ABLATION OF LOWER-MEDIUM-DEEP LESSIONS USING ULTRA-HIGH RADIO FREQUENCY (HF) POWER FOR ULTRA-SHORT DURATION

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to radiofrequency (RF) ablation, and particularly to cardiac RF ablation.BACKGROUND OF THE INVENTION

[0002] Techniques for optimizing radiofrequency (RF) ablation treatments were previously proposed in patent literature. For example, U.S. Patent Application Publication 2009 / 0093802 describes systems and methods for transeptal cardiac procedures. A method for treating a patient in accordance with a particular embodiment includes positioning a tissue penetrating guidewire adjacent to a cardiac septum, directing pulses of energy to the guidewire, and advancing the guidewire into and through the septum by moving the guidewire in a distal direction in a series of discrete steps. Individual steps can be of a predetermined distance measured outside the patient's body. The method can further include passing a catheter over the guidewire after the guidewire has passed through the septum.

[0003] As another example, U.S. Patent Application Publication 2004 / 0172110 describes an RF heating balloon catheter that is capable of cauterizing a target lesion in an atrial vestibule. The RF heating balloon catheter comprises an inflatable balloon capable of coming into contact with a target lesion when inflated, an RF electrode serving as a counter to a surface electrode attached to a surface of a subject's body and being placed in a wall of the balloon or inside the balloon to supply RF power between the surface electrode and the RF electrode, a temperature sensor capable of sensing temperature inside the balloon, a guide shaft projecting from the extremity of the inner tube and capable of holding the balloon on the target lesion, and a guidewire extended through the catheter tube and the guide shaft.

[0004] U.S. Patent 9,962,217 describes tissue ablation systems and methods in which a cardiac catheter incorporates a pressure detector for sensing a mechanical force against the distal tip when engaging an ablation site. Responsively to the pressure detector, a controller computes an ablation volume according to relationships between the contact pressure against the site, the power output of an ablator, and the energy application time. The system applies a specified dosage of energy for an application time and at a power level to the tissue for ablation thereof, wherein at least one of the application time of the dosage and the power level depend on the mechanical force.

[0005] US 2017 / 065329 A1 describes an electrosurgical system that includes an electrosurgical probe connected to a control console, wherein the probe is capable of coagulating and ablating tissue depending on a selected operating mode. Before operating the system, probe-specific data stored in a memory device associated with the probe is read by a processing device in the console. The data includes source impedance values specific to a coagulation or cutting mode of operation. A constant duty cycle value for a modulated cutting mode also is provided. Depending on the operating mode selected, an RF generator adjusted to have a predetermined source impedance value provides a voltage value to the probe. During the duty-cycled mode, the RF generator generates an instantaneous voltage value output for a duty cycle portion that is less than 100% of a time period, which value is no less than a maximum continuous average voltage value for the electrosurgical probe.

[0006] WO 2015 / 192027 A1 describes catheter systems, tools and methods for the selective and rapid application of DC voltage pulses to drive irreversible electroporation for minimally invasive transurethral prostate ablation. In one embodiment, a switch unit is used to modulate and apply voltage pulses from a cardiac defibrillator, while in another, the system controller can be configured to apply voltages to an independently selected multiplicity or subsets of electrodes. Devices are disclosed for more effective DC voltage application including the infusion of cooled fluid to elevate the irreversible electroporation threshold of urethral wall tissue and to selectively ablate regions of prostate tissue alone.

[0007] US 10322286 B2 describes a system that includes a pulse waveform generator and an ablation device coupled to the pulse waveform generator. The ablation device includes at least one electrode configured for ablation pulse delivery to tissue during use. The pulse waveform generator is configured to deliver voltage pulses to the ablation device in the form of a pulsed waveform. A first level of a hierarchy of the pulsed waveform includes a first set of pulses, each pulse having a pulse time duration, with a first time interval separating successive pulses. A second level of the hierarchy of the pulsed waveform includes a plurality of first sets of pulses as a second set of pulses, a second time interval separating successive first sets of pulses, the second time interval being at least three times the duration of the first time interval.

[0008] WO 2018 / 006086 A1 describes systems and methods that utilize RF energy to treat a patient's skin (e.g., dermis and hypodermis) or other target tissue including at a depth below a tissue surface (e.g., skin surface, mucosal surfaces of the vagina or esophagus). In various aspects, the methods and systems described herein can provide a RF-based treatment in which the deposition of RF energy can be selectively controlled to help ensure heating uniformity during one or more of body sculpting treatment (lipolysis), skin tightening treatment (laxity improvement), cellulite treatment, vaginal laxity or rejuvenation treatment, urinary incontinence treatment, fecal incontinence treatment, all by way of non-limiting examples. In various aspects, the systems can comprise one or more sources of RF energy (e.g., a RF generator), a treatment applicator comprising one or more electrode arrays configured to be disposed in contact with a tissue surface, and a return electrode (e.g., a neutral pad) to the tissue surface.

[0009] US 10405920 B2 describes a method, including selecting a first maximum radiofrequency (RF) power to be delivered by an electrode within a range of 70W-100W, and selecting a second maximum RF power to be delivered by the electrode within a range of 20W-60W. The method also includes selecting an allowable force on the electrode within a range of 5 g-50 g, selecting a maximum allowable temperature, of 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 8-45 ml / min. The method further includes performing an ablation of tissue using the selected values by initially using the first power, switching to the second power after a predefined time between 3 s and 6 s, and terminating the ablation after a total time for the ablation between 10 s and 20 s.

[0010] US 2018 / 289284 A1 describes systems, devices and methods of determining orientation of a distal end of a medical instrument (e.g., electrode-tissue orientation of an RF ablation catheter). One or more processors may be configured to receive temperature measurements from each of a plurality of temperature-measurement devices distributed along a length of the distal end of the medical instrument and determine the orientation from a group of two or more possible orientation options based on whether temperature measurement values or characteristics of temperature response determined from the temperature measurement values satisfy one or more orientation criteria.SUMMARY OF THE INVENTION

[0011] The invention is defined by the appended claims and is directed to a system for cardiac tissue ablation. Methods described herein are not explicitly recited in the wording of the claims, but are considered as useful for understanding the invention.

[0012] The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which:BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a schematic, pictorial illustration of a system for ultrahigh-power ultrashort-duration (UPUD) cardiac radiofrequency (RF) ablation therapy, in accordance with an embodiment of the present invention; and Fig. 2 is a flow chart that schematically illustrates steps of an algorithm performed in the operation of the ultrahigh-power ultrashort-duration (UPUD) RF ablation system of Fig. 1, according to an embodiment of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS OVERVIEW

[0014] Cardiac radiofrequency (RF) ablation systems may vary 20 the rate of ablative power during ablation in an attempt to achieve an exact lesion depth. Some systems may vary both the RF power and irrigation rate, as well as the time duration of ablation, while ensuring that the temperature of the ablated tissue does not exceed a maximum value or falls below a minimal value.

[0015] However, during ablation of, for example, thin tissues, the tissue may have poor temperature response (e.g., tissue temperature may rise / fall unexpectedly). As a result, the system may correspondingly vary the amount of energy it applies to tissue, which may result in an uncontrolled lesion depth. For example, in typical

[0016] protocols that apply several tens of watts for a time duration up to ten seconds, an uncontrolled conductive heating mechanism in the tissue may cause an uncontrolled lesion depth.

[0017] In some cases, other control readings, such as impedances, may be inaccurate, leading to incorrect tuning of RF power and duration of ablation, such as applying too little power for too long a time, resulting in inefficient ablation and possible side effects, such as blood clots.

[0018] Embodiments of the present invention that are described hereinafter operate an ablation system in a constant ultrahigh-power ultrashort-duration (UPUD) mode.

[0019] The disclosed UPUD ablation protocols use an ultrahigh rating of ablating RF power (a preset ablation power level of 400 watts) that is applied to tissue for ultrashort time duration (a preset ablation time of 0.5 to 0.7 seconds or 0.8 to 0.9 seconds) to achieve a preplanned lesion. The ultrashort ablation time ensures that the high power is concentrated in the desired lesion area, so as to considerably reduce risk of collateral damage from energy that escapes the desired area, for example damage caused by conductive heating via tissue.

[0020] With the disclosed UPUD-mode of RF ablation the resulting lesion depth mainly depends on the resistive heating of the tissue and not the conductive heating of tissue, so as to achieve high level of reproducibility of lesion parameters. In particular, the difference between the aforementioned conventional ablation protocols and the disclosed UPUD protocols is significant especially in areas where it is hard to maintain a stable position of the catheter, for example, at a ridge between a pulmonary vein and an appendage.

[0021] The capability to generate and apply RF ablation in a time duration comparable with a single heartbeat significantly reduces requirements over catheter stability for long duration (e.g., for ten heartbeats). The relaxed requirement, in turn, reduces the effort and time a physician needs to spend in order to stabilize the catheter for achieving an accurate, effective lesion. In an embodiment, the RF ablation duration is set to not exceed a single heartbeat period (a single cardiac cycle) of the patient. The heartbeat period may be pre-measured for the particular patient, or a general upper bound suitable for all patients can be set.

[0022] In some embodiments, a processor running an algorithm during the ablation monitors the temperature, and, if temperature exceeds an allowable maximal temperature value (e.g., a prespecified high temperature limit) the processor halts the ablation procedure. Additionally or alternatively, during the ablation the processor monitors contact force between catheter and tissue, and if contact force falls below a prespecified value, which causes ablation efficiency to fall, the processor halts the ablation procedure.

[0023] With multi-electrode catheters, embodiments of the invention are able to apply approximately 400 watts for each of the electrodes for a typical required time duration being, as noted above, in the sub-second range. The disclosed UPUD ablation can produce, for example, a ring of accurate lesions that are highly localized.

[0024] The disclosed UPUD RF ablation technique may thus improve the clinical outcome of catheter-based RF ablation procedures.SYSTEM DESCRIPTION

[0025] Fig. 1 is a schematic, pictorial illustration of a system 20 for ultrahigh-power ultrashort-duration (UPUD) cardiac radiofrequency (RF) ablation therapy, in accordance with an embodiment of the present invention. Typically, a memory 45 of system 20 stores numerous ablation protocols for different clinical scenarios, such as the protocol described in Fig. 2.

[0026] As seen, a physician 26 inserts a catheter 28 through a blood vessel into a chamber of a heart 24 of a subject 22, and manipulates the catheter so that a distal end 32 of the catheter contacts cardiac tissue in an area that is to be treated. A tip electrode 51 of catheter 28, seen in inset 25, comprises one or more temperature sensors 50, which measure the temperature of the electrode. In some embodiments this temperature is used to estimate the temperature in the vicinity of the ablated tissue. Tip electrode 51 further comprises one or more contact force sensors 53, which measure a force exerted by tip electrode 51 on tissue. A method to estimate an instantaneous contact force exerted by an ablation probe against the tissue is described in U.S. Patent application 16 / 403,865, filed May 6, 2019, entitled "Adapting Irrigation rate in Radiofrequency (RF) Ablation in Response to Contact-Force Variation," which is assigned to the assignee of the present patent application. Alternatively, any other suitable technique can be used for estimating the contact force exerted by tip electrode 51 on the tissue.

[0027] After positioning distal end 32 at an ablation site, and ensuring that the tip is in contact with cardiac tissue, operator 26 actuates an ultrahigh-power ultrashort-duration (UPUD) RF energy generator 44 in a control console 42 to supply RF power via a cable 38 to distal end 32. Meanwhile, an irrigation pump 48 supplies a cooling fluid, such as normal saline solution, via a tube 40 and a lumen in catheter 28 to the distal end. Typically, both before and during the ablation, a display 46 displays values of the ablation parameters, such as those listed in Tables I-II below, to physician 26.

[0028] Timing ultrahigh-power ultrashort-duration (UPUD) RF and irrigation may be coordinated in order to give the appropriate volume of irrigation during the ultrashort ablation, so as to cool the tip of the catheter and the tissue without overloading the heart with excessive irrigation fluid.

[0029] In order to operate system 20, a processor 41 includes a number of modules used by the processor to operate the system. These modules comprise a temperature module 52, a power setting module 54, an irrigation module 55, and a contact force module 57, the functions of which are described below. In particular, processor 41 runs a dedicated algorithm as disclosed herein, included in Fig. 2, which enables processor 41 to perform the disclosed steps, as further described below.

[0030] Although the pictured embodiment relates specifically to the use of a tip ablation device for ablation of heart tissue, the methods described herein may alternatively be applied in ablation devices comprising multiple ablation electrodes where each electrode is independently controlled by processor 41 and operates according to RF power and duration specified in UPUD protocols, such as described in Fig. 2.APPLYING ULTRAHIGH RF POWER FOR ULTRASHORT DURATIONS

[0031] Fig. 2 is a flow chart that schematically illustrates steps of an algorithm performed in operation of ultrahigh-power ultrashort-duration (UPUD) RF ablation system 20 of Fig. 1, according to an embodiment of the present invention. The process begins at an ablation parameter presetting step 60, in which physician 26 presets ablation power and time duration. Step 60 may involve generating different protocols for different clinical scenarios, and storing the protocols, for example, in memory 45 of system 20.

[0032] The aforementioned ablation parameters, and other preset paraments, are set as shown in Tables I-II. Typically, for the RF power per electrode, an operator of the system only sets the ultrahigh RF power, while a minimal RF power is automatically set by the system to zero for safety reasons.

[0033] Tables I-II bring different possible settings that may be used to optimize lesion depth and minimize collateral damage, depending on the clinical need. Table-I Low Lesion DepthParameter Value / Range Preset ablation power level400 WPreset ablation time0.5 s - 0.7 sAllowable maximal temperature65 °CSampling rate of contact force5 Hz - 70 HzPreset irrigation flow rate2-30 ml / min Table-II Medium Lesion Depth Parameter Value / Range Preset ablation power level400 WPreset ablation time0.8 s - 0.9 sAllowable maximal temperature65 °CSampling rate of contact force5 Hz - 70 HzIrrigation flow rate2-30 ml / min

[0034] Ablation parameters setting step 60 is implemented before physician 26 performs an ablation, e.g., by using or modifying a predefined UPUD ablation protocol.

[0035] At the beginning of an ablation session, 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.

[0036] 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.

[0037] At RF delivery step 66, physician 26 operates system 20, with a particular ablation protocol that physician 26 selected, for which the parameter values were selected in steps 60 and 62. The task of physician 26 is to perform the preset ablation protocol by applying (e.g., with electrode 51) the target rate of power during the ultrashort time duration defined, for example, in UPUD protocols comprising ablation parameters shown in Tables I-II.

[0038] In some embodiments, the pulse duration is set so as not to exceed a single heartbeat duration (a single cardiac cycle) of the patient. Performing ablation in a single heartbeat is advantageous, for example, in that it is considerably easier to maintain the catheter stable for the duration of the procedure. In an embodiment, processor 41 pre-measures the heartbeat period of the specific patient being treated, and ensures that the pulse duration does not exceed the pre-measured heartbeat duration. Alternatively, the pulse duration may be set to be shorter than a global duration (e.g., some sub-second duration) that is suitable generally for all patients.

[0039] Display 46 of system 20 may be configured to display to physician 26, by methods which are known in the art, the progress of the RF delivery to the electrode. The display of the progress may be graphical, such as a simulation of the dimensions of a respective lesion as it is produced by the ablation, and / or by way of an alphanumeric display.

[0040] During the RF delivery procedure, processor 41 uses temperature module 52 and contact force module 57 to perform a number of checks on the progress of the procedure.

[0041] In some embodiments, temperature is checked (68), and if temperature exceeds the allowable maximal value according to Table I, the processor ceases delivery of power and halts the ablation procedure, at an ablation termination step 72. Additionally or alternatively, contact force is checked (70), and if contact force falls below a prespecified value, the processor ceases delivery of power and halts the ablation procedure, at an ablation termination step 72.

[0042] The example flow chart shown in Fig. 2 is chosen purely for the sake of conceptual clarity. The present embodiment also comprises additional steps of the algorithm, such as checking a flow of irrigation, which have been omitted from the disclosure herein purposely on order to provide a more simplified flow chart.

[0043] Although the embodiments described herein mainly address cardiac applications, the methods and systems described herein can also be used in ablating other organs of the body, such as in renal and prostate ablation. It will thus be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are within the scope of the appended claims.

Claims

1. A system (20) for cardiac tissue ablation, the system (20) comprising: a memory (45), which is configured to store values of an ultrahigh-power ultrashort-duration (UPUD) ablation protocol that specifies a radiofrequency (RF) ablation signal having (i) a preset ablation power level of 400 Watts and (ii) a preset ablation time of 0.5 to 0.7 seconds or 0.8 to 0.9 seconds, for creating a specified lesion in tissue in a body of a patient (22); wherein the UPUD ablation protocol further comprises a maximal temperature of 65 °C, a sampling rate of contact force of 5 to 70 Hz, and a preset irrigation flow rate of 2 to 30 ml / min; an ablation probe, which is configured to make contact with the tissue; an ultrahigh-power ultrashort-duration (UPUD) generator (44), which is configured to generate the RF ablation signal; and a processor (41), which is configured to control the generator (44) and the ablation probe to apply the RF ablation signal to the tissue according to the UPUD protocol, which delivers the ablation power having the specified target ablation power and duration.

2. The system (20) according to claim 1, wherein the processor (41) is further configured to control the probe, during application of the RF ablation signal, to: monitor a temperature in a vicinity of the tissue; and if the monitored temperature exceeds a predefined maximal temperature, halt the ablation signal.

3. The system (20) according to claim 1, wherein the processor (41) is further configured to control the probe, during application of the RF ablation signal, to: monitor a contact force that the probe exerts on tissue; and if the monitored contact force falls below a prespecified value, halt the RF ablation signal.