Abstract:
A stent assembly ( 10 ) comprises a stent component ( 12 ). The stent component ( 12 ) includes a primary arm ( 14 ) defining a first open passage; and at least one secondary arm ( 16 ) extending at an angle from the primary arm ( 14 ), the at least one secondary arm ( 16 ) being integrally formed with the primary arm ( 14 ) as a one piece unit and the secondary arm ( 16 ) defining a second open passage in communication with the passage of the primary arm ( 14 ). An outer sheath ( 20 ) surrounds and constrains the stent component ( 12 ) in a constricted configuration to facilitate insertion of the stent component  12  into a vascular system of a patient. The outer sheath ( 20 ) is removable from the stent component ( 12 ) to enable the stent component ( 12 ) to adopt its operative configuration when the stent component ( 12 ) is at its desired position in the vascular system of the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from U.S. Provisional Patent Application No. 60/820,066 filed on 21 Jul. 2006, the contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    This invention relates, generally, to a stent assembly and, more particularly, to a bifurcated stent assembly, to a stent and to a stent delivery system for, and a method of, positioning a stent assembly at a site in a patient&#39;s body. 
       BACKGROUND 
       [0003]    The use of stents to treat lesions caused by the build up of plaque in a patient&#39;s vascular system is known. However, a lesion often occurs at a bifurcation in the vascular system. The treatment of such lesions is complex. In the past, two separate stents have been used where one of the stents is passed through an aperture in a side wall of the other stent. Thus, a clinician has to manoeuvre multiple stents which presents additional challenges. 
         [0004]    The use of two separate stents can also increase the risk of impeding blood flow, especially to the branch artery. Another problem associated with the use of a separate stent branching from a primary stent is the effect of the stent in the side branch hanging into the main vessel increasing the risk of thrombosis. 
         [0005]    Due to the complexity of using two separate stents, some clinicians take the chance of ignoring side branch stenosis. In addition, since lesions rarely occur exactly at the bifurcation but may occur above or below the bifurcation another problem is the effect of shifting the plaque as a result of insertion of the stent or a balloon from one bifurcated vessel into the other. 
         [0006]    It is therefore desirable to have a device specifically designed for treating lesions at bifurcations in the vasculature. 
       SUMMARY 
       [0007]    Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
         [0008]    According to a first aspect of the invention, there is provided a stent assembly which comprises 
         [0009]    a stent component including
       a primary arm defining a first open passage; and   at least one secondary arm extending at an angle from the primary arm, the at least one secondary arm being integrally formed with the primary arm as a one piece unit and the secondary arm defining a second open passage in communication with the passage of the primary arm; and       
 
         [0012]    an outer sheath surrounding and constraining the stent component in a constricted configuration to facilitate insertion of the stent component into a vascular system of a patient, the outer sheath being removable from the stent component to enable the stent component to adopt its operative configuration when the stent component is at its desired position in the vascular system of the patient. 
         [0013]    In a preferred embodiment, the stent component is bifurcated, being substantially Y-shaped or T-shaped. 
         [0014]    Thus, the outer sheath may be shaped to accommodate the bifurcated stent component. The sheath may be tubular having an enlarged distal portion to accommodate the secondary arm of the stent component in a constrained, side-by-side position relative to the primary arm. Instead, the outer sheath may comprise a plurality of interconnected deployment tubes configured to be coincident with the arms of the stent component, at least a portion of the outer sheath being frangible for enabling the outer sheath to be removed from the stent component. In particular, the outer sheath may have a shape complementary to that of the stent component. The frangible portion of the outer sheath may be defined by a zone of weakness extending along at least a part of at least one of the tubes. 
         [0015]    One of the outer sheath and the stent component may include a rupture assisting element which facilitates rupturing of the frangible portion of the outer sheath. The rupture assisting element may be arranged in a crook between the primary arm and the secondary arm and may be in the form of a toothed arrangement carried either by the stent component or the outer sheath. In the latter case, the toothed arrangement may be configured to bear against the crook of the stent component to force the parts of the outer sheath on opposite sides of the frangible portion apart upon commencement of withdrawal of the outer sheath from the stent component. 
         [0016]    The secondary arm may branch off the primary arm intermediate an inlet opening and an egress opening of the passage of the primary arm. 
         [0017]    In an embodiment, the stent component may be a self expanding component made from a shape memory alloy such as Nitinol. In another embodiment, the stent component may be an expansible component which expands under the assistance of a radially outwardly directed force. For example, the stent component may be expanded by inflating a balloon inserted into the component. 
         [0018]    Further, the stent component may be polymer coated. In addition, or instead, the stent component may be coated with anti-coagulants, anti-infection surface treatment agents, or other drugs. 
         [0019]    According to a second aspect of the invention, there is provided a stent component which comprises 
         [0020]    a primary arm defining a first open passage; 
         [0021]    at least one secondary arm extending at an angle from the primary arm, the at least one secondary arm defining a second open passage in communication with the passage of the primary arm; and 
         [0022]    a rupture assisting element which engages a frangible portion of an outer sheath to assist in rupturing the frangible portion, the rupture assisting element being arranged in a crook between the primary arm and the secondary arm. 
         [0023]    The primary arm and the secondary arm may be formed integrally as a one-piece unit. 
         [0024]    According to a third aspect of the invention, there is provided a stent component which comprises 
         [0025]    a primary arm having a wall portion and defining a first open passage having an inlet opening and an egress opening with at least one intermediate opening being defined in the wall portion; and 
         [0026]    a secondary arm associated with the, or each, intermediate opening of the primary arm, the, or each, secondary arm being adjustably attached to the primary arm in register with its associated intermediate opening and the, or each, secondary arm defining a second open passage in communication with the first open passage of the primary arm. 
         [0027]    The, or each, secondary arm may be hingedly attached to the primary arm. More particularly, the, or each, secondary arm is hingedly attached to the primary arm by a pair of opposed hinge elements. This allows for independent radial expansion of the primary arm and the, or each, secondary arm. 
         [0028]    According to a fourth aspect of the invention, there is provided a stent delivery system for positioning a stent assembly at a site in a patient&#39;s body, the system comprising 
         [0029]    an introducer; 
         [0030]    a stent assembly, as described above, displaceably received within the introducer; and 
         [0031]    a guide mechanism extending through the introducer and each arm of the stent assembly for guiding the stent assembly relative to the introducer into position at a desired site in a patient&#39;s body. 
         [0032]    More particularly, the stent assembly may be displaceably arranged relative to the introducer to be displaced from a first position in which the assembly is received within the introducer and a second position in which the assembly projects from a distal end of the introducer. 
         [0033]    The introducer may be a delivery tube having a bore, at least a distal part of the bore being divided into at least two conduits by a septum arrangement. The septum arrangement may be a breakable septum arrangement. 
         [0034]    The guide mechanism may comprise an elongate guide element extending through each arm of the stent assembly. 
         [0035]    A distal end of each elongate element may carry a trap for entrapping dislodged material. The trap may be a collapsible trap. 
         [0036]    At least one of the guide elements may be one of pre-shaped and steerable. 
         [0037]    According to a fifth aspect of the invention, there is provided a method of positioning a stent assembly at a site in a patient&#39;s body, the method comprising 
         [0038]    feeding an introducer containing the stent assembly, as described above, and a guide mechanism to the site at the patient&#39;s body; 
         [0039]    causing the guide mechanism to extend from a distal end of the introducer so that each of a plurality of elongate guide elements of the guide mechanism is received in a blood vessel at the site; 
         [0040]    ejecting the stent assembly from a distal end of the introducer with each arm of the assembly being guided into one of the blood vessels along its associated guide element; and 
         [0041]    removing the outer sheath of the assembly to enable each arm of the assembly to be expanded to inhibit restenosis of its associated blood vessel. 
         [0042]    The method may include ejecting the stent assembly from the introducer by withdrawing the introducer in a proximal direction, withdrawal of the introducer causing breaking of a septum arrangement arranged at a distal end of the introducer between the arms of the stent assembly. 
         [0043]    Further, the method may include removing the outer sheath of the assembly by breaking a frangible portion of the outer sheath. The method may include breaking the frangible portion of the outer sheath by urging the sheath proximally relative to the stent component, a rupture assisting element of the stent component engaging the frangible portion of the outer sheath. 
         [0044]    The method may include deploying a trap at a distal end of each guide element to entrap material dislodged from the site. The trap is a collapsible trap and the method may include collapsing the trap after positioning of the stent component to facilitate withdrawal of the guide mechanism. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0045]      FIG. 1  shows a three dimensional view of an embodiment of a stent assembly; 
           [0046]      FIG. 2  shows a schematic, sectional side view of a part of the stent assembly; 
           [0047]      FIG. 3  shows a three dimensional view of a stent component of the assembly; 
           [0048]      FIG. 4  shows a schematic end view of a part of an embodiment of a stent delivery system; 
           [0049]      FIGS. 5   a - 5   d  show various stages in the positioning of the stent component at a site in a patient&#39;s body; and 
           [0050]      FIG. 6  shows a schematic, sectional side view of a part of another embodiment of a stent component. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0051]    In the drawings, reference numeral  10  generally designates an embodiment of a stent assembly. The assembly  10  comprises a stent component  12  ( FIG. 3 ). The stent component  12  comprises a primary arm  14  and a secondary arm  16  projecting from the primary arm  14  at a predetermined, acute angle to form a bifurcated stent component  12 . The primary arm  14  defines a first, open passage  18 . The secondary arm  16  defines a second, open passage  19  opening into, and in communication with, the passage  18  of the primary arm  14 . 
         [0052]    The assembly  10  further includes an outer sheath  20  which has a shape complementary to that of the stent component  12 . Thus, the outer sheath  20  is similarly bifurcated to accommodate the stent component  12 . More particularly, the outer sheath  20  has a first, or primary, tube  22  which accommodates the primary arm  14  of the stent component  12  and a second, or secondary, tube  24  which accommodates the secondary arm  16  of the stent component  12 . 
         [0053]    The outer sheath  20  surrounds and contains the stent component  12  in a constricted configuration to facilitate insertion of the stent assembly  10  into an introducer  26  ( FIG. 4 ) of a stent delivery system  30  ( FIGS. 5   a - 5   d ) and will be described in greater detail below with reference to  FIGS. 5   a - 5   d  of the drawings. 
         [0054]    The outer sheath  20  has a frangible portion  32 . More particularly, the frangible portion  32  is a zone of weakness formed in the outer sheath  20  on facing parts of the tubes  22  and  24 . In the illustrated embodiment the zone of weakness  32  is a line of perforations. The zone of weakness could instead be an actual break or discontinuity in the wall of the sheath  20  which, upon removal of the introducer  20  from the assembly  10 , opens to permit removal of the sheath  20  from the stent component  12 . 
         [0055]    The junction of the secondary arm  16  with the primary arm  14  of the stent component  12  defines a crook  34 . A rupture assisting element  36  ( FIG. 2 ), in the form of a tooth-like formation, is received in the crook  34  of the stent component  12 . The rupture assisting element  36  is aligned with the zone of weakness  32  in the outer sheath  20 . Consequently, when the outer sheath  20  is urged in the direction of arrow  38  ( FIG. 2 ), the rupture assisting element  36  engages the zone of weakness  32  of the outer sheath  20  causing rupturing of the zone of weakness  32  to facilitate withdrawal of the outer sheath  20  from the stent component  12 , as will be described in greater detail below. 
         [0056]    In another embodiment, the tooth-like formation is directed oppositely to that illustrated and is carried by the outer sheath  20  to be received in the crook  34  of the stent component  12 . The tooth-like formation is configured to bear against the crook  34  of the stent component  12  to force parts of the outer sheath  20  on opposite sides of the zone of weakness  32  apart upon commencement of withdrawal of the outer sheath  20  from the stent component  12 . 
         [0057]    The stent delivery system  30  comprises the introducer  26  for introducing the stent assembly  10  into the vasculature of the patient undergoing treatment. The introducer  26  is a tubular member. A distal end of the introducer  26  is divided into two conduits  40  and  42  ( FIG. 4 ) by a septum  44 . In use, the septum  44  is received between the primary arm  14  and the secondary arm  16  of the stent component  12 , while the stent component  12  is enshrouded in the outer sheath  20  to maintain separation of the arms  14  and  16 . The septum  44  is of a breakable material and, when the introducer  26  is withdrawn from the vasculature of the patient, the septum  44  breaks to facilitate withdrawal of the introducer  26 . 
         [0058]    The stent assembly  10  is inserted into the introducer  26  via a proximal end (not shown) of the introducer  26  and is positioned at a distal end  46  of the introducer  26 . The introducer  26  is inserted into the vasculature and is steered through the vasculature to the site to be treated. In particular, the assembly  10  is for use in treating a lesion  54  occurring at a bifurcation  48  in the vasculature of the patient such as, for example, at the bifurcation between the external carotid artery  50  and the internal carotid artery  52 . Thus, in use, the introducer  26  of the system  30  is steered so that the distal end  46  of the introducer terminates proximally of the bifurcation  56 . 
         [0059]    A guide mechanism  58 , comprising a pair of guide elements, or wires,  60 ,  62 , is extended from the distal end  46  of the introducer  26 . The wire  60  of the guide mechanism  58 , which feeds into the external carotid artery  50 , passes through the passage  18  of the primary arm  14  of the stent component  12 . The wire  62 , which feeds into the internal carotid artery  52 , passes through the passage of the secondary arm  16  of the stent component  12 . It will therefore be appreciated that the guide wires  60  and  62  are arranged on opposed sides of the septum  44  of the introducer  26 . Further, the guide wire  62  may be pre-shaped with a kink  63  ( FIG. 5   b ) to facilitate insertion of the guide wire  62  into the artery  52 . 
         [0060]    Each guide wire  60 ,  62  carries a collapsible trap  64  at its distal end. Prior to deployment of the stent component  12  from within the introducer  26 , the traps  64  are opened, as shown in  FIG. 5   c  of the drawings, to entrap material dislodged by releasing or ejecting the stent component  12  from the distal end  46  of the introducer  26 . 
         [0061]    Once the traps  64  have been opened, the stent assembly  10  is urged out of the distal end  46  of the introducer  26  to the position shown in  FIG. 5   c  of the drawings. When the introducer  26  is withdrawn proximally relative to the stent assembly  10 , the tubes  22 ,  24  of the outer sheath  20  splay outwardly to facilitate insertion of the tubes  22 ,  24  into their associated arteries  50 ,  52  respectively. Thus, the tube  22  of the outer sheath  20  is received in the external carotid artery  50  while the tube  24  of the outer sheath  20  is received in the internal carotid artery  52 . 
         [0062]    A drawstring  66 , or the like, is connected to a proximal end of the outer sheath  20 . The outer sheath  20  is urged in the direction of arrow  38 . The zone of weakness  32 ′ comes into contact with the rupture assisting element  36  of the stent component  12  causing rupturing of the zone of weakness  32  and facilitating removal of the outer sheath  20  from the stent component  12 . Removal of the outer sheath  20  enables the stent component  12  to expand radially to adopt its desired position at the site in the patient&#39;s body where restenosis of the site is to be inhibited. 
         [0063]    The stent component  12  can be implemented in a number of ways. In one embodiment, the stent component  12 , which is of a unitary, one-piece construction, is of a shape memory alloy material such as Nitinol. In this embodiment, the outer sheath  20  constricts the stent component  12  facilitating its insertion into the introducer  26  and its placement at the desired site. Once the outer sheath  20  has been removed, the Nitinol adopts its pre-formed shape which, in this case, is an expanded configuration. This holds the stent component  12  in the desired position at the site. 
         [0064]    In another embodiment of the invention, the stent component  12  is of an expansible bio-metal mesh. Once the outer sheath  20  has been removed, a balloon (not shown), in a deflated condition, is inserted into each arm  14 ,  16  of the stent component  12 . The balloon is then inflated to cause a radially outwardly directed force to be exerted on the arms  14  and  16  of the stent component  12  causing the arms  14  and  16  to expand to their desired size. 
         [0065]    In both embodiments, instead of the rupture assisting element  36 , the outer sheath may be ruptured by inflating the balloon prior to removal of the outer sheath  20 . Inflation of the balloon causes rupturing of the outer sheath  20  at the zone of weakness  32  facilitating withdrawal of the outer sheath  20 . 
         [0066]      FIG. 6  shows a further embodiment of the stent component  12 . With reference to the previous drawings, like reference numerals refer to like parts unless otherwise specified. In this embodiment, the secondary arm  16  of the stent component  12  is adjustably attached to the primary arm  14 . A radially expansible wall portion  68  of the primary arm  14  defines an intermediate opening  70 . The secondary arm  16  is attached to the primary arm  14  so that it is in register with the intermediate opening  70  of the primary arm  14 . 
         [0067]    It will be appreciated that, in the case of all the embodiments, the stent component  12  could have a plurality of secondary arms  16  associated with the primary arm. In the case of this embodiment, therefore, the wall portion  68  of the primary arm could define more than one intermediate opening  70  with each intermediate opening  70  having a secondary arm  16  associated with it. 
         [0068]    The secondary arm  16  is hingedly attached to the primary arm  14 . More particularly, the secondary arm  16  is attached to the primary arm  14  by a pair of opposed hinge elements  72  (One of the hinge elements  72  is visible in shown in  FIG. 6 . The other hinge element is aligned with the visible hinge element). This allows the primary arm  14  and the secondary arm  16  to expand radially independently with respect to each other. 
         [0069]    In the case of this embodiment, the guide wires  60  and  62  guide the primary arm  14  and the secondary arm  16 , respectively, into their associated arteries  50  and  52 . The angle of the secondary arm  16  relative to the primary arm  14  is governed by the angle of the arteries  50  and  52 . The angle of the secondary arm  16  relative to the primary arm  14  automatically adjusts to accommodate variations in angles between blood vessels. Due to the presence of the guide wires  60  and  62 , there is no need to control or preset the angle of the secondary arm  16  relative to the primary arm  14 . 
         [0070]    It will be appreciated that, while the stent assembly  10  and the system  30  have been described with reference to their application to the carotid arteries of a patient, the stent assembly  10  and system  30  are able to be used in any other part of the vasculature of a patient&#39;s body where bifurcations occur such as, for example, in the coronary arteries. 
         [0071]    It is an advantage of the invention that a stent assembly  10  and system  30  are provided which can be used for the treatment of the build up of plaque at bifurcations in a patient&#39;s vasculature and can be used without difficulty. In particular, the use of a stent assembly  10  of unitary construction facilitates placement of the stent assembly  10 . Due to the use of a one-piece stent component  12 , the likelihood of shifting plaque from one vessel to another at the bifurcation is minimised. Also, the use of the one-piece stent component  12  minimises the risk of thrombus occurring at the bifurcation. In addition, a system  30  is provided which facilitates positioning and placement of the stent assembly  10  at the desired location in the patient&#39;s vasculature. 
         [0072]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.