Abstract:
A tip for a medical device includes a hollow body having a window, a sensor positioned within the hollow body and oriented such that its active surface is pointed towards the window, and a membrane positioned within a beam path of the sensor. The membrane passes energy without preventing an outer surface of the hollow body of the tip from coming in contact with tissue, thus allowing the hollow body to deliver therapy to an adjacent tissue and/or diagnose adjacent tissue. The membrane can cover the window or the sensor. The membrane is desirably permeable to an irrigant, such that a suitable level of irrigant outflow from the window is maintained, and thin enough that it minimizes attenuation of energy passing to and/or from the sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/927,289, filed 14 Jan. 2014, which is hereby incorporated by reference as though fully set forth herein. 
     
    
     BACKGROUND 
       [0002]    The instant disclosure relates to medical devices. In particular, the instant disclosure relates to sensor-bearing tips that can be mounted to medical devices for use in the human body, such as diagnostic and therapeutic catheters. 
         [0003]    Catheters are used in a variety of diagnostic and therapeutic procedures, for example to diagnose and/or treat conditions such as atrial arrhythmias. For example, a catheter carrying one or more electrodes can be deployed and manipulated through a patient&#39;s vasculature and, once located at the intended site, radiofrequency (“RF”) energy can be delivered through the electrodes to ablate tissue. Alternatively, or in addition, the electrodes can be used to create a map of the electrophysiological activity of the patient&#39;s heart. Further, the electrodes can be used to localize (that is, determine the position and orientation of) the catheter as it is deployed and manipulated to the intended site. 
         [0004]    In some catheters, an additional sensor, such as an ultrasound sensor or optical sensor, is provided in the catheter tip to provide additional information during performance of the primary diagnosis or therapy. For example, RF ablation catheters can include one or more ultrasound sensors, located within the hollow tip of the catheter, that can be used to monitor the progress of a lesion forming in the tissue being treated and/or to confirm one or more characteristics of the lesion once created. 
         [0005]    Extant sensor-bearing tip medical devices, however, are subject to various issues, including excessive irrigant outflow, the passage of debris from the interior of the medical device into the patient&#39;s body, and distortion of signals to and/or from the sensors. Although there are known solutions to some of these problems, they very often exacerbate others (e.g., a rigid cover can be used to prevent the passage of debris, but increases signal distortion). 
       BRIEF SUMMARY 
       [0006]    Disclosed herein is a tip for a medical device that includes: a hollow body including a window; a sensor including an active surface positioned within the hollow body and oriented such that the active surface is pointed towards the window; and a membrane positioned within a beam path of the sensor, wherein the membrane passes energy without preventing an outer surface of the hollow body of the tip from coming in contact with tissue. The membrane can be positioned such that it covers the window, for example by securing it to either an outer surface of the hollow body or an inner surface of the hollow body. The membrane can also have its outer edge proximate the perimeter of the window. Alternatively, the membrane can take the form of a balloon secured within the hollow tip. 
         [0007]    In other aspects, the membrane can be positioned such that it covers the sensor. For example, the membrane can be adjacent to the sensor or adhered to the sensor, such as by chemically vapor depositing the membrane material onto the sensor. 
         [0008]    In some embodiments, the sensor is an acoustic sensor and the membrane is an acoustically-transmissive membrane. 
         [0009]    The sensor can sense energy coming from tissue and, in some embodiments, can transmit energy to the tissue and sense returning and/or reflected energy. The energy emitted by the sensor can be a different form of energy than the energy used by the tip to provide diagnosis and/or therapy. For example, the sensor can emit ultrasonic energy, and the tip can use radiofrequency energy to provide ablation therapy. 
         [0010]    In some embodiments, the membrane is permeable to an irrigant. This can be accomplished, for example, by using a hydrophilic material for the membrane, by treating the membrane to be hydrophilic, by using a porous (e.g., micro- or macro-porous) material for the membrane, and/or by forming irrigation holes in the membrane (e.g., by laser drilling). 
         [0011]    Typically, the membrane will be flexible. It can also exhibit elastomeric, viscoelastomeric, or plastic properties when deformed. 
         [0012]    Certain advantages can be achieved by making the membrane thin, including the minimization of acoustic distortion and the attenuation of energy passing through the membrane (e.g., passing to and/or from the sensor). Thus, for example, the membrane can have a thickness of no more than 30 microns, such as between 5 microns and 25 microns or between 10 microns and 20 microns. 
         [0013]    Also disclosed herein is a medical device including: an elongate tubular body having a distal section and including a lumen extending along its length; a hollow tip, including a window, attached to the distal end of the elongate tubular body, wherein the lumen of the elongate tubular body is in fluid communication with an interior of the hollow tip; a sensor disposed within the hollow body, wherein the sensor comprises an active surface oriented towards the window; and a membrane positioned between the active surface of the sensor and the window. The membrane can be secured to the hollow tip or, alternatively, to the elongate tubular body. 
         [0014]    In another aspect, a tip for a medical device includes: a hollow body including a window; a sensor including an active surface positioned within the hollow body and oriented such that the active surface is pointed towards the window; a membrane deposited upon and overlying the sensor; and an irrigant dam positioned to restrict outflow of irrigant from the window. The membrane can include a chemically vapor deposited poly(p-xylylene), such as Parylene™. 
         [0015]    The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  depicts an exemplary catheter including a sensor-bearing hollow tip. 
           [0017]      FIG. 2  illustrates an exemplary sensor-bearing hollow tip mounted to a catheter body in close up and partial cut-away view. 
           [0018]      FIG. 3  illustrates a first embodiment of a sensor-bearing hollow tip as disclosed herein mounted to a catheter body in close up and partial cut-away view. 
           [0019]      FIG. 4  illustrates a second embodiment of a sensor-bearing hollow tip as disclosed herein mounted to a catheter body in close up and partial cut-away view. 
           [0020]      FIG. 5  illustrates a third embodiment of a sensor-bearing hollow tip as disclosed herein mounted to a catheter body in close up and partial cut-away view. 
           [0021]      FIG. 6  illustrates a fourth embodiment of a sensor-bearing hollow tip as disclosed herein mounted to a catheter body in close up and partial cut-away view. 
           [0022]      FIG. 7  illustrates a fifth embodiment of a sensor-bearing hollow tip as disclosed herein mounted to a catheter body in close up and partial cut-away view. 
           [0023]      FIG. 8  is a close up view of the ring-shaped dam shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The present disclosure provides sensor-bearing tips for use in medical devices and medical devices including the same. The tips can have a diagnostic or therapeutic function, with the sensor(s) used to monitor such function. For purposes of illustration, several exemplary embodiments will be described in detail herein in the context of a radiofrequency (“RF”) ablation catheter including an acoustic sensor (e.g., a pulse-echo transducer) that can be used to monitor the progress of the lesion being formed in an adjacent tissue. It should be understood, however, that the methods, apparatuses, and systems described herein can be utilized in other contexts (e.g., optical sensors). 
         [0025]      FIG. 1  is a schematic diagram of an ablation system  100  including an exemplary catheter  10 . As shown in  FIG. 1 , catheter  10  generally includes an elongate tubular body  12  having a proximal end  14  and a distal end  16 . Tubular body  12  defines a lumen  18  (not visible in  FIG. 1 , but shown in  FIGS. 2-7 ). Although only a single lumen  18  is depicted in the figures, this is only for the sake of clarity of illustration; tubular body  12  can have any number of lumens  18  without departing from the scope of the instant teachings. 
         [0026]    Proximal end  14  of tubular body  12  is attached to a catheter control handle  20 . Catheter control handle  20  can include, for example, an actuator (not shown) coupled to suitable structure (e.g., pull wires and/or pull rings) within tubular body  12  in order to effect the deflection of distal end  16 . It can also include connections to additional components of ablation system  100  as discussed in further detail below. Insofar as the construction of catheter control handle  20  will be familiar to those of ordinary skill in the art and a detailed understanding thereof is not necessary to make and use the teachings herein, however, no further description need be provided. 
         [0027]    A hollow tip  22  is attached to distal end  16  of tubular body  12 . Tip  22  can be a diagnostic tip, a therapeutic tip, a hybrid diagnostic and therapeutic tip, or any other type of tip that may be desirable for a given application of catheter  10 . 
         [0028]    For example, tip  22  can include an RF ablation element, such as a tip electrode. As such, catheter  10  can be connected with an ablation energy source  120 , such as an RF generator. 
         [0029]      FIG. 2  is a close-up and partial cross-section of hollow tip  22  (and a portion of tubular body  12  proximate distal end  16 ) against a tissue surface  24 . As shown in  FIG. 2 , lumen  18  of tubular body  12  is in fluid communication with the interior  26  of hollow tip  22 , which is defined by a wall  28  of hollow tip  22 . An irrigant (e.g., saline) or other fluid can be delivered from fluid source  124  (shown in  FIG. 1 ), through lumen  18 , and into hollow tip  22 , for example for cooling purposes, for energy transmission purposes, and/or for acoustic matching purposes. 
         [0030]    Wall  28  of hollow tip  22  further includes a window or (“beam hole”)  30  (e.g., a break in wall  28 ). Window  30  allows for the passage of energy to and/or from a sensor  32 , which, in some embodiments, is an ultrasound transducer, disposed within interior  26  of hollow tip  22  along a beam path  34 . It is therefore desirable for window  30  to be larger than the active surface  36  of sensor  32 , which is oriented towards window  30 , to minimize or eliminate diffraction and/or attenuation of energy passing to and/or from sensor  32  by reducing the likelihood that incoming and/or outgoing energy will pass through or otherwise impinge the edges of wall  28  defining window  30 . 
         [0031]    As illustrated, sensor  32  is mounted to an acoustic backer  38 , but any suitable structure to secure sensor  32  within hollow tip  22  can be employed. Backer  38  can be acoustically attenuative, such that any acoustic energy that propagates backwards from sensor  32  towards backer  38 , rather than towards tissue  24 , is attenuated. This also allows acoustic sensor  32  to have a short acoustic ring-down time, making it suitable for the transmission of short pulses for pulse-echo lesion sensing. 
         [0032]    Window  30  also allows for irrigant to pass out of interior  26  of hollow tip  22 , for example for tissue cooling purposes, energy transmission purposes, and/or for energy coupling to adjacent tissue. The irrigant, such as saline, can benefit the coupling and transmission of both RF ablation energy and pulse-echo acoustic energy to (and, in the case of pulse-echo energy, from) tissue  24 . Tissue  24  may naturally distend into window  30 . 
         [0033]    A transducer pinger  128  (see  FIG. 1 ), which might have more than one channel, supplies pinging energy, such as electrical energy pulses, to sensor  32  (e.g., an ultrasound transducer). A control unit  130  (also shown in  FIG. 1 ) is provided for controlling the ablation and the acoustic pinging during ablation. For instance, control unit  130  can be configured to carry out duty cycling or synchronization for both ablation and pinging. An acoustic pinger echo analyzer or acoustic receiver  132  is provided to condition and analyze the data collected by sensor  32  to provide one or more of lesion feedback, tissue thickness or proximity measurement, tip contact force monitoring, and pre-pop detection. The information can be presented to a practitioner (e.g., using a graphical user interface) to provide real-time assessment of the ablation. The information may additionally or alternatively be utilized by the system itself without operator intervention, for example as input to a feedback control loop to avoid steam pops and/or to achieve a desired lesion depth. 
         [0034]    Thus, one aspect disclosed herein is directed to an RF ablation catheter with one or more acoustic transducers therein or thereon, wherein the acoustic transducer is capable of at least one of acoustic lesion feedback, catheter tip-force monitoring, tissue thickness or proximity measurement, or pre-pop warning. The catheter is capable of delivering an RF ablating tip to a patient&#39;s tissue to be ablated. These aspects and others are described in U.S. patent application publication no. 2012/0265069, which is hereby incorporated by reference as though fully set forth herein. 
         [0035]    A fully-open window  30 , however, has certain attendant disadvantages. For example, it allows for a very substantial volume of irrigant outflow, which can starve smaller irrigation passageways (e.g., apertures that are not also intended to pass energy to and/or from a sensor) of irrigant. This results in decreased irrigant backpressure in hollow tip  22 , which can in turn lead to increased bubble formation due to a reduced boiling point, particularly when the temperature of hollow tip  22  increases during use (e.g., where hollow tip  22  functions as a radiofrequency (“RF”) ablation electrode). Similarly, a fully-open window  30  presents no obstacles to the passage of potentially harmful debris into the patient&#39;s body if, for example, a portion of sensor  32  were to break off 
         [0036]    Though extant devices mitigate some of these concerns (e.g., a rigid polymeric acoustic covering over window  30  reduces the risk of debris passing into the patient&#39;s body), they do so at the expense of other desirable aspects (e.g., a rigid polymeric acoustic covering over window  30  can defocus and attenuate ultrasonic energy passing therethrough and/or limit the outflow of irrigant to such an extent that blood coagulates at window  30  or the tissue becomes dewetted). The embodiments disclosed herein advantageously allow the simultaneous achievement of multiple desirable attributes—including, without limitation, an appropriate volume of irrigant outflow, the prevention of debris escape, avoidance of beam distortion, and the minimization of window-edge diffraction and/or attenuation of energy passing to and/or from sensor  32 —by placing a membrane within beam path  34  of sensor  32  (that is, between active surface  36  of sensor  32  and tissue  24 ). 
         [0037]    A first embodiment of a sensor-bearing hollow tip  300  is depicted in  FIG. 3 . As shown in  FIG. 3 , a membrane  310  covers window  30 . In particular, membrane  310  is secured to the inner surface  311  of wall  28 , for example by thermoforming an outer periphery  313  of membrane  310  to wall  28  under heat and pressure or by securing the outer periphery  313  of membrane  310  to wall  28  with a suitable adhesive. Outer periphery  313  of membrane  310  is proximate the perimeter of window  30 ; that is, membrane  310  is roughly the same size and shape (e.g., round, oval, or other shape) as window  30 . 
         [0038]    A second embodiment of a sensor-bearing hollow tip  400  is depicted in  FIG. 4 . The embodiment of  FIG. 4  is similar to that of  FIG. 3 , except that membrane  410  is secured to the outer surface  411  of wall  28 , for example by thermoforming an outer periphery  413  of membrane  410  to wall  28  under heat and pressure or by securing outer periphery  413  of membrane  410  to wall  28  with a suitable adhesive. Outer periphery  413  of membrane  412  is proximate the perimeter of window  30 ; that is, membrane  410  is roughly the same size and shape as window  30 . 
         [0039]    A third embodiment of a sensor-bearing hollow tip  500  is depicted in  FIG. 5 . As shown in  FIG. 5 , a membrane  510  is secured proximate sensor  32 , for example to acoustic backer  38 . To inflate membrane  510 , there is an inlet (e.g., passageway  511 ) to deliver irrigant (or another suitable inflation fluid) to the space  513  between membrane  510  and sensor  32 /acoustic backer  38 ). 
         [0040]      FIG. 6  depicts another embodiment of a hollow tip  600 . In the embodiment of  FIG. 6 , membrane  610  comprises a balloon (or bladder) that is inflated against the inner surface of wall  28 , for example under pressure of an irrigant or other suitable inflation fluid, when in use. Membrane  610  can be secured to elongate tubular body  12 , for example by thermoforming membrane  610  to elongate tubular body  12  under heat and pressure at one or more locations interior to hollow tip  600 . 
         [0041]    It is desirable for membranes  310 ,  410 ,  510 ,  610  to be wettable by irrigant (e.g., saline), for example by using a material that is either naturally hydrophilic to the irrigant or has been treated to be hydrophilic to the irrigant. 
         [0042]    It is also desirable for membranes  310 ,  410 ,  510 ,  610  to be permeable to the irrigant (that is, membranes  310 ,  410 ,  510 ,  610  should permit the irrigant to pass through its thickness). For example, a microporous, micropermeable, or foamlike material can be used for membrane  310 ,  410 ,  510 ,  610 . Alternatively or additionally, a plurality of irrigation holes  312 ,  412 ,  512 ,  612  can be provided in membranes  310 ,  410 ,  510 ,  610  respectively, for example by laser-drilling or punching. Because irrigant flow out of windows  30  will be limited, however, by the presence of permeable membranes  310 ,  410 ,  510 ,  610  there remains net positive irrigant pressure inside hollow tip  300 ,  400 ,  500 ,  600 , which in turn suppresses bubble formation, boil-over, and thrombus formation. 
         [0043]    Where sensor  32  is an acoustic sensor, membranes  310 ,  410 ,  510 ,  610  can be acoustically-transmissive. Suitable materials for membranes  310 ,  410 ,  510 ,  610  include, without limitation, polyether ether ketone (“PEEK”) (e.g., the APTIV™ films of Victrex), polyethylene terephthalate (“PET”), polyvinyl chloride (“PVC”), nylon, urethane, polyethylene, latex, and silicone. 
         [0044]    Membranes  310 ,  410 ,  510 ,  610  are flexible, in order to attain a curvilinear shape in window  30 , for example under pressure of an irrigant. In addition to being flexible, membranes  310 ,  410 ,  510 ,  610  can be elastomeric (e.g., deforming elastically under irrigant pressure), viscoelastomeric (e.g., deforming elastically under irrigant pressure, but returning to its relaxed state after a time delay), plastic (e.g., deforming plastically under irrigant pressure), or may exhibit a combination of the foregoing properties. 
         [0045]    According to certain aspects, membranes  310 ,  410 ,  510 ,  610  have a thickness of no more than about 30 microns. For example, membranes  310 ,  410 ,  510 ,  610  can each have a thickness between about 5 microns and about 25 microns, or between about 10 microns and about 20 microns. At these dimensions, acoustic distortion and attenuation of energy passing to and/or from sensor  32  are minimized, but the membrane itself remains able to withstand the irrigant pressure. 
         [0046]    The embodiments discussed above offer the advantages of simultaneously allowing a desirable volume of irrigant outflow, preventing debris escape, avoiding beam distortion, providing excellent acoustic coupling to wetted tissue, and minimizing diffraction and attenuation of energy passing to and/or from sensor  32 . Each embodiment also offers additional advantages beyond those discussed above. For example, in hollow tips  300  and  600 , the bond between membrane  310 ,  610  and wall  28  or elongate tubular body  12  is protected from abrasion against tissue  24  when catheter  10  is in use. 
         [0047]    As another exemplary advantage of the embodiment illustrated in  FIG. 3 , because membrane  310  is only slightly larger than window  30 , there is less interference with the ability of an irrigant delivered to hollow tip  300  to cool the interior of wall  28  before flowing out of hollow tip  300  (e.g., through irrigant holes  312  or additional irrigation passageways (not shown) in wall  28 ). 
         [0048]    Hollow tips  400 ,  500 , and  600  offer the additional exemplary advantage of easier installation of membrane  410 ,  510 ,  610  resulting from the ability to see the point(s) at which the membrane is bonded during assembly. That is, unlike membrane  310 , membranes  410 ,  510 , and  610  are not attached to wall  28  at a blind point. 
         [0049]    Still another embodiment of hollow tip  700  is shown in  FIG. 7 . As shown in  FIG. 7 , a membrane  710  is placed closely around sensor  32  and acoustic backer  38 . Indeed, membrane  710  can be directly deposited upon sensor  32  and acoustic backer  38 . Membrane  710  can be used in conjunction with a ring-shaped dam  712 , formed, for example, of a compressible rubber or foam material, at or near window  30  to control the flow of irrigant out of hollow tip  700 . As shown in  FIG. 8 , ring-shaped dam  712  can include a plurality of flow passageways  714  designed to promote a suitable volume of irrigant outflow from window  30 . 
         [0050]    Membrane  710  can be a chemically vapor-deposited layer of a poly-para-xylylene, such as Parylene™, and, in particular, Parylene™ C. Such materials are desirably pin-hole free and can be precisely deposited over irregular surfaces substantially conformally. Membrane  710  can have a thickness of between about 10 microns and 15 microns. 
         [0051]    Additional exemplary advantages (e.g., beyond the prevention of debris escape and the other advantages discussed above) of membrane  710  include increased mechanical capture of sensor  32  in the event of breakage, increased high voltage leakage protection, and ease of assembly. 
         [0052]    In addition, membrane  710  does not distend towards tissue under irrigant pressure. Instead, membrane  710  remains bonded to sensor  32  and acoustic backer  38 . 
         [0053]    Although several embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. 
         [0054]    For example, although the exemplary embodiments are discussed and illustrated in connection with a single sensor, the teachings herein are equally applicable to devices including additional sensors and/or more than a single window. Indeed, certain aspects disclosed herein are particularly advantageous in medical devices including several sensors (e.g., three radially-looking sensors arranged circumferentially about the hollow tip at about 120° intervals and a fourth forward-looking sensor). 
         [0055]    All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. 
         [0056]    It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.