Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1999-08-25
2003-02-18
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001350
Reexamination Certificate
active
06520987
ABSTRACT:
BACKGROUND OF THE INVENTION
1.—Field of the Invention
This invention generally relates to expandable intravascular prosthetic devices, also known as stents, that are usually implanted in a patient s body lumen such as an artery to maintain the patency of the lumen after balloon angioplasty.
2.—Description of the Prior Art
a) Stents in Clinical Practice
Stents are usually cylindrically shaped devices which function is to maintain patency or to expand a segment of a body lumen such as an artery. They are particularly useful for preventing a torn or injured arterial lining from occluding a fluid passageway, or for supporting a vessel segment in the presence of suboptimal results following balloon angioplasty. Coronary stenting is gaining widespread acceptance in the treatment of atherosclerotic coronary artery disease. Since the first report by Sigwart et al. of the placement of metallic stents in coronary arteries, coronary stenting has been shown to optimize the geometry of the coronary lumen after balloon angioplasty, to reduce procedural complications and the need for urgent coronary bypass surgery (as a bail-out strategy) and to decrease the rate of restenosis. Coronary stenting is considered by many interventional cardiologists as the therapy of choice for venous graft stenoses. This device is also increasing in popularity for de novo native coronary lesions (primary stenting). Two recent randomized clinical trials comparing stenting with standard balloon angioplasty in primary lesions have demonstrated the efficacy of the Palmaz-Schatz™ stent in reducing the rate of angiographically detected restenosis. In one of these trials, there was both angiographic and clinical benefit, as reflected by; a reduction in major clinical endpoints, especially repeated revascularization of the target lesion.
b) Types of Permanent Stents
Self-expanding Stents
The first stent available for clinical use consisted of a stainless-steel alloy with a self-expanding, spring-like mesh design. The stent was maintained in a constrained and elongated conformation at the distal portion of a delivery catheter by an overlying sheath. When released (by withdrawing the overlying sheath), the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the artery wall. This type of stent is known as the Wallstent™. Although very flexible and providing excellent fluid dynamics, this self-expanding stent was found by some investigators to be deficient since, when deployed, it could exert an undue, permanent stress on the vessel wall. Moreover, significant longitudinal shortening is observed during radial self-expansion, which may result in inappropriate stent placement or inadequate dissection coverage.
Balloon-expandable Stents
The limitations encountered with the Wallstent™ lead to the development of various stents which were controllably expandable within a blood vessel. Generally, in these systems (often called “balloon-expandable stents”) the stent, mounted and crimped on a deflated angioplasty balloon, is delivered to the target area of a blood vessel by a catheter system. Once the stent has been properly positioned (under fluoroscopic guidance), the balloon is expanded thereby expanding the stent so that the latter is urged in place against the vessel wall. At this point, the balloon is deflated, withdrawn and subsequently removed.
Balloon-expandable stents which have gained some notoriety are the Palmaz-Schatz™ stent, the ACS Multilink™ stent, the Wiktor™ stent and the Gianturco-Roubin Flex-Stent™. The Palmaz-Schatz™ and the ACS Multilink™ balloon expandable stents share the common design of a carved stainless-steel cylinder. The Palmaz-Schatz™ stent consists of two rigid stainless-steel slotted tubes joined by a single filament to aid in flexibility. The slotted configuration, when balloon-expanded, deploys as a meshwork. However, despite its articulation, the Palmaz-Schatz stent is known to lack flexibility for delivery in tortuous vessel anatomy and for expansion in angulated lesions. The ACS Multilink™ stent is somewhat similar to the latter, but differs in the increased number of bridges interconnecting identical corrugated rings. In comparison with the Palmaz-Schatz™ stent, the ACS Multilink™ stent has a better flexibility, a more operator-friendly delivery system and less longitudinal shortening during radial expansion.
The Wiktor™ stent, and the Gianturco-Roubin Flex-Stent™ share the common design of a monofilament wire wrapped around an angioplasty balloon catheter. Although they differ from each other in their material, coil structure, radiopacity and degree of wall coverage, they both offer a good flexibility for negotiating tortuous vessels and minimal longitudinal shortening during radial expansion. However, the major drawback is related to the hazard of inadvertent unraveling during manipulation and balloon withdrawal, due to their monofilament design. Other reported disadvantages are the relatively large wire spacing and some degree of recoil after expansion, which may be the reasons why restenosis after use of this type of stent is rather frequent.
All of the stents described above share the common design of being monotubular and thus best suited for delivery in the straight segment of a body passageway. These stents are inappropriate for placement in a bifurcation or a passageway having side branches since: a) the risk of closure of the side branch is increased and b) the side branch will be substantially inaccessible.
The presence of a bifurcation or a major side branch is well recognized as a contraindication for conventional stents.
Indeed, the Physician Guide published in support of the Palmaz-Schatz stent states: “ . . . no attempt should be made following placement of a Palmaz-Schatz stent to access a side branch with a guide wire or a balloon, as such attempts may result in additional damage to the target vessel or the stent. Attempts to treat obstructed side branches within stented segments can result in balloon entrapment, necessitating emergency bypass surgery.”
Thus, it would be desirable to have an expandable, steerable stent that could prevent obstruction and allow access to side branches, particularly in the field of interventional cardiology. It would be also desirable whether such a stent could be easy to install.
SUMMARY OF THE INVENTION
The present invention provides a longitudinally flexible permanent intravascular prosthesis, made of a plastically deformable metal alloy, for implantation in a body lumen and expandable from a contracted condition to an expanded condition, comprising: a plurality of adjacent rings independently expandable in the radial direction and interconnecting members between adjacent rings. The stent comprises two types of rings, each formed by a plurality of either hexagonal or inverted hexagonal elements. The two types of rings are arranged alternately in alignment over the longitudinal axis of the stent, so as to limit spacing between rings and to provide sufficient vessel wall coverage. Two interconnecting members are used to join adjacent rings, positioned at 0° and 180° in the transverse (cross-sectional) axis to provide flexibility between two rings in one plane; the next pair of interconnecting members is shifted 90° from the previous one to provide flexibility to the next attached ring in the perpendicular plane. Thus, this alternately interconnecting member disposition provides a relative flexibility along the longitudinal axis in either the contracted or the expanded state. This particular design has also the property to limit longitudinal expansion or contraction during radial deployment.
The stent is to be mounted and crimped over a balloon catheter, delivered in a contracted state within a body lumen such a patient s artery and expanded passively by the radial forces on the inflating balloon catheter.
A generally tubular stent according to the invention is formed from a deformable material and consists of a plurality of ring-shaped elements of the same radius joined to
Prebilic Paul B.
Swabey Ogilvy Renault
Symbiotech Medical, INC
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