Patent Description:
Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in various tissue regions in or near the heart, for example, the atria and/or and adjacent structures such as areas of the pulmonary veins, and left and right atrial appendages. Regardless of the sources, unwanted signals are conducted abnormally through heart tissue where they can initiate and/or maintain arrhythmia.

Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathways for such signals. More recently, it has been found that by mapping the electrical properties of the heart muscle in conjunction with the heart anatomy, and selectively ablating cardiac tissue by application of energy, it is possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.

A typical ablation procedure involves the insertion of a catheter having electrode(s) at its distal end into a heart chamber. An indifferent electrode is provided, generally adhered to the patient's skin. Radio frequency (RF) current is applied to the electrode(s), and flows between the surrounding media, i.e., blood and tissue and the indifferent electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue, as compared to blood which has a higher conductivity than the tissue. Heating of the tissue occurs due to Joule heating. If the tissue is heated sufficiently, protein denaturation occurs; this in turn forms a lesion within the heart muscle which is electrically non-conductive.

A focal catheter works well, for example, when ablating a line of block in the atria. However, for tubular regions in or around the heart, this type of catheter is cumbersome, skill dependent, and time consuming. For example, when the line of block is to be made about a circumference of the tubular region, it is difficult to manipulate and control the distal end of a focal catheter so that it effectively ablates about the circumference. In current practice a line of block is accomplished by maneuvering the catheter from point to point and is highly dependent on the skill of the operator and can suffer from incomplete isolation of target areas such as the pulmonary vein ostia. However, done well, it can be very effective.

Catheters with circular ablation assemblies (or "lasso-type" catheters) are known. This type of catheter comprises a catheter body having at its distal end an ablation assembly with a preformed generally circular curve with an outer surface and being generally transverse to the axis of the catheter body. In this arrangement, the catheter has at least a portion of the outer circumference of the generally circular curve in contact with the inner circumference or ostium of a tubular region in or near the patient's heart, e.g., a pulmonary vein. However, one drawback with catheters of this type may be the relatively fixed size or circumference of the circular ablation assembly, which may not match the circumference of the tubular region undergoing treatment. Further, the variance in anatomy observed between subjects makes it difficult for a "one size fits all" approach.

Ablation catheters with inflatable assemblies or balloons are also known. Such balloons may include electrodes positioned on the outer surface of the balloons for ablating tissue and are typically inflated with a pressurized fluid source. More recently, inflatable catheter electrode assemblies have been constructed with flex circuits to provide the outer surface of the inflatable electrode assemblies with a multitude of very small electrodes. Examples of catheter balloon structures are described in<CIT>, titled Balloon for Ablation Around Pulmonary Vein.

Flex circuits or flexible electronics involve a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, Liquid Crystal Polymer (LCP), PEEK or transparent conductive polyester film (PET). Additionally, flex circuits can be screen printed silver circuits on polyester. Flexible printed circuits (FPC) are made with a photolithographic technology. An alternative way of making flexible foil circuits or flexible flat cables (FFCs) is laminating very thin (<NUM>) copper strips in between two layers of PET. These PET layers, typically <NUM> thick, are coated with an adhesive which is thermosetting, and will be activated during the lamination process. Single-sided flexible circuits have a single conductor layer made of either a metal or conductive (metal filled) polymer on a flexible dielectric film. Component termination features are accessible only from one side. Holes may be formed in the base film to allow component leads to pass through for interconnection, normally by soldering.

However, where irrigation is desired or needed to cool and dilute the tissue region being ablated by an inflatable electrode assembly, perforation or the formation of irrigation apertures in a balloon membrane layer and an outer flex circuit substrate layer has posed numerous challenges. Where the apertures are formed in each layer separately, alignment of the apertures thereafter between the two layers has its difficulties. Where the apertures are formed in the two layers affixed to each other, methods for forming apertures in one layer may degrade or damage the other layer, especially where the two layers are constructed of material with different melting temperatures, such as Pellethane and polyimide. Patchworking the balloon structure with sections of perforated membrane and sections of perforated substrate can cause the balloon to misshapen, especially where the materials have different durometers.

Accordingly, a need exists for a method of constructing a catheter having an inflatable member or balloon with flex circuits and yet provides a plurality of irrigation apertures for irrigation of fluid from inside the balloon to outside. It is desirable that such method allows for the of irrigation apertures with uniformity and/or accuracy, without undesirable degradation or damage to the balloon membrane and flex circuit substrate, while enabling the balloon to maintain a desirable shape or configuration while inflated.

<CIT> discusses a catheter and catheter system that may be used to treat disease tissue by gentle heating in combination with gentle or standard dilation. An elongate flexible catheter body with a radially expandable balloon having a plurality of electrodes engages tissue including diseased tissue when the structure expands.

Additional relevant prior art is disclosed in <CIT> and <CIT>.

The invention is defined by the scope of independent claims <NUM>, <NUM> and <NUM>. Embodiments of the present invention include a method of constructing an inflatable irrigated electrode assembly for an electrophysiology catheter. In some embodiments, the method comprises: providing a flex circuit having a substrate with a pre-formed aperture, the substrate constructed of a material with a greater heat resistance; providing an inflated balloon member with a flexible membrane, the membrane constructed of a material with a lesser heat resistance; affixing the substrate to the membrane with adhesive; the adhesive having a lower melting temperature than the flex circuit substrate, and applying heat through the pre-formed aperture of the substrate, the heat having a temperature sufficient to melt a portion of the membrane and the adhesive without degrading, damaging or melting the substrate, the portion of the membrane melted forming an aperture in the membrane.

In some embodiments, the substrate is constructed of a thermoset material or a material having a higher melting temperature relative to the lower melting temperature of the material from which the membrane is constructed, for example, polyimide.

In some embodiments, the membrane is constructed of thermoplastic polyurethane.

In some embodiments, the membrane is constructed of a flexible and elastic material.

In some embodiments, the heat applied reflows the portion of the membrane and the adhesive forming the aperture in the membrane.

In some embodiments, the applying heat includes inserting a soldering iron into the preformed aperture.

In some embodiments, the applying heat includes inserting a hot wire into the preformed aperture.

In some embodiments, the applying heat includes directing an energy beam from a laser into the pre-formed aperture to melt the target portion of the membrane.

In some embodiments, a method of constructing an inflatable electrode assembly configured for irrigation, comprises: providing a flex circuit having a substrate with a pre-formed aperture, the substrate constructed of a thermoset material or a material having a first melting temperature; providing a balloon member with a membrane, the membrane having a second melting temperature lower than the first melting temperature of the substrate; affixing the substrate to the membrane with an adhesive having a third melting temperature also lower than the first melting temperature, wherein a surrounding portion of the substrate around the pre-formed aperture masks a surrounding portion of the membrane and the adhesive so as to expose a target portion of the membrane; and applying heat to the target portion of the membrane through the pre-formed aperture of the substrate, wherein the heat applied, without degrading, damaging or melting the substrate, melts the target portion of the membrane and the adhesive in forming an aperture in the membrane.

In some embodiments, the heat applied creates a temperature between the first melting temperature of the membrane and the second and third melting temperatures of the substrate and the adhesive.

In some embodiments, the aperture in the membrane is larger than the pre-formed aperture in the substrate.

In some embodiments, affixing the substrate to the membrane includes applying an adhesive between the membrane and the surrounding portion of the substrate, wherein the heat applied through the aperture of the substrate reflows the membrane and the adhesive.

In some embodiments, a method of constructing an inflatable electrode assembly configured for irrigation, comprising: providing a flex circuit having a substrate with a pre-formed aperture, the substrate constructed of a thermoset material or a material having a higher melting temperature; providing an inflated balloon member with a flexible membrane, the membrane having a lower melting temperature; adhering the substrate to the membrane with adhesive, the adhesive also having a lower melting temperature than the substrate, wherein a first surrounding portion of the substrate around the pre-formed aperture frames an exposed target portion of the membrane and the adhesive while masking a second surrounding portion of membrane and the adhesive around the exposed target portion; and applying heat to the target portion of the membrane through the pre-formed aperture of the substrate, the heat creating a temperature sufficient to melt the target portion of membrane and the adhesive without melting or thermally damaging or degrading the first surrounding portion of the substrate.

These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:.

As shown in <FIG>, the catheter <NUM> comprises an elongated catheter shaft <NUM>, an inflatable electrode assembly <NUM> with a balloon member <NUM> having one or more flex circuits <NUM> on its outer surface, and a deflection control handle <NUM> attached to the proximal end of the catheter body <NUM>. The catheter <NUM> may function in combination with a distal electrode assembly, for example, a lasso electrode assembly <NUM>, for which the inflatable electrode assembly <NUM> can function as an anchor and/or stabilizer when the lasso electrode assembly <NUM> is in use, such as when inserted in a pulmonary vein PV of the left atrium, as shown in <FIG>.

With reference to <FIG>, each flex circuit on the balloon member <NUM> has an elongated electrode <NUM>, configured with, for example, a longitudinal spine <NUM> and a plurality of fingers <NUM> that extend transversely from opposite sides of the spine. As show in <FIG>, the electrode <NUM> of each flex circuit <NUM> is configured for circumferential contact with tissue in a tubular region or ostium when the balloon member <NUM> is pressurized to expand the inflatable electrode assembly <NUM> by fluid from a remote fluid source (not shown). The fluid is delivered by an irrigation tubing <NUM> that extends from the control handle <NUM>, along the length of the catheter body <NUM> and into an interior cavity of the balloon member <NUM>. It is understood that the inflatable electrode assembly <NUM> assumes a collapsed configuration when entering a patient's vasculature and is expanded by inflation for deployment at a target site. In accordance with a feature of the present invention, the inflatable electrode assembly <NUM> is configured with a plurality of irrigation apertures <NUM> which advantageously allows fluid from inside the interior cavity of the balloon member <NUM> to pass to outside of the assembly <NUM> during deployment, for various purposes, including cooling surrounding tissue, improving lesion formation and minimizing the creation of char on or near the assembly <NUM>. Although <FIG> illustrates the flow of fluid as stream jets <NUM>, it is understood that the fluid may exit the irrigation apertures <NUM> at any desirable or appropriate rate, ranging between fluid seepage or weeping to stream jets.

As shown in <FIG>, the balloon member <NUM> has a membrane <NUM> which is flexible and if appropriate or desired, also elastic. The membrane <NUM> is constructed of a thermoplastic material with a low durometer ranging between about 50A and 55D, and preferably between about 80A and 50D. A suitable material includes Pellethane, a medical-grade thermoplastic polyurethane elastomer, with superior resilience, low temperature properties and exceptionally smooth surfaces.

Fixedly attached to an outer surface of the balloon membrane <NUM>, for example, by an adhesive, are the plurality of flex circuits <NUM>. As shown in <FIG>, each flex circuit <NUM> may be connected at its distal end to the other flex circuits by a hub or circular portion <NUM> during manufacture, forming a flex circuit web with radially extending flex circuits. The hub <NUM> is removed prior to affixation of the flex circuit onto the balloon member. As shown in <FIG>, each flex circuit <NUM> has a main portion which carries the electrode <NUM>, a proximal tail portion <NUM> which extends toward a proximal end of the assembly <NUM>. A proximal tail end (not shown) may be tucked under and affixed by a proximal ring <NUM> to help fasten the flex circuit <NUM> on the outer surface of the balloon membrane <NUM>.

As shown in <FIG>, each flex circuit has a sheet substrate <NUM> which supports the electrode <NUM> and other components including solder patches and thermocouple wires. In accordance with a feature of the present invention, the substrate <NUM> is constructed of any suitable material with a greater heat resistance than that of the membrane <NUM> of the balloon member <NUM>. As used herein, heat resistance refers to the ability of a material to withstand high temperatures at which the material melts, degrades or is damaged. For example, a material that begins to melt at a lower temperature has a lesser heat resistance, whereas a material that begins to melt at a higher temperature has a greater heat resistance.

In some embodiments, the substrate is constructed of a thermoset material or a material that can withstand a temperature higher than the melting temperature of the construction material of the balloon membrane <NUM> by approximately 100C or more. A suitable material includes polyimide, which is any of a class of polymers with an imido group, that is resistant to high temperatures, wear, radiation, and many chemicals.

In accordance with a feature of the present invention, each flex circuit <NUM> is preperforated or otherwise formed with apertures <NUM> by a suitable process prior to affixation to the balloon membrane <NUM>. In other words, apertures <NUM> are preformed in the substrate <NUM> of the flex circuit <NUM> prior to and separately from apertures <NUM> formed in the balloon membrane <NUM>. A suitable substrate perforation process includes laser cutting, including laser perforation and laser micro perforation. Rather than puncturing or tearing the substrate <NUM>, as is typical with mechanical perforation machines, which tends to weaken the material, laser micro-perforation burns through the substrate <NUM>, where the result is a cleaner, smaller, rounder, more precise hole. Laser perforating systems operate by using a focused laser pulse to vaporize a very small, well-defined and controlled area or point to form a hole while sealing the hole's edges and strengthening the material around it. With laser micro perforation, hole diameters down to about 5microns can be achieved. The apertures <NUM> formed in the substrate <NUM> via laser perforation have diameters ranging between about <NUM> micrometers and <NUM> micrometers, and preferably are about <NUM> micrometers ( <NUM>" and <NUM>", and preferably are about <NUM>').

After the flex circuits <NUM> have been perforated with apertures <NUM>, the flex circuits <NUM> are affixed to the outer surface of the balloon membrane <NUM> by a suitable adhesive <NUM>, as shown in <FIG>. The adhesive <NUM> is allowed to flow between the substrate <NUM> and the membrane <NUM> to provide full coverage in order to maximize adhesion. In some embodiments, the balloon member <NUM> is inflated by the application of positive air pressure into the balloon member <NUM> during the affixation of the flex circuits <NUM> to the outer surface of the balloon membrane <NUM>.

For ease in describing the method of the present invention, reference is made to <FIG>, where a surrounding portion <NUM> surrounds a pre-formed aperture <NUM> in the substrate <NUM>. With the substrate <NUM> affixed to the membrane <NUM> (both shown in an exploded view in <FIG>), the preformed aperture <NUM> frames or circumscribes a respective target portion <NUM> of the membrane at which an aperture <NUM> can be formed in the membrane <NUM>. The surrounding portion <NUM> of the substrate <NUM>, when affixed to the membrane <NUM>, masks a surrounding portion <NUM> of membrane <NUM> that surrounds the target portion <NUM>.

After the adhesive affixing the membrane <NUM> and the substrate <NUM> together has flowed and cured, a heating element <NUM> is applied to the target portion <NUM> of the membrane <NUM> as accessed through the pre-formed aperture <NUM>, with the surrounding portion <NUM> of the substrate <NUM> blocking and protecting the masked surrounding portion <NUM> of the membrane <NUM> from the applied heat. In this manner, the pre-perforated substrate <NUM> of the flex circuit <NUM> when affixed to the balloon membrane <NUM> serves as a template wherein the pre-formed aperture <NUM> in the substrate <NUM> provides a guide by which an aperture <NUM> in the balloon membrane <NUM> is formed. The pre-formed apertures <NUM> in the substrates <NUM> of the flex circuits <NUM> advantageously provide an exact and direct guide as to the locations of the apertures <NUM> in the balloon membrane <NUM>.

In some embodiments, the heat applied may provide or create a temperature of about <NUM>-400C, but preferably around 250C. In some embodiment, a source of the heat may be a heating or heated element, for example, a fine tipped soldering iron or a heated fine wire. The heat may also be provided by an energy beam, such as a laser that can provide localized heating (nonexcimer) by absorption of the adhesive <NUM> and the balloon membrane <NUM> sufficient to melt the adhesive <NUM> and balloon membrane <NUM>, and not the substrate <NUM> of the flex circuit <NUM> masking the membrane <NUM>.

The heat applied creates a temperature sufficient to melt and reflow the balloon membrane <NUM>. Because the substrate <NUM> has a higher melting temperature, it is unaffected by the heat and it provides a precise orifice size after the material of the balloon membrane <NUM> reflows away from the heat source. Where the adhesive <NUM> is reflowable, the heat applied also reflows the adhesive <NUM> away from the aperture <NUM>.

The reflow is achieved by initial mechanical displacement of the melted materials, but is further helped by surface tension of the melted materials which will form a rim around the underside of the preformed aperture <NUM>.

Accordingly, the reflowing of the adhesive <NUM> and the balloon membrane <NUM> via heat applied through the pre-formed apertures <NUM> of the flex circuit <NUM> can result in apertures <NUM> in the balloon membrane <NUM> that have at least the same or greater size or diameters than the apertures <NUM>.

Embodiments of the method of manufacturing of the present invention provide a number of benefits and advantages. For example the use of localized heat minimizes or avoids the use of aids in the manufacture or assembly of the balloon member <NUM> and the flex circuits <NUM>, including the avoidance of using an inner inflated balloon to provide structural support to the balloon member <NUM>. Moreover, there is little difficulty aligning the pre-formed apertures <NUM> of the substrate <NUM> with the apertures <NUM> formed in the balloon membrane <NUM> because the pre-perforated flex circuit <NUM> is adhered directly on the balloon membrane <NUM> after which the apertures <NUM> are formed, reducing if not eliminating any possibility of misalignment. Furthermore, the use of a heating element in reflowing the balloon membrane <NUM> and the adhesive <NUM> provides a physical barrier to any reflowed materials blocking or resealing the newly-formed aperture <NUM> in the balloon membrane <NUM>. No puncture or drilling is involved so there is no risk of creating debris that may detach from the catheter.

In the embodiment of <FIG>, the electrode <NUM> of the flex circuit <NUM> has one or more voids or cutouts <NUM> along the spine <NUM>. One cutout 54A is filled with, for example, tungsten-loaded epoxy <NUM> to serve as markers visible under fluoroscopy. Other smaller cutouts 54B serve as blind vias to provide electrical connections for the electrode <NUM> from one side (topside) of the substrate <NUM> to the other side (underside) of the substrate. Another cutout 54C frames a pre-formed aperture <NUM> in the substrate <NUM> previously formed by laser-cutting before affixation to the balloon membrane <NUM>.

After the flex circuit <NUM> has been affixed to the balloon membrane <NUM> by the adhesive <NUM>, and the adhesive has cured, a heating element <NUM> is inserted through the preformed aperture <NUM> of the substrate <NUM> to melt the membrane <NUM> framed by the preformed aperture <NUM>. The heating element <NUM> reflows both the adhesive <NUM> and the membrane <NUM> and away from the heating element <NUM> to form the aperture <NUM> in the membrane <NUM> that is generally aligned and coaxial with the preformed aperture. The pre-formed aperture <NUM> in the substrate <NUM> and the subsequent aperture <NUM> formed in the membrane <NUM> together provide an irrigation aperture in the inflatable electrode assembly allowing irrigation fluid to pass from inside the balloon member to outside of the inflatable electrode assembly.

Claim 1:
A method of constructing an inflatable irrigated electrode assembly (<NUM>) for an electrophysiology catheter (<NUM>), the method comprising:
providing a flex circuit (<NUM>) having a substrate (<NUM>) with a pre-formed aperture (<NUM>), the substrate having a higher heat resistance;
providing an inflated balloon member (<NUM>) with a flexible membrane (<NUM>), the membrane (<NUM>) having a lower heat resistance;
affixing the substrate (<NUM>) to the membrane (<NUM>) with adhesive (<NUM>);
applying heat through the pre-formed aperture (<NUM>) of the substrate (<NUM>), the heat creating a temperature sufficient to melt a portion of membrane (<NUM>) and the adhesive (<NUM>) without melting the substrate (<NUM>), the portion of the membrane (<NUM>) and the adhesive (<NUM>) melted forming an aperture (<NUM>) in the membrane (<NUM>) and adhesive (<NUM>); and
wherein the aperture (<NUM>) in the membrane (<NUM>) is larger than the pre-formed aperture (<NUM>) in the substrate (<NUM>) due to reflow of the membrane (<NUM>) and the adhesive (<NUM>).