Ablate low- to medium-depth lesions using ultra-high radiofrequency (RF) power in ultra-short durations

Abstract

The present invention is entitled "Ablation of low-medium depth lesions in ultrashort duration using ultra-high radiofrequency (RF) power." The present invention discloses a method for ablation of body tissue, the method comprising defining an ultra-high power ultra-short duration (UPUD) ablation protocol, the ultra-high power ultra-short duration (UPUD) ablation protocol specifying an ablation signal having (i) a target ablation power of at least 400 watts and (ii) a pulse duration of no more than three seconds for producing a specified ablation lesion in tissue within a patient's body. Contact is achieved between an ablation probe and the tissue. Using the ablation probe, an ablation signal is applied to the tissue according to the UPUD protocol, the UPUD protocol delivering the ablation signal having the specified target ablation power and duration.

Description

Technical Field

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

[0002] Techniques for optimizing radiofrequency (RF) ablation therapy have previously been proposed in the patent literature. For example, U.S. Patent Application Publication 2009 / 0093802 describes a system and method for a transseptal cardiac procedure. A method for treating a patient according to a specific embodiment includes positioning a tissue penetrating guidewire near the septum, directing an energy pulse to the guidewire, and advancing the guidewire into and through the septum by moving the guidewire in a series of discrete steps in a distal direction. Each step may have a predetermined distance measured outside the patient's body. The method may also include transmitting a catheter via the guidewire after the guidewire has passed through the septum.

[0003] As another example, U.S. Patent Application Publication No. 2004 / 0172110 describes an RF heating balloon catheter capable of cauterizing a target lesion in the atrial vestibule. The RF heating balloon catheter includes: an inflatable balloon capable of contacting the target lesion when inflated; an RF electrode, which serves as a counter electrode to a surface electrode attached to the surface of the subject's body and is placed in the wall of the balloon or inside the balloon to provide RF power between the surface electrode and the RF electrode; a temperature sensor capable of sensing the temperature inside the balloon; a guide shaft extending from the distal end of an inner tube and capable of holding the balloon on the target lesion; and a guide wire extending through the catheter and the guide shaft.

[0004] U.S. Patent 9,962,217 describes a tissue ablation system and method in which a cardiac catheter incorporates a pressure sensor for sensing a mechanical force against the distal tip when engaging an ablation site. A controller responds to the pressure sensor to calculate an ablation volume based on the relationship between the contact pressure at the site, the ablator's power output, and the energy application time. The system applies a prescribed dose of energy to the tissue at a specific application time and a specific power level to ablate the tissue, wherein at least one of the application time and power level of the dose depends on the mechanical force. Summary of the Invention

[0005] An embodiment of the present invention provides a method for ablation of body tissue, the method comprising defining an ultra-high power ultra-short duration (UPUD) ablation protocol, the ultra-high power ultra-short duration (UPUD) ablation protocol specifying an ablation signal having (i) a target ablation power of at least 400 watts and (ii) a pulse duration of no more than three seconds for producing a specified 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 according to the UPUD protocol, the UPUD protocol delivering the ablation signal having the specified target ablation power and duration.

[0006] In some embodiments, defining the UPUD ablation protocol includes setting the pulse duration to no longer than one second. In other embodiments, defining the UPUD ablation protocol includes setting the pulse duration to no longer than a single heartbeat cycle of the patient.

[0007] In some embodiments, the method further comprises monitoring the temperature of the tissue adjacent to the ablation signal during application of the ablation signal, and

[0008] If the monitored temperature exceeds a predefined maximum temperature, the ablation signal is stopped.

[0009] In another embodiment, the method further comprises monitoring a contact force applied by the probe to the tissue during application of the ablation signal, and stopping the ablation signal if the monitored contact force drops below a pre-specified value.

[0010] According to an embodiment of the present invention, there is further provided a system for ablation of body tissue, the system comprising

[0011] A memory, an ablation probe, an ultra-high power ultra-short duration (UPUD) generator, and a processor. The memory is configured to store values ​​of an ultra-high power ultra-short duration (UPUD) ablation protocol, the ultra-high power ultra-short duration (UPUD) ablation protocol specifying an ablation signal having (i) a target ablation power of at least 400 watts and (ii) a pulse duration of no more than three seconds for producing a specified ablation lesion in tissue within a patient's body. The ablation probe is configured to make contact with the tissue. The UPUD 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 to the tissue according to the UPUD protocol, which delivers an ablation power having a specified target ablation power and duration.

[0012] 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

[0013] Figure 1is a schematic, pictorial illustration of a system for ultra-high power, ultra-short duration (UPUD) cardiac radiofrequency (RF) ablation therapy according to an embodiment of the present invention; and

[0014] Figure 2 To schematically illustrate an embodiment of the present invention Figure 1 A flow chart of the steps of an algorithm performed during operation of an ultra-high power ultra-short duration (UPUD) RF ablation system. DETAILED DESCRIPTION

[0015] Overview

[0016] Cardiac radiofrequency (RF) ablation systems can vary the rate of ablation power during ablation in an attempt to achieve precise lesion depth. Some systems can vary the RF power and irrigation rate, as well as the duration of ablation, while ensuring that the temperature of the ablated tissue does not exceed a maximum value or drop below a minimum value.

[0017] However, during ablation of thin tissue, for example, the tissue may have a poor temperature response (e.g., the tissue temperature may rise / fall unexpectedly). As a result, the system may vary the amount of energy it applies to the tissue accordingly, which may result in uncontrolled lesion depth. For example, in a typical protocol where tens of watts are applied for a duration of up to ten seconds, uncontrolled conductive heating mechanisms in the tissue may result in uncontrolled lesion depth.

[0018] In some cases, other control readings such as impedance may be inaccurate, resulting in incorrect tuning of RF power and ablation duration, such as applying too little power for too long, which can lead to inefficient ablation and possible side effects such as blood clots.

[0019] The embodiments of the present invention described below operate the ablation system in a constant ultra-high power ultra-short duration (UPUD) mode. Typically, the UPUD ablation protocols disclosed herein use ultra-high rated ablation RF power (e.g., at least 400 watts per ablation electrode) applied to tissue for an ultra-short duration (e.g., no more than three seconds and typically only lasting a sub-second duration of 0.5-0.9 seconds, depending on the target lesion depth) to achieve pre-planned lesions. The ultra-short ablation time ensures that the high power is concentrated in the desired lesion area to significantly reduce the risk of collateral damage (e.g., damage caused by conductive heating of the tissue) from energy escaping the desired area.

[0020] Using the UPUD mode of RF ablation disclosed in the present invention, the resulting lesion depth is primarily determined by impedance heating of the tissue rather than conductive heating of the tissue, thereby achieving a high level of reproducibility in lesion parameters. Specifically, the difference between the conventional ablation protocol described above and the UPUD protocol disclosed in the present invention is significant, especially in areas where maintaining a stable catheter position is difficult, such as the ridge between the pulmonary veins and the atrial appendage.

[0021] The ability to generate and apply RF ablations within a duration comparable to a single heartbeat significantly reduces the need for the catheter to remain stable for long durations (e.g., ten heartbeats). The reduced need, in turn, reduces the effort and time a physician needs to spend stabilizing the catheter to achieve accurate and effective ablation lesions. In one embodiment, the RF ablation duration is set to not exceed a single heartbeat cycle (single cardiac cycle) of the patient. The cardiac cycle can be pre-measured for a specific patient, or a universal upper limit can be set that applies to all patients.

[0022] In some embodiments, a processor running an algorithm monitors temperature during ablation and stops the ablation procedure if the temperature exceeds a maximum temperature value allowed (e.g., a pre-specified high temperature limit). Additionally or alternatively, during ablation, the processor monitors the contact force between the catheter and the tissue and stops the ablation procedure if the contact force drops below a pre-specified value that results in a decrease in ablation efficiency.

[0023] For multi-electrode catheters, embodiments of the present invention can apply approximately 400 watts to each of the electrodes for typical desired durations in the sub-second range as described above. The disclosed UPUD ablation can produce, for example, a ring of highly localized, precise lesions.

[0024] The disclosed UPUD RF ablation technology may therefore improve the clinical outcomes of catheter-based RF ablation procedures.

[0025] System Description

[0026] Figure 1 FIG2 is a schematic diagram illustrating a system 20 for ultra-high power ultra-short duration (UPUD) 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] As seen, physician 26 inserts catheter 28 through a blood vessel into a chamber of the heart 24 of subject 22 and manipulates the catheter so that the distal end 32 of the catheter contacts the heart tissue in the area to be treated. Figure 1The tip electrode 51 of the catheter 28 shown in FIG. 1 includes one or more temperature sensors 50 that measure the electrode temperature. In some embodiments, this temperature is used to estimate the temperature near the ablated tissue. The tip electrode 51 also includes one or more contact force sensors 53 that measure the force applied by the tip electrode 51 to the tissue.

[0028] Methods for estimating the instantaneous contact force applied by the ablation probe against tissue are described in U.S. patent application Ser. No. 16 / 403,865, entitled “Adapting Irrigation rate in Radiofrequency (RF) Ablation in Response to Contact-Force Variation,” filed May 6, 2019, which is assigned to the assignee of the present patent application and the disclosure of which is incorporated herein by reference. Alternatively, any other suitable technique may be used to estimate the contact force applied by the tip electrode 51 on the tissue.

[0029] After positioning the distal tip 32 at the ablation site and ensuring that the tip is in contact with the cardiac tissue, the operator 26 activates an ultra-high power ultra-short duration (UPUD) RF energy generator 44 in the console 42 to supply RF power to the distal tip 32 via 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 ablation parameters, such as those listed in Tables I-II below, to the physician 26.

[0030] The timing of ultra-high power ultra-short duration (UPUD) RF and irrigation can be adjusted to provide the appropriate volume of irrigation fluid to cool the catheter tip and tissue during the ultra-short ablation period without adding excessive irrigation fluid to the heart.

[0031] In order to operate the system 20, the processor 41 includes a plurality of modules used by the processor to operate the system. These modules include a temperature module 52, a power setting module 54, a flushing module 55, and a contact force module 57, the functions of which are described below. Specifically, the processor 41 operates as disclosed herein and includes Figure 2 The dedicated algorithm in the embodiment enables the processor 41 to perform the steps disclosed in the present invention, as further described below.

[0032] Although the illustrated embodiments are specifically directed to ablating cardiac tissue using a tip ablation device, the methods described herein may alternatively be applied to an ablation device comprising a plurality of ablation electrodes, each of which is independently controlled by a processor 41 and operates according to the RF power and duration specified in a UPUD protocol, such as Figure 2 As stated.

[0033] Applying ultra-high RF power for ultra-short durations

[0034] 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 an ultra-high power ultra-short duration (UPUD) RF ablation system 20. The process begins with an ablation parameter preset step 60, during which the physician 26 presets the ablation power and duration. Step 60 may involve generating different protocols for different clinical scenarios and storing the protocols in, for example, the memory 45 of the system 20.

[0035] In some embodiments, the above ablation parameters and other preset parameters are set as shown in Tables I-II. Typically, for the RF power of each electrode, the operator of the system only sets the ultra-high RF power, and for safety reasons, the system automatically sets the minimum RF power to zero.

[0036] Tables I-II provide different possible settings that can be used to optimize lesion depth while minimizing collateral damage, depending on clinical needs.

[0037] parameter Value / Range Preset ablation power levels 400W Preset ablation time 0.5s-0.7s Maximum allowable temperature 65℃ Contact force sampling rate 5Hz-70Hz Preset flush flow rate 2ml / min-30ml / min

[0038] Table-I Low ablation depth

[0039] parameter Value / Range Preset ablation power levels 400W Preset ablation time 0.8s-0.9s Maximum allowable temperature 65℃ Contact force sampling rate 5Hz-70Hz Flushing flow rate 2ml / min-30ml / min

[0040] Table II Ablation Lesion Depth

[0041] The ablation parameter setting step 60 is performed before the physician 26 performs ablation, for example, by using or modifying a predefined UPUD ablation protocol.

[0042] At the start of ablation therapy, in a probe introduction step 62 , physician 26 inserts catheter 28 into a desired location in heart 24 using a catheter position tracking system incorporated into system 20 .

[0043] Next, physician 26 makes physical contact between electrode tip 51 and target cardiac tissue at an electrode-tissue contact step 64. Processor 41 receives contact force indicative signals from sensors on catheter 28 and determines the instantaneous contact force.

[0044] At RF delivery step 66, physician 26 operates system 20 using the particular ablation protocol selected by physician 26, for which parameter values ​​were selected in steps 60 and 62. Physician 26 is tasked with executing the preset ablation protocol by applying (e.g., using electrode 51) the target power for an ultra-short duration defined, for example, in a UPUD protocol including the ablation parameters shown in Tables I-II.

[0045] The values ​​given in Tables I-II are example values, and any other suitable values ​​can be used in alternative embodiments. Generally speaking, the power level applied to each electrode is at least 400W, and the pulse duration does not exceed three seconds. In most practical implementations, the pulse duration does not exceed one second.

[0046] In some embodiments, the pulse duration is set to no longer than a single heartbeat cycle of the patient (a single cardiac cycle). Performing ablation in a single heartbeat is advantageous, for example, because it is significantly easier to keep the catheter stable for the duration of the procedure. In one embodiment, the processor 41 pre-measures the heartbeat cycle of the specific patient being treated and ensures that the pulse duration does not exceed the pre-measured heartbeat cycle. Alternatively, the pulse duration can be set to be shorter than a universal duration (e.g., a sub-second duration) that is generally applicable to all patients.

[0047] Display 46 of system 20 can be configured to display the progress of RF delivery to the electrodes to 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 ablation) and / or by an alphanumeric display.

[0048] During the RF delivery protocol, the processor 41 performs a number of checks on the progress of the protocol using the temperature module 52 and the contact force module 57. In some embodiments, the temperature is checked (68), and if the temperature exceeds an allowable maximum value according to Table 1, the processor ends the delivery of power and stops the ablation protocol at an ablation termination step 72. Additionally or alternatively, the contact force is checked (70), and if the contact force drops below a pre-specified value, the processor ends the delivery of power and stops the ablation protocol at an ablation termination step 72.

[0049] Figure 2 The exemplary flow chart shown in is chosen purely for the sake of conceptual clarity. This embodiment also includes additional steps of the algorithm, such as checking the flushing flow rate, which have been intentionally omitted from the disclosure herein in order to provide a more simplified flow chart.

[0050] Although the embodiments described herein are primarily directed to cardiac applications, the methods and systems described herein may also be used to ablate other organs of the body, such as kidney and prostate ablation.

[0051] 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 values ​​of an ultra-high power ultra-short duration UPUD ablation protocol specifying a radio frequency (RF) ablation signal having (i) a target ablation power of at least 400 watts and (ii) a pulse duration of no more than three seconds for producing a specified ablation lesion in tissue within a patient; an ablation probe configured to come into contact with the tissue; an ultra-high power ultra-short duration UPUD generator configured to generate the RF ablation signal; and a processor configured to control the UPUD generator and the ablation probe to apply the RF ablation signal to the tissue according to the UPUD ablation protocol, the UPUD ablation protocol delivering the ablation power having the specified target ablation power and duration, The processor pre-measures the patient's heart cycle and ensures that the duration of the RF ablation signal does not exceed the pre-measured heart cycle of the patient.

2. The system of claim 1, wherein the pulse duration does not exceed one second.

3. The system of claim 1 , wherein the processor is further configured to control the ablation probe during application of the RF ablation signal to: monitoring the temperature near the tissue; and If the monitored temperature exceeds a predefined maximum temperature, the RF ablation signal is stopped.

4. The system of claim 1 , wherein the processor is further configured to control the ablation probe during application of the RF ablation signal to: monitoring the contact force applied by the ablation probe on the tissue; and If the monitored contact force drops below a pre-specified value, the RF ablation signal is stopped.

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