Systems and methods for temperature control in irrigation ablation

Abstract

The present invention is titled Systems and Methods for Temperature Control in Irrigation Ablation. A catheter ablation system includes: a catheter probe having a distal end, the catheter probe including: a temperature sensor; a plurality of irrigation holes; and an ablation electrode; a radio frequency (RF) heating controller coupled to the catheter probe and configured to supply RF energy to the ablation electrode to control the ablation electrode to emit heat at a target power; an irrigation controller coupled to the catheter probe and configured to supply irrigation fluid through the catheter probe at a continuously adjustable irrigation flow rate to exit through the irrigation holes; and an operating console having a processor and a memory, the memory storing instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate based on the target power and the target average temperature.

Description

Technical Field

[0001] Aspects of embodiments of the present invention relate to procedures using radiofrequency ablation and systems for performing such procedures. Background Art

[0002] Cardiac arrhythmias, specifically atrial fibrillation, have been common and dangerous medical conditions, particularly in the elderly population. In patients with normal sinus rhythm, the heart, which consists of the atria, ventricles, and excitatory conduction tissues, beats in a synchronous, patterned manner in response to electrical stimuli. In patients with cardiac arrhythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normal conduction tissue as in patients with normal sinus rhythm. Instead, abnormal regions of cardiac tissue conduct abnormally to adjacent tissues, disrupting the cardiac cycle into an asynchronous rhythm. Such abnormal conduction has previously been known to occur in various regions of the heart, such as, for example, in the sinoatrial (SA) node region, along the conduction pathways of the atrioventricular (AV) node and His bundle, or in the myocardial tissue forming the ventricular and atrial chamber walls.

[0003] Cardiac arrhythmias, including atrial arrhythmias, can be of the multiple reentrant wave type, characterized by multiple asynchronous loops of electrical impulses that are distributed around the atrial chamber and typically self-propagating. Alternatively, or in addition to the multiple reentrant wave type, cardiac arrhythmias can also have a focal source, such as when isolated tissue regions within the atrium beat autonomously in a rapid, repetitive manner.

[0004] Electrode catheters have been commonly used in medical practice for many years. The diagnosis and treatment of cardiac arrhythmias with the aid of electrode catheters include mapping the electrical properties of cardiac tissue and selectively ablating cardiac tissue by applying energy. Such ablation can stop or alter the propagation of unwanted electrical signals from one part of the heart to another. Ablation methods disrupt unwanted electrical pathways by forming non-conductive ablation lesions. A variety of energy delivery forms for forming ablation lesions have been disclosed, including the use of microwaves, lasers, and more commonly, radiofrequency energy to form conduction blocks along the walls of cardiac tissue.

[0005] In use, an electrode catheter is inserted into a major vein or artery (e.g., the femoral artery) and then guided into the ventricle. A reference electrode is provided, typically taped to the patient's skin or disposed on the ablation catheter or another catheter. Radiofrequency (RF) current is applied to the ablation electrode of the catheter and flows through the surrounding medium (i.e., blood and tissue) to the reference electrode. The distribution of the current depends on the amount of contact of the electrode surface with tissue compared to blood, which has a higher conductivity than tissue.

[0006] Heating of tissue occurs due to the resistivity of the tissue. The tissue is heated sufficiently to cause cell destruction in the cardiac tissue, resulting in the formation of a non - electrically conductive ablation lesion in the cardiac tissue. During this process, heating of the ablation electrode also occurs due to conduction from the heated tissue to the electrode itself. If the electrode temperature becomes high enough, possibly above 60 °C, a thin transparent coating of dehydrated blood can form on the surface of the electrode. If the temperature continues to rise, the dehydrated layer of the blood can become thicker and thicker, leading to blood coagulation on the electrode surface. Since dehydrated biological materials have a higher resistance than tissue, the impedance to the flow of electrical energy into the tissue also increases. If the impedance increases sufficiently, impedance rise occurs, and the catheter must be removed from the body and the tip electrode cleaned.

[0007] During the normal application of RF current, the circulating blood provides some cooling for the ablation electrode. Another method is to actively cool the ablation electrode by flushing it with saline, for example, at room temperature, rather than relying on the relatively passive physiological cooling provided by the blood. Since the intensity of the RF current is no longer limited by the interface temperature, the current can be increased. This results in ablation lesions that tend to be larger and more spherical, typically measured to be about 10 mm to 12 mm.

[0008] RF ablation is typically performed at a continuous power level of about 20 watts - 50 watts, with a contact force of approximately 10 g and under flushing. The ablation time depends on the size of the ablation lesion to be achieved and is typically about 1 minute. Generally speaking, a higher power level will reduce the time required to form a specific ablation lesion. However, due to the risk of forming steam pops, large continuous power values are usually not available. Summary of the Invention

[0009] Aspects of embodiments of the present invention relate to systems and methods for controlling a flush pump of a flush catheter ablation system. Specifically, some aspects of embodiments of the present invention relate to controlling the flow rate of fluid provided to tissue through a catheter probe to control the temperature at the contact point between the tip of the catheter probe and biological tissue.

[0010] According to one embodiment of the present invention, a catheter ablation system includes: a catheter probe having a distal end, the catheter probe including: a temperature sensor; a plurality of irrigation apertures; and an ablation electrode; a radio frequency (RF) heating controller coupled to the catheter probe and configured to supply RF energy to the ablation electrode to control the ablation electrode to emit heat at a target power; an irrigation controller coupled to the catheter probe and configured to supply irrigation fluid through the catheter probe at a continuously adjustable irrigation flow rate to exit through the irrigation apertures; and an operation console having a processor and a memory, the memory storing instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate based on the target power and the target average temperature.

[0011] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an irrigation flow rate selected from more than two different irrigation flow rates.

[0012] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate in the form of a continuously variable quantity.

[0013] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to a value within a continuous range.

[0014] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an initial irrigation flow rate based on the target power and the target average temperature during a pre-ablation time period.

[0015] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an adjusted flow rate during a power ramp-up time period after the pre-ablation time, the adjusted flow rate being set based on: the target power; the target average temperature; the initial irrigation flow rate; the temperature slope measured by the temperature sensor during the pre-ablation time; the temperature slope measured by the temperature sensor during the power ramp-up time; and the temperature rise measured since the start of ablation by the temperature sensor.

[0016] The memory of the operation console may further store instructions which, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate using a proportional integral derivative control loop based on the current temperature measured by the temperature sensor and the target average temperature.

[0017] The target average temperature may be constant relative to the target power.

[0018] The target average temperature can be set to increase linearly with respect to the target power.

[0019] According to one embodiment of the present invention, a method for controlling a catheter ablation system, the catheter ablation system comprising: a catheter probe having a distal end, the catheter probe comprising: a temperature sensor; a plurality of irrigation holes; and an ablation electrode; a radio frequency (RF) heating controller coupled to the catheter probe and configured to supply RF energy to the ablation electrode to control the ablation electrode to emit heat at a target power; and an irrigation controller coupled to the catheter probe and configured to supply irrigation fluid through the catheter probe at a continuously adjustable irrigation flow rate to exit through the irrigation holes, the method comprising: receiving, via an operation console, a target power and a target average temperature, the operation console being configured to receive a signal from the temperature sensor and control the RF heating controller and the irrigation controller; and controlling, via the operation console, the irrigation controller to set the irrigation flow rate based on the target power and the target average temperature.

[0020] The method may further comprise controlling the irrigation controller to set the irrigation flow rate to an irrigation flow rate selected from more than two different irrigation flow rates.

[0021] The method may further comprise controlling the irrigation controller to set the irrigation flow rate in the form of a continuously variable amount.

[0022] The method may further comprise controlling the irrigation controller to set the irrigation flow rate to a value within a continuous range.

[0023] The method may further comprise controlling the irrigation controller to set the irrigation flow rate to an initial irrigation flow rate based on the target power and the target average temperature during a pre-ablation time period.

[0024] The method may further comprise controlling the irrigation controller to set the irrigation flow rate to an adjusted flow rate during a power ramp-up time period after the pre-ablation time, the adjusted flow rate being set based on: the target power; the target average temperature; the initial irrigation flow rate; the temperature slope measured by the temperature sensor during the pre-ablation time; the temperature slope measured by the temperature sensor during the power ramp-up time; and the temperature rise measured by the temperature sensor since the start of ablation.

[0025] The method may further comprise controlling the irrigation controller to set the irrigation flow rate using a proportional-integral-derivative control loop based on the current temperature measured by the temperature sensor and the target average temperature.

[0026] The target average temperature may be constant with respect to the target power.

[0027] The target average temperature can be set to increase linearly with respect to the target power. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings, together with the description, illustrate exemplary embodiments of the invention and, together with the description, are used to explain the principles of the invention.

[0029] Figure 1A is a schematic diagram of an invasive medical procedure using an ablation device according to an embodiment of the invention.

[0030] Figure 1B is a schematic block diagram showing the components of an ablation device according to an embodiment of the invention.

[0031] Figure 2A is a cross-sectional view along the length of a probe according to an embodiment of the invention.

[0032] Figure 2B is according to an embodiment of the invention along Figure 2A a cross-sectional view of the marked Cut IIB-IIB in

[0033] Figure 2C is a perspective view of a section of the distal end of a probe according to an embodiment of the invention.

[0034] Figure 2D is a schematic cross-sectional view of a force sensor incorporated into the proximal portion of the distal end of a probe according to an embodiment of the invention.

[0035] Figure 3A is a graph showing the variation of temperature, power, requested flush flow rate, and actual flush flow rate over time in an animal study using a flush catheter ablation system with a comparative flush pump controller in a first operating mode.

[0036] Figure 3B is a graph showing simulated temperature, power, requested flush flow rate, and actual flush flow rate for matching animal study data using a flush catheter ablation system with a comparative flush pump controller as shown in Figure 3A in a first operating mode.

[0037] Figure 3C is a graph showing simulated temperature, power, requested flush flow rate, and actual flush flow rate for matching animal study data using a flush catheter ablation system with a comparative flush pump controller in a second operating mode of Figure 3A

[0038] Figure 4A is a graph showing the constant temperature operating mode of an ablation system according to an embodiment of the invention. ​

[0039] Figure 4B It is a diagram showing the linearly increasing temperature operation mode of an ablation system according to an embodiment of the present invention.

[0040] Figure 5 It is a flowchart of a method for controlling the output flow rate according to an embodiment of the present invention.

[0041] Figure 6 It is a schematic diagram of a simulation framework according to an embodiment of the present invention.

[0042] Figure 7A 、 Figure 7B and Figure 7C are diagrams showing the simulation performance of a flushing control method according to an embodiment of the present invention. Detailed Description

[0043] In the following detailed description, only certain exemplary embodiments of the present invention are shown and described by way of illustration. As those skilled in the art will recognize, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0044] Figure 1A It is a schematic diagram of an invasive medical procedure using an ablation device 12 according to an embodiment of the present invention. This procedure is performed by a physician 14, and by way of example, it is assumed that the procedure in the following description involves ablation of a part of the myocardium 16 of the heart of a human patient 18. However, it should be understood that the embodiments of the present invention are not limited to this particular procedure and can also be applied to substantially any ablation procedure regarding biological tissue.

[0045] To perform ablation, the physician 14 inserts a probe 20 into the patient's lumen such that the distal end 22 of the probe 20 enters the patient's 18 heart. The distal end 22 includes one or more electrodes 24 mounted on the outer side of the distal end 22, and the electrodes 24 contact corresponding positions of the myocardium 16. The probe 20 also has a proximal end 28. Referring to Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D , the distal end 22 of the probe is described in more detail below.

[0046] The ablation device 12 is controlled by a system processor 46 located in an operating console 48. The operating console 48 includes controls 49 through which a physician 14 communicates with the processor 46. During a procedure, the processor 46 typically uses any method known in the art to track the position and orientation of the distal end 22 of the probe 20. For example, the system processor 46 may use a magnetic tracking method in which a magnetic transmitter outside the patient 18 generates signals in coils located in the distal end 22 of the probe 20. The system uses this tracking method.

[0047] Software for the processor 46 can be loaded for execution electronically by the processor 46 and can be loaded, for example, from a non-transitory memory within the operating console 48 or from an external source (e.g., via a network). Alternatively or in addition, the software can be provided via a non-transitory tangible medium such as an optical, magnetic, or electronic storage medium. The trajectory of the distal end 22 is typically displayed on a screen 62 in the form of a graphical representation 60 of the patient 18's heart, where the graphical representation can be a three-dimensional (3-D) model. The process of performing ablation using the device 12 is also typically displayed on the screen 62 in the form of a graph 64 and / or data 66 including text and numbers.

[0048] Figure 1B is a schematic block diagram showing the components of an ablation device according to an embodiment of the present invention. To operate the device 12, the system processor 46 communicates with a memory 50 that stores modules used by the processor 46 to operate the device 48. Thus, the memory 50 includes a temperature module 52, a power control module 54, a force module 56, and a flush module 58, the functions of which are described in more detail below. The software modules in the memory can be configured to receive data from or control the corresponding hardware of the ablation device 12. For example, the temperature module 52 can be configured to read temperature data from one or more temperature sensors 78 (e.g., thermocouples, thermistors, etc.) at the distal end 22 of the probe 20. The force module 56 can be configured to read force data from sensors in the distal end 22 of the probe 20. The power control module 54 can be configured to control an RF generator 55 to control the radiofrequency power (e.g., radiofrequency current) supplied to myocardial tissue 16 through the ablation electrode 24A. The flush module 58 can be configured to control a flush pump 59 to deliver a fluid (e.g., saline, heparin, or other diagnostic and therapeutic fluids, such as neuroinhibitors and neurostimulants) to the patient's tissue (e.g., myocardial tissue 16) through the probe 20.

[0049] A temperature sensor 78 on the distal end 22 of the probe 20 (e.g., via the screen 62) provides feedback to the physician 14 regarding the quality of the contact between the ablation electrode 24A (described in more detail below) and the myocardial tissue 16 at the distal tip of the probe 20. Detecting the temperature using the temperature module 52 also allows the processor 46 to control the RF generator 55 based on the temperature.

[0050] For example, in some embodiments, the ablation device 12 operates in an operating mode where the physician sets the power (e.g., 30 W), and the temperature module 52 implements a safety feature where the processor 46 controls the RF generator 55 (via the power control module 54) to stop delivering power when the temperature module 52 detects that the temperature at the tip has exceeded a threshold, thereby avoiding or reducing the likelihood of overheating of the myocardial tissue 16. As another example, in some embodiments, the ablation device 12 can operate in a mode where the physician sets a target temperature, and the detected temperature is used to increase or decrease the power output by the RF generator 55 (up to the maximum power) to maintain a constant temperature.

[0051] As described above, the flush module 58 is also used to control the flush pump 59 to deliver a fluid (e.g., saline) to the patient's tissue. The fluid flowing through the flush supply flows through flush holes at the distal end of the tip, thereby cooling the tip of the probe 20 (e.g., the distal end 22), thus reducing the chance of overheating and conducting heat to the patient's tissue. The liquid also cools the surface of the patient's tissue, thereby reducing other adverse effects such as carbonization and overheating.

[0052] Prior art for controlling the flush flow rate is relatively discrete (e.g., binary). A comparative flush control system automatically switches between two preset flow rates: a low flow rate (e.g., 2 mL / minute) and a high flow rate (e.g., 17 mL / minute or 30 mL / minute). The switching can be automatically controlled based on conditions such as the output power of the RF generator 55.

[0053] The optimal flow rate depends on tissue characteristics such as the thickness of the tissue. For example, in the case of thin tissue, if the flow rate is too high, the flush may cause excessive cooling of the tissue, thereby preventing ablation of the tissue and preventing the formation of an effective ablation lesion to achieve the desired physiological treatment effect. On the other hand, in the case of very thick tissue, the same flow rate may not be sufficient to cool the tip. This can cause overheating of the tip (e.g., the temperature at the tip exceeds the threshold), thereby causing the processor 46 to control the RF generator 55 to reduce the output, which also results in insufficient heat being delivered to the tissue to perform ablation.

[0054] However, these comparative flush control systems can lead to instability (e.g., temperature fluctuations) and can operate in a manner that is not intuitive to the physician, as described in more detail below.

[0055] Accordingly, aspects of embodiments of the present invention relate to systems and methods for controlling a flush flow rate in accordance with ablation conditions, as described in more detail below.

[0056] Aspects of embodiments of the present invention may be implemented in a flush ablation catheter system that includes a probe or catheter body 20 having a distal end 22 inserted into a patient. Figure 2A , Figure 2B , Figure 2C and Figure 2D Schematically shows the distal end 22 of the probe 20 suitable for use with an ablation system 12 in accordance with an embodiment of the present invention. However, embodiments of the present invention are not limited to use with a probe having the specific structure depicted in Figure 2A , Figure 2B , Figure 2C and Figure 2D but may instead be applied to other flush ablation catheters. Figure 2A is a cross-sectional view along the length of the probe 20, Figure 2B is a cross-sectional view along Figure 2A the cut IIB-IIB marked in Figure 2C is a perspective view of a section of the distal end 22 of the probe 20, and Figure 2D is a schematic cross-sectional view of a force sensor 90 incorporated into the proximal portion 92 of the distal end 22.

[0057] Referring to Figure 2A and Figure 2B , the probe or catheter body 20 includes an elongated tubular construction having a single, axial or central lumen. The catheter body 20 is flexible, i.e., bendable, but substantially incompressible along its length. The catheter body 20 may have any suitable construction and may be made of any suitable material. For example, the outer wall of the catheter body may be made of polyurethane or PEBAX. The outer wall may include an embedded braided mesh of stainless steel or the like to increase the torsional stiffness of the catheter body 20 such that when the control handle attached to the catheter body is rotated, the intermediate section of the catheter 20 will rotate in a corresponding manner.

[0058] The insertion tube 70 extends along the length of the probe 20 and is connected at the terminus of its distal end 22 to a conductive top cap electrode 24A that is used for ablation. The conductive top cap electrode 24A is also referred to herein as the ablation electrode. The conductive top cap electrode 24A has an approximately planar conductive surface 84 at its distal end and a substantially circular edge 86 at its proximal end. There are typically other electrodes, such as electrode 24B, proximal to the ablation electrode 24A. Typically, the insertion tube 70 comprises a flexible biocompatible polymer, while the electrodes 24A, 24B comprise a biocompatible metal, such as gold or platinum. The ablation electrode 24A typically has flushing holes or flushing cavities 72 through it. In one embodiment, there are thirty-six (36) holes 72 evenly distributed over the ablation electrode 24A.

[0059] The electrical conductor 74 transmits radiofrequency (RF) electrical energy from the ablation module 54 ( Figure 1A ) through the insertion tube 70 to the ablation electrode 24A, and thus, the electrical conductor 74 energizes the ablation electrode 24A to ablate myocardial tissue 16 in contact with the electrode. As described in more detail below, the power control module 54 controls the level (e.g., wattage) of RF power supplied to the ablation electrode 24A from the RF generator 55. During an ablation procedure, flushing fluid (e.g., saline) flowing out through the flushing holes 72 flushes the tissue under treatment (e.g., myocardial tissue 16), and the flushing module 58 controls the flow rate of the fluid. The flushing fluid is delivered to the ablation electrode 24A through a tube within the insertion tube 70.

[0060] The temperature sensors 78 are mounted at locations axially and circumferentially arranged around the distal tip of the probe 20 within the conductive top cap electrode 24A. In one embodiment, the conductive top cap electrode 24A includes six temperature sensors, with one set of three temperature sensors at a distal location near the tip and another set of three temperature sensors at a slightly more proximal location. This distribution is shown by way of example, and more or fewer numbers of sensors can be mounted in any suitable location within the conductive top cap electrode 24A. The temperature sensors 78 can be thermocouples, thermistors, or any other suitable type of miniature temperature sensor. The temperature sensors 78 are connected by leads that run through the length of the insertion tube 70 to provide temperature signals to the temperature module 52.

[0061] In one embodiment, the conductive top cap electrode 24A has a relatively thick sidewall 73 (e.g., about 0.5 mm thick) to provide desired thermal insulation between the temperature sensor 78 and the flushing fluid within the tip's central cavity 75. The flushing fluid exits the cavity 75 through the holes 72. The sensor 78 is mounted on a rod 77 that is fitted into a longitudinal orifice 79 in the sidewall 73. The rod 77 can be made of a plastic material such as polyimide and can be held in place at their distal ends by an adhesive 81 such as epoxy resin. U.S. Patent Application Publication No. 2014 / 0171821 to Govari et al. describes a catheter having a temperature sensor mounted in a configuration similar to that described above, and this application is incorporated herein by reference. The above arrangement provides a series of six sensors 78, but in other arrangements, other numbers of sensors will be apparent to those skilled in the art, and all such arrangements and numbers are included within the scope of the present invention.

[0062] In the description herein, it is assumed that the distal end 22 defines a set of orthogonal axes (e.g., along the x, y, and z axes), where the axis 94 of the distal end corresponds to the z axis in the set. For simplicity and by way of example, it is assumed that the y axis is in the plane of the page, it is assumed herein that the x - y plane corresponds to the plane defined by the circle 86, and it is assumed that the origin of the x, y, and z axes is the center of the circle.

[0063] Figure 2D FIG. 7 is a schematic cross - sectional view of a force sensor 90 according to an embodiment of the present invention. The sensor 90 includes a spring 94, which is assumed herein to include a plurality of coils 96 that connect the top cap 24A to the proximal end 92. A position sensor 98 is fixed to the distal side of the spring 94, and it is assumed herein to include one or more coils coupled to the force module 56 through conductors 100.

[0064] An RF transmitter 102 (typically a coil) is fixed to the proximal side of the spring 94, and RF energy for the transmitter is provided from the force module 56 via a conductor 104. The RF energy from the transmitter passes through the sensor 98, generating a corresponding signal in the conductors 100 of the sensor.

[0065] In operation, when a force is applied to the top cap 24A, the sensor 98 moves relative to the transmitter 102, and this movement causes a change in the sensor signal (e.g., a change in capacitance). The force module 56 uses the change in the sensor's signal to provide a measure of the force on the top cap 24A. This measure typically provides the magnitude and direction of the force. A more detailed description of a sensor similar to sensor 90 is provided in U.S. Patent Application Publication No. 2011 / 0130648, and the entire disclosure of this patent application is incorporated herein by reference. While Figure 2DA single force sensor is shown, but embodiments of the present invention are not limited thereto. For example, in some embodiments, multiple springs 94 with corresponding sensors 98 may be arranged along the axis 94 of the distal end 22 (e.g., along the z-axis) to provide information about the angle of the force applied to the distal end 22.

[0066] Figure 3A is a graph showing the variation of temperature, power, requested flush flow rate, and actual flush flow rate over time in an animal study using an ablation system for a flush catheter with a comparative flush pump controller in a first operating mode. As discussed above, the comparative flush pump controller has discrete or binary flush flow control, where the flush pump operates in a "low flow" mode (e.g., Figure 3A 4 mL / min in Figure 3A and a "high flow" mode (e.g.,

[0067] Collect data from the flush pump controller Figure 3A shown in Figure 3A which is configured to operate in a first mode corresponding to a "low" output power (in this example, less than or equal to 35 W). In this first mode, flushing is typically provided at a low baseline flow rate of 4 mL / min and the flow rate is temporarily increased to a high flow rate of 15 mL / min based on detected temperature changes (as Figure 3A shown, the thin dashed line corresponds to the requested flow rate requested by the flush module 58, and the thin solid line indicates the actual flow rate output by the flush pump 59). For example, at about 6 seconds, the measured temperature (shown by the medium solid line in Figure 3A exceeds the maximum temperature threshold of 50 °C (shown by the medium dashed line in Figure 3A shown). Accordingly, the flush pump temporarily changes the flow rate to the high flow rate (15 mL / min) for about 1 second. In the case shown in Figure 3A shown, the output power (shown by the thick solid line in

[0068] Figure 3B is a graph showing simulated temperature, power, requested flush flow rate, and actual flush flow rate for matching the animal study data using an ablation system for a flush catheter with a comparative flush pump controller shown in Figure 3A in a first operating mode. As can be seen in Figure 3B the model generally tracks inFigure 3A The behavior observed for a given combination of a target power of 35 W and a target temperature of 50°C.

[0069] In many cases, such as in Figure 3A the case shown in Figure 3A Neither a low flow rate (e.g., 4 mL / min) nor a high flow rate (e.g., 15 mL / min) is an optimal flow rate, resulting in frequent changes in the flow rate during ablation and also resulting in temperature instability. As can be seen in

[0070] Figure 3C is a diagram showing the simulated temperature, power, requested flush flow rate, and actual flush flow rate for matching animal study data using a flush catheter ablation system with a Figure 3A comparative flush pump controller in a second operating mode. In this example, the second operating mode corresponds to a "high" output power (e.g., above 35 W, specifically 36 W in Figure 3C as shown by the thick dashed line). When operating in this high output power mode, the processor 46 sets the baseline flush flow rate to a high flow rate (e.g., 15 mL / min) and temporarily switches to a low flow rate (4 mL / min) when the temperature is below the target value (42°C in this example). As previously mentioned, the optimal flow rate is generally neither 4 mL / min nor 15 mL / min, which is observed by the frequent switching of the flow rate during the ablation process of approximately 35 seconds shown in Figure 3C As Figure 3C shown, the temperature fluctuates (or is unstable) during the ablation process and varies in the range of approximately 41°C to approximately 44°C.

[0071] In addition, the behavior of the system changes in a non-intuitive manner to the user (e.g., a physician) because the baseline flow rate switches from a low flow rate to a high flow rate when the physician changes the power setting from a value in the "low power" range to a value in the "high power" range. For example, when the RF output power is changed from 35 W to 36 W, the flow rate will suddenly change from a low baseline rate to a high baseline rate. This non-linearity in the system response is non-intuitive, at least because a small change in the expected output power (2 W) is generally expected to result in a small change in the system behavior. The main reason for this non-intuitive behavior here is that the physician generally expects an increase in power to be associated with an increase in temperature. However, here, since the default flow rate is switched from 4 to 15, the physician will actually observe a decrease in the average temperature when switching from the low power mode to the high power mode. In addition, the temperature behavior is not constant and depends on factors such as force, quality of contact, tissue thickness, etc. Therefore, different ablations can produce different temperature responses, further increasing the non-intuitiveness of the comparison method.

[0072] Accordingly, aspects of embodiments of the present invention relate to controlling the flush flow rate in a manner that provides a more predictable temperature response over a range of power and temperature settings, contact force, tissue thickness, etc., and also provides a more stable temperature at the catheter tip.

[0073] Aspects of embodiments of the present invention relate to the use of a flush pump 59 that is capable of adjusting the flow rate (e.g., capable of continuous adjustment or capable of adjustment in small increments, such as 1 mL / min or less), as controlled in real-time or near real-time by a processor 46. This fine control of the flow rate allows the ablation system 12 to achieve various temperature responses regardless of tissue heat transfer properties, contact force, catheter position, and power settings. For example, Figure 4A is a diagram showing the constant temperature operation mode of an ablation system according to an embodiment of the present invention. As Figure 4A shown, embodiments of the present invention are capable of stably maintaining the temperature at a value supplied by the user (e.g., supplied by a physician) throughout the entire RF output power range (e.g., 20 W to 50 W) of the ablation system 12.

[0074] Aspects of embodiments of the present invention are described herein as setting the flow rate to a value within a continuous range. However, embodiments of the present invention are not limited to cases where the flow rate is fully continuously adjustable. As used herein, the term "continuous" includes cases where fine control of the flushing flow rate is possible (e.g., at a resolution of 1 mL / min). For example, in a digital control system, the flow rate can be specified by an unsigned integer representing the current flow rate in milliliters per minute (mL / min). In the context of this patent application, such a digital control system can still be said to provide "continuous" control considering the ability to finely control the flushing flow rate. However, embodiments of the present invention are not limited to this, and can also include finer resolutions (e.g., 0.5 mL / min or 0.1 mL / min) or slightly coarser resolutions (e.g., 2 mL / min).

[0075] Figure 4B is a diagram showing a linearly increasing temperature operation mode of an ablation system according to an embodiment of the present invention. As Figure 4B shown, in some embodiments of the present invention, the desired average temperature is defined as a linear function of the target output power (e.g., in Figure 4B , as the RF output power increases from 20 W to 50 W, the average temperature linearly increases from 40 °C to 50 °C).

[0076] Figure 5 is a flowchart of a method 500 for controlling the output flow rate according to an embodiment of the present invention. In operation 510, the flushing module 58 sets an initial pre-ablation flow rate F i . Starting with an initial flow rate (F t ) close to the optimal flow rate for a given target power (P d ) and target average temperature (T i ) reduces or prevents temperature oscillations and allows for faster convergence to the desired target temperature. In some embodiments of the present invention, after setting the target power (P t ) and target average temperature (T d ), once the physician 14 presses the "start" button, this initial flow rate is supplied. The "start" button is typically pressed about two seconds before ablation begins to allow for effective flushing at the catheter tip. In some embodiments of the present invention, the initial flow rate (F i ) is calculated as a function of the target power (P t ) and target average temperature (T d ) (F i = f(P t , T d))), where the function f is obtained by fitting a regression model to real-world data, data generated by a simulation model, or a combination thereof (e.g., real-world data enhanced by simulation).

[0077] In one embodiment of the present invention, a relatively accurate prediction of the good or optimal initial flow rate is calculated by the following regression formula:

[0078]

[0079] As a specific example, the above formula calculates that for P t = 50 W and T d = 45 °C, the initial flow rate F i = 10 mL / min. For P t = 30 W and T d = 45 °C, the initial flow rate calculated by the formula is F i = 6 mL / min.

[0080] After setting the initial flow rate, in operation 520, the temperature module 52 measures the temperature detected by the temperature sensor 78 before ablation (during the "pre-ablation time") and during the first few seconds of ablation. These temperature measurements reflect the heat transfer rates of the blood and tissue specific to the ablation performed (e.g., the viscosity of the blood and the thickness of the tissue). These temperature measurements include the temperature slope during the pre-ablation time (S n ), the temperature slope during the power ramp-up period (e.g., during the period from 1 second after the start of ablation to 2 seconds after the start of ablation) (S p ), and the temperature rise (T r ) measured since the start of ablation (e.g., within the first three seconds).

[0081] In operation 530, the flushing module calculates the adjusted flow rate (F a ) based on the temperature measurements made in operation 520. In some embodiments, this flow rate adjustment is performed, for example, during the power ramp-up period three seconds after the start of ablation when the temperature has not yet reached its target value, and allows the flushing module to improve the accuracy of the predicted flow rate to match the specific conditions of the current ablation for generating the desired average temperature.

[0082] In one embodiment of the present invention, a relatively accurate prediction of the good or optimal adjusted flow rate (F a ) is calculated by the following regression formula:

[0083]

[0084] During implementation, the correction is typically relatively small (e.g., a few mL / min) and in many cases is zero. Thus, in some embodiments of the present invention, because the calculated initial flow rate F i can provide a temperature that is accurate enough relative to the desired average temperature Td, operations 520 and 530 are omitted.

[0085] The regulated flow rate F a (and in some embodiments, the initial flow rate F i ) enables the temperature to be relatively accurate and predictable. However, in some cases, the quality of the contact between the catheter tip 22 and the tissue 16 can change during ablation, resulting in a change in the measured temperature. While some physicians use the measured temperature as an indicator of the contact quality (e.g., to indicate whether the physician needs to adjust the position of the catheter tip to maintain good contact), in some cases, the physician may find it desirable to maintain a constant temperature even after the contact quality has changed.

[0086] Accordingly, some aspects of the embodiments of the present invention relate to further regulating the flow rate by applying a proportional-integral-derivative (PID) control loop to control the flow rate based on the temperature error relative to the desired average temperature T d . According to one embodiment of the present invention, in operation 550, the flush module 58 uses a low gain to calculate the change in flow rate ΔF at a given time t, as calculated by the following formula:

[0087]

[0088] After updating the regulated flow rate F a to a new flow rate (F a = F a + ΔF) based on the change in flow rate ΔF, the processor 46 determines whether ablation continues (e.g., whether the physician is still pressing the trigger to apply RF power to perform ablation). If so, the processor 46 returns to operation 550 to continue regulating the flow rate (in some embodiments, after a delay such as 1 second). If ablation does not continue, the process of controlling the flow rate ends (e.g., stops flushing or returns to the baseline constant rate).

[0089] Accordingly, some embodiments of the present invention enable the flush module to regulate the fluid flow rate to compensate for large and / or rapid changes in temperature.

[0090] Some aspects of embodiments of the present invention relate to systems and methods for simulating tissue temperature responses, where such simulations are used to calculate the coefficients of the regression models described above with respect to operations 510 and 530. In some embodiments of the present invention, the regression models are calculated from ablation data recorded under various different settings (e.g., power, temperature, and flush flow rate settings) and contact and tissue properties (e.g., thickness, heat capacity, and thermal conductivity). However, due to the small number of animal studies performed and because in some cases the only available data comes from ablation systems with flush pumps configured to deliver fluid at discrete flow rates (e.g., 4 mL / min, 8 mL / min, and 15 mL / min), it may be difficult to obtain sufficiently realistic data.

[0091] Accordingly, some aspects of embodiments of the present invention relate to generating simulated data to generate realistic data for training regression models. According to one embodiment of the present invention, a tissue temperature model is defined as a function of physical parameters, which include: tissue mass (volume), which is related to the loss of power and contributes to the temperature rise; tissue heat transfer coefficient (α), which defines the ratio of the energy lost to the environment (by heat conduction) and does not contribute to the temperature rise; and flush cooling efficiency coefficient (β), which controls the rate at which the flush contributes to tissue cooling (e.g., can reflect tip design, occlusion of flush holes, etc.).

[0092] Figure 6 is a schematic diagram of a simulation framework according to one embodiment of the present invention. As Figure 6 shown, the framework 600 includes models of the patient tissue temperature response model 610 and the RF generator model 630 described above. The RF generator model 630 is configured to have a target power and a target temperature and generate an output flush flow rate and an output RF power. These flow rates and RF powers are supplied to the tissue temperature response model 610, which generates a temperature response and supplies the temperature response back to the RF generator model 630. Accordingly, the RF generator model 630 uses the received temperature to update its flush flow rate and power output (e.g., using techniques of a comparative ablation system).

[0093] In one embodiment, the parameters or coefficients of the above formulas for operations 510 and 530 are derived by calculating the statistical distribution of model parameters from available real-world data (e.g., animal study data). These distributions are then stretched (e.g., the parameters are adjusted) to increase the likelihood that rare cases not measured in the real-world data are better represented in the simulated data. A large number of simulated ablations are then performed using Monte Carlo techniques by randomly sampling parameter sets from the stretched statistical distribution of the parameters and "measuring" the steady-state temperature produced by these parameters. In one embodiment, for each simulation, the simulated ablation starts at an initial flow rate and is subsequently switched to another flow rate in order to collect simulated data for fitting the model for calculating the initial flow rate (corresponding to operation 510) and for fitting the model for calculating the adjusted flow rate (corresponding to operation 530).

[0094] In one embodiment of the invention, the steady-state thermal energy E0 of the tissue mass at body temperature is calculated according to the following equation:

[0095] E0 = C·m(273 + T0)

[0096] where T0 is the tissue steady-state temperature, m is the effective tissue mass affected by ablation (assuming that most of the energy is absorbed as heat), and C*m is the heat capacity of the tissue mass m in joules per kelvin.

[0097] In one embodiment, the energy state of the system at time n in the simulation is calculated based on the following formula:

[0098] E[n] = E[n - 1] + P[n]Δt - α(E[n - 1] - E0)Δt - βC s F[n]Δt(T[n] - T r )

[0099] where E[n - 1] is the energy state at time n - 1, P[n]Δt is the energy delivered during Δt seconds (the time in seconds between steps n and n - 1), α(E[n - 1] - E0)Δt is the energy lost to the environment during Δt seconds due to heat transfer (in the case of non-flushing), and βC s F[n]Δt(T[n] - T r ) represents the energy lost to flushing, where β is the flushing efficiency coefficient, C s is the heat capacity of the flushing fluid (e.g., saline), F[n] is the flow rate at time n (mL / second), T[n] is the tissue temperature (kelvin) and T r is the temperature of the fluid (kelvin) (e.g., room temperature).

[0100] In the above equation, α represents the tissue heat transfer rate, which is a function of the effective area of the catheter tip, blood flow, tissue properties, etc., and will thus vary with time in a dynamic system. For a more realistic model, in some embodiments, α is modeled as a stochastic process (band-limited white noise with a mean α0, a standard deviation σ, and a low-pass cutoff frequency f0).

[0101] In one embodiment, the instantaneous temperature T[n] is updated according to the following formula:

[0102]

[0103] Figure 7A 、 Figure 7B and Figure 7C are diagrams showing the simulated performance of the flushing control method according to an embodiment of the present invention. Figure 7A is a simulation in which the target power is set to 35 W, the target temperature is set to 47 °C, and the maximum temperature is set to 50 °C. As Figure 7A 、 Figure 7B and Figure 7C shown, compared with the oscillating temperature of the comparative examples shown in Figure 3A 、 Figure 3B and Figure 3C the measured temperature is relatively stable over time. Further, as Figure 7A 、 Figure 7B and Figure 7C shown, temperature control is achieved while maintaining a constant power output and with a relatively small change in the flushing flow rate. Since the control system has a more predictable (e.g., linear) response to changes in operating parameters (e.g., output power) and environmental changes (e.g., changes in tip contact quality), the adaptive flushing flow control according to an embodiment of the present invention achieves improved temperature stability and improved usability for the physician.

[0104] Although the present invention has been described in connection with certain exemplary embodiments, it should be understood that the present invention is not limited to the disclosed embodiments. On the contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents.

Claims

1. A catheter ablation system, comprising: A catheter probe having a distal end, the catheter probe comprising: A temperature sensor; A plurality of irrigation holes; and An ablation electrode; A radio frequency (RF) heating controller coupled to the catheter probe and configured to supply RF energy to the ablation electrode to control the ablation electrode to emit heat at a target power; An irrigation controller coupled to the catheter probe and configured to supply irrigation fluid through the catheter probe at a continuously adjustable irrigation flow rate for exiting through the irrigation holes; and An operation console having a processor and a memory, the memory storing instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate based on the target power and the target average temperature, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an initial irrigation flow rate based on the target power and the target average temperature during a pre-ablation time period, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an adjusted flow rate during a power ramp-up time period after the pre-ablation time, setting the adjusted flow rate based on: The target power; The target average temperature; The initial irrigation flow rate; The temperature slope measured by the temperature sensor during the pre-ablation time period; The temperature slope measured by the temperature sensor during the power ramp-up time; and The temperature rise measured by the temperature sensor since the start of ablation.

2. The catheter ablation system according to claim 1, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to an irrigation flow rate selected from more than two different irrigation flow rates.

3. The catheter ablation system according to claim 1, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate by a continuously variable amount.

4. The catheter ablation system according to claim 1, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate to a value within a continuous range.

5. The catheter ablation system according to claim 1, wherein the memory of the operation console further stores instructions that, when executed by the processor, cause the processor to control the irrigation controller to set the irrigation flow rate using a proportional-integral-derivative control loop based on the current temperature measured by the temperature sensor and the target average temperature.

6. The catheter ablation system according to claim 1, wherein the target average temperature is constant with respect to the target power.

7. The catheter ablation system according to claim 1, wherein the target average temperature is set to increase linearly with respect to the target power.

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