Stretch-resistant vaso-occlusive coils

Abstract: This is an implantable vaso-occlusive device. It is typically a vaso-occlusive coil comprised of a primary helically wound coil which may then be wound into a secondary shape. Central to the invention is the use of a stretch-resisting member fixedly attached within at least a portion of the primary coil. The stretch-resisting member may be formed into coil tips at the ends of the coil by melting the polymeric fibers or alloys or by attaching the fibers with a glue. This stretch-resisting member is for the primary purpose of preventing stretching of the coil during movement of that coil, e.g., by retrieval or repositioning after deployment. The device typically has a self-forming secondary shape made from a pre-formed primary linear helically wound coil, although it need not have the secondary form. External fibers may be attached to the device and affixed to the pre-formed linear member to increase. The vaso-occlusive member may be also be covered with a fibrous braid. The device is typically introduced into the body through a catheter. The device is passed axially through the catheter sheath and assumes its secondary form upon exiting the catheter.

Description: This invention is an implantable vaso-occlusive device. It is typically a vaso-occlusive coil comprised of a primary helically wound coil which may then be wound into a secondary shape. Central to the invention is the use of a stretch-resisting member extending through the lumen formed is fixedly attached to the coil in at least two locations. This stretch-resisting member is for the primary purpose of preventing stretching of the coil during movement of that coil, e.g., by retrieval or repositioning after deployment. The device typically has a self-forming secondary shape made from a pre-formed primary linear helically wound coil, although it need not have the secondary form. External fibers may be attached to the device and affixed to the pre-formed linear member to increase thrombogenicity. The vaso-occlusive member may be also be covered with a fibrous braid. The device is typically introduced into the body through a catheter. The device is passed axially through the catheter sheath and assumes its secondary form upon exiting the catheter. Vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. One widely used vaso-occlusive device is a helical wire coil having windings which may be dimensioned to engage the walls of the vessels. Other less stiff, helically coiled devices have been described, as well as those involving woven braids. For instance, US Patent No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded, convoluted configuration when relaxed. The stretched condition is used in placing the coil at the desired site (by its passage through the catheter) and the coil assumes a relaxed configuration -- which is better suited to occlude the vessel --once the device is so placed. Ritchart et al. describes a variety of shapes. The secondary shapes of the disclosed coils include "flower" shapes and double vortices. A random secondary shape is described, as well. Vaso-occlusive coils having attached fibrous elements in a variety of secondary shapes are shown in US Patent No. 5,304,194, to Chee et al. Chee et al. describes a helically wound device having a secondary shape in which the fibrous elements extend in a sinusoidal fashion down the length of the coil. These coils, as with Ritchart et al., are produced in such a way that they will pass through the lumen of a catheter in a generally straight configuration and, when released from the catheter, form a relaxed or folded shape in the lumen or cavity chosen within the human body. The fibrous elements shown in Chee et al. enhance the ability of the coil to fill space within the vasculature and to facilitate formation of embolus and subsequent allied tissue. There are a variety of ways of discharging shaped coils and linear coils into the human vasculature. In addition to those patents which apparently describe only the physical pushing of a coil out into the vasculature (e.g., Ritchart et al.), there are a number of other ways to release the coil at a specifically chosen time and site. US Patent No. 5,354,295 and its parent, 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device. A variety of mechanically detachable devices are also known. For instance, US Patent No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. US Patent No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil. US Patent No. 5,261,916, to Engelson, shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. US Patent 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. US Patent No. 5,312,415, to Palermo, also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil. US Patent No. 5,350,397, to Palermo et al., shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold unto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil. Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, in US Patent Application 07/978,320, filed November 18, 1992, entitled "Ultrasoft Embolization Coils with Fluid-Like Properties" by Berenstein et al. also published as WO-A-9410936, is found a coil having little or no shape after introduction into the vascular space. None of these devices are helical coils which contain a stretch-resisting member contained therein. US-A-5 217 484 discloses a vaso-occlusive device. The deployment tip attached to the proximal end of the primary coil takes the form either of a pair of radially expandable jaws which clamp around a radial enlargement at the distal end of the pusher, or a radial enlargement which is clamped by radially expandable jaws provided at the distal end of the pusher. In both cases, when the deployment tip is pushed distally out of the distal tip of a constraining catheter, the jaws expand radially to unclamp the radial enlargement, releasing the primary coil from the pusher. US-A-5 122 136 discloses a device in accordance with the preamble of claim 1. According to the present invention there is provided a vaso-occlusive device comprising: an outer helically wound primary coil having a first end, a second end and an axis between said first and second ends, said coil defining a lumen between said first and second ends; and a deployment tip attached to at least one of said first and second ends, said deployment tip comprises an electrolytically detachable end adapted to detach from a pusher by imposition of a current on said pusher; characterised in that the device further comprises a stretch-resisting member extending through at least a portion of said lumen and fixedly attached to said primary coil in at least two axially separated locations other than the first and second coil ends, the device being so constructed and arranged that, following the coil's deployment and prior to detachment, the coil may be withdrawn using the pusher, with the stretch-resisting member preventing stretching of said coil during such withdrawal. The primary helix, with its included stretch-resistant member, may be wound into a secondary form and heat-treated to preserve that form, desirably prior to the step of including the stretch-resisting member into the coil. The secondary form may be one which, when ejected from a delivery catheter, forms a specific shape. Such a shape might, e.g., fill a vascular cavity such as an aneurysm, or perhaps, a fistula. The stiffness of the various parts of the coil may be tailored to enhance the utility of the device for specific applications. Fibrous materials may be woven into the member or tied or wrapped onto it. The device may be used simply by temporarily straightening the device and introducing it into a suitable catheter, the catheter already having been situated so that its distal opening is at the selected site in the body. The device is then pushed through the catheter and, upon its ejection from the distal end of the catheter into the vascular cavity, assumes its relaxed or secondary shape. The device is typically used in the human vasculature to form emboli but may be used at any site in the human body where an occlusion such as one produced by the inventive device is needed. The present invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings. None of the drawings shows a device which, in the exact form illustrated, is in accordance with the present invention in that none employs (1) an electrolytically severable joint and (2) a stretch-resisting member attached to the primary coil in at least two axially separated locations other than the coil ends. Nevertheless, when modified to include electrolytically severable joints and stretch-resisting members which are attached to the primary coil in at least two axially separated locations other than the coil ends, these devices may be brought into accordance with the present invention. Figure 1A shows a side view, partial cutaway of a vaso-occlusive coil having a generally linear fibrous stretch-resisting member. Figure 1B shows a side view, partial cutaway of a vaso-occlusive coil having a generally linear wire stretch-resisting member. Figure 1C shows a side view, partial cutaway of a vaso-occlusive coil having a generally helical stretch-resisting member. Figures 2A, 2B, and 2C show side view, partial cutaways of typical ends of vaso-occlusive coils. Figures 3A and 3B show, in side view, partial cutaways of electrolytically severable joints suitable for use in vaso-occlusive coils made according to the invention. Figure 4 shows a "C" shaped secondary shape for a vaso-occlusive device. Figure 5 shows a clover-leaf secondary shape for a vaso-occlusive device. Figure 6 shows a double-looped secondary shape for a vaso-occlusive device. Figure 7 shows attachment of external fibrous material to a vaso-occlusive device. Figure 8 shows attachment of external braided fibrous material to a vaso-occlusive device. Figures 9A-9D show a procedure for introducing a vaso-occlusive coil such as found in the other Figures into an aneurysm. Figures 1A, 1B and 1C show side-view partial cross-sections (or cutaways) of devices (100,200,210). The devices shown in Figures 1A and 1B are made up of a helically wound outer coil (102,202) having a first end (104,204) and a second end (106,206). We refer to this form as the "primary" winding or shape. These devices include a stretch-resisting member (108,208,214) which is shown to be fixedly attached both to the first end (104,204) and to the second end (106,206). In Figures 1A and 1B the stretch-resisting member (108,208) is attached to both ends. The devices of Figures 1A and 1B are not in accordance with the present invention. To be in accordance with the present invention the stretch-resisting member must be attached to at least two points on the coil other than the coil ends. The stretch-resisting member (108) of the device shown in Figure 1A is fibrous and desirably polymeric. It may be a thermoplastic or thermosetting and comprise a bundle of threads or a single filament melted onto, glued, or otherwise fixedly attached to the vaso-occlusive coil (100). In some instances, it may also be desirable to include one or more metallic strands in the stretch-resisting member (108) to provide stiffness or electrical conductance for specific applications. The stretch-resisting member (208) of the device shown in Figure 1B is a simple wire or "ribbon" which is soldered, brazed, glued, or otherwise fixedly attached to the first end (204), second end (206), or to the coil at one or more locations intermediate to those the ends. The device shown in Figure 1C includes a stretch-resisting member (214) which is comprised of a helically wound coil which is soldered, brazed, glued, or otherwise fixedly attached to the first end (204) or second end (206) or in one or more intermediate locations. The stretch-resisting member (214) in this configuration provides a greater measure of lateral flexibility than the wire variation (208 in Figure 1B). It may be wound in either the same direction as is the outer coil (202) or in the alternate direction. A modest drawback to this device is that it will stretch more than the Figure 1B device when axially stressed. The materials used in constructing the vaso-occlusive coil (102, 202) and the stretch resisting member (108, 208, 214) may be any of a wide variety of materials; preferably, a radio-opaque material such as a metal or a polymer is used. Suitable metals and alloys for the wire making up the primary coil (102, 202) and the stretch-resisting member (108, 208, 214) include the Platinum Group metals, especially platinum, rhodium, palladium, rhenium, as well as tungsten, gold, silver, tantalum, and alloys of these metals. These metals have significant radio-opacity and in their alloys may be tailored to accomplish an appropriate blend of flexibility and stiffness. They are also largely biologically inert. Highly preferred is a platinum/tungsten alloy, e.g., 8% tungsten and the remainder platinum. The ribbon or coil stretch-resisting members (208, 214) may also be of any of a wide variety of stainless steels if some sacrifice of radio-opacity and flexibility may be tolerated. Very desirable materials of construction, from a mechanical point of view, are materials which maintain their shape despite being subjected 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 (38-42 weight % zinc); copper/zinc alloys containing 1-10 weight % of beryllium, silicon, tin, aluminum, or gallium; or nickel/aluminum alloys (36-38 atomic % aluminum). Particularly preferred are the alloys described in US Patent Nos. 3,174,851; 3,351,463; and 3,753,700. Especially preferred is the titanium/nickel alloy known as "nitinol". These arc very sturdy alloys which will tolerate significant flexing without deformation even when used as very small diameter wire. If a superelastic alloy such as nitinol is used in the device, the diameter of the coil wire may be significantly smaller than that used when the relatively more ductile platinum or platinum/tungsten alloy is used as the material of construction. The coils may be made of radiolucent fibers or polymers (or metallic threads coated with radiolucent or radio-opaque fibers) such as Dacron (polyester), polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoroethylene), Nylon (polyamide), or even silk. Should a polymer be used as the major component of the vaso-occlusive coil member, it is desirably filled with some amount of a radio-opaque material such as powdered tantalum, powdered tungsten, bismuth oxide, barium sulfate, and the like. The coil material is first wound into a primary coil (102, 202). The primary coil is typically linear after it has been wound. Generally speaking, when the coil (102, 202) is a metallic coil and that coil is a platinum alloy or a superelastic alloy such as nitinol, the diameter of the wire used in the production of the coil (102, 202) will be in the range of 0.0064 and 0.152 mm (0.00025 and 0.006 inches). The wire is wound into a primary coil (102, 202) having a primary diameter of between 0.076 and 0.635 mm (0.003 and 0.025 inches). For most neurovascular indications, the preferable primary coil (102, 202) diameter is 0.2 to 0.46 mm (0.008 to 0.018 inches). We have generally found that the coil wire may be of sufficient diameter to provide a hoop strength to the resulting device sufficient to hold the device in place within the chosen body site, lumen'or cavity, without substantially distending the wall of the site and without moving from the site as a result of the repetitive fluid pulsing found in the vascular system. The axial length of the primary coil will usually fall in the range of 0.5 to 100 cm, more usually 2.0 to 40 cm. Depending upon usage, the coil may well have 10-75 turns per centimeter, preferably 10-40 turns per centimeter. All of the dimensions here are provided only as guidelines and are not critical to the invention. However, only dimensions suitable for use in occluding sites within the human body are included in the scope of this invention. Once the primary coil (102, 202) is wound, the stretch-resisting member (108, 208) is inserted into the lumen of the primary coil (102, 202) and secured to the coil as desired. Suitable polymeric materials for the polymeric stretch-resisting member (108) can be either thermosetting or thermoplastic. Thermoplastics are preferred because they allow simplification of the procedure for constructing the device (100) since they may be melted, for example using simple devices such as soldering irons, to form the ends. Thermosetting plastics would typically be held in place by an adhesive. Suitable polymers include most biocompatible materials which may be made into fibers but include polyester such as polyethyleneterephthalate (especially Dacron) and polyamides including the Nylons, polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoro-ethylene), or even silk. Especially preferred because of the long history of safe and effective usage in the human body is fibrous polyethyleneterephthalate (PET) sold as Dacron. Figure 2A shows a side-view partial cross-section of one end of a coil (100). Figure 2A also shows the helically wound outer coil (102) having an end (106) which is formed from a formerly molten fiber which also makes up the stretch-resisting member (114). An end of this type may be considered to have modestly higher vaso-occluding properties than a metallic end. Other functional equivalents to this structure include ends (106) formed of glues such as epoxies and their equivalents, and which are mechanical in nature. However, to be in accordance with the present invention a device must have its stretch-resisting member attached to the primary coil in at least two axially separated locations other than the coil ends. Feature 2B shows an external knot (112) which fixes the length of the coil member (102) and keeps it from stretching; Figure 2C shows a reformed mass formerly molten polymer or of glue which is of a diameter larger than the inner diameter of coil (102) and prevents the coil from stretching. The knot (112) and block (114) are not shown to be attached to the coil (102) but may be. To be in accordance with the present invention a device must have its stretch-resisting member attached to the primary coil in at least two axially separated locations other than the coil ends. The devices shown in Figures 1A, 1B, 1C and 2A, 2B and 2C are designed to be deployed by use of a pusher and a catheter in the manner discussed in Ritchart et al, discussed above, and as illustrated are thus not in accordance with the present invention. To be in accordance with the present invention a device must be electrolytically detachable from the pusher used to deploy it. When the ends of the devices are adapted to accept an electrolytically severable joint of the type discussed in US Patent No. 5,354,295 and its parent, 5,122,136, both to Guglielmi and Sepetka, described above, and when the stretch-resisting member is attached to the primary coil in at least two axially separated locations other than the coil ends, the resultant devices are in accordance with the present invention. Figures 3A and 3B depict, in partial cross-section, devices each provided with an electrolytically severable joint of the aforementioned type. The vaso-occlusive coil (130,230) is attached to a fill member (132,232). The fill member (132,232) preferably comprises a thermoplastic formed into place or an epoxy or the like and adheres, in turn, both to the stretch resistant member (134,234) and the core wire (136,236). The core wire (136,236) in this variation has an enlarged member which is embedded in the fill member (132,232). The core wire (136,236) is insulated, typically with a combination of polytetrafluoroethylene and parylene (polyparaxyxylene), except for a small sacrificial joint (138,238) which is intended to be the site of the electrolysis as the joint (138,238) is eroded or severed and the coil deployed into the body site. As was noted above, the devices of this invention may have the simple linear shape shown in Figures 1 and 2 or may have shapes which are not so simple. Figures 4 to 6 show what are termed "secondary" shapes in that they are formed from the primary coil by the simple act of winding the primary coil on a form of a desired shape and then beat treating the so-formed shape. Figure 4 shows a "C" shaped coil assembly (160) having a stretch-resistant member (162). Figure 5 shows a clover-leaf shaped coil assembly (164) also having a stretch-resistant member (162). Figure 6 shows a double-loop coil assembly (166). These are indicative of the various secondary shapes suitable for this invention. Additionally, these devices may also be used in conjunction with various external fiber adjuncts. Figure 7 shows a partial side-view of a linear variation of the inventive device (170) having filamentary material (172) looping through the coil (174). This method of attachment is described in greater detail in US Pat. Nos. 5,226,911 and 5,304,194, to Chee et al. A further description of a desirable fiber attachment is shown in US Pat. application No. 08/265,188, to Mirigian et al, filed June 24, 1994 and published as EP-A-715503, belonging to the prior art by virtue of Article 54(3) EPC. Figure 9 shows a partial cutaway of a device (180) having a braided covering (182) of a filamentary material and a stretch-resisting member (184). This method of enveloping a coil is described in greater detail in US Pat. Nos. 5,382,259, to Phelps et al. The fibrous woven or braided tubular materials may be made from a biocompatible materials such as Dacron (polyester), polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoroethylene), Nylon (polyamide), or silk. The strands forming the braid should be reasonably heavy, e.g., having tensile strength of greater than about 0.66N (0.15 pounds). The materials mentioned, to the extent that they are thermoplastics, may be melted or fused to the coils. Alternatively, they may be glued or otherwise fastened to the coils. Preferred materials are Dacron. Figures 9A-9D depict a common deployment method suitable for introduction of the vaso-occlusive devices of the present invention. It may be observed that these procedures are not significantly different than those described in the Ritchart et al. patent mentioned above. Although the vaso-occlusive device illustrated in Figures 9A-9D is not shown as having an electrolytically severable joint, it will be appreciated that the deployment method is applicable to inventive vaso-occlusive devices with such joints. Specifically, Figure 9A shows the distal tip of a delivery catheter (310) which is within the opening (312) of an aneurysm (314) found in an artery (316). The distal or end section of the vaso-occlusive device (318) is shown within the catheter (310). In Figure 9B, the distal end portion of the vaso-occlusive device (318) has exited the distal end of the catheter (310) and has wound into a secondary shape within the aneurysm (314). Figure 9C shows the completion of the formation of the secondary shape within the aneurysm (314). Figure 9D shows the separation of the vaso-occlusive device (318) from the pusher, placement within the aneurysm (314), and the withdrawal of the catheter from the mouth of the aneurysm. Once the inventive coil is in place in an aneurysm or other site, there may be an occasion during which the coil must be moved or even withdrawn. For instance, in Figure 9D, the coil might extend through the mouth (312) of the aneurysm into the artery. Occlusion would not be desirable in the artery. A device such as the endovascular snare shown in US Pat. No. 5,387,219, to Rappe, may then be used to grasp the exposed coil and move it or retrieve it from the body. The stretch-resisting member of this invention prevents the coil from stretching into a single strand of wire and multiplying in length.

Claims: A vaso-occlusive device comprising: an outer helically wound primary coil (130,230) having a first end, a second end and an axis between said first and second ends, said coil defining a lumen between said first and second ends; and a deployment tip attached to at least one of said first and second ends, said deployment tip comprises an electrolytically detachable end adapted to detach from a pusher by imposition of a current on said pusher; characterised in that the device further comprises a stretch-resisting member extending through at least a portion of said lumen and fixedly attached to said primary coil in at least two axially separated locations other than the first and second coil ends, the device being so constructed and arranged that, following the coil's deployment and prior to detachment, the coil may be withdrawn using the pusher, with the stretch-resisting member preventing stretching of said coil during such withdrawal. The device of claim 1, wherein said stretch-resisting member comprises at least one fiber. The device of claim 1, wherein said stretch-resisting member comprises multiple fibers. The device of any one of the preceding claims, wherein said stretch-resisting member comprises a wire. The device of any one of the preceding claims, wherein said stretch-resisting member comprises a helical coil. The device of any preceding claim, wherein said helically wound primary coil has a secondary form. The device of any one of the preceding claims, wherein said helically wound primary coil comprises a metal selected from the group consisting of platinum, palladium, rhodium, gold, tungsten, and their alloys. The device of claim 7, wherein said helically wound primary coil comprises an alloy of platinum and tungsten. The device of any one of claims 1 to 6, wherein said helically wound primary coil comprises an alloy selected from the group consisting of stainless steels and super-elastic alloys. The device of claim 9, wherein said helically wound primary coil comprises a nickel-titanium super-elastic alloy. The device of any one of the preceding claims, additionally comprising external filamentary material attached to said primary coil. The device of any one of the preceding claims, wherein the stretch-resisting member comprises a polymer. The device of claim 12, wherein the polymer contains a radio-opaque filler. The device of claim 12 or claim 13, wherein the stretch-resisting member comprises a thermoplastic. The device of claim 14, wherein said thermoplastic comprises polyethylene terephthalate. The device of claim 14 or claim 15, wherein said thermoplastic also forms a cap located on at least one end of said primary coil. The device of claim 16, wherein said cap is of the same diameter as said primary coil. The device of claim 16 or claim 17, wherein said thermoplastic forms caps at both ends of said primary coil. The device of any one of claims 1 to 11, wherein the stretch-resisting member comprises a ribbon. The device of claim 19, wherein said ribbon comprises a metal selected from the group consisting of platinum, palladium, rhodium, gold, tungsten, and their alloys. The device of claim 20, wherein said ribbon comprises an alloy of platinum and tungsten.

Inventors: ENGELSON ERIK T, GIA SON M, KEN CHRISTOPHER G M, ENGELSON, ERIK T., GIA, SON M., KEN, CHRISTOPHER G.M.
Applicants: TARGET THERAPEUTICS INC, TARGET THERAPEUTICS, INC.
Application year: 1996
Main classification: A61B17
IPC codes: A61F2, A61B17, A61B19