Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Reexamination Certificate
2001-08-13
2003-11-25
O'Connor, Cary E. (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
C623S001300, C623S001350
Reexamination Certificate
active
06652572
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to endovascular graft systems for the repair of aneurysms. In particular, this invention relates to an endovascular graft system for use in repairing abdominal aortic aneurysms.
BACKGROUND OF THE INVENTION
Aortic aneurysms represent a significant medical problem for the general population. Aneurysms within the aorta presently affect between two and seven percent of the general population and the rate of incidence appears to be increasing. This form of vascular disease is characterized by a degradation in the arterial wall in which the wall weakens and balloons outward by thinning. If untreated, the aneurysm can rupture resulting in death within a short time.
The traditional treatment for patients with an abdominal aortic aneurysm is surgical repair. This is an extensive operation involving transperitoneal or retroperitoneal dissection of the aorta and replacement of the aneurysm with an artificial artery known as a prosthetic graft. This procedure requires exposure of the aorta through an abdominal incision extending from the lower border from the breast bone down to the pubic bone. The aorta is clamped both above and below the aneurysm so that the aneurysm can be opened and the prosthetic graft of approximately the same size as the aorta is sutured in place. Blood flow is then re-established through the prosthetic graft. The operation requires a general anesthesia with a breathing tube, extensive intensive care unit monitoring in the immediate post-operative period along with blood transfusions and stomach and bladder tubes. All of this imposes stress on the cardiovascular system. This is a high-risk surgical procedure with well-recognized morbidity and mortality.
More recently, significantly less invasive clinical approaches to aneurysm repair known as endovascular grafting have been proposed. (See, Parodi, J. C., et al. “Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,” 5 Annals of Vascular Surgery, 491 (1991)). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft in the endoluminal position (within the lumen of the artery). By this method, the graft is attached to the internal surface of an arterial wall by means of attachment devices such as expandable stents, one above the aneurysm and a second below the aneurysm.
Although endovascular grafting represents a desirable improvement over traditional surgical repair, current endovascular graft systems suffer from certain deficiencies. For example, current endovascular graft systems typically are unsuitable for use in an aneurysm which is torturous. Aneurysms in the aorta create tortuosity as they grow. Aneurysms grow both in diameter and length, thus “pushing” the adjacent upper and lower portions of the arteries upward and downward, respectively. Since the aorta is relatively “fixed” at the renal arteries, the portion of the aorta below and near the renal arteries becomes bent and curved in order to accommodate the added length. A similar phenomenon occurs below the aneurysm in the iliac arteries, leading to tortuous iliacs. As many as 20% of aortic aneurysms may have so much tortuosity that they are unable to be fitted with an endovascular graft of this kind. Such systems are unable to conform to the curved walls of the vasculature due to the tortuosity caused by the growing aneurysm.
A specific problem is the “angulation” or bend in the neck of the aorta, where it meets the upper part of the aneurysm. This angulation may result in several problems which limit the effectiveness of traditional endovascular graft systems which do not have designs that conform to the tortuosity and angulation above the aneurysm. First, since these systems are typically anchored above the aneurysm with a stent, a portion of the stent may extend into the blood flow path, creating turbulence which may result in blood clotting. It is well-known that in coronary vessels, stents used to treat constrictive lesions must be well apposed to the wall of the vessel to prevent the possibility of thrombosis. Second, a non-conforming upper stent will not place the upper end of the graft in good apposition to the aortic wall, making it difficult to obtain a good seal with a conventional endovascular graft system. Such is illustrated in
FIG. 2
, showing a generic endovascular graft attached to a conventional non-conforming expanded metal stent in the neck of a tortuous aortic neck. Since this conventional stent will not conform to the tortuosity of the aorta, an upper edge
1
of the stent extends into the blood flow path increasing the chance of thrombosis. Further, a lower edge
2
is not apposed to the wall of the aorta so that the graft material
3
affixed to it does not properly seal. A third problem with non-conforming attachment systems is that once placed in tortuous or angulated aneurysmal anatomy, they are unstable and can “pop-out” of position. The attachment system shown in
FIG. 2
is an example of an unstable attachment system. Conventional endovascular graft systems having an attachment system intended to project across and above the renal artery ostia also pose a different problem since the attachment system obstructs the renal arteries making it difficult, if not impossible, to effect a repair on a renal artery once the stent is in place.
Thus, a need exists for a prosthetic endovascular graft system which will permit stable conformance to bends within an aneurysm, while providing a good seal to the vasculature.
SUMMARY OF THE INVENTION
This invention is an endovascular graft system comprising an attachment member which conforms to the contours of the vessel adjacent an aneurysm, permitting a good seal and robust anchoring of the graft with the vasculature. The attachment member is a stent-like structure which will be referred to herein either as an attachment member, an aortic attachment member or a stent.
In one aspect, this invention is an aortic attachment member capable of expanding from a first delivery configuration to a second deployed configuration for placement in a vessel of a patient's vascular system, the attachment member comprising a cranial zone having a first radial strength, a caudal zone having a second radial strength, and an intermediate zone comprising multiple longitudinal struts located between the cranial and caudal zones, the intermediate zone having a third radial strength. The cranial and caudal zones are separated by and joined by the longitudinal struts. The third radial strength can be lower than the first or second radial strengths. The cross-sectional area of the longitudinal struts is preferably smaller than the cross-sectional area of the material making up the caudal or cranial zones. Preferably, the cross-sectional area is reduced by reducing both the strut width and thickness. Preferably, the caudal and cranial zones have struts patterned in a Z-shape. Alternatively, the cranial zone may have struts shaped in a diamond configuration. The radial strength of the caudal and cranial zones may be approximately equal. In a preferred embodiment, the caudal zone further comprises barbs to assist in anchoring the attachment member. The cranial zone may also comprise barbs to further assist in anchoring the attachment member.
In another aspect, this invention is an endovascular graft system capable of expanding from a first delivery configuration to a second deployed configuration for placement in a vessel of a patient's vascular system. The endovascular graft system comprises an aortic attachment member having a cranial zone and a caudal zone, each having a first radial strength, and an intermediate zone having multiple joining longitudinal struts located between and connecting the cranial and caudal zones, the intermediate zone having a second radial strength which is less than the first radial strength, the cranial and caudal zones being formed from a self-expanding material. The system further includes a conduit formed of a graft material affixed to the caudal zone of the attachment member.
Drontle John R.
Keith Peter T.
Kugler Chad J.
Cordis Corporation
O'Connor Cary E.
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