinally spaced from the corresponding channel entrance  130 . As best shown in  FIG. 6 , each of the channel exits  132 A,  132 B, and  132 C is longitudinally or axially spaced from the corresponding channel entrance  130 A by a different length or amount. In other words, the channel exit  132 A is located closer to the channel entrance  130 A than the channel exit  132 B is to the channel entrance  130 A, and the channel exit  132 B is located closer to the channel entrance  130 A than the channel exit  132 C is to the channel entrance  130 A. While each channel entrance  130  is shown with three (3) corresponding channel exits  132 , this is by way of example and not limitation, and each channel entrance  130  may have more or fewer corresponding channel exits  132 . The reason for having more than one channel exit  132  per channel entrance  130  and for the channel exits  132  to be longitudinally spaced is for at least one of the channel exits to  132  to be open at different stages of deployment of the stent-graft prosthesis  100 , as will be explained in more detail below. Further,  FIG. 6  shows that the valve assembly/flap (described in more detail below) of channel exit  132 A overlaps with channel exit  132 B (hence channel exit  132 B is shown dashed). Similarly, the valve assembly/flap of channel exit  132 B overlaps with channel exit  132 C. This overlap is better seen in  FIGS. 10 , for example. However, this is not meant to be limiting and the flaps need not overlap. Moreover, while the corresponding channel entrance  130  and channel exits  132  are described as circumferentially aligned, this is not meant to be limiting, and the corresponding channel entrance  130  and channel exits  132  need not be circumferentially aligned. 
     In an embodiment, each of the channel entrances  130  and/or each of the channel exits  132  may include a valve assembly  135 , coupled thereto, as shown in  FIGS. 7 and 8 . Each valve assembly  135  includes an open state and a closed state. When the valve assembly  135  is in the open state, the valve assembly  135  is configured to permit blood flow there through. The open state of each valve assembly  135  corresponds to the partially expanded state of the adjacent body stent  124  of the channel entrance  130  or the channel exit  132  to which the valve assembly  135  is coupled, as will be described below. When the valve assembly  135  is in the closed state, the valve assembly  135  is configured to prevent blood flow there through. The closed state of each valve assembly  135  corresponds to the radially collapsed and the radially expanded configurations of the adjacent body stent  124  of the channel entrance  130  or the channel exit  132  to which the valve assembly  135  is coupled, as will also be described below. Each valve assembly  135  may be coupled to the corresponding channel entrance  130  or channel exit  132  by methods such as, but not limited to adhesives, sewing, fusing, or any other suitable method. 
     In an embodiment, each valve assembly  135  is a flap valve assembly  135 . Each flap valve assembly  135  has a generally triangular shape when in the open state, as shown in  FIG. 7 , and a generally flat, rectangular shape when in the closed state, as shown in  FIG. 8 . As best viewed in  FIG. 7 , each flap valve assembly  135  includes a collar  136 . A first edge  138  of the collar  136  is coupled to a first edge  140  (see  FIG. 6 ) of the channel entrance  130  or a first edge  142  (see  FIG. 6 ) of the channel exit  132 . When coupled to the channel entrance  130  or the channel exit  132 , the flap valve assembly  135  changes shape as the portion of the stent graft prosthesis  100  adjacent the channel exit  130  or the channel exit  132  transitions from the radially compressed state, to the partially expanded state, and then to the radially expanded state. Thus, as explained in more detail below, when the portion of the stent-graft prosthesis  100  adjacent a channel entrance  130  or a channel exit  132  to which the flap valve assembly  135  is coupled is in the radially compressed configuration for delivery, the flap valve assembly  135  is closed. When the portion of the stent-graft prosthesis  100  adjacent a channel entrance  130  or a channel exit  132  to which the flap valve assembly  135  is coupled radially expands from the radially compressed state to the partially expanded state, the flap valve assembly transitions to the open state. When the portion of the stent-graft prosthesis  100  adjacent a channel entrance  130  or a channel exit  132  to which the flap valve assembly  135  is coupled expands to the radially expanded configuration, the flap valve assembly  135  correspondingly transitions to the closed state, preventing blood flow through the corresponding channel entrance  130  or channel exit  132 . 
     In an embodiment, each valve assembly  135  extends longitudinally, generally parallel to the central longitudinal axis LA of the graft material  102 , as best shown in  FIG. 4 . Thus, each valve assembly  135  at each channel entrance  130  extends from the channel entrance  130  distally inside of the graft material  102  (i.e., within the graft-lumen  114 ). Further, each valve assembly  135  at each channel exit  132  extends from the channel exit  132  outside the graft material  102  of the stent-graft prosthesis  100 . 
     While described herein with a valve assembly  135  at each channel entrance  130  and each channel exit  132 , this is not meant to be limiting, and in other embodiments, each channel entrance  130  and each channel exit  132  may or may not have a valve assembly  135 . Moreover, while each valve assembly  135  has been described as a flap valve assembly  135 , this is by way of example and not limitation, and each valve assembly  135  may have a valve design other than a flap valve. Further, each valve assembly  135  may be of a similar or different valve design in any combination. 
     The operation of the stent-graft prosthesis  100  will now be explained with reference to  FIGS. 9-12 , which are sectional cutaway views of a vessel illustrating the delivery, positioning and deployment of the stent-graft prosthesis  100  at the site of a vessel abnormality, which in  FIGS. 9-12  is an aneurysm. However, this is by way of example and not limitation and embodiments of the stent-graft prosthesis  100  may be utilized with other vessel abnormalities including, but not limited to dissections and transections. 
     Referring now to  FIG. 9 , the stent-graft prosthesis  100  is disposed on a distal portion of a delivery system  500  in the radially compressed configuration. The delivery system  500  includes at least an outer sheath  502  and an inner shaft  504  having a tip capture mechanism  506  mounted thereon. The proximal end  111  of the stent-graft prosthesis  100  is releasably coupled to the tip capture mechanism  506 . The stent-graft prosthesis  100  is mounted on the inner shaft  504  and the outer sheath  502  encapsulates, covers, or restrains the stent-graft prosthesis  100  in the radially compressed configuration for delivery thereof. The delivery system  500  is advanced to a desired treatment location of an aneurysm AN in a vessel VS. In embodiments hereof, the delivery system  500  may be similar to the Captiva Delivery System, manufactured by Medtronic Vascular, Inc. of Santa Rosa, California, or a delivery system as described in U.S. Patent Application Publication No. 2009/0276027 to Glynn, or U.S. Pat. No. 8,882,828 to Kinkade et al., each of which is incorporated by reference herein in its entirety. 
     Once the stent-graft prosthesis  100  is at the desired treatment location within the vessel VS, the stent-graft prosthesis  100  may be deployed from the delivery system  500 . The outer sheath  502  of the delivery system  500  is retracted to release a portion the stent-graft prosthesis  100 . The released portion of the stent-graft prosthesis  100  radially expands within the vessel VS and the stent-graft prosthesis  100  transitions to a partially expanded configuration. When in the partially expanded configuration shown in  FIG. 10 , a first or tip-capture portion  150  of the stent-graft prosthesis  100 , including at least the proximal end  111 , is restrained in the radially compressed state by the tip capture mechanism  506 . A second or distal constrained portion  152  including at least the distal end  113  is restrained in the radially compressed state by the outer sheath  502 . At the deployment moment shown in  FIG. 10 , the distal restrained portion  152  further includes the body stents  124 E and  124 F. A third or expanded portion  154  of the stent-graft prosthesis  100  expands to the radially expanded state to conformingly engage the inner wall of the vessel VS. In  FIG. 10 , the expanded portion  154  includes the body stent  124 B. A fourth or tapered inlet portion  156  is disposed between the tip-capture portion  150  and the expanded portion  154  and is held in the partially expanded state by the tip-capture portion  150  in the radially compressed configuration and the expanded portion  154  in the radially expanded configuration. The tapered inlet portion  156  includes the seal stent  122 , the body stent  124 A, and the channel entrances  130 . A fifth or tapered outlet portion  158  is disposed between the expanded portion  154  and the distal constrained portion  152  and is held in the partially expanded state by the expanded portion  154  in the radially expanded configuration and the distal constrained portion  152  in the radially compressed configuration. The tapered outlet portion  158  includes the body stents  124 C and  124 D, and the channel exits  132 A and  132 B, respectively. 
     When in the partially expanded configuration of  FIG. 10 , the stent-graft prosthesis  100  generally occludes the lumen LU of the vessel VS. Thus, as can be seen in  FIG. 10 , absent the channel entrances  130 , blood pressure against the stent-graft prosthesis may cause the stent-graft prosthesis  100  to move during deployment. Also, blood flow past the stent-graft prosthesis  100  is blocked, thereby depriving blood flow to vessels downstream of the stent-graft prosthesis  100 . However, when in the partially expanded configuration of  FIG. 10 , blood flow is enabled through the channels  106 . In particular, as explained above, the channel entrances  130  are disposed in the tapered inlet portion  156  of the partially deployed stent-graft prosthesis  100 , distal of the first end  110  of the graft material  102 . In this partially expanded state of the tapered inlet portion  156 , the channel entrances  130  and the associated valve assemblies  135  are open, thus enabling blood flow into the channel lumen  134  (i.e., the graft lumen  114 ). Similarly, the tapered outlet portion  158  is in the partially expanded state. Therefore, the channel exits  132 A,  132 B disposed at the tapered outlet portion  158 , and their associated valve assemblies  135 , are open, thereby enabling blood flow out of the channel lumen  134  through the channel exits  132 A,  132 B. Thus, blood from an upstream side UP of the stent-graft prosthesis  100  is permitted to travel through the channels  106  to the downstream side DW of the stent-graft prosthesis  100 . More precisely, blood on the upstream side UP of the stent-graft prosthesis  100  enters through the channel entrances  130 , travels through the channel lumen  134 , and exits to the downstream side DW of the stent-graft prosthesis  100  through the channel exits  132 A and  132 B. The flow of blood through the channels  106  from the upstream side UP to the downstream side DW of the stent-graft prosthesis  100  relieves pressure associated with pulsatile blood flow on the upstream side UP of the stent-graft prosthesis  100 , and more specifically on the outer surface  120  of the graft material  102  of the tapered inlet portion  156  of the stent-graft prosthesis  100 . The flow of blood through the channels  106  from the upstream side UP to the downstream side DW of the stent-graft prosthesis  100  also provides blood supply to vessels downstream of the stent-graft prosthesis  100 . When the pressure associated with the pulsatile blood flow is relieved on the upstream side UP by the channels  106  during deployment of the stent-graft prosthesis  100 , the stent-graft prosthesis  100  can be more precisely positioned. In addition, the position of the stent-graft prosthesis  100  can be more easily maintained during deployment of the stent-graft prosthesis  100 . 
     The blood flow explained above is at the stage of deployment shown in  FIG. 10 . As the outer sheath  502  continues to be retracted to release the stent-graft prosthesis  100 , the blood flow from the upstream side UP to the downstream side DW of the stent-graft prosthesis  100  through the channels  106  is maintained. In particular, as each successive body stent  124  is released from the outer sheath  502  during deployment of the stent-graft prosthesis  100 , each released body stent  124  expands first to a partially expanded state and then to a radially expanded state. More specifically, as each body stent  124  expands to the partially expanded state, each body stent  124  transitions from the distal constrained portion  152  of the stent-graft prosthesis  100  to the tapered outlet portion  158  of the stent-graft prosthesis  100 . In the example of  FIG. 10 , the next body stent  124  to be released would be the body stent  124 E. When the body stent  124 E is released and permitted to expand to the partially expanded state, the body stent  124  of the tapered outlet portion  158  closest to the first end  111 , in the example of  FIG. 10 , the body stent  124 C, is concurrently permitted to expand to the radially expanded state and transitions to the expanded portion  154 , as shown in  FIG. 11 . As body stent  124 C radially expands to the radially expanded state, the channel exits  132 A and their associated valve assemblies  135  are closed due to the expansion. At the stage shown in  FIG. 11 , body stent  124 D has also radially expanded to the radially expanded state, thereby closing channels exits  132 B and their associated valve assemblies  135 . Further, when the body stent  124 E expands to the partially expanded state upon release from the outer sheath  502 , the corresponding valve assemblies  135  of the adjacent channel exits  132 C transition from the closed state to the open state to permit blood to exit the channels  106  therethrough, as shown in  FIG. 11 . Thus, blood flow through the channels  106  is maintained during the deployment of the stent-graft prosthesis  100 , with blood entering the channel entrances  130 , traveling through the channel lumen  134 , and exiting one or more of the channel exits  132 A,  132 B, and  132 C as the stent-graft prosthesis  100  is deployed. 
     When final deployment of the stent-graft prosthesis  100  is desired, the outer sheath  502  is retracted to release the second end  113  of the stent-graft prosthesis  100 , as shown in  FIG. 11A . In this configuration, the channel exits  132 A,  132 B,  132 C are all closed, but the channel entrances  130  are open because first end  111  of the stent-graft prosthesis  100  is captured by the tip capture mechanism  506 . Blood flows into the channel entrances  130 , into the graft lumen  114 , and exits through the second end  113  of the stent-graft prosthesis  100  distal of the aneurysm AN. The tip capture mechanism  506  is then actuated to release the first end  111  of the stent-graft prosthesis  100  to transition the stent-graft prosthesis  100  to the radially expanded configuration within the vessel VS, as shown in  FIG. 12 . When in the radially expanded configuration, each of the channel entrances  130  and each of the channel exits  132  are in the closed state and blood is permitted to flow through the graft lumen  114  from the proximal end  111  to the distal end  113  of the stent-graft prosthesis  100 , thereby isolating the aneurysm AN from blood normal pressure and reducing the chance of vessel rupture. 
       FIG. 11B  shows an embodiment wherein the first end  111  of the stent-graft prosthesis  100  is in the radially expanded configuration (tip capture mechanism  506  has been actuated) and the second end  113  of the stent-graft prosthesis  100  is still captured in the sheath  502 . This can occur between the step shown in  FIG. 11  and the full release of the stent-graft prosthesis  100  as shown in  FIG. 12 . Thus, instead of releasing the second end  113  first, as shown in  FIG. 11A , the first end  111  is released first. However, in other embodiments, the first end  111  of the stent-graft prosthesis  100  may be radially expanded prior to any other portion of the stent-graft prosthesis  100  in order to allow radial expansion of the seal stent  122  to secure the stent-graft. In either situation, with the first end  111  in the radially expanded configuration, blood enters the graft lumen  114 . In a conventional stent-graft, with the second, downstream end still captured in delivery system, the blood is trapped within the graft lumen. With the stent-graft prosthesis  100  disclosed herein, however, blood may exit the graft lumen  114  through the channel exits  132 . If the stent-graft prosthesis  100  is to be used in a method wherein the first end  111  is radially expanded prior to the remainder of the stent-graft prosthesis  100 , as described, then the channel entrances  130  are not needed. 
       FIGS. 13-19  illustrate a stent-graft prosthesis  200  in accordance with another embodiment hereof In the embodiment shown, the stent-graft prosthesis  200  includes a graft material  202 , a frame  204 , and a plurality of channels  206  (not shown in  FIG. 13 —see  FIG. 15-16 ). The stent-graft prosthesis  200  has a radially compressed configuration for delivery, a radially expanded configuration when deployed, and a partially expanded configuration when transitioning between the radially compressed and the radially expanded configurations. The stent-graft prosthesis  200  is of a closed-web configuration. However, the stent graft prosthesis  200  may instead be an open web configuration. 
     The graft material  202  is of a generally tubular shape having a central longitudinal axis L A , a first end or edge  210 , a second end or edge  212 , and a graft lumen  214  extending from the first end  210  to the second end  212 , as shown in  FIG. 13 . The graft material  202  has a longitudinal length  216 , which may vary based upon the application. The graft material  202  further includes an inner surface  218  and the outer surface  220 . In an embodiment, the first end  210  of the graft material  202  may be referred to as a proximal or an upstream end or edge  210  of the graft material  202 . In the embodiment shown, the first end  210  of the graft material is also a first, proximal or upstream end or edge  211  of the stent-graft prosthesis  200 . The second end  212  of the graft material  202  may be referred to as a distal or a downstream end or edge  212  of the graft material  202 . In the embodiment shown, the second end  212  of the graft material  202  is also a second, distal or downstream end or edge  213  of the stent-graft prosthesis  200 . For a stent-graft prosthesis for an abdominal aortic aneurysm delivered from the femoral artery, the proximal or upstream end  211  of the stent-graft prosthesis  200  is the end that is coupled to a tip capture mechanism of a delivery system. The graft material  202  may be formed from any suitable graft material as previously described with respect to the graft material  102 . 
     As shown in  FIG. 13 , the frame  204  includes a sealing or seal stent  222  and a plurality of body stents  224 . The frame  204  is configured to support the graft material  202 . In the embodiment illustrated in  FIG. 13 , the stent-graft prosthesis  200  is shown in the radially expanded configuration and includes one (1) seal stent  222  adjacent to the first end  210 , and eight (8) body stents  224  axially spaced between the first end  210  and the second end  212  of the graft material  102 . Although shown with eight (8) body stents  224 A,  224 B,  224 C,  224 D,  224 E,  224 F,  224 G, and  224 H, it will be understood that the stent-graft prosthesis  200  may include more or fewer of body stents  224  depending upon the desired length  216  of the stent-graft prosthesis  200  and/or the intended application. The seal stent  222  and each of the body stents  224  are self-expanding and each includes a radially compressed state for delivery, a radially expanded state when deployed, and a partially expanded state when transitioning between the radially compressed state and the radially expanded state. The seal stent  222  and each of the body stents  224  may be a sinusoidal patterned ring including a plurality of crowns or bends  226  and a plurality of struts or straight segments  228  with each crown  226  being formed between a pair of adjacent struts  228 . While shown with a particular pattern, the seal stent  222  and the body stents  224  may have different patterns and configurations. As described in more detail below, the body stents  224  are disposed on the outer surface  220  of the graft material  202 . 
     The seal stent  222  is coupled to the graft material  202 . When the stent-graft prosthesis  200  is in the radially expanded configuration, the seal stent  222  is configured with sufficient radial spring force to conformingly and sealingly engage a wall of a vessel to prevent blood flow between the wall of the vessel and the outer surface  220  of the graft material  202 . The seal stent  222  may be coupled to the graft material  202  by stitches, sutures, or any other suitable method. In the embodiment shown in  FIG. 13 , the seal stent  222  is coupled to the outer surface  220  of the graft material  102 . However, in alternate embodiments, the seal stent  222  may be coupled to the inner surface  218  of the graft material  202 . 
     In the embodiment illustrated in  FIG. 14 , which is a body stent  224  cut and flattened for illustrative purposes, each body stent  224  includes four (4) first segments  260 . Each first segment  260  is circumferentially separated from an adjacent first segment  260  by a second segment  262 . Thus, the body stent  224  includes four (4) second segments  262 . Each first segment  260  includes one (1) crown  226   a  and two (2) adjacent struts  228 . Each second segment  262  includes one (1) crown  226   b  and two adjacent struts  228 . Further, there is a crown  226   c  where each first segment  260  meets an adjacent second segment  262 . While each body stent  224  is described as having four (4) first segments  260  and four (4) second segments  262 , this is by way of example and not limitation, and each body stent  224  may have more or fewer of first and second segments  260 ,  262 . Additionally, while each first segment  260  and second segment  262  is described with one (1) crown  226  and two (2) adjacent struts  228 , this, too, is by way of example and not limitation, and each first segment  260  and/or each second segment  262  may have more crowns  226  and adjacent struts  228 . Even further, while the crown  226   a  of each first segment  260  is facing a specific direction, and the crown  226   b  of each second segment  262  is facing in the same direction, this is not meant to be limiting, and each crown  226   a / 226   b  of each first section  260  and second section  262  may alternatively face the opposite direction in any combination. 
     Each second segment  262  is coupled to the outer surface  220  of the graft material  202  by methods such as, but not limited to stitches, sutures, or any other suitable method. Each first segment  260  is not coupled to the graft material  202 . As shown in  FIGS. 15 and 16 , and explained in more detail below, each of the channels  206  is formed between an outer surface  220  of the graft material  202  at the location of one of the first segments  260  and a vessel wall when the stent-graft prosthesis  200  is in a partially expanded configuration. 
     When each body stent  224  is assembled as part of the frame  204  of the stent-graft prosthesis  200 , as best shown in  FIG. 15 , which is a perspective illustration of the stent-graft prosthesis  200  in the partially expanded configuration, the first segments  260  of each body stent  224  are circumferentially aligned with the first segments  260  of a longitudinally adjacent body stent  224 . 
     Each channel  206  is configured to relieve pressure associated with pulsatile blood flow on the stent-graft prosthesis  200  during implantation within a body vessel. Accordingly, each channel  206  is configured to permit blood flow from an upstream side of the stent-graft prosthesis  200  to a downstream side of the stent-graft prosthesis  200  when the stent-graft prosthesis is in the partially expanded configuration, as shown in  FIG. 15 . The partially expanded configuration, as used herein, means that a portion or portions of the stent-graft prosthesis  200  is/are in a radially compressed state and at least a portion of the stent-graft prosthesis  200  is in a radially expanded state, as will be described in more detail below. In the embodiment shown in  FIG. 15 , the first end  211  is the upstream side of the stent-graft prosthesis  200  and the second end  213  is the downstream side of the stent-graft prosthesis  200 . 
     As best shown in  FIG. 15 , each channel  206  includes a channel lumen  234  extending from a channel entrance  230  distal of the first end  210  of the graft material  202  to a channel exit  232  proximal of the second end  212  of the graft material  202 . Each channel entrance  230  is formed at the first body stent  224  distal of the first end  211  that includes first segments  260  that are unattached to the graft material  202 . In the embodiment shown in  FIG. 15 , the first body stent distal of the first end  211  that includes first segments  260  that are unattached to the graft material  202  is the body stent  224 B (i.e., the second body stent). However, this is not meant to be limiting and the channel entrances  230  may be formed at other body stents depending on, for example, the locations of the body stents, their spacing, the expanded diameter of the stent-graft prosthesis  200 , and other factors that would be recognized by those skilled in the art. The formation of the channel exits  232  will be discussed in more detail below. Each channel entrance  230  is configured to permit blood flow to the corresponding channel lumen  234  and each channel exit  232  is configured to permit blood flow from the corresponding channel lumen  234  when the stent-graft prosthesis  200  is in the partially expanded configuration. 
     As best shown in  FIG. 16 , the stent-graft prosthesis  200  includes four (4) channels  206 . As noted above, each channel lumen  234  is formed between the outer surface  220  of the graft material  202  and the adjacent wall of the vessel at the locations of the first segments  260  when the stent-graft prosthesis  200  is in the partially expanded configuration. While described with four (4) channels  206 , this is by way of example and not limitation, and there may be more or fewer channels  206 . 
       FIGS. 17-19 , which are sectional cutaway views of a vessel illustrating the delivery, positioning and deployment of the stent-graft prosthesis  200  at the site of a vessel abnormality, will be referenced to explain the operation of the stent-graft prosthesis  200 . While the vessel abnormality of  FIGS. 17-19  is an aneurysm, it will be understood that this is by way of example and not limitation and embodiments of the stent-graft prosthesis  200  may be utilized with other vessel abnormalities including, but not limited to dissections and transections. 
     Referring now to  FIG. 17 , a distal portion of a delivery system  500  is shown with the stent-graft prosthesis  200  disposed in a radially compressed configuration thereon. The stent-graft  200  has been advanced to a desired treatment site of a vessel VS, which in this example is the location of an aneurysm AN. The delivery system  500  includes at least an outer sheath  502  and an inner shaft  504  having a tip capture mechanism  506  mounted thereon. The first end  211  of the stent-graft prosthesis  200  is releasably coupled to the tip capture mechanism  506 . The stent-graft prosthesis  200  is mounted on the inner shaft  504  and the outer sheath  502  encapsulates, covers, or restrains the stent-graft prosthesis  200  in the radially compressed configuration for delivery thereof. In embodiments hereof, the delivery system  500  may be similar to the Captiva Delivery System, manufactured by Medtronic Vascular, Inc. of Santa Rosa, Calif., or as a delivery system as described in U.S. Patent Application Publication No. 2009/0276027 to Glynn, or U.S. Pat. No. 8,882,828 to Kinkade et al., previously incorporated by reference in their entirety. 
     Once the stent-graft prosthesis  200  is at the desired treatment location within the vessel VS, the stent-graft prosthesis  200  may be deployed from the delivery system  500 . The outer sheath  502  of the delivery system  500  is retracted to release a portion of the stent-graft prosthesis  200 . The released portion of the stent-graft prosthesis  200  radially expands within the vessel VS and the stent-graft prosthesis  200  transitions to the partially expanded configuration. As shown in  FIG. 18A , a first or tip-capture portion  250  of the stent-graft prosthesis  200 , including at least the first end  211 , is restrained in the radially compressed state by the tip-capture mechanism  506 . A second or distal restrained portion  252  is restrained in the radially compressed state by the outer sheath  502 . At the deployment moment shown in  FIG. 18A , the distal restrained portion  252  includes the body stents  224 G and  224 H. A third or expanded portion  254  of the stent-graft prosthesis  200  expands to the radially expanded state to conformingly engage an inner wall of the vessel VS. In  FIG. 18A , the expanded portion  254  includes the body stents  224 B- 224 F. A fourth or tapered inlet portion  256  is disposed between the tip-capture portion  250  and the expanded portion  254  and is held in the partially expanded state by the tip-capture portion  250  in the radially compressed state and the expanded portion  254  in the radially expanded state. In the embodiment shown, the tapered inlet portion  256  includes the body stent  224 A. A fifth or tapered outlet portion  258  is disposed between the expanded portion  254  and the distal restrained portion  252 , and is held in the partially expanded state by the expanded portion  254  in the radially expanded state and the distal restrained portion  252  in the radially compressed state. In the state of deployment shown in  FIG. 18A , the tapered outlet portion  258  includes the body stent  224 F, but this varies as the stent-graft prosthesis  200  is being deployed, as explained in more detail below. 
     The lumen LU of the vessel VS is generally occluded when the stent-graft prosthesis  200  is in the partially expanded configuration and disposed therein. Thus, as can be seen in  FIG. 18A , absent the channel entrances  230 , blood pressure against the stent-graft prosthesis  200  may cause the stent-graft prosthesis  200  to move during deployment. However, when in the partially expanded configuration of  FIG. 18A , blood flow is enabled through the channels  206 . In particular, as explained above, the channel entrances  230  are disposed in the tapered inlet portion  256  of the partially deployed stent-graft prosthesis  200 . In this partially expanded state of the tapered inlet portion  256 , the blood flows along the exterior surface  220  of the graft material  202  where the graft material  202  is attached to the body stent  224 A. As the blood flows past the body stent  224 A, the graft material  202  is not attached to the first segments of the body stent  224 B. Thus, the blood flow forces the graft material  202  radially inward away from the first segments  260  of the body stent  224 B, thereby creating the channel entrances  230  and enabling blood flow into the channel lumen  234 . Similarly, the tapered outlet portion  258  is in the partially expanded state. Therefore, the channel exits  232  are disposed at the tapered outlet portion  258 . In particular, the channel exits  232  are formed between the most distal body stent  224  of the expanded portion  254  and the most proximal body stent  224  of the tapered outlet portion  258 . Thus, in the embodiment shown in  FIG. 18A , the channel exits  232  are formed between the body stent  224 E and the body stent  224 F, as shown. The channel exits  232  are formed at this location because the graft material  202  at the first segments  260  of the body stent  224 E hangs below the body stent  224 E. However, because the body stent  224 F is only partially expanded, the graft material  202  at the body stent  224 F is adjacent the body stent  224 F. Thus, any blood flow in the channel lumen  234  escapes the channel lumen  234  and a channel exit  232  is formed.  FIG. 18C  is a partial cross-sectional view of a portion of  FIG. 18A  showing this feature. 
     Thus, blood from an upstream side UP of the stent-graft prosthesis  200  is permitted to travel through each channel  206  to the downstream side DW of the stent-graft prosthesis  200 . More precisely, blood on the upstream side UP of the stent-graft prosthesis  200  pushes the graft material  202  radially inward, away from the uncoupled portions of the body stents  224 , thereby opening each channel  206 . Blood flow enlarges each channel  206  when the stent-graft prosthesis  200  is in the partially expanded configuration. Blood enters each channel  206  through the corresponding channel entrance  230 , flows through the channel lumen  234  outside of the outer surface  220  of the graft material  202 . Radially outside of the outer surface  220  of the graft material at the channel lumens  234  are the respective first segment  260  of the each body stent  224  and the adjacent wall of the vessel VS. Thus the channels  234  are formed between the outer surface  220  of the graft material  202  and the first segment  260  of each body stent  224  in the radially expanded state/the adjacent wall of the vessel VS. The blood exits to the downstream side DW of the stent-graft prosthesis  200  through the corresponding channel exit  232 . The flow of blood through the channel  206  from the upstream side UP to the downstream side DW of the stent-graft prosthesis  200  relieves pressure associated with pulsatile blood flow on the upstream side UP of the stent-graft prosthesis  200 . More specifically, when the stent-graft  200  is in the partially expanded configuration, the channels  206  relieve upstream pressure against the outer surface  220  of the graft material  202  at the tapered inlet portion  256 . When the pressure associated with the pulsatile blood flow is relieved on the upstream side UP by the channel  206  during deployment of the stent-graft prosthesis  200 , the stent-graft prosthesis  200  can be more accurately positioned and easily maintained during deployment. 
     It will be understood that as the outer sheath  502  is retracted, the body stents  224  are sequentially released and the number of body stents  224  of the third portion  254  increases. With the channel exit  232  of each channel  206  being defined by the body stent  224  in the radially expanded state nearest the second end  213 , which is a part of the expanded portion  254 , the channel exit  232  for each channel  206  effectively moves longitudinally toward the second end  212  as the stent-graft  200  is deployed. For example,  FIG. 18B  shows the outer sheath  502  further retracted as compared to  FIG. 18A . Thus, in  FIG. 18B , the body stent  224 F has expanded from the partially expanded state in the tapered outlet portion  258  to the expanded stated in the expanded portion  254 . Further, the body stent  224 G has been released from the outer sheath  502  and has transitioned from the radially compressed state of the distal restrained portion  252  to the partially expanded state of the distal outlet portion  258 . Thus, the channel exits  232  have moved towards the second end  213  of the stent-graft prosthesis  200 , as shown in  FIG. 18B . 
     When final deployment of the stent-graft prosthesis  200  is desired, the outer sheath  502  is retracted to release the second end  213  of the stent-graft prosthesis  200 , thereby enabling the second end  213  to radially expand to the radially expanded configuration. Further, the tip capture mechanism  506  is actuated to release the first end  211  of the stent-graft prosthesis  200  such that the first end  211  expands to the radially expanded configuration. With both the first and second ends  211 ,  213  expanded, the stent-graft prosthesis  200  is in the radially expanded configuration within the vessel VS, as shown in  FIG. 19 . The full retraction of the sheath  502  and release of the first end  211  from the tip-capture mechanism  506  may simultaneously or sequentially. When the first end  211  of the stent-graft prosthesis  211  is released from the tip-capture mechanism  506 , the seal stent  222  and the body stent  224 A expand to the radially expanded configuration. When in the radially expanded configuration, the seal stent  220  conformingly seals to the wall of the vessel VS, preventing blood flow between the graft material  202  and the wall of the vessel VS. Because both the seal stent  222  and the body stent  224 A do not have first segments  260  with the graft material  202  uncoupled thereto, blood is blocked from entering the channel entrances adjacent the body stent  224 B. Similarly, because the body stent  224 H does not have first segments  260  with the graft material  202  uncoupled thereto, the channel exits  236  adjacent the body stent  224 G are closed. Further, when the stent-graft  200  is in the radially expanded configuration, blood flows from the first end  210 , through the graft lumen  214 , and exits through the second end  212 . Blood flow through the graft lumen  214  forces the graft material  202  radially outward against first segments  260  of the body stents  224  and the wall of the vessel VS, collapsing the channels  206  (not visible in  FIG. 19 ). 
     While various embodiments of 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. Thus, the breadth and scope of the present invention should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. 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. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the detailed description. All patents and publications discussed herein are incorporated by reference herein in their entirety.