Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent combined with surgical delivery system
Reexamination Certificate
2000-10-31
2002-08-06
Nguyen, Dinh X. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent combined with surgical delivery system
C623S001230, C600S139000, C600S141000, C604S523000, C604S525000, C604S534000, C604S535000
Reexamination Certificate
active
06428566
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to expandable endoprosthesis devices, generally called stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel, to maintain the patency thereof. Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis.
Stents are generally tubular shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as a coronary artery. Stents are usually delivered in a radially compressed condition to the target site and then deployed at that location into a radially expanded condition to support the wall of the vessel and help maintain it dilated. They are particularly suitable for urging a segment of a dissected arterial lining radially outwardly in a lumen to maintain a fluid passageway there through.
A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally on a balloon catheter; helically wound coiled springs manufactured from an expandable heat sensitive metal; and self-expanding stents inserted in a compressed state for deployment into a body lumen.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the wall of the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed, for example, from shape memory metals such as nickel-titanum (NiTi) alloys, which will respond to elevated temperature or the like to expand from a radially compressed state when the stent is advanced out of the distal end of the delivery catheter into the blood vessel. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent. Other self-expanding stents may use stress-induced martensite (SIM) alloys to allow the stent to move between contracted and expanded positions.
Typical stent delivery systems for implanting expandable stents at the target site generally include a dilatation catheter having an inflatable balloon or other expandable means mounted at the distal end thereof. The expandable stent is radially compressed onto the balloon for delivery within a body lumen. Some prior art stent delivery systems for implanting balloon expandable stents utilize an outer delivery sheath that is initially placed over the compressed stent prior to delivery. A delivery sheath is sometimes used to prevent the compressed stent from moving axially along the balloon portion of the dilatation catheter while being advanced within the patient's vasculature. Once the catheter is in place, the physician can retract the outer sheath to expose the stent and expandable balloon. The physician can then inflate the balloon portion of the dilatation catheter to cause the compressed stent to expand radially to a larger diameter to be left in place within the artery at the target site.
In the case of implanting self-expanding stents at the target site, typical delivery systems include an inner lumen upon which the compressed or collapsed stent is mounted and an outer restraining sheath that is initially placed over the compressed stent prior to deployment. When the stent is to be deployed in the body vessel, the outer sheath is moved in relation to the inner lumen to “uncover” the compressed stent, allowing the stent to move to its expanded condition. Some delivery systems utilize a “push-pull” technique in which the outer sheath is retracted while the inner tubing 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 stent, the inner tubing must remain stationary, thereby preventing the stent from moving axially within the body lumen.
Prior art stent delivery systems are benefitted by the function of the delivery sheath in preventing the collapsed stent from moving axially along the inner lumen of the delivery catheter while being advanced within the patient's vasculature. In addition, sometimes the stent cannot be deployed for a variety of reasons, so it must be able to be pulled back into the guiding catheter without being “stripped off” of the dilatation or delivery catheter. Further, despite the care given during placement, stents can become dislodged from the delivery system. The consequences of losing a stent range from embarrassment to a life threatening situation requiring immediate surgery. The use of a delivery sheath can help alleviate such problems.
The delivery sheath also helps prevent the stent from abrading the body lumen wall as the stent is being manipulated into the target area. With no delivery sheath, the struts of the stent would be exposed to the walls of the patient's vasculature and could possibly cause trauma to the walls or cause pieces of plaque to break from the stenosis. Abrasive forces in the area of the stenosis are not desirable due to the possible formation of embolic debris that would be released into the patient's blood stream. Such debris could possibly occlude smaller blood vessels leading to vital organs such as the brain. Thus, for a variety of reasons, the outer sheath remains in place over the compressed stent until the physician has manipulated the catheter into the proper location within the patient's vasculature. Once in position, the physician can retract the outer sheath to expose the stent and allow it to safely expand within the body lumen at the target site.
It follows that it is beneficial for the delivery sheath to have a low profile with no obtrusions and that the sheath be made of a low-friction, flexible material. Such construction would facilitate the insertion of the stent delivery system into small inner diameter guide catheters and body lumens and would minimize trauma to the lumens as the delivery system is being maneuvered into tight, difficult-to-reach areas in the patient's vasculature.
When used with a self-expanding stent delivery system, the delivery sheath must serve an additional purpose of resisting the radial force being applied to the sheath by the stent as it is held in its collapsed condition. In some self-expanding stent designs, the radial force applied by a collapsed stent can be quite substantial. As a result, the delivery sheath must have sufficient strength to support the collapsed stent against expansion. Additionally, since a stent delivery system may be placed in storage for a considerable length of time, the sheath must be capable of restraining the stent during that period. The prolonged exposure of the sheath to an expansive force can ultimately deform the sheath (referred to as creep), which can render the delivery system useless for implantation in a patient.
The path to the deployment site within a patient's body lumen may be relatively tortuous, involving navigation through various curves and turns of the patient's vasculature, which requires longitudinal flexibility in order to accommodate the turns without inflicting trauma to the walls of the lumen. In the past, this requirement for flexibility dictated a relatively thin wall sheath and placed the constraint on the designer trading off sheath strength for flexibility. There thus exists a need for a sheath which affords sufficient radial strength to maintain the self-expanding stent compressed during deployment, but yet has sufficient flexib
Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Miller Cheryl
Nguyen Dinh X.
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