Patent Application
20080319388
1. Field of the Invention
The present invention relates to a delivery system and method for deployment of a medical device, e.g., a self-expanding vascular device, in the vasculature of a patient. More particularly, a delivery system having a sheath with portions specifically positioned relative to a balloon positioned therein is described.
2. Background of the Invention
As is known, treatment of vascular blockages due to any one of a number of conditions, such as arteriosclerosis, often comprises balloon dilatation and treatment of the inner vessel wall by placement of a stent. These stents are positioned to prevent restenosis of the vessel walls after the dilatation. Other devices, often referred to as drug eluting stents, are now being used to deliver medicine 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 expansion of the balloon causes the compressed prosthesis to expand to a larger diameter and then left in place within the vessel at the target site. 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. When the actuating wire is pulled to retract the outer sheath and deploy the prosthesis, the inner lumen must remain stationary, preventing the prosthesis from moving axially within the body vessel.
There have been, however, problems associated with these delivery systems. For example, systems that rely on a “push-pull design” can experience movement of the collapsed prosthesis within the body vessel when the inner lumen is pushed forward. This movement can lead to inaccurate positioning and, in some instances, possible perforation of the vessel wall by a protruding end of the prosthesis. Systems that utilize an actuating wire design will tend to move to follow the radius of curvature when placed in curved anatomy of the patient. As the wire is actuated, tension in the delivery system can cause the system to straighten. As the system straightens, the position of the prosthesis changes because the length of the catheter no longer conforms to the curvature of the anatomy. This change of the geometry of the system within the anatomy can also lead to inaccurate prosthesis positioning.
Other 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. As shown in U.S. Pat. No. 6,656,213, the stent may be 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. In other embodiments, the balloon is outside the stent and the sheath is around both the balloon and the stent.
To facilitate the rupturing of the sheath, it is further known to provide perforations in the sheath. The intention of the perforations is to make the rupturing or separation of the sheath easier upon expansion of the balloon. While the perforations may help to control the rupturing of the sheath by providing a “weak” portion, the dynamics of sheath rupturing are still not well controlled.
There is, therefore a need for a mechanism to reliably deliver a self-expanding stent, enclosed in a sheath, with repeatable and known operating characteristics.
In one embodiment, a delivery system comprises a catheter having a distal end and a proximal end; a balloon, in a deflated condition, positioned at the distal end of the catheter, the balloon comprising at least two wing portions wrapped about the distal end of the catheter, and a sheath positioned about the balloon, wherein the sheath comprises a weakened portion located on the positioned sheath in a predetermined relation to the at least two wing portions of the balloon.
The weakened portion of the positioned sheath may comprise a plurality of substantially linearly arranged perforations oriented substantially parallel to a longitudinal axis of the sheath.
The weakened portion of the positioned sheath may be 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.
The weakened portion of the positioned sheath may be located at a position that is approximately equidistant between sequentially adjacent circumferential points where the at least two wings press against the positioned sheath as the balloon is inflated.
Upon inflation of the balloon, in one embodiment, each wing of the at least two wings presses against the positioned sheath at a respective wing pressure location about the circumference of the sheath; and the weakened portion of the positioned sheath is located at a position that is approximately half the distance, around the circumference, between adjacent wing pressure locations.
The weakened portion of the positioned sheath may comprise an initial cut in the sheath extending proximally a predetermined distance from a distal edge of the sheath.
In yet another embodiment, the predetermined location of the weakened portion may be within 20% of a midpoint between sequentially adjacent circumferential points where the at least two wings press against the positioned sheath as the balloon is inflated.
In one embodiment, the delivery system may comprise: a self-expanding medical device positioned at the distal end of the catheter, wherein the self-expanding medical device is maintained in a compressed state by the positioned sheath.
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.
n another embodiment the balloon is a dual-wing balloon having first and second wings, 1 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 another 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 wingbase 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 wingbase portion of the next adjacent wing.
In yet another embodiment a system comprises: a catheter having a distal end and a proximal end; a balloon, in a deflated condition, positioned at the distal end of the catheter and wrapped about the distal end of the catheter, the balloon comprising at least two wing portions; a medical device, having a compressed state and an expanded state, positioned about the balloon; and a sheath, comprising sheath material, positioned about the medical device to hold the medical device in the compressed state, the sheath material comprising a predetermined sheath portion, wherein the predetermined sheath portion is located at a position as a function of positions of the at least two wing portions of the balloon.
The balloon may be one of: a bi-wing structure with only two wings; and a tri-wing structure with three wings.
In yet another embodiment a method of providing an ostial protection device delivery system comprises: providing a catheter having a distal end and a proximal end; positioning a deflated balloon at the distal end of the catheter, the balloon comprising wing portions; wrapping the wing portions about the distal portion of the catheter so as to facilitate inflation of the balloon; providing an ostial protection device about the deflated balloon; positioning an elongate tubular sheath, the sheath having a proximal end and a distal end oriented with the catheter, the sheath comprising a predefined sheath portion, about the ostial protection device and the balloon to hold the ostial protection device in a compressed state; and orienting the predefined sheath portion in a predetermined relationship as a function of locations of the folded wing portions of the balloon.
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:
A medical device delivery system, as shown in
A cross section of the system 10, along line 1B-1B, is presented in
Referring to
Alternatively, the sheath 18 may be created by weakening a portion of the sheath 18 by chemical and/or mechanical means. Still further, the perforation 200 may comprise one or more holes, where each hole is created by the removal of sheath material. While the perforation 200 is shown here at the distal end of the sheath 18, of course, one of ordinary skill in the art would understand that were the sheath 18 to be connected to the catheter 12 at the distal end of the sheath 18, then the perforation 200 may be positioned at a proximal end of the sheath 18. Further, more than one perforation 200 may be provided, for example, one at each of the proximal and distal ends of the sheath 18, respectively.
As an alternative to the perforation 200, a single initial cut 602, as shown in
The sheath is made from a material having a grain, or fibers, that can be longitudinally oriented, for example, PTFE. In general, the sheath 18, upon expansion of the balloon 14, will tear along the perforation 200 or initial cut 602 in substantially a straight line following a longitudinal axis of the sheath 18 as defined, generally, by the catheter 12.
The expansion of the balloon causes the sheath to rupture. Once the sheath ruptures, the stent expands and is released into the vessel. The balloon pressure that will cause a sheath 18 to split, however, is not consistent in previously known systems. Tests have shown that the sheaths from a batch of balloon-mounted systems will not always split at the same balloon pressure.
Experiments were conducted by the present inventors, using an external polymer sheath 18, made from PTFE, and a PTCA balloon catheter. In the test setup, the PTCA balloon catheter included a 2.0 mm by 30 mm nylon balloon 14. The particular type of balloon 14 that was used in these experiments exhibited semi-compliant behavior, in that it has a compliance of approximately 5% at 2 mm with 6 atmospheres of nominal pressure, i.e., the balloon diameter ranges from 1.9 mm to 2.1 mm at 6 atmospheres. The external polymer sheath 18 was provided in two sizes: a) 0.043 inches inner diameter by 0.002 inches wall thickness; and b) 0.047 inches inner diameter by 0.002 inches wall thickness. The sheath was positioned substantially as shown in
Five samples of each of sheath type a) and sheath type b) were externally loaded onto the 2.0 mm by 30 mm PTCA balloon catheter. The balloon was inflated in one atmosphere intervals to a pressure until the polymer sheath fully split, i.e., the sheath split along the full length of the 30 mm PTCA balloon. As shown in Table 1 below, for sheath type (a) the balloon pressure needed to fully split the sheath ranged from 4 to 8 atmospheres. The sheath of type (b) exhibited a full split with balloon pressures that ranged from 7 to 18 atmospheres.
This inconsistency in the balloon pressure required to fully split the polymer sheath appears to hinder the effectiveness of the sheath for delivery of a device. The wide range of balloon pressure values required to fully split the sheath renders a construction substantially as represented in
The present inventors 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. A deflated PTCA catheter balloon 30, shown in a perspective view in
Referring to
The present inventors have observed that placement of the perforation 200 or split 602 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.
As found by the inventors of the present invention, there is an optimum area or areas on the circumference of the sheath at which to place the perforation 200 (running longitudinally) or initial cut 602. These locations around the circumference are determined by the folded balloon.
Referring to
When the perforation 200 or initial cut 602 is placed anywhere within one of the areas 42, 44, the sheath 40 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 40. It has been observed, however, that a split or perforation may be placed in each of the areas 42, 44 to facilitate separation of the sheath 40.
A second set of experiments was performed where sheaths, with the same construction as those previously described, are provided around the PTCA balloon except that the perforation or initial cuts are placed in one of the areas 42, 44, i.e., relative to the orientation of the balloon 30. Once again, the balloon is inflated in increments of 1 atmosphere. As shown in Table 2, the balloon pressure necessary to fully split the sheath 40 was repeatedly 5 atmospheres.
The specific placement of the initial cut 602 or perforation 200 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 present inventors have recognized that the folds or wings 32, 34 of the PTCA balloon 30 play a role in splitting the sheath 40, due to the placement of the split 602 or perforation 200. 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 40 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 40 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 40, 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 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 perforation or slit 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
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. 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.
While the present invention has been described with respect to a bi-folded balloon, the invention is not limited to an embodiment 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 one or more initial cuts or series of perforations 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.
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.
