Abstract:
An ablation catheter having distal and proximal ends for performing ablation on a human tissue region comprises at least one electrode. These elements are formed on a conductive sheet situated at the distal end of the catheter. A flex circuit assembly couples the at least one electrode to a measurement and power circuit attached to the proximal end of the catheter. The measurement and power circuit supplies power to the at least one electrode via the flex circuit.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to catheters and other medical probes and, more specifically, to using flex circuits and etched electrodes in these devices.  
       BACKGROUND OF THE INVENTION  
       [0002]     Certain catheters or surgical probe shafts employ a set of braided insulated copper wires that form an intertwined, complicated cross-hatched design running the length of the catheter or probe. This braided shaft then serves as a conduit for radio frequency (RF) current that is delivered to the electrodes to ablate tissue, as well as to sense electrophysiological signals that are in turn transmitted along those same lines to a monitoring system.  
         [0003]     Another pair of copper wires is often soldered to a copper-constantan thermocouple junction located on a gold band proximal to each electrode. This gold band has a high thermal conductivity and the thermocouple junction quickly equilibrates to the sensed environmental temperature at the gold band. The thermocouple junction forms a temperature-to-voltage transducer and the two copper wires transmit information back to the energy source for feedback-control of RF energy delivery.  
         [0004]     Material and labor costs may increase in the assembly process as the number of electrodes increases with conventional methods of assembly. For example, the number of braided wires for a 24-electrode catheter/probe with 24 thermocouples adds up to 72 wires. The “count and cut” process used during assembly to extricate and expose the correct wire along the shaft to solder onto an electrode or thermocouple has become increasingly time-consuming to perform these labor-intensive production steps. When one electrode or one thermocouple connection fails during final electrical testing at the factory, the entire catheter/probe has to be counted as scrap if the fault cannot be reworked.  
       SUMMARY OF THE INVENTION  
       [0005]     An ablation catheter having etched electrodes connected to the proximal end of the catheter by a flex circuit enables the braided wire assembly used in previous systems to be replaced by printed circuit board technology. Thermal sensing elements (e.g., thermocouples or thermistors) may also be connected. The catheter is easy to fabricate because of the use of the flex circuits in conjunction with etched electrodes and thermal sensing elements such as thermocouples. The use of etching to construct the electrodes allows electrodes having very precise dimensions to be constructed. Alternatively, coiled electrodes can be used.  
         [0006]     In many of these embodiments, a catheter having distal and proximal ends for performing ablation on a human tissue region comprises at least one etched electrode. In addition, at least one thermal sensing element may be used. These elements are formed from a conductive sheet and situated at the distal end of the catheter. Alternatively, coiled electrodes can be used.  
         [0007]     A flex circuit assembly couples the at least one etched electrode and the at least one thermocouple sensor to a measurement and power circuit attached to the proximal end of the catheter. The measurement and power circuit supplies power, senses impedance at the electrode-tissue interface and controls electrical current flow to the at least one etched electrode via the flex circuit. The thermal sensing element supplies thermal information indicative of conditions at the human tissue interface to the measurement and power circuit, to control the amount of electrical current to be delivered to the tissue.  
         [0008]     The flex circuit assembly may include plurality of identical flex circuit sub-portions. The sub-portions may be attached together and bent to form a cylindrically shaped assembly. Furthermore, multiple layers of flex circuits may be used. In addition, the measurement and power circuit may be comprised of a PC board, an energy source, and monitoring equipment (e.g., monitoring and control circuits for energy delivery).  
         [0009]     The etched electrodes may be coated with a conductive gel to aid in the ablation or other medical procedure. Also, the electrodes may be infused with anti-coagulant chemicals that are time released during the course of an ablation procedure. Further, the thermal sensing element may be comprised of gold bands and copper-constantan junctions. Mass production time and costs are reduced.  
         [0010]     Thus, the present system and method allows for the replacement of complex braided wire arrangements with a flex circuit arrangement. The structures described herein are simple to construct and easy to modify when adjustments are needed and/or when failures of components occur after the flex circuit assembly is placed inside a catheter shaft.  
         [0011]     In addition, the approaches described herein are useful in a variety of medical therapy applications. For instance, the embodiments described herein can also be employed for the treatment of cardiac arrhythmias such as atrial fibrillation (AF) and ventricular tachycardia (VT). Minimally invasive access or endocardial access methods can be employed with probes/catheters using these approaches. The electrodes described herein can also be used to sense electrical activity from the heart, and the proximal connection of the probe/catheter shaft can be attached to a computerized mapping system. In addition, the present approaches are useful in other tissue desiccation and ablation procedures, for example, in oncology to selectively heat and destroy cancerous tumors. Other uses in different organ systems are possible. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1   a  is perspective view of a flex circuit assembly for use in an ablation catheter showing a single electrode thermocouple pair according to the present invention;  
         [0013]      FIG. 1   b  is a front view of a flex circuit of  FIG. 1  showing twenty four electrode-thermocouple pairings according to the present invention;  
         [0014]      FIG. 1   c  is a perspective view showing a three-layered flex circuit assembly according to the present invention;  
         [0015]      FIG. 2   a  is a perspective view of a flex circuit assembly with etched electrodes and thermocouples formed into a cylinder according to the present invention;  
         [0016]      FIG. 2   b  is a perspective view of a flex circuit assembly with coiled electrodes and thermocouples formed into a cylinder according to the present invention;  
         [0017]      FIG. 3   a  is a perspective view of a flex circuit assembly with etched electrodes and thermocouples formed into a cylinder according to the present invention;  
         [0018]      FIG. 3   b  is a perspective view of a flex circuit assembly with coiled electrodes and thermocouples formed into a cylinder according to the present invention;  
         [0019]      FIG. 4  is a perspective view of a flex circuit assembly fitted into an ablation catheter according to the present invention; and  
         [0020]      FIG. 5  is a cross-sectional view taken along line  304  of  FIG. 3   a  according to the present invention;  
         [0021]      FIGS. 6   a - c  are cross-sectional views of a catheter using three flex circuit layers according to the present invention;  
         [0022]      FIG. 7  is a perspective view of the catheter using three flex circuit layers of  FIG. 6  according to the present invention; and  
         [0023]      FIG. 8  is perspective view of a flex circuit sheet showing the electrodes etched directly onto a conductive sheet according to the present invention. 
     
    
       [0024]     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of the various embodiments of the present invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]     The present system and method allows for the replacement of complex braided wire arrangements with a flex circuit arrangement in catheters and other medical devices. Medical devices constructed according to these approaches are relatively simple to fabricate. Mass production time and costs are also reduced.  
         [0026]     The approaches described herein can be used in a variety of medical procedures. For example, the approaches described herein can be employed for the treatment of cardiac arrhythmias such as atrial fibrillation (AF) and ventricular tachycardia (VT). Minimally invasive access or endocardial access methods can also be performed with the probes/catheters described in this application. The electrodes utilized in the approaches described herein can also be used to sense electrical activity from the heart, and the proximal connection of the probe/catheter shaft can be attached to a computerized mapping system. In addition, these approaches can be used in tissue desiccation and ablation procedures, for example, in oncology, to selectively destroy cancerous tumors.  
         [0027]     Referring now to  FIG. 1   a , one example of a flex circuit  100  used in an ablation catheter is described. A flex circuit pattern is printed on a flat sheet  104  with solder pins  106  at one edge of the sheet  104 . The pins  106  point perpendicular to the surface of the sheet  104 . The pins  106  correspond to connections for electrodes and thermal sensing elements (e.g., thermocouples). The pins are shown in  FIG. 1  as being parallel to the surface of the sheet  104 , but are bent or formed perpendicular to the sheet when the sheet is folded into a cylinder. The following description is made with respect to the thermal sensing elements being thermocouples. However, it will be understood by those skilled in the art that the thermal sensing elements may include not only thermocouples, but thermistors or any other thermal sensing device.  
         [0028]     A conductive circuit  110  is established on the pattern and is connected to the pins  106 . For example, a metallic conductive circuit  110  is established using techniques that are known in the art. In this case, the conductive circuit  110  includes three lines that conduct electrical energy.  
         [0029]     In addition, as described with respect to  FIGS. 1   b  and  1   c , repeated similar patterns of the conductive circuits can be printed onto flex circuit boards. In addition, as described below, this arrangement can be formed into a cylinder and placed into the shaft of a catheter or medical probe.  
         [0030]     Conducting circuit elements  110  of the sheet  104  are electrically insulated from each other and from the exposed surfaces of the flex sheet  104 . Preferably, the inter-wire spacings for RF energy and current delivery are predetermined to comply with applicable regulatory, EMC and safety compliance standards.  
         [0031]     Referring now to  FIG. 1   b , a circuit including 24 electrode and thermocouple pairs is shown. A first electrode thermocouple pair  106  (electrode E 1  and thermocouple TC 1 ) has corresponding conductive paths  110 , which couple the electrode and thermocouples to a connector  150  at the proximal end of the catheter. A second electrode thermocouple pair  120  (electrode E 2  and thermocouple TC 2 ) has corresponding conductive paths  112 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter. A third electrode thermocouple pair  122  (electrode E 3  and thermocouple TC 3 ) has corresponding conductive paths  114 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter. For simplicity, the fourth through twenty-third pairs of electrodes and thermocouples are not shown in  FIG. 1   b . Finally, a twenty-fourth electrode thermocouple pair  124  (electrode E 24  and thermocouple TC 24 ) has corresponding conductive paths  116 , which couple the electrode and thermocouples to the connector  150  at the proximal end of the catheter.  
         [0032]     It will be understood that the electrode thermocouple pairs and their conductive paths can be split across multiple layers of circuit boards. In other words, the first eight pairs may be placed on a first flex circuit board, the second eight pairings on a second flex circuit board, and the third eight pairings placed on a third flex circuit board. The three boards are stacked onto each other and then formed into a cylinder. Preferably, the three groupings are offset lengthwise from each other when the three layers are rolled into a cylinder for placement in the catheter.  
         [0033]     Referring now to  FIG. 1   c , a multi-layered flex circuit assembly is described. A first assembly  180 , second assembly  182 , and third assembly  184  are formed into concentric cylinders with assembly  180  being the outermost protective layer assembly. Assembly  182  is inside assembly  180  and assembly  184  is inside assemblies  180  and  182 . Electrode solder points E 1 , E 2 , and E 3  are formed on the assembly  180 . Other electrode solder points up to and including electrodes En are formed on the other assemblies. The assemblies  180 ,  182 , and  184  are electrically insulated from each other by homogenous polyimide material layers (not shown in  FIG. 1   c ) that are typically used in multi-layer flex circuit boards.  
         [0034]     In addition, thermocouple solder points T 1 , T 2  and T 3  are formed on assembly  180 . Other thermocouple solder points up to and including Tn are formed on the assemblies  182  and  184 . Conductive lines  186  are coupled to the respective electrodes and thermocouples. The electrodes and thermocouples are attached to the actual solder points.  
         [0035]     Referring now to  FIG. 2   a , the flex sheet  100  is shown folded into a cylinder  206 . For example, the flex sheet  100  may be folded around a shape-forming mandrel  202 , with the pins  106  at the sheet edge pointing away from the mandrel  202 . In this case, the underside of the edge of the flex sheet  100  with pins  106  is adhered to the top surface of the other edge of the same sheet  100 , so that the sheet takes on a cylindrical form. The pins  106  are soldered onto etched electrodes  204 . The pins  106  (shown exaggerated in  FIG. 2   a  for clarity) protrude perpendicularly along one longitudinal edge of the cylinder  206 .  
         [0036]     A thermocouple band  208  is also constructed. In one example, the thermocouple band  208  may be constructed of a gold band to give the band a high thermal conductivity. These bands can be constructed using techniques known by those skilled in the art.  
         [0037]     The example described herein with respect to  FIG. 2   a  (and also  FIGS. 3   a  and  5 ) utilizes a single set of electrodes and thermocouple band. However, multiple electrodes and bands can also be used. It will also be understood that multiples of the unit assembly can be organized in a linear pattern to form a linear mapping and ablation electrode array.  
         [0038]     Preferably, metal etching is used for the production of the electrodes  204  to produce coiled groove, thereby creating a spring-like electrode component. Several techniques may be employed to etch metal sheets into different structural forms.  
         [0039]     In one example process, a computer-aided design (CAD) drawing of the electrode coil pattern is generated. This drawing serves as the CAD image that is a faithful replica of the electrode. The drawing is printed onto a transparency film.  
         [0040]     A cylindrical section of metal (e.g. platinum iridium) cut to a specific length is cleaned thoroughly. Then, a photo resist coating is applied to the outer surface so that it is photo-sensitive.  
         [0041]     The CAD image is then overlaid onto the photo-sensitized metal surface and exposed to a ultra-violet (UV) light source. The metal cylinder is thereafter deposited into a developing solution to create a hardened image of the desired coil pattern on the metal cylinder surface.  
         [0042]     The metal surface is then treated with an etchant, such as an acid. The etchant eats away the rest of the surface that is devoid of the hardened image, to create a spiral-shaped coil structure that can function as ablation and mapping electrodes  204 . If the desired spiral groove is too fine for acid or other form of chemical etching, then an alternate fabrication technique is to employ three dimensional etching of the spiral pattern via a precision laser cutting process.  
         [0043]     Yet another alternate process is to etch the electrodes directly onto the flex circuit board. This approach assumes dissimilar metals are layered onto the board, e.g. platinum for electrodes, copper for conduction lines by an appropriate manufacturing process.  
         [0044]     Referring now to  FIG. 2   b , another example of a flex circuit assembly is described. In this case, the assembly is the same as that shown and described with respect to  FIG. 2   a  except that the etched electrodes  204  are replaced with coiled electrodes  204 .  
         [0045]     In one example, the coiled electrodes  204  may be 0.005″ gauge (0.003″ to 0.006″ range with one preferred type being a 0.005″ gauge) platinum iridium wire that is wound into a spring-like structural unit. These units may be 3 mm to 6 mm long and have outer diameters ranging from approximately 3 Fr to 5 Fr. Other dimensions are also possible.  
         [0046]     Referring now to  FIG. 3   a , the etched electrodes  204  and thermocouple band  208  are inserted over the cylindrical structure formed by folding the flex circuit. The electrodes  204  and thermocouple  208  are soldered at the respective protruding pin sites  106  that were spaced out by design to provide the desired inter-electrode and electrode-thermocouple spacing.  
         [0047]     At one stage of the manufacturing process, the electrodes  204  can be coated with a conductive gel or other ionic material that improves tissue-electrode contact. At the same time, the electrodes  204  may be infused with anti-coagulant chemicals that are time released during the course of an ablation procedure.  
         [0048]     Multiple layers of such unit assemblies may be utilized to reduce overall catheter or medical probe shaft diameter. These layers can be electrically insulated from each other by a homogenous polyimide material that is typically used in multi-layer flex circuit boards.  
         [0049]     An inner hollow shaft  302  of the resulting cylinder from this flex circuit catheter shaft can serve as a conduit for a guide wire or stylet with deflectable mechanism, permitting the linear assembly of electrodes  204  and thermocouples  208  to be shaped and conformed to a tissue surface to afford excellent electrode-tissue contact that ensures optimal coupling of RF energy with the tissue. The conductive annular gold band for the thermocouple and the etched electrode are then slid along the shaft and soldered over their respective solder points.  
         [0050]     The flex circuit assembly is rolled and placed in the shaft of the catheter. The end of the flex circuit assembly plugs into a connector. The connector is coupled to at least one PC card, which interfaces the arrangement to power and measurement equipment.  
         [0051]     Referring now to  FIG. 3   b , another example of a flex circuit assembly is described. In this case, the assembly is the same as that shown and described with respect to  FIG. 3   a  except that the etched electrodes  204  are replaced with coiled electrodes  204 .  
         [0052]     As with the coiled electrodes of  FIG. 2   a , the coiled electrodes  204  of  FIG. 3   b  may be 0.005″ gauge (0.003″ to 0.006″ range with one preferred type being a 0.005″ gauge) platinum iridium wire that is wound into a spring-like structural unit. These units may be 3 mm to 6 mm long and have outer diameters ranging from approximately 3 Fr to 5 Fr. Other dimensions are also possible.  
         [0053]     Referring now to  FIG. 4 , one example of a catheter system using the flex circuit and etched electrodes and thermocouples is described. A catheter  400  includes the cylindrical flex circuit assembly  408  that has been described with respect to  FIGS. 1-3  above. The cylindrical assembly  408  forms the distal end of the catheter  400  and is inserted into the telescopic structure  406  having a handle, which forms the proximal end of the catheter  400 .  
         [0054]     Etched electrodes  402  are constructed and soldered onto the cylindrical assembly  408  as has been described elsewhere in the application. Alternatively, coiled electrodes may be used. In addition, thermocouples  404  are soldered onto the cylindrical assembly  408  as has also been described elsewhere in the application. The cylindrical assembly  408  may include sub-portions of flex circuits that are attached together to form the assembly  408 .  
         [0055]     An inner hollow shaft (not shown in  FIG. 4 ) of the cylinder  408  (i.e., the flex circuit catheter shaft) may serve as a conduit for a guide wire or stylet with deflectable mechanism (not shown), permitting the linear assembly of electrodes  402  and thermocouples  404  to be shaped and conform to a tissue surface. This gives excellent electrode-tissue contact that ensures optimal coupling of RF energy with tissue  410 . The conductive annular gold band for the thermocouples  404  and the etched electrode  402  may then be slid along the shaft and soldered over their respective solder points.  
         [0056]     A power and measurement circuit  408  is coupled to the catheter  400  via a personal computer (PC) board  407 . The power and measurement circuit  408  supplies electrical energy to the catheter and its electrodes  402  that can be used, for example, for ablation procedures. The impedance signals received at the electrodes and the information received by the thermocouples reporting tissue temperature can be relayed back to the power and measurement circuit  408  via the cylindrical assembly  408 . The power and measurement circuit  408  can receive information from the thermocouples and display this information to an operator for manual feedback control. In addition, the power and measurement circuit  408  can receive operating instructions from an automated processing unit for feedback and control to adjust various operating parameters pertaining to the RF current being emitted from the catheter  400 , such as the power or current delivered to the tissue  410 .  
         [0057]     Referring now to  FIG. 5 , a cross-sectional view of the cylindrical assembly  208  taken along line  304  in  FIG. 3   a  is described. A guide wire  502  is in the middle of the hollow shaft  504  of the assembly  408 . The electrodes  204  and thermocouple (not shown in  FIG. 5 ) are soldered at the respective protruding pin sites  106  that were spaced at predetermined distances by design to provide the desired inter-electrode and electrode-thermocouple spacing along the side of the catheter.  
         [0058]     Referring now to  FIG. 6   a - c  and  FIG. 7 , one example of an assembly using multiple layers of flex circuits is described.  FIGS. 6   a - c  show cross sectional drawings taken along lines  708 ,  710 , and  712  of  FIG. 7  respectively. A first flex circuit assembly  602 , second flex circuit assembly  604 , and third flex circuit assembly  606  are concentrically located with assembly  602  on the outside, assembly  604  inside of assembly  602  and assembly  606  inside assembly  604 .  
         [0059]     The assemblies  602 ,  604 , and  606  are electrically insulated from each other by a homogenous polyimide material layers  608  and  610  that is typically used in multi-layer flex circuit boards. Pin  612  is coupled to the flex circuit assembly  602 . Pin  614  extends through the assembly  602  and is coupled to the flex circuit assembly  604 . Pin  616  extends through the assemblies  602  and  604  and is coupled to the flex circuit assembly  606 . Although only one pin is shown for each assembly (for convenience in viewing), it will be understood that multiple pins for the multiple layers  602 ,  604 , and  606  can be used. In addition, additional pins for thermocouples may also be included. The inner pins  614  and  616  may have holes drilled through the various layers so that the pins  614  and  616  reach above the surface of the cylinder.  
         [0060]     Referring now to specifically to  FIG. 7 , the assembly of  FIG. 6  shows electrodes and thermocouples  702  coupled to the pins  612 . Electrodes and thermocouples  704  are coupled to the pins  614 . Further, electrodes and thermocouples  706  are coupled to the pins  616 . Since multiple layers are used, the overall catheter or medical probe shaft diameter is reduced.  
         [0061]     Referring now to  FIG. 8 , one example of a flex circuit  800  used in an ablation catheter is described where the electrodes are etched directly onto the flex sheet. A flex circuit pattern is printed on a flat sheet  804 . Electrodes  806  are constructed on the sheet  804  directly and electrically contact a conductive circuit element  810  on the flex sheet  804 . Dissimilar metals are layered onto the board, for instance, platinum for electrodes and copper for the conduction circuit element  810 , by an appropriate manufacturing process.  
         [0062]     Conductive circuit elements  810  of the sheet  804  are electrically insulated from each other and from the exposed surfaces of the flex sheet  804 . Preferably, the inter-wire spacings for RF energy and current delivery are predetermined to comply with applicable regulatory, EMC and safety compliance standards.  
         [0063]     Thus, the present system and method allows for the substitution of a flex circuit assembly for complex braided wire arrangements. It is simple to construct and incorporate into a catheter, surgical probe, or other medical device. Potentially, during the assembly process, a technician can easily replace damaged parts of the circuit with new flex circuit components as required. The etched electrodes provide for more precise dimensions to be provided for the electrodes than were possible in the previous arrangements.  
         [0064]     While there has been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true scope of the present invention.