Patent Application
20110218608
Today, there are a wide range of intravascular prostheses on the market for use in the treatment of aneurysms, stenosis, and other vascular disorders. Stents, stent grafts, and other vascular prostheses are well known for treating a myriad of diseases and illnesses in vasculature. For percutaneous interventions, many vascular prostheses are inserted into the body within a catheter and accurately and safely deployed at the desired treatment site.
Previously known self-expanding vascular prostheses can be retained in a catheter delivery configuration using an outer sheath; the prosthesis then self-expands when the outer sheath is retracted. See, for example, US patent application publication number US 2008/0021657 A1, assigned to the assignee of this application. Due to this configuration, several potentially undesirable effects are present during deployment of the prosthesis. Because the outer sheath is restraining the prosthesis, the frictional force between the prosthesis and outer sheath must be overcome to deploy the stent. The frictional force may be prohibitive to sheath withdrawal, and may shift the position of the prosthesis. Alternatively, self-expanding vascular prostheses can be secured to the outer surface of a delivery catheter; the prosthesis is then released from the delivery catheter at the target site within the patient. See, for example, U.S. Pat. Nos. 5,772,668 and 6,514,285.
This application is directed to systems in which self expanding vascular prosthesis are retained in their radially contracted states through the use of an outer delivery sheath. Portions of the vascular prosthesis may be secured to an inner delivery catheter, as in US 2008/0021657 A1, or an inner delivery catheter may not be used.
It is typically desirable that the vascular prosthesis have a high outward acting force to improve in vivo performance. However, this high outward acting force can result in a high frictional force during deployment, and requires the outer sheath, sometimes called the outer delivery sheath, to be strong both radially and longitudinally. A high deployment force is undesirable from safety, ergonomic, and control perspectives, e.g. placement accuracy. A high deployment force requires the use of stronger materials and/or a thicker outer sheath. These material and dimensional constraints are undesirable; the stronger materials are often more expensive and less flexible than traditional materials, and a thicker outer sheath moreover results in a larger device profile. Additionally, with a high deployment force, the outer sheath is more likely to stretch and neck down, resulting in additional deployment difficulties.
The vascular prosthesis is generally restrained in the outer sheath from the time the vascular prosthesis is loaded, packaged, sterilized, transported, and then deployed by the end-user. The device must remain operational following exposure to all of these environments, which can vary dramatically in temperature, humidity, and mechanical impact. Throughout these different environments, the self-expanding vascular prosthesis maintains a residual outward acting force. The changes in humidity and temperature can cause changes in the dimensions and physical properties of the device, resulting in undesirable deployment characteristics of the device. For example, sterilization through the use of ethylene oxide gas is a common sterilization procedure that requires elevated temperatures and high humidity to adequately sterilize the device. These conditions may cause the materials used in the device to expand and weaken, allowing the vascular prosthesis to expand radially and embed into the outer sheath, resulting in higher deployment forces and potential increases in profile. Additionally, the prosthesis material may have material properties such that elevated temperature results in the vascular prosthesis exerting a higher outward force against the outer sheath causing a further likelihood of higher deployment forces.
One example of a vascular prosthesis delivery system comprises a radially self expandable vascular prosthesis and a delivery sheath. The delivery sheath has a lumen. The lumen has a smaller diameter storage region and a larger diameter delivery region. A vascular prosthesis is housed within the storage region and is movable into the delivery region for delivery of the vascular prosthesis at a target site within a patient. The delivery force required to move the vascular prosthesis from the delivery region into the patient can be less than the force required to move the vascular prosthesis from the storage region into the delivery region. In some examples, the delivery sheath comprises a main delivery sheath and an extension cartridge mountable to the main delivery sheath, the extension cartridge comprising the smaller diameter storage region. In some examples, the smaller diameter storage region and the larger diameter delivery region are each generally constant diameter regions. In some examples, the storage region defines a tapered lumen, the tapered lumen expanding in diameter in a distal direction. In some examples, the storage and delivery regions are generally coextensive and define a tapered lumen expanding in diameter in a distal direction.
One example of a method for storing a vascular prosthesis and delivering the vascular prosthesis to a target site within a patient comprises the following. A vascular prosthesis delivery system is obtained, the vascular prosthesis delivery system comprising radially self expandable vascular prosthesis stored within a smaller diameter storage region of a lumen of a delivery sheath. The vascular prosthesis is moved from the smaller diameter storage region into a larger diameter delivery region of the lumen of the delivery sheath. The vascular prosthesis is moved from the larger diameter delivery region to a target site within a patient. Whereby the force required to move the vascular prosthesis from the delivery region into the patient can be less than the force required to move the vascular prosthesis from the storage region into the delivery region. In some examples, the obtaining step is carried out with the delivery sheath comprising a main delivery sheath and an extension cartridge mountable to the main delivery sheath, the extension cartridge comprising the smaller diameter storage region; this example further comprises removing the extension cartridge from the main delivery sheath after the vascular prosthesis is moved from the storage region to the delivery region. In some examples, the obtaining step is carried out with the smaller diameter storage region defining a tapered smaller diameter storage region, the tapered smaller diameter storage region expanding in diameter in a distal direction, and wherein the first moving step is carried out with the vascular prosthesis being moved from the tapered smaller diameter storage region into the larger diameter storage region. In some examples, the obtaining step is carried out so that the storage and delivery regions comprise a generally coextensive storage/delivery region, the storage/delivery region being a tapered storage/delivery region expanding in diameter in a distal direction.
Other features, aspects and advantages of the present invention can be seen on review of the drawings, the detailed description, and the claims which follow.
The following description will typically be with reference to specific structural embodiments and methods. It is to be understood that there is no intention to limit the invention to the specifically disclosed embodiments and methods but that the invention may be practiced using other features, elements, methods and embodiments. Preferred embodiments are described to illustrate the present invention, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a variety of equivalent variations on the description that follows. Like elements in various embodiments are commonly referred to with like reference numerals.
One aspect of the present invention is the recognition of the drawbacks of previously known devices created by the vascular prosthesis exerting an outward radial force on the outer delivery sheath, discussed above, which causes embedding of the vascular prosthesis into the outer delivery sheath with the resultant increased and unpredictable delivery force. It would be desirable to provide an implantable vascular prosthesis delivery system with optimal delivery flexibility and profile, a low, predictable deployment force, and accurate vascular prosthesis placement.
Referring now to
Alternating helical section 21 can be formed from a solid tubular member or sheet comprised of a shape memory material, such as nickel-titanium alloy (commonly known in the art as Nitinol). However, it should be appreciated that alternating helical section 21 may be constructed from any suitable material or processes recognized in the art. The prosthesis may then be laser cut or photoetched, using techniques that are known in the art, to define a specific pattern or geometry in the deployed configuration. Alternating helical section 21 can be cut or etched from the tube or sheet material so that helical portions 24a, 26a, 24b, 26b are integrally formed as a single monolithic body. However, it should be appreciated that separate helical portions may be mechanically coupled, such as by welding, soldering or installing mechanical fasteners to construct alternating helical section 21. An appropriate heat treatment then may be applied to alternating helical section 21 of vascular prosthesis 20 so that the device may be configured to self-deploy from a contracted delivery configuration to the expanded deployed configuration.
Referring now to
Consequently, apices 28a and 28c are tightly wound onto the shaft of the delivery catheter and the remainder of each helical portion 24, 26 is wound against the shaft so that each turn of each portion 24, 26 slightly overlaps an adjacent turn. As a result, apex 28b and the distal and proximal ends of alternating helical section 21 are located furthest radially outward on the rolled alternating helical section 21 and are not secured to the delivery device. The overlap of the turns of helical portions 24, 26 is indicated by dashed lines in
The present invention can be carried out with vascular prosthesis being constructed in a manner other than vascular prosthesis 20. For example, instead of being a ribbon-like material, the vascular prosthesis may be a wire having a round or other cross-sectional shape and may not have overlapping elements. Also, instead of having alternating helical sections, the entire prosthesis may be wound in a single direction. In another example, the vascular prosthesis is not helically wound but may be circumferentially wrapped; see
Referring to
Retainers 36 may be eyelets, notches, or similar structures in catheter body 32. A retaining wire, not shown, may be used to hold the prosthesis 20 to the catheter body 32. The retaining wire may be of a material such as high-strength polymer or Nitinol metallic wire. The retaining wire may run down the primary lumen of the catheter body 32 which may be sized to traverse over a guidewire 38. Alternatively, the retaining wire may be placed in a secondary, small diameter lumen.
Referring to
The following deployment mechanisms described apply to any self-expanding prosthesis configuration. The prosthesis may comprise a super-elastic material, such as Nitinol, or any suitable material recognized in the art, including polymers and biodegradable materials. The prosthesis design may consist of an alternating helix pattern as described above, such as a serpentine pattern as depicted in
A first example of the invention will be discussed with reference to
According to this example of this present invention, the vascular prosthesis 20 is captured inside of a constraining apparatus, cartridge 52, which can be separate from the catheter assembly. The vascular prosthesis 20 may be wrapped, then loaded into this temporary cartridge 52 that is sterilized separately from the rest of the device. Before clinical use and deployment, the cartridge 52 with the vascular prosthesis 20 loaded therein, is temporarily attached to the outer delivery sheath 42 and becomes an extension of outer delivery sheath 42. The cartridge 52 may be linked by friction fitting over the outer delivery sheath 42 of the catheter assembly, an o-ring feature, a clamshell design of the cartridge, the use of mating luers, or other appropriate connection mechanism. The cartridge 52 may be made from a lubricious material with sufficient strength to resist the prosthesis 20 from embedding into the inner surface of the cartridge during sterilization. Materials may include PTFE, FEP, polyimide-impregnated PTFE, Delrin®, polyethylene, Nitinol, or a composite such as a PTFE-lined braided tubing. As shown in
Alternatively, the cartridge 52 can be attached to the proximal end of the catheter assembly, not shown, and the prosthesis 20 can be transferred distally to its pre-delivery location using a pusher element. In this example, the lumen 60 of outer delivery sheath 42 also preferably has an internal diameter equal to or greater than the cartridge internal diameter. Again, a change in diameter of just 0.025 mm (0.001″) or 0.05 mm (0.002″) over the stent length is sufficient, but a change 0.076 mm (0.003″) or more is preferable. After transfer into the outer delivery sheath 42, the cartridge 52 is removed from the outer delivery sheath 42 and the loaded catheter assembly 50 is placed into the vessel. A pusher wire or alternate inner shaft may then be used to transfer the prosthesis along the catheter assembly into the treatment zone.
Cartridge 52 may be attached to the outer delivery sheath 42 during manufacturing. The cartridge 52 may be linked by a friction-fitting over the outer delivery sheath 42, an o-ring feature, a clamshell design of the cartridge, the use of mating luers, or an alternative mechanism. An inner delivery catheter 30 may be placed through both the outer delivery sheath 42 and the cartridge 52. The vascular prosthesis 20 may be loaded on the inner delivery catheter 30 and transferred into the cartridge 52. The entire system, including the outer delivery sheath 42, inner delivery catheter 30, the vascular prosthesis 20, and the cartridge 52, are then sterilized together or independently. At the clinical site, the vascular prosthesis 20 is transferred into the final sheath location 56 within outer delivery sheath 42 from the cartridge 52. If the cartridge 52 is attached to the proximal end of the outer delivery sheath 42, the vascular prosthesis 20 is pushed into or pulled through the lumen 60 of the outer delivery sheath and the cartridge 52 is removed. If the cartridge 52 is attached to the distal end 58 of the outer delivery sheath 42, the vascular prosthesis 20 may be pulled into the outer delivery sheath 42 from its proximal end using the delivery catheter 30. Alternatively, the vascular prosthesis 20 may be pushed into the outer delivery sheath 42 from the distal end 58 using a tool, such as a pusher wire, to advance the vascular prosthesis 20 through the cartridge 52.
In this example, vascular prosthesis 20 is initially secured to the delivery catheter 30 and can be released from the inner delivery catheter when the vascular prosthesis is outside of the outer delivery sheath 42. However, the invention can also be practiced when the vascular prosthesis 20 is not secured to an inner delivery catheter 30 so that it is pushed out of the distal end 58 of sheath 42 using other mechanisms, such as a pusher wire.
Another example of the invention relates to providing outer delivery sheath 42 with different internal diameters such that, as shown in
Differences in diameters between the storage region 54 and the delivery region 56 may be as little as 0.025 mm (0.001″) or 0.05 mm (0.002″), but preferably 0.076 mm (0.003″) or greater. The amount of the differences in diameters will depend at least in part upon the materials used, the forces exerted by vascular prosthesis 20 and the subsequent amount of embedding by vascular prosthesis 20 into outer delivery sheath 42. The thickness of stent 20 in the contracted state is preferably greater than the diameter change of the outer delivery sheath 42. This enables a pushing feature on the inner delivery catheter 30 at the proximal end of stent 20 to continuously contact the stent from the cartridge 52 or storage region 54 to the distal end of the delivery region 56. Contracted stent thickness may be achieved through individual wall thickness of stent 20 or the wrapping of stent 20 resulting in multiple layers. Alternatively, the stent 20 may be in intimate contact with the inner delivery catheter 30, e.g. through the use of a retaining wire.
A further example of the invention will be discussed with reference to
In an alternative example, shown in
The sheath 42 may include, but is not limited to a metallic matrix of braid or coil, a PTFE liner, and a high-strength laminate layer. There are multiple methods of producing a tapered profile on the inner diameter of the sheath 42. The sheath may be laminated or stretched over a mandrel with the tapered outer diameter profile. The mandrel may be produced via multiple manufacturing methods including, but not limited to centerless grinding or Swiss screw machining. Additionally, stepped internal diameters may be incorporated with the tapered internal diameter. Therefore, tapering region 68 may include a single type of tapered segment or, for example, any combination of straight tapered segments, curved tapered segments and stepped tapered segments. The stepped tapered segments typically include generally axially directed surfaces and generally radially directed surfaces.
To further limit deployment force in the tapering delivery sheath concept exemplified in
The invention has been discussed in terms of smaller diameter storage regions and larger diameter delivery regions. In some examples, such as in
The above descriptions may have used terms such as above, below, top, bottom, over, under, et cetera. These terms may be used in the description and claims to aid understanding of the invention and not used in a limiting sense.
While the present invention is disclosed by reference to the preferred embodiments and examples detailed above, it is to be understood that these examples are intended in an illustrative rather than in a limiting sense. It is contemplated that modifications and combinations will occur to those skilled in the art, which modifications and combinations will be within the spirit of the invention and the scope of the following claims.
Any and all patents, patent applications and printed publications referred to above are incorporated by reference.
This application claims the benefit of U.S. provisional patent application No. 61/241,345 filed 10 Sep. 2009, the disclosure of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61241345 | Sep 2009 | US |
