Abstract:
A bifurcated vascular prosthesis including a tubular main branch extended by at least two sub-branches, wherein at least one part of the main branch has an expandable strengthener in the form of an expandable annular section; and each sub-branch has at least one expandable zone longitudinally offset to avoid overlapping of corresponding longitudinally offset expandable zones between sub-branches.

Description:
This application is a Continuation-in-Part of PCT/FR97/00931, filed May 28, 1997. 
    
    
     FIELD OF THE INVENTION 
     This invention features vascular prostheses designed to treat aortic aneurisms via the endoluminal route. The endovascular prostheses currently proposed are designed, in a first embodiment, for repairs, by means of a straight prosthetic tube attached at either end by an endoprosthesis. In another known embodiment, the repair is achieved by means of an aortic bifurcation whose form is similar to that of the anatomical layout. 
     BACKGROUND 
     In the prior art, an expanding prosthesis is also known, described in the French patent FR2678508. This document describes a device for reinforcing vessels in the human body, of the type which has an extended strengthener which runs along the inside of the vessel to be reinforced. In the invention, in order to allow unbroken junctions to be formed especially at the bifurcations, at least two devices are used with self-locking spirals which allow unbroken junctions to be created. 
     Another document of the prior art, published under the number EP508473 describes a bifurcated endovascular prosthesis, formed by a main branch and flexible sub-branches. The drawback with this type of prosthesis which is the closest state of the art is that to make surgical implantation possible, numerous models are required to suit the diameters and lengths of the aorta and the iliac arteries. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is to overcome these drawbacks and to offer a prosthesis whereby one model can be adapted to suit a wide range of vascular sections. Another objective is to offer a prosthesis which can be surgically implanted rapidly, in order to reduce the length and cost of the operation. 
     To this end, the invention features first of all a bifurcated vascular prosthesis, formed by a tubular main branch and extended by means of two tubular sub-branches, characterised in that at least one part of the main branch has expandable strengtheners. 
     The main branch will preferably be made from an expandable material, such as PTFE, reinforced by an expandable annular section. 
     The inlet of the main branch is advantageously formed of a stripped reinforced tubular section wherein a part of the expandable material (PTFE) has been stripped away to reveal the reinforcing material. This stripped section provides better adherence for the prosthesis. 
     In a first embodiment, the sub-branches are free and not reinforced. The main branch is advantageously expandable up to a diameter of around 28 mm, and the sub-branches are conically shaped, the end of which measures approximately 10 mm in diameter. 
     In a second embodiment, the main branch is extended by means of two reinforced sub-branches which are expandable up to a diameter of 10 mm, the expandable zones being offset longitudinally, and the sub-branches being of different lengths in order to avoid the reinforced zones overlapping. 
     Advantageously in both embodiments, the sub-branches are each extended by means of expandable reinforced annular sections, the length of which can be adjusted to suit the distal attachment to the iliac arteries. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description will become clearer upon reading the following description, referring to the non-restrictive examples of embodiments, where: 
     FIG. 1 shows a cross-sectional view of a first embodiment of the invention; 
     FIG. 2 shows a cross-sectional view of a second embodiment of the invention; 
     FIGS. 3 and 4 show cross-sectional views of two embodiments of extensions of the sub-branches of the prosthesis; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a cross sectional view of a first embodiment of the invention. 
     The prosthesis has a main branch ( 1 ) and two sub-branches ( 2 ,  3 ). The main branch is made up of a tubular section, made from an expandable material such as PTFE and reinforced at the top by an expandable annular section. The middle section ( 1 ′) of the main branch is made of reinforced PTFE, which extends to the sub-branches ( 2 ,  3 ) via a section ( 1 ″) made of non-reinforced PTFE. The main branch can be expanded up to a diameter of approximately 28 mm. The proximal end ( 4 ) of the main branch is reinforced but a part of the expandable material (PTFE) has been stripped away in order to improve the adherence to the aortic artery. This main branch forms a bifurcation extended by the two free, non-reinforced sub-branches ( 2 ,  3 ). Their cross section reduces slightly to create a conical shape of around 10 mm in diameter at the end, thus improving the distal adherence. 
     This assembly is mounted onto a guide balloon catheter ( 6 ), which allows the main branch to be dilated up to 28 mm, depending on the type of balloon and the insufflation pressure, and the sub-branches are coiled. This prepared assembly is passed via the, iliac artery ( 10 ) into the aneurism ( 7 ), with the stripped proximal end positioned just below the renal arteries ( 8 ). At this point, the main branch ( 1 ) is expanded by pressurising the balloon ( 6 ). The balloon ( 6 ) is then removed, leaving the two sub-branches ( 2 ,  3 ) in the aneurism. These sub-branches ( 2 ,  3 ) are then extended under the pressure of the blood circulation. Each sub-branch ( 2 ,  3 ) of the bifurcation is then extended by means of straight modules of known type, whose length can be altered to suit the adherence to each iliac artery ( 10 ,  10 ′). 
     These straight modules are advantageously expandable modules formed by expandable annular segments encased in an expandable material, such as PTFE. 
     These modules will be dilated to suit the diameter of the iliac artery. 
     FIG. 2 shows a second embodiment. 
     The main branch ( 1 ) and the two sub-branches ( 2 ,  3 ) are formed of expandable segments encased in an expandable material, such as PTFE. The two sub-branches ( 2 ,  3 ) have longitudinally offset reinforced zones ( 21 ,  21 ′) to avoid any overlapping which would result in an excess thickness preventing it from being introduced into the vascular system. Consequently, sub-branch ( 3 ) is longer than sub-branch ( 2 ). The non-reinforced part of the prosthesis junction can be pre-dilated. 
     The assembly is mounted onto an expanding device which allows firstly the main branch to be dilated with a main balloon ( 6 ) up to 28 mm, depending on the insufflation pressure, then the first sub-branch ( 2 ) up to 10 mm using another balloon ( 25 ). The second sub-branch ( 3 ) is then expanded by means of a third balloon ( 26 ). It is also possible to use the same balloon to expand firstly the main branch, then one of the sub-branches. 
     As previously described, the sub-branches ( 2 ,  3 ) are extended by straight modules ( 11 ,  12 ) formed by annular segments which are adjustable in length encased in an envelope of expandable material, such as PTFE. 
     FIG. 3 shows an embodiment of the extension of the sub-branch where the proximal end of a modular extension ( 27 ) has a conical, non-reinforced part ( 28 ) connected to the distal end ( 29 ) of the main branch. 
     FIG. 4 shows an embodiment of the extension of the sub-branch where the proximal end of a modular extension ( 27 ) has a reinforced part ( 30 ) connected to the reinforced end ( 31 ) of the main branch. 
     The above descriptive examples of the invention are non-restrictive. The specialist will be able to produce different embodiments without escaping from the inventive concept.