Patent Publication Number: US-2019192222-A1

Title: Open-irrigated ablation catheter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Non Provisional application Ser. No. 15/195,995 filed Jun. 28, 2016, which claims priority to Provisional Application No. 62/186,359, filed Jun. 29, 2015, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to medical devices. More specifically, the invention relates to devices and systems for performing ablation and mapping functions. 
     BACKGROUND 
     Aberrant conductive pathways disrupt the normal path of the heart&#39;s electrical impulses. For example, conduction blocks can cause the electrical impulse to degenerate into several circular wavelets that disrupt the normal activation of the atria or ventricles. The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms called arrhythmias. Ablation is one way of treating arrhythmias and restoring normal conduction. The sources of the aberrant pathways (called focal arrhythmia substrates) are located or mapped using mapping electrodes situated in a desired location. After mapping, the physician may ablate the aberrant tissue. In radio frequency (RF) ablation, RF energy is directed from the ablation electrode through tissue to an electrode to ablate the tissue and form a lesion. 
     SUMMARY 
     In an Example 1, an open-irrigated catheter system comprises a catheter body; a tip assembly, coupled to a distal end of the catheter body, and having an exterior wall that defines an interior region within the tip assembly, wherein the exterior wall includes a plurality of proximal irrigation ports and a plurality of distal irrigation ports, and wherein the exterior wall is conductive for delivering radio frequency (RF) energy for an RF ablation procedure; at least one fluid chamber defined within the interior region, wherein the at least one fluid chamber is in fluid communication with at least one of the plurality of proximal irrigation ports and the plurality of distal irrigation ports; and at least one fluid lumen extending from a fluid source, through the catheter body, to the tip assembly, wherein the at least one fluid lumen is in fluid communication with the at least one fluid chamber. 
     In an Example 2, the system of Example 1, wherein the plurality of proximal irrigation ports comprises at least 12 irrigation ports. 
     In an Example 3, the system of Example 2, wherein the plurality of proximal irrigation ports comprises at least 36 irrigation ports. 
     In an Example 4, the system of any of Examples 1-3, wherein the plurality of proximal irrigation ports is arranged in an evenly-spaced array positioned circumferentially around a proximal portion of the tip assembly. 
     In an Example 5, the system of Example 4, wherein the array comprises at least one row. 
     In an Example 6, the system of Example 5, the array comprising a first row of irrigation ports and a second row of irrigation ports, wherein the second row is aligned with the first row to form a plurality of pairs of longitudinally-aligned irrigation ports. 
     In an Example 7, the system of Example 5, the array comprising a first row of irrigation ports and a second row of irrigation ports, wherein the second row is offset from the first row. 
     In an Example 8, the system of any of Examples 1-7, wherein the at least one fluid chamber comprises a proximal fluid chamber and a distal fluid chamber, wherein the proximal fluid chamber is in fluid communication with the plurality of proximal irrigation ports, and wherein the distal fluid chamber is in fluid communication with the plurality of distal irrigation ports. 
     In an Example 9, the system of Example 8, wherein the at least one fluid lumen comprises a first fluid lumen and a second fluid lumen, wherein the first fluid lumen is in fluid communication with the proximal fluid chamber and wherein the second fluid lumen is in fluid communication with the distal fluid chamber. 
     In an Example 10, the system of Example 9, wherein the fluid source provides a first stream of fluid to the proximal fluid chamber and a second stream of fluid to the distal fluid chamber, wherein the second stream of fluid is provided at a greater flow rate than the first stream of fluid. 
     In an Example 11, the system of Example 8, wherein the at least one fluid lumen comprises a single fluid lumen that is in fluid communication with the proximal fluid chamber, the system further comprising a fluid path extending between the proximal fluid chamber and the distal fluid chamber such that the proximal fluid chamber is in fluid communication with the distal fluid chamber. 
     In an Example 12, the system of Example 11, further comprising a distal insert, wherein the fluid path is defined within the distal insert. 
     In an Example 13, the system of any of Examples 1-12, wherein the external wall includes a plurality of mapping-electrode openings, and wherein the system further comprises a plurality of mapping electrodes, wherein each of the plurality of mapping electrodes is positioned within one of the plurality of mapping-electrode openings. 
     In an Example 14, the system of any of Examples 1-13, wherein the plurality of distal irrigation ports comprises six distal irrigation ports, wherein the six distal irrigation ports are evenly-spaced circumferentially around a distal portion of the tip assembly. 
     In an Example 15, the system of any of Examples 1-14, wherein each of the proximal irrigation ports includes a diameter of between 0.00254 cm (0.001 in.) and 0.01016 cm (0.004 in.). 
     In an Example 16, an open-irrigated catheter system comprises a catheter body; a tip assembly, coupled to a distal end of the catheter body, and having an exterior wall that defines an interior region within the tip assembly, wherein the exterior wall includes a plurality of proximal irrigation ports and a plurality of distal irrigation ports, and wherein the exterior wall is conductive for delivering radio frequency (RF) energy for an RF ablation procedure; at least one fluid chamber defined within the interior region, wherein the at least one fluid chamber is in fluid communication with at least one of the plurality of proximal irrigation ports and the plurality of distal irrigation ports; and at least one fluid lumen extending from a fluid source, through the catheter body, to the tip assembly, wherein the at least one fluid lumen is in fluid communication with the at least one fluid chamber. 
     In an Example 17, the system of Example 16, wherein the plurality of proximal irrigation ports comprises at least 12 irrigation ports. 
     In an Example 18, the system of Example 17, wherein the plurality of proximal irrigation ports comprises at least 36 irrigation ports. 
     In an Example 19, the system of Example 16, wherein the plurality of proximal irrigation ports is arranged in an evenly-spaced array positioned circumferentially around a proximal portion of the tip assembly. 
     In an Example 20, the system of Example 19, wherein the array comprises at least one row. 
     In an Example 21, the system of Example 20, the array comprising a first row of irrigation ports and a second row of irrigation ports, wherein the second row is aligned with the first row to form a plurality of pairs of longitudinally-aligned irrigation ports. 
     In an Example 22, the system of Example 20, the array comprising a first row of irrigation ports and a second row of irrigation ports, wherein the second row is offset from the first row. 
     In an Example 23, the system of Example 16, wherein the at least one fluid chamber comprises a proximal fluid chamber and a distal fluid chamber, wherein the proximal fluid chamber is in fluid communication with the plurality of proximal irrigation ports, and wherein the distal fluid chamber is in fluid communication with the plurality of distal irrigation ports. 
     In an Example 24, the system of Example 23, wherein the at least one fluid lumen comprises a first fluid lumen and a second fluid lumen, wherein the first fluid lumen is in fluid communication with the proximal fluid chamber and wherein the second fluid lumen is in fluid communication with the distal fluid chamber. 
     In an Example 25, the system of Example 24, wherein the fluid source provides a first stream of fluid to the proximal fluid chamber and a second stream of fluid to the distal fluid chamber, wherein the second stream of fluid is provided at a greater flow rate than the first stream of fluid. 
     In an Example 26, the system of Example 23, wherein the at least one fluid lumen comprises a single fluid lumen that is in fluid communication with the proximal fluid chamber, the system further comprising a fluid path extending between the proximal fluid chamber and the distal fluid chamber such that the proximal fluid chamber is in fluid communication with the distal fluid chamber. 
     In an Example 27, the system of Example 26, further comprising a distal insert, wherein the fluid path is defined within the distal insert. 
     In an Example 28, the system of Example 16, wherein the external wall includes a plurality of mapping-electrode openings, and wherein the system further comprises a plurality of mapping electrodes, wherein each of the plurality of mapping electrodes is positioned within one of the plurality of mapping-electrode openings. 
     In an Example 29, the system of Example 16, wherein the plurality of distal irrigation ports comprises six distal irrigation ports, wherein the six distal irrigation ports are evenly-spaced circumferentially around a distal portion of the tip assembly. 
     In an Example 30, the system of Example 16, wherein each of the proximal irrigation ports includes a diameter of between 0.00254 cm (0.001 in.) and 0.01016 cm (0.004 in.). 
     In an Example 31, an open-irrigated catheter comprises a tip assembly having an exterior wall that defines an interior region within the tip assembly, wherein the exterior wall includes a plurality of proximal irrigation ports and a plurality of distal irrigation ports, and wherein the exterior wall is conductive for delivering radio frequency (RF) energy for an RF ablation procedure; at least one fluid chamber defined within the interior region, wherein the at least one fluid chamber is in fluid communication with at least one of the plurality of proximal irrigation ports and the plurality of distal irrigation ports; and at least one fluid lumen extending from a fluid source, through the catheter body, to the tip assembly, wherein the at least one fluid lumen is in fluid communication with the at least one fluid chamber. 
     In an Example 32, the catheter of Example 31, wherein the at least one fluid chamber comprises a proximal fluid chamber and a distal fluid chamber, wherein the proximal fluid chamber is in fluid communication with the plurality of proximal irrigation ports, and wherein the distal fluid chamber is in fluid communication with the plurality of distal irrigation ports. 
     In an Example 33, the catheter of Example 32, wherein the at least one fluid lumen comprises a first fluid lumen and a second fluid lumen, wherein the first fluid lumen is in fluid communication with the proximal fluid chamber and wherein the second fluid lumen is in fluid communication with the distal fluid chamber. 
     In an Example 34, the catheter of Example 33, wherein the fluid source provides a first stream of fluid to the proximal fluid chamber and a second stream of fluid to the distal fluid chamber, wherein the second stream of fluid is provided at a greater flow rate than the first stream of fluid. 
     In an Example 35, the catheter of Example 31, wherein the plurality of distal irrigation ports comprises six distal irrigation ports, wherein the six distal irrigation ports are evenly-spaced circumferentially around a distal portion of the tip assembly. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an illustrative mapping and ablation system that includes an open-irrigated catheter in accordance with embodiments of the invention. 
         FIGS. 2A-2D  depict an illustrative tip assembly for a mapping and ablation catheter in accordance with embodiments of the invention. 
         FIGS. 3A-3B  depict an illustrative tip assembly for a mapping and ablation catheter in accordance with embodiments of the invention. 
         FIG. 4  depicts an illustrative tip assembly for a mapping and ablation catheter in accordance with embodiments of the invention. 
         FIG. 5  depicts an illustrative tip assembly for a mapping and ablation catheter in accordance with embodiments of the invention. 
         FIG. 6  depicts an illustrative tip assembly for a mapping and ablation catheter in accordance with embodiments of the invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Embodiments of the disclosure relate to a radiofrequency (RF) ablation catheter system. In embodiments, the catheter may be a hybrid catheter, which may be configured to be used for both localized mapping and ablation functions. The hybrid catheter may be configured to provide localized, high resolution ECG signals during ablation. This localized mapping may enable the ablation procedure to be more precise than that which can be achieved with conventional, non-hybrid ablation catheters. The catheter has an open-irrigated catheter design. A cooling fluid, such as a saline, is delivered through the catheter to a tip assembly having a tissue ablation electrode, where the fluid exits through irrigation ports defined in the tissue ablation electrode to cool the electrode and surrounding tissue during ablation. Clinical benefits of such a catheter may include, but are not limited to, controlling the temperature and reducing coagulum formation on the tip of the catheter, preventing impedance rise of tissue in contact with the catheter tip, and maximizing potential energy transfer to the tissue. Additionally, the localized intra cardiac electrical activity can be recorded in real time or near-real time at the location of energy delivery. 
     A number of adverse effects may be encountered with open-irrigated RF ablation catheters and may include, for example, excessive heating of a proximal portion of the tissue ablation electrode (e.g., due to edge effect), current density concentrations (e.g., due to geometric discontinuities, radius changes, etc.), and/or the like. Some developments to address these issues have included the addition of proximal irrigation ports similar in size to the distal irrigation ports, and the replacement of larger distal irrigation ports with a large number of very small irrigation ports dispersed throughout the ablation electrode. Both of these solutions may provide some mitigation of proximal heating due to edge effect, but have a tendency to change the current pathway due to the cloud of cooling fluid that forms around the electrode. This can either result in current loss, as the current shunts through the ionic fluid and away from the target tissue, or result in excessive tissue heating, which may be a byproduct of a localized saline cloud driving too much current into the tissue. 
     Embodiments of the invention provide an open-irrigated catheter design that includes distal irrigation ports and much smaller proximal irrigation ports (that may be referred to as “micro-holes”), thereby providing cooling fluid flow to cool the proximal portion of the electrode, while maintaining the desired current pathways due to the more forceful flow of fluid from the larger distal irrigation ports.  FIG. 1  depicts a mapping and ablation system  100  that includes an open-irrigated ablation catheter  102 , according to embodiments of the invention. The illustrated catheter  102  includes a tip assembly  104  having a tissue ablation electrode  105 , with mapping microelectrodes  106 , proximal irrigation ports  108 , and distal irrigation ports  110 . The catheter  102  includes a catheter body  112  and a proximal catheter handle assembly  114 , having a handle  116 , coupled to a proximal end  118  of the catheter body  112 . The tip assembly  104  is coupled to a distal end  120  of the catheter body  112 . 
     In some instances, the mapping and ablation system  100  may be utilized in ablation procedures on a patient and/or in ablation procedures on other objects. In various embodiments, the ablation catheter  102  may be configured to be introduced into or through the vasculature of a patient and/or into or through any other lumen or cavity. In an example, the ablation catheter  102  may be inserted through the vasculature of the patient and into one or more chambers of the patient&#39;s heart (e.g., a target area). When in the patient&#39;s vasculature or heart, the ablation catheter  102  may be used to map and/or ablate myocardial tissue using the microelectrodes  106  and/or the tissue ablation electrode  105 . In embodiments, the tissue ablation electrode  105  may be configured to apply ablation energy to myocardial tissue of the heart of a patient. 
     According to embodiments, the tissue ablation electrode  105  may be, or be similar to, any number of different tissue ablation electrodes such as, for example, the IntellaTip MiFi,™ or the Blazer™ Ablation tip, both of which are available from Boston Scientific of Marlborough, Mass. In embodiments, the tissue ablation electrode  105  may have any number of different sizes, shapes, and/or other configuration characteristics. The tissue ablation electrode  105  may be any length and may have any number of the microelectrodes  106  positioned therein and spaced circumferentially and/or longitudinally about the tissue ablation electrode  105 . In some instances, the tissue ablation electrode  105  may have a length of between one (1) mm and twenty (20) mm, three (3) mm and seventeen (17) mm, or six (6) mm and fourteen (14) mm. In one illustrative example, the tissue ablation electrode  105  may have an axial length of about eight (8) mm. In another illustrative example, the tissue ablation electrode  105  may include an overall length of approximately 4-10 mm. In embodiments, the tissue ablation electrode  105  may include an overall length of approximately 4 mm, 4.5 mm, and/or any other desirable length. In some cases, the plurality of microelectrodes  106  may be spaced at any interval about the circumference of the tissue ablation electrode  105 . In one example, the tissue ablation electrode  105  may include at least three microelectrodes  106  equally or otherwise spaced about the circumference of the tissue ablation electrode  105  and at the same or different longitudinal positions along the longitudinal axis of the tissue ablation electrode  105 . 
     In embodiments, the catheter  102  may include a deflectable catheter region  124  configured to allow the catheter  102  to be steered through the vasculature of a patient, and which may enable the tissue ablation electrode  105  to be accurately placed adjacent a targeted tissue region. A steering wire (not shown) may be slidably disposed within the catheter body  112 . The handle assembly  114  may include one or more steering members  126  such as, for example, rotating steering knobs that are rotatably mounted to the handle  116 . Rotational movement of a steering knob  126  relative to the handle  116  in a first direction may cause a steering wire to move proximally relative to the catheter body  112  which, in turn, tensions the steering wire, thus pulling and bending the catheter deflectable region  124  into an arc; and rotational movement of the steering knob  126  relative to the handle  116  in a second direction may cause the steering wire to move distally relative to the catheter body  112  which, in turn, relaxes the steering wire, thus allowing the catheter  102  to return toward its original form. To assist in the deflection of the catheter  102 , the deflectable catheter region  124  may be made of a lower durometer plastic than the remainder of the catheter body  112 . 
     According to embodiments, the catheter body  112  includes one or more cooling fluid lumens (not shown) and may include other tubular element(s) to provide desired functionality to the catheter  102 . The addition of metal in the form of a braided mesh layer sandwiched in between layers of plastic tubing may be used to increase the rotational stiffness of the catheter  102 . 
     The illustrated system  100  includes an RF generator  128  used to generate RF energy for use during an ablation procedure. The RF generator  128  may include an RF source  130  that produces the RF energy and a controller  132  for controlling the timing, level, and/or other characteristics of the RF energy delivered through the tip assembly  104 . The RF generator  128  may be configured to deliver ablation energy to the ablation catheter  102  in a controlled manner in order to ablate the target tissue sites. Ablation of tissue within the heart is well known in the art, and thus for purposes of brevity, the RF generator  128  will not be described in further detail. Further details regarding RF generators are provided in U.S. Pat. No. 5,383,874, which is expressly incorporated herein by reference in its entirety for all purposes. 
     The illustrated system  100  also includes a fluid source  134 , having a fluid reservoir  136  and a pump  138  for providing cooling fluid, such as a saline, through the catheter  102  and out through the irrigation ports  108  and  110 . A mapping signal processor  140  may be connected to the electrodes  106 , also referred to herein as microelectrodes. The mapping signal processor  140  and electrodes  106  may be configured to detect electrical activity of the heart. This electrical activity may be evaluated to analyze an arrhythmia and to determine where to deliver the ablation energy as a therapy for the arrhythmia. Although the mapping processor  140  and RF generator  128  are shown as discrete components, they can alternatively be incorporated into a single integrated device. 
     One of ordinary skill in the art will understand that various components such as, for example, aspects of the RF generator  128 , the fluid source,  134 , and/or the mapping signal processor  140 , may be implemented using software, hardware, and/or firmware. Various methods of operation may be implemented as a set of instructions contained on a computer-accessible medium capable of directing a processor to perform the respective method. 
     The RF ablation catheter  102  as described may be used to perform various diagnostic functions to assist the physician in an ablation treatment. For example, in some embodiments, the catheter  102  may be used to ablate cardiac arrhythmias, and at the same time provide real-time assessment of a lesion formed during RF ablation. Real-time assessment of the lesion may involve any of monitoring surface and/or tissue temperature at or around the lesion, reduction in the electrocardiogram signal, a drop in impedance, direct and/or surface visualization of the lesion site, and imaging of the tissue site (e.g., using computed tomography, magnetic resonance imaging, ultrasound, etc.). In addition, the presence of the microelectrodes within the RF tip electrode can operate to assist the physician in locating and positioning the tip electrode at the desired treatment site, and to determine the position and orientation of the tip electrode relative to the tissue to be ablated. 
     Illustrative catheters that may be used as the catheter  102  may include, among other ablation and/or mapping catheters, those described in U.S. patent application Ser. No. 12/056,210 filed on Mar. 26, 2008, and entitled HIGH RESOLUTION ELECTROPHYSIOLOGY CATHETER, and U.S. Pat. No. 8,414,579 filed on Jun. 23, 2010, entitled MAP AND ABLATE OPEN IRRIGATED HYBRID CATHETER, which are both hereby incorporated herein by reference in their entireties for all purposes. Alternatively, or in addition, catheters that may be used as the catheter  102  may include, among other ablation and/or mapping catheters, those described in U.S. Pat. No. 5,647,870 filed on Jan. 16, 1996, as a continuation of U.S. Serial No. 206,414, filed Mar. 4, 1994 as a continuation-in-part of U.S. Serial Number 33,640, filed Mar. 16, 1993, entitled MULTIPLE ELECTRODE SUPPORT STRUCTURES, U.S. Pat. No. 6,647,281 filed on Apr. 6, 2001, entitled EXPANDABLE DIAGNOSTIC OR THERAPEUTIC APPARATUS AND SYSTEM FOR INTRODUCING THE SAME INTO THE BODY, and U.S. Pat. No. 8,128,617 filed on May 27, 2008, entitled ELECTRICAL MAPPING AND CRYO ABLATING WITH A BALLOON CATHETER, which are all hereby incorporated herein by reference in their entireties for all purposes. 
       FIGS. 2A-2D  illustrate a hybrid catheter  200 , according to embodiments of the invention, having proximal and distal irrigation ports and three microelectrodes used to perform a mapping function. The illustrated catheter  200  includes a tip assembly  202 , having a tip body  204 , and an open-irrigated ablation electrode  206  used to perform mapping and ablation functions. In embodiments, the ablation functions may be performed, in part, by the ablation electrode  206 , which may function as an RF electrode. The mapping functions may be performed, at least in part, by mapping electrodes  208 . 
     With particular reference to  FIG. 2B , the illustrated tip assembly  202  includes a generally hollow ablation electrode  206  having a distal insert  210  disposed therein and configured to separate a proximal fluid chamber  212  and distal fluid chamber  214 . The tip assembly  202  has an open interior region  216  defined by an exterior wall  218  of the tip assembly  202 . Fluid flow through the chambers  212  and  214  may be used to provide internal, targeted cooling of portions of the ablation electrode  206 . In the illustrated embodiments, the hollow tip body  204  has a generally cylindrical shape, but in other embodiments, the tip body  204  may have any number of different shapes such as, for example, an elliptical shape, a polygonal shape, and/or the like. By way of an example and not limitation, embodiments of the tip assembly  202  may have a diameter on the order of about 0.08-0.1 inches, a length on the order of about 0.2-0.3 inches, and an exterior wall  218  with a thickness on the order of about 0.003-0.004 inches. 
     As the terms are used herein with respect to ranges of measurements (such as those disclosed immediately above), “about” and “approximately” may be used, interchangeably, to refer to a measurement that includes the stated measurement and that also includes any measurements that are reasonably close to the stated measurement, but that may differ by a reasonably small amount such as will be understood, and readily ascertained, by individuals having ordinary skill in the relevant arts to be attributable to measurement error, differences in measurement and/or manufacturing equipment calibration, human error in reading and/or setting measurements, adjustments made to optimize performance and/or structural parameters in view of differences in measurements associated with other components, particular implementation scenarios, and/or the like. 
     According to embodiments, the distal insert  210  may be made of plastic components such as, for example, Ultem. Various distal insert embodiments include design elements configured for self-positioning the distal insert during manufacturing. Such embodiments may facilitate reducing the number of processing steps to join the distal insert to the tip electrode. Additionally, various distal insert embodiments may be configured for self-alignment and configured to isolate electrical components from the irrigation fluid. Some embodiments are configured for self-alignment, some embodiments are configured to isolate electrical components from the irrigation fluid, and some embodiments are configured for both self-alignment and for isolating electrical components from the irrigation fluid. Various designs of distal inserts as described above are described in U.S. Pat. No. 8,414,579, the entirety of which is hereby incorporated by reference herein for all purposes. 
     In embodiments, the ends of the distal insert  210  may be encapsulated with adhesives to provide a seal between the proximal and distal chambers  212  and  214 . In embodiments, the distal insert  210  may include openings or apertures  220 , each opening 220 sized to receive a microelectrode  208  and a corresponding noise artifact isolator  222 . These microelectrodes  208  may be used to image localized intra-cardiac activity. The microelectrodes  208  may, for example, be used to record high resolution, precise localized electrical activity, to prevent excessive heating of the ablation electrode  206 , to allow greater delivery of power, to prevent the formation of coagulum and to provide the ability to diagnose complex ECG activity. In embodiments, the microelectrodes  208  are small, independent diagnostic sensing electrodes embedded within the walls of the ablation electrode  206  of the RF ablation catheter  200 . The noise artifact isolator  222  electrically isolates the small electrodes  208  from the conductive exterior wall  218  of the ablation electrode  206 . According to embodiments, the noise artifact isolator  222  may be a polymer-based material sleeve and/or adhesive that encapsulates the microelectrodes  208 . The isolator  222  isolates the noise entrance creating a much cleaner electrogram during an RF ablation mode. These electrically-isolated microelectrodes  208  are able to sense highly localized electrical activity, avoid a far-field component, and simultaneously achieve the ability to ablate tissue without noise artifact during RF mode. 
     The illustrated distal insert  210  also includes a fluid conduit or passage  224  to permit fluid to flow from the proximal fluid reservoir  212  to the distal fluid reservoir  214 , a thermocouple opening 226 sized to receive a thermocouple  228 , and openings 230 sized to receive electrical conductors  232  used to provide electrical connections to the microelectrodes  208 . Also illustrated is a thermocouple wire  234  connected to the thermocouple  228 . According to embodiments, the distal insert  210  may be fabricated from stainless steel, a polymer, and/or the like. In embodiments, a proximal insert (not shown) may be disposed in an interior region  236  of a proximal portion  238  of the tip body  204 . The proximal insert may, in embodiments, prevent fluid from flowing back out of the proximal fluid chamber  212 , and may include apertures for the wires, conductors, and one or more fluid conduits. 
     According to embodiments, the ablation electrode  206  may be formed from a conductive material. For example, some embodiments use a platinum-iridium alloy. Some embodiments use an alloy with approximately 90% platinum and 10% iridium. The conductive material of the ablation electrode  206  is used to conduct RF energy used to form legions during the ablation procedure. In embodiments, the ablation electrode  206  includes a plurality of distal irrigation ports  240  near the distal end  242  of the ablation electrode  206 , and a plurality of proximal irrigation ports  244  near the proximal end  246  of the ablation electrode  206 . By way of example and not limitation, in embodiments, the distal irrigation ports  240  may each have a diameter approximately within a range of 0.01 to 0.02 inches. Fluid, such as a saline solution, flows from the distal fluid reservoir  214 , through these ports  240 , to the exterior of the catheter  200 . This fluid is used to cool the ablation electrode  206  and the tissue near the electrode  206 . This temperature control may facilitate reduction of coagulum formation on the tip of the catheter  200 , prevents impedance rise of tissue in contact with the catheter tip, and increases energy transfer to the tissue because of the lower tissue impedance. 
     According to embodiments, the proximal irrigation ports  244  are configured to facilitate a fluid flow out of the ablation electrode  206  to minimize char formation on the proximal region of the ablation electrode  206 . Providing proximal irrigation ports may also facilitate minimizing risk of thrombus and the potential for emboli. According to embodiments, the proximal irrigation ports are relatively small as compared, for example, to the distal irrigation ports. For example, in embodiments, each of the proximal irrigation ports  244  may have a diameter of approximately 0.00254 cm (0.001 in.) to 0.01016 cm (0.004 in.). In this manner, conventional flow characteristics associated with distal irrigation ports may be maintained, so as to maintain effective RF conduction for ablation. That is, for example, the proximal irrigation ports may be configured to provide a flow rate sufficient for achieving desired cooling results external to the ablation electrode  206 , while maintaining desired flow characteristics from the distal irrigation ports. The arrangement, size, and/or number of proximal irrigation ports may be adjusted based on the characteristics of the distal irrigation ports, the fluid chambers, the tip, and/or the like. In embodiments, the catheter  200  may include 6 distal irrigation ports  240  and between 12 and 36 proximal irrigation ports  244 . In other embodiments, the catheter may include more than 36 proximal irrigation ports  244  such as, for example, 54 ports, 72 ports, and/or the like. 
     Various embodiments isolate the microelectrode signal wires from the cooling fluid circulating in the proximal chamber of the hollow ablation electrode, and thus are expected to reduce the noise that is contributed form the internal cooling fluid circulation. The fluid seal can be provided without bonding or adhesive. The electrical components within the tip are isolated form the cooling flow of irrigation fluid while the irrigation fluid maintains internal cooling of the proximal and distal portions of the tip electrode. Further, such designs may have the potential of increasing the accuracy of the temperature readings from the thermocouple, and are described in U.S. Pat. No. 8,414,579, incorporated above. 
       FIGS. 3A and 3B  illustrate a hybrid catheter  300 , according to embodiments of the invention, having a plurality of distal irrigation ports  302  and a plurality of proximal irrigation ports  304 . The hybrid catheter  300  includes a tip assembly  306 , having an ablation electrode  308 . The ablation electrode  308  includes an external wall  310  that encloses an interior region  312 . The interior region includes a proximal fluid chamber  314  and a distal fluid chamber  316 , separated by a distal insert  318 . A plurality of mapping electrodes  320  may be disposed in the external wall  310 . A cooling lumen  322  extends from a fluid source (not shown) to the distal fluid chamber  316 , and provides fluid to the proximal and distal fluid chambers  314  and  316 . As shown, for example, the cooling lumen  322  includes holes  324  to enable a portion of the fluid that is provided to the cooling lumen  322  to pass into the proximal fluid chamber  314  to cool a proximal portion  326  of the ablation electrode  308 . The fluid from the proximal chamber  314  also is passed out of the ablation electrode  308  via the proximal irrigation ports  304 . The remainder of the fluid provided to the cooling lumen  322  passes to the distal fluid chamber  316  and at least a portion of that fluid is passed out of the ablation electrode  308  via the distal irrigation ports  302 . 
     According to embodiments, a catheter may include a separate cooling lumen for providing fluid to each of the proximal and distal fluid chambers. In embodiments, both cooling lumens may be coupled to the same fluid source and/or a separate fluid source.  FIG. 4  illustrates a perspective cutaway view of a hybrid catheter tip assembly  400 , according to embodiments of the invention, having an ablation electrode  402 . The ablation electrode  402  includes an external wall  404  that encloses an interior region  406 . The interior region  406  includes a proximal fluid chamber  408  and a distal fluid chamber  410 , separated by a distal insert  412 . A plurality of mapping electrodes  414  may be disposed in the external wall  404 . The external wall  404  may also include a plurality of distal irrigation ports  416  and a plurality of proximal irrigation ports  418 . A first cooling lumen  420  extends from a fluid source (not shown) to the proximal fluid chamber  408 , and provides fluid to the proximal fluid chamber  418 . A second cooling lumen  422  extends from a fluid source (not shown) to the distal fluid chamber  410 , and provides fluid to the distal fluid chamber  410 . The fluid from the proximal chamber  408  is passed out of the ablation electrode  402  via the proximal irrigation ports  418  and the fluid from the distal fluid chamber  410  is passed out of the ablation electrode  402  via the distal irrigation ports  416 . 
     Electrical signals, such as electrocardiograms (ECGs), are used during a cardiac ablation procedure to distinguish viable tissue from not viable tissue. If ECG amplitudes are seen to attenuate during the delivery of RF energy into the tissue, the delivery of RF energy into that specific tissue may be stopped. However, noise on the ECG signals makes it difficult to view attenuation. It is currently believed that internal cooling fluid circulation, cooling fluid circulating externally in contact with other electrodes, and/or fluid seepage in between the electrodes and their housing may cause the noise on this type of ablation catheter. 
       FIG. 5  depicts a hybrid catheter  500  in accordance with embodiments of the invention. The catheter  500  may be, include, or be similar to, the catheter  102  depicted in  FIG. 1 , the catheter  200  depicted in  FIGS. 2A-2D , the catheter  300  depicted in  FIGS. 3A and 3B , and/or the catheter tip assembly  400  depicted in  FIG. 4 . The illustrated catheter  500  includes a tip assembly  502  coupled to a distal end  504  of a catheter body  506 . The catheter body  506  includes a plurality of ring electrodes  508 . In embodiments, the catheter body  506  may include three ring electrodes  508  or any other desirable number of ring electrodes  508 . As illustrated, the tip assembly  502  includes an ablation electrode  510  having a plurality of mapping electrodes  512 , a plurality of distal irrigation ports  514 , and a plurality of proximal irrigation ports  516 . The proximal irrigation ports  516  are arranged in a first row  518  and a second row  520 . Each row  518  and  520  may include a plurality of proximal irrigation ports  516  evenly spaced circumferentially around the ablation tip electrode  510 . In embodiments, the ablation electrode  510  may include one row of proximal irrigation ports  516 , two rows of proximal irrigation ports  516 , three rows of proximal irrigation ports  516 , four rows of proximal irrigation ports  516 , or any other desired number of rows, each row having any number of proximal irrigation ports that may, for example, be evenly spaced circumferentially. 
     The proximal irrigation ports  516  depicted in  FIG. 5 , and described above, may be arranged in multiple rows, where each row is offset from an adjacent row. According to embodiments, proximal irrigation ports may be arranged in circumferential rows that are aligned to form multiple longitudinal columns of at least two irrigation ports.  FIG. 6  depicts a hybrid catheter  600  in accordance with embodiments of the invention. The catheter  600  may be, include, or be similar to, the catheter  500  depicted in  FIG. 5 . The illustrated catheter  600  includes a tip assembly  602  coupled to a distal end  604  of a catheter body  606 . The catheter body  606  includes a plurality of ring electrodes  608 . In embodiments, the catheter body  606  may include three ring electrodes  608  or any other desirable number of ring electrodes  608 . As illustrated, the tip assembly  602  includes an ablation electrode  610  having a plurality of mapping electrodes  612 , a plurality of distal irrigation ports  614 , and a plurality of proximal irrigation ports  616 . The proximal irrigation ports  616  are arranged in a first row  618  and a second row  620 . Each row  618  and  620  may include a plurality of proximal irrigation ports  616  evenly spaced circumferentially around the ablation electrode  610 . The proximal irrigation ports  616  may be arranged in circumferential rows  618  and  620  that are aligned to form multiple longitudinal columns  622  of at least two irrigation ports  616  each. The ablation electrode  610  may include any desired number of rows and/or columns of proximal irrigation ports  616 . 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.