Abstract:
A method for inserting a stent into the delivery sheath of a stent/graft deployment catheter. The stent has V hooks on its proximal end which are positively engageable by projections attached to a stent/graft deployment catheter plunger. The proximal end of the stent is manually squeezed over the V hooks such that the V hooks engage the projections. The catheter is passed through the center of a funnel. While maintaining pressure on the stent and the V hooks, the plunger is withdrawn so as to pull the stent into the delivery sheath through the center of the funnel. The funnel guides the stent into the delivery sheath and gradually compresses the stent as it approaches the delivery sheath.

Description:
This is a divisional application of Ser. No. 09/053,393 filed Apr. 1, 1998, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an improved stent and stent/graft deployment catheter. More particularly, the invention relates to a stent which is capable of being loaded into the delivery sheath of a stent/graft deployment catheter without suffering any structural damage and which is uniformly radially compressed during packing. 
     2. Description of the Prior Art 
     An abdominal aortic aneurysm (AAA) is a sac caused by an abnormal dilatation of the wall of the aorta as it passes through the abdomen. The aorta is the main artery of the body, supplying blood to all organs and parts of the body except the lungs. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen, and finally divides into the iliac arteries which supply blood to the pelvis and lower extremities. 
     The AAA ordinarily occurs in the portion of the aorta below the kidneys. When left untreated, the aneurysm will eventually cause the sac to rupture with ensuing fatal hemorrhaging in a very short time. The repair of abdominal aortic aneurysms has typically required major abdominal surgery in which the diseased and aneurysmal segment of the aorta is bridged with a prosthetic device, such as a synthetic graft. 
     As with all major surgeries, there are many disadvantages to the above mentioned surgical technique, the foremost of which is the high mortality and morbidity rate associated with surgical intervention of this magnitude. Other disadvantages of conventional surgical repair include the extensive recovery period associated with such surgery; difficulties in suturing the graft to the aorta; the unsuitability of the surgery for many patients, particularly older patients exhibiting comorbid conditions; and the problems associated with performing the surgical procedure on an emergency basis after the aneurysm has already ruptured. 
     In view of the above mentioned disadvantages of conventional surgical repair techniques, techniques have been developed for repairing AAAs by intraluminally delivering an aortic graft to the aneurysm site through the use of a catheter based delivery system, and securing the graft within the aorta using an expandable stent. Since the first documented clinical application of this technique was reported by Parodi et al. in the Annals of Vascular Surgery, Volume 5, pages 491-499 (1991), the technique has gained more widespread recognition and is being used more commonly. 
     Problems have been encountered accurately deploying the stent/graft. These problems are partially due to the method of packing the stent/graft into the delivery sheath of the deployment catheter. Currently, the stent/graft is manually radially compressed and pushed into the delivery sheath. This stent/graft compress and push method is problematic for a number of reasons. First, this process often leads to breakage of the stent struts. A stent with broken struts may not expand as designed, and as a result, will not properly bridge the AAA upon deployment. Second, this compress and push method of stent/graft packing produces a non-uniformly compressed stent. Unless all of the stent cells are equally compressed the stent/graft may not expand as designed upon exposure to the patient&#39;s blood, and as a result, the stent/graft will not adequately bridge the AAA. Another drawback of the present compress and push method of stent/graft packing is that it is very time consuming and difficult, and therefore, it is inappropriate for large scale production. 
     Therefore, the need exists for an improved method for inserting a stent/graft into the delivery sheath of a deployment catheter. Furthermore, the need exists for an improved stent and a stent/graft deployment catheter which is capable of being loaded with a stent/graft using the improved stent/graft packing method. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to produce a method for inserting a stent/graft which overcomes the deficiencies of the prior art compress and push packing method. 
     It is another object of the invention to produce a stent/graft deployment catheter capable of pulling a uniformly compressed stent/graft into its delivery sheath without damaging the stent/graft. 
     It is a further object of the invention to produce a stent with V hooks capable of being pulled into the delivery sheath of the stent/graft deployment catheter. 
     The invention is a method for inserting an improved stent into the delivery sheath of an improved stent/graft deployment catheter. The stent has V hooks on its proximal end which are positively engageable by projections attached to a stent/graft deployment catheter plunger. The proximal end of the stent is manually squeezed over the V hooks such that the V hooks engage the projections. The catheter is passed through the center of a funnel. While maintaining pressure on the stent and the V hooks, the plunger is withdrawn so as to pull the stent into the delivery sheath through the center of the funnel. The funnel guides the stent into the delivery sheath and uniformly compresses the stent as it approaches the delivery sheath. 
     To the accomplishment of the above and related objects the invention may be embodied in the form illustrated in the accompanying drawings. Attention is called to the fact, however, that the drawings are illustrative only. Variations are contemplated as being part of the invention, limited only by the scope of the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like elements are depicted by like reference numerals. The drawings are briefly described as follows. 
     FIG. 1 is longitudinal cross section of a distal portion of a prior art stent/graft deployment catheter. 
     FIG. 2 is a plan view of a stent/graft being inserted into a delivery sheath via the prior art compress and push packing method. 
     FIG. 3 illustrates a longitudinal cross section of the prior art catheter of FIG. 1 percutaneously inserted into a patient&#39;s blood vessel. 
     FIG. 4 is a plan view of an unrolled stent having four V hooks. 
     FIG. 5 is a plan view of an unrolled stent having two V hooks. 
     FIG. 6 is perspective view of a stent/graft being compressed so as to positively engage the stent&#39;s V hooks with a plunger&#39;s L projections. 
     FIG. 7 is a longitudinal cross section of a stent/graft which is partially inserted in a delivery sheath and partially enveloped by a funnel. 
     FIG. 8 is a longitudinal cross section of a stent/graft having V hooks fully compressed and inserted into a delivery sheath. 
     FIG. 9 illustrates a longitudinal cross section of a stent/graft deployment catheter having a grabber housing and without the inner tube and the tip. 
     FIG. 10 illustrates a plan view of a distal surface of the grabber housing of FIG.  9 . 
     FIG. 11 illustrates a longitudinal cross section of a distal portion of an alternative embodiment of the invention incorporating spring biased projections. 
     FIG. 12 illustrates a perspective view of a stent/graft being loaded into the delivery sheath of the catheter illustrated in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a longitudinal cross section of a co-axial prior art stent/graft deployment catheter  21 . Said catheter  21  is comprised of a catheter body  10 , a tip  50 , an inner tube  40 , a stent/graft  30 , and a plunger  20 , all of which are co-axial and have proximal and distal ends. Only the distal portion of the deployment catheter  21  is shown for clarity. The catheter body  10  is slidingly disposed about the inner tube  40  and has a delivery sheath  42 , a tube portion  43 , and an inner surface  70 . The plunger  20  is slidingly disposed about the inner tube  40  and is slidingly disposed within the catheter body  10 . The distal end of the inner tube  40  is attached to the tip  50 . The stent/graft  30  is slidingly disposed about the inner tube  40  and within the delivery sheath  42  of the catheter body  10  and is between the proximal end of the tip  50  and the distal end of the plunger  20 . The stent/graft  30  has an outer surface  60  and a lumen  52  extending from its proximal end to its distal end. The stent/graft lumen  52  is occupied by a distal portion  41  of the inner tube  40 . The delivery sheath  42  is located between the tip  50  and the tube portion  43  of the catheter body  10 . The inner and outer diameters of the delivery sheath  42  and the tube portion  43  are the same. 
     FIG. 2 illustrates a perspective view of the stent/graft  30  being inserted by hand  38  into the delivery sheath  42  via the prior art compress and push method. The plunger  20 , the inner tube  40 , and a proximal portion  39  of the stent/graft  30  can be seen through the delivery sheath  42  wall as dotted lines. The catheter body  10  has been pulled back exposing the distal portion  41  of the inner tube  40 . The stent/graft  30  is disposed about the distal portion  41  of the inner tube  40  as is pinched by hand  38  and pushed into the delivery sheath  42 . The stent/graft  30  is made from a shape memory alloy, such as Nitinol, and is cooled below its transformation temperature allowing it to be compressed without permanent structural damage. 
     The stent/graft deployment catheter  21  may be inserted percutaneously or via a surgical cut-down method into a blood vessel. FIG. 3 illustrates a longitudinal cross section of the prior art catheter  21  percutaneously inserted in a blood vessel  55  of a patient  54 . The delivery sheath  42  is still down stream of an aneurysm  56  in need of repair and has fully exited an insertion sheath  57 . If inserted percutaneously, as illustrated in FIG. 3, a guide wire  58  is first advanced through an insertion site  53  into the blood vessel  55  of the patient  54 . Next, a dilator sheath assembly (dilator not shown) is disposed about the guide wire  58  and the distal portion of the dilator is used to dilate the insertion site  53 . After dilation of the insertion site  53  the dilator is removed while the insertion sheath  57  is held in place in the blood vessel  55  of the patient  54 . Next, the catheter  21  is inserted into the introducer sheath  57  and is advanced forward into the blood vessel  55  of the patient  54 . Upon proper positioning of the tip  50  in the blood vessel  55  the plunger  20  is held in place while the catheter body  10  is pulled away from the tip  50  exposing the entire stent/graft  30  to blood. Upon contact with blood the stent/graft  30  expands such that the diameter of the stent/graft lumen  52  becomes larger than the outer diameter of the tip  50 . The expanded stent/graft  30  becomes fixed in place in the blood vessel  55  and thus bridges the aneurysm  56 . The inner tube  40  is then pulled away from the stent/graft  30  such that the tip  50  passes through the stent/graft lumen  52 . Finally, the catheter  21  is removed from the patient  54 . Note that there are many other types of self-expandable stent/grafts on the market including heat sensitive and spring-like stent/grafts. Note further that one major function of the introducer sheath  57  is to control bleeding at the insertion site  53  of the patient  54  during the entire procedure. 
     The prior art compress and push packing method may damage the stent/graft  30  and produce a non-uniformly compressed stent which may not adequately bridge the aneurysm  56  upon deployment. FIG. 4 illustrates a plan view of an unrolled improved stent  2  having four V hooks  37  which is capable of being inserted in a uniformly compressed state and without structural damage. The stent  2  comprises nine parallel struts  36  which are connected by heart shaped cross members  35 . Each V hook  37  is connected to the end of two adjacent struts  36 . Stents that are 20 mm in diameter or greater generally require at least four V hooks for proper insertion into a delivery sheath. Stents that are less than 20 mm in diameter only require two V hooks. An unrolled stent  2  having only two V hooks  37  is illustrated in FIG.  5 . 
     FIGS. 6-8 illustrate the improved method of packing the improved stent  2  (shown in FIG. 5) using an improved stent/graft deployment catheter  21  having two L projections  22  projecting from a distal end  107  of the plunger  20 . As can be seen in FIG. 6, the improved stent/graft deployment catheter  21  is first advanced through the center of a funnel  24 . The catheter body  10  is then pulled back exposing the distal portion  41  of the inner tube  40  and a distal portion  23  of the plunger  20 . The remaining portion of the plunger  20  is disposed within the catheter body  10  and is shown as dotted lines. Next, the L projections  22  are placed between the V hooks  37 . The stent/graft  30  is the compressed lightly by hand  38  such that the V hooks  37  are positively engaged by the L projections  22 . While maintaining said engagement the catheter  21  is moved to the left, relative to the catheter body  10 , such that the stent/graft  30  contacts the funnel  24 . Next, while holding the catheter body  10 , the plunger  20  is moved to the left forcing the stent/graft  30  into the delivery sheath  42 . As soon as the portion of the stent/graft  30  immediately to the right of the V hooks  37  is enveloped by the delivery sheath  42  the hand  38  releases the stent/graft  30 . The plunger  20  is pulled until the entire stent/graft  30  is disposed within the delivery sheath  42 , as illustrated in FIG.  8 . FIG. 8 illustrates a longitudinal cross section of a distal portion of the improved stent/deployment catheter  21  without the inner tube  40  after the stent/graft  30  has been completely inserted. Note that the stent/graft  30  may be made from a shape memory alloy, such as Nitinol. Prior to packing a shape memory alloy stent/graft, the body of the stent/graft must be cooled below its transformation temperature in order to allow it to be compressed without incurring any structural damage. 
     FIG. 7 illustrates a longitudinal cross section of the stent/graft  30  partially inserted in the delivery sheath  42  and partially enveloped by the funnel  24 . The V hooks  37  are positively engaged by the L projections  22 . The funnel  24  guides the stent/graft  30  into the delivery sheath  42 . As the plunger  20  is moved left relative to the catheter body  10 , the funnel  24  uniformly compresses the stent/graft  30 . 
     An alternate embodiment of the invention involves adding a component to the catheter  21  rather than altering the plunger  20  itself. FIG. 9 illustrates a longitudinal cross section of a distal portion of a stent/graft deployment catheter  21  without the inner tube  40  (shown in FIG. 6) and the tip  50  (shown in FIG.  6 ). A grabber housing  25  is attached to the distal end of the plunger  20  and is disposed about the inner tube  40 . The grabber housing  25  has two L projections projecting from a distal surface  26 . The stent/graft  30  is inserted in the same manner as illustrated in FIGS. 6-8. FIG. 10 illustrates a plan view of the distal surface  26  of the grabber housing  25 . 
     An alternate embodiment of the grabber housing  25  or the improved stent/graft deployment catheter  21  may have the L projections  22  inset in the grabber housing  25  or the plunger  20 . Alternatively, the L projections  22  may comprise springs attached to the grabber housing  25  or plunger  20 , as illustrated in FIG.  11 . FIG. 11 illustrates a longitudinal cross section of a distal portion of an alternative embodiment of the invention incorporating spring biased projections. A proximal portion  27  of the L projection  22  is attached to the plunger  20  or to a grabber housing (not shown). A distal portion  28  of the L projection  22  is connected to the proximal portion  27  by a coil portion  29 . The coil portion  29  permits the distal portion  28  to move between a position generally parallel to a longitudinal axis  105  of the catheter  21  and a position at an angle to said axis  105  (the equilibrium position). The L projections  22  lie in grooves  106  in the plunger  20  when forced into apposition generally parallel to the axis  105  of the catheter  21 . FIG. 12 illustrates a perspective view of a stent/graft  30  being loaded into the delivery sheath  42  of the catheter  21  illustrated in FIG.  11 . During packing of the stent/graft  30  into the delivery sheath  42  the plunger  20  is positioned such that the L projections  22  are partially enveloped by the delivery sheath  42 . Next, the stent/graft  30  is manually compressed such that the V hooks  37  positively engage the L projections  22 . This engagement is accomplished by squeezing the portion of the stent/graft  30  adjacent to the V hooks  37 , placing said portion between the L projections  22 , and releasing the stent/graft  30  such that the L projections  22  and the V hooks positively engage when the stent/graft  30  partially springs back to its uncompressed state. Next, the plunger  20  is moved to the left relative to the catheter body  10  such that the L projections  22  are forced by the delivery sheath  42  towards the axis  105  of the catheter  21  and such that the delivery sheath  42  envelopes first the L projections  22  and then the stent/graft  30 . Note, that unlike the other embodiments of the invention described above, once the V hooks  37  are engaged by the L projections  22  and as long as a sufficient portion of the distal portion  28  is enveloped by the delivery sheath  42 , the stent/graft  30  no longer has to be manually compressed to maintain the positive engagement. Once the stent/graft  30  is enveloped by the delivery sheath  42  (after having passed through a funnel  24 , as described above) the L projections  22  apply a restoring force against the delivery sheath  42 . Upon deployment of the stent/graft  30  said restoring force causes the L projections  22  to spring open, i.e. away from the axis of the catheter  21 , disengaging the V hooks  37 , and thus, allowing the stent/graft  30  to expand unhindered. 
     Note that the use of two, three, four or more L projections, in any of the above mentioned embodiments, to engage a multi-hooked stent is contemplated.