Irrigated catheter having a porous tip electrode

A porous tip electrode catheter is provided. The porous tip electrode comprises a porous material through which fluid can pass. The porous tip electrode is covered with a thin coating of conductive metal having openings through which fluids can pass.

FIELD OF THE INVENTION

The present invention is directed to an irrigated catheter having a porous tip electrode.

BACKGROUND OF THE INVENTION

Electrode catheters have been in common use in medical practice for many years. They are used to 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., the 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 the usefulness of the catheter.

In certain applications, it is desirable to have the ability to inject and/or withdraw fluid through the catheter. One such application is a cardiac ablation procedure for creating lesions which interrupt errant electrical pathways in the heart. Traditionally, this has been accomplished with an irrigated tip catheter.

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 patient's skin. Radio frequency (RF) current is applied to the tip electrode, and flows through the surrounding media, 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 resistivity. 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. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself. If the electrode temperature becomes sufficiently high, possibly above 60° C., a thin transparent coating of dehydrated blood can form on the surface of the electrode. If the temperature continues to rise, this dehydrated layer of blood can become progressively thicker resulting in blood coagulation on the electrode surface. Because dehydrated biological material has a higher electrical resistance than endocardial tissue, impedance to the flow of electrical energy into the tissue also increases. If the impedance increases sufficiently, an impedance rise occurs and the catheter must be removed from the body and the tip electrode cleaned.

In a typical application of RF current to the endocardium, circulating blood provides some cooling of the ablation electrode. However, there is typically a stagnant area between the electrode and tissue which is susceptible to the formation of dehydrated proteins and coagulum. As power and/or ablation time increases, the likelihood of an impedance rise also increases. As a result of this process, there has been a natural upper bound on the amount of energy which can be delivered to cardiac tissue and therefore the size of RF lesions. Historically, RF lesions have been hemispherical in shape with maximum lesion dimensions of approximately 6 mm in diameter and 3 to 5 mm in depth.

In clinical practice, it is desirable to reduce or eliminate impedance rises and, for certain cardiac arrythmias, to create larger lesions. One method for accomplishing this is to monitor the temperature of the ablation electrode and to control the RF current delivered to the ablation electrode based on this temperature. If the temperature rises above a pre-selected value, the current is reduced until the temperature drops below this value. This method has reduced the number of impedance rises during cardiac ablations but has not significantly increased lesion dimensions. The results are not significantly different because this method continues to rely on the cooling effect of the blood which is dependent on the location within the heart and the orientation of the catheter to the endocardial surface.

Another method is to irrigate the ablation electrode, e.g., with physiologic saline at room temperature, to actively cool the ablation electrode instead of relying on the more passive physiological cooling provided by the blood. Because the strength of the RF current is no longer limited by the interface temperature, current can be increased. This results in lesions which tend to be larger and more spherical, usually measuring about 10 to 12 mm.

The clinical effectiveness of irrigating the ablation electrode is dependent upon the distribution of flow within the electrode structure and the rate of irrigation flow through the tip. Effectiveness is achieved by reducing the overall electrode temperature and eliminating hot spots in the ablation electrode which can initiate coagulum formation. More channels and higher flows are more effective in reducing overall temperature and temperature variations, i.e., hot spots. The coolant flow rate must be balanced against the amount of fluid that can be injected into the patient and the increased clinical load required to monitor and possibly refill the injection devices during a procedure. In addition to irrigation flow during ablation, a maintenance flow, typically a lower flow rate, is required throughout the procedure to prevent backflow of blood into the coolant passages. Thus, reducing coolant flow by utilizing it as efficiently as possible is a desirable design objective.

One method for designing an ablation electrode which efficiently utilizes coolant flow is the use of a porous material structure. One such design is described in U.S. Pat. No. 6,405,078 to Moaddeb et al., the entire disclosure of which is incorporated herein by reference. Moaddeb describes the use of sintered metal particles to create a porous tip electrode. In addition, Moaddeb uses a non-conductive insert implanted into the porous tip electrode for mounting a thermocouple, lead wire and/or irrigation tube within the porous tip electrode. However, during irrigation the sintered metal particles can disintegrate and break away from the electrode structure. Consequently, a desire arises for a porous electrode having increased structural integrity.

SUMMARY OF THE INVENTION

In one embodiment, the invention is directed to an irrigated catheter having a porous tip electrode. The catheter comprises a catheter body and a tip section. The catheter body has an outer wall, proximal and distal ends, and a lumen extending therethrough. The tip section comprises a segment of flexible tubing having proximal and distal ends and at least one lumen therethrough. The proximal end of the tip section is fixedly attached to the distal end of the catheter body. The porous tip electrode is fixedly attached to the distal end of the tubing of the tip section. The tip electrode comprises a porous material through which fluid can pass.

The porous tip electrode comprises sintered non-conductive material. The sintered material may be made from any suitable non-conductive polymer or ceramic material. The sintered particles comprise both small particles and large particles, the large particles having a mean diameter at least about 2.5 times greater, and preferably, about 4 times greater, than the mean diameter of the small particles. The use of differently sized particles helps control the porosity of the sintered material, promotes uniform flow of fluid through the porous material, and minimizes fluid pressure drop through the material. The porous tip electrode is covered with a thin metal coating that is webbed, or otherwise porous, with openings through which fluid can pass to the outer surface of the tip electrode. The sintered polymeric or ceramic material has improved resistance to disintegration during irrigation. The metal coating improves overall structural stability of the tip electrode and serves as an electrode for conducting radio-frequency energy to the target tissue.

The catheter further comprises an irrigation tube having proximal and distal ends. The irrigation tube extends through the central lumen in the catheter body, with the distal end of the irrigation tube in fluid communication with the proximal end of the passage in the tip electrode. By this design, the fluid can flow through the irrigation tube, into the passage in the tip electrode and through the porous material and porous coating of the tip electrode to the outer surface of the tip electrode. A temperature sensing means is mounted in a blind hole in the tip electrode. A puller wire is mounted in the tip section. An electrode lead wire is electrically connected to the proximal end of the tip electrode.

DETAILED DESCRIPTION OF THE INVENTION

In a particularly preferred embodiment of the invention, there is provided a steerable catheter having an irrigated tip. As shown inFIGS. 1 to 4, catheter10comprises an elongated catheter body12having proximal and distal ends, a tip section14at the distal end of the catheter body12, and a control handle16at the proximal end of the catheter body12.

With reference toFIG. 2, the catheter body12comprises an elongated tubular construction having a single, axial or central lumen18. The catheter body12is flexible, i.e., bendable but substantially non-compressible along its length. The catheter body12can be of any suitable construction and made of any suitable material. A presently preferred construction comprises an outer wall22made of a polyurethane or PEBAX. The outer wall22comprises an imbedded braided mesh of high-strength steel, stainless steel or the like to increase torsional stiffness of the catheter body12so that, when the control handle16is rotated, the tip section14of the catheter10will rotate in a corresponding manner. The outer diameter of the catheter body12is not critical, but is preferably no more than about 8 french, more preferably about 7 french, still more preferably about 5 french. Likewise, the thickness of the outer wall22is not critical, but is thin enough so that the central lumen18can accommodate an irrigation tube, a puller wire, lead wires, and any other wires, cables or tubes. The inner surface of the outer wall22is lined with a stiffening tube20, which can be made of any suitable material, such as polyimide or nylon. The stiffening tube20, along with the braided outer wall22, provides improved torsional stability while at the same time minimizing the wall thickness of the catheter, thus maximizing the diameter of the central lumen18. The outer diameter of the stiffening tube20is about the same as or slightly smaller than the inner diameter of the outer wall22. Polyimide tubing is presently preferred for the stiffening tube20because it may be very thin walled while still providing very good stiffness. This maximizes the diameter of the central lumen18without sacrificing strength and stiffness. A particularly preferred catheter has an outer wall22with an outer diameter of from about 0.090 inches to about 0.098 inches and an inner diameter of from about 0.061 inches to about 0.065 inches and a polyimide stiffening tube20having an outer diameter of from about 0.060 inches to about 0.064 inches and an inner diameter of from about 0.051 inches to about 0.056 inches.

As shown inFIGS. 3A,3B, and4, the tip section14comprises a short section of tubing19having three lumens30,32and34. The tubing19is made of a suitable non-toxic material that is preferably more flexible than the catheter body12. A presently preferred material for the tubing19is braided polyurethane, i.e., polyurethane with an imbedded mesh of braided high-strength steel, stainless steel or the like. The outer diameter of the tip section14, like that of the catheter body12, is preferably no greater than about 8 french, more preferably about 7 french, still more preferably about 5 french. The size of the lumens is not critical. In a particularly preferred embodiment, the tip section14has an outer diameter of about 7 french (0.092 inches) and the first lumen30and second lumen32are generally about the same size, each having a diameter of from about 0.020 inches to about 0.024 inches, preferably about 0.022 inches, with the third lumen34having a slightly larger diameter of from about 0.032 inches to about 0.038 inches, preferably about 0.036 inches.

A preferred means for attaching the catheter body12to the tip section14is illustrated inFIG. 2. The proximal end of the tip section14comprises an outer circumferential notch24that receives the inner surface of the outer wall22of the catheter body12. The tip section14and catheter body12are attached by adhesive (e.g. polyurethane glue) or the like. Before the tip section14and catheter body12are attached, however, the stiffening tube20is inserted into the catheter body12. The distal end of the stiffening tube20is fixedly attached near the distal end of the catheter body12by 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 body12and the distal end of the stiffening tube20to permit room for the catheter body12to receive the notch24of the tip section14. A force is applied to the proximal end of the stiffening tube20, and, while the stiffening tube20is under compression, a first glue joint (not shown) is made between the stiffening tube20and the outer wall22by a fast drying glue, e.g. Super Glue®. Thereafter, a second glue joint (not shown) is formed between the proximal ends of the stiffening tube20and outer wall22using a slower drying but stronger glue, e.g. polyurethane.

At the distal end of the tip section14is a tip electrode36. Preferably, the tip electrode36has a diameter about the same as the outer diameter of the tubing19. The tip electrode36is formed of any suitable non-conductive polymer, such as polyethylene or Teflon®, or ceramic material, in which holes are drilled. The porous non-conductive material can be made using any conventional technique. For example, the porous non-conductive material can be machined from a rod of the material. Preferably, however, the non-conductive polymer comprises sintered polymer particles86formed from polyethylene or Teflon®, as best depicted inFIG. 8. As used herein, the term “sinter” refers to the process of bonding adjacent particles in a powder mass or compacting the particles by heating them to a temperature below the melting point of the main constituent at a predetermined and closely controlled time-temperature regime, including heating and cooling phases, in a protective atmosphere. The sintered polymer particles86permit passage of a cooling fluid through the tip electrode, as described in more detail below. The porosity of the sintered material is controlled by the amount of particle compacting in the mold or glue, the particle size, and the particle distribution.

A particularly preferred sintering process involves providing polyethylene or Teflon® powder particles in a certain sieve fraction, e.g., in the range of from about 5 microns to about 250 microns. The particles are preferably in the range of from about 10 microns to about 100 microns. In a particularly preferred embodiment, at least two different sized particles can be provided. For example, particles in the range of from about 15 microns to about 30 microns, and more preferably about 20 microns, in combination with particles in the range of from about 80 microns to about 110 microns, and more preferably about 100 microns, could be used. When two different sized particles are used, preferably the larger particles have a mean diameter at least about 2.5 times greater than the mean diameter of the smaller particles, and more preferably at least about 4 times greater. Alternatively, a single particle size can be used, which can give a denser packing and result in a higher pressure drop across the porous electrode. Whatever polymer is used, the particles are preferably rounded, and more preferably spherical, so as to provide a tip electrode surface that is not rough. However, the particles can be irregularly shaped, i.e. having differing shapes, which is a low cost alternative.

In a preferred process, the particles are put into a mold, such as a ceramic mold, having the desired electrode shape. If desired, the particles can be mixed with a suitable binder prior to being put into the mold. When a binder is used, the mold containing the binder and particles is placed into a low temperature oven and heated to a temperature sufficient to evaporate the binder. The particles are then sintered under vacuum or air at a temperature ranging from about 80° C. to about 160° C., although the temperature can vary depending on the composition of the porous polymer. However, the temperature should be below the melting point of the composition. The resulting tip electrode is then removed from the mold and assembled onto the flexible tubing of the tip section.

A tip electrode prepared in accordance with this method is depicted inFIG. 8. In particular,FIG. 8illustrates the porosity of the tip electrode when particles of different sizes are used. Although the drawings of the tip electrode, such asFIGS. 3A and 3B, do not depict the porous sintered material in detail, it is to be understood that where the body of the tip electrode is described as being made of a porous sintered material, it appears generally as depicted inFIG. 8. The drawings, such asFIGS. 3A and 3B, are provided to more clearly show the additional components in the tip section.

As shown inFIGS. 3A and 3B, the tip electrode36has two cavities extending therein, namely a primary fluid passage35and a blind hole31that correspond in size and location to the lumens34and30, respectively, in the tip section14. The primary fluid passage35extends substantially all the way through the sintered material of the tip electrode36, preferably ending just before the distal end of the tip electrode36. The blind hole31extends only a part of the way through the sintered material of the tip electrode36, preferably about half the length of the tip electrode36or less. For example, for a 3.5 mm tip electrode36, the blind hole31is about 0.088 inches long.

Disposed over the surface of the porous tip electrode is a thin metal coating84, as depicted inFIG. 10. The metal coating84serves to impart improved structural integrity to the porous tip electrode36while also serving as an electrode for distributing radio-frequency energy to the target tissue. The metal coating also prevents substantial contact of the non-conductive porous material of the tip electrode with the target tissue. The metal coating84can be made of any conductive metal, e.g. platinum or gold. Preferably, the metal coating84is made of a platinum-iridium alloy, e.g. 90% Platinum/10% Iridium, applied to the surface of the porous tip electrode36by a deposition process impregnating a thin layer of platinum-iridium alloy onto the porous surface of the tip electrode36. The thickness of the metal coating84may vary as desired, but is sufficiently thin to maintain a porous electrode surface, and sufficiently thick to maintain a conductive surface. For example, the metal coating84may have a thickness ranging from 0.2 μm to about 2 μm. Preferably, as shown inFIG. 10, the metal coating84is webbed or otherwise porous with openings85in the metal coating84through which irrigation fluids can pass.

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 electrode36is attached to the tubing19by polyurethane glue or the like. The wires and tubes that extend into the tip electrode36, described in more detail below, help to keep the tip electrode in place on the tubing19of the tip section14.

In the embodiment shown inFIGS. 3A and 3B, there are three ring electrodes39mounted on the tubing19proximal to the tip electrode36. It is understood that the presence and number of ring electrodes39may vary as desired. Each ring electrode39is slid over the tubing19and fixed in place by glue or the like. The ring electrodes39can be made of any suitable material, and are preferably machined from platinum-iridium bar (90% platinum/10% iridium).

The tip electrode36and ring electrodes39are each connected to a separate lead wire44. The lead wires44extend through the first lumen30of tip section14, the central lumen18of the catheter body12, and the control handle16, and terminate at their proximal ends in an input jack (not shown) that may be plugged into an appropriate monitor (not shown). The portion of the lead wires44extending through the central lumen18of the catheter body12, control handle16and proximal end of the tip section14may be enclosed within a protective sheath49, which can be made of any suitable material, preferably polyimide. The protective sheath49is preferably anchored at its distal end to the proximal end of the tip section14by gluing it in the first lumen30with polyurethane glue or the like. The lead wires44are attached to the tip electrode36and ring electrodes39by any conventional technique. For example, as described below, the tip electrode36, in one embodiment, may have a distal section70having a greater diameter than the diameter of proximal section68. In this embodiment, as depicted inFIG. 6, connection of a lead wire44to the tip electrode is accomplished, for example, by coiling the lead wire44around the proximal portion of the tip electrode36and gluing it in place to the metal coating84with polyurethane glue or the like.

Connection of a lead wire44to a ring electrode39is preferably accomplished by first making a small hole through the tubing19. Such a hole can be created, for example, by inserting a needle through the tubing19and heating the needle sufficiently to form a permanent hole. A lead wire44is then drawn through the hole by using a microhook or the like. The ends of the lead wire44are then stripped of any coating and soldered or welded to the underside of the ring electrode39, which is then slid into position over the hole and fixed in place with polyurethane glue or the like.

An irrigation tube is provided within the catheter body12for infusing fluids, e.g. saline, to cool the tip electrode36. The irrigation tube may be made of any suitable material, and is preferably made of polyimide tubing. A preferred irrigation tube has an outer diameter of from about 0.032 inches to about 0.036 inches and an inner diameter of from about 0.027 inches to about 0.032 inches.

With reference toFIGS. 2 and 3A, the irrigation tube comprises multiple tube segments. A first irrigation tube segment46extends through the central lumen18of the catheter body12and terminates in the proximal end of the third lumen34of the tip section14. The distal end of the first irrigation tube segment46is anchored in the third lumen34by polyurethane glue or the like. The proximal end of the first irrigation tube segment46extends through the control handle16and terminates in a luer hub47or the like at a location proximal to the control handle. A second irrigation tube segment48is provided at the distal end of the third lumen34and extends into the primary fluid passage35of the tip electrode36. The second irrigation tube segment48is anchored by polyurethane glue or the like within the third lumen34of the tip section14and in the primary fluid passage35. The second irrigation tube segment48provides additional support to maintain the tip electrode36mounted on the tubing19. In practice, fluid is injected into the first irrigation tube segment46, through the third lumen34, through the second irrigation tube segment48, into the primary fluid passage35of the tip electrode36, and out through the porous material of the tip electrode. Because the primary fluid passage35extends distally a greater length than the blind hole31, the fluid can pass outwardly on all sides of the distal end of the primary fluid passage35.

The fluid introduced through the catheter is preferably a biologically compatible fluid, and may be in a gaseous or liquid state. Suitable fluids include saline, water, carbon dioxide, nitrogen, and helium. In addition to, or instead of, being used to cool the tip electrode, the infused fluid also forms a buffer layer to maintain biological materials, such as blood, at a distance from the tip electrode, thereby minimizing contact of the tip electrode with the biological material. This buffer layer reduces coagulation of biological materials and regulates the impedance or resistance to energy transfer of the tissue near the tip electrode-during ablation.

The rate of fluid flow through the catheter may be controlled by any suitable fluid infusion pump or by pressure. A suitable infusion pump is the FLOGARD™ available from Baxter. The rate of fluid flow through the catheter preferably ranges from about 0.5 ml/min to about 30 ml/min, more preferably from about 5 ml/min to about 15 ml/min. Preferably, the fluid is maintained at about room temperature.

As shown inFIG. 7, a temperature sensing means41is provided for the tip electrode36and, if desired, the ring electrodes39. Any conventional temperature sensing means41, e.g., a thermocouple or thermistor, may be used. With reference toFIG. 3B, a preferred temperature sensing means41for the tip electrode36comprises a thermocouple formed by a wire pair. One wire of the wire pair is a copper wire41a, e.g., a number40copper wire. The other wire of the wire pair is a constantan wire43, which gives support and strength to the wire pair. The wires41aand43of the wire pair are electrically isolated from each other except at their distal ends where they contact each other and are twisted together, covered with a short piece of plastic tubing45, e.g. polyimide, and covered with epoxy. The plastic tubing45is then attached by polyurethane glue or the like in the first blind hole31of the tip electrode36. The wires41aand43extend through the first lumen30in the tip section14. Within the catheter body12, the wires41aand43may extend through the protective sheath49with the lead wires44. The wires41aand43then extend out through the control handle16and to a connector (not shown) connectable to a temperature monitor (not shown).

Alternatively, the temperature sensing means41may be a thermistor. A suitable thermistor for use in the present invention is Model No. AB6N2-GC14KA143E/37C sold by Thermometrics (New Jersey). The temperature sensing means may also be used as a feedback system to adjust the flow rate of the fluid through the catheter to maintain a desired temperature at the tip electrode.

A puller wire50extends through the catheter body12, is anchored at its proximal end to the control handle16, and is anchored at its distal end to the tip section14. The puller wire50is 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 wire50. The puller wire50preferably has a diameter ranging from about 0.006 inches to about 0.010 inches.

A compression coil52is situated within the catheter body12in surrounding relation to the puller wire50. The compression coil52extends from the proximal end of the catheter body12to the proximal end of the tip section14. The compression coil52is made of any suitable metal, preferably stainless steel. The compression coil52is tightly wound on itself to provide flexibility, i.e., bending, but to resist compression. The inner diameter of the compression coil52is preferably slightly larger than the diameter of the puller wire50. The Teflon® coating on the puller wire50allows it to slide freely within the compression coil52. If desired, particularly if the lead wires44are not enclosed by a protective sheath49, the outer surface of the compression coil52can be covered by a flexible, non-conductive sheath, e.g., made of polyimide tubing, to prevent contact between the compression coil52and any other wires within the catheter body12.

The compression coil52is anchored at its proximal end to the proximal end of the stiffening tube20in the catheter body12by glue joint51and at its distal end to the tip section14by glue joint53. Both glue joints52and53preferably 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 body12and the central lumen18. Such a hole may be formed, for example, by a needle or the like that punctures the outer wall22of the catheter body12and stiffening tube20which is heated sufficiently to form a permanent hole. The glue is then introduced through the hole to the outer surface of the compression coil52and wicks around the outer circumference to form a glue joint about the entire circumference of the compression coil52.

The puller wire50extends into the second lumen32of the tip section14. The puller wire50is anchored at its distal end to the tip section14. Preferably, an anchor is fixedly attached to the distal end of the puller wire50, as depicted inFIGS. 3A and 9. The anchor is preferably formed by a metal tube55, e.g. a short segment of hypodermic stock, which is fixedly attached, e.g. by crimping, to the distal end of the puller wire50. The tube55has a section that extends a short distance beyond the distal end of the puller wire50. A cross-piece53made of a small section of stainless steel ribbon or the like is soldered or welded in a transverse arrangement to the distal end of the tube section55, which is flattened during the operation. This creates a T-bar anchor. A notch is created in the side of the tip section14, resulting in an opening into the second lumen32into which the puller wire50extends. The anchor lies partially within the notch. Because the length of the ribbon forming the cross-piece53is longer than the diameter of the opening into the lumen32, the anchor cannot be pulled completely into the lumen32. The notch is then sealed with polyurethane glue or the like to give a smooth outer surface. Within the second lumen32of the tip section14, the puller wire50extends through a plastic, preferably Teflon® sheath56, which prevents the puller wire50from cutting into the wall of the tubing19when the tip section is deflected.

In an alternative arrangement, as shown inFIG. 5, a single lumen side arm58is fluidly connected to the central lumen18near the proximal end of the catheter body12. The first irrigation tube segment46extends through the catheter body12and out the side arm58, where it terminates in a luer hub (not shown) or the like. The side arm58is preferably made of the same material as the outer wall22, but preferably has a greater thickness, e.g. 0.0275 inches. Where the side arm58meets the catheter body12, a molded joint can be provided to provide additional strength and support. The molded joint can be made of any suitable biocompatible material, and is preferably made of polyurethane.

Longitudinal movement of the puller wire50relative to the catheter body12, which results in deflection of the tip section14, is accomplished by suitable manipulation of the control handle16. A suitable control handle for use with the present invention is described in U.S. Pat. No. 6,120,476, the disclosure of which is incorporated herein by reference.

In another preferred embodiment according to the invention, an electromagnetic sensor64is provided in the distal end of the tip section14. As shown inFIG. 9, in this embodiment the tip electrode36is connected to the tubing19of the tip section14by means of a plastic housing66, preferably made of polyetheretherketone (PEEK). The tip electrode36has a proximal section68and a distal section70. The proximal section68of the tip electrode36has an outer diameter less than the outer diameter of the distal section70. Thus, in the depicted embodiment, the proximal section68forms a recessed stem that fits inside the distal end of the plastic housing66, and the distal section70is exposed. The proximal section68is bonded to the housing66by polyurethane glue or the like. The proximal end of the plastic housing66is bonded with polyurethane glue or the like to the distal end of the tubing19of the tip section14. Preferably, the plastic housing66is about 1 cm long.

In this embodiment, the tip electrode36preferably has a total length ranging from about 6 mm to about 9 mm, more preferably about 7 mm. For a 7 mm long tip electrode, the distal section70and proximal section68each preferably have a length of about 3.5 mm. The proximal section68is formed of a solid metal material. The distal section70is formed of a porous material, as described above. However, the tip electrode36could be modified so that a portion of the proximal section68, which is formed of a solid material, is exposed along with the distal section70, which is formed of a porous material. Alternatively, a portion of the distal section70could form a part of the stem that extends into the housing66. However, in the preferred embodiment, the entire porous distal section70is exposed and the entire solid proximal section68is contained within the housing66.

A generally hollow cavity72is formed in the proximal end of the proximal section68of the tip electrode36. The electromagnetic sensor64is mounted partially in the plastic housing66, partially in the cavity72, and partially in the flexible tubing19, in a manner similar to that described in U.S. Pat. No. 6,120,476, the disclosure of which is incorporated herein by reference.

The tip electrode36has a fluid passage35and a blind hole31that extend longitudinally from the cavity72. The second irrigation tube segment48, puller wire50, thermocouple wires41and43, and tip electrode lead wire44are mounted in the tip electrode. The electromagnetic sensor64is connected to an electromagnetic sensor cable65, which extends through the third lumen34of the tip section14, through the central lumen18of the catheter body12, and into the control handle16. The electromagnetic sensor cable65then extends out the proximal end of the control handle16within 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 handle16, for example, as described in U.S. Pat. No. 5,964,757, the disclosure of which is incorporated herein by reference. The electromagnetic sensor cable65comprises 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. Suitable electromagnetic sensors for use with the present invention are described, for example, in U.S. Pat. Nos. 5,558,091, 5,443,489, 5,546,951, 5,568,809 and 5,391,199 and International Publication No. WO 95/02995, the disclosures of which are incorporated herein by reference. A preferred electromagnetic sensor64has a length of from about 6 mm to about 7 mm and a diameter of about 1.3 mm.

Preferably, in this embodiment, the catheter body does not comprise a stiffening tube20, because additional space is needed within the central lumen10to include the electromagnetic sensor cable. The catheter body in this embodiment has an outer diameter preferably no greater than about 8 french, more preferably from about 7 french to about 7.5 french, and if desired, no greater than about 5 french.

In the above-described embodiments, the tip electrode is described as having a fluid passage and a blind hole. As would be recognized by one skilled in the art, the tip electrode could have only a fluid passage into which all of the tubes, wires, etc. extend. However, such a design is less desirable because the thermocouple would be in direct contact with the fluid, which can result in an inaccurate temperature reading.

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. Such a design is described in U.S. Pat. No. 6,123,699, the disclosure of which is 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 principle, 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 for the following claims, which are to have their fullest and fairest scope.