Abstract:
A delivery system for delivering an endoluminal implant to a distal deployment location inside a body lumen from a proximal access location outside the lumen. The system comprises the implant, a catheter, and a slidable sheath having an advanced position in which the sheath covers the implant and a retracted position in which the implant is exposed. The catheter comprises a stabilizer having a distal end adjacent the implant proximal end and/or a catheter tip attached to a central core slideably disposed relative to the implant and having a proximal end adjacent the implant distal end. The catheter tip proximal end and/or the stabilizer distal end comprises a docking section adapted to releasably engage a portion of the implant. Each docking section has an engagement geometry comprising a flared engagement surface that extends inside a short axial length of the implant or a pocket having a bottleneck geometry.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 09/573,273, filed May 18, 2000, now U.S. Pat. No. 6,858,034 which claims priority from U.S. Provisional Patent Application Ser. No. 60/134,971, filed on May 20, 1999, both of which are herein incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates generally to endoluminal grafts or “stents” and, more specifically, to stent delivery systems or “introducers”. 
   BACKGROUND OF THE INVENTION 
   A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft. As used herein, however, the term “stent” is a shorthand reference referring to a covered or uncovered such stent. 
   A stent may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an intraluminal stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a stent deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient&#39;s skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the stent deployment location, the introducer is manipulated to cause the stent to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the stent), whereupon the stent expands to a predetermined diameter in the vessel into the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration. 
   Referring now to  FIGS. 1A and 1B , there is shown a prior art, pre-loaded stent delivery system  10  for housing and deploying a compressed stent  14 . Stent delivery system  10  comprises an outer sheath  12  and a conventional pusher or stabilizer  16  loaded proximal to the stent. As used herein, the term “proximal” refers to the end closer to an access location outside the body whereas “distal” refers to the farther from the access location. Delivery system  10  also typically comprises a catheter tip  20  at the distal end and a pusher handle  25  located at the proximal end outside the body lumen. The catheter tip may be attached to central core  23  that runs through central lumen  22  within pusher  16 . Central core  23  may guide the delivery system through the body lumen over a guidewire (not shown) to the area to be repaired, or may be adapted for inflating a balloon (if applicable), and/or for flushing the system. The delivery system may additionally have radiopaque markers at selected locations therein to be used for fluoroscopic guidance of the system through the body lumen. 
   To deploy stent  14 , delivery system  10  is threaded through the body lumen to the desired location for stent deployment. Outer sheath  12  is then retracted, and pusher  16  acts as a stabilizer to keep stent  14  from retracting with the sheath. As outer sheath  12  retracts, stent  14  is exposed and expands into place against the body lumen to be repaired. The stent may be a self-expanding stent, such as a stent made of shape-memory nitinol (nickel-titanium) wire as are well-known in the art, or the stent may require inflation of a balloon to expand it against the walls of the body lumen, as is also well-known in the art. 
   Regardless of the type of stent or delivery system, the portion of delivery system  10  that houses compressed stent  14  typically has increased mass and rigidity as compared to the rest of delivery system  10 . Thus, referring now to  FIG. 2 , when introducing delivery system  10  through tortuous anatomy, kinking of the delivery system may occur in region  17  of the system where pusher  16  and stent  14  interface, due to the rigidity of both the stent and the pusher. Kinking along kink angle “a” may develop as a result of the rigidity of compressed stent  14 , whereas kinking along kink angle “b” may develop as a result of the rigidity of pusher  16 . The resulting kink angle a+b is therefore dependent upon the material properties of both the compressed stent  14  and pusher  16 . Similar kinking may also occur in region  18  where stent  14  and tip  20  interface. 
   Such kinking may prevent or hamper proper deployment of stent  14  because creases  15  that develop where sheath  12  is bent may prevent retraction of the sheath. Such creases  15  present a problem not only where stent  14  is intended for deployment in the tortuous portion of the body lumen, but also may persist even after the delivery system  10  is ultimately navigated past the tortuous portion of the lumen to a remote deployment site. Also, the discontinuity of the contact surface between stent  14  and pusher  16  could lead to an improper or inaccurate deployment of the stent. Where kinking causes such creases  15  in sheath  12  that prevent deployment, delivery system  10  must be retracted from the body and discarded, and the introduction process must start again with a new introducer. Thus, there is a need in the art to prevent such kinking in stent delivery systems. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention comprises a delivery system for delivering a endoluminal implant to a distal deployment location inside a body lumen from a proximal access location outside the body lumen. The delivery system comprises the implant having a proximal end and a distal end; a catheter comprising at least one of a stabilizer having a distal end located adjacent the implant proximal end, a catheter tip attached to a central core slideably disposed relative to the implant and having a proximal end located adjacent the implant distal end, or a combination thereof; and a slidable sheath having an advanced position in which the sheath covers the implant and a retracted position in which the implant is exposed. At least one of the catheter tip proximal end or the stabilizer distal end comprises a docking section adapted to releasably engage a portion of the implant, each docking section comprising an engagement geometry for engaging the implant, each docking section engagement geometry comprising a flared engagement surface that extends inside a short axial length of the implant or a pocket having a bottleneck geometry. 
   Another aspect of the invention comprises a system for retaining a portion of a medical implant on a delivery member until performance of a predetermined release action. The system comprises the delivery member, comprising an outer sheath and an inner tubular member for engaging a portion of the implant, the sheath having an advanced position in which the sheath covers the implant, and a retracted position in which the implant is exposed. The inner tubular member has an axis and one or more flexible fingers, the one or more flexible fingers having an unrestrained configuration with the sheath in the retracted configuration in which the fingers are biased angularly outward from the inner tubular member axis, and a restrained configuration with the sheath in the advanced configuration in which the fingers are adapted to engage a portion of the implant. Each finger comprises an end member having a different cross sectional geometry than a remainder of the finger. 
   Yet another aspect of the invention comprises a delivery system for delivering an endoluminal implant, the delivery system comprising the implant having a proximal end and a distal end and a catheter comprising at least one of a stabilizer, a catheter tip, or a combination thereof, the stabilizer having a distal end located adjacent the implant proximal end, the catheter tip having a proximal end located adjacent the implant distal end and attached to a central core slideably disposed relative to the implant. At least one of the catheter tip proximal end or the stabilizer distal end comprises a docking section adapted to releasably engage a portion of the implant, the docking section comprising a pocket adapted to releasably contain a limited length of one end of the compressed implant inserted therein. The pocket comprises an annular pocket having an inner wall located radially inward of the compressed implant and an outer wall located radially outward of the compressed implant, the inner wall and the outer wall both terminating at a substantially same axial location relative to the implant. 
   Still another aspect of the invention comprises a delivery system comprising the implant; a catheter comprising at least one of a stabilizer having a distal end located adjacent the implant proximal end and/or a catheter tip attached to a central core slideably disposed relative to the implant and having a proximal end located adjacent the implant distal end; and a slidable sheath having an advanced position in which the sheath covers the implant and a retracted position in which the implant is exposed. At least one of the catheter tip proximal end or the stabilizer distal end comprises a docking section adapted to releasably engage a portion of the implant, the docking section comprising an engagement geometry for engaging the implant, in which the docking section engagement geometry comprises (a) a pocket having an outer wall located radially outward of the compressed implant and (b) a radial protrusion that engages the implant. In one embodiment, the docking section radial protrusion protrudes inward from the pocket outer wall. In another embodiment, the docking section pocket comprises a flared end rim radially biased outward relative to the compressed stent and adapted for the inward protrusion to releasably grip a limited length of the proximal end of the stent in pushing engagement therewith when the flared end rim is inwardly compressed by the sheath to a non-flared diameter. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. 

   
     BRIEF DESCRIPTION OF DRAWING 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
       FIG. 1A  is a longitudinal section schematic illustration of an exemplary stent delivery system of the prior art. 
       FIG. 1B  is an enlarged portion of  FIG. 1A . 
       FIG. 2  is a longitudinal section schematic illustration of an exemplary stent delivery system of the prior art in a kinked state due to the varying rigidity along the system. 
       FIG. 3  is a longitudinal section schematic illustration of a portion of an exemplary stent delivery system of the present invention, showing the stent in a compressed state cradled in the docking section pockets of both the catheter tip and the pusher. 
       FIG. 4  is a longitudinal section schematic illustration of the pusher of  FIG. 3  shown in a deployed state after retraction of the outer sheath. 
       FIG. 5  is a flowchart depicting an exemplary method of deploying a stent in accordance with the present invention. 
       FIG. 6  a longitudinal section schematic illustration of exemplary docking sections of the present invention, showing the stent in a compressed state with a pusher docking section and a catheter docking section inserted in the ends thereof. 
       FIGS. 7A and 7B  are an end view and a side view, respectively, of an exemplary docking section of the present invention comprising a set of fingers. 
       FIGS. 8A and 8B  are an end view and a side view, respectively, of an exemplary docking section of the present invention comprising an annular pocket. 
       FIG. 8C  is an end view of an exemplary docking section of the present invention, showing a docking section comprising an annular pocket defined by a plurality of fingers. 
   

   DETAILED DESCRIPTION OF INVENTION 
   Referring now to the drawing, wherein like reference numerals refer to like elements throughout,  FIGS. 3-4  illustrate an exemplary stent delivery system  10 ′ of the present invention, having an exemplary docking pusher  16 ′ and docking catheter tip  20 ′. As shown in  FIG. 3 , stent delivery system  10 ′ comprises an outer sheath  12 , central lumen  22 , and central core  23 , similar to delivery systems known in the art. As used herein, the term “system” shall encompass both a completed assembly which is capable of deploying a stent or a sub-assembly which is capable of deploying a stent when combined with other components. Docking pusher  16 ′ and catheter tip  20 ′, however, comprise docking sections  42  and  42 ′ respectively, each docking section having a pocket  40  and  40 ′, respectively. Docking section  42  located at pusher distal end  28  is adapted to hold proximal end  30  of compressed stent  14 , whereas docking section  42  located at catheter tip proximal end  29  is adapted to hold distal end  31  of compressed stent  14 . Docking section  42  or  42 ′ may be a discrete section connected to, respectively, pusher  16 ′ or catheter tip  20 ′, as shown in  FIGS. 3 and 4  with respect to pusher  16 ′, or may be a hollowed section integral to the rest of the pusher or catheter tip, as shown in the figures with respect to catheter tip  20 ′. Other docking section configurations or means for engaging the compressed stent end with the pusher or catheter tip may also be used, as described herein later. 
   The term “pusher” is used herein throughout, although such device may also be referred to in the art as a “stabilizer”, because the method of deploying the stent may not actually comprise “pushing” the stent out of the sheath, but rather “stabilizing” the stent (holding it in place and preventing it from moving) while the outer sheath is retracted. Thus, use of the term “pusher” herein refers to such a device adapted for any method of deploying known in the art, including as a stabilizer, and the term “pusher” is not intended as a limitation thereof. 
   Docking pusher  16 ′ and docking catheter tip  20 ′ overcome kinking in the body lumen because a certain amount of compressed stent  14  is actually docked or cradled inside pocket  40  or  40 ′, creating a smooth transition between the stent and the pusher or catheter tip. The pusher and stent and/or catheter tip and stent in such docked configurations thus move together at their respective interface points while navigating the tortuous anatomy of the body lumen, by minimizing any area of weakened rigidity to prevent kinks. 
   In addition, as long as rim  44  of docking section  42  in pusher  16 ′ grips stent  14 , the stent may be “recaptured” or “recovered” even once it has been partially deployed. For instance, if a medical professional determines that a partially deployed stent  14  needs to be repositioned, pusher  16 ′ may be pulled back within sheath  12  or the sheath advanced to recover the partially deployed stent. Then, the deployment process can start over. Other embodiments having other means for releasably engaging the stent may offer similar recapture capabilities. 
   Also, because of the docked arrangement between stent  14  and pusher  16 ′, the stent may be rotated, pushed, or pulled both before and during deployment, unlike with conventional deployment systems where the pusher can only transmit force in a pushing direction. For example, where the stent architecture has a particular feature intended for alignment with a particular part of the body lumen, such as a particularly flexible portion of the stent to be aligned with a tortuous portion of the body lumen, the stent can be rotated, pushed, or pulled to effect this alignment. Additionally, in the configuration shown in  FIG. 3  where docking section  42  pinches stent  14  against central core  23 , creating friction, there is less undesired movement of the stent inside the delivery system as compared to non-docked prior configurations. Additionally, the use of a docking section in the catheter tip may facilitate placement of the distal end of the stent in a predetermined location. 
   As shown in  FIG. 3 , stent  14  is held within pocket  40  of docking section  42  of pusher  16 ′ and pinched inwardly by end rim  44 . When compressed within sheath  12 , docking section  42  has a bottleneck shape created by inward protrusions  48  of end rim  44  that define a neck with a smaller diameter than the remainder of pocket  40 , as shown in  FIG. 3 . End rim  44  of docking section  42  thus has a normal radial bias outward that is compressed and confined within the walls of sheath  12  during introduction to the body. As shown in  FIG. 4 , once the target zone has been reached, outer sheath  12  is retracted. When sheath  12  is retracted beyond end rim  44  of docking section  42 , rim  44  springs open into an outwardly flared configuration and releases proximal end  30  of stent  14 . Accordingly, docking section  42  may comprise any material, such as stainless steel, that provides flared end rim  44  with the requisite “springiness” to pinch inward when compressed and to spring open when the sheath is retracted. Although illustrated with respect to the pusher docking section  42  in  FIG. 4 , this outwardly-flared configuration may also be applicable to catheter tip docking section  42 ′; however, as shown in  FIG. 3 , a non-outwardly-biased, cylindrical configuration is preferred, as described below. 
   Instead of having a bottleneck shape when compressed within sheath  12  and radially flared and biased outward when not housed within the sheath, end rim  44 ′ of docking section  42 ′ in catheter tip  20 ′ is cylindrical in shape and capable of holding stent  14  within pocket  40 ′ merely by frictional engagement. Prior to retraction of sheath  12  to deploy stent  14 , central core  23  and tip  20 ′ attached thereto may, in some cases, need to be advanced distally so that the stent disengages from the pocket  40 ′. Such a non-radially-biased pocket may also be provided on docking section  42  of pusher  16 ′. In such case, stent  14  may be partially deployed and anchored into the walls of a body lumen so that the stent has sufficient frictional resistance against the body lumen to enable pusher  16 ′ to be retracted to disengage the stent from within the non-flared pocket without dislocating the stent. 
   The step of advancing catheter tip  20 ′ prior to retraction of sheath  12  may also be performed to facilitate stent delivery even where docking section  42 ′ includes a radially-biased end rim (not shown). Such a radially-biased end rim on catheter tip  20 ′, however, may present difficulty in preparing delivery system  10 ′ for retraction from the body after deployment unless there is some mechanism to re-compress the end rim back inside sheath  12 . Without such re-compression of the radially-biased end rim back inside the sheath, such as is possible with respect to pusher  16 ′ merely by retracting the pusher to pull end rim  44  back inside sheath  12 , the radially-biased end rim may protrude from the streamlined shape of the delivery system at the catheter end during retraction and provide a catching point that may damage the body lumen. Thus, a non-radially-biased end rim  44 ′ is preferred for catheter tip  20 ′. 
   Docking section  42  may include a radiopaque marker  46 , to provide increased radiographic “vision” of the pusher end, and when combined with a similar marker (not shown) on the proximal end of stent  14 , to visualize relative movement of pusher and stent as stent  14  disengages from pusher  16 ′. Similar markers  46  may also be provided for similar purposes on the catheter tip docking section  42 ′ and on the stent distal end (not shown). “Radiopaque marker” as used herein encompasses any discrete area of different radiopacity as compared to a surrounding area. 
   Pusher docking sections, catheter tip docking sections, stent delivery systems, and methods incorporating such pushers and/or catheter tips may take a wide variety of forms other than that described specifically above. A particular stent delivery system may include only a pusher docking section, only a catheter tip docking section, or both. The essence of any such docking section is that it releasably engages an end of the stent over some axial length in a manner whereby that engagement is releasable upon stent deployment. The term “releasably engaging” denotes that the engagement between the docking section and the stent is not permanent, but rather is releasable in the sense that the stent is released from the docking section when the outer sheath is retracted or when the pusher or catheter tip is advanced or retracted away from the stent. The pusher docking section is either biased radially outward or defines a pocket in which the portion of the stent proximal end is nested. 
   The length of the stent engaged by the docking section of this invention should be sufficiently long, taking into account the stent diameter and flexibility as well as the tortuosity of the lumen to be traversed during its deployment, to maintain a pushing engagement notwithstanding the tortuosity for which the stent is designed. Such pushing engagement enables transmission of a pushing force applied thereto, such as from the pusher to the stent, or from the stent to the catheter tip. The length of the stent engaged by the docking section should be sufficiently short, however, and/or the angle of radial flare a (as shown in  FIG. 4 ) sufficiently great, so as to facilitate reliable release of stent  14  when sheath  12  is retracted. The dimensions and mechanical features of individual docking section designs may be readily determinable by those skilled in the art. 
   In particular, the docking section may comprise an axially-extending engagement surface which extends over a short axial length of the stent either on the interior or exterior thereof. Such surface may define the interior of pocket  40  previously described and shown in  FIGS. 3 and 4 , or an insert adapted to be inserted within the stent end to engage the stent end, as shown in  FIG. 6 . 
   As shown in  FIG. 6 , docking section  142 ′ of catheter tip  120  is a reduced diameter section (i.e., an insert) of catheter  120  that fits within distal end  31  of compressed stent  14 . Docking section  142  of pusher  116  fits within proximal end  30  of compressed stent  14 , and is radially biased outward to firmly hold stent  14  against sheath  12 . Such bias outward to radially urge the stent proximal end  29  against the inner surface of the deployment sheath  12  further facilitates pusher  116  and stent  14  moving as one without pulling away from one another. Although docking section  142 ′ having merely a reduced diameter section is illustrated in  FIG. 6  with respect to catheter tip  120  whereas radially-biased-outward docking section  142  is illustrated with respect to pusher  116 , either configuration is applicable to both the catheter tip and the pusher. As described above, however, a non-biased configuration is generally preferred at the catheter tip for ease of delivery system retraction. 
   In another exemplary embodiment, shown in  FIGS. 7A and 7B , docking section  242  of pusher  216  may comprise engagement means in the form of a set of fingers  244 . Fingers  244  may define a pocket adapted for surrounding the stent, as shown in  FIGS. 7A and 7B . Referring now to  FIGS. 8A and 8B , in yet another embodiment, docking section  342  of pusher  316  may comprise pocket  340  in the form of an annular pocket between inner wall  341  and outer wall  343  adapted for insertion of the stent proximal end (not shown). Inner wall  341  may define a hollow or solid cylinder, or may be in the form of fingers that insert within the stent. Outer wall  343  may be solid as shown in  FIGS. 8A and 8B , or may be in the form of outer fingers. As shown in  FIG. 8C , another embodiment may comprise a plurality of inner fingers  441  and outer fingers  443  that define the inner wall and outer wall, respectively. Another embodiment, not shown, may comprise only inner fingers  441 . Such inner fingers, outer fingers, or combination thereof may be radially biased outward. Although docking sections  242 ,  342 , and  442  are described and shown in  FIGS. 7A-8B  with respect to pushers, similar docking section configurations may be provided for catheter tips. 
   The invention also comprises a method for pre-loading a stent delivery system, as described below relative to  FIGS. 3 and 4 . The method comprises loading at least compressed stent  14  and pusher  16 ′ within outer sheath  12 , including releasably engaging a portion of stent proximal end  30  with docking section  42  at pusher  16 ′ distal end  28 , stent distal end  31  with docking section  42 ′ at catheter tip  20 ′ proximal end  29 , or a combination thereof. The method may include disposing a portion of the corresponding stent end  30  or  31  within a pocket  40  in docking section  42  or  42 ′. 
   The invention further comprises a method for deploying a stent in accordance with the flowchart depicted in  FIG. 5  and the drawings shown in  FIGS. 3 and 4 . The method comprises in step  100 , introducing a pre-loaded stent delivery system  10 ′ to a body lumen. Delivery system  10 ′ comprises a compressed stent  14  having a proximal end  30  and a distal end  31 , a pusher  16 ′ having a distal end  28 , a catheter tip  20 ′ having a proximal end  29  and attached to a central core  23  slideably disposed within pusher  16 ′. At least one of pusher  16 ′ or catheter tip  20 ′ have a docking section  42  or  42 ′ adapted to releasably engage the stent end over some length thereof, such as with pocket  40  and/or  40 ′ within which the stent end is disposed. Outer sheath  12  overlies compressed stent  14 , pusher  16 ′, and each docking section  42  and/or  42 ′. Next, in step  105 , the stent delivery system is navigated to a desired location for deploying stent  14 , and finally, in step  110 , outer sheath  12  is retracted to deploy the stent from the outer sheath and from docking section  42  and/or  42 ′ into the desired location. Where catheter tip  20 ′ has a docking section  42 ′, the method may further comprise advancing central core  23  and the catheter tip  20 ′ attached thereto prior to retracting sheath  12 , to further facilitate release of stent  14  from the docking section. Where pocket  40  has an end rim  44  that is radially biased outward and adapted to be inwardly compressed to grip the stent end when loaded within outer sheath  12 , as shown in  FIGS. 3 and 4 , the method may further comprise the end rim expanding outward during evacuation of the stent from the pocket. Where, as is shown in  FIG. 6 , docking section  142  and/or  142 ′ comprise a reduced diameter section adapted for inserting within the end of stent  14 , the method may further comprise the stent expanding away from the reduced diameter section. 
   While the present invention has been described with respect to specific embodiments thereof, it is not limited thereto. Therefore, the claims that follow are intended to be construed to encompass not only the specific embodiments described but also all modifications and variants thereof which embody the essential teaching thereof.