fig1 - 3 show portions of a stent - graft deployment system 10 . fig1 illustrates the system 10 without a stent - graft while fig2 and 3 show close up views of the deployment system tip which are loaded with a stent - graft 15 , 15 a . this system could also deploy a stent alone or some other form of endoprosthesis . the subsequent use of “ stent - graft ” herein should be understood to include other forms of endoprosthesis . ideally , the stent - groft deployment system 10 comprises a tapered tip 12 , 12 a , 12 b that is flexible and able to provide trackability in tight and tortuous vessels , and can bend easily once the primary sheath 20 is retracted . other tip shapes such as bullet - shaped tips could also be used . the system 10 includes a primary sheath 20 ( preferably made of a semi - rigid material such as ptfe ) initially covering a secondary sheath 14 ( preferably made of woven polyethylene terephthalate ( pet )). the secondary sheath 14 is more flexible than the retractable primary sheath 20 . the deployment system 10 is able to separately retract the primary and secondary sheaths . the primary sheath should have enough stiffness to provide adequate trackability and column strength as the system 10 tracks through tortuous vessels to avoid buckling or kinking . the secondary sheath utilizes its greater flexibility ( at the expense of column strength ) to improve trackability and pushability , particularly through areas having tight radiuses . so , where prior deployment systems utilizing just a semi - rigid primary sheath were prone to kinking while tracking through an area with a tight radius . use of the secondary sheath avoids kinking or changes in shape and reduces resistance to deployment ( reduced advancement force ) while tracking through vessels with tight curves . the deployment system 10 also includes a stent - graft 15 initially retained within the secondary sheath 14 . as described herein , the stent - graft 15 is preferably a self - expanding , nitinol / dacron stent - graft system designed for endovascular exclusion of thoracic aortic aneurisms ( taa ). the deployment system 10 includes a cup 16 as shown in fig2 or alternatively steel runners 17 as shown in fig3 that eventually release the stent - graft by its mere self - expansion to act as a means for retaining the stent - graft 15 in place during deployment . although the means for retaining shown in fig3 is on the “ backend ” of the stent - graft , it can alternatively or additionally be on a “ tip end ” of the stent - graft and attached to one or more of several coaxial tubes . a handle or a hub 22 is fixed to the primary sheath 20 , a second handle or hub ( 24 ) near a proximal end of the stent - graft deployment system 10 is fixed to the secondary sheath , and a catheter shaft including a shaft handle 26 is connected to and aids the advancement of the system 10 and acts as a deployment means . in addition , the deployment system 10 shown includes a flush port 28 and a radiopaque marker 18 allowing for accurate positioning of the delivery system prior to deployment of the stent - graft in the proximal position . referring to fig4 - 8 and fig1 - 15 , the stent - graft deployment system 10 is shown in various stages as it is advances over a guide wire 111 ( as shown in fig1 - 14 ) and the stent - graft is deployed . fig4 - 8 , in particular , illustrate the stent - graft deployment system 10 as it would operate or function outside or apart from the body . fig1 - 15 illustrate the stent - graft deployment system as it would operate when tracking over a guide wire 111 within a body and particularly through a target area ( vessel ) having a tight curvature or radius ( 21 ). fig4 and 10 both illustrate the stent - graft deployment system 10 with the primary sheath 20 covering the secondary sheath 14 . the flexible secondary sheath 14 is arranged within the semi - rigid sheath 20 when the semi - rigid sheath 20 is in a non - retracted position as shown in fig4 . as shown in fig5 , the stent - graft 15 is constrained solely by the flexible secondary sheath 14 and further illustrates a handle or hub 22 coupled to the semi - rigid sheath 20 serving as a first arrangement for retracting the semi - rigid sheath 20 and exposing the flexible secondary sheath 14 as well as an inner tube 25 coupled to the flexible secondary sheath 14 serving as a second arrangement for retracting the flexible secondary sheath and enabling the stent - graft to expand . it should be noted that the exposed portion of the flexible secondary sheath 14 could have a diameter larger than the semi - rigid primary sheath 20 that surrounded the flexible secondary sheath 14 previously . the larger diameter of the exposed portion of the flexible secondary sheath 14 is a contributory factor in reducing the force needed to retract the secondary sheath . once the flexible secondary sheath 14 is exposed , the end of stent - graft deployment system 10 beyond the semi - rigid sheath has greater flexibility ( than the portion of the system within the semi - rigid sheath 20 ) as it tracks across the guidewire . the first arrangement described above could comprise ( as previously mentioned ) the handle or hub 22 coupled to the semi - rigid sheath 20 enabling the relative axial movement of the semi - rigid sheath 20 over a remainder of the stent - graft deployment system and the second arrangement could comprise an inner tube 25 coupled to the flexible secondary sheath 14 that enables relative axial movement of the flexible secondary sheath 14 relative to the semi - rigid sheath 20 and the longitudinal axis of the catheter . such as where operation of the second handle 24 causes axial pulling of the proximal end of the flexible secondary sheath 14 , to create a tension in the material / fabric of the secondary sheath to cause retraction that causes the cylindrically configured sheath to retract along the longitudinal axis of the catheter to provide a substantially circularly uniform deployment of the stent graft starting at its distal end ( relative to the catheter ). in any event , once the secondary sheath 14 is exposed or outside the primary sheath , the system 10 can be advanced over the guide wire 111 with a lower advancement force since the secondary sheath is designed to be quite flexible particularly in areas with tight radiuses ( 21 ) as shown in fig1 . the tight arch 21 is meant to represent any area or vessels with tight radiuses such as the thoracic arch . referring to fig6 and 13 , in each instance the primary sheath has been retracted and the secondary sheath is shown partially retracted with the stent - graft 15 being partially deployed . as the secondary sheath retracts , more and more of the stent - graft is deployed as shown in fig6 - 8 and fig1 - 15 . fig8 and 14 illustrate the stent - graft deployment system 10 with the secondary sheath 14 completely retracted and the stent - graft 15 fully deployed . in fig1 the stent - graft deployment system 10 has been removed . the stent - graft deployment system 10 can also be thought of as a device for implanting a radially self - expanding endoprosthesis 15 having an outer sheath 20 . as previously explained , the outer sheath 20 is more rigid and axially maneuverable relative to an inner sheath 14 and wherein the outer sheath 20 is disposed over the inner sheath 14 in a first position ( as shown in fig5 ) and exposes the inner sheath 14 in a second position ( as shown in fig6 - 8 ). the system 10 can also include an elongated catheter 25 coupled to the inner sheath 14 , wherein the inner sheath 14 is constructed to retain the radially self - expanding endoprosthesis 15 in a first position and enable deployment of the radially self - expanding endoprosthesis 15 in a second position . referring to fig9 , a flow chart illustrates a method 100 of deploying a stent - graft includes the steps of providing a stent - graft deployment system with a stent - graft 102 , tracking the stent - graft deployment system over a guide wire to a location before a target area 104 , which may include a curved portion , and retracting the primary sheath to expose a secondary sheath within the target area while the primary sheath is retracted or held as the secondary sheath is exposed 106 . the stent - graft is moved to its location within the target area or until its location within the target area is confirmed . it should be noted that once the primary sheath is retracted and the secondary sheath is exposed , the secondary sheath ( being of a relatively more flexible material than the primary sheath ) will provide greater flexibility in tracking through the remainder of the target area regardless of the curvature or tortuous nature of the vessel . the method further includes the steps of further tracking the stent - graft deployment system to place the secondary sheath in the curved portion of the target area 108 , and retracting the secondary sheath to at least partially deploy the stent - graft in the target area 110 . this step may include deploying or releasing the stent - graft from the delivery system using a release mechanism 112 . the device may also be considered to have a first predeployment configuration wherein said first and second sheaths surround the stent graft to be deployed , and a second partial deployment configuration where the primary sheath is fully retract so that the primary sheath no longer constrains the stent graft to be deployed , while the secondary sheath still constrains the stent graft to be deployed , and third fully deployed configuration where said stent graft is fully released from the primary and secondary sheaths . wherein the relative movement of the tubular ( substantially cylindrical sheaths ) is such that the axial centerline of the cylinder forming the sheaths is moved without the sheaths being everted between their respective predeployment configurations and their respective post deployment configurations such that the axial centerline of the cylinder of each sheath moves in substantially one motion ( in a linear movement along a curving path ) along the axial centerline of the catheter along which it is moved the present configuration is well suited for introducing the stent - graft deployment system into a femoral artery and advancing the stent - graft deployment system through an iliac artery into the aorta for repair of an aortic aneurysm and more specifically in tracking the stent - graft deployment system through a portion of an thoracic arch when the secondary sheath has been exposed after the retraction of the primary sheath and without any kinking of the primary sheath . additionally , the description above is intended by way of example only and is not intended to limit the spirit and scope of the invention and its equivalents as understood by persons skilled in the art .
a stent - graft deployment system includes a stent - graft , a flexible catheter tip attached to a catheter shaft , a retractable primary sheath containing the stent - graft in a first constrained small diameter configuration around the catheter shaft near the flexible tip . the stent - graft deployment system further includes a flexible secondary sheath disposed within the retractable primary sheath and also containing the stent - graft , wherein when the primary sheath is removed from around the stent - graft , the flexible secondary sheath contains the stent - graft in a second constrained small diameter configuration around the catheter shaft near the flexible tip . the removal of the secondary sheath releases the stent - graft from a radial constraint so that stent - graft deployment may proceed .