Abstract:
An electrophysiology catheter includes a tube having a proximal end, a distal end, and a lumen therebetween. The tube is preferably comprised of multiple sections of different flexibility, arranged so that the flexibility of the catheter increases from the proximal end to the distal end. There is a first generally hollow electrode member at the distal end. At least one magnetically responsive element is disposed at least partially in the hollow electrode, for orienting the distal end of the catheter with an externally applied magnetic field. Multiple magnets can be distributed over the distal portion of the device. The end electrode can have openings for delivering irrigating fluid, and/or a sleeve can be provided around the tube to create an annular space for the delivering of irrigating fluid. A temperature sensor can be provided to control the operation of the catheter. A localization coil can also be included to sense the position and orientation of the catheter.

Description:
This is a continuation of U.S. patent application Ser. No. 10/443,113, filed May 21, 2003, now U.S. Pat. No. 6,980,843, issued Dec. 27, 2005 the disclosure of which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   This invention relates to electrophysiology catheters, and in particular to a magnetically guidable electrophysiology catheter. 
   Electrophysiology catheters are elongate medical devices that are introduced into the body and are used for sensing electrical properties of tissues in the body; applying electrical signals to the body for example for cardiac pacing; and/or applying energy to the tissue for ablation. An electrophysiology catheter typically has a proximal end, a distal end, and at least one, and preferably at least two electrodes on its distal end. Recently, electrophysiology catheters have been made with electrodes having openings in their distal ends for passage of normal saline solution which cools the surface tissues to prevent blood clotting. These electrodes can be difficult to navigate into optimal contact with the tissues using conventional mechanical pull wires. 
   SUMMARY OF THE INVENTION 
   Electrophysiology catheters in accordance with the principles of this invention of this invention are particularly adapted for magnetic navigation. The electrophysiology catheter comprises a tube having a proximal end, a distal end, and a lumen therebetween. Of course, solid catheters could also be used. The tube is preferably comprised of multiple sections of different flexibility, each section being more flexible than its proximal neighbor, so that the flexibility of the catheter increases from the proximal end to the distal end. A first generally hollow electrode member is located at the distal end of the tube. The first electrode has a generally cylindrical sidewall and a dome-shaped distal end. There is preferably a second electrode spaced proximally from the first electrode, and there may be a plurality of additional ring electrodes proximal to the first electrode. In accordance with the principles of this invention, several magnetically responsive members are spaced along the length of the catheter. Flexible portions of the catheter are disposed between the magnetically responsive elements. Each of the flexible portions can have a different bending stiffness which, by the inverse relationship between bending stiffness and flexibility, defines the flexibility of each flexible portion. Moreover, because the flexible portions can have different flexibilities, the various flexible portions can have different turn radii, which can be optimized for their particular location within the catheter. The distal end portion of the catheter remains flexible to facilitate navigating the catheter within the body. 
   The magnetically responsive members can be permanent magnets, permeable magnets, electromagnetic coils, or combinations thereof and will hereinafter be referred to as magnet members. Each magnet member is sized and shaped so that it can orient the part of the catheter in which it is included inside the body under the application of a magnetic field from an external source magnet. The magnet member is preferably responsive to a magnetic field of 0.1 T, and more preferably less. The interplay between the strength and orientation of each magnet member and the flexibility and length of each flexible segment allows segments of the catheter to be oriented in a selected direction at the location of each magnet member with the applied magnetic field. Because of the ability to design flexible segments of the catheter for a particular catheter function, the catheter may navigate and advance through delicate structures in the body inaccessible to most other catheters. 
   One particularly demanding catheter function, electrical mapping and RF ablation therapy for restoration of normal electrical activity in cardiac chambers, requires a catheter which can extend trans-septally through a puncture in the septal wall of the heart from the right side to the left side and touch the anterior right lateral portions of the circumference of the Mitral Valve. Such navigation places particular demands on the catheter because the navigation requires a sharp, 180 degree navigation of the catheter within the narrow confines of the left ventricle. However, the current state of the art provides no such catheter that is easy to navigate around the Mitral Valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a side view of a catheter in accordance with a preferred embodiment of the present invention; 
       FIG. 2A  is a cross sectional view of a portion of a catheter with a first alternate magnetic member in accordance with the principles of this invention; 
       FIG. 2B  is a cross sectional view of a portion of a catheter with a second alternate magnetic member in accordance with the principles of this invention; 
       FIG. 2C  is a cross sectional view of a portion of a catheter with a third alternate magnetic member in accordance with the principles of this invention; and 
       FIG. 3  is a side view of the catheter of Figure a flexed by a magnetic field. 
   

   Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   A first embodiment of an electrophysiology catheter constructed according to the principles of this invention is indicated generally as  20  in  FIG. 1 . The electrophysiology catheter  20  has a proximal end  22  and a distal end  24 . The catheter  20  preferably includes a hollow flexible tube  26  with a sidewall  28  and a lumen  30  therethrough. A longitudinal axis  32  extends generally through the lumen  30  in the center of the device. The tube  26  is preferably made from a flexible biocompatible materials such as Pebax™. 
   As shown in  FIG. 1 , the catheter  20  can have a dome-shaped end electrode  34  on its distal end, and one or more ring electrodes  36  and  38  which extend around the distal end portion of the tube  26 . The ring electrodes may actually have a slit therein to reduce eddy currents when the catheter moves in an applied magnetic field. Lead wires  40  extend proximally from the electrodes  34 ,  36 , and  38  to conduct electrical signals, from the electrodes to a signal processing unit at the proximal end when the catheter is used in sensing and mapping, and to the electrodes  34 ,  36 , and  38  when the catheter is used for ablating tissue. Some of the electrodes can be dedicated for use in recording of electrophysiological electrical activity, others of the electrodes can be used for delivering RF energy to sites within a patient for therapeutic purposes. The electrodes can be disposed over magnetic or nonmagnetic sections of the catheter  20 . When placed over a magnetic section of the catheter, the magnet helps apply and control the contact force between the tissue and the electrode, but some or all of the electrodes could be placed over a non-magnetic portion of the catheter as well. 
   The distal end  24  of the catheter  20  can include a thermocouple or thermistor  42 . Leads  44  extend from the thermocouple or thermistor  42  to the proximal end of the catheter. The thermocouple or thermistor  42  allows temperature at the distal end of the catheter to be measured, so that the local effects of the operation of the RF therapy delivery. 
   As shown in  FIG. 1  the catheter  20  has magnetic members  46 ,  48 , and  50  which may be made from or include a permanently magnetized material with a fixed magnetic dipole moment, or a shaped magnetically permeable material that responds magnetically to an applied field so that magnetically induced moments act on the magnetic members  46 ,  48 , and  50 . The magnetic members  46 ,  48 , and  50  can be contained within the lumen  30 ; embedded in the side wall  28  of the catheter  20 ; or affixed to the side wall  28  in the form of a sleeve around the tube  26 . The magnet members  46 ,  48 , and  50  are preferably made from a permanent magnetic material, such as Neodymium-Iron-Boron (Nd—Fe—B) or Samarium-Cobalt, or a permeable magnetic material, such as Hiperco. If any of the magnetic members  46 ,  48 , and  50  is made of a magnetically permeable material, they may be designed in a shape that is inherently flexible, for instance a helically wound coil coaxial with the longitudinal axis of the catheter. 
   The strongest currently available magnetic material, Neo  53  is well suited for use to form the magnetic members  46 ,  48 , and  50 . The use of even stronger magnetic materials for the magnetic members is within the spirit and scope of the present invention. 
   The magnetic members  46 ,  48 , and  50  can take any size and shape, provided that they provide sufficient response to the applied magnetic field. As shown in  FIG. 2 , the magnetic members  46   48 , and  50  can be sized and shaped to accommodate the leads  40  and  44  within the lumen  30 . A second embodiment includes sleeve shaped magnetic members  42 ′ ( FIG. 2 ) which may be disposed anywhere on the outside of the tube  26 . In the embodiment shown in  FIG. 2 , the sleeve shaped magnetic members  46 ′ have an inside diameter of between about 0.008 and 0.15 inches to receive the tube  26 , and an outside diameter of between about 0.010 and 0.18 inches; and a length of between about 0.020 and 0.8 inches. The dimensions of the magnet  46 ′ will depend on the size of the tube  26  size, the tube material, catheter function, and the number of leads  40  and  44  in the lumen  30 . 
   The sleeve-shaped magnetic members  46 ′ can also be used to aid in connecting tube sections  26   a  and  26   b , as is illustrated in  FIG. 2 . As show in  FIG. 2A , the tube portions  26   a  and  26   b  can be flexible segments. Moreover, because the tube portions  26   a  and  26   b  can be made separately, from different materials, in difference sizes and configurations. For example, the tube segment  26   a  and  26   b  can comprise multiple layers which result in different properties for these sections. Thus, the design of the tube segments  26   a  and  26   b  can facilitate adapting the catheter to particular catheter functions and/or to facilitate navigating the catheter to a specific location or configuration for a particular function or procedure. 
   Alternatively, the magnetic members may have a generally spherical configuration, indicated as  46 ″ in  FIG. 2B , with a passage therethrough for mounting the magnet members  46 ″ over the catheter  20 . In yet another alternative, the magnetic members may be helically shaped, for example helical member  46 ′″ disposed in the lumen  30 , which may be, formed from a magnetic wire. 
   The various magnetic properties of the magnetic members  42 ′,  42 ″, and  42 ″, including the identity of the magnetic material, magnetic permeability, magnetic volume, magnetic orientation, and magnetic polarity of each magnetic member  42  can be selected to adapt the responsiveness of the magnetic members to an applied magnetic field. 
   As to the positions of the magnetic members along the tube  26 , in the embodiment shown in  FIG. 1 , the distal-most magnetic member  46  can be placed within 15 mm of the distal end  24  with satisfactory results. Magnet members  48  and  50  are preferably disposed within 3 to 80 mm of the proximal end of distal-most magnetic member  46 . In some embodiments the magnet members are positioned near locations on the catheter  20  where the flexibility of the tube  26  changes (e.g. at the location where tube segments  26   a  and  26   b  meet). 
   The tube  26  is preferably comprised of flexible portions  52 ,  54 ,  56 , and  58 . Each of the portions can have different size and shape and a mechanical properties. The portions  52 ,  54 ,  56 , and  58  can be different regions in a one-piece tube, or the portions can be comprised of one or more separate pieces joined together to form tube. By varying the mechanical properties of each flexible segment, such as the Young&#39;s modulus (by selection of the material), bending moment of inertia (by altering the cross sectional geometry of the tube), or the length, the properties of the catheter  20  can be adapted to particular catheter functions and/or to facilitate navigating the catheter to a specific location or configuration for a particular function or procedure. 
   Accordingly, the deflection of the distal end of a flexible portion is governed by the beam bending equation:
 
ε= lmB  sin(θ−ε)/ EI   (1)
 
where ε is the tip angular deflection, l is the length of the deflected distal portion of the device, m is the magnetic dipole moment of the magnetic member at the distal end of said flexible portion, θ is the field orientation angle with respect to the proximal end of the length l, and B is the applied magnetic field. The beam bending equation is useful to illustrate the properties which affect the deflection over even relatively large distances. Accordingly, the bending stiffness (EI/l) and its inverse, the flexibility, of the flexible portions determine the amount by which the distal end of a flexible portion deflects when a magnetic field is applied to the catheter  20 . By selecting the material, the cross sectional geometry, and the length of the flexible segments, the deflection of the distal ends of the flexible portions can be adapted to particular catheter functions and/or to facilitate navigating the catheter to a specific location or configuration for a particular function or procedure.
 
   The strength of the applied magnetic field and the magnetic dipole moment of the magnetic member determine the magnetically induced moment that acts on the magnetic member when a magnetic field is applied to the catheter. The magnetic members  42 ,  44 , and  46  transfer the moments to the flexible segments via the mechanical couplings between the flexible segments  52 ,  54 ,  56 , and  58  and the magnetic members. Thus the selection of the magnetic properties of the magnetic members and the selection of the mechanical properties of the flexible segments also affects how much the distal end of each flexible segment will deflect when the magnetic field is applied to the catheter. Large flexible segment deflections, greater than about 0.1 inch per inch, are desirable because they provide for the smaller turning radii desired for highly navigable catheters  20 . 
   The leads  40  and  44  can contribute to the bending stiffness of the catheter  20  ( FIG. 1 ). Thus, the number, size, and bending stiffness of wires within the lumen  30  should generally be minimized to maximize the flexibility of the flexible segments  140 ,  142 ,  144 , and  150  although, in other embodiments, the presence of wiring within the lumen  28  may beneficially decrease the flexibility of the flexible segments. While a single, generally round lumen  30  has been shown and described herein, tubes and/or lumens of other shapes, and multiple lumens can be provided to control the flexibility of the catheter and/or to adapt the catheter for particular functions and/or to facilitate navigating the catheter to a specific location or configuration for a particular function or procedure. 
   An alternate construction is shown in  FIG. 3 , such that when a magnetic field is applied to the catheter  20 , the catheter bends in an amount and direction depending on the strength of the applied magnetic field, the properties of the magnet elements, and the property of the flexible portions of the tube. The direction of the applied magnetic field is indicated by arrow  40 . Upon the application of a magnetic field to the catheter, a magnetically induced moment acts on each magnetic member  46 ,  48 , and  50 . These moments tend to turn the magnetic members  46 ,  48 , and  50  in a direction determined by the polarity of the magnet and the direction of the magnetic field. That is, a moment acts on the magnetic members  46 ,  48 , and  50  which tends to orient the magnetic members in the direction of the magnetic field  40 . Thus, magnetic members  46 ,  48 , and  50 , if unrestrained by the flexible portions  52 ,  54 ,  56 , and  58  would orient themselves with the applied magnetic field  40 . As shown in  FIG. 3 , the magnetic field  40  turns the magnetic members  46 ,  48 , and  50  in a counterclockwise direction, causing a corresponding counter clockwise flexing of the catheter  20 . 
   The magnitudes of the moments depend on the strength of the applied magnetic field and the magnetic properties of the individual magnetic members  46 ,  48 , and  50 . Because the flexible segments  52 ,  54 ,  56 , and  58  have some finite bending stiffness, equilibrium develops between the magnetically induced moments acting on each magnetic member  46 ,  48  and  50  and the resisting torques caused by the bending stiffness of the flexible members  52 ,  54 ,  56 , and  58  Thus, the catheter  20  will flex through a particular angle and stop with the magnetically induced moments in equilibrium with the resisting torques. 
   A second embodiment of a catheter constructed according to the principles of this invention is indicated generally as  100  in  FIG. 3 . Catheter  100  has a proximal end  102 , a distal  104 , and a tubular sidewall  106  having a lumen  108 . Catheter  100  could include various electrodes and thermistors described above with respect to catheter  20 , but these are omitted in  FIG. 3  for clarity. The catheter  100  comprises a plurality of portions of differing flexibility, in accordance with a design to facilitate configuring the catheter with an externally applied magnetic field to assume a desired shape, or to reach a desired location in a subject&#39;s body. As shown in  FIG. 3 , there are at least five portions  110 ,  112 ,  114 ,  116 , and  118 . These portions can either be different areas of a continuous tube, or they can separate sections formed into a tube. There are also a plurality of magnetically responsive elements, similar to elements  46 ,  48 , and  50 . As shown in  FIG. 3 , there are five elements  120 ,  122 ,  124 ,  126 , and  128 . 
   When a magnetic field is applied to the distal end portion of the catheter, the magnetically responsive elements  120 ,  122 ,  124 ,  126  and  128  tend to align their permanent magnetization (or induced magnetization) direction with the direction of the applied field. The flexible portions  110 ,  112 ,  114 ,  116 , and  118  apply some resistance to the magnet elements that tends to prevent them from aligning with the applied magnetic field. By providing a plurality of magnetically responsive elements connected by a plurality of flexible portions, the catheter  100  can be designed to assume a particular configuration upon the application of a magnetic field. 
   When a magnetic field is applied to the distal end portion of the catheter, the magnetically responsive elements  120 ,  122 ,  124 ,  126 , and  128  tend to align their permanent magnetically (or induced magnetization) direction with the direction of the applied field. The flexible portions  110 ,  112 ,  114 ,  116 , and  118  apply some resistance to the magnet elements that tend to prevent them from aligning with the applied magnetic field, and thereby establishes a lag between the tip direction and the applied field direction. By providing a plurality of magnetically responsive elements connected by a plurality of flexible portion, the catheter  100  can designed to assume a particular configuration upon the application of a magnetic field. The modulus a elasticity (IMB/EI) for each flexible segment is preferably greater than about 0.1, such that the free length of the distal end (of about 0.5 cm) can align within 20 degrees of a magnetic field even where the field is applied in a direction substantially perpendicular to the axial length of the medical device. When the field is applied in a direction substantially perpendicular to the elongate direction of the un-deformed device, the lag (or angle) between tip element and the applied field is less than about 20 degress, and the lag between each successively proximal element and the applied field is less than 35 degrees. The body portion of the medical device applies a torque (ie.—resistance to bending) of no more than about 0.01 N m to resist orientation of the with an applied field. 
   The magnetic properties of the magnetically responsive elements can also be selected to adapt the catheter to particular functions. For instance, in the preferred embodiment, the magnetization direction of the magnetically responsive elements would preferably be aligned with the axis of the catheter. Aligning the polarity of the magnets enables the catheter to flex through 180 degrees because all of the magnetically induced moments on the magnetic members operate in the same direction. Accordingly, the magnetically induced moments act cumulatively along the length of the catheter, navigating the catheter in an ever tighter curve. Such a reducing radius curve allows the catheter to reach areas in the body, for example the anterior, right, lateral portions of the Mitral Valve, which prior art catheters have difficulty in accessing. By selecting the size and position of the magnets and the stiffness of the flexible portion, the device can extend trans-septally through a puncture in the septal wall of the heart from the right side to the the left side, and touch the anterior right lateral portions of the circumference of the Mitral Valve. Another advantage of a reducing radius catheter over the prior art is that the catheter is softer. Accordingly, pressure which could damage soft tissue is minimized thereby easing patient trauma and improving chances for full patient recovery. It should be noted that this softer, more flexible catheter can also be stiffened by the application of a magnetic field that will cause the magnetic element to remain aligned with the field, and thereby make the catheter&#39;s bending resistance four time larger in the presence of the field, as compared to the bending resistance of the catheter in the absence of a field. 
   In some embodiments the magnetization direction might vary from this arrangement so that the catheter takes on a designed shape upon the application of a magnetic field. It is also possible that although aligned with axis of the catheter, the polarities of adjacent magnets alternate, i.e. so that the north pole of one magnet faces the south pole of an adjacent magnet. By placing the magnetically responsive members in opposition catheters can be constructed which will snake through obstructions, first navigating in one direction, then navigating in the other, and so forth. 
   Thus the present invention provides a family of highly navigable catheters well suited for reaching areas of the body inaccessible to prior art catheters. The small turning radii available via the invention allow navigation around acute angles and within small, confined chambers within the body. Also, by providing a reducing radius curvature catheter, the invention avoids physician fatigue and internal patient injury induced by the prior art catheters. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.