US20110093037A1 - Compliant electrode for patent foramen ovale closure device - Google Patents

Abstract

A medical device for use in delivering RF energy to a tissue opening is disclosed. In one embodiment, the medical device comprises a compliant electrode. The compliant electrode can include a shape memory material, such as NITINOL, to facilitate the electrode having at least one relaxed orientation. The electrode can be deployed from a delivery shaft inside the left atrium, for example, of a heart through the delivery shaft. The electrode can be configured to substantially conform to the tissue proximate the tissue opening. After energy is applied to the tissue between the left and right electrodes, the left electrode can be removed from the left atrium by being received back into the delivery shaft and the delivery shaft thereafter removed from the opening.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a divisional of application Ser. No. 11/534,953, filed Sep. 25, 2006, and entitled COMPLIANT ELECTRODE FOR PATENT FORAMEN OVALE CLOSURE DEVICE, pending, which claims the priority of provisional application Ser. No. 60/720,913, filed on Sep. 26, 2005, and entitled COMPLIANT ELECTRODE FOR PFO CLOSURE DEVICE, the disclosures of each which are also incorporated by reference herein in their entireties.
BACKGROUND OF THE INVENTION
• 1. The Field of the Invention
• The present invention relates generally to implanting medical devices within a patient. More particularly, the present invention relates to the field of patent foramen ovale (“PFO”) closure devices.
• 2. The Relevant Technology
• FIGS. 1A-1C depict various views of a heart.Heart10 is shown in a cross-section view inFIG. 1A. In a normal heart, theright atrium30 receives systemic venous blood from thesuperior vena cava15 and theinferior vena cava25 and then delivers the blood via thetricuspid valve35 to theright ventricle60. However, inheart10, there is a septal defect betweenright atrium30 andleft atrium40 of a patient's heart which is referred to as a patent foramen ovale (“PFO”). PFO is a birth defect that occurs when an opening between the upper two chambers of the heart fail to close after birth to a lesser or greater degree. This birth defect is sometimes also known as a “hole in the heart.”
• Other problems with this condition are that a blood clot may travel freely between the left or right atria of the heart, and end up on the arterial side. This could allow the clot to travel to the brain, or other organs, and cause embolization, or even a heart attack. These and other similar defects (septal or otherwise), where some tissue needs to be closed to function properly include the general categories of atrial septal defects (“ASDs”), ventricular septal defects (“VSCs”) and patent ductus arterosus (“PDA”), and so forth.
• The PFO, which is an open flap on the septum between the heart's right and left atria, is generally identified at50. In a normal heart,left atrium40 receives oxygenated blood from the lungs viapulmonary arteries75 and then delivers the blood to theleft ventricle80 via thebicuspid valve45. However, inheart10 some systemic venous blood also passes fromright atrium30 throughPFO50, mixes with the oxygenated blood inleft atrium40 and then is routed to the body fromleft ventricle80 viaaorta85.
• During fetal development of the heart, theinterventricular septum70 dividesright ventricle60 andleft ventricle80. In contrast, the atrium is only partially partitioned into right and left chambers during normal fetal development as there is a foramen ovale. When the septum primum52 incompletely fuses with the septum secundum54 of the atrial wall, the result is a PFO, such as thePFO50 shown inFIGS. 1A-1C, or an atrial septal defect referred to as an ASD.
• FIG. 1C provides a view of the crescent-shaped, overhanging configuration of the typical septum secundum54 from withinright atrium30. Septum secundum54 is defined by itsinferior aspect55, corresponding with the solid line inFIG. 1C, and itssuperior aspect53, which is its attachment location toseptum primum52 as represented by the phantom line. Septum secundum54 and septum primum52 blend together at the ends of septum secundum54; these anterior and posterior ends are referred to herein as “merger points” and are respectively identified at56aand56p. The length of the overhang of septum secundum54, the distance betweensuperior aspect53 andinferior aspect55, increases towards the center portion of the septum secundum54 as shown.
• Atunnel58 is defined by portions of septum primum52 and septum secundum54 between themerger points56aand56pwhich have failed to fuse. Thetunnel58 is often at the apex of the septum secundum54 as shown. When viewed withinright atrium30, the portion of septum secundum54 to the left oftunnel58, which is referred to herein as theposterior portion57pof the septum secundum54, is longer than the portion of the septum secundum54 to the right oftunnel58, which is referred to herein as theanterior portion57aof the septum secundum54. In addition to being typically longer, the left portion also typically has a more gradual taper than the right portion, as shown. The area defined by the overhang of theanterior portion57aof septum secundum54 and theseptum primum52 and extending from theanterior merger point56atowardtunnel58 is ananterior pocket59a. Similarly, the area defined by the overhang of theposterior portion57pof septum secundum54 and theseptum primum52 and extending from theposterior merger point56ptowardtunnel58 is aposterior pocket59p.
• Conventional treatments for PFO (and related conditions), have generally involved invasive surgery, which presents a different, new set of risks to a patient. Although there are some less invasive treatments for PFO, these have typically been less efficient at closing the PFO opening than techniques involving invasive surgery. Accordingly, there is a continuing need for improved methods and devices for closing the PFO opening. In particular, there is a need for improved methods and devices for deploying PFO closure anchors in a patient.
BRIEF DESCRIPTION OF THE DRAWINGS
• To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
• FIG. 1A is a cross-sectional view of a heart;
• FIG. 1B is an enlarged cross-section view of septum primum and the septum secundum and a PFO tunnel between the septum primum and the septum secundum;
• FIG. 1C is a perspective view of the septum secundum with the tunnel and the septum primum shown in phantom;
• FIG. 2 is a perspective view of an electrode according to one configuration of the present invention;
• FIG. 3 is a top view of the electrode ofFIG. 2;
• FIG. 4A is a side view of the electrode ofFIG. 2 as the electrode is being deployed;
• FIG. 4B is a side view of the electrode ofFIG. 2 as the electrode is further deployed;
• FIG. 4C is a side view of the electrode ofFIG. 2 as the electrode is substantially deployed to a trained orientation;
• FIG. 5A is a cross-sectional view of the electrode ofFIG. 2 in an internal tissue opening;
• FIG. 5B is a perspective view illustrating the electrode in the left atrium;
• FIG. 6 is a bottom view of an alternative embodiment of an electrode according to the present invention;
• FIG. 7 is a bottom view of an alternative embodiment of an electrode according to the present invention;
• FIG. 8 is a bottom view of an alternative embodiment of an electrode according to the present invention;
• FIG. 9A is a bottom view of an alternative embodiment of an electrode according to the present invention; and
• FIG. 9B is a bottom view of the electrode ofFIG. 9B.
BRIEF SUMMARY OF THE DISCLOSURE
• The invention relates to a medical device for reducing the size of an internal tissue opening utilizing energy, such as radio frequency energy. In one embodiment, the medical device can include a left electrode having a plurality of arms trained to a predetermined orientation. The arms can transition from a constrained orientation to a relaxed orientation, i.e., predetermined orientation, during deployment and/or use of the medical device. The flexibility of the arms and resultant increased surface contact of the electrode with the tissue adjacent to, around, and/or associated with the PFO can increase the effectiveness of a “tissue weld” as energy is applied between the left electrode positioned against a left atrial wall of a heart and a right electrode positioned against the right atrial wall of the heart.
• In one embodiment, the arms can include a shape memory material, such as NITINOL, such that the arms can be deformed and will thereafter return to their predetermined, trained, or relaxed orientation. As such, the arms can be configured to be received back into a delivery shaft after the “tissue weld” and the delivery shaft can be removed from the opening. In this manner, the left electrode can be removed from the left atrium of the heart with minimal disturbance of the tissue weld.
• The arms can be configured so as to provide coverage of a portion of the tissue wall proximate to the internal tissue opening, such as, but not limited to, a PFO. For example, the arms can be configured to be compliant and exhibit a nonlinear force versus deflection characteristic. The nonlinear force versus deflection characteristic is such that as the plurality of arms become substantially coplanar, the stiffness of the electrode increases through the inter-contacting of the plurality of arms. As the stiffness of the electrode increases, the likelihood that the plurality of arms will pull through an internal tissue opening is reduced. In this manner, the proportion of arm that is in contact with the tissue proximate to the opening is increased.
• Various features can be implemented to facilitate placement of the left electrode against the atrial wall of the left atrium. For example, the arms can include a ball portion at the distal tip of each of the arms to reduce the likelihood of the arms inadvertently puncturing the heart. Also, the arms can include a hook positioned in the distal ends of each of the arms to engage a loop portion of a different arm.
• These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
DETAILED DESCRIPTION OF THE INVENTION
• The present invention extends to systems, methods, and apparatus for a device that is suitable for reducing the size of an internal tissue opening. By way of explanation, the devices disclosed herein can be used for any internal tissue opening, although frequent reference is made herein to closing a PFO opening of a heart tissue using a right atrial anchor and a left atrial anchor for purposes of simplicity. Accordingly, it will be understood that references to PFO openings are not limiting of the invention.
• In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known aspects of PFO closure devices or medical devices in general have not been described in particular detail in order to avoid unnecessarily obscuring the present invention. In addition, it is understood that the drawings are diagrammatic and schematic representations of certain embodiments of the invention, and are not limiting of the present invention nor are they necessarily drawn to scale.
• Illustrative embodiments of the invention relate to delivering radio frequency or RF energy to the septal wall of the heart to treat a defect known as a patent foramen ovale (PFO). In order to treat this type of defect it is desirable to have an electrode system that holds the walls of the flap-like defect together while energy is applied to “weld” the defect closed, i.e. damage the tissue to stimulate tissue growth in the area.
• In one embodiment, the medical device can include an electrode configured to increase the effectiveness of the tissue weld. The effectiveness of the tissue weld can be increased by configuring the electrode to contact, and in some instances conform with, the tissue of the atrium proximate the opening of the PFO. Furthermore, the electrode can be configured to be collapsible to a small cross section to remove the electrode from the welded tissue opening without substantially interfering with the new weld.
• In one embodiment, the electrode can include a plurality of arms trained to a predetermined orientation. The plurality of arms can include a shape memory material, such as NITINOL, which can be trained to orient themselves in a predetermined shape. The plurality of arms can be configured to be straightened as they are received into a delivery shaft, and then assume their predetermined shape as they are extended from the delivery shaft. Stated another way, the arms can be set with a relaxed orientation that is desirable for tissue contact or conformance; the arms being biased to return to the relaxed orientation when the arms are in the constrained orientation within the delivery shaft.
• As such, as used herein, relaxed orientation refers to the predetermined or trained shape of the material; constrained orientation refers to an orientation other than the relaxed orientation, such as, for example, when an arm is forced into a shape different than the shape of the relaxed orientation. For example, the arms can be trained to include one or more curves or the arms can be trained to be substantially straight. Furthermore, the arms can be trained to have multiple relaxed orientations, wherein the relaxed orientations are dependent upon a characteristic, such as temperature. In this example, certain temperature ranges can correspond to a specific relaxed orientation. Another example can include the arms having a substantially straight relaxed orientation during a first temperature range and having a curved relaxed orientation, such as illustrated in any of FIGS.2 and6-9A, during a second temperature range. Also, it will be appreciated that the entire arm can be trained, or a portion or multiple portions of the arm can be trained.
• The plurality of arms can be configured so as to provide coverage of a portion of the arterial wall proximate to the internal tissue opening, such as a PFO. For example, the plurality of arms can be configured with a nonlinear force versus deflection characteristic. The nonlinear force versus deflection characteristic results in increased stiffness of the electrode as the plurality of arms become substantially coplanar. As the stiffness of the electrode increases due to the inter-connection of the plurality of arms, the likelihood that the plurality of arms will pull through an internal tissue opening is reduced. In this manner, a practitioner can apply pressure to the electrode thus resulting is the plurality of arms being positioned against the opening of the PFO. In a similar manner, the plurality of arms can be configured to be compliant. The compliancy of the plurality of arms can increase the density of the plurality of arms in the proximity of the internal tissue opening.
• The plurality of arms can include various other features to facilitate placement of the electrode against the arterial wall of the atrium. For example, the plurality of arms can include a ball portion at the distal tip of the plurality of arms. The ball portion can be configured to reduce the likelihood of the plurality of arms inadvertently puncturing the tissue of the arterial wall.
• With reference now to the illustrated embodiments,FIG. 2 is a perspective view of a deployedelectrode100 in a relaxed orientation. The following discussion is made with respect to a left electrode that can be disposed in theleft atrium40 of the heart10 (FIG. 1). It will be understood, however, that the features and functions of the electrode can also be adapted for a right electrode positionable within the right atrium30 (FIG. 1) or in any other lumen of the patient.
• In the illustrated embodiment,electrode100 includes one ormore arms102 extending radially from an axialtubular housing106.Arms102 can extend radially fromhousing106 due toarms102 being trained to have the illustrated relaxed orientation. For example, in the illustrated embodiment,arms102 can be trained to extend radially fromhousing106 and then curve back around so as to form a bulb shape with an optionally partially flattened bottom as shown inFIG. 2A.
• Housing106 can be configured to secure proximal ends ofarms102 together such that movement ofhousing106 can result in movement ofarms102. Alternatively,housing106 can be configured so as to enablearms102 to move throughhousing106 such thatarms102 can move relative tohousing106. Furthermore,housing106 can be configured such that those portions ofrespective arms102 which extend out fromhousing106 are trained portions ofarms102; however,housing106 can be configured to house both trained and/or non-trained portions ofarms102. Housing106 can be configured to facilitate deployment ofelectrode100, as will be discussed more fully herein.
• In one embodiment,electrode100 can include from 4 to 10 arms made of a Shape Memory Material (SMM), such as superelastic NITINOL. NITINOL is a nickel titanium alloy that belongs to a class of materials called Shape Memory Alloys (SMA), which in turn belongs to the broader class of SMM. SMMs have a shape memory effect in which they can be made to remember a particular shape. Once the material has been made to remember a particular shape, i.e. set or trained, the material can be bent out of shape and then upon unloading from strain or heating the material will return to its set, relaxed or trained orientation. While various methods of setting or training a material are known, one way in which material can be trained is through a heating process. In one embodiment, arms150, which comprise NITINOL materials, can be trained to remember a certain shape, can then be straightened, for example in a shaft, catheter or other tube, and then released from the catheter or tube to return to the trained shape. Other SMM's can include a magnetic shape memory alloy which can change their shape in response to a change in a magnetic field. Furthermore, the SMM can be a shape memory polymer, such as a “smart plastic” which can hold different shapes at different temperatures.
• Arms102 can be wrapped, coated, or filled with a biocompatible radiopaque material such as platinum to enhance the visibility of the device under fluoroscopy. Furthermore,arms102 can include marker bands attached thereto to enhance visibility under fluoroscopy. The distal ends of thearms102 may have a ball formed at the tip to reduce the possibility of an arm inadvertently perforating the heart. An example of aball224 is shown with respect toarm220 ofFIG. 9B.Ball224 can also be configured to provide enhanced visibility under fluoroscopy.
• With reference now toFIG. 3,arms102 can include ahook104 at the distal end ofrespective arms102.Hooks104 can be configured to engage one or moredifferent arms102 so as to inter-connectarms102. Furthermore, the relaxed orientation ofarms102 can be such that hooks104 are positioned under the loop portion so as to inter-connectarms102 together as thearms102 become coplanar. Inter-connecting ofarms102 together in this manner can increase the nonlinear deflection characteristic of thearms102 and/or theelectrode100.
• FIGS. 4A to 4C illustrate deployment ofelectrode100. With respect toFIG. 4A, adelivery shaft152, such as a left anchor delivery shaft, is illustrated havingarms102 ofelectrode100 extending out therefrom. As shown in the illustration, arms can be positioned within leftanchor delivery shaft152 in a substantially straightened manner. Asarms102 are advanced out of leftanchor delivery shaft152,arms102 can then begin to return to their relaxed orientation, for example, such as the basket-like shape as illustrated inFIG. 4C. As will be appreciated by one of ordinary skill in the art, becausearms102 are substantially straightened relative to the relaxed orientation as illustrated inFIG. 4C within leftanchor delivery shaft152,electrode100 can be delivered and/or deployed through a small hole relative to the size of the deployed orientation ofelectrode100.
• It will be understood by one of ordinary skill in the art in view of the disclosure provided herein thatarms102 can have multiple relaxed orientations. For example, in an alternative embodiment,arms102 can have a substantially straight first relaxed orientation and a curved second relaxed orientation, wherein respective relaxed orientations are dependent upon a characteristic, such as temperature. It may be desirable to havearms102 be in a first relaxed orientation while being inserted into a atrium of a patient and thereafter be changed to the second relaxed orientation for positioning against the wall of the atrium.
• Electrode100 can be advanced out ofdelivery shaft152 by a variety of means or manners. For example, in one embodiment, the proximal end ofhousing106 can be received in the distal end ofdelivery shaft152. Housing106 can then be moved throughdelivery shaft152 until the proximal end ofhousing106 extends from the proximal end ofdelivery shaft152 andarms102 are received withindelivery shaft152. At this point,housing106 can be moved distally with respect todelivery shaft152, thus causingarms102 to extend from or deploy fromdelivery shaft152. Alternatively,arms102 can extend throughdelivery shaft152 and extend out from the proximal end ofdelivery shaft152. In this embodiment, the proximal ends ofarms102 can be coupled together so as to maintain the overall shape ofelectrode100 as formed byarms102. The coupled ends ofarms102 can be moved distally with respect todelivery shaft152 to deploy the trained portions ofarms102.
• Arms102 can be positioned withinhousing106 and/ordelivery shaft152 in a manner that enableshousing106 and/ordelivery shaft152 to have a reduced diameter. For example,arms102 can be configured so as to fit inhousing106 and/ordelivery shaft152 in an organized manner, or in other words substantially reduce overlapping ofarms102. In this manner, the diameter ofhousing106 and/ordelivery shaft152 can be reduced. As will be appreciated by one of ordinary skill in the art in view of the disclosure provided herein, the diameter ofhousing106 and/ordelivery shaft152 can correspond with the size of the remaining tissue opening after the tissue weld. Accordingly, a smaller diameter ofhousing106 and/ordelivery shaft152 can result in a smaller resulting opening after the tissue weld.
• FIG. 5A illustrates anexample device300 utilizing an electrode in accordance with the present invention. Furthermore,FIGS. 5A and 5B illustrate the positioning of an electrode in the left atrium of a patient. In the illustrated embodiment,device300 can include aleft electrode314, aright electrode311 and adelivery sheath302 configured to facilitate positioning of left andright electrodes314,311. Elements associated withleft electrode314 can include a plurality ofshape memory arms316, adelivery shaft310 configured to house at least a portion ofarms316, a leftelectrode delivery tube306 configured to receivedelivery shaft310 therein, whereindelivery shaft310 can translate and/or rotate therein, andinsulation308 on the outer surface of leftelectrode delivery tube306.
• Elements associated withright electrode311 can include a plurality ofshape memory arms312 and aright electrode catheter304. In the illustrated embodiment,arms312 can be coupled toright electrode catheter304. Furthermore,right electrode catheter304 can receive leftelectrode delivery tube306 therein such that leftelectrode delivery tube306 can translate and/or rotate inright electrode catheter304.
• For simplicity of discussion, only twoarms316 ofleft electrode314 and twoarms312 ofright electrode311 are illustrated. However, it will be appreciated by one of ordinary skill in the art in view of the disclosure provided herein that left and right electrode can include more than two arms.
• As shown in the illustrated embodiment, various elements associated withleft electrode314 can be inserted through the opening of the PFO. For example,delivery shaft310 and leftelectrode delivery tube306 which can enclose at least a portion of leftanchor delivery shaft310, can be received within an opening of the PFO. An approach for transcatheter treatment of a PFO is through the femoral vein and the inferior venacava into the right atrium of the heart. As such, it will be advantageous for the member or electrode that passes through the PFO into the left atrium to have a low crossing profile thus requiring only a small hole to withdraw the device through after the energy delivery and/or “tissue welding” have been accomplished.
• In the illustration,delivery sheath302 can be outside aright electrode catheter304. Whenright electrode catheter304 is extended fromdelivery sheath302,right electrode311 can be deployed such thatarms312 can extend. Whenright electrode catheter304 is withdrawn intodelivery sheath302,arms312 can collapse and enter theright electrode catheter304.
• Leftelectrode delivery tube306 can be inside theright electrode catheter304 and can haveinsulation308 in its exterior surface to electrically insulate between theright electrode catheter304 and the conductive leftelectrode delivery tube306 and theconductive delivery shaft310. Alternatively, insulation can be positioned on the interior surface of leftelectrode delivery tube306 or can be positioned on the exterior surface ofdelivery shaft310. Furthermore, insulation can be positioned on the interior and exterior surface of leftelectrode delivery tube306 and the exterior surface ofdelivery shaft310, or any combination thereof.
• Delivery shaft310 can have various shapes, but can be tubular at the distal opening so thatleft electrode314 opens radially when deployed. When leftelectrode314 is extended fromdelivery shaft310, thearms316 ofleft electrode314 can assume their trained or predetermined orientation. When leftelectrode314 is withdrawn intodelivery shaft310,arms316 return to a straightened orientation. In this manner,left electrode314 can have an increased surface area outsidedelivery shaft310 than would otherwise be possible to insert in a patient. In other words, leftelectrode314 of the present invention can be pushed out of and pulled back into a tube with a diameter of about 1 mm, for example, and yet expand to a diameter of about 20 mm, for example, and have enough strength to hold the atrial walls together during energy delivery and strongly resist pulling through the PFO.
• Witharms312 ofright electrode311 andarms316 ofleft electrode314 being positioned in this manner, energy can be applied to the tissue which is betweenarms312 andarms316. The application of energy in this manner can cause tissue damage. Causing tissue damage in this manner can initiate tissue regrowth so as to weld the tissue together. After such treatment,delivery shaft310 can be advanced back through the small remaining hole in the PFO and leftelectrode314 can be pulled intodelivery shaft310 and leftanchor delivery shaft310 withdrawn without substantially disturbing the weak “tissue weld” that has been created by the procedure.
• FIG. 5B illustrates the positioning ofelectrode314 against the left atrial wall of the heart. As shown in the illustrated embodiment,electrode314 is somewhat flattened against the tissue of the heart proximate theopening58. In this manner, a portion ofarms316 can contact a portion ofseptum primum52 andseptum secundum54. As a bottom surface, such as the surface depicted with reference to108, is pressed against tissue,arms316 can be configured to collapse so as to form a surface area pattern, such as illustrated inFIG. 5B. More particularly, in one embodiment, withdrawingdelivery shaft310 andarms316 together can result inarms316 contacting the underlying tissue. Contact ofarms316 with the underlying tissue can result in the curved portion ofarms316 to flatten. Asarms316 flatten, the contact area betweenarms316 and the underlying surface can be increased. The increased contact area can facilitate the application of energy to the underlying tissue to thereby stimulate tissue regrowth.
• FIG. 6 is a bottom view ofelectrode100 illustrating thepattern arms102 may form asarms102 are flattened by being positioned against tissue. As shown in the illustrated embodiment, hooks104 are positioned under loop portions ofarms102. As will be appreciated by one of ordinary skill in the art in view of the disclosure provided herein, a variety of types and configurations of electrodes can be utilized without departing from the spirit and scope of the invention. For example,FIG. 7 is a bottom view of an alternative embodiment of anelectrode having arms200. In this embodiment, aninward curve202 may be utilized. Theinward curve202 may be positioned at the distal ends ofarms200. In this manner,arms200 may obtain a denser electrode pattern nearer the center of the device.FIG. 8 illustrates yet another embodiment of anelectrode having arms210, whereinarms210 can extend radially.
• It will be understood by one of ordinary skill in the art in view of the disclosure provided herein that while certain embodiments of invention include seven arms, the number of arms can be modified without departing from the spirit and scope of the invention. For example, in one embodiment, electrode includes 10 arms. Alternatively, electrode includes 5 arms. Likewise, the pattern of arm can be modified without departing from the invention.
• FIG. 9A illustrates another example of anarm220 configuration in a left electrode. In this embodiment, thearms220 can have a predetermined orientation such thatarms220 extend from adelivery shaft222, curve around and then extend toward and then cross a central axis of thedelivery shaft222. In this manner, extension of thearms220 can be restrained bydelivery shaft222.FIG. 9B is presented to more clearly illustrate this point with only asingle arm220 depicted to show howarm220 crosses central axis ofdelivery shaft222, such thatdelivery shaft222 can constrainarm220. Furthermore,FIG. 9B illustratesball224 being positioned at a distal end ofarm220, it being understood thatball224 can be implemented into any electrode design disclosed herein.
• As illustrated in the figures, embodiments of the invention can utilize larger radius curves in the arms with respect to the delivery shaft. Utilization of a larger radius curve can result in lower stresses and better fatigue characteristics as well as reduced forces required to pull the electrode into a catheter, delivery shaft or housing.
• By way of example, a device with 7, 0.008″ diameter NiTi arms wrapped with 0.001×0.003 platinum ribbon can be delivered through a tube with a bore of .0.037″, which is slightly less than 1 mm or 3 French.
• One advantage of the invention is that the device can be compliant. The compliancy of the electrode can result in a more even pressure distribution over a potentially irregular surface, such as with the atrial wall at the entrance to the PFO. Furthermore, the compliancy of the electrode can result in the application of substantially even pressure to the atrial wall when the electrode is tilted at an angle to the wall.
• The compliance of the electrode has a nonlinear force versus deflection characteristic which can result in the arms becoming stiff as the arms of the electrode become coplanar. This can provide to the user a tactile feel that the device is engaged against the atrial tissue. Furthermore, the compliancy of the electrode can reduce the likelihood of the electrode inadvertently being pulled through the PFO during use.
• The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. Exemplary claims have been included herein to illustrate embodiments of the invention. Although exemplary claims are presented, the invention is not limited to these claims, and the applicant reserves the right to present different or other claims in the future in view of the embodiments of the invention described herein.

Claims (5)

1. A method for reducing the size of an internal tissue opening comprising the steps of

providing a first electrode comprising a plurality of compliant arms, said plurality of arms each comprising a trained portion, said trained portion comprising a shape memory material, wherein said trained portion has a relaxed orientation;

extending said trained portion from a delivery shaft into a left atrium of a patient;

positioning a second electrode in a right atrium of the patient;

inducing tissue regrowth by applying energy between said first electrode and said second electrode.

2. A method as recited in claim19, further comprising the step of removing said first electrode from said left atrium through an opening no larger than the outer diameter of the distal end of said delivery shaft.

3. A method as recited in claim19, further comprising the step of pulling said trained portion back into said delivery shaft.

4. A method as recited in claim19, wherein said trained portion comprises the entire arm.

5. A method as recited in claim19, wherein said trained portion comprises less than the entire arm.

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