Embolic coil deployment system with improved embolic coil

A medical device for placing an embolic coil at a preselected location within a vessel comprising a positioning catheter having a distal tip for retaining the embolic coil which when pressurized with a fluid expands outwardly to release the coil at the preselected position and including an embolic coil having a relatively flexible proximal portion which resists stretching.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a medical device for placing an embolic
 coil at a preselected location within a vessel of the human body, and more
 particularly, relates to a catheter having a distal tip for retaining the
 embolic coil in order to transport the coil to a preselected position
 within the vessel and a control mechanism for releasing the embolic coil
 at the preselected position.
 2. Description of the Prior Art
 For many years flexible catheters have been used to place various
 devices-within the vessels of the human body. Such devices include
 dilatation balloons, radiopaque fluids, liquid medications and various
 types of occlusion devices such as balloons and embolic coils. Examples of
 such catheter devices are disclosed in U.S. Pat. No. 5,108,407, entitled
 "Method And Apparatus For Placement Of An Embolic Coil"; U.S. Pat. No.
 5,122,136, entitled, "Endovascular Electrolytically Detachable Guidewire
 Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms,
 Vascular Malformations And Arteriovenous Fistulas." These patents disclose
 devices for delivering embolic coils to preselected position within vessel
 of the human body in order to treat aneurysms or alternatively to occlude
 the blood vessel at the particular location.
 Coils which are placed in vessels may take the form of helically wound
 coils, or alternatively, may be random wound coils, coils wound within
 other coils or many other such coil configurations. Examples of various
 coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled,
 "Vascular Occlusion Assembly; U.S. Pat. No. 5,382,259, entitled,
 "Vasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous
 Coverings." Embolic coils are generally formed of a radiopaque metallic
 materials, such as platinum, gold, tungsten or alloys of these metals.
 Often times several coils are placed at a given location in order to
 occlude the flow of blood through the vessel by promoting thrombus
 formation at the particular location.
 In the past, the proximal end of embolic coils have been placed within the
 distal end of the catheter and when the distal end of the catheter is
 properly positioned the coil may then be pushed out of the end of the
 catheter with, for example a guidewire, to release the coil at the desired
 location. This procedure of placement of the embolic coil is conducted
 under fluoroscopic visualization such that the movement of the coil
 through the vasculature of the body may be monitored and the coil may be
 placed in the desired location. With these placements systems there is
 very little control over the exact placement of the coil since the coil
 may be ejected to a position some distance beyond the end of the catheter.
 As is apparent, with these latter systems, when the coil has been released
 from the catheter it is difficult, if not impossible, to retrieve the coil
 or to reposition the coil.
 Numerous procedures have been developed to enable more accurate positioning
 of coils within a vessel. Still another such procedure involves the use of
 a glue or solder for attaching the embolic coil to a guidewire which, is
 in turn, placed within a flexible catheter for positioning the coil within
 the vessel at a preselected position. Once the coil is at the desired
 position, the coil is restrained by the catheter and the guidewire is
 pulled from the proximal end of the catheter to thereby cause the coil to
 be detached from the guidewire and released from the catheter system. Such
 a coil positioning system is disclosed in U.S. Pat. No. 5,263,964,
 entitled, "Coaxial Traction Detachment Apparatus And Method."
 Another coil positioning system utilizes a catheter having a socket at the
 distal end of the catheter for retaining a ball which is bonded to the
 proximal end of the coil. The ball, which is larger in diameter than the
 outside diameter of the coil, is placed in a socket within the lumen at
 the distal end of the catheter and the catheter is then moved into a
 vessel in order to place the coil at a desired position. Once the position
 is reached, a pusher wire with a piston at the end thereof is pushed
 distally from the proximal end of the catheter to thereby push the ball
 out of the socket in order to thereby release the coil at the desired
 position. Such a system is disclosed in U.S. Pat. No. 5,350,397, entitled,
 "Axially Detachable Embolic Coil Assembly." One problem with this type of
 coil placement system which utilizes a pusher wire which extends through
 the entire length of the catheter and which is sufficiently stiff to push
 an attachment ball out of engagement with the socket at the distal end of
 the catheter is that the pusher wire inherently causes the catheter to be
 too stiff with the result that it is very difficult to guide the catheter
 through the vasculature of the body.
 Another method for placing an embolic coil is that of utilizing a heat
 releasable adhesive bond for retaining the coil at the distal end of the
 catheter. One such system uses laser energy which is transmitted through a
 fiber optic cable in order to apply heat to the adhesive bond in order to
 release the coil from the end of the catheter. Such a method is disclosed
 in U.S. Pat. No. 5,108,407, entitled, "Method And Apparatus For Placement
 Of An Embolic Coil." Such a system also suffers from the problem of having
 a separate element which extends throughout the length of the catheter
 with the resulting stiffness of the catheter.
 Still another method for placing an embolic coil is disclosed in co-pending
 U.S. patent application Ser. No. 09/177,848, entitled "Embolic Coil
 Hydraulic Deployment System," filed on Oct. 21, 1998 and assigned to the
 same assignee as the present patent application. This patent application
 discloses the use of fluid pressure which is applied to the distal tip of
 the catheter for expanding the lumen in order to release the embolic coil.
 Various embolic coil designs have been proposed for use with coil
 deployment systems such as the stretch resistant vaso-occlusive coil
 disclosed in U.S. Pat. No. 5,853,418, entitled "Stretch Resistant
 Vaso-occlusive Coils," which discloses a helically wound coil having a
 polymeric stretch resisting member extending through the lumen of the coil
 and fixedly attached to both the distal end and the proximal end of the
 coil. While the stretch resisting member prevents the coil from being
 stretched during use, this member which extends throughout the length of
 the coil tends to significantly reduce the flexibility of the coil. This
 reduced flexibility may present problems because in order to place
 vaso-occlusive coils into a desired location and have the coil property
 employ it is very important that the coil be very flexible.
 SUMMARY OF THE INVENTION
 The present invention is directed toward a vascular occlusive coil
 deployment system for use in placing an embolic coil at a preselected site
 within a vessel which includes an elongated, flexible catheter having a
 distal tip for retaining the coil so that the coil may be moved to the
 preselected position within the vessel. The catheter has a lumen which
 extends therethrough the length of the catheter and also includes a distal
 end which is formed of a material having a durometer such that when a
 fluid pressure of about 90 to 450 pounds per square inch (psi) is applied
 to the interior of the catheter, the walls of the distal tip expand
 outwardly, or radially, to thereby increase the lumen of the distal tip of
 the catheter. The proximal end of the embolic coil is placed into the
 lumen of the distal tip of the catheter and is retained by the distal tip
 of the catheter. A hydraulic injector, such as a syringe, is coupled to
 the proximal end of the catheter for applying a fluid pressure to the
 interior of the catheter. When the coil is placed at a desired position
 within a vessel, fluid pressure is then applied to the interior of the
 catheter by the hydraulic injector to thereby cause the walls of the
 distal tip to expand outwardly to thereby release the coil for placement
 in the vessel.
 In order to prevent the proximal portion of the coil, which is held by the
 distal tip of the catheter, from stretching and unwinding, to thereby
 cause a premature release of the coil, the proximal portion of the coil is
 modified in a manner so as to "lock" adjacent turns of the coil together
 to thereby prevent such stretching or unwinding. The coil preferably takes
 the form of a tightly wound helical coil having a proximal end, a distal
 end and a lumen extending therethrough. The coil includes a seal plug
 which is disposed in fluid-tight engagement within the coil lumen at the
 proximal end of the coil. In addition, the coil includes a support wire
 which extends along the central axis of the coil lumen for a length
 substantially less than the length of the coil and in which one end of the
 support wire is fixedly attached to the seal plug and the other end of the
 support wire is fixedly attached to at least one of the turns of the coil
 at a point substantially remote from the distal end of the coil. With this
 design, all of the turns of the coil between the proximal end of the coil
 and the point on the coil where the support wire is attached are tightly
 secured to each other thereby preventing this proximal portion of the coil
 from stretching or unwinding while still being very flexible.
 In accordance with another aspect of the present invention, the flexible
 catheter is comprised of a proximal section and a relatively short distal
 section. The proximal section is formed of a material which is
 sufficiently flexible to be passed through the vasculature of the human
 body and is of a durometer which essentially resists outward expansion
 when a fluid pressure on the order of about 90 to 450 psi is applied to
 the interior of the catheter. The distal section of the catheter is formed
 of a material which is also sufficiently flexible to be passed through the
 vasculature of the body, yet is of a durometer which is significantly
 lower than the durometer of the proximal section and exhibits the property
 of expanding outwardly, or radially, when such a fluid pressure is applied
 to the interior of the catheter to thereby permit the release of the
 embolic coil.
 In accordance with still another aspect of the present invention, the
 distal section of the catheter has a durometer in a range of between about
 25 D and 55 D.
 In still another aspect of the present invention, the embolic coil is
 comprised of a helical coil having a proximal end, a distal end, and a
 lumen extending therethrough. A seal plug is disposed within the lumen of
 the proximal end of the coil in fluid-tight engagement. The proximal end
 of the coil is disposed in a fluid-tight engagement within the lumen of
 the distal section of the catheter and is retained by the lumen of the
 catheter for subsequent release.
 In another aspect of the present invention, the hydraulic injector for
 applying a fluid pressure to the interior of the catheter takes the form
 of a syringe which is coupled to the proximal end of the catheter for,
 upon movement of the piston, creating a fluid pressure which is applied to
 the interior of the catheter to thereby cause the release of the embolic
 coil.
 In accordance with another aspect of the present invention, the embolic
 coil may take the form of other types of implantable devices, such as a
 vascular filter.
 In another aspect of the present invention, there is provided a method for
 placing an embolic coil with a selected site within a vessel of the body
 comprising the steps of advancing a catheter through the vasculature of
 the body to place an embolic coil which is retained within the lumen of
 the distal tip of the catheter to a preselected site, applying a fluid
 pressure to the interior of the catheter to thereby cause the distal tip
 of the catheter to expand radially outwardly to release the embolic coil
 at the preselected site, and withdrawing the catheter from the vasculature
 system.
 With the coil design of the present invention the proximal portion of the
 coil is prevented from stretching or unwinding to thereby prevent the
 premature release of the coil from the catheter deployment system.
 These aspects of the invention and the advantages thereof will be more
 clearly understood from the following description and drawings of a
 preferred embodiment of the present invention:

DESCRIPTION OF A PREFERRED EMBODIMENT
 FIG. 1 generally illustrates the vascular occlusive coil deployment system
 100 which is comprised of a hydraulic injector or syringe 102, coupled to
 the proximal end of a catheter 104. An embolic coil 106 is disposed within
 the lumen of the distal end 108 of the catheter. The proximal end of the
 coil 106 is tightly held within the lumen of the distal section 108 of the
 catheter 104 until the deployment system is activated for release of the
 coil. As may be seen, the syringe 102 includes a threaded piston 110 which
 is controlled by a handle 112 for infusing fluid into the interior of the
 catheter 104. Also as illustrated, the catheter 104 includes a winged hub
 114 which aids in the insertion of the is catheter into the vascular
 system of the body.
 FIG. 2 illustrates in more detail the distal end of the catheter 104. The
 catheter 104 includes a proximal section 116 and the distal section 108.
 The proximal section 118 of the embolic coil 106 is disposed within the
 distal section 108 of the catheter and is tightly held within the lumen
 120 of this distal section 108 prior to release of the coil. As may be
 appreciated, FIG. 2 illustrates the vascular occlusive coil deployment
 system prior to activation of the piston of the syringe and prior to
 release of the coil.
 The embolic coil 106 may take various forms and configurations and may even
 take the form of a randomly wound coil, however, with the helical wound
 coil as illustrated in FIG. 2, the coil is provided with a weld bead or
 seal plug 122 which is disposed in a lumen 123 which lumen extends
 throughout the length of the coil 106. The seal plug 122 serves to prevent
 the flow of fluid through the lumen of the coil 106 so that when the coil
 106 is placed in fluid-tight engagement with the lumen 120 the coil serves
 to provide a fluid-tight seal at the distal end of the catheter 104. A
 liquid silicone material 130a is injected into the space surrounding the
 support wire 130 to fill the proximal portion of the lumen of the coil.
 The silicone material is then cured to seal the proximal end of the coil
 to prevent fluid leakage through the turns of the coil. The cured remains
 flexible with the result that the proximal end of the coil remains
 flexible.
 Preferably, the proximal section 116 and the distal section 108 of the
 catheter 104 are formed of materials having different durometers. The
 proximal section 116 is preferably formed of Pebax material having a
 durometer in a range of about 62 D to 75 D. The proximal section is
 sufficiently flexible to transverse the vasculature of the human body, but
 is sufficiently rigid such that when a fluid pressure of approximately 90
 to 450 psi is applied to the interior of this section of the catheter
 there is very little, if any, radial expansion of the walls of this
 section. On the other hand, the distal section 108 of the catheter is
 preferably formed of polymer material with a relatively low durometer
 which, exhibits the characteristic that when a fluid pressure of
 approximately 90 to 450 psi is applied to the interior of the catheter the
 walls of the distal section 108 expand radially, somewhat similar to the
 action of a balloon inflating, to thereby release the proximal end 118 of
 the coil 106. As may be appreciated, there are numerous materials which
 could be used to fabricate the proximal section 116 and distal section 108
 of the catheter 104, however, the distal section 108 is preferably formed
 from a block copolymer such as Pebax having a durometer of between 25 D
 and 55 D with a durometer of 40 D being the preferred durometer.
 FIGS. 3 and 4 generally illustrate the coil release mechanism in action for
 the vascular occlusive catheter deployment system. More particularly, as
 shown in FIG. 3, when a hydraulic pressure is applied to the interior 124
 of the catheter 104 the relatively low durometer distal section 108 of the
 catheter begins to expand radially, much as a balloon expands during the
 process of inflation. As the distal section 108 continues to expand
 radially there comes a point as illustrated in FIG. 4 in which the coil
 106 becomes disengaged from the lumen of the distal section 108 and the
 coil is then released from the catheter and is deployed at that location
 within the vessel.
 As illustrated in FIG. 5, when the coil 106 has been released from the
 catheter 104 the catheter may then be withdrawn leaving the coil
 positioned at the desired site.
 As illustrated in FIG. 6, the vaso-occlusion or embolic coil 106 is formed
 by winding a platinum alloy wire into a tightly wound helical
 configuration. The diameter of the wire is generally in the range of about
 0.0015 inches to 0.008 inches. The outside diameter of the coil 106 is
 preferably in a range of about 0.006 inches to 0.055 inches. While the
 particular embolic coil 106 illustrated in FIG. 6 is shown as being a
 straight coil it should be appreciated that embolic coils take the form of
 various configurations and may take the form of a helix, a random shape
 configuration or even a coil within a coil configuration.
 With the embodiment of the coil deployment system disclosed in this
 application it may be noted that the first several turns on the proximal
 end of the embolic coil 106 are retained or held by the distal tip of the
 catheter as the coil is moved in position. Often times it is necessary to
 move a coil to a certain position within the vasculature and then to
 withdraw the coil back to a more proximal position within the vasculature.
 During the movement of a coil through the vasculature, particularly when
 the coil is withdrawn to a more proximal position within the vasculature,
 it is possible to stretch or unwind the turns of the coil. If the turns of
 the coil which are held by the distal tip of the deployment catheter are
 stretched or unwound the result is that the outside diameter of the coil
 decreases with the result that the coil may be prematurely released from
 the deployment system.
 In order to prevent the proximal portion of the coil 106 from stretching or
 unwinding, a platinum support wire 130 is welded to the proximal sealing
 plug 122. The other end of the platinum support wire 130 is bonded by
 welding to one of the turns of the coil at a position relatively close to
 the proximal end of the catheter. Preferably, the embolic coil is of a
 length in a range of about 1.5 centimeters to 30 centimeters. The length
 of the support wire is of a length in the range of about 0.5 millimeters
 to about 4 millimeters and the diameter of the support wire is between
 about 0.0007 and 0.002 inches. With this arrangement, the overall
 flexibility of the embolic coil 106 is maintained while providing a means
 for preventing the stretching or unwinding of the gripped portion of the
 coil. As may be appreciated, the proximal sealing plug may take the form
 of a welded bead which is formed at the end of the support wire 130. Also,
 the support wire may be attached to the weld bead and to the turns of the
 coil by soldering, welding, or by the use of an adhesive. The support wire
 could be formed of various different materials including polymers or
 composites. A liquid silicone material 130a is injected into the space
 surrounding the support wire 130 to fill the proximal portion of the lumen
 of the coil. The silicone material is then cured to seal the proximal end
 of the coil to prevent fluid leakage through the turns of the coil.
 With the vascular occlusive coil deployment system of the present invention
 it is possible to place an embolic coil very precisely at a desired
 location within a vessel. Once the coil has been placed in that location
 by use of the catheter, the catheter may be activated by applying a
 hydraulic pressure to the interior of the catheter to thereby cause the
 catheter to release the coil and deposit the coil very accurately at the
 desired location.
 As is apparent, there are numerous modifications of the preferred
 embodiment described above which will be readily apparent to one skilled
 in the art, such as many variations and modifications of the coil
 including numerous coil winding configurations, or alternatively other
 types of implant devices, such as a vascular filter. Also, there are
 obviously variations of the syringe arrangement for applying a fluid
 pressure to the interior of the catheter, including many other fluid
 pressure generating systems for increasing the pressure within the
 interior of a catheter in order to cause the distal section of the
 catheter to expand. These modifications would be apparent to those having
 ordinary skill in the art to which this invention relates and are intended
 to be within the scope of the claims which follow.