Patent Application
20050246008
The present invention relates to a two-part delivery system for implantable vascular prostheses, wherein the delivery system provides reduced profile and enhanced flexibility to negotiate narrow vessels and tortuous anatomy.
Vascular stenting has become a practical method of reestablishing blood flow to diseased vasculature. Conventional stent delivery systems have problems negotiating vessels having reduced diameters and vessels that require tortuous or challenging anatomy to be traversed. Today there are a wide range of intravascular prostheses on the market for use in the treatment of aneurysms, stenosis, and other vascular irregularities. Balloon expandable and self-expanding stents are well known for restoring patency in a stenosed vessel, e.g., after an angioplasty procedure, and the use of coils and stents are known techniques for treating aneurysms.
Previously-known vascular prostheses and stents generally are retained in a contracted delivery configuration on or within a delivery system, which typically includes a guide wire, delivery catheter and sheath. Alternatively, the delivery system may include a catheter that includes one or more locking mechanisms that retain the stent on the catheter until it is desired to deploy the stent.
U.S. Pat. No. 4,665,918 to Garza provides a typical example of a delivery system for a self-expanding stent, and includes an inner member and sheath that cooperate to define a compartment that holds the stent in a contracted delivery configuration. The inner member includes a guide wire lumen that permits the delivery system to be advanced along a pre-positioned guide wire. Once positioned at the desired location within a vessel, the inner member is held stationary, while the sheath is retracted proximally, thereby permitting the stent to self-expand.
U.S. Pat. No. 4,733,665 to Palmaz describes a typical previously-known delivery system for a balloon expandable stent, that includes a balloon catheter and sheath. The stent is compressed onto the balloon of the balloon catheter; the sheath ensures that the stent does not come free from the catheter until the stent is located at the desired location within the vessel.
Due to the increased profile associated with employing a sheath to retain the stent on the delivery system, many previously-known delivery systems sought to eliminate the sheath. For example, U.S. Pat. No. 5,314,444 to Gianturco describes a delivery system wherein the stent is tightly compressed onto the balloon of the balloon catheter, whereby the sheath was omitted. Similarly, U.S. Pat. No. 4,553,545 to Maass and U.S. Pat. No. 5,147,370 to McNamara describe delivery systems for self-expanding helical stents that employed locking members disposed within the catheter to lock the ends of the stent in place until the stent was maneuvered through the vessel to its destination.
While such previously-known systems eliminated the sheath of the delivery system, the use of locking mechanisms required that the diameter of the catheter increase, so that little overall reduction in delivery profile was accomplished. Likewise for balloon expandable stent delivery systems, the ability to reduce the overall profile of the delivery system was limited by of thickness of the stent compressed onto the deflated balloon, the balloon inflation lumen diameter and guide wire lumen diameter, and need to make the inflation lumen walls sufficiently thick to withstand the inflation pressures required to deploy the stent.
For the foregoing reasons, even the best previously-known stent delivery systems generally have been limited to a minimum diameter of about 6 French. In addition, as noted above, previously-known delivery systems employ a layering of the sheath (if present), stent and inner member or balloon catheter. Notwithstanding the development of improved materials over the last two decades, the overall rigidity of the combined stent and delivery system has remained relatively high. This in turn has limited the ability to access smaller vessels and negotiate highly tortuous anatomy.
In addition to the foregoing drawbacks of previously-known stent delivery systems, the acceptance of self-expanding stents has been limited by problems peculiar to the design of such stents. Specifically, self-expanding stents may experience large length changes during expansion (referred to as “foreshortening”) and may shift within the vessel prior to engaging the vessel wall, resulting in improper placement.
Where the stent has a helical coil configuration, as described for example in PCT Publication WO 00/62711 to Rivelli, friction between the turns of the stent and the sheath or between individual turns of the stent, may cause the turns to bunch up, or overlap with one another, during deployment. U.S. Pat. No. 4,768,507 to Fischell et al. and U.S. Pat. No. 6,576,006 to Limon et al., each describe the use of a groove disposed on an inner member of the delivery system to prevent such axial movement, but such arrangements detrimentally increase the profile of the delivery system. Moreover, those delivery systems do not address the issue of stent foreshortening.
In view of the aforementioned drawbacks of previously-known stent delivery systems, it would be desirable to provide a delivery system and methods that provide a reduced profile, thereby enabling the delivery system to negotiate small diameter vessels.
It also would be desirable to provide a delivery system and methods that provide low rigidity in the delivery configuration, thereby allowing the delivery system to negotiate highly tortuous anatomy.
It further would be desirable to provide a stent delivery system for self-expanding stents and methods of use that provide a desired degree of foreshortening (including zero foreshortening) of the stent during deployment.
In view of the foregoing, it is an object of the present invention to provide a delivery system and methods that provide a reduced profile, thereby enabling the delivery system to negotiate small diameter vessels.
It is another object of this invention to provide a delivery system and methods that provide low rigidity in the delivery configuration, thereby allowing the delivery system to negotiate highly tortuous anatomy.
It is a further object of the present invention to provide a stent delivery system for self-expanding stents and methods of use that provide a desired degree of foreshortening (including zero foreshortening) of the stent during deployment.
In accordance with the principles of the present invention, a two-part delivery system is provided that includes a loader tube/delivery wire component (preloaded with a stent) and a separately inserted sheath. In a preferred embodiment, the stent or other implantable device is compressed onto the delivery wire and retained in a contracted delivery configuration by the loader tube. The delivery wire preferably has a diameter in a range of 0.014 to 0.035″, and may be constructed in a manner similar to conventional guide wires. The loader tube preferably is relatively short, e.g., 10 cm, and is disposed adjacent to the distal end of the delivery wire.
In one preferred embodiment, the sheath is constructed of a thin-walled material with a non-stick interior liner, e.g., such as polytetrafluoroethylene, and has the same inner diameter as the inner diameter of the loader tube. This permits that loader tube to be coupled to the sheath so that the stent may be transferred from the loader tube to the sheath while the stent is retained in the contracted delivery configuration. Because the stent is not stored in the sheath, as in previously known systems, but only passes in a transitory manner through the sheath during delivery, the wall thickness of the sheath may be substantially thinner than in previously known delivery systems and substantially more flexible.
In accordance with a further aspect of the invention, the sheath is configured to be inserted to a desired position into a vessel along a conventional pre-placed guide wire. Once the sheath is positioned, the conventional guide wire is withdrawn. The delivery wire then is inserted into the proximal end of the sheath, and the loader tube is coupled to the proximal end of the sheath. The delivery wire (and attached stent) then are advanced from the loader tube through the sheath. Once the stent is located at a desired position within a vessel, the delivery wire is held stationary and the sheath is retracted to deploy the stent.
The foregoing method of the present invention thus permits the sheath to be separately advanced through highly tortuous anatomy. Because the sheath does not contain the stent when originally advanced through the patient's vessel, it is much less rigid than previously-known delivery systems. In addition, once the distal end of the sheath is inserted to a desired location within a vessel, the loader tube permits the stent to be pushed into and through the sheath in the contracted state. This feature ensures that there is no increase in the profile of the delivery system, and permits stents of the present invention to be delivered using sheaths as small as 3 French.
According to a further aspect of the invention, especially for use with helical ribbon stents, the delivery wire includes a winding section dimensioned to receive the stent. The winding section preferably comprises a guide that defines a pitch of the stent to facilitate consistent and accurate winding of the helical portion of the stent around the delivery wire. The winding section preferably is configured to provide zero or a desired degree of foreshortening, so that the length of the stent undergoes a predictable amount of change during deployment.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which:
The present invention is directed to a delivery system for use with implantable vascular prostheses for a wide range of applications, such as treating aneurysms, maintaining patency in a vessel, and allowing for the controlled delivery of therapeutic agents to a vessel wall. In a preferred embodiment, the delivery system is configured for use with a stent having a helical ribbon portion joined, at its distal end, to a radially self-expanding anchor portion, such as depicted in
Referring to
Vascular prosthesis 10 preferably is formed from a solid tubular member comprising a shape memory material, such as nickel-titanium alloy (commonly known in the art as Nitinol). The solid tubular member then is laser cut, using techniques that are per se known in the art, to a desired deployed configuration, as depicted in
In the illustrated embodiment, distal section 14 has a generally zig-zag configuration in the deployed state, wherein the zig-zag configuration preferably is formed by laser cutting a solid tube to form a pattern comprising plurality of arcuate struts 18 joined at apices 20. Distal section 14 is designed to be deployed from the delivery catheter of the present invention first to fix the distal end of the stent at a desired known location within a vessel. In this manner, subsequent deployment of helical section 12 of the stent may be accomplished with greater accuracy.
Helical section 12 preferably comprises a helical mesh configuration that includes a plurality of substantially flat turns 22. Plurality of turns 22 may include a multiplicity of openings, as illustrated by openings 24. It should be understood that the configuration of helical section 12 depicted in
Referring to
Delivery wire 32 may comprise a conventional guide wire more than 100 cm in length (e.g., 120 cm) and having a diameter in a range of about 0.014 to 0.035″. In a preferred embodiment, the delivery wire further comprises winding section 34 at its distal end including guide 35. Guide 35 defines a pitch that facilitates consistent and accurate winding body portion 12 of the vascular prosthesis around delivery wire 32. Delivery wire 32 preferably includes atraumatic coil tip 36, distal marker 37 adjacent to coil tip 36 and proximal marker 38. Distal marker 37 is radiopaque and may be used to identify the location of the distal end of the stent under fluoroscopic guidance. Proximal stop 38 also preferably is radiopaque, and provides an abutment surface against which the proximal end of the stent may engage during retraction of sheath 40.
Winding section 34 corresponds to the length spanned by guide 35 between distal marker 37 and proximal stop 38. The winding section is dimensioned to receive vascular prosthesis 10, which in
Still referring to
Loader tube 50 comprises a substantially cylindrical tube having lumen 51, side port 52, optional hemostatic valve 53, and luer-type coupling 54 at distal end 55. Loader tube 50 comprises a relatively rigid material, such as polycarbonate and has a length of approximately 10 cm. In accordance with the principles of the present invention, lumen 51 has an inner diameter selected to retain vascular prosthesis 10 compressed about delivery wire 32. The inner diameter of lumen 51 is substantially equal to the inner diameter of lumen 41 of sheath 40. When is it desired to place vascular prosthesis 10, it may be pushed, still in the contracted state, from loader tube 50 and into and through sheath 40 using delivery wire 32. Non-stick liner 47 of sheath 40 facilitates movement of the stent between loader tube 50 and sheath 40.
Coupling 44 of sheath 40 accepts coupling 54 of loader tube 50 to enable transfer of the contracted stent from the loader tube into sheath 50. Illustratively, coupling 44 comprises a threaded section that mates with threads disposed on coupling 54 of loader tube 50. Alternatively, the couplings may comprise conventional luer-type connectors.
Hemostatic valves 45 and 53 prevent excessive backflow through the proximal ends of the sheath and loader tube, respectively, during coupling of the two components and advancement of the stent and delivery wire. Hemostatic valves 45 and 53 comprise conventional valve bodies having perforated elastomeric disks that self-seal under compression. Side port 52 of loader tube 50 permits an irrigation fluid, such as saline, or fluoroscopic dye to be introduced during stent delivery for diagnostic purposes.
Referring now to
Referring to
The specific steps for winding the vascular prosthesis onto delivery wire 32 in a proximal to distal direction are as follows: First, the tail of helical portion 12 of the stent is located and fixed at the proximal end of winding section 34 with the distal edge of the stent abutted against helical ledge 39. Next, helical portion 12 is wrapped around the delivery wire using the helical ledge to control the pitch and overlap of the turns. Loader tube 50 then is advanced over the vascular prosthesis to retain the helical portion in the contracted position on delivery wire 32. If the stent includes anchor portion 14, as depicted in
Alternatively, stent 10 may be wound onto delivery wire 32 in a distal to proximal direction, as follows: First, the anchor portion of the stent is placed on delivery wire in a desired location, and the joint between anchor portion and the helical body portion of the stent is temporarily fixed to the inner member. Next, the helical portion of the stent is wrapped around the delivery wire in abutment to the helical ledge of the delivery wire. When the stent is completely wrapped around the delivery wire, loader tube 50 is advanced over the stent while rotating the loader tube in the direction in which the stent is wound. The loader tube then is advanced up to the joint where the anchor portion joins the helical portion. Next, the anchor portion is compressed into contact with the delivery wire and the loader tube is again advanced, while being rotated in the direction of the wrap, until it covers the anchor portion. The loader tube and delivery wire, with pre-loaded stent, then may be packaged and sterilized for use.
When the stent is loaded in accordance with the foregoing method, helical ledge 39 not only mitigates foreshortening, but in addition, prevents the proximal edge of the stent from sliding in the proximal direction during stent deployment.
When disposed in loader tube 50, vascular prosthesis 10 is constrained within lumen 51 so that it cannot expand or unwind during sliding translation of delivery wire 32 within the loader tube. Hemostatic valve 32 may be used to lock delivery wire 32 in position in loader tube 50 until it is desired to deploy the vascular prosthesis.
A method of stenting a target location within a vessel is now described. First, a conventional guide wire is advanced into a patient's vessel under fluoroscopic guidance until the distal tip is disposed at the target location, e.g., having a stenosis or aneurysm. Generally, if angioplasty of the stenosis is to be performed, a balloon catheter then is inserted along the guide wire and inflated to disrupt the stenosis. The balloon catheter then is deflated and the balloon catheter is withdrawn, leaving the guide wire in place.
Sheath 40 then is advanced over the guide wire so that atramautic tip is positioned at the target location. This may be determined, for example, by injecting radiographic dye through lumen 41 or by direct visualization of radiopaque marker 46. Once the distal end of the sheath is at the desired location, the conventional guide wire is withdrawn, leaving the sheath in place.
Next, as shown in
Referring to
More specifically, as sheath 40 is retracted proximally, anchor section 14 of the stent self-expands into engagement with the vessel wall within or distal to lesion L. When released from the constraint provided by the sheath, the struts of anchor section 14 expand in a radial direction to engage the interior of vessel V. After anchor section 14 is secured to the vessel wall distal of lesion L, sheath 40 is further retracted proximally to cause helical section 12 to unwind and deploy to its predetermined shape within vessel V. Once the last turn of the helical section is deployed, sheath 40 is withdrawn from the patient's vessel. Delivery wire 32 may be removed, or alternatively used as a guide wire for a balloon catheter to be inserted into the vessel to further expand the stent, if desired.
Referring now to
In most interventional procedures, satisfactory stent placement requires predictable placement of the distal and proximal ends of the stent within a target vessel. Previously-known ribbon-type self-deploying stents, however, have encountered limited clinical acceptance due to problems associated with foreshortening and inaccurate placement.
Specifically, previously-known ribbon-type stents often are wound down around a delivery catheter in either an “edge to edge” manner (where the edges of adjacent turns lie next to one another) or with an overlap (or “shingled”), and then covered with a sheath that restrains the stent in the contracted delivery configuration. When wound “edge to edge,” the stent may be significantly longer in the contracted delivery configuration than in the deployed configuration, and thus result in significant foreshortening when deployed.
On the other hand, when the turns of the stent are permitted to overlap in the contracted delivery configuration, the turns of the stent may lock or bind within the delivery system during deployment. Further still, in either method of contracting the stent to its contracted delivery configuration, the stent has a tendency to jump or hop forwards or backwards when deployed, resulting in poor control. Thus, previously-known ribbon-type stents generally are perceived to be capable of less accurate deployment than conventional balloon expandable stents.
Guide 35 of delivery wire 32 of the present invention resolves this problem by controlling winding of the stent to a predetermined contracted delivery configuration, and likewise controlling unwinding of the stent during deployment to mitigate foreshortening.
In accordance with the principles of the present invention, it has been discovered that certain trigonometric relationships may be utilized whereby the sent may be wrapped to its reduced delivery diameter, and experience little or no foreshortening during deployment. These relationships are derived below, and then implemented in the delivery catheters of the present invention, as set forth below.
Referring now to the lower portion of
The strip has a width (ω) and an edge length (E); these are physical characteristics of the stent that do not change. On the other hand, the diameter (d), wrap angle (θ), number of revolutions (n), and axial length (L) are interrelated characteristics that vary depending upon the helical configuration of the stent. For example, the diameter of the stent varies between the contracted delivery configuration and deployed configuration, which also may effect the wrap angle, number of revolutions, and axial length.
From inspection of
Referring now to
F=(L1+ω/cos θ1)−(L2+ω/cos θ2)
F=(L1−L2)+(ω/cos θ1−ω/cos θ2)
From inspection of
F=(E sin θ1−E sin θ2)+(ω/cos θ1−ω/cos θ2)
F=E(sin θ1−sin θ2)+ω(1/cos θ1−1/cos θ2)
Of primary interest in the context of the present invention is the case where there is no foreshortening (F=0) when the stent transitions from diameter d1 to diameter d2. By setting the above equation equal to zero, it will be observed that the edge component of the equation E(sin θ1−sin θ2) and the width component ω(1/cos θ1−1/cos θ2) must either be equal to zero, or be equal and opposite. For meaningful wrap angles (0<θ<90), both components will always have the same sign. Thus, in order for the equation to balance, both components of the equation must be equal to zero. This leads to the conclusion that for there to be no foreshortening during stent deployment, the two wrap angles must be equal: θ1=θ2. Accordingly, for a stent wrapped into a helical configuration, where strip width X and total edge length E are constant, the amount of foreshortening between two different configurations is dependant on wrap angle alone. Thus, to eliminate foreshortening between any two helical configurations, both configurations must have the same wrap angle θ.
Provision of the helical ledge directly on the exterior surface of the delivery wire as in the embodiment of
While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.
The present application is a continuation-in-part application of co-pending, commonly assigned U.S. patent application Ser. No. 10/836,909, filed Apr. 30, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10836909 | Apr 2004 | US |
| Child | 10925756 | Aug 2004 | US |
