Patent Publication Number: US-2021161453-A1

Title: Electrophysiology catheter design

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of and claims priority to U.S. patent application Ser. No. 16/039,919, filed Jul. 19, 2018, entitled ELECTROPHYSIOLOGY CATHETER DESIGN, and is a continuation of and claims priority to U.S. patent application Ser. No. 15/164,445, filed May 25, 2016, entitled ELECTROPHYSIOLOGY CATHETER DESIGN, now patented as U.S. Pat. No. 10,039,467, which is a divisional of and claims priority to U.S. patent application Ser. No. 13/750,133, filed Jan. 25, 2013, entitled ELECTROPHYSIOLOGY CATHETER DESIGN, now patented as U.S. Pat. No. 9,370,311, which is related to and claims the benefit of U.S. Provisional Patent Application Ser. No. 61/684,385, filed Aug. 17, 2012, entitled MONOPHASIC ACTION POTENTIAL CATHETER DESIGN, and is related to and claims the benefit of U.S. Provisional Patent Application Ser. No. 61/727,163, filed Nov. 16, 2012, entitled MONO-PHASIC ACTION POTENTIAL ELECTROGRAM CATHETER, the entirety of which all is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     n/a 
     FIELD OF THE INVENTION 
     The present invention relates to a device and system for improved mapping and tissue ablation that may be manufactured at a reduced cost and complexity. 
     BACKGROUND OF THE INVENTION 
     Medical procedures are available for treatment of a variety of cardiovascular conditions, such as cardiac arrhythmias, atrial fibrillation, and other irregularities in the transmission of electrical impulses through the heart. As an alternative to open-heart surgery, many medical procedures are performed using minimally invasive surgical techniques, where one or more slender implements are inserted through one or more small incisions into a patient&#39;s body. Such procedures may involve the use of catheters or probes having multiple sensors, electrodes, or other measurement and treatment components to treat the diseased area of the heart, vasculature, or other tissue. Minimally-invasive devices are desirable for various medical and surgical applications because they allow for shorter patient recovery times compared to surgery, and for precise treatment of localized discrete tissues that are otherwise difficult to access. For example, catheters may be easily inserted and navigated through the blood vessels and arteries, allowing non-invasive access to areas of the body with relatively little trauma, while other minimally-invasive probes or instruments may be inserted into small openings and directed through targeted anatomy without significant impact or disruption to surrounding tissue. 
     One such example of a minimally invasive therapy involves the treatment of cardiac arrhythmias or irregular heartbeats in which physicians employ specialized cardiac assessment and treatment devices, such as a mapping and/or ablation catheter, to gain access to interior regions of a patient&#39;s body. Such devices may include tip electrodes or other ablating elements to create lesions or other anatomical effects that disrupt or block electrical pathways through the targeted tissue. In the treatment of cardiac arrhythmias, a specific area of cardiac tissue having aberrant electrical activity (e.g. focal trigger, slow conduction, excessively rapid repolarization, fractionated electrogram, etc.) is typically identified first before subsequent treatment. This localization or identification can include obtaining unipolar or bipolar electrograms, or monophasic action potential (“MAP”) electrograms of a particular cardiac region. Monophasic action potential recordings document the onset of local tissue depolarization, during repolarization, and the general action potential morphology. The MAP signal is generated by measurement between two electrodes, the first being in contact with the blood but generally not in contact with the myocardium, and the second being in contact with the myocardium, with high enough local pressure to depolarize the underlying myocytes. This increased local pressure preferably is created by a relatively prominent, yet small surface area electrode in stable contact with the myocardium. 
     MAP signals may be obtained by temporarily depolarizing selected tissue, with responsive electrical activity being recorded or otherwise monitored for an indication of local depolarization timing, refractory period duration, and any aberrant electrical activity. After mapping and diagnosing aberrant tissue, a physician may decide to treat the patient by ablating the tissue. Accurate mapping of the cardiac tissue using bipolar, unipolar, or MAP electrogram signals can reduce the number of ablations necessary to treat an aberrant electrical pathway, and can make the executed ablations more effective. In addition, MAP recordings can substantially improve the ability to determine the timing of local tissue activation which is often ambiguous when recorded using standard intracardiac electrodes. 
     The accuracy of MAP signal measurement largely depends on quality of contact between one or more mapping electrodes and the heart tissue. For example, motion artifacts caused by a beating heart and nonuniform ventricular contraction can significantly distort detected MAP signals, as movement of the heart will vary the pressure of (and therefore alter the contact between) the mapping electrodes on the heart tissue as well as resulting in unstable sliding contact of the electrodes. Currently known diagnostic cardiac electrophysiology catheters do not accurately and reliably detect MAP signals. 
     Further, combination mapping and ablation devices reduce procedure time and complexity by eliminating the need to employ separate mapping and ablation devices for each task. Combination mapping and ablation devices also increase ablation accuracy, because once aberrant tissue (the “target tissue”) is found, ablation can begin immediately without having to remove the mapping device and relocate the target tissue with the ablation device. It is desirable to include one or more larger electrodes for radiofrequency (RF) ablation, so the large electrode area can provide a large surface area for dissipation into the blood pool of heat absorbed from the tissues. When smaller electrodes, and therefore a smaller active surface area, are used, the electrodes are more likely to incur local overheating, which can lead to thermal denaturation of blood proteins, producing adherent or embolic coagulum or other undesirable effects downstream of the electrodes and the treatment site. Conversely, more accurate electrograms and MAP recordings may be obtained with smaller mapping electrodes. 
     To provide more effective and efficient medical treatments, it is thus desirable to optimize the apparatus and method of use to ensure more uniform contact between a mapping device and cardiac tissue when recording MAP signals. It is also desirable to have a catheter that can both record monophasic action potentials, and subsequently ablate the local tissue if desired. It is further desirable to provide a mapping apparatus that is simple and cost effective to manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method, device, and system for improved mapping and/or ablation of a target tissue region, while reducing manufacturing cost and complexity. In a first embodiment, the device may generally include an elongate body and a distal assembly affixed to the elongate body and including a treatment electrode having a first surface, a conductive mapping region, and a selectively conductive ablation region. The selectively conductive ablation region may be conductive of high-frequency current and substantially non-conductive of low-frequency current. The treatment electrode may be composed of metal, such as platinum, platinum alloys, gold, gold alloys, gold with a coating of tantalum, copper with a coating of tantalum, aluminum, tungsten, titanium, tantalum, hafnium, niobium, silver, zirconium, and combinations thereof. The selectively conductive ablative region may include an oxide layer on the treatment electrode first surface. For example, the treatment electrode may be composed of gold and the selectively conductive ablative region may include a layer of oxidized tantalum. Further, the selectively conductive ablative region may be larger than the conductive mapping region. In another embodiment, the treatment electrode may include a coiled region that is prominent from the elongate body, for example, treatment electrode may be a coiled hypotube electrode. The perimeter of the hyptotube electrode may include one or more substantially angular bends and/or one or more protuberances to further enhance local small area contact pressure with tissue. In another embodiment, the device may include two treatment electrodes, each treatment electrode being substantially disposed about a circumference of the elongate body, the conductive mapping regions of the treatment electrode being coaxial with the longitudinal axis of the elongate body, and the conductive mapping region of each treatment electrode being distal of the selectively conductive ablation region of each electrode. In another embodiment, the elongate body of the device may define a distal region, and the device may further comprise two or more treatment electrodes, each treatment electrode being substantially disposed within a discrete circular sector of the distal tip. 
     In another embodiment, the device may include an elongate body defining a distal portion, a proximal portion, and a longitudinal axis, and an assembly affixed to the distal portion of the elongate body and defining an anterior face lying in a plane that is substantially orthogonal to the longitudinal axis of the elongate body, the assembly including a plurality of electrodes, each electrode having a first surface, an electrically conductive mapping region, and a thermally conductive and electrically insulated region. The assembly may be a carrier arm, and the electrically conductive mapping region of the mapping electrode may be positioned on the anterior face of the curved carrier arm. The device may further include two carrier arms, the anterior faces of the carrier arms being coplanar and perpendicular to each other. The thermally conductive and electrically insulated region may include a layer of at least one of pyrolytic graphite, graphite, graphene, diamond, diamond-like carbon (DLC) coating, alumina, sapphire, zirconia, tantala, titania, beryllium oxide, polymer composites containing thermally conductive particles, nanoparticles, self-assembling nanoparticles, nanomaterials and composites, olive oil, medical grade silicone oil, and combinations thereof on the first surface. Further, the thermally conductive and electrically insulated region may be composed of gold or gold alloy, and may include a layer of at least one of pyrolytic graphite, graphite, graphene, diamond, diamond-like carbon coating, alumina, sapphire, zirconia, tantala, titania, beryllium oxide, polymer composites containing thermally conductive particles, nanoparticles, self-assembling nanoparticles, nanomaterials and composites, olive oil, medical grade silicone oil, and combinations thereof on the first surface. 
     In another embodiment, the device may include an elongate body defining a distal portion and a proximal portion, and an assembly affixed to the distal portion of the elongate body and including a plurality of conductive protuberant metal electrode portions and a plurality of substantially insulated portions. Each of the plurality of protuberant electrode portions and plurality of substantially insulated portions may circumscribe the distal assembly housing, and the distalmost electrode portion may have the smallest circumference, and the proximalmost electrode portion has a largest circumference, of the plurality of electrode portions. Further, the plurality of protuberant electrode portions may be alternated with the plurality of substantially insulated portions. The plurality of protuberant metal electrode portions and the plurality of substantially insulated portions may be composed of a metal selected from the group consisting of platinum, platinum alloys, gold, gold alloys, gold with a coating of tantalum, copper with a coating of tantalum, copper with a coating of gold, aluminum, tungsten, titanium, tantalum, hafnium, niobium, zirconium, and mixtures thereof, and each of the plurality of substantially insulated portions includes an outer layer of oxidized aluminum, tungsten, titanium, tantalum, hafnium, niobium, zirconium, and mixtures thereof. 
     The method may generally include providing a device including a distal assembly comprising one or more conductive regions and one or more selectively conductive regions, the one or more conductive regions and one or more selectively conductive regions being in electrical communication with a high-frequency energy source, and the one or more selectively conductive regions being conductive of conductive of high-frequency energy and substantially non-conductive of low-frequency electric current, positioning the distal assembly in contact with an area of target tissue, recording at least one electrogram from the area of target tissue with the conductive region of the distal assembly, determining whether the at least one electrogram indicates the presence of an aberrant electrical pathway within the area of target tissue, and when the presence of an aberrant electrical pathway within the area of target tissue is indicated, transmitting a high-frequency energy to the conductive region and the selectively conductive region, the conductive region and selectively conductive region ablating at least a portion of the area of target tissue. For example, the high-frequency energy may be radiofrequency energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  shows a medical system including a catheter having a distal assembly; 
         FIG. 2  shows a first embodiment distal assembly; 
         FIG. 3  shows a bulbed wire of the distal assembly of  FIG. 2 ; 
         FIG. 4  shows a schematic diagram of an electrochemical cell for use in conjunction with anodizing and annealing bulbed wires, such as forming a tantalum pentoxide layer on a tantalum surface; 
         FIG. 5  shows a simplified depiction of a holder adapted to contain bulbed wires for use in conjunction with a process for imparting further corrosion resistance or selective electrical conductivity to the bulbed wires of  FIG. 2 ; 
         FIG. 6A  shows a second embodiment of a distal assembly; 
         FIG. 6B  shows a third embodiment of a distal assembly; 
         FIG. 7A  shows a fourth embodiment of a distal assembly; 
         FIG. 7B  shows a fifth embodiment of a distal assembly; 
         FIG. 8  shows a sixth embodiment of a distal assembly; 
         FIG. 9A  shows a seventh embodiment of a distal assembly; 
         FIG. 9B  shows an eighth embodiment of a distal assembly; 
         FIG. 9C  shows a ninth embodiment of a distal assembly; 
         FIG. 10A-10H  show various configurations of a tenth embodiment of a distal assembly; 
         FIG. 11  shows an eleventh embodiment of a distal assembly; 
         FIG. 12A  shows a twelfth embodiment of a distal assembly; and 
         FIG. 12B  shows a view of the anterior face of an embodiment of the distal assembly of  FIG. 12A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term “distal assembly” refers to a distal portion of a medical device that has mapping and/or ablation functionality. If the medical device includes an elongate body, at least a portion of the distal assembly may be distal of the elongate body (for example, as shown in  FIGS. 9A-10 ), or the distal assembly may be substantially affixed on, disposed about, or integral to the distal portion of the medical device (for example, as shown in  FIGS. 2 and 6A-7B ). 
     As used herein, the term “selectively conductive metal” refers to a metal with an oxide form or coating that behaves like a capacitor, passing high-frequency currents and pulsed energy but blocking transmission of direct current and low-frequency signals. The metal, for example, aluminum, tungsten, titanium, tantalum, hafnium, niobium, zirconium (and alloys thereof), as well as gold or copper with a thin film of tantalum, or copper with a thin film of gold, may be fully electrically conductive. The oxide of that metal, on the other hand, may have low resistance to high-frequency current flow, thus being selectively conductive, and a high resistance to low-frequency or direct current flow, thus having selectively insulative properties. 
     Referring now to  FIG. 1 , a medical system  10  including a catheter  12  having a distal assembly  14  is shown. The system  10  may generally include a medical device  12  (such as a catheter or surgical probe) coupled to a console  16  or other operating equipment. The catheter  12  has a distal assembly  14  positionable at or near a target tissue region. The catheter  12  may have an elongate body or catheter shaft  18  with a proximal portion  20 , a distal portion  22 , and may define a lumen therebetween (not shown in  FIG. 1 ). The distal portion  22  of the elongate body  18  may include one or more reference electrodes  24  in electrical communication with the distal assembly  14  and console  16 . The console  16  may include one or more computers  26  for storing data, interpreting signals received from the device (for example, determining whether received signals indicate an aberrant electrical activity within a patient&#39;s heart), generating alerts, controlling the system, and the like, and may also include one or more fluid reservoirs  27 , vacuums, power sources, and the like. The elongate body  18  may be both flexible and resilient, with sufficient column strength and torsional rigidity facilitating steady contact with tissue to improve signal fidelity in mapping contacted tissue. The catheter  12  may also have a handle  28  affixed to the proximal portion  20  of the elongate body, which may include one or more fluid inlet and outlet ports, actuators, connectors, and other control and/or connecting elements. 
     The distal assembly  14  is coupled to the distal portion  22  of the elongate body  18 , and includes one or more mapping and/or ablation electrodes  30 , each comprising an electrode head  32  and electrode wire  34 . The one or more electrodes  30  may be permanently affixed to an electrode assembly housing  36  (as shown and described in  FIGS. 2-5 ). The distal assembly  14  may be operable at least for mapping a target tissue region, but may also be operable as a treatment assembly. For example, the console  16  may include a radio frequency (RF) generator or high voltage pulsed energy generator  38  in electrical communication with one or more of the electrodes  30  or the electrode assembly housing  36  such that the distal assembly  14  may also be used to ablate or electroporate a target tissue region. The catheter  12  and system  10  may be configured for use with any of a variety of energy modalities, including cryoablation, RF ablation, and electroporation. Further, the catheter  12  and system  10  may be configured for mapping tissue, for example, recording and processing electrograms from cardiac tissue. 
     Referring generally to  FIGS. 2-10 , embodiments of the distal assembly  14  and methods for manufacturing are shown and described. In all embodiments, the distal assembly  14  offers a cost effective and quality performance advantage over currently known devices. For example, although all embodiments may provide more accurate mapping, the distal assembly  14  of  FIG. 2  may offer combined mapping and ablation functionality in a space-saving configuration with fewer components and manufacturing steps, whereas the distal assemblies  14  of  FIGS. 6A, 6B, and 8-10  may further offer the advantage of having combined functionality without the need for creating each component from a different material. Further, the distal assembly  14  of  FIGS. 8-10  may offer the advantage of including features that enhance contact between mapping electrodes and tissue. Finally, the distal assemblies  14  of  FIGS. 7A and 7B  may offer the advantage of including a single electrode that has both mapping and ablation functionality. 
     The distal assemblies  14  of  FIGS. 2-10  may include components (for example, mapping and/or electrodes and/or a housing assembly) that are composed of a selectively conductive material. Metal oxides such as tantalum pentoxide may be referred to as “selectively conductive metals.” Tantalum pentoxide, for example, is selectively conductive. That is, it has the unique ability to block direct current (DC) while allowing high-frequency current conduction (such as radiofrequency energy). Tantalum pentoxide passes high-frequency current preferentially but blocks DC transmission. Metals such as tantalum, aluminum, tungsten, titanium, haffnium, niobium, zirconium, and mixtures thereof, which have oxides that are selectively conductive. Additionally, doped semiconductors such as p-type and n-type doped silicon and gallium, and composite materials made from ceramics as well as conductive polymers, metal-polymers, metal-ceramic composites, and some nanomaterials may also be selectively conductive. Further, tantalum (Ta) and tantalum compounds such as grain-stabilized tantalum (TaKS), tantalum pentoxide (Ta 2 O 5 ), tantalum-tungsten (TaW), capacitor quality tantalum (TaK), or similar are highly corrosion resistant. Tantalum compounds also display excellent cold ductility, high melting point (for example, Ta has a melting point of 3,017° C.), outstanding resistance against aqueous solutions and metal melts, superconductivity, and a high level of biocompatibility. Further, TaKS, for example, is radiopaque, making it well suited for use in catheters that must be located within and navigated through a patient&#39;s body. Tantalum and tantalum compounds can be even more durable than MP35N (a nickel-cobalt-chromium-molybdenum alloy commonly used material for medical implantable devices such as catheter wires that is nonmagnetic, has high tensile strength, good ductility and toughness, and excellent corrosion resistance) and is less expensive than platinum. Additionally, as shown in  FIGS. 7A and 7B , the distal assembly  14  may include a single electrode  30 , wherein at least a portion of which is composed of a tantalum compound (for example, Ta 2 O 5 ) and at least a portion of which is composed of a different material (for example, gold, gold alloy, copper coated with gold, or platinum). As a result, the tantalum portion of the electrode may be used to ablate or electroporate tissue using, for example, RF energy (for example, renal, liver, or prostate tissue), whereas the non-tantalum portion of the electrode may be used to deliver a direct current stimulus to or record direct current from the tissue. 
     Referring now to  FIG. 2 , a first embodiment of a distal assembly  14  is shown. The distal assembly  14  may include a housing  36  and one or more electrodes  30 , such as monophasic action potential (MAP) electrodes, each positioned a radial distance from the longitudinal axis  40  of the housing  36 . If two electrodes  30  are used, the electrodes  30  may be positioned opposite each other. If three or more electrodes  30  are used (for example, four electrodes are shown in  FIG. 2 ), the electrodes  30  may have a radial symmetry about the housing longitudinal axis  40 . 
     The distal assembly  14  shown in  FIG. 2  may have been formed according to the method shown and described in  FIGS. 3-5 . For example, one or more bulbed wires  42  comprising a bulb portion  44  and a wire portion  46  may be created (as shown and described in  FIG. 3 ). The wire  46  portion of each bulbed wire  42  may then be anodized (as shown and described in  FIG. 4 ), and the bulb portion  44  of each bulbed wire  42  may be composed of the non-anodized material or be electroplated, sputtered, or ion-embedded with a corrosion-resistant material or material having other beneficial properties (as shown and described in  FIG. 5 ). 
     Once one or more bulbed wires  42  have been treated (for example, anodized and electroplated), the wires  42  may be placed into and bonded to an electrode assembly housing (referred to as the “assembly housing”)  36 . For example, four bulbed wires  42  may be used. At this stage (that is, when the bulbed wires  42  are seated within the mapping assembly housing  36 ), the bulbed wires are referred to as electrodes  30 , comprising electrode heads  32  and electrode wires  34 . In the embodiment shown in  FIG. 2 , the electrodes  30  and electrode assembly housing  36  are collectively referred to as the distal assembly  14 . However, not all embodiments include a housing  36  (for example, the embodiments of  FIGS. 6A, 6B, 9, and 10A-10C ). The assembly housing  36  includes an anterior face  48  from which the one or more electrode heads  32  may protrude. Alternatively, the electrode heads  32  may be mounted within the assembly housing  36  such that the electrode heads  32  are substantially flush with the anterior face  48  of the electrode housing  36 . For example, the assembly housing  36  may include a socket sized to receive each electrode  30  such that the electrode head  32  is seated within the socket and the electrode wire  34  passes through an opening in the socket and into the elongate body, once the housing is coupled to an elongate body. The electrodes  30  may be affixed to the electrode assembly housing  36  using adhesive, thermoplastics, or other known techniques. 
     The distal assembly  14  of  FIGS. 2-5  may be particularly suited for diagnostic purposes, i.e. mapping. However, the distal assembly  14  alternatively may be used as part of a combination ablation and mapping device  12 . For example, the assembly housing  36  may be in electrical communication with an energy source (such as RF energy) and composed of an electrically conductive material, or coated or cladded with an electrically conductive material, so that the electrodes  30  may be used for mapping and the housing  36  (which may have a larger “footprint” than the mapping electrodes) may be used for ablation. In this case, a thin insulative layer could be incorporated to electrically isolate the electrode heads  32  from the assembly housing  36 . For example, an insulative layer could be disposed within the sockets of the assembly housing  36 . Alternatively, the assembly housing  36  and electrodes  30  may be composed of a conductive material, but the housing  36  may include an outer layer of a selectively conductive material. Additionally or alternatively, the assembly housing  36  may be composed of a low-durometer, resilient material such as silicone, a polymer or conductive polymer, air-filled balloon, gel, fiber composite, or the like, that conforms to irregular geometries while ensuring contact between the electrode head  32  and target tissue region. For example, as the heart beats, the deformable housing may absorb the pressure to preserve contact between the electrode head and target tissue region. 
     Once assembled, the distal assembly  14  may be coupled to the distal portion  22  of the elongate body  18 , with the electrode wires  34  providing electrical connection between the distal assembly  14  and catheter  12  and/or system  10 . Thus, the entire distal assembly  14  may include as little as two components (for example, if a single electrode and distal assembly housing were used). In a non-limiting embodiment, the distal assembly  14  as shown in  FIG. 2  may include six components: four electrodes  30 , the assembly housing  36 , and a reference electrode  24 . The assembly housing  36  and electrodes  30  may be composed of the same material. This embodiment includes fewer components than known mapping assemblies, at least in the electrodes, which reduces cost and assembly time while providing higher reliability. 
     Referring now to  FIG. 3 , a bulbed wire  42  of the distal assembly  14  of  FIG. 2  is shown. The bulbed wire  42  may be manufactured or molded from a volume of metal such that a bulb  44  or substantially spherical shape is formed at one end (referred to as the “bulb”), such as by cold forming and/or extrusion. The bulb  44  may become the electrode head  32  (as shown and described in, for example,  FIGS. 2, 4 and 5 ), so it may have any dimensions suitable for the final mapping assembly. Having a single-piece electrode head  32  and electrode wire  34  eliminates the need to weld an electrode to a wire. A two-piece system is also feasible, but would increase cost and manufacture time and complexity. The bulbed wire  42  may be composed of a highly corrosion-resistant material, such as tantalum or tantalum compound (such as Ta 2 O 5  or TaKS). 
     Referring now to  FIG. 4 , a schematic diagram of an electrochemical cell  50  for use in conjunction with anodizing and annealing bulbed wires  42  is shown. Once the bulbed wire  42  of  FIG. 3  is formed, the wire portion  46  may be anodized to create a thin oxide layer on the external surface of the wire portion  46 . For example, the insulating layer may be approximately 1 μm thick. During the anodizing process, the wire portion  46  is placed into a container  52  containing an electrolytic solution  54  such as H 3 PO 4 , H 2 SO 4 , ammonium tartrate, or the like. The container  52  may also include a cylindrical mesh electrode  56 , and the wire portion  46  to be oxidized may be disposed through the center of the cylindrical mesh electrode  56 . The mesh  56  and wire  46  may be coupled to a controllable power source  58 . Then, a current (direct, alternating, or pulsed) may be passed through the solution  54 , creating an oxide layer about the wire  46 . This oxide layer further protects the wire against corrosion and imparts a conductive barrier to electrically isolate the wire from adjacent components and structures. The wire portions  46  of multiple bulbed wires  42  may be anodized at once. Although the entire structure can be anodized, the preferred embodiment anodizes only the regions of the assembly that will be adjacent to other conductive structures to provide an insulative barrier. For example, the wire  46  and bulb  44  may be composed of tantalum, and only the wire  46  may then be anodized to create an oxide layer. This process may be used for components of any of the distal assemblies shown and described herein that include an oxide layer. 
     Referring now to  FIG. 5 , a schematic diagram of a holder  60  adapted to contain bulbed wires  42  for use in conjunction with a process for imparting further corrosion resistance to the bulbed wires  42  of  FIG. 3  is shown. After being anodized, one or more materials may be deposited on the bulbs  44  to enhance electrical conductivity, provide added corrosion resistance, or impart other beneficial qualities. For example, iridium oxide may be electrodeposited on the bulbs  44  or nickel-titanium alloy may be sputtered onto the bulbs  44 . Additionally or alternatively, sputtering may be used to deposit nickel-titanium alloy, gold, gold alloy, platinum or platinum-based alloy, or the like. However, other materials and techniques may be used. For example, the wire  42  may be composed of gold with a tantalum coating. The tantalum coating on the bulb  44  may be etched, and the exposed gold may then be anodized or electroplated, sputtered, or ion-embedded with a coating of platinum-iridium. Prior to treating the bulbs  44  (for example, by electrodeposition or sputtering), one or more bulbed wires  42  may be placed into a holder or container  60  to hold them in place. The holder or container  60  may be adapted to hold any number of wires  42 , and may generally hold the wires  42  such that the bulbs  44  are accessible on the top of the holder  60  (as shown in  FIG. 3 ). Once the wires  42  are in place, the bulbs  44  may be treated. 
     Referring now to  FIGS. 6A and 6B , a second and third embodiment of a distal assembly  14  is shown. In both embodiments, the electrode head  32  (the conductive portion) and the electrode wire  34  (the insulated portion) are not only composed of the same material, but are also created from a single piece of material (collectively referred to as an “electrode”). This may reduce manufacturing cost and complexity. Additionally, more than one electrode wires  34  may be used within a catheter body  18  without the need for including insulation material between the wires. 
     In the embodiment shown in  FIG. 6A , a plurality (for example, three) electrode wires  34  are disposed within a medical device, such as a catheter elongate body  18 . Each wire  34  may be composed of a metal (for example, tantalum or TaKS) and include an outer insulative oxide layer (for example, tantalum pentoxide). When low-frequency or DC voltage flows through the wire, the wire  34  will function as an insulated conductor of energy. Therefore, no additional insulative material is required within the medical device to electrically insulate each wire  34  from the others. This may not only increase the available space within the medical device for other components such as pull wires, push rods, etc., but may also decrease manufacturing cost and complexity. Each wire  34  may extend through internal portion of the elongate body  18  for a distance, and then exit the wall of the elongate body  18  at an exit point  62 . From the exit point  62 , the wire  34  may then be disposed about an exterior distal portion in one or more coils  64 , which may be referred to as an electrode head  32 . Unlike the wire  34 , this external coiled portion  64  may not include an oxidative layer, and therefore may be electrically conductive. Further, the coiled portion  64  may have a hydrophilic coating to reduce the likelihood of air collecting within the turns of the coils. The electrodes  30  may be made as shown and described in  FIGS. 3-5 . Additionally, a housing or at least a portion of a medical device (for example, an elongate body) may be overmolded onto the electrodes to provide a seal at the exit point  62 . The distal tip  66  of the elongate body  18  may have an atraumatic rounded or blunt configuration to prevent injury to the patient during mapping and/or ablation procedures. 
     The embodiment shown in  FIG. 6B  has substantially the same configuration as the embodiment shown and described in  FIG. 6A , except that a hypotube  68  instead of a wire may be used. Like the wire of the embodiment in  FIG. 6A , the hypotube  68  may comprise an electrode  30  (conductive portion) and a “wire”  34  (insulated portion); however, unlike the embodiment in  FIG. 6A , the hypotube  68  may contain a volume of coolant or saline solution for cooling the electrode  30  portion of the hypotube  68  during ablation procedures (for example, during RF ablation). The conductive portions of both embodiments shown in  FIGS. 6A and 6B  may be used for mapping and/or ablation. The small diameter hypotube provides increased local tissue contact pressure against the endocardium in any orientation, providing reliable MAP recording capability. 
     Referring now to  FIGS. 7A and 7B , a fourth and fifth embodiment of the distal assembly  14  are shown. These embodiments include an electrode  30  that has both mapping and ablation functionality. As shown in  FIG. 7A , one or more electrodes  30  may be disposed about the distal portion  22  of a medical device, such as the flexible, elongate body  18  of a catheter. Although  FIG. 7A  shows two electrodes  30 , any number of electrodes  30  may be used. Each electrode  30  may include a conductive region  70  and a region that is selectively conductive  72 . As described herein, the electrode  30  may be composed of a highly conductive metal such as gold and may include a thin film coating of a metal such as tantalum, and the selectively conductive region  72  may include an outer oxide layer, whereas the conductive region  70  does not. The oxide layer may be an oxide of aluminum, tungsten, titanium, tantalum, hafnium, niobium, zirconium (and alloys thereof). The oxide layer in the case of tantalum pentoxide may be between approximately 10 nm and approximately 5000 nm, preferably approximately 100 nm to approximately 1000 nm. Further, the conductive region may have a layer of conductive material such as gold or gold alloy sputtered, ion-embedded, or electrodeposited on an outer surface. The conductive region  70  may have a smaller surface area than the selectively conductive region  72 . As a non-limiting example, two electrodes  30  may be positioned on the device distal end such that the conductive regions  70  are each located on the distal end of the electrode  30 , and the electrodes  30  are spaced a distance apart by the material of the device (for example, a catheter elongate body), which material provides insulation between electrodes. Further, a fluid lumen  74  may be disposed within the elongate body  18  that is in fluid communication with a source of saline or similar fluid for cooling the electrodes  30 . During use, measurement by the electrodes  30  of a low-frequency intracardiac electrogram or direct current voltage will be only from the portions of the electrodes in the conductive region  70 , whereas the selectively conductive region  72  is insulated by the oxide layer and does not measure electrograms. As described above, smaller electrodes  30  are less likely to corrode under high voltage and produce more accurate electrograms. Activating the electrodes  30  with high-frequency pulses or RF energy may cause the entire electrode  30 , both conductive  70  and selectively conductive regions  72 , to function as an ablation electrode having a larger footprint than that of the electrode when the selectively conductive region  72  is insulated during mapping procedures. 
     The embodiment shown in  FIG. 7B  generally functions in the same manner as the embodiment shown in  FIG. 7A .  FIG. 7B , however, shows two electrodes  30  radially arranged about the distal portion  22  of the device (although any number of electrodes may be used). That is, each electrode  30  may be substantially disposed within a discrete circular sector of the distal region  22  of the device, for example, an elongate body  18 . The fluid lumen  74  may define an opening  76  at the distal tip  66  of the device, and the conductive region  70  of each electrode  30  may be closest to the lumen opening  76  or distal tip  66  to facilitate mapping when the selectively conductive region  72  is insulated. When the selectively conductive region  72  is conductive, the entirety of each electrode  30  may function as an ablation electrode. In both  FIGS. 7A and 7B , the fluid lumen  74  containing saline or similar nontoxic fluid may be open to the environment, and the saline may be allowed to exit the device into the patient&#39;s bloodstream through the lumen opening  76 . Alternatively, the fluid lumen may be in communication with a source of refrigerant that is expanded to cool the electrodes  30 , and that is recovered by a vacuum after it is expanded in the distal portion  22  of the device proximate the electrodes  30 . 
     Referring now to  FIG. 8 , a sixth embodiment of a distal assembly is shown. The distal assembly  14  may have a generally conical shape, but may include one or more protruding electrode rings  78  (for example three protruding electrode rings  78  are shown in  FIG. 8 ). The protruding electrode rings  78  may have rounded edges to prevent injury to the patient. Between the protruding electrode rings  78  may be one or more recessed insulated portions  80 . The protruding electrode rings  78  and recessed insulated portions  80  may be composed of the same material. For example, the protruding electrode rings  78  and recessed insulated portions  80  may be composed of a metal (for example, tantalum), and the recessed insulated portions  80  may have an oxide layer (for example, tantalum pentoxide) or may have a coating of an electrically insulating and thermally conductive material (for example, diamond-like carbon). As a non-limiting example, the oxide layer or the layer of thermally conductive material may be between approximately 10 nm to approximately 5000 nm. The protruding electrode rings  78  may function as mapping electrodes, and the protrusions may enhance contact and establish a higher local pressure between the rings and tissue, thereby enhancing depolarization of the tissue during mapping procedures and providing more reliable and accurate mapping (for example, MAP) signal recording. Additionally, if the insulated portions  80  are composed of a selectively conductive material, both the protruding electrode rings  78  and insulated portions  80  may also be capable of functioning as a single, larger ablation electrode. Alternatively, the insulated portions  80  could be composed of a different material. Even though this may add to manufacturing cost and complexity, the configuration of the distal assembly would still function to produce better mapping signals. 
     Referring now to  FIGS. 9A-9C , a seventh, eighth, and ninth embodiment are shown. All three embodiments may include a coiled hypotube electrode  68  disposed about the distal portion  22  of a medical device, such as an elongate body  18  of a mapping and/or ablation catheter. It will be understood that the drawings show only a single winding but additional, more proximal windings may be included in an ablation device. In such embodiments, the proximal windings may be made selectively conductive as described previously. The hypotube  68  in each embodiment may be in fluid communication with a source of saline or similar fluid (as described in  FIGS. 7A and 7B ), or with a cryogenic fluid, for cooling the hypotube electrode  68 . The small diameter hypotube may provide increased local tissue contact pressure against the endocardium in any orientation, providing reliable MAP recording capability. The hypotube  68  may be coiled or wound around the distal portion  22  of the elongate body  18 , the hypotube  68  winding at least approximately 360° about the distal portion  22  of the elongate body  18 . Alternatively, the hypotube may include a coil or winding  82  that is distal from the elongate body  18  (as shown in  FIGS. 9A-9C ). Alternatively, the hypotube may include multiple coils or windings  82  that are disposed about the distal portion of the elongate body or that are distal from the elongate body  18 . Further, the hypotube  68  of each embodiment may be composed of a metal (for example, tantalum or stainless steel plated with gold or gold alloy) and include one or more alternating selectively conductive regions  72  or more proximal hypotube windings (not shown), having an oxide layer (for example, tantalum pentoxide). As a non-limiting example, the oxide layer may have a thickness of between approximately 10 nm to approximately 5000 nm, preferably approximately a thickness of 100 nm to approximately 1000 nm. The exposed (non-oxidized) conductive regions  70  may be smaller (that is, have less surface area) than the oxidized selectively conductive regions  72  to enhance signal quality during mapping when recording intracardiac electrograms. Finally, all embodiments may include one or more thermocouples or thermisters  84  in contact with the hypotube  68  to monitor temperature of the hypotube  68 . 
     The hypotube of  FIG. 9A  may include a coil  82  that has a substantially smooth circumference without any bumps, ridges, or textures. Conversely, the hypotube  68  of  FIG. 9B  may include a plurality of elements  86  that are prominent from (or protrude from) a surface of the hypotube  68  to further enhance local small area contact pressure with tissue at the site of contact with each of the prominent elements  86 , thus enhancing MAP signal recording capability by increasing local pressure on the tissue under the prominent elements  86 . Each prominent element  86  may extend from a surface of the hypotube  68 , for example, the outer circumference or perimeter of the hypotube. Although four prominent elements  86  are shown in  FIG. 9A , it will be understood that any number of prominent elements  86  may be used to enhance contact between the hypotube  68  and tissue of interest. 
     Likewise, the hypotube  68  of  FIG. 9C  may be bent to include one or more substantially angular bends  88 . Each bend  88  may be prominent from (or protrude from) the outer circumference of the hypotube  68 , thus creating prominent sites about the hypotube  68  to further enhance local small area contact pressure with tissue and improving MAP signal recording capability. Although  FIG. 9C  shows three protuberant bends  88 , it will be understood that any number of bends may be included to enhance MAP signal recording capability when the device is positioned in most any orientation against tissue of interest. Alternatively, the embodiments shown in  FIGS. 9A-9C  may be made entirely with a conductive surface and without the selectively conductive areas. 
     Referring now to  FIGS. 10A-10H , various configurations of a tenth embodiment of a distal assembly  14  are shown. The embodiment shown in  FIGS. 10A-10H  may have the general appearance of a catheter such as the Pulmonary Vein Ablation Catheter (PVAC) sold by Ablation Frontiers (Medtronic Inc., Minneapolis, Minn.), which is an over-the-wire circular mapping and ablation catheter. The PVAC device may include a carrier arm  90  bearing one or more electrodes, typically having either nine or ten electrodes  30 . Although  FIGS. 10B-10H  show and describe only two electrodes  30  on the carrier arm  90 , the features of the described electrodes  30  will also apply to any other electrodes  30  included on the carrier arm  90 . The electrodes  30  may be conductive, and the carrier arm  90  may be composed of a non-conductive material  91  (as shown in  FIG. 10A ). Alternatively, the embodiments of  FIGS. 10A-10H  may not include individual electrodes, but rather a flexible curved carrier arm  90  that is composed of a metal, such as gold, with an electrically insulated but thermally conductive coating (for example, diamond-like carbon) or with a selectively conductive coating (for example, gold with a thin film coating of tantalum that is oxidized to form tantalum pentoxide), with one or more alternating uncoated conductive regions  70 . As a non-limiting example, the oxide layer may be between approximately 10 nm to approximately 5000 nm, preferably approximately 100 nm to approximately 1000 nm. The exposed or uncoated conductive regions  70  may be smaller (that is, have less surface area) than the oxidized selectively conductive regions  72  (or electrically insulated but thermally conductive regions) to enhance signal quality during mapping when intracardiac electrogram voltage is measured. Alternatively, the conductive regions  70  and selectively conductive regions  72  may be the same size. As a non-limiting example in which electrodes  30 , are borne on the carrier arm  90 , the carrier arm  90  may have a diameter of approximately 25 mm, and each of the electrodes  30  and portions of the carrier arm  90  between the electrodes  30  may be approximately 3 mm wide. Further, the carrier arm  90  may include ten electrodes affixed thereto. 
     A first end  92  of the carrier arm  90  may be affixed to, for example, an elongate body  18  of the device, whereas a second end  94  of the carrier arm  90  may be affixed to a guidewire sheath  96  that is slidably receivable within the device. Therefore, the carrier arm  90  may be transitionable from a substantially linear delivery configuration when the guidewire sheath  96  is extended to a curved treatment configuration when the guidewire sheath  96  is retracted or partially retracted. For example,  FIG. 10A  shows the guidewire sheath  96  being partially retracted, and the carrier arm  90  extending approximately 360° between the first end  92  and the second end  94  of the carrier arm  90 . 
       FIG. 10B  shows a close-up view of a portion of the carrier arm  90 , wherein the conductive regions  70  are entirely conductive. The entire carrier arm  90  may be non-conductive or selectively conductive in order to ablate or electroporate tissue when high-frequency or pulsed current is applied (for example, RF voltage). Alternatively, the carrier arm  90  may be electrically insulated and thermally conductive, as described for  FIGS. 10C-10H . Further, although  FIG. 10B  shows electrodes  30  affixed to the carrier arm  90 , the electrodes  30  may be integral to the carrier arm  90 , as described above in  FIG. 10A . In the example shown in  FIG. 10B , the conductive electrodes  30  are affixed to the carrier arm  90 , and the carrier arm  90  is selectively conductive  72 . Further, the conductive  70  electrodes  30  shown in  FIG. 10B  may wrap all the way around the circumference of a cross section of the carrier arm  90 . The figure also shows a portion of an electrogram signal (inset). 
       FIGS. 10C-10H  show close-up views of carrier arm  90  portions wherein the electrodes  30  are partially conductive. That is, the electrodes  30  are conductive only in certain areas, in particular, areas that will be in contact with target tissue (for example, an anterior or tissue-facing surface  48  of the carrier arm  90 ). For example, the electrodes  30  may be composed of a material, such as gold or gold alloy, that is affixed to the outer surface of the carrier arm  90  (which may be non-conductive  91 , selectively conductive  72 , or electrically insulated but thermally conductive  97 ; depicted in the figures as “92/72/97”), and only a portion of the electrode  30  may be uncoated or exposed (that is, conductive). The remaining portions  100  of the electrodes  30  may be selectively conductive (for example, composed of gold with a thin film outer layer of tantalum that has been oxidized to form tantalum pentoxide) or electrically insulated but thermally conductive (for example, having an outer layer of diamond-like carbon). The electrically insulative but thermally conductive outer layer may dissipate heat to the bloodstream yet prevent energy loss to the non-tissue-facing surfaces that are not in tissue contact. The electrically insulative but thermally conductive layer may be a thin coating of one or more materials such as thermal pyrolytic graphite, graphite, graphene, diamond, diamond-like carbon (DLC) coatings, alumina, sapphire, zirconia, tantala, titania, beryllium oxide, polymer composites containing thermally conductive particles, nanoparticles, self-assembling nanoparticles, nanomaterials and composites, biocompatible thermally conductive fluids like olive oil, medical grade silicone oil, and similar materials. Further, this layer may be between approximately 10 nm and approximately 5000 nm. 
     Alternatively, the electrodes  30  may be integral to the carrier arm  90 , with the conductive regions  70  being exposed or not having an outer oxide layer or layer of electrically insulated but thermally conductive material (for example, diamond-like carbon). In either configuration, the non-tissue-facing surfaces of both the electrode  30  and the carrier arm  90  (for example, if the carrier arm  90  is selectively conductive) may include an electrically isolated but thermally conductive layer, with only the anterior or tissue-facing surfaces of the electrodes  30  being conductive. Further, in all embodiments, the conductive regions  70  may be smaller than the non-conductive or selectively conductive portions, or they may be the same size. None of the figures shown herein may be drawn to scale.  FIGS. 10C-10H  also show a portion of an enhanced electrogram signal (inset) that may be achieved using the devices of  FIGS. 10C-10H . 
     In  FIGS. 10C-10E , the conductive regions  70  of the electrodes  30  may be linear. In  FIGS. 10F-10H , the conductive regions  70  may be substantially circular. In  FIGS. 10G and 10H , the circular conductive regions  70  may be raised or may protrude from the surface of the carrier arm  90  in a prominent bump  102 . As discussed in  FIGS. 9B and 9C , this prominent bump  102  may further enhance electrogram signal quality. Further, when very minimal or open signal filtering is applied (for example, approximately 0.5 Hz to approximately 1000 Hz), the prominent bump  102  may produce a monophasic action potential when referenced against a non-tissue-facing reference electrode  24 , as shown in  FIG. 10H . The reference electrode  24  may be located on the distal portion of the elongate body  17  (as shown in  FIG. 10A ) or on a non-tis sue-facing surface of the carrier arm  90  (not shown). 
     Referring now to  FIG. 11 , an eleventh embodiment of a distal assembly is shown. The device may be a focal catheter having a rounded distal tip  66 . A mapping and ablation electrode  30  may be disposed over the distal tip  66  and portion of the distal portion  22  of the elongate body  18 , as shown. The electrode  30  may include a conductive region  70  and a non-conductive or selectively conductive region  104 . In one configuration, the region  104  may be selectively conductive. Both the conductive  70  and selectively conductive  104  regions may be composed of a metal such as gold or gold alloy, and the selectively conductive region  104  may, for example, have a thin film layer of tantalum over the gold and the tantalum layer may be oxidized to tantalum pentoxide. As a non-limiting example, the oxide layer may be between approximately 10 nm to approximately 5000 nm, preferably approximately 100 nm to approximately 1000 nm. In this case, the conductive region  70  may be used for mapping procedures and the entire electrode  30  may be used for ablation or electroporation procedures (as described in more detail in, for example,  FIG. 2 ). In another configuration, the region  104  may be non-conductive. The entire electrode  30  may be composed of a conductive metal (for example, gold or gold alloys), but the non-conductive region  104  may have a coating with a material that is highly thermally conductive but is fully electrically insulative, such as thermal pyrolytic graphite, graphite, graphene, diamond, diamond-like carbon (DLC) coatings, alumina, sapphire, zirconia, tantala, titania, beryllium oxide, polymer composites containing thermally conductive particles, nanoparticles, self-assembling nanoparticles, nanomaterials and composites, biocompatible thermally conductive fluids like olive oil, medical grade silicone oil, and similar materials. In this case, the device may provide enhanced electrogram signal quality (due to the smaller region of the electrode  30  that is used for mapping procedures and the interference-mitigating effect of the coating), a high cooling capability, and a reduced loss of ablation or electroporation energy to the bloodstream. 
     Referring now to  FIGS. 12A and 12B , a twelfth embodiment of a distal assembly is shown. The distal assembly  14  may include one or more carrier arms  106  bearing one or more mapping and/or ablation electrodes  30 . One carrier arm  106  is shown in  FIG. 12A  for simplicity; however, two or more carrier arms  106  may be used. For example,  FIG. 12B  shows the anterior or tissue-facing surface  48  of distal assembly  14  including two carrier arms  106 . Each carrier arm  106  may include a first portion  108  at the anterior or tissue-facing surface  48  of the carrier arm  106  on which the one or more mapping and/or ablation electrodes  30  are borne, and two second portions  110  that are coupled to the device  12 . The distal assembly  14  may further include one or more reference electrodes  24 . Each of the electrodes  30  may include a conductive region  70  and a region that is electrically insulated but highly thermally conductive  97 . For example, both the conductive region  70  and the insulated region  97  may be composed of gold or gold alloy, whereas the insulated region  97  may include a thin film coating or layer of a material such as diamond-like carbon (DLC). Although not shown in  FIG. 12A or 12B , the electrode  30  may be composed of gold with a thin film surface of tantalum, and may include selectively conductive regions  72  in which the tantalum layer is oxidized to form tantalum pentoxide. These selectively conductive regions  72  may largely correspond to the insulated regions  97  shown in  FIGS. 12A and 12B . As a non-limiting example, the oxide layer may be between approximately 10 nm to approximately 5000 nm, preferably approximately 100 nm to approximately 1000 nm. 
     The point at which the first  108  and second  110  portion of each carrier arm  106  meet may form an acute angle. The second portion  110  of each arm  106  may be affixed to a shaft that is slidably movable within the elongate body  16  of the device  12 , or affixed directly to the elongate body  18 . Further, the distal assembly  14  may be composed of a resilient and deformable material, and may assume a first position for delivery (not shown) and a second position for mapping and/or treatment (as shown in  FIG. 12A ). When in the second expanded position, the first portion  108  of each arm  106  may lie in a plane that is substantially orthogonal to the longitudinal axis of the device  12 . Still further, the resilient and deformable material may be biased toward either the first or second position and may be steerable by one or more pull wires, guide wires, rods, or other steering mechanisms controllable at or proximal to the handle  28  of the device  12 . The one or more electrodes  30  may be capable of transmitting both low-frequency and high-frequency current, and may be suited for mapping, ablation, and/or electroporation. 
     The embodiments shown and described in  FIGS. 10 and 12 , in particular, may be suited for anatomical placement, such that certain areas of the electrode  30  will be tissue contacting while other areas will only be in contact with the blood. The Medtronic Ablation Frontiers Pulmonary Vein Ablation Catheter® (PVAC) is an example of such a device as shown and described in  FIGS. 10A-10H , and the Medtronic Ablation Frontiers Multi-Array Ablation Catheter® (MAAC) is an example of such a device as shown and described in  FIGS. 12A and 12B . The exposed fully electrically conductive regions  70  of the electrodes  30  are specifically placed in areas of the electrode  30  that will contact cardiac muscle that is to be electrically mapped and potentially ablated. In some embodiments, the non-cardiac muscle facing portions of the electrode  30  may be coated with the electrically insulative material that is also highly thermally conductive. Two important functions are served by the coating: during mapping, the non-cardiac muscle (tissue) facing surfaces do not collect far-field electrical signals that degrade quality of local electrograms; and, during ablation (for example, RF ablation) or electroporation, the non-muscle facing surfaces do not waste energy to the blood but these surfaces serve to dissipate heat collected by the tissue facing side of the electrode, through the electrode and into the flowing blood. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.