Expandable bifurcated stent

Abstract: An expandable bifurcated stent comprising a proximal end and a distal end in communication with one another, the proximal end comprising a primary passageway and the distal end comprising a pair of secondary passageways, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent, said primary passageway being connected to each of the secondary passageways at a reinforced intersection point.

Description: TECHNICAL FIELD The present invention relates to an expandable bifurcated stent. BACKGROUND ART Stents are generally known. Indeed, the term "stent" has been used interchangeably with terms such as "intraluminal vascular graft" and "expansible prosthesis". As used throughout this specification the term "stent" is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g. a lumen or artery). In the past six to eight years, the use of stents has attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term "body passageway" is intended to have a broad meaning and encompasses any duct (e.g. natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like. Initial stents were self-expanding, spring-like devices which were inserted in the body passageway in a contracted state. When released, the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the body passageway. Such stents were known in the art as the Wallstent™. The self-expanding stents were found by some investigators to be deficient since, when deployed, they could place undue, permanent stress on the walls of the body passageway. This lead to the development of various stents which were controllably expandable at the target body passageway so that only sufficient force to maintain the patency of the body passageway was applied in expanding the stent. Generally, in these later systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (the target area of the body passageway can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded thereby expanding the stent so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to maintain the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing). A stent which has gained some notoriety in the art is known as the Palmaz-Schatz™ Balloon Expandable Stent (hereinafter referred to as "the Palmaz-Schatz stent"). This stent is discussed in a number of patents including United States patents 4,733,665, 4,739,762, 5,102,417 and 5,316,023. Another stent which has gained some notoriety in the art is known as Gianturco-Roubin Flex-Stent™ (hereinafter referred to as "the Gianturco-Roubin stent"). This stent is discussed in a number of patents including United States patents 4,800,882, 4,907,336 and 5,041,126, the contents of each of which are hereby incorporated by reference. Other types of stents are disclosed in the following patents: United States patent 5,035,706 (Gianturco et al.), United States patent 5,037,392 (Hillstead), United States patent 5,147,385 (Beck et al.), United States patent 5,282,824 (Gianturco), Canadian patent 1,239,755 (Wallsten), and Canadian patent 1,245,527 (Gianturco et al.). All of the stents described in the above-identified patents share the common design of being mono-tubular and thus, are best suited to be delivered and implanted in-line in the body passageway. These known stents are inappropriate for use in a bifurcated body passageway (e.g. a body passageway comprising a parent passageway that splits into a pair of passageways). Further, these stents are inappropriate for use in a body passageway having side branches since: (i) accurate placement of the stent substantially increases the risk to the patient, (ii) the risk of passageway closure in the side branches is increased, and (iii) the side branches will be substantially inaccessible. Indeed the Physician Guide published in support of the Palmaz-Schatz stent states on page 32 (the contents of which are hereby incorporated by reference): " ... no attempt should be made following placement of a PALMAZ-SCHATZ stent to access the side branch with a guide wire or a balloon, as such attempts may result in additional damage to the target vessel or the stent. Attempts to treat obstructed side branches within stented segments can result in balloon entrapment, necessitating emergency bypass surgery." Thus, when installed, the Palmaz-Schatz stent admittedly shields side branches emanating from the target area of the body passageway effectively permanently. This can be problematic since the only way to treat blockage or other problems associated with the side branches is to perform the type of surgery which installation of the stent was intended to avoid. This contraindication for conventional mono-tubular stents is corroborated by a number of investigators. See, for example, the following: 1. Interventional Cardiovascular Medicine: Principles and Practice (1994); Publisher: Churchill Livingstone Inc.; pages 221-223 (Ohman et al.), 487-488 (Labinaz et al.), 667-668 (Bashore et al.) and 897 (Bailey et al.), including references cited therein; 2. Gianturco-Roubin Flex-Stent™ Coronary Stent: Physician's Guide; page 2, Paragraph 3 under WARNINGS; 3. Circulation , Vol. 83, No. 1, January 1991 (Schatz et al.); entitled "Clinical Experience With the Palmaz-Schatz Coronary Stent"; pages 148-161 at page 149; and 4. American Heart Journal, Vol. 127, No. 2, February 1994 (Eeckhout et al.); entitled "Complications and follow-up after intracoronary stenting: Critical analysis of a 6-year single-center experience"; pages 262-272 at page 263. Further, some investigators have attempted to install individual stents in each branch of the bifurcated body passageway. However, this approach is fraught with at least two significant problems. First, implantation of three individual stents, together with the expansive forces generated upon implantation results in subjecting the central walls of the bifurcated body passageway to undue stress which may lead to post-procedural complications. Second, since the central walls of the bifurcated body passageway are not supported by the individual stents, this area of the passageway is left substantially unprotected and susceptible to blockage. One particular problem area with bifurcated body passageways is the occurrence of bifurcation lesions within the coronary circulation. Generally, these legions may be classified as follows: Type Characteristic A Prebranch stenosis not involving the ostium of the side branch; B Postbranch stenosis of the parent vessel not involving the origin of the side branch; C Stenosis encompassing the side branch but not involving the ostium; D Stenosis involving the parent vessel and ostium of the side branch; E Stenosis involving the ostium of the side branch only; and F Stenosis discretely involving the parent vessel and ostium of the side branch. See Atlas of Interventional Cardiology (Popma et al.), 1994, pages 77-79. The presence of bifurcation lesions is predictive of increased procedural complications including acute vessel closure. Detailed classification of other bifurcated body passageways is relatively undeveloped given the lack of non-surgical treatment approaches. A bifurcated stent as in the preamble of claim 1 is known from document US-A-4 994 071. It would be desirable to have an improved expandable bifurcated stent since this would be useful in treating aneurysms, blockages and other ailments. It would also be desirable if such a stent was relatively easy to install. DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a novel expandable bifurcated stent which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art. Accordingly, the present invention provides an expandable bifurcated stent as specified in claim 1. In another of its aspects, the present invention provides an expandable stent as in the dependent claims. Thus, the present invention relates to the provision of an expandable bifurcated stent. As used throughout this specification, the term "bifurcated stent" is intended to have a broad meaning and encompasses any stent having a primary passageway to which is connected at least two secondary passageways. Thus, trifurcated stents are encompassed herein. Further, one of the secondary passageways can be a continuation of the primary passageway with the result that the other secondary passageway is essentially a side branch to the primary passageway. The Applicants have also discovered that the use of a specific repeating pattern in a porous stent is particularly advantageous. Generally, the repeating pattern is a polygon having a pair of side walls substantially parallel to the longitudinal axis of the stent passageway in question, a first concave-shaped wall and a second convex-shaped wall connecting the side walls, the first wall and the second wall being equidistant along an axis which is parallel to the longitudinal axis of the stent passageway in question. As used throughout this specification, the terms "concave-shaped" and "convex-shaped" are intended to have a broad meaning and a shape having apex. Thus, the apex can be the top of a smooth curve. Alternatively, the apex can be a point or top of a segmented line. The important point is that the apex of the concave-shaped wall is directed into the polygon whereas the apex of the convex-shaped wall is directed away from the polygon. The advantages associated with the use of such a repeating pattern include the following: 1. The stent is controllably expandable; 2. The stent is flexible and thus, can be deliver via and/or implanted in curved body passageways; and 3. Access to side branches is maintained, unlike the Palmaz-Schatz stent described hereinabove. The stent of the present invention can further comprise coating material therein. The coating material can be one or more of a biologically inert material (i.e. to reduce the thrombogenicity of the stent), a medicinal composition which leaches in the wall of the body passageway after implantation (e.g. to provide anticoagulant action and the like). BRIEF DESCRIPTION OF THE DRAWING Embodiments of the present invention will be described with reference to the accompanying drawings wherein like numerals designate like parts and in which: Figure 1 illustrates a perspective view of a bifurcated stent in a first, contracted position; Figure 2 illustrates an enlarged perspective view of the bifurcated stent of Figure 1 in a second, expanded position; Figure 3 illustrates an expanded two-dimensional representation of the repeating patterns present in the stents illustrated in Figure 1-2; Figure 4 illustrates a cross-section of a bifurcated body passageway into which the bifurcated stent of Figure 1 is being delivered; Figure 5 illustrates a cross-section of a bifurcated body passageway in which the bifurcated stent of Figure 1 is positioned in a first, contracted position; and Figure 6 illustrates a cross-section of a bifurcated body passageway in which the bifurcated stent of Figure 1 positioned in a second, expanded position. BEST MODE FOR CARRYING OUT THE INVENTION With reference to Figure 1, there is illustrated a stent 10. Stent 10 comprises a proximal end 15 and a distal end 20. Proximal end 15 comprises a primary passageway 25. Distal end 20 comprises a pair of secondary passageways 30,35. Secondary passageways 30,35 are connected to primary passageway 25 at an intersection point 40. As will be appreciated by those of skill in the art, the length of primary passageway 25 and secondary passageways 30,35 is particularly restricted and is select to optimize both deliverability of the stent (shorten) and vessel coverage (lengthen). With reference to Figure 2, there is illustrated an enlarged perspective view of the bifurcated stent illustrated in Figure 1 in a second, expanded position. As illustrated, secondary passageways 30,35 are split apart more than they are when the bifurcated stent is in the first, contracted position (Figure 1). As illustrated, primary passageway 25 and secondary passageways 30,35 are porous. The porosity of these passageways is defined by a plurality of intersecting members 45. Intersecting members 45 define a first repeating pattern designated A and a second repeating pattern designated B in Figure 2. The nature of first repeating pattern A and second repeating pattern B will be discussed in more detail hereinbelow with reference to Figure 3. With reference to Figure 3, there is illustrated an enlarged two-dimensional representation of first repeating pattern A and second repeating pattern B. These repeating patterns are illustrated with respect to a longitudinal axis 50 which is representative of the longitudinal axis which would be present in each of primary passageway 25, secondary passageways 30,35 discussed above with reference to Figures 1 and 2. As illustrated, repeating pattern A is a polygon comprising a pair of side walls 55,60. Side walls 55.60 are substantially parallel to longitudinal axis 50. Side walls 55.60 are connected by a concave-shaped wall 65 and a convex-shaped wall 70. As illustrated, concave-shaped wall 65 is made up of a trio of segments 66,67,68. In the illustrated embodiment, segment 67 is the apex of concave-shaped wall 65. Convex-shaped wall 70 is made up of a trio of segments 71,72,73. In the illustrated embodiment, segment 72 is the apex of convex-shaped wall 70. It will be appreciated by those of skill in the art that the provision of first repeating pattern A, as illustrated, necessarily defines and provides for second repeating pattern B. It will also be appreciated by those of skill in the art that second repeating pattern B is a mirror image of first repeating pattern A taken along an axis (not shown) substantially normal to longitude general axis 50. It will be further appreciated by those of skill in the art that the shape of concave-shaped wall 65 and/or convex-shaped wall 70 can be modified without departing from the function and performance of the stent. For example, the trio of segments can be replaced by a suitably curved or arcuate wall. Alternatively, more than three segments can be used to define concave-shaped wall 65 and/or convex-shaped wall 70. It will be further appreciated by those of skill in the art that various walls of first repeating pattern A and second repeating pattern B may be omitted (and even desired) at selected points along the body of the stent within the scope of the appended claims. For example, it is possible to omit one or both of side walls 55,60 at selected points along the body of the stent with a view to improving the longitudinal flexibility of the stent. Further, it is possible to omit one or more of segments 71,72,73 at selected points along the body of the stent with a view to improving the lateral flexibility of the stent. With further reference to Figure 2, the intersection point 40 is an annular arrangement of second repeating pattern B in which first, a reinforcing bar 75 has been disposed between side walls 55,60 to connect segments 67 and 72 and second, a reinforcing segment 80 is provided midway between and has a similar shape to concave-shaped wall 65 and convex-shaped wall 70. These two areas of modification serve to reinforce intersection point 40. This facilitates alleviation of stresses under which this area of stent 10 is placed when it is expanded. It will of course be appreciated by those of skill in the art that modifications can be made to the design of intersection point 40 within the scope of the appended claims. For example, the flexibility of stent 10 at intersection point 40 can be modified by judicious addition or omission of further reinforcing bars 75 and/or reinforcing segments 80. With reference to Figures 4 and 5, there is illustrated a bifurcated body passageway 150 comprised of a proximal passageway 155 and a pair of distal passageways 160,165. As illustrated, bifurcated body passageway 150 comprises a Type "D" Bifurcation lesion having characteristic blockages 170,175,180. Stent 10 is delivered to bifurcated body passageway 150 in the following manner. Initially, a pair of guidewires 185,190 are inserted into proximal passageway 155 such that guidewire 185 enters distal passageway 160 and guidewire 190 enters distal passageway 165. The manner by which the guidewires are inserted is conventional and within the purview of a person skilled in the art. As illustrated, stent 10 is positioned in association with a pair of catheters 195,200 (for clarity, the interior of stent 10 is not shown). Catheter 195 has associated with it a balloon 205. Catheter 200 has associated with it a balloon 210. Balloons 205,210 substantially fill primary passageway 25 of stent 10. Balloon 205 substantially fills secondary passageway 30 of stent 10. Balloon 210 substantially fills secondary passageway 35 of stent 10. The stent/catheter/balloon combination is delivered through proximal passageway 155 with the aid of guidewires 185,190. As the stent/catheter/balloon combination approaches distal passageways 160,165, predisposition of guidewires 185,190 serves to separate secondary passageways 30,35 to be disposed in distal passageways 160,165, respectively. Thus, as illustrated in Figure 5, stent 10 is positioned in place. Once stent 10 is in position, balloons 205,210 are expanded resulting in implantation of stent 10 in the corresponding interior surfaces of proximal passageway 155 and distal passageways 160,165. Upon implantation of stent 10, balloons 205,210 are collapsed. Thereafter, catheters 195,200 and guidewires 185,190 have been removed leaving the implanted stent 10 shown in Figure 6. As illustrated in Figure 6, blockages 170,175,180 are bulged radially outwardly in combination with the appropriate portions of proximal passageway 155 and distal passageways 160,165 resulting in a reduction in the overall blockage in bifurcated body passage 150. It will be apparent to those of skill in the art that implantation of stent 10 can be accomplished by various other means. For example, it is contemplated that it is possible to substitute the pair of catheter/balloon combinations illustrated in Figures 4 and 5 with a single, bifurcated catheter/balloon design which mimics the design of the stent. Thus, in this modification, the balloon and guidewire would be design to mimic the bifuracted design of the stent. As further alternative, it is contemplated that the stent can be made of a suitable material which will expand when bifurcated body passageway 150 is flushed with a liquid having an elevated temperature (e.g. 65,6°-71,1°C or 150°F-160°F). Further, stent 10 can be designed to expand upon the application of mechanical forces other than those applied by a balloon/catheter. Still further, stent 10 can be designed self-expanding to be implanted as described above. In this embodiment, the radially outward force exerted on the stent would be generated within the stent itself. Still further, the stent depicted in Figures 1-2 can be modified to omit, on a selected basis, first repeating pattern A and/or second repeating B with a view to improve flexibility of the stent and to allow access to other structures (e.g. side branches/arteries) outside the bounds of the stent.

Claims: A bifurcated stent (10) comprising a proximal end (15) and a distal end (20) in communication with one another, the proximal end (15) comprising a primary passageway (25) and the distal end (20) comprising a pair of secondary passageways (30,35), the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent (10), characterized in that the primary passageway (25) is connected to the each of the secondary passageways (30,35) at a reinforced intersection point (40) in the unexpanded state of the stent (10). The bifurcated stent defined in claim 1, wherein the intersection point (40) is porous. The bifurcated stent defined in claim 2, wherein the porosity of the intersection point (40) is defined by a plurality intersecting members. The bifurcated stent defined in claim 3, wherein the intersecting members define a repeating pattern (A) which comprises a pair of side walls (55,60) substantially parallel to the longitudinal axis (50) of the primary passageway (25), a first concave-shaped wall (65) and a second convex-shaped wall (70) connecting the side walls (55,60) and a reinforcing bar (75) disposed between and substantially parallel to the pair of side walls (55,60). The bifurcated stent defined in any one of the preceding claims, wherein the reinforced intersection point (40) is annular. The bifurcated stent defined in any one of the preceding claims, wherein at least one of the primary passageway (25) and secondary passageways (30,35) is porous. The bifurcated stent defined in claim 6, wherein the porosity is defined by a plurality intersecting members in the form of a first repeating pattern (A) comprising a polygon having a pair of side walls (55,60) substantially parallel to the longitudinal axis (50) of the primary passageway (25), a first concave-shaped wall (65) and a second convex-shaped wall (70) connecting the side walls (55,60). The bifurcated stent defined in claim 7, wherein the first wall (65) and the second wall (70) have a flat apex (67,72). The bifurcated stent defined in any one of claims 7 or 8, wherein the intersecting members define a second repeating pattern (B). The bifurcated stent defined in claim 9, wherein the second repeating pattern (B) is a substantial mirror image of the first repeating pattern (A) taken along an axis substantially normal to the longitudinal axis (50) of the primary passageway (25).

Inventors: PENN IAN M, RICCI DONALD R, PENN, IAN M., RICCI, DONALD R.
Applicants: DIVYSIO SOLUTIONS ULC
Application year: 1995
Main classification: A61F2
IPC codes: A61F2