Abstract:
A stent or stent-graft deployment apparatus or mechanism configured so that, when activated, the stent or stent-graft progressively expands in a direction from its end which is proximally positioned to the deployment instrument, such as a percutaneous catheter, to its end which is distally positioned to the deployment instrument. The stent or stent-graft deployment mechanism includes a tether or slip line configuration which reduces the likelihood of snagging between the line and stent member. A method is also provided for deploying a stent or stent-graft within a mammalian lumen which includes expanding the stent or stent-graft in such a proximal-to-distal direction. The apparatus and method of the present invention minimize the likelihood of the stent or stent-graft from being displaced from the desired site before it is somewhat secured in the vessel during deployment.

Description:
This is a continuation of application Ser. No. 08/620,273, filed on Mar. 22, 1996, now abandoned, which is a continuation-in-part application for application Ser. No. 08/572,436, entitled Stent-Graft Deployment Apparatus and Method, filed on Dec. 14, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to implants for repairing ducts and passageways in the body. More specifically, the invention relates to an apparatus and procedures for deploying a stent-graft in mammalian vasculature. 
     A variety of stent or stent-graft designs and deployment mechanisms have been developed. For various reasons, many of these stent-grafts tend to become displaced from the intended deployment site within a lumen upon deployment prior to being secured within the lumen. Thus, there is a need to improve stent or stent-graft deployment placement accuracy and reliability within a vessel. Additionally, there exists a need to improve upon the reliability of the devices used for deployment of the stent-grafts. 
     SUMMARY OF THE INVENTION 
     The present invention involves medical devices and method(s) for deploying an expandable stent or stent-graft within mammalian lumens. According to the present invention, a medical device comprises a stent (or stent-graft) which has a proximal portion and a distal portion, and means for progressively deploying or expanding the stent, preferably a tether or slip line, which is releaseably coupled to the stent. The line is arranged such that when it is released from the stent, the stent progressively expands in a direction from its proximal portion to its distal portion. In order to accomplish progressive expansion of the stent, according to one variation of the slip-line embodiment the line is preferably arranged in a sack knot configuration. According to a further aspect of the slip line embodiment, the line has a fixed end associated with the distal portion of the stent and a release end associated with the proximal portion of the stent. The release end of the line is pullable to actuate expansion of the stent. 
     The position of the line and the sack knot configuration can eliminate the need for doubling back the line to minimize the risk of snagging between the line and the stent device, thus, increasing deployment reliability. According to another aspect of the present invention, the stent or stent-graft described above may be placed within a lumen from a direction against the flow of fluid (e.g., blood). The stent expands or unfolds in a direction from its downstream end to its upstream end relative to the fluid flow. Thus, the present invention may minimize the likelihood of the device being displaced from the desired site before it is somewhat secured in the vessel during deployment. 
     According to another aspect of the invention, a delivery member, such as a catheter or guide wire, may be used to place the stent or stent-graft at the intended delivery site. When used with a catheter, the stent is releasably coupled, as described above, adjacent to the catheter&#39;s shaft portion, with the stent&#39;s proximal end being adjacent to the distal end of the catheter&#39;s shaft portion. 
     A preferred method of the present invention involves placing a folded stent device attached to a stent delivery member, such as a catheter, at a desired site within a mammalian lumen, and then progressively unfolding the stent device in a direction away from the stent delivery member. 
    
    
     The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings and appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic perspective view of a folded stent-graft held in position by a tether line in a sack knot configuration in accordance with the principles of the present invention. 
     FIG. 2 shows an enlarged view of a stent fold line using the tether line in the sack knot configuration of FIG.  1 . 
     FIG. 3A is a perspective view of the stent-graft FIG. 1 in an unfolded state. 
     FIG. 3B is an enlarged perspective view of a mid-portion of the stent-graft of FIG.  3 A. 
     FIGS. 4A,  4 B, and  4 C diagrammatically show a method of deploying a stent-graft according to the present invention for deploying the stent graft shown in FIG.  1   
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings generally, wherein like numerals indicate like elements throughout the several drawings, and to FIG. 1 in particular, there is shown a diagrammatic perspective view of an exemplary stent-graft  300  folded and constrained by means of a stent tether or slip line configuration  308  (See FIG. 2) in accordance with the principles of the present invention. Although a particular stent-graft will be described, it should be understood that this description is for the purpose of presenting an example, and that other stent-graft constructions can be used. The stent fold line  302  configurations and deployment methods of the present invention, which are discussed in detail below with respect to FIGS. 1,  2 , and  4 A-C, may be employed with a variety of stent-graft configurations such as that illustrated in FIGS. 3A and 3B. The exemplary stent-graft configuration of FIGS. 3A and 3B is discussed first in order to shed light on the description of the deployment apparatus and methods of the present invention. 
     FIG. 3A shows an expandable stent-graft  300 . Expandable stent-graft  300  generally includes a thin-walled tube or graft member  4 , an expandable stent member  6 , and a coupling member  8  for coupling the stent and graft members together. Stent member  6 , disposed between generally tubular graft member  4  and coupling member  8 , provides a support structure for graft member  4  to minimize the likelihood of graft member  4  collapsing during use. 
     Expandable stent member  6  is generally cylindrical and comprises a helically arranged undulating member  10  having a plurality of helical turns  12  and preferably comprising nitinol wire, although other materials may be used, as described in detail below. Undulating helical member  10  forms a plurality of undulations  14  which are preferably aligned so that they are generally “in phase” with each other as shown in the drawings. A linking member  20  is provided to maintain the phased relationship of undulations  14  during compression and deployment as well as during bending of the stent member  6 . As more clearly shown in the enlarged sectional view of FIG. 3B, linking member  20  is laced or interwoven between undulations in adjacent turns of helical member  10  and, thus, acquires a helical configuration as well. Linking member  20  preferably comprises a biocompatible polymeric or metallic material having sufficient flexibility to be readily folded upon itself. 
     Coupling member  8 , which secures the stent member to the graft member  4 , covers only a portion of the stent member  6 . Alternatively, coupling member  8  can be described as preferably interconnecting less than entirely the inner or outer surface of stent member  6  to graft member  4  (e.g., it covers less than all of the outer surface of stent member  6  when graft member  4  is positioned inside stent member  6 ). With this construction, regions of the stent member do not interface with the coupling member when the stent-graft is an uncompressed state, for example. This is believed to advantageously reduce sheer stresses between the stent member and the coupling member when the stent-graft undergoes bending or compression, thereby reducing the risk of tearing the graft or coupling member or causing delamination between the stent and graft members. 
     Coupling member  8  preferably has a generally broad or flat surface for interfacing with the stent  6  and graft members  4 , and is arranged in a helical configuration. This broad surface increases the potential bonding surface area between coupling member  8  and graft member  4  to enhance the structural integrity of the stent-graft. The increased bonding surface area also facilitates minimizing the thickness of the coupling member. It has been found that a coupling member  8  in the form of a generally flat ribbon or tape, as shown in the enlarged sectional view of FIG. 3B, provides preferable results. 
     In FIG. 3B, coupling member  8  is shown formed with multiple helical turns  23 , each being spaced from the turns adjacent thereto, thereby forming coupling member-free stress relief zones  24  between adjacent turns. The coupling member also preferably is arranged to provide a generally uniform distribution of stress relief zones  24 . In the illustrated embodiment, coupling member  8  is helically wound around stent member  6  with its helical turns  23  aligned with the stent member turns  12 . 
     Coupling member  8  also preferably covers a substantial portion of each undulation  14  so as to minimize the likelihood of stent member  6  lifting away from graft member  4 . As shown, the coupling member may be constructed with a constant width and arranged with uniform spacing between the turns. Coupling members having widths of 0.025, 0.050, and 0.075 inches have been applied to the illustrated stent member having a peak-to-peak undulation amplitude of about 0.075 inch with suitable results. However, it has been found that as the coupling member band width increases, the stent-graft flexibility generally is diminished. It is believed that a coupling member width of about one-fourth to three-fourths the amplitude of undulations  14 , measured peak-to-peak, is preferred (and more preferably one-third to two-thirds) to optimize flexibility. Coupling member  8  (or separate pieces thereof) preferably also surrounds the terminal end portions  16  and  18  of stent-graft  2  to secure the terminal portions of graft member  4  to the support the structure formed by stent member  6 . 
     It should be noted that the above-described stent-graft configuration of FIGS. 3A and 3B is only exemplary. Other stent-graft configurations and constructions can be used with the present invention, such as those disclosed in PCT Publication WO 95/26695, which is hereby incorporated by reference herein in its entirety. 
     The scope of materials suitable for the stent and graft members and the linking member described above as well as deployment mechanisms will be discussed in detail below. 
     Stent Materials 
     The stent member is constructed of a reasonably high strength material, i.e., one which is resistant to plastic deformation when stressed. Preferably, the stent member comprises a wire which is helically wound around a mandrel having pins arranged thereon so that the helical turns and undulations can be formed simultaneously. Other constructions also may be used. For example, an appropriate shape may be formed from a flat stock and wound into a cylinder or a length of tubing formed into an appropriate shape. 
     In order to minimize the wall thickness of the stent-graft, the stent material should have a high strength-to-volume ratio. Designs as depicted herein provide stents which may be longer in length than conventional designs. Additionally, the designs do not suffer from a tendency to twist (or helically unwind) or to shorten as the stent-graft is deployed. As will be discussed below, materials suitable in these stents and meeting these criteria include various metals and some polymers. 
     A percutaneously delivered stent-graft must expand from a reduced diameter, necessary for delivery, to a larger deployed diameter. The diameters of these devices obviously vary with the size of the body lumen into which they are placed. For instance, the stents may range in size from 2.0 mm in diameter for neurological applications to 40 mm in diameter for placement in the aorta. Typically, expansion ratios of 2:1 or more are required. These stents are capable of expansion ratios of up to 5:1 for larger diameter stents. The thickness of the stent materials obviously varies with the size (or diameter) of the stent and the ultimate required yield strength of the folded stent. These values are further dependent upon the selected materials of construction. Wire used in these variations are typically of stronger alloys, e.g., nitinol and stronger spring stainless steels, and have diameters of about 0.002 inches to 0.005 inches. For the larger stents, the appropriate diameter for the stent wire may be somewhat larger, e.g., 0.005 to 0.020 inches. For flat stock metallic stents, thicknesses of about 0.002 inches to 0.005 inches is usually sufficient. For the larger stents, the appropriate thickness for the stent flat stock may be somewhat thicker, e.g., 0.005 to 0.020 inches. 
     The stent-graft is fabricated in the expanded configuration. In order to reduce its diameter for delivery the stent-graft would be folded along its length, similar to the way in which a PCTA balloon would be folded. It is desirable, when using super-elastic alloys which also have temperature-memory characteristics, to reduce the diameter of the stent at a temperature below the transition-temperature of the alloys. Often the phase of the alloy at the lower temperature is somewhat more workable and easily formed. The temperature of deployment is desirably above the transition temperature to allow use of the super-elastic properties of the alloy. 
     There are a variety of disclosures in which super-elastic alloys such as nitinol are used in stents. See, U.S. Pat. Nos. 4,503,569, to Dotter; 4,512,338, to Balko et al.; 4,990,155, to Wilkoff; 5,037,427, to Harada, et al.; 5,147,370, to MacNamara et al.; 5,211,658, to Clouse; and 5,221,261, to Termin et al. None of these references suggest a device having discrete, individual, energy-storing torsional members. 
     Jervis, in U.S. Pat. Nos. 4,665,906 and 5,067,957, describes the use of shape memory alloys having stress-induced martensite properties in medical devices which are implantable or, at least, introduced into the human body. 
     A variety of materials variously metallic, super elastic alloys, and preferably nitinol, are suitable for use in these stents. Primary requirements of the materials are that they be suitably springy even when fashioned into very thin sheets or small diameter wires. Various stainless steels which have been physically, chemically, and otherwise treated to produce high springiness are suitable as are other metal alloys such as cobalt chrome alloys (e.g., ELGILOY®), platinum/tungsten alloys, and especially the nickel-titanium alloys generically known as “nitinol”. 
     Nitinol is especially preferred because of its “super-elastic” or “pseudo-elastic” shape recovery properties, i.e., the ability to withstand a significant amount of bending and flexing and yet return to its original form without deformation. These metals are characterized by their ability to be transformed from an austenitic crystal structure to a stress-induced martensitic structure at certain temperatures, and to return elastically to the austenitic shape when the stress is released. These alternating crystalline structures provide the alloy with its super-elastic properties. These alloys are well known but are described in U.S. Pat. Nos. 3,174,851, 3,351,463, and 3,753,700. Typically, nitinol will be nominally 50.6% (±0.2%) Ni with the remainder Ti. Commercially available nitinol materials usually will be sequentially mixed, cast, formed, and separately cold-worked to 30-40%, annealed, and stretched. Nominal ultimate yield strength values for commercial nitinol are in the range of 30 psi and for Young&#39;s modulus are about 700 Kbar. The &#39;700 patent describes an alloy containing a higher iron content and consequently has a higher modulus than the Ni—Ti alloys. 
     Nitinol is further suitable because it has a relatively high strength to volume ratio. This allows the torsion members to be shorter than for less elastic metals. The flexibility of the stent-graft is largely dictated by the length of the torsion segments and/or torsion arms. The shorter the pitch of the device, the more flexible the stent-graft structure can be made. Materials other than nitinol are suitable. Spring tempered stainless steels and cobalt-chromium alloys such as ELGILOY® are also suitable as are a wide variety of other known “super-elastic” alloys. 
     Although nitinol is preferred in this service because of its physical properties and its significant history in implantable medical devices, we also consider it also to be useful in a stent because of its overall suitability with magnetic resonance imaging (MRI) technology. Many other alloys, particularly those based on iron, are an anathema to the practice of MRI causing exceptionally poor images in the region of the alloy implant. Nitinol does not cause such problems. 
     Other materials suitable as the stent include certain polymeric materials, particularly engineering plastics such as thermotropic liquid crystal polymers (“LCP&#39;s”). These polymers are high molecular weight materials which can exist in a so-called “liquid crystalline state” where the material has some of the properties of a liquid (in that it can flow) but retains the long range molecular order of a crystal. The term “thermotropic” refers to the class of LCP&#39;s which are formed by temperature adjustment. LCP&#39;s may be prepared from monomers such as p,p′-dihydroxy-polynuclear-aromatics or dicarboxy-polynuclear-aromatics. The LCP&#39;s are easily formed and retain the necessary interpolymer attraction at room temperature to act as high strength plastic artifacts as are needed as a foldable stent. They are particularly suitable when augmented or filled with fibers such as those of the metals or alloys discussed below. It is to be noted that the fibers need not be linear but may have some preforming such as corrugations which add to the physical torsion enhancing abilities of the composite. 
     Linking Member Materials 
     Flexible link  20 , which is slidably disposed between adjacent turns of the helix may be of any appropriate filamentary material which is blood compatible or biocompatible and sufficiently flexible to allow the stent to flex and not deform the stent upon folding. Although the linkage may be a single or multiple strand wire (platinum, platinum/tungsten, gold, palladium, tantalum, stainless steel, etc.), the use of polymeric biocompatible filaments is preferable. Synthetic polymers such as polyethylene, polypropylene, polyurethane, polyglycolic acid, polyesters, polyamides, their mixtures, blends and copolymers are suitable; preferred of this class are polyesters such as polyethylene terephthalate including DACRON® and MYLAR® and polyaramids such as KEVLAR®, polyfluorocarbons such as polytetrafluoroethylene with and without copolymerized hexafluoropropylene (TEFLON® or GORE-TEX®), and porous or nonporous polyurethanes. Natural materials or materials based on natural sources such as collagen may also be used. 
     Graft Member Materials 
     The tubular component or graft member of the stent-graft may be made up of any material which is suitable for use as a graft in the chosen body lumen. Many graft materials are known, particularly known are those used as vascular graft materials. For instance, natural materials such as collagen may be introduced onto the inner surface of the stent and fastened into place. Desirable collagen-based materials include those described in U.S. Pat. No. 5,162,430, to Rhee et al, and WO 94/01483 (PCT/US93/06292), the entirety of which are incorporated by reference. Synthetic polymers such as polyethylene, polypropylene, polyurethane, polyglycolic acid, polyesters, polyamides, their mixtures, blends and copolymers are suitable; preferred of this class are polyesters such as polyethylene terephthalate including DACRON® and MYLAR® and polyaramids such as KEVLAR®, polyfluorocarbons such as polytetrafluoroethylene (PTFE) with and without copolymerized hexafluoropropylene (TEFLON® or GORE-TEX®), and porous or nonporous polyurethanes. Especially preferred are the expanded fluorocarbon polymers (especially PTFE) materials described in British. Pat. Nos. 1,355,373, 1,506,432, or 1,506,432 or in U.S. Pat. Nos. 3,953,566, 4,187,390, or 5,276,276, the entirety of which are incorporated by reference. 
     Included in the class of preferred fluoropolymers are polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), copolymers of tetrafluoroethylene (TFE) and perfluoro (propyl vinyl ether) (PFA), homopolymers of polychlorotrifluoroethylene (PCTFE), and its copolymers with TFE, ethylene-chlorotrifluoroethylene (ECTFE), copolymers of ethylene-tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), and polyvinyfluoride (PVF). Especially preferred, because of its widespread use in vascular prostheses, is expanded PTFE. 
     In addition, one or more radio-opaque metallic fibers, such as gold, platinum, platinum-tungsten, palladium, platinum-iridium, rhodium, tantalum, or alloys or composites of these metals like may be incorporated into the device, particularly, into the graft, to allow fluoroscopic visualization of the device. 
     The tubular component may also be reinforced using a network of small diameter fibers. The fibers may be random, braided, knitted, or woven. The fibers may be imbedded in the tubular component, may be placed in a separate layer coaxial with the tubular component, or may be used in a combination of the two. 
     A preferred material for the graft and coupling members is porous expanded polytetrafluorethylene. An FEP coating is one preferred adhesive that is provided on one side of the coupling member. 
     Manufacture of the Stent-Graft 
     The following example is provided for purposes of illustrating a preferred method of manufacturing a stent-graft such as the one shown in FIGS. 3A and 3B. It should be noted, however, that this example is not intended to limit the invention. 
     The stent member wire is helically wound around a mandrel having pins positioned thereon so that the helical structure and undulations can be formed simultaneously. While still on the mandrel, the stent member is heated to about 460° F. for about 20 minutes so that it retains its shape. 
     Wire sizes and materials may vary widely depending on the application. The following is an example construction for a stent-graft designed to accommodate a 6 mm diameter vessel lumen. The stent member comprises a nitinol wire (50.8 atomic % Ni) having a diameter of about 0.007 inch. In this example case, the wire is formed to have sinusoidal undulations, each having an amplitude measured peak-to-peak of about 0.100 inch and the helix is formed with a pitch of about 10 windings per inch. The inner diameter of the helix (when unconstrained) is about 6.8 mm. The linking member can be arranged as shown in the drawings and may have a diameter of about 0.006 inch. 
     In this example, the graft member is porous expanded polytetrafluorethylene (PTFE), while the coupling member is expanded PTFE coated with FEP. The coupling member is in the form of a flat ribbon (as shown in the illustrative embodiments) that is positioned around the stent and graft members as shown in FIG.  3 B. The side of the coupling member or ribbon that is FEP coated faces the graft member to secure it to the graft member. The intermediate stent-graft construction is heated to allow the materials of the ribbon and graft member to merge and self-bind as will be described in more detail below. 
     The FEP-coated porous expanded PTFE film used to form the ribbon shaped coupling member preferably is made by a process which comprises the steps of: 
     (a) contacting a porous PTFE film with another layer which is preferably a film of FEP or alternatively of another thermoplastic polymer; 
     (b) heating the composition obtained in step (a) to a temperature above the melting point of the thermoplastic polymer; 
     (c) stretching the heated composition of step (b) while maintaining the temperature above the melting point of the thermoplastic polymer; and 
     (d) cooling the product of step (c). 
     In addition to FEP, other thermoplastic polymers including thermoplastic fluoropolymers may also be used to make this coated film. The adhesive coating on the porous expanded PTFE film may be either continuous (non-porous) or discontinuous (porous) depending primarily on the amount and rate of stretching, the temperature during stretching, and the thickness of the adhesive prior to stretching. 
     The thin wall expanded PTFE graft used to construct this example is of about 0.1 mm (0.004 in) thickness and has a density of about 0.5 g/cc. The microstructure of the porous expanded PTFE contains fibrils of about 25 micron length. A 3 cm length of this graft material is placed on a mandrel the same diameter as the inner diameter of the graft. The nitinol stent member having about a 3 cm length is then carefully fitted over the center of the thin wall graft. 
     The stent-member was then provided with a ribbon shaped coupling member comprised of the FEP coated film as described above. The coupling member was helically wrapped around the exterior surface of the stent-member as shown in FIG.  3 B. The ribbon shaped coupling member was oriented so that its FEP-coated side faced inward and contacted the exterior surface of the stent-member. This ribbon surface was exposed to the outward facing surface of the thin wall graft member exposed through the openings in the stent member. The uniaxially-oriented fibrils of the microstructure of the helically-wrapped ribbon were helically-oriented about the exterior stent surface. 
     The mandrel assembly was placed into an oven set at 315° C. for a period of 15 minutes after which the film-wrapped mandrel was removed from the oven and allowed to cool. Following cooling to approximately ambient temperature, the mandrel was removed from the resultant stent-graft. The amount of heat applied was adequate to melt the FEP-coating on the porous expanded PTFE film and thereby cause the graft and coupling members to adhere to each other. Thus, the graft member was adhesively bonded to the inner surface of helically-wrapped coupling member  8  through the openings between the adjacent wires of the stent member. The combined thickness of the luminal and exterior coverings (graft and coupling members) and the stent member was about 0.4 mm. 
     The stent-graft was then folded in order to prepare it for delivery. To accomplish this a stainless steel wire which was at least about two inches longer than the stent-graft was inserted through the lumen of the stent-graft. The stent-graft was flattened and the stainless steel wire positioned at one end of the stent-graft. A second stainless steel wire of about the same length was placed on the outer surface of the stent-graft adjacent to the first stainless steel wire. The wires were then mounted together into a fixture, tensioned and then rotated, thereby folding the stent-graft. As the stent-graft rotates it is pressed into a “C” shaped elongated stainless steel clip in order to force it to roll upon itself. The folded stent-graft is then advanced along the wire out of the clip into a glass capture tube. A removable tether line, which is used to constrain the stent-graft in the rolled configuration for delivery is applied to the stent-graft at this point by gradually advancing the stent-graft out of the capture tube and lacing the tether line through the stent-graft structure. After this step is completed, the stent-graft is pulled off of the first wire and transferred onto the distal end of the catheter shaft or tubing for delivery. 
     Prior to folding, the stent-graft was cooled to about −30° C. so that the nitinol was fully martensitic and, thus, malleable. This is done to allow the stent-graft to be more easily folded. Cooling is accomplished by spray soaking the graft with chilled gas such as tetrafluroethane. Micro-Dust™ dry circuit duster manufactured by MicroCare Corporation (Conn) provides suitable results. The spray canister was held upside down to discharge the fluid as a liquid onto the stent-graft. 
     Deployment of the Stent-Graft 
     The stent-graft may be delivered percutaneously, typically through the vasculature, after having been folded to a reduced diameter. Once reaching the intended delivery site, it may be expanded to form a lining on the vessel wall. 
     When a stent-graft having torsion members, as described above, is folded, crushed, or otherwise collapsed, mechanical energy is stored in torsion in those members. In this loaded state, the torsion members have a torque exerted about them and consequently have a tendency to untwist. Collectively, the torque exerted by the torsion members as folded down to a reduced diameter must be restrained from springing open. The stent-member preferably has at least one torsion member per fold. The stent-graft is folded along its longitudinal axis and restrained from springing open. As is apparent from the foregoing, the stent-graft is a self-expanding stent-graft. The stent-graft is then deployed by removing the restraining mechanism, thus allowing the torsion members to spring open against the vessel wall. The attending physician will select an appropriately sized stent-graft. Typically, the stent-graft will be selected to have an expanded diameter of up to about 10% greater than the diameter of the lumen at the deployment site. 
     FIGS. 4A-C diagrammatically show a procedure for deploying a stent-graft assembly, constructed according to the present invention, using a percutaneous dual-lumen catheter assembly  314 . Catheter assembly  314  includes a catheter or delivery member shaft portion  325 , a hub portion  327 , and a tip portion  312 . Extending coaxially within shaft portion  325  are two parallel channels, a guidewire channel  331  and a tether line channel  329 . Shaft portion  325  has a distal end portion  310 . Extending through guidewire channel  331  and beyond distal end portion  310  is a guidewire tube  318 . Running through and extending distally beyond the end of guidewire tube  318  is guidewire  319 . Axially mounted on the distal end of guidewire tube  318  are a proximal barrier  321  and a distal barrier  320 . 
     Referring particularly to FIG. 4A, catheter assembly  314  has been inserted into a selected site within a body lumen  350 . A stent-graft, such as stent-graft  300  described in conjunction with FIGS. 3A and B, is folded about guidewire tube  318  and is held axially in place prior to deployment between distal and proximal barriers  320 ,  321 . Tether wire  306  extends through loops  308  and through tether line channel  329  and hub portion  327  of catheter  314  to outside the body. Tether wire  306  may be outside proximal barrier  321  or extend therethrough as shown in FIG.  4 A. 
     Deployment of stent-graft  300  is accomplished by actuating or pulling tether wire  306  in the direction of arrow  370 , as shown in FIG.  4 B. FIG. 4B shows partial removal of tether wire  306  from loops  308  to partially deploy and expand the stent-graft  300  onto the selected site. With this configuration, stent-graft  300  can be described as opening or deploying in a hub-to-tip direction with respect to catheter  314  and in a proximal-to-distal direction with respect to the stent-graft itself (i.e., the end of the stent-graft proximate to distal end  310  of shaft portion  325  opens first). FIG. 4C shows tether wire  306 , the loops thereof which have been completely retracted from the interior of stent-graft  300  which is now in its fully unfolded, deployed state within lumen  350 . 
     The hub-to-tip or proximal-to-distal deployment method of the present invention, described above with respect to FIGS. 4A-C, is accomplished in part by the manner in which the tether or slip line is configured to the stent-graft. FIGS. 1 and 2 show a preferred embodiment of the tether line configuration of the present invention. In FIG. 1, stent-graft  300  is shown having a proximal portion  330  and a distal portion  332 . When stent-graft  300  is used for its intended purpose in conjunction with a deployment means, such as the catheter assembly  314  illustrated in FIGS. 4A-C, proximal portion  330  is positioned proximate to and associated with distal end  310  of catheter assembly  314 . As such, distal portion  332  of stent-graft  300  is positioned proximate to and associated with the tip portion  312  of catheter assembly  314 . 
     Stent-graft  300  is held in position by a tether or slip line  306  in a sack knot configuration in accordance with the present invention. FIG. 1 shows the use of a single stent fold  302 . The fixed end portion  306 ′ of slip line  306  is associated with distal end  332  of stent-graft  300  and a row of eyelets  324 . Conversely, the release end  322  of slip line  306  is associated with proximal end  330  of stent-graft  300 . The eyelets are preferably formed by pulling local portions of linking member  20  away from the fold line, threading slip line  306  therethrough, and then releasing the respective portion of linking member  20 . The eyelets may then be tied or otherwise fixed to the stent. 
     FIG. 2 shows the stent fold line  306 ″ having the herringbone pattern of the “sack knot” configuration used to close the fold in stent  300  in FIG.  1 . This knot is the one used to hold, for example, burlap sacks of feed grain closed prior to use which allow ease of opening when the sack is to be opened. Slip line  306  has a fixed end  306 ′ and a release end  322 . Loops of slip line  306  pass through the eyelets  324  on the side of the stent fold associated with the fixed end  306 ′. It should also be noted that the fixed end  306 ′ is not typically tied to stent  300  so as to allow removal of the slip line after deployment. Additionally, the eyelets  324  and  326  are desirable but optional. The eyelets  324  and  326  may be wire or polymeric thread or the like tied to the stent structure at the edge of the stent fold. Alternatively, eyelets  324  and  326  may be formed from linking member  20 , as discussed above, to form the loops through which slip line  306  passes. In a further configuration, slip line  306  may be woven into the stent structure, for example, into undulations  14  as shown in FIG.  3 A. 
     Release end  322  of slip line  306  is positioned so that, when the stent-graft deployment or release mechanism (not shown) is associated with stent-graft  300 , it is in the vicinity of the proximal portion  330  of stent-graft  300 . Thus, when release end  322  is pulled in the direction of arrow  334 , the stent-graft  300  unfolds from the proximal end  330  to the distal end  332  (see FIG.  4 B). 
     Alternatively, the loops of the slip line may pass through eyelets  326  on the side of the stent fold associated with release end  322 , as depicted in phantom in FIG.  2 . With this latter arrangement, release end  322  is pulled in the direction of arrow  336 , and stent-graft  300  unfolds in the opposite direction, from distal end  332  towards proximal end  330 . However, this distal-to-proximal unfolding arrangement, due to the extra folded-back length of tether line leading to release end  322 , is more likely to cause the tether line to become entangled upon deployment of the stent-graft. 
     The preferred proximal-to-distal deployment arrangement eliminates the extra folded-back length of the tether line leading to the release end and, thus, may reduce the likelihood of snagging between the slip line and stent member. This arrangement also provides less fluid flow resistance when the stent-graft is deployed against the flow of blood (i.e., from a downstream to upstream direction), which in turn improves positioning accuracy during deployment, particularly in the course of an aortic procedure. Other means, within the scope of the invention, are contemplated to be employed to hold the stent device in an unfolded or constricted configuration and to activate the proximal-to-distal deployment arrangement of the present invention. These means include adhesive tape having a perforation which facilitates easy tear-away, a Velcro strip that can be peeled away from a stent device, a zipper or clasp mechanism, or any other suitable interlocking-type mechanism having a pull actuator. 
     The disclosures of any publications, patents and published patent applications referred to in this application are hereby incorporated by reference. 
     The above is a detailed description of a particular embodiment of the invention. The full scope of the invention is set out in the claims that follow and their equivalents. Accordingly, the claims and specification should not be construed to unduly narrow the full scope of protection to which the invention is entitled.