WO1994024931A1

WO1994024931A1 - Electrode-carrying catheter and method of making same

Info

Publication number: WO1994024931A1
Application number: PCT/US1994/004746
Authority: WO
Inventors: Josef K. Winkler
Original assignee: Arrow International Investment Corp.
Priority date: 1993-05-05
Filing date: 1994-05-02
Publication date: 1994-11-10
Also published as: ZA943074B; AU6821994A

Abstract

An electrode carrying catheter (10) of high flexibility along substantially its entire length includes an elongate, flexible tube (12) defining a proximal end (14), a distal end (16), and an electrically insulative outer tubular surface (20) intermediate the ends (14) and (16). At least one electrode (30), formed of a thin, flexible layer of an electrically conductive ink, is disposed on the tube (12). Flexible conductors (29) conduct electrical signals between the proximal end (14) of the tube (12) and each of the electrodes (30a) and (30b), the conductors (29) including electrically conductive adhesive (34) disposed intermediate each of the electrodes (30a) and (30b) and the tube (12).

Description

ELECTRODE-CARRYING CATHETER AND METHOD OF MAKING SAME

BACKGROUND OF THE INVENTION The present invention relates to electrode-carrying catheters, and more particularly to an electrode-carrying catheter having a high level of flexibility along its entire length.

Electrode-carrying catheters are well known in the medical art. Typically such catheters are made by applying metal strips on the outer side and/or distal (front) surfaces

10 of a flexible tube of non-conductive plastic, each side strip acting as a side electrode and each distal strip acting as an end electrode. The presence of the metal strips limits the natural flexibility of the tubing so that the catheter is not of high flexibility throughout its entire length, and this ¹⁵ presents problems in threading the catheter into the human body over a guidewire since the diminished flexibility may limit the ability of the catheter to conform to the travel path defined by the guidewire, leading to blood vessel trauma.

Those skilled in the medical arts will appreciate that

^2ϋ such electrode-carrying catheters find diagnostic and therapeutic utility in a wide variety of different applications. For example, mapping catheters are used diagnostically to produce a wave function of the heart's electrical impulses so that a doctor can determine proper

^*. *_ functioning or fault, and location of the fault, in the heart.

Ablative catheters are used therapeutically to destroy tissue in the heart causing tachycardia, utilizing radio frequency current catheter ablation. Such catheters are also used for heart pacing purposes and for analgesia in various parts of the body. Depending upon the particular application for which the catheter is used, it may be desirable for the catheter to carry one or more side electrodes, one or more end electrodes, or a combination thereof. The use of a plurality of smaller electrodes rather than a single large electrode enables higher current densities to be obtained and frequently enables superior electrical contact with the tissue, both of these being highly desirable factors in connection with ablative catheters in particular, where larger areas of radio frequency ablation in the tissue are desirable.

Electrically conductive wires have never proven to be entirely satisfactory as the electrodes since a functional electrode requires a much larger surface area than can be provided by a flexible wire. Further, unless provisions are made to fix the wire relative to the catheter tube, it is extremely difficult to ensure that the wire is held in place so as to assure a reliable electrical contact. While a wire could be held in place by use of an electrically conductive adhesive securing the wire to the tube, it would be extremely difficult to create an electrode by applying an adhesive in a thin layer over a large surface area, as would be necessary to ensure that the electrode layer is flexible. While a biocompatible conductive paint has the advantage of being easily applied in an extremely thin layer to the tube outer surface by printing techniques, so as to ensure flexibility thereof and cover the wire, there are other problems associated with such conductive paint. While the flexible, thin layer of conductive ink painted on the tube outer surface forms a good electrical connection with the wire, the conductive paint does not form a reliable physical connection with the typical wire as necessary to ensure that the passage of the catheter through the human body along the guidewire to the proposed working site does not to some degree remove, separate or abrade away the thin layer of conductive paint.

Accordingly, it is an object of the present invention to provide in one embodiment an electrode-carrying catheter of high flexibility substantially along its entire length.

Another object is to provide such a catheter which can mount a large number of electrodes.

A further object is to provide such a catheter wherein there is a reliable electrical contact between any conductive strip or wire extending from the proximal end to an electrode, the electrode has a sufficiently large surface area for electrode functioning, and all exposed surfaces are biocompatible. It is also an object of the present invention to provide such a catheter which is easily and inexpensively manufactured. It is another object to provide processes for the manufacture of such catheters.

It is a further object to provide in another embodiment an electrode-carrying catheter which has metal band electrodes flush with the catheter wall.

It is a final object to provide an easy and economical process for the manufacture and assembly of such a catheter.

SUMMARY OF THE INVENTION It has now been found that the above and related objects of the present invention are obtained in an electrode-carrying catheter of high flexibility along substantially its entire length. The catheter comprises an elongate, flexible tube defining a proximal end, a distal end, and an electrically insulative outer tubular surface intermediate the ends. At least one electrode, formed of a thin, flexible layer of an electrically conductive ink, is disposed on the tube. Conducting means are provided for conducting electrical signals between the proximal end of the tube and each of the electrodes, the conducting means including electrically conductive adhesive disposed intermediate each of the electrodes and the tube. The catheter may include as the electrodes at least one end electrode disposed on the distal end, at least one side electrode disposed on the outer tubular surface, or combinations thereof. In a first preferred embodiment, the tube is hollow, and the conducting means includes at least one flexible, electrically conductive wire disposed in the tube hollow, each wire being in electrical contact with a respective one of the electrodes via the adhesive. Where the catheter includes as the electrodes at least one side electrode disposed on the outer tubular surface, it further comprises beneath at least some of the side electrodes a slot defined in the outer tubular surface. The outer tubular surface defines an aperture at opposite ends of the slot, one of the wires passing outwardly through one of the apertures and inwardly through the other of the apertures and making electrical contact therebetween with a respective one of the side electrodes via the adhesive. The adhesive is disposed intermediate the wire, the slot and the side electrode and blocks the pair of apertures. Where the catheter includes as the electrodes at least one end electrode disposed on a non-conductive flexible cap closing the distal end, the cap defines beneath at least some of the end electrodes a slot and an aperture at opposite ends of the slot. One of the wires passes forwardly through one of the apertures and rearwardly through the other of the apertures and makes electrical contact therebetween with a respective one of the end electrodes via the adhesive. The adhesive is disposed intermediate the wire, the slot, and the end electrode and blocks the pair of apertures. In second and third preferred embodiments, the conducting means comprises at least one flexible, uninsulated, electrically conductive wire embedded within the tube, each of the wires being in electrical contact with a respective one of the electrodes via the adhesive. In the second embodiment, the tube is extruded to define a plurality of lumens, and each of the wires is disposed in a respective one of the lumens. In the third embodiment, the tube is over-extruded over each of the wires. In a fourth preferred embodiment, the conducting means is plastic and at least in part integral with the tube. The conducting means comprises a non-conductive flexible core, a plurality of co-extruded flexible strips of electrically conductive material disposed around and insulated from one another by the non-conductive core, and a non-conductive flexible exterior peripheral surface about the strips and core. The peripheral surface defines a removed section beneath each of the electrodes to facilitate electrical contact between the strips and respective ones of the electrodes via the adhesive.

In a fifth preferred embodiment, the tube includes a flexible non-conductive core and a flexible non-conductive outer layer about the core. The conducting means includes, intermediate the core and the outer layer, a longitudinally-spaced plurality of flexible, uninsulated, electrically conductive wires helically wound around and into the core and insulated from one another by the core. The outer layer defines a removed section beneath each of said electrodes to facilitate electrical contact between the wires and respective ones of the electrodes via the adhesive. Preferably the outer layer is over-extruded over the wires and the core.

Preferably in each embodiment the adhesive is a flexible adhesive.

The present invention additionally encompasses a process for manufacturing each embodiment. The process for manufacturing the first embodiment comprises the steps of providing a flexible, elongate, insulative hollow tube having a sidewall between a proximal end and a distal end. The outer peripheral surface of the sidewall defines at least one slot, and the sidewall defines at each end of each slot an aperture therethrough. Alternatively or in addition thereto, a flexible, insulative cap of plastic is secured on the distal end, the front outer surface of the cap defining at least one slot and the cap defining at each end of each slot an aperture therethrough. In any case, for each slot, a single electrically conductive wire is threaded through both apertures associated with the slot, and the portion of the wire exposed adjacent the slot is stripped and forced into the slot. Electrically conductive adhesive is then applied to fill the slot and block the adjacent two apertures. Finally, a flexible, thin layer of electrically conductive ink is printed at least over the adhesive in the slot. The process for manufacturing the second embodiment comprises the steps of extruding a flexible, elongate tube with a plurality of axially extending lumens therein, and inserting an uninsulated, flexible, electrically conductive wire in each of the lumens. The outer surface of the tube is then removed at a plurality of spaced locations so as to expose a portion of each of the wires. The tube material removed is replaced at each location with electrically conductive adhesive, and finally a flexible, thin layer of electrically conductive ink is printed at least over the adhesive at each location.

The process for manufacturing the third embodiment comprises the steps of over-extruding a flexible, elongate tube over a plurality of spaced apart uninsulated, flexible, electrically conductive wires. The outer surface of the tube is removed at a plurality of spaced locations so as to expose a portion of each of the wires. The tube material removed is replaced at each location with an electrically conductive adhesive, and a flexible, thin layer of electrically conductive ink is printed at least over the adhesive at each location. The process for manufacturing the fourth embodiment comprises the steps of co-extruding a flexible, insulating central core of plastic and a plurality of flexible, electrically conductive strips of plastic around the core such that each of the strips is insulated from adjacent strips by the core. A flexible, thin layer of insulating plastic is extruded over the co-extrusion to form an outer layer, and a portion of each strip is exposed through the outer layer at a respective location. The exposed strip portion at each location is covered with electrically conductive adhesive, and a flexible, thin layer of electrically conductive ink is printed at least over the adhesive at each location.

The process for manufacturing the fifth embodiment comprises the steps of extruding a flexible, non-conductive, elongate core with a soft outer surface, and then helically winding a spaced apart plurality of flexible, uninsulated, electrically conductive wires about and at least partially into the core outer surface. A flexible, non-conducting outer layer is over-extruded over the wires and the core, and the outer layer is removed at a plurality of spaced locations so as to expose a portion of each of the wires. The outer layer material removed at each location is then replaced with electrically conductive adhesive, and a flexible, thin layer of electrically conductive ink is printed over the adhesive at each location. Preferably the soft outer surface of the core is formed by over-extruding a soft layer over the core, the soft layer being relatively softer than the core.

Also encompassed by the present invention is an electrode-carrying catheter having an outer tubular surface and a ring electrode flush therewith. The catheter comprises an elongate, flexible tube defining a proximal end, a distal end, and an electrically insulative outer tubular surface intermediate the ends. At least one electrically conductive ring electrode is crimped on the outer tubular surface so as to be flush therewith. Conducting means are provided for conducting electrical signals between the proximal end and each of the electrodes, the conducting means including electrically conductive adhesive disposed intermediate each of the electrodes and the tube.

Further encompassed by the present invention is a process for manufacturing an electrode-carrying catheter having a tubular outer surface and a ring electrode flush therewith. The process comprises the steps of providing a flexible, electrically insulative, elongate tube having disposed therein a plurality of spaced apart, flexible, electrically conductive conductors, and electrically conductive adhesive replacing the outer surface of the tube at a plurality of spaced locations so as to be in electrical contact with a portion of each of the conductors. A respective electrically conductive ring electrode is disposed over each location and then the electrode is crimped to the tube at a plurality of points such that the ring electrode is collapsed into the tube and flush therewith.

BRIEF DESCRIPTION OF THE DRAWING

The above and related objects, features, and advantages of the present invention will be more fully understood by reference to the following detailed description of the presently preferred, albeit illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawing wherein: FIG. IA is a fragmentary sectional view of a catheter according to a first embodiment of the present invention;

FIG. IB is a fragmentary top plan view thereof, to a slightly enlarged scale; FIG. 1C is a fragmentary sectional view taken along the line 1C-1C of FIG. IA, to a slightly enlarged scale;

FIG. 2A is a fragmentary side elevational view of a second embodiment of the present invention;

FIG. 2B is a sectional view thereof taken along the line 2B-2B of FIG. 2A;

FIG. 3A is a fragmentary side elevational view of a third embodiment of the present invention;

FIG. 3B is a sectional view thereof taken along the line 3B-3B of FIG. 3A; FIG. 4A is a fragmentary side elevational view of a fourth embodiment of the present invention;

FIG. 4B is a sectional view thereof taken along the line 4B-4B of FIG. 4A;

FIG. 5A is a fragmentary side elevational view of a fifth embodiment of the present invention;

FIG. 5B is a sectional view thereof taken along the line 5B-5B of FIG. 5A;

FIG. 6A is a fragmentary side elevational view of a sixth embodiment of the present invention; FIG. 6B is a sectional view thereof taken along the line 6B-6B of FIG. 6A; and FIG. 6C is a fragmentary sectional view thereof taken along the line 6C-6C of FIG. 6B, to a greatly enlarged scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. IA, therein illustrated is an electrode-carrying catheter according to a first embodiment of the present invention, generally designated by the reference numeral 10. While the configuration and dimensions of the catheter will vary with the intended application for the catheter, it is generally of the same overall width and length of the known catheters for the same application. However, unlike the known catheters, the catheter 10 of the present invention is characterized by a high degree of flexibility along its entire length, even where the electrodes are disposed.

The catheter 10 is formed of an elongate, flexible tube generally designated 12. The tube 12 defines a proximal end 14, a distal end 16, and a sidewall 19 connecting the ends 14, 16 and having an electrically insulative outer surface 20. The tube 12 is hollow and defines a hollow 22 extending substantially along its entire length. The tube may be formed of polyurethane or any of the other flexible, electrically insulative materials commonly used in catheter construction such as polyvinyl chlorides, polyesters and various copolymers.

Referring now to FIGS. IB and 1C as well, at least one electrode 30 is disposed on the tube 12. The electrode may be a side electrode 30a disposed on the outer surface 20 (one side electrode being illustrated in FIG. IA) , an end electrode 30b disposed on the distal or front end and more particularly on a cap 32 disposed on the distal end (one end electrode being illustrated in FIG. IA) , or a combination thereof. Particular electrodes 30 may extend axially or transversely (i.e., circumferentially) relative to the tube axis as preferred for a given application. The side electrode 30a may extend fully around the circumference of the tube 12 (as illustrated) or merely over an arc thereof, and the end electrode 306 may extend over a full diameter of the cap 32 or only over a portion thereof (as illustrated).

A preferred biocompatible electrically conductive ink for use as the electrode is available under the trade name 102-05F from Creative Materials Incorporated of Tyngsboro, Massachusetts 01879. This ink is about 85% by weight silver (cured), has a high resistance to abrasion and scratching, exhibits high solvent resistance and hydrolytic stability, and may be thinned as necessary with conventional solvents (such as butyl cellosolve acetate) as necessary to provide a desirable viscosity for printing. In order to enable the ink to be applied as a very thin layer exhibiting a desired level of flexibility, it is preferably applied at a viscosity of about 500 cps. After application, the ink may be cured for one hour at HCC, although shorter times and lower temperatures may also be used. Alternatively, other inks exhibiting like 'characteristics may be employed as the electrodes.

Conducting means generally designated 29 are provided for conducting electrical signals between the proximal end 14 and each of the electrodes 30a, 30a, 30b. The conducting means 29 are illustrated in FIG. IA only for the end electrode 30b and one of the two side electrodes 30a (namely, the upper one) . The conducting means 29 includes electrically conductive adhesive 34 securing together each of the electrodes 30a, 30b and the tube 12 (or, more precisely in the case of the end electrode 30b, the cap 32). However, as clearly seen in FIGS. IB and 1C, the adhesive 34 is completely covered by the electrode 30 in each instance.

A preferred electrically conductive adhesive 34 is a high temperature (250^βC), silver conductive epoxy adhesive available under the trade name No. 101-42 from Creative Materials Incorporated. It provides high electrical conductivity, superior durability and a versatile cure schedule. Most importantly, the mixed adhesive has the viscosity of a smooth paste at 75^βF. After the adhesive is applied to the tube, it is cured, for example, with a hot press ground to the radius of the catheter at 250-330^βF for thirty seconds. The hot press not only cures the adhesive, but also forms a smooth surface finish suitable for receipt thereon of the electrode. Preferably the adhesive 34 is originally applied slightly in excess of the amount required so that it protrudes slightly outwardly from the outer surface 20 of the tube 12. Then subsequently, as part of the curing process, the hot press causes the outer surface of the adhesive to conform to the outer curvature of the tube and assume the smooth finish well suited to receive the thin layer of ink forming the electrode 30. Alternatively, a variety of other adhesives exhibiting like characteristics (e.g., Polymer Adhesive EP21TDCS from Master Bond Inc. of Hackensack, New Jersey 07601) may be employed, with the same or different curing techniques.

The electrodes 30 are applied to the outer surface of the tube 12 and the adhesive 34 at desired locations by means of printing, painting, dipping or the like. Printing, and especially pad printing, is especially preferred as an extremely thin layer of ink is applied thereby, without any deleterious affect on the flexibility of the catheter tube 12.

Referring now to FIGS. 1A-1C, therein illustrated is the first embodiment of the present invention wherein the tube 12 is hollow and the conducting means 29 includes at least one insulated electrically conductive wire 33 (e.g., 34 gauge copper wire) disposed in the tube hollow 22. Each of the wires 33 is in electrical contact with a respective one of the electrodes 30a or 30b by means of the adhesive 34.

Where the catheter 10 includes at least one side electrode 30a disposed on the outer tubular surface 20, beneath at least one of the side electrodes 30a, there is a slot 40a (best seen in FIG. 1C) and an aperture 42a (best seen in FIG. IA) at opposite ends of the slot 40a and extending through the sidewall 19 into the hollow 22. One of the wires 33 (and in particular, as illustrated in FIG. IA, wire 33a) passes from hollow 22 outwardly through one of the apertures 42a, travels along the slot 40a, and then passes inwardly through the other of the apertures 42a. Intermediate the two apertures 42a, the wire 33a makes electrical contact with the side electrode 30a by means of the adhesive 34. It will be appreciated that the slot 40a and apertures 42a are occupied by the wire 33a, the adhesive 34, or both. The adhesive 34 is disposed intermediate the wire 33a, the slot 40a, and the side electrode 30a and furthermore blocks (with the wire 33a) the apertures 42 through which the wire 33a has been threaded.

Where the catheter 10 includes at least one end electrode 30b as one of the electrodes 30 thereof, a non-conductive flexible cap 32 is disposed across the distal end 16 of the tube 12 in order to close the same. The cap 32 may be formed of the same material as the tube 12 or a different material, e.g., a flexible non-conductive epoxy. The cap 32 defines, beneath at least one of end electrodes 30b in the outer front surface of the cap 32, a slot 40b and an aperture 42b at opposite ends of the slot 40b extending through the cap 32 into the hollow 22. One of the wires 33 (and in particular, as illustrated in FIG. IA, wire 33b) passes forwardly through one of the apertures 42b, travels along the slot 40b, and then passes rearwardly through the other of the apertures 42b. Between the apertures 42b, the wire 33b makes electrical contact with the end electrode 30b by means of the adhesive 34. The adhesive 34 is disposed intermediate the wire 33b, the slot 40b and the end electrode 30b and furthermore blocks (with the wire 33b) the apertures 42b through which the wire 33b has been threaded.

While the slot 40a is illustrated as extending longitudinally and the slot 40b is illustrated as extending transversely, the orientation of the various slots will depend upon the particular application intended for the catheter. Thus the slot 40a may alternatively extend circumferentially or transversely, and the slot 40b may alternatively extend at least to some degree longitudinally.

As the first embodiment defines no structure ensuring electrical separation between the various wires 33, the wires 33 are necessarily insulated to prevent shorting if they come into contact. Accordingly, after a single insulated electrically conductive wire is threaded through both of the apertures 42 associated with a given slot 40, the portion of the wire 33 adjacent the slot 40 is stripped of its insulative cover in order to expose the same for electrical contact. The stripped portion is then forced into the slot 40 (e.g., by pulling on the ends of the wire 33), after which electrically conductive adhesive 34 is applied to fill the portion of the slot not occupied by the wire 33 and to block the adjacent two apertures 42 not already occupied by the wire 33. Only after this is the flexible, thin layer of electrically conductive ink (which forms the electrode 30) printed over the adhesive 34 in the slot 40 and the adjacent area of the tube 12, as desired.

Referring now to FIGS. 2A and 2B, therein illustrated is a second embodiment 100 of the present invention wherein the tube 112 has a proximal end 114, a distal end 116 and a sidewall 119 therebetween defining an outer tubular surface 120. At least one side electrode 130 is disposed along the length of the tubular outer surface 120 (two electrodes 130 being illustrated in FIG. 2A) . A unique feature of this embodiment 100 is that the tube 112 is extruded to define a plurality of lumens 131 or axial passageways extending between the proximal and distal ends 114, 116. Only four such lumens 131 are illustrated in the sidewall 119 of the hollow tube 112 of FIG. 2, but a lesser or greater number of lumens 131 may be provided. Indeed the tube 112 may be solid and the entire cross sectional area of the tube 112 may be formed with the lumens 131 therein. After the tube 112 (with its lumens 131) has been extruded, an uninsulated, flexible, electrically conductive wire 133 is inserted into each of the lumens 131 as part of the conducting means 129. Then the outer surface 120 of the tube 112 is removed at a plurality of spaced locations so as to expose a portion of each of the wires 133 at its respective location. The tube material can be removed by various techniques such as skiving, drilling, grinding, or chemical etching. The removed tube material at each location is then replaced with ^•electrically conductive adhesive 134 as part of the conducting means 129. Finally, a flexible, thin layer of electrically conductive ink 130 is printed over the adhesive 134 at each location and, as desired, adjacent portion of the tubular outer surface 119. The adhesive 134 at each location is disposed intermediate the wire 133, the tube 112 and the ink forming the electrode 130.

As each wire 133 is enclosed by its own lumen 131, the wire 133 requires no insulation. The absence of any insulation on the wire 133 facilitates the effecting of an electrical connection between the wire 133 and the electrode 130, as it is only necessary to remove the tube material (and not any wire insulation) . While the tube 112 has been illustrated as hollow, a solid tube 112 (except for the lumens 131) may also be employed, especially where the number of electrodes 130 to be disposed on the tube outer surface 120 mandates the presence of a large number of wires 133 within the tube 112.

As will be appreciated by those skilled in the art, the second embodiment 100 avoids both the initial added expense of insulated wires and the subsequent added expense of manually removing insulation therefrom at various locations in order to permit electrical connections thereto. Further, it is easier to thread the various wires 133 into the respective lumens 131 than to have to thread each wire through an aperture, along a slot, and back through another aperture, as in the first embodiment 10. Finally, as each wire 133 is disposed within its own lumen 131, greater protection and support is afforded to each individual wire 133.

Referring now to FIGS. 3A and 3B, therein illustrated is a third embodiment of the present invention, generally designated by the reference numeral 200. The third embodiment is substantially similar to the second embodiment, and hence like elements will be designated by like reference numerals. The major difference is that, whereas in the second embodiment 100 the tube 112' is extruded with lumens 131 through which the wires 133 must then be inserted, in the third embodiment 200 the tube 112' is over-extruded (sometimes called "co-extruded") over each of the wires 133. During the over-extrusion process, the wires 133 are drawn along from idler supply rolls by the extruded plastic.

Then the outer surface 120 of the tube 112' is removed at a plurality of spaced locations so as to expose a portion of each of the wires 133 at its respective location. The tube material can be removed at the desired locations by various techniques such as skiving, drilling or grinding, but chemical etching is preferred as it lessens the chance of damaging fragile copper wires 133 and the quantity of tubing material removed is consistent. For chemical etching, the tube is marked to leave exposed only the locations to be etched away. For example, appropriate amounts of urethane tubing material may be removed in about thirty minutes with tetrahydrofurane solvent.

The removed tube material at each location is then replaced with electrically conductive adhesive 134 as part of the conducting means 129. Finally, a flexible, thin layer of electrically conductive ink 130 is printed over the adhesive 134 at each location and, as desired, adjacent portion of the tubular outer surface 119. The adhesive 134 at each location is disposed intermediate the wire 133, the tube 112' and the ink forming the electrode 130.

The third embodiment 200 is greatly more economical to manufacture than either the first or second embodiments 10,100. Whereas both the first and second embodiments 10,100 require a substantial amount of manual handling after the tube has been formed in order to thread the wires 33 through the apertures 42 and the wires 133 through the lumens 131, respectively, this tedious precision work is not necessary in the third embodiment 200 where the tube 112" is over-extruded over the wires 133.

Referring now to FIGS. 4A and 4B, therein illustrated is a fourth embodiment of the present invention, generally designated by the reference numeral 300. The fourth embodiment 300 is a wireless version of the second embodiment 100 and the third embodiment 200. The tube 112" is solid and defines a proximal end 114, a distal end 116, and a sidewall 119 defining an outer surface 120. The tube 112" is formed of plastic and is composed initially of a co-extrusion of a flexible, insulating central core 302 (illustrated in FIG. 4B in the configuration of a cross) and a plurality of flexible, electrically conductive strips 304 (which take the place of the wires 133 of the second and third embodiments). The conductive strips 304 are disposed around the core 302 such that each of the strips 304 is insulated from adjacent strips 304 by the core 302 (as illustrated in FIG. 4B, by the arms of the core cross). Finally, a flexible, thin insulating layer 306 is extruded over the co-extrusion to form the outer layer 306 of the tube 112" defining outer surface 119. Thus the conductive strips are isolated from one other and the environment by means of the core 302 and the outer layer 306.

It will be appreciated that, while only four strips 304 have been illustrated in FIG. 4, the number of strips 304 can be varied as desired for particular applications, with the core 302, of course, being appropriately varied in configuration to provide insulative isolation for each strip 304. The core 302 and the outer layer 306 are preferably non-conductive polyurethane, while the strips 304 are preferably a conductive polyurethane. As in the second and third embodiments 100, 200, the outer surface of the tube 112" (here the outer layer 306) is then removed at a plurality of spaced locations so as to expose a portion of each strip 304 (instead of a portion of each embedded wire 133) at a respective location. The exposed strip portion is then covered at each location with electrically conductive adhesive 134, and finally a flexible, thin layer of electrically conductive ink 130 is printed over the adhesive 134 at each location and, as desired, adjacent portions of the outer layer 306 of tube 112".

Both the third and fourth embodiments 200, 300 offer substantial savings in the costs of manufacturing as there is no need to thread wires through apertures or lumens. Depending on the availability and cost of the conductive plastics, however, the fourth embodiment 300 may be especially cost effective, even relative to the third embodiment 200, since it does not require the use of wires at all.

Referring now to FIGS. 5A and 5B, therein illustrated is a fifth embodiment of the present invention, generally designated by the reference numeral 400. The fifth embodiment 400 has a tube 112"' which defines a proximal end 114, a distal end 116, and a sidewall 119 defining an outer surface 120. The tube 112"' is composed initially of an extrusion of a flexible, insulating central core 402 (illustrated in FIG. 5B in the configuration of a cylinder) having a flexible, insulating soft layer 404 over the outer surface of the core 402. The soft outer surface 404 of the core 402 may be formed by . over-extruding a soft layer 404 over the core 402, the soft layer being relatively softer than the core. As part of the conducting means, flexible, uninsulated, electrically 5 conductive wires 133 (three wires 133a, 133b, 133c being shown) are helically wound around and into the soft layer 404 of the core 302. The wires 133 are longitudinally spaced apart such that each of the wires 133 is insulated from the two adjacent wires 133 by portions of the soft layer 404 of the core (as 0 illustrated in FIG. 5B) . In order to preclude accidental movement of the spaced apart plurality of wires 133 prior to over-extrusion of an outer layer thereover, the wires 133 are helically wound around the soft layer 404 about core 402 so that they at least partially embed themselves within the soft 5 layer 404. Finally, a flexible, thin insulating layer 406 is over-extruded over the extrusion 402, 404 and any exposed portion of wires 133 to form the outer layer 406 of the tube 112"' defining outer surface 119. Thus the conductive wires 133 are isolated from one other and the environment by means of o the core 402, the soft layer 404, and the outer layer 406.

It will be appreciated that, while only three wires 133 have been illustrated in FIG. 5, the number of wires 133 can be varied as desired for particular applications. It will also be appreciated that the core 402 may be hollow or define a 5 central axial lumen therein, thereby to enable passage of a conductive wire 133 from the proximal end to the distal end where it may be in electrical communication with an end electrode 130. If the soft layer of 404 is of sufficient thickness to receive and electrically isolate the wires 133 totally embedded therein and is furthermore subsequently treatable (e.g., curable or modifiable) to provide an abrasion-resistant surface, the outer layer 406 may be dispensed with entirely and the soft layer thus treated after the wire embedding step.

As in the second, third and fourth embodiments 100, 200, 300, the outer surface of the tube 112"' (here the exterior layer 404) is then removed, here preferably by grinding, at a plurality of spaced locations so as to expose a portion of each embedded wire 133 at a respective location. The exposed wire portion is then covered at each location with electrically conductive adhesive 134, and finally a flexible, thin layer of electrically conductive ink 130 is printed over the adhesive 134 at each location.

In order to provide flexible end electrodes in the second, third, fourth and fifth embodiments 100, 200, 300, 400, a flexible, electrically insulative cap (not shown) is preferably disposed over the distal end 116 of the tube. The cap may be of appreciable thickness, apertured therethrough under the end electrode, and provided with conductive adhesive joining the end electrode through the aperture to a wire 133 or conductive strip 304. For example, the exterior of the cap may be similar in shape to the cap 32 of the first embodiment 10. Alternatively, a flat, unapertured layer 132 of insulative plastic (such as the plastic from which the tube 120 itself is formed or an epoxy) is used to seal the lumens 131 at the distal end in the second embodiment 100 or electrically isolate the distal ends of the wires 133 of the third and fifth embodiments 200, 400 or the strips 304 of the fourth embodiment 300.

In each embodiment it is essential that the adhesive 34,134 be disposed intermediate the electrode and the wire 33,133 or conductive strip 304 so that, when the ink is applied to form the electrode, it cannot enter the aperture 31, the lumen 131, or the slight interface gap which is frequently found between the different materials of an over-extrusion or co-extrusion (e.g., between a wire 133 and the plastic 133 over-extruded over the wire). Otherwise, the ink may be drawn by capillary action from the outer surface of the tube into the aperture, lumen, or interface gap, thereby distorting the thin layer of ink printed on the outer surface as the electrode. Because the relatively thin, fluid-like ink forming the electrode is of substantially lower viscosity than the relatively thick, pasty adhesive, it is more likely to be drawn into any exposed capillary volume. Thus, preferably the ink has a viscosity less than about 2,000 cps (preferably 100-2,000 cps), while the adhesive has a viscosity greater than about 2,000 cps (preferably 2,000-100,000 cps). As a reference point, glycerin and honey have a viscosity of about 2,000 cps. For pad printing an ink viscosity of 100-200 cps is preferred, and the ink may be thinned as necessary to provide a suitable viscosity.

It will be appreciated that, in each embodiment, the adhesive 34, 134 is cured before application of the electrode 30, 130 thereover. Thus the adhesive does not actively physically secure together the electrode and another element - e.g., the wire 33,133, strip 304 or tube 12, 112. In all embodiments, however, the adhesive provides a passive electrical connection between an electrode and another element - e.g., the wire 33, 131 or strip 304.

It will also be appreciated that the outer surface 20,120 of the sidewall 19,119 (including outer layer 306, 406) may have the portions at the particular locations removed therefrom simultaneously. The locations at which the tubing material is to be removed are predetermined by the desired location of the electrodes. In each embodiment except the first, before removal of the tubing material the wires 133 or conductive strips 304 are already in place and in fixed spatial disposition relative to one another. Accordingly, once the location of one wire or strip is determined (perhaps by inspection of the distal end where they are initially visible), then the location of all of the remaining wires is known. Thus, grinding elements of a grinding machine, for example, can be appropriately positioned relative to the known wire or strip, and the tubing material simultaneously removed at each location. A catheter according to the present invention made using, as the electrically conductive adhesive 34,134, a non-flexible adhesive still exhibits a high level of flexibility along substantially its entire length as the adhesive forms only a small deposit at each electrode location. However, when the catheter is bent in a manner which exceeds the level of high flexibility, the non-flexible adhesive tends to crack rather than simply separate from the tube or electrode. Cracking of the adhesive typically does not interfere with its function of adhering itself to one or more surfaces, but it does potentially interfere with and render unreliable its function as an electrical connection between an electrode and another element. Accordingly, care must be taken with the catheter made using a non-flexible adhesive such as those mentioned above (i.e., Creative Materials No. 101-42 and Master Bond Polymer Adhesive EP21TDCS) to ensure that the flexing of the catheter is maintained within predetermined limits. Accordingly, in a variant of the present invention applicable to each of its embodiments, the conductive adhesive 34,134 is preferably also flexible. The flexible adhesive must, of course, be compatible with the ink used for the electrodes 30,130, the material of tubing 12,112 and the electrically conductive wires 33,133 or strip 304. Preferred flexible, electrically conductive adhesives include those available under the trade name 107-25 from Creative Materials Incorporated (an adhesive/sealant material having a carbon filler and a paste consistency when cured) and under the trade name CS408-2 from Emerson & Cummings of Woburn, Massachusetts 01888 (a one-component silver-filled thermoplastic epoxy base adhesive having an uncured viscosity at 25°C of 24,000 cps). 5 The very thin layer of ink forming the electrode

30,130 according to the present invention extends only very slightly above (i.e., radially outwardly of) the outer surface of the tube. Thus, the electrode is more nearly flush with the outer surface of the tube than the conventional electrode made _Q of a metal band or ring which has been slipped over the tube outer surface, slid along its length to an appropriate location, and then secured thereto by adhesive. Other conventional processes for forming electrodes may be employed to provide an electrode which is flush with the outer surface 5 of the catheter, but the processes required are arduous, time- consuming and/or require further processing. For example, in one process, metal bands and sleeves therebetween are slipped over the tube outer surface with the sleeves maintaining the appropriate spacing between adjacent electrodes; this requires _Q the use of additional pieces (namely, the sleeves) and an arduous assembly process. Another process requires the tubing to be stretched to lower the outer diameter thereof, metal bands placed over the stretched tubing and disposed in appropriate spatial relationship, and the tubing then heated 5 and released. The metal bands sink into the heat-softened tubing outer surface as the tubing resumes its original configuration (except where the metal bands are embedded therein) . This technique requires additional stretching, heating and cooling steps.

Accordingly, in a variant of the present invention useful where the high level of flexibility enabled by the use of a flexible electrode is not essential and the emphasis is on the smoothness of the catheter outer surface (that is, the electrodes being flushed with the outer tubular surface) , the present invention provides an electrode-carrying catheter which is made by a crimping process which offers a significant advantage over conventional processes for producing a catheter with a flush outer surface by sharply reducing labor requirements and simplifying assembly. The crimped electrode technique may be applied to any of the aforementioned embodiments of the present invention as the crimping process is performed only after the electrically conductive adhesive (whether flexible or not) has replaced the removed tube material.

Accordingly, referring now to FIGS. 6A, 6B and 6C, purely for expository purposes the crimped electrode variation is illustrated in connection with a catheter 500 having a proximal end 114, a distal end 116, and a sidewall 119 with an outer surface 120 extending between the two ends 114, 116. Flexible, uninsulated, electrically conductive wires 133 extend longitudinally and are embedded within the tubing 112. A portion of the tubing material is removed and replaced by conductive adhesive 134, the adhesive 134 then being cured. A metal band or ring electrode 530, preferably formed of a biocompatible metal such a platinum, is slid along the length of the tubing 112 to an appropriate location. The inner diameter of the electrode 530 is slightly larger than the outer diameter of the tubing 112 to enable the electrode 530 to slide over the catheter and over the top of the adhesive 134 at the location. A crimping machine (not shown) is then employed to crimp the outer diameter of the electrode 530 down to the outer diameter of the tubing 112. To this end, the crimping machine is provided with a circumferentially spaced plurality of crimping points (for example, 12 points equidistantly spaced about a circumference) which simultaneously crimp and collapse the band 530 so that the crimped or collapsed band 530 retains its original circular configuration but with a reduced diameter. It will be appreciated that because the crimping operation squeezes the band 530 flush with the tubing outer surface 120, an extremely smooth catheter/electrode interface is obtained. Typically no subsequent smoothing of the exterior surface of the tubing at the catheter/electrode interface is required. The presence of the electrode 530 does not increase the diameter of the tubing 112. As used herein, the terms "insulating", "insulative", "non-conducting" and "non-conductive" are synonyms.

To summarize, the present invention provides an electrode-carrying catheter of high flexibility along substantially its entire length, the catheter being capable of mounting a large number of electrodes. There is reliable electrical contact between any conductive strip or wire extending from the proximal end to an electrode, with the electrode having a sufficiently large surface area for electrode functioning, and all exposed surfaces being biocompatible. The catheter is easily and inexpensively manufactured. In another embodiment the present invention provides a catheter with a flush ring electrode and a simple and economical method of manufacture thereof. Now that the preferred embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be construed broadly and limited only by the appended claims, and not by the foregoing specification.

Claims

WE CLAIM :

1. An electrode-carrying catheter of high flexibility along substantially its entire length, comprising:

(A) an elongate, flexible tube defining a proximal end, a distal end, and an electrically insulative outer tubular surface intermediate said ends;

(B) at least one electrode formed of a thin, flexible layer of an electrically conductive ink and disposed on said tube; and (C) conducting means for conducting electrical signals between said proximal end and each of said electrodes, said conducting means including electrically conductive adhesive disposed intermediate each of said electrodes and said tube.

2. The catheter of Claim 1 including as said electrodes at least one end electrode disposed on said distal end.

3. The catheter of Claim 1 including as said electrodes at least one side electrode disposed on said outer tubular surface.

4. The catheter of Claim 1, wherein said tube is hollow, and said conducting means includes at least one flexible, insulated, electrically conductive wire disposed in said tube hollow, each said wire being in electrical contact with a respective one of said electrodes via said adhesive.

5. The catheter of Claim 4, including as said electrodes at least one side electrode disposed on said outer tubular surface, and further comprising beneath at least one of said side electrodes a slot defined in said outer tubular surface, said outer tubular surface defining an aperture at opposite ends of said slot, one of said wires passing outwardly through one of said apertures and inwardly through the other of said apertures and making electrical contact therebetween with a respective one of said side electrodes via said adhesive.

6. The catheter of Claim 5, wherein said adhesive is disposed intermediate said wire,_, said slot and said side electrode, and blocks said pair of apertures.

7. The catheter of Claim 4, further comprising a non-conductive flexible cap closing said distal end and including as said electrodes at least one end electrode disposed on said cap, said cap defining beneath at least one of said end electrodes a slot and an aperture at opposite ends of said slot, one of said wires passing forwardly through one of said apertures and rearwardly through the other of said apertures and making electrical contact therebetween with a respective one of said end electrodes via said adhesive.

8. The catheter of Claim 7, wherein said adhesive is disposed intermediate said wire, said slot, and said end electrode, and blocks said pair of apertures.

9. The catheter of Claim 1, wherein said conducting means is formed of plastic and is at least in part integral with said tube, said conducting means comprising a non-conductive flexible core, a plurality of flexible strips of electrically conductive material co-extruded with, disposed around, and insulated from one another by said core, and a non-conductive flexible exterior peripheral surface about said strips and core, said peripheral surface defining a removed section beneath each of said electrodes to facilitate electrical contact between said strips and respective ones of said electrodes via said adhesive.

10. The catheter of Claim 1, wherein said conducting means comprises at least one flexible, uninsulated, electrically conductive wire embedded within said tube, each of said wires being in electrical contact with a respective one of said electrodes via said adhesive.

11. The catheter of Claim 10, wherein said tube is over-extruded over each of said wires.

12. The catheter of Claim 10, wherein said tube is extruded to define a plurality of lumens, and each of said wires is disposed in a respective one of said lumens.

13. The catheter of Claim 1, wherein said tube includes a flexible non-conductive core and a flexible non-conductive outer layer about said core, said conducting means including, intermediate said core and said outer layer, a longitudinally-spaced plurality of flexible, uninsulated, electrically conductive wires helically wound around and into said core and insulated from one another by said core (and from the environment by said outer layer), said outer layer defining a removed section beneath each of said electrodes to facilitate electrical contact between said wires and respective ones of said electrodes via said adhesive.

14. The catheter of Claim 13, wherein said outer layer is over-extruded over said wires and said core.

15. The catheter of Claim 1 wherein said adhesive is a flexible adhesive.

16. A process for manufacturing an electrode-carrying catheter of high" flexibility substantially along its entire length, comprising the steps of:

(A) over-extruding a flexible, elongate tube over a plurality of spaced apart uninsulated, flexible, electrically conductive wires;

(B) removing the outer surface of the tube at a plurality of spaced locations so as to expose a portion of each of the wires; (C) replacing the tube material removed at each location with electrically conductive adhesive; and

(D) printing a flexible, thin layer of electrically conductive ink at least over the adhesive at each location.

17. A process for manufacturing an electrode-carrying catheter of high flexibility substantially along its entire length, comprising the steps of:

(A) extruding a flexible, elongate tube with a plurality of axially extending lumens therein; (B) inserting an uninsulated, flexible, electrically conductive wire in each of the lumens;

(C) removing the outer surface of the tube at a plurality of spaced locations so as to expose a portion of each of the wires; (D) replacing the tube material removed at each location with electrically conductive adhesive; and

(E) printing a flexible, thin layer of electrically conductive ink at least over the adhesive at each location.

18. A process for manufacturing an electrode-carrying catheter of high flexibility substantially along its entire length, comprising the steps of:

(A) co-extruding a flexible, insulating central core of plastic and a plurality of flexible, electrically conductive strips of plastic around the core such that each of the strips is insulated from adjacent strips by the core;

(B) extruding a flexible, thin, insulating layer of plastic over the co-extrusion to form an outer layer; (C) exposing a portion of each strip through the outer layer at a respective location;

(D) covering the exposed strip portion at each location with electrically conductive adhesive; and

19. A process for manufacturing an electrode-carrying catheter of high flexibility substantially along its entire length, comprising the steps of: (A) providing a flexible, elongate, insulative hollow tube having a sidewall between a proximal end and a distal end, the outer peripheral surface of the sidewall defining at least one slot and the sidewall defining at each end of each slot an aperture therethrough;

(B) for each slot, threading a single electrically conductive wire through both apertures associated with the slot;

(C) for each slot, stripping the portion of the wire exposed adjacent the slot and forcing the stripped portion into the slot;

(D) for each slot, filling the slot and blocking the adjacent two apertures with electrically conductive adhesive; and (E) for each slot, printing a flexible, thin layer of electrically conductive ink at least over the adhesive in the slot.

20. A process for manufacturing an electrode-carrying catheter of high flexibility substantially along its entire length, comprising the steps of:

(A) providing a flexible, elongate, insulative, hollow tube having a sidewall between a proximal end and a distal end;

(B) securing a flexible, insulative cap of plastic on the distal end, the front outer surface of the cap defining at least one slot and the cap defining at each end of each slot an aperture therethrough;

(C) for each slot, threading a single electrically conductive wire through both apertures associated with the slot;

(D) for each slot, stripping the portion of the wire exposed adjacent the slot and forcing the stripped portion into the slot;

(E) for each slot, filling the slot and blocking the adjacent two apertures with electrically conductive adhesive; and

(F) for each slot, printing a flexible, thin layer of electrically conductive ink at least over the adhesive in the slot.

21. A process for manufacturing an electrode-carrying catheter of high flexibility along substantially its entire length, comprising the steps of:

(A) extruding a flexible, non-conductive, elongate core with a soft outer surface; (B) helically winding a spaced apart plurality of flexible, uninsulated, electrically conductive wires about and at least partially into the core outer surface;

(C) over-extruding a flexible, non-conducting outer layer over the wires and the core; (D) removing the outer layer at a plurality of spaced locations so as to expose a portion of each of the wires;

(E) replacing the outer layer material removed at each location with electrically conductive adhesive; and

5 (F) printing a flexible, thin layer of electrically conductive ink over the adhesive at each location.

22. The process of Claim 21 wherein the soft outer surface of the core is formed by over-extruding a soft layer over the core, the soft layer being relatively softer than the 0 core.

23. An electrode-carrying catheter having an outer tubular surface and a ring electrode flush therewith, comprising:

(A) an elongate, flexible tube defining a 5 proximal end, a distal end, and an electrically insulative outer tubular surface intermediate said ends;

(B) at least one electrically conductive ring electrode crimped on and flush with said outer tubular surface; and o (C) conducting means for conducting electrical signals between said proximal end and each of said electrodes, said conducting means including electrically conductive adhesive disposed intermediate each of said electrodes and said tube.

24. A process for manufacturing an electrode-carrying catheter having a^' tubular outer surface and a ring electrode flush therewith, comprising the steps of:

(A) providing a flexible, electrically insulative, elongate tube having disposed therein a plurality of spaced apart, flexible, electrically conductive conductors and electrically conductive adhesive replacing the outer surface of the tube at a plurality of spaced locations so as to be in electrical contact with a portion of each of the conductors; and

(B) disposing a respective electrically conductive ring electrode over each location and crimping the electrode to the tube at a plurality of points such that the ring electrode is collapsed into the tube and flush therewith.