Patent Description:
In some ablation procedures, a catheter is inserted into a heart, and an ablation electrode at the distal end of the catheter is used to deliver an ablating signal to the tissue.

<CIT> describes a catheter adapted for ablation having multiple dedicated irrigation tubings to supply fluid to their respective electrode or set of electrodes. The tubings provide parallel flow pathways through the catheter where irrigation fluid is delivered to irrigated tip and/or ring electrodes which can accomplish uni-polar or bi-polar ablation. Such separate and dedicated fluid pathways allow fluid to be delivered to the corresponding electrode or set of electrodes at different flow rates. An integrated ablation system using such catheter has an ablation energy source and an irrigation pump with multiple pump heads that can operate independently of each other. An integrated irrigation tubing set is included to extend between the fluid source and the catheter, with each pump head being able to act on a different tubing that delivers fluid to a different electrode or set of electrodes.

<CIT>
, describes a catheter or lead having a flexible printed circuit for conveying signals and/or energy. Each trace may be in electrical connection with one or more external electrical contacts. More specifically, each trace is typically electrically connected to a single contact. The traces and contacts may assist in diagnosis and/or detection of bio-electrical signals emitted by organs, and may transmit such signals to a connector or diagnostic device affixed to the catheter. The external electrical contacts may detect bioelectric energy or may deliver electrical or thermal energy to a target site.

<CIT> describes a flex-PCB catheter device that is configured to be inserted into a body lumen. The flex-PCB catheter comprises an elongate shaft, an expandable assembly, a flexible printed circuit board (flex-PCB) substrate, a plurality of electronic components and a plurality of communication paths. The elongate shaft comprises a proximal end and a distal end. The expandable assembly is configured to transition from a radially compact state to a radially expanded state. The plurality of electronic elements are coupled to the flex-PCB substrate and are configured to receive and/or transmit an electric signal. The plurality of communication paths are positioned on and/or within the flex-PCB substrate. The communication paths selectively couple the plurality of electronic elements to a plurality of electrical contacts configured to electrically connect to an electronic module configured to process the electrical signal. The flex-PCB substrate can have multiple layers, including one or more metallic layers. Acoustic matching elements and conductive traces can be includes in the flex-PCB substrate.

<CIT> describes a medical probe, including a flexible insertion tube, having a distal end for insertion into a body cavity of a patient and which is configured to be brought into
contact with tissue in the body cavity. The probe further includes a sensor tube of an elastic material, contained inside the distal end of the insertion tube and configured to deform in response to forces exerted by the tissue on the distal end. The probe also includes a plurality of strain gauges fixedly attached to a surface of the sensor tube at different, respective locations and configured to generate respective signals in response to deformations of the sensor tube.

<CIT> discloses a catheter including an inner tip member defining a fluid delivery lumen extending therethrough, and an outer tip member disposed about the inner tip member. The inner and outer tip members define a gap therebetween in fluid communication within the fluid delivery lumen.

<CIT> discloses an ablation electrode assembly including an inner core member and an outer shell surrounding the inner core member. The inner core member and the outer shell define a space or separation region therebetween. Irrigation fluid flows within the space.

<CIT> discloses a catheter apparatus with a tip electrode and an insulation member. The elements of the tip assembly provides a fluid flow path that allows the fluid to be heated prior to exiting the tip assembly. The tip assembly includes an inlet lumen, a fluid heating space connected to the inlet lumen, and a plurality of fluid outlets connected to the fluid heating space. The inlet lumen, which extends through the insulation member, is connected to the outlets by the fluid heating space. The fluid heating space is defined by a space between the tip electrode and the insulation member. <CIT> discloses an electrode including a closed end sharpened to its one end and a hollow tube type electrode extended long in the length direction from the other end of the closed end. An insulation member is installed on the outer circumference of the hollow electrode except for the part connected to the closed end. A hollow refrigerant tube is installed in the hollow electrode for circulation of refrigerants.

The invention is defined in the independent claim.

There is provided, an apparatus, including:.

In some embodiments, each of the microelectrodes includes:.

In some embodiments, the apparatus further includes a plurality of temperature sensors coupled to the PCB, each of the temperature sensors being thermally coupled to the conducting element of a respective one of the microelectrodes.

In some embodiments, the microelectrodes are fittingly situated within the microelectrode apertures.

In some embodiments, the microelectrodes are fixed to respective perimeters of the microelectrode apertures.

In some embodiments, the apparatus further includes a catheter handle at a proximal end of the catheter, wherein the PCB is coupled to the catheter handle.

In some embodiments, the apparatus further includes a structure disposed within a lumen of the tip electrode and configured to inhibit retraction of the microelectrodes through the microelectrode apertures by supporting the PCB.

In some embodiments, a distal end of the structure is positioned within <NUM> of a distal face of the tip electrode.

In some embodiments, the structure is annular.

In some embodiments, the tip electrode is further shaped to define a plurality of fluid apertures configured to allow passage of a fluid therethrough.

In some embodiments, the PCB is positioned within a lumen of the tip electrode such as to define a space, between the PCB and an inner surface of the tip electrode, for passage of the fluid to the fluid apertures.

In some embodiments, the space is less than <NUM> in a radial direction.

In some embodiments, at least some of the microelectrodes are located along a distal face of the tip electrode.

In some embodiments, the at least some of the microelectrodes that are located along the distal face of the tip electrode are oriented obliquely with respect to the distal face of the tip electrode.

In some embodiments, at least some of the microelectrodes are located along a circumferential face of the tip electrode.

There is further provided, not explicitly claimed but nevertheless considered useful for understanding the invention, a method, including:.

In some embodiments, the method further includes, while passing the ablating signal into the tissue, passing a fluid through a plurality of fluid apertures in the tip electrode.

In some embodiments, passing the fluid through the fluid apertures includes passing the fluid through the fluid apertures via a space between the PCB and the tip electrode.

In some embodiments, passing the fluid through the fluid apertures includes passing the fluid through the fluid apertures via a conduit that is supporting the PCB.

In some embodiments, the method further includes measuring a temperature of the tissue, using a plurality of temperature sensors that are thermally coupled to respective conducting elements of the microelectrodes.

There is further provided, an apparatus, including:.

In some embodiments, each of the strain gauges is coupled to an outer surface of the respective one of the bridges.

In some embodiments, each of the strain gauges is coupled to an inner surface of the respective one of the bridges.

In some embodiments, the tube is shaped to define one or more slots at respective longitudinal positions along the tube, each of the slots separating between a respective pair of the segments.

In some embodiments, each of the slots includes a circumferential portion that passes circumferentially along the tube, and two longitudinal portions that pass longitudinally along the tube at respective ends of the circumferential portion, and a respective one of the bridges is between the two longitudinal portions of the slot.

In some embodiments, each of the slots is, circumferentially, between <NUM> and <NUM> degrees long.

In some embodiments, the apparatus further includes a tip electrode at a distal end of the catheter, the tube being electrically coupled to the tip electrode.

In some embodiments, the tip electrode and the tube are formed of a single piece of material.

In some embodiments, the tube is metallic.

In some embodiments, the apparatus further includes at least one printed circuit board (PCB) disposed within the tube and configured to carry the signals from the strain gauges.

In some embodiments, the strain gauges are mounted on the PCB.

In some embodiments, the apparatus further includes a structure that supports the PCB, the structure being coupled to the tube.

In some embodiments, the structure includes a plurality of tabs, and the structure is coupled to the tube by virtue of the tabs fitting into complementary apertures in the tube.

In some embodiments, the structure includes a conduit configured to allow passage of a fluid therethrough.

In some embodiments, the strain gauges include three strain gauges disposed at different respective circumferential positions along the tube.

In some embodiments, the passing the fluid through the plurality of fluid apertures includes passing the fluid through the plurality of fluid apertures via the tube.

In some embodiments, estimating the force includes:.

In some embodiments, the method further includes, using a printed circuit board (PCB) disposed within a lumen of the catheter, carrying the signals to a proximal end of the catheter.

There is further provided an apparatus, including:.

In some embodiments, the structure is configured such that fluid flows through the space in a distal direction.

In some embodiments, the structure is configured such that the fluid flows through the space in a proximal direction.

In some embodiments, the structure includes a conduit.

In some embodiments, the conduit is configured such that the fluid exits a distal opening of the conduit, and is then deflected into the space by a distal face of the tip electrode.

In some embodiments, a majority of the fluid apertures are in a circumferential face of the tip electrode.

In some embodiments, the distal opening of the conduit is positioned within <NUM> of the distal face of the tip electrode.

In some embodiments, the structure is shaped to define one or more circumferential openings, such that the fluid flows into the space through the circumferential openings.

In some embodiments, at least part of the space is less than <NUM> in a radial direction.

In some embodiments, causing the fluid to flow in the longitudinal direction includes causing the fluid to flow in a distal direction.

In some embodiments, causing the fluid to flow in the longitudinal direction includes causing the fluid to flow in a proximal direction.

In some embodiments, the structure includes a conduit, and the method further includes causing the fluid to flow through the conduit prior to flowing through the space.

In some embodiments, the method further includes causing the fluid to exit a distal opening of the conduit, and to be deflected into the space by a distal face of the tip electrode.

In some embodiments, the method further includes causing the fluid to flow into the space through one or more circumferential openings in the structure.

Embodiments described herein include an ablation catheter for use in ablating tissue, such as intracardiac tissue. The catheter comprises a tip electrode at the distal end of the catheter, which is used to deliver ablating signals to the tissue. The catheter further comprises a plurality of microelectrodes, which are coupled to at least one printed circuit board (PCB) disposed within the lumen of the catheter. The microelectrodes are fittingly situated within microelectrode apertures in the tip electrode. During the ablation procedure, the microelectrodes may be used to acquire signals from the tissue, in order to help assess the electrical activity of the tissue. These signals may be carried by the PCB to the proximal end of the catheter.

Advantageously, the microelectrodes, and the PCB to which they are coupled, serve a structural role, in addition to the functional role described above. In particular, the fit of the microelectrodes within the microelectrode apertures, and the attachment of the microelectrodes to the PCB, inhibits the tip electrode from migrating from the rest of the catheter, such that it may not be necessary to have a separate "safety wire" holding the tip electrode. Typically, a conduit, or other support, within the tip electrode supports the PCB, such that the microelectrodes do not migrate from the microelectrode apertures.

During the ablation procedure, it is typically desired to pass an irrigating fluid into the blood surrounding the catheter, in order (i) to draw heat from the ablating tip, and (ii) to help prevent blood clots from forming. Hence, the tip electrode is typically shaped to define a plurality of fluid apertures, for passage of an irrigating fluid therethrough. Advantageously, embodiments described herein allow for a large amount of heat exchange between the tip electrode and the irrigating fluid, by providing, for passage of the fluid, a narrow space between the PCB and the tip electrode, along the inner surface of the tip electrode. As the fluid is forced through this narrow space prior to exiting from the fluid apertures, a large amount of heat is absorbed from the tip electrode. In some embodiments, to pass the fluid through the narrow space, the fluid is deflected by the distal inner face of the tip electrode.

To increase the efficacy and/or safety of the ablation procedure, it is typically helpful to regulate the force applied to the tissue by the catheter. To this end, the catheter described herein typically further comprises a slotted tube, which is disposed within the lumen of the catheter, near the distal end of the catheter. A plurality of slots along the tube divide the tube into separate segments, each neighboring pair of the segments being spanned by a respective bridge. A plurality of strain gauges are coupled, respectively, to the bridges. As the catheter pushes against the tissue at the contact point between the tip electrode and the tissue, the force applied to the catheter by the tissue causes the bridges to bend. The strain gauges measure this bending, and output signals in response thereto. Based on these signals, the magnitude and direction of the force may be estimated, such that the force may be appropriately regulated.

Reference is initially made to <FIG>, which is a schematic illustration of a procedure using an ablation catheter <NUM>. <FIG> depicts a physician <NUM> using catheter <NUM> to perform an ablation of tissue within a heart <NUM> of a subject <NUM>. Catheter <NUM> comprises a catheter shaft <NUM>, at a distal end of which is disposed a tip electrode <NUM>. During the ablation procedure, tip electrode <NUM> is inserted into heart <NUM>. Tip electrode <NUM> is then brought into contact with the intracardiac tissue, and ablating signals are passed, via the tip electrode, into the tissue.

A console <NUM>, which is connected to the ablation catheter via a catheter handle <NUM> at the proximal end of the catheter, includes a signal generator ("SIG GEN") <NUM>, which generates the ablating signals, a processor ("PROC") <NUM>, which receives and processes signals received from the distal end of the catheter, and a pump <NUM>, which pumps irrigating fluid to the distal end of the catheter. During the procedure, anatomical information, and/or any other relevant information, may be displayed on a monitor <NUM>.

Tip electrode <NUM> is shaped to define a plurality of microelectrode apertures <NUM>, within which, respectively, a plurality of microelectrodes <NUM> are fittingly situated. (Typically, the microelectrodes are electrically and thermally isolated from the tip electrode. ) In general, any number of microelectrode apertures <NUM> - and hence, microelectrodes <NUM> - may be located along the distal face <NUM> of the tip electrode, and/or the circumferential face <NUM> of the tip electrode. In some embodiments, for example, catheter <NUM> comprises six microelectrodes - three at distal face <NUM>, and three at circumferential face <NUM>, the latter three microelectrodes being spaced apart from each other by approximately <NUM> degrees. Each of the microelectrodes may either be flush with the outer surface of the tip electrode, or alternatively, may protrude from the outer surface. (Such protrusion may facilitate a more accurate temperature reading by a temperature sensor located beneath the microelectrode, as described below, by bringing the temperature sensor closer to the tissue from which the reading is acquired. ) Upon the tip electrode being placed in contact with the tissue, the tip electrode passes an ablating signal into tissue, while the microelectrodes acquire intracardiac electrocardiogram (ECG) signals from the tissue. Alternatively or additionally, the microelectrodes may be used to pass current into the tissue for impedance measurements, which may be used, for example, for impedance-based location-sensing.

Typically, tip electrode <NUM> is further shaped to define a plurality of fluid apertures <NUM>, which are configured to allow passage of a fluid therethrough. During the ablation procedure, while ablating signals are being passed into the tissue, an irrigating fluid is delivered to, and passed through, fluid apertures <NUM>, as further described below. The fluid apertures are typically much smaller than the microelectrode apertures, and are typically located mostly (or entirely) along the circumferential face of the tip electrode, i.e., typically most, or all, of the fluid apertures pass through the circumferential face.

Typically, catheter <NUM> further comprises a slotted tube <NUM>, which is typically situated at a distal portion of the catheter, such as immediately proximally to, and/or partly underneath, tip electrode <NUM>. (For example, the proximal end of the tip electrode may slide over the distal portion of the tube. ) As described in detail below, tube <NUM> is shaped to define one or more slots <NUM> at respective longitudinal positions along the tube, each of slots <NUM> separating between two respective segments of the tube, such that the segments are at least partly disconnected from each other. Each pair of neighboring segments is spanned by a bridge <NUM>. One or more strain gauges <NUM> are coupled to bridges <NUM>, each strain gauge <NUM> being configured to measure the strain in the bridge to which the strain gauge is coupled. As described above, these measurements may be used to estimate the force applied to the tissue by the catheter during the ablation procedure. Typically, slotted tube <NUM> is metallic; for example, the slotted tube may be manufactured from any suitable metallic alloy, such as nitinol.

Although, in <FIG>, the slotted tube and strain gauge are seen through a transparent portion of the outer surface of the catheter, it is noted that the portion of the outer surface of the catheter that covers the slotted tube is not necessarily transparent. It is further noted that, in some embodiments, the slotted tube is not covered, such that the slotted tube itself constitutes part of the outer wall of the catheter, as shown in <FIG>, which is described below.

In some embodiments, catheter <NUM> further comprises one or more ring electrodes <NUM> on the surface of the catheter. Ring electrodes <NUM> may be used, for example, for ECG-signal acquisition, or injection of current for impedance-based location-sensing.

Reference is now made to <FIG>, which is a schematic illustration of the distal end of catheter <NUM>, in accordance with some embodiments of the present invention. (In <FIG>, tip electrode <NUM> is hidden, such that the components of the catheter underneath the tip electrode are visible.

Typically, at least one flexible PCB <NUM> is disposed within the lumen of the catheter. For example, <FIG> shows a single PCB <NUM>, comprising three splines that are folded over such that the splines extend proximally from the distal end <NUM> of PCB <NUM>. PCB <NUM> typically runs through the lumen of the catheter, such that the PCB is covered by catheter shaft <NUM>, i.e., the PCB is typically not exposed. In some embodiments, PCB <NUM> extends from the distal end of the catheter to catheter handle <NUM>, and is directly coupled to the catheter handle. In other embodiments, the proximal end of PCB <NUM> is connected to a cable, and the cable is coupled to the catheter handle. In either case, the coupling of the PCB to the catheter handle - whether a direct coupling, or a coupling via a cable - anchors the PCB (and hence, the tip electrode, as further described below) to the catheter handle.

As shown in <FIG>, microelectrodes <NUM> are coupled to the PCB, and the PCB carries signals from the microelectrodes to the proximal end of the catheter. In some embodiments, PCB <NUM> also carries signals to the distal end of the catheter. For example,
PCB <NUM> may carry current, for injection into tissue, to ring electrodes <NUM> (<FIG>). Alternatively or additionally, PCB <NUM> may carry signals, such as current signals for injection for impedance measurements, to the microelectrodes, and/or ablating signals to the tip electrode via an electrical coupling between tube <NUM> and tip electrode.

Typically, each microelectrode comprises a conducting element <NUM> and an isolating wall <NUM>. Isolating wall <NUM>, which is typically glued to PCB <NUM>, surrounds conducting element <NUM>, thus electrically- and thermally-isolating the conducting element from the tip electrode. Conducting element <NUM> is typically electrically coupled to PCB <NUM> (e.g., by being directly connected to the PCB), such that ECG signals detected by the conducting surface may be carried by the PCB from the distal end of the catheter. In some embodiments, as shown, each microelectrode is cylindrically shaped, whereby isolating wall <NUM> has an annular shape, and the outer surface of conducting element <NUM>, which forms the top of the cylinder, is circular. Typically, the diameter of the microelectrode apertures in the tip electrode is only slightly larger than that of the microelectrodes, such that the microelectrodes fit snugly into the apertures. Alternatively or additionally, during the manufacture of catheter <NUM>, the microelectrodes may be glued to, or otherwise fixed to, the respective perimeters of the microelectrode apertures. Thus, the microelectrodes are securely coupled to the tip electrode.

Typically, temperature sensors <NUM>, such as thermistors, are also coupled to the PCB, and the PCB further carries signals from temperature sensors <NUM>. Typically, each temperature sensor is located within a respective isolating wall <NUM>, beneath the outer surface of a respective conducting element <NUM>. (For clarity, in <FIG>, the conducting element of one of the microelectrodes is hidden, revealing a temperature sensor <NUM>. ) In such embodiments, conducting elements <NUM> are thermally coupled to the temperature sensors (e.g., by contacting the temperature sensors), such that the conducting elements conduct heat from the tissue to the temperature sensors, thus facilitating the measuring of the tissue temperature by the temperature sensors.

Although the tip electrode is typically fastened to the remainder of the catheter (e.g., by being fastened to tube <NUM>), a fallback securement mechanism for the tip electrode may be desired. Advantageously, as noted above, the PCB, together with the microelectrodes, serve as such a fallback securement mechanism, by anchoring the tip electrode to the remainder of the apparatus. For example, the tip electrode may be anchored to the catheter handle, by virtue of the PCB - which is attached to the microelectrodes, which are securely coupled to the tip electrode - being connected to the catheter handle. It may thus be unnecessary to attach a safety wire, or any other dedicated fallback securement mechanism, to the tip electrode. The PCB thus provides structural stability to the catheter, in addition to carrying signals to and/or from the distal end of the catheter.

In some embodiments, one or more of the microelectrodes at distal face <NUM> are oriented obliquely (e.g., at <NUM> degrees) with respect to distal face <NUM>. Such an orientation further helps to anchor the tip electrode in place, by inhibiting the tip electrode from sliding distally.

Typically, PCB <NUM> is supported by a conduit <NUM>, which, aside from supporting PCB <NUM> (and hence inhibiting the microelectrodes from retracting, i.e., sliding inward from the surface of the tip electrode into the lumen of the tip electrode), also allows passage of fluid therethrough. Conduit <NUM> is shaped to define a distal opening <NUM>, i.e., an opening at the distal end of the conduit, through which, as further described below, irrigating fluid may pass. As shown in <FIG>, conduit <NUM> may be coupled to slotted tube <NUM>, e.g., via tabs <NUM> of the conduit that fit into complementary apertures <NUM> in the slotted tube.

Alternatively or additionally to conduit <NUM>, PCB <NUM> may be supported by any other structure, such as an annular supporting structure, that prevents radially-inward migration of the microelectrodes.

Reference is now made to <FIG>, which is a schematic illustration of slotted tube <NUM>. As described above, slotted tube <NUM> is shaped to define one or more slots <NUM>, at respective longitudinal positions along the tube, which divide the tube into a plurality of segments. For example, in <FIG>, three slots divide the tube into four segments - a first segment 72a, a second segment 72b, a third segment 72c, and a fourth segment 72d. Typically, the slotted tube is formed by laser-cutting the slots into an uncut tube.

Each of slots <NUM> typically includes, in addition to a circumferential portion <NUM> that passes circumferentially along the tube, two longitudinal portions <NUM> that pass longitudinally along the tube at respective ends of circumferential portion <NUM>. (Longitudinal portions <NUM> thus "cut into" the segments. ) Between the two ends of each longitudinal portion <NUM> lies a respective bridge <NUM>, which spans the pair of neighboring segments separated by the slot. In response to forces applied to the catheter, bridges <NUM> bend. Typically, each of the slots runs along a large majority of the circumference of the tube, such that each bridge <NUM> is relatively narrow. For example, each slot may be, circumferentially, between <NUM> and <NUM> degrees long (i.e., each slot may pass along <NUM>-<NUM> degrees of the circumference of the tube), such that bridge <NUM> is between <NUM> and <NUM> degrees wide. The relative narrowness of the bridges facilitates the bending of the bridges.

As shown in <FIG>, strain gauges <NUM> are typically coupled to bridges <NUM>, such that each strain gauge spans a respective pair of segments. (In <FIG>, the rightmost strain gauge is not shown, due to this strain gauge being located at a portion of the tube that faces away from the viewer. ) The bending of each bridge <NUM> causes a signal to be output by the strain gauge that is coupled to the bridge, the signal indicating the strain in the bridge. The signals from the strain gauges are carried, by PCB <NUM>, to the proximal end of the catheter.

For example, each strain gauge shown in <FIG> comprises a resistor <NUM>. As the shape of the strain gauge changes due to the strain in the bridge, the resistance of resistor <NUM> changes. Via PCB <NUM>, a voltage may be applied across the strain gauge, such that the measured current flowing through the strain gauge indicates the change in resistance of the strain gauge, and hence, the strain in the bridge. Alternatively, a current may be applied across the strain gauge, such that the measured voltage across the strain gauge indicates the change in resistance of the strain gauge. This measured voltage or current is referred to herein as the "signal," output by the strain gauge, that indicates the strain in the bridge.

Based on the signals from strain gauges <NUM> that indicate the strain measurements, the force that is being applied to the catheter may be estimated. In particular, by placing three strain gauges at different respective circumferential positions along the tube, three separate, independent strain measurements may be obtained. Based on these three strain measurements, the direction of the force, in addition to the magnitude of the force, may be ascertained. For example, as shown, the three strain gauges may be spaced equiangularly along the tube, such that <NUM> degrees separates between the respective middles of any two of the strain gauges.

In some embodiments, as shown, strain gauges <NUM> are coupled to the outer surfaces of the bridges. In such embodiments, connecting elements (not shown) may connect the strain gauges to the PCB disposed within the tube, such that the PCB may carry the signals from the strain gauges. In other embodiments, strain gauges <NUM> are coupled to the inner surfaces of the bridges. In such embodiments, the strain gauges may be mounted on the PCB.

Reference is now made to <FIG>, which is a schematic illustration of a longitudinal cross-section of the distal end of catheter <NUM>, in accordance with some embodiments of the present invention.

As described above, during the ablation procedure, pump <NUM> delivers irrigating fluid to the distal end of the catheter. <FIG> shows an example flow pattern of this irrigating fluid, as the irrigating fluid approaches, and then passes through, tip electrode <NUM>. First, the fluid passes through tube <NUM>, and then through conduit <NUM>. Next, the fluid passes through opening <NUM> of the conduit and through an opening <NUM> at the distal end of the PCB. The fluid thus reaches distal face <NUM> of the tip electrode, and is subsequently deflected, by the inner surface <NUM> of distal face <NUM>, into a space <NUM> that lies between (i) the PCB and conduit, and (ii) the tip electrode. (Space <NUM> is typically situated primarily adjacent to circumferential face <NUM> of the tip electrode. ) After flowing, through space <NUM>, along the inner surface of the tip electrode, the fluid reach fluid apertures <NUM>, and exits from the tip electrode via the fluid apertures.

Typically, the fluid, as it flows distally through the lumen of the catheter, is contained by the catheter, such that all, or at least a substantial majority of, the fluid reaches opening <NUM> of the conduit, and then flows proximally through space <NUM>, as described above. In this regard, it is noted that any slots <NUM> adjacent to tab <NUM> are typically relatively narrow, such that relatively little fluid escapes from slots <NUM>. It is further noted that any fluid that escapes through slots <NUM>, between segments of tube <NUM>, typically does not reach space <NUM>; rather, the path of this fluid is blocked by tip electrode <NUM>.

Notwithstanding the above, in some embodiments, catheter <NUM> comprises a fluid-delivery tube, which delivers fluid to the distal end of the catheter. For example, the distal end of such a fluid-delivery tube may be connected to the proximal end of conduit <NUM>, such that fluid flows through the fluid-delivery tube to conduit <NUM>, and then through conduit <NUM> as described above. Alternatively, for example, the distal end of such a fluid-delivery tube may be immediately proximal to (e.g., within <NUM> of) inner surface <NUM>, such that the fluid reaches inner surface <NUM> immediately upon exiting the fluid-delivery tube.

In some embodiments, catheter <NUM> does not comprise conduit <NUM>. In such embodiments, the portion of the PCB that is distal to tube <NUM> may be closed (i.e., the openings between the PCB splines may be closed), such that the PCB functions as a conduit, in that the fluid flows through the PCB to the distal face of the tip electrode.

Typically, the PCB and conduit are positioned within the tip electrode such that space <NUM> is relatively narrow. For example, the portion of the space that is between the PCB and the tip electrode may be less than <NUM> in the radial direction, i.e., the width W1 of the space, measured between the PCB and the inner surface of the tip electrode, may be less than <NUM>. (Assuming the thickness of the PCB is approximately <NUM>, this implies that the portion of the space between conduit <NUM> and the inner surface of the tip electrode may be less than <NUM>. ) The narrowness of space <NUM> forces the fluid to flow near the inner surface of tip electrode <NUM>, along a large portion of this surface, such that a relatively large amount of heat is transferred from the tip electrode to the fluid.

Typically, the majority of the fluid apertures are in the circumferential face of the tip electrode, rather than the distal face, such that relatively little fluid escapes from the catheter, prior to flowing through space <NUM>. Thus, a relatively large amount of heat may be transferred from the tip electrode to the fluid. For example, in some embodiments, distal face <NUM> does not have any fluid apertures, such that all of the fluid is forced into space <NUM>. Alternatively, some fluid apertures may be positioned within distal face <NUM>.

Typically, distal opening <NUM> is positioned relatively close to distal face <NUM>, e.g., within <NUM> of the distal face. Typically, the distal end of the conduit is flush with the distal end of the PCB, with distal opening <NUM> being aligned with distal opening <NUM> of the PCB. Thus, all of the fluid exiting through distal opening <NUM> is forced through distal opening <NUM>, emerging from distal opening <NUM> within a small distance D1, which may be less than <NUM>, of distal face <NUM>.

Were the conduit positioned more proximally, some of the fluid exiting from opening <NUM> might flow directly to the fluid apertures, without first flowing along the inner surface of the tip electrode. By positioning the conduit near the distal face, therefore, the fluid is forced to flow along the inner surface of the tip electrode, prior to exiting from the tip electrode.

As described above, <FIG> shows a flow pattern according to which the fluid flows, along the inner surface of the tip electrode, mainly in a proximal direction. Alternatively or additionally, the fluid may flow in the opposite longitudinal direction, i.e., the distal direction, along the inner surface of the tip electrode. For example, tabs <NUM>, and/or other portions of conduit <NUM> (or of any other structure positioned within the tip electrode), may be shaped to define one or more circumferential (or "side") openings <NUM>, such that the irrigating fluid flows through openings <NUM> into space <NUM>, flows distally through space <NUM>, and exits through the fluid apertures. (In such embodiments, the distal end of the conduit is typically closed, such that fluid does not flow directly to the distal face of the tip electrode. ) In such embodiments, the majority, or all, of the fluid apertures may be located on the distal face of the tip electrode, such that most, or all, of the fluid forced into space <NUM> flows along most of the length of the tip electrode, prior to exiting from the tip electrode.

Reference is now made to <FIG>, which is a schematic illustration of an ablation catheter, in accordance with some embodiments of the present invention. In the embodiment shown in <FIG>, tip electrode <NUM> and tube <NUM> are formed from a single piece of material, e.g., a single piece of nitinol, such that the tip electrode is continuous with the tube. (Stated differently, in the embodiment of <FIG>, the distalmost segment of tube <NUM> functions as the tip electrode. ) This embodiment thus differs from previously-described embodiments, in which the tip electrode and the tube are manufactured separately, and are then physically and/or electrically coupled to one another. Advantages of such a design include simplicity of, and reduced cost of, manufacture.

Claim 1:
Apparatus, comprising:
a catheter (<NUM>);
a tip electrode (<NUM>), at a distal end of the catheter, shaped to define a plurality of fluid apertures (<NUM>); and
a structure, within the tip electrode, configured such that fluid passed distally through a lumen of the catheter flows in a longitudinal direction through a space (<NUM>) between the structure and an inner surface of the tip electrode, prior to exiting through the fluid apertures, wherein the structure comprises a conduit (<NUM>) configured such that at least some of the fluid exits a distal opening (<NUM>) of the conduit, and is then deflected into the space by a distal face (<NUM>) of the tip electrode, and wherein the structure is configured such that the fluid exits the fluid apertures directly from the space between the structure and the inner surface of the tip electrode,
characterised in that
the structure is shaped to define one or more circumferential openings (<NUM>), such that at least some of the fluid flows into the space through the circumferential openings.