Abstract:
An assembly for occluding a vascular site (e.g., an aneurysm) of a human or veterinary patient includes a vaso-occlusive member, a pusher member having a distal end and a severable junction located proximal to the distal end, and a pivotable coupling that couples the pusher member to the occlusive member. A delivery catheter can be used to deliver the vaso-occlusive member to the vascular site. A method of using the assembly to occlude an aneurysm having an aneurysmal sac and an aneurysmal neck, includes locating the catheter within the aneurysmal neck, and manipulating the pusher member to place the vaso-occlusive member within the aneurysmal sac. The method further includes severing the severable junction to detach the vaso-occlusive member from the pusher member. As a result, an axial force is applied by the vaso-occlusive member in a proximal direction, which buckles the pivotable coupling to laterally deflect the axial force. The lateral deflection of the axial force caused by the buckling of the pivotable coupling prevents the catheter from being displaced from the aneurysmal neck by the axial force.

Description:
RELATED APPLICATION DATA  
       [0001]    The present application claims the benefit under 35 U.S.C. §120 to U.S. patent application Ser. No. 11/022,189, filed Dec. 22, 2004. The foregoing application is hereby incorporated by reference into the present application in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]    The present invention relates to assemblies for implanting vaso-occlusive devices in-vivo for establishing an embolus or vascular occlusion in a vessel of a human or veterinary patient. 
       BACKGROUND OF THE INVENTION  
       [0003]    Vaso-occlusive devices or implants are used for a wide variety of reasons. They are often used for treatment of intra-vascular aneurysms. This is to say that the treatment involves the placement of a vaso-occlusive device in an aneurysm to cause the formation of a clot and eventually of a collagenous mass containing the vaso-occlusive device. These occlusions seal and fill the aneurysm thereby preventing the weakened wall of the aneurysm from being exposed to the pulsing blood pressure of the open vascular lumen. Treatment of aneurysms in this fashion is a significant improvement over the surgical method typically involved. 
         [0004]    A common vaso-occlusive device is a soft, helically wound coil. A typical commercial coil will be formed by winding a platinum wire strand about a primary mandrel and applying a heat treatment to impart a primary winding coil shape. The relative stiffness of the coil will depend, among other things, on the diameter of the wire strand, the diameter of the primary mandrel, and the pitch of the primary windings. The device is then wrapped around a secondary mandrel, and again heat treated to impart a secondary shape. For example, U.S. Pat. No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a primary, linear helical configuration when stretched and a folded, and a convoluted, secondary configuration when relaxed in a minimal energy configuration. The stretched condition is used in placing the coil at the desired site (by its passage through a delivery catheter) and the coil assumes a relaxed configuration—which is better suited to occlude the vessel—once the device is so placed. 
         [0005]    It is well-known to detach such vaso-occlusive coil devices from a delivery wire using a mechanical detachment mechanism. For example, U.S. Pat. No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. U.S. Pat. No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil. U.S. Pat. No. 5,261,916, to Engelson, shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. U.S. Pat. No. 5,304,195, to Twyford et al., shows a pusher-vaso-occlusive coil assembly having an affixed, proximally extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengage when expelled from the distal tip of the catheter. 
         [0006]    It is also well-known to use an electrolytically severable joint to release vaso-occlusive coils at the vessel site. For example, Guglielmi et al. shows an embolism forming device and procedure for using that device which employs an electrolytically severable joint. Specifically, Guglielmi et al. desirably places a finely wound platinum coil into a vascular cavity such as an aneurysm. The coil is delivered endovascularly using a catheter such as those described above. After placement in the aneurysm, the coil is severed from its insertion core wire by the application of a small electric current to that core wire. The deliverable coils are said to be made of a platinum material. Proximal of the embolic coil, as noted above, is a core wire which is typically stainless steel. The core wire is used to push the platinum embolic coil into vascular site to be occluded. Other variations of the Guglielmi et al. technology are found in U.S. Pat. No. 5,354,295. 
         [0007]    Current electrolytically detachable coil products employ a relatively inflexible bridge assembly that connects the proximal end of the vaso-occlusive coil to the distal end of the pusher wire assembly. When the coil is detached from the pusher wire, the force the pusher wire has been exerting on the coil (and aneurysm wall) pushes back on the pusher wire assembly, which can displace the tip of the introducer catheter out of the aneurysm. This is because the PET sleeve does not laterally buckle or flex, but instead axially transmits the push-back force against the distal tip of the delivery catheter. Having the catheter tip displaced from the aneurysm requires the physician to relocate the catheter tip prior to placement of a further occlusive device, which undesirably extends the duration of the procedure. 
       SUMMARY OF THE INVENTION  
       [0008]    In accordance with one aspect of the invention, an assembly is provided for establishing an embolus or vascular occlusion in a vessel of a human or veterinary patient. The assembly generally includes a vaso-occlusive member (e.g., a coil), a pusher member having a distal end and a severable junction (e.g., a mechanically or electrolytically severable junction) located proximal to the distal end, and a pivotable coupling that couples the pusher member to the occlusive device. The assembly may optionally comprise a catheter in which the pusher member is slidably disposed. If the vaso-occlusive member comprises a coil, the assembly may optionally comprise a stretch-resisting member, in which case, the pivotable coupling may anchor the stretch-resisting member within the lumen of the coil. Besides optionally providing anchoring for a stretch-resisting member, the pivotable coupling may also include an element that electrically insulates the pusher member distal end from vaso-occlusive member. The pivotable coupling may be fashioned in any one of a variety of manners. 
         [0009]    In one embodiment, the pivotable coupling comprises a flexible sleeve (e.g., one made of an elastomeric material) coupled between the pusher member distal end and vaso-occlusive member. The pivotable coupling may also comprise a proximal coil coupled to the pusher member distal end, and a distal coil coupled to the vaso-occlusive member, in which case, the sleeve is disposed over the proximal and distal coils. 
         [0010]    In another embodiment, the pivotable coupling comprises a proximal link member (e.g., a hook or loop) coupled to the pusher member distal end, and a distal link member (e.g., a hook or loop) coupled to the vaso-occlusive member, wherein the proximal and distal link members pivotably engage each other. The pivotable coupling may also comprise a proximal coil coupled to the pusher member distal end, and a distal coil coupled to the vaso-occlusive member, in which case, the proximal link member is disposed on a distal end of the proximal coil, and the distal link member is disposed on a proximal end of the distal coil. 
         [0011]    In still another embodiment, the pivotable coupling comprises a first ball member coupled to the pusher member distal end, a second ball member coupled to the vaso-occlusive member, and a sleeve (e.g., a braid or mesh) holding the first and second ball members. The pivotable coupling may also comprise a coil mounted to the vaso-occlusive member, in which case, the first ball member is formed onto the pusher member distal end, and the second ball member is formed on a proximal end of the coil. 
         [0012]    In yet another embodiment, the pivotable coupling comprises a first coil coupled between the pusher member distal end and the vaso-occlusive member. The first coil comprises open-pitched windings between which spaces reside. The vaso-occlusive member comprises a vaso-occlusive coil comprising proximal windings disposed within the spaces between some of the open-pitched windings. At least some of the spaces between the open-pitched windings remain empty. The pivotable coupling may comprises a second coil coupled between the pusher member distal end and the first coil, in which case, the second coil comprises distal windings disposed within the spaces between some of the open-pitched windings. 
         [0013]    In accordance with another aspect of the invention, a method of occluding a vascular site (e.g., an aneurysm) using the vaso-occlusive assembly is provided. The method comprises manipulating the pusher member to place the vaso-occlusive member adjacent the vascular site. If the vascular site is an aneurysm, the delivery catheter can be placed within the aneurysmal neck, and the pusher member can be manipulated to place the vaso-occlusive member within the aneurysmal sac. The method further comprises severing the severable junction to detach the vaso-occlusive member from the pusher member. As a result, an axial force is applied by the vaso-occlusive member in a proximal direction, which buckles the pivotable coupling to laterally deflect the axial force. If the catheter is in an aneurysmal neck, the lateral deflection of the axial force caused by the buckling of the pivotable coupling will prevent the catheter from being displaced from the aneurysmal neck by the axial force. 
         [0014]    Other features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]    The drawings illustrate the design and utility of preferred embodiments of the present invention, in which similar elements are referred to by common reference numerals. In order to better appreciate how the above-recited and other advantages and objects of the present inventions are obtained, a more particular description of the present inventions briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0016]      FIG. 1  is a cross-sectional view of a vaso-occlusive assembly constructed in accordance with a preferred embodiment of the present inventions; 
           [0017]      FIG. 2  is a cross-sectional view of the vaso-occlusive assembly of  FIG. 1 , particularly illustrating operation of a pivotable coupling within the assembly; 
           [0018]      FIG. 3  is a cross-sectional view of a vaso-occlusive assembly constructed in accordance with another preferred embodiment of the present inventions; 
           [0019]      FIG. 4  is a cross-sectional view of the vaso-occlusive assembly of  FIG. 3 , particularly illustrating operation of a pivotable coupling within the assembly; 
           [0020]      FIG. 5  is a cross-sectional view of a vaso-occlusive assembly constructed in accordance with still another preferred embodiment of the present inventions; 
           [0021]      FIG. 6  is a cross-sectional view of the vaso-occlusive assembly of  FIG. 5 , particularly illustrating operation of a pivotable coupling within the assembly; 
           [0022]      FIG. 7  is an exploded view of a pivotable coupling and vaso-occlusive coil used in the vaso-occlusive assembly of  FIG. 5 ; 
           [0023]      FIG. 8  is a cross-sectional view of a vaso-occlusive assembly constructed in accordance with yet another preferred embodiment of the present inventions; 
           [0024]      FIG. 9  is a cross-sectional view of the vaso-occlusive assembly of  FIG. 8 , particularly illustrating operation of a pivotable coupling within the assembly; 
           [0025]      FIG. 10  is an exploded view of a pivotable coupling and vaso-occlusive coil used in the vaso-occlusive assembly of  FIG. 8 , and 
           [0026]      FIGS. 11A-11C  illustrate a method of using the vaso-occlusive assembly of  FIG. 1  to occlude an aneurysm. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Referring to  FIG. 1 , a vaso-occlusive assembly  10  constructed in accordance with a preferred embodiment is illustrated. For purposes of orientation, the term “proximal” as it qualifies an element generally refers to the left end of the element, and the term “right” as it refers to an element generally refers to the right end of the element, as shown in the figures. The vaso-occlusive assembly  10  generally comprises a delivery device  12 , which includes an elongated tubular catheter  16  and a pusher member  18 , and a vaso-occlusive device  14  detachably associated with the distal end of the delivery device  12 , and in particular, the distal end of the pusher member  18 . 
         [0028]    The catheter  16  comprises an elongated tubular member  20  having a delivery lumen  22  in which the pusher member  18 , and thus, the vaso-occlusive device  14 , is slidably disposed. The tubular member  20  can be composed of any suitable flexible and biocompatible material that allows it to be introduced through the tortuous vasculature of a patient to the vascular occlusion site. The pusher member  18  has a severable junction  24  that operates to selectively detach the vaso-occlusive device  14  from the delivery device  12 . In the illustrated embodiment, the severable junction  24  is an electrolytically severable junction that is susceptible to electrolysis, and thus, disintegrates when the core wire  18  is electrically charged in the presence of an ionic solution, such as blood or most other bodily fluids. 
         [0029]    To provide the electrical charge, the catheter  16  further comprises an annular electrode  26  mounted on the tubular member  20  at the distal end of the delivery lumen  22  and electrical conductors  28  (two shown) axially extending through the wall of the tubular member  20  in contact with the electrode  26 . The electrode  26  comprises a conductive biocompatible material, such as stainless steel, titanium, copper, platinum, gold, silver, or alloys thereof. Thus, when the electrolytically severable junction  24  is disposed outside of the catheter  16  in contact with the bodily fluids of the patient, electrical energy can be transmitted through the conductors  28  to the electrode  26 , where it is transmitted to the portion of the core wire  18  in contact with the electrode  26 . The electrical energy is then transmitted through the core wire  18  to the electrolytically severable junction  24 , which undergoes electrolysis until it severs to detach the vaso-occlusive device  14  from the delivery device  12 . Further details regarding the use of electrolytic joints are described in U.S. Pat. Nos. 5,354,295, 5,122,136, and 5,941,888, which are expressly incorporated herein by reference. 
         [0030]    It should be noted that other types of severable junctions, such as mechanically severable junctions, can also be used to connect the vaso-occlusive device  14  to the pusher member  18 . Various mechanical mechanisms are described in U.S. Pat. Nos. 5,234,437, 5,250,071, 5,261,916, 5,304,195, 5,312,415, and 5,350,397, which are expressly incorporated herein by reference. 
         [0031]    Referring still to  FIG. 1 , the vaso-occlusive device  14  includes a vaso-occlusive member  30  having a lumen  32  extending therethrough, a stretch-resisting member  34  extending within the lumen  32  of the vaso-occlusive member  30  to prevent axial stretching of the vaso-occlusive member  30 , and a pivotable coupling  36  that operates to affix the vaso-occlusive member  30  to the core wire  18 , while providing a pivot point  38  about which the distal end of the pusher member  18  and the vaso-occlusive member  30  pivot in order to deflect an axial force otherwise applied to the delivery device  12  by the vaso-occlusive device  14  after the junction  24  has been severed. In the illustrated embodiment, the pivotable coupling  36  also serves as an anchoring assembly that facilitates anchoring of the stretch-resisting member  34  within the vaso-occlusive member  30 . 
         [0032]    The vaso-occlusive member  30  has a sufficient small size that enables it to be advanced through the delivery catheter  16  and access the targeted vascular site. The materials used in constructing the vaso-occlusive member  30  may be any of a wide variety of materials, and preferably, a radio-opaque and biologically compatible material. Suitable metallic materials include the Platinum Group metals, especially platinum, rhodium, palladium, rhenium, as well as tungsten, gold, silver, tantalum, and alloys of these metals. Highly preferred is a platinum/tungsten alloy, e.g., 8% tungsten and the remainder platinum. Certain polymers can also be used as a suitable material for the vaso-occlusive member  30  either alone or in conjunction with radio-opaque markers, e.g., by filling the polymer with radio-opaque material, such as powdered tantalum, powdered tungsten, bismuth oxide, barium sulfate, and the like. 
         [0033]    In the illustrated embodiment, the primary vaso-occlusive member  30  takes the form of a helical coil with windings  40 , although other suitable members, such as a ribbon, a braided member, or the like can be used. The shape and constituent of the vaso-occlusive coil  30  will depend upon the use to which the coil will be placed. For occluding peripheral or neural sites, the diameter of the wire used in the production of the coil  30  is preferably in the range of 0.001 to 0.006 inches, and the outer diameter of the vaso-occlusive coil  30 , itself, is preferably in the range of 0.003 and 0.025 inches. For most neurovascular applications, an outer diameter between 0.008 and 0.018 inches provides sufficient hoop strength to hold the vaso-occlusive coil  30  in place within the selected body site, without substantially distending the wall of the site and without moving from that site as a result of the repetitive fluid pulsing found in the vascular system. The axial length of the wire used to make the vaso-occlusive coil  30  will usually fall in the range of 0.5 and 100 cm, more typically within the range of 2.0 and 40 cm. The axial length of the vaso-occlusive coil  30  will usually fall within the range of 2 mm and 40 cm. It should be noted that all of the dimensions provided for the vaso-occlusive coil  30  are provided only as guidelines, and the invention, in its broadest aspects, should not be limited thereto. Rather, only dimensions that are suitable for use in occluding sites within the human body are included in the scope of the invention. It should be appreciated that while the length of the vaso-occlusive coil  30  is shown in  FIG. 1  as being on the same order of length as the pivotable coupling  26 , the length of the vaso-occlusive coil  30  will typically be many orders greater than that of the pivotable coupling  26 . 
         [0034]    Depending on the desired therapeutic effect and the shape of the site to be treated, the vaso-occlusive coil  30  may be treated or accessorized in numerous ways in order to enhance its therapeutic effect. For example, the vaso-occlusive coil  30  may be made to form various secondary shapes, often through the use of heat treatment, that may be better suited to fill a particular treatment site, as disclosed in U.S. Pat. Nos. 5,853,418 and 6,280,457, which are expressly incorporated herein by reference. Alternatively, the vaso-occlusive coil  30  may have little or no shape after introduction into the vascular space, as disclosed in U.S. Pat. No. 5,690,666, which is expressly incorporated herein by reference. In addition, external materials may be added to the outside of vaso-occlusive coil  30  in an effort to increase its thrombolytic properties. For example, fibrous materials can be tied or braided onto the outside of the vaso-occlusive coil  30 . These alternative embodiments are disclosed in U.S. Pat. Nos. 5,226,911, 5,304,194, 5,354,295, 5,382,259, 5,549,624, and 6,280,457, which are expressly incorporated herein by reference. 
         [0035]    Referring still to  FIG. 1 , the stretch-resisting member  34  is affixed between the distal end of the vaso-occlusive coil  30  and the distal end of the pivotable coupling  36  within the lumen  22  of the vaso-occlusive coil  30  in a tensile relationship to prevent axial stretching of the vaso-occlusive coil  30 . In the illustrated embodiment, the stretch-resisting member  34  comprises a distal cap  42  affixed outside of the distal end of the vaso-occlusive coil  30 , and a looped thread  44  coupled to the pivotable coupling  36  in a tensile relationship, such that the distal cap  42  is proximally urged against the distal end of the vaso-occlusive coil  30 . The distal cap  42 , which has a diameter greater than the diameter of the coil lumen  22 , can be formed by gluing or melting the distal end of the stretch-resisting member  34 . Alternatively, the stretch-resisting member  34  may be tied in a knot (not shown), which may or may not be attached to the vaso-occlusive coil  30 . 
         [0036]    In the illustrated embodiment, the stretch-resisting member  34  is fibrous and desirably polymeric. Suitable polymeric materials can be either thermosetting or thermoplastic and can comprise a bundle of threads or a single filament. Themoplastics are preferred, because they allow simplification of the procedure for constructing the stretch-resisting member, e.g., by allowing the distal cap  42  to be formed by melting using a simple tool, such as a soldering iron. Suitable polymers include most biocompatible materials that may be made in fibers, including thermoplastics, e.g., polyesters, such as polyethyleneterephthalate (PET), especially Dacron®; polyamides, including Nylon®; polyolefins, such as polyethylene, polyprophylene, polybutylene, their mixtures, alloys, block, and random copolymers; fluoropolymers (polytetrafluoroethylene (PTFE)), or even silk or collagen. The stretch-resisting member  34  may be composed from materials, such as dissolvable sutures, for instance, polylactic acid or polyglycolic acid, to encourage cell growth in an aneurysm after introduction. Highly preferred is polypropylene, for instance, in the form of 10-0 and 9-0 polypropylene suture material. The diameter of the looped thread  44  is typically between about 0.0001 inches and 0.01 inches. 
         [0037]    Alternatively, rather than using plastics, a wide variety of stainless steels can be used if some sacrifice in flexibility can be tolerated. Stretch-resisting members of this type are described in U.S. Pat. No. 5,853,418, which is expressly incorporated herein by reference. Very desirable materials of construction, from a mechanical point of view, are materials that maintain their shape despite being subject to high stress. Certain “super-elastic alloys” include various nickel-titanium alloys (48-58 atomic % nickel and optionally containing modest amounts of iron); copper/zinc alloys containing 1-10 weight % of beryllium, silicon, tin, aluminum, or gallium; or nickel/aluminum alloys (36-38 atomic % aluminum). 
         [0038]    The pivotable coupling  36  comprises a proximal mounting coil  46  formed of a series of windings  50 , a distal mounting coil  48  formed of a series of windings  52 , and a flexible sleeve  54  for coupling the mounting coils  46 ,  48  together. The proximal mounting coil  46  is mounted around the distal end of the core wire  18  just distal to the severable junction  24 , and the distal mounting coil  48  is mounted within the lumen  22  of the vaso-occlusive coil  30 . The distal-most winding  52  of the distal mounting coil  48  is formed into a loop or hook  56 , which is suitably connected to the looped thread  44  of the stretch-resisting member  34 , thereby maintaining the stretch-resisting member  34  in a tensile state. 
         [0039]    The mounting coils  46 ,  48  can be composed of the same material as the vaso-occlusive coil  30 , but in the illustrated embodiment, are composed of platinum or platinum alloy. In the illustrated embodiment, the diameter of the wire used to make the mounting coils  46 ,  48  is smaller than the diameters of the wire used to make the vaso-occlusive coil  30  in order to minimize the profile of the pivotable coupling  36 . The outer diameter of the distal mounting coil  48  is preferably about the same size as the diameter of the primary coil lumen  22 , so that the distal mounting coil  48  and vaso-occlusive coil  30  snugly fit together. 
         [0040]    The pivotable coupling  36  further comprises a core wire extension  58  around which the distal mounting coil  48  is mounted to provide the distal end of the pivotable coupling  36  the compressive strength necessary to prevent buckling when mounted within the lumen  22  of the vaso-occlusive coil  30 . The mounting coils  46 ,  48  can be affixed to the core wire  18 , core wire extension  58 , and vaso-occlusive coil  30  using suitable means, such as interference fitting, welding, or bonding. 
         [0041]    The sleeve  54  is suitably mounted around the mounting coils  46 ,  48 , and is composed of a highly flexible, yet axially strong material, such that it is configured to axially connect the mounting coils  46 ,  48 , while allowing the mounting coils  46 ,  48  to pivot relative to each other about the pivot point  38 , as illustrated in  FIG. 2 . Suitable materials for the sleeve  54  include elastomeric polymers, which can be heat shrunk or otherwise bonded over the mounting coils  46 ,  48 . Fibrous material may also be embedded within the sleeve  54  to increase its axial strength. The pivot point  38  can either be coincident within a space between the ends of the mounting coils  46 ,  48  or a highly flexible material, such as an elastomeric polymer, that can be bonded between the mounting coils  46 ,  48 . As previously discussed, the outer diameters of the respective mounting coils  46 ,  48  are preferably the same, so that the sleeve  54  fits over the mounting coils  46 ,  48  in a uniformly snug manner. 
         [0042]    Besides integrating the mounting coils  46 ,  48  in an axially fixed, but pivotably, relationship, the sleeve  54  also serves to electrically insulate the mounting coils  46 ,  48 , as well as the distal end of the core wire  18  and the core wire extension  58 , from the bodily fluids in which they would otherwise be in contact with, so that the electrolytic process is focused at the severable junction  24 . In addition, the proximal-most windings  40  of the vaso-occlusive coil  30  in which the distal mounting coil  48  is affixed can be coated with an electrically insulative material, such as polyurethane or the like, to prevent potential electrical contact between the vaso-occlusive coil  30  and the core wire  18 . 
         [0043]    Optional electrically conductive coils (not shown) can be mounted to the coil wire  18  between the pivotable coupling  36  and the severable junction  24  to provide a means to determine when the vaso-occlusive device  14  has detached from the core wire  18 . That is, the electrically conductive coils provide an increased conductance between the core wire  18  and an external electrode, the substantial reduction of which can be measured when the conductive coils are eliminated from the electrical circuit after the conductive coils (along with the vaso-occlusive device  14 ) separates from the core wire  18 . 
         [0044]    Referring now to  FIG. 3 , a vaso-occlusive assembly  110  constructed in accordance with another preferred embodiment is illustrated. The vaso-occlusive assembly  110  is similar to the previously described vaso-occlusive assembly  10 , with the exception that it comprises a vaso-occlusive device  114  that includes a different pivotable coupling  36  for affixing the vaso-occlusive coil  30  to the core wire  18 . Like the previously described pivotable coupling  36 , the pivotable coupling  136  illustrated in  FIG. 3  has a proximal mounting coil  146  with windings  150  affixed to the distal end of the core wire  18  and a distal mounting coil  148  with windings  152  affixed within the lumen  22  of the vaso-occlusive coil  30 . These mounting coils  146 ,  148 , however, are not connected together via a sleeve-based pivotable coupling, but rather a link-based pivotable coupling  136 . 
         [0045]    In particular, the pivotable coupling  136  comprises a loop member  154  disposed through the lumen of the distal mounting coil  148 , so that proximal and distal eyelets  156 ,  158  respectively extend from the opposite sides of the distal mounting coil  148 . The loop member  154  may be suitably affixed within the lumen of the distal mounting coil  148  using an interference fit or by bonding or welding. The pivotable coupling  136  also comprises a hook  160  formed from the distal-most winding  150  of the proximal mounting coil  146 . The hook  160  is linked around the proximal eyelet  156  of the loop member  154  to axially connect the mounting coils  146 ,  148  to each other, while allowing the mounting coils  146 ,  148  to pivot relative to each other about a pivot point  138 , as illustrated in  FIG. 4 . Significantly, the hook  160  and proximal eyelet  156  are not welded or bonded together, so as to not hinder the pivoting action of the coupling  136 . 
         [0046]    Like the previously described pivotable coupling  36 , the pivotable coupling  136  in this case also serves as an anchoring assembly for anchoring the stretch-resisting member  34  within the vaso-occlusive coil  30 . In particular, the distal eyelet  158  of the looped member  154  connects to the looped thread  44  of the stretch-resisting member  34  to maintain the stretch-resisting member  34  in a tensile state. The mounting coil  146 , the proximal loop  156  of the looped member  154 , and the proximal-most windings  40  of the vaso-occlusive coil  30  can be coated with an electrically insulative material (not shown), such as polyurethane or the like, to prevent potential electrical contact between the vaso-occlusive coil  30  and the core wire  18 . Optionally, the mounting coil  146  can be left bare to provide a means to determine when the vaso-occlusive device  114  has detached from the core wire  18 . 
         [0047]    Referring now to  FIG. 5 , a vaso-occlusive assembly  210  constructed in accordance with still another preferred embodiment is illustrated. The vaso-occlusive assembly  210  is similar to the previously described vaso-occlusive assemblies  10 ,  110 , with the exception that it comprises a vaso-occlusive device  214  with a different pivotable coupling  236  for affixing a modified vaso-occlusive coil  230  to the core wire  18 . In particular, the pivotable coupling  236  comprises a mounting coil  246  having windings  250  affixed to proximal-most windings  240  of the vaso-occlusive coil  230  (mounting coil  246  and vaso-occlusive coil  230  shown separately in  FIG. 7 ), a pair of ball elements  256 ,  260  disposed on the respective distal end of the core wire  18  and proximal-most winding  250  of the mounting coil  246 , and a flexible sleeve  254  for coupling the ball elements  256 ,  260  together. 
         [0048]    The mounting coil  246  and vaso-occlusive coil  230  are designed to be affixed to each other in an interlocking manner. In particular, the windings  246  of the mounting coil  230  and the proximal-most windings  240  of the vaso-occlusive coil  230  are open-pitched (best shown in  FIG. 7 ), so that the mounting coil windings  246  can be disposed within spaces  242  between the open vaso-occlusive coil windings  240 , and the vaso-occlusive coil windings  230  can likewise be disposed within spaces  252  between the open mounting coil windings  250 . It can be appreciated, that the mounting coil  246  and vaso-occlusive coil  230  can be interlocked together using a twisting action, as illustrated in  FIG. 7 . To ensure that the mounting coil  246  and vaso-occlusive coil  230  remain interlocked, they may be suitably welded or bonded together. The composition and dimensions of the vaso-occlusive coil  230  may be similar to those of the previously described vaso-occlusive coil  30 . 
         [0049]    The mounting coil  246  preferably has a sufficient strength and stiffness that allows it to be integrated with the vaso-occlusive coil  230  in a robust manner. To this end, the windings  250  of the mounting coil  246  are doubled up, so that the spaces  252  only exist between pairs of windings  250 . That is, there are twice as many windings  250  as spaces  252 , thereby effectively increasing the strength of the mounting coil  246  relative to the vaso-occlusive coil  230 . To provide additional strength, the wire used to make the mounting coil  246  has an increased diameter relative to the diameter of the wire used to make the vaso-occlusive coil  230 . 
         [0050]    The outer diameters of the respective vaso-occlusive coil  230  and mounting coil  246  are selected to be the same, so that the outer profile of the combined assembly is uniform. The dimensions of the spaces  242  between the open windings  240  of the vaso-occlusive coil  230  will depend on the size and number of windings  250  of the mounting coil  246 , and the dimensions of the spaces  252  between the windings  250  of the mounting coil  246  will likewise depend on the size and number of windings  240  of the vaso-occlusive coil  230 . In the illustrated embodiment, the width of the spaces  242 ,  252  of one coil  230 ,  246  will be selected to conveniently accommodate the windings  250 ,  240  of the other coil  246 ,  230 , so that a substantial axial force is not exerted on the respective windings of the coils  230 ,  246 . Thus, the width of the spaces  242  between the windings  240  of the vaso-occlusive coil  230  will be about equal to twice the diameter of the wire used to make the mounting coil  246 , whereas the width of the spaces  252  between the windings  250  of the mounting coil  246  will be about equal to the diameter of the wire used to make the vaso-occlusive coil  230 . 
         [0051]    The ball members  256 ,  260  may be formed, e.g., by melting the ends of the respective core wire  18  and mounting coil  246 . The sleeve  254  is suitably mounted around the ball members  254 ,  260 , and is composed of a highly flexible, yet axially strong material, such that it is configured to axially connect the ball members  254 ,  260  while allowing the ball members  254 ,  260  to pivot relative to each other about a pivot point  238 , as illustrated in  FIG. 6 . 
         [0052]    The pivotable coupling  236 , like the pivotable couplings  36 , 136  described above, additionally serves as an anchoring assembly that anchors the stretch-resisting member  34  within the vaso-occlusive coil  230 . To this end, the doubling of the mounting coil windings  250  naturally forms an eyelet  255  (best shown in  FIG. 7 ) at the distal end of the mounting coil  246  that is suitably connected to the looped thread  44  of the stretch-resisting member  34 , thereby maintaining the stretch-resisting member  34  in a tensile state. 
         [0053]    In the illustrated embodiment, the sleeve  254  comprises a mesh material to provide the sleeve  254  with maximum flexibility. Because, the mesh sleeve  254  does not electrically isolate the ball members  256 ,  260 , the ball members  256 ,  260  can be coated with an electrically insulative material (not shown), such as polyurethane or the like, to prevent potential electrical contact between the vaso-occlusive coil  230  and the core wire  18 . Optionally, the proximal ball member  256  can be left bare to provide a means to determine when the vaso-occlusive device  214  has detached from the core wire  18 . 
         [0054]    Referring now to  FIG. 8 , a vaso-occlusive assembly  310  constructed in accordance with yet another preferred embodiment is illustrated. The vaso-occlusive assembly  310  is similar to the previously described vaso-occlusive assemblies  10 ,  110 ,  210 , with the exception that it comprises a vaso-occlusive device  314  with a different pivotable coupling  336  for affixing a modified vaso-occlusive coil  330  to the core wire  18 . In particular, the pivotable coupling  336  comprises a proximal mounting coil  346  with windings  350  affixed to the distal end of the core wire  18 , and a distal mounting coil  338  within windings  352  affixed to the windings  350  of the proximal mounting coil  346  and windings  340  of the vaso-occlusive coil  330  (mounting coils  346 ,  348  and vaso-occlusive coil  330  shown separately in  FIG. 10 ). 
         [0055]    Like the previously described mounting coil  246  and vaso-occlusive coil  230 , the mounting coils  346 ,  348  and vaso-occlusive coil  330  are designed to be affixed to each other in an interlocking manner. In particular, the distal-most windings  350  of the proximal mounting coil  346 , all of the windings  350  of the distal mounting coil  346 , and the proximal-most windings  340  of the vaso-occlusive coil  330  are open-pitched (best shown in  FIG. 10 ). In this manner, the distal-most coil windings  350  of the proximal mounting coil  346  can be disposed within spaces  356  between the proximal-most windings  352  of the distal mounting coil  348 , and the proximal-most windings  352  of the distal mounting coil  348  can likewise be disposed within spaces  354  between the distal-most coil windings  350  of the proximal mounting coil  346 . In a similar manner, the proximal-most windings  340  of the vaso-occlusive coil  330  can be disposed within the spaces  356  between the distal-most windings  352  of the distal mounting coil  348 , and the distal-most windings  352  of the distal mounting coil  348  can likewise be disposed within spaces  342  between the proximal-most windings  340  of the vaso-occlusive coil  330 . 
         [0056]    It can be appreciated, that the distal and proximal mounting coils  346 ,  348  and vaso-occlusive coil  330  can be interlocked together using a twisting action, as illustrated in  FIG. 10 . To ensure that the distal and proximal mounting coils  346 ,  348  and vaso-occlusive coil  330  remain interlocked, they may be suitably welded or bonded together. The composition and dimensions of the vaso-occlusive coil  330  may be similar to those of the previously described vaso-occlusive coil  30 . 
         [0057]    The outer diameters of the distal and proximal mounting coils  346 ,  348  and vaso-occlusive coil  330  are selected to be the same, so that the outer profile of the combined assembly is uniform. In the same manner described above with respect to the mounting coil  246  and vaso-occlusive coil  230 , the dimensions of the spaces between the open windings of each coil will depend on the size and number of the windings of the coil that interlocks with the respective coil. 
         [0058]    The number of windings of the distal mounting coil  348  is greater than the combined number of windings of the proximal mounting coil  346  and vaso-occlusive coil  330 , so that the spaces between the windings at the center of the distal mounting coil  346  remain empty. In this manner, a pivot point  338  about which the proximal and distal portions of the distal mounting coil  348  may pivot, is formed in the center of the distal mounting coil  348 . 
         [0059]    The pivotable coupling  336 , like the pivotable couplings  36 ,  136 ,  236  described above, additionally serves as an anchoring assembly that anchors the stretch-resisting member  34  within the vaso-occlusive coil  330 . To this end, the proximal mounting coil  346  is formed by coiling the distal end of the core wire  18  onto itself, as illustrated in  FIG. 10 . An eyelet  358  is formed at the distal end of the proximal mounting coil  348  where the core wire  18  coils back is suitably connected to the looped thread  44  of the stretch-resisting member  34 , thereby maintaining the stretch-resisting member  34  in a tensile state. 
         [0060]    The proximal and distal mounting coils  346 ,  348  and the proximal-most windings  340  of the vaso-occlusive coil  330  can be coated with an electrically insulative material (not shown), such as polyurethane or the like, to prevent potential electrical contact between the vaso-occlusive coil  330  and the core wire  18 . The distal portion of the core wire  18  extending through the proximal mounting coil  346  may also be coated with an electrically insulative material. Optionally, this portion of the core wire  18  can be left bare to provide a means to determine when the vaso-occlusive device  314  has detached from the core wire  18 . 
         [0061]    Although the pivotable couplings of the previous vaso-occlusive assemblies have been described as being located distal to the severable junction, pivotable couplings can also be located proximal to the severable junction. 
         [0062]    Having described the structure of the vaso-occlusive assemblies, the operation of the vaso-occlusive assembly  100  in occluding a vascular site, and in particular, an aneurysm  400  originating from a parent blood vessel  402 , will now be described with reference to  FIGS. 11A-11C . The vaso-occlusive assemblies  110 ,  210 ,  310  can similarly be used to occlude the aneurysm  400 , but for purposes of brevity, only the use of the vaso-occlusive assembly  10  will be described. 
         [0063]    First, in a conventional manner, the catheter  16 , which houses the core wire  18  and vaso-occlusive coil  14 , is introduced through the vasculature of the patient and manipulated until the distal end of the catheter  16  resides within a neck  402  of the aneurysm  400  ( FIG. 11A ). At this point, the vaso-occlusive coil  14  is positioned at the distal end of the catheter  16  in its undeployed state. The core wire  18  is then pushed in the distal direction, causing the vaso-occlusive coil  14  to extend out of the distal end of the catheter  16  and deploy within a sac of the  404  of the aneurysm  400  ( FIG. 11B ). A current is then applied to the core wire  18  (via the electrode  26  illustrated in  FIG. 1 ), which causes the severable junction  24  to disintegrate via electrolysis, after which the vaso-occlusive coil  14  detaches from the core wire  18  ( FIG. 11C ). During detachment, the vaso-occlusive coil  14  creates an axial force in the proximal direction that causes the flexible coupling  36  to buckle, thereby deflecting the axial force in the lateral direction, so that the catheter  16  is not displaced from the aneurysmal neck  404  by the axial force. 
         [0064]    Additional vaso-occlusive coils  14  can be deployed within the aneurysmal sac  402  in a similar manner to completely occlude the aneurysm  400 . After occlusion of the aneurysm  400  is completed, the vaso-occlusion assembly  10  is removed from the vasculature of the patient. 
         [0065]    Although particular embodiments of the present invention have been shown and described, it will be understood that it is not intended to limit the present invention to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present inventions are intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present invention as defined by the claims.