Abstract:
Embolic coil implant systems and methods whereby coils are mechanically detachable are disclosed. The coils include a retention element that may be releasably retained within the distal end of an implant tool. The implant tool may include a fulcrum configured to engage a first filament and prevent the release of the coil when the first filament is engaged. Alternatively, an urging means and aperture may be disposed within the sidewall of the implant tool, and a first filament may, in conjunction with the aperture and sidewall, releasably retain the coil until the first filament is withdrawn. The implant tool may also include an alignment member for aligning the first filament.

Description:
PRIORITY 
       [0001]    This application claims priority to prior Provisional Application No. 61/080,742, filed Jul. 15, 2008, and Provisional Application No. 61/083,111, filed Jul. 23, 2008, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the fields of systems and methods for implanting an intravascular implant device, and more specifically to systems and methods for implanting embolic coils. 
       BACKGROUND 
       [0003]    Coil embolization is a commonly practiced technique for treatment of brain aneurysm, arterio-venous malformation, and other conditions for which vessel occlusion is a desired treatment option, such as, for example, in the occlusion of a tumor “feeder” vessel. A typical occlusion coil is a wire coil having an elongate primary shape with windings coiled around a longitudinal axis. In the aneurysm coil embolization procedure, a catheter is introduced into the femoral artery and navigated through the vascular system under fluoroscopic visualization. The coil in the primary shape is positioned within the catheter. The catheter distal end is positioned at the site of an aneurysm within the brain. The coil is passed from the catheter into the aneurysm. Once released from the catheter, the coil assumes a secondary shape selected to optimize filling of the aneurysm cavity. Multiple coils may be introduced into a single aneurysm cavity for optimal filling of the cavity. The deployed coils serve to block blood flow into the aneurysm and reinforce the aneurysm against rupture. 
         [0004]    One form of delivery system used to deliver an embolic coil through a catheter to an implant site includes a wire and a coil attached to the wire. The coil (with the attached wire) is advanced through a catheter as discussed above. To release the coil into an aneurysm, current is passed through the wire, causing electrolytic detachment of the coil from the wire. A similar system is used to deliver a coil to the site of an arterio-venous malformation or fistula. The subject system provides a mechanical alternative to prior art electrolytic detachment systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a side elevation view of an embolic coil implant system; 
           [0006]      FIG. 2  is a side elevation view of the embolic coil of the implant system of  FIG. 1 ; 
           [0007]      FIG. 3A-3C  are a series of side elevation views of the portion of the coil identified by region  3 - 3  in  FIG. 2 , illustrating the properties of the pre-tensioned stretch resistant wire. 
           [0008]      FIG. 4A  illustrates the proximal portion of the coil engaged with the distal portion of the detachment shaft and wire. 
           [0009]      FIG. 4B  is similar to  FIG. 4A  and illustrates the proximal portion of the coil and the distal portion of the shaft and wire following detachment. 
           [0010]      FIGS. 5A through 5G  are a sequence of drawings schematically illustrating the steps of occluding an aneurysm using the system of  FIGS. 1 through 4B . 
           [0011]      FIGS. 6A and 6B  schematically illustrate steps of detaching the coil from the detachment shall and wire in accordance with the method of  FIGS. 5A through 5G . 
           [0012]      FIG. 7  is an elevation view of an alternate embodiment of a detachment system, in which the distal end of the pusher tube is shown partially transparent. 
           [0013]      FIG. 8  is a perspective view of the embodiment of  FIG. 7 . 
           [0014]      FIG. 9  is a plan view of the system of  FIG. 7 , showing the coil detached from the pusher tube. 
           [0015]      FIG. 10  is an elevation view of the system of  FIG. 7 , showing the coil detached from the pusher tube. 
           [0016]      FIG. 11  is a side elevation view of yet another embodiment of a detachment system according to the invention, in which the distal end of the pusher tube is shown partially transparent. 
           [0017]      FIG. 12  is a plan view of the embodiment of  FIG. 11 . 
           [0018]      FIG. 13  is a bottom view of the embodiment of  FIG. 11 . 
           [0019]      FIG. 14  is a side elevation view of the embodiment of  FIG. 11  following a step in detachment of the embolic coil. 
           [0020]      FIG. 15  is a side elevation view of the embodiment of  FIG. 11  following detachment of an embolic coil. 
           [0021]      FIG. 16  is a side elevation view of yet another alternative embodiment according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Referring to  FIG. 1 , general components of an embolic coil implant system  10  include a microcatheter  12 , insertion tool  14 , and embolic coil  16 . These components may be provided individually or packaged together. Additional components of the system may include a guide catheter insertable into the vasculature via an access point (e.g., femoral puncture), and an associated guide wire for facilitating advancement of the guide catheter. 
         [0023]    Microcatheter  12  is an elongate flexible catheter proportioned to be received within the lumen of a corresponding guide catheter and advanced beyond the distal end of the guide catheter to the cerebral vasculature where an aneurysm to be treated is located. Suitable dimensions for the microcatheter include inner diameters of 0.010 “to 0.045”, outer diameters of 0.024″ to 0.056″, and lengths from 75 cm to 175 cm. One preferred embodiment utilizes the following dimensions: 0.025 in ID, 0.039 in Distal OD (3 F), 0.045 in Proximal OD (3.5 F), and length of 145-155 cm. Marker bands  18  facilitate fluoroscopic visualization of the microcatheter position during the course of an implantation procedure. Microcatheter  12  includes a lumen  20  proportioned to receive the embolic coil  16  and the shaft of the insertion tool  14 . When the coil is within the lumen of the microcatheter, the surrounding lumen walls restrain the coil in the generally elongated shape shown in  FIG. 1 . Release of the coil from the microcatheter allows the coil to assume its secondary shape. 
         [0024]    Details of the embolic coil  16  are shown in  FIG. 2 . Coil  16  is formed of a wire  22  coiled to have a primary coil diameter D 1  of approximately 0.020 inches, although smaller diameters, and diameters as large as 0.035 inches, may instead be used. The pitch of the coil may be uniform as shown, or it may vary along the length of the coil, or different sections of the coil may be formed to have different pitches. The wire material selected for the coil is preferably one capable of fluoroscopic visualization, such as Platinum/Iridium, Platinum/Tungsten, or other suitable material. In one embodiment, the wire forming the coil has a diameter of approximately 0.0015-0.0020 inches. Coil  16  is then formed into a secondary three-dimensional shape. The secondary shape can be helical, spherical, multi-lobal or any other shape desired to fill the aneurysm void. ‘The process for forming this shape is to temperature set the stretch resistant wire  30  into the desired shape. The stretch-resistant member could be a shape-memory polymer or metal such as nitinol. Stretch-resistant member  30  can be in a diameter range of 0.0005″ to 0.003″. 
         [0025]    One or more reduced-diameter windings  24  are positioned at the proximal end of the coil  16 , forming a stop  26 . An atraumatic distal tip  28 , which may be formed of gold or tin solder or other material, is mounted to the distal end of the coil  16 . A stretch resistant wire  30  or other type of elongate filament or strand is attached to the distal tip  28  and extends through the coil  16 . Stretch resistant wire  30  includes an element  32  on its proximal end that is sufficiently broad that it will not pass through the lumen of the windings of stop  26 , but will instead rest against the stop  26 . Element  32  may be a ball (e.g., formed of gold/tin solder, PET, platinum, titanium or stainless steel) as shown, or an alternative element having features that will engage with or be unable to pass the stop  26  or other parts of the proximal portion of the coil  16 . The stretch resistant wire helps to maintain the pitch of the coil even when the coil is placed under tension. During implantation, the stretch resistant wire helps in repositioning of the coil (if needed). The stretch resistant wire makes the coil easier to retract, and maintains close positioning of coil windings during manipulation of the coil. 
         [0026]    Stretch resistant wire  30  is pre-tensioned, so that the ball  32  naturally sits firmly against the stop  26  as shown in  FIG. 3A . When tension is applied to the wire  30  as shown in  FIG. 3B , and then released as in  FIG. 3C , the ball will return to its firm seating against the stop. The stretch resistant wire prevents the coil from stretching when deployed, repositioned, or withdrawn from the aneurysm. This stretch resistant wire will not yield when placed in tension during repositioning. Conversely, stretch resistant wire will prevent compaction of adjacent coils, likely improving long term performance of coil  16  following implantation. Stretch resistant wire  30  will have a yield strength approximately 0.5 lbs. In a preferred embodiment, the stretch resistant wire is shape set to give the embolic coil  16  its predetermined secondary shape. In other words, the shape set of the wire will cause the coil  16  to assume the secondary shape ( FIG. 5C ) once it is advanced from the microcatheter  12 . In alternative embodiments, the coil itself, or both the coil and the wire may be shape set to give the coil its secondary shape. 
         [0027]    Referring again to  FIG. 1 , insertion tool  14  includes a flexible elongate tubular shaft  34 , and a handle  36  on the proximal portion of the shaft  34 . An actuator  38  on the handle  36  is manipulatable by a user to effect detachment of an embolic coil from the shaft  34  as will be discussed in detail below. Although the actuator is shown in this drawing as a slidable button, any number of other types of slidable, rotatable, pivotable, depressible, etc., actuators may instead be used using techniques well known in the art. Although the handle  36  is shown coupled to insertion tool  14 , in other embodiments, the handle  36  may be attached and removed for use with multiple coils to effect detachment. 
         [0028]      FIGS. 4A and 4B  show cross-section views of the distal portion of the shaft  34 . As shown, a detachment wire  40  or other type of elongate filament or strand extends through the lumen of the shaft  34 . During use, shaft  34  would be inserted through microcatheter  12  to the aneurysm. A pair of engaging elements  42  is positioned on the wire  40 . Engaging elements  42  are elements that will couple the detachment wire  40  to the stretch resistant wire  30 , preferably by engaging the element  32 . In the illustrated embodiment, the engaging elements  42  are spaced apart elements having a broader diameter than the wire. Suitable examples include spaced apart beads  42  deposited onto the wire. These may be formed of gold/tin solder, PET, stainless steel, or alternate materials. 
         [0029]    As shown in  FIG. 4A , embolic coil  16  is coupled to the insertion tool  14  by positioning ball  32  between the engaging elements  42  within the shaft  34 . The ball  32  is constrained between the engagement elements  42  and the surrounding walls of the shaft lumen. This positioning retracts the ball  32  proximally relative to the coil  16 , adding tension to the stretch resistant wire  30 . 
         [0030]    Referring to  FIG. 4B , to release the embolic coil  16  from the insertion tool  14 , the actuator is manipulated to cause relative advancement of the detachment wire  40  relative to the shaft  34 . In other words, the actuator may withdraw the shaft and/or advance the wire  40 . Other embodiments may be provided without an actuator, in which case the user may manually advance the wire  40  and/or retract the shaft  34 . The more proximal sections of the wire  40  and/or shaft  34  may be thicker than the distal sections as shown in  FIGS. 6A and 6B  to facilitate manual actuation by the user&#39;s fingers or by an actuator. 
         [0031]    The relative movement between the shaft and wire causes the distal portion of the wire  40  to extend from the shaft, thereby releasing the constraints on the ball  32 . The ball  32  and attached stretch resistant wire  30  retract towards the coil  16 , and the ball  32  comes to rest at the stop  26 . 
         [0032]      FIGS. 5A through 5G  illustrate use of the system to implant the coil  16 . Prior to implantation, the coil is coupled to the insertion tool  14  as illustrated in  FIG. 1 . 
         [0033]    The microcatheter  12  is introduced into the vasculature using a percutaneous access point, and it is advanced to the cerebral vasculature. As discussed above, a guide catheter and/or guide wire may be used to facilitate advancement of the microcatheter. The microcatheter is advanced until its distal end is positioned at the aneurysm A.  FIG. 5A . 
         [0034]    The coil  16  is advanced through the microcatheter  12  to the aneurysm A.  FIG. 5B . The coil and insertion tool may be pre-positioned within the microcatheter  12  prior to introduction of the microcatheter  12  into the vasculature, or they may be passed into the proximal opening of the microcatheter lumen after the microcatheter has been positioned within the body. The insertion tool  14  is advanced within the microcatheter  12  to deploy the coil from the microcatheter into the aneurysm A. As the coil exits the microcatheter, it assumes its secondary shape as shown in  FIG. 5C  due to the shape set of the stretch resistant wire  30 . 
         [0035]    Referring to  FIG. 6A , the detachment wire  40  may include fluoroscopically visible markers that indicate to the user when the coil has been advanced sufficiently for detachment. For example, the user may watch for alignment of a marker  44  on the wire  40  with the markers  18  on the microcatheter. Note, however, that the detachment step may be performed with the proximal end of the coil inside or outside the microcatheter. 
         [0036]    At the appropriate time, the coil is released from the insertion tool by withdrawing the shaft  34  relative to the detachment wire  30  to cause the distal end of the wire to extend from the shaft  34 .  FIGS. 5D and 6B  illustrate retraction of the shaft  34  while holding the wire  30  stationary, although the detachment may instead be performed by advancing the wire while holding the shaft stationary, or by combined motion of retracting the shaft and advancing the wire. The coil detaches from the wire  30 , and the ball  32  of the coil  16  retracts into contact with the stop  26 .  FIG. 5E . The insertion tool  14  is withdrawn from the microcatheter  12 .  FIG. 5F . If additional coils are to be implanted, an insertion tool  14  with an attached coil is passed into the microcatheter  12  and the steps of  FIGS. 5B through 5E  are repeated. The method is repeated for each additional coil need to sufficiently fill the aneurysm A. Once the aneurysm is fully occluded, the microcatheter  12  is removed.  FIG. 5G . 
         [0037]      FIGS. 7-10  illustrate an alternative embodiment of an insertion tool  114  that may be used to deploy the embolic coil  16  in the manner similar to that shown in  FIGS. 5A-5G . 
         [0038]    Referring to  FIG. 7 , the insertion tool  114  comprises an elongate pusher tube  116  having a tubular distal tip  118  (shown partially transparent in  FIG. 7 ). A fulcrum  120  having a slot  122  (best shown in  FIG. 9 ) is cut into a side wall of the distal tip  118 . The distal end of the fulcrum can be moved into an inwardly-extending position in which it extends into the lumen of the distal tip  118  as shown in  FIGS. 7 and 8 . The fulcrum  120  is shape set to return to an open (or neutral) position generally flush with the pusher tube wall ( FIG. 9 ) when it is released from the inwardly-extending position. A pull wire  126  is extendable through the lumen of the pusher tube  116  and into the slot  122  in the fulcrum  120  to retain the fulcrum in the inwardly-extending position shown in  FIGS. 7 and 8 . 
         [0039]    The distal tip  118  is preferably formed of shape memory material such as nitinol, shape memory polymer, or an injection molded material having elastic properties. The more proximal sections of the pusher tube  116  can be made of polymeric tubing, with the distal tip  118  mounted to polymeric tubing. In the illustrated embodiment, the distal tip  118  includes a plurality of proximally-extending fingers  124  laminated into the polymeric tubing of the pusher tube  116  to secure the distal tip in place. 
         [0040]    To couple the pusher tube  116  and coil  16  for use, the pull wire  126  is introduced into the pusher tube. Ball  32  is separated slightly from the coil  16  and is inserted into the pusher tube  116  and held in place while the fulcrum  120  is pressed into the inwardly-extending position to prevent movement of the ball  32  out of the distal tip  118 . The pull wire  126  is passed through the slot  122  to retain the fulcrum in the inwardly-extending position. 
         [0041]    To deploy the coil  16 , the coil and pusher tube  116  are passed through a delivery catheter as described above. At the site of the aneurysm, the pusher tube  116  is advanced to push the coil out of the delivery catheter. The pull wire  126  is pulled proximally from the slot  122  of the fulcrum  120 , allowing the fulcrum  120  to return to its open position and out of contact with the ball  32 . As with the previous embodiments, the ball  32  retracts into contact with the proximal end of the coil  16  and in doing so exits the proximal end of the pusher tube  116 . 
         [0042]      FIGS. 11-15  illustrate another alternate embodiment of a detachment system.  FIGS. 11 ,  14  and  15  illustrate detachment system  200  following successive steps to detach embolic coil  206  from insertion tool  214 . Beginning with  FIG. 11 , a side elevation view of the distal end of insertion tool  214  is shown as partially transparent. Insertion tool  214  comprises an elongate pusher tube  216  having a tubular distal tip  218 , and side wall  204  defining lumen  208  therethrough. Side wall  204  is cut, molded, or otherwise configured to define paddle  240 , partial aperture  244  surrounding a portion of paddle  240 , and shoulder  246 . Paddle  240  and partial aperture  244  may be of various alternative sizes and/or shapes. An example of a suitable shape for paddle  240  can be seen in a plan view in  FIG. 12 , which also reveals a possible position of ball  232  prior to deployment of system  200 . As explained in greater detail below, prior to deployment of system  200  to release coil  206 , ball  232  has freedom of movement within lumen  208 , both axially and rotationally. The exact position of ball  232  will consequently vary from that illustrated in  FIG. 12 . 
         [0043]    Also cut or otherwise configured or disposed upon a side wall  204  is alignment member  228 , shown in the example of  FIG. 11  as opposite paddle  240 . As seen from a bottom view of the device in  FIG. 13 , alignment member is illustrated as a loop cut from sidewall  204 . Alternatively, an alignment member may be formed by placing one or more circumferential cuts into the sidewall to define a band and bending the band inwardly into the lumen. It will be appreciated that alignment member  228  may alternatively be, for example, a hook, tab, or any other suitable structure for guiding the position of pull wire  226 . Pull wire  226  is axially moveable within alignment member  228 , however, alignment member  228  helps prevent unintended longitudinal translation of pull wire  226 . 
         [0044]    In preparation for deploying system  200 , pull wire  226  is loaded through alignment member  228 , through lumen  208 , until it reaches ball  232 , or as far as coil  206 . Prior to loading coil  206 , pull wire  226 , which may be tapered, may be threaded through the distal end of insertion tool  214  to permit loading of ball  232 , and then retracted slightly to releasably retain coil  206 . When positioned within distal tip  218  via alignment member  228 , and occupying lumen  208  pull wire  226  urges ball  232  against paddle  240 , and ball has freedom of movement within aperture  244 . Partial aperture  244  permits paddle  240  to be urged slightly out of the plane of sidewall  204 , and paddle  240  in turn places some pressure on ball  232 . Ball  232  is prevented by shoulder  246  from exiting the distal tip  218 . Though ball  232  is retained within distal tip of insertion tool  214  prior to deployment of system  200 , ball  232  advantageously has both axial and rotational freedom of movement within the distal tip  218  of insertion tool  214  prior to retraction of pull wire  226  by an operator. 
         [0045]    As shown in  FIG. 14 , during deployment of detachment system  200 , pull wire  226  is retracted proximally of ball  232 . (Alternatively, insertion tool  214  may be moved distally to pull wire  226 .) Once pull wire  226  is proximal of ball  232 , ball  232  is urged by paddle  240  into the lumen  208  of insertion tool  214 . Axial movement of ball  232  is no longer restricted in a distal direction by shoulder  246 , and ball  232  (and hence coil  206 ) is free to exit distal tip  218 .  FIG. 15  illustrates coil  206  following its exit from distal tip  218 . 
         [0046]      FIG. 16  illustrates a similar detachment mechanism which operates generally according to the same principles of the embodiment described in relation to  FIGS. 11-15  above. However, in the embodiment illustrated in  FIG. 16 , paddle  340  is oriented perpendicularly to the longitudinal access of insertion tool  214 . Further, no aperture surrounds paddle  340 . Other, alternative configurations of paddle  340  are also possible according to the invention.