Abstract:
Apparatus for medical treatment or diagnosis in a body cavity of a mammalian subject includes an elongate probe, having an outer surface and comprising a distal portion, which is adapted for insertion into the body cavity. An electrode strip includes an elongate insulating substrate, which is wrapped around the distal portion of the probe so as to define a helix having distal and proximal ends and a length therebetween, the substrate being fixed to the outer surface of the probe over substantially all of the length of the helix. A plurality of electrodes are disposed along the length of the helix and fixed to the substrate. Electrical conductors are coupled to the electrodes and run along the substrate over the length of the helix so as to communicate with circuitry in a location proximal to the distal portion of the probe.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to invasive medical devices, and specifically to devices for mapping electrical activity in the heart.  
       BACKGROUND OF THE INVENTION  
       [0002]     Catheters with electrode arrays on their outer surfaces are known in the art. For example, U.S. Pat. No. 6,063,022, whose disclosure is incorporated herein by reference, describes a catheter with an array of electrophysiological sensing electrodes spaced along its length. The catheter also comprises position sensors, for use in determining the location of the electrodes within the body. The electrodes and position sensors can thus be used to generate a map of physiological activity as a function of position within the body cavity. In another embodiment described in this patent, the catheter comprises an array of radio frequency (RF) ablation electrodes.  
         [0003]     Typically, in order to produce an electrode array on the catheter, a set of wires is threaded through a lumen of the distal portion of the catheter, and each of the electrodes is electrically coupled to a respective one of the wires. Assembly of such catheters is generally an expensive, labor-intensive process, which typically includes: (a) forming holes in the shaft of the catheter at the location of each electrode; (b) threading a set of wires through a lumen in the distal portion of the catheter; (c) manually drawing each wire through a respective hole in the shaft; (d) attaching each wire to a respective electrode; (e) pulling each wire back into the shaft; and (f) gluing each electrode to the outer surface of the shaft over its respective hole.  
         [0004]     Some catheters carry electrode arrays that can be expanded when the catheter is inside a chamber of the heart, in order to enable rapid mapping of electrical activity or RF ablation in the chamber. For example, U.S. Pat. No. 5,279,299, whose disclosure is incorporated herein by reference, describes a catheter having an expandable device, which is secured to the distal extremity of the catheter and is movable between a contracted position and an expanded position. The electrodes are mounted on the expandable device so that when the expandable device is moved to the expanded position in a chamber of the heart, the electrodes are moved into engagement with the wall of the chamber. In one embodiment, the expandable element has the form of a single flexible elongate strip, which is wrapped in a spiral fashion around the catheter and is movable between contracted and expanded positions.  
         [0005]     Other catheters use strip electrodes, rather than arrays of individual electrodes, on their outer surface. For example, U.S. Pat. No. 6,090,104, whose disclosure is incorporated herein by reference, describes a catheter having at least one spirally wrapped flat ribbon electrode. Each such electrode has an associated lead wire that can be connected to a source of energy for ablation or connected to a recording system to produce electrophysiological signals for diagnosis. The catheter is steerable by use of a puller wire connected to the distal section of the catheter and connected to a handle with means for controlling the movement of the puller wire.  
       SUMMARY OF THE INVENTION  
       [0006]     Embodiments of the present invention provide improved means and methods for fixing an electrode array to the distal portion of an invasive probe, such as a catheter. An electrode strip is wound in a helix around a distal portion of the probe and is fixed to the outer surface of the probe over substantially the entire length of the helix. The strip comprises an insulating substrate, with electrodes disposed along the length of the substrate. Electrical conductors running along the substrate couple the electrodes to circuitry inside the probe or to wires in the probe that connect to circuitry outside the proximal end of the probe.  
         [0007]     The use of the electrode strip in this manner makes it possible to attach an array of electrodes to the probe simply and economically, without the need to create multiple holes in the probe or to run a wire to each electrode, as in devices known in the art. In embodiments of the present invention, only a single hole is typically made in the probe, for connecting the conductors at the proximal end of the electrode strip to the wires or circuits inside the probe.  
         [0008]     Typically, the distal portion of the probe is bendable, generally for purposes of steering the probe inside the body. Bending the catheter can exert tensile and shear forces on the strip at the outside of the bend. Since the electrodes and conductors on the electrode strip are generally inelastic, these tensile forces could cause damage to the strip, such as loss of electrical contact with the electrodes. To avoid this problem, in some embodiments of the present invention, at least the distal portion of the probe comprises a relatively soft, elastic material, while the substrate of the electrode strip is strong and substantially inelastic. When the probe bends, the pressure exerted on the probe by the electrode strip at the outside of the bend causes substantial deformation of the elastic material. The tensile and shear forces exerted on the electrode strip are thus substantially reduced.  
         [0009]     There is therefore provided, in accordance with an embodiment of the present invention, apparatus for medical treatment or diagnosis in a body cavity of a mammalian subject, the apparatus including:  
         [0010]     an elongate probe, having an outer surface and including a distal portion, which is adapted for insertion into the body cavity; and  
         [0011]     an electrode strip, including: 
        an elongate insulating substrate, which is wrapped around the distal portion of the probe so as to define a helix having distal and proximal ends and a length therebetween, the substrate being fixed to the outer surface of the probe over substantially all of the length of the helix;     a plurality of electrodes, disposed along the length of the helix and fixed to the substrate; and     electrical conductors, coupled to the electrodes and running along the substrate over the length of the helix so as to communicate with circuitry in a location proximal to the distal portion of the probe.        
 
         [0015]     Typically, the distal portion of the probe is adapted to bend and includes an elastic material, which substantially deforms due to a pressure exerted thereon by the electrode strip when the distal portion is bent, while the electrode strip is substantially inelastic, so that the electrode strip does not substantially deform due to a tensile force exerted thereon when the distal portion is bent. In a disclosed embodiment, the apparatus includes a glue applied between the substrate and the outer surface of the probe so as to fix the substrate to the probe, wherein the glue is sufficiently elastic so as to accommodate a relative motion between the electrode strip and the outer surface when the distal portion is bent.  
         [0016]     In some embodiments, the substrate includes a flexible circuit substrate, and the electrodes and conductors are printed on the substrate by a printed circuit fabrication process. In one embodiment, the substrate has an inner side, which is fixed to the outer surface of the probe, and an outer side, upon which the electrodes are disposed, and the conductors are disposed along the inner side of the substrate. In another embodiment, the conductors are disposed along the outer side of the substrate.  
         [0017]     Typically, the probe includes a cable passing therethrough in communication with the circuitry, and the conductors are coupled to the cable at the proximal end of the helix. In one embodiment, the probe includes a multiplexer, coupled between the conductors and the cable so as to select the electrodes to be coupled to the cable.  
         [0018]     In some embodiments, the electrodes are spaced substantially evenly over the length of the helix, while in other embodiments, the electrodes are grouped in two or more clusters over the length of the helix.  
         [0019]     In one embodiment, the probe includes a catheter, which is adapted to be inserted into a chamber of a heart of the subject. Typically, the electrodes are adapted to sense electrical signals within a wall of the heart, and the conductors are adapted to convey the signals to the circuitry. Alternatively, the electrodes are adapted to receive electrical energy from the conductors and to apply the electrical energy to a wall of the heart.  
         [0020]     There is also provided, in accordance with an embodiment of the present invention, a method for producing a medical device, the method including:  
         [0021]     providing an elongate probe, which is adapted for insertion into the body cavity;  
         [0022]     wrapping an electrode strip around the probe so as to define a helix having distal and proximal ends and a length therebetween, the strip including an elongate insulating substrate having a plurality of electrodes fixed thereto and disposed along the length of the helix and further having electrical conductors, coupled to the electrodes, running along the substrate over the length of the helix so as to communicate with circuitry associated with the probe; and  
         [0023]     fixing the substrate to an outer surface of the probe over substantially all of the length of the helix.  
         [0024]     There is additionally provided, in accordance with an embodiment of the present invention, a method for medical diagnosis, including:  
         [0025]     inserting an elongate probe into a body cavity of a mammalian subject, the probe having an elongate insulating substrate wrapped around a distal portion of the probe so as to define a helix having distal and proximal ends and a length therebetween, the substrate being fixed to an outer surface of the probe over substantially all of the length of the helix, wherein a plurality of electrodes are disposed along the length of the helix and fixed to the substrate, and wherein electrical conductors are coupled to the electrodes and run along the substrate over the length of the helix;  
         [0026]     disposing the probe in the body cavity so that the electrodes sense electrophysiological activity within the cavity; and  
         [0027]     receiving and processing signals from the electrodes via the conductors.  
         [0028]     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a schematic, pictorial illustration of a cardiac catheterization system, in accordance with an embodiment of the present invention;  
         [0030]      FIG. 2  is a schematic side view of a distal portion of a catheter with an electrode strip fixed thereto, in accordance with an embodiment of the present invention;  
         [0031]      FIG. 3  is a schematic, pictorial view of an electrode strip, in accordance with an embodiment of the present invention;  
         [0032]      FIG. 4  is a schematic cutaway view of a heart with a catheter inserted therein, in accordance with an embodiment of the present invention;  
         [0033]      FIG. 5  is a schematic frontal view of an electrode strip, in accordance with an embodiment of the present invention;  
         [0034]      FIG. 6  is a schematic, sectional view of a portion of a catheter having an electrode strip fixed thereto, in accordance with an embodiment of the present invention;  
         [0035]      FIG. 7  is a schematic frontal view of an electrode strip, in accordance with another embodiment of the present invention; and  
         [0036]      FIG. 8  is a block diagram that schematically shows multiplexing circuitry inside a catheter, in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0037]      FIG. 1  is a schematic, pictorial illustration of a cardiac catheterization system  20 , in accordance with an embodiment of the present invention. System  20  comprises an elongate probe, typically a catheter  22 , which is inserted by a user through a vein or artery of a human or other mammalian subject  26  into a chamber of a heart  24  of the subject. Catheter  22  is coupled at its proximal end to a console  28 , which receives electrical signals from electrodes fixed to the distal end of the catheter inside the heart, as described hereinbelow. The console may use these signals to create a map of electrical activity in the heart, as is known in the art. Alternatively or additionally, the console may be configured to provide electrical energy, typically RF energy, to the electrodes in order to ablate areas of the endocardium, as is likewise known in the art.  
         [0038]      FIG. 2  is a schematic side view of a distal portion  30  of catheter  22 , in accordance with an embodiment of the present invention. An electrode strip  32  is wound in a helix around the distal portion of the catheter. The electrode strip comprises an array of electrodes  34 , which are electrically exposed on the outer surface of the strip. The strip typically has a width of about 2 mm, a length between about 10 cm and about 12 cm, and a thickness of about 0.03 mm. Typically, there are about twenty-five electrodes  34  on the strip. Alternatively, electrode strips of this sort may be produced in larger or smaller sizes, and with greater or smaller numbers of electrodes. Catheter  22  may comprise other elements in distal portion  30 , which are not shown in the figures, including a steering mechanism and sensors of other types, such as position sensors. Such elements are described, for example, in the above-mentioned U.S. Pat. No. 6,063,022.  
         [0039]      FIG. 3  is a schematic pictorial illustration of a segment of electrode strip  32 , showing portions of both an outer side  46  and an inner side  48  of the strip, in accordance with an embodiment of the present invention. Strip  32  comprises a micro-flex circuit, produced on a flexible, non-conductive substrate, typically a biocompatible plastic, such as polyimide. Electrodes  34  are deposited on the outer side of the substrate, typically using methods of printed circuit production known in the art. The electrodes are connected through the substrate to conductive traces  50  on inner side  48  of strip  32 . The traces are typically arranged such that each of the traces is electrically coupled to exactly one of the electrodes on the opposite side of the strip. Traces  50  are typically about 11 μm wide and 1 μm thick, on 22 μm centers. The traces may be formed near the center line of strip  32  in order to minimize shear forces on the traces. Further details of the construction of strip  32  are shown below in  FIGS. 5, 6  and  7 .  
         [0040]     Returning now to  FIG. 2 , in order to assemble catheter  22 , the distal end of electrode strip  32  is secured to distal portion  30  of catheter  22  in the vicinity of a distal tip  36  of the catheter. The strip may be secured, for example, by using a fastener  38 , such as a pin or screw, or by gluing its distal end to the catheter. Strip  32  is then spirally wrapped tightly about distal portion  30  of the catheter, and is permanently secured thereto along the length of the strip, by means such as glue. The proximal end of the electrode strip is inserted into catheter  22  through an aperture  42  (which is subsequently sealed). Inside the catheter, traces  50  are electrically coupled to a cable  44  or other signal transfer medium, which connects at the proximal end of catheter  22  to console  28 . Cable  44  may comprise, for example, a MicroFlat ribbon cable (produced by W. L. Gore &amp; Associates, Elkton, Md.), which contains individual wires having a one-to-one correspondence with traces  50 . Alternatively, multiple traces may be multiplexed onto a single wire, as described hereinbelow with reference to  FIG. 8 .  
         [0041]      FIG. 4  is a schematic, cutaway illustration of heart  24 , showing distal portion  30  of catheter  22  inserted inside a chamber  55  of the heart, in accordance with an embodiment of the present invention. The distal portion of the catheter is brought into contact with the inner wall of chamber  55 , causing electrodes  34  on strip  32  to receive electrical signals from the myocardium. Alternatively, electrodes  34  may be configured to receive electrical signals within chamber  55  without physically contacting the heart wall, as described, for example, in U.S. Pat. No. 6,400,981, whose disclosure is incorporated herein by reference.  
         [0042]      FIG. 5  is a schematic frontal view of an electrode strip  60 , in accordance with an embodiment of the present invention. This strip may be used interchangeably with strip  32 , shown in the preceding figures. Strip  60  comprises electrode pads  62  formed on a polyimide substrate  64 . The substrate is typically about 1.8 mm wide and 12.5 μm thick. The electrode pads themselves are about 1.3×1.5 mm across, and are spaced about 1.4 mm apart. The pads are fabricated on the substrate by methods of flexible printed circuit production known in the art. The pads may be produced, for example, by depositing a thin layer of nickel chromium (typically about 0.5 nm thick), overlaid by about 1 μm of gold. To reduce the impedance of the electrodes, pads  62  may be plated with a variety of materials, as are known in the art, such as platinum, platinum black, iridium oxide, activated iridium, or titanium nitride. It will be understood, however, that all the dimensions and materials cited here are provided by way of example, and other materials, dimensions and methods for construction of electrode strips will be apparent to those skilled in the art.  
         [0043]     Traces  50  are printed on substrate  64  and connect electrode pads  62  to corresponding contact pads  66 , at a proximal end  68  of strip  60 . The traces in this embodiment are printed on the same (outer) side of the substrate as are the electrode pads, passing along the margins of the substrate outside pads  62 , as shown in the enlarged inset in  FIG. 5 . In order to maximize the available area of pads  62 , without making strip  60  any wider than necessary, traces are preferably very narrow, typically on the order of 10 μm wide. Typically, end  68  is inserted into catheter  22 , and contact pads  66  are used for connecting the traces to cable  44 , as described above. A distal end  70  of strip  60  may be strengthened for secure fastening to distal portion  30  of catheter  22 .  
         [0044]      FIG. 6  is a schematic, sectional view of catheter  22 , showing a detail of distal portion  30  of the catheter with electrode strip  60  fixed thereto, in accordance with an embodiment of the present invention. As noted above, in this illustration, traces  50  are formed alongside electrode pads  60  on the outer surface of substrate  64 . The traces are overlaid by an additional protective layer  74 , such as another 12.5 μm layer of polyimide. Thus, the total thickness of strip  60  is about 26 μm. Assuming the radius of catheter is about 1 mm, the ratio of the radius of curvature of strip  60  to its thickness is about  40 . Alternatively, traces  50  may be printed on the inner surface of substrate  64 , as described above. For the sake of visual clarity, the dimensions in  FIG. 6  are not shown to scale. It will be understood in any case that the dimensions given above are provided solely by way of example, and larger or smaller dimensions may similarly be used, depending on application requirements and material characteristics.  
         [0045]     Strip  60  is wrapped tightly around an outer wall  76  of catheter  22 , and is fastened to wall  76  along substantially the entire length of the strip, typically by a layer of medical-grade glue  78 . For example, glue  78  may comprise a two-part polyurethane mix, such as a mixture of Vorite®  689  and Polycin®  640 -M 1  (produced by G. R. O&#39;Shea, Itasca, Ill.). The inventors found that a mixture of 81.8:100 (Polycin:Vorite) of these materials gave satisfactory results. Alternatively, a cyanoacrylic or urethane acrylate adhesive, such as  201 -CTH (Dymax Corporation, Torrington, Conn.) may be used. Substrate  64  of strip  60  typically has a high tensile strength, which may be on the order of 400,000 psi, and a high Young&#39;s modulus, so that the strip resists stretching or breaking when subjected to tensile or shear forces. Such forces may be generated when catheter  22  is bent, as shown in  FIG. 4 , particularly on the outside of the bend. If strip  60  were sufficiently elastic to stretch under these forces, conductors  50  or electrodes  62  might tear or suffer other damage.  
         [0046]     In order to reduce the tensile force exerted on strip  60 , wall  76  may be formed of an elastic material, such as a suitable medical-grade polyurethane or PVC. For example, the wall may be made from a PELLETHANE thermoplastic polyurethane elastomer (Dow Chemical, Midland, Mich.). Such a wall material is soft enough to deform inward under the pressure exerted thereon by the portion of strip  60  that is on the outside of a bend in the catheter. Glue  78  preferably has high tensile strength, as well (typically at least 1,500 psi), to avoid detachment of substrate  64  from wall  76  when the catheter bends. Unlike the substrate, the glue may be chosen to allow stretching of the glue layer, typically by up to about 175%, under the shear force that is exerted between substrate  64  and wall  76 .  
         [0047]      FIG. 7  is a schematic frontal view of an electrode strip  80 , in accordance with another embodiment of the present invention. In this embodiment, electrodes  62  are clustered in groups along the length of substrate  64 , rather than being evenly distributed as in  FIG. 5 . The strip characteristics illustrated in  FIGS. 3, 5  and  7  are shown here solely by way of example, and other electrode configurations, shapes and sizes may also be used, as will be apparent to those skilled in the art.  
         [0048]      FIG. 8  is a block diagram that schematically illustrates a multiplexer  90  in catheter  22 , for connecting traces  50  to cable  44 , in accordance with an embodiment of the present invention. The use of the multiplexer reduces the number of wires that must be passed through catheter  22  to console  28 , thereby allowing the catheter to be made thinner and more flexible, or leaving room to accommodate other functional elements inside the catheter. Multiplexer  90  may comprise an analog/digital converter, which converts the electrode signals on traces  50  to digital samples. In this case, the multiplexer may also comprise a digital multiplexer, using substantially any suitable digital multiplexing technique, such as time division, frequency division, or code division multiplexing. Alternatively, multiplexer  90  may comprise analog multiplexing circuitry, such as a switch, for selecting the signals from traces  50  to be conveyed over cable  44  at any given time. When multiplexer  90  is used, cable  44  typically comprises about five to seven wires, as opposed to the much larger number of wires that would be required otherwise.  
         [0049]     Although the fabrication and use of electrode strips are described hereinabove mainly with reference to cardiac catheter  22 , the principles of the present invention may similarly be applied to elongate probes that are used in examining and treating other body organs and cavities, as well. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.