Detachable endovascular occlusion device activated by alternative electric current

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DETACHABLE ENDOVASCULAR OCCLUSION DEVICE ACTIVATED'BYALTERNATING ELECTRIC CURRENT THE REGENTS OF THE UNIVERSITY OF CALIFORNIAC:23318

Patent

Guglielmi et al. (UCLA)

P281-D

DETACHABLE ENDOVASCULAR OCCLUSION DEVICE ACTIVATED BY

ALTERNATING ELECTRIC CURRENT

Background of the Invention 1. Field of the Invention

The invention relates to the field of electrocoagulation, and in particular tothe use of alternating currents to form endovascular occlusions. 2. Description of the Prior Art

Occlusion of vascular structures by endovascular catheters is currentlyrealized though the use of detachable balloons, injectable glue, detachable orpushable coils, and injectable particles. Detachable balloons are of such a naturethat they can only be practically used in large vessels. The use of injectable glue islimited by the difficulty of controllable delivery to the desired occlusion site.Detachable and pushable coils are effective, but in some cases are not sufficientlythrombogenic. The use of injectable particles suffers from their relative invisibilityin fluoroscopy and the difficulty in controlling their ultimate disposition at thedesired occlusion site. In many prior art technologies the coagulation wire must beripped out of the clot, usually causing considerable disruption or even reopening theocclusion.

The use of both alternating and direct current for creating electrocoagulationis well known. See, Gold et al., "Transarterial Electrocoagulation Therapy of aPseudoaneurysm in the Head of the Pancreas," American Journal of Roentgenology, 1

Patent

Guglielmi et al. (UCLA)

P281-D

Volume 125, No. 2, at 422 (1975); Thompson et al., 'Vessel Occlusion withTranscatheter Electrocoagulation: Initial Clinical Experience," Diagnostic Radiology at335 (November 1979); Thompson et al., 'Transcatheter Electrocoagulation: ATherapeutic Angiographic Technique for Vessel Occlusion," Investigative Radiology at 5 146 (March-April 1977); Phillips, ’Transcatheter Electrocoagulation of Blood Vessels,"

Investigative Radiology at 295 (September-October 1973); and Phillips et al.,"Experimental Closure of Ateriovenous Fistula by Transcatheter Electrocoagulation,"Diagnostic Radiology 115:319 (May 1975). However, each of these experimentalinvestigations were generally performed in larger vessels and did not establish 10 controllability, nor efficacy for use in smaller vessels.

Therefore, what is needed is a clinical occlusive device which is visible, biocompatible, controllable in that it can be detached at will at a desired site evendistal to the delivery microcatheter, which is directable, efficacious in coagulatingblood and vessel and usable in small vessels without the risk of causing disruption or 15 reopening the occlusion at the end of the treatment.

Brief Summary of the Invention

The invention is an apparatus for selectively providing endovascularocclusion in a patient comprising a delivery wire guidable to or near an 20 endovascular occlusion site. A detachable coil is temporarily and selectivelycoupled to the delivery wire. An alternating current generator selectively is coupledto the detachable coil to provide current to the coil to effect electrocoagulation. Asa result, a controllable occlusive apparatus efficacious and usable in small vessels isprovided. 2

Patent

Guglielmi et al. (UCLA)

P281-D

The apparatus further comprises a direct current generator selectivelycoupled to the detachable coil. A switch selectively couples either the alternatingcurrent generator and direct current generator to the detachable coil or both. In thepreferred embodiment the coil is a GDC coil. The alternating and direct currentgenerators are variably controllable and the controllable alternating currentgenerator is frequency controllable.

The apparatus further comprises a sensing circuit for determining when apredetermined state of electrocoagulation is achieved at or near the detachable coil.The sensing circuit senses impedance of the detachable coil within the patient. Theapparatus further comprises a control circuit for selectively initiating detachment ofthe coil when the sensing circuit determines the predetermined state ofelectrocoagulation has been achieved.

The alternating current generator serves to ohmically heat the detachablecoil and surrounding blood tissues and/or dielectricly heat the detachable coil andsurrounding blood tissues at a radio frequency.

The invention is also defined as an apparatus for creating an endovascularocclusion at a selectively occlusion site comprising a conductive delivery wire and aselectively disposable and detachable conductive coil coupled to the delivery wireand disposable by the delivery wire at or near the occlusion site. An alternatingcurrent signal source is electrically coupled to the delivery wire and coil forproviding a source of heating energy at the coil. As a result, the apparatus is acontrollable occlusive device usable and efficacious in small vessels.

The detachable coil is electrolytically detachable or mechanically detachable.The apparatus further comprises a control circuit for determining when apredetermined degree of electrocoagulation has occurred at the coil and then for 3

Patent

Guglielmi et al. (UCLA)

P281-D

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detaching the coil from the delivery wire. A direct current signal source iselectrically coupled to the detachable coil and the control circuit turns thealternating current signal source off when the predetermined degree ofelectrocoagulation has occurred and turns the direct current signal source on to 5 detach the coil from the delivery wire.

The invention is also characterized as a method of forming a vascularocclusion comprising providing a conductive delivery wire and disposing aconductive coil coupled to the delivery wire at or near a selected occlusion site. Analternating current is applied to the coil to coagulate the occlusion site. A 10 determination is made whether a predetermined amount of electrocoagulation hasoccurred at the occlusion site. The alternating current through the coil isterminated when the step of determining establishes that the predeterminedelectrocoagulation has occurred. The coil is then detached from the delivery wire toleave the coil at the occlusion site. As a result, an occlusion is efficaciously provided 15 in a small vessel.

In the preferred embodiment, detaching the coil from the delivery wire isperformed automatically and the coil is electrotytically separated from the deliverywire.

The invention may be better visualized by now turning to the following20 drawings wherein like elements are referenced by like numerals.

Brief Description of the Drawings

Figure 1 is an idealized diagram of the apparatus of the invention.

Figure 2 is an enlarged view of one embodiment of the catheter for use in25 connection with the apparatus of Figure 1. 4

Patent

Guglielmi et al. (UCLA)

P281-D

The invention and its various embodiments may now be better understood byturning to the following detailed description.

Detailed Description of the Preferred Embodiments 5 An apparatus is provided for electrocoagulating blood and tissue at an occlusion site by means of application of an alternating signal or current through adetachable conductive coil on the end of a delivery wire. A Guglielmi DetachableCoil (GDC) is preferably used in the combination with radio frequency energy tocause local heating at the coil. Once carbonization of blood at the detachment zone 10 of the GDC coil occurs, the impedance of the entire system increases. Theimpedance increase is detected to automatically turn off the alternating current andthen to apply a direct current to electrolytically detach the GDC coil from thedelivery wire.

The apparatus of the invention uses a detachable microcatheter coil system 15 and a source of alternating and direct electric current. The electrolyticallydetachable coil system is commercialized by Target Therapeutics of California·, asthe Guglielmi Detachable Coil System (hereinafter defined as the GDC coil orsystem) and includes a source of direct current coupled to a microcatheter-guided • wire with a mechanically or electrolytically detachable distal coil. Any. one of the 20 embodiments described in U.S. Patents 5,122,136; 5,226,911; and/or 5,354,295 may be used in the present apparatus. All of the U.S. Patents 5,122,136; 5,226,911;and 5,354,295 are incorporated herein by reference as if set forth in their entirety. 5

Patent

Guglielmi et al. (UCLA)

P281-D

Mechanical means for detachment of the coil from the catheter is disclosed in U.S.Patents 5,234,437 and 5,261,916 also incorporated herein by reference.

Figure 1 is a highly diagrammatic depiction of the apparatus as applied toform an endovascular occlusion. The GDC system, generally denoted by reference 5 numeral 10, includes a guidable microcatheter 12, which in the illustratedembodiment is a tracker endovascular catheter as manufactured by TargetTherapeutics, Inc. of Fremont, California. A GDC coil 14 is positioned at orproximate to a selected occlusion site 16, which is typically in a small vessel. GDCcoil 14 is generally fabricated from platinum and may assume any physical shape, 10 form or composition described in the foregoing incorporated patent references orknown in the art. For example, GDC coil 14 may be straight, curved, circular, spiral,biased to form a preferred shaped, or completely limp and pliable, and may. incorporate fibers or other equivalent micro-obstructive structures. The apparatusof Figure 1 is particularly useful for arterial feeder occlusion of arteriovenous 15 malformations, arteriovenous fistulae and vascular tumors.

For example, in the embodiment of Figure 2, microcatheter 12 is shown as carrying an insulated guidewire 18 extending from catheter tip 20. At apredetermined position, insulated guidewire 18 is stripped of its insulation toprovide a bare wire 22 connected at junction 24 to GDC coil 14. 20 GDC coil 14 is positioned at or near site 16 and an alternating signal generator 26 is connected through switching circuit 28 to a proximal end of deliverywire 22. As is conventional in the art, the alternating current is applied at afrequency, voltage, current repetition time, wave shape and other signalcharacteristic as may be desired to induce electrocoagulation of blood and body 25 tissue in contact with and in the immediate vicinity of the uninsulated exposed 6

Patent

Guglielmi et al. (UCLA)

P281-D portion of GDC coil 14 and wire 22 at the distal end of microcatheter 12. Noelectrocoagulation occurs in contact with or in the immediate vicinity of theinsulated portion 18 of delivery wire 22. A ground electrode 30 is provided to the patient through means of aconductive dermal adhesive pad, symbolically shown in Figure 1 schematically as anelectrical ground 30. The alternating signal or current applied through GDC coil 14induces heating in the proximity of the noninsulated platinum portion of the GDCcoil and/or the tissue such as the arterial or vessel wall and blood surrounding GDCcoil 14. The insulated portion of the delivery wire should extend to almost 0.5mm ofthe solder joint 24 holding coil 14, so that when alternating current or RF is applied,a clot will form substantially only around the detachable coil 14 and not the deliverywire. The frequency which is contemplated as being used and the present apparatusincludes very low frequencies just above direct current to radio frequencies spanningthe spectrum from less than 1 Hertz to many Gigahertz. For example, a frequencycan be chosen to match a radio frequency absorption peak for any of theconstituents at occlusion site 16, such as water. The proteins of the vascularstructure or the blood are denatured by the heat and the shrinkage of the vascularwall and/or clotting of blood will occur. For example, it is well known that collagenfibers in the vascular wall are shrinkable at temperatures above 60 degreescentigrade.

The power provided by alternating signal generator 26 is variable by theoperator through an interface unit 32 coupled thereto either directly or throughswitching circuit 28. Variability of the power, the voltage, current and repetitionrate through interface 32 of the output of alternating current generator 26 is used toachieve vascular occlusion without damaging the vessel wall, and to minimize or 7

Patent

Guglielmi et al. (UCLA)

P281-D even substantially avoid unintended or unwanted heating of the surrounding tissues.Alternating signal generator 26 is a variable alternating current generator with avoltage now only in the range of 0 to 70 volts and is preferably battery operated withrechargeable batteries. The waveform shape is selectable through interface 32 andtypically may be sine wave, square wave, triangular wave or customized shapes witha variable frequency pulse rate.

The waveform of the alternating current signal is continuously monitoredthrough interface 32 and vessel occlusion is instantly detected by changes in theshape of the waveform due to carbonization of the blood on the detachment zone inthe proximity of junction 24 on GDC coil 14. This waveform change due to bloodcarbonization is determined by a change in the impedance of the system shown inFigure 1. Therefore, interface 32 is contemplated as included an impedancedetector which will automatically sound an audible signal to the operator or triggeran automatic turn off of the alternating current generator 26. Once sufficientcoagulation has been determined to have occurred, GDC coil 14 is detached asdescribed in the incorporated patent references by means of a direct currentgenerated by direct current generator 34 and coupled through switching circuit 28 todelivery wire 22. Switching circuit 28 may be manually activated by the operator, orautomatically programmed to switch over to deliver the proper direct currentseparating current at the completion of alternating current electrocoagulation. GDC coils 14 are particularly effective in the apparatus of Figure 1. Incontrast to other types of endovascular coils, GDC coils 14 are detachable in placeand distal from delivery catheter 12 after vessel occlusion has been achieved. Coilsof various sizes, ranging from 0.005 to 0.2 inch in diameter, various shapes andconfigurations and softness utilizing platinum wire diameters in the range of 0.001 to 8

Patent

Guglielmi et al. (UCLA)

P281-D 0.004 or more inch can be used as desired for coil 14. Platinum wires with differentelectrical resistances may be utilized.

Although the embodiment of Figure 1 has been shown with alternatingcurrent generator 26 and direct current generator 34 as separate units, it is expressly 5 contemplated that both units, as well as interface 32 together with an impedancedetection circuit as described above, will be integrally incorporated within a singlecircuit. The impedance detector subcircuit thus automatically will turn off thealternating current signal and activate the direct current signal to detach the GDCcoil 14. In this embodiment, the operator, after setting the initial parameters, need 10 only then to turn on a single activate switch to cycle through a complete procedure.Acoustic or audio visual feedback can be provided to display both alternatingcurrent vessel occlusion and detachment of GDC coil. 14. For example, both thedirect current and alternating current components of the signal may be digitallygenerated through a personal computer software controlled interface. Power levels 15 are low, being typically in the range of 0.1 to 20 watts so that the use of broadbandgenerators is feasible. Alternatively, interface 32 may be used to selectively coupletwo or more separate generators to catheter 12 to completely cover the desirefrequency bands discussed above.

While a conventional guidewire 22 is adequate for transmission of direct 20 current to MHz signals, it is conceivable that power losses at higher frequencies inthe GHz bands may become unacceptable. Therefore, guidewire 22 in these casesmay be alternatively fabricated in the form of a flexible micro-coaxial cable,microwave transmission stripline or other transmission means now known or laterdevised as may be appropriate for carrying the power levels and frequencies 25 disclosed. 9

Patent

Guglielmi et al. (UCLA)

P281-D

Many alterations and modifications may be made by those having ordinaryskill in the art without departing from the spirit and scope of the invention.Therefore, it must be understood that the illustrated embodiment has been set forthonly for the purposes of example and that it should not be taken as limiting theinvention as defined by the following claims.

The words used in this specification to describe the invention and its variousembodiments are to be understood not only in the sense of their commonly definedmeanings, but to include by special definition structure, material or acts beyond thescope of the commonly defined meanings. The definitions of the words or elementsof the following claims are, therefore, defined in this specification to include notonly the combination of elements which are literally set forth, but all equivalentstructure, material or acts for performing substantially the same function insubstantially the same way to obtain substantially the same result.

In addition to the equivalents of the claimed elements, obvious substitutionsnow or later known to one with ordinary skill in the art are defined to be within thescope of the defined elements.

The claims are thus to be understood to include what is specificallyillustrated and described above, what is conceptionally equivalent, what can beobviously substituted and also what essentially incorporates the essential idea of theinvention. 10