Embodiments of the present disclosure relate generally to medical devices suitable for use in body tissue modulation and ablation. In particular, embodiments of the instant disclosure relate to structures and methods for cooling medical devices employed in tissue modulation and ablation.
Radio frequency ablation (RFA) is a relatively new medical procedure in which tissue is ablated using the heat generated from the radio frequency waves. Unlike the conventional procedures, the RF current does not interfere with the nervous or cardiac system and can be used as a minimally invasive procedure without a general anesthetic. Further, RFA procedures generally require image guidance, such as X-ray screening, CT scan, or ultrasound.
Many nerves, such as renal nerves, run in close proximity to blood vessels and thus can be accessed intravascularly through the blood vessel walls. This treatment, however, may result in thermal injury to the artery walls. The treatment can also produce undesirable side effects, such as blood damage and clotting, and the high temperature can produce protein fouling of the electrode. One of the ways to reduce thermal damage involves cooling the nerve ablation region by natural blood flow through the renal artery. An alternate approach for reducing artery wall damage involves placing the RF electrodes a short distance away from the artery wall. Though effective, that process requires precise spacing of electrodes from the artery wall, which is difficult to achieve.
Therefore, there exists a need for a system which reduces vessel wall damage by cooling the RF electrodes and places them automatically at a controlled distance from the vessel wall.
One embodiment pertains to an ablative catheter system comprising an elongate member having a proximal end and a distal end. The elongate member may be a catheter and include one or more lumens extending along its length. An end-effector may be disposed at the distal end of the elongate member, the end-effector including an expandable frame and a membrane supported on the frame. The membrane may be configured to partially occlude fluid flow upon frame expansion. One or more electrodes may be placed on the end-effector and are configured to ablate or otherwise modulate tissue. The system also includes a control member configured to translate the end-effector between a collapsed state and the frame expansion state. Such a control member may be a sheath, a pull wire or the like.
Upon expansion, the membrane increases radially in size from a proximal end and may have a generally conical shape and may further include pleats or other concavities. In some embodiments, the membrane is non-pourous or is otherwise generally impervious to blood flow. The membrane may be impermeable to radio-frequency energy. The membrane may extend distally from the distal end of the elongate member or may be spaced longitudinally from the distal end of the elongate member.
The one or more electrodes are placed on an outer surface of the membrane, an inner surface of the membrane, on the expandable frame, a separate electrode-carrying structure or other suitable location. The electrodes are preferably placed so that, upon expansion of the end-effector in a vessel having walls, the one or more electrodes are spaced apart from the vessel wall. The expandable frame may include a plurality of struts. The plurality of struts may extend from the distal end of the elongate member to a distal end of the membrane. The plurality of struts may extend from the distal end of the elongate member distally past a distal end of the membrane. Upon expansion, the plurality of struts and the membrane form a generally conical shape. The distal ends of the struts may include distal ends that are turned inwardly or have some other atraumatic feature.
In some contemplated embodiments, the expandable frame may include a first section and a second section distal the first section, and wherein the expandable frame has an expanded configuration wherein the first section increases radially in size distally and the second section decreases radially in size distally (and so form a double-cone or football-shaped frame). The expandable frame comprises longitudinally struts that converge to a distal end of the second section. The membrane may be disposed proximal the second section or may be disposed on the first and second sections. The expandable frame comprises an atraumatic distal end.
The control member may be coupled to the proximal end of the end-effector and may extend proximally within the lumen of the elongate member. Alternatively, the control member may be a tube or sheath that is slidable over the end-effector to move the end-effector between a closed position and an open position or to allow an end-effector that is biased in an open position to assume the open position upon withdrawal of the sheath.
Some embodiments pertain to a method of performing an intravascular procedure, comprising the steps of providing a system comprising elongate member having a distal region including an expandable end-effector having a blood impermeable membrane and an electrode, positioning the end-effector intravascularly at a region of interest, expanding the membrane to partially occlude blood flow and form pleats in the membrane, and activating the electrode. The membrane may have a proximal end and a distal end such that the membrane has a perimeter at the distal end that is larger than the perimeter at the proximal end. A system used in the method may be any of the systems described herein.
An example medical device for modulating nerve activity may include a sheath. An elongate shaft may be disposed in the sheath. The shaft may have a distal end. An expandable frame may be attached to the shaft. The frame may include a plurality of struts and a membrane attached to the struts. The frame may be configured to shift between an expanded configuration and a collapsed configuration. The membrane may be configured to partially occlude blood flow through a blood vessel when the frame is in the expanded configuration. One or more electrodes coupled to the frame.
Another example medical device for modulation of renal nerve activity may include a sheath. An elongate shaft may be slidably disposed within the sheath. The shaft may have a distal region. A self-expanding umbrella frame may be attached to the shaft. The frame may include a plurality of struts and a membrane attached to the struts. The frame may be configured to shift between a collapsed configuration when the frame is disposed within the sheath and a conical configuration when the sheath is disposed proximally of the frame. One or more electrodes may be coupled to the frame. The membrane may define a plurality of pleated regions that extend radially inward relative to the struts when the frame is in the conical configuration. The pleated regions may be configured to increase blood flow adjacent to the electrodes.
Method for modulating renal nerves are also disclosed. An example method may include providing a renal nerve modulation device. The renal nerve modulation device may include a sheath. An elongate shaft may be slidably disposed within the sheath. The shaft may have a distal region. A self-expanding umbrella frame may be attached to the shaft. The frame may include a plurality of struts and a membrane attached to the struts. The frame may be configured to shift between a collapsed configuration when the frame is disposed within the sheath and a conical configuration when the sheath is disposed proximally of the frame. One or more electrodes may be coupled to the frame. The membrane may define a plurality of pleated regions that extend radially inward relative to the struts when the frame is in the conical configuration. The pleated regions may be configured to increase blood flow adjacent to the electrodes. The method may also include advancing the renal nerve modulation device through a blood vessel to a position within a renal artery and proximally retracting the sheath relative to the frame. Proximally retracting the sheath relative to the frame may shift the frame from the collapsed configuration to the conical configuration. The method may also include activating at least one of the one or more electrodes.
The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify these embodiments.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.
For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this 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 terms “about” may include 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).
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.
It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include one or more particular features, structures, and/or characteristics. However, such recitations do not necessarily mean that all embodiments include the particular features, structures, and/or characteristics. Additionally, when particular features, structures, and/or characteristics are described in connection with one embodiment, it should be understood that such features, structures, and/or characteristics may also be used connection with other embodiments whether or not explicitly described unless clearly stated to the contrary.
The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.
Certain treatments require the temporary or permanent interruption or modification of select nerve function. One example treatment is renal nerve ablation, which is sometimes used to treat conditions related to hypertension and/or 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 of the nerves running to the kidneys may reduce or eliminate this sympathetic function, which may provide a corresponding reduction in the associated undesired symptoms.
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 treatment locations and/or applications where nerve modulation and/or other tissue modulation including heating, activation, blocking, disrupting, or ablation are desired, such as, but not limited to: blood vessels, urinary vessels, or in other tissues via trocar and cannula access. For example, the devices and methods described herein can be applied to hyperplastic tissue ablation, cardiac ablation, pulmonary vein isolation, tumor ablation, benign prostatic hyperplasia therapy, nerve excitation or blocking or ablation, modulation of muscle activity, hyperthermia or other warming of tissues, etc.
An end-effector 114 may be disposed at the distal end of the elongate member 106. Generally, end-effector 114 is configured to shift between an expanded form or configuration and a collapsed form or configuration (suitable for being maneuvered through body lumens within the body lumen 102). In at least some embodiments, end-effector 114 may be configured to shift between the expanded configuration and the collapsed configuration by shifting the position of the elongate member 106 relative to a sheath 112. For example, elongate member 106 may be positioned so that the end-effector 114 is positioned distally of the sheath 112. When so positioned, the end-effector 114 may shift to the expanded configuration (e.g., as shown in
When in the expanded configuration, end-effector 114 may be shaped like a cone or otherwise have a generally conical shape. End-effector 114 partially occludes the interior of vessel 102 either by having a distal end that is smaller than the cross-section of the body lumen 102 and/or by including pleats or folds.
End-effector 114 may include a frame (indicated generally at 120) that includes a plurality of struts 118 and a membrane 116 lying over and secured to the struts 118. Each strut 118 may extend from the distal end of the elongate member 106, where each strut 118 is fixed. The number and length of the struts 118 depends upon the particular application, as will be understood by those in the art. In the embodiment illustrated, six struts 118 are employed, each strut being about 1-5 cm long. Variations are contemplated, however, that include any suitable number of struts 118 including one, two, three, four, five, six, seven, eight, nine, ten, or more struts 118.
The end-effector 114 may be equipped with a control member that may urge each strut 118 to the expanded state shown in
When freed from restraint, the control member may cause a portion of each strut 118 to move radially away from the longitudinal axis of elongated member 106, pushing membrane 116 outwardly. That expansion continues until the struts 118 are at their furthest expanded state or have encountered the wall 104 of the body vessel. When the struts 118 bear on walls 104, the membrane 116 can be described as forming a pleated structure, with the membrane portions lying between struts 118 assuming cupped or concave forms. In other words, the pleated regions of the membrane 116 may extend radially inward relative to the struts 118 and/or frame 120. Such a configuration allows the membrane to partially occlude the vessel while channeling the blood flow through the pleats. When doing so, the flow of blood may increase along the pleats and/or along electrodes 124 positioned generally along the frame 120. This may be desirable for a number of reasons. For example, the increased blood flow along the electrodes 124 may aid in dissipating heat that might be generated during activation of the electrodes 124.
As indicated above, one or more electrodes 124 may be provided along the frame 120 and may be located on the outside surface of membrane 116, on the inside surface of membrane 116, on the struts 118, on a separate electrode bearing structure or other suitable location. In at least some embodiments, electrodes 124 are RF (radio frequency) electrodes. Other electrodes are contemplated including laser electrodes, microwave electrodes, ultrasound transducers, or the like. Electrodes 124 may be sized and located to provide a desired RF field, capable of accomplishing the desired nerve ablation. In the illustrated embodiment, electrodes 124 are located between each pair of struts 118, spaced from the distal end of the membrane 116. In the illustrated configuration, electrodes may be formed of a metal electro-deposited or painted on the membrane. Furthermore, each electrode 124 is appropriately connected to an RF energy source (not shown). Alternative locations for electrodes may be the tips of struts 118, on the inner side of membrane 116, or any other suitable location. The electrodes 124 are illustrated as oblongs, but may be oval, circular, or other suitable shape.
In alternative embodiments, electrodes 124 can be attached to other structures, rather than directly on the frame 120. For example, an electrode 124 can be suspended by a separate support strut, or between two struts. Additionally, the frame 120 may be configured as a double cone (e.g., as shown in
Struts 118 can be formed of any material possessing requisite characteristics of resilience and stiffness. Suitable materials include nitinol or other shape-memory or highly elastic materials, or stainless steel, or other alloys, or elastic polymer, or combinations. Where struts 118 are designed to impinge upon walls 104, each strut 118 may have sufficient contact area to minimize mechanical trauma to the vessel wall. For example, each strut 118 may have a wall-contacting pad or may be curved inwardly at the distal end to form a convex atraumatic contact with the vessel wall 104.
The membrane 116 may be formed of a relatively thin, flexible material, such as polyester, fluoropolymer, or other polymers, flexible metallic structures, coatings, or combinations. As will be appreciated from considering the description of operation below, the material for membrane 116 can be selected to be impermeable to bodily fluids or to permit a desired amount of seepage or leakage. Materials such as non-porous versions of embolic protection filter membrane materials produce impermeable membranes. The membrane material can be attached to struts 118 by any suitable attachment means or method, such as adhesive, thermal bond, or the like.
When deployed within the body lumen 102, membrane 116 at least partially occludes the flow of blood or other fluid within the lumen. The degree of occlusion can be controlled by the extent to which the distal ends of struts 118 expand, by the shape of the membrane 116 between adjacent struts 118, and by the material of membrane 116. For example, struts 118 can be designed to expand completely within body lumen 102, impinging upon walls 104, or that expansion can be controlled to leave some degree of space between the distal tips of struts 118 and walls 104. Further, the shape of membrane 116 lying between adjacent struts 118 can be scalloped (depicted generally at reference number 110) to permit a desired amount of flow around the deployed frame 120, as shown in
An effect of reducing the cross-sectional area of lumen 102 in a relatively localized area is an increase in the flow velocity within the lumen at that localized area. This increased velocity concomitantly increases the cooling effect of the fluid. Because the remaining flow is almost totally confined to the portion of the lumen adjacent to the walls 104, the increased cooling capacity of the fluid results in improved heat removal from the vessel walls 104. In that manner, ablation effectiveness may be improved while minimizing danger to surrounding tissue. For example, the fluid flow past the frame 120 illustrated in
In this embodiment, RF electrodes to 224 are positioned on the struts 218 rather than on the surface of membrane 216. A number of alternative positions for location of the RF electrodes 224 are contemplated based on the delivery of a desired RF field at a target location.
As depicted, the inner expansion member 326 may be placed proximal of the A-A′ plane, such that the electrodes are spaced apart from both the inner inflatable member 326 and the vessel wall 304. During nerve ablation, the elongate member is advanced to the site of operation in a collapsed state. Once there, the operator may inflate the inner expansion member 326 to expand the frame 314 within the blood vessel and place the RF electrodes 324 some distance apart from the vessel wall 304. This off-wall positioning of electrodes along with increased blood velocity provided by the expanded frame 314 increases convective cooling of RF electrodes 324 and reduces vessel wall injury and blood damage.
As can be seen by inspection of
In its collapsed state, seen in
It should be apparent that the medical device of the present disclosure may be used to carry out a variety of medical or non-medical procedures, including surgical and diagnostic procedures in a wide variety of bodily locations. For example, ablation of tissue associated with a variety of body organs, such as esophagus, stomach, bladder, or the urethra could be accomplished using the method discussed above. In addition, at least certain aspects of the disclosed embodiments may be combined with other aspects of the embodiments, or removed altogether, without departing from the scope of the disclosure.
Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/548,608, filed Oct. 18, 2011, the entirety of which is incorporated herein by reference.
Number | Date | Country | |
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61548608 | Oct 2011 | US |