Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1999-08-31
2003-04-01
Thaler, Michael H. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
Reexamination Certificate
active
06540774
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 cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as coronary artery. Stents are usually delivered in a compressed condition to the target site and then deployed at that location into an expanded condition to support the vessel and help maintain it in an open position. They are particularly suitable for use in supporting and holding back a dissected arterial lining which can occlude the 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 into a compressed state for deployment into a body lumen. One of the difficulties encountered in using prior art stents involve maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery and accommodate the often tortuous path of the 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 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 from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. 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.
Details of prior art expandable stents can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); U.S. Pat. No. 4,512,1338 (Balko et al.); U.S. Pat. No. 4,553,545 (Maass, et al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco); U.S. Pat. No. 5,514,154 (Lau, et al.); U.S. Pat. No. 5,421,955 (Lau et al.); U.S. Pat. No. 5,603,721 (Lau et al.); U.S. Pat. No. 4,655,772 (Wallsten); U.S. Pat. No. 4,739,762 (Palmaz); and U.S. Pat. No. 5,569,295 (Lam), which are hereby incorporated by reference.
Further details of prior art self-expanding stents can be found in U.S. Pat. No. 4,580,568 (Gianturco); and U.S. Pat. No. 4,830,003 (Wolff, et al.), which are hereby incorporated by reference.
Expandable stents are delivered to the target site by delivery systems which often use balloon catheters as the means for expanding the stent in the target area. One such stent delivery system is disclosed in U.S. Pat. No. 5,158,548 to Lau et al. Such a stent delivery system has an expandable stent in a contracted condition placed on an expandable member, such as an inflatable balloon, disposed on the distal portion of an elongated catheter body. A guide wire extends through an inner lumen within the elongated catheter body and out its distal end. A tubular protective sheath is secured by its distal end to the portion of the guide wire which extends out of the distal end of the catheter body and fits over the stent mounted on the expandable member on the distal end of the catheter body.
Some prior art stent delivery systems for implanting self-expanding stents include an inner lumen upon which the compressed or collapsed stent is mounted and an outer restraining sheath which 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 into the target area.
The positioning of the stent at the desired location in the body lumen is often critical since inaccurate placement can affect the performance of the stent and the success of the medical procedure. The positioning of the stent before, during, and after its implantation and expansion is generally monitored by external monitoring equipment, such as a fluoroscope, which allows the physician to place the stent in the exact target site. Radiopaque markers placed on the ends of the catheters of the stent delivery system often are utilized to help locate the stent on the catheter during deployment. Additionally, the stent itself can be made from a radiopaque material. For this reason, it is desirable for the stent to be moderately radiopaque. Stents which lack sufficient radiopacity are usually more difficult to position accurately and assess with angiography. Therefore, even a physician using the best available stent delivery systems may not be capable of accurately positioning the stent if there are problems visualizing the stent on the fluoroscope.
Currently, many stents in use are formed from stainless steel or nickel-titanium type alloys which are not always readily visible on the medical imaging instrument. With these materials, the radiopacity of the stent is highly dependant on the amount of metal in the stent. Stents which have thicker struts are generally more radiopaque than stents with thinner struts. However, the strut of the stent cannot be too thick or wide, since the stent must be capable of expanding radially to a larger diameter during deployment. Generally, stents having wider struts are more radiopaque then stents with narrower struts, however, if the strut width is increased in areas subject to high stresses, the strain created in the material at these areas could increase dramatically and may cause cracks in the stent to form, which is highly undesirable.
To increase radiopacity, radiopaque markers have been placed on stents to attempt to provide a more identifiable image for the physician. One such surgical stent featuring radiopaque markers is disclosed in U.S. Pat. No. 5,741,327 (Frantzen) which utilizes radiopaque marker elements attached to the ends of a radially expandable surgical stent to increase the visibility of the stent. However, there are certain drawbacks in utilizing radiopaque markers since some markers may restrict the ability of the stent to fully expand radially and can cause an unwanted protrusion from the surface of the stent which can possibly pierce the wall of the body lumen. Additionally, radiopaque markers can either fail to provide an adequate outline of the stent or illuminate the stent so brightly that fine details such as blood vessels or other bodily structures are obscured when an image is obtained. When the stent is made from highly radiopaque metals such as tantalum or platinum, often the radiopacity of the stent is too high and there is a need to decrease the radiopacity to allow adequate visualization of the surrounding blood vessels, especially at the target location where the PCTA or the PTA procedure has been performed.
The design of the strut pattern of the stent can sometimes lead to unwanted complications during the stent deployment. For example, in some instances, the forces of the body lumen on the fully expanded stent can cause the ends of the stent to collapse somewhat causing the stent to take the form of a “cigar” shap
Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Thaler Michael H.
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