Patent Application
20090112159
The present invention relates to a delivery system for a self-expanding medical device. More particularly, the delivery system is provided with a profiled sheath allowing for better system positioning of the medical device and which has an initiation slit oriented with respect to a balloon portion of the delivery system.
As is known, treatment of vascular blockages due to any one of a number of conditions, such as arteriosclerosis, often involves balloon dilatation and treatment of the inner vessel wall by placement of a stent. The stent is positioned to prevent restenosis of the vessel walls after the dilatation. Drug eluting stents are now available where medicine is delivered to the vessel wall to also help reduce the occurrence of restenosis.
These stents, i.e., tubular prostheses, typically fall into two general categories of construction. The first category of prosthesis is made from a material that is expandable upon application of a controlled force applied by, for example, a balloon portion of a dilatation catheter upon inflation. The second category of prosthesis is a self-expanding prosthesis formed from, for example, shape memory metals or super-elastic nickel-titanium (NiTi or Nitinol) alloys, that will automatically expand from a compressed or restrained state when the prosthesis is advanced out of a delivery catheter and into the blood vessel.
Some known prosthesis delivery systems for implanting self-expanding stents include an inner lumen upon which the compressed or collapsed prosthesis is mounted and an outer restraining sheath that is initially placed over the compressed prosthesis prior to deployment. When the prosthesis is to be deployed in the body vessel, the outer sheath is moved in relation to the inner lumen to “uncover” the compressed prosthesis, allowing the prosthesis to move to its expanded condition. Some delivery systems utilize a “push-pull” type technique in which the outer sheath is retracted while the inner lumen is pushed forward. Still other systems use an actuating wire that is attached to the outer sheath.
Delivery systems are known where a self-expanding stent is kept in its compressed state by a sheath positioned about the prosthesis. A balloon portion of the delivery catheter is provided to rupture the sheath and, therefore, release the prosthesis. For example, in U.S. Pat. No. 6,656,213, the stent is provided around the balloon, with the sheath around the stent, that is, the balloon, stent, and sheath are co-axially positioned, such that expansion of the balloon helps to expand the self-expanding stent as well as rupture the sheath.
There have been issues, however, with the sheath having an adverse effect on the vessel as the delivery system is positioned. In some instances, the sheath has been “caught” on lesions that are found in the vessel.
There is, therefore, a need for a sheath that does not interfere with positioning of the delivery system.
Embodiments of the present invention serve to minimize any adverse effects of the sheath on either the positioning of the delivery system or the vessel itself. The sheath is made with a profile and leading edge that, as the delivery system is distally moved through a vessel, does not interfere with positioning. The profiled sheath also reduces incidences of the sheath catching on lesions in the vessel. Further, an initiation slit provided on the sheath is oriented with respect to a balloon portion of the delivery system.
In one embodiment, a delivery system includes a catheter having a distal end and a proximal end; a balloon positioned at the distal end of the catheter, the balloon comprising at least two wing portions wrapped about the distal end of the catheter; a medical device, having a compressed state and an expanded state, positioned about the balloon portion; and a sheath positioned about the medical device to hold the medical device in the compressed state. The sheath has a distal sheath portion located at a distal end of the sheath, the distal sheath portion having a first diameter and a first longitudinal length; a transition portion, of a second longitudinal length, having a distal end located adjacent the proximal end of the distal sheath portion, the distal end of the transition portion being of the first diameter and having a proximal end with a second diameter greater than the first diameter; a body portion of a third longitudinal length, having a distal end adjacent a proximal end of the transition portion, the body portion being of the second diameter; and an opening provided in an outer surface of the sheath. The opening is located on the positioned sheath in a predetermined relation to the at least two wing portions of the balloon.
The opening of the positioned sheath is located at a position where a total force exerted by expansion of the at least two wing portions against the positioned sheath, upon inflation of the balloon, is at its greatest.
In one embodiment, the balloon is a dual-wing balloon having first and second wings, each wing having a respective wing-tip portion and a wing-base portion, wherein the balloon is wrapped about the catheter in a bi-fold orientation, and wherein the opening in the sheath is located between the wing-tip portion of the first wing and the wing-base portion of the second wing.
In one embodiment, the balloon is a dual-wing balloon having first and second wings, each wing having a respective wing-tip portion and a wing-base portion, and wherein the balloon is wrapped about the catheter in a U-fold orientation, and wherein the opening in the sheath is located between the wing tip of the first wing and the wingtip of the second wing.
In one embodiment, the balloon is a tri-wing balloon having three wings, each wing having a respective wingtip portion and wing base portion, wherein the balloon is wrapped about the catheter such that a wingtip portion of a first wing is folded toward a wing-base portion of a next adjacent wing, and wherein the opening in the sheath is located between the wingtip portion of the first wing and the wing-base portion of the next adjacent wing.
The above and further advantages of the present invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which:
The present invention is directed to a sheath that is profiled, i.e., shaped, to reduce instances of interference between a distal edge of the sheath and a vessel and/or any lesion or lesions that might be present in the vessel. Embodiments of the sheath and its implementation will be described below in more detail.
Reference is now made to
The device 100 includes a cap or flared portion 102, an anchor portion 104, and an articulating portion 106. The anchor portion 104 is configured to fit into a side-branch vessel and the cap portion 102 is configured to selectively protect at least part of an ostial region. The articulating portion 106 flexibly connects the anchor portion 104 to the cap portion 102, such that various angles of articulation are possible between each of the three portions. The articulating portion 106 includes connectors 110 connecting to the cap portion 102 and to the anchor portion 104.
The device 100 may be formed of a generally elastic, super-elastic, in-vivo stable and/or “shape-memorizing” material. Such a material is able to be initially formed in a desired shape, e.g., during an initial procedure performed at a relatively high temperature, deformed, e.g., compressed, and then released to assume the desired shape. The device 100 may be formed of Nickel-Titanium alloy (“Nitinol”) that possesses both super-elastic and shape-memorizing properties. Biocompatible non-elastic materials, such as stainless steel, for example, may be also used. Other combinations of materials and processes would be understood by one of ordinary skill in the art.
The device 100 may be formed from a wire or cut from a single tube of material. The device 100 may be formed from a single piece of material or may be assembled in sections. In general, each section comprises a plurality of struts 108 arranged in a manner of peaks and valleys familiar to those of ordinary skill in the art.
The struts 108 may have a cross-section that is, but not limited to, circular, oval, rectangular, or square. One of ordinary skill in the art will understand the options available with respect to the cross-section chosen for the struts 108 depending upon the intended application of the device.
The self-expanding device 100 may be delivered via a system that uses a sheath and a balloon portion of a delivery catheter. In general, as explained in more detail below, the device 100 is compressed and loaded in a low-profile or crimped state about a balloon portion and surrounded by a sheath. To deliver the device the balloon portion is inflated, causing the sheath to rupture and release the constrained device 100 into its expanded condition within the vessel.
A medical device delivery system 200, as shown in
A cross-section view of the system 200, along line 3-3, is presented in
The sheath 218 may be made from a material having a grain, or fibers, that can be longitudinally oriented, for example, PTFE, Nylon, PEBAX, polypropylene, and the like. Other materials may be used for the sheath as easily understood by one of ordinary skill in the art.
Referring now to
The sheath 218 is made from a plastic material and, as above, is generally cylindrical, i.e., a hollow tube. Once the sheath 218 ruptures, however, it is no longer a cylinder and has a form that covers less than all of the circumference of the now-expanded stent 100. Referring to
Referring now to
Turning now to
The inventors of the present application have noted that adjustment of either the inner diameter of the sheath or the wall thickness of the material from which the sheath is made, does not sufficiently reduce the occurrence of fish-mouth. It appears that the initiation slit 402 is one of the leading factors that contributes to the size of the fish-mouth. In one series of experiments, the length of the initiation slit 402 was reduced from 1.5 mm to 0.5 mm and the amount of fish-mouth width, i.e., diameter, was substantially reduced. While the amount of fish-mouthing was reduced, however, the benefit of a lower and consistent pressure of the balloon portion necessary to consistently open, i.e., rupture, the sheath 218, was negatively affected. Thus, merely reducing the length of the initiation slit 402, while it does reduce the width of the fish-mouth, prevents consistent release of the device at a lower balloon pressure.
A profiled sheath 900, as shown in
In the present description, reference to “width” is referring to the diameter of the tubular sheath. Further, while there is reference to “portions,” e.g., distal lead portion 906, the profiled sheath 900 is, in one embodiment, of a unitary construction. The claims appended hereto, however, should not be limited to this construction unless expressly recited therein.
The sheath 900 is made from material similar to that referenced above with respect to the known sheath 218. Further, the grain direction of this material is oriented in a longitudinal direction along the profiled sheath 900 running from the distal end 902 to the proximal end 904.
An initiation opening 912 is provided across a junction or boundary between the distal lead portion 906 and the cone/transition portion 908. A distal-most part of the opening 912 is located a distance D from the distal end 902 of the sheath 900. Thus, the opening 912 is “set back” from the distal end 902 of the sheath 900. It is advantageous to position the opening 912 across the boundary between the distal lead portion 906 and the cone/transition portion 908. The opening 912 need not, however, be symmetrically positioned across the boundary.
The opening 912 may be implemented as a slice in the sheath material, where no material has been removed, and where there are sharp edges at each end of the opening 912. The sharp edges assist in the consistent splitting of the sheath. The opening 912 may be created by a slicing operation or a punching operation. The opening 912 may be implemented by operation of a sharp blade or a slicing laser device could be used. Alternatively, the opening 912 may result from an operation where material is removed, i.e., “punched out.”
Referring now to
In operation, as the balloon portion 214 is inflated, the opening 912 will expand as shown in
A profiled sheath 900 is made from any suitable material for a sheath as has been described above. To make the profiled sheath, the material is initially provided as a cylindrical tube of material 1202 and is attached to one end of a mandrel 1204, as shown in
The RF coil 1212 is activated while at the same time a pulling force is applied to the free end 1210 in a direction Y, as shown in
Once the desired profile has been obtained, the narrowed portion of the tube is then cut and the opening 912 is created, as shown in
As shown in the flowchart of
While an RF coil has been described for softening the sheath material, a heater, microwave device, steam device, or infrared (IR) laser could also be used. Choosing the apparatus or method for softening the sheath material is within the capabilities of one of ordinary skill in the art.
The effectiveness of the sheath for delivery of a device will be significantly reduced if the delivery system requires too wide a range of balloon pressure to fully split the polymer sheath. The wide range of balloon pressure values required to fully split the sheath renders a system as being too variable to validate and subsequently too variable to use in everyday procedures.
The present inventors have recognized that the bi-folded wings of a PTCA catheter balloon could be used to aid in better controlling the splitting dynamics of the sheath. For reference, a deflated PTCA catheter balloon 30 is shown in a perspective view in
Referring to
The placement of the initiation opening 912 to take advantage of the mechanical leverage provided from the folded wings 32, 34 of the balloon 30 will aid in establishing a consistent and repeatable splitting of the sheath at a specific pressure, or relatively narrow range of pressures, of the balloon. In known systems, the split or perforation on the sheath were randomly placed, irrespective of any geometry of the balloon around which the sheath was disposed.
There is an optimum area or areas on the circumference of the sheath at which to place the initiation opening 912 (running longitudinally. These locations around the circumference are determined by the folded balloon.
Referring to
When the initiation opening 912 is placed anywhere within one of the areas 42, 44, the sheath 900 will split at a uniform and consistent and repeatable pressure of the balloon. It should be noted that one initial cut or perforation in either of the areas 42, 44 is sufficient to initiate the full split of the sheath 900. It has been observed, however, that a split or perforation may be placed in each of the areas 42, 44 to facilitate rupture or separation of the sheath 900.
The specific placement of the initiation opening 912 with respect to the folded geometry or orientation of the balloon provides consistent and repeatable sheath splitting performance. The repeatability and consistency of obtaining a full split provides an advantage with respect to using a delivery system with a balloon expandable sheath to deliver a self expanding medical device.
Thus, the folds or wings 32, 34 of the PTCA balloon 30 play a role in splitting the sheath 900, due to the placement of the initiation opening 912. Further, optimum positions about the circumference of the sheath can be predetermined as a function of the balloon's placement and folded geometry about the catheter.
Referring to
The placement areas 42, 44 located about the circumference of the sheath 900 may be considered to be defined as located generally halfway between circumferentially adjacent points where the balloon wings 32, 34 exert a respective force against the sheath 900 upon inflation of the balloon. The placement areas 42, 44, in one embodiment, are located along the circumference of the sheath within a portion of the circumference that is in a range of 40-60% of the distance between the points 52, 54.
Alternatively, the location of the placement areas 42, 44 may be described as being located between a wing tip 36 and a wing base 38 of adjacent wings of the balloon. As shown in
The balloon 30, as shown in
When folded, and placed within a sheath 900, as shown in cross-section in
In yet another embodiment, as shown in
A method 1000 for assembling a delivery system as described above is shown, generally, in
Returning to step 1006, if the balloon is of a dual-wing construction then control passes to step 1016 where the balloon is folded. At step 1018 it is determined as to whether or not the balloon was folded in a bi-fold configuration or a U-fold configuration. If it is determined that it is the former configuration then control passes to step 1010 and operation continues as described above. If, however, it is the U-fold configuration then, at step 1020, the sheath is wrapped around a balloon. Subsequently, step 1022, the location between adjacent wing tips about the circumference of the sheath is determined. Finally, step 1024, the initiation opening is placed in the determined location.
An alternate method 1100 for assembling a system in accordance with another embodiment of the present invention will now be described with respect to the flowchart shown in
While an embodiment of the present invention has been described with respect to a bi-folded balloon, the invention is not limited to embodiments with a balloon that only has two wings. The present invention can be implemented with any balloon having two or more wings where the initial cut or perforation are placed in the sheath with respect to those points on the sheath at which the wings of the balloon exert force against the sheath as the balloon is being inflated.
Thus, in accordance with the teachings of the present invention, the placement of an initial cut in a sheath that is provided to constrain a self expanding device, for example, a stent prior to delivery, is determined with respect to a geometry and orientation of a folded balloon around which the sheath is provided.
It is to be understood that the present invention is not limited in its application to the details of construction and the arrangement of the components set forth in the foregoing description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Specifically, while the foregoing description is with respect to a flared ostial protection device, the profiled sheath described here can equally be applied to systems that deliver other types of devices, e.g., a straight or “non-flared” cylindrical main-branch stent.
Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
It is further appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.
Although various exemplary embodiments of the present invention have been disclosed, it will be apparent to those skilled in the art that changes and modifications can be made that will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be apparent to those reasonably skilled in the art that other components performing the same functions may be suitably substituted.
