Monophasic catheter with microelectrodes and method of using same for localized detection of signals - Patents.com

Abstract

A catheter having an ablation electrode with at least one microelectrode configured to detect monophasic action potential signals and a force sensor configured to detect the contact force of the microelectrode against a tissue surface can be used to acquire pre-ablation and post-ablation MAP signals having monophasic characteristics to determine the presence or absence of monophasic characteristics in the latter when assessing the quality or success of the ablation procedure and lesion formation.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 842,439, filed May 2, 2019, the entire contents of which are incorporated herein by reference.

[0002] FIELD OF THEINVENTION FIELD OF THE DISCLOSURE This disclosure relates generally to electrophysiology catheters, and more particularly to irrigated ablation catheters. [Background technology]

[0003] Electrical activity at a point in the heart is usually measured by advancing a multi-electrode catheter to simultaneously measure electrical activity at multiple points in the heart chamber. The recording resulting from the time-varying electrical potentials measured by one or more electrodes is known as an electrogram. Electrograms can be measured with unipolar or bipolar leads and are used, for example, to measure the onset of electrical propagation at a point, known as the local activation time. Various electrode designs are known for different purposes. In particular, catheters with basket-shaped electrode arrays are known and described, for example, in U.S. Pat. No. 5,772,590, the disclosure of which is incorporated herein by reference.

[0004] Electrograms are biphasic and global signals, therefore a sensor within the ventricle can detect local electrical activity, i.e., far-field electrical activity, i.e., ambient electrical activity radiating away from the sensor, that can distort or obscure signals radiating at or near the sensor location. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, in some cases, it is desirable to obtain a local signal in the form of a monophasic action potential signal. The monophasic action potential (MAP) is an extracellularly recorded waveform that can reproduce the repolarization time course of the transmembrane action potential (TAP) with high fidelity. Applicants have recognized the need to provide a catheter capable of obtaining a local signal in the form of a MAP signal. [Means for solving the problem]

[0006] MAPs have been used electrophysiologically to allow for a better understanding of tissue responses at the cellular level. MAPs can reproduce the repolarization time course of the transmembrane action potential (TAP) with high fidelity using active and non-active electrodes. An embodiment of the present invention includes a catheter with a microelectrode and a thermocouple so that the microelectrode can be utilized to study MAPs on local tissue to induce local therapeutic injury on the tissue.

[0007] An embodiment of the present invention obtains a MAP signal by using an aspiration catheter with a sensing catheter to create a localized trauma in the tissue that causes a response in a measurable signal from the tissue. The MAP signal is used to indicate the effects of drugs, disease or healthy tissue, among other diagnostic indicators. An embodiment of the present invention also obtains a MAP signal by applying pressure to the tissue using a catheter to obtain a reversible localized injury on the tissue. Either of these techniques allows the medical provider to infer the cellular level response (i.e., signal) due to the localized trauma so that a therapeutic response can be devised.

[0008] An embodiment of the invention includes a catheter with multiple microelectrodes with thermocouples to obtain a MAP signal by using contact force-applying microelectrodes to provide an optimal force to the tissue (for reversible localized injury) while measuring a response signal from the tissue with the force-applying microelectrodes. The MAP signal can be measured similarly to non-force-applying microelectrodes.

[0009] The microelectrodes have a roughened or fractured surface that allows for extraction of high signal relative to noisy electrical signals from localized tissue damage, while allowing for consistent force application by the contact force sensor via the smaller surface area over which the microelectrodes are applied.

[0010] In some embodiments, the catheter comprises: an elongated catheter shaft; a distal portion, an ablation electrode having a sidewall and an outer surface, the sidewall having at least one aperture; at least one microelectrode configured to sense monophasic action potential signals, the microelectrode having a distal sensing portion protruding from an outer surface of the electrode and a proximal portion extending through a single hole; and a force sensor configured to sense a contact force of the at least one microelectrode against the tissue surface.

[0011] In some embodiments, the distal sensing portion has a spherical configuration.

[0012] In some embodiments, the distal sensing portion protrudes a predetermined distance from the distal end of the ablation electrode.

[0013] In some embodiments, the distal sensing portion has a fractured surface.

[0014] In some embodiments, the distal sensing portion has a coating from the group consisting of silver chloride, iridium oxide, and titanium oxide.

[0015] In some embodiments, the distal sensing portion has an etched surface.

[0016] In some embodiments, the distal sensing portion has a width in the range of about 0.014 mm to 0.015 mm.

[0017] In some embodiments, the distal sensing portion is configured to cause reversible localized damage to tissue.

[0018] In some embodiments, the distal portion includes a plurality of microelectrodes, each microelectrode having a respective distal sensing portion and a respective proximal portion, each proximal portion extending through a respective hole formed in a sidewall of the ablation electrode.

[0019] In some embodiments, the sidewall of the ablation electrode includes at least one blind channel and at least one thermocouple wire pair within the blind channel.

[0020] In some embodiments, the thermocouple wire pair has a non-linear configuration to provide at least one contact surface with the inner surface of the blind passage.

[0021] In some embodiments, the method of using a catheter having a plurality of microelectrodes includes: - placing a catheter having one or more microelectrodes in tissue contact at a first location along a desired ablation pattern; - acquiring a pre-ablation MAP signal sensed by one or more microelectrodes at a first location, the MAP signal having a monophasic characteristic; - performing an ablation with the catheter at a first location; - acquiring a post-ablation MAP signal sensed by a microelectrode at a first location; - repositioning the catheter having one or more microelectrodes in tissue contact at a second location along the desired ablation pattern only when the post-ablation MAP signal lacks monophasic characteristics.

[0022] In some embodiments, the method comprises: - re-performing the ablation at the first location when at least a portion of the monophasic characteristic remains present in the post-ablation MAP signal. [Brief description of the drawings]

[0023] These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a schematic, pictorial illustration of a catheter ablation system, according to an embodiment. [Diagram 2] FIG. 2 is a side perspective view of a distal portion of a single-phase capable catheter having multiple microelectrodes suitable for use with the system of FIG. 1, according to an embodiment. [Diagram 3] FIG. 3 is a side cross-sectional view of the distal portion of FIG. 2. [Figure 4A] Pre-ablation ECG with microelectrodes detecting the MAP signal. [Figure 4B] 3D electroanatomical map and post-ablation ECG with microelectrodes in the absence of MAP signal after successful ablation. [Figure 4C] 13 is a post-microelectrode ablation ECG after movement of the microelectrode to a new tissue target location. [Diagram 5] FIG. 3 is a side cross-sectional view of the distal portion of FIG. 2 with the sensing portion of the microelectrode generally embedded in tissue with sufficient force to create a reversible localized lesion for detecting an ECG signal having MAP characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. The description clearly enables one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is currently contemplated to be the best mode of carrying out the invention.

[0025] The term "about" or "approximately" as used herein with respect to any numerical value or range of values ​​indicates an appropriate and suitable dimensional tolerance that allows a portion of a component or a collection of components to function for its intended purpose as described herein. More specifically, "about" or "approximately" can refer to a range of values ​​of ±20% of the recited value, e.g., "about 90%" can refer to a range of values ​​of 71% to 99%. Additionally, as used herein, the terms "patient," "host," "user," and "subject" refer to any human or animal subject and are not intended to limit the system or method to use in humans, although use of the invention in human patients represents a preferred embodiment.

[0026] overview 1 and 2, a catheter 10 that can be used in minimally invasive procedures such as ablation of cardiac tissue includes an elongated catheter shaft 12 and a short deflection section 14 distal to the catheter shaft 12, which can be deflected in one or two directions. A preferred embodiment of the catheter shaft 12 and deflection section 14 is described in U.S. Patent Application No. 15 / 925,521, filed March 19, 2018, entitled CATHETER WITH MULTIFUNCTIONAL MICROINJECTION-MOLDED HOUSING, the entire disclosure of which is incorporated herein by reference. Distal to the deflection section 14 is a distal portion 15 that includes a force sensor 40 and a tip electrode 21 that supports a plurality of microelectrodes 17 and a plurality of thermocouples 18. The catheter also includes a control handle 16 proximal to the catheter shaft 12.

[0027] System Description 1 is a schematic, pictorial diagram of a catheter ablation system 100. In system 100, a catheter 10 is inserted into the vascular system of a patient 11 and into a heart chamber 13. The catheter is used by an operator 19 of system 100 during a procedure that typically includes performing an ablation of the patient's cardiac tissue.

[0028] The operations, functions, and behavior of the system 100 are managed by a system controller 130, which includes a processing unit 132 in communication with a memory 134 in which software for the operation of the system 100 is stored. In some embodiments, the controller 130 is an industry-standard personal computer that includes a general-purpose computer processing unit. However, in some embodiments, at least some of the operations, functions, or behavior of the controller are implemented using custom-designed hardware and software, such as, for example, an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). In some embodiments, the controller 130 is managed by an operator 19 using a pointing device 136 and a graphical user interface (GUI) 138, which allow the operator to set parameters of the system 100. The GUI 138 also typically displays the results of the procedure to the operator on a display monitor 140.

[0029] The software in memory 134 may be downloaded to the controller in electronic form, for example over a network. Alternatively or additionally, the software may be provided on a non-transitory tangible medium, such as an optical, magnetic, or electronic storage medium.

[0030] The electrical components, including the electrodes, thermocouples, and position (location or orientation) sensors of the distal portion 15, are connected to the system controller 130 by conductors passing through the catheter shaft 12 and the deflection section 14. In addition to being used for ablation, the electrodes may perform other functions known in the art. The system controller 130 may distinguish currents related to different functions of the electrical components by frequency multiplexing. For example, radio frequency (RF) ablation forces are delivered at frequencies on the order of several hundred kHz, while the position sensing frequency can be at a frequency of about 1 kHz. A method for assessing the location of the distal portion 15 using impedance measured to the electrodes is disclosed in U.S. Pat. No. 8,456,182, entitled "Current Localization Tracker," by Bar-Tal et al., which is incorporated herein by reference in its entirety.

[0031] 1, system controller 130 includes a force module 148, an RF ablation module 150, an irrigation module 152, a tracking module 154, a temperature sensing module 156, and a MAP module 157. System controller 130 uses force module 148 to generate signals and measure signals provided to and received from force sensors 40 in distal portion 15 to measure the magnitude and direction of forces on distal portion 15. System controller 130 uses ablation module 150 to monitor and control ablation parameters, such as the level of ablation power applied via one or more electrodes of distal portion 15. Ablation module 150 includes an RF generator (not shown) and controls the power / wattage and duration of the ablation applied.

[0032] Typically, during ablation, heat is generated in one or more electrodes activated by the ablation module 150, as well as in the surrounding area. To dissipate the heat and improve the efficiency of the ablation process, the system controller 130 monitors the temperature of different portions / surfaces of the distal portion 15 and supplies irrigation fluid to the distal portion 15. The system controller 130 uses the irrigation module 152 to monitor and control irrigation parameters, such as the flow rate and temperature of the irrigation fluid. In some embodiments, the system controller 130 uses the irrigation module 152 in response to the temperature sensing module 156 in managing "hot spots" or uneven heating on the surface of the distal portion 15 by controlling and adjusting movable internal components of the distal portion 15, as described in more detail below.

[0033] The system controller 130 monitors the location and orientation of the distal portion 15 relative to the patient 11 using a tracking module 154. The monitoring can be performed by any tracking method known in the art, such as that provided in the Carto3® system manufactured by Biosense Webster, Irvine, Calif. Such a system uses a radio frequency (RF) magnetic transmitter external to the patient 11 and a responsive element (see, for example, position sensor 50) in the distal portion 15. Alternatively or additionally, tracking can be performed by measuring the impedance between one or more electrodes of FIG. 3 and patch electrodes attached to the skin of the patient 11, such as those also provided in the Carto3® system. For simplicity, elements specific to tracking and used by the module 154, such as the elements and patch electrodes mentioned above, are not shown in FIG. 1.

[0034] System controller 130 uses MAP module 157 to receive and process MAP signals sensed by the microelectrodes when using active and non-active electrodes to recreate the repolarization time course of the transmembrane action potential (TAP) with high fidelity. As described in more detail below, pre- and post-ablation MAP signals can provide guidance to the system operator when moving the catheter to create a continuous line of lesion or block.

[0035] 2 and 3, the distal portion 15 includes a shell cap electrode 21 configured with a proximal neck 22, a cylindrical sidewall 23, and a distal end 24 enclosing an internal chamber 25 having a proximal opening at the neck 22 configured to receive an insert 20 occupying the proximal opening. The cap electrode 21 is configured for one or more functions including, for example, ablation. The sidewall 23 includes a plurality of radial irrigation openings 33 that allow fluid within the chamber 25 to exit outside the cap electrode 21. The sidewall 23 also includes a plurality of longitudinal through holes 26 disposed at equiangular positions about a central longitudinal axis 27 of the distal portion 15. In the illustrated embodiment, three holes 26 are located at approximately 0, 120, and 240 degrees about the axis 27, although it is understood that the number of holes may vary, for example, from two to five, as needed or desired. Each hole 26 has a proximal opening and a distal opening, and each hole 26 extends the length of the sidewall between the neck 22 and the distal end 24 of the cap electrode 21. The cap electrode 21 may be constructed from any suitable material, including, for example, platinum-palladium.

[0036] Extending into each hole 26 is a respective microelectrode 17 having an elongated stem 28 and a distal sensing portion 29 exposed and configured to contact tissue. The microelectrodes 17 may be constructed of any suitable material, including, for example, platinum-iridium. In particular, as shown in FIG. 5 , the stem 28 of each microelectrode 17 is configured to extend a predetermined distance distal to the distal end 24 of the cap electrode 21 such that the distal sensing portion 29 can contact and invaginate the tissue T with an optimal force to cause reversible local trauma to sense the MAP signal without causing permanent damage. The distal sensing portions 29 of the microelectrodes 17 have their contact surfaces that protrude above the surface topology of the electrode 21 such that the distal sensing portions 29 can be generally embedded within the tissue. At each distal end of the hole 26, a recess 30 is formed in the distal end 24 of the cap electrode 21. The recess 30 may be filled with a material, for example, polyurethane, to seal and pot the distal portion of the stem 28 within the recess 30.

[0037] In some embodiments, the distal sensing portion 29 of the microelectrode 17 is configured to have a spherical or bulbous configuration that can be substantially completely enclosed by surrounding tissue, for example, to avoid sensing extracellular or far-field signals. The microelectrode profile serves to cause reversible piercing to study MAP at the tissue site. With multiple microelectrodes, multiple separate local tissue regions can be studied simultaneously. The distal sensing portion configuration may include an oval or elliptical configuration. In some embodiments, the distal portion 29 has a width or diameter W of about 0.014 mm and 0.015 mm, and the stem 28 has a length of about 0.100 mm. The protruding distance D of the distal sensing portion 29 measured from the distal surface of the distal sensing portion 29 to the distal surface of the distal tip 24 is about 0.023 mm. The protruding distance allows the microelectrode to access the local tissue depth MAP.

[0038] In some embodiments, the surface of the distal sensing portion 29 is mechanically prepared to minimize signal noise through cleaning methods and surface coatings. In some embodiments, the surface of the distal sensing portion 29 is roughened, for example, by plasma etching, or coated with one or more coatings of, for example, fractured material, silver chloride, iridium oxide, or titanium nitride to provide micron-sized cracks and crevices to increase the surface area of ​​the distal portion. Iridium oxide can provide up to 100 times greater surface area. Titanium nitride can provide up to 1000 times greater surface area. Mechanical roughening by plasma etching can provide up to 10 times greater surface area. Such fractured surface area allows for extraction of high signal to noise electrical signals from localized tissue trauma.

[0039] Each stem 28 is surrounded by an elongated insulating support member 31 having a lumen 32, e.g., a polyimide tube, generally coextensive with the stem within the respective bore 26. The member 31 electrically insulates the entire microelectrode 17 from the electrode 21. The fit between the stem 28 and the lumen 32, and between the support member 31 and the bore 26, may be a tight or interference fit. The distal end of the insulating support member 31 is configured with a flange 34 for sealing the bore 26 and the lumen 32. At the proximal end of the stem 28, an electrical connection is provided, e.g., by welding, to a respective lead wire 35. The proximal opening of each bore 26 leads to the neck 22 of the cap electrode 21 such that the lead wire 35 can extend proximally into the neck 22, along the deflection section 14 and the catheter shaft 12, toward the control handle 16.

[0040] The sidewall 23 of the cap electrode 21 also has a number of blind passages 36 at equiangular positions about the central longitudinal axis 27 offset from the position of the bore 26, each accommodating a respective thermocouple (TC) wire pair 18, e.g., a constantan wire and a copper wire pair. In some embodiments, six blind passages 36 are located in the sidewall to accommodate six pairs of TCs 18, e.g., at 15, 75, 135, 195, 255 and 315 degrees about the axis 27. The twisted distal ends of the wire pairs forming the distal junction of each TC 18 are accommodated within a respective tube 39, e.g., a hypotube, having a predetermined length longer than the length of the blind passage. The longer length of the hypotube and distal junction, and the larger diameter of the blind passage 36, allow the hypotube and distal junction to be forced into a non-linear shape inside the blind passage, thereby ensuring contact between the hypotube and the inner wall of the blind passage for more accurate temperature sensing of the cap electrode 21. The proximal opening of each blind passage opens into the neck 22 of the cap electrode 21 so that the wire pairs of the TC 18 can pass up the catheter shaft 12 proximally to the neck and along the catheter deflection section 14 and into the control handle 16.

[0041] In some embodiments, the insert 20 is configured in part as an irrigation fluid flow diverter having one or more radial channels 37 that provide fluid communication between the chamber 25 and the distal end of an irrigation lumen 52 that extends along the length of the catheter between the distal section 15 and the control handle 16. An irrigation module 152 of the system controller 130 (FIG. 1) controls the flow of irrigation fluid through the irrigation lumen 52 and into the chamber 25.

[0042] The insert 20, which occupies the neck 22 of the cap electrode 21, may be formed with a blind hole for receiving the distal end of a lead wire 55 for energizing the insert 20 and the cap electrode 21. A lateral channel may also be formed through which a safety wire 38 passes to connect the cap electrode 21 to the catheter 10 as a safety measure. In some embodiments, the distal portion 15 includes a force sensor 40 whose distal end is connected to the proximal end of the insert. Similar aspects of the force sensor are described in U.S. Pat. No. 8,357,152 (Govari et al., issued Jan. 22, 2013) and U.S. Patent Application No. 2011 / 0130648 (Beeckler et al., filed Nov. 30, 2009), both of which disclosures are incorporated herein by reference. The force sensor 40 includes a resilient coupling member 41 forming a spring joint between the distal and proximal ends of the coupling member, with a central lumen 42 passing therethrough. Coupling member 41 typically has one or more helices 43 cut into member 41 so that member 41 acts as a spring.

[0043] Coupling member 41 is mounted within and covered by a non-conductive, biocompatible sheath 44, typically formed from a flexible plastic material. Configuring the coupling member to have as large an outer diameter as possible typically increases the sensitivity of force sensor 40. Additionally, and as described below, the relatively large diameter tubular coupling member 41, and its relatively thin wall, provides a relatively wide central lumen 42 through which components pass in and out of distal portion 15. During an RF ablation procedure, significant heat may be generated in distal portion 15, and therefore sheath 44 may comprise a heat resistant plastic material, such as polyurethane, whose shape and resilience are substantially unaffected by exposure to heat.

[0044] In some embodiments, the force sensor 40 includes a distal coil 45 (FIG. 3) housed in the insert 20 distal to the spring joint, and three proximal coils 46 (not shown) proximal to the spring joint. The coils provide an accurate reading of any dimensional changes of the spring joint of the force sensor 40, including the axial displacement and angular deflection of the joint. These coils are a type of magnetic transducer that may be used in embodiments of the present invention. "Magnetic transducer" means, in the context of this patent application and in the claims, a device that generates a magnetic field in response to an applied current or outputs an electrical signal in response to an applied magnetic field. Although the embodiments of the present application describe coils as magnetic transducers, in alternative embodiments, other types of magnetic transducers may be used, as would be apparent to one of ordinary skill in the art.

[0045] In some embodiments, the distal coil 45 is driven by current through a cable (not shown) from the system controller 130 and the force module 148 to generate a magnetic field. This magnetic field is received by the proximal coil 46, which is fixed at the same axial distance from the coil 45, but at different angular positions about the longitudinal axis 27, e.g., 0, 120, and 240 degrees about the axis 27. The proximal coil 46 generates electrical signals in response to the magnetic field transmitted by the distal coil 45. These signals are conveyed by a cable (not shown) to the system controller 130, which processes the signals using the force module 148 to measure the displacement of the spring junction parallel and concentric with the axis 27, and to measure the angular deflection of the junction from the axis. From the measured displacement and deflection, the system controller 130 can estimate the magnitude and direction of the force on the spring junction of the coupling member 41, typically using pre-determined calibration tables stored in the force module 148. In particular, the force sensor 40 enables the multiple microelectrodes 17 to apply a consistent force against tissue, although it will be understood that in some embodiments, the catheter 10 need not have a force sensor.

[0046] The system controller 130 measures and detects the location and orientation of the distal end 12 using a tracking module 154 (FIG. 1). The detection method can be by any conventional process known in the art. In some embodiments, a magnetic field generated external to the patient 11 (e.g., by a generator positioned under the patient's bed) generates an electrical signal in a position sensor 50 housed in a lumen 42 of the coupling member 41 generally proximal to the spring joint. As will be appreciated by those skilled in the art, the position sensor 50 includes sensing coils X, Y, and Z (which in some embodiments is one of coils 46). The system controller 130 processes the electrical signal to assess the location and orientation of the distal portion 15. Alternatively, the magnetic field may be generated at the distal portion 15 and the electrical signal generated by the magnetic field may be measured external to the patient 11.

[0047] In use, the catheter 10 is introduced into the patient's vasculature and the distal portion 15 is advanced to a region of interest, e.g., a heart chamber. The system controller 130 accomplishes diagnostic procedures, including mapping. For example, the position sensor 50 generates signals that are processed by the tracking module 154 in determining the location and orientation of the distal portion 15. The tip electrode 21, the distal ring electrode 53, or the proximal ring electrode 54 sense electrical activity of the cardiac tissue, the generated signals being processed by the processing unit 132. A 3D electrophysiological map may be created from these processed signals, and ablation tissue sites are identified and targeted. The system controller 130 can then accomplish therapeutic procedures. For example, the operator manipulates the distal portion 15 so that the tip electrode 21 contacts the targeted tissue site. Contact between the tip electrode 21 and the tissue results in the application of a force that displaces the distal portion 15 relative to the proximal end of the coupling member 41 of the force sensor 40. Such displacement causes the proximal coil 46 to generate a signal that is processed by the force module 148, for example, to verify contact of the distal portion 15 and tissue in preparation for ablation.

[0048] Before and / or during ablation, the irrigation module 152 controls the delivery and rate of irrigation fluid to the distal portion 15 by a pump (not shown) that delivers irrigation fluid from a fluid source (not shown) through the irrigation lumen 52. The ablation module 150 delivers RF energy to the cap electrode 21, which heats the target tissue to form a lesion. One or more of the thermocouples TC18 generate signals representative of the temperature of the respective surrounding tissue and fluid. In response to the sensed temperature, the system controller 130, in some embodiments, may communicate with the ablation module 150 to adjust the power delivery and / or with the irrigation module 152 to adjust the rate of fluid delivery or adjust the position of the flow director 58 to its most distal, more distal, or less proximal position as appropriate to avoid hot spots, charring, or thrombosis. Thus, the irrigation fluid can be directed to exit the irrigation opening 33 at one or more selected flow rates.

[0049] By pressing one or more microelectrodes 17 against tissue with sufficient force to embed the respective one or more distal sensing portions 29 into the tissue to cause reversible local trauma or damage, the one or more microelectrodes 17 can detect a MAP signal. As shown in FIG. 4A, three pre-ablation ECG signals detected by the microelectrodes 17 designated μ1-μ2, μ2-μ3, and μ3-μ1, respectively, exhibit a monophasic characteristic that distinguishes them from the biphasic ECG signals detected by the other electrodes. In contrast, as shown in FIG. 4B, three post-ablation ECG signals detected by the same microelectrodes do not exhibit monophasic activity; these signals are generally flat lines while the other electrodes continue to detect signals. Once the ablation procedure forms an effective lesion, the microelectrodes do not detect a MAP signal indicating that the target tissue has been successfully necrosed. In FIG. 4C, the distal portion 15 of the catheter has been moved so that the same microelectrodes are embedded in a new target location. Thus, the ECG signals detected by the microelectrodes again exhibit a monophasic characteristic. Thus, in some embodiments, the method of ablation using a catheter having microelectrodes described above comprises: - placing a catheter having one or more microelectrodes in tissue contact at a first location along a desired ablation pattern; - acquiring a pre-ablation ECG signal sensed by one or more microelectrodes at a first location, the ECG signal having monophasic action potential characteristics; - performing an ablation with the catheter at a first location; - obtaining a post-ablation ECG signal sensed by a microelectrode at a first location; - repositioning the catheter having one or more microelectrodes in tissue contact at a second location along the desired ablation pattern only when the post-ablation ECG signal at the first location lacks monophasic action potential characteristics.

[0050] The method also includes: - re-performing the ablation at the first location when at least a portion of the monophasic characteristic remains present in the ECG signal after ablation.

[0051] The above method may be particularly useful when a continuous line of lesion or block is desired, such as pulmonary vein isolation.

[0052] The preceding description has been presented with reference to certain representative embodiments of the present invention. Those skilled in the art to which the present invention pertains will appreciate that modifications and variations of the described structures may be made without significantly departing from the principles, spirit and scope of the present invention, and that the drawings are not necessarily drawn to scale. It will be further understood that any one feature of one embodiment may be used in place of or in addition to features of other embodiments. Therefore, the above description should not be interpreted as relating only to the exact structure described and illustrated in the accompanying drawings. Rather, it should be interpreted as consistent with and supporting the following claims, which are intended to have their fullest and most accurate scope.

[0053] [Embodiment] (1) A catheter comprising: an elongated catheter shaft; a distal portion, an ablation electrode having a sidewall and an exterior surface, the sidewall having at least one aperture; at least one microelectrode configured to sense monophasic action potential signals, the microelectrode having a distal sensing portion protruding from the outer surface of the electrode and a proximal portion extending through the one hole; a distal portion including a force sensor configured to sense a contact force of the at least one microelectrode against a tissue surface. (2) The catheter of embodiment 1, wherein the distal sensing portion has a spherical configuration. (3) The catheter of embodiment 1, wherein the distal sensing portion protrudes a predetermined distance from the distal end of the ablation electrode. (4) The catheter of embodiment 1, wherein the distal sensing portion has a fractured surface. (5) The catheter of embodiment 1, wherein the distal sensing portion has a coating from the group consisting of silver chloride, iridium oxide, and titanium oxide.

[0054] (6) The catheter of embodiment 1, wherein the distal sensing portion has an etched surface. (7) The catheter of claim 1, wherein the distal sensing portion has a width in the range of about 0.014 mm to 0.015 mm. (8) The catheter of embodiment 1, wherein the distal sensing portion is configured to cause reversible localized damage to tissue. (9) The catheter of embodiment 1, wherein the distal portion includes a plurality of microelectrodes, each microelectrode having a respective distal sensing portion and a respective proximal portion, the respective proximal portions extending through respective holes formed in the sidewall of the ablation electrode. (10) The catheter of embodiment 1, wherein the side wall of the ablation electrode includes at least one blind passage and at least one thermocouple wire pair within the blind passage.

[0055] (11) The catheter of embodiment 10, wherein the thermocouple wire pair has a nonlinear configuration to provide at least one contact surface with an inner surface of the blind passage. (12) A method of using a catheter having a plurality of microelectrodes, comprising: placing a catheter having one or more microelectrodes in tissue contact at a first location along a desired ablation pattern; acquiring a pre-ablation MAP signal sensed by the one or more microelectrodes at the first location, the MAP signal having a monophasic characteristic; performing an ablation with the catheter at the first location; obtaining a post-ablation MAP signal sensed by the microelectrode at the first location; and repositioning the catheter with the one or more microelectrodes in tissue contact at a second location along the desired ablation pattern only when the post-ablation MAP signal lacks the monophasic characteristic. (13) The method of embodiment 12, further comprising re-performing ablation at the first location when at least a portion of the monophasic characteristic remains present in the post-ablation MAP signal.

Claims

1. A catheter comprising: an elongated catheter shaft; a distal portion, an ablation electrode having a sidewall and a distal end, the sidewall having at least one aperture, the distal end including a distal surface and a curved surface between the distal surface and the sidewall; at least one microelectrode configured to sense monophasic action potential signals, the at least one microelectrode having a distal sensing portion protruding from the curved surface of the ablation electrode and an elongated stem extending through the one hole, the distal sensing portion directed toward a distal side of the catheter relative to the elongated stem; a force sensor configured to sense a contact force of the at least one microelectrode against a tissue surface; the elongate stem is configured to extend distally a predetermined distance from the distal end of the ablation electrode; A catheter, wherein the distal sensing portion is spherical with a diameter in the range of 0.014 mm to 0.015 mm, the diameter of the distal sensing portion being greater than the diameter of the elongate stem.

2. The catheter of claim 1 , wherein the distal sensing portion has a surface with micron-sized gaps formed therein.

3. The catheter of claim 1 , wherein the distal sensing portion has a coating from the group consisting of silver chloride, iridium oxide, and titanium oxide.

4. The catheter of claim 1 , wherein the distal sensing portion has an etched surface.

5. 10. The catheter of claim 1, wherein the distal sensing portion is configured to cause reversible localized damage to the tissue by forcing the at least one microelectrode into the tissue with sufficient force to embed the distal sensing portion within the tissue.

6. 2. The catheter of claim 1, wherein the distal portion comprises a plurality of microelectrodes, each microelectrode having a respective distal sensing portion and a respective proximal portion, the respective proximal portions extending through a respective hole formed in the sidewall of the ablation electrode.

7. The catheter of claim 1 , wherein the sidewall of the ablation electrode includes at least one blind channel and at least one thermocouple wire pair within the blind channel.

8. The catheter of claim 7 , wherein the thermocouple wire pair has a non-linear configuration to provide at least one contact surface with an inner surface of the blind passage.

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