Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Bifurcated
Reexamination Certificate
2000-10-06
2004-05-04
Isabella, David J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Bifurcated
C623S001150, C623S001110, C623S001230, C606S194000
Reexamination Certificate
active
06730119
ABSTRACT:
BACKGROUND OF THE INVENTION
A stent is used to provide a prosthetic intraluninal wall, e.g., in the case of a stenosis to provide an unobstructed conduit for blood through the area of the stenosis. An endoluminal prosthesis comprises a stent which carries a prosthetic graft layer of fabric or other material and is used in the instant invention to treat an aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of distal embolization or rupture of the distended wall of the aneurysm.
Typically, a stent or endoluminal prosthesis is implanted in a blood vessel at the site of the aneurysm by minimally invasive techniques in which the stent is compressed along its long axis and is delivered by catheter to the site where it is required. A cut down technique in which the blood vessel to be used as conduit is exposed by minor surgical means. Various catheters or sheaths are inserted through small openings made in the conduit blood vessel. The stent is directed into the correct position and the catheter is withdrawn. The catheter's withdrawal allows the stent to re-expand to a predetermined diameter in the vessel.
Aneurysms in vessel walls at or near bifurcations pose additional problems because the intraluminal support provided by the stent must extend from the main vessel into both branches of the bifurcation. This requirement complicates the procedures for introducing the catheters for positioning the stent(s), as well as insertion and placement of the stent components to conform to the configuration of the bifurcation. Stent branches must be joined with the main stent in the correct configuration and without leakage at any juncture. It is also desirable to conduct additional procedures to thrombose the material in the aneurysm cavity and to ensure re-endotheliazation of the stent walls.
A number of prostheses are known for treating the formation of aneurysms in bifurcated body lumens. A typical previously practiced bifurcated prosthesis comprises a hollow tubular graft having a main section and first and second legs or extensions. For example, in open surgery to repair an abdominal, aortic aneurysm, the main section of the prosthesis is sutured to the aorta below the renal arteries, and the first and second branches of the graft are sutured to the corresponding iliac arteries. Surgical implantation of known prostheses poses a major risk of mortality and morbidity, and open surgical implantation frequently cannot be performed on patients in poor health.
Even if surgery is deemed of acceptable risk, the cumulative mortality of patients with spontaneous rupture of abdominal aortic aneurysms is approximately seventy-five percent (75%), despite emergency surgical treatment. The likelihood of rupture is under five percent in aneurysms less than 5 cm in diameter; however, in aneurysms larger than this, surgery is required to reduce the risk of spontaneous rupture and hemorrhage. The mortality of such surgery ranges between four and eight percent (4-8%). The highest risk occurs in patients greater than sixty-nine (69) years of age with chronic obstructive pulmonary disease, left ventricular hypertrophy or a history of cerebral vascular disease. In an attempt to lower the mortality of aneurysm repair, percutaneous treatment of aortic aneurysms has been attempted. Attempts using covered stent grafts to treat the aneurysm have been approximately eighty-five percent (85%) successful. Some patients undergoing this procedure require conversion in open surgical operations. Other serious complications occur in approximately ten percent (10%) of the patients so treated. Many of these patients develop a post implantation syndrome consisting of leukocytosis and elevated C-reactive protein levels. Other difficulties with covered stent grafts include difficulty in placement of the grafts, potential for obliteration of branch vessel ostia with the stent graft which in turn might compromise flow to lumbar or visceral arteries.
In attempts to overcome the drawbacks associated with surgically implanted grafts, a number of methods and devices have been developed to implant such grafts percutaneously. Komberg, U.S. Pat. No. 4,562,596 describes a bifurcated graft for intraluminal, percutaneous implantation. The graft comprises a hollow tubular main portion connected to a first leg and a shorter second leg. The main portion includes a plurality of barbs that impale the healthy tissue of the aorta to maintain the graft in position. Such grafts have a drawback in their inability to provide a fluid tight seal at the ends of the graft. Without adequate sealing, bypass flow paths (endo leaks) may develop between the graft and the aneurysm wall, which may eventually cause rupture of the aneurysm.
Chuter, U.S. Pat. No. 5,387,235 describes a bifurcated graft having a main portion connected to first and second legs. The main portion, first and second legs each include a barbed self-expanding anchor ring that engages healthy tissue in either the aorta or the iliac arteries to retain the graft in position. These types of devices have a drawback that the diameter of the delivery system must be large enough to accommodate the combined diameters of each of the anchor deployment mechanisms. Thus, it may not be possible to use the device taught in the Chuter '235 patent in patients having small diameter femoral or iliac arteries.
Yet another drawback of previously known bifurcated grafts is the difficulty encountered in pulling the legs of the graft into the branch vessels. While a number of methods have been described in the prior art for accomplishing this task, these methods generally involve snaring a guide wire, either in the iliac artery or in the abdominal aorta, to place a guide wire for deploying the leg of the graft in the contralateral branch.
Shmulewitz, U.S. Pat. No. 5,961,548 describes a bifurcated graft, and methods of implantation that provide positive sealing between the graft and healthy tissue proximal and distal of the graft site. Shmulewitz further describes methods of implantation of a bifurcated graft that enable smaller diameter delivery systems to be employed than are taught in the prior art as well as enhancement of the ease with which the legs of the graft may be deployed in the branches of a bifurcated body lumen.
The drawback presented in the graft and methods taught in Shmulewitz '548 is that the stent graft is covered, which has four major problems:
(1) Covered stent grafts are 22 F or greater and must be inserted by surgical cutdown due to the obligate nature of increased bulkiness of a stent covering combined with the metallic substrate being incompressible and, therefore, unable to be compressed below 22 F.
(2) Covering the stent graft completely eliminates blood flow to the side branches, such as the lumbars from the central lumen. This elimination of blood flow has produced paraplegia in animal models. However, retrograde collateral flow from the lumbars is not prevented. This leads to endo leaks with the potential for aneurysm expansion in humans who have been implanted with similar devices.
(3) In patients with short cuffs of normal aorta below the renal arteries, completely covered stent grafts are not able to achieve secure placement and are therefore prone to dislodgment and axial migration with subsequent endo leaking and aneurysm expansion and rupture.
(4) The second covered stent graft is designed to dock minimally within the first. There are several other similar designs, which have a very high incidence of left iliac side branch graft dissociation in time due to healing and/or expansion of the aneurysm. This disassociation of the left iliac side branch portion from the main graft results in leakage of blood into the aneurysm cavity, further expansion of the aneurysm and late, often fatal, aneurysm rupture.
Rhodes, U.S. Pat. No. 5,843,160, describes expandable, intraluminal prosthesthes for the treatment of aneurysmal or occlusive disease at a bifurcation of a vessel, duct or lumen. Each prosthesis taught by Rhodes includes three ex
Board of Regents of the University of Texas System
Chattopadhyay Urmi
Isabella David J.
Skolnick Malcolm H.
Wisner Mark R.
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