Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
2002-05-07
2004-11-09
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001150
Reexamination Certificate
active
06814750
ABSTRACT:
TECHNICAL FIELD
The invention pertains to implantable medical devices and, in particular, to a self-expanding prosthetic device for sustaining a vessel or hollow organ lumen.
BACKGROUND OF THE INVENTION
Various diseases of blood vessels or hollow organs cause a stenosis or complete obturation (occlusion) of their lumen, which results in a decrease or complete loss of their functional attributes. The wide spread of diseases of this kind demands an elaboration of quite new methods of medical treatment.
Devices for sustaining a blood vessel or hollow organ lumen typically have a tubular shaped frame body which is introduced in the vessel or hollow organ and fixed in the necessary place to sustain its lumen. The problem of designing such devices has already a twenty year history. Nevertheless, a universally reliable device satisfying all necessary requirements has as yet not been created.
A device for sustaining a vessel or hollow organ lumen should satisfy the following requirements:
effectively fulfill the function of recovering and sustaining the vessel or hollow organ lumen;
have a reliable and simple delivery control system;
have a wide range of sizes from 3 to 50 mm and more;
have biological compatibility with organism tissues;
be useable in different anatomical areas of vessels and hollow organs;
cause minimum trauma during and after operation; and
have a stiff construction to counteract in situ external compression forces.
An attempt to create a device compatible with tissues was undertaken in USSR Patent No. 1237201, dated Feb. 15, 1986. This known device for sustaining the vessel or hollow organ lumen represents a wire frame having a tubular shaped body. The frame is formed by a wire element, having round or square cross-section and arranged in a cylindrical helical line. The frame has a shape of a helical cylindrical spring and it is furnished with fixing elements to keep it on the device for delivery into the vessel or hollow organ. Each fixing element is made in the form of a loop, one of which is formed at the initial section of the wire element, and the other at its final section. The facility for delivering the above device to a vessel or hollow organ comprises an introducer in the form of an X-ray contrast tube and another X-ray contrast tube of a lesser diameter, on whose surface the device is secured by means of a connecting element. The material of the frame wire is an alloy of the titanium-nickel system, which is biologically compatible with the organism tissues.
The device known from the USSR patent is reliable in use. However, it is expedient to use the known device in vessels or hollow organs having a diameter of not more than 8 mm, which is conditioned by the value of the ultimate strain of the frame material limited by 8% (the so-called strain limit of shape memory effect), as well as by the demand of minimizing the puncture hole (hole in vessel through which the device is introduced into an organ). Furthermore, the device can withstand only limited external compression forces.
The use of the known device in vessels and hollow organs with a diameter exceeding 8 mm, and without exceeding the ultimate strain of the frame material, would demand a decrease of the thickness of the wire frame elements, which would result in a further loss of stiffness of the frame. Alternatively, it would be necessary to increase the diameter of the puncture hole, which in turn would cause intolerable trauma to the vascular or hollow organ walls. Thus, the mentioned construction of the device for sustaining a vessel or hollow organ lumen is applicable only for vessels or hollow organs whose diameter is less than 8 mm, which sharply narrows the field of its application.
The execution of the function of effectively recovering and sustaining a vessel or hollow organ lumen by the described device demands an arrangement of the coils of the wire frame with a minimum lead to prevent germination of atherosclerotic patches, or counteract the occlusion. However, the making of the frame with a minimum lead between coils results in a loss of its stiffness in the vessel or hollow organ. As a result, external compression forces effect a change of the frame's arrangement in the vessel, i.e., the frame's longitudinal axis gets arranged at an angle to the vessel axis, or in an increase of the lead between coils. Both in the first and second cases, the frame stops functioning, and the vessel or hollow organ lumen gets reduced.
As it was described above, the frame is furnished with fixing elements on the front and rear ends. The fixing elements are made in the form of loops lying in the plane perpendicular to the frame axis in such a manner that the partial overlapping of the frame lumen occurs. As a result, turbulent flows in the blood current are formed and facilitate the appearance of various complications such as atherosclerotic formations.
The described facility of frame delivery is reliable enough in the process of introduction of the frame to the affected area. However, at installation of the frame with the aid of this facility one of the fixing loops gets released. The frame, being constrained in a reduced diameter until this moment, gets released and uncoils in the direction opposite to the direction of coiling at its fixing, acquiring its initial shape. In the process of uncoiling, which is uncontrolled, trauma to the vascular or hollow organ walls may occur, which has an unfavorable affect on the result of operation. In addition, the frame can occupy an arbitrary position in the vessel that is uncontrolled by the surgeon.
The described frame has the shape of a helical cylindrical spring. If we examine the frame section in a plane perpendicular to the frame axis and passing through the coil surface, it is seen that the frame coil located in the plane has a break, which decreases the frame stiffness under the effect of radially acting forces.
Another device for sustaining a vessel or hollow organ lumen is known (Ann Radiol, 1988, 31, n.2, 100-103), and it has a tubular shaped wire frame formed by a wire element, which in development represents a saw-tooth line. In order to permit a change in the stiffness of the frame, the latter is bound at the tops by a caprone thread.
The branches of the wire element are arranged along the longitudinal axis of the tubular frame, which provides for a constancy of the frame's linear dimensions at the delivery and installation of the frame in the affected place of the vessel or hollow organ. To fix the frame in the vascular or hollow organ walls, provision is made for fixing elements in the form of hooks.
In the described construction, use is made of materials whose ultimate elastic strain makes up tenths of a percent. The delivery system represents an X-ray contrast tube accommodating a pusher, which is a piston with a rod. For transportation (delivery), the device is placed in the X-ray contrast tube, and by means of the rod the surgeon acts upon the piston interacting with the device.
The described device has found a wide application for sustaining the lumen of the affected areas of veins, in which there are no atherosclerotic processes. The use of this device in arterial vessels is hardly possible because of the large distances between the wire elements, which may result in germination of atherosclerotic patches and, as a consequence, in an ineffective use of this device.
The latter known device is used for sustaining the lumen of the affected areas of veins whose diameter is within 15 to 30 mm. In this case, a wire of a large diameter is used to impart the necessary stiffness to the construction. If this device were to be used in smaller vessels or hollow organs having a diameter from 3 to 15 mm it would be necessary to decrease the wire thickness (diameter). However, the loss in diameter thickness may hardly provide an effective means for sustaining the lumen.
Due to the arrangement of the wire branches in the peripheral direction of the tubular frame body, the given construction is stable and has a high stiffness in the axial direc
Hansen Palle
Kadnikov Andrej A.
Kavteladze Zaza A.
Kirts Beth Ann
Korshok Aleksandr P.
Godlewski Richard J.
Snow Bruce
William Cook Europe A/S
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