Energy-directed radiofrequency (RF) ablation

Abstract

The present invention is entitled "Energy-Directed Radiofrequency (RF) Ablation." The present invention provides a method for ablating body tissue, comprising defining a target amount of ablative energy required to create a designated ablation lesion in tissue within a patient's body. Contact is established between an ablation probe and the tissue. Using the ablation probe, an ablation signal is applied to the tissue, the ablation signal delivering the target amount of ablative energy for a minimum duration allowed within a defined maximum power constraint.

Description

Technical Field

[0001] The present invention relates generally to radiofrequency (RF) ablation, and in particular to cardiac RF ablation. Background Art

[0002] Techniques for controlling RF ablation have been previously proposed in the patent literature. For example, U.S. Patent Application Publication 2004 / 0158237 describes an integrated multi-energy ablation system that allows a variety of ablation procedures to be performed without exchanging catheters. The present invention provides a console that is connected to one or more energy processing devices, such as catheters or probes, via an energy delivery umbilical system. The integrated ablation station is designed to be compatible with commercial catheters and allows for continuous or simultaneous ablation and mapping procedures to be performed when deeper and wider lesion capabilities and / or a wider temperature ablation spectrum are required. Incorporating a closed fluid circulation system allows for circulating fluid to cool the RF catheter ablation electrode during radiofrequency energy delivery.

[0003] As another example, U.S. Patent Application Publication No. 2017 / 0209208 describes a method comprising selecting a first maximum radiofrequency (RF) power to be delivered by an electrode within a range of 70 W-100 W, and selecting a second maximum RF power to be delivered by the electrode within a range of 20 W-60 W. The method also comprises selecting an allowable force on the electrode within a range of 5 g-50 g, selecting a maximum allowable temperature of the tissue to be ablated within a range of 55° C.-65° C., and selecting an irrigation rate for providing irrigation fluid to the electrode within a range of 8 mL / min-45 mL / min. The method also comprises performing ablation of the tissue by initially using the first power using the selected value, switching to the second power after a predefined time between 3 s and 6 s, and terminating the ablation after a total ablation time between 10 s and 20 s.

[0004] U.S. Patent Application Publication No. 2012 / 0157890 describes body tissue ablation performed by inserting a probe into the body of a living subject, advancing the probe to contact tissue within the body, generating energy at a power output level, and delivering the generated energy into the tissue via the probe. While delivering the generated energy, the ablation is also performed by determining a measured temperature of the tissue and a measured power level of the delivered energy, and controlling the power output level as a function of the measured temperature and the measured power level. The present invention also describes associated apparatus for performing the ablation. Summary of the Invention

[0005] One embodiment of the present invention provides a method for ablation of body tissue, comprising defining a target amount of ablative energy required to produce a designated ablation lesion in tissue within a patient's body, establishing contact between an ablation probe and the tissue, and applying an ablation signal to the tissue using the ablation probe, the ablation signal delivering the target amount of ablative energy for a minimum duration allowed within a defined maximum power constraint.

[0006] In some embodiments, the method further comprises applying an irrigation fluid proximate the tissue during application of the ablation signal.A temperature is monitored proximate the tissue, and if the monitored temperature exceeds a defined maximum temperature limit, a flow rate of the irrigation fluid is increased.

[0007] In some embodiments, the method further includes reducing the power of the ablation signal and extending the duration of the ablation signal if the monitored temperature exceeds the defined maximum temperature limit but the flow rate of the irrigation fluid exceeds a defined maximum flow rate limit.

[0008] In one embodiment, monitoring the temperature comprises measuring a temperature of an electrode delivering the ablation signal to the tissue. In another embodiment, the method further comprises extending the ablation duration until a predetermined amount of ablation energy is reached to be applied to the tissue.

[0009] In some embodiments, the method further comprises applying an irrigation fluid proximate to the tissue during application of the ablation signal, monitoring temperature proximate to the tissue, and if the monitored temperature exceeds a defined maximum temperature limit, reducing the power of the ablation signal to maintain the temperature within the maximum temperature limit to a given tolerance.

[0010] In some embodiments, the method further includes increasing irrigation flow to reduce the temperature to below the maximum temperature limit if the power of the ablation signal decreases during application of the ablation signal, and then increasing the power of the ablation signal to the maximum power target.

[0011] In one embodiment, the method further comprises stopping the ablation signal if the target amount of ablation energy is not met during an allowed duration during application of the ablation signal.

[0012] According to an embodiment of the present invention, a system for ablation of body tissue is further provided, the system comprising a memory, an ablation probe, a generator, and a processor. The memory is configured to store a value of a target amount of ablation energy required to produce a specified ablation lesion in tissue within a patient's body. The ablation probe is configured to contact the tissue. The generator is configured to generate an ablation signal. The processor is configured to control the generator and the ablation probe to apply the ablation signal having the target amount of ablation energy to the tissue for a minimum duration allowed within a defined maximum power constraint.

[0013] The present invention will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic, illustrative diagram of a system for cardiac radiofrequency (RF) ablation therapy according to an embodiment of the present invention; and

[0015] Figure 2 To schematically illustrate an embodiment of the present invention Figure 1 Flowchart of the steps of the algorithm performed during the operation of the RF ablation system. DETAILED DESCRIPTION

[0016] Overview

[0017] Cardiac radiofrequency (RF) ablation systems can vary the amount of ablation energy and the corresponding lesion depth. To achieve this, such systems can simultaneously vary the irrigation rate and RF power input, as well as the ablation duration, while ensuring that the temperature of the ablated tissue does not exceed a maximum value. However, during ablation, such as during ablation of thin tissue, the tissue may sometimes have a poor temperature response (e.g., the temperature may rise or fall unexpectedly). The amount of energy (which varies accordingly) can lead to uncontrolled ablation lesion depth.

[0018] The embodiments of the present invention described below operate the ablation system in a constant energy mode, wherein a predetermined amount of ablative RF energy is applied to the tissue in the shortest possible time to achieve a pre-planned lesion depth within constraints. (Short ablation times help focus the energy in the desired lesion area, i.e., reduce the amount of energy that escapes the desired area). A maximum RF power level is set, resulting in a nominal time for ablation. During ablation, the temperature is monitored to maintain it within an allowable temperature range, including high and low temperature limits.

[0019] During ablation, irrigation flow rate and power output level are adjusted to maintain the maximum possible RF power while keeping the temperature within its allowed range. In some embodiments, when the applied RF power level is reduced, the ablation time is extended so that a preset amount of ablation RF energy target is met.

[0020] Typically, a processor running an algorithm for ablation commands an increased irrigation flow rate within the allowed flow rate range so that the ablation power can be maintained at the highest possible level allowed by the preset upper power limit and temperature range. In other words, power reduction is only used as a last resort when it is impossible to stay below the maximum temperature limit using irrigation alone.

[0021] In some embodiments, the disclosed method includes the steps of: (a) defining a target amount of ablation energy required to produce a specified ablation lesion in tissue within a patient; (b) making contact between an ablation probe and the tissue; and (c) using the ablation probe, applying an ablation signal to the tissue that delivers the target amount of ablation energy during a minimum duration allowed within a defined maximum power constraint.

[0022] In some embodiments, during application of the ablation signal, the disclosed method further comprises applying an irrigation fluid proximate the tissue and monitoring a temperature proximate the tissue. If the monitored temperature exceeds a defined maximum temperature limit, the processor commands an increase in the flow rate of the irrigation fluid.

[0023] If the monitored temperature exceeds the defined maximum temperature limit, but the flow rate of the irrigation fluid exceeds a defined maximum flow rate limit, the processor commands a reduction in the power of the ablation signal and an extension of the duration of the ablation signal.

[0024] The disclosed RF ablation techniques allow for maintaining maximum RF power levels for shorter durations, depending on the target amount of RF energy to be placed in tissue, and thus can improve the clinical outcomes of catheter-based RF ablation procedures.

[0025] System Description

[0026] Figure 1 FIG2 is a schematic diagram illustrating a system 12 for cardiac radiofrequency (RF) ablation therapy according to an embodiment of the present invention. Typically, the memory 45 of the system 20 stores a plurality of ablation protocols for different clinical scenarios, such as Figure 2 The protocol described in .

[0027] Physician 26 inserts catheter 28 through a blood vessel into a chamber of heart 24 of subject 22 and manipulates the catheter so that distal end 32 of the catheter contacts the area of ​​endocardium to be treated. The tip electrode 51 of catheter 28, seen in inset 25, includes one or more temperature sensors 50 that measure the electrode temperature. In some embodiments, this temperature is used as an estimate of the temperature near the ablated tissue.

[0028] After positioning the distal tip 32 at the ablation site and ensuring that the tip contacts the endocardium, the operator 26 activates the RF energy generator 44 in the console 42 to supply RF energy to the distal tip 32 through the cable 38. Simultaneously, an irrigation pump 48 supplies a cooling fluid, such as a saline solution, to the distal tip through the lumen in the tube 40 and the catheter 28. Typically, before and during ablation, a display 46 displays the values ​​of the ablation parameters, such as those listed in Tables I-IV below, to the physician 26.

[0029] The operation of the RF energy generator and the irrigation pump can be adjusted to provide an appropriate volume of irrigation fluid to cool the catheter tip and tissue during the ablation procedure without adding excessive irrigation fluid to the heart. Each temperature sensor within the temperature sensor 50 provides feedback to the console 42 for use in, for example, controlling the RF energy dose and / or irrigation volume.

[0030] In order to operate the system 12, the processor 41 includes a plurality of modules that are used by the processor to operate the system. These modules include a temperature module 52, a power control module 54, and a flushing module 55, the functions of which are described below. Specifically, the processor 41 operates as disclosed herein including Figure 2 , which enables the processor 41 to perform the disclosed steps, as further described below.

[0031] Although the illustrated embodiment is specifically directed to ablating cardiac tissue using a tip ablation device, the methods described herein may alternatively be applied to an ablation device including multiple ablation electrodes, when the operation of each electrode is independently controlled by processor 41 .

[0032] Energy-directed RF ablation

[0033] Figure 2 To schematically illustrate an embodiment of the present invention Figure 1 FIG2 is a flow chart illustrating the steps of an algorithm executed in the operation of the RF ablation system 20. The process begins at an ablation parameter preset step 60, in which the physician 26 presets each of the variable ablation parameters described above, and specifically sets a target amount of ablation energy. Such steps may involve generating multiple protocols for different clinical scenarios, wherein such protocols are stored, for example, in the memory 45 of the system 20.

[0034] In some embodiments, the ablation parameters are set as shown in one of Tables I - IV. Typically, for RF power, the operator of the system only sets the maximum RF power, while the system automatically sets the minimum RF power to zero for safety reasons.

[0035] Tables I-IV provide four different settings that can be used to optimize lesion depth while minimizing collateral damage, depending on clinical needs, such as:

[0036] Table I - Low Depth (less than 2mm)

[0037] Table II - Medium Depth (2mm-3.5mm)

[0038] Table III—High Depth (3.5mm-5.0mm)

[0039] Table IV - Excess Depth (greater than 5.0 mm)

[0040] Low Depth Parameters:

[0041]

[0042] Table I

[0043] Medium depth parameters:

[0044]

[0045] Table II

[0046] High Depth Parameters:

[0047]

[0048] Table III

[0049] Ultra-high depth parameters:

[0050]

[0051] Table IV

[0052] The ablation parameter setting step 60 is performed before the physician 26 performs ablation.

[0053] At the start of ablation therapy, physician 26 inserts catheter 28 into the desired location in heart 24 using the catheter position tracking system incorporated into system 20 in a probe introduction step 62. At this step, physician 26 brings catheter 28 into contact with the target cardiac tissue.

[0054] At impedance determination step 64, processor 41 uses power control module 54 to check whether the impedance of electrode 51 is greater than a preset impedance value. If so, the system stops the ablation procedure of electrode 51 in termination step 66. If step 64 returns a negative value, control of the algorithm continues to RF ablation step 68.

[0055] At the RF delivery step 68, the physician 26 operates the system 20 using the particular ablation protocol selected by the physician, with the parameter values ​​selected in step 60. The physician 26 is tasked with executing the preset ablation protocol by applying (e.g., using the electrodes 51) a target amount of energy during the minimum duration allowed, for example, as shown in Table 1. The display 46 of the system 20 can be configured to display the progress of RF delivery to the electrodes to the physician 26 by methods known in the art. The display of progress can be graphical (such as a simulation of the corresponding lesion size resulting from the ablation) and / or via an alphanumeric display.

[0056] During the RF delivery procedure, processor 41 uses temperature module 52 to perform multiple checks on the progress of the procedure as shown in the flowchart by decision steps 70, 74, and 78. Irrigation module 55 and power control module 54 perform the modifications shown in the flowchart by modifying steps 72 and 76.

[0057] In an alternative embodiment, the temperature is checked, and if the temperature reaches a pre-specified target, the processor instructs the generator to reduce power to keep the temperature within the pre-specified temperature target. If the system identifies a power reduction exceeding a given power (e.g., a 1W reduction), the flush flow rate is increased to prevent the power reduction. Increasing the flow rate can increase power while maintaining the target temperature.

[0058] At a first temperature decision step 70, the processor uses the temperature module 52 to check whether the measured tissue temperature deviates from the allowed preset temperature range selected in step 60. If the temperature decision step 70 returns an affirmative answer, then at an irrigation modification step 72, the irrigation control module 55 modifies the irrigation flow rate to bring the temperature within the allowed range.

[0059] At a second temperature decision step 74, the processor uses the temperature module 52 to again check whether the measured tissue temperature deviates from the allowable preset temperature range selected in step 60. If the temperature decision step 74 returns a positive answer, the power control module 54 modifies the power to the electrode 51 at a power modification step 76 to bring the temperature within the allowable range.

[0060] If the modifications to steps 72 and 76 are unsuccessful in controlling tissue temperature according to Table I, the system stops the ablation procedure of electrode 51 at termination step 66 .

[0061] If any of decision steps 70 , 74 , or 78 returns a negative answer, control proceeds to an ablation decision step 80 .

[0062] At ablation decision step 80, processor 41 checks whether the amount of ablation energy deposited by a given electrode, set in step 60, has been reached. If it has been reached, the process ends. If the energy has not been reached or exceeded, control passes to duration decision step 82, in which processor 41 checks whether the maximum ablation time set in step 60 has been reached or exceeded. If the maximum preset time has been reached, the system stops the procedure on electrode 51 in termination step 66. Otherwise, the process loops back to decision step 64.

[0063] For simplicity and clarity, decision steps 64, 70, 74, 78, 80, and 82 are presented sequentially in the flowchart. However, typically, the system performs these steps in parallel using the power control module.

[0064] Figure 2 The exemplary flow chart shown in is chosen solely for conceptual clarity. Embodiments of the present invention also include additional steps of the algorithm, such as checking the level of contact force of the electrode 51 with the tissue, which have been intentionally omitted from the disclosure herein in order to provide a more simplified flow chart.

[0065] In one embodiment, the method disclosed herein further includes the following steps during application of the ablation signal: applying an irrigation fluid in the vicinity of the tissue, monitoring the temperature in the vicinity of the tissue, and if the monitored temperature exceeds a defined maximum temperature limit, reducing the power of the ablation signal to maintain the temperature within the maximum temperature limit to a given tolerance.

[0066] In another embodiment, the disclosed method further comprises the steps of, during application of the ablation signal, increasing the irrigation flow to reduce the temperature to below the maximum temperature limit if the power of the ablation signal is reduced, and subsequently increasing the power of the ablation signal to the maximum power target.

[0067] In another embodiment, the disclosed method further includes stopping the ablation signal if the target amount of ablation energy is not met during an allowed duration during the application of the ablation signal.

[0068] Although the embodiments described herein primarily discuss cardiac applications, the methods and systems described herein may also be used, for example, to ablate other organs of the body.

[0069] It should therefore be understood that the embodiments described above are cited by way of example, and that the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and subcombinations of the various features described above, as well as variations and modifications thereof, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art. The documents incorporated by reference into this patent application are considered an integral part of this application, except that if any term defined in these incorporated documents conflicts with a definition explicitly or implicitly given in this specification, only the definition in this specification shall be considered.

Claims

1. A system for ablation of body tissue, the system comprising: a memory configured to store a value of a target amount of ablation energy required to create a designated ablation lesion in tissue within a patient; an ablation probe configured to contact tissue; a generator configured to generate an ablation signal; and a processor configured to control the generator and the ablation probe to apply the ablation signal having the target amount of ablation energy to the tissue for a minimum duration allowed within a defined maximum power constraint; as well as controlling the probe during application of the ablation signal to: applying an irrigation fluid proximate to the tissue; monitoring a temperature in the vicinity of the tissue; increasing the flow rate of the flushing fluid if the monitored temperature exceeds a defined maximum temperature limit; as well as If the monitored temperature exceeds the defined maximum temperature limit, but the flow rate of the irrigation fluid exceeds a defined maximum flow rate limit, the processor is further configured to control the generator to reduce the power of the ablation signal and extend the duration of the ablation signal. 2 . The system of claim 1 , wherein the monitored temperature is the temperature of an electrode that delivers the ablation signal to the tissue.

3. The system of claim 1, wherein the processor is further configured to control the generator to extend the ablation duration until a preset amount of ablation energy is reached to be applied to the tissue.

4. The system of claim 1 , wherein the processor is further configured to: applying an irrigation fluid proximate to the tissue; monitoring the temperature of the vicinity of the tissue; and If the monitored temperature exceeds a defined maximum temperature limit, the power of the ablation signal is reduced to maintain the temperature within the maximum temperature limit up to a given tolerance.

5. The system of claim 4 , wherein the processor is further configured to: during application of the ablation signal, if the power of the ablation signal is decreasing, increase irrigation flow to reduce the temperature to below the maximum temperature limit, and then increase the power of the ablation signal to the maximum power target. 6 . The system of claim 1 , wherein the processor is further configured to stop the ablation signal if the target amount of ablation energy is not met during the allowed duration.

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