Abstract:
An irrigated tip electrode design includes a shell generally surrounding a plug which jointly define a chamber that is fed with fluid by a lumen. The fluid is distributed to the outer surface of the tip electrode through fluid passages. The chamber is advantageously isolated from a region of the tip electrode occupied by electrical and/or electromagnetic components in the tip electrode. Lumens occupied by the these components terminate in blind holes that have no communication with the chamber. A method of fabricating includes providing a shell configured from a rod to provide an open interior cavity, sealing and partially filling the cavity with a plug to form a chamber, then forming fluid passages between the cavity and an outer surface of the tip electrode, and providing a lumen through which fluid can enter the chamber and exit therefrom through the fluid passages.

Description:
FIELD OF INVENTION  
       [0001]     The present invention relates to improved steerable electrode catheters having an irrigated tip, and methods of manufacturing the same.  
       BACKGROUND OF INVENTION  
       [0002]     Electrode physiology catheters applying radio frequency energy ablation have been used to treat heart arrhythmias caused by aberrant electrical activity in the heart tissue. In particular, the catheters are configured with tip electrodes that deliver RF energy to the heart tissue to heat and kill it by ablation. The scarred tissue no longer conducts the errant excitation waves and effectively isolates these waves from other areas in the heart.  
         [0003]     For tissue ablation, there are several motivations to deliver the RF energy through the catheter tip, including i) the natural tendency for the tip of the catheter to contact the wall of the heart chamber, ii) the physician&#39;s ability to manipulate the tip to the desired location and hold it in place with sufficient pressure to facilitate both stability and RF current flow to the tissue, and iii) the desire to afford sufficient surface area for tip/tissue interface cooling by blood flow around the tip electrode to avoid cutting or charring the tissue. Given the foregoing factors, the tip electrode of the catheter is often the instrument of choice for RF ablation.  
         [0004]     Irrigated tip electrode catheters are a known improvement for their ability to cool the tip/tissue interface and/or dilute the adjacent blood by irrigation. Such catheters are configured to emit a cooling liquid, such as normal saline or dextrose/saline solution, out tiny holes in the tip electrode at or near the tip/tissue interface. The liquid cools the tip tissue interface and lowers the adjacent “hematacrit,” both of which in turn greatly reduce thrombus formation and charring at the interface.  
         [0005]     The design of hole patterns can be crucial for efficient irrigation, that is, the achievement of sufficient cooling without seriously loading the patient with coolant. With proper design of the hole patterns, it is possible to achieve efficient irrigation with insignificant local blood dilution. Accordingly, it is possible to achieve a much improved RF lesion with greatly reduced danger of thrombus formation from charring.  
         [0006]     However, a challenge with irrigated tip electrodes is the need to isolate the irrigation liquid from the electrical components attached to and imbedded in the tip electrode, which can include the lead wires, electrical or electromagnetic sensors and/or temperature sensors. A further compounding challenge is the spatial confinement in the tip region which mandates efficient use of the limited space to house the above components. The fabrication of the irrigated tip electrode therefore involves multiple factors, including combining irrigation control for maximum cooling efficiency, sealing off irrigation components from the electrical components, providing sufficient space in the tip electrode for all these components, and avoiding detachment of the tip electrode from the catheter.  
         [0007]     It is therefore desirable to provide a catheter with efficient and effective irrigation such as where irrigation holes are situated around the extreme distal end of the tip electrode and the irrigation paths in the tip electrode are of generally equal and short lengths. It is further desirable that such a catheter provides for separate and isolated compartments between the irrigation and electrical components. It is also desirable to provide a method of fabricating such a catheter where there is irrigation control for maximum cooling efficiency, the irrigation is sealed off from the electrical components, there is sufficient space to house all the irrigation and electrical components and/or the tip electrode is securely attached to the catheter.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides an irrigated tip for attachment to an ablation catheter, and a method of manufacture therefor. The irrigated tip electrode has a shell and a plug which jointly define a chamber that is fed by an irrigation lumen. In particular, the shell is configured with an interior cavity that is sealed and partially filled by the plug whose distal end is proximal of the distal end of the interior cavity to define a plenum chamber in the tip electrode. An irrigation lumen is configured in the tip electrode to supply the plenum chamber with irrigation fluid that is then distributed to the outer surface of the tip electrode through fluid passages.  
         [0009]     A detailed embodiment of the present invention, an irrigated tip catheter has a catheter body, a control handle and a deflectable tip section. In particular, the catheter body has a proximal end and a distal end and the control handle is at the proximal end of the catheter body. The tip section is at the distal end of the catheter body and comprises a tip electrode having a shell and a plug that jointly define a sealed chamber which receives through a lumen fluid that is distributed through fluid passages to outside of the tip electrode. The chamber is advantageously isolated from a region of the tip electrode occupied by electrical and/or electromagnetic components in the tip electrode. In particular, lumens occupied by the these components terminate in blind holes that have no communication with the chamber.  
         [0010]     The present invention also includes a method of fabricating an irrigated tip electrode. One method comprises providing a shell configured from a rod to provide an open interior cavity, forming fluid passages between the cavity and an outer surface of the tip electrode, sealing and partially filling the cavity with a plug to form a chamber, and providing a lumen through which fluid can enter the chamber and exit therefrom through the fluid passages.  
         [0011]     In a more detailed embodiment, the method includes drilling of the rod to form the shell and press-fitting the plug into the shell to form a generally monolithic structure. The method may also include drilling the monolithic structure to form an irrigation lumen, where such drilling can occur at or near an interface between the plug and the shell.  
         [0012]     In another more detailed embodiment, the method may include inserting the plug into the interior cavity until a proximal end of the plug is flush with a proximal end of the shell, and forming at least one additional lumen in the monolithic structure whose distal end is proximal of the plenum chamber. Moreover, the at least one additional lumen may be devoid of communication with the irrigation lumen and the plenum chamber within the tip electrode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:  
         [0014]      FIG. 1  is a side view of a catheter according to an embodiment of the invention.  
         [0015]      FIG. 2  is a side cross-sectional view of a catheter body according to the invention, including the junction between the catheter body and tip section. It is noted that the first, third and fourth lumens of the tip section are shown in a single representational cross sectional view in order to facilitate the discussion herein. However, it will be understood by one of ordinary skill in the art that no single plane intersects all the lumens shown.  
         [0016]      FIG. 3  is a side cross-sectional view of a catheter tip section showing an embodiment of an irrigated tip electrode.  
         [0017]      FIG. 3A  is an opposite side cross-sectional view of the catheter tip section of  FIG. 3 .  
         [0018]      FIG. 4  is a cross-sectional view of the tip section of  FIG. 2  taken along line  4 - 4 .  
         [0019]      FIG. 5  is a cross-sectional view of the tip electrode of  FIG. 3  taken along line  5 - 5 .  
         [0020]      FIG. 6  is a side cross-sectional view of an alternative embodiment of a catheter body according to the invention having a side arm. It is again noted that the first, third and fourth lumens of the tip section are shown in a single representational cross sectional view in order to facilitate the discussion herein. However, it will be understood by one of ordinary skill in the art that no single plane intersects all the lumens shown.  
         [0021]      FIG. 7  is side view of a shell and a plug prior to placement of the plug in the shell in forming the tip electrode in one embodiment.  
         [0022]      FIG. 7A  is a side view of the shell and the plug of  FIG. 7  after placement of the plug in the shell.  
         [0023]      FIG. 7B  is an end view of the shell and plug of  FIG. 7A .  
         [0024]      FIG. 7C  is a side view of the shell and the plug of  FIG. 7B  with lumens drilled.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     In an embodiment of the invention, there is provided a steerable bi-directional catheter having an irrigated tip. As shown in  FIGS. 1-7 , catheter  10  comprises an elongated catheter body  12  having proximal and distal ends, a deflectable tip section  14  at the distal end of the catheter body  12 , and a control handle  16  at the proximal end of the catheter body  12 .  
         [0026]     With reference to  FIGS. 1 and 2 , the catheter body  12  comprises an elongated tubular construction having a single, axial or central lumen  18 . The catheter body  12  is flexible, i.e., bendable but with substantially torsional stiffness. The catheter body  12  can be of any suitable construction and made of any suitable material. A presently preferred construction comprises an outer wall  22  made of a polyurethane or PEBAX. The outer wall  22  comprises an imbedded 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 tip section  14  of the catheter  10  will rotate in a corresponding manner.  
         [0027]     Extending through the single lumen  18  of the catheter body  12  are lead wires, an infusion tube, a first compression coil through which a first puller wire extends for uni-directional deflection, if not also a second compression coil through which a second puller wire extends for bidirectional deflection. A single lumen catheter body is often preferred over a multi-lumen body because it has been found that the single lumen body permits better tip control when rotating the catheter. The single lumen permits the lead wires, infusion tube, and the puller wire(s) each surrounded by the compression coil(s) to float freely within the catheter body. If such wires and tube were restricted within multiple lumens, they tend to build up energy when the handle is rotated, resulting in the catheter body having a tendency to rotate back if, for example, the handle is released, or if bent around a curve, to flip over, either of which are undesirable performance characteristics.  
         [0028]     The outer diameter of the catheter body  12  is not critical, but is preferably no more than about 8 french, more preferably 7 french. Likewise the thickness of the outer wall  22  is not critical, but is thin enough so that the central lumen  18  can accommodate an infusion tube, at least one puller wire, lead wires, and any other wires, cables or tubes. The inner surface of the outer wall  22  is lined with a stiffening tube  20 , which can be made of any suitable material, such as polyimide or nylon. The stiffening tube  20 , along with the braided outer wall  22 , provides improved torsional stability while at the same time minimizing the wall thickness of the catheter, thus maximizing the diameter of the central lumen  18 . The outer diameter of the stiffening tube  20  is about the same as or slightly smaller than the inner diameter of the outer wall  22 . Polyimide tubing is presently preferred for the stiffening tube  20  because it may be very thin walled while still providing very good stiffness. This maximizes the diameter of the central lumen  18  without sacrificing strength and stiffness.  
         [0029]     An embodiment of the catheter has the outer wall  22  with an outer diameter of from about 0.090 inch to about 0.094 inch and an inner diameter of from about 0.061 inch to about 0.065 inch and the polyimide stiffening tube  20  having an outer diameter of from about 0.060 inch to about 0.064 inch and an inner diameter of from about 0.051 inch to about 0.056 inch.  
         [0030]     At least one puller wire  42  for deflecting the tip section  14  extends through the catheter body  12 , is anchored at its proximal end to the control handle  16 , and is anchored at its distal end to the tip section  14 . The puller wire  42  is made of any suitable metal, such as stainless steel or Nitinol, and is preferably coated with Teflon.RTM. 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 inches.  
         [0031]     A compression coil  44  is situated within the catheter body  12  in surrounding relation to the puller wire  42 . The compression coil  44  extends from the proximal end of the catheter body  12  to the proximal end of the tip section  14 . The compression coil  44  is made of any suitable metal, preferably stainless steel. The compression coil  44  is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil  44  is preferably slightly larger than the diameter of the puller wire  42 . Teflon.RTM. coating on the puller wire  42  allows it to slide freely within the compression coil  44 . If desired, particularly if electrode lead wires are not enclosed by a protective sheath, the outer surface of the compression coil  44  can be covered by a flexible, non-conductive sheath  39 , e.g., made of polyimide tubing, to prevent contact between the compression coil  44  and any other wires within the catheter body  12 .  
         [0032]     The compression coil  44  is anchored at its proximal end to the proximal end of the stiffening tube  20  in the catheter body  12  by glue joint  50  and at its distal end to the tip section  14  by glue joint  51 . Both glue joints  50  and  51  preferably comprise polyurethane glue or the like. The glue may be applied by means of a syringe or the like through a hole made between the outer surface of the catheter body  12  and the central lumen  18 . Such a hole may be formed, for example, by a needle or the like that punctures the outer wall  22  of the catheter body  12  and the stiffening tube  20  which is heated sufficiently to form a permanent hole. The glue is then introduced through the hole to the outer surface of the compression coil  44  and wicks around the outer circumference to form a glue joint about the entire circumference of the compression coil  44 .  
         [0033]     A suitable means for attaching the catheter body  12  to the tip section  14  is illustrated in  FIG. 2 . The proximal end of the tip section  14  comprises an outer circumferential notch  24  that receives the inner surface of the outer wall  22  of the catheter body  12 . The tip section  14  and catheter body  12  are attached by glue or the like. Before the tip section  14  and catheter body  12  are attached, however, the stiffening tube  20  is inserted into the catheter body  12 . The distal end of the stiffening tube  20  is fixedly attached near the distal end of the catheter body  12  by forming a glue joint  23  with polyurethane glue or the like. Preferably a small distance, e.g., about 3 mm, is provided between the distal end of the catheter body  12  and the distal end of the stiffening tube  20  to permit room for the catheter body  12  to receive the notch  24  of the tip section  14 . A force is applied to the proximal end of the stiffening tube  20 , and, while the stiffening tube  20  is under compression, a first glue joint (not shown) is made between the stiffening tube  20  and the outer wall  22  by a fast drying glue, e.g. Super Glue.RTM. Thereafter a second glue joint  26  is formed between the proximal ends of the stiffening tube  20  and outer wall  22  using a slower drying but more permanent glue, e.g., polyurethane.  
         [0034]     If desired, a spacer can be located within the catheter body between the distal end of the stiffening tube and the proximal end of the tip section. The spacer provides a transition in flexibility at the junction of the catheter body and tip section, which allows this junction to bend smoothly without folding or kinking. A catheter having such a spacer is described in U.S. patent application Ser. No. 08/924,616, entitled “Steerable Direct Myocardial Revascularization Catheter”, the disclosure of which is incorporated herein by reference.  
         [0035]     As shown in  FIGS. 3, 3A  and  4 , the tip section  14  comprises a tip electrode  36 , and a short section of tubing  19  having multiple off-axis lumens, e.g., three or four or more lumens. The tubing  19  is made of a suitable non-toxic material that is preferably more flexible than the catheter body  12 . A presently preferred material for the tubing  19  is braided polyurethane, i.e., polyurethane with an embedded mesh of braided stainless steel or the like, but the tubing  19  can comprise a plastic core, an inner plastic layer surrounding the core, a braided stainless steel mesh surrounding the inner layer, and an outer plastic layer surrounding the braided mesh. A suitable tubing is described in U.S. Pat. No. 6,569,114.  
         [0036]     The outer diameter of the tip section  14 , like that of the catheter body  12 , is preferably no greater than about 8 french, more preferably 7 french. The size of the lumens is not critical. In one embodiment, the tip section  14  has an outer diameter of about 7 french (0.092 inch) and the tubing  19  contains four lumens. The diameters of a first lumen  30  and a second lumen  32  are similar in size, and are each preferably 0.018 inch. The diameters of a third lumen  34  and a lumen  35  are also similar in size and are each preferably 0.029 inch.  
         [0037]     Carried on the tip section  14  are ring electrodes  38  whose lead wires  40  extend through the third lumen  34  of the tip section, and a thermocouple whose wires  41  and  45  (one of which can serve as the tip electrode lead wire in an alternative embodiment) also extend through the third lumen  34 . The tip section  14  also carries an electromagnetic navigation sensor  47  that is generally located in the tip electrode  36 . A cable  55  for the sensor  47  extends from the sensor  47  through the lumen  34 . A nonconducting sheath  49  can be provided in the lumen  34  for isolating and insulating the wires  40 ,  41  and  45 . Extending through the fourth lumen  35  of the tip section  14  is an infusion tube  88  extending from the control handle  16  and catheter body  12  and into the tip electrode  36 .  
         [0038]     Extending through the first and second lumens  30  and  32  are puller wires  42   a  and  42   b , respectively, for bidirectional deflection of the tip section  14 . Each puller wire has its respective plastic, preferably Teflon.RTM., sheath  81 , which prevents the puller wire from cutting into the wall of the tip section  14  when the tip section is deflected.  
         [0039]     As shown in the embodiment of  FIGS. 3 and 3 A, the tip electrode  36  is connected to the tubing  19  of the tip section  14  by means of a plastic housing  21 , preferably made of polyetheretherketone (PEEK). The proximal end of the tip electrode  36  is notched circumferentially to form a neck  31 , which fits inside the distal end of the plastic housing  21  and is bonded to the housing  21  by polyurethane glue or the like. As discussed further below, the wires, cable and irrigation tube that extend into the tip electrode  36  help keep the tip electrode in place on the tip section.  
         [0040]     The proximal end of the plastic housing  21  is bonded with polyurethane glue or the like to the distal end of the tubing  19  of the tip section  14 . The distal end of the tubing  19  is notched circumferentially to form a stem  33  which fits inside the proximal end of the housing  21 . The plastic housing can be about 1 cm long and the tip electrode  36  can have a diameter about the same as the outer diameter of the tubing  19  and housing  21 .  
         [0041]     In accordance with a feature of the present invention, the tip electrode  36  has multiple off-axis lumens. In the illustrated embodiment, there are a first lumen  64 , a second lumen  66 , a third lumen  68  and a fourth lumen  62 . The first, second and third lumens terminate in respective blind holes  74 ,  76  and  78 . The fourth lumen  62  however extends through and into a plenum chamber  37  provided in the distal end of the tip electrode. Significantly, the lumens  64 ,  66 ,  68  and the blind holes  74 ,  76 ,  78  are isolated and spatially separated from the plenum chamber and are as shown in the illustrations proximal of the plenum chamber. Thus, fluid entering and occupying the plenum chamber has no communication with these lumens or holes or, more importantly, the components received therein. Moreover, the relative distal and proximal orientation of the chamber and these components efficiently utilizes the limited space in the tip electrode without compromising their function or operation.  
         [0042]     The plenum chamber is in communication with the outer surface of the tip electrode  36  via multiple fluid passages  59  that extend radially from the plenum chamber. The plenum chamber advantageously occupies most if not all of the cross-section of the distal end of the tip electrode  36  such that the travel path of each fluid passage  59  through the distal end of the tip electrode is generally short and generally equal. As such, the irrigation fluid is evenly distributed from the plenum chamber to the outer surface of the tip electrode despite the relatively small hole size or cross section of the fluid passages which may be about 0.010 inch to 0.016 inch in diameter. There may be at least four, and more preferably, at least six fluid passages  59  in the tip electrode. However, it is understood by one of ordinary skill in the art that the number and configuration of the fluid passages can be varied as desired or appropriate.  
         [0043]     To supply the fluid to the plenum chamber, the infusion tube  88  extends through the central lumen  18  of the catheter body  12 , the fourth lumen  35  of the tip section  14  and the lumen  62  of the tip electrode. The distal end of the tube  88  can be proximal of the plenum chamber or it can extend into the plenum chamber  37 . The infusion tube  88  is anchored in the lumen  62  by polyurethane glue or the like. The fluid transported can be used for infusing fluids, e.g., saline, to cool the tip electrode  36 , in particular, the tip/tissue interface during ablation. The tip electrode may also be configured to infuse drugs or to collect tissue or fluid samples. The infusion tube may be made of any suitable material, and is preferably made of polyimide tubing. A preferred infusion tube has an outer diameter of from about 0.032 inch to about 0.036 inch and an inner diameter of from about 0.028 inch to about 0.032 inch.  
         [0044]     As better shown in  FIG. 5 , the lumens  62  and  68  are generally aligned along one diameter d″ of the tip electrode and the lumens  64  and  66  are generally aligned along another diameter d′ orthogonal to the diameter d″. Described differently, the lumens  62  and  64  occupy a first pair of opposing quadrants and the lumens  66  and  68  occupy a second pair of opposing quadrants. Moreover, the lumens of the tip electrode  36  are generally axially aligned with the lumens of the tubing  14 . In particular, the lumen  62  is generally axially aligned with the lumen  35 , the lumen  64  with the lumen  30 , the lumen  66  with the lumen  32 , and the lumen  68  and the lumen  34 .  
         [0045]     A preferred tip electrode  36  has an effective length, i.e., from its distal end to the distal end of the housing  21 , ranging between about 3.0 to 5.0 mm, and an actual length, i.e., from its distal end to its proximal end, of about 4.0 to 6.0 mm.  
         [0046]     In the embodiment shown, the three ring electrodes  38  are mounted on the housing  21 . It is understood that the presence and number of ring electrodes  38  may vary as desired and such additional ring electrodes  38  can be mounted on the tubing  19 . Each ring electrode  38  is slid over the housing  21  and/or the tubing  19  and fixed in place by glue or the like.  
         [0047]     The tip electrode  36  can be made of any suitable material, and are preferably machined from platinum-iridium bar (90% platinum/10% iridium). The tip electrode  36  and ring electrodes  38  are each connected to a separate lead wire  40 . The lead wires  40  extend through the third lumen  34  of tip section  14 , the central lumen  18  of the catheter body  12 , and the control handle  16 , and terminate at their proximal end in an input jack (not shown) that may be plugged into an appropriate monitor (not shown). As mentioned, the portion of the lead wires  40  extending through the proximal end of the tip section  14 , the central lumen  18  of the catheter body  12  and the control handle  16  are enclosed within a protective sheath  49 , which can be made of any suitable material, preferably polyimide. The protective sheath  49  is anchored at its distal end to the proximal end of the tip section  14  by gluing it in the third lumen  34  with polyurethane glue or the like.  
         [0048]     The lead wires  40  and the ring electrodes  38  are attached to the tip section  14  by any conventional technique. Connection of a lead wire to the tip electrode  36  is accomplished, for example, by welding the lead wire  40  into the hole  76  in the tip electrode  36  (see  FIG. 3A  which shows the tip electrode without the housing  21 , the tubing  19  or the ring electrode  38 ). Connection of a lead wire  40  to a ring electrode  38  is preferably accomplished by first making a small hole through the tubing  19  and/or the housing  21  ( FIG. 3 ). Such a hole can be created, for example, by inserting a needle through the tubing  19  and/or housing  21  and heating the needle sufficiently to form a permanent hole. A lead wire  40  is then drawn through the hole by using a microhook or the like. The ends of the lead wire  40  are then stripped of any coating and soldered or welded to the underside of the ring electrode  38 , which is then slid into position over the hole and fixed in place with polyurethane glue or the like.  
         [0049]     The temperature sensing means provided in the tip section  14  may also be a thermistor such as Model No. AB6N2-GC14KA143E/37C sold by Thermometrics (New Jersey). In the thermocouple however of the illustrated embodiment of  FIG. 3 , the wire  41  is a number “40” copper wire, and the wire  45  is a number “40” constantan wire, which gives support and strength to the wire pair. The wires  41  and  45  of the wire pair are electrically isolated from each other except at their distal ends where they contact and are twisted together, covered with a short piece of plastic tubing  43 , e.g., polyimide, and covered with epoxy. The plastic tubing  43  is then attached in the blind hole  74  of the tip electrode  36 , by polyurethane glue or the like. The wires  41  and  45  then extend out through the control handle  16  and to a connector (not shown) connectable to a temperature monitor (not shown).  
         [0050]     The lead wires  40  and the thermocouple wires  41  and  45  extend through the nonconductive covering  49  that extends also through the lumen  34  of the tubing  19  as mentioned above and through the housing  21  where the distal end of the lead wires are connected to their respective ring electrodes  38  and to the tip electrode  36 .  
         [0051]     The puller wire  42   a  extends from the lumen  30  in the tubing  19 , through the housing  21  and into the lumen  64  of the tip electrode  36  and is anchored at its distal end in the blind hole  74 . Similarly, the puller wire  42   b  extends from the lumen  32  in the tubing  19 , through the housing  21  and into the lumen  66  of the tip electrode and is anchored at its distal end in the blind hole  76 . A preferred method for anchoring the puller wires within the blind holes is by crimping metal tubing  46  of hypodermic stock to the distal end of the puller wire  42  and soldering the metal tubing  46  inside the blind holes. Anchoring the puller wires  42  within the tip electrode  36  provides additional support, reducing the likelihood that the tip electrode  36  will fall off the tip section  14 . Alternatively, one or both of the puller wires  42  can be attached to the side of the tip section  14 .  
         [0052]     The cable  55  for the electromagnetic navigation sensor  47  extends through the lumen  34  of the tubing  19 , and through the housing  21 , its distal end connected to the sensor  47 . The sensor  72  is fixedly attached within the tip electrode  36  and the plastic housing  21  by polyurethane glue or the like.  
         [0053]     Referring to  FIG. 1 , the proximal end of the cable  55  extends out the proximal end of the control handle  16  within an umbilical cord  78  to a sensor control module  75  that houses a circuit board (not shown). The cable  55  comprises multiple wires encased within a plastic covered sheath. In the sensor control module  75 , the wires of the electromagnetic sensor cable  55  are connected to the circuit board which amplifies the signal received from the electromagnetic sensor  47  and transmits it to a computer (not shown) in a form understandable by the computer  
         [0054]     The proximal end of the first infusion tube  88  extends through the control handle  16  and terminates in a luer hub  90  or the like at a location proximal to the control handle. In practice, fluid may be injected into the infusion tube  88  through the luer hub  90  ( FIG. 1 ), and flows through the infusion tube  88 , through the fourth lumen  35  and through the lumen  62 , into the plenum chamber  37  and out the fluid passages  59  in the tip electrode. Again, the fluid passage may have other configurations as desired. For example, the fluid passages  59  may include a longitudinal hole that extends out the distal end of the tip electrode  36 , or the tip electrode  36  may be porous enough to allow fluids to pass to the outer surface of the tip electrode, the interconnecting pores forming the fluid passage.  
         [0055]     In an alternative arrangement, as shown in  FIG. 6 , a single lumen side arm  94  is fluidly connected to the central lumen  18  near the proximal end of the catheter body  12 . The infusion tube  88  extends through the catheter body  12  and out the side arm  94 , where it terminates in a luer hub  90  ( FIG. 1 ) or the like. The side arm  94  is preferably made of the same material as the outer wall  22 , but preferably has a greater thickness, e.g., 0.055 inch. Where the side arm  94  meets the catheter body  12 , a molded joint can be provided to provide additional strength and support The molded joint can be made of any suitable biocompatable material, and is preferably made of polyurethane.  
         [0056]     The lumens  30  and  32  of the tubing  19  in the tip section receiving the puller wires  42   a  and  42   b , respectively, may be in adjacent quadrants, but are preferably in opposing quadrants as illustrated. If desired, the distal ends of one or both of the puller wires may be anchored to the side wall of the catheter tip section for example as, described in U.S. patent application Ser. No. 08/924,611, now U.S. Pat. No. 6,123,699, the entire disclosure of which is incorporated herein by reference. Moreover, the first puller wire may be anchored proximal to the anchor location of the second puller wire.  
         [0057]     A catheter construction comprising multiple puller wires including control handle construction is disclosed in U.S. patent application Ser. No. 08/924,611, Entitled “Omni-Directional Steerable Catheter”, the entire disclosure of which is incorporated herein by reference. Such application describes a suitable control handle for manipulating two or more puller wires. Other suitable control handles are disclosed in U.S. Pat. No. 6,602,242, the entire disclosure of which is incorporated herein.  
         [0058]     In accordance with a feature of the invention, the tip electrode is attached to the tip section through multiple attachment means. In the illustrated embodiment, the attachment means and structures include at least the infusion tube, and the puller wires, if not also the wire of the navigation sensor, to provide at least three if not four structure or points of attachment, each of which extends between the tubing  19  and the tip electrode  38 . To that end, the hypodermic stock anchoring the distal end of the puller wires can be of a greater length, e.g., at least 3.0 mm, preferably ranging between 3.0 mm and 4.0 mm for greater anchoring capabilities to the tip electrode. In any case, these generally tensile structures of attachment can remain even if the housing  21  is absent in the instance the tubing  19  and the tip electrode  36  are attached directly to each other or indirectly by or through another component.  
         [0059]      FIG. 7  illustrates the tip electrode  36  in an initial process of manufacture. The tip electrode  36  is configured from a first rod  82  which is notched circumferentially at its proximal end to form the neck  31  (see also  FIGS. 3 and 3 A) and a body  85 . The distal end of the body  85  is milled to form an atraumatic end  86 , e.g., a generally rounded conical shape. The interior of the rod is then drilled to form a shell  90  with predetermined thicknesses h 1  around the neck and h 2  around the body and a depth or length L 1  defining an open interior cavity  92 . The cavity  92  has a generally cylindrical proximal portion with a predefined length and diameter, and a generally conical or half-spherical distal portion. The conical distal portion may have a distal conical tip cross-section  93  spanning about 118 degrees. The rod may be constructed of any suitable material with sufficient structural strength and/or electrical conductivity, and is preferably of a noble metal alloy, for example 90/10 PT/IR.  
         [0060]     Formed of the same or comparable material of which the shell is formed, a second rod or plug  96  has a generally elongated configuration with a generally circular cross-section. The plug  96  having a diameter d suitable for a press fit into the interior cavity  92  is inserted into the shell  90  to seal and partially fill the cavity. To that end, although the predetermined diameter d is generally equal or slightly larger than the predetermined diameter of the interior cavity, the plug has a predetermined length L 2  that is lesser than the predetermined length L 1  of the shell  90 . As such, when the plug is inserted into the shell (see  FIG. 7A ), the plug can be positioned relative to the shell with its proximal end flush with the proximal end of the shell while its distal end is proximal of an edge location  99  by a predetermined distance X equaling at least about three times the diameter of the fluid passage  59 . As such, the depth of the plenum chamber (from the distal end of the plug  96  to the distal end of the plenum chamber) is advantageously minimal compared to the length of the shell, which maximizes the region in the tip electrode proximal the plenum chamber for housing other components in the tip electrode.  
         [0061]     It is understood by one of ordinary skill in the art that the proximal ends of the shell and the plug need not be flush if that is not a consideration for drilling of the lumens and blind holes in the tip electrode described further below. In any case, the press fit between the rod  96  and the shell  90  forms a fluid-tight seal such that the plenum chamber  37  and the lumen  62  opening into the plenum chamber are sealed from electrical components and any potting compound and solder that may be used in the tip electrode. In particular, fluid in the plenum chamber is limited to leaving the chamber through only the fluid passages  59  and/or the infusion tube  88  that feeds into the plenum chamber.  
         [0062]     The press fit also renders the plug and the shell a generally monolithic structure such that drilling can be accomplished on the proximal face of the structure without regard to an interface  103  between the plug and the shell (see  FIG. 7B ), particularly where the proximal ends of the plug and shell after assembly are flush with each other. Drilling can be initiated at the proximal face toward the distal end to form the lumens  62  and  68  (lumens  66  and  68  not shown) and the blind hole  78  (blind holes  74  and  76  not shown) for receiving the various electrical and nonelectrical components provided the tip electrode. In the illustrated embodiment of  FIG. 7B , drilling occurs at four locations generally along two orthogonal diameters d′ and d″ of the cross section of the structure, forming the lumens  62 ,  64 ,  66  and  68 . Given the confined space in the tip electrode, the lumens  64  and  66  are shown overlapping or otherwise in communication with the lumen  68 , but only to a limited degree such that the function and operation of each lumen and the contents thereof are not adversely affected. That is, the overlap (between longitudinal edges  101  and  102  better shown in  FIGS. 3, 3A  and  5 ) is not so large that the respective components of neighboring lumens can significantly commingle or become tangled with each other. It is understood by one of ordinary skill in the art that this need not be so as the lumens can be configured without any overlap.  
         [0063]     By situating one or more of the lumens  62 ,  64 ,  66 ,  68  to traverse the interface  103  between the plug and the shell (best seen in  FIG. 5 ), further strength and integrity can be imparted to the interface and bonding between the plug and the shell. As such, space in the tip electrode can be more efficiently utilized where the lumens are drilled after the plug and shell have been assembled. However, it is understood by one of ordinary skill in the art that the plug  96  can be drilled before it is press fitted into the shell  90 . In any case, there should be no overlap between the lumen  62  and any of the lumens  62 ,  64 ,  68 , so that there is no opportunity for the fluid carried in the tube  88  to come in contact with the respective components of the lumens  62 ,  64 ,  68 .  
         [0064]     The fluid passages  59  in the distal end of the shell  90  are formed from laser or electrical discharge machining (EDM) drilling, which can occur from the outer surface of the tip electrode toward the plenum chamber, prior to or after assembly of the plug  96  and shell  92  (although it is generally preferred that the drilling occurs before the plug is inserted so that any drilling debris inside the shell can be more easily removed). To ensure that each fluid passage has substantially the same travel path from the plenum chamber to the outer surface of the tip electrode, the drilling which creates the interior cavity  92  should be conducted in a manner that ensures the thickness of the distal end  86  is generally uniform, such as drilling centrally along the longitudinal axis of the rod  82 .  
         [0065]     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. It is further understood that the drawings are not necessarily to scale.  
         [0066]     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.