fig1 shows a side view of a generic catheter assembly ( 100 ) made using the inventions described herein . in general , the assembly employs a catheter body ( 102 ) which has a distal end ( 104 ) and a proximal end ( 106 ). the catheter may be of the design noted above in referring to engelson ( u . s . pat . no . 4 , 739 , 768 ), although it is not critical that such catheter body design be used in this invention . other catheter bodies are also suitable in various circumstances . whatever the catheter design , however , there must exist at least one lumen passing between distal end ( 104 ) and proximal end ( 106 ). passing through the lumen of catheter body ( 102 ) are a collection of components . in particular , detachable coil ( 108 ) emanates from distal end ( 104 ) as the coil is deployed . a pusher ( 110 ) may be used to push the detachable coil ( 106 ) from the distal end ( 104 ) of the catheter body ( 102 ). when used , core wire ( 112 ) extends from the catheter body &# 39 ; s distal end ( 106 ) through pusher ( 110 ) and into the center of detachable coil ( 108 ). in this configuration , the circuit for electrolytically detaching a desired portion of detachable coil ( 108 ) passes through a conductive path found in the pusher ( 110 ) and the core wire ( 112 ). a small gap desirably is found between the detachable coil ( 102 ) and the electrode found on the distal region of the core wire ( 112 ). the power supply ( 114 ) is found in fig1 . in general , we have found that tapered core wires ( 112 ) are especially suitable for this inventive procedure and device in that they tend to lessen the friction of the core wire against the various interior parts of the catheter assembly ( 100 ). the core wire ( 112 ) will typically be covered with an insulating material ( as will be discussed in more detail below ) with an insulating material such as polyfluorocarbons ( e . g ., teflon ), polyurethane , polyethylene , polypropylene , or other suitable polymeric material . the electrode , which will also be discussed in more detail below , is not covered with the electrical insulator and is of a material that should not dissolve in the blood upon imposition of the voltage . indeed , the core wire ( 112 ) should , in the region of its distal section , at least , be of a metal which is more noble than that found in the detachable coil ( 108 ). the core wire ( 112 ) is typically 10 - 50 mils . in diameter and is of stainless steel or the like . we have found that gold plating the distal tip provides significant resistance to electrolytic disposition . the core wire ( 112 ) and , indeed , the entire catheter assembly ( 100 ), is typically between 50 and 300 cm . in length . obviously , the length of the catheter assembly ( 100 ) is chosen based upon the use to which the device is to be placed . fig2 shows one variation of the invention in which the core wire ( 116 ) is immobile with respect to the distal end ( 104 ) of the catheter body . as was noted above , core wire ( 116 ) is coated with an insulator up to the region of the distal electrode ( 118 ). distal electrode ( 118 ) is , of course , left uncoated so to allow an electrical path to form through the liquid surrounding it to the detachable coil ( 108 ). the pusher ( 110 ) is also depicted in fig1 . this variation of the device operates in the following fashion . the pusher ( 110 ) pushes the detachable coil ( 108 ) through the catheter body ( 104 ) until the desired length of detachable coil ( 104 ) has emanated through the distal end of the catheter lumen . the immobile core wire ( 116 ) does not move with respect to catheter body ( 104 ). this variation permits the attending physician to understand that the length of the detachable coil ( 108 ) which extends beyond the tip of the catheter is the length of detachable coil ( 108 ) which will be left at the selected vasoocclusive site . it should be apparent that the electrode ( 118 ) found at the tip of immobile core wire ( 116 ) should , at once , be both open to the fluid in the vasculature so to allow the electrolysis to take place but also not be allowed to contact the interior of coil ( 108 ) lest a direct short take place . a shroud or protector is desirably placed over the electrode ( 118 ). the core wire ( 116 ) itself is insulated proximally of the electrode ( 118 ). preferably such inherently slippery polymers as polyfluorocarbons ( such as ptfe , fep ), polysulfones or the like are desirable as such coatings . fig3 shows another variation of the invention . as was the case with fig2 the distal end ( 104 ) of the catheter body is shown as is pusher ( 110 ). in this instance , the detachable coil ( 108 ) may be electrolytically severed outside of the catheter body distal tip ( 104 ). this is accomplished by use of a movable core wire ( 120 ) by &# 34 ; movable &# 34 ; we mean that it may be axially moved within the inner lumen of coil ( 108 ) and with respect to the distal tip of ( 104 ) of catheter body . this variation clearly allows the attending physician to trim the length of detachable coil ( 108 ) at some determinable point outside of the catheter . this may be desirable , for instance , when occluding an aneurysm . in this way , the distal tip of ( 104 ) of the catheter body is positioned near the opening of the aneurysm , the proper length of detachable coil ( 108 ) is then placed through the mouth of the aneurysm into the sac , and the electrode ( 122 ) on core wire ( 120 ) is then inserted just into the aneurysm so that during electrolytic dissolution of a small section of the coil , the dissolution takes place within the aneurysm sac beyond the aneurysm neck . this prevents any small sections of coil remaining out in the artery to form other non - desired emboli . fig4 shows another variation of the inventive device in which no core wire is used . as was the case with the variations shown in fig2 and 3 , the device employs a pusher ( 110 ) and a detachable coil ( 108 ). however , in lieu of the electrode found interior to the detachable coil ( 108 ) found in fig2 and 3 , the electrode ( 124 ) in this variation is found on the interior of catheter distal section ( 126 ). this configuration has many of the same benefits as does the variation shown in fig2 in that the attending physician is cognizant of the amount of coil to be left at the desired occluded site because that amount of coil equals that amount seen emanating from the distal tip ( 126 ) of the catheter body . the catheter body in this variation has included within its wall ( or otherwise provided for ), a conductor which extends from the proximal end of the catheter ( 106 ) ( in fig1 ) to the electrode ( 124 ). it should be apparent that pusher ( 110 ) completes the circuit through the detachable coil ( 108 ) either by inclusion of a conductive wire in the wall of the pusher ( 110 ) or by a discrete wire passing through the lumen of the pusher . in the variations shown in fig2 and 3 , it is more desirable to place the conductor in the wall of the pusher since in that way , the movement of core wire ( 116 ) ( in fig2 ) and core wire ( 120 ) ( in fig3 ) is not impeded . in the variation shown in fig4 the conductor associated with the proximal end of detachable coil ( 108 ) may either be placed within the wall of pusher ( 110 ) or through the lumen found in the midsection . indeed , in certain short catheter assemblies ( 100 ) ( in fig1 ) may be completely metallic . it is within purview of this invention that other means of conducting electricity to the proximal end of the detachable coil ( 108 ) are reasonable , but such does not form the core idea of this invention . as was the case in the variation found in fig3 the electrode ( 122 ) should be provided with a protector or shroud to allow the contact of the metallic electrode ( 122 ) with blood but not to allow the electrode to contact the interior of coil ( 108 ). also as was the case with immobile core wire ( 116 ), the core wire ( 120 ) is insulated proximally of the metallic tip ( 122 ) preferably with a lubricious polymer . the detachable coil ( 108 ) shown in each of the drawings above is shown to be a coil . indeed , it may be a coil or it may be some other vasoocclusive form such as a braid or a combination of braids and coils . a coil is desired because it more readily severs electrolytically at a single point . electrolytic dissolution of multi - fibered braid is complicated by the presence of multiple electrolysis points . the diameter of the wire used in such braid is typically much smaller than would be used in a coil but , again , the dissolution process is inherently more complicated . additionally , it is within the purview of this invention to cover the vasoocclusive device or connect the vasoocclusive device with fibrous materials . the fibrous materials may be materials which cause the vasoocclusive better to form a thrombus . fibrous materials such as dacron and the like are acceptable . fibrous adjuvants such as found in u . s . patent application no . 07 / 965 , 973 , to phelps et al ., or in u . s . pat . no . 5 , 226 , 911 to chee et al . entitled &# 34 ; vasoocclusion coil with attached fibrous elements &# 34 ; the entirety of which are incorporated by reference , are acceptable . fig5 and 6 show a typical layout involving the inventive device as was generally described in the figures above but particularly with regard to fig3 . in fig5 a core wire ( 120 ) having an electrode ( 118 ) at its distal section is coated with an insulation material such as teflon throughout its length except at the electrode ( 118 ). this core wire ( 120 ) is placed within pusher ( 110 ). as was noted above , the core wire ( 120 ) is typically of a diameter of approximately 10 - 30 mils ., although such size is not critical . in the embodiment shown in fig5 the core wire ( 120 ) is tapered to its distal end . the vasoocclusive coil ( 104 ) is pushed from the catheter into the aneurysm sac ( 130 ) through aneurysm neck ( 132 ). preferably , detachable vasoocclusive device ( 108 ) when a coil , forms a secondary loop after it leaves the end of the catheter . the most distal end ( 134 ) of detachable coil ( 108 ) may also have an end plug or tip of some type simply to prevent punctures of the aneurysm as it is introduced into the aneurysm sac . as noted , the detachable coil ( 108 ) may be prebiased to form a cylinder or a conical envelope . the coil may be heat treated or crimped or otherwise physically treated to form a random shape after it is ejected from the catheter . it is desirable that a significant volume of the aneurysm be filled with the vasoocclusive device . consequently , it is desirable that the device be quite flexible so to allow its conformance to the inner wall of the aneurysm without puncture . in any event , once the coil is properly placed within the aneurysm and the attending physician positions the electrode ( 118 )&# 39 ; so to trim a proper amount of the detachable coil ( 108 ) into the aneurysm , a modest voltage is then applied to the device . in particular , a positive electric current of approximately 0 . 1 to 2 milliamps at 0 . 1 to 5 . 0 volts is applied to core wire ( 120 ) so to form a thrombus within aneurysm sac ( 130 ). the negative pole of power supply ( 114 ) is attached to the conductor passing through or along the pusher ( 110 ). after the thrombus ( 140 ) has been formed ( as shown in fig6 ) and the aneurysm occluded , the core wire ( 120 ) with its electrode ( 118 ) is withdrawn as is the distal portion of the catheter ( 104 ). this removal typically takes place within three to ten minutes , leaving aneurysm sac ( 132 ) occluded as is shown in fig6 . the process is typically practiced under fluoroscopic control with local anesthesia . a transfemoral catheter ( of which ( 104 ) is the distal section ) is utilized to treat a cerebral aneurysm . in much heavier patients , the catheter may be introduced into the carotid artery . many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of this invention . therefore it must be understood that the concept of electrolytically determining the length of a vasoocclusive device such as described herein is the concept of this invention and may be provided for in a variety of shapes . the illustrated embodiments have been used only for the purposes of clarity and should not be taken as limiting the invention as defined by the following claims .
this invention is an apparatus for creating an endovascular occlusion by the formation of thrombi in arteries , veins , aneurysms , vascular malformations , and arteriovenous fistulas . in particular , the invention is an assembly for electrolytically severing a portion of the endovascular device such as a coil via the use of electrolysis . the vasoocclusive device is introduced through a catheter and is intended to remain at the desired thrombus formation site . the invention further includes a method for the introduction of the device and its electrolytic separation .