Abstract:
This disclosure concerns release mechanisms for medical implants, particularly embolic coils and the like, which utilize bulbous elements and receiving elements to constrain the bulbous elements. In some cases, the receiving elements are sized and shaped to help constrain the bulbous element axially and/or radially, and may work in concert with constraining elements and/or release wires that are optionally moveable independently of the receiving elements.

Description:
PRIORITY 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 to U.S. Provisional Patent Application Ser. No. 62/237,904, filed Oct. 6, 2015, which is incorporated by reference in its entirety and for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This application relates to the field of medical devices and medical procedures. More particularly, the application is related to devices and methods for occluding body lumens such as blood vessels. 
       BACKGROUND 
       [0003]    Therapeutic embolization or occlusion of blood vessels may be used to treat a variety of vascular and non-vascular conditions including cerebral and peripheral aneurysms, arteriovenous malformation, uterine fibroids and various tumors. One commonly used agent for embolizing blood vessels is the embolic coil, a permanently implanted coiled wire structure which, when implanted into a blood vessel, occludes the vessel by causing thrombosis where it is deployed. Embolic coils may have different lengths and/or cross-sectional diameters, in order to fit into and occlude vascular structures of varying sizes. In use, the coils are delivered through a microcatheter in a narrow-diameter elongated configuration (e.g. to fit within a 3 Fr catheter lumen). Once deployed into the vessel, the coil may assume a complex 3-D shape such as a helix, a spiral, a J-shape, or a birds-nest shape, and may include thrombogenic fibers or bundles of fibers along its length. Embolic coils are highly flexible, and can be delivered through narrow or tortuous vascular structures, but when occlusion of relatively large vascular structures is desired, multiple coils may be necessary to achieve full occlusion. 
         [0004]    These coils have typically been placed at the desired site using a catheter and a pusher. The site is first accessed by the catheter. In treating peripheral or neural conditions requiring occlusion, the sites are accessed with flexible, small diameter catheters, which may be guided to the site through the use of guidewires and/or flow-directed means such as balloons at the distal end of the catheter. Once the site has been accessed, the catheter lumen is cleared (i.e., the guidewire is removed if a guidewire has been used), and the coil is placed in the proximal end of the catheter and advanced through the catheter with a pusher. When the coil reaches the distal end of the catheter it is advanced into the vessel and deployed. This technique of plunging the coil from the distal end of the catheter has undesirable limitations. First, because of the plunging action of the pusher during deployment, the positioning of the coil at the site cannot be controlled to a fine degree of accuracy. Second, once plunged from the catheter, it is difficult to reposition or retrieve the coil if desired. Indeed, another device, called a retriever, must be threaded through the catheter to snare the coil to reposition or retrieve it. 
         [0005]    The coil is typically connected to the pusher or another structure within the catheter and must be detached. This detachment is typically facilitated by the use of an electrolytically severable link or a mechanical coupling. While current detachment mechanisms are generally reliable, they may not release the coil when triggered 100% of the time. In the case of mechanical detachment mechanisms in particular, improving detachment reliability may involve undesirable trade-offs such as increasing the size and/or cost of parts used in detachment mechanisms. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention, in its various aspects, provides improved mechanical coil detach systems which achieve 100% detachment and which minimize the trade-offs between 100% detachment and increased size and/or expense. 
         [0007]    In one aspect, the present invention relates to a system for treating a patient which includes a catheter defining a lumen, a pusher assembly slidably disposed within the lumen, a constraining element slidably disposed within the lumen and moveable independently of the pusher assembly, which constraining element has a tubular distal end disposable about a distal portion of the pusher assembly, and an embolic coil with a proximal end comprising a bulbous element. The pusher assembly, in preferred embodiments, includes a distal receiving element having a first portion defining a first planar surface extending radially and a second portion defining an elongated planar surface extending substantially perpendicular to and distally from the planar surface, the elongated planar surface having a protrusion extending away from the planar surface. In some embodiments, the inner diameter of the tubular distal end of the constraining element is closely toleranced to the combined outer diameter of the bulbous element of the embolic coil and the second portion of the distal receiving element (for instance, the inner diameter is, in some cases, not more than 133% of (a) an outer diameter of the bulbous element of the embolic coil, plus (b) a thickness of the second portion of the distal receiving element). Similarly, in some embodiments, the protrusion extends a distance from the elongated planar surface that is less than 50% of a diameter of the bulbous element. More generally, in certain embodiments, the combination (i.e. the combined thickness) of the extension of the protrusion from the elongated planar surface and the second portion of the distal receiving element is greater than or equal to a difference between the inner diameter of the tubular distal end of the constraining element and the combined outer diameter of the bulbous element of the embolic coil and the second portion of the distal receiving element. In some cases, the bulbous element is connected to the embolic coil by one of a wire and a rod extending axially along a central axis of the coil, and wherein the wire or rod extends axially along a central axis of the embolic coil when the bulbous element and receiving element are engaged and disposed within the lumen of the tubular distal end of the constraining element. The constraining element and pusher assembly may be arranged within the lumen in several different ways to permit smooth catheter operation and/or to minimize the potential for mechanical interference between those parts. For instance, in some cases the constraining element includes a wire or a rod disposed proximally of the tubular distal end, the wire or rod extending parallel to the pusher assembly, in which case the pusher assembly is disposed coaxially within the catheter lumen. In other cases, the constraining element includes a coiled segment disposed proximally of the tubular distal end, in which case the pusher assembly is disposed coaxially within a lumen defined by the coiled segment. In still other cases, the constraining element includes a wire or a rod disposed proximally of the tubular distal end and disposed coaxially within the catheter lumen and the pusher assembly includes an elongated portion extending parallel to the wire and through a proximal aperture within the tubular distal end. In various cases, the distal receiving element is a single piece. In preferred cases, the embolic coil is secured to the catheter by contacting the bulbous element and the distal receiving element and advancing the constraining element at least partially over the bulbous element and the distal receiving element and, optionally, the coil is released by moving at least one of the pusher assembly and the constraining element relative to the other. In some cases, the pusher assembly and constraining element can be retracted from the catheter and replaced with a pusher assembly and constraining element engaged with a second embolic coil. The system according to this aspect can be used in medicine, for instance for the treatment of vascular conditions, and can be included in kits for use by medical personnel. 
         [0008]    In another aspect, the present invention relates to a system for treating a patient which includes a catheter defining a first lumen, a pusher assembly slidably disposed within the first lumen and having a tubular distal element defining a second lumen, which tubular distal element includes a slot formed in a wall thereof, a release wire slidably disposed within the first lumen and moveable independently of the pusher assembly, and an embolic coil with a proximal end comprising a bulbous element. In various embodiments according to this aspect, the tubular distal end has an inner diameter that is less than a combined diameter of the bulbous element plus a diameter of the release wire, and wherein the release wire is disposable (i.e. it can be positioned) near an inner wall of the tubular distal element opposite the slot so as to displace the bulbous element into the slot. The pusher assembly can include, in some cases, a wire or a rod disposed proximally of the tubular distal end and coaxially within the catheter lumen, in which case the release wire extends parallel to the pusher assembly, or the pusher can include a coiled segment disposed proximally of the tubular distal end, in which case the release wire can be disposed coaxially within a lumen defined by the coiled segment. 
         [0009]    In yet another aspect, the present invention relates to a method of treating a patient by inserting into that patient&#39;s body a catheter having a pusher assembly, distal receiving element, constraining element and embolic coil with a bulbous element as described above. Once inserted, at least one of the pusher assembly and the constraining element is moved relative to the other, thereby permitting the bulbous element to separate from the distal receiving element. As above, in some cases the inner diameter of the tubular distal end of the constraining element is not more than 133% of the outer diameter of the bulbous element of the embolic coil plus the thickness of the second portion of the distal receiving element, the protrusion extends a distance from the elongated planar surface that is less than 50% of a diameter of the bulbous element, and/or the combination of the extension of the protrusion from the elongated planar surface and the second portion of the distal receiving element is greater than or equal to a difference between the inner diameter of the tubular distal end of the constraining element and the combined outer diameter of the bulbous element of the embolic coil and the second portion of the distal receiving element. The bulbous element can be connected to the embolic coil by one of a wire and a rod extending axially along a central axis of the coil, such that the wire or rod extends axially along a central axis of the embolic coil when the bulbous element and receiving element are engaged and disposed within the lumen of the tubular distal end of the constraining element. The method can also include a step of retracting the pusher assembly, and may also include a step of retracting the constraining element prior to the retraction of the pusher assembly. In some cases, the pusher assembly and the constraining element are withdrawn from the catheter, and a pusher assembly and constraining element engaged with a bulbous element of a second embolic coil is reinserted into the catheter. Finally, in some cases the method includes positioning at least part of the embolic coil within a vascular structure to be occluded. 
     
    
     
       DRAWINGS 
         [0010]    Aspects of the invention are described below with reference to the following drawings in which like numerals reference like elements, and wherein: 
           [0011]      FIG. 1  shows a schematic view of a delivery catheter according to certain embodiments of the present invention. 
           [0012]      FIGS. 2A, 2B and 2C  show schematic views of the catheter of  FIG. 1  at three points during the detachment process. 
           [0013]      FIG. 3  shows a schematic depiction of a receiving element as used in the delivery catheter of  FIGS. 1 and 2 . 
           [0014]      FIGS. 4A , B, C, D, E and F show, in schematic form, various alternative configurations of delivery catheters according to the embodiments of the present invention. 
       
    
    
       [0015]    Unless otherwise provided in the following specification, the drawings are not necessarily to scale, with emphasis being placed on illustration of the principles of the invention. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    An exemplary catheter assembly  100 , as shown in  FIG. 1 , includes a generally tubular catheter  105 , an embolic coil  110  (though any other implantable medical device of similar size may be used) having, at its proximal end, a ball or other bulbous element  111 , a pusher assembly  115  slidably disposed within the catheter  105  and having, at its distal end, a receiving element  116  that is sized to engage the ball  111 . The catheter assembly  100  also includes a constraining element  120  that is slidable within the catheter lumen independently of the pusher assembly  115  and which constrains the axial or radial movement of the ball  111  when it is engaged with the receiving element  116 . 
         [0017]    The constraining element  120  depicted in  FIGS. 1 and 2  has a generally tubular distal end and has an inner diameter that is slightly larger than the combined width of the ball  111  and the receiving element  115  when the two are engaged (e.g. 10% larger, 20% larger, 30% larger, 40% larger or 50% larger). Together with a lip or ridge  116   a  on the receiving element, the constraining element  120  helps limit both the axial and radial movement of the ball  111  when it is engaged with the receiving element  116  and is contained within the lumen of the constraining element  120 . This arrangement is shown in  FIG. 2A  and is used to advance the coil  110  through the distal end of the catheter  105 . 
         [0018]    As  FIG. 2B  illustrates, as the coil  110  is advanced through the distal end of the catheter  105 , the constraining element  120  remains positioned over the ball  111  and the receiving element  116  of the pusher assembly  115 , permitting the placement of the coil  110  prior to its release. When release of the coil is desired, the constraining element  120  is retracted over the pusher assembly  115  or, alternatively, the pusher assembly  115  is advanced through the constraining element  120 ; in either case, the ball  111  is exposed ( FIG. 2C ), thereby releasing the embolic coil  110 . 
         [0019]    The catheter assembly  100  shown in  FIGS. 1 and 2  has several advantageous characteristics, including without limitation the following: it is 100% detachable yet it allows a user to recapture the coil  110  by engaging the receiving element  116  with the ball  111  and advancing the constraining element  120  over both. At the same time, the simple design has a small overall diameter that will tend to preserve the flexibility of the catheter assembly  100  and can be implemented using materials that are currently used to produce delivery catheters. 
         [0020]    Turning now to  FIG. 3 , an exemplary receiving element  116  includes a proximal axially constraining surface  116   b  and a radially constraining surface  116   c  which in turn includes, at its distal end, a ridge or lip  116   a  that serves to further limit the axial movement of the ball  111  and therefore the coil  110  when the constraining element  120  is extended over the ball  111  and the receiving element  116 . Each of the proximal axially constraining surface  116   b,  the radially constraining surface  116   c  and the lip or ridge  116   a  are generally continuous with one another (such that the receiving element  116  can be fabricated as a single piece) and preferably have relatively flat (in the case of the radial and axial constraining surface), even surfaces. 
         [0021]    The receiving element  116  depicted in  FIG. 3  is superficially similar to the design of Engelson disclosed in U.S. Pat. No. 5,261,916 (which is incorporated by reference in its entirety and for all purposes herein), but the skilled artisan will appreciate that Engelson utilizes a pusher with an enlarged cylindrical tip having both an axial bore and a radial slot to receive the ball of the embolic coil, such that the coil is constrained both proximally and distally by a body having a diameter equal to or greater than the diameter of the ball. In the embodiment of  FIGS. 1-3 , however, the lip  116   a  is significantly smaller than the diameter of the ball  111 . For instance, in one case the ball  111  has a diameter of approximately 0.012″ (0.30 mm), while the lip or ridge  116   a  may have a convex curved surface with a radius of 0.0035″ (0.09 mm). More generally, the lip  116   a  preferably extends a distance that is equal to or, preferably, slightly greater than the difference between the inner diameter of the constraining element  120  and the combined outer diameters of the receiving element  116  and the ball  111  when the two are engaged. This configuration limits radial displacement of the ball  111  and the proximal end of the embolic coil  110  during the delivery process, aiding accurate placement of the coil  110  with a relatively low risk of coil movement during release. At the same time, the distance is not so great as to reduce the mechanical clearance of the ball  111  or the connector between the ball  111  and the coil  110  when it is engaged with the receiving element  116  and the constraining element  120 . 
         [0022]    While the embodiments presented above exemplify certain aspects of the present invention, it is not limited in scope to those aspects. For instance, the constraining element  120  is depicted throughout  FIGS. 1, 2 and 3  as a cylindrical body having constant inner and outer diameters and extending the entire length of the catheter assembly  100 . This arrangement has the advantages described above, but the resulting catheter assembly  100  may be comparatively stiff, as the constraining element is preferably robust to deformation or “ovalization” that could potentially allow the ball  111  to migrate during delivery. 
         [0023]    In situations where embolic coils are to be delivered through tortuous and/or narrow diameter vessels, a more flexible catheter may be desired; this is achieved in various embodiments by altering the diameter, length or rigidity of the constraining element  120  along the length of the catheter assembly  100 . For instance, in some cases, the diameter of the constraining element  120  is maximized at its distal end so as to encompass the ball  111  and the receiving element  116 , then decreases proximally. Alternatively, the distal portion of the constraining element  120  may be made more rigid than the proximal portion (e.g. by means of greater wall thickness, incorporation of a rigid material such as a reinforcing fiber or braid, or a rigid bushing) allowing the distal end to resist ovalization while the proximal end retains flexibility. And, in yet another alternative illustrated in  FIGS. 4A-B , the distal constraining element  120  has a length that is significantly less than the length of the catheter  105  and is connected, at its proximal end, to a wire or other structure  121  that enables the constraining element  120  to be pushed or pulled relative to the catheter  105  and/or the pusher assembly  115 . In the embodiments shown in  FIGS. 1-3 , the constraining element  120  and the pusher assembly are arranged coaxially (i.e. the pusher assembly  115  is centered) along substantially all of the length of the catheter assembly  100 ; in the embodiment of  FIG. 4A , the wire  121  is centered, and the constraining element includes an off-center proximal aperture  122  to accommodate the pusher assembly  115 . Alternatively, if the pusher assembly  115  is centered, the proximal aperture  122  is located more centrally, while the wire  121  is off-center as shown in  FIG. 4B . 
         [0024]    In addition to improved flexibility, the relatively short constraining element  120  shown in  FIGS. 4A-B , as well the embodiments described below, facilitate of fluid injection through the delivery catheter  105 : the use of a tubular constraining element  120  of relatively short length may reduce the fluid pressure necessary to inject fluid through the catheter  105 , by providing a comparatively larger inner diameter across most of its length. By contrast, the diameter of the lumen available for fluid flow is reduced along the entire length of the catheter  105  when the constraining element  120  is a tube extending the entire length of the catheter  105 . 
         [0025]    Embolic coil  110  will, in certain embodiments, have both a primary helical structure and a complex secondary structure, such as a helix, an ovoid shape, a J-shape, etc., as described in U.S. Pat. No. 5,639,277 to Mariant, et al, which is incorporated by reference herein for all purposes. Because the coil  110  tends to assume the secondary shape when unconstrained, it may expand while disposed within the lumen of the catheter  105  and, as the coil  110  is advanced through the catheter  105 , it may tend to twist. One potential complication of the designs of  FIGS. 4A-B , and those described below, is that this twisting may cause the wire  121  to twist, potentially twisting around the pusher assembly  115 . In order to prevent twisting of the wire  121  and the pusher assembly  115 , the catheter optionally includes constraining elements such as small bushings, or wire rings, which limit the circumferential and/or radial movement of one or both of the wire  121  and the pusher assembly  115 . These wires, bushings, etc. are preferably positioned at multiple places along the length of the catheter  105 , thereby ensuring that the wire  121  and the pusher assembly  115  do not mechanically interfere with one another along the length of the catheter  105  during the delivery process. 
         [0026]    In another group of embodiments, a pusher assembly including a receiving element provides both radial and axial constraint of the ball with the aid of a wire or other narrow body that urges the ball and the receiving element together. For instance, in  FIGS. 4C-D , a catheter assembly  400  includes a catheter  405  for delivering an embolic coil  410  having a proximal ball  411 , which catheter includes a pusher assembly  415  with a tubular receiving element  416  having an axial bore defining a lumen and a slot  417  cut into the side-wall of the receiving element  416  that is sized to accommodate part or all of the ball  111 . The assembly also includes a release wire  420  slidably disposed in the catheter  405  that is independent of the pusher assembly  415 . The release wire  420  is positioned to urge the ball  411  toward the slot  417 , providing axial and radial constraint of the ball  411  during delivery. As discussed above, either the pusher assembly  415  or the release wire  420  can be centered, in which case the other is off-center. In either case, the release wire  420  and the pusher assembly  415  are optionally constrained to prevent tangling or crossing at one or more points along the length of the catheter  405 , for instance by one or more wire rings, or by the use of a guidewire lumen or slit within the catheter  405  (not shown). 
         [0027]    In use, the catheter assembly  400  operates by “pull release”: in order to deploy the coil  410 , the pusher assembly  415  and the release wire  420  are advanced distally relative to the catheter  405 ; once the coil is suitably positioned, the release wire  420  is retracted proximally, thereby releasing the coil  410 . 
         [0028]    Turning now to  FIGS. 4E-F , in some cases, the pusher assembly and constraining element are arranged coaxially, with the pusher element  115  being central and extending through a hollow central portion  130  of the constraining element  120  ( FIG. 4E ). Alternatively, as shown in  FIG. 4F , the release wire  420  can extend through a hollow central portion  430  of the pusher assembly  416 . The hollow central portion  130   430  can be a coil or other suitable hollow body through which the pusher assembly  115  or the release wire  420 , respectively, is be slidably disposed. 
         [0029]    The phrase “and/or,” as used herein should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. 
         [0030]    The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts. 
         [0031]    As used in this specification, the term “substantially” or “approximately” means plus or minus 10% (e.g., by weight or by volume), and in some embodiments, plus or minus 5%. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology. 
         [0032]    Certain embodiments of the present invention have been described above. It is, however, expressly noted that the present invention is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described herein are also included within the scope of the invention. Moreover, it is to be understood that the features of the various embodiments described herein were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express herein, without departing from the spirit and scope of the invention. In fact, variations, modifications, and other implementations of what was described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention. As such, the invention is not to be defined only by the preceding illustrative description.