Controlling cardiac ablation using blood electrical conductivity

Abstract

To control operation parameters of ablation catheters which perform tissue ablation procedures.SOLUTION: Methods and systems provide assessments of the size of lesions to be ablated into tissue, such as cardiac tissue. The lesion size assessments are based on parameters including blood conductivity, hot-spot temperature, catheter tip temperature, and current data of the radiofrequency (RF) ablation energy being used, such as power, duration, temperature, irrigation and contact force.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 617,780, filed on January 5, 2024, the disclosure of which is incorporated herein by reference.

[0002] (Field of the Invention) The present disclosure generally relates to tissue ablation procedures, and more specifically to controlling the operating parameters of an ablation catheter that performs tissue ablation procedures.

Background Art

[0003] Some medical procedures require the application of ablation signals to the tissue of a patient's organ. For example, radiofrequency (RF) ablation signals can be applied to heart tissue at the ablation site to treat arrhythmias. Irreversible electroporation (IRE) / pulse - field ablation (PFA) procedures utilize high - voltage pulses for catheter - based cardiac ablation to treat conditions such as symptomatic atrial fibrillation due to local tissue necrosis.

Brief Description of the Drawings

[0004] A more complete understanding of the present disclosure will be obtained by reading the following detailed description of the embodiments of the present disclosure in conjunction with the drawings.

Figure 1

Figure 2

Figure 3

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[0005] Overview Ablation catheters are used to create ablated lesions of dead or necrotic tissue for various procedures. As used herein, the term "ablation" refers to radiofrequency (RF) ablation procedures, or irreversible electroporation (IRE) procedures, sometimes referred to as pulsed field ablation (PFA). These procedures are intended to form lesions at a target location within the heart (also referred to herein as the ablation site), thereby treating cardiac arrhythmias, by applying one or more high voltage monopolar or bipolar electrical pulses to one or more electrodes in contact with the tissue to be ablated.

[0006] For example, in RF ablation procedures, the parameters applied to the ablation catheter and generator include power, duration, temperature, perfusion, and contact force. These parameters are defined, for example, to obtain a desired lesion of a desired depth and lateral size (e.g., diameter) within the tissue.

[0007] During ablation, a portion of the energy is absorbed by the blood pool. For example, in RF ablation of the myocardium, approximately 75 - 80%, which is the majority of the current and power generated by the generator, flows into and is absorbed by the blood, and only a small amount, 20 - 25%, enters the tissue. This absorption is thought to be caused by the surface area of the tip of the ablation catheter in contact with the blood, which is much larger than the effective surface area in contact with the tissue, and the blood conductivity is higher than the tissue conductivity.

[0008] When performing ablation treatment, the depth and lateral size of the lesion vary from patient to patient. To account for differences between patients, the ablation parameters are adjusted based on the individual patient. However, it is difficult to predict the ablation parameters for each patient. A further difficulty in predicting lesion size is that the range of blood conductivity in humans is very wide (e.g., the blood impedance experienced by the electrodes varies between 100 and 150 ohms), which significantly affects the amount of energy flowing through the tissue during RF ablation.

[0009] For example, generally, the higher the blood conductivity, the more the RF energy (ablation current) emitted from the ablation catheter flows into the blood (and is absorbed there) rather than into the tissue to be ablated.

[0010] To accurately calculate the desired lesion size for an individual patient's tissue, the orientation of the ablation catheter needs to be analyzed in terms of the nature of the contact between the ablation catheter tip and the tissue, and the patient's blood conductivity should be known. The blood conductivity can be determined from a blood sample prior to the ablation procedure. Based on these two factors, the ablation catheter and its generator can be controlled to produce a lesion of the desired depth and lateral size such that the lesion is uniform among patients.

[0011] Lesion size assessment is performed by an algorithm that uses parameters including blood conductivity, catheter tip temperature, and current data of the RF ablation energy used such as power, duration, temperature, perfusion, and contact force. It has been found that substantially more accurate lesion assessment is achieved by using the actual measured value of blood conductivity together with the measured catheter tip temperature, impedance, and contact force.

[0012] Description of the System Referring to FIG. 1, there is schematically shown an exemplary catheter-based electrophysiology mapping and ablation system 10 that includes a plurality of catheters, which are percutaneously inserted by a physician 24 through a patient's vasculature into a cardiac chamber or vascular structure of the heart 12. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near the desired location in the heart 12. Thereafter, one or more catheters can be inserted into the delivery sheath catheter to reach the desired location within the heart 12. The plurality of catheters may include catheters dedicated to sensing intracardiac electrogram (IEGM) signals, catheters dedicated to ablation, and / or catheters dedicated to both sensing and ablation.

[0013] An exemplary catheter 14 configured to sense IEGM is illustrated herein. The physician 24 can place the distal tip 28 of the catheter 14 in contact with the heart wall to sense a target site in the heart 12. For ablation, the physician 24 can similarly place the distal end of an ablation catheter in contact with a target site for ablation of tissue. For example, the ablation catheter may comprise a SMARTTOUCH™ or VARIPULSE™ catheter produced by Biosense Webster Inc. (Irvine, California).

[0014] The catheter 14 is, for example, a catheter that optionally includes one or more electrodes 26 distributed over a plurality of splines 22 at the distal tip 28 and configured to sense IEGM signals. The electrodes 26 can be used to perform impedance measurements from which blood conductivity can be derived and adjusted by the workstation 55 and the processor. For example, impedance measurement estimates can use the impedance measured between at least any two catheter electrodes 26.

[0015] The catheter 14 can further include one or more position sensors, such as indicated by the position sensor 29, which is embedded within or near the distal tip 28. The position sensor 29 functions to track the position and orientation of the distal end 28 of the catheter 14. Optionally, the position sensor 29 is a magnetic-based position sensor that includes one to three magnetic coils for sensing the three-dimensional (3D) position and orientation of the catheter 14 and the catheter tip 28.

[0016] The magnetic position sensor 29 can operate in conjunction with a position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predetermined working volume. The real-time position of the distal tip 28 of the catheter 14 can be tracked based on the magnetic field generated by the position pad 25 and sensed by the magnetic-based position sensor 29. Details of the magnetic-based position sensing technology used by the catheter 14 and the magnetic position sensor 29 are described, for example, in U.S. Patent Nos. 5,539,199; 5,443,489; 5,558,091; 6,172,499; 6,239,724; 6,332,089; 6,484,118; 6,618,612; 6,690,963; 6,788,967; and 6,892,091.

[0017] The system 10 includes one or more electrode patches 38 positioned on the patient 23 for skin contact to establish position referencing of the position pad 25 and impedance-based tracking of the electrodes 26. In the case of impedance-based tracking, a current is directed to the electrodes 26 and sensed at the electrode skin patches 38 such that the position of each electrode can be triangulated via the electrode patches 38. Details of the impedance-based position tracking technology are described in U.S. Patent Nos. 7,536,218; 7,756,576; 7,848,787; 7,869,865; and 8,456,182.

[0018] The recorder (11) records and displays the electrocardiogram 21 captured by the body surface ECG electrodes 18 and the intracardiac electrogram (IEGM) captured by the electrodes 26 of the catheter 14. The recorder 11 may include pacing capabilities for pacing the heart rhythm and / or may be electrically connected to an independent pacemaker.

[0019] The system 10 may include an ablation energy generator (RF generator) 50 adapted to deliver ablation energy to one or more electrodes at the distal tip of a catheter configured to ablate. The ablation energy may be delivered by the catheter 14 or by an additional ablation catheter (not shown). The energy generated by the ablation energy generator 50 includes, but is not limited to, radiofrequency (RF) energy, or pulsed field ablation (PFA) energy (including unipolar or bipolar high voltage DC pulses that can be used to perform irreversible electroporation (IRE) / pulsed field ablation (PFA)), or combinations thereof. The energy generated, e.g., RF energy, is based on various ablation parameters including, e.g., the contact properties of the catheter tip 28 and the blood conductivity (σ) of the patient 23.

[0020] The Patient Interface Unit (PIU) 30 is an interface configured to establish electrical communication between the catheter, other electrophysiological devices, a power source, and a workstation 55 for controlling the operation of the system 10. The electrophysiological devices of the system 10 may include, for example, a plurality of catheters, position pads 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generator 50, and recorder 11. Optionally, the PIU 30 further includes the ability to implement real-time calculation of the catheter position and perform ECG calculations.

[0021] The workstation 55 includes a memory, a processor unit 101a (e.g., one or more processors including a central processing unit (CPU)) with the memory or a storage device 101b (FIG. 2), and appropriate operating software stored therein. The processor unit 101a and the memory 101b also include and / or provide, for example, user interface capabilities through which a user can manually or automatically input various parameters such as blood conductivity, the temperature of the ablation catheter tip 28 (also referred to as the tip temperature), the hot spot temperature (the hot spot temperature is the area of the maximum or highest temperature of the internal and ablated damage), the target temperature (t), etc. through the PIU 30. Here, t is less than 140° C. Celsius, etc. The workstation 55 also includes a proportional-integral-derivative (PID) control module 108 (FIG. 2) and, via its processor, also executes software for the damage assessment algorithm 102 (FIG. 2).

[0022] The workstation 55 also provides multiple functions such as, for example, (1) modeling the endocardial anatomical structure in three dimensions (3D) and rendering it to display a model or an electroanatomical map 20 on a display device 27, (2) displaying on the display device 27 an activation sequence (or other data) compiled from the recorded potential map 21 with a representative visual indicator or image superimposed on the rendered electroanatomical (EA) map 20, (3) displaying the real-time positions and directions of multiple catheters within the heart chamber, (4) displaying on the display device 27 sites of interest such as where ablation energy has been applied, and (5) providing parameters optimal for ablation including these, such as the contact quality of the catheter tip and the patient's blood conductivity. One commercially available product embodying the elements of the system 10 is available as the CARTO (trademark) 3 system, obtainable from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0023] The workstation 55 typically includes a general-purpose computer, which is programmed with software to perform the functions described herein. The software can be downloaded to the computer in electronic form, for example, via a network, or alternatively or additionally, provided and / or stored on a non-transitory tangible medium such as magnetic memory, optical memory, or electronic memory.

[0024] Ablation Control System and Damage Assessment Model FIG. 2 schematically shows an ablation control system 100 as part of a feedback control loop 100x. The ablation control system 100 is a subsystem within the main system 10 and is, for example, within the workstation 55. The system 100 includes components that execute a damage assessment algorithm 102, such as a processor 101a and associated storage device / memory 101b. The system 100 also includes a target temperature module 104, a mixer 106, and a proportional-integral-derivative (PID) control module (PID controller 108). The components 101a, 101b, 102, 104, 106, 108 of the system 100 communicate electronically and / or data communicate directly or indirectly with each other, for example.

[0025] Processor 101a includes one or more processors, including a microprocessor, to control the operation of damage assessment algorithm 102, target temperature module 104, mixer 106, and / or PID control module 108, and to perform the functions and operations detailed herein. Typically, processor 101a includes a general-purpose computer, which is programmed with software to perform the functions described herein. The software can be downloaded to the computer in electronic form via a network, for example, or alternatively or additionally, provided and / or stored on a non-transitory tangible medium such as magnetic memory, optical memory, or electronic memory. The processor is a conventional processor, including, for example, a hardware processor such as those used in servers, computers, and other computerized devices. For example, the processor may include x86 processors from AMD (Advanced Micro Devices (registered trademark)), as well as Intel (registered trademark), Xenon (registered trademark), and Pentium (registered trademark) processors from Intel, and any combination thereof.

[0026] Storage device / memory 101b includes any conventional storage medium. Storage device / memory 204 stores machine-executable instructions executed by processor 101a to execute the disclosed process.

[0027] Damage assessment algorithm 102 is the blood conductivity

[0028]

Number

[0029] The blood conductivity (σ) in Siemens / meter (S / M) units from the blood in the blood pool of the patient 23 can be obtained by one or more of the following methods. 1. Direct measurement - The direct measurement of blood conductivity is performed using a probe such as the Eutech (trademark) ECTestr11 Dual Range Conductivity Tester manufactured by Thermo Scientific to measure a blood sample. The blood sample is, for example, at least 5 cc of venous blood from the femoral vein, and the sample is measured by the probe. 2. Red blood cell (RBC) count - The red blood cell count is taken from a blood sample from the patient, such as the blood sample detailed above for "direct measurement". The correlation is shown in detail, for example, in FIG. 1 of Texter, Jr., et al., "The Electrical Conductivity of Blood-II. Relation and Cell Count", in Blood, Volume 5, Issue 11, November 1950, Pages 1036 - 1048, which document is incorporated herein by reference in its entirety. The correlation converts the red blood cell count to the value of the aforementioned conductivity in S / m units. 3. Impedance Measurement between Ring Electrodes 26 of Catheter 14 - This method includes measuring the blood impedance between at least two catheter electrodes 26 and, optionally, converting the values obtained for impedance measurement to conductivity, for example, using a graph or calibration table, as detailed in U.S. Patent Nos. 10,398,348 and 11,596,324 of the same owner, the entire disclosures of which are incorporated herein by reference.

[0030] The temperature at the catheter tip is measured by one or more temperature sensors located at the tip of the catheter. The temperature measurement values are continuously updated, for example, at a rate of 20 Hz.

[0031] For the purpose of algorithm 102, the catheter penetration depth is first estimated based on the contact force between the ablation electrode and the patient's tissue surface and / or the impedance measurement values.

[0032] The damage assessment algorithm 102, also known as the damage size assessment algorithm, outputs the damage size, which is projected onto the electroanatomical (EA) map 20 for observation by the physician 24 and / or the operator in the control room. The hot spot temperature to be compared with the target temperature is also output, and the difference between them (calculated by, for example, mixer 106) is input to the PID control module 108.

[0033] The hot spot temperature is calculated, for example, by a thermal model as described in the appendix. The hot spot temperature is the maximum temperature within the ablated area of the tissue, such as determined based on measurements made by the temperature sensor 110 within the ablation catheter tip.

[0034] The target temperature is determined by processor 101a based on a temperature sufficient for ablation that does not result in a steam pop, as disclosed in, for example, U.S. Patent No. 9,241,756 of the same owner, the disclosure of which is incorporated herein by reference, and is typically less than 140 degrees Celsius. Alternatively, the target temperature may be stored in a database or PID module 108, such as in a look-up table (LUT).

[0035] The PID controller 108 receives an "error" value and functions to control the current supply of RF energy necessary to ablate an ablation spot of a size determined by the damage assessment algorithm 102 based on this value. For example, the PID controller 108 calculates an output signal to control the RF ablation energy and its pulses generated by the RF generator 50. The calculated pulses are used by the ablation catheter 14 to ablate a damage of a desired dimension in accordance with a damage size calculation as determined (e.g., calculated) by the algorithm 102.

[0036] Referring now to FIG. 3, a flowchart showing in detail a computer-implemented process, such as that performed by the damage assessment algorithm 102, is shown. See also the elements shown in FIGS. 1 and 2. The process and sub-processes of FIG. 3 are computerized processes executed by the system 10 and subsystem 100. The processes and sub-processes described above are executed, for example, continuously, automatically, e.g., in real time.

[0037] The evaluation of the damage starts at start block 302. The processor is programmed with physical parameters and material properties such as the thermal and electrical properties of the material at the tip 28 of the ablation catheter 14. The processor is also programmed to sample at regular intervals, for example, at a rate of 20 times per second, from six different probes (e.g., sensors 29) at the tip 28 of the catheter 14.

[0038] Moving to block 304, the positioning of ablation catheter 14 begins with physician 24 inserting ablation catheter 14 into the tissue to be ablated. Physician 24 may use any suitable method to select the ablation site within the tissue. For example, in cardiac ablation, physician 24 can choose to ablate the site of the arrhythmia, as is known in the art.

[0039] Following probe positioning, the process moves to block 306, where processor 101a estimates the initial penetration depth of the tip 28 of catheter 14 into the tissue using, for example, one or more of a) impedance, contact force, and / or temperature measurements, and b) blood conductivity measurements. For example, impedance is determined by impedance measurements from two or more electrodes 26 on catheter 14. For example, using a tissue proximity indication (TPI) algorithm, the impedance between electrodes 26 can be measured to estimate the penetration depth of catheter 14 / catheter tip 28, and the TPI algorithm is detailed in U.S. Patent No. 10,398,348.

[0040] Contact force is determined by measurements on a force gauge (not shown) near catheter tip 28 that measures the contact force on the tissue with a resolution of, for example, 1 gram. Temperature measurements can be made, for example, as disclosed in J. Kosuth, et al., "Chamber-Specific Radiofrequency Lesion Dimension Estimation Using Novel Catheter-Based Tissue Interface Temperature Sensing", in JACC: Clinical Electrophysiology, Vol. 3, No. 10, pages 1092 - 1102 (2017), for example, by the penetration of tip 28 into the tissue (equal to the surface coverage rate of the tip by the tissue), the disclosure of which is incorporated herein by reference.

[0041] The process moves to block 308, where the RF generator 50 is operated to apply an ablation current to the tissue. The RF power level generated by the RF generator 50 is controlled by the current level applied to the generator 50. The energy generated by the RF generator 50 is delivered to the tissue at the ablation site via the ablation catheter 14. Typically, when RF energy is applied to the tissue, the ablation catheter 14 makes measurements of temperature, impedance, and force that are delivered to the processor(s) 101a.

[0042] Moving to block 310, the processor(s) 101a creates a finite element (FE) model using the estimated depth of the tip 28 and blood conductivity (σ) (from block 306), as well as the current actual temperature and impedance measurements taken at the catheter tip 28. The FE model includes calculated temperature and impedance values in a plurality of sub-regions of a 3D region called the temperature domain. The temperature domain typically includes regions of tissue, such as regions and hot spots, the tip 28 and sensors of the catheter 14, and regions in the immediate vicinity of the tissue where liquids such as blood and irrigating saline may be present. Note that sensors at the tip 28 of the ablation catheter 14 are present in some of the sub-regions of the FE model. An exemplary FE model is disclosed in "Chamber-Specific Radiofrequency Lesion Dimension Estimation Using Novel Catheter-Based Tissue Interface Temperature Sensing" by J. Kosuth et al. in JACC: Clinical Electrophysiology, as detailed above. The implementation of the FE model in this embodiment is further described in the appendix.

[0043] The process moves to block 312, where processor 101a compares the calculated temperature and impedance values of the FE model with the actual measured values of the probe sensor. If there is no match at block 312, the processor re-estimates the tip penetration depth in re-estimation step 314, loops back to step 310, and the process resumes from there. The loop of re-estimating the penetration depth at block 314 repeats the process of block 306 and adjusts it in combination with the FE model (block 310) until processor 101a finds a match at block 312.

[0044] If there is a match at block 312, the process proceeds to block 316, where a real-time model of the predicted hot spot temperature and pressure progression as a function of time is created for a given blood conductivity and lesion size. The real-time model is based at least on the tip (probe) penetration depth estimated at block 306 or 314 (which is a "free parameter" of the model), and the ablation current used to operate RF generator 50. The model typically includes the predicted change curves of temperature and / or pressure at the hot spot. Alternatively, the model may consist of a table of temperature / pressure and time points. Further alternatively, the model can include any other suitable form such as a mathematical formula.

[0045] Based on the model and a predetermined temperature / pressure threshold, the process moves to block 318, and at block 320 it is determined whether the hot spot temperature determined here meets the target temperature. The target temperature is the desired temperature for the ablation spot, which is high enough to cause tissue necrosis while avoiding steam pops, and is obtained, for example, from a look-up table.

[0046] Return to block 318. If the hot spot temperature does not meet the target temperature (programmed into system 100), the process moves to block 322. At block 322, the PID controller (PID control module 108) changes the current supply to RF generator 50 to the tip of catheter 28 according to the difference between the hot spot temperature and the target temperature. Next, the process moves to block 316 and resumes from there.

[0047] Alternatively, at block 318, if the hot spot temperature meets the target temperature, the process moves to block 324. At block 324, the processor determines whether ablation is complete. For example, to determine whether ablation is complete, physician 24 may end ablation if the amount of energy applied to the tissue (e.g., the product of RF power and duration) exceeds a predetermined threshold.

[0048] Alternatively or additionally, physician 24 may determine the end of ablation by examining any suitable information presented on display 27 during the ablation process. Further alternatively or additionally, the processor may automatically determine the end of ablation using, for example, the method described in U.S. Patent No. 8,900,225, the disclosure of which is hereby incorporated by reference in its entirety.

[0049] At block 324, when ablation is complete, the process (method) of damage assessment algorithm 102 ends at end step 326.

[0050] Otherwise, in block 324, if ablation is not complete, the processor loops back to step 310 to readjust the FE model if a deviation from the model occurs. Factors that can cause an FE model deviation include, for example, tissue-probe relative motion generated by the heartbeat and respiratory motion of patient 23. Note that after adjustment of the FE model in step 310, respective updates to the real-time model in block 316 and to the predicted occurrence time of the steam pop event in block 320 may continue.

[0051] This process may be repeated as desired.

[0052] Alternatively or additionally, physician 24 may adjust the position or depth of insertion of catheter 14 into the tissue, or may temporarily remove the catheter from contact with the tissue. Physician 24 can apply increased force to catheter 14 to insert it deeper into the tissue if the prediction model shows a slowly rising temperature / pressure curve. However, if the model indicates an impending steam pop event, physician 24 may partially or completely remove catheter 14 from the tissue. Further alternatively or additionally, physician 24 can control the perfusion rate and / or any other suitable means that can affect the rate of temperature / pressure change in response to the model metrics. Physician 24 may also respond in various ways in parallel to reducing the risk of a steam pop event.

[0053] FIG. 4 shows a flowchart of a process for determining whether a patient is a suitable candidate for ablation based on blood conductivity. For example, if the blood conductivity is less than a particular value, less than about 4 microsiemens (S) / centimeter (mS / cm), more ablation current flows through the tissue compared to a normal blood conductivity of about 6.5 mS / cm. When this large amount of current reaches the tissue, the tissue is heated more quickly, resulting in greater damage with risk factors such as steam pops, carbonization, and / or esophageal overheating.

[0054] The process begins at block 402, where the blood conductivity is obtained by one of the processes detailed above. The process moves to block 404, where it is determined whether the blood conductivity measurement is less than a threshold value, for example, less than 4 mS / cm.

[0055] If the answer at block 404 is "yes", the process moves to block 406, where a temperature-induced (e.g., controlled) catheter is selected for the treatment. The temperature sensor of such a catheter continuously monitors the temperature at the tip where ablation occurs. This real-time feedback enables the treatment to be adjusted quickly enough according to how the patient's tissue responds in order to avoid damage to healthy tissue. Next, the process moves to block 408 and the ablation treatment proceeds.

[0056] Alternatively, if the answer at block 404 is "no", the process moves directly to block 408 and the ablation treatment proceeds.

[0057] From block 408, the process moves to block 410, where the ablation treatment ends.

[0058] The examples described herein mainly address ablation of heart tissue, but other tissues can also be ablated by the devices and methods disclosed herein.

[0059] The implementation of the methods and / or systems of the embodiments of the present disclosure can involve performing and / or completing the selected tasks manually, automatically, or a combination thereof. Further, according to the actual instrumentation and equipment of the methods and / or systems of the embodiments of the present disclosure, some of the selected tasks can be implemented by hardware, by software, by firmware, or a combination thereof, using an operating system or a cloud-based platform.

[0060] For example, the hardware for performing a selected task according to an embodiment of the present disclosure can be implemented as a chip or a circuit. As software, a selected task according to an embodiment of the present disclosure can be implemented as a plurality of software instructions executed by a computer using any suitable operating system. In an exemplary embodiment of the present disclosure, one or more tasks according to an exemplary embodiment of the method and / or system described herein are executed by a data processor such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and / or data, and / or a non-volatile storage device for storing instructions and / or data, such as a non-transitory storage medium such as a magnetic hard disk and / or a removable medium. Optionally, a network connection is also provided. A display and / or a user input device such as a keyboard or a mouse are also optionally provided.

[0061] For example, any combination of one or more non-transitory computer-readable (storage) media can be utilized in accordance with the examples enumerated above of the present disclosure. This non-transitory computer-readable (storage) media may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, but is not limited to, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (an inclusive list) of the computer-readable storage medium would include, hereinafter, namely, an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of the present disclosure, the computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0062] The computer-readable signal medium may include, for example, a propagated data signal in which the computer-readable program code is embodied, either in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electromagnetic, optical, or any suitable combination thereof. The computer-readable signal medium is any computer-readable medium that is not a computer-readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

[0063] As will be appreciated with reference to the paragraphs provided above and the drawings referenced therein, various examples of computer-implemented methods are provided herein, some of which can be performed by various examples of the apparatus and system described herein, and some of which can be performed in accordance with instructions stored on a non-transitory computer-readable storage medium described herein. Further, some examples of the computer-implemented methods provided herein can be performed by other apparatus or systems and can be performed in accordance with instructions stored on a computer-readable storage medium other than those described herein, as will be apparent to those skilled in the art with reference to the examples described herein. Any reference to a system and a computer-readable storage medium with respect to the following computer-implemented methods is provided for purposes of explanation and is not intended to limit any of such systems or any of such non-transitory computer-readable storage media with respect to any of the examples of the computer-implemented methods described above. Similarly, any reference to the following computer-implemented methods with respect to a system and a computer-readable storage medium is provided for purposes of explanation and is not intended to limit any of the computer-implemented methods disclosed herein.

[0064] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible embodiments of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, segment, or portion of instructions comprising one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, and the combinations of blocks in the block diagrams and / or flowchart diagrams, as well as the block diagrams and / or flowchart diagrams themselves, can be implemented by a dedicated hardware-based system that performs a particular function or operation, or by a combination of dedicated hardware and computer instructions. The descriptions of the various embodiments of the present disclosure are presented for purposes of illustration, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

[0065] Damage assessment algorithm The disclosed damage assessment algorithm (102) is used to evaluate damage parameters using the temperature measured by a therapeutic catheter. The damage parameters are the damage size (width and depth) and the maximum temperature (hot spot) occurring within the tissue.

[0066] The algorithms described in the following sections are executed in real time, but are based on offline-compiled data, look-up tables (LUTs), and pre-collected material properties. This contributes to both the relative simplicity of the algorithms and their speed without significantly degrading the accuracy of the algorithms.

[0067] The thermal time scale (the time it takes for the temperature front to propagate in the spatial scale of interest, or the time it takes for the temperature field to change significantly) is on the order of a few seconds, so the fluctuations in the measurements due to heartbeat and respiration have little effect on lesion formation.

[0068] Heartbeat and respiratory movements cause movement of the catheter relative to the tissue, which in turn causes changes in the measured temperature as the sensor moves relative to the lesion.

[0069] Conversely, heat generation within the tissue can remain stable, aided by the large heat capacity of the tissue.

[0070] Thus, tissue heat capacity acts as a low-pass filter that averages out the fluctuations.

[0071] Basic operating principle Offline (generate a lookup table (LUT) model): ● Perform all simulations for the relevant ablation settings (current, catheter insertion / depth, impedance, ablation time, blood conductivity, etc.).

[0072] Execution time 1. Start ablation and measure data (temperature, impedance) from the catheter sensor. 2. The behavior of the measured values is unique and similar to the values generated by a specific simulation (in the sense that they are generated using a specific catheter depth, current, material properties, etc.). The data for this simulation can be retrieved from the relevant lookup table. 3. The simulation output lookup table contains non-directly measured parameters, including the range and shape of the temperature field within the tissue, and the measured values that the inventors would have obtained if reality were identical to the simulation. By continuously comparing the measured temperature with the simulated temperature, an optimal simulation scenario database is selected, from which the damage size and the maximum temperature (hot spot) are extracted.

[0073] Simulation and Model Generation The following parameters are required to perform the simulations necessary to generate the data used by the algorithm. 1. Catheter tip structure including insert and temperature sensor. 2. Range of power / current applied during ablation. 3. Range of catheter penetration depth / angle defining the contact shape. 4. Material properties (e.g., thermal / electrical conductivity, temperature range, perfusion flow rate, etc.) 5. Ablation site characteristics (beyond RA, RV, tissue geometry, and presence of fat layer / lung / pericardium, etc.). 6. Range of blood conductivity.

[0074] Combinations of multiple parameters from the above set are used to generate a database that constitutes the algorithm input (i.e., LUT).

[0075] All models are run at currents within the range used in electrophysiology ablation practice, assuming an ablation duration of up to 125 seconds.

[0076] Each simulation generates a time-dependent temperature field. These results can be analyzed for data relevant to the algorithm, such as damage width / depth (damage boundary defined as the 57C isotherm, and maximum tissue temperature (hot spot)).

[0077] After completion of the simulations covering all parameter combinations and variations, the following results are extracted into the algorithm input database. ● Damage depth ● Damage width ● Temperature measured ● Temperature at the hottest tissue spot.

[0078] All parameters are compiled as a table in the following format. Value (time = t, penetration = D, current = I, conductivity = C) Therefore, each value corresponds to a specific time, catheter penetration depth, ablation current, and blood conductivity.

[0079] Each parameter is described as a function of (t, D, I, C) by using linear interpolation of the values within the (t, D, I, C) set. This provides a continuous function used as an algorithm to predict the progression of damage.

[0080] Data preprocessing Maximum measured temperature Of all temperature measurement values (e.g., six measurement values in the QDOT catheter), only the maximum value is transferred to the algorithm. The implicit assumption is that the sensor with the highest measured temperature is the sensor closest to the damage and is therefore most suitable for evaluating the damage.

[0081] Instantaneous loss of contact: As long as the catheter tip is in contact with the tissue and the ablation current heats the tissue, the local decrease in tissue temperature cannot be rapid.

[0082] Therefore, if the measured temperature shows a rapid decrease, it can be assumed that the measured temperature decrease is due to the instantaneous loss of contact by the measuring sensor and not due to the true decrease in tissue temperature. This intermittent contact represents the tissue temperature between its "high" points, and only these points accurately represent the tissue temperature.

Example

[0083] (Example 1) A method for ablating a patient's tissue using an ablation catheter (14), the method comprising obtaining (402) a value of the blood conductivity of blood in a blood pool associated with the ablation catheter and the tissue to be ablated. The ablation energy required to ablate the tissue is calculated (316) based on ablation parameters including the value of the blood conductivity. The size of the lesion generated by the ablation energy is evaluated (310) based on the calculated ablation energy.

[0084] (Example 2) Calculating the ablation energy (316) further includes applying to the calculation the hot spot temperature of the ablated lesion, the method according to Example 1.

[0085] (Example 3) Evaluating the lesion size (310) further includes estimating (306) the initial penetration depth of the tip of the catheter into the tissue and creating a finite element (FE) model of the three-dimensional (3D) temperature distribution in the tissue using the estimated initial penetration depth and the value of the blood conductivity, as well as the current actual temperature and impedance measurements taken at the tip, and estimating (316) the size of the lesion from the temperature distribution, the method according to Example 1.

[0086] (Example 4) The method according to Example 3, including adjusting (322) the ablation energy based on the size of the lesion.

[0087] (Example 5) The method according to Example 1, including selecting (406, 408) a catheter type based on the obtained value of the blood conductivity.

[0088] (Example 6) Obtaining the value of the blood conductivity (402) includes determining the blood conductivity value from a blood sample of the patient prior to ablation, the method according to Example 1.

[0089] (Example 7) Evaluating the size of the lesion (310) involves using a pre - created look - up table of entries regarding lesion depth, lesion width, measured temperature, and temperature at the hottest tissue spot, the method described in Example 1.

[0090] (Example 8) Evaluating the size of the lesion (310) involves evaluating the depth and lateral size of the lesion, the method described in Example 1.

[0091] (Example 9) A system (10) for ablating a patient's tissue using an ablation catheter (14), comprising an interface (30) and a processor (101a). The interface is configured to obtain (402) a value of the blood conductivity of the blood of a blood pool associated with the ablation catheter and the tissue to be ablated. The processor (101a) is configured to calculate (316) the ablation energy required to ablate the tissue based on ablation parameters including the value of the blood conductivity, and to evaluate (310) the size of the lesion generated by the ablation energy based on the calculated ablation energy.

[0092] As used herein, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include plural referents.

[0093] Certain features of the invention are described in the context of separate embodiments for clarity, but it should be understood that these may also be presented in combination in a single embodiment. Conversely, various features of the disclosure are described in the context of a single example for brevity, but these may also be provided separately, or in any suitable partial combination, or in any other described embodiment of the disclosure as may be suitable. Specific features described in the context of various embodiments should not be considered essential features of those embodiments, except where the embodiment would not be operable without those elements.

[0094] 〔Embodiment〕 (1) A method for ablating a patient's tissue using an ablation catheter, the method comprising: obtaining a value of the blood conductivity of blood in a blood pool associated with the ablation catheter and the tissue to be ablated; calculating ablation energy required to ablate the tissue based on ablation parameters including the value of the blood conductivity; evaluating the size of damage generated by the ablation energy based on the calculated ablation energy. (2) The method according to embodiment 1, wherein calculating the ablation energy further comprises applying a hot spot temperature of the ablated damage to the calculation. (3) The method according to embodiment 1, wherein evaluating the damage size further comprises estimating an initial penetration depth of the tip of the catheter into the tissue, creating a finite element (FE) model of a three-dimensional (3D) temperature distribution within the tissue using the estimated initial penetration depth and the value of the blood conductivity, and the current actual temperature and impedance measurement values taken at the tip, and estimating the size of the damage from the temperature distribution. (4) The method according to embodiment 3, comprising adjusting the ablation energy based on the size of the damage. (5) The method according to embodiment 1, comprising selecting a catheter type based on the obtained value of blood conductivity.

[0095] (6) The method according to embodiment 1, wherein obtaining the value of the blood conductivity includes determining the value of the blood conductivity from a blood sample of the patient before the ablation. (7) The method according to embodiment 1, wherein evaluating the size of the lesion includes using a pre - created look - up table of entries regarding lesion depth, lesion width, measured temperature, and temperature at the hottest tissue spot. (8) The method according to embodiment 1, wherein evaluating the size of the lesion includes evaluating the depth and lateral size of the lesion. (9) A system for performing ablation of a patient's tissue using an ablation catheter, the system comprising: an interface configured to obtain a value of blood conductivity of blood in a blood pool associated with the ablation catheter and the tissue to be ablated; a processor, wherein the processor is configured to: calculate ablation energy required to ablate the tissue based on ablation parameters including the value of the blood conductivity; evaluate the size of a lesion generated by the ablation energy based on the calculated ablation energy. (10) The system according to embodiment 9, wherein the processor is configured to calculate the ablation energy by applying the hot - spot temperature of the ablated lesion to the calculation.

[0096] (11) The processor is configured to estimate an initial penetration depth of the tip of the catheter into the tissue, create a finite element (FE) model of a three-dimensional (3D) temperature distribution within the tissue using the estimated initial penetration depth and the value of the blood conductivity, and the current actual temperature and impedance measurement values taken at the tip, and evaluate the damage size by estimating the size of the damage from the temperature distribution, the system of embodiment 9. (12) The processor is configured to adjust the ablation energy based on the size of the damage, the system of embodiment 11. (13) The processor is configured to select a catheter type based on the obtained value of the blood conductivity, the system of embodiment 9. (14) The interface is configured to obtain the value of the blood conductivity by determining the value of the blood conductivity from a blood sample of the patient prior to the ablation, the method of embodiment 9. (15) The processor is configured to evaluate the size of the damage by using a pre-created look-up table of entries regarding damage depth, damage width, measured temperature, and temperature at the hottest tissue spot, the system of embodiment 9.

[0097] (16) The processor is configured to evaluate the size of the damage by evaluating the depth and lateral size of the damage, the system of embodiment 9.

Claims

1. A system for performing ablation of a patient's tissue using an ablation catheter, the system comprising: an interface configured to obtain a value of the blood conductivity of blood in a blood pool associated with the ablation catheter and the tissue to be ablated; a processor, wherein the processor is configured to: calculate ablation energy required to ablate the tissue based on ablation parameters including the value of the blood conductivity; evaluate the size of damage generated by the ablation energy based on the calculated ablation energy.

2. A method for performing ablation of a patient's tissue using an ablation catheter, the method comprising: obtaining a value of the blood conductivity of blood in a blood pool associated with the ablation catheter and the tissue to be ablated; calculating ablation energy required to ablate the tissue based on ablation parameters including the value of the blood conductivity; evaluating the size of damage generated by the ablation energy based on the calculated ablation energy.

3. The method according to claim 2, wherein calculating the ablation energy further comprises applying a hot spot temperature of the ablated damage to the calculation.

4. Evaluating the damage size further comprises estimating an initial penetration depth of the tip of the catheter into the tissue, creating a finite element (FE) model of the three-dimensional (3D) temperature distribution in the tissue using the estimated initial penetration depth, the value of the blood conductivity, and the current actual temperature and impedance measurement values at the tip, and estimating the size of the damage from the temperature distribution.

5. The method according to claim 4, further comprising adjusting the ablation energy based on the size of the damage.

6. The method according to claim 2, further comprising selecting a catheter type based on the obtained value of the blood conductivity.

7. The method of claim 2, wherein obtaining the value of the blood conductivity includes determining the value of the blood conductivity from a blood sample of the patient prior to the ablation. **Claim 8** The method of claim 2, wherein evaluating the size of the lesion includes using a pre-made look-up table of entries regarding lesion depth, lesion width, measured temperature, and temperature at the hottest tissue spot. **Claim 9** The method of claim 2, wherein evaluating the size of the lesion includes evaluating the depth and lateral size of the lesion.

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