Patent Publication Number: US-2019183570-A1

Title: Catheter with liquid-cooled control handle

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of, and claims priority to and the benefit of U.S. application Ser. No. 15/073,510 filed Mar. 17, 2016, now U.S. Pat. No. 10,213,254, which is a continuation of, and claims priority to and the benefit of U.S. application Ser. No. 14/666,247 filed Mar. 23, 2015, now U.S. Pat. No. 9,289,259, which is a continuation of, and claims priority to and the benefit of U.S. patent application Ser. No. 12/942,880 filed Nov. 9, 2010, now U.S. Pat. No. 8,986,303, the entire contents of all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to catheters and, in particular, to a catheter with an improved control handle. 
     BACKGROUND 
     Catheters have been in common use in medical practice for many years. Applications of catheters include stimulating and mapping electrical activity in the heart and ablating sites of aberrant electrical activity. Such catheters are also referred to as electrode catheters. In use, an electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the location of interest within the body, e.g., the chamber of the heart where aberrant electrical activity within the heart is located. 
     A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. Lesions created by such cardiac ablation procedure effectively interrupt errant electrical pathways in the heart. 
     Catheters typically have an elongated catheter body, a deflectable section distal the catheter body and tip section distal the deflectable section. A typical ablation catheter provides irrigation at the tip electrode for a number of reasons, including the avoidance of charring and the desire for larger lesions. By irrigating the ablation electrode, such as with room temperature physiologic saline, the ablation electrode is actively cooled instead of more passive physiological cooling by blood flow. Because the strength of the RF current is no longer limited by the interface temperature, current can be increased for larger and more spherical lesions. 
     A control handle proximal the catheter body serves primarily to house deflection mechanism coupled to puller wires extending through catheter and provide an interface by which a user can manipulate the deflection mechanism. Where irrigation is provided, an irrigation tubing extends through the control handle to pass fluid from a fluid source to a distal end of the catheter. The control handle also normally houses a printed circuit board supporting various circuits and chips configured for signal processing from and/or to the distal section or tip electrode, including, for example, amplification of signals from an electromagnetic position sensor and/or digitizing circuits for digitizing a voltage signal of the thermocouple. An EPROM chip may also be included to shut down the circuit board after the catheter has been used so as to prevent reuse of the catheter, or at least the electromagnetic sensor. 
     Current catheters with a control handle containing a PC board rely on natural convection within a closed chamber of the control handle to provide cooling of the PC board. As catheters become more advanced and capable, the internal electronics become more involved, often resulting in greater thermal waste energy loads. Increases in thermal waster energy result in increased thermal temperatures in the control handle and ultimately high handle temperatures which can negatively affect user comfort. 
     Small fans are often used on PC boards to increase the convective heat loss of the board. However, because control handles are typically sealed, the heat load will increase the handle temperature. In order for fans to be effective in a catheter handle, inlet and outlet grates or ports should be integrated into the catheter handle. But such features may diminish the aesthetics of the handle. Heat pipes can also be integrated into the handle to increase heat transfer from the mounted integrated circuits, but again the heat will tend to remain in the handle increasing handle temperature. Self pumping micro fluidic heat exchangers may also be used but, like heat pipes, they will release heat energy into the handle resulting in increased handle temperatures. 
     As irrigation fluid at room temperature ranges between about 20-25 C (or 68-77 F), which is significantly lower than the normal human body temperature of 37 C (or 98.6 F), and it is known to pass irrigation fluid through the control handle, it would be desirable to provide an improved control handle that uses the irrigation fluid flowing therethrough to help cool the PC board and lower the temperature inside the control handle by transporting the heat out of the control handle. Such increased heat transfer will result in lower operating temperature of the PC board and hence a cooler control handle. 
     SUMMARY 
     The present invention is directed to an electrophysiologic catheter adapted for use in a patient&#39;s heart with an improved control handle. Catheters typically have a catheter body and a control handle which houses a heat source, including integrated circuits mounted on a printed circuit board, which can produce undesirable thermal waste energy loads that accumulate in the control handle causing discomfort to a user. In accordance with a feature of the present invention, the catheter includes a heat transfer assembly to better dissipate heat in the control handle. The heat transfer assembly includes a pump, a reservoir containing a coolant, a heat transfer member, and a coolant transport network transporting coolant between at least the reservoir and the heat transfer member. In one embodiment, the heat transfer member is located within the control handle as a heat exchanger on the circuit board to receive the coolant for transferring heat from the integrated circuits to the coolant. In another embodiment, at least one heat transfer member is located on the circuit board directly surrounding the integrated circuits to internally cool the integrated circuit within the control handle. A second heat transfer member is located outside of the control handle as a heat exchanger. The heat transfer member of this embodiment may be an IC heat transfer unit, a cover heat transfer unit or a heat transfer assembly. Either embodiment may be configured with a closed a coolant transport network or an open coolant transport network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and aspects of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a catheter, including a heat transfer assembly, according to an embodiment of the present invention. 
         FIG. 2A  is a side cross-sectional view of the catheter of  FIG. 1 , including a junction of a catheter body and an intermediate section, along a first diameter. 
         FIG. 2B  is a side cross-sectional view of the catheter of  FIG. 1 , including a junction of a catheter body and an intermediate section, along a second diameter generally perpendicular to the first diameter. 
         FIG. 2C  is an end cross-sectional view of the catheter of  FIGS. 2A and 2B , taken along line C-C. 
         FIG. 3  is a side cross-sectional view of the catheter of  FIG. 1 , including a junction between an intermediate section and a connector tubing, with a tip electrode. 
         FIG. 4  is a side cross-sectional view of the control handle of  FIG. 1 , including a piston with a thumb control. 
         FIG. 5  is a schematic diagram of a catheter, including a heat transfer assembly, according to an alternate embodiment of the present invention. 
         FIG. 6  is an perspective view of a printed circuit board within a control handle of the catheter of  FIG. 5 , according to one embodiment of the present invention. 
         FIG. 7 a    is a side view of a heat transfer member in the form of an IC heat transfer unit of the present invention, according to one embodiment. 
         FIG. 7 b    is a side view of a heat transfer member in the form of a cover heat transfer unit of the present invention, according to one embodiment. 
         FIG. 7 c    is a side view of a heat transfer member in the form of a heat transfer assembly of the present invention, according to one embodiment. 
         FIG. 8  is a schematic of a catheter, including a heat transfer assembly, according to another alternate embodiment of the present invention. 
         FIG. 9  is a schematic of a catheter, including a heat transfer assembly, according to yet another alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described more fully hereinafter, in which exemplary embodiments are shown. This disclosure may, however, be embodied in many different forms and is not be construed as limited to the exemplary embodiments set forth herein. Here, when a first element is described as being coupled or connected to a second element, the first element may be directly connected to the second element or indirectly connected to the second element via one or more third elements. 
       FIG. 1  illustrates a catheter  10  according to an embodiment of the present invention. The catheter  10  includes an elongated catheter shaft or body  12  having proximal and distal ends, an intermediate section  14  with uni- or bi-directional deflection distal of the catheter shaft  12 , a tip section  15  with a tip electrode  17  at a distal end of the intermediate section, and a control handle  16  at the proximal end of the catheter shaft  12 . Advantageously, the catheter includes a heat transfer assembly employing a reservoir of coolant and a pump to provide cooling of integrated circuits housed in the control handle by means of forced convection. 
     As shown in  FIGS. 2A and 2B , the catheter body  12  comprises an elongated tubular construction having a single, axial or central lumen  19 . The catheter body  12  is flexible, i.e., bendable, but substantially non-compressible along its length. The catheter body  12  can be of any suitable construction and made of any suitable material. A presently preferred construction comprises an outer wall  20  made of polyurethane or PEBAX. The outer wall  20  comprises an embedded braided mesh of stainless steel or the like to increase torsional stiffness of the catheter body  12  so that, when the control handle  16  is rotated, the intermediate section  14  of the catheter  10  is able to rotate in a corresponding manner. 
     The outer diameter of the catheter body  12  is not critical, but is preferably no more than about 9 french, more preferably about 7 french. Likewise, the thickness of the outer wall  20  is not critical, but is thin enough so that the central lumen  19  can accommodate puller wires, one or more lead wires, and any other desired wires, cables or tubes. If desired, the inner surface of the outer wall  20  is lined with a stiffening tube  21  to provide improved torsional stability. In one embodiment, catheter  10  has an outer wall  20  with an outer diameter of from about 0.090 inches to about 0.094 inches and an inner diameter of from about 0.061 inches to about 0.065 inches. 
     The intermediate section  14  comprises a short section of tubing  22  having multiple lumens, as also shown in  FIG. 2C . In one embodiment, a first lumen  30  carries one or more lead wires  50 , temperature sensor (e.g., thermocouple wires  43  and  44 ) for monitoring tissue temperature in the tip electrode  17 , and a cable  74  for an electromagnetic position  75  sensor housed in the tip section  14 . A second lumen  32  carries a puller wire for at least deflection along one direction in a plane. An opposing third lumen  34  can carry a second puller wire if bi-directional deflection along a second, opposing direction in the plane of the first deflection is desired. A fourth lumen  35  carries an irrigation tube  61  for supplying fluid to the tip electrode. The tubing  22  is made of a suitable non-toxic material that is preferably more flexible than the catheter body  12 . In one embodiment, the tubing  22  is braided polyurethane, i.e., polyurethane with an embedded mesh of braided stainless steel or the like. The number of lumens or the size of each lumen is not critical, but is sufficient to house the lead wires, puller wire(s), electromagnetic sensor cable, thermocouple wires and/or irrigation tubing depending on the embodiment. 
     A preferred means for attaching the catheter body  12  to the intermediate section  14  is illustrated in  FIGS. 2A and 2B . The proximal end of the intermediate section  14  comprises an outer circumferential notch  26  that receives the inner surface of the outer wall  20  of the catheter body  12 . The intermediate section  14  and catheter body  12  are attached by glue or the like. 
     If desired, a spacer (not shown) can be located within the catheter body  12  between the distal end of the stiffening tube  21  and the proximal end of the intermediate section  14 . The spacer provides a transition in flexibility at the junction of the catheter body and intermediate section, which allows the junction to bend smoothly without folding or kinking. A catheter having such a spacer is described in U.S. Pat. No. 5,964,757, the entire disclosure of which is incorporated herein by reference. 
     As illustrated in  FIG. 3 , the tip section  15  includes the tip electrode  17  which may be connected to the tubing  22  of the intermediate section  14  by means of a single lumen connector tubing  23 . The connector tubing provides space for the electromagnetic position sensor  75  and the various components extending from the tubing  22  to reorient themselves as needed for anchoring in the tip electrode  17 . To that end, a distal surface of the tip electrode is provided with blind holes. In the disclosed embodiment, blind hole  61  is provided to receive a distal end of the tip electrode lead wire  40 , blind hole  63  to receive a distal end of the thermocouple wires  43  and  44 , and blind hole  65  to receive a distal end of the electromagnetic sensor  75 . Irrigation passage  66  is also formed in the tip electrode to receive a distal end of the irrigation tubing  61 . The passage  66  is in communication with transverse branches  67  and fluid ports  69  allowing fluid delivered through the tubing  61  to pass to outside of the tip electrode. 
     As shown in  FIG. 2B , the puller wire  42  is provided for uni-directional deflection of the intermediate section  14 . The puller wire  42  extends through the catheter body  12 , and is anchored at its proximal end to the control handle  16 , and at its distal end to the tubing  22  near the distal end of the intermediate section  14  by means of a T-bar anchor  71 , as generally described in U.S. Pat. Nos. 5,893,885 and 6,066,125, the entire disclosures of which are incorporated herein by reference. The puller wire is made of any suitable metal, such as stainless steel or Nitinol, and are preferably coated with Teflon® or the like. The coating imparts lubricity to the puller wire  42 . The puller wire  42  preferably has a diameter ranging from about 0.006 to about 0.010 inch. 
     A compression coil  72  is situated within the catheter body  12  in surrounding relation to the puller wire  42 , as shown in  FIG. 2B . The compression coil  72  extends from the proximal end of the catheter body  12  to the proximal end of the intermediate section  14 . The compression coil is made of any suitable metal, preferably stainless steel and is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil is preferably slightly larger than the diameter of the puller wire. The Teflon® coating on the puller wire allows it to slide freely within the compression coil. The outer surface of the compression coil is covered by a flexible, non-conductive sheath  78 , e.g., made of polyimide tubing. 
     Longitudinal movement of the puller wire  42  relative to the catheter body  12 , which results in deflection of the intermediate section  14 , is accomplished by suitable manipulation of the control handle  16 . Examples of suitable control handles for use in the present invention are disclosed in U.S. Pat. Nos. Re 34,502, 5,897,529, and 7,377,906, the entire disclosures of which are incorporated herein by reference. In the embodiment of  FIG. 4 , a distal end of the control handle  16  comprises a piston  54  with a thumb control  56  for manipulating the puller wire  42  for uni-directional deflection of the intermediate section  14 , although it is understood that the present invention is readily adaptable to a control handle with two puller wires for bi-directional deflection. 
     Connected to the piston  54  by means of a shrink sleeve  28  is the proximal end of the catheter body  12 . The irrigation tubing  61 , the puller wire  42 , the lead wire  40 , the thermocouple wires  43  and  44  and the electromagnetic sensor cable  74  extend proximally from the catheter body through the piston  54 . The puller wire  42  is anchored to an anchor pin  36  located proximal to the piston  54 . The lead wire  40 , thermocouple wires  43  and  44  and electromagnetic sensor cable  74  extend through a first tunnel  58 , located near the side of the control handle  16 . The electromagnetic sensor cable  74  connects to a circuit board  64  in the proximal end of the control handle. Wires  73  connect the circuit board  64  to, for example, a mapping and/or ablation system, including a computer and imaging monitor (not shown). 
     Within the piston  54 , the electromagnetic sensor cable  74  and lead wires  40  are situated within a transfer tube  27   a , and the puller wire  42  is situated within another transfer tube  27   b  to allow longitudinal movement of the wire and cable near the glue joint  53 . The irrigation tubing  61  extends proximally through the shrink sleeve  28  where its proximal end is in communication with the heat transfer assembly  50  via a distal conduit  68   a  which extends through a second tunnel  60  situated near the side of the piston  54  opposite the anchor pin  36 . 
     The control handle  16  houses a heat source, including the printed circuit (PC) board  64  on which are mounted multiple integrated circuits serving various functions such as local amplification and/or processing of signals, including signals from the electromagnetic sensor and/or the thermocouple housed in the distal section of the catheter. An EPROM chip may also be included to limit the catheter or at least the position sensor to a single use. 
     In the embodiment of  FIGS. 1 and 4 , the heat transfer assembly  50  is configured as an open system employing the reservoir  51  and the pump  52  (e.g., an infusion pump), a coolant transport network with fluid conduits  68   a  and  68   b , and/or other mechanisms and components typically employed for delivering fluid through the catheter to the tip electrode. As described above, irrigation fluid is delivered in the irrigation tubing  61  of the catheter  10 . In the present invention, the heat transfer assembly advantageously uses the fluid, e.g., irrigation saline, as a coolant to cool the PC board in the control handle. In the embodiment illustrated in  FIG. 1 , the infusion pump  52  pumps the fluid from the reservoir  51  through the proximal fluid conduit  68   b  passing into the control handle  16 . A distal end of the conduit  68   b  terminates at and feeds into an inlet of a heat transfer unit, for example, a heat exchanger  90  (or heat sink) mounted on or near integrated circuits  80  on the PC board  64 , especially high power output integrated circuits. An outlet of the heat exchanger feeds to a proximal end of the distal fluid conduit  68   a  whose distal end is in communication with a proximal end of the irrigation tubing  61  inside the piston  54 . As shown in  FIG. 4 , the distal fluid conduit  68   a  is anchored to the inside of the control handle  16  by glue joint  53 . 
     The heat transfer assembly  50  applies the principle of forced convection to cool the PC board  64  and hence the control handle  16 . As the integrated circuits  80  on the PC board heat up during use of the catheter, the heat generated is transferred to the heat exchanger  90 . As irrigation fluid transported by the proximal conduit  68   b  flows through the heat exchanger  90 , the heat transferred to the heat exchanger is further transferred to the fluid thereby cooling the heat exchanger. 
     As understood in the art, the heat exchanger  90  is configured to dissipate thermal waste energy from the PC board  64  to the irrigation fluid from the reservoir  51  by maximizing surface area between the open space in the control handle and the irrigation fluid, while minimizing resistance to fluid flow through the heat exchanger  90 . The heat exchanger can take any suitable form, including a plate heat exchanger or a tubular heat exchanger, with parallel-flow, counter-flow, or cross-flow as desired or appropriate. The heat exchanger is constructed of any suitable material that is thermally conductive for optimal heat transfer. The material should also be biocompatible and suitable for ETO sterilization, including, for example, stainless steel or noble metal plated copper, such that contact between the irrigation fluid and the heat exchanger material does not compromise the fluid in terms of sterility and biocompatibility when it exits from the ports in the tip electrode and enters the patient&#39;s body. 
     Where the irrigation fluid is at room temperature, for example, ranging between about 20-25 C (or 68-77 F), the heat exchanger  90  can be expected to raise the temperature of the fluid by about 5 degrees, to about 25-30 C or (77-86 F). Since normal human body temperature is about 37 C (or 98.6 F), there is little risk of introducing overheated fluid into the patient, or of overheating the patient over the course of the catheter procedure. However, if desired, temperature control over the fluid can be provided by means of a cooling unit  57 , including, for example, a radiator, a compressor, and an expansion valve, that pre-cools the fluid from the reservoir by a predetermined amount before it enters the control handle and the heat exchanger so that the temperature of the fluid exiting the heat exchanger and/or the control handle is generally predetermined before it exits the tip electrode and enters the patient&#39;s body. 
     In an alternate embodiment shown in  FIG. 5 , a heat transfer assembly  50   a  is configured as a closed system, wherein the coolant is recirculated by the coolant transport network between one or more heat transfer units, such as IC heat transfer units  100 ,  200  and/or  250  provided on the PC board  64 , and a remote heat exchanger  92  connected via a coolant feed conduit  69   b  and a coolant return conduit  69   a . Coolant-cooled integrated circuits are known in the art and are described in U.S. Pat. Nos. 7,400,502 and 5,360,993, the entire contents of which are incorporated by reference.  FIG. 7 a    illustrates an embodiment of a connector heat transfer unit (or hereinafter an IC heat transfer unit)  100  of the prior art, which is depicted with a heat generating component  101 , such as an integrated circuit or chip, inserted into the connector heat transfer unit  100 . The IC heat transfer unit  100  may be of a variety of shapes and sizes, but these will be determined principally by the size and electrical conductor configuration of the heat generating component and the motherboard (or PC board) to which the connector heat transfer unit will be coupled. All of the following embodiments of the IC heat transfer unit can be deployed in an application where the IC heat transfer unit is not mechanically attached to any type of motherboard and, it will be understood, that the IC heat transfer unit may be electrically connected to the mother board in any suitable manner. The IC heat transfer unit may be composed of any number of materials but a lightweight, electrical insulating material is desirable. 
     In  FIG. 7 a   , the electrical conductors or pins  102  of the chip  101  are inserted into receptacles  104 . A cavity  103  is disposed in the IC heat transfer unit  100  such that a surface of the cavity in thermally coupled to the surface of the chip  101 . This surface of the cavity may be composed of any good heat conducting material, such as copper, to transfer heat from the heat generating component to a coolant flowing through the cavity. The heat transfer unit  101  is configured with an inlet pathway  106  and an outlet pathway  108  for fluid entry and exit from the cavity. As understood by one of ordinary skill in the art, the configuration of the cavity and the pathways can be varied as needed or desired to alter fluid flow efficiency. 
     The IC heat transfer unit pins  109  electrically connect the receptacles  104  to the PC board, for example, by soldering. It will be appreciated that any suitable means may be used to connect the pins of chip  101  to the PC board and the IC heat transfer unit is not limited to the receptacles  104  and pins  109  described above. For example, the connector heat transfer unit  100  may have a plurality of holes for pins  102  to be inserted into and through and then soldered to the PC board. 
     The surface of the cavity  103 , thermally coupled to the heat generating component  101 , is depicted as  110 . The surface  110  may be comprised of any good heat conducting material, such as copper. This surface  110  is preferably coupled to the heat generating component  101  by means of a thermal paste having good thermal transfer characteristics. Alternatively, the heat generating component  101  may be held in place within the connector heat transfer unit  100  and thermal coupling of the component  101  to the surface  110  achieved by use of one or more clips, not shown, from the connector heat transfer unit  100  to the component  101  or by a one or more clamp assemblies, not shown. In any case, it is preferable to apply thermal paste to the coupling of surface  110  with the component to insure maximum heat transfer. It should also be appreciated that the present invention encompasses many other possibilities for thermally coupling the component  101  to the surface  110  including, but not limited to, application of mechanical force, such as a clamping motion, to create a positive force between the component  101  and the surface  110  and thus improve thermal conductivity. 
     The electrical conductors or pins  102  of most commercial heat generating components, such as microprocessors, for example, are typically copper coated with precious metals. Thus, in addition to being good electrical conductors, they are also good heat conductors. Similarly, the receptacles  104  and electrical conductors or pins  109  may be comprised of similar materials with both good electrical and heat transfer characteristics. The IC heat transfer unit  100  may then be comprised of a material with good electrical insulation characteristics and good heat transfer characteristics to provide cooling and/or additional cooling of the chip  101 . A wide variety of materials, such as a hard silicone, for example, can be used for this purpose in the IC heat transfer unit  100 . Specifically, heat from the chip  101  is transferred to the electrical conductors or pins  102 . Some of this heat may be transferred from the pins  102 , directly and/or indirectly through the receptacles  104  and pins  109 , for example, to the IC heat transfer unit  100  and then on to the cavity  103  where the coolant flowing there through will absorb some or all of this heat for dissipation. A thermal paste can be applied to the electrical conductors or pins  102  to insure maximum heat transfer to the body of the IC heat transfer unit  100  directly, or indirectly through the receptacles  104  and pins  109 , for example. It should also be appreciated that pins  102  and the IC heat transfer unit  100  can be thermally coupled via other means including, but not limited to, application of mechanical force to create pressure in a clamping motion. 
     In yet another alternative for coupling the surface  110  to the chip  101 , the surface  110  may be open or partially open allowing the coolant to come into direct contact with the chip  101 , which normally is encased and protected by an IC pack (not shown) and thereby eliminating the thermal resistance of both the surface  110  and the thermal paste or other thermal connection medium used. In this situation, for example, the surface  110  could be in the form of a flange around the perimeter of the cavity  103 . When the flange is coupled and sealed to the chip  101 , the cavity is sealed and coolant will come in direct contact with the chip  101  without leaks or spills. 
     Referring now to  FIG. 7 b   , a cover heat transfer unit  200  for the IC heat transfer unit  100  is depicted which provides additional cooling of the chip  101 . The cover heat transfer unit  200  has many similarities to the IC heat transfer unit  100 , including a cavity  203 . Entrances and exits for the coolant to and from the cavity  203  are provided by inlet pathway  206  and by outlet pathway  208 , respectively. The electrical conductors or pins  202  of the chip  101  are shown. Cavity  203  has a surface  210  which is thermally coupled to the chip  101 . 
     Whenever possible, it is desirable to orient the heat transfer units  100  and  200  so that the respective inlet is situated below the respective outlet. This orientation allows the cooling system to take advantage of convective circulation of the coolant since heated coolant will naturally rise and cooled coolant will naturally drop. In this manner, the thermodynamics of the coolant can assist forced circulation, by a pump for example, and provide additional cooling of the heat generating components even after power is shut down. 
     A function of cover heat transfer unit  200  is to provide cooling to an additional surface of the chip  101 . As shown in the embodiment of  FIG. 7 c   , when a cover heat transfer unit  200  is used in conjunction with IC heat transfer unit  100  in forming a heat transfer module  250  to secure and cool a single chip, surface  210  is transferring heat from one side of the chip to a coolant while surface  110  is transferring heat from an opposite side of the chip to a coolant. Use of the cover heat transfer unit  200  then can provide dramatic increases in cooling power or capacity when combined with the IC heat transfer unit  100 . 
     The IC heat transfer unit  220  includes a cavity  223 ; a surface  230  of the cavity  223  thermally coupled to the chip  216 ; a plurality of receptacles or electrical contacts  224  to accept electrically the electrical conductors  217  of the chip  216 ; and a plurality of pins or electrical conductors  229 , electrically connecting the receptacles  224  to the PC board via, for example, by wave soldering. 
     The chip  216  may be held in place within the module  250  and thermal coupling of the component to the surfaces  110  and  210  achieved by any number of methods. For example, one or more screws  212  threaded into one or more mating receptacles  213  may be utilized. Alternatively, or in addition, one or more spring clips, or any of a variety of mechanical fasteners to create a clamping force, not shown, from the IC heat transfer unit  220  to the cover  200  and/or adhesives may be utilized. In any case, it is preferable to apply a thermally conductive material to the coupling of surface  230  with the component  216  and to the coupling of surface  210  to the opposite side of the chip  216  to insure maximum heat transfer. 
     In yet another alternative for coupling the surfaces  230  and  210  to the chip  216 , either one or both of the surfaces  230  and  210  may be open or partially open allowing the coolant to come into direct contact with the chip  216  and thereby eliminating the thermal resistance of both the surfaces  230  and  210  and the thermal resistance of thermal paste or other thermal connection medium used. In this situation, for example, either or both of surfaces  230  and  210  could be in the form of a flange around the perimeter of the cavities  223  and  203 , respectively. When the flanges are coupled and sealed to opposite sides of heat generating component  216 , the cavities are sealed and coolant will come in direct contact with the component on opposite sides there of without leaks or spills. 
     In operation, cooled coolant received from a heat exchange unit is applied to inlet pathways  105  and  205 . It flows through into the cavities  103  and  203 . Heat from the chip  101  is absorbed into the coolant and heats the coolant. The heated coolant then flows through outlet pathways  108  and  208  and is then directed back to the heat exchange unit for cooling. It will be appreciated and understood that other methods of receiving the coolant, directing the coolant through and out of the heat transfer module  250  may be utilized. 
     The heat transfer assembly in a closed or isolated configuration allows for more selection of a coolant since the coolant is not entering the patient&#39;s body. A fluid with an ideal coefficient of variation (COV) for use includes Propylene-Glycol. When used with an irrigated catheter, such a closed or isolated configuration allows for higher mass flow rates of coolant resulting increased convective heat transfer and a decrease in the thermal load to irrigation fluid preventing possible loss in irrigation effectiveness at the tip electrode. 
     As understood by one of ordinary skill in the art, additional cooling mechanisms, such as air-cooled heat sinks or heat pipes for example (not shown), can be coupled to a free surface of the chip  101  to provide for additional cooling, if desired. It is further understood that the handle  16  and PC board may have any suitable shapes and sizes. As one of ordinary skill in the art, the location of the circuit board within the handle can vary depending on the structures and components within the handle, such as mechanisms for controlling deflection of the intermediate section  14  and various wires, cables and tubings that extend through the control handle and distally along the catheter shaft and beyond. 
     The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. Any feature of any one embodiment can be used in any other embodiment in the place of or in addition to other features. For example, although the first embodiment described herein features a catheter having an open system with a heat transfer assembly employing at least one heat exchanger mounted on the PC board and the second embodiment features a catheter having a closed system with at least one board-mounted heat transfer module, the present invention includes embodiments where the catheter has a closed system with a heat transfer assembly employing at least one heat exchanger mounted on the PC board (see  FIG. 8 ), as well as a catheter having a open system with at least one board-mounted heat transfer module (see  FIG. 9 ). As understood by one of ordinary skill in the art, the drawings are not necessarily to scale. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims which are to have their fullest and fair scope.