Patent Publication Number: US-2005119644-A1

Title: Articulating catheter tip with wedge-cuts

Description:
FIELD OF THE INVENTION  
      The present invention pertains generally to surgical instruments. More particularly, the present invention pertains to medical catheters designed to cool contacted body tissue to extremely low (i.e. cryogenic) temperatures. The present invention is particularly, but not exclusively, useful as a cryocatheter having a segment that can be reshaped in situ to contact and cool internal target tissue having a complex surface geometry in a one-step process.  
     BACKGROUND OF THE INVENTION  
      There are many applications in which it is desirable to contact and cool tissue having a complex (e.g. non-flat) surface geometry. One such application is the ablation of a circumferential band of tissue surrounding the ostium of a pulmonary vein where the pulmonary vein connects with the left atrium. This band of tissue can be ablated in a procedure to treat a somewhat common heart ailment known as atrial fibrillation.  
      Research has shown that atrial fibrillation is due to abnormal electrical signals that pass through (or originate at) the tissue surrounding the ostia of the pulmonary veins where the pulmonary veins connect with the left atrium. Once the circumferential band of tissue surrounding the affected ostium has been ablated, the destroyed tissue is no longer able to initiate or conduct any type of electrical signal. Accordingly, ablation can be used to prevent abnormal electrical signals from the pulmonary veins from reaching the heart.  
      One technique that has been used to cryoablate the circumferential band of tissue has involved sequentially ablating tissue at a plurality of relatively small locations around the periphery of the ostium. To perform this procedure, the cold cryotip of the cryoablation catheter must be repeatedly moved (i.e. reoriented) to sequentially contact portions within a band of tissue. In theory, these ablations can combine to establish an effective circumferential ablation band. However, in practice, this complex process often results in a non-uniform or discontinuous circumferential lesion that does not adequately block all of the abnormal electrical signals from entering the heart. Moreover, this procedure is time consuming because it requires extensive manipulation of the cryotip around the ostium. The result is a somewhat lengthy procedure that increases patient discomfort and increases the probability that complications may result from the procedure.  
      The present invention contemplates the cryoablation of a circumferential band of tissue in a single-step (i.e. the entire band of tissue is ablated simultaneously). This requires contacting the circumferential band of tissue with a contacting element having a relatively large-diameter, somewhat cylindrical shaped contact surface. The problem, however, has been the non-invasive delivery of a contacting element having this relatively large, bulky shape to the treatment site. In particular, the human vasculature is curved, branched and contains vessels having relatively small inner diameters. As a consequence, it is necessary to design a catheter having a relatively low profile to allow the distal end of the catheter to navigate through the complex vasculature. With this in mind, it would be desirable for a catheter to have a relatively low profile for transit through the vasculature and a relatively large contact surface to allow for a one-step cryoablation. To solve this dilemma, the present invention contemplates a contacting element that can be reshaped in-situ from a relatively low profile shape to a shape suitable for contacting a circumferential band of tissue.  
      In light of the above, it is an object of the present invention to provide a system and method for performing a non-invasive, single-step cryoablation of a circumferential shaped band of tissue in the vasculature of a patient. Another object of the present invention is to provide a system and method for treating atrial fibrillation by cryoablating the peripheral tissue surrounding the ostium of a pulmonary vein where the pulmonary vein connects to the left atrium. Still another object of the present invention is to provide a system and method for cryoablating tissue in the vasculature of a patient in a relatively quick, efficient and reliable manner.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to an articulating catheter for cryoablating target tissue at a treatment site. In particular, the articulating catheter can be used to cryoablate target tissue having a curved (i.e. non-flat) surface. For the present invention, the articulating catheter includes an elongated, thermally conductive tube that has an outer surface and is formed with a plurality of transverse notches. With this cooperation of structure, the tube is reconfigurable between a first configuration wherein the tube is substantially cylindrical and a second configuration in which at least a portion of the outer surface of the tube is shaped to substantially conform with the surface of the target tissue.  
      In greater structural detail, each notch establishes a first edge and an opposed second edge. In the first configuration, each edge is inclined relative to a plane that is substantially perpendicular to a longitudinal axis defined by the cylindrical shaped tube. On the other hand, when the tube is in the second configuration, the first edge of each notch is juxtaposed with the second edge of the notch, and the tube is no longer cylindrical.  
      In an exemplary embodiment on the articulating catheter, the notches can be configured such that the tube is curved in the second configuration and establishes an inner radius of curvature, ρ inner , relative to a central axis and an outer radius of curvature, ρ outer , relative to the central axis. More specifically, the portion of the tube that is distanced from the central axis by the distance ρ outer , constitutes a continuous, thermally conductive band that can be placed in contact with target tissue having a curved surface and cooled to cryoablate the target tissue.  
      In a typical arrangement, the tube is configured in the first configuration and attached to a cryo-element having an expansion chamber. A catheter tube is then used to advance the cryo-element and tube to the treatment site whereupon the tube can be reconfigured into the second configuration. For example, a pull-wire attached to the distal end of the tube can be actuated to reconfigure the tube. Once reconfigured, the conforming portion of the tube is placed in contact with the target tissue. Next, a refrigerant can be passed through the catheter tube and expanded in the expansion chamber to cool the cryo-element and tube. The cooling can be continued until the target tissue is effectively cryo-ablated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:  
       FIG. 1  is a perspective view of a system for cryoablating internal target tissue shown operationally positioned in a patient;  
       FIG. 2  is perspective view of a distal portion of the cryoablation system shown in  FIG. 1 ;  
       FIG. 3  is side plan view of a reshapeable contact segment shown in a first configuration in which the contact segment is cylindrically shaped;  
       FIG. 4  is a front plan view of the reshapeable contact segment shown in  FIG. 3 ;  
       FIG. 5  is a side plan view of the reshapeable contact segment shown in  FIG. 3 , shown after reconfiguration into a second configuration in which a portion of the outer surface of the contact segment is shaped to substantially conform with the surface of the target tissue;  
       FIG. 6  is a cross-sectional view of a distal portion of the cryoablation system shown in  FIG. 1 , as seen along the line  6 - 6  in  FIG. 2 ;  
       FIG. 7  is a perspective view of a distal portion of the cryoablation system shown in  FIG. 1 , shown in the straight configuration and positioned at a treatment site in the vasculature of a patient; and  
       FIG. 8  is a perspective view of a distal portion of the cryoablation system shown in  FIG. 1 , shown in the curved configuration and positioned at a treatment site in the vasculature of a patient.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Referring initially to  FIG. 1 , a system  20  for ablating internal target tissue of a patient  22  is shown. As shown, the system  20  includes a catheter  24  that extends from a proximal end  26  that remains outside the patient&#39;s body during the procedure to a distal end  28 . From  FIG. 1  it can be seen that the distal end  28  of the catheter  24  has been inserted into the patient  22  through an artery such as the femoral artery and advanced through the patient&#39;s vasculature until the distal end  28  is positioned in the upper body of the patient  22 .  FIG. 1  further shows that the proximal end  26  of the catheter  24  is connected to a catheter handle  30 , which in turn is connected to a fluid refrigerant supply unit  32  via one or more umbilicals  34   a - c.    
      Referring now to  FIG. 2 , the cryotip (i.e. the distal portion) of the catheter  24  is shown in greater detail. As shown, the catheter  24  includes a catheter tube  36 , contact segment  38  and a cryo-element  40 .  FIG. 2  also shows that the contact segment  38  extends from a distal end  42  (which is attached to the cryo-element) to a proximal end  44  (which is attached to the distal end  46  of the catheter tube  36 ). For the system  20 , both the cryo-element  40  and the contact segment  38  are made of thermally conductive materials. Further, the cryo-element  40  is attached to the distal end  42  of the contact segment  38  to establish a thermally conductive interface therebetween which allows heat to flow between the contact segment  38  and cryo-element  40 .  
      A better understanding of the contact segment  38  can be obtained with cross-reference to  FIGS. 2 and 3 . As seen there, the contact segment  38  includes an elongated, thermally conductive tube  48  that has an outer surface  50  and is formed with a plurality of transverse notches  52 , for which exemplary notches  52   a  and  52   b  have been labeled. Typically, the tube  48  is made of a stainless steel material and the notches  52  are cut in the stainless steel tube  48  using a precision laser. As explained in more detail further below, the tube  48  is reconfigurable between a first configuration (shown in  FIGS. 2 and 3 ) wherein the tube  48  is substantially cylindrical and a second configuration (shown in  FIG. 5 ) in which at least a portion of the outer surface  50  of the tube  48  is shaped to substantially conform with the surface of the target tissue.  
      As best seen in  FIGS. 3 and 4 , each notch  52  establishes a first edge  53  and an opposed second edge  54 . For the embodiment shown, each edge  53 ,  54  is inclined relative to a plane (such as a plane containing line  56 ) that is substantially perpendicular to a longitudinal axis  58  defined by the tube  48  when the tube  48  is in the first configuration (i.e. when the tube  48  is cylindrical shaped). It can further be seen that the first edge  53  and second edge  54  of each notch  52  meet at a respective first corner  60  and second corner  62 .  
      For the embodiment shown, the notches  52  are arranged with their respective first corners  60   a,b  lying substantially along a common line, such as reference line  64 , that extends parallel to the longitudinal axis  58  when the tube  48  is in the first configuration (as shown in  FIG. 3 ). It is to be appreciated that for notches  52  of uniform shape and size, the second corners  62  will also lie along a common line that extends parallel to the longitudinal axis  58 . This cooperation of structure allows the tube  48  to deflect in a single plane when reconfigured from the first configuration to the second configuration. However, those skilled in the pertinent art will recognize that by varying the shape, size and/or alignment of the notches  52 , a tube  48  can be made to deflect in more than one plane. For example, the notches  52  can be arranged wherein a first section of the tube  48  deflects in a first plane and a second section of the tube  48  deflects in a second plane.  
       FIG. 5  shows the tube  48  after it has been reconfigured into the second configuration. As shown in  FIG. 2 , a pull-wire  66  attached to the distal end of the tube  48  at attachment point  68  can be actuated to reconfigure the tube  48  in the second configuration. When the tube  48  is configured as shown in  FIG. 5 , the first edge  53  of each notch  52  is juxtaposed with the second edge  54  of the notch  52 , and the tube  48  is no longer cylindrical. For the exemplary embodiment shown in  FIG. 5 , the notches  52  are configured such that the tube  48  is curved in the second configuration and establishes an inner radius of curvature, ρ inner , relative to a central axis  70  and an outer radius of curvature, ρ outer , relative to the central axis  70 . More specifically, the portion  72  of the tube  48  that is distanced from the central axis  70  by the distance ρ outer , constitutes a continuous, thermally conductive band that can be placed in contact with target tissue having a curved surface and cooled to cryoablate the target tissue.  
      A more detailed understanding of the interactive cooperation between the contact segment  38  and the cryo-element  40  can be obtained with reference to  FIG. 6 . As shown, the cryo-element  40  surrounds and defines an expansion chamber  74 . A supply tube  76  is provided that extends from a proximal end  78  to a distal end  80 . As shown in  FIG. 1 , the proximal end  78  of the supply tube  76  is connected to a refrigerant supply unit  32  via umbilical  34   a.  Cross-referencing  FIGS. 1 and 6 , it can be seen that from the proximal end  78 , the supply tube  76  passes through the handle  30 , the catheter tube  36 , the contact segment  38  and projects slightly into the expansion chamber  74 . A restriction  82  can be positioned in the supply tube  76  at the distal end  80  to restrict the flow of refrigerant. A refrigerant return line  84  is arranged co-axially with the supply tube  76  to direct expanded refrigerant from the expansion chamber  74  to the refrigerant supply unit  32 . Alternative arrangements (not shown) can include locating the cryo-element  40  at the proximal end  44  of the contact segment  38 , or locating cryo-elements  40  at both the distal end  42  and the proximal end  44  of the contact segment  38 .  
     Operation  
      The operation of the system  20  can best be appreciated with reference to  FIGS. 7 and 8  which show a treatment site at the ostium  86  of a pulmonary vein  88  where the pulmonary vein  88  connects to the left atrium  90 . Referring to  FIG. 7 , the contact segment  38  is initially placed in the first configuration in which the contact segment  38  is cylindrical and somewhat straight. This configuration allows the distal portion of the catheter  24  to be somewhat easily navigated through the vasculature to the treatment site. During transit through the vasculature, a curve can be imparted to the contact segment  38  (using the pull-wire  66  shown in  FIG. 2 ) to steer the distal portion of the catheter  24  to the treatment site. The catheter tube  12  is used to advance the contact segment  38  to the treatment site. At the treatment site, the distal portion of the catheter  24  is positioned near the target tissue to be cryoablated.  
      At the treatment site, the pull-wire ( FIG. 2 ) can be activated to reconfigure the contact segment  38  in the second configuration, such as the configuration as shown in  FIG. 8 . In the second configuration, the portion  72  of the contact segment  38  is shaped as a continuous, thermally conductive band that can be placed in contact with a circumferential band of tissue surrounding the ostium  86  of a pulmonary vein  88  where the pulmonary vein  88  connects with the left atrium  90 .  
      Once the contact segment  38  has been positioned at the treatment site, configured in the second configuration and placed in contact with the target tissue, a fluid refrigerant, such as Nitrous Oxide, from the refrigerant supply unit  32  is transferred through the supply tube  76  and into the expansion chamber  74  ( FIG. 6 ) of the cryo-element  40 . Inside the expansion chamber  74 , the fluid undergoes endothermic expansion to absorb heat from the cryo-element  40  (and the contact segment  38  and target tissue). Typically, a fluid refrigerant is used that transitions from a liquid state to a gaseous state as it expands into the expansion chamber  74 . Heat absorbed by the refrigerant during this phase transition (i.e. latent heat) cools the cryo-element  40 , which in turn cools the contact segment  38 , which cools and cryoablates the target tissue. After expansion, the gaseous fluid refrigerant can pass through the return line  84  ( FIG. 6 ) and exit the patient  22  ( FIG. 1 ).  
      After the target tissue has been cryoablated, the contact segment  38  can be warmed and reconfigured (using the pull-wire  66 ) to place the contact segment  38  into the first configuration (as shown in  FIG. 7 ). For example, the contact segment  38  can passively absorb ambient heat at the treatment site to warm the contact segment  38 . It will be appreciated, however, that the contact segment  38  can also be warmed by any other devices or methods known to those skilled in the pertinent art. Once in the first configuration, the contact segment  38  can then be withdrawn from the treatment site and removed from the patient.  
      While the particular articulating catheter tip with wedge-cuts as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.