Patent Publication Number: US-2015066118-A1

Title: Intravascular Neuromodulation Device Having a Spiral Track and Associated Methods

Description:
TECHNICAL FIELD 
     The present technology relates generally to intravascular neuromodulation and associated methods. In particular, several embodiments are directed to devices positionable along spiral tracks for intravascular renal neuromodulation and associated methods. 
     BACKGROUND 
     The sympathetic nervous system (SNS) is a primarily involuntary bodily control system typically associated with stress responses. Fibers of the SNS innervate tissue in almost every organ system of the human body and can affect characteristics such as pupil diameter, gut motility, and urinary output. Such regulation can have adaptive utility in maintaining homeostasis or preparing the body for rapid response to environmental factors. Chronic activation of the SNS, however, is a common maladaptive response that can drive the progression of many disease states. Excessive activation of the renal SNS in particular has been identified experimentally and in humans as a likely contributor to the complex pathophysiology of hypertension, states of volume overload (such as heart failure), and progressive renal disease. For example, radiotracer dilution has demonstrated increased renal norepinephrine (“NE”) spillover rates in patients with essential hypertension. 
     Cardio-renal sympathetic nerve hyperactivity can be particularly pronounced in patients with heart failure. For example, an exaggerated NE overflow from the heart and kidneys of plasma is often found in these patients. Heightened SNS activation commonly characterizes both chronic and end stage renal disease. In patients with end stage renal disease, NE plasma levels above the median have been demonstrated to be predictive of cardiovascular diseases and several causes of death. This is also true for patients suffering from diabetic or contrast nephropathy. Evidence suggests that sensory afferent signals originating from diseased kidneys are major contributors to initiating and sustaining elevated central sympathetic outflow. 
     Sympathetic nerves innervating the kidneys terminate in the blood vessels, the juxtaglomerular apparatus, and the renal tubules. Stimulation of the renal sympathetic nerves can cause increased renin release, increased sodium (Na+) reabsorption, and a reduction of renal blood flow. These neural regulation components of renal function are considerably stimulated in disease states characterized by heightened sympathetic tone and likely contribute to increased blood pressure in hypertensive patients. The reduction of renal blood flow and glomerular filtration rate as a result of renal sympathetic efferent stimulation is likely a cornerstone of the loss of renal function in cardio-renal syndrome (i.e., renal dysfunction as a progressive complication of chronic heart failure). Pharmacologic strategies to thwart the consequences of renal efferent sympathetic stimulation include centrally acting sympatholytic drugs, beta blockers (intended to reduce renin release), angiotensin converting enzyme inhibitors and receptor blockers (intended to block the action of angiotensin II and aldosterone activation consequent to renin release), and diuretics (intended to counter the renal sympathetic mediated sodium and water retention). These pharmacologic strategies, however, have significant limitations including limited efficacy, compliance issues, side effects, and others. Recently, intravascular devices that reduce sympathetic nerve activity by applying an energy field to a target site in the renal blood vessel (e.g., via radio frequency ablation) have been shown to reduce blood pressure in patients with treatment-resistant hypertension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure. Furthermore, components can be shown as transparent in certain views for clarity of illustration only and not to indicate that the illustrated component is necessarily transparent. For ease of reference, throughout this disclosure identical reference numbers may be used to identify identical or at least generally similar or analogous components or features. 
         FIG. 1  is a partially schematic diagram of a neuromodulation system configured in accordance with an embodiment of the present technology. 
         FIG. 2  is a longitudinal cross-sectional view of an intravascular therapeutic assembly in a delivery state (e.g., low-profile or collapsed configuration) and carried within a delivery element in accordance with an embodiment of the present technology. 
         FIG. 3A  is a perspective view of the intravascular therapeutic assembly of  FIG. 2  having a spiral-shaped track in a deployed state (e.g., expanded configuration) within a renal artery of a patient in accordance with a further embodiment of the present technology. 
         FIG. 3B  is a transverse cross-sectional view of the intravascular therapeutic assembly taken along line  3 B- 3 B of  FIG. 3A . 
         FIG. 4A  is a transverse cross-sectional view of an intravascular therapeutic assembly configured in accordance with an embodiment of the present technology. 
         FIG. 4B  is a transverse cross-sectional view of an intravascular therapeutic assembly configured in accordance with another embodiment of the present technology. 
         FIG. 5  schematically illustrates modulating renal nerves with an intravascular therapeutic assembly configured in accordance with an embodiment of the present technology. 
         FIG. 6A  is a longitudinal cross-sectional view of an intravascular therapeutic assembly and guidewire in a delivery state (e.g., low-profile or collapsed configuration) in accordance with another embodiment of the present technology. 
         FIG. 6B  is a perspective view of the intravascular therapeutic assembly of  FIG. 6A  with the guidewire partially withdrawn and showing the therapeutic assembly in a deployed state (e.g., expanded configuration) within a renal artery of a patient in accordance with a further embodiment of the present technology. 
         FIG. 7  is a flowchart of a method for delivering and deploying an intravascular therapeutic assembly in accordance with an embodiment of the present technology. 
         FIG. 8  is a flowchart of another method for delivering and deploying an intravascular therapeutic assembly in accordance with an embodiment of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is directed to apparatuses, and methods for achieving electrically- and/or thermally-induced renal neuromodulation (i.e., rendering neural fibers that innervate the kidney inert or inactive or otherwise completely or partially reduced in function) by percutaneous transluminal intravascular access. In particular, embodiments of the present technology relate to therapeutic assemblies having track elements and treatment devices (e.g., treatment catheters) slidably engaged with the track elements. The therapeutic assemblies include at least one neuromodulation element (e.g., at least one electrode) that can be located, for example, at a distal portion of the treatment device. After deployment in a target blood vessel of a human patient, a distal portion of the track element is transformable between a delivery or low-profile state (e.g., a generally straightened shape) to a deployed state (e.g., a radially expanded, generally spiral/helical shape) such that the track element defines a spiral-shaped track in apposition with an inner wall of the target blood vessel (e.g., renal artery). 
     The treatment device can include a treatment catheter or another elongate member that slidably engages the track element such that movement of the of the treatment device relative to the track element translates the neuromodulation element(s) along the track element to position the neuromodulation element(s) at various treatment positions within the target blood vessel. In one embodiment, for example, the track element can be a wire (e.g., nitinol wire) that is accommodated within a lumen of the treatment device (e.g., treatment catheter, microcatheter, tubular sheath, etc.) and has an expandable, pre-formed, helical shape at a distal portion thereof. Accordingly, movement of the treatment device proximally or distally along the deployed and stationary track element can displace the neuromodulation element both angularly or circumferentially and longitudinally relative to a longitudinal axis of the target blood vessel. 
     The neuromodulation element(s) are in electrical communication with an energy source or energy generator external to the patient such that energy is delivered via the neuromodulation element(s) to portions of a renal artery after being advanced thereto along a percutaneous transluminal path (e.g., a femoral artery puncture, an iliac artery and the aorta, a radial artery, or another suitable intravascular path). Suitable energy modalities include, for example, electrical energy, radio frequency (RF) energy, pulsed electrical energy, or thermal energy. The treatment device carrying the neuromodulation element(s) can be sized, shaped and have suitable flexibility such that the neuromodulation element(s) are in constant apposition with the interior wall of the renal artery when the track element is in the deployed (e.g., spiral/helical) state. The pre-formed spiral/helical shape of the deployed portion of the track element carrying the treatment device allows blood to flow through the assembly during therapy, which is expected to help prevent occlusion of the renal artery during activation of the neuromodulation element(s). 
     Previous energy-delivery catheter systems for inducing neuromodulation that include arrays of electrodes can be expensive to manufacture. For example, multiple electrodes require separate wiring of each electrode as well as complex algorithms and design of the energy generator. Additionally, repositioning and specific lesion placement on the interior wall of the renal artery are challenging and time consuming when using conventional energy-delivery catheter systems. In contrast, a self-expanding spiral frame over which an elongate member (e.g., sheath, treatment catheter, microcatheter, etc.) can travel provides a simple design that is easy to deploy and use compared to the conventional catheter devices. Moreover, the neuromodulation element can, in some embodiments, include a single electrode that can be moved proximally or distally along the track element while the track element remains in situ. The movement can be achieved via a pull or push mechanism that slides the neuromodulation element along the spiral-shaped track to easily select and access new ablation or treatment locations. Additionally, because movement of the neuromodulation element along the track element is achievable to access a plurality of treatment locations (both circumferentially and longitudinally displaced from each other), a single neuromodulation element can be deployed on the treatment device. This design aspect avoids the separate wiring that multiple electrodes would require, which is expected to reduce manufacturing time and material costs associated with additional separate electrodes and wiring, as well as reduce the complexity of the control algorithm typically necessary to operate more than one independent electrode or energy delivery elements. 
     Specific details of several embodiments of the technology are described below with reference to  FIGS. 1-7 . Although many of the embodiments are described below with respect to devices, systems, and methods for intravascular modulation of renal nerves using spiral-shaped track elements, other applications and other embodiments in addition to those described herein are within the scope of the technology. Additionally, several other embodiments of the technology can have different configurations, components, or procedures than those described herein. A person of ordinary skill in the art, therefore, will accordingly understand that the technology can have other embodiments with additional elements, or the technology can have other embodiments without several of the features shown and described below with reference to  FIGS. 1-7 . 
     As used herein, the terms “distal” and “proximal” define a position or direction with respect to the treating clinician or clinician&#39;s control device (e.g., a handle assembly). “Distal” or “distally” are a position distant from or in a direction away from the clinician or clinician&#39;s control device. “Proximal” and “proximally” are a position near or in a direction toward the clinician or clinician&#39;s control device. 
     Selected Examples of Neuromodulation Systems 
       FIG. 1  is a partially schematic illustration of a renal neuromodulation system  10  (“system  10 ”) configured in accordance with an embodiment of the present technology. The system  10  includes an intravascular catheter  12  operably coupled to an energy source or energy generator  30  (e.g., a RF energy generator). The catheter  12  can include an elongated shaft  14  having a proximal portion  16  and a distal portion  20 . The catheter  12  also includes a handle  18  at the proximal portion  16 . The catheter  12  can further include a therapeutic assembly or treatment section  100  (shown schematically) at the distal portion  20  (e.g., attached to the distal portion  20 , defining a section of the distal portion  20 , etc.). As explained in further detail below, the therapeutic assembly  100  can include a treatment device  120  slidably engaging a distal portion of track element  110 . In the exemplary over-the-wire (“OTW”) embodiment shown in  FIG. 1 , the proximal end of track element  110  extends from an exit port  15  in handle  18 . The treatment device  120  can be an elongate member (e.g., a sheath, a treatment catheter, etc.) with one or more neuromodulation elements or energy delivery elements  122  disposed at a distal end thereof. In one embodiment, the neuromodulation or energy delivery element  122  can be an electrode for delivering energy at a target treatment site and providing therapeutically-effective electrically- and/or thermally-induced renal neuromodulation. 
     As explained in greater detail below, the therapeutic assembly  100  is configured to be intravascularly delivered to a target blood vessel (e.g., a renal blood vessel) of a human patient in a low-profile configuration. Upon delivery to the target treatment site, the therapeutic assembly  100  is further configured to be transformed into an expanded state (e.g., the distal portion of track element  110  is deployed into a generally spiral/helical configuration as shown schematically in  FIG. 1 ) to place the track element  110  into apposition with an inner wall of the blood vessel. 
     Alternatively, the deployed state may be non-spiral provided that the deployed state places the track element and specifically one or more energy delivery elements  122  in vessel wall apposition for delivering the energy to the treatment site. The treatment device  120  can then be slidably moved along the track element  110  to position the neuromodulation or energy delivery element  122  at desired location(s) for modulating target nerves proximate to the inner wall of the blood vessel, thereby providing therapeutically-effective electrically- and/or thermally-induced renal neuromodulation. 
     The therapeutic assembly  100  may be transformed between the delivery and deployed states using a variety of suitable mechanisms or techniques (e.g., self-expansion). In one specific example, the distal portion of track element  110  can be a pre-formed, self-expanding wire that will transform into the deployed state or arrangement when unrestricted (e.g., by retracting a guide catheter, straightening sheath, etc.). 
     The proximal end of the treatment device  120  is carried by or affixed to the distal portion  20  of the elongated shaft  14 . A distal end of the track element  110  may include an atraumatic tip  112 . In some embodiments, the distal end of the catheter  12  may include an atraumatic tip for preventing intravascular trauma during delivery of the therapeutic assembly  100  to the treatment site. The distal end of the catheter  12  may also be configured to engage another element of the system  10  or catheter  12 . For example, the distal end of the catheter  12  may define a passageway for receiving a guidewire for delivery of the treatment device using OTW or rapid exchange (“RX”) techniques. Further details regarding such arrangements are described below with reference to  FIGS. 6A and 6B . 
     The neuromodulation element(s)  122  can be electrically coupled to the energy source  30  via a cable  32 , and the energy source  30  (e.g., a RF energy generator) can be configured to produce a selected modality and magnitude of energy for delivery to the treatment site via the neuromodulation element  122  carried by the treatment device  120 . As described in greater detail below, one or more supply wires (not shown) can extend along the elongated shaft  14  or through a lumen in the shaft  14  to the therapeutic assembly  100  and supply the treatment energy to the neuromodulation element  122 . 
     A control mechanism  40 , such as foot pedal or handheld remote control device, may be connected to the energy source  30  to allow the clinician to initiate, terminate and, optionally, adjust various operational characteristics of the energy source  30 , including, but not limited to, power delivery. The remote control device can be positioned in a sterile field and operably coupled to the therapeutic assembly  100 , and specifically to the neuromodulation element  122 , and can be configured to allow the clinician to activate and deactivate the energy delivery to the neuromodulation element  122 . In other embodiments, the remote control device may be built into the handle assembly  18 . 
     The energy source or energy generator  30  can be configured to deliver the treatment energy via an automated control algorithm  34  and/or under the control of a clinician. For example, the energy source  30  can include computing devices (e.g., personal computers, server computers, tablets, etc.) having processing circuitry (e.g., a microprocessor) that is configured to execute stored instructions relating to the control algorithm  34 . In addition, the processing circuitry may be configured to execute one or more evaluation/feedback algorithms  35 , which can be communicated to the clinician. For example, the energy source  30  can include a monitor or display  36  and/or associated features that are configured to provide visual, audio, or other indications of power levels, sensor data, and/or other feedback. The energy source  30  can also be configured to communicate the feedback and other information to another device, such as a monitor in a catheterization laboratory. 
     The system  10  can also include one or more additional sensors (not shown) located proximate to or within the neuromodulation element  122 . For example, the system  10  can include temperature sensors (e.g., additional thermocouples, thermistors, etc.), impedance sensors, pressure sensors, optical sensors, flow sensors, and/or other suitable sensors connected to one or more supply wires (not shown) that transmit signals from the sensors and/or convey energy to the therapeutic assembly  100 . 
     Selected Examples of Therapeutic Assemblies and Related Devices 
       FIG. 2  is an longitudinal cross-sectional view of a portion of the intravascular therapeutic assembly  100  in a delivery state (e.g., a low-profile or collapsed configuration) in accordance with an embodiment of the present technology, and  FIG. 3A  is a perspective view of the therapeutic assembly  100  of  FIG. 2  in a deployed state or expanded configuration within a renal artery RA (or other target blood vessel) of a patient. As noted above, the therapeutic assembly  100  can be transformed or actuated between the delivery state ( FIG. 2 ) and the deployed state (e.g., a radially expanded, generally spiral/helical configuration,  FIG. 3A ). 
     Referring to  FIGS. 2 and 3A  together, the therapeutic assembly  100  includes the treatment device  120  carried by and slidably engaged with the distal portion of track element  110 . The treatment device  120  includes the neuromodulation element  122  positioned at or near a distal portion  124  thereof for delivering therapeutically effective energy to target tissue (e.g., one or more nerves) of the patient. In the deployed state, the therapeutic assembly  100  is configured to place the distal portion of track element  110  and neuromodulation element  122  in apposition with an interior wall of the renal artery RA. The treatment device  120  comprises a treatment catheter, a microcatheter, or other elongate member (e.g., a sheath) having a lumen  126  therethrough defining a passageway for receiving the track element  110 . The track element  110  accordingly provides a guide for the treatment device  120  as it moves over the track element  110 . 
     Referring to  FIG. 2 , and in one embodiment, the therapeutic assembly  100  may be restrained in the delivery state (e.g., a generally straight or collapsed configuration) within the lumen of a tubular sheath or delivery element  130 . The delivery element  130  can have a suitable radial and bending stiffness for restraining the distal portion of track element  110  in the low-profile and generally straight or non-spiral configuration (e.g., the delivery state). In some embodiments, for example, the delivery element  130  may comprise a guide catheter or a straightening sheath sized and shaped to restrain one or more components of the therapeutic assembly  100  in the low-profile state for delivery to the target treatment site within the renal artery RA. In the collapsed, low-profile configuration, the geometry of the therapeutic assembly  100  is configured to facilitate movement through the delivery element  130  to the treatment site. Persons of skill in the art of catheters will understand that delivery element  130 , if it is a guide catheter, will typically have a pre-formed curved region (not shown) near the distal end. Thus, the delivery state of the therapeutic assembly  100  will be reduced, i.e. “low” in transverse profile, but not necessarily straight as it passes through the curved region of the guide catheter. Therapeutic assembly  100 , in the low-profile configuration is sufficiently flexible to pass through the guide catheter, including the curved region. In some embodiments, the delivery element  130  may be 8 Fr or smaller (e.g., a 6 Fr guide catheter) to accommodate small renal arteries during delivery of the therapeutic assembly  100  to the treatment site. In other embodiments, however, the delivery element  130  may have a different size. 
     In some methods of using the neuromodulation system  10 , the intravascular catheter  12  may be delivered and deployed over a guidewire  50  (shown in  FIG. 5 ), rather than with a delivery element  130 . The guidewire  50  can then be exchanged within lumen  126  for the track element  110 , the pre-formed distal portion of which will tend to take its helical shape in the treatment site, thereby deforming the treatment device  120  into a similar helical shape such that at least the neuromodulation element  122  is placed in apposition with an interior wall of the renal artery RA. After forming suitable treatment zones or lesions on the inner wall of renal artery RA, the track element  110  may be partially or fully withdrawn or exchanged within lumen  126  for guidewire  50  to allow treatment device  120  to relax to a straighter configuration for removal from the patient. One of ordinary skill in the art will recognize a plurality of delivery protocols for delivering and deploying the therapeutic assembly  100  at the target treatment site, several of which are described further below and with respect to  FIGS. 7 and 8 . 
     As best seen in  FIG. 3A , after delivery to the target treatment site (e.g. renal artery RA), the distal portion of track element  110  of the therapeutic assembly  100  may be deployed to its expanded, spiral-shaped configuration. In one embodiment, for example, the distal portion of track element  110  may be deployed by moving the delivery element  130  (e.g., sheath;  FIG. 2 ) and therapeutic assembly  100  relative to each other such that the therapeutic assembly  100  including the distal portion of track element  110  is exposed distally beyond the delivery element  130 . The distal portion of track element  110  can be configured to assume the expanded configuration when in an unbiased (e.g., unrestrained) condition. The delivery element  130  ( FIG. 2 ), for example, can be pulled proximally while the therapeutic assembly  100  is held stationary with respect to the treatment site. Alternatively, the therapeutic assembly  100  can be pushed distally beyond a distal end  134  of the delivery element  130  while the delivery element  130  is held stationary with respect to the treatment site. 
     The spiral-shaped configuration of the distal portion of track element  110  is further illustrated in  FIG. 3B , which is a transverse cross-sectional view of the therapeutic assembly  100  along the line  3 B- 3 B of  FIG. 3A . Referring to  FIGS. 3A and 3B  together, the distal portion of track element  110  defines a spiral track tending to contact the interior wall of the renal artery RA. In one embodiment, the distal portion of track element  110  can have a pre-set spiral/helical configuration such that the distal portion of track element  110  self-expands to a deployed geometry within the renal artery RA. The helix of track element  110  has a transverse dimension about its central axis CA that is at least approximately equal to a renal artery inner diameter D 1  ( FIGS. 3A and 3B ) and a maximum length in the direction of the central axis CA that is preferably less than or can be accommodated by the renal artery length (not shown). In other embodiments, however, the track element  110  may have a different arrangement and/or different dimensions. 
     In one embodiment, the track element  110  may be formed from suitable shape memory material, such as nitinol (nickel-titanium alloy) wire. In other embodiments, however, the track element  110  can be composed of different materials and/or have a different arrangement. For example, the track element  110  may be formed from other suitable materials such as metal wire (e.g., stainless steel), shape memory polymers, electro-active polymers, etc., that are pre-formed or pre-shaped into the desired deployed state ( FIGS. 3A and 3B ). Alternatively, the track element  110  may be formed from multiple materials such as a composite of one or more polymers and metals. 
     Referring again to  FIGS. 3A and 3B  together, the treatment device  120  is disposed over the distal portion of track element  110  such that, when the distal portion of track element  110  assumes its pre-set spiral/helical shape, the treatment device  120  is sufficiently flexible to conform to the helical shape of track element  110  such that at least neuromodulation element  122  can be placed in apposition with the interior wall of the renal artery RA. Treatment device  120  is moveable over the relatively stationary track element  110  for positioning or re-positioning element  122  at one or more treatment locations along the interior wall of the renal artery RA. In one embodiment, for example, the treatment device  120  can include a flexible tube  128  and at least the pre-shaped spiral/helical distal portion of track element  110  can be received within the lumen  126  of tube  128 . The flexible tube  128  may be composed of a polymer material such as polyamide, polyimide, polyether block amide copolymer sold under the trademark PEBAX, polyethylene terephthalate (PET), polypropylene, an aliphatic, polycarbonate-based thermoplastic polyurethane sold under the trademark CARBOTHANE, or a polyether ether ketone (PEEK) polymer. The material properties and dimensions of the tube  128  are selected to provide the necessary flexibility for the tube  128  to readily deform between a relaxed, substantially straight shape and a shape that conforms to the helical deployed shape of the distal portion of track element  110 . In other words, the tube  128  is more flexible than the track element  110  such that the shape of the combined components is defined by the shape of the track element  110 . In some embodiments, the lumen  126  is sized to provide sufficient clearance with the track element  110  to reduce friction between the catheter  12  and the track element  110 . In various embodiments, a lubricant or lubricious coating (not shown) can be included on either or both of the sliding surfaces, or may be applied between the track element  110  and the catheter  12  to facilitate relative movement therebetween. 
     In an alternative embodiment, the catheter  12  may include an operative wire (not shown) to facilitate pushing or pulling the treatment device  120  relative to the track element  110 . The operative wire can extend proximally from the treatment device  120  (e.g. as an alternative to the shaft  14 ) to be accessible, for example, to a clinician outside the patient when the therapeutic assembly  100  is being delivered and deployed. In other embodiments, however, the treatment device  120  may have a different arrangement and/or different features. 
     In one embodiment, the neuromodulation element  122  can be an electrode configured to deliver energy (e.g., electrical energy, RF energy, pulsed electrical energy, non-pulsed electrical energy, thermal energy, etc.) across the wall of the renal artery RA. In a specific embodiment, the neuromodulation element  122  can deliver a thermal RF field to targeted renal nerves adjacent the wall of the renal artery RA. Referring to  FIGS. 2-3B  together, the neuromodulation element  122  can include a band electrode surrounding the distal end  124  of the treatment device  120  such as at the distal end of the flexible tube  128 . For example, the neuromodulation element  122  can be a band electrode bonded to the tube  128  using an adhesive. In other embodiments, the treatment device  120  can include more than one neuromodulation element  122 . For example, the device  120  may include 2 or 3 electrodes (not shown) or, in yet another embodiment, an array of electrodes such as a series of separate band electrodes spaced along the treatment device  120  and bonded to the flexible tube  128 . Although band or tubular electrodes are illustrated, in other embodiments disc or flat electrodes may also be employed. In still another embodiment, electrodes having a spiral or coil shape may be utilized. The neuromodulation element  122  may be formed from any suitable metallic material (e.g., gold, platinum, an alloy of platinum and iridium, etc.). In other embodiments, however, the number, arrangement, and/or composition of the neuromodulation element(s)  122  may vary. For example, the neuromodulation element  122  may be placed on the treatment device  120  at another location proximal to the distal portion  124  of the treatment device  120 . 
     The neuromodulation element  122  is electrically connected to an external energy source (such as energy source  30 ,  FIG. 1 ) by a conductor or bifilar wire (not shown) extending through catheter  12 . The neuromodulation element  122  may be welded or otherwise electrically coupled to its energy supply wire, and the wire can extend the entire length of the catheter  12  (e.g. inside, outside or within a wall of the treatment device  120  and shaft  14 ) such that a proximal end thereof is coupled to the energy source  30  ( FIG. 1 ). In some embodiments, the therapeutic assembly  100  may also include an insulating layer (e.g., a layer of PET or another suitable material) over the track element  110  to further electrically isolate the material (e.g., nitinol wire) of the track element  110  from the wires (not shown). 
     In some embodiments, the therapeutic assembly  100  can include radiopaque markers  140  or other indicia for facilitating navigation of the assembly  100  through the vasculature as well as positioning of the neuromodulation element  122  at one or more desired treatment locations within the renal artery RA using x-ray imaging techniques known in the art.  FIG. 3A  illustrates an embodiment where radiopaque markers  140  are mounted to an outer surface of the distal portion  124  of the treatment device  120 . In other embodiments, not shown, the track element  110  can also include radiopaque markers  140  (e.g., made with radiopaque ink). In certain aspects, at least a portion of the track element  110  and/or the treatment device  120  can be made from platinum and/or other radiopaque materials (e.g., platinum/iridium alloy metal coil wrapped around the elongate member). 
     In operation and referring to  FIGS. 1-3B  together, after the distal portion of track element  110  is self-expanded or otherwise deployed to its pre-set spiral/helical configuration in apposition with the interior wall of the renal artery RA, the treatment device  120  can be slid in either a proximal or distal direction along the relatively stationary track element  110  to position the neuromodulation element  122  at a desired treatment location. Therapeutically-effective energy can then be delivered via the neuromodulation element  122  across the wall of the renal artery RA to targeted renal nerves (not shown) at one or more treatment locations. For example, neuromodulatory energy can be delivered at a first treatment location followed by sliding the treatment device  120  in either a proximal or distal direction along the track element  110  to place the neuromodulation element  122  at a second treatment location transposed circumferentially and longitudinally offset from the first treatment location along the renal artery RA. This step can be followed by delivering energy via the neuromodulation element  122  across the wall of the renal artery RA to targeted renal nerves at the second treatment location. Further steps can include sliding the treatment device  120  along the track element  110  to one or more additional treatment locations and again delivering energy to target nerves. 
     In some embodiments, the second treatment location can be longitudinally spaced away from the first treatment location along the renal artery RA in either a proximal or distal direction. Sliding the treatment device  120  between first and second treatment locations can also translate the second treatment location circumferentially about the interior wall of the blood vessel with respect to the first treatment location. For example, as the treatment device  120  slides along the spiral-shaped track provided by the distal portion of the track element  110  ( FIG. 3A ), the neuromodulation element  122  is transposed circumferentially and longitudinally on the interior wall of the renal artery RA. Accordingly, energy can be delivered at one or more discrete treatment locations to form a helical pattern of lesions or treatment zones along the interior wall of the renal artery. In some embodiments, the treatment zones may overlap. In other embodiments, however, the lesions may be spaced sufficiently such that they do not overlap. In still further embodiments, energy can be delivered while sliding the treatment device  120  along the spiral-shaped track element  110  to form a continuous or approximately continuous helical lesion. 
       FIGS. 4A and 4B  are transverse cross-sectional views of the therapeutic assembly  100  illustrating various arrangements of the treatment device  120  surrounding the track element  110 . In one arrangement, and as shown in  FIG. 4A , the track element  110  can be a wire having a generally circular cross-sectional shape, and the treatment device  120  can be an elongate member with a generally circular cross-sectional shape and having the lumen  126  for accommodating the track element  110 . In this arrangement, the treatment device  120  may be a treatment catheter or other microcatheter having the flexible tube  128  that is configured to slidably engage the track element  110 .  FIG. 4B , however, shows an alternative arrangement wherein the track element  110  has a generally rectangular cross-sectional shape.  FIG. 4B  also depicts an embodiment of the treatment device  120  that does not include a tube  128 , but instead incorporates a non-circumferential sleeve  428  that only partially encloses the track element  110 . In addition to the arrangements shown in  FIGS. 4A and 4B , those of ordinary skill in the art will recognize that there may be other suitable arrangements for providing a track or rail configured to be placed in apposition with the interior wall of the target blood vessel and a treatment device configured to engage and slidably move along the track or rail to position a neuromodulation element coupled thereto at a plurality of treatment locations. 
     Selected Examples of Methods for Delivery and Deployment of Therapeutic Assemblies 
     Several suitable delivery methods are disclosed herein and discussed further below; however, one of ordinary skill in the art will recognize a plurality of methods suitable to deliver the therapeutic assembly  100  to the treatment site and to deploy the distal portion of track element  110  from the delivery configuration to the deployed configuration. With respect to the embodiment illustrated in  FIGS. 1-3B , the track element  110  may be delivered to the treatment site through or within a guide catheter or straightening sheath (e.g., the delivery element  130  shown in  FIG. 2 ). The sheath may be pre-placed across the treatment site with or without use of a guidewire, and the track element  110 , with or without catheter  12  mounted thereabout, can then be passed through the sheath. Alternatively, track element  110  with or without catheter  12  mounted thereabout can be pre-loaded into the sheath such that the assembled components can be advanced simultaneously through the patient&#39;s vasculature. In any case, during delivery, the straightening sheath can partially or fully restrain the distal portion of track element  110  in the delivery configuration. When the distal portion of track element  110  is within the target site, the straightening sheath may be at least partially withdrawn or retracted to permit the distal portion of track element  110  to transform into the deployed configuration. 
       FIG. 5  (with additional reference to  FIG. 1 ) illustrates at least one step of modulating renal nerves with an embodiment of the system  10 . The therapeutic assembly  100  is shown positioned within the renal plexus RP and catheter  12  is shown in an intravascular path P extending from a percutaneous access site in a femoral (illustrated), brachial, radial, or axillary artery to a targeted treatment site within a respective renal artery RA. As illustrated, a section of the proximal portion  16  of the catheter shaft  14  is exposed externally of the patient even as the therapeutic assembly  100  has been advanced fully to the targeted treatment site in the patient. By manipulating the proximal portion  16  of the shaft  14  from outside the intravascular path P, the clinician may advance the shaft  14  through the sometimes tortuous intravascular path P and remotely manipulate the distal portion  20  of the shaft  14 . 
     In the method step illustrated in  FIG. 5 , the therapeutic assembly  100  extends intravascularly to the treatment site over a guidewire  50  using an OTW technique. The guidewire  50  may comprise any suitable medical guidewire sized to slidably fit within the lumen  126  of catheter  12 . In one particular embodiment, for example, the guidewire  50  may have a diameter of 0.356 mm (0.014 inch). When the guidewire  50  is used for delivery of the therapeutic assembly  100  to the treatment site, deployment of the track element  110  can be accomplished by exchanging the guidewire  50  for the track element  110  within the lumen  126  of the catheter  12 . This exchange can be accomplished through the open proximal end of lumen  126  at exit port  15  in handle  18  (See  FIG. 1 ). Thus, in  FIG. 5 , the exposed element is labeled as either guidewire  50  or track element  110 . 
     In another method of delivery,  FIG. 6A  illustrates a transverse cross-sectional view of a portion of the intravascular therapeutic assembly  100  wherein both a guidewire  50  and track element  110  are disposed within treatment device  120 .  FIG. 6B  is a perspective view of the therapeutic assembly  100  of  FIG. 6A  in a deployed state (e.g., expanded configuration) within a renal artery RA (or other target blood vessel) of a patient. As illustrated, both guidewire  50  and track element  110  are slidably disposed in lumen  126 , which will necessarily be somewhat larger than the earlier embodiment wherein only one of guidewire  50  or track element  110  are present in lumen  126 . In another embodiment (not shown) guidewire  50  and track element  110  can be slidably disposed in separate, dedicated lumens. The guidewire  50  may be sufficiently stiff to keep treatment device  120  relatively straight and thereby restrain the track element  110  in the delivery state. It will be understood that, without additional bending stiffness provided by either guidewire  50  or delivery element  130  (of the previous method), treatment device  120  will tend to conform to the shape of track element  110 . When the guidewire  50  is partially refracted or withdrawn from the treatment site, as illustrated in  FIG. 6B , the track element  110  provides a shape-recovery force sufficient to overcome the straightening force provided by a distalmost portion  52  of the guidewire  50  such that the track element  110  can deploy into its spiral/helical shaped configuration and deform treatment device  120  along with it. Further, because the distalmost portion  52  of the guidewire  50  can remain at least partially within the therapeutic assembly  100  while in the deployed state (e.g.,  FIG. 6B ), the guidewire  50  can impart additional structural integrity to the positioning of the spiral-shaped portion during treatment. This feature is expected to help mitigate or reduce problems associated with keeping the therapeutic assembly  100  in place during treatment (e.g., help with vasoconstriction). 
     In an alternate method step, the guidewire  50  including the distalmost portion  52  may be withdrawn completely from the therapeutic assembly  100  while remaining within the shaft  14  (not shown) to permit the transformation of therapeutic assembly  100 . In yet another method step, the guidewire  50  may be withdrawn completely from the shaft  14 . In any of the foregoing examples, the clinician can withdraw the guidewire  50  sufficiently to observe transformation of the therapeutic assembly  100  to the deployed configuration and/or until an X-ray image shows that the distal tip of the guidewire  50  is at a desired location relative to the therapeutic assembly  100  (e.g., at least partially withdrawn from the therapeutic assembly  100 , or completely withdrawn from the therapeutic assembly  100 , etc.). In some methods, the extent of withdrawal of the guidewire  50  can be based, at least in part, on the clinician&#39;s judgment with respect to the selected guidewire and the extent of withdrawal necessary to achieve deployment of the therapeutic assembly  100 . 
     After formation of lesions or treatment zones suitable for achieving neuromodulation, and in accordance with one method, the therapeutic assembly  100  may be transformed back to the low-profile delivery configuration by axially advancing the guidewire  50  relative to the therapeutic assembly  100  (e.g., within the lumen  126  of the treatment device  120 ). Following advancement of the guidewire  50 , the track element  110  can be withdrawn from the renal artery RA, or in another embodiment, the guidewire  50  can be exchanged for the track element  110  in lumen  126  of the treatment device  120  ( FIG. 6 ). Once the guidewire  50  is in position at the treatment site and the therapeutic assembly  100  is in the low-profile delivery configuration, the treatment device  120  can be pulled back with or over the guidewire  50 . In further embodiments, a guide catheter or straightening sheath (e.g., shown as delivery element  130  in  FIG. 2 ) can be axially advanced relative to the therapeutic assembly  100  to transform the track element  110  back to the delivery configuration. In one embodiment, for example, the guide catheter or straightening sheath may be advanced until the distal tip of the catheter or sheath is generally aligned with the distal end of the track element  110 . In other embodiments, however, the distalmost portion of the catheter or sheath may be advanced to a different location relative to the therapeutic assembly  100  to achieve transformation of the track element  110  back to a low-profile configuration. 
     Image guidance, e.g., computed tomography (CT), fluoroscopy, intravascular ultrasound (IVUS), optical coherence tomography (OCT), intracardiac echocardiography (ICE), or another suitable guidance modality, or combinations thereof, may be used to aid the clinician&#39;s positioning and manipulation of the therapeutic assembly  100 . For example, a fluoroscopy system (e.g., including a flat-panel detector, x-ray, or c-arm) can be rotated to accurately visualize and identify the target treatment site. In other embodiments, the treatment site can be determined using IVUS, OCT, and/or other suitable image mapping modalities that can correlate the target treatment site with an identifiable anatomical structure (e.g., a spinal feature) and/or a radiopaque ruler (e.g., positioned under or on the patient) before delivering the catheter  12  and/or the therapeutic assembly  100 . Further, in some embodiments, image guidance components (e.g., IVUS, OCT) may be integrated with the catheter  12 , the track element  110 , the treatment device  120  and/or run in parallel with the catheter  12  to provide image guidance during positioning and removal of the therapeutic assembly  100 . For example, image guidance components (e.g., IVUS or OCT) can be coupled to at least one of the therapeutic assembly  100  to provide three-dimensional images of the vasculature proximate the target site to facilitate positioning or deploying the therapeutic assembly  100  within the target renal blood vessel. 
       FIG. 7  is a block diagram illustrating a method  700  of delivering and deploying the therapeutic assembly  100  described above with reference to  FIGS. 1-6  at a target treatment site for modulating renal nerves. In one embodiment, the method  700  can include transluminally delivering a catheter in a low-profile delivery configuration within a renal artery of a human patient (block  702 ). The catheter can comprise a therapeutic assembly that includes a track element and a treatment device carried by the track element. The treatment device can include a neuromodulation element at a distal portion thereof. The method  700  can also include transforming the catheter from the delivery configuration to a deployed configuration (block  704 ). In the deployed configuration, the track element has a radially expanded, generally helical shape configured to place the treatment device and at least the neuromodulation element carried thereon proximate to a renal nerve. In one arrangement, the treatment device can include a sleeve with a lumen for receiving the track element therethrough. When the track element is in the radially expanded, helical shape, the sleeve is configured to slide over the stationary track to position the neuromodulation element at one or more treatment locations along the renal artery. 
     In one embodiment, the catheter can include a guide catheter or straightening sheath configured to hold the track element in the delivery configuration. Accordingly, the step of transforming the catheter can include a step of at least partially withdrawing the guide catheter (or the straightening sheath) to expose the track element within an interior lumen of the renal artery. In certain embodiments, the therapeutic device components as illustrated in  FIGS. 1-4B  and  6  above can be configured to fit within an 8 Fr guide catheter or smaller (e.g., 7 Fr, 6 Fr, etc.) to access small peripheral vessels. In additional embodiments, and as described above with respect to  FIGS. 5 and 6 , the method  700  can optionally include delivering the catheter to the renal artery over a guidewire (not shown). In one embodiment, delivering the catheter over a guidewire can also include exchanging the guidewire for the therapeutic assembly within the catheter. 
     The method  700  can further include modulating the renal nerve (block  706 ). In this step, energy can be delivered to the renal nerve via the neuromodulation element at a first treatment location along the renal artery. The treatment device can then be moved along the relatively stationary track element to position the neuromodulation element at a second treatment location along the renal artery, and energy can be delivered to the renal nerve via the neuromodulation element at the second treatment location. For example, the treatment device can slide along the relatively stationary track element having the generally helical shape to position the neuromodulation element at the one or more treatment locations along an inner wall of the renal artery. Moving the treatment device transposes the neuromodulation element circumferentially and longitudinally relative to a longitudinal axis of the renal artery. In one embodiment, the neuromodulation element can emit RF energy for modulating the renal nerve adjacent the inner wall of the renal artery at the targeted treatment locations. Delivering energy at the first and second treatment locations can form an interrupted lesion along the inner wall of the renal artery. In other embodiments, however, energy can be delivered during movement of the treatment device to form a continuous lesion along the inner wall. In certain other embodiments, modulation of the renal nerve can occur by delivering energy via the neuromodulation element at a single treatment location. 
       FIG. 8  is a block diagram illustrating another method  800  of delivering and deploying the therapeutic assembly  100  described above with reference to  FIGS. 1-6  at a target treatment site for modulating renal nerves. For example, the method  800  can include intravascularly positioning a therapeutic assembly at a treatment site within a target blood vessel of a human patient (block  802 ). The therapeutic assembly can comprise a track element in a low-profile delivery configuration and an elongate member over the track element. The elongate member can comprise an electrode disposed a distal portion thereof. The method  800  can also include transforming the track element from the delivery configuration to a deployed configuration, wherein, in the deployed configuration, the track element comprises a spiral track tending to be in apposition with an inner wall of the target blood vessel (block  804 ). In one embodiment, the track element can be maintained in the delivery configuration with a delivery element (e.g., guide catheter, straightening sheath, etc.), and the step of transitioning the track element can include at least partially withdrawing or retracting the delivery element. The method  800  can further include sliding the elongate member over the track element to position the electrode at a treatment location along the spiral track (block  806 ). The method  800  can also include delivering energy via the electrode to modulate target nerves proximate to the inner wall of the target blood vessel (block  808 ). 
     Additional Embodiments 
     Features of the catheter device components described above and illustrated in  FIGS. 1-6B  can be modified to form additional embodiments configured in accordance with the present technology. For example, neuromodulation system  10  can provide delivery of any of the therapeutic assemblies  100  illustrated in  FIGS. 2-4B ,  6 A, and  6 B using one or more additional delivery elements such as guide catheters, straightening sheaths, and/or guidewires. Similarly, the therapeutic assemblies described above and illustrated in  FIGS. 1-3B ,  6 A and  6 B showing only a single neuromodulation element can also include additional electrode elements, wires, and energy delivery features positioned along the treatment device. 
     Various method steps described above for delivery and deployment of the therapeutic assembly components also can be interchanged to form additional embodiments of the present technology. For example, while the method steps described above are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments. 
     Renal Neuromodulation 
     Renal neuromodulation is the partial or complete incapacitation or other effective disruption of nerves innervating the kidneys. In particular, renal neuromodulation comprises inhibiting, reducing, and/or blocking neural communication along neural fibers (i.e., efferent and/or afferent nerve fibers) innervating the kidneys. Such incapacitation can be long-term (e.g., permanent or for periods of months, years, or decades) or short-term (e.g., for periods of minutes, hours, days, or weeks). Renal neuromodulation is expected to efficaciously treat several clinical conditions characterized by increased overall sympathetic activity, and in particular conditions associated with central sympathetic over-stimulation such as hypertension, heart failure, acute myocardial infarction, metabolic syndrome, insulin resistance, diabetes, left ventricular hypertrophy, chronic and end stage renal disease, inappropriate fluid retention in heart failure, cardio-renal syndrome, osteoporosis, and sudden death. The reduction of afferent neural signals contributes to the systemic reduction of sympathetic tone/drive, and renal neuromodulation is expected to be useful in treating several conditions associated with systemic sympathetic over activity or hyperactivity. Renal neuromodulation can potentially benefit a variety of organs and bodily structures innervated by sympathetic nerves. 
     Various techniques can be used to partially or completely incapacitate neural pathways, such as those innervating the kidney. The purposeful application of energy (e.g., electrical energy, thermal energy) to tissue by energy delivery element(s) or components such as those described in conjunction with the intravascular treatment assemblies above, can induce one or more desired thermal heating effects on localized regions of the renal artery and adjacent regions of the renal plexus, which lay intimately within or adjacent to the adventitia of the renal artery. The purposeful application of the thermal heating effects can achieve neuromodulation along all or a portion of the renal plexus. 
     The thermal heating effects can include both thermal ablation and non-ablative thermal alteration or damage (e.g., via sustained heating and/or resistive heating). Desired thermal heating effects may include raising the temperature of target neural fibers above a desired threshold to achieve non-ablative thermal alteration, or above a higher temperature to achieve ablative thermal alteration. For example, the target temperature can be above body temperature (e.g., approximately 37° C.) but less than about 45° C. for non-ablative thermal alteration, or the target temperature can be about 45° C. or higher for the ablative thermal alteration. 
     More specifically, exposure to thermal energy (heat) in excess of a body temperature of about 37° C., but below a temperature of about 45° C., may induce thermal alteration via moderate heating of the target neural fibers or of vascular structures that perfuse the target fibers. In cases where vascular structures are affected, the target neural fibers are denied perfusion resulting in necrosis of the neural tissue. For example, this may induce non-ablative thermal alteration in the fibers or structures. Exposure to heat above a temperature of about 45° C., or above about 60° C., may induce thermal alteration via substantial heating of the fibers or structures. For example, such higher temperatures may thermally ablate the target neural fibers or the vascular structures. In some patients, it may be desirable to achieve temperatures that thermally ablate the target neural fibers or the vascular structures, but that are less than about 90° C., or less than about 85° C., or less than about 80° C., and/or less than about 75° C. Regardless of the type of heat exposure utilized to induce the thermal neuromodulation, a reduction in renal sympathetic nerve activity (RSNA) is expected. 
     Conclusion 
     The above detailed descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments. 
     From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. 
     Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.