Abstract:
An artery, vein, aneurysms vascular malformation or arterial fistula is occluded through endovascular occlusion by the endovascular insertion of a platinum wire and/or tip into the vascular cavity. The vascular cavity is packed with the tip to obstruct blood flow or access of blood in the cavity such that the blood clots in the cavity and an occlusion if formed. The tip may be elongate and flexible so that it packs the cavity by being folded upon itself a multiple number of times, or may pack the cavity by virtue of a filamentary or fuzzy structure of the tip. The tip is then separated from the wire mechanically or by electrolytic separation of the tip from the wire. The wire and the microcatheter are thereafter removed leaving the tip embedded in the thrombus formed within the vascular cavity. Movement of wire in the microcatheter is more easily tracked by providing a radioopaque proximal marker on the microcatheter and a corresponding indicator marker on the wire. Electrothrombosis is facilitate by placing the ground electrode on the distal end of the microcatheter and flowing current between the microcatheter electrode and the tip. 
     REEAXMINATION RESULTS The questions raised in reexamination request  90 / 007 , 231 , filed Oct.  4 ,  2004  have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by  35  U.S.C.  307  as provided in  37  CFR  1 . 570 (e), for ex parte reexaminations, or the reexamination certificate required by  35  U.S.C.  316  as provided in  37  CFR  1 . 99 (e) for inter partes reexaminations.

Description:
This application is a continuation of application Ser. No. 08/801,795 filed Feb. 14, 1997, issued as U.S. Pat. No. 5,885,578, which in turn was  is a continuation of application Ser. No. 08/485,821, field Jun. 6, 1995, now abandoned, which is a divisional of application Ser. No.  08 / 311 , 508 , filed on Sep.  23 ,  1994 , issued as U.S. Pat. No.  5 , 540 , 680 , which is a continuation application of application Ser. No.  07 / 840 , 211  filed on Feb.  24 ,  1992 , issued as U.S. Pat. No.  5 , 354 , 295 , and which in its turn was  is a continuation-in-part application of application Ser. No. 07/492,717, filed Mar. 13, 1990, issued as U.S. Pat. No. 5,122,136. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and apparatus for endovascular electrothrombic formation of thrombi in arteries, veins, aneurysms, vascular malformations and arteriovenous fistulas. 
     2. Description of the Prior Art 
     Approximately 25,000 intracranial aneurysms rupture every year in North America. The primary purpose of treatment for ruptured intracranial aneurysm is to prevent rebleeding. At the present time, three general methods of treatment exist, namely an extravascular, endovascular and extra-endovascular approach. 
     The extravascular approach is comprised of surgery or microsurgery of the aneurysm or treatment site for the purpose of preserving the parent artery. This treatment is common with intracranial berry aneurysms. The methodology comprises the step of clipping the neck of the aneurysm, performing a sutureligation of the neck, or wrapping the entire aneurysm. Each of these surgical procedures is performed by intrusive invasion into the body and performed from outside the aneurysm or target site. General anesthesia, craniotomy, brain retraction and arachnoid dissection around the neck of the aneurysm and placement of a clip are typically required in these surgical procedures. Surgical treatment of vascular intracranial aneurysm can expect a mortality rate of 4-8% with a morbidity rate of 18-20%. Because of the mortality and morbidity rate expected, the surgical procedure is often delayed while waiting for the best surgical time with the result that an additional percentage of patients will die from the underlying disease or defect prior to surgery. For this reason the prior art has sought alternative means of treatment. 
     In the endovascular approach, the interior of the aneurysm is entered through the use of a microcatheter. Recently developed microcatheters, such as those shown by Engelson. “Catheter Guidewire”, U.S. Pat. No. 4,884,579 and as described in Engelson, “Catheter for Guidewire Trackzng”, U.S. Pat. No. 4,739,768 (1998), allow navigation into the cerebral arteries and entry into cranial aneurysm. 
     In such procedures a balloon is typically attached to the end of the microcatheter and it is possible to introduce the balloon into the aneurysm, inflate it, and detach it, leaving it to occlude the sac and neck with preservation of the parent artery. While endovascular balloon embolization of berry aneurysms is an attractive method in situations where an extravascular surgical approach is difficult, inflation of a balloon into the aneurysm carries some risk of aneurysm rupture due to possible over-distention of portions of the sac and due to the traction produced while detaching the balloon. 
     While remedial procedures exist for treating a ruptured aneurysm during classical extravascular surgery, no satisfactory methodology exists if the aneurysm breaks during an endovascular balloon embolization. 
     Furthermore, an ideal embolizing agent should adapt itself to the irregular shape of the internal walls of the aneurysm. On the contrary, in a balloon embolization the aneurysmal wall must conform to the shape of the balloon. This may not lead to a satisfactory result and further increase the risk of rupture. 
     Still further, balloon embolization is not always possible. If the diameter of the deflated balloon is too great to enter the intracerebral arteries, especially in the cases where there is a vasospasm, complications with ruptured intracranial aneurysms may occur. The procedure then must be deferred until the spasm is resolved and this then incurs a risk of rebleeding. 
     In the extra-intravascular approach, an aneurysm is surgically exposed or stereotaxically reached with a probe. The wall of the aneurysm is then performed from the outside and various techniques are used to occlude the interior in order to prevent it from rebleeding. These prior art techniques include elecrothrombosis, isobutyl-cyanoacrylate embolization, hog-hair embolization and ferromagnetic thrombosis. 
     In the use of electrothrombosis for extra-intravascular treatment the tip of a positively charged electrode is inserted surgically into the interior of the aneurysm An application of the positive charge attracts white blood cells, red blood cells, platelets and fibrinogen which are typically negatively charged at the normal pH of the blood. The thrombic mass is then formed in the aneurysm about the tip. Thereafter, the tip is removed, See Mullan, “Experiences with Surgical Thrombosis of Intracranial Berry Aneurysms and Carotid Cavemous Fistulas”: J. Neurosurg., Vol. 41, December 1974; Hosobuchi, “Electrothrombosis Carotid-Cavemous Fistula”,J. Neurosurg., Vol. 42, January 1975; Afaki et al., “Electrically Induced Thrombosis for the Treatment of Intracranial Anewysms and Angiomas”, Excerpta Medica International Congress Series, Amsterdam 1965, Vol. 110, 651-654; Sawyer et al., “Bio-Electric Phenomena as an Etiological Factor in Intravascular Thrombosis”, Am. J. Physiol., Vol. 175, 103-107 (1953); J. Piton et al., “Selective Vascular Thrombosis Induced by a Direct Electrical Current; Animal Experiments”, J. Neuroradiology. Vol. 5, pages 139-152 (1978). However, each of these techniques involves some type of intrusive procedure to approach the aneurysm from the exterior of the body. 
     The prior art has also devised the use of a liquid adhesive isobutylcyanoacrylate (IBCA) which polymerizes rapidly on contact with blood to form it firm mass. The liquid adhesive is injected into the aneurysm by puncturing the sac with a small needle. In order to avoid spillage into the parent artery during IBCA injection, blood flow through the parent artery must be momentarily reduced of interrupted. Alternatively, an inflated balloon may be placed in the artery at the level of the neck of the aneurysm for injection. In addition to the risks caused by temporary blockage of the parent artery, the risks of seepage of such a polymerizing adhesive into the parent artery exists, if it is not completely blocked with consequent occlusion of the artery. 
     Still further, the prior art has utilized an air gun to inject hog hair through the aneurysm wall to induce internal thrombosis. The success of this procedure involves exposing the aneurysm sufficiently to allow air gun injection and has not been convincingly shown as successful for throbic formations. 
     Ferromagnetic thrombosis in the prior art in extraintravascular treatments comprises the stereotactic placement of a magnetic probe against the sac of the aneurysm followed by injection into the anuerysm by an injecting needle of iron microspheres. Aggregation of the microspheres through the extravascular magnet is followed by interneuysmatic throbus. This treatment has not been entirely successful because of the risk of fragmentation of the metallic thrombus when the extravascular magnet is removed. Suspension of the iron powder in methyl methymethacrylate has been used to prevent fragmentation. The treatment has not been favored, because of the need to puncture the aneurysm, the risk of occlusion of the parent artery, the use of unusual and expensive equipment, the need for a craniectomy and general anesthesia, and the necessity to penetrate cerebral tissue to reach the aneurysm. 
     Endovascular coagulation of blood is also well known in the art and a device using laser optically generated heat is shown by O&#39;Reilly, “Optical Fiber with Attachable Metallic Tip for Intravascular Laser Coagulation of Arteries, Veins, Aneurysms, Vascular Malformation and Arteriovenous Fistulas”, U.S. Pat. No. 4,735,201 (1988). See also, O&#39;Reilly et al., “Laser Induced Thermal Occlusion of Berry Aneurysms: Initial experimental Results”, Radiology, Vol. 171, No. 2, pages 471-74 (1989). O&#39;Reilly places a tip into an aneurysm by means of an endovascular microcatheter. The tip is adhesively bonded to a optic fiber disposed through the microcatheter. Optical energy is transmitted along the optic fiber from a remote laser at the proximal end of the microcatheter. The optical energy heats the tip of cauterize the tissue surrounding the neck of the aneurysm or other vascular opening to be occluded. The catheter is provided with a balloon located on or adjacent to its distal end to cut off blood flow to the site to be cauterized and occluded. Normally, the blood flow would carry away the heat at the catheter tip, thereby preventing cauterization. The heat in the tip also, serves to melt the adhesive used to secure the tip to the distal end of the optical fiber, If all goes well, the tip can be separated from the optical fiber and left in place in the neck of the aneurysm, provided that the cauterization is complete at the same time as the hot melt adhesive melts. 
     A thrombus is not formed from the heated tip. Instead, blood tissue surrounding the tip is coagulated. Coagulation is a denaturation of protein to form a connective-like tissue similar to that which occurs when the albumen of an egg is heated and coagulates from a clear running liquid to as opaque white solid. The tissue characteristics and composition of the coagulated tissue is therefore substantially distinct from the thrombosis which is formed by the thrombotic aggregation of white and red blood cells, platelets and fibrinogen. The coagulative tissue is substantially softer than a thrombic mass and can therefore more easily be dislodged. 
     O&#39;Reilly&#39;s device depends at least in part upon the successful cauterization timed to occur no later than the detachment of the heat tip from the optic fiber. The heated tip must also be proportionally sized to the neck of the aneurysm in order to effectively coagulate the tissue surrounding it to form a blockage at the neck. It is believed that the tissue in the interior of the aneurysm remains substantially uncoagulated. In addition, the hot melt adhesive attaching the tip to the optic fiber melts and is dispersed into the adjacent blood tissue where it resolidifies to form free particles within the intracranial blood stream with much the same disadvantages which result from fragmentation of a ferromagnetic electrothrombosis. 
     Therefore, what is needed is an apparatus and methodology which avoids each of the shortcomings and limitations of the prior art discussed above. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a method for forming an occlusion within a vascular cavity having blood disposed therein comprising the steps of endovascularly disposing a wire and/or tip near an endovascular opening into the vascular cavity. The wire may include a distinguishable structure at its distal end, which is termed a tip, in which case the remaining portion of the wire may be termed a guidewire. The term “wire” should be understood to collectively include both guidewires and tips and simply wires without distinct tip structures. However, the tip may also simply be the extension of the wire itself without substantial distinction in its nature. A distal tip of the wire is deposited into the vascular cavity to pack the cavity to mechanically form the occlusion within the vascular cavity about the distal tip. The distal tip is detached from the guidewire (or wire) to leave the distal tip within the vascular cavity. As a result, the vascular cavity is occluded by the distal tip, and by any thrombus formed by use of the tip. 
     In one embodiment, the step of detaching the distal tip from the guidewire (or wire) comprises the step of mechanically detaching the distal tip from the guidewire (or wire). 
     In another embodiment, the guidewire and tip (or wire) are used within a microcatheter and in the step of detaching the distal tip from the guidewire (or wire), the guidewire and tip (or wire) are longitudinally displaced within the microcatheter. The microcatheter has radio-opaque proximal and tip markers. The guidewire and tip (or wire) have collectively a single radio-opaque marker. The displacement of the guidewire and tip (or wire) moves the single radio-opaque marker to the proximity of the proximal marker on the microcatheter. At this point the tip will be fully deployed in the vascular cavity and tip separation may proceed. It is not necessary then in this embodiment to be able to see actual deployment of the tip before operation. The tip member allows and enhances direct observation of the correct placement of the catheter tip into the opening of the vascular cavity. 
     In one embodiment the step of disposing the tip (or wire) into the vascular cavity to pack the cavity comprises the step of disposing a tip (or wire) having a plurality of filaments extending therefrom to pack the cavity. 
     In another embodiment the step of disposing the tip (or wire) into the vascular cavity to pack the cavity comprises the step of disposing a long flexible tip (or wire) folded upon itself a multiple number of times to pack the cavity. 
     The invention can also be characterized as a method for forming an occlusion within a vascular cavity having blood disposed therein comprising the steps of endovascularly disposing a wire within a microcatheter near an endovascular opening into the vascular cavity. The microcatheter has a distal tip electrode. The distal tip of the wire is disposed into the vascular cavity to pack the cavity to form the occlusion within the vascular cavity about the distal tip of the wire by applying a current between the distal tip electrode and the distal end of the wire packed into the cavity. The distal tip of the wire is detached from the wire to leave the distal tip of the wire within the vascular cavity. As a result, the vascular cavity is occluded by the distal tip, and by any thrombus formed by use of the tip. 
     The invention is also a wire for use in formation of an occlusion within a vascular cavity used in combination with a microcather comprising a core wire, and a detachable elongate tip portion extending the core wire for a predetermined lineal extent. The tip portion is adapted to be packed into the vascular cavity to form the occlusion in the vascular cavity and coupled to the distal portion of the core wire. As a result, endovascular occlusion of the vascular cavity can be performed. 
     In one embodiment, the elongate tip portion is a long and substantially pliable segment adapted to be multiply folded upon itself to substantially pack said vascular cavity. 
     In another embodiment, the elongate tip portion is a segment adapted to be disposed in said vascular cavity and having a plurality of filaments extending therefrom to substantially pack said vascular cavity when disposed therein. 
     In still another embodiment, the microcather has a pair of radioopaque markers disposed thereon and the core wire has a radioopaque maker disposed thereon. The marker on the core wire is positioned in the proximity of one of the pair of markers on the microcatheter when the core wire is fully deployed. The other marker on the core wire marks the position of the catheter tip. 
     The invention is still further characterized as a microcatheter system for use in formation of an occlusion within a vascular cavity comprising a microcatheter having a distal end adapted for disposition in the proximity of the vascular cavity. The distal end has an electrode disposed thereon. A conductive guidewire is disposed in the microcatheter and longitudinally displaceable therein. The guidewire comprises a core wire, and an elongate tip portion extending the core wire for a predetermined lineal extent. The tip portion is adapted to be packed into the vascular cavity to form the occlusion in the vascular cavity. The tip portion is coupled to the distal portion of the core wire. The occlusion is formed by means of applying a current between the tip portion and the electrode on the microcatheter when the tip portion is disposed into the vascular cavity. As a result, endovascular occlusion of the vascular cavity can be performed. 
     More generally speaking, the invention is a method for forming an occlusion within a vascular cavity having blood disposed therein comprising the steps of disposing a body into the cavity to substantially impede movement of blood in the cavity. The body is employed in the cavity to form the occlusion within the vascular cavity. As a result, the vascular cavity is occluded by the body. 
     The step of disposing the body in the vascular cavity comprises the step of packing the body to substantially obstruct the cavity. 
     In one embodiment the step of packing the cavity with the body comprises the step of obstructing the cavity with a detachable elongate wire tip multiply folded upon itself in the cavity. 
     The step of disposing the body into the vascular cavity comprises disposing in the vascular cavity means for slowing blood movement in the cavity to initiate formation of the occlusion in the cavity. 
     In another embodiment the step of packing the cavity with the body comprises the step of obstructing the cavity with a body having a compound filamentary shape. 
     The step of employing the blood in the vascular cavity to form the occlusion comprises the step of applying an electrical current to the body or mechanically forming the occlusion in the body or simultaneously. 
     The invention is also wire for use in formation of an occlusion within a vascular cavity used in combination with a microcatheter. The invention comprises a core wire and a detachable elongate tip portion extending the core wire for a predetermined lineal extent. The core wire is adapted to being packed into the vascular cavity to form the occlusion in the vascular cavity and is coupled to the distal portion of the core wire. The tip portion includes a first segment for disposition into the cavity and a second segment for coupling the first portion to the core wire. The second segment is adapted to be electrolysized upon application of current. An insulating coating is disposed on the first segment. The second segment is left exposed to permit selective electrolysis thereof. As a result, endovascular occlusion of the vascular cavity can be performed. 
     The invention can better be visualized by now turning to the following drawings wherein like elements are referenced by like numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an enlarged partially cross-sectioned side view of a first embodiment of the distal end of the guidewire and tip of the invention 
         FIG. 2  is an enlarged longitudinal cross section of a second embodiment of the guidewire and tip of the invention. 
         FIG. 3  is an enlarged side view of a third embodiment of the invention with a microcatheter portion cut away in a longitudinal cross-sectional view. 
         FIG. 4  is a simplified depiction of the wire of  FIG. 3  shown disposed within a simple cranial aneurysm. 
         FIG. 5  is a depiction of the wire of  FIG. 4  shown after electrolytic detachment of the tip. 
         FIG. 6  is plan view of another embodiment of the guidewire and tip portion wherein the type is provided with a plurality of polyester filamentary hairs. 
         FIGS. 7 and 8  are a diagrammatic depictions of the use of the invention wherein position markers have been provided on the catheter and wire to assist in proper fluoroscopic manipulation. 
         FIG. 9  is a simplified cross-sectional view of the catheter and wire showing a ground electrode disposed on the distal tip of the catheter. 
       The invention and its various embodiments are best understood by now turning to the following detailed description. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An artery, vein, aneurysm, vascular malformation or arterial fistula is occluded through endovascular occlusion by the endovascular insertion of a platinum tip into the vascular cavity. The vascular cavity is packed with the tip to obstruct blood flow or access of blood in the cavity such that the blood clots in the cavity and an occlusion if formed. The tip may be elongate and flexible so that it packs the cavity by being folded upon itself a multiple number of times, or may pack the cavity by virtue of a filamentary or fuzzy structure of the tip. The tip is then separated from the wire mechanically or by electrolytic separation of the tip from the wire. The wire and the microcatheter are thereafter removed leaving the tip embedded in the thrombus formed within the vascular cavity. Movement of wire in the microcatheter is more easily tracked by providing a radioopaque proximal marker on the microcatheter and a corresponding indicator marker on the wire. Electrothrombosis is facilitate by placing the ground electrode on the distal end of the microcatheter and flowing current between the microcatheter electrode and the tip. 
     When the tip is separated from the wire by electrolytic separation of the tip from the wire, a portion of the wire connected between the tip and the body of the wire is comprised of stainless steel and exposed to the bloodstream so that upon continued application of a positive current to the exposed portion, the exposed portion is corroded away at least at one location and the tip is separated from the body of the wire. 
       FIG. 1  is an enlarged side view of a first embodiment of the distal end of the wire and tip shown in partial cross-sectional view. A conventional Teflon laminated or similarly insulated stainless steel wire  10  is disposed within a protective microcatheter (not shown). Stainless steel wire  10  is approximately 0.010-0.020 inch (0.254-0.508 mm) in diameter. In the illustrated embodiment, wire  10  is tapered at its distal end to form a conical section  12  which joins a section  14  of reduced diameter which extends longitudinally along a length  16  of wire  10 . Section  16  then narrows gradually down to a thin threadlike portion  18  beginning at a first bonding location  20  and ending at a second bonding location  22 . 
     The stainless steel wire  10 , comprised of that portion disposed within the microcatheter body, tapered section  12 , reduced diameter section  16  and threadlike section  18 , is collectively referred to as a core wire which typically is 50-300 cm in length. 
     In the illustrated embodiment the portion of the core wire extending from tapered section  12  to second bonding location  22  is collectively referred to as the grinding length and may typically be between 20 and 50 cm. in length. 
     Reduced diameter portion  14  and at least part of sections  12  and first bonding location  20  may be covered with an insulating Teflon laminate  24  which encapsulates the underlying portion of wire  10  to prevent contact with the blood. 
     A stainless steel coil  26  is soldered to the proximate end of threadlike portion  18  of wire  10  at first bonding location  20 . Stainless steel coil  26  is typically 3 to 10 cm. in length and like wire  10  has a diameter typically between 0.010 to 0.020 inch (0.254-0.508 mm). 
     The distal end of stainless steel coil  26  is soldered to the distal end of threadlike portion  18  of wire  10  and to the proximal end of a platinum secondary coil  28  at second bonding location  22 . Secondary coil  28  itself forms a spiral or helix typically between 2 to 10 mm in diameter. The helical envelope formed by secondary coil  28  may be cylindrical or conical. Like wire  10  and stainless steel coil  26 , a secondary coil  28  is between approximately 0.010 and 0.020 inch (0.254-0.508 mm) in diameter. The diameter of the wire itself forming stainless steel coil  26  and coil  28  is approximately between 0.001-0.005 inch. 
     The distal end of secondary coil  28  is provided with a platinum soldered tip  30  to form a rounded and smooth termination to avoid puncturing the aneurysm or tearing tissue. 
     Although prebiased to form a cylindrical or conical envelope, secondary coil  28  is extremely soft and its overall shape is easily deformed. When inserted within the microcatheter (not shown), secondary coil  28  is easily straightened to lie axially within the uicrocatheter. Once disposed out of the tip of the microcatheter, secondary coil  28  formed the shape shown in FIG.  1  and may similarly be loosely deformed to the interior shape of the aneurysnm. 
     As will be described below in greater detail in connection with the third embodiment of  FIG. 3 , after placement of secondary coil  28  within the interior of the aneurysm a direct current is applied to wire  10  from a voltage source exterior to the body. The positive cleavage on secondary coil  28  within the cavity of the aneurysm causes a thrombus to form within the aneurysm by electrothrombosis. Detachment of the tip occurs either: (1) by continued application of current for a predetermined time when the portion  18  is exposed to blood; or (2) by movement of the wire to expose portion  18  to blood followed by continued current application for a predetermined time. Ultimately, both threadlike portion and stainless steel coil  26  will be completely disintegrated at least at one point, thereby allowing wire  10  to be withdrawn from the vascular space while leaving secondary coil  28  embedded within the thrombus formed within the aneurysm. 
       FIG. 2  illustrates in enlarged partially cross-sectional view a second embodiment of the invention. Stainless steel core  32  terminates in a conical distal portion  34 . Stainless steel coil  36 , shown in cross-sectional view, is soldered to distal portion  34  of wire  32  at bonding location  38 . The opposing end of the stainless steel coil  36  is provided with a soldered, rounded platinum tip  40 . In the illustrated embodiment, stainless steel core wire  32  is approximately 0.010 inch in diameter with the length of stainless steel coil  36  being approximately 8 cm. with the longitudinal length of platinum tip  40  being between 3 and 10 mm. The total length of wire  32  from tip  40  to the proximal end is approximately 150 cm. 
     The embodiment of  FIG. 2  is utilized in exactly the same manner as described above in connection with  FIG. 1  to form a thrombic mass within an aneurysm or other vascular cavity. The embodiment of  FIG. 2  is distinguished from that shown in  FIG. 1  by the absence of the extension of stainless core  32  through coil  36  to tip  44 . In the case of the embodiment of  FIG. 2  no inner core or reinforcement is provided within stainless steel coil  36 . Threadlike portion  18  is provided in the embodiment of  FIG. 1  to allow increased tensile strength of the wire. However, a degree of flexibility of the wire is sacrificed by the inclusion even of threadlike tip  18 , so that the embodiment of  FIG. 2  provides a more flexible tip, at least for that portion of micro-guidewire constituting the stainless steel coil  36 . 
     It is expressly understood that the helical secondary coil tip of the embodiment of  FIG. 1  could similarly be attached to stainless steel coil  36  of the embodiment of  FIG. 2  without departing from the spirit and scope of the invention. 
     Thinned and threadlike portion guidewires disposed concentrically within coiled portions are well known and are shown in Antoshkiw, “Disposable Guidewire”, U.S. Pat. No. 3,789,841 (1974); Sepetka et al., “Guidewire Device”, U.S. Pat. No. 4,832,047 (1989); Engleson, “Catheter Guidewire”, U.S. Pat. No. 4,884,579 (1989); Samson et al., “Guidewire for Catheters”, U.S. Pat. No. 4,538,622 (1985); and Samson et al., “Catheter Guidewire with Short Spring Tip and Method of Using the Same”. U.S. Pat. No. 4,554,929 (1985). 
     Turn now to the third embodiment of the invention as shown in FIG.  3 .  FIG. 3  shows an enlarged side view of a wire, generally denoted by reference numeral  42 , disposed within a microcatheter  44  shown in cross-sectional view. Like the embodiment of  FIG. 1 , a stainless steel coil  46  is soldered to a conical portion  48  of wire  22  at a first bonding location  50 . A thin threadlike extension  52  is then longitudinally disposed within stainless steel coil  46  to a second bonding location  54  where stainless steel wire  46  and threadlike portion  52  are soldered to a soft platinum coil  56 . Platinum coil  56  is not prebiased, nor does it contain any internal reinforcement, but is a free end and open coil similar in that respect to stainless steel coil  36  of the embodiment of FIG.  2 . 
     However, platinum coil  56  is particularly distinguished by its length of approximately 1 to 50 cm. and by its flexibility. The platinum or platinum alloy used is particularly pliable and the diameter of the wire used to form platinum coil  56  is approximately 0.001-0.005 inch in diameter. The distal end of platinum coil  56  is provided with a smooth and rounded platinum tip  58  similar in that respect to tips  30  and  40  of  FIGS. 1 and 2 , respectively. 
     When coil  56  is disposed within microcatheter  44 , it lies along the longitudinal lumen  60  defined by microcatheter  44 . The distal end  62  of microcather  60  is then placed into the neck of the aneurysm and the wire  42  is advanced, thereby feeding tip  58  in platinum coil  56  into aneurysm  64  until bonding location  50  resides in the neck of the aneurysm as best depicted in the diagrammatic cross-sectional view of FIG.  4 . 
       FIG. 4  illustrates the insertion of the embodiment of  FIG. 3  within a vessel  66  with distal tip of microcatheter  44  positioned near neck  68  of aneurysm  64 . Coil  56  is fed into aneurysm  64  until at least a portion of stainless steel coil  46  is exposed beyond the distal tip  62  of microcatheter  44 . A positive electric current of approximately 0.01 to 2 milliamps at 0.1-6 volts is applied to wire  42  to form the thrombus. Typically a thrombus will form within three to five minutes. The negative pole  72  of voltage source  70  is typically placed over and in contact with the skin. 
     After the thrombus has been formed and the aneurysm completely occluded, tip  58  and coil  56  are detached from wire  42  by electrolytic disintegration of at least one portion of stainless steel coil  46 . In the illustrated embodiment this is accomplished by continued application of current until the total time of current application is almost approzimately four minutes. 
     At least one portion of stainless steel coil  46  will be completely dissolved through by electrolytic action within 3 to 10 minutes, usually about  4  minutes. After separation by electrolytic disintegration, wire  42 , microcatheter  44  and the remaining portion of coil  46  still attached to wire  42  are removed from vessel  66 , leaving aneurysm  64  completely occluded as diagrammatically depicted in  FIG. 5  by thrombus  74 . It will be appreciated that the time of disintegration may be varied by altering the dimensions of the portions of the wire and/or the current 
     The process is practiced under fluoroscopic control with local anesthesia at the groin. A transfemoral microcatheter is utilized to treat the cerebral aneurysm. The platinum is not affected by electrolysis and the remaining portions of the microcatheter are insulated either by a Teflon lamination directly on wire  42  and/or by microcatheter  44 . Only the exposed portion of the wire  46  is affected by the electrolysis. 
     It has further been discovered that thrombus  74  continues to form even after detachment from wire  42 . It is believed that a positive charge is retained on or near coil  56  which therefore continues to attract platelets, white blood cells, red blood cells and fibrinogen within aneurysm  64 . 
     Although the foregoing embodiment has been described as forming an occlusion within a blood-filled vascular cavity by means of electrothrombosis, the above disclosure must be read to expressly include formation of the occlusion by mechanical mechanisms without resort to the application of electrical current. A mechanical mechanism which can be safely disposed into the vascular cavity to impede, slow or otherwise initiate clotting of the blood or formation of the occlusion is within the scope of the invention. The insertion within the vascular cavity and maintenance therein of an object with an appropriate blood-clotting characteristics can and does in many cases cause the formation of an occlusion by itself. Depicted in  FIG. 6  is an embodiment of the invention wherein such mechanical thrombosis can be achieved. Wire  10  has a tapering end portion  14  covered with a Teflon laminate  24  similar to that described in connection with the embodiment of FIG.  1 . Wire  10  is attached by means of a mechanical coupling  100  to a platinum coil  102  which has a plurality of filaments or fine hairs  104  extending therefrom. In the illustrated embodiment, hairs  104  have a length as may be determined from the size of the vascular cavity in which coil  102  is to be used. For example, in a small vessel hair lengths of up to 1 mm are contemplated. An example of polyester filaments or hairs attached to a coil which was not used in electrothrombosis may be seen in the copending application entitled Vasoocclusion Coil with Attached Fiberous Elements, filed Oct. 2, 1991, Ser. No. 07/771,013. 
     Coil  102  has sufficient length and flexibility that it can be inserted or coiled loosely into the vascular cavity. The length of coil  102  need not be so long that the coil itself is capable of being multiply folded on itself and fill or substantially fill the vascular cavity. Hairs  104  extending from coil  102  serve to substantially pack, fill or at least impede blood flow or access in the vascular cavity. Hairs  104 , which are generally inclined backwardly away from extreme tip  106  when delivered, are thus easily able to slide forward with little friction through restrictions in the vessels and aneurysm. Additionally, hairs  104  do not have sufficient length, strength or sharpness to provide any substantial risk or potential for a puncture of the thin vascular wall. The plurality of hairs  104 , when coiled within the vascular cavity, provide an extremely large surface for attachment of blood constituents to encourage and enhance the formation of a mechanical occlusion within the vascular opening. 
     In the preferred embodiment, coil  102  is mechanically coupled to thin tapered portion  104  of wire  10  by means of a small drop of polyester  100 . Polyester may be substituted for the gold solder of the previously described embodiments in order to reduce concern or risk of toxic reactions in the body. 
     Tip portion  104  may also be mechanically separated from wire  10  by means other than electrolysis. One method is make the connection between tip  104  and wire  10  by means of a spring loaded mechanical clasp (not shown). The clasps are retained on tip  104  as long as the clasps remain inside of the catheter, but spring open and release tip  104  when extended from the catheter. The catheter and clasps may then be removed from the insertion site. This type of mechanical connection is described in the copending application entitled, “Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Coupling”, filed Dec. 12, 1991 with Ser. No. 07/806,979 which is incorporated herein by reference and assigned to Target Therapeutics Inc. An alternative nonresilient mechanical ball and clasp capturing mechanism is described in the copending application entitled “Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Ball and Keyway Coupling”, filed Dec. 12, 1991 with Ser. No. 07/806,912 which is also incorporated herein by reference and assigned to Target Therapeutics Inc. 
     In another embodiment wire  10  and tip portion  104  screw into each other and can be unscrewed from each other by rotation of the catheter or wire with respect to tip  104 . An extendable sheath (not shown) in the microcatheter is advanced to seize tip  104  to prevent its rotation with wire  10  during the unscrewing process. This type of mechanical connection is described in the copending application entitled “Detachable Pusher-Vasoocclusive Coil Assembly with Threaded Coupling”, filed Dec. 12, 1991 with Ser. No. 07/806,898 which is incorporated herein by reference and assigned to Target Therapeutics Inc. 
     In any case the specific means disclosed here of mechanically detaching tip  104  from wire  10  forms no part of the present invention apart from its combination as a whole with other elements of the invention. Specific disclosure of the mechanical means of detachment have been set forth only for the purposes of providing an enabling disclosure of the best mode presently known for practicing the claimed invention. 
     Even where the occlusion is not formed by electrothrombosis, separation of tip  104  may be effected by electrolysis. In such situations, the electrolysing current may be concentrated on the sacrificial stainless steel portion of tip  104  by disposition of an insulative coating on the remaining platinum portion. For example, tip  104  may be provided with a polyethylene coating save at least a portion of the stainless length. This has the effect of decreasing the time required to electrolytically sufficiently disintegrate the steel portion to allow detachment of the platinum tip, which is an advantageous feature in those cases where a large aneurysm must be treated and a multiple number of coils must be deployed within the aneurysm. 
     Notwithstanding the fact that wire  10  and platinum coil  102  in the embodiment  FIG. 6  or wire  10  and platinum coil  28 ,  36  and  56  in the embodiments of  FIGS. 1-5  are radiopaque, there is still some difficulty when manipulating the device under fluoroscopy to be able to determine the exact position or movement of the probe relative to the aneurysm. This is particularly true when a large number of coils are deployed and one coil then radiographically hides another.  FIG. 7  illustrates an improvement of, for example, the embodiment of  FIGS. 4 and 5 . Microcatheter  144  is positioned so that its distal end  162  within vessel  66  is positioned at the opening aneurysm  64 . Microcatheter  144  is provided with radiopaque marker  108  at distal tip  162 , a tip marker. Moving toward the proximal end of microcatheter  144  is a second radiopaque marker  110 , a proximal marker. Radiopaque markers  108  and  110  are, for example, in the form of radiopaque rings made of platinum, approximately 1-3 mm in longitudinal length along the axis of microcatheter  144 . Rings  110  and  108  are typically separated by about 3 cm on microcatheter  144 . Similarly, wire  10  has a radiopaque marker  112  defined on it such that marker  112  on wire  10  is approximately with aligned with marker  110  on microcatheter  14  when coil  56  is fully deployed into aneurysm  64 . Typically, full deployment will place the solder or connection point  54  of the order of 2-3 mm past opening  68  of aneurysm  64 . Distal marker  108  on microcatheter  144  is used to facilitate the location of the microcatheter tip, which can often be obscured by the coils which have been previously deployed. The coils are a varying lengths depending on the application or size of the aneurysm or vascular cavity being treated. Coil lengths of 4-40 cm are common. Therefore, even though the thinness of coil  56  may make it difficult to see under standard fluoroscopy and even though the fineness of wire  10  may similarly be obscured or partly obscured, radiopaque markers  108 ,  110  and  112  are clearly visible. Manipulation of wire  10  to proximal marker  110  can then easily be observed under conventional fluoroscopy even when there are some loss of resolution or fluoroscopic visual obstruction of the coil. 
     Further, in the previous embodiments, such as that shown in  FIGS. 4 and 5 , when electrothrombosis is used to form the occlusion within aneurysm  64 , coil  56  is used as the electrical anode while the cathode is a large skin electrode  72  typically conductively applied to the groin or scalp.  FIG. 9  illustrates an alternative embodiment wherein microcatheter  144  is supplied with an end electrode  114  coupled to an electrical conductor  116  disposed along the length of microcatheter  144 . Wire  116  is ultimately led back to voltage source  70  so that ring electrode  114  is used as the cathode during electrothrombosis instead of an exterior skin electrode  72 . With the embodiment of  FIG. 9  the electrical currents and electrical current paths which are set up during the electrothrombosis formation are local to the site of application which allows even smaller currents and voltages to be used to initiate electrothrombosis than in the situation when an exterior skin electrode must be utilized. The electrothrombosic current distributions are also better controlled and localized to the site of the thrombus formation. The possibility of stray thrombus formations occurring at unwanted sites or uncontrolled and possibly unwanted electrical current patterns being established elsewhere in the brain or body is therefor largely avoided. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the shape of the tip or distal platinum coil used in combination with the wire according to the invention may be provided with a variety of shapes and envelopes. In addition thereto, the composition of the micro-guidewire tip may be made of elements other than platinum including stainless steel beryllium, copper and various alloys of the same with or without platinum. Still further, the diameter of the wire, various of the wire described above and the stainless steel coil immediately proximal to the detachable tip may be provided with differing diameters or cross sections to vary the times and current magnitudes necessary in order to effectuate electrolytic detachment from the tip. Still further, the invention may include conventional electronics connected to the proximal end of the wire for determining the exact instant of detachment of the distal tip from the wire. 
     Therefore, the illustrated embodiment has been set forth only for the purposes of clarity and example and should not be taken as limiting the invention as defined by the following claims, which include all equivalent means whether now known or later devised.