Patent Publication Number: US-2013231659-A1

Title: Off-wall and contact electrode devices and methods for nerve modulation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/605,649, filed Mar. 1, 2012, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to medical devices, and methods for manufacturing medical devices. More particularly, the present disclosure pertains to methods and apparatuses for modulating nerves through the walls of blood vessels. 
     BACKGROUND 
     Certain treatments require temporary or permanent interruption or modification of select nerve functions. One example treatment is renal nerve ablation, which is sometimes used to treat conditions related to congestive heart failure. The kidneys produce a sympathetic response to congestive heart failure, which among other effects, increases the undesired retention of water and/or sodium. Ablating some nerves running to the kidneys may reduce or eliminate this sympathetic function, providing a corresponding reduction in the associated undesired symptoms. For example, a renal nerve ablation procedure is often used to lower the blood pressure of hypertensive patients. 
     Many nerves (and nervous tissue such as brain tissue), including renal nerves, run along the walls of or in close proximity to blood vessels and these nerves can be accessed intravascularly through the blood vessel walls. In some instances, it may be desirable to ablate or otherwise modulate perivascular renal nerves using a radio frequency (RF) electrode. Such treatment, however, may result in thermal injury to the vessel at the electrode and other undesirable side effects such as, but not limited to, blood damage, clotting, and/or protein fouling of the electrode. To prevent such undesirable side effects, some techniques attempt to increase the distance between the vessel walls and the electrode. In these systems, however, the electrode may inadvertently contact the vessel walls. 
     Therefore, there remains room for improvement and/or alternatives in providing systems and methods for intravascular nerve modulation. 
     SUMMARY 
     The disclosure is directed to several alternative designs and methods of using medical device structures and assemblies. 
     Accordingly, some embodiments pertain to a system for nerve modulation, including an elongate shaft having a proximal end, a distal end, and a nerve modulation assembly at the distal end. The nerve modulation assembly has a collapsed configuration and an expanded configuration. The system may further include an inner basket having a proximal end and a distal end and multiple electrode struts joined to each other at the proximal end of the inner basket and extending to the distal end of the inner basket. Each electrode strut includes an electrode. The electrodes may be monopolar or bipolar. The electrodes of the system may be powered with a single power controller for all electrodes or use dedicated power controllers for each electrode. The power to the electrodes might be delivered simultaneously to all electrodes or in some sequential pattern. In addition, an outer basket having a proximal end and a distal end and a plurality of spacer struts joined to each other at the proximal end of the outer basket and extending to the distal end of the outer basket. The inner basket and the outer basket are disposed at the distal end of the elongate shaft, wherein in the expanded configuration, the plurality of spacer struts extend further radially from the elongate axis than the plurality of electrode struts. 
     An example system for nerve modulation may include an elongate shaft having a longitudinal axis, a proximal end, a distal end, and a nerve modulation assembly disposed at the distal end. The nerve modulation assembly may have a collapsed configuration and an expanded configuration. The nerve modulation assembly may include an inner basket and an outer basket. The inner basket may include a proximal end and a distal end. The inner basket may also include a plurality of electrode struts joined to each other at the proximal end of the inner basket and extending to the distal end of the inner basket. Each electrode strut may include an electrode. The outer basket may include a proximal end and a distal end. The outer basket may also include a plurality of spacer struts joined to each other at the proximal end of the outer basket and extending to the distal end of the outer basket. The inner basket and the outer basket may be disposed at the distal end of the elongate shaft. When the nerve modulation assembly is in the expanded configuration the plurality of spacer struts may extend further radially outward from the longitudinal axis of the shaft than the plurality of electrode struts. 
     Another example system for nerve modulation may include an elongate shaft having a proximal end, a distal end and a nerve modulation assembly at the distal end. The nerve modulation assembly may include a basket configured to shift between a collapsed configuration and an expanded configuration. The basket may have a proximal end and a distal end. The basket may include a plurality of inner struts and a plurality of outer struts. Each of the inner struts may include an electrode portion and an electrically insulated portion. The basket may be disposed at the distal end of the elongate shaft. 
     Another example system for nerve modulation may include an elongate shaft having a proximal end and a distal end. A basket assembly configured to move between a collapsed configuration and an expanded configuration may be disposed adjacent to the distal end of the elongate shaft. The basket assembly may include an inner basket having a proximal end and a distal end and comprising a first plurality of struts. At least one of the first plurality struts may include an electrode. The basket assembly may also include an outer basket having a proximal end and a distal end and comprising a second plurality of struts. The second plurality of struts may include an insulating material. In the expanded configuration the outer basket may have a cross-sectional profile larger than a cross-sectional profile of the inner basket. 
     The summary of some example embodiments is not intended to describe each disclosed embodiment or every implementation of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic view illustrating a renal nerve modulation system in situ. 
         FIG. 2A  is a schematic view of an exemplary ablative catheter system with an ablative member in the expanded state. 
         FIG. 2B  illustrates the ablative member of  FIG. 2A  in a collapsed position. 
         FIG. 3A  illustrates the distal end of an exemplary ablative catheter system in an expanded position within a blood vessel. 
         FIG. 3B  is a cut away sectional view of the ablative member of  FIG. 2A . 
         FIG. 4  illustrates the distal end of an alternate ablative catheter system in an expanded position within a blood vessel. 
         FIG. 5  is cross-sectional view of an embodiment of an ablative catheter system with an ablative member in an expanded state within a blood vessel. 
         FIG. 6  is cross-sectional view of an embodiment of an ablative catheter system with an ablative member in an expanded state within a blood vessel. 
         FIG. 7  is an isometric view of the distal portion of an example ablative catheter system with an ablative member in the expanded state. 
         FIG. 8  is an isometric view of the distal portion of an example ablative catheter system with an ablative member in the expanded state. 
         FIG. 9  is an isometric view of the distal portion of an example ablative catheter system with an ablative member in the expanded state. 
         FIG. 10A  is an isometric view of the distal portion of an example ablative catheter system with an ablative member in the expanded state. 
         FIG. 10B  is an end view of the distal portion of the example ablative catheter system of  FIG. 10A  with an ablative member in the expanded state. 
         FIGS. 11A and 11B  are isometric views of the distal portion of an ablative catheter system shown in an expanded state and a collapsed state, respectively. 
         FIG. 12  is an isometric view of the distal portion of an ablative catheter system shown in an expanded state. 
         FIG. 13  is an isometric view of the distal portion of an ablative catheter system shown in an expanded state. 
         FIG. 14  is an isometric view of the distal portion of an ablative catheter system shown in an expanded state. 
     
    
    
     While embodiments of the present disclosure are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular embodiments described. One the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure. 
     DETAILED DESCRIPTION 
     For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in the specification. 
     All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the term “about” may be indicative as including numbers that are rounded to the nearest significant figure. 
     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     Although some suitable dimension ranges and/or values pertaining to various components, features, and/or specifications are disclosed, one of skill in the art, incited by the present disclosure, would understand desired dimensions, ranges and/or values many deviate from those expressly disclosed. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The detailed description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. The illustrative embodiments depicted are intended only as exemplary. Selected features of any illustrative embodiment may be incorporated into an additional embodiment unless clearly stated to the contrary. 
     While the devices and methods described herein are discussed relative to renal nerve modulation, it is contemplated that the devices and methods may be used in other applications where ablation or modulation are desired such as nerve modulation and/or ablation near other vessel lumens. 
     In some instances, it may be desirable to ablate perivascular renal nerves with targeted tissue heating. However, as energy passes from an electrode to the desired treatment region the energy may heat the fluid (e.g. blood) and tissue as it passes. As more energy is used, higher temperatures in the desired treatment region may be achieved, but may result in some negative side effects, such as, but not limited to, thermal injury to the vessel wall, blood damage, clotting, and/or electrode fouling. Positioning the electrode away from the vessel wall may provide some degree of passive cooling by allowing blood to flow past the electrode while still allowing the electrode elements to target nerves within about 2.5 mm of the luminal surface, where the perivascular renal nerves are located. An appropriate amount of energy may properly ablate the nerve tissue while causing no damage to the vessel wall or to deep tissue such as muscle tissue or the intestinal walls. 
       FIG. 1  is a schematic view of an illustrative renal nerve modulation system  100  in situ. System  100  may include one or more conductors  102  for providing power to a nerve modulation assembly  104  disposed within a catheter sheath or guide catheter  106 . A proximal end of the conductor  102  may be connected to a control and power element  108 , which supplies the necessary electrical energy to activate the one or more electrodes (not shown) at or near a distal end of the nerve modulation assembly  104 . In some instances, return electrode patches  110  may be supplied on the struts or at another conventional location on the patient&#39;s body to complete the circuit. In bipolar designs, the ground electrodes may be present on the device near the distal end. The control and power element  108  may include monitoring elements to monitor parameters such as power, temperature, voltage, amperage, impedance, pulse size and/or shape and other suitable parameters as well as suitable controls for performing the desired procedure. In some instances, the power element  108  may control a radio frequency (RF) electrode. The electrode may be configured to operate at a frequency of approximately 460 kHz. It is contemplated that any desired frequency in the RF range may be used, such as, for example, from 400-900 kHz. However, it is contemplated that different types of energy outside the RF spectrum may be used as desired, such as, for example, but not limited to ultrasound, microwave, and laser. 
       FIGS. 2A and 2B  are schematics of an exemplary ablative catheter system  200  according to embodiments of the present disclosure. More particularly,  FIG. 2A  is a side view of the catheter system  200  in an expanded state, while  FIG. 2B  is a side view of the catheter system  200  in a collapsed or compressed state. The ablative catheter system  200  includes catheter sheath  106  having a proximal end  204  and a distal end  206 , an elongate member  208  having a proximal end  210  and a distal end  212 , and an expandable ablative member, such as the nerve modulation assembly  104  coupled to the elongate member&#39;s distal end  212 . The catheter system  200  may further include a handle  216  coupled to the sheath&#39;s proximal end  204 . 
     The sheath  106  may be substantially circular, formed of any suitable biocompatible material such as polyurethane, polyether block amide, polyimide, nylon, polyester, polyethylene, or any other such polymeric materials. The sheath  106  may also be a composite structure comprising a polymer matrix and a braid that is also a polymer or metal. Other suitable cross-sectional shapes such as elliptical, oval, polygonal, or irregular may also be contemplated. Moreover, the sheath  106  may be flexible along its entire length or adapted for flexure along portions of its length. Alternatively, the sheath&#39;s distal end  206  may be flexible while the remaining sheath may be rigid. Flexibility allows the sheath  106  to maneuver in the circuitous vasculature, while rigidity provides the necessary rigidity to allow the operator to urge the sheath  106  forward. The diameter of the sheath  106  may vary according to the desired application, but it is generally smaller than the typical diameter of a patient&#39;s vasculature. Moreover, the diameter of the sheath  106  may depend on the diameter of the elongate member  208  and the nerve modulation assembly  104 . 
     The elongate member  208 , as described previously, extends along the elongate axis from the proximal end  204  of the sheath  106 . Further, the elongate member&#39;s proximal end  210  may be connected to the handle  216  and its distal end  212  may be connected to the nerve modulation assembly  104 . The connection to the handle  216  and the nerve modulation assembly  104  may be temporary or permanent. Examples of temporary connection include snap-fit, Luer-lock, or screw-fit devices. Examples of permanent or semi-permanent connection include welding or gluing. It will be understood that various other connection mechanisms may be incorporated to connect the various members. In other instances, the elongate member  208  may not be connected to the handle  216 . Instead, the handle  216  may include one or more ports (not shown) and the elongate member  208  may be inserted in the catheter sheath&#39;s lumen through the port. Using an independent elongate member  208  and nerve modulation assembly  104  allows operators to use the catheter sheath  106  for other procedures or to insert guidewires for guiding and urging the catheter to the desired location. 
     In one embodiment, the elongate member  208  is a conductor covered by an insulative material. The proximal end of the conductor may be connected to a power source  218  such as an external power generator or battery incorporated in the handle  216 . The distal end of the conductor may be connected to the nerve modulation assembly  104 . 
       FIG. 2A  illustrates the nerve modulation assembly  104  in an expanded state. In general, the nerve modulation assembly  104  is configured as a bi-level basket having an outer basket that contacts the blood vessel walls and an inner basket that includes electrodes for ablation purposes. Electrodes positioned on the inner basket of the nerve modulation assembly  104  remain spaced from the vessel wall. Depending on the desired application, electrodes may be placed in any desired position on the inner basket of the nerve modulation assembly  104 . The nerve modulation assembly  104  is discussed in detail in the following section in connection with  FIGS. 3A and 3B . 
       FIG. 2B  is a schematic illustrating the distal portion of the ablative catheter system  200  with the nerve modulation assembly  104  in the compressed state. From this state, the ablative member may be expanded using numerous techniques depending on the properties of the ablative member. These techniques may be applied on each of the inner and outer basket, expanding the baskets to the desired degree. For instance, the ablative member  104  may be self-expandable or expanded by some external force such as a pull wire. Self-expandable members may be formed of any material that is in a compressed state when force is applied and in an expanded state when force is released. Such members may be formed of steel or of shape memory alloys such as Nitinol or any other self-expandable material. 
     Many techniques may be utilized to compress a self-expandable member and keep it in the compressed state. According to one technique, the nerve modulation assembly  104  is present within the sheath  106  for deployment (shown in  FIG. 2B ). The inner diameter of sheath  106  is smaller than the expanded state of nerve modulation assembly  104 , keeping it in the compressed state. Once the assembly  104  exits the sheath  106 , however, the pressure is released, and the modulation assembly  104  expands. It will be understood that in such situations, the material and thickness of the sheath  106  is selected such that it applies a greater force on the nerve modulation assembly  104  than the force exerted by the modulation assembly  104  on the sheath  106 . If the sheath  106  material is too thin or too elastic, it may not be sufficient to hold the nerve modulation assembly  104  in the compressed state, and the nerve modulation assembly  104  may expand within the sheath  106  itself. Alternatively, if the sheath  106  is too rigid or thick, it may not be able to traverse the circuitous vasculature path, causing injury to the vessel walls. Therefore, it may be often preferred to select a suitable material and thickness keeping both aspects in mind. 
     According to another technique, pull wires (not shown) may be utilized. Pull wires may be attached to the ablative member&#39;s distal end or proximal end. In some instances, pull wires may be connected to both the inner and the outer basket. This may allow a user to selectively control the configuration of each basket individually. When the pull wire is pulled in a certain axial direction (distally or proximally), it places a tensile force on the nerve modulation assembly  104 , stretching it longitudinally and keeping it in the compressed state. When the pull wire is released, the tensile force is released permitting the nerve modulation assembly  104  to enter the expanded state. For example, if the pull wire is attached to the ablative member&#39;s distal end, pulling the wire distally elongates (compresses) the nerve modulation assembly  104  and releasing the pull wire, releases the force on the nerve modulation assembly  104 , expanding it. Moreover, a member to pull, push, or release the pull wire may be configured in the device&#39;s handle  216  allowing operators to easily expand or compress the nerve modulation assembly  104 , as required. Alternatively, the actuation mechanism may be present at the proximal end  210  of the elongate member  208 . 
     Where nerve modulation assembly  104  is expanded by some external force, the nerve modulation assembly  104  does not expand on its own. Thus, an expanding mechanism may be required to impose an outward radial force on the modulation assembly  104  to expand it. Such expansion mechanism (not shown) may include balloons inflated by fluids, or dilators. Other such expansion mechanism may also be utilized without departing from the scope of the present disclosure. For example, springs or levers may be utilized to expand the nerve modulation assembly  104 . Similarly, the nerve modulation assembly  104  itself may be formed of pivotal structures connected to one another. For instance, the modulation assembly  104  may be formed of multiple wires interconnected along pivotal joints. An outward force on the pivotal point expands the various wires connected to the point, expanding the nerve modulation assembly  104 . 
     The expansion of the nerve modulation assembly  104  should be such that it does not cause damage to the artery by exerting a large force on the vessel walls. To prevent such large expansion diameters, the nerve modulation assembly  104  may include visualization features such as radiopaque struts or markers to visualize the extent of expansion using standard fluoroscopy methods. Further, the nerve modulation assembly  104  may include a force or expansion-limiting component that prevents the modulation assembly  104  from expanding beyond a certain limit. Often, the expansion limit may be set during manufacturing of the modulation assembly  104 . For example, operators may know the average size of renal arteries, and they may ensure the basket does not expand beyond the average artery size. For example, the diameter of the expanded modulation assembly  104  may be maintained below about 4 French. The expansion-limiting component may be employed on both the inner and outer basket, as desired. 
     The following figures and description illustrate a specific exemplary configuration of the nerve modulation assembly  104 . 
       FIG. 3A  is a schematic illustrating a distal portion of the ablative catheter system  200  within a blood vessel in a patient&#39;s body. Here, the nerve modulation assembly  104 , having a proximal end  304  a distal end  306 , is in the expanded state. The nerve modulation assembly  104  generally forms a double basket, including an outer basket  308  and an inner basket  310 . The outer basket  308  is longer than and encloses the inner basket  310  such that the surface of the inner basket  310  is spaced away from the vessel wall  302 , thus never making contact with vessel wall  302 . The inner basket  310  includes electrodes  312  positioned on its surface, as desired. The inner basket  310  may be longitudinally centered as shown in  FIG. 3A  or may be longitudinally offset with respect to the outer basket  308 . The electrodes  312  may be centered on the inner basket  310  as shown in  FIG. 3A  or may be offset or angled on the inner basket  310 . 
     The outer basket  308  includes multiple spacer struts  314  and the inner basket  310  includes multiple electrode struts  316 . The struts  314 ,  316  are joined together along the longitudinal axis at their proximal and distal ends. In the illustrated embodiment, struts  314 ,  316  axially extend from the proximal end  304  to the distal end  306 . In other embodiments, however, struts  314 ,  316  may follow a spiral or helical path from the proximal end  304  to the distal end  306 . It will be understood that other basket  308 ,  310  configurations are also within the scope of the present disclosure. In addition, the number of struts  314 ,  316  constituting the inner basket  310  and outer basket  308  may vary, as desired. For example, the outer and inner baskets  308 ,  310  may include 5 struts each. In an aspect, the outer basket  308  may include 6 struts, while the inner basket  310  may include only 4 struts. These are just examples. It is contemplated that either the outer basket  308  or the inner basket  310  may have any number of struts  314 ,  316  desired. 
     Struts  314 ,  316  generally remain substantially parallel to the longitudinal axis in the compressed state, and radially expand in the expanded state. A center portion of struts  314  and  316  expand to form baskets. As shown, the outer basket  308  expands to a greater degree as compared to the inner basket  310 , keeping the inner basket struts  316  spaced apart from the vessel walls  302 . 
     Each strut  314 ,  316  may be formed of a single wire extending from the proximal end to the distal end. Alternatively, the struts  314 ,  316  may be formed of multiple wires twisted or braided along the length of the nerve modulation assembly  104 . Moreover, the multi-wire struts  314 ,  316  may extend along the entire length of the retracting member and the sheath, or only the length of the retracting member. In other cases, portions of the struts  314 ,  316  may be formed of single wires, while other portions may be formed of multiple wires. In yet other cases, the thickness of the wires may be uniform along the length of the struts. Alternatively, the wires may be thicker in the middle and thinner at the proximal and distal portions of the struts  314 ,  316 , or vice-versa. 
     Each strut  314 ,  316  may assume varying shape and configuration. For example, struts  314 ,  316  may be round, flat ribbons, solid wires, or hollow tubes. In addition, all struts  314 ,  316  may be identical, or different struts  314 ,  316  may be shaped differently. If round struts are used, it may be desirable to bias the strut to expand in the desired direction by a forming method or localized plastic deformation. Flat ribbons may have a width (tangent to the circumference of the device) greater than the thickness (the dimension along a radius) to ensure bowing in the proper direction when expanded. Alternatively, a predetermined bias may be built into the strut  314 ,  316 . 
     In general, spacer struts  314  may be made any suitable insulative material acting as electrical spacers. Struts  316 , however, may be made of a conductive material with an insulative cladding. A portion of the struts  316  may be bare wire acting as electrodes  312 . For example, a center portion of the struts  316  may be without a cladding, while all other portions may have the insulative cladding. Alternatively, the struts  316  may also be made of completely insulative material and external electrodes  312  may be attached to portions of the nerve modulation assembly  104 . For example, one or more wireless or wired electrodes connected to the power source may engage with the one or more struts  316 . 
       FIG. 3B  is a schematic of a cross-section of the nerve modulation assembly  104  of  FIG. 3A  showing the electrodes  312  and the spacer struts  314 . In  FIG. 3B , the struts  314  of the outer basket  308  have been connected with a circular line and the struts  316  of the inner basket  310  have also been connected with a circular line to illustrate the outer profile of both the outer and inner baskets  308 ,  310 . However, this is merely exemplary. The struts  314 ,  316  are not necessary interconnected. Further, diagonal lines connecting outer struts  314  offset from inner struts  316  have been included to illustrate the struts  314 ,  316  may be offset from one another, although this is not required. When fully expanded, the spacer struts  314  may contact or nearly contact the vessel wall  302 , while electrodes  312  positioned on the inner basket  310  confined within the outer basket  308 , preventing contact between vessel walls  302  and electrodes  312 . 
     Further, the electrodes  312  may each be connected to a power supply, such as power source  218 , such that each electrode may be operated separately and current may be maintained to each electrode  312 . The power source may activate each electrode  312  one at a time. The next electrode is activated only after a first electrode is activated and deactivated. Alternatively, the electrodes  312  may be activated simultaneously. 
     When electrical signals are passed through the struts  316 , the bare portions behave as electrodes  312 . Therefore, based on the required number and position of electrodes  312 , portions of the nerve modulation assembly  104  may be left bare. 
     Electrodes  312  may be positioned on struts  316  in any suitable manner, designed to provide ablative RF energy to selected areas adjacent the target vessel. In some embodiments, all electrodes  312  may be positioned on the center portion of each internal strut  316 . Alternatively, electrodes  312  may be staggered so that all the electrodes  312  are not located at the same axial level. Such an arrangement may allow electrodes  312  to target different ablation sites. For example, the electrode  312  for one strut  316  may be in the central portion, for another strut  316  may be in the proximal portion, and for a third strut  316  may be in the distal portion. In addition, the number of electrodes  312  on struts  316  may vary. In an embodiment, only one of the struts  316  may include bare electrodes  316 . Alternatively, some or all of the struts  316  may include the electrodes  312 . Different alternatives of the electrodes  312  may be contemplated. For example, bare electrode portions  312  on struts  316  may be identically or differently shaped such as round or oblong paddles. 
       FIG. 4  illustrates an alternate embodiment of the ablative catheter system  400  depicting the nerve modulation assembly  104  deployed within the blood vessel  302 . The nerve modulation assembly  104 , extending from the distal end of the sheath  106 , is configured to assume an expanded configuration. 
     A number of elements of ablative system  400  are similar to those shown in  FIG. 2  such as the outer basket  308 , inner basket  310 , and struts  314 ,  316 . Here, the ablative catheter system  400  includes a wider electrode  402  (as compared to the struts  316 ), as opposed to system  200 , where the electrodes  312  are bare wires having a cross-section smaller than the remaining strut portion. In the illustrated embodiment, the electrodes  402  may be oblong, paddle, or suitably shaped having a cross-section wider than the proximal portion of the struts  316 . 
     The rigidity and characteristics of the material used to form the nerve modulation assembly  104  determine expandability of the nerve modulation assembly&#39;s  104 . For example, the thickness of the material may vary between the central portion, and the distal and proximal portions, causing the central portion to deviate greater than the proximal and distal portions. In addition, the outer and inner struts  314 ,  316  may expand to a different degree. For example, the spacer struts  314  may expand more so than the electrode struts  316 , creating spaces between the electrode struts  316  and the vessel wall  302 . To this end, the material composition may vary between the central and end portions of each strut and between spacer and electrode struts  314 ,  316 , varying the expandability of these portions. In some embodiments, stainless steel may be used to form one portion, while tungsten, platinum, palladium, or a suitable polymer may be used to form other portions. Other techniques to vary the expandability of the struts may be employed just as easily, as understood by those of skill in the art. 
     Further, the degree of expansion, the materials used, and the thickness of the struts  314 ,  316  may vary within the struts without departing from the scope of the present disclosure. Moreover, different levels of expansion may be carried out for the different inner struts  316  so that the electrodes  312  are at a varied distance from the artery walls. 
     It will be understood that other variations in configuration are possible as long as the nerve modulation assembly  104  includes insulated portions in contact with the vessel wall and bare electrode portions  312  away from the vessel wall. For example, the nerve modulation assembly  104  may be made of expandable conductor wires shaped as an ellipse or a circle. The elliptical or circular member may be stored in a compressed state within the sheath  106 , and when the nerve modulation assembly  104  is actuated to extend beyond the distal end  206  of the sheath  106  the nerve modulation assembly  104  may expand. In this type of nerve modulation assembly  104 , the electrodes  312  may be positioned at the distal or proximal end of the nerve modulation assembly  104 . Alternatively, the inner struts may have a zigzag shape, bends, or bumps to position the electrodes  312  as desired. 
     For example,  FIG. 5  is a cross-sectional view of an example system disposed in an expanded state within a blood vessel  550 . The outer basket  508  comprises five spacer struts  514  that have a ribbon-shaped cross-sectional profile. An inner basket  510  comprises five electrode struts  512  that also have a ribbon-shaped cross-sectional profile. The electrode struts  512  of the inner basket  510  are offset from the spacer struts  514  of the outer basket, although this is not required. Furthermore, while the system is described as including five space struts  514  and five electrode struts  512 , it is contemplated that there may be any number of struts desired in either the outer basket  508  or the inner basket  510 . Additionally, the dimensions illustrated in  FIG. 5  are merely examples. The struts  512 ,  514  may take any shape and/or size desired. Similarly, the spacing between the vessel wall  550  and the electrode struts  512  may be any distance desired. The embodiment is otherwise similar to that described with respect to  FIGS. 3A and 3B . 
       FIG. 6  is a cross-sectional view of an example system disposed in an expanded state within a blood vessel  650 . The outer basket  608  comprises five spacer struts  614  that have a ribbon-shaped cross-sectional profile. An inner basket  610  comprises five electrode struts  612  that also have a ribbon-shaped cross-sectional profile. The electrode struts  612  of the inner basket  610  are in line with the spacer struts  614  of the outer basket, although this is not required. Furthermore, while the system is described as including five space struts  614  and five electrode struts  612 , it is contemplated that there may be any number of struts desired in either the outer basket  608  or the inner basket  610 . Additionally, the dimensions illustrated in  FIG. 6  are merely examples. The struts  612 ,  614  may take any shape and/or size desired. Similarly, the spacing between the vessel wall  650  and the electrode struts  612  may be any distance desired. The embodiment is otherwise similar to that described with respect to  FIGS. 3A and 3B . 
       FIGS. 7 and 8  illustrate a portion of example ablative catheter systems with an ablative member in the expanded state. Systems  700  and  800  each have inner baskets  710 , 810  and outer baskets  708 , 808  that comprise struts having a ribbon profile. The expandable portion of inner basket  710  of system  700  is confined by a distal ring  720  and a proximal ring  722 . Both rings  720  and  722  are within the outer basket  708 . A pull wire  724  has a distal stop  726  and is freely slidable within a lumen  728  of the system  700 . When the pull wire is moved proximally relative to a catheter  730  attached to the baskets, the baskets  708 ,  710  are moved to the expanded shape shown in  FIG. 7 . In the embodiment of  FIG. 8 , the pull wire  824  is fixed to the distal end  826  of the system  800 . A proximal end  834  of the outer basket  808  is fixed to a catheter (not shown) that extends proximally over the pull wire  824 . Relative proximal movement of the pull wire  824  relative to the catheter causes the baskets  808 , 810  to expand to the expanded configuration shown in  FIG. 8 . Distal and proximal stops  820 , 822  on the inner basket  810  within the outer basket  808  cause the radial expansion of the inner basket to be less than that of the outer basket. The electrode struts  712 ,  812  of the systems  700 ,  800  are electrically connect to a power source. 
     The active portions of the electrode struts  712 ,  812  may vary. For example, the whole of a strut  712  from ring  720  to  722  may be bare and act as an electrode or only a portion of the strut may be bare and act as an electrode. The non-electrode portions are coated with an electrically insulating material. A proximal portion, middle portion or distal portion may be the active electrode portion. In some embodiments, only an inner portion of the strut is the active electrode portion and the outer surface (and, in some embodiments, the edges between the inner and outer surfaces) are electrically insulated. In some of these embodiments as well, only a portion of the inner surface is the active electrode portion. For example, in one embodiment, the active electrode portion is the middle portion of the inner surface and the remainder of the strut  712  is insulated. It can be appreciated that the electrode struts of subsequent embodiments may readily include these variations discussed herein. 
       FIG. 9  illustrates a portion of an ablative catheter system  900  with an ablative member in the expanded state. In some instances, the inner basket  910  and outer basket  908  of system  900  may be formed from the same tubular precursor by a plurality of longitudinal slots cut in the tubular precursor. It is contemplated the size of the longitudinal slots may be varied to achieve the desired basket shape. In other instances, the inner basket  910  may be formed from a first tubular precursor and the outer basket  908  may be formed from a second tubular precursor. It is contemplated that the inner basket  910  may be formed from a smaller tubular precursor than the outer basket  908 , although this is not required. The proximal ends of the five struts  912  of the inner basket  910  are joined by a fixation element  922  that is distal a fixation element  944  that joins the proximal ends of the five struts  914  of the outer basket  908 . While the inner and outer baskets  910 ,  908  are described as including five struts  912 ,  914 , it is contemplated that the baskets  908 ,  910  may include any number of struts desired. Elements  922  and  944  are fixed relative to each other and slide over a pull wire  924  that is fixed to the distal end  926  of the system  900 . Element  944  is further fixed to a catheter (not shown) that extends proximally over the pull wire  924 . The electrode struts  912  of the inner basket  910  are electrically connected to a power source. The spacer struts  914  of the outer basket  908  are electrically insulated. The system may be biased to a closed state such that pulling on the pull wire  924  expands the system or biased to an open state such that pushing on the pull wire  924  collapses the system from an expanded state. 
       FIGS. 10A and 10B  illustrate an isometric and an end view, respectively, of the distal portions of an ablative catheter system  1000  that is similar to system  900  except as otherwise noted. The system  1000  may include an inner basket  1010  and an outer basket  1008 . The inner basket  1010  may include, but is into limited to, three electrode struts  1012  that have wider active electrode portions  1060 . The proximal strut portion  1062  and distal strut portion  1064  of each electrode strut  1012  may be insulated such that portion  1060  is the only active portion of the electrode strut. Each electrode strut  1012  may also include a stiffer proximal base portion  1066  and stiffer distal base portion  1068  that exhibit greater resistance to the compressive bending force of the pull wire  1024 . The greater stiffness of portions  1066 ,  1068  may be imparted by additional material or a different cross-sectional profile. Pull wire  1024  is fixed to the distal end of the device and relative movement between the pull wire  1024  and the proximal end  1044  of the baskets  1008 ,  1010  may cause expansion of the device. The outer basket  1008  may include, but is not limited to, six spacer struts  1014 . A central portion of each spacer strut  1014  is bent away from the nearest electrode portion  1060 , as illustrated in  FIG. 10B . The system may be biased to a closed state such that pulling on the pull wire  1024  expands the system or biased to an open state such that pushing on the pull wire  1024  collapses the system from an expanded state. 
       FIGS. 11A and 11B  are isometric views of the distal portion of an ablative catheter system  1100  shown in an expanded state and a collapsed state, respectively. System  1100  is an ablative system where the electrodes may contact the vessel wall. A pull wire  1124  is fixed to the distal end of the system and proximal movement of the pull wire  1124  relative to the proximal end of the system causes expansion. A first pair of struts  1102  and  1104  is fixed proximally and distally and by rings  1106 ,  1108 . In some instances, the first pair of struts  1102 ,  1104  may be positioned generally opposite from one another. For example, the first strut  1102  may be configured to contact the vessel wall at a first location and the second strut  1104  may be configured to contact the vessel wall approximately 180° from the first location. A second pair of struts  1110  and  1112  is likewise fixed proximally and distally and by rings  1114 ,  1116 . In some instances, the second pair of struts  1110 ,  1112  may be positioned generally opposite from one another. For example, the third strut  1110  may be configured to contact the vessel wall at a first location and the fourth strut  1112  may be configured to contact the vessel wall approximately 180° from the first location. Thus, when the system is expanded, alternating apexes  1118 ,  1120 ,  1122 ,  1123 ,  1126 ,  1128 ,  1130  and  1132  are created. Apexes  1120 ,  1122 ,  1126  and  1132  are insulated and thus do not act as electrodes. Apexes  1118 ,  1123 ,  1128  and  1130  are bare and thus act as electrodes. The pattern of bare apexes forms a helical pattern with an active electrode approximately every 90 degrees. It can be appreciated that the profile of the strut  1102 ,  1104 ,  1110 ,  1112  at the electrode apexes may be altered if desired. For example, the apexes may be shaped as portions  1060  of  FIGS. 10A and 10B . Conductors  1132  (not all illustrated) provide power to the struts  1102 ,  1104 ,  1110 ,  1112  and a hollow catheter  1032  extends proximally over the pull wire  1124 . The system may be biased to a closed state such that pulling on the pull wire  1124  expands the system or biased to an open state such that pushing on the pull collapses the system from an expanded state. 
     The system  1200  shown in  FIG. 12  is similar to that of system  1100  except that the struts may be formed from a single tubular member and the electrode portions of the struts form a more compact ablation pattern. In some embodiments, apex portions  1212 ,  1214 ,  1216 ,  1218  may be insulated while apex portions  1220 ,  1222 ,  1224 ,  1226  are bare and thus able to act as electrodes. In other embodiments, the apex portions  1212 ,  1214 ,  1216 ,  1218 ,  1220 ,  1222 ,  1224 ,  1226  are all insulated while the area of the tubular member (proximate to and including waist  1228 ) may be bare and able to act as electrodes. In a contemplated variation, the struts are formed separately and attached to a central ring (corresponding to waist  1228 ). The electrode apexes  1212 ,  1214 ,  1216 ,  1218 ,  1220 ,  1222 ,  1224 ,  1226  may also be changed from the ribbon profile shown. For example, they may be shaped like portions  1060  of  FIG. 10A . The struts are fixed proximally to a tubular member and distally to the distal end of the system. A pull wire  1230  is likewise fixed to the distal end and slidable within the tubular member. The system may be biased to a closed state such that pulling on the pull wire  1230  expands the system or biased to an open state such that pushing on the pull wire  1230  collapses the system from an expanded state. 
       FIGS. 13 and 14  are isometric views of example embodiments of non-contact ablative catheter systems. The term “non-contact” is meant to signify that no active or electrically emitting portion of the electrode touches a vessel wall when the system is properly used in a blood vessel of conventional shape. Each system includes struts that are expanded by the use of a pull wire. The systems may be biased to a closed state such that pulling on the pull wire expands the system or biased to an open state such that pushing on the pull wire collapses the system from an expanded state. The pull wire and the struts are fixed together at their distal ends. The struts are fixed to a tubular member through which the pull wire slides at their proximal ends. The struts may have a uniform cross-section such as the illustrated flat ribbon or may have another desired shape. For example, the struts may widen at the active electrode portions. The struts may further be shaped to expand in a particular manner. For example, the struts of  FIG. 13  are illustrated as having a flat central section when expanded. The struts may be altered to have the football shaped expansion profile of  FIG. 14 , for example. 
     In system  1300  of  FIG. 13 , each strut  1302  has an outer face  1304  that faces radially outwardly, an inner face  1306  that faces radially inwardly and may include two side faces  1308 ,  1310  that join the inner and outer faces. The outer face  1304  and the two side faces  1308 ,  1310  of each strut are covered with an electrically insulating material. The inner face  1306  is free from the electrically insulating material and is thus free to act as an electrode. In some instances, the inner face  1306  may be 100% free from insulating material. In other instances, the inner face  1306  may be partially covered with insulating material. For example, the inner face  1306  may be approximately 90% free from insulating material, approximately 80% free from insulating material, approximately 70% free from insulating material, approximately 60% free from insulating material, approximately 50% free from insulating material, approximately 40% free from insulating material, approximately 30% free from insulating material, approximately 20% free from insulating material, or approximately 10% free from insulating material. These are just examples. In some embodiments, the electrically insulating material covers the outer face  1304  and contiguous portions of the side faces  1308 ,  1310  while portions of the side faces  1308 ,  1310  contiguous with the inner face  1306  are bare. In some embodiments, the distal and proximal portions of the inner face  1306  are also covered with an electrically insulating material. 
     In system  1400 , each strut  1402  includes an apex portion  1404  that is electrically insulated and a distal base portion  1406  and a proximal base portion  1408  that are also electrically insulated. Each strut  1402  also includes bare portions  1410  and  1412  that are free from insulating material and thus can act as electrodes. Each bare portion  1410 , 1412  is spaced from the center of the apex portion  1404  and is thus kept spaced from a vessel wall when system  1400  is expanded. In some embodiments, the inner face of the apex portion  1404  is free from insulating material or is only partially insulated so that the inner face of the apex portion  1404  may act as an electrode as well. In some instances, the inner face may be 100% free from insulating material. In other instances, the inner face may be approximately 90% free from insulating material, approximately 80% free from insulating material, approximately 70% free from insulating material, approximately 60% free from insulating material, approximately 50% free from insulating material, approximately 40% free from insulating material, approximately 30% free from insulating material, approximately 20% free from insulating material, or approximately 10% free from insulating material. These are just examples. 
     It is further contemplated that the size of the apex portion  1404  may vary depending on the desired application. In some instances, an outer surface of the apex portion  1404  may comprise at least 20% of the outer surface of the strut  1402 . In other instances, the outer surface of the apex portion  1404  may comprise at least 30%, at least 40%, at least 50%, or at least 60%, of the outer surface of the strut  1402 . These are just examples. In some embodiments, the outer surface of the apex portion  1404  may comprise no more than 60% of the outer surface of the strut  1402   
     To monitor the temperature of the any of the electrodes herein and the blood vessel walls, one or more sensors, such as temperature sensors, may be placed at different portions of the nerve modulation assembly  104 . For instance, one sensor may be placed near the electrode to monitor electrode fouling or electrode temperature, and another sensor may be placed in the portion contacting the vessel wall to measure the temperature at the blood vessel. External devices connected to the sensors may be configured to raise alerts if any of the sensors detect temperatures over a preconfigured threshold value. If an alert is raised, operators may discontinue ablation or reduce power until the temperature at the electrode or at the vessel wall returns under the threshold value. Alternatively, operators may simply monitor the temperatures and discontinue operation when temperatures exceed a certain value. In an alternate embodiment, the impedance of the electrodes may be measured by the control and power element to monitor the procedure. 
     The shape of nerve modulation assembly  104  described in the present disclosure may eliminate the possible problems associated with an electrode touching the artery walls and causing injury there. Further, being spaced from the vessel walls, the electrode may circumferentially radiate RF energy, equally ablating the nerves surrounding the artery. It may be preferred to space the electrodes as close as possible to the vessel wall without actually touching the vessel wall with the bare metal of the electrodes. Such a configuration may minimize the power requirements of the device while reducing or eliminating excessive heating of deeper surrounding tissues. 
     In use, any of the systems may be introduced percutaneously as is conventional in the intravascular medical device art. For example, a guidewire may be introduced percutaneously through a femoral artery and navigated to a renal artery using standard radiographic techniques. The catheter sheath  106  may be introduced over the guide wire and the guide wire may be withdrawn. The elongate member and the ablative member may then be introduced in the sheath  106  and urged distally to the desired location. Once there, the sheath may be retracted proximally to allow the ablative member to expand or the ablative member may be urged distally to extend beyond the distal end of the sheath. 
     The outer and inner basket may be actuated simultaneously or actuated separately. In one embodiment, once the nerve modulation assembly  104  extends from the sheath  106 , both the inner and outer basket may expand to their desired configuration. Alternatively, the outer basket may be actuated first so that the outer basket may snuggly fit with the vessel walls. The inner basket may then be actuated based on the configuration of the outer basket, ensuring that the degree of expansion of the inner basket is less than the outer basket. 
     The electrodes may then be activated to ablate nerve tissue. During this procedure, the ablative member may continuously monitor the impedance and/or temperature at the electrodes and the vessel walls. Further, the electrodes may be activated sequentially or simultaneously, as desired. Radiography techniques may be utilized to monitor the tissue being ablated. Once the tissue is sufficiently ablated, the catheter sheath may be advanced or the ablative member may be retracted to compress the ablative member and retrieve it from the patient&#39;s body. Alternatively, the ablative member may be repositioned to perform further ablative procedures as desired. 
     Those skilled in the art will recognize that the present disclosure may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departure in forma and detail may be made without departing from the scope and spirit of the present disclosure as described in the appended claims.