Intravascular endoprothesis

Abstract: The intravascular stent intended for implantation in a stenotic area or zone of obstruction of a blood vessel consists of a flat sheet (1) which is perforated to form a kind of a reticulated or lattice type structure with undeformable links (2) and made of malleable material. Said sheet (1) is temporarily rolled up and locked in a spiral with a relatively small diameter (d) on a deflated angioplasty balloon (6) mounted on the end of a catheter (7) and is held in said rolled-up state by a tie (8) laced into overlapping links. Once the device is in place in the restricted area of the blood vessel to be treated and after tie (8) is removed, the rolled sheet (1) is expanded to a desired diameter (D) by inflating balloon (6) and is then held in this expanded state by integrated holding flaps (5) which, after the balloon is deflated, extend through the links and engage the edges thereof under the pressure of the vessel.

Description: BACKGROUND OF THE INVENTION The present invention is directed to a system for treating stenosis or obstruction in a blood vessel or other body lumen according to the preamble of Claim 1. Such a system is known from DE-A-3640745. There are different kinds of intravascular endoprostheses, commonly called stents, which have the common characteristic of being presented into a patient's blood vessel or other body cavity or lumen in the shape of a cylindrical cuff, the wall of which forms a kind of lattice of deformable mesh in order to permit its diametrical expansion and contraction. This is seen in DE 3640745 (Strenecker), EPA 0221570 (Palmaz), U.S. Patent 4,740,207 (Kreamer), U.S. Patent 3,868,956, and Japanese Application 57-89859. In the first reference a lattice-like stent with a thread for holding it to a catheter is presented. The stent has in addition, end fastening means for locking it into an expanded diameter position. In the second reference an expandable stent is again disclosed, the stent being retained by a cather by fixation devices. The stent may expand to various diameters depending upon the environment in which it is placed. In U.S. Patent 4,740,207 (Kreamer), the stent is made of stainless steel sheet and appears originally in a rolled-up form of smaller diameter. After being introduced into the area of the vessel to be treated, it is expanded by means of an angioplasty balloon on the distal end of a catheter which is disposed on the interior of the rolled-up stent. The balloon is inflated with a fluid to the desired diameter which usually corresponds to the maximum expansion of which said balloon is capable. In another type, such as described in U.S. Patent 3,868,956, and Japanese Application 57-89859 published June 4, 1982, the stent is made of thermo-expandable material such as nitinol which is dilated by heat after being implanted. Finally, in a recently developed type, the stent is made of stainless steel wires of good elastic quality which are interwoven into a mesh, the diameter of which is selected to be slightly larger than the normal inner diameter of the vessel to be treated, so that it can exert a residual radial pressure on the arterial wall after being implanted. Before being introduced into the patient's blood vessel and while advancing the stent into the area of the blood vessel to be treated, the stent is reduced in diameter by stretching longitudinally and kept compressed on the catheter by a withdrawable sleeve. Once the device is implanted, the progressive withdrawal of said membrane permits the deployment of the stent in the vascular lumen. Of these three known kinds of stents, the second, the one made of thermo-expandable material, presents the great inconvenience because it is difficult to manipulate and implant, and its expansion is hard to control and not reliable. The above inconvenience does not exist in the stents made of stainless steel wire, but they still present a defect in that their expansion to a desired maximum diameter takes place at the cost of a proportional shortening of their length. This shortening, which follows the geometrical deformation of the lattice mesh being expanded in the transverse direction of the cylinder and reduced in the direction of its length, has the effect of making the accurate implantation of the device at its desired location very difficult. The structure of an open weave, stainless steel wire results in loose wires at the ends of the cylinder which can be traumatizing to the arterial tissue and can result in a fibrous change therein and the formation of an intraluminal scar which can be the beginning of another stenosis. The invention has the purpose of eliminating these inconveniences, particularly to provide a stent which can be easily and accurately placed in the desired arterial location with considerably less trauma than the prior art devices. SUMMARY OF THE INVENTION This invention is directed to a system for treating stenosis or obstruction in a blood vessel or other body lumen, according to Claim 1. The intravascular endoprosthesis or stent consists of a flat rectangular sheet intended to be rolled up into a spiral of small diameter around the catheter and held in the small diameter rolled-up state by a temporary holding means. It is then expanded to a greater diameter by unrolling, after the temporary holding means has been eliminated. In this manner, the transition from the wound-up condition with a relatively small diameter to the unwound, expanded form of large diameter takes place without a reduction in the length of the endoprosthesis or stent because this dimensional change is obtained by unrolling rather than by dimensional deformation of its wall. This results in its implantation being simple and considerably more exact in the desired area. Therefore, the use of a woven metal wire structure is no longer necessary to obtain the expansion and/or reduction of diameter of the stent and this allows for the possible use of a plain sheet for special applications. However, when an open reticulated structure is required, it is still possible to provide the flat sheet forming the stent with apertures arranged to give it the appearance of a lattice with regular non-deformable links. In both cases, whether plain or perforated sheet is used, the surface of the stent wall is smooth and the ends of the sheet are free of metal fibers which result in it being implanted with little or no trauma to the blood vessel. Additionally, the flat inner surface of the stent makes for a smooth flow of the fluid. These effects comply simply and reliably with the requirements set. The advantages provided by this invention will be shown more clearly in the following detailed description, especially concerning the potential use of non-thrombogenic and degradable materials instead of stainless steel. BRIEF DESCRIPTION OF THE DRAWINGS The enclosed exemplary drawings show one embodiment of the invention and one structural variation thereof. FIG. 1a is a schematic perspective view of a stent in a wound-up state embodying features of the invention; FIG. 1b is a perspective view of the stent shown in FIG. 1a in an unwound, expanded state; FIG. 2 is a transverse cross section of the embodiment shown in FIG. 1a; FIG. 3 is a transverse cross section of the embodiment shown in FIG. 1a in an expanded condition; FIG. 4 is a partial plan view of a structural detail of the wall of the stent shown in FIGS. 1-3; and FIG. 5 is a partial view of structural details of a variation in the wall of the stent. DETAILED DESCRIPTION OF THE INVENTION The stent shown in FIGS. 1 to 4 consists of a flat rectangular sheet of biocompatible, malleable material, temporarily rolled up to form a cylinder 1 as shown in FIG. 1a. This rolled sheet 1 has an array of apertures which give it the appearance of a lattice 2 with non-deformable square links, the two parallel sides 3 of which are oriented in the longitudinal direction of the thus-formed cylinder. One angle of the reticulated structure is detailed in FIG. 4. The covered edge 4 of the rolled sheet 1 is provided with holding flaps or fingers 5 which project outwardly from the longitudinal axis of the finished cylinder in order to engage links 2 of the latticework overlapping them. In the embodiment shown, flaps 5 are spaced two by two within links 2 in order to facilitate their engagement in the latter. In the left side of FIG. 1, and according to its section in FIG. 2, the stent is shown rolled up into a spiral having a relatively small diameter (d) over a deflated angioplasty balloon 6 which is mounted on the leading end of catheter 7; the two latter elements, the balloon and the catheter, being those commonly used for implantation of a stent. The means to temporarily hold the stent in its rolled-up state is a holding wire 8 which is laced through the links of the last two layers of the spiral formed by the rolled sheet 1, close to the outer overlapping edge 9. The wire 8 is designed so that it can be removed by pulling from the outside. In FIG. 1b, and according to its section shown in FIG. 3, the stent is shown in the expanded state with a larger diameter (D). It is expanded by inflating the angioplasty balloon 6 after pulling out the holding wire. For the sake of clarity, balloon 6 and catheter 7 are not shown in FIG. 1b. During inflation of the angioplasty balloon 6, the holding flaps 5 which are inclined in the direction opposite to that in which sheet 1 is unrolling slide from link to link without engaging the latter. When the angioplasty balloon 6 is deflated, the pressure of the blood vessel surrounding the stent has a tendency to re-roll the sheet 1 from which it is made. However, upon contraction of the sheet, holding flaps 5 which point in the direction of this re-rolling engage the first links of the lattice they encounter, hooking themselves into the edges of the latter, as can be seen in FIGS. 1b and 3. The stent is thus held firmly and cleanly without trauma in its expanded state in the vessel. Of course, the rollable width of sheet 1 and the size of the lattice links are a function of the maximum diameter to which the angioplasty balloon 6 can be inflated and should be calculated so that after the maximum inflation of the balloon, edge 4 bearing flaps 5 is still overlapped by at least the last row of links of the opposite overlapping edge 9. The design of the stent in a rolled sheet as described presents the advantage that it can easily be unrolled and rolled up on the angioplasty balloon 6 without modifying the latter. The square form of links 2 of the lattice provides great radial stability of the cylinder, and that is of interest for the treatment of straight-line vessels. But the square form is not limitative. Thus, for example, in order to facilitate the introduction of the endoprosthesis into an injured blood vessel, relatively high flexibility can be obtained with diamond-shaped links, such as links 10 of the variation shown in FIG. 5. In this alternative embodiment, the small axes (a) of the diamond-shaped links point in the longitudinal direction of the cylinder. The holding flaps intended to oppose the re-rolling tendencies of the stent under the pressure of the vessel after the angioplasty balloon 6 has been deflated are raised extensions 11 of the sharp angles of links 10 on the covered edge 4 of the sheet. The raised extensions 11 hook into the corresponding inner angles of the links which overlap them. The holes which provide the rolled sheet 1 with a lattice-like or reticulated structure can have any desired geometrical shape, depending on the particular effect sought and the mode of application of the stent, without eliminating the lattice-like appearance. The principle of expansion by unrolling provides the advantage of preventing any shortening of the stent, whatever the shape of the apertures. The drawing shows the favorable effect already indicated, as compared to the present state of the art, with an absence of free traumatizing wires at the ends of the stent cylinder, the latter presenting only geometrical elements, namely squares 2 and diamonds 10, the same effect being shared by all other shapes. The system for holding the stent in its expanded state with a large diameter (D), which is effected by the self-locking holding flaps 5 or 11, eliminates the requirement for material with good elastic characteristics. This allows for the advantageous use of malleable and non-thrombogenic materials and eventually resorbable materials. The holding system of the invention can also be used with a plain rolled sheet requiring only that perforations be provided for the flaps to engage in the overlapping edge of the sheet. Another advantage of this invention is that it permits the use of a stent formed of all kinds of materials such as metals and synthetic and ceramic materials, provided those materials are biocompatible. The use of synthetic materials allows for a wider choice of a coating formed of compatible products or materials which prevent cell proliferation inside the stent. In the case of a material having very good elastic characteristics it is possible to shape the cylindrical sheet 1 so that its expansion by unrolling is obtained by its own elasticity. The final shape of the expanded device has the appearance of an open cylinder. Upon implantation, the elasticity of the material thus opposes itself to the pressure of the vessel until the two forces are in balance.

Claims: A system for treating stenosis or obstruction in a blood vessel or other body lumen, said system comprising: a stent including a flat sheet (1) which may be rolled up into a spiral to a reduced diameter (d) around a catheter (7), the stent having overlapping inner and outer longitudinal sections (9, 4); an expander (6) to expand the stent by unrolling the sheet to a larger diameter (D) when it is positioned in the area of stenosis or obstruction such that there is an overlap of the longitudinal edges (4, 9) of said sheet; radially extending fingers (5)(11) provided on the inner overlapping longitudinal section (4) of the sheet (1) which interfit with corresponding means in the outer overlapping longitudinal section (9) of the sheet for locking the stent in the expanded condition. a removable device (8) to temporarily hold the stent (1) in its state of reduced diameter (d) on the catheter (7), a means to release the removable device (8) so that said expander (6) may expand the stent to the larger diameter (D) said system being characterized by: said sheet having apertures so arranged as to give it a reticulated, lattice-like appearance with undeformable links (2, 10); said removable device (8) consisting of a wire laced through said links (2, 10) of at least the last two layers of the spiral formed sheet (1) rolled upon itself; and said radially extending fingers (5, 11) interfitting through said links (2, 10) in the outer overlapping section (9) of the sheet for locking the stent in the expanded condition. The system according to claim 1 characterized by the fact that said stent is made of elastic material and that its expansion by unrolling is caused by its own elasticity. The system according to claim 1 characterized by the fact that said stent is made of malleable material and that its expansion by unrolling is obtained by inflating an interior angioplasty balloon (6) mounted on and around the catheter, said balloon (6) being said expander. The system according to any one of the preceding claims characterized by the fact that said radially extending fingers (5, 11) consist of a selected number of raised flaps arranged along the covered longitudinal edge (4) of the cylinder in the expanded state, which point in a radially outward direction to the latter and which extend through the first of the links (2, 10) they encounter in the overlapping sheet (1) when the angioplasty balloon is deflated. The system according to any one of the preceding claims characterized by the fact that the links of the rolled sheet are diamond shaped (10) with the small axis (a) thereto pointing in the longitudinal direction of the stent. The system according to any one of claims 1 through 5 characterized by the fact that the links of the rolled sheet are square-shaped (2) and the two parallel sides (3) thereof are oriented in the longitudinal direction of the stent.

Inventors: SIGWART ULRICH, SIGWART, ULRICH
Applicants: ADVANCED CARDIOVASCULAR SYSTEM, ADVANCED CARDIOVASCULAR SYSTEMS, INC.
Application year: 1990
Main classification: A61F2
IPC codes: A61F2