CA2129745C - Method and apparatus for advancing catheters - Google Patents
Method and apparatus for advancing catheters Download PDFInfo
- Publication number
- CA2129745C CA2129745C CA002129745A CA2129745A CA2129745C CA 2129745 C CA2129745 C CA 2129745C CA 002129745 A CA002129745 A CA 002129745A CA 2129745 A CA2129745 A CA 2129745A CA 2129745 C CA2129745 C CA 2129745C
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- Prior art keywords
- catheter
- electrode
- disposed
- distal end
- electrode array
- Prior art date
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/14—Probes or electrodes therefor
- A61B18/149—Probes or electrodes therefor bow shaped or with rotatable body at cantilever end, e.g. for resectoscopes, or coagulating rollers
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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- A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/14—Probes or electrodes therefor
- A61B18/1492—Probes or electrodes therefor having a flexible, catheter-like structure, e.g. for heart ablation
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M25/00—Catheters; Hollow probes
- A61M25/01—Introducing, guiding, advancing, emplacing or holding catheters
- A61M25/0105—Steering means as part of the catheter or advancing means; Markers for positioning
- A61M25/0133—Tip steering devices
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- A—HUMAN NECESSITIES
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- A61B18/1402—Probes for open surgery
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- A61B2017/00026—Conductivity or impedance, e.g. of tissue
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- A61B2017/00097—Temperature using thermocouples one of the thermometric elements being an electrode or the heating element
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- A61B2017/00238—Type of minimally invasive operation
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- A61B2017/003—Steerable
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- A61B2017/22001—Angioplasty, e.g. PCTA
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- A61B2017/22038—Implements for squeezing-off ulcers or the like on the inside of inner organs of the body; Implements for scraping-out cavities of body organs, e.g. bones; Calculus removers; Calculus smashing apparatus; Apparatus for removing obstructions in blood vessels, not otherwise provided for with a guide wire
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- A61B2018/00005—Cooling or heating of the probe or tissue immediately surrounding the probe
- A61B2018/00011—Cooling or heating of the probe or tissue immediately surrounding the probe with fluids
- A61B2018/00029—Cooling or heating of the probe or tissue immediately surrounding the probe with fluids open
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- A61B2018/0016—Energy applicators arranged in a two- or three dimensional array
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- A61B2018/00053—Mechanical features of the instrument of device
- A61B2018/00184—Moving parts
- A61B2018/00196—Moving parts reciprocating lengthwise
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- A61B2018/00315—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body for treatment of particular body parts
- A61B2018/00345—Vascular system
- A61B2018/00351—Heart
- A61B2018/00392—Transmyocardial revascularisation
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- A61B2018/00678—Sensing and controlling the application of energy using a threshold value upper
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- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
- A61B18/1206—Generators therefor
- A61B2018/1213—Generators therefor creating an arc
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- A61B18/04—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating
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- A61B18/12—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by heating by passing a current through the tissue to be heated, e.g. high-frequency current
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- A61B2018/1497—Electrodes covering only part of the probe circumference
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- A61B18/14—Probes or electrodes therefor
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- A61B90/36—Image-producing devices or illumination devices not otherwise provided for
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Abstract
A catheter comprises a catheter body (10) having a proximal end, a distal end, and an electrode array disposed near he distal end (12). The electrode array includes a plurality of isolated electrode terminals (18). The electrode array and a common electrode (16) are connected to a high frequency power supply (32) anc9 the common electrode (16) may be located on the catheter, may be secured separately to a patient's skin, or may be formed as part of a movable guidewire. By contacting the electrode array against a target location in the patient's body, the target location may be selectively heated, with the current density being contacted at the points of contact between the electrode terminals (18) and the tissue or stenotic material. For example, by positioning the common electrode within a stenotic region and contacting a leading surface of the stenotic region with the electrode array, the stenotic material can be heated by applying a high frequency voltage between the electrode array and the common electrode. The stenotic region can thus recanalized by advancing the distal end of the catheter body through the heated stenotic material.
Description
~ ~~r~l~
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n~ a~g ~~s ~~ ~c~ c c~~~~~
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.:, va .;
7~i~l.d of th~ 7~ne~nition The present invention relates generally to the 1,~ construction and use of catheters for interventional and diagnostic procedures. Tn particular, the present invention relates to methods and apparatus for advancing catheters through restrictions and occlusions within body 15 lumens and cavities.
tether~sclerosis is a form of arteriosclerosis ch is characterised by irregularly distributed ~h~
i o~ . , ~ep~~~,~eCy ~n th~r~all~ of a patent ~ aid arterl.~w~ a ~uch depose.ts fret~uently fibs~se and calcgfy ~~rer tame, i " ~~ perd.oiAOly c~~pr~~~.~~ng the. pat~~snt' a~ he~~s h number ~f cathete=based apparoaches have been developed for d~.agn~sing and treating ether~sclerosis and :, ~er f~rms ~f arteriosclerosis: The m~st common ~hgerventional technis~ue for treating atheroscierosis is 2~ ~~ll~on angi.oplasty where ~ .balloon-tipped catheter is i~trerduc~d ~o the vascular system, and the balloon S]~panded w~.thln a r~..gl~n ~f .~atenAS~4..~,~ o ~ther r where , f or ~ntervent~.onal techn~.ques ~.nclaide atherectomy exaDnple, a catheter hav~.ng a cupshaped rotating cutter i .'~ ~ 1S lntr~du&~"ed t~ the vaL~cular System and used t~ 6e~Tere '~, and capture at least a p~rt~on ~f ~he sten~t~c material.
~ther ~.ntexvent~onal techn~.c~ues lnclu~e laser ablation, mechanical. abrasion, chemical. dissolution, and the like.
catheter-based diagnostic techniques include ultrasonic ~5 i~a~ixag where an ultrasonic transducer disposed at the tal end ~f a vascular catheter is introduced~to the di s region of stenosis.
With most of these techniques, it is necessary to advance the distal end of the catheter at least partly through the stenosed region before the interventional or diagnostic procedure can be commenced. While such initial advancement is often not a problem, it can be very problematic when the occlusion is severe and little or no lumen remains to receive the catheter. Under such circumstances, it is necessary to at least partly recanalize the occlusion before the catheter procedure can begin.
A number of methods for recanalizing severe occlusions have been proposed, including the use of hot-tipped catheters, laser catheters, and drill-tipped catheters. In general, these approaches rely on very aggressive treatment of the stenotic material to open up a passage, where such aggressive techniques can expose the blood vessel wall to significant injury, for example, vessel perforation. The risk of injury is exacerbated by the unconstrained path which the catheter can follow.
An improved technique for advancing a severe angioplasty catheter into and optionally through a severe occlusions is described in U.S. Patent No. 4,998,933, which has common inventorship with the present application. A first electrode is disposed at or near the distal tip of the angioplasty catheter and a second electrode is provided on an electrically conductive guidewire. After the guidewire is at least partly advanced into a stenotic material, a high frequency voltage can be applied between the guidewire electrode and the catheter tip electrode in order to generate heat within the stenotic material lying between said electrodes. As the stenotic material is heated, it is 2a softened, thereby allowing easier advancement of the angioplasty catheter.
Although a substantial improvement in the art, the catheter described in U.S. Patent No. 4,998,933 can NO 93/13816 ~ '~ ~ '~ ~ ~ ~ ~ PCT/gJS92/1126~
1'C'1"1U~92111265 z ._ . .
n~ a~g ~~s ~~ ~c~ c c~~~~~
a ..
. ;;
.:, va .;
7~i~l.d of th~ 7~ne~nition The present invention relates generally to the 1,~ construction and use of catheters for interventional and diagnostic procedures. Tn particular, the present invention relates to methods and apparatus for advancing catheters through restrictions and occlusions within body 15 lumens and cavities.
tether~sclerosis is a form of arteriosclerosis ch is characterised by irregularly distributed ~h~
i o~ . , ~ep~~~,~eCy ~n th~r~all~ of a patent ~ aid arterl.~w~ a ~uch depose.ts fret~uently fibs~se and calcgfy ~~rer tame, i " ~~ perd.oiAOly c~~pr~~~.~~ng the. pat~~snt' a~ he~~s h number ~f cathete=based apparoaches have been developed for d~.agn~sing and treating ether~sclerosis and :, ~er f~rms ~f arteriosclerosis: The m~st common ~hgerventional technis~ue for treating atheroscierosis is 2~ ~~ll~on angi.oplasty where ~ .balloon-tipped catheter is i~trerduc~d ~o the vascular system, and the balloon S]~panded w~.thln a r~..gl~n ~f .~atenAS~4..~,~ o ~ther r where , f or ~ntervent~.onal techn~.ques ~.nclaide atherectomy exaDnple, a catheter hav~.ng a cupshaped rotating cutter i .'~ ~ 1S lntr~du&~"ed t~ the vaL~cular System and used t~ 6e~Tere '~, and capture at least a p~rt~on ~f ~he sten~t~c material.
~ther ~.ntexvent~onal techn~.c~ues lnclu~e laser ablation, mechanical. abrasion, chemical. dissolution, and the like.
catheter-based diagnostic techniques include ultrasonic ~5 i~a~ixag where an ultrasonic transducer disposed at the tal end ~f a vascular catheter is introduced~to the di s region of stenosis.
With most of these techniques, it is necessary to advance the distal end of the catheter at least partly through the stenosed region before the interventional or diagnostic procedure can be commenced. While such initial advancement is often not a problem, it can be very problematic when the occlusion is severe and little or no lumen remains to receive the catheter. Under such circumstances, it is necessary to at least partly recanalize the occlusion before the catheter procedure can begin.
A number of methods for recanalizing severe occlusions have been proposed, including the use of hot-tipped catheters, laser catheters, and drill-tipped catheters. In general, these approaches rely on very aggressive treatment of the stenotic material to open up a passage, where such aggressive techniques can expose the blood vessel wall to significant injury, for example, vessel perforation. The risk of injury is exacerbated by the unconstrained path which the catheter can follow.
An improved technique for advancing a severe angioplasty catheter into and optionally through a severe occlusions is described in U.S. Patent No. 4,998,933, which has common inventorship with the present application. A first electrode is disposed at or near the distal tip of the angioplasty catheter and a second electrode is provided on an electrically conductive guidewire. After the guidewire is at least partly advanced into a stenotic material, a high frequency voltage can be applied between the guidewire electrode and the catheter tip electrode in order to generate heat within the stenotic material lying between said electrodes. As the stenotic material is heated, it is 2a softened, thereby allowing easier advancement of the angioplasty catheter.
Although a substantial improvement in the art, the catheter described in U.S. Patent No. 4,998,933 can NO 93/13816 ~ '~ ~ '~ ~ ~ ~ ~ PCT/gJS92/1126~
cause unwanted shorting of electrical energy by the blood ' and blood vessel wall during the application of the high frequency voltage. The catheter employs a single discrete electrode at its distal tip. So long a~ the tip electrode fully contacts the stenotic material, the induced heat will be substantially limited to the stepotic material. If a portion (or ally of the electrode is exposed to the blood vessel wall and/or blood, however, current will begin to flow through the 1t~ blood vessel tissue and/or blood, causing the undesired , ,3 shorting of electrical current. Moreover, since both the blood vessel wall and the blood have higher electrical canductivities than the stenotic material, they wall carry the current in preference to the stenotic material.
For these reasons, it would be desirable to provide improved apparatus and methods for advancing vascular catheters past severe occlusions in blood vessels and other body lumens. In particular, it would be desirable to provide improved catheters of the type described in U:S. Patent No. A,998,933, where the catheter more electively heats the atheroa~atous material. It would be further desirable if such catheters were abla to discriminate between the atheromatous ~ass'and the blood vessel wall -i 25 (preferentially heating and ablating the former) so that ., d selectively pass through the atheroma the catheter wou~
.
as the catheter is advanced through the lumen of the blood vessel. The catheters and methods of the present invention should be compatible with a wide variety of 3Q interventior~al and diagnostic devices, particularly being compatible with angiop.lasty catheters.
De~~crimtion of the Hackarouna I~rt U:S. Patent No. 4,998,933; is described above.
European Patent Publication 182 689 and U.S. Patent No.
35 752 describe angioplasty balloon catheters having , ;
means for interxaally heating the balloons. A "hot tip"
catheter having a metal tip heated by a laser is WO 93/13816 PGT/US92/11co5 described in Cumberlant et al. (1986) Lancet i: 1457-1459. U.S. Patent No. 4,654,024, describes a catheter having an electrically heated tip for melting atheroma.
U.S. Patent No. 4,796,622, describes a catheter having a tip which is heated by an exothermic reaction. A
catheter having a high speed rotating abrasive element at its distal tip is described in U.S. Patent No. 4,857,046.
U.S. Patent No. 4,709,698, describes the placement of electrode pairs on the surface of a dilatation balloon to heat atheroma as the balloon is expanded.
BUI~ARY OF THE INDENTION
The present invention provides apparatus for localized heating of target locations within a patient's body, such as atheromatous mass in blood vessels, tissue, and the like. The method and apparatus are particularly useful for advancing a catheter through an occluded region in a blood vessel or other body lumen, more particularly through stenotic regions in blood vessels which are fully or almost fully occluded with stenotic material. Catheter apparatus according to the present invention include a catheter body having a proximal end, a distal end, and an electrode array disposed near the distal end. The electrode array includes a plurality of isolated electrode terminals typically forming the distal tip of the catheter. A
common electrode is provided and contacted with the patient's body to complete an electrically conductive path with the electrode array. The common electrode may be disposed on the catheter body proximally of the electrode array, or may be disposed distally of the electrode array, typically on or as part of a movable guidewire. As a third alternative, the common electrode 'may be provided as a discrete member which can be attached externally to the patient's skin. In each case, heating of the stenotic or other occluding material or high resistance tissue can be achieved by contacting the electrode array with the tarter location, e.g., a ieadinc portion of the stenotic material. By then applying high frequency voltage between the electrode array and the common electrode, heating of the target location will result.
For these reasons, it would be desirable to provide improved apparatus and methods for advancing vascular catheters past severe occlusions in blood vessels and other body lumens. In particular, it would be desirable to provide improved catheters of the type described in U:S. Patent No. A,998,933, where the catheter more electively heats the atheroa~atous material. It would be further desirable if such catheters were abla to discriminate between the atheromatous ~ass'and the blood vessel wall -i 25 (preferentially heating and ablating the former) so that ., d selectively pass through the atheroma the catheter wou~
.
as the catheter is advanced through the lumen of the blood vessel. The catheters and methods of the present invention should be compatible with a wide variety of 3Q interventior~al and diagnostic devices, particularly being compatible with angiop.lasty catheters.
De~~crimtion of the Hackarouna I~rt U:S. Patent No. 4,998,933; is described above.
European Patent Publication 182 689 and U.S. Patent No.
35 752 describe angioplasty balloon catheters having , ;
means for interxaally heating the balloons. A "hot tip"
catheter having a metal tip heated by a laser is WO 93/13816 PGT/US92/11co5 described in Cumberlant et al. (1986) Lancet i: 1457-1459. U.S. Patent No. 4,654,024, describes a catheter having an electrically heated tip for melting atheroma.
U.S. Patent No. 4,796,622, describes a catheter having a tip which is heated by an exothermic reaction. A
catheter having a high speed rotating abrasive element at its distal tip is described in U.S. Patent No. 4,857,046.
U.S. Patent No. 4,709,698, describes the placement of electrode pairs on the surface of a dilatation balloon to heat atheroma as the balloon is expanded.
BUI~ARY OF THE INDENTION
The present invention provides apparatus for localized heating of target locations within a patient's body, such as atheromatous mass in blood vessels, tissue, and the like. The method and apparatus are particularly useful for advancing a catheter through an occluded region in a blood vessel or other body lumen, more particularly through stenotic regions in blood vessels which are fully or almost fully occluded with stenotic material. Catheter apparatus according to the present invention include a catheter body having a proximal end, a distal end, and an electrode array disposed near the distal end. The electrode array includes a plurality of isolated electrode terminals typically forming the distal tip of the catheter. A
common electrode is provided and contacted with the patient's body to complete an electrically conductive path with the electrode array. The common electrode may be disposed on the catheter body proximally of the electrode array, or may be disposed distally of the electrode array, typically on or as part of a movable guidewire. As a third alternative, the common electrode 'may be provided as a discrete member which can be attached externally to the patient's skin. In each case, heating of the stenotic or other occluding material or high resistance tissue can be achieved by contacting the electrode array with the tarter location, e.g., a ieadinc portion of the stenotic material. By then applying high frequency voltage between the electrode array and the common electrode, heating of the target location will result.
5 Accordingly, the present invention provides a catheter system comprising:
a catheter body having a proximal end and a distal end;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of electrically isolated electrode terminals disposed over a contact surface;
a common electrode; and means for applying a high frequency voltage between the electrode array and the common electrode, wherein current flow to each electrode terminal is individually controlled in response to changes in impedance between the electrode terminal and the common electrode.
In a further aspect, the present invention provides a catheter comprising:
a catheter body having a proximal end, a distal end, and a guidewire lumen;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of isolated electrode terminals disposed over a contact surface;
means for connecting the isolated electrode terminals to a high frequency power supply; and a plurality of current limiting resistors, with at least one resistor connected in series between each electrode terminal and the power supply.
The present invention also provides a catheter system comprising:
a catheter guide having a proximal end, a distal end, a lumen therethrough, and a common electrode disposed on an exterior distal surface;
a catheter body disposed within the lumen of the catheter guide, said catheter body having a proximal end, 5a a distal end, and an electrode array disposed over a contact surface at the distal end, said electrode array including a plurality of electrically isolated electrode terminals; and means for individually connecting the electrode terminals to a high frequency power supply along isolated high impedance conductive paths;
whereby the common electrode and the electrode array may be connected to a high frequency power supply to efficiently deliver energy to a patient surface contacted by the electrode array and electrically exposed to the common electrode.
According to a particular aspect of the present invention, heating is directed primarily to the target location by limiting the current flow through each electrode terminal in the electrode array. In this way, more power is applied to the high resistance (low conductivity) tissue or stenotic material relative to the low resistance (high conductivity) blood and blood vessel wall. Current flow may be limited by active or passive devices, with an exemplary system employing a plurality of current limiting resistors, with at least one current limiting resistor in series with each electrode terminal.
The catheter of the present invention may be used alone in order to heat a target location e.g., to recanalize a stenotic region within a blood vessel.
Optionally, the catheter may be used in combination with other interventional or diagnostic devices in order to provide a multiple step treatment and/or diagnostic procedure. In particular, it will be possible to provide the electrode array of the present invention in combination with or at the distal end of catheters which employ other interventional and/or diagnostic elements, such as dilatation balloons, lasers, ultrasonic transducers, and the like. By employing catheters having such additional capabilities, the need to exchange catheters is reduced or eliminated.
A particular advantage of catheters constructed in Sb accordance with the principles of the present invention is that they can be "self-guiding" when introduced through a blood vessel. Since the electrode array heats atheromatous material in preference to the blood vessel wall, the catheter can be advanced without substantial concern over damage to the blood vessel wall. That is, the path of the catheter will be preferentially pCT/U~92/11 ~~ g3/a~~a~ 12 9'~ ~
._ . .
through the atheroma, necessarily limiting damage to the blood vessel wall.
The catheter of the present invention will 'i preferably include a temperature measuring or sensing ..
element near its distal tip, preferably within the electrode array, in order to measure the temperature at .
.
the interface between the electrode array and the tissue ''a or stenotic material being treated. More preferably, a plurality of temperature measuring elements will be Z,0 distributed through the electrode array in order to determine the temperature profile of the interface.
Temperature information obtained from the temperature measuring elements can be used to control the power output to the electrodes in order to control the temperature of the stenoti.c material within a desired range.
1~RTEF DEBCRIP'f~ON DF fRE DRAWII~1C~8 .! Fig. 1. is ~ perspective view of a catheter .;
system constructed in accordance with the principles of ; ~ 20 the present inventi~n, where the catheter includes a ..
s dilatati~n balloon.
,;, Fig. 2 is an enlarged view of the distal end of the catheter of 'Fig. 1, shown in section.
F~q..3 is'an egad view of the distal tip of the '25 catheter of Figs : ~. end 2 .
Figs. 4~8 a:llustrate the use of the catheter of Js Figs: 1.-3 in the recanalizati~n of a stenosed region within a blood vessel according to the method of the , '' present invention 3tD Fig: 9 is a schematic illustration of a current v li3niting power supgly: useful as part of the catheter systean of the present invention.
Fig. 10 is a sec~nd embodiment of a catheter :' system constructed in accordance with the principles of 35 the present invention.
dig: I2 illustrates use of the catheter of Fig. 10 a.n the recanalization of a stenosed region within ,;,..-..,~a'VU 93/13816 212 ~'~ 4 ~ ~~'fm~~xmzb~
a blood vessel according to the method of the present invention.
a Fig. 12 illustrates a third embodiment of a :;
catheter constructed in accordance with the principles of ,, 5 the present invention in combination with an anchoring ' catheter sheath.
::
Fig. 13 illustrates the use of the catheter and catheter sheath of Fig. 1.2 in the recanalization of a stenosed region within a blood vessel according to the .10 method of the present invention. .
'' DES~FtI~TION iDF' '~E &'NEF'ER~tED FM.80DIMENT
this invention provides a method and apparatus for selectively heating a target location within a patient's body, such as solid tissue, a body lumen, or 15 the like, particularly including atheromatous material which partially or fully rcludes a blood vessel or other body lumen. In addition .~ blood vessels, body lumens which may be treated by tire method and apparatus of the present inv~nti~n include the urinary tract (which for 20 example may be ~ccl~ded by an enlarged prostrate in males), the fallopian tubes (which may be occluded and cause infertility), and the like. For convenience, the remaining disclosure will He directed specifically at the treatment of blood rressels but it will be appreciated .25 that the apparatus and methods can be applied equally .i well to other body hamens and passages.
The stenotic ~nate~ial in blood vessels will be atheroma or athero~matous plaque, and may be relatively soft (fresh) or may be in advance stages of ra '~ 3a atherosclerosis and hardened. The present' invention'uses an electrode array including a plurality of independently c~ntrolled electrodes distributed over the distal portion of a catheter to apply heat seiectavely to the stenotic material while limiting the unwanted heating of the blood and/or surrounding vessel wall. Since the atheromatous mass in tie occluded blood vessel is preferentially heated and softened relative to the vessel wall, the path ;fyl~~" -WO 93/l3~Ib PCT/US92/11 ~?
,; 8 ' ' of the advancing catheter tip will be naturally confined in the lumen, away from the blood vessel wall. The electrode array will usually include at least two electrode terminals, more usually at least ZO electrade .
terminals, and preferably at least 36 electrode .
~
the stenotic material .
terminals, or more. Prs a result, is selectively softened, or weakened, permitting l~
~recanalize the blood advancement of the catheter to vessel lumen. Accordingly, this invention provides a l0 method and apparatus for effectively penetrating a partially or totally occluded blood vessel by simultaneously applying both (1) heat to the stenotic material surrounding the tip of the catheter and (2) pressure against the heated stenotic material using the catheter itself. Optionally, subsequent recanalization procedures may be performed using either the same or a :,;
v' dif f erent catheter .
The present invention includes a means for guiding the catheter along a pathway approximating the central region of the occluded blood vessel. The guiding ,~ means is usually an electrically conducting wire that contains or serves as a common electrade for the heating means. The guiding means is extensible from the tip of the catheter and is located within and concentric to the y 25 catheter conveniently being in the form of a movable or fixed guidewire, usually being a movable guidewire. The electrode array is disposed proximally to the common electrode and positioned on or near the tip of the .
catheter.
~~i 30 Each :individual electrode in this array is electrically insulated from all other electrodes in the array and is connected to its own power source or vaonraection which limits or interrupts current flow to the electrode when low resistivity material (e.g. blood) , 35 causes a lower resistance path between the common electrode and the individual electrode. The tip of the catheter is thus composed of many independent electrode '6~V0 93/13816 ~ 2 ~. ~ ~'~ 4 5 PCT/US92/11265 terminals designed to deliver electrical energy in the vicinity of the tip. The selective heating of the ', stenotic material is achieved by connecting each individual electrode terminal and the common electrode (e. g. on a guidewire) to an independent power source, which may be a substantially constant current power source. The application of high frequency voltage between the common electrode and the electrode array results in the conduction of high frequency current from each individual electrode terminal to the said common electrode. The current flow from each individual :3 electrode terminal to the common electrode is controlled by either active or passive means, or a combination :thereof, to selectively heat the stenotic material while minimizing the undesirable heating of the blood or the ,,;
vessel wall.
This invention takes advantage of the differences in electrical resistivity between the stenotic material (atheromatous mass), blood, and blood vessel wall. By way of example, for any selected level . of applied voltage, if the electrical conduction path y~.. . , between the common electrode (e.g. guidewire) and one of -the individual electrode terminals within the electrode ,. arra~r is blood or blood vessel wall-(each having a is y y), said current relativel low~electrical resistivit control means connected to individual electrode will limit current flow so that the heating of intervening blood or blood vessel wall is minimized. In contrast, if the electrical conduction path between the Gammon ~~ 30 electrode and one of the'individua'1 electrode terminals' wathir. the electrode array is atheromatous mass (having a relatively higher electrical resistivity), said current control means connected to said individual electrode will ny allow current f low suf f icient f or the heating and , subsequent thermal softening or weakening o~ the intermediate atheromatous mass.
a catheter body having a proximal end and a distal end;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of electrically isolated electrode terminals disposed over a contact surface;
a common electrode; and means for applying a high frequency voltage between the electrode array and the common electrode, wherein current flow to each electrode terminal is individually controlled in response to changes in impedance between the electrode terminal and the common electrode.
In a further aspect, the present invention provides a catheter comprising:
a catheter body having a proximal end, a distal end, and a guidewire lumen;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of isolated electrode terminals disposed over a contact surface;
means for connecting the isolated electrode terminals to a high frequency power supply; and a plurality of current limiting resistors, with at least one resistor connected in series between each electrode terminal and the power supply.
The present invention also provides a catheter system comprising:
a catheter guide having a proximal end, a distal end, a lumen therethrough, and a common electrode disposed on an exterior distal surface;
a catheter body disposed within the lumen of the catheter guide, said catheter body having a proximal end, 5a a distal end, and an electrode array disposed over a contact surface at the distal end, said electrode array including a plurality of electrically isolated electrode terminals; and means for individually connecting the electrode terminals to a high frequency power supply along isolated high impedance conductive paths;
whereby the common electrode and the electrode array may be connected to a high frequency power supply to efficiently deliver energy to a patient surface contacted by the electrode array and electrically exposed to the common electrode.
According to a particular aspect of the present invention, heating is directed primarily to the target location by limiting the current flow through each electrode terminal in the electrode array. In this way, more power is applied to the high resistance (low conductivity) tissue or stenotic material relative to the low resistance (high conductivity) blood and blood vessel wall. Current flow may be limited by active or passive devices, with an exemplary system employing a plurality of current limiting resistors, with at least one current limiting resistor in series with each electrode terminal.
The catheter of the present invention may be used alone in order to heat a target location e.g., to recanalize a stenotic region within a blood vessel.
Optionally, the catheter may be used in combination with other interventional or diagnostic devices in order to provide a multiple step treatment and/or diagnostic procedure. In particular, it will be possible to provide the electrode array of the present invention in combination with or at the distal end of catheters which employ other interventional and/or diagnostic elements, such as dilatation balloons, lasers, ultrasonic transducers, and the like. By employing catheters having such additional capabilities, the need to exchange catheters is reduced or eliminated.
A particular advantage of catheters constructed in Sb accordance with the principles of the present invention is that they can be "self-guiding" when introduced through a blood vessel. Since the electrode array heats atheromatous material in preference to the blood vessel wall, the catheter can be advanced without substantial concern over damage to the blood vessel wall. That is, the path of the catheter will be preferentially pCT/U~92/11 ~~ g3/a~~a~ 12 9'~ ~
._ . .
through the atheroma, necessarily limiting damage to the blood vessel wall.
The catheter of the present invention will 'i preferably include a temperature measuring or sensing ..
element near its distal tip, preferably within the electrode array, in order to measure the temperature at .
.
the interface between the electrode array and the tissue ''a or stenotic material being treated. More preferably, a plurality of temperature measuring elements will be Z,0 distributed through the electrode array in order to determine the temperature profile of the interface.
Temperature information obtained from the temperature measuring elements can be used to control the power output to the electrodes in order to control the temperature of the stenoti.c material within a desired range.
1~RTEF DEBCRIP'f~ON DF fRE DRAWII~1C~8 .! Fig. 1. is ~ perspective view of a catheter .;
system constructed in accordance with the principles of ; ~ 20 the present inventi~n, where the catheter includes a ..
s dilatati~n balloon.
,;, Fig. 2 is an enlarged view of the distal end of the catheter of 'Fig. 1, shown in section.
F~q..3 is'an egad view of the distal tip of the '25 catheter of Figs : ~. end 2 .
Figs. 4~8 a:llustrate the use of the catheter of Js Figs: 1.-3 in the recanalizati~n of a stenosed region within a blood vessel according to the method of the , '' present invention 3tD Fig: 9 is a schematic illustration of a current v li3niting power supgly: useful as part of the catheter systean of the present invention.
Fig. 10 is a sec~nd embodiment of a catheter :' system constructed in accordance with the principles of 35 the present invention.
dig: I2 illustrates use of the catheter of Fig. 10 a.n the recanalization of a stenosed region within ,;,..-..,~a'VU 93/13816 212 ~'~ 4 ~ ~~'fm~~xmzb~
a blood vessel according to the method of the present invention.
a Fig. 12 illustrates a third embodiment of a :;
catheter constructed in accordance with the principles of ,, 5 the present invention in combination with an anchoring ' catheter sheath.
::
Fig. 13 illustrates the use of the catheter and catheter sheath of Fig. 1.2 in the recanalization of a stenosed region within a blood vessel according to the .10 method of the present invention. .
'' DES~FtI~TION iDF' '~E &'NEF'ER~tED FM.80DIMENT
this invention provides a method and apparatus for selectively heating a target location within a patient's body, such as solid tissue, a body lumen, or 15 the like, particularly including atheromatous material which partially or fully rcludes a blood vessel or other body lumen. In addition .~ blood vessels, body lumens which may be treated by tire method and apparatus of the present inv~nti~n include the urinary tract (which for 20 example may be ~ccl~ded by an enlarged prostrate in males), the fallopian tubes (which may be occluded and cause infertility), and the like. For convenience, the remaining disclosure will He directed specifically at the treatment of blood rressels but it will be appreciated .25 that the apparatus and methods can be applied equally .i well to other body hamens and passages.
The stenotic ~nate~ial in blood vessels will be atheroma or athero~matous plaque, and may be relatively soft (fresh) or may be in advance stages of ra '~ 3a atherosclerosis and hardened. The present' invention'uses an electrode array including a plurality of independently c~ntrolled electrodes distributed over the distal portion of a catheter to apply heat seiectavely to the stenotic material while limiting the unwanted heating of the blood and/or surrounding vessel wall. Since the atheromatous mass in tie occluded blood vessel is preferentially heated and softened relative to the vessel wall, the path ;fyl~~" -WO 93/l3~Ib PCT/US92/11 ~?
,; 8 ' ' of the advancing catheter tip will be naturally confined in the lumen, away from the blood vessel wall. The electrode array will usually include at least two electrode terminals, more usually at least ZO electrade .
terminals, and preferably at least 36 electrode .
~
the stenotic material .
terminals, or more. Prs a result, is selectively softened, or weakened, permitting l~
~recanalize the blood advancement of the catheter to vessel lumen. Accordingly, this invention provides a l0 method and apparatus for effectively penetrating a partially or totally occluded blood vessel by simultaneously applying both (1) heat to the stenotic material surrounding the tip of the catheter and (2) pressure against the heated stenotic material using the catheter itself. Optionally, subsequent recanalization procedures may be performed using either the same or a :,;
v' dif f erent catheter .
The present invention includes a means for guiding the catheter along a pathway approximating the central region of the occluded blood vessel. The guiding ,~ means is usually an electrically conducting wire that contains or serves as a common electrade for the heating means. The guiding means is extensible from the tip of the catheter and is located within and concentric to the y 25 catheter conveniently being in the form of a movable or fixed guidewire, usually being a movable guidewire. The electrode array is disposed proximally to the common electrode and positioned on or near the tip of the .
catheter.
~~i 30 Each :individual electrode in this array is electrically insulated from all other electrodes in the array and is connected to its own power source or vaonraection which limits or interrupts current flow to the electrode when low resistivity material (e.g. blood) , 35 causes a lower resistance path between the common electrode and the individual electrode. The tip of the catheter is thus composed of many independent electrode '6~V0 93/13816 ~ 2 ~. ~ ~'~ 4 5 PCT/US92/11265 terminals designed to deliver electrical energy in the vicinity of the tip. The selective heating of the ', stenotic material is achieved by connecting each individual electrode terminal and the common electrode (e. g. on a guidewire) to an independent power source, which may be a substantially constant current power source. The application of high frequency voltage between the common electrode and the electrode array results in the conduction of high frequency current from each individual electrode terminal to the said common electrode. The current flow from each individual :3 electrode terminal to the common electrode is controlled by either active or passive means, or a combination :thereof, to selectively heat the stenotic material while minimizing the undesirable heating of the blood or the ,,;
vessel wall.
This invention takes advantage of the differences in electrical resistivity between the stenotic material (atheromatous mass), blood, and blood vessel wall. By way of example, for any selected level . of applied voltage, if the electrical conduction path y~.. . , between the common electrode (e.g. guidewire) and one of -the individual electrode terminals within the electrode ,. arra~r is blood or blood vessel wall-(each having a is y y), said current relativel low~electrical resistivit control means connected to individual electrode will limit current flow so that the heating of intervening blood or blood vessel wall is minimized. In contrast, if the electrical conduction path between the Gammon ~~ 30 electrode and one of the'individua'1 electrode terminals' wathir. the electrode array is atheromatous mass (having a relatively higher electrical resistivity), said current control means connected to said individual electrode will ny allow current f low suf f icient f or the heating and , subsequent thermal softening or weakening o~ the intermediate atheromatous mass.
6 PCf/US92/112 , a0 2129' 4~
The application of a high frequency voltage between the common electrode and the electrode array for appropriate intervals of time substantially weakens the selectively heated atheromatous mass, allowing the .
catheter to penetrate and pass through the obstruction, thus recanalixing the blood vessel. Once the partially .
or fully occluded blood vessel has been opened to allow ''i passage of the catheter, the~catheter can be advanced to 'j position a dilatation balloon (or other interventional or diagnostic element) within the occluding material. The dilatation balloon can then be used for angioplasty :' treatment in a substantially conventional manner.
Direct (Joulian) heating of the stenotic material by conduction of high frequency current softens '~'i15 the material ever a distributed region. The volume of this distributed region is precisely controlled by the geomet=ical separation between the common. electrode (e. g.
the guidewire) and the electrode array. The rate of heating of the stenotic material is controlled by the appla.ed voltage level. The use of high frequency current a for Joulian heating also minimizes induced stimulation of ~uscl~e tissue or nerve tissue in the vicinity of the mass '~" being hewed.- In addition, high frequencies minimize the risk of interfering with the natural pacing of the heart ,wi , in circumstances where the catheter of the present invention'is used'in he coronary arteries.
The power applied to the common electrode and the electrode array will be at high frequency, typically hetween about 50 kHz and 2 biz, usually being between about 100 kHz a,nd I ~I~giz, 'and preferably being between ._ about 200 kliz and 400 kHz. The voltage applied will usually be in the range from about two volts to 100 ; volts, preferably being in the range fram about five volts to 90 volt, and more preferably being 'in the~range 3~ from about seven volts to 70 volts. Usually, the voltage applied will be adjustable; frequently in response to a :,d temperature controller which maintains a desired VVO 93/1316 - ~ ~ ~ r~ ~ '~ pCf/~1592111265 temperature at the interface between the electrode array and the stenotic material. The desired temperature at the interface between the electrode array and the stenotic material will usually be in the range from about 3~°C to x.00°C, more usually from about 3&°C to 8.0°~C, and preferably from about 40°C to 70°C.
A particular advantage of the present invention is that the heating means can be configured to a wide range of catheter sixes appropriate to the particular sixe of tine occluded blood vessel or other body lumen or cavity being recanalixed, typically in the range of diameters from 0.04 to 0.4 inches. The present invention can also incorporate a guidewire which can function as both a means for controlling and guiding the path of the catheter in the conventional manner, as well as to concentrate the thermal power density dissipated directly into the stenotic material by serving as the common electrode:
''' The preferred power source of the present ::, 'a ~0 invention carp deliver a high frequency voltage selectable , .
to generate power levels ranging from several milliwatts t~ 5~ watts, depending'o~ the size of the stenotic material being heated, the sixe of the blood vessel being ~ecanalixed, and the rate.of advancement of the heating means through the stenotic materiel. The power source aalows tie user to select the voltage level according to the sp~ci:fic requirements of a particular angioplasty or ~tlaer pre~cedure .
'' The power source will be current limited or otherwise controlled s~ that undesired heating of blood, blood vessel wall, and other low electrical resistance materials does not ~ccur. In the exemplary embodiment described belora, current limiting resistors are placed in ~,, series with each independent electrode, where the resistor is 'sired' to provide an at least equal, and preferably greater, resistance than would normally be provided by the stenotic material. Thus, the electrode 1W~ 93/3815 ~~ PCT/L15921I1,"~~~..
sees a substantially constant current source so that power dissipation through a low resistance path, e.g.
blood, will be substantially diminished.
1~s an alternative to the current limitinr~
resistors, a controlled power supply may be prov~.ded which interrupts the current flow to an individual electrode in the array when the resistance between that electrode and the common electrode falls below a y threshold level. The control could be implemented by placing a switch in series with each electrode,.where the switch is turned on and off based on the sensed current flow through the electrode, i.e. when the current flow exceeds a preselected limit, the switch would be turned off. The current limit could be selectable by the user and preferably would be preset at the time of manufacture ;,;a of. the power source: Current flow could be periodically ..;, se;~sed and reestablished when the stenotic material resistance is again present. Particular control system deigns f~r implementing this strategy are well within :, ~ 0 the ski l l ~:n thh art .
1~ an exemplary embodiment as shown in a catheter 1.0 includes a guidewire 16 which Figure 1 , functions both as a means'for guiding the catheter into the intended p~siti~ra, as well as a common electrode.
~5 The entire guidewire may be an electrode, or it may contain an elects~de. Referring to Figures 1 and 2, the ,~a . Catheter 10 alSO inCluds all aZray Of eleCtr~de , te~ninals 18 disposed on the distal tip 12 of the catheter l0. The electrode terminals 18 are eleetrically 30 isolated from each other and from the common electrode 16: Proximally from the tip 12, the catheter 10 includes j a conventional dilatation (angioplasty) balloon 20 ' generally concentric with the shaft of the catheter 10.
Still referring to Figures 1 and 2, each of the terminals 35 l8 is connected to the impedance matching network 22 by .
means of the individually insulated conductors 52. The proximal portion of the catheter 10 is also equipped with " ~:~tJO 93/1381b 2 '~ ~'~ ~ PCT/US92/112b5 the fluid port 24 communicating with balloon 20. The guidewire is axially movable in an electrically insulating guidewire lumen tube 46, said lumen tube 46 being contained in, and concentric to, the catheter 10.
.':;
The proximal end 42 of the guidewire is sealed against fluid leaks by a fluid seal 28. The proximal portion of .:, the catheter l0 also has a connector 26 for providing the -. electrical connections to the matching network 22.
r A power source 32 provides a high frequency voltage to the electrode terminals 18 by means~of a cable : 38 connectable to the connector 26. The power source 32 ~
C has a controller 34 to change the applied voltage level ''' as well as a selector 36 for selection of the highest temperature at the tip l2 of the catheter 10 during its lained later. Finally, the proximal portion as ex use p , of the guidewire electrode 42 is connected to the power source 32 by a detachable connector 30 and cable 40.
In the embodiment shown in Figures 1, 2, and 3, temperature sensors 48 are provided in the distal tip 12 of the catheter 10, typically thermocouple pairs (e. g.
chromel and alumel~. Said temperature sensors 48 and connected to the power source 32 by thermocouple wires 50 extending the length of the catheter 10 and by the cable 38 connected through the connector 26. The temperature sensors 48 at the tip 12 of the-catheter 10 are connected v to a'feedback c~ntrol system in power source 32 to adjust the power outgut so that the user selectable temperature "' is not exceeded during the use of the catheter in recanalization of an occluded blood vessel. Fower output ~, 30 could be c~ntrolled by any conventional technique, such , as control of voltage, currento duty cycle, or the like.
The selectable temperature is selected by the user by i . adjusting selector 36 prcwided in the power source 32.
Referring to Figure 2, the distal tip 12 of the catheter 10 of the preferred embodiment contains the exposed terminals of the electrode terminals 18 and the temperature sensors 48. The terminals 18 and temperature ' :: : , ... : ' ..;;i. .. : ;~., . ., : ~ ;::, .. ..:
WO 93/13816 pC'f/US92/lla;- i ~~.~~~r~ ~C~ , 14 -s''~en~sorsl 48 are secured in a matrix of suitable insulating material (e. g. epoxy) 54 and formed in a generally tapered or hemispherical shape, preferably being a conical or "nose cone" configuration. Proximal to the tapered tip 12, the temperature sensor wires 50 and ;', electrode wires 52 are contained in a jacket 44 of cylindrical shape covering the ,length of the catheter 10.
"' An end view of the catheter 10 at the tip 12 is illustrated in Figure 3. Referring to Figures 2 and 3, electrode terminals l8 are electrically insulated from each other and from temperature sensors 48, and are secured together in a bundle by the electrically insulating material 54: Proximal to the tip 12, the thermocouple wires 5o and electrode wires 52 are '~'' 15 contained in a suitable jacket 44 of cylindrical shape covering the length of the catheter 10. The central portion of the catheter l0 contains the electrically insulating guidewire lumen tube 46 which provides a lumen for the guidewire l6: The distal end of the said tube 46 optionally eac~tends beyond he tip 12 to provide a tip offset l4. The intended purpose of said tip offset 14 is to provide a minimum separation between the said common electrode on guidewire 16 and array of electrodes 18, usually being at least 0.02 inches, more usually being at least O:IS inches; and sometimes being 0.25 inches or greater:
;.; Figure 4 illustrates how the catheter 10 can be applied to recanalize a blood vessel 56 occluded with an atheromatous plaque 58. ,In this ease, the,guidewire 16, ~
~ 30 is first advanced to the site of the atheromatous plaque -r 58, arid the catheter 10 is then moved over the guidewire ~, 16 to contact a leading edge of the plaque. Next, the guidewire 16 is advanced through the plaque 58 under I
fluoroscopic guidance; exposing a length 60 ~f the ~ guidewire which,is electrically conducting.
Referring next to Figure 5, the distal tip 12 ~f the catheter 10 comprising the array of electrode ~~~V~ 93/13816 PC'f/US92/11265 2~.2~'~4~
15 ._ ..
terminals 18 as urged against the atheromatous plaque 58.
°i A high frequency voltage is applied between the common ''~' electrode an guidewire 16 and each of the electrode terminals 18. The resulting electrical current flows between the said common electrode 16 and the electrode v% terminals 18 through the atheromatous plaque 58, as r'~"~ illustrated by current flux lines 62, pue to the electrical resistance of the atheromatous plaque 58, the localized current flow heats the plaque 58 in a zone 64.
, ~''?
, ., 1 10 The localized heating is adjusted by varying the level and duration of the high frequency voltage.
.~
The tip offset 14 maintains a minimum distance , between the electrode l8 and the common electrode s,;3 (guidewire) 16. The zone of heating 64 within the plaque 58 is deffined by the boundary of the current flux lines '.1 52. The atheromatous plaque material softens in the heated zone 64, which facilitate the forward axial advancement of the catheter tip 12 through said heated '' zone. Said movement of the tip 12 effects the ,.;;20 displacement of the plaque material, thereby recanalizing (creating an opening through) the previously occluded blood vessel 56. The catheter 10 is advanced through the softened plaque until a channel is created in the occluding mass.. The catheter 10 is withdrawn leaving a vessel recanalized allowing an improved flow of blood therethrough.
After the catheter 10 has been advanced through the heated plaque, if necessary, the balloon 20 can be inflated with'agapropriate flaid to appropriate pressures to effect conventional angioplasty.
There are situations ~,rhere a guidewire cannot be completely advance~'~ ::ross a stenosed region 58, as , ~ure .. In such cases, the common illustrated in Fic ~;. , electrode (guidewire) 16 is partially penetrated into the 35.. atheromatous;plaque 58' to the extent possible. The array of electrodes l8 is contacted against the wall of ;,.;
plaque 58', and the tip offset 14 creates a minimum PCf/L'S921aI-~._.
ewe g3/a~sab ._ 16 spacing between the common electrode 26 and the electrode array so that some heating of plaque will occur. The catheter 10 and the common electrode 16 can then be alternately advanced until a channel is created through the entire region of plaque 58'. Once again, ' conventional balloon angiopl~sty can be performed once the balloon 20, in its deflated position, has been advanced across the plaque ~58'.
A central aspect of the present invention is the ability of the catheter 10 to deliver electrical energy effectively only to the intended areas, i.e. the atheromatous material, and not to the blood or the blood vessel. Such directed energy transfer results in selective heating of the atheromatous material which allows the catheter to be ''self-guiding" as described above. When the tip l2 of the catheter 10 is pressed against a region of stenotic material, some of the electrode terminals l8 will be in contact with atheroma, while other electr~de terminals may be in contact with ZO blood, and yet ethers may be in contact with the blood vessel wall. These situations are illustrated in Figures 7 and 80 ~a~h ~f the electrode termixrals 18 experiences an electrical impedance whack is characteristic of the material which. is disp~sed between the zndividu~l electrode terminal and the common electrode. The present invention takes advantage of the fact that the electrical resistivity of typical atherama is higher than that of s~
.l bl~~d or blood vessel walle Thus, if the current~passing throutgh each of the electr~de terminals 18 is limited to a substantially constant'valute, the regions of higher ,-~ electrical resistivity will generate more ~oulian heating {power = I2R. where I is the current through resistance R} than a region ~f lower electrical resistivity.
Therefore, the atheromatous plaque of the stenotic region will be selectively heated up while the blood and blood .t vessel wall will experience a minimal rise in :,,... ..... ,. :.: _ .:, . . ~ ~-,- . ,.; . ,. : : -.., ,. _:~ , ....
,.. , . . , . , . , , . ,.. .. . a ,. . ,: _ .. , ;~.
. . - .. , . . , , . , .". .. . ... : ., . : ... .
- ~ ~ ~ ~ ~ ~ ~ PGT/US92/112b5 ~?WO 93/ 1381 b ._ . . . 17 temperature. Thus, the catheter will selectively advance through the atheroma which has been heated and softened.
The heating selectivity of the present invention is accomplished by selecting the electrical resistance of the various components which comprise the pathway of the electrical current 62 between the common electrode (guidewire) 16 and each of the electrode terminals l8 in the electrode array located at the tip 12 of the catheter 10. By way of example, the electrical resistivity of blood at body temperature is iri the range from 148 to 176 Ohm-cm at a frequency up to 120 kHz (Geddes et al. (1967) Med. B.ioh. Eng. 5:271-293). The electrical resistivity of human cardiac and skeletal muscle (which approximates the structure of the blood vessel wall) is in the range of 100 to 456 Ohm-cm at 3 frequencies in the .range l00 to 1000 kHz. (Geddes et al.
(196?), supra).
In contrast, atheromatous mass generally resembles fat-like deposits and contains cholesterol, ~ 20 lipids, and lipidophages. Based on its primarily fat=
wy like composition, the atheromatous mass has a relatively '' ,y > high electrical resistivity as compared with blood. The ~
electrical resistivity'of fat--like substances in human has been reported in the range of 1,000 to 3,000 Ohm-cm '~ 25 at frequencies ranging from 100 to 1,000 kHz (Geddes et . al., (1967), supra): This invention utilizes the ..e, 'r ixEherent two to den fold difference in electrical y resistivities to selectively heat the atheromatous plaque , in a blood vessel.
30 Each of the electrode terminals 18 is connected to an individual source of current by means of wires 52.
A current limiting network providing the controlled or ,~;
constant curren~, as described above, is contained in a ,,, junction box Z2: The network can be composed of either 35 active or passive electronic components to perform its ~.;j intended function: By way of example, and not intending to limit the scope and spirit of this invention, a ;::.. .. :. . ~ ' : . . . ' .:', , ~ ~~;~, r r'~.~ , . . ~ ~ " . .' ~ ', .; :
. , :: , , m. . i. ..
P~'/US9211y~.'.
WO 93! 13816 ~.~~g~ ~5 ._ . .
I network composed of passive circuit elements, i.e.
resistors, is illustrated in Fig. 9. Referring to Figs. 1, 2, and 9, a constant current network 22 consists of a multiplicity of resistors 72 which are same in number as the electrode terminals 18. Each resistor is connected between a power source 32 (by the connector 26 and cable 38) and the corresponding electrode terminal 18 (by wire 52). The current will be maintained substantially constant so long as each resistor impedance is sufficiently higher than the load impedance. Suitable '~ resistor values will be in the range from 500 tt to 50,000 t~, usually being in the range from 1,000 n to 25,000 n, preferably being in the range from 3,000 n to 25,000 n.
.~'15 Still referring to Figs. 1 and 9, each ,,,~, electrodewcerminal l8'is connected to a load represented by the atheromablood, or blood vessel wall. More specifically; he load impedance 74 of the atheroma is designated by A, the load impedance 76 of blood is ;~ 20 denoted by B, and load impedance 78 of vessel wall is denoted by W respectively. As the current passes through these components; it is received by the common electrode (guidewire) 1'6 which is in turn connected to the power source 32 by connector 30 and cable 40. The level of the < 2~ current flowing in the circuits is controlled by the v~lt~ge applied between the proximal end of the resistor network 22 and the common electr~de (guidewire) 16.
The'expected power delivered to each of the loads (i.e. atheroma, blood, and vessel wall tissue) can 30 be calculated based~on exemplary values for the different :.-;
parameters as enumerated below Catheter diameter (5.French), D 1.56 mm .'~ Number of Electrodes' Terminals 18 , n 35 Site of the-'electrode 18 tip, d 0.004" dia. .
Resistance of the network resistor 72, R 10,000 Ohms ampe~snce 74 of atheroma, A 3,000 Ohms .,s '~"re~.~.
~~ 93/t3896 _ ~ ~ ~ ~ ~ ~ ~ PC'f/US92/112fi5 Tmpedance 76 of blood, B 200 Ohms Tmpedance 78 of vessel wall, W 500 Ohms Applied voltage from source 32 W: 4o Volts, RM8 Calculated power dissipation per eleetrode in:
Atheroma 28 milliwatts Blood 3 milliwatts Vessel Wall 7 milliwatts Calculating power (I2R) from the abode, the power dissipation in the atheromatous plaque is approximately ten times that in blood and four times that in blood vessel wall respectively. Taking into account the heat capacities of various components, the expected temperature in the atheromatous plaque will be considerably greater than in the blood or blood vessel wall.
The desired temperature rise of the atheromatous,pl~que to effect desired recanalization is ~f the order of 9.0° to 6~°. Based on the above calculation; a 10° to 60°C increase in the temperature of the atheromatous plaque using'the apparatus and method of the present inventa.on will result in a corresponding rise of blo~d temp~ra~ure in the range of 1°C to 6°C caused by ,4 25 the current fl~wing direetly through the blood>
Once a sufficient temperature rise is accomplished ~.n the atheromatous plaque, the mechanical strength of the said mass is substantially reduced in the localized region. surrounding the tip 12 0~ the catheter i0. This allows the catheter 10 to be advanced incrementally through the plaque by applying a ~" longitudinal g~ree on the portions of the catheter 10 external to the patient. This force is transmitted along the length of the catheter 10 to the tip region 12 to create a 'eboring pressure" sufficient to penetrate the plaque 58. T~s the blood vassal wall is not equivalently heated or softened, the catheter will preferentially 'W~ 93/13 ~~ ~~ PCT/IJS92/11~. .
._.. 20 advance through the plaque 58 following a path of its own creation.
The method of controlling the heating by the thermally assisted angioplasty catheter of this invention can also be accomplished by temperature feedback control mechanism. The temperature of the atheroma in contact with the tip 12 is sensed by temperature sensing elements such as means of thermocouple pairs (Fig. 3) 48. A
feedback control loop contained in the power source 32 allows the adjustment of the necessary voltage applied so that the required temperature rise in the atheroma is accomplished. Conversely, by continuously monitoring the temperature of the atheroma being heated, the appropriate voll:.age level is continuously maintained such that the user-selected temperature is never exceeded.
Chile the above description provides a full and '';~i complete disci~sure ~f a preferred embodiment of the 'vi' invention, various anodifications, alternative COnstruct~.onS, and equivalents may be employed. F~r exaunple, the power could be communicated to the e~.ectrodes by:~ires imbedded in the catheter Mall. Also, the temperature sensing nay be achieved using fiber optics with infraxed sensing teehniqu~, a thex-mocouple, a ther-mi~tor or-other temperature sensing means.
Alt~rnati.vely, by proper selection of metals used for :; ( 1 ) a~ultipl3,city of electrodes and leads ( e. g .
Ccnst~entan ) arid ( 2 ) guidewire ( a . g steel ) , each individual electrode can function as a thermocouple in c~njunction with the singular guidewire. The measure~ent ~0 of the direct current voltage between the guidewire and ~ the multiplicity of electrodes indicates the maximum , temt~erataare which occurs at any location on the catheter ti~p This inf~rrmation can then be used in the feedback control loop as described above to assure an improved 3~ , safe upper limit on the operating temperature during the use of the apparatus of the present invention.
,.;,,z ~~~V~ 93/13816 ~ ~ ~ ~ ~ ~ J PCT/US92/11265 z ~ ._ . .
;;~~ A more preferred embodiment of the catheter of this invention is shown in Fig. 10. In this embodiment, 'r the catheter 80 is substantially similar in construction to that of Fig. l, except that a second electrode.82 is provided for on the body 84 of the catheter shaft instead 'h I
:9 of the guidewire being the second electrode. During use .e1 of the catheter 80 in therapy, this second electrode 82 is intended to be in electrical cantact with the blood in the artery. The location of the second electrode 82 is shown to be near the proximal end of the catheter 80, but could also be disposed more distally.
Still referring to Fig. 10, guidewire 86 is ;;t~
connected to the current-limiting circuitry in power source 94 in a manner similar to the electrical 'i ~ connection of tip electrodes 90. During use of the catheter 80, the gui~lewire 86 becomes an additional electrode working in conjunction with the other tip '; electrodes. In this emlaodi.ment, no offset between the ,~ guidewire 86 and the electrode array 90 is required.
Referring now to Fig. 11; the catheter 80 is '' advanced over the guidewire 86 to the site of a total occlusion 88 -in the artery, 89. The electrode array 90 and the guidewire 86 are connected to the power source 9~
r= (Fig. 10)', and'the second ~lectr~de 82 is connected to an e' 25 opposite polarity terminal of the power source. ey applying power to the electrodes 9o and 82, current flux ~; lines !32 are formed and distributed in the occlusion 88.
v The,highest current density exists at the immediate vicinity of the tip electrode array 90, thereby producing ,~; 30 maximum heating of the atheroma in contact with the cathet~x~ tip: A return path for tlhe electrical current from the tip electrodes 90 to the second electrode 82 is defined through the blood in the blood vessel, the blood vessel wall, and/or the surrounding tissue. However, the 35 ' e~xrrent is most likely-to flow through the blood and , blood vessel wall as these components have much lower res~.stivity as c~mpared to other body tissue. The second 1~0 93f 13$16 ~ PC'T/US92111;. ~~~~ j electrode 82 is designed to be long with a large surface . area to ensure low density of current flux lines at said a second electrode.
r As the current passes through, the temperature S of the occluding material 88 is raised, thereby softening 'e, the occlusion. The catheter 80~;.along the guidewire 86 is advanced through tha.s softened:atheroma until the vessel is recanalized. A final recanalization step can then be :, performed by balloon dilatation or other currently 'i 10 available therapeutic techniques. ' vi It is understood that the plaque in the total .'',j occlusions can be dense and somewhat hard to push a catheter through even though it is heated. In order to facilitate the mechanical advancement of the catheter 15 through the praque, another embodiment of the catheter system of the present invention is illustrated in Fig.
12. The catheter IO of Fig. 1 or catheter 80 of Fig. 10 v is placed in ~ sheath catheter 96. The distal end of the sheath eatheter 96 indludes one or a plurality of ~0 expanding means 98, such as infratable balloons. The proximal endbf the sheath catheter 96 includes the '~ necessary bl~od scaling means and balloon expanding ~aorts: The shaft of the sheath datheter 96 includes the necessary lumens) for expanding said ballo~n(s) 98.
The purpose of the sheath catheter 96 is to provide an anchor for the main catheter 10 or 80 while in use. Specificarly referring to Fig. 13, the catheter system (domprising of the sheath catheter 96 and the main catheter iQ or 80) is advanced to the site of the 3~ occlusion 102 (Fig. 11). The balloons) 98 are inflated end the sheath catheter 96 is thus anchored in position in the blood'vessel proximate to the occlusion. The main catheter 10 or 80 is then advanced inside the sheath catheter 96 against the occlusion 102. The main catheter 35 tip 90 is then energized, and further advanced through : the softened atheroma. The sheath catheter 96 with inflated balloons) 98 thus serves as an anchoring means :~'j.
'7V~ 93/13816 ~ ~ ~ ~ ~ ~ ~ ~CT/US92/11265 ._ .. 23 .
assisting in the advancing of the main catheter 10 or 80 through the occlusion 102.
Although the foregoing invention has been described in detail f or purposes of clarity of .
understanding, it mill be obvious that certain modifications nay be practiced within the scope of the appended claims.
.y ..;,.,f
The application of a high frequency voltage between the common electrode and the electrode array for appropriate intervals of time substantially weakens the selectively heated atheromatous mass, allowing the .
catheter to penetrate and pass through the obstruction, thus recanalixing the blood vessel. Once the partially .
or fully occluded blood vessel has been opened to allow ''i passage of the catheter, the~catheter can be advanced to 'j position a dilatation balloon (or other interventional or diagnostic element) within the occluding material. The dilatation balloon can then be used for angioplasty :' treatment in a substantially conventional manner.
Direct (Joulian) heating of the stenotic material by conduction of high frequency current softens '~'i15 the material ever a distributed region. The volume of this distributed region is precisely controlled by the geomet=ical separation between the common. electrode (e. g.
the guidewire) and the electrode array. The rate of heating of the stenotic material is controlled by the appla.ed voltage level. The use of high frequency current a for Joulian heating also minimizes induced stimulation of ~uscl~e tissue or nerve tissue in the vicinity of the mass '~" being hewed.- In addition, high frequencies minimize the risk of interfering with the natural pacing of the heart ,wi , in circumstances where the catheter of the present invention'is used'in he coronary arteries.
The power applied to the common electrode and the electrode array will be at high frequency, typically hetween about 50 kHz and 2 biz, usually being between about 100 kHz a,nd I ~I~giz, 'and preferably being between ._ about 200 kliz and 400 kHz. The voltage applied will usually be in the range from about two volts to 100 ; volts, preferably being in the range fram about five volts to 90 volt, and more preferably being 'in the~range 3~ from about seven volts to 70 volts. Usually, the voltage applied will be adjustable; frequently in response to a :,d temperature controller which maintains a desired VVO 93/1316 - ~ ~ ~ r~ ~ '~ pCf/~1592111265 temperature at the interface between the electrode array and the stenotic material. The desired temperature at the interface between the electrode array and the stenotic material will usually be in the range from about 3~°C to x.00°C, more usually from about 3&°C to 8.0°~C, and preferably from about 40°C to 70°C.
A particular advantage of the present invention is that the heating means can be configured to a wide range of catheter sixes appropriate to the particular sixe of tine occluded blood vessel or other body lumen or cavity being recanalixed, typically in the range of diameters from 0.04 to 0.4 inches. The present invention can also incorporate a guidewire which can function as both a means for controlling and guiding the path of the catheter in the conventional manner, as well as to concentrate the thermal power density dissipated directly into the stenotic material by serving as the common electrode:
''' The preferred power source of the present ::, 'a ~0 invention carp deliver a high frequency voltage selectable , .
to generate power levels ranging from several milliwatts t~ 5~ watts, depending'o~ the size of the stenotic material being heated, the sixe of the blood vessel being ~ecanalixed, and the rate.of advancement of the heating means through the stenotic materiel. The power source aalows tie user to select the voltage level according to the sp~ci:fic requirements of a particular angioplasty or ~tlaer pre~cedure .
'' The power source will be current limited or otherwise controlled s~ that undesired heating of blood, blood vessel wall, and other low electrical resistance materials does not ~ccur. In the exemplary embodiment described belora, current limiting resistors are placed in ~,, series with each independent electrode, where the resistor is 'sired' to provide an at least equal, and preferably greater, resistance than would normally be provided by the stenotic material. Thus, the electrode 1W~ 93/3815 ~~ PCT/L15921I1,"~~~..
sees a substantially constant current source so that power dissipation through a low resistance path, e.g.
blood, will be substantially diminished.
1~s an alternative to the current limitinr~
resistors, a controlled power supply may be prov~.ded which interrupts the current flow to an individual electrode in the array when the resistance between that electrode and the common electrode falls below a y threshold level. The control could be implemented by placing a switch in series with each electrode,.where the switch is turned on and off based on the sensed current flow through the electrode, i.e. when the current flow exceeds a preselected limit, the switch would be turned off. The current limit could be selectable by the user and preferably would be preset at the time of manufacture ;,;a of. the power source: Current flow could be periodically ..;, se;~sed and reestablished when the stenotic material resistance is again present. Particular control system deigns f~r implementing this strategy are well within :, ~ 0 the ski l l ~:n thh art .
1~ an exemplary embodiment as shown in a catheter 1.0 includes a guidewire 16 which Figure 1 , functions both as a means'for guiding the catheter into the intended p~siti~ra, as well as a common electrode.
~5 The entire guidewire may be an electrode, or it may contain an elects~de. Referring to Figures 1 and 2, the ,~a . Catheter 10 alSO inCluds all aZray Of eleCtr~de , te~ninals 18 disposed on the distal tip 12 of the catheter l0. The electrode terminals 18 are eleetrically 30 isolated from each other and from the common electrode 16: Proximally from the tip 12, the catheter 10 includes j a conventional dilatation (angioplasty) balloon 20 ' generally concentric with the shaft of the catheter 10.
Still referring to Figures 1 and 2, each of the terminals 35 l8 is connected to the impedance matching network 22 by .
means of the individually insulated conductors 52. The proximal portion of the catheter 10 is also equipped with " ~:~tJO 93/1381b 2 '~ ~'~ ~ PCT/US92/112b5 the fluid port 24 communicating with balloon 20. The guidewire is axially movable in an electrically insulating guidewire lumen tube 46, said lumen tube 46 being contained in, and concentric to, the catheter 10.
.':;
The proximal end 42 of the guidewire is sealed against fluid leaks by a fluid seal 28. The proximal portion of .:, the catheter l0 also has a connector 26 for providing the -. electrical connections to the matching network 22.
r A power source 32 provides a high frequency voltage to the electrode terminals 18 by means~of a cable : 38 connectable to the connector 26. The power source 32 ~
C has a controller 34 to change the applied voltage level ''' as well as a selector 36 for selection of the highest temperature at the tip l2 of the catheter 10 during its lained later. Finally, the proximal portion as ex use p , of the guidewire electrode 42 is connected to the power source 32 by a detachable connector 30 and cable 40.
In the embodiment shown in Figures 1, 2, and 3, temperature sensors 48 are provided in the distal tip 12 of the catheter 10, typically thermocouple pairs (e. g.
chromel and alumel~. Said temperature sensors 48 and connected to the power source 32 by thermocouple wires 50 extending the length of the catheter 10 and by the cable 38 connected through the connector 26. The temperature sensors 48 at the tip 12 of the-catheter 10 are connected v to a'feedback c~ntrol system in power source 32 to adjust the power outgut so that the user selectable temperature "' is not exceeded during the use of the catheter in recanalization of an occluded blood vessel. Fower output ~, 30 could be c~ntrolled by any conventional technique, such , as control of voltage, currento duty cycle, or the like.
The selectable temperature is selected by the user by i . adjusting selector 36 prcwided in the power source 32.
Referring to Figure 2, the distal tip 12 of the catheter 10 of the preferred embodiment contains the exposed terminals of the electrode terminals 18 and the temperature sensors 48. The terminals 18 and temperature ' :: : , ... : ' ..;;i. .. : ;~., . ., : ~ ;::, .. ..:
WO 93/13816 pC'f/US92/lla;- i ~~.~~~r~ ~C~ , 14 -s''~en~sorsl 48 are secured in a matrix of suitable insulating material (e. g. epoxy) 54 and formed in a generally tapered or hemispherical shape, preferably being a conical or "nose cone" configuration. Proximal to the tapered tip 12, the temperature sensor wires 50 and ;', electrode wires 52 are contained in a jacket 44 of cylindrical shape covering the ,length of the catheter 10.
"' An end view of the catheter 10 at the tip 12 is illustrated in Figure 3. Referring to Figures 2 and 3, electrode terminals l8 are electrically insulated from each other and from temperature sensors 48, and are secured together in a bundle by the electrically insulating material 54: Proximal to the tip 12, the thermocouple wires 5o and electrode wires 52 are '~'' 15 contained in a suitable jacket 44 of cylindrical shape covering the length of the catheter 10. The central portion of the catheter l0 contains the electrically insulating guidewire lumen tube 46 which provides a lumen for the guidewire l6: The distal end of the said tube 46 optionally eac~tends beyond he tip 12 to provide a tip offset l4. The intended purpose of said tip offset 14 is to provide a minimum separation between the said common electrode on guidewire 16 and array of electrodes 18, usually being at least 0.02 inches, more usually being at least O:IS inches; and sometimes being 0.25 inches or greater:
;.; Figure 4 illustrates how the catheter 10 can be applied to recanalize a blood vessel 56 occluded with an atheromatous plaque 58. ,In this ease, the,guidewire 16, ~
~ 30 is first advanced to the site of the atheromatous plaque -r 58, arid the catheter 10 is then moved over the guidewire ~, 16 to contact a leading edge of the plaque. Next, the guidewire 16 is advanced through the plaque 58 under I
fluoroscopic guidance; exposing a length 60 ~f the ~ guidewire which,is electrically conducting.
Referring next to Figure 5, the distal tip 12 ~f the catheter 10 comprising the array of electrode ~~~V~ 93/13816 PC'f/US92/11265 2~.2~'~4~
15 ._ ..
terminals 18 as urged against the atheromatous plaque 58.
°i A high frequency voltage is applied between the common ''~' electrode an guidewire 16 and each of the electrode terminals 18. The resulting electrical current flows between the said common electrode 16 and the electrode v% terminals 18 through the atheromatous plaque 58, as r'~"~ illustrated by current flux lines 62, pue to the electrical resistance of the atheromatous plaque 58, the localized current flow heats the plaque 58 in a zone 64.
, ~''?
, ., 1 10 The localized heating is adjusted by varying the level and duration of the high frequency voltage.
.~
The tip offset 14 maintains a minimum distance , between the electrode l8 and the common electrode s,;3 (guidewire) 16. The zone of heating 64 within the plaque 58 is deffined by the boundary of the current flux lines '.1 52. The atheromatous plaque material softens in the heated zone 64, which facilitate the forward axial advancement of the catheter tip 12 through said heated '' zone. Said movement of the tip 12 effects the ,.;;20 displacement of the plaque material, thereby recanalizing (creating an opening through) the previously occluded blood vessel 56. The catheter 10 is advanced through the softened plaque until a channel is created in the occluding mass.. The catheter 10 is withdrawn leaving a vessel recanalized allowing an improved flow of blood therethrough.
After the catheter 10 has been advanced through the heated plaque, if necessary, the balloon 20 can be inflated with'agapropriate flaid to appropriate pressures to effect conventional angioplasty.
There are situations ~,rhere a guidewire cannot be completely advance~'~ ::ross a stenosed region 58, as , ~ure .. In such cases, the common illustrated in Fic ~;. , electrode (guidewire) 16 is partially penetrated into the 35.. atheromatous;plaque 58' to the extent possible. The array of electrodes l8 is contacted against the wall of ;,.;
plaque 58', and the tip offset 14 creates a minimum PCf/L'S921aI-~._.
ewe g3/a~sab ._ 16 spacing between the common electrode 26 and the electrode array so that some heating of plaque will occur. The catheter 10 and the common electrode 16 can then be alternately advanced until a channel is created through the entire region of plaque 58'. Once again, ' conventional balloon angiopl~sty can be performed once the balloon 20, in its deflated position, has been advanced across the plaque ~58'.
A central aspect of the present invention is the ability of the catheter 10 to deliver electrical energy effectively only to the intended areas, i.e. the atheromatous material, and not to the blood or the blood vessel. Such directed energy transfer results in selective heating of the atheromatous material which allows the catheter to be ''self-guiding" as described above. When the tip l2 of the catheter 10 is pressed against a region of stenotic material, some of the electrode terminals l8 will be in contact with atheroma, while other electr~de terminals may be in contact with ZO blood, and yet ethers may be in contact with the blood vessel wall. These situations are illustrated in Figures 7 and 80 ~a~h ~f the electrode termixrals 18 experiences an electrical impedance whack is characteristic of the material which. is disp~sed between the zndividu~l electrode terminal and the common electrode. The present invention takes advantage of the fact that the electrical resistivity of typical atherama is higher than that of s~
.l bl~~d or blood vessel walle Thus, if the current~passing throutgh each of the electr~de terminals 18 is limited to a substantially constant'valute, the regions of higher ,-~ electrical resistivity will generate more ~oulian heating {power = I2R. where I is the current through resistance R} than a region ~f lower electrical resistivity.
Therefore, the atheromatous plaque of the stenotic region will be selectively heated up while the blood and blood .t vessel wall will experience a minimal rise in :,,... ..... ,. :.: _ .:, . . ~ ~-,- . ,.; . ,. : : -.., ,. _:~ , ....
,.. , . . , . , . , , . ,.. .. . a ,. . ,: _ .. , ;~.
. . - .. , . . , , . , .". .. . ... : ., . : ... .
- ~ ~ ~ ~ ~ ~ ~ PGT/US92/112b5 ~?WO 93/ 1381 b ._ . . . 17 temperature. Thus, the catheter will selectively advance through the atheroma which has been heated and softened.
The heating selectivity of the present invention is accomplished by selecting the electrical resistance of the various components which comprise the pathway of the electrical current 62 between the common electrode (guidewire) 16 and each of the electrode terminals l8 in the electrode array located at the tip 12 of the catheter 10. By way of example, the electrical resistivity of blood at body temperature is iri the range from 148 to 176 Ohm-cm at a frequency up to 120 kHz (Geddes et al. (1967) Med. B.ioh. Eng. 5:271-293). The electrical resistivity of human cardiac and skeletal muscle (which approximates the structure of the blood vessel wall) is in the range of 100 to 456 Ohm-cm at 3 frequencies in the .range l00 to 1000 kHz. (Geddes et al.
(196?), supra).
In contrast, atheromatous mass generally resembles fat-like deposits and contains cholesterol, ~ 20 lipids, and lipidophages. Based on its primarily fat=
wy like composition, the atheromatous mass has a relatively '' ,y > high electrical resistivity as compared with blood. The ~
electrical resistivity'of fat--like substances in human has been reported in the range of 1,000 to 3,000 Ohm-cm '~ 25 at frequencies ranging from 100 to 1,000 kHz (Geddes et . al., (1967), supra): This invention utilizes the ..e, 'r ixEherent two to den fold difference in electrical y resistivities to selectively heat the atheromatous plaque , in a blood vessel.
30 Each of the electrode terminals 18 is connected to an individual source of current by means of wires 52.
A current limiting network providing the controlled or ,~;
constant curren~, as described above, is contained in a ,,, junction box Z2: The network can be composed of either 35 active or passive electronic components to perform its ~.;j intended function: By way of example, and not intending to limit the scope and spirit of this invention, a ;::.. .. :. . ~ ' : . . . ' .:', , ~ ~~;~, r r'~.~ , . . ~ ~ " . .' ~ ', .; :
. , :: , , m. . i. ..
P~'/US9211y~.'.
WO 93! 13816 ~.~~g~ ~5 ._ . .
I network composed of passive circuit elements, i.e.
resistors, is illustrated in Fig. 9. Referring to Figs. 1, 2, and 9, a constant current network 22 consists of a multiplicity of resistors 72 which are same in number as the electrode terminals 18. Each resistor is connected between a power source 32 (by the connector 26 and cable 38) and the corresponding electrode terminal 18 (by wire 52). The current will be maintained substantially constant so long as each resistor impedance is sufficiently higher than the load impedance. Suitable '~ resistor values will be in the range from 500 tt to 50,000 t~, usually being in the range from 1,000 n to 25,000 n, preferably being in the range from 3,000 n to 25,000 n.
.~'15 Still referring to Figs. 1 and 9, each ,,,~, electrodewcerminal l8'is connected to a load represented by the atheromablood, or blood vessel wall. More specifically; he load impedance 74 of the atheroma is designated by A, the load impedance 76 of blood is ;~ 20 denoted by B, and load impedance 78 of vessel wall is denoted by W respectively. As the current passes through these components; it is received by the common electrode (guidewire) 1'6 which is in turn connected to the power source 32 by connector 30 and cable 40. The level of the < 2~ current flowing in the circuits is controlled by the v~lt~ge applied between the proximal end of the resistor network 22 and the common electr~de (guidewire) 16.
The'expected power delivered to each of the loads (i.e. atheroma, blood, and vessel wall tissue) can 30 be calculated based~on exemplary values for the different :.-;
parameters as enumerated below Catheter diameter (5.French), D 1.56 mm .'~ Number of Electrodes' Terminals 18 , n 35 Site of the-'electrode 18 tip, d 0.004" dia. .
Resistance of the network resistor 72, R 10,000 Ohms ampe~snce 74 of atheroma, A 3,000 Ohms .,s '~"re~.~.
~~ 93/t3896 _ ~ ~ ~ ~ ~ ~ ~ PC'f/US92/112fi5 Tmpedance 76 of blood, B 200 Ohms Tmpedance 78 of vessel wall, W 500 Ohms Applied voltage from source 32 W: 4o Volts, RM8 Calculated power dissipation per eleetrode in:
Atheroma 28 milliwatts Blood 3 milliwatts Vessel Wall 7 milliwatts Calculating power (I2R) from the abode, the power dissipation in the atheromatous plaque is approximately ten times that in blood and four times that in blood vessel wall respectively. Taking into account the heat capacities of various components, the expected temperature in the atheromatous plaque will be considerably greater than in the blood or blood vessel wall.
The desired temperature rise of the atheromatous,pl~que to effect desired recanalization is ~f the order of 9.0° to 6~°. Based on the above calculation; a 10° to 60°C increase in the temperature of the atheromatous plaque using'the apparatus and method of the present inventa.on will result in a corresponding rise of blo~d temp~ra~ure in the range of 1°C to 6°C caused by ,4 25 the current fl~wing direetly through the blood>
Once a sufficient temperature rise is accomplished ~.n the atheromatous plaque, the mechanical strength of the said mass is substantially reduced in the localized region. surrounding the tip 12 0~ the catheter i0. This allows the catheter 10 to be advanced incrementally through the plaque by applying a ~" longitudinal g~ree on the portions of the catheter 10 external to the patient. This force is transmitted along the length of the catheter 10 to the tip region 12 to create a 'eboring pressure" sufficient to penetrate the plaque 58. T~s the blood vassal wall is not equivalently heated or softened, the catheter will preferentially 'W~ 93/13 ~~ ~~ PCT/IJS92/11~. .
._.. 20 advance through the plaque 58 following a path of its own creation.
The method of controlling the heating by the thermally assisted angioplasty catheter of this invention can also be accomplished by temperature feedback control mechanism. The temperature of the atheroma in contact with the tip 12 is sensed by temperature sensing elements such as means of thermocouple pairs (Fig. 3) 48. A
feedback control loop contained in the power source 32 allows the adjustment of the necessary voltage applied so that the required temperature rise in the atheroma is accomplished. Conversely, by continuously monitoring the temperature of the atheroma being heated, the appropriate voll:.age level is continuously maintained such that the user-selected temperature is never exceeded.
Chile the above description provides a full and '';~i complete disci~sure ~f a preferred embodiment of the 'vi' invention, various anodifications, alternative COnstruct~.onS, and equivalents may be employed. F~r exaunple, the power could be communicated to the e~.ectrodes by:~ires imbedded in the catheter Mall. Also, the temperature sensing nay be achieved using fiber optics with infraxed sensing teehniqu~, a thex-mocouple, a ther-mi~tor or-other temperature sensing means.
Alt~rnati.vely, by proper selection of metals used for :; ( 1 ) a~ultipl3,city of electrodes and leads ( e. g .
Ccnst~entan ) arid ( 2 ) guidewire ( a . g steel ) , each individual electrode can function as a thermocouple in c~njunction with the singular guidewire. The measure~ent ~0 of the direct current voltage between the guidewire and ~ the multiplicity of electrodes indicates the maximum , temt~erataare which occurs at any location on the catheter ti~p This inf~rrmation can then be used in the feedback control loop as described above to assure an improved 3~ , safe upper limit on the operating temperature during the use of the apparatus of the present invention.
,.;,,z ~~~V~ 93/13816 ~ ~ ~ ~ ~ ~ J PCT/US92/11265 z ~ ._ . .
;;~~ A more preferred embodiment of the catheter of this invention is shown in Fig. 10. In this embodiment, 'r the catheter 80 is substantially similar in construction to that of Fig. l, except that a second electrode.82 is provided for on the body 84 of the catheter shaft instead 'h I
:9 of the guidewire being the second electrode. During use .e1 of the catheter 80 in therapy, this second electrode 82 is intended to be in electrical cantact with the blood in the artery. The location of the second electrode 82 is shown to be near the proximal end of the catheter 80, but could also be disposed more distally.
Still referring to Fig. 10, guidewire 86 is ;;t~
connected to the current-limiting circuitry in power source 94 in a manner similar to the electrical 'i ~ connection of tip electrodes 90. During use of the catheter 80, the gui~lewire 86 becomes an additional electrode working in conjunction with the other tip '; electrodes. In this emlaodi.ment, no offset between the ,~ guidewire 86 and the electrode array 90 is required.
Referring now to Fig. 11; the catheter 80 is '' advanced over the guidewire 86 to the site of a total occlusion 88 -in the artery, 89. The electrode array 90 and the guidewire 86 are connected to the power source 9~
r= (Fig. 10)', and'the second ~lectr~de 82 is connected to an e' 25 opposite polarity terminal of the power source. ey applying power to the electrodes 9o and 82, current flux ~; lines !32 are formed and distributed in the occlusion 88.
v The,highest current density exists at the immediate vicinity of the tip electrode array 90, thereby producing ,~; 30 maximum heating of the atheroma in contact with the cathet~x~ tip: A return path for tlhe electrical current from the tip electrodes 90 to the second electrode 82 is defined through the blood in the blood vessel, the blood vessel wall, and/or the surrounding tissue. However, the 35 ' e~xrrent is most likely-to flow through the blood and , blood vessel wall as these components have much lower res~.stivity as c~mpared to other body tissue. The second 1~0 93f 13$16 ~ PC'T/US92111;. ~~~~ j electrode 82 is designed to be long with a large surface . area to ensure low density of current flux lines at said a second electrode.
r As the current passes through, the temperature S of the occluding material 88 is raised, thereby softening 'e, the occlusion. The catheter 80~;.along the guidewire 86 is advanced through tha.s softened:atheroma until the vessel is recanalized. A final recanalization step can then be :, performed by balloon dilatation or other currently 'i 10 available therapeutic techniques. ' vi It is understood that the plaque in the total .'',j occlusions can be dense and somewhat hard to push a catheter through even though it is heated. In order to facilitate the mechanical advancement of the catheter 15 through the praque, another embodiment of the catheter system of the present invention is illustrated in Fig.
12. The catheter IO of Fig. 1 or catheter 80 of Fig. 10 v is placed in ~ sheath catheter 96. The distal end of the sheath eatheter 96 indludes one or a plurality of ~0 expanding means 98, such as infratable balloons. The proximal endbf the sheath catheter 96 includes the '~ necessary bl~od scaling means and balloon expanding ~aorts: The shaft of the sheath datheter 96 includes the necessary lumens) for expanding said ballo~n(s) 98.
The purpose of the sheath catheter 96 is to provide an anchor for the main catheter 10 or 80 while in use. Specificarly referring to Fig. 13, the catheter system (domprising of the sheath catheter 96 and the main catheter iQ or 80) is advanced to the site of the 3~ occlusion 102 (Fig. 11). The balloons) 98 are inflated end the sheath catheter 96 is thus anchored in position in the blood'vessel proximate to the occlusion. The main catheter 10 or 80 is then advanced inside the sheath catheter 96 against the occlusion 102. The main catheter 35 tip 90 is then energized, and further advanced through : the softened atheroma. The sheath catheter 96 with inflated balloons) 98 thus serves as an anchoring means :~'j.
'7V~ 93/13816 ~ ~ ~ ~ ~ ~ ~ ~CT/US92/11265 ._ .. 23 .
assisting in the advancing of the main catheter 10 or 80 through the occlusion 102.
Although the foregoing invention has been described in detail f or purposes of clarity of .
understanding, it mill be obvious that certain modifications nay be practiced within the scope of the appended claims.
.y ..;,.,f
Claims (33)
1. A catheter system comprising:
a catheter body having a proximal end and a distal end;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of electrically isolated electrode terminals disposed over a contact surface;
a common electrode; and means for applying a high frequency voltage between the electrode array and the common electrode, wherein current flow to each electrode terminal is individually controlled in response to changes in impedance between the electrode terminal and the common electrode.
a catheter body having a proximal end and a distal end;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of electrically isolated electrode terminals disposed over a contact surface;
a common electrode; and means for applying a high frequency voltage between the electrode array and the common electrode, wherein current flow to each electrode terminal is individually controlled in response to changes in impedance between the electrode terminal and the common electrode.
2. A catheter system as in claim l, wherein the comanon electrode is disposed on the catheter body proximally of the electrode array.
3. A catheter system as in claim 1, wherein the common electrode comprises a wire extending distally from the catheter body.
4. A catheter system as in claim 1, wherein the common electrode comprises means for external attachment to a patient's body.
5. A catheter system as in claim 1, further comprising an interventional element disposed proximally of the electrode array on the catheter body.
6. A catheter system as in claim 5, wherein the interventional element comprises a dilatation balloon.
7. A catheter system as in claim 1, further comprising means for measuring temperature disposed near the distal end of the catheter body.
8. A catheter system as in claim 7, wherein the means for measuring temperature comprises a plurality of temperature sensing elements disposed within the electrode array.
9. A catheter system as in claim 7, whereby the means for applying the high frequency voltage comprises means for controlling the voltage based on the temperature sensed by the temperature sensing means.
10. A catheter system as in claim 1, further comprising means for individually limiting current flow through each electrode terminal in order to control current flow.
11. A catheter system as in claim 10, wherein the means for limiting current flow comprises a plurality of current limiting resistors located within the catheter body with at least one resistor connected to each electrode terminal.
12. A catheter system as in claim 10, wherein the means for limiting current flow comprises a plurality of current limiting resistors located within the voltage applying means, with at least one resistor connected to each electrode terminal.
13. A Catheter system as in claim 1, wherein the contact surface is a tapered surface at the distal end of the catheter body.
14. A catheter system as in claim 13, wherein the tapered surface is of nosecone configuration.
15. A catheter comprising:
a catheter body having a proximal end, a distal end, and a guidewire lumen;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of isolated electrode terminals, disposed over a contact surface;
means for connecting the isolated electrode terminals to a high frequency power supply; and a plurality of current limiting resistors, with at least one resistor connected in series between each electrode terminal and the power supply.
a catheter body having a proximal end, a distal end, and a guidewire lumen;
an electrode array disposed near the distal end of the catheter body, said array including a plurality of isolated electrode terminals, disposed over a contact surface;
means for connecting the isolated electrode terminals to a high frequency power supply; and a plurality of current limiting resistors, with at least one resistor connected in series between each electrode terminal and the power supply.
16. A catheter as in claim 15, wherein the current limiting resistors are disposed in the catheter body.
17, A catheter as in claim 15, wherein the current limiting resistors are disposed in the high frequency power supply and a plurality of conductors are disposed in the catheter body for connecting the resistors to the power supply.
18. A catheter as in claim 15, further comprising an interventional element disposed proximally of the electrode army on the catheter body.
19. A catheter as in claim 18, wherein the interventional element comprises a dilatation balloon.
20. A Catheter as in claim 18, further comprising means for measuring temperature disposed near the distal end of the catheter body.
21. A catheter as in claim 20, wherein the means for measuring temperature comprises a plurality of temperature sensing elements distributed within the electrode array.
22. A catheter as in claim 15, further comprising a movable guidewire slidable disposed within the guidewire lumen, wherein said guidewire is electrically isolated from the electrode array and includes a common electrode and means for connecting the common electrode to a high frequency power supply.
23. A catheter as in claim 15, further comprising a common electrode disposed an the catheter body proximally of the electrode array.
24. A catheter as in claim 15, wherein the current limiting resistors have a resistance in the range from 500 .OMEGA. to 50, 000 .OMEGA..
25. A catheter as in claim 15, wherein the electrode array is disposed over a tapered surface at the distal end of the catheter body.
26. A catheter as in claim 25, wherein the tapered surface is of nosecone configuration.
27. A catheter system comprising a catheter guide having a proximal end, a distal end, a lumen therethrough, and a common electrode disposed on an exterior, distal surface;
a catheter body disposed within the lumen of the catheter guide; said catheter body having a proximal end; a distal end; and an electrode array disposed over a contact surface at the distal end, said electrode array including a plurality of electrically isolated electrode terminals; and means for individually connecting the electrode terminals to a high frequency power supply along isolated high impedance conductive paths;
whereby the common electrode and the electrode array may be connected to a high frequency power supply to efficiently deliver energy to a patient surface contacted by the electrode array and electrically exposed to the common electrode.
a catheter body disposed within the lumen of the catheter guide; said catheter body having a proximal end; a distal end; and an electrode array disposed over a contact surface at the distal end, said electrode array including a plurality of electrically isolated electrode terminals; and means for individually connecting the electrode terminals to a high frequency power supply along isolated high impedance conductive paths;
whereby the common electrode and the electrode array may be connected to a high frequency power supply to efficiently deliver energy to a patient surface contacted by the electrode array and electrically exposed to the common electrode.
28. A catheter system as in claim 27, wherein the catheter guide comprises an inflatable balloon disposed near its distal end.
29. A catheter system as in claim 27, further comprising a guidewire received in a guidewire lumen in the catheter body, wherein the guidewire is electrically coupled to the electrode array.
30. A catheter system as in claim 27, wherein the means for connecting comprises a plurality of current limiting resistors connected in parallel between the individual electrode terminals and a common pole of the power supply.
31. A catheter systems as in claim 30, wherein the current limiting resistors are disposed in the distal end of the catheter body.
32. A catheter system as in claim 28, wherein the contact surface is tapered.
33. A catheter system as in claim 32, wherein the tapered surface is of nosecone configuration.
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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US81757592A | 1992-01-07 | 1992-01-07 | |
US07/817,575 | 1992-01-07 | ||
US07/958,977 | 1992-10-09 | ||
US07/958,977 US5366443A (en) | 1992-01-07 | 1992-10-09 | Method and apparatus for advancing catheters through occluded body lumens |
PCT/US1992/011265 WO1993013816A1 (en) | 1992-01-07 | 1992-12-28 | Method and apparatus for advancing catheters |
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CA2129745A1 CA2129745A1 (en) | 1993-07-08 |
CA2129745C true CA2129745C (en) | 2001-02-20 |
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Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002129745A Expired - Lifetime CA2129745C (en) | 1992-01-07 | 1992-12-28 | Method and apparatus for advancing catheters |
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US (1) | US5366443A (en) |
EP (2) | EP0882430B1 (en) |
AT (2) | ATE173903T1 (en) |
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CA (1) | CA2129745C (en) |
DE (2) | DE69227783T2 (en) |
NZ (1) | NZ246503A (en) |
WO (1) | WO1993013816A1 (en) |
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WO1993013816A1 (en) | 1993-07-22 |
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