Patent Publication Number: US-6663573-B2

Title: Bipolar mapping of intracardiac potentials using recessed electrodes

Description:
This is a division of application Ser. No. 09/612,490 filed Jul. 7, 2000, now U.S. Pat. No. 6,408,199. 
     The present invention is related to other commonly owned U.S. patent applications: U.S. Ser. No. 09/611,849, entitled Catheter with Tip Electrode Having a Recessed Ring Electrode Mounted Thereon; U.S. Ser. No. 09/611,617, entitled Mapping and ablation Catheter; U.S. Ser. No. 09/612,487, entitled Multi-Electrode Catheter, System and Method; and U.S. Ser. No. 09/612,606, entitled System and Method for Detecting Electrode-Tissue Contact; all commonly owned by the assignee of the present invention and the disclosures of each are incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a method for measuring electrical activity in the heart and a catheter useful for performing the method. 
     BACKGROUND OF THE INVENTION 
     Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. 
     In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is. 
     In healthy humans the heartbeat is controlled by the sinoatrial node (“S-A node”) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (“A-V node”) which in turn transmits the electrical signal potentials throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of or damage to the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as cardiac arrhythmia. 
     Electrophysiological ablation is a procedure often successful in terminating cardiac arrhythmia. This procedure involves applying sufficient energy to the interfering tissue to ablate that tissue thus removing the irregular signal pathway. However, before the ablation procedure can be carried out, the interfering tissue must first be located. 
     One location technique involves an electrophysiological mapping procedure whereby the electrical signals emanating from the conductive endocardial tissues are systematically monitored and a map is created of those signals. By analyzing that map, the interfering electrical pathway can be identified. A conventional method for mapping the electrical signals from conductive heart tissue is to percutaneously introduce an electrophysiology catheter (electrode catheter) having mapping electrodes mounted on its distal extremity. The catheter is maneuvered to place these electrodes in contact with or in close proximity to the endocardium. By monitoring the electrical signals at the endocardium, aberrant conductive tissue sites responsible for the arrhythmia can be pinpointed. 
     Once the origination point for the arrhythmia has been located in the tissue, the physician may use an ablation procedure to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities and restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. 
     Conventional unipolar electrode catheters utilize a primary tip or ring electrode that cooperates with a reference electrode outside the patient&#39;s body. Such catheters are known to map inaccurate electrical readings due to the reference electrode being located outside the patient&#39;s body. 
     Previous attempts have been made to design a bipolar electrode catheter having two electrodes within the patient&#39;s body. However, such catheters also have limited accuracy. Specifically, both electrodes pick up near field electrical signals emanating from the conductive endocardial tissues due to their contact with the heart tissue, and far-field electrical signals which propagate from other regions of the heart due to their contact with the blood. The far-field signals interfere with the near-field signals, making accurate measurement of the near-field signals difficult. Accordingly, a need exists for a bipolar electrode catheter that more accurately measures near-field signals. 
     U.S. Pat. No. 5,749,914 to Janssen discloses a catheter for removing obstructions from a tubular passageway in a patient. In one embodiment, Janssen describes a catheter having a distal end with a recessed annular ridge that defines a groove in which a plurality of electrodes are seated. The electrodes are sized so that they are recessed within the annular ridge. A return electrode is located on the catheter proximal to the recessed electrodes. The electrodes are connected to a radio-frequency energy source that generates and supplies current to the electrodes to ablate constructive material. Janssen nowhere teaches or suggests, however, using this catheter to map electrical activity in the heart. 
     U.S. Pat. No. 4,966,597 to Cosman discloses a cardiac ablation electrode catheter with a thermosensing detector at a position in the distal end of the catheter. In one embodiment, the ablation electrode has an insulative exterior with openings that provide exposed electrode surfaces. Each of the electrode surfaces can be independently connected to different contacts, which are then connected to a voltage source, or the electrode surfaces can all be connected together. A temperature-measuring conductor is attached to one or more of the electrode surfaces. The object of the invention described in Cosman is to provide a cardiac catheter for tissue ablation with ultra-fast faithful recording of temperature in the affected tissue. Cosman nowhere discloses, however, obtaining electrical signals with different electrodes and comparing the signals to obtain near-field electrical activity information. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a catheter having two electrodes for bipolar mapping and a method for using the catheter. In one embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart. The method comprises introducing into the heart a catheter comprising an elongated tubular body having a distal region and a circumferential recess along the length of the distal region. A first electrode is mounted on the distal region in close proximity to the circumferential recess. A second electrode is mounted within the circumferential recess. The method further comprises positioning the distal region at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart. 
     In another embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart comprising introducing into the heart a catheter comprising an elongated body having an outer diameter and a distal region, a first electrode mounted on the distal region, and a second electrode mounted on the distal region in close proximity to and electrically isolated from the first electrode, the second electrode having an outer diameter less than the outer diameter of the portion of the distal region on which it is mounted. The distal region is positioned at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart. 
     In still another embodiment, the invention is directed to a method for measuring near-field electrical activity at a location in a heart comprising introducing into the heart a catheter comprising an elongated body having a distal region, a first electrode mounted on the distal region, and a second electrode mounted on the distal region in close proximity to and electrically isolated from the first electrode. The second electrode is covered by a blood-permeable membrane that prohibits direct contact between the second electrode and surrounding heart tissue. The distal region is positioned at the location in the heart so that the first electrode is in direct contact with heart tissue and the second electrode is not in direct contact with heart tissue but is in contact with blood. A first signal is obtained with the first electrode, and a second signal is obtained with the second electrode. The first signal and the second signal are compared to obtain the near-field electrical activity at the location in the heart. 
     In yet another embodiment, the invention is directed to a catheter comprising an elongated body having a distal region. A first electrode is mounted on the distal region. A second electrode is mounted on the distal region in close proximity to and electrically isolated from the first electrode. The second electrode is covered by a blood-permeable membrane that, in use, prohibits direct contact between the second electrode and surrounding heart tissue. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a side view of an embodiment of the catheter of the invention. 
     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. 
     FIG. 3 is a side cross-sectional view of a catheter tip section showing a tip electrode and a recessed ring electrode. 
     FIG. 4 is a side cross-sectional view of an alternative tip section according to the invention having a ring electrode covered by a blood-permeable material. 
     FIG. 5A is a side cross-sectional view of another alternative tip section according to the invention having a first ring electrode and a second ring electrode that is recessed. 
     FIG. 5B is a side cross-sectional view of another alternative tip section according to the invention having a first ring electrode and a second ring electrode that is covered by a blood-permeable membrane. 
     FIG. 6 is a side cross-sectional view of another alternative tip section according to the invention, the tip section including an electromagnetic location sensor. 
     FIG. 7 is an end cross-sectional view of the tip section depicted in FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     In a particularly preferred embodiment of the invention, there is provided a steerable catheter having two electrodes for making bipolar measurements. As shown in FIGS. 1 to  3 , catheter  10  comprises an elongated catheter body  12  having proximal and distal ends, a 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 . 
     With reference to FIG. 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 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  22  made of a polyurethane, or PEBAX. The outer wall  22  comprises an imbedded braided mesh of high-strength steel, 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. The outer diameter of the catheter body  12  is not critical, but is preferably no more than about 8 french (1 mm=3 french), more preferably about 7 french, still more preferably about 5 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, a 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. A particularly preferred catheter has an outer wall  22  with an outer diameter of from about 0.090 inch to about 0.098 inch and an inner diameter of from about 0.061 inch to about 0.065 inch and a 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. If desired, the stiffening tube  20  can be eliminated. As would be recognized by one skilled in the art, the catheter body construction can be modified as desired. 
     As shown in FIG. 3, the tip section  14  comprises a short section of tubing  19  having two lumens  30  and  32 . 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 high-strength steel, stainless steel or the like. 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, still more preferably about 5 french. The size of the lumens is not critical and can vary depending on the specific application. 
     A preferred 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 adhesive (e.g., polyurethane 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 (not shown) 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®. Thereafter a second glue joint (not shown) is formed between the proximal ends of the stiffening tube  20  and outer wall  22  using a slower drying but stronger glue, e.g., polyurethane. 
     At the distal end of the tip section  14  is a tip electrode  36 . Preferably the tip electrode  36  has a diameter about the same as the outer diameter of the tubing  19 . The tip electrode  36  can be made from any suitable material, such as platinum, gold, iridium or stainless steel, and is preferably machined from platinum-iridium bar (90% platinum/10% iridium). 
     A preferred tip electrode has a length ranging from about 2.5 mm to about 8 mm, preferably about 3.5 mm. Preferably the tip electrode  36  is attached to the tubing  19  by polyurethane glue or the like. The wires that extend into the tip electrode  36 , described in more detail below, help to keep the tip electrode in place on the tubing  19  of the tip section  14 . 
     In the embodiment shown in FIG. 3, there is a ring electrode  39  mounted within a circumferential recess  26  in the tubing  19  of the tip section  14 . The recess  26  is located near the distal end of the tip section  14  and in close proximity to the tip electrode  36 . As used herein, “in close proximity” means a distance suitable for conducting bipolar mapping. Preferably the recess  26  is spaced apart from the tip electrode  36  a distance no greater than about 4 mm, more preferably from about 0.1 mm to about 2 mm, still more preferably from about 0.5 mm to about 1.0 mm. The width and depth of the recess  26  are designed such that, when the tip section  14  is positioned on its side against the adjacent heart tissue, the tissue des not come into contact with the ring electrode  39 . Preferably, the width of the recess  26  ranges from about 0.5 mm to about 4 mm, more preferably from about 1 mm to about 3 mm, with the depth of the recess  26  preferably ranging from about 0.25 mm to about 1.5 mm, more preferably from about 0.5 mm to about 1 mm. 
     In a preferred embodiment, the ring electrode  39  comprises a resilient ribbon-shaped conductive material that is wrapped within the recess  26  and fixed in place by glue or the like. The ring electrode  39  can be made of any suitable conductive material, such as those discussed above for the tip electrode. The width of and thickness of the ring electrode  39  are suitable for fitting within the recess  26  so that the outer surface of the ring electrode  39  is recessed within the recess  26 . In other words, the ring electrode  39  has an outer diameter less than the outer diameter of the tubing  19  of the tip section  14 . Preferably, the outer diameter of the ring electrode  39  is at least about 10%, more preferably from about 20% to about 50%, less than the outer diameter of the portion of the tip section  14  on which it is mounted. The ring electrode  39  has a width preferably ranging from about 0.5 mm to about 4 mm, more preferably from about 1 mm to about 3 mm. In an alternative embodiment, the ring electrode  39  is in the form of a snap ring, where the width and thickness of the ring  39  are suitable for fitting within the recess  26 , as described above. 
     The tip electrode  36  and ring electrode  39  are each connected to a separate lead wire  44 . The lead wires  44  extend through the first lumen  30  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 signal processing unit (not shown). The portion of the lead wires  44  extending through the central lumen  18  of the catheter body  12 , control handle  16  and proximal end of the tip section  14  may be enclosed within a protective sheath  49 , which can be made of any suitable material, preferably polyimide. The protective sheath  49  is preferably anchored at its distal end to the proximal end of the tip section  14  by gluing it in the first lumen  30  with polyurethane glue or the like. 
     The lead wires  44  are attached to the tip electrode  36  and ring electrode  39  by any conventional technique. Connection of a lead wire  44  to the tip electrode  36  is accomplished, for example, by soldering the lead wire  44  into a first blind hole  31  of the tip electrode, as shown in FIG.  3 . 
     Connection of a lead wire  44  to a ring electrode  39  is preferably accomplished by first making a small hole through the tubing  19 . Such a hole can be created, for example, by inserting a needle through the tubing  19  and heating the needle sufficiently to form a permanent hole. A lead wire  44  is then drawn through the hole by using a microhook or the like. The ends of the lead wire  44  are then stripped of any coating and soldered or welded to the underside of the ring electrode  39 , which is then slid into position over the hole and fixed in place with polyurethane glue or the like. 
     A puller wire  50  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  50  is made of any suitable metal, such as stainless steel or Nitinol, and is preferably coated with Teflon® or the like. The coating imparts lubricity to the puller wire  50 . The puller wire  50  preferably has a diameter ranging from about 0.006 to about 0.010 inches. 
     A compression coil  52  is situated within the catheter body  12  in surrounding relation to the puller wire  50 . The compression coil  52  extends from the proximal end of the catheter body  12  to the proximal end of the tip section  14 . The compression coil  52  is made of any suitable metal, preferably stainless steel. The compression coil  52  is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil  52  is preferably slightly larger than the diameter of the puller wire  50 . The Teflon® coating on the puller wire  50  allows it to slide freely within the compression coil  52 . If desired, particularly if the lead wires  44  are not enclosed by a protective sheath  49 , the outer surface of the compression coil  52  can be covered by a flexible, non-conductive sheath  46 , e.g., made of polyimide tubing, to prevent contact between the compression coil  52  and any other wires within the catheter body  12 . 
     The compression coil  52  is anchored at its proximal end to the proximal end of the stiffening tube  20  in the catheter body  12  by glue joint  51  and at its distal end to the tip section  14  by glue joint  53 . Both glue joints  51  and  53  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  52  and wicks around the outer circumference to form a glue joint about the entire circumference of the compression coil  52 . 
     The puller wire  50  extends into the second lumen  32  of the tip section  14 . The puller wire  50  is anchored at its distal end to the tip electrode  36  within a second blind hole  33  by weld or the like. A preferred method for anchoring the puller wire  50  within the tip electrode  36  is by crimping metal tubing  54  to the distal end of the puller wire  50  and soldering the metal tubing  54  inside the second blind hole  33 . Anchoring the puller wire  50  within the tip electrode  36  provides additional support for the tip electrode on the flexible plastic tubing  19 , reducing the likelihood that the tip electrode will separate from the tubing. Alternatively, the puller wire  50  can be attached to the side of the tip section  14 . Such a design is described in U.S. patent application Ser. No. 08/924,611 (filed Sep. 5, 1997), the disclosure of which is incorporated herein by reference. Within the second lumen  32  of the tip section  14 , the puller wire  50  extends through a plastic, preferably Teflon®, sheath  56 , which prevents the puller wire  50  from cutting into the wall of the tubing  19  when the tip section is deflected. 
     Longitudinal movement of the puller wire  50  relative to the catheter body  12 , which results in deflection of the tip section  14 , is accomplished by suitable manipulation of the control handle  16 . A suitable control handle design for use with the present invention is described in allowed U.S. patent application Ser. No. 08/982,113, filed Dec. 1, 1997, the disclosure of which is incorporated herein by reference. 
     In operation, the present invention is ideal for mapping the heart and ablating accessory signal pathways causing arrhythmias. To perform this function, the distal end of the catheter  10  is inserted into a vein or artery and advanced into the heart. To assist in positioning the tip section  14  of the catheter  10  at a desired position within the heart, the puller wire  50  and control handle  16  are used to deflect the tip section  14 . Once the tip section  14  has been positioned at or near the desired location of the heart tissue, the electrical activity of the heart may be identified, evaluated or mapped, and electrophysiological sources of arrhythmia may be identified and/or treated. 
     Electrical activity within the heart is detected using the tip electrode  36  and ring electrodes  39  of the catheter  10 . The catheter  10  of the present invention is designed such that the tip electrode  36  is in direct contact with the heart tissue. Thus, the tip electrode  36  senses both the local activation energy (near-field signals) at the point of contact with the heart tissue and far field activation energy (far-field signals) received by the electrode through the blood. 
     As described above, the ring electrode  39  is recessed relative to the tip section  14  to be protected from direct contact with the heart tissue, but permitting contact with surrounding blood. The close proximity of the ring electrode  39  to the tip electrode  36  enables the ring electrode  36  to receive approximately the same far-field signals as the tip electrode  36 . However, the ring electrode  39  does not pick up the local activation potential (near-field signals). The signals received by the tip electrode  36  and the ring electrode  39  are sent to a suitable signal processing unit. 
     Within the signal processing unit, the signal detected by the ring electrode  39 , which is only far-field signals, is subtracted from the signal detected by the tip electrode  36 , which includes both near-field and far-field signals. Thus, the near-field signals can be more accurately determined. This improved method of detecting electrical activity allows the physician or operator to determine the location of the arrhythmiogenic focus more accurately for ablating and other purposes. 
     Alternate bipolar electrode designs can also be provided having one electrode in contact with blood but not the heart tissue. For example, as shown in FIG. 4, the ring electrode  39  is covered by a membrane  60  that is permeable to the blood, but that prevents direct physical contact between the ring electrode and the heart tissue. In this embodiment the ring electrode  39  is mounted on the tubing  19  proximal to and in close proximity to the tip electrode  39 . The ring electrode  39  is slid over the tubing  19  and fixed in place by glue or the like. The membrane  60  is wrapped around the ring electrode  39  and glued in place onto the tip section  14  by polyurethane or the like. The membrane  60  is preferably in the form of a perforated film or a woven or nonwoven fabric. The membrane  60  preferably comprises a biocompatible polymer. Examples of suitable biocompatible polymers for use in connection with the invention include polyolefins such as polypropylene, polyurethane, polyetheramide, polyetherimide, polyimide, fluoropolymers such as polytetrafluoroethylene, silicones and the like, and combinations thereof. The blood-permeable membrane  60  thus allows the blood to permeate the membrane  60  and contact the ring electrode  39 , while protecting the ring electrode  39  from direct contact with the heart tissue. 
     In alternative embodiments, as shown in FIGS. 5A and 5B, ring electrode pairs may be provided instead of the tip electrode/ring electrode combinations described above. In these embodiments, the ring electrode pair  61  includes first and second ring electrodes  64  and  66  mounted in close proximity to each other. In one alternative embodiment, the first ring electrode  64  is mounted on the outer surface of the tubing  19  to make direct contact with adjacent heart tissue. The second ring electrode  66  is displaced within a recess  65  proximal to the first electrode  64  such that the second electrode  66  is recessed from the outer surface of the tubing  19  to prevent direct contact with adjacent heart tissue, in a manner as described above. 
     In another alternative embodiment, the first ring electrode  64  is mounted on the outer surface of the tubing  19 , to make direct contact with adjacent heart tissue. The second ring electrode  66  is mounted on the tubing  19  proximal to the first electrode  64 . A blood-permeable membrane  60  is wrapped around the second electrode  66 , in a manner as described above, to protect the second electrode  66  from direct contact with adjacent heart tissue. 
     As would be recognized by one skilled in the art, the relative locations of the ring electrodes can vary. For example, in the embodiment of FIG. 5A, the second electrode  66 , which is recessed, can be distal to the first electrode  64 . Also, additional ring electrodes can be provided for any of the above-described embodiments. 
     In an alternative embodiment, the catheter further includes a location sensor, preferably an electromagnetic location sensor. As shown in FIGS. 6 and 7, the tip section  14  includes a third lumen  34 . The electromagnetic sensor  72  is mounted in part in the distal end of the tubing  19  and in part in a blind hole in the tip electrode  36 . Suitable electromagnetic sensors for use in connection with the present invention are described in U.S. patent application Ser. No. 09/160,063 (entitled “Miniaturized Position Sensor”) and U.S. Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951, 5,568,809, and 5,391,199, the disclosures of which are incorporated herein by reference. The electromagnetic sensor  72  is connected to a electromagnetic sensor cable  74 , which extends through the third lumen  34  of the tip section  14 , through the central lumen  18  of the catheter body  12 , and into the control handle  16 . The electromagnetic sensor cable  74  then extends out the proximal end of the control handle  16  within an umbilical cord (not shown) to a sensor control module (not shown) that houses a circuit board (not shown). Alternatively, the circuit board can be housed within the control handle  16 , for example, as 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. The electromagnetic sensor cable  74  comprises multiple wires encased within a plastic covered sheath. In the sensor control module, the wires of the electromagnetic sensor cable are connected to the circuit board. The circuit board amplifies the signal received from the electromagnetic sensor and transmits it to a computer in a form understandable by the computer by means of the sensor connector at the proximal end of the sensor control module. Also, because the catheter is designed for single use only, the circuit board preferably contains an EPROM chip which shuts down the circuit board approximately 24 hours after the catheter has been used. This prevents the catheter, or at least the electromagnetic sensor, from being used twice. If desired, the sensor  72  can be contained within a rigid plastic housing, e.g., made of polyetheretherketone (PEEK), that is mounted between the tip electrode  36  and the flexible tubing  19 . Such a design is described in U.S. Pat. No. 5,938,603, the disclosure of which is incorporated herein by reference. 
     To use the electromagnetic sensor  72 , the patient is placed in a magnetic field generated, for example, by situating under the patient a pad containing coils for generating a magnetic field. A reference electromagnetic sensor is fixed relative to the patient, e.g., taped to the patient&#39;s back, and the catheter containing a the electromagnetic location sensor is advanced into the patient&#39;s heart. Each sensor preferably comprises three small coils which in the magnetic field generate weak electrical signals indicative of their position in the magnetic field. Signals generated by both the fixed reference sensor and the second sensor in the heart are amplified and transmitted to a computer which analyzes the signals and then displays the signals on a monitor. By this method, the precise location of the sensor in the catheter relative to the reference sensor can be ascertained and visually displayed. The sensor can also detect displacement of that catheter that is caused by contraction of the heart muscle. A preferred mapping system includes a catheter comprising multiple electrodes and an electromagnetic sensor, such as the NOGA-STAR catheter marketed by Biosense Webster, Inc., and means for monitoring and displaying the signals received from the electrodes and electromagnetic sensor, such as the Biosense-NOGA system, also marketed by Biosense Webster, Inc. 
     Using this technology, the physician can visually map a heart chamber. This mapping is done by advancing the catheter tip into a heart chamber until contact is made with the heart wall. This position is recorded and saved. The catheter tip is then moved to another position in contact with the heart wall and again the position is recorded and saved. By combining the electromagnetic sensor and electrodes, a physician can simultaneously map the contours or shape of the heart chamber and the electrical activity of the heart. 
     If desired, the catheter can be multidirectional, i.e., having two or more puller wires to enhance the ability to manipulate the tip section in more than one direction or to form two or more different curves. A description of such a design is described in U.S. patent application Ser. Nos. 08/924,611 (filed Sep. 5, 1997), 09/130,359 (filed Aug. 7, 1998), 09/143,426 (filed Aug. 28, 1998), 09/205,631 (filed Dec. 3, 1998), and 09/274,050 (filed Mar. 22, 1999), the disclosures of which are incorporated herein by reference. 
     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. 
     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.