US20070276361A1 - Method and apparatus for adjusting electrode dimensions - Google Patents

Abstract

Extendable and expandable ablation electrodes are disclosed. Electrophysiology catheter systems include ablation electrodes that maintain a reduced cross-sectional profile during introduction into a patient and are extendable and/or expandable once positioned at a lesion site. The expanded electrodes having a larger length or and/or diameter can help to produce large lesions. Controllability of the dimensions of the ablation electrodes may be improved.

Description

RELATED APPLICATIONS
• This application claims priority under 35 U.S.C. § 19(e) to U.S. Provisional Application Ser. No. 60/458,489, entitled “Electrode for Electrophysiology Catheter Having an Eccentric Surface”, filed on Mar. 28, 2003, U.S. Provisional Application Ser. No. 60/458,490, entitled “Electrophysiology Catheter Allowing Adjustment Between Electrode and Tissue Gap”, filed on Mar. 28, 2003, U.S. Provisional Application Ser. No. 60/458,491, entitled “Shape Shifting Electrode Geometry for Electrophysiology Catheters”, filed on Mar. 28, 2003, U.S. Provisional Application Ser. No. 60/458,643, entitled “Method and Apparatus for Selecting Temperature/Power Set Points in Electrophysiology Procedures”, filed on Mar. 28, 2003, and U.S. Provisional Application Ser. No. 60/458,856, entitled “Catheter Tip/Electrode Junction Design for Electrophysiology Catheters” filed on Mar. 28, 2003, all five of which are each incorporated herein by reference in their entireties.
BACKGROUND OF INVENTION
• 1. Field of Invention
• The invention relates to medical devices and methods for performing ablation procedures. More particularly, the invention relates to methods and apparatus for extending and/or retracting ablation electrode surfaces in vivo.
• 2. Discussion of Related Art
• The human heart is a very complex organ, which relies on both muscle contraction and electrical impulses to function properly. The electrical impulses travel through the heart walls, first through the atria and then the ventricles, causing the corresponding muscle tissue in the atria and ventricles to contract. Thus, the atria contract first, followed by the ventricles. This order is essential for proper functioning of the heart.
• Over time, the electrical impulses traveling through the heart can begin to travel in improper directions, thereby causing the heart chambers to contract at improper times. Such a condition is generally termed a cardiac arrhythmia, and can take many different forms. When the chambers contract at improper times, the amount of blood pumped by the heart decreases, which can result in premature death of the person.
• Techniques have been developed which are used to locate cardiac regions responsible for the cardiac arrhythmia, and also to disable the short-circuit function of these areas. According to these techniques, electrical energy is applied to a portion of the heart tissue to ablate that tissue and produce scars which interrupt the reentrant conduction pathways or terminate the focal initiation. The regions to be ablated are usually first determined by endocardial mapping techniques. Mapping typically involves percutaneously introducing a catheter having one or more electrodes into the patient, passing the catheter through a blood vessel (e.g. the femoral vein or artery) and into an endocardial site (e.g., the atrium or ventricle of the heart), and deliberately inducing an arrhythmia so that a continuous, simultaneous recording can be made with a multichannel recorder at each of several different endocardial positions. When an arrythormogenic focus or inappropriate circuit is located, as indicated in the electrocardiogram recording, it is marked by various imaging or localization means so that cardiac arrhythmias emanating from that region can be blocked by ablating tissue. An ablation catheter with one or more electrodes can then transmit electrical energy to the tissue adjacent the electrode to create a lesion in the tissue. One or more suitably positioned lesions will typically create a region of necrotic tissue which serves to disable the propagation of the errant impulse caused by the arrythromogenic focus. Ablation is carried out by applying energy to the catheter electrodes. The ablation energy can be, for example, RF, DC, ultrasound, microwave, or laser radiation.
• Atrial fibrillation together with atrial flutter are the most common sustained arrhythmias found in clinical practice.
• Another source of arrhythmias may be from reentrant circuits in the myocardium itself. Such circuits may not necessarily be associated with vessel ostia, but may be interrupted by means of ablating tissue either within the circuit or circumscribing the region of the circuit. It should be noted that a complete ‘fence’ around a circuit or tissue region is not always required in order to block the propagation of the arrhythmia; in many cases simply increasing the propagation path length for a signal may be sufficient. Conventional means for establishing such lesion ‘fences’ include a multiplicity of point-by-point lesions, dragging a single electrode across tissue while delivering energy, or creating an enormous lesion intended to inactivate a substantive volume of myocardial tissue.
• The size of a lesion is dependent on many factors, including energy emission and electrode size. Generally, higher applications of electrical power and larger electrodes lead to larger lesion sizes. However, overly high energy delivery can lead to undesirable effects such as tissue desiccation or charring, and in some circumstances, blood coagulation. Increased electrode dimensions present problems with insertion into a patient and introduction into the heart because the larger dimensions can make it difficult to maneuver a catheter through arteries and veins.
SUMMARY OF INVENTION
• Embodiments of the present invention encompass apparatus and method for creating lesions in heart tissue (ablating) to create a region of necrotic tissue which serves to disable the propagation of errant electrical impulses caused by an arrhythmia. Embodiments of the present invention also encompass apparatus and methods for adjusting the dimensions of ablation electrodes that are positioned in a patient.
• In one embodiment, a catheter comprises a longitudinal catheter shaft for positioning an ablation electrode within a patient's body. An ablation electrode is disposed on the shaft and has an outer surface. The electrode is convertible from a first configuration in which the electrode outer surface has a first axial size and a first radial size to a second configuration in which the electrode outer surface has a second axial size and maintains the first radial size.
• According to another embodiment, a catheter comprises a longitudinal catheter shaft for positioning an ablation electrode within a patient's body. An ablation electrode is disposed on the shaft and has an outer surface. The electrode is convertible from a first configuration in which the electrode outer surface has a first axial size and a first radial size to a second configuration in which the electrode outer surface has a second radial size and maintains the first axial size.
• In a further embodiment, a catheter comprises a longitudinal catheter shaft for positioning an ablation electrode within a patient's body. An ablation electrode is disposed on the shaft, and the electrode has a continuous outer ablating surface area that is adjustable. The electrode is substantially comprised of metal.
• According to another embodiment, a catheter shaft comprises an outer shaft portion having a longitudinal passage extending through an outer surface, an inner shaft portion, and an electrode surface with a first end and a second end. The first end is coupled to the inner shaft portion, and the second end is coupled to the outer shaft portion. The electrode surface passes through the longitudinal passage. One of the outer shaft portion and the inner shaft portion is rotatable relative to the other of the outer shaft portion and the inner shaft portion, and relative rotation of the inner shaft portion and the outer shaft portion extends the electrode surface in a radial direction away from the outer shaft portion.
• According to another embodiment, a catheter shaft comprises an outer shaft portion having a passage extending through an outer surface, an inner shaft portion, an ablation electrode member configured to pass through the passage, and a biasing element that biases the electrode member.
BRIEF DESCRIPTION OF DRAWINGS
• The accompanying drawings are not intended to be drawn to scale. In the drawings, like components that are illustrated in various figures are represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:
• FIG. 1 illustrates a catheter system according to embodiments of the present invention;
• FIG. 2 illustrates a perspective view of a portion of a catheter shaft and an electrode according to one embodiment of the present invention;
• FIG. 3 illustrates a perspective view of the embodiment shown inFIG. 2 with the electrode extended axially.
• FIG. 4 illustrates a perspective view of a portion of a catheter shaft and an electrode according to another embodiment of the invention;
• FIG. 5 illustrates the embodiment shown inFIG. 4 with an electrode surface expanded radially;
• FIG. 6 illustrates a perspective view of another embodiment of a portion of a catheter shaft with an electrode surface in a retracted configuration;
• FIG. 7 illustrates a cross-sectional view of the embodiment shown inFIG. 6 in a retracted configuration;
• FIG. 8 illustrates a cross-sectional view of the embodiment shown inFIG. 6 in an expanded configuration;
• FIG. 9 illustrates a perspective view of a portion of a catheter shaft and an electrode that includes extendable fins according to another embodiment of the invention;
• FIG. 10 illustrates a cross-sectional view of the embodiment shown inFIG. 9 with the fins in a retracted configuration;
• FIG. 11 illustrates a cross-sectional view of the embodiment shown inFIGS. 9 and 10 with the fins in an extended configuration;
• FIG. 12 illustrates a cross-sectional view of another embodiment of an electrode that includes extendable fins in a retracted configuration; and
• FIG. 13 illustrates a cross-sectional view of the embodiment shown inFIG. 12 with the fins in an extended configuration.
DETAILED DESCRIPTION
• This invention is not limited in its application to the details of construction and the arrangement of components and acts set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing”, “involving”, and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.
• In ablation procedures, lesion size may be improved by increasing the surface extension of an ablation electrode. By extending the surface geometry of the electrode radially, the reach of the electrical potential field created by the ablation electrode extends further into the ablation domain. It is desirable, however, to limit the cross-sectional size of catheters being inserted into patients. As a catheter is maneuvered through the vasculature, small sizes and flexibility are preferred.
• Longer electrode sizes can also improve the uniformity of lesions by reducing the number of electrodes used. With a single, long electrode, overlapping electric fields and gaps in tissue ablation may be reduced. Longer electrodes, however, can reduce the flexibility of catheters, which may be undesirable when maneuvering a catheter within a patient.
• Embodiments of the invention include expandable electrodes that may provide large surface areas for ablation procedures, but may maintain reduced cross-sectional profiles when being maneuvered through a patient's veins or arteries.
• System Overview
• Reference is now made toFIG. 1, which figure illustrates an overview of an ablation catheter system in accordance with embodiments of the present invention. The system includes acatheter10 having ashaft portion12, acontrol handle14, and aconnector portion16. Acontrol module8 is connected toconnector portion16 via cable6. An ablation energy supply4 may be connected to controlmodule8 viacable3.Control module8 is used to control ablation energy provided by ablation energy supply4 tocatheter10. Ablation energy may include, as examples, RF, microwave, DC, ultrasound, or laser radiation. Although illustrated as separate devices, ablation energy supply4 andcontrol module8 may be incorporated into a single device.
• In this description, various aspects and features of embodiments of the present invention will be described. The various features of the embodiments of the invention are discussed separately for clarity. One skilled in the art will appreciate that the features may be selectively combined in a device depending upon the particular application. Furthermore, any of the various features may be incorporated in a catheter and associated methods of use for ablation procedures.
• Catheter Overview
• Still referring toFIG. 1,catheter10 may include a distal tip electrode18 and/or one ormore ring electrodes20. Distal tip electrode18 may be affixed to the distal tip ofshaft12 in such a manner as to not move relative to the distal tip, or distal tip electrode18 may be moveable relative toshaft12.Catheter10 may be a steerable device.FIG. 1 illustrates the distal tip portion18 being deflected by the mechanism contained within control handle14. Control handle14 may include a rotatable thumb wheel (not shown) which can be used by a user to deflect the distal end of the catheter. The thumb wheel (or any other suitable actuating device) is connected to one or more pull wires which extend throughshaft portion12 and are connected to the distal end18 of the catheter at an off-axis location, whereby tension applied to one or more of the pull wires causes the distal portion of the catheter to curve in a predetermined direction or directions.
• Electrodes with Adjustable Dimensions
• In producing long lesions, it may be desirable to use a continuous electrode that extends longitudinally along a catheter shaft. A series of ring electrodes that are spaced axially from one another may not reach all targeted tissue with adequate electrical potential. The potential fields of the series of electrodes do not necessarily sufficiently reach one another and certain volumes of tissue may not receive transmitted energy. Attempts to ablate those tissue volumes by increasing the power applied to the ring electrodes might result in overlapping potential fields that could lead to tissue overheating.
• A single, long electrode may help to create a continuous lesion with a more uniform temperature and/or power distribution. Because electrodes are typically made with stiff materials such as metals, long electrodes can reduce the maneuverability of the catheter through arteries and veins. It would be desirable to have a maneuverable catheter that positions ablation electrodes able to produce continuous lesions.
• Referring now toFIG. 2, one embodiment of an axially extendableablation electrode assembly100 is illustrated. In a retracted configuration, the shorter axial length of anelectrode102 does not reduce the maneuverability of the catheter as much as a longer electrode of similar stiffness might. In an extended configuration, the longer length of the electrode may be capable of producing long lesions in a target tissue volume which are more uniform than lesions created by a series of separate electrodes.
• In the retracted configuration, as illustrated, anouter electrode portion104 encompassesinner electrode portions106 and108. Twoadditional electrode portions110 and112 are not visible in this configuration, but are illustrated inFIG. 3. Alongitudinal slot114 is disposed alongshaft12 such thatinner electrode portion108 may be connected to pullwires116 and118. Any suitable barrier may be included inlongitudinal slot114 to prevent penetration of blood but allowinner electrode portion108 to remain connected to pullwires116 and118.
• In some embodiments, one electrode portion, such as theinnermost electrode portion108, is connected to anelectrical lead120 that delivers energy toelectrode102. The other electrode portions may remain electrically connected to ablation energy supply4 by staying in electrical contact with an adjacent electrode portion regardless of whetherelectrode assembly100 is in the retracted or extended configuration. In other embodiments, each electrode portion may be separately connected toelectrical lead120.
• Electrode102 is shown in an axially extended configuration inFIG. 3.Inner electrode portions106 and108 may be moved alongcatheter shaft12 by pulling onpull wire116. This pulling may be achieved with any suitable actuating device oncontrol handle14. Pullwire116 may be attached to only one inner electrode portion, such asinner electrode portion108, which then pulls oninner electrode portion106 upon reaching a certain extension. In other embodiments, pullwire116 may be attached to multiple electrode portions, or there may be multiple pull wires. In this embodiment, pullwire118 is used to retractinner electrode portion108. Pullwire118 may pass through a pulley (not shown) or around a standoff (not shown) insideshaft12 so that tension applied in the direction of control handle14 movesinner electrode portion108 towardouter electrode portion104.
• Instead of passingpull wires116,118 throughslot114, pullwires116,118 may be attached to slidable magnets on an inner surface ofshaft12. Magnetically coupling these magnets to magnets attached to the electrode portions allows thepull wires116,118 to move the electrode portions without the use of a slot or other passage. In other embodiments, a series of electromagnets mounted internally or externally onshaft12 may be consecutively energized to move electrode portions alongshaft12.
• Oneouter electrode portion104 and fourinner electrode portions106,108,110,112 are provided in the embodiment illustrated inFIGS. 2 and 3, but a greater or lesser number of inner electrode portions may be included.Inner portions106,108,110,112 do not necessarily have to be positioned entirely withinouter electrode portion104 in a retracted configuration. In some embodiments, extended configurations may provide forelectrode portions104,106,108,110,112 that do not form a singlecontinuous electrode102. In these embodiments, the electrode portions may be axially spaced from one another upon extension.
• Typically, the further an ablation electrode extends radially from an catheter shaft, the larger the volume of tissue that can be ablated because a larger electrode can extend the potential field further into the domain than a smaller electrode. The diameter of an ablation electrode is limited, however, because the catheter and electrodes move through a patient's arteries and/or veins. An electrode with a large diameter also may be difficult to initially introduce into a patient.
• One embodiment of anelectrode assembly200 that extends an ablation electrode surface radially is illustrated inFIGS. 4 and 5. In a retracted configuration, shown inFIG. 4, anelectrode surface202 is held closely to anouter shaft portion204 such that a cross-sectional profile ofelectrode assembly200 is not much larger thanshaft12. In an expanded configuration, as illustrated inFIG. 5,electrode surface202 is extended radially away fromshaft12. In the expanded configuration,electrode surface202 may have a larger cross-sectional profile and extends further fromshaft12 than a non-expandable electrode that is sized to be maneuverable within a patient.
• Of course in some embodiments, even in an expanded configuration,electrode assembly200 may be smaller than non-expandable electrodes which are sized to be maneuverable within a patient. Control of the size ofelectrode surface202 may be one objective for the use of an electrode assembly such aselectrode assembly200, rather than increasing electrode size beyond a typically maneuverable size. By using a metal plate, metal sheet, or other stiff materials in constructing an electrode assembly, the dimensions and/or placement of an electrode surface may be known or measured to a greater accuracy than electrode surfaces associated with balloon inflation or flexible surfaces.
• In the embodiment illustrated inFIG. 4,outer shaft portion204 is positioned over aninner shaft portion206.Electrode surface202, which in this embodiment is a flexible metal plate, is attached toouter shaft portion204 along afirst end208. The metal plate extends aroundouter shaft portion204, passes through aslot210, and a second end (not shown inFIG. 4) of the metal plate attaches toinner shaft portion206.
• Rotation ofouter shaft portion204 relative toinner shaft portion206 adjustselectrode surface202 between the retracted configuration and the expanded configuration. In the embodiment illustrated inFIG. 4,inner shaft portion206 comprisesshaft12. In other embodiments,inner shaft portion206 may comprise an element that is not a part ofshaft12 or not integral toshaft12.
• Electrode surface202 includes an electrically-conductive material such as platinum, silver, gold, chromium, aluminum, tungsten, or any other suitable electrically-conductive material. In some embodiments,electrode surface202 is substantially comprised of an electrically-conductive material such as metal, that is,electrode surface202 is not made up of a non-conductive material that is coated with a conductive material.
• In another embodiment, illustrated inFIGS. 6-8,outer shaft portion204 isshaft12, whileinner shaft portion206 extends axially for approximately the length ofelectrode surface202. With this arrangement,electrode surface202 may be held directly againstshaft12 such that the cross-sectional profile ofelectrode assembly200 is slightly larger than the cross-sectional profile ofshaft12.FIG. 6 showselectrode surface202 in a retracted configuration. Of course,inner shaft portion204 may extend for a greater length thanelectrode surface202.
• FIG. 7 shows a cross-section ofelectrode assembly200 in a retracted configuration.Inner shaft portion206 is rotated clockwise to pull a section ofelectrode surface202 insideouter shaft portion204 through aslot210 inouter shaft portion204. Because of the reduced length ofelectrode surface202 that remains on the exterior ofouter shaft portion204,electrode surface202 moves inwardly towardouter shaft portion204 and decreases the overall diameter ofelectrode assembly200.
• Electrode surface202 is attached toouter shaft portion204 by passingfirst end208 of electrode surface through aslot212 inouter shaft204 and fixingfirst end208 to aninside surface214 ofouter shaft portion204. Similarly,second end209 may be attached toinner shaft portion206 by passingsecond end209 through aslot216 ininner shaft portion206. As should be evident to one of skill in the art, other suitable methods of attachingfirst end208 andsecond end209 to their respective shaft portions may be employed.
• FIG. 8 showselectrode assembly200 in an expanded configuration.Inner shaft portion206 is rotated counterclockwise to force a section ofelectrode surface202 outside ofouter shaft portion204 throughslot210. With a longer length ofelectrode surface202 exterior to theouter shaft portion204, the diameter ofelectrode assembly300 is increased.
• In some embodiments, electrode assemblies may be provided that allow adjustment of electrode dimensions in both the radial direction and the axial direction. Such embodiments may include combinations of structures disclosed herein or equivalents.
• An electrode surface that extends fromshaft12 along certain radii may allow for deeper embedding of an electrode surface into tissue. Additionally, electric fields may be more directed than with cylindrical electrodes.
• One embodiment of anelectrode assembly300 that allows for the extension and retraction of an electrode surface along certain radii is illustrated inFIG. 9. In this embodiment, twofins302 are extendable fromshaft12. Twofins302 are shown in this embodiment, but any suitable number of fins may be used such as one fin, three fins, four fins, etc. With retractable fins,shaft12 may be maneuvered through the patient with a limited cross-sectional diameter. Once satisfactorily positioned,fins302 may be extended. As shown inFIG. 10,fins302 may be attached to aninner shaft portion306 that is rotatable relative to anouter shaft portion304. In this embodiment,outer shaft portion302 isshaft12. In other embodiments,inner shaft portion306 may beshaft12 andouter shaft portion204 may comprise a collar that is mounted aroundshaft12.
• In the illustrated embodiment ofFIGS. 9-11, rotation ofinner shaft portion304 clockwise relative toouter shaft portion306 pullsfins302 inwardly throughslots310 inouter shaft portion304.
• Fins302 may be constructed with an electrically-conductive material that is flexible enough to be extended and retracted throughslots310. In further embodiments,fins302 may be constructed of a non-electrically conducting material, such as a plastic or a rubber, that is coated with an electrically-conductive coating.
• As shown inFIG. 11, clockwise rotation ofinner shaft portion306 relative toouter shaft portion304pushes fins302 throughslots310 to extend them beyond anouter surface318 ofouter shaft portion304.Fins302 may be of any suitable shape, and they may extend further in the circumferential direction than an axial direction.
• Referring now toFIG. 12,electrode assembly400 includes a cam arrangement to extendfins402. In this arrangement, aneccentric shaft406 is rotated to pushfins402 beyond anouter surface418 ofshaft12. A biasing element, such as aspring420, presses against aninner surface422 ofshaft12 and astop424 that is attached tofin402. In this manner, wheneccentric shaft406 is oriented as shown inFIG. 12,fins402 are urged inward ofouter surface418. Wheneccentric shaft406 is oriented as shown inFIG. 13,fins402 are urged outward ofouter surface418. In some embodiments, rotation ofeccentric shaft406 may be achieved with an actuator oncontrol handle14.
• Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Claims (31)

1. A catheter comprising:

a longitudinal catheter shaft for positioning an ablation electrode within a patient's body; and

an ablation electrode disposed on the shaft and having an outer surface, wherein the electrode is convertible from a first configuration in which the electrode outer surface has a first axial size and a first radial size to a second configuration in which the electrode outer surface has a second axial size and maintains the first radial size.

2. The catheter according toclaim 1, wherein the ablation electrode comprises a first electrode portion and a second electrode portion, the second electrode portion having a length and being moveable in the axial direction of the catheter, wherein in the first configuration more of the second electrode portion length is contained within the first electrode portion than in the second configuration.

3. The catheter according toclaim 2, wherein in the first configuration, the second electrode portion length is fully contained within the first electrode portion.

4. The catheter according toclaim 2, wherein the ablation electrode comprises a third electrode portion that is at least partially contained within the second electrode portion in the first configuration.

5. The catheter according toclaim 2, wherein a pull wire is connected to the second electrode portion.

6. The catheter according toclaim 1, wherein the ablation electrode is a ring electrode.

7. The catheter according toclaim 6, wherein the first electrode portion and the second electrode portion are cylindrical.

8. A catheter comprising:

a longitudinal catheter shaft for positioning an ablation electrode within a patient's body; and

an ablation electrode disposed on the shaft and having an outer surface, wherein the electrode is convertible from a first configuration in which the electrode outer surface has a first axial size and a first radial size to a second configuration in which the electrode outer surface has a second radial size and maintains the first axial size.

9. The catheter according toclaim 8, further comprising an inner shaft portion and an outer shaft portion, the outer shaft portion having a longitudinal slot, wherein

the ablation electrode comprises a flexible, electrically-conductive plate having a first end and a second end; and

the first end is attached to the outer shaft portion, the plate passes through the longitudinal slot, and the second end is attached to the inner shaft portion.

10. The catheter according toclaim 9, wherein rotation of the inner shaft portion relative to the outer shaft portion converts the electrode from the first configuration to the second configuration.

11. A catheter comprising:

a longitudinal catheter shaft for positioning an ablation electrode within a patient's body; and

an ablation electrode disposed on the shaft, the electrode having a continuous outer ablating surface area, wherein the outer ablating surface area is adjustable; and wherein

the electrode is substantially comprised of metal.

12. The catheter according toclaim 11, wherein the electrode is substantially comprised of at least one of: platinum; silver; gold; chromium; aluminum and tungsten.

13. The catheter according toclaim 11, wherein the electrode is substantially comprised of a combination of at least two of: platinum; silver; gold; chromium; aluminum and tungsten.

14. A catheter comprising:

a longitudinal catheter shaft for positioning an ablation electrode within a patient's body; and

an ablation electrode comprising a metal sheet disposed on the shaft, the metal sheet forming an electrode outer surface that is substantially continuous along both a longitudinal direction and a circumferential direction; wherein

the electrode is convertible from a first configuration in which the electrode outer surface has a first radial size to a second configuration in which the electrode outer surface has a second radial size.

15. The catheter according toclaim 14, wherein the ablation electrode is cylindrical.

16. An ablation electrode for ablating tissue, comprising:

a first ablation electrode portion configured for mounting on a catheter shaft, the first ablation electrode portion having an outer surface configured to emit electrical energy; and

a second ablation electrode portion configured for mounting on the catheter shaft, the second ablation electrode portion having a surface configured to emit electrical energy; wherein

the second ablation electrode portion is moveable from a first position substantially inside the first ablation electrode portion to a second position substantially outside the first ablation electrode portion.

17. The ablation electrode according toclaim 16, further comprising a third ablation electrode portion configured for mounting on the catheter shaft, the third ablation electrode portion having a surface configured to emit electrical energy, wherein

the third ablation electrode portion is moveable from a first position substantially inside the second ablation electrode portion to a second position substantially outside the second ablation electrode portion.

18. The ablation electrode according toclaim 16, in combination with a longitudinal catheter shaft for positioning an ablation electrode within a patient's body, wherein the first ablation electrode and the second ablation electrode are mounted on the catheter shaft.

19. The combination according toclaim 18, further comprising a pull wire configured to move the second electrode portion.

20. A catheter shaft comprising:

an outer shaft portion having a longitudinal passage extending through an outer surface;

an inner shaft portion;

an electrode surface with a first end and a second end, the first end coupled to the inner shaft portion, and the second end coupled to the outer shaft portion, wherein

the electrode surface passes through the longitudinal passage;

one of the outer shaft portion and the inner shaft portion is rotatable relative to the other of the outer shaft portion and the inner shaft portion; and

relative rotation of the inner shaft portion and the outer shaft portion extends the electrode surface in a radial direction away from the outer shaft portion.

21. The catheter shaft according toclaim 20, wherein relative rotation of the inner shaft portion and the outer shaft portion retracts the electrode surface in a radial direction toward the outer shaft portion.

22. The catheter shaft according toclaim 20, wherein the inner shaft portion and the outer shaft portion are cylindrical.

23. The catheter shaft according toclaim 20, wherein the electrode surface comprises at least one of: platinum; silver; gold; chromium; aluminum and tungsten.

24. A catheter shaft comprising:

an outer shaft portion having a passage extending through an outer surface;

an inner shaft portion;

an ablation electrode member configured to pass through the passage; and

a biasing element that biases the electrode member.

25. The catheter shaft according toclaim 24, wherein the inner shaft portion is configured to urge the ablation electrode member through the passage in a direction away from the inner shaft portion when the inner shaft portion rotates.

26. The catheter shaft according toclaim 25, wherein the biasing element is configured to bias the electrode member toward the inner shaft member.

27. The catheter shaft according toclaim 26, wherein the passage is a longitudinal slot.

28. the catheter shaft according toclaim 27, wherein the ablation electrode member is a fin.

29. The catheter shaft according toclaim 27, comprising two ablation electrode members.

30. The catheter shaft according toclaim 27, wherein the two ablation electrode members extend in opposite directions to one another.

31. The catheter according toclaim 24, wherein the ablation electrode member is comprised substantially of metal.

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