Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
2000-10-13
2003-07-08
Lindsey, Rodney M. (Department: 3765)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001130, C623S001200
Reexamination Certificate
active
06589275
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a medical devices and more particularly to a stent having at least one tubular member which has a longitudinal direction and comprises several longitudinally consecutive cylindrical spring members interconnected by connecting members, the individual cylindrical spring members each being an endless wire of a zigzag configuration having arm sections extending between elbow sections, and the tubular member being self-expanding from a radially compressed state with a relatively small diameter to a state with a larger diameter.
Such a stent device is known from EP 0 480 667. The cylindrical spring members constructed from an endless wire of a zigzag configuration are commonly called Z-stents sold by Cook Incorporated, Bloomington, Ind. or Gianturco stents, and they have proved to be very applicable for percutaneous transluminal insertion in a vessel in a radially compressed state and subsequent release and self-expansion at the desired site in the vessel in the vascular system. These stents can be compressed to a very compact state with an advantageously small diameter during insertion while retaining a strong self-expanding effect. In the known stent device, two cylindrical spring members (Z-stents) may be arranged at either end of a graft, and they may be interconnected by means of a single rigid bar extending in parallel with the longitudinal direction of the tubular member from an elbow section on one stent to an elbow section on the other stent. This stent device is suitable for cutting off an aneurysm, the two stents being arranged in the healthy vessel on either side of the aneurysm and pressing the graft out towards the vessel wall so that the aneurysm is cut off from the vessel.
It is possible to join several stents into long stent devices, but it may be difficult to obtain sufficient flexibility in the stent device for the insertion along curved vessel paths to perform suitably without problems. In a stent device invented by Chuter, see EP 0 539 237, several Z-stents are joined by providing the elbow sections with eyes in which a bar with thickened end sections is inserted. The bar permits the eyes to be displaced away from each other until they are stopped by the end sections so that one stent can be turned in an angular direction in relation to the other. At long-term implantation, however, the device may perhaps become damaged due to wear as a consequence of stent movements caused by the persistent pulsating loadings occurring in blood vessels.
Other prior-art stent devices are balloon-expandable and have several stent bodies joined by connecting members. Such devices have no actual resilient effect and depend fully on inflation of the balloon to be dilated to the correct diameter for fastening to the vessel wall to become suitable. During a period of time, the vessel geometry may change and negatively affect the fastening of the rigid, balloon-expandable stent body.
As an example of such non-self-expandable stent device can be mentioned EP 0 335 341, which provides joining of several stents by means of connecting members extending approximately in the circumferential direction between elbow sections on two adjacent stents. In the expanded state, this device has no particular longitudinal rigidity.
As another example of a non-self-expanding stent device can be mentioned EP 0 712 614, in which a graft is fastened to the vessel at either end by means of a stent formed by wave-shaped annular wires, the apex areas of which are interconnected by means of connecting members extending in the longitudinal direction of the tubular member. The fastening of the connecting members to the apex areas and the wave shape of the annular wires prevent a force acting axially on an annular wire from being transferred to a more remote annular wire, and at the same time the problems are further increased because an axial compression leads to local expansion of the diameter of the tubular member. At long-term placing in a vessel, some of the annular wires may be displaced in the longitudinal direction of the vessel in relation to others of the annular wires, while the intermediate annular wire(s) is/are slowly deformed to a larger diameter, and the vessel wall locally yields and grows to a correspondingly larger diameter. Furthermore, the two stents are not interconnected, and thus one graft end may migrate in relation to the other graft end. Moreover, the balloon-expandable stents suffer from the disadvantage that the flow through the vessel is completely cut off while the balloon is inflated for expansion of the stent.
It is a problem of the known stent devices that they are either too yielding to radial pressure or too rigid to permit bending of the longitudinal axis of the tubular member. A suitable rigidity to radial pressure is of importance to obtain the primary effect of keeping the vessel lumen open, while bending flexibility is important during the transluminal insertion of the device, when the highest possible bending flexibility is desired to prevent frictional locking against the vessel wall in areas with strong vessel curves. The desire for high bending flexibility may also be relevant to the properties in the implanted state, where the device may inflict injuries on the vessel if the bending rigidity is too great.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a stent device that fulfils the desires of a suitable rigidity to radial pressure and a suitably high bending flexibility even when many consecutive stents are interconnected. It is further an object to provide a stent device that has a smaller tendency towards migration in the vessel over a long period following implantation than the prior-art devices.
In view thereof the stent device according to the present invention is characterized in that between the cylindrical spring member and the succeeding cylindrical spring member in the longitudinal direction there are at least three resilient connecting members firmly fastened to the arm sections of the cylindrical spring members at a distance from the elbow sections.
By fastening the resilient connecting members to the arm sections at positions at a distance from the elbow sections, the connecting members become longer, and the greater length reduces the rigidity of the connecting members to transverse deflection. When the tubular member is curved, the connecting members on the inside of the curve can more easily deflect with simultaneous reduction of the distance between the two nearest cylindrical spring members (in the following also called Z-stents). Mounting of the connecting member a distance inwards on the arm section provides the advantage that both the associated elbow sections become free to deflect in relation to the connecting member, which gives the Z-stent a more uniform deformation course in which the elbow section facing away from the connecting member is prevented from deflecting strongly radially outwards, which might otherwise result in an undesirable point load on the vessel wall.
It is important that the ends of the connecting members are firmly fastened to the arm sections. This reduces the long-term wear damage to the stent material, and the connection between the interconnected arm sections becomes rigid so that an axially directed pressure influence on a Z-stent is transmitted to the succeeding Z-stents via the pressure-transmitting connecting members. This latter effect is very important to reduce or prevent migration of stents after implantation. If a vessel wall area begins to yield at a stent in the stent body and to lose its grip thereon, for example as a consequence of a persistent pulsating blood pressure from only one side of the stent device, displacement of the stent in the longitudinal direction of the vessel is prevented by means of the pressure-rigid connecting members to the succeeding stent. Thus, the entire tubular member with the many joined stents assists in keeping all the stents in place, and longitudinal influences on the vessel wall are distributed
Ivancev Krasnodar
Rasmussen Erik Edelbo
Godlewski Richard J.
Lindsey Rodney M.
William Cook Eurpoe ApS
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