Endovascular electrolytically detachable wire for thrombus formation

0001The invention relates to a wire for use in combination with a microcatheter to form an occlusion within a vascular novelty.

0002Approximately 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.

0003The 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 suture-ligation 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 anaesthesia, 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.

0004In the endovascular approach, the interior of the aneurysm is entered through the use of a microcatheter. Recently developed microcatheters, such as those shown by <b>Engelson</b>, <i>"Catheter Guidewire",</i> U.S. Patent 4,884,579 and as described in <b>Engelson</b>, <i>"Catheter for Guidewire Tracking",</i> U.S. Patent 4,739,768 (1988), allow navigation into the cerebral arteries and entry into a cranial aneurysm.

0005In 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.

0006While 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.

0007Furthermore, 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 increases the risk of rupture.

0008Still 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.

0009In the extra-intravascular approach, an aneurysm is surgically exposed or stereotaxically reached with a probe. The wall of the aneurysm is then perforated from the outside and various techniques are used to occlude the interior in order to prevent it from rebleeding. These prior art techniques include electrothrombosis, isobutyl-cyanoacrylate embolization, hog-hair embolization and ferromagnetic thrombosis.

0010In 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 <b>Mullan</b>, <i>"Experiences with Surgical Thrombosis of Intracranial Berry Aneurysms and Carotid Cavernous Fistulas",</i> J. Neurosurg., Vol. 41, December 1974; <b>Hosobuchi</b>, <i>"Electrothrombosis Carotid-Cavernous Fistula",</i> J. Neurosurg., Vol. 42, January 1975; <b>Araki et al</b>., <i>"Electrically Induced Thrombosis for the Treatment of Intracranial Aneurysms and Angiomas",</i> Excerpta Medica International Congress Series, Amsterdam 1965, Vol. 110, 651-654; <b>Sawyer et al.</b>, <i>"Bio-Electric Phenomena as an Etiological Factor in Intravascular Thrombosis",</i> Am. J. Physiol., Vol. 175, 103-107 (1953); <b>J. Piton et al</b>., <i>"Selective Vascular Thrombosis Induced by a Direct Electrical Current; Animal Experiments",</i> 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.

0011The prior art has also devised the use of a liquid adhesive, isobutyl-cyanoacrylate (IBCA) which polymerizes rapidly on contact with blood to form a 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 or 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 etists, if it is not completely blocked with consequent occlusion of the artery.

0012Still 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 thrombic formations.

0013Ferromagnetic thrombosis in the prior art in extra-intravascular treatments comprises the stereotactic placement of a magnetic probe against the sac of the aneurysm followed by injection into the aneurysm by an injecting needle of iron microspheres. Aggregation of the microspheres through the extravascular magnet is followed by interneuysmatic thrombus. 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.

0014Endovascular coagulation of blood is also well known in the art and a device using laser optically generated heat is shown by <b>O'Reilly</b>, <i>"Optical Fiber with Attachable Metallic Tip for Intravascular Laser Coagulation of Arteries, Veins, Aneurysms, Vascular Malformation and Arteriovenous Fistulas",</i> U.S. Patent 4,735,201 (1988). See also, <b>O'Reilly et al.</b>, <i>"Laser Induced Thermal Occlusion of Berry Aneurysms: Initial Experimental Results",</i> Radiology, Vol. 171, No. 2, pages 471-74 (1989). <b>O'Reilly</b> 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 to 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.

0015A 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 an 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.

0016<b>O'Reilly's</b> 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.

0017WO-A-91/13592, upon which the preamble of claim 1 is based, discloses a microcatheter system for use in the formation of an occlusion within a vascular cavity. The system comprises a microcatheter having a distal end adapted for disposition in the proximity of a vascular cavity. The system further comprises a conductive wire for disposal in the microcatheter and for longitudinal displacement therein. This conductive wire comprises a core wire and an elongated tip portion coupled to a distal portion of the core wire. The tip portion extends the core wire for a predetermined linear extent and is, in use, positioned in the vascular cavity. In use, the elongate tip portion is used as an electrical anode while a large skin electrode, applied to the groin or scalp, is used as the electrical cathode. Upon causing current to flow between the cathode and the anode the elongate tip portion is separable from the core wire by electrolytic separation. Following separation, the core wire and microcatheter are removed leaving the tip portion within the vascular cavity.

0018According to the present invention there is provided a wire for use in combination with a microcatheter to form an occlusion within a vascular cavity, the wire comprising: <ul id="ul0001" list-style="none" compact="compact"><li>a core wire; and</li><li>a detachable elongate tip portion coupled to a distal portion of the core wire, the tip portion extending the core wire for a predetermined lineal extent and being adapted to be positioned, in use, in a vascular cavity to form an occlusion in the vascular cavity, whereby endovascular occlusion of the vascular cavity can be performed;</li><li>characterised in that the detachable elongate tip portion has a plurality of filaments or fine hairs extending therefrom.</li></ul>

0019In the preferred embodiment of wire according to the present invention, described hereinafter in conjunction with Figure 6, the filaments or fine hairs are arranged to substantially pack, fill or at least impede blood flow or access in the vascular cavity when the tip portion is displaced therein. The filaments or fine hairs are up to one millimetre in length and are made of polyester.

0020The core wire and the detachable elongate tip portion may advantageous be coupled by polyester.

0021The elongate tip portion may be a coil, preferably a platinum coil.

0022The elongate tip portion may be detachable from the core wire by mechanical means. For example, the elongate tip portion may be releasably connected to the core wire by a spring-loaded mechanical clasp. The elongate tip portion may, however, instead by detachable from the core wire by electrolytic disintegration of part of the wire.

0023The invention can be better visualized by now turning to the following drawings in which like elements are referenced by like numerals. <ul id="ul0002" list-style="none" compact="compact"><li>Figure 1 is an enlarged partially cross-sectioned side view of a first embodiment of the distal end of a prior art guidewire and tip.</li><li>Figure 2 is an enlarged longitudinal cross-section of a second embodiment of a prior art guidewire and tip.</li><li>Figure 3 is an enlarged side view of a third embodiment of a prior art guidewire and tip with a microcatheter portion cut away in longitudinal cross-sectional view.</li><li>Figure 4 is a simplified depiction of the wire of the prior art microcatheter system of Figure 3, shown disposed within a simple cranial aneurysm.</li><li>Figure 5 is a depiction of the wire of the prior art microcatheter system of Figure 4, shown after electrolytic detachment of the tip.</li><li>Figure 6 is a plan view of an embodiment of a wire in accordance with the present invention, in which the detachable elongate tip portion is provided with a plurality of polyester filamentary hairs.</li><li>Figures 7 and 8 are diagrammatic depictions of the use of a microcatheter system in which the detachable elongate tip portion does not have a plurality of filaments or fine hairs as required by the present invention, position markers being provided on the catheter and wire to assist in proper fluoroscopic manipulation.</li><li>Figure 9 is a simplified cross-sectional view of a catheter and wire in which the detachable elongate tip portion is not provided with a plurality of filaments or fine hairs as required by the present invention, a ground electrode being shown disposed on the distal tip of the catheter.</li></ul>

0024An 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.

0025When 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.

0026Figure 1 is an enlarged side view of a first embodiment of the distal end of a prior art 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.

0027The 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.

0028In 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.

0029Reduced diameter portion 14 and at least part of sections 12 and first bonding location 20 may be covered with an insulating Teflon (a registered trade mark) laminate 24 which encapsulates the underlying portion of wire 10 to prevent contact with the blood.

0030A 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).

0031The 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, secondary coil 28 is between approximately 0.010 and 0.020 inch (0.254-0508 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.

0032The 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.

0033Although 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 microcatheter. Once disposed out of the tip of the microcatheter, secondary coil 28 forms the shape shown in Figure 1 and may similarly be loosely deformed to the interior shape of the aneurysm.

0034As will be described below in greater detail in connection with the third embodiment of Figure 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 charge 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 kill 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.

0035Figure 2 illustrates in enlarged partially cross-sectional view a second prior art embodiment. 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 0.25 mm (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 proximate end is approximately 150 cm.

0036The embodiment of Figure 2 is utilized in exactly the same manner as described above in connection with Figure 1 to form a thrombic mass within an aneurysm or other vascular cavity. The embodiment of Figure 2 is distinguished from that shown in Figure 1 by the absence of the extension of stainless core 32 through coil 36 to tip 40. In the ease of the embodiment of Figure 2 no inner core or reinforcement is provided within stainless steel coil 36. Threadlike portion 18 is provided in the embodiment of Figure 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 Figure 2 provides a more flexible tip, at least for that portion of the micro-guidewire constituting the stainless steel coil 36.

0037It is expressly understood that the helical secondary coil tip of the embodiment of Figure 1 could similarly be attached to stainless steel coil 36 of the embodiment of Figure 2.

0038Thinned and threadlike portion guidewires disposed concentrically within coiled portions are well known and are shown in <b>Antoshkiw</b>, <i>"Disposable Guidewire",</i> U.S. Patent 3,789,841 (1974); <b>Sepetka et al</b>., <i>"Guidewire Device",</i> U.S. Patent 4,832,047 (1989); <b>Engelson</b>, <i>"Catheter Guidewire",</i> U.S. Patent 4,884,579 (1989); <b>Samson et al</b>., <i>"Guidewire for Catheters",</i> U.S. Patent 4,538,622 (1985); and <b>Samson et al</b>., <i>"Catheter Guidewire with Short Spring Tip and Method of Using the Same",</i> U.S. Patent 4,554,929 (1985).

0039Turn now to the third prior art embodiment as shown in Figure 3. Figure 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 Figure 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 and open coil similar in that respect to stainless steel coil 36 of the embodiment of Figure 2.

0040However, 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 to diameter of the wire used to form platinum coil 56 is approximately 0.025-0.13mm (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 Figures 1 and 2, respectively.

0041When coil 56 is disposed within microcatheter 44, it lies along the longitudinal lumen 60 defined by microcatheter 44. The distal end 62 of microcatheter 60 is then placed into the neck of the aneurysm and the wire 42 is advanced, thereby feeding tip 58 of 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 Figure 4.

0042Figure 4 illustrates the insertion of the embodiment of Figure 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.

0043After 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 approximately four minutes.

0044At 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 Figure 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.

0045The 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 (a registered trade mark) lamination directly on wire 42 and/or by microcatheter 44. Only the exposed portion of the wire 46 is affected by the electrolysis.

0046It 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.

0047Although 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 Figure 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 (a registered trade mark) laminate 24 similar to that described in connection with the embodiment of Figure 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 US-A-5 226 911, entitled Vasoocclusion Coil with Attached Fiberous Elements.

0048Coil 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.

0049In this 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.

0050Tip 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 US-A-5 304 195, entitled, "Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Coupling". An alternative nonresilient mechanical ball and clasp capturing mechanism is described in US-A-5 261 916, entitled "Detachable Pusher-Vasoocclusive Coil Assembly with Interlocking Ball and Keyway Coupling".

0051In 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 US-A-5 234 437, entitled "Detachable Pusher-Vasoocclusive Coil Assembly with Threaded Couplings".

0052In 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.

0053Even 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 steel 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.

0054Notwithstanding the fact that wire 10 and platinum coil 102 in the embodiment Figure 6 or wire 10 and platinum coil 28, 36 and 56 in the embodiments of Figures 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. Figure 7 illustrates an improvement of, for example, the embodiment of Figures 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 he 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.

0055Further, in the previous embodiments, such as the prior art embodiments shown in Figures 4 and 5, when electrothrombosis is used to form the occlusion within vascular 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. Figure 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 Figure 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 therefore largely avoided.

0056It 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.