Abstract:
An introducer sheath has multiple distal slots allowing for translation of a catheter within a cardiac cavity. A pair of longitudinal slots are provided on opposite sides of the sheath near the distal end. A portion of the catheter may deploy from one of the slots while the ablation tip deploys from the opposing slot. The sheath design provides greater maneuverability for the catheter in a direction orthogonal to the tissue to be ablated, while restricting lateral movement of the catheter. The longitudinal direction of the slots further aids in the formation of linear lesions using the catheter.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     a. Field of the Invention  
         [0002]     The instant invention is directed toward an introducer sheath for use in delivering a catheter for endocardial applications. The introducer sheath has multiple distal slots allowing for translation of the catheter within a cardiac cavity.  
         [0003]     b. Background Art  
         [0004]     Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures an introducer sheath is inserted into a vessel located near the surface of a human body and is guided to a specific location within the body. A catheter is then inserted into the sheath and guided to the desired location for examination, diagnosis, and treatment. For example, one procedure often referred to as “catheter ablation” utilizes a catheter to convey an electrical stimulus to a selected location within the human body to create tissue necrosis. Another procedure oftentimes referred to as “mapping” utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body.  
         [0005]     In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node located in the right atrium to the atrialventricular (AV) node and then along a well defined route which includes the His-Purkinje system into the left and right ventricles. Sometimes abnormal rhythms occur in the atrium which are referred to as atrial arrhythmia. Three of the most common arrhythmia are ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmia can result in significant patient discomfort and even death because of a number of associated problems, including the following: (1) an irregular heart rate, which causes a patient discomfort and anxiety; (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure; and (3) stasis of blood flow, which increases the vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause for the arrhythmia although it is believed that the principal mechanism is one or a multitude of stray circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included significant usage of various drugs. In some circumstances drug therapy is ineffective and frequently is plagued with side effects such as dizziness, nausea, vision problems, and other difficulties.  
         [0006]     An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia involves the ablation of tissue in the heart to cut off the path for stray or improper electrical signals. Such procedures are performed many times with an ablation catheter. Typically, the introducer sheath is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the introducer sheath reaches the desired location for the ablation procedure in the heart. The ablation catheter is then delivered through the introducer sheath to the procedure location. The ablation catheters commonly used to perform these ablation procedures produce lesions and electrically isolate or render the tissue non-contractile at particular points in the cardiac tissue by physical contact of the cardiac tissue with an electrode of the ablation catheter and application of energy. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate arrhythmia.  
         [0007]     One difficulty in obtaining an adequate ablation lesion using conventional ablation catheters is the constant movement of the heart, especially when there is an erratic or irregular heart beat. Another difficulty in obtaining an adequate ablation lesion is caused by the inability of conventional catheters to obtain and retain uniform contact with the cardiac tissue across the entire length of the ablation electrode surface. Without such continuous and uniform contact, any ablation lesions formed may not be adequate.  
         [0008]     It is well known that benefits may be gained by forming lesions in tissue if the depth and location of the lesions being formed can be controlled. In particular, it can be desirable to elevate tissue temperature to around 50° C. until lesions are formed via coagulation necrosis, which changes the electrical properties of the tissue. For example, when sufficiently deep lesions are formed at specific locations in cardiac tissue via coagulation necrosis, undesirable ventricular tachycardias and atrial flutter may be lessened or eliminated. “Sufficiently deep” lesions means transmural lesions in some cardiac applications.  
         [0009]     Current techniques for creating continuous linear lesions in endocardial applications include, for example, dragging a conventional catheter on the tissue, using an array electrode, or using pre-formed electrodes. Ablation catheters are not presently designed to be translated within the atria while ablating to form linear lesions. Further, introducer sheaths of present design provide little assistance to the ablation procedure other than delivering the catheter to the appropriate cardiac cavity. Present catheter designs either require significant technical skill on the part of the surgeon in guiding and placing the catheter by sensitive steering mechanisms. Because of the technical difficulty of operating catheters with such steering mechanisms, ablation procedures can be very time consuming, sometimes taking over three hours or more. Such an extended length of time can exacerbate patient discomfort, both physically and emotionally. In addition, x-ray fluoroscopy is often used throughout the procedure to locate the distal end of the catheter to ensure that it is in the proper location. Clinicians are therefore exposed to significant amounts of radiation on a regular basis because of the lengthy time required for these procedures with present technology.  
         [0010]     A particular difficulty encountered with existing ablation catheters is assurance of adequate tissue contact. All of these devices comprise rigid electrodes that do not always conform to the tissue surface, especially when sharp gradients and undulations are present, such as at the ostium of the pulmonary vein in the left atrium and the isthmus of the right atrium between the inferior vena cava and the tricuspid valve. Consequently, continuous linear lesions are difficult to achieve. With present rigid catheters of uniform construction, it can be quite difficult to maintain sufficient contact pressure until an adequate lesion has been formed. This problem is exacerbated on contoured or trabecular surfaces. If the contact between the electrode and the tissue cannot be properly maintained, a quality lesion is unlikely to be formed.  
         [0011]     Thus, there remains a need for an ablation instrument that addresses these issues with the existing designs and that permits the formation of uniform spot and continuous linear lesions, including transmural lesions, on smooth or contoured surfaces, and that provides an ease of use not found in previous designs.  
         [0012]     The information included in this background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention is to be bound.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     The present invention is an introducer sheath for use with an ablation catheter in endocardial application. The introducer sheath is particularly advantageous for use with a catheter in the ablation of a sloped, trabecular surface of endocardial tissue in the right atrium. The introducer sheath has multiple distal slots allowing for translation of the catheter within the cardiac cavity. A pair of longitudinal slots are provided on opposite sides of the sheath near the distal end to allow the catheter to deploy within the cardiac cavity. A portion of the catheter may deploy from one of the slots while the ablation tip deploys from the opposing slot. The sheath design provides greater maneuverability for the catheter in a direction orthogonal to the tissue to be ablated, while restricting lateral movement of the catheter. The longitudinal direction of the slots further aids in the formation of linear lesions using the catheter.  
         [0014]     In one embodiment of the invention, the introducer sheath is composed of a proximal portion, a distal portion, and a spanning member. The spanning member is proximal and adjacent to the distal portion and distal and adjacent to the proximal portion. The spanning member further defines a first longitudinal slot along one side of the introducer sheath and a second longitudinal slot along an opposite side of the introducer sheath. The first slot may be longitudinally offset from the second slot. The first slot may also be the same length as the second slot and oriented symmetrically with the second slot. The width of the first slot allows for deployment of a catheter through the first slot; and the width of the second slot allows for deployment of the catheter through the second slot simultaneously with deployment of the catheter through the first slot.  
         [0015]     In another embodiment, the sheath is composed of an elongated shaft and a spanning member interposed along the elongated shaft. The spanning member is proximal to a distal end of the sheath. The spanning member further defines a first longitudinal slot in a sidewall of the spanning member and a second longitudinal slot in the sidewall of the spanning member spaced circumferentially opposite the first longitudinal slot. The width of the first slot allows for deployment of a catheter through the first slot and the width of the second slot allows for deployment of the catheter through the second slot simultaneously with deployment of the catheter through the first slot.  
         [0016]     Other features, details, utilities, and advantages of the present invention will be apparent from the following more particular written description of various embodiments of the invention as further illustrated in the accompanying drawings and defined in the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is an isometric view of an ablation catheter according to one embodiment of the present invention with a sheath substantially cut away.  
         [0018]      FIG. 2  is an isometric view of the ablation catheter of  FIG. 1  detailing several component sections of the catheter.  
         [0019]      FIG. 3  is a top isometric view of an introducer sheath for use with the ablation catheter of  FIG. 1  detailing several component sections of the sheath.  
         [0020]      FIG. 4  is a bottom isometric view of the introducer sheath of  FIG. 3  detailing several component sections of the sheath.  
         [0021]      FIG. 5  is an isometric view of the catheter of  FIG. 1  carried within the sheath of  FIG. 3 .  
         [0022]      FIG. 6  is an isometric view of the catheter of  FIG. 1  unfurling from within the sheath of  FIG. 3 .  
         [0023]      FIG. 7  is a cross-section view, taken along line  7 - 7  of  FIG. 5 , of the catheter ablation electrode carried within the sheath.  
         [0024]      FIG. 8  is a cross-section view, taken along line  8 - 8  of  FIG. 5 , of the catheter and ablation electrode within the sheath.  
         [0025]      FIG. 9  is a cross-section view, taken along line  9 - 9  of  FIG. 6 , of the catheter and ablation electrode unfurling from within the sheath.  
         [0026]      FIG. 10  is an enlarged view of the circled region of  FIG. 9  detailing a brush electrode and revealing a conductor making electrical contact with the filaments comprising the brush electrode, and depicting a secondary lead (e.g., for a thermocouple) extending adjacent to the conductor and becoming embedded within the brush filaments.  
         [0027]      FIG. 11  is an isometric schematic of the various component materials forming the catheter of the present invention.  
         [0028]      FIG. 12  is a cross-section of a catheter formed of the material components of  FIG. 1 .  
         [0029]      FIGS. 13 and 14  are isometric schematics of the ablation catheter and sheath of  FIGS. 1-10  depicting a method of creating a linear lesion in the right atrium.  
         [0030]      FIG. 15  is an isometric schematic of an alternate embodiment of the ablation catheter of the present invention with a ball electrode depicted in situ in the right atrium. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Several embodiments of an endocardial ablation system  2 , including an ablation catheter  4  with an armature-type suspension system, an introducer sheath  6 , and an ablation electrode  8 , according to the present invention is depicted in the figures. As described further below, the endocardial ablation system  2  of the present invention provides a number of advantages, including, for example, mitigating electrode-tissue contact problems. The suspension system of the ablation catheter  4  facilitates enhanced tissue contact in difficult environments (e.g., during ablation of a contoured or trabecular surface on a beating heart), whether creating a spot lesion or a continuous linear lesion, by facilitating contact of the ablation electrode  8  with surface contours of endocardial tissue. This is particularly useful for treatment of atrial flutter where it is desirable to create a linear lesion along the trabecular slope of the isthmus between the ostium of the inferior vena cava and the tricuspid valve in the right atrium.  
         [0032]      FIG. 1  is an isometric view of one embodiment of a catheter  4 , emerging from a sheath  6  that has been cut away, with an ablation electrode  8  attached to the distal end of the catheter  4 . (As used herein, “proximal” refers to a direction away from the body of a patient and toward the clinician. In contrast, “distal” as used herein refers to a direction toward the body of a patient and away from the clinician.) The catheter  4 , sheath  6 , and ablation electrode  8  together form the endocardial ablation system  2  depicted in detail  FIGS. 5-9 . The catheter  4  is designed for insertion within a main lumen  10  of the sheath  6  (see  FIG. 3 ). Axiomatically, the diameter of the main lumen  10  is sized to accommodate the outer diameter of the catheter  4 .  
         [0033]     As shown in  FIG. 2 , the catheter  4  is a component-built catheter, in this embodiment divided into three sections, a proximal section  14 , a suspension section  16 , and a distal section  18 . The suspension section  16  is located between the proximal section  14  and the distal section  18 . In this embodiment, both the proximal section  14  and the distal section  18  are of a more rigid construction than the suspension section  16 , which is comparatively pliant. While more rigid than the suspension section  16 , the proximal section  14  and the distal section  18  may each have different levels of stiffness or rigidity. In other embodiments it may be desirable to include additional component sections of varying degrees of rigidity depending upon the need of the procedure to be performed. For example, a distal tip of the distal section  18  might be formed of a soft or pliable material to minimize abrasion of the endocardial tissue. If desirable, certain of the component sections may be formed with curved shapes to assist the placement of the catheter  4  based upon the anatomy of the heart. For example, as shown in  FIG. 2 , the distal section  18  has a slight curve at its proximal end. The suspension section  16  may also have a curve to initiate the orientation of the distal section  18  of the catheter  4  out of the lower port  28 . The arc or radius of curvature of a particular section may be selected to allow the catheter  4  to appropriately “fit” in various sizes of heart cavities, to position the catheter  4  with respect to a particular tissue location for ablation application, or to orient the attached ablation electrode  8  at a particular angle or direction. However, each of the sections of the catheter  4  is pliant compared to the sheath  6  and, when introduced into the sheath  6 , each of the sections of the catheter  4  is constrained by the sheath  6  and conforms to the orientation of the sheath  6 .  
         [0034]     As shown in  FIG. 2 , the catheter  4  may be formed from sections of different materials.  FIGS. 11 and 12  depict one exemplary embodiment for forming such a component catheter. The catheter wall  44  may be formed of several layers of materials to ultimately create a composite structure. In the embodiment of  FIGS. 11 and 12  the catheter wall is composed of an inner tube  70  of plastic, which is initially surrounded by a cylindrical braid  72  of metal fibers, for example, stainless steel fibers. The metallic braid  72  is included in the catheter wall  44  to add stability to the catheter  4  and also to resist radial forces that might crush the catheter  4 . The metallic braid  72  also provides a framework to translate torsional forces imparted by the clinician on the proximal section  14  to the distal end to rotate the catheter  4  for appropriate orientation of the ablation electrode  8 . The choice of a flat, angled braid pattern for the metallic braid  72  as depicted adds hoop strength to the catheter  4  without impacting the flexibility of the catheter  4 . Based upon the exemplary configuration of  FIG. 2 , three collinear sections of equal diameter plastic tubing abutted together surround the metallic braid  72 . A first tube  74  is composed of a first plastic material, a second tube  76  is composed of a second plastic material, and a third tube  78  is composed of a third plastic material.  
         [0035]     The component plastic sections of the catheter wall  44  may be composed, for example, of Pebax® resins (AUTOFINA Chemicals, Inc., Philadelphia, Pa.), or other polyether-block co-polyamide polymers, wherein different formulas are used to create the desired material stiffness within each section of the catheter  44 . These sections of different material enable the catheter  16  to have, for example, different mechanical properties (e.g., flexibility) at different locations along the catheter shaft. For example, the proximal section  14  of the catheter wall  44  may be formed by the first tube  74  having a relatively stiffer material formulation than the suspension section  16 , allowing for greater transfer of control exerted at the proximal end of the catheter  4  to the distal end. The suspension section  16  may be formed by the second tube  76  having a relatively more pliant material formulation than the first tube  74  of the proximal section  14  to provide a level of suspension to the distal tip  18  as further described below. The distal section  18  may be formed by the third tube  78  having a relatively more rigid material formulation to create greater stiffness than the suspension section  16  as well to provide appropriate support to the ablation electrode  8 . The inner tube  70  is generally chosen to have a relatively pliant material formulation. In an exemplary embodiment, the first tube  74  may have a hardness of  72  Shore A, the second tube may have a hardness of  55  Shore A, the third tube may have a hardness of  65  Shore A, and the inner tube may have a hardness of  40  Shore A. The distal section  18  may further be composed of a radiopaque marker to allow a clinician to visualize the position of the tip of the catheter  4  in the heart.  
         [0036]     Once the appropriate material qualities of the plastic for each of the inner, first, second, and third tubes  70 ,  74 ,  46 ,  48  are chosen, the catheter wall  44  can be fabricated. As previously described, the inner tube  70  is first surrounded by the metallic braid  72 . The first, second, and third tubes  74 ,  76 ,  78  are then placed around the metallic braid  72  and are abutted together, end-to-end. The first, second, and third tubes  74 ,  76 ,  78  may then be covered by a shrink wrap tube (not shown), if desired, to maintain the close abutment between the adjacent ends of the first, second, and third tubes  74 ,  76 ,  78 . The layered structure of the inner tube  70 , the metallic braid  72 , the first, second, and third tubes  74 ,  76 ,  78 , and the shrink wrap is then heated to a temperature at which the plastic materials composing each of the inner, first, second, and third tubes  70 ,  74 ,  76 ,  78  begins to melt. The plastic of the inner tube  70  flows through the interstices of the metallic braid  72  from the inside. Similarly, the plastic of the first, second, and third tubes  74 ,  76 ,  78  flows through the interstices of the metallic braid  72  from the outside. In this manner, the inner tube  70  is welded to the first, second, and third tubes  74 ,  76 ,  78  and the metallic braid  72  is encapsulated between them to form the catheter wall  44  as shown in  FIG. 12 . Similarly, the adjacent ends of the first tube  74  and second tube  76  are welded together and the adjacent ends of the second tube  76  and the third tube  78  are welded together. If the shrink wrap tube is used, it encapsulates the entire catheter wall  44  of the component catheter  4 . As indicated above, the various sections of the catheter  4  may be provided with preset curves. Such curvature can be imparted to the catheter  4 , for example, by placing a mandrel of a desired form in the catheter  4  and thermally setting the desired curvature to the catheter wall  44 . Although the catheter wall  44  depicted in the figures (and as shown in cross-section in  FIG. 12 ) has a circular cross section, the cross-section of the catheter wall  44  may be other than circular.  
         [0037]     The introducer sheath  6  may similarly be composed of several component sections of different materials as indicated in  FIGS. 3 and 4 . A proximal portion  20  of the sheath  6  is connected with a spanning member  22 , which is in turn connected with an anchor member  24 , which forms the distal end of the sheath  6 . Similar to the catheter  4 , the proximal portion  20  and the anchor member  24  may be composed, for example, of Pebax® resins. In this application, the hardness of the plastic formulations may be greater than that of the catheter  4  in order to guide the catheter  4  within the main lumen  10  and anchor lumen  12  of the sheath  6 . The proximal portion  20  and the anchor member  24  may be of the same or different material formulations with similar or different hardness measurements depending upon the needs of the particular procedure to be performed.  
         [0038]     The spanning member  22  may be composed of a stiffer material than both the proximal portion  20  and the anchor member  24  of the sheath  6  in order to maintain the integrity of the sheath  6 . Two opposing linear slots are formed in the wall of the spanning section  22  of the sheath  6  to create the upper port  26  and the lower port  28 . The linear slots may be between 2 and 4 cm in length. In one exemplary embodiment, these linear slots may each be about 3 cm in length. The formation of such linear slots in the sheath  6  weakens the wall of the sheath  6  because of the significant amount of material removed from the spanning member  22 . In order to provide adequate strength, the spanning member  22  may be composed, for example, of a stainless steel tube covered with an aseptic plastic, with an arc-shaped length of material removed on opposite sides of the tube. These arc shaped lengths form the upper port  26  and the lower port  28 , respectively, which are defined along the length by thin rectangular walls of remaining material. In alternate embodiments, the upper port  26  may be longer that the lower port  28  or vice versa. The proximal and distal ends of these rectangular walls are integral with tubular caps, which are attached to the proximal portion  20  of the sheath  6  on the proximal end and the anchor member  24  on the distal end. The increased structural rigidity of the spanning member  22  facilitates the stability of the sheath  6  to act as a platform for deployment of the catheter  4  from the upper port  26  and lower port  28 .  
         [0039]     In an alternate embodiment, the spanning member  22  may be formed of a shape-memory metal in order to provide sufficient tensile strength and alternately flexibility to negotiate the vasculature to reach the heart and enter an atrial chamber. For example, NiTinol, a nickel-titanium (NiTi) alloy with shape-memory properties may be used for the spanning member  22 . Shape-memory metals, such as NiTinol are materials that have been plastically deformed to a desired shape before use. Then upon heat application, either from the body as the catheter is inserted into the vasculature or from external sources, the fixation element is caused to assume its original shape before being plastically deformed. NiTinol and other shape-memory alloys are able to undergo a “martensitic” phase transformation that enables them to switch from a “temporary” shape to a “parent” shape at temperatures above a transition temperature. Below that temperature, the alloy can be bent into various shapes. Holding a sample in position in a particular parent shape while heating it to a high temperature programs the alloy to remember the parent shape. Upon cooling, the alloy adopts its temporary shape, but when heated again above the transition temperature the alloy automatically reverts to its parent shape. Alternately, or in addition, shape-memory materials may also be super elastic—able to sustain a large deformation at a constant temperature—and when the deforming force is released they return to their original undeformed shape.  
         [0040]     Common formulas of NiTinol have transformation temperatures ranging between −100 and +110° C., have great shape-memory strain, are thermally stable, and have excellent corrosion resistance, which make NiTinol exemplary for use in medical devices for insertion into a patient. For example, the spanning section  22  may be designed using NiTinol with a transition temperature around or below room temperature. Before use the sheath  6  is stored in a low-temperature state. By flushing the sheath  6  with chilled saline solution, the NiTinol spanning section  22  can be kept in its deformed state while positioning the sheath  6  at the desire site. When appropriately positioned, the flow of chilled saline solution can be stopped and the sheath  6  warmed by body heat, or warm saline can be substituted to allow the NiTinol to recover its “preprogrammed” shape.  
         [0041]     The anchor member  24  extends distally beyond the spanning member  22 . Increased stiffness of the anchor member  24  also helps provide increased structural integrity of the sheath  6 . The anchor member  24  may be pressed or anchored against tissue in a cavity of the heart, for example, an atrium wall  56  as shown in  FIGS. 13-15 , to help stabilize the endocardial ablation system  2  while the heart is beating. The anchor member  24  may be composed of a polymer of greater hardness and/or stiffness than the proximal portion  20  of the sheath  6  or it may even be composed of stainless steel or another suitable material to provide the desired rigidity and structural integrity. The anchor member  24  may terminate with an atraumatic distal tip  58  of a softer material to mitigate possible damage to the atrial wall  56 . The distal tip  58  of the anchor member may further have a radiopaque marker to help in identifying the location of the distal end of the sheath  6  during a procedure.  
         [0042]     In the particular embodiment of  FIGS. 1, 2 , and  6 - 10 , a brush electrode  8  is depicted as the ablation electrode  8 . A continuous linear lesion  54  (as shown in  FIGS. 13-14 ) is able to be formed because of the superior ability of the filaments  40  of the brush electrode  8  to maintain contact with the tissue  52  and to transfer ablative energy to the tissue  52 . In an alternative embodiment, for example, as shown in  FIG. 15 , the catheter  4  may incorporate a ball electrode  8 ′ as the ablation electrode. Although not as capable of conforming to trabecular surfaces as the brush electrode  8 , the ball electrode  8 ′ may be desired for use in certain circumstances for creating spot ablations. Other electrode tips known in the industry may alternately be used if so desired.  
         [0043]     The novel brush electrode  8  of the type depicted in  FIGS. 1, 2  and  6 - 10  was originally disclosed in U.S. patent application Ser. No. 10/808,919 filed 24 Mar. 2004, entitled  Brush Electrode and Method for Ablation , which is hereby incorporated by reference in its entirety as though fully set forth herein. As shown in greater detail in  FIGS. 7-10 , the brush electrode  8  may be composed of a plurality of filaments  40 , either conductive or nonconductive, arranged in a bundle and protruding from the distal section  18  of the catheter  4 . Such a flexible brush electrode  8  provides enhanced tissue contact, particularly for use on contoured or trabecular surfaces.  
         [0044]     The filaments  40  may be constructed from a variety of different materials, including nonconductive materials, semi-conductive materials, and conductive materials. For example, the filaments  40  may be formed from metal fibers, metal plated fibers, carbon compound fibers, and other materials. Very thin, carbon fibers may be used. Relatively thicker but less conductive Thunderon® acrylic fibers (Nihon Sanmo Dyeing Company Ltd., Kyoto, Japan) may also be used for the brush electrode filaments  40 . Nylon fibers coated with conductive material may also be used. Filaments  40  constructed from metal plated fibers, like coated nylon fibers, may comprise flattened areas around their outer surfaces, resulting in the filaments  40  having noncircular cross-sectional shapes. The brush filaments  40  may be insulated from each other, or they may be in electrical contact with each other. Conductive or nonconductive fluids may flow interstitially between and among the filaments  40  themselves or along the outer surface of the filaments  40 .  
         [0045]     An embedded portion  48  of the filaments  40  forming the brush electrode  8  may be contained within the catheter lumen  30  at the distal tip  18  of the catheter  4  while an exposed portion  46  may extend distally from the distal tip  18 . The exposed portion  46  of the brush electrode  8  may project a few millimeters from the distal tip  18  of the catheter  4 . The distance that the exposed portion  46  of the brush electrode  8  extends from the distal tip  18  of the catheter  18  varies depending upon a number of factors including the composition of the filaments  40  comprising the brush electrode  8  and the particular area to be treated with the brush electrode  8 . The distal tip  18  of the catheter  4  may itself be conductive or nonconductive.  
         [0046]      FIG. 7  is a cross-section view of the ablation system  2  as shown in  FIG. 5  with the catheter  4  and the brush electrode  8  contained within the main lumen  10  and anchor lumen  12  of the sheath  6 .  FIG. 9  is similarly a cross-section view of the ablation system  2  as shown in  FIG. 6 , in this instance with the catheter  4  and the brush electrode  8  unfurling from the lower port  28  and upper port  26  of the sheath  6 . As depicted in  FIGS. 7 and 9 , the catheter houses a conductor  32  having an insulated portion  34  and an uninsulated portion  36  that carries ablative energy (e.g., radio frequency current) from an energy source in a controller (not shown) to the brush electrode  8 . The conductor  32  extends within the catheter lumen  30  along a longitudinal axis of the catheter  4 . The conductor  32  may comprise, for example, insulated copper wire with an uninsulated portion  36  in electrical contact with the brush electrode  8 .  
         [0047]     In this embodiment, the uninsulated portion  36  of the conductor  32  is formed or tied in a loop or noose  38  around the embedded portion  48  of the filaments  40  of the brush electrode  8 , as shown to better advantage in  FIGS. 8 and 10 . At the loop or noose  38 , ablative energy is transferred from the conductor  32  to the conductive filaments  40  of the brush electrode  8 . In this embodiment, the uninsulated portion  36  of the primary conductor  32  is connected to the embedded portion  48  of the brush electrode  8  so that the connection between the conductor  32  and the brush electrode  8  is protected within the catheter wall  44 . A lead  42  may extend substantially parallel to the conductor  32 . A distal end of the lead  42  is embedded with the filaments  40  comprising the brush electrode  8 , as shown in  FIGS. 8 and 10 . The lead  60 , when present, may be operatively connected to a sensor embedded in the brush electrode  8  (e.g., a thermal sensor, an ultrasound sensor, or a pressure sensor).  
         [0048]      FIG. 10  is an enlarged view of the circled region of  FIG. 9 . As shown in  FIG. 10 , the brush electrode  8  may have a relatively flat working surface  50  at the distal end  32  of the brush electrode  8 . In other words, in this depicted embodiment, all of the filaments  40  comprising the brush electrode  8  extend approximately the same distance from the distal section  18  of the catheter  4 . Thus, the brush tip provides a relatively flat working surface  50  comprising the longitudinal ends of the filaments  40 . The catheter wall  44  of the distal section  18  of the catheter  4  provides mechanical support for the filaments  40  and may also provide electrical shielding.  
         [0049]     The filaments  40  may alternatively be trimmed to provide a variety of configurations and shapes for the working surface  30  of the brush electrode  8 , which may provide advantages for special applications of the brush electrode  8 . For example, a blade-shape may be formed by creating an edge of longer filaments of the brush electrode  8  resulting in a line of contact with the tissue. Alternatively, the brush electrode  8  may have a wedge-shaped working surface  50  to facilitate angular placement and increase the area of the working surface  50 . This configuration may be advantageous for point applications of ablative energy. As another example, the working surface  50  of the brush electrode  8  may have a concave portion or channel, which may be beneficial for wrap-around applications and provide advantages when ablating curved surfaces like the outer surface of a blood vessel. Alternatively, the working surface  50  of the brush electrode  8  may have a convex, trough-shaped tip, which may be beneficial, for example, when reaching into troughs or depressions on a contoured surface. The working surface  50  of the brush electrode  8  may also be domed, hemispherical, a frustum, or conical, coming nearly to a point at the most distal end of the brush electrode  8 , with its longest filaments  40  proximal to the longitudinal axis of the catheter  4 . The brush electrode  8  is depicted in many of the drawings with a circular cross section, but it may have different cross-sectional configurations.  
         [0050]     In one embodiment, conductive or nonconductive fluid may flow through the catheter lumen  30  from a fluid source (e.g., a pump and reservoir in a controller) to the brush electrode  8 . When the fluid flows through the brush electrode  8 , it creates a wet-brush electrode in which impinging jets of fluid traveling interstitially impact the tissue  52  at an interface between the tissue  52  and the brush electrode  8  to help control temperature changes at the interface. When using conductive fluid and either conductive or nonconductive filaments  40 , the brush electrode  8  may act as a virtual electrode. If there is no direct contact between conductive filaments and the tissue  52 , or the filaments  40  are entirely nonconductive, the conductive fluid flowing through the catheter lumen  30  makes the electrical contact at the interface between the brush electrode  8  and the tissue  52 .  
         [0051]     The brush electrode  8  according to the present invention delivers ablative energy to the tissue via the conductive filaments  40  alone, via the conductive fluid alone, or via both the conductive filaments  40  and the conductive fluid. In the latter two configurations, the brush electrode  8  is referred to as a wet-brush electrode. Since it is possible for the conductive fluid to escape from the exposed portion of the wet-brush electrode before reaching the working surface  50  at the distal tip of the wet-brush electrode, there is some ablative energy leakage to the surrounding blood. The leakage of ablative energy to the surrounding blood is in part due to direct contact between the blood and the conductive filaments and in part due to the conductive fluid escaping between the filaments  40  to the surrounding blood, particularly when substantial splaying of the filaments  40  occurs.  
         [0052]     As the catheter  4  is further deployed from the sheath  6 , the curved section  16  continues to furl and also translates linearly in the direction of the anchor member  58  as indicated by comparison of the positions of the catheter  4  in each of  FIGS. 9-11 . The deployment of the catheter  4  maintains the distal tip  18  and the attached ablation electrode  8  in contact with the trabecular slope  26  of the isthmus  24 .  
         [0053]     The creation of a linear lesion  54  in the tissue  52  of the isthmus  64  of the right atrium  60  is depicted schematically in  FIGS. 13 and 14 . In this procedure, a linear series of ablation lesions is created from the annulus of the tricuspid valve  28  to the inferior vena cava  22  in the isthmus  24  of the right atrial tissue  52  bordering the Eustachian ridge. This isthmus  24  of tissue is critical to the large right atrial reentrant circuit responsible for atrial flutter. The ablation lesions  54  damage atrial tissue  52  preventing the conduction of electrical impulses through the critical isthmus  24 . When the line of conduction block is complete, the atrial flutter circuit is shorted and the arrhythmia is cured.  
         [0054]     As shown in  FIG. 13 , the sheath  6  is positioned as desired in the heart, for example, in the right atrium  60  with the distal tip  58  of the anchor member  24  set securely against the atrial wall  56 . This placement of the sheath  6  fixes the position of the ablation system  2  and minimizes movement of the ablation system  2  with respect to the heart when the heart beats. A linear lesion  54  is initiated by the deployment of the catheter  4  from the lower port  62  of the sheath  6 . When moved proximally out of the anchor lumen  12  such that the ablation electrode  8  is between the spanning members  22 , the distal section  18  of the catheter  4  drops from the lower port  38  as the suspension section  16  is not rigid enough to support the distal section  18 . In addition, as described above, the suspension section  16  may also be formed with a preset curvature that directs the distal section out of the sheath  6  through the lower port  28 . The suspension section  14  bends to create a curved or angled relationship between the proximal section  14  and the distal section  18 .  
         [0055]     As the distal section  18  drops out of the lower port  28  of the sheath  6 , the ablation electrode  8  is oriented toward the sloped isthmus  24  and is placed in contact with the tissue  52 , initially on the isthmus  64  adjacent the tricuspid valve  68 . Once the ablation electrode contacts the tissue  52 , the catheter  4  may further be pushed distally to orient the distal section  18  generally orthogonally to the tissue  52 . In order to achieve this orthogonal orientation, the suspension section  16  and the proximal end of the distal section  18  may push through the upper port  26  in the sheath  6 . Because the suspension section  16  is of a relatively pliable construction, the suspension section  16  is able to bend easily to allow the distal section  18  to orient appropriately. By creating an orthogonal orientation, a greater surface area of the working surface  50  of the ablation electrode  8  is placed in contact with the tissue  52 . Upon activation of a source of ablative energy connected with the ablation electrode  8 , the tissue  52  is necrotized and a lesion  54  is formed. As the catheter  4  is further manipulated.  
         [0056]     To create a linear lesion along the isthmus  64  of the right atrium  60 , the catheter  4  is further manipulated in a similar manner to both relocate the ablation electrode  8  along trabecular surface  36  of the isthmus  2  and maintain the orientation of the distal section  18  generally orthogonal to the tissue  52 . From the initial position the catheter  4  may be pulled proximally through the main lumen  10 . This movement relaxes the distal section  18  from the orthogonal position and increases the angle formed by the suspension section  16  between the proximal section  14  and the distal section  18  to generally “flatten” the catheter  4 . In this manner, the distal section  18 , and consequently the ablation electrode  8 , is pulled along the isthmus  64 . Once moved proximally a small amount to reposition the ablation electrode  8 , the catheter  4  may then be moved distally within the main lumen  10 . The ablation electrode  8  interfaces with the tissue  52  to maintain its new position, thereby forcing the distal section  18  to again be pushed into a position generally orthogonal to the tissue  52 . The distal section  18  is able to return to an orthogonal position because of the flexibility of the suspension section  16 , which again forms a smaller angle between the proximal section  14  and the distal section  18  of the catheter  4 . This orthogonal orientation again increases the surface area contact of the working surface  50  of the ablation electrode  8  with respect to the tissue  52 .  
         [0057]     As the ablation electrode is moved along the trabecular slope  66  of the isthmus  64 , the distance between the sheath  6  and the tissue  52  decreases. However, the sheath  6  does not interfere with the placement of the ablation electrode  8  because the upper port  26  allows the suspension section  16  and the distal section  18  to extend above the sheath  6  as indicated in  FIG. 14 . The spanning members  22  further aid the positioning of the ablation electrode  8  by restricting lateral movement of the catheter  4  with respect to the sheath  6 . The pliability of the suspension section  16  acts as an armature-type suspension, allowing the ablation electrode  8  to easily follow the undulations of a trabecular surface. By maintaining a close interface between the ablation electrode  8  and the endocardial tissue  52  on the isthmus  64  along a linear path as shown in  FIGS. 13 and 14 , a continuous linear lesion  54  may be created.  
         [0058]     In this manner, the endocardial ablation system  2  of the present invention provides a simple mechanism to direct an ablation electrode to treat a sloped trabecular surface  26  along the isthmus  24  between the inferior vena cava  62  and the tricuspid valve  68  in the right atrium  60 . The preset curves of the suspension section  16  and the distal section  18  maintain the orientation of the ablation electrode  8  toward the trabecular slope  66 . Further, because of the pliability of the suspension section  16 , the distal section  18  may be oriented orthogonally to the isthmus  64  at any point along the trabecular slop  66 , regardless of the distance between the sheath  6  and the tissue  52  of the isthmus at a particular point. This allows the ablation catheter  8  to contact any portion of the trabecular slope  66  desired. This is achievable by merely introducing the catheter  4  into the right atrium  60  through the sheath  6  and manipulating the catheter  4  proximally and distally. Thus, the endocardial ablation system  2  of the present invention is relatively easy for a clinician to use compared to the extensive training required to manipulate a steerable catheter or other similar device.  
         [0059]     Alternatively, the ablation electrode may embody other electrode forms to achieve particular desired results. For example,  FIG. 15  depicts an embodiment of the present invention in which a ball electrode  8 ′ is integrated with the distal section  18  of the catheter  4 . A catheter  4  according to the present invention incorporating a ball electrode  8 ′ can similarly be manipulated in conjunction with the sheath  6  of the present invention to ablate tissue  52  and create a lesion  54 . Different ablation electrodes in addition to the brush electrode  8  and ball electrode  8 ′ including, for example, virtual electrodes, may also be used depending upon the application or ablation effect desired. However, the advantages of the armature-type suspension system of the endocardial ablation system  2  of the present invention for maintaining tissue contact are applicable regardless of the electrode chosen for use.  
         [0060]     Although various embodiments of this invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. All directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the basic elements of the invention as defined in the following claims.