Device for temperature-controlled short-duration ablation using resistive heating

Abstract

The present invention, entitled "Temperature-Controlled Short-Duration Ablation Using Resistive Heating," discloses a method comprising performing tissue ablation using a first, high RF power for a short duration; pausing the RF power for a predetermined period; and applying a second, high RF power for a short duration, thereby forming an ablation lesion with a larger surface area and greater depth through resistive heating and thermal delay. The high RF power may range from 75W to 95W, and the short duration may range from 4 seconds to 5 seconds.

Description

[0001] Cross-references to Related Patent Applications

[0002] This patent application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 841,754, filed May 1, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates generally to surgery and, in particular, to surgery using radiofrequency ablation. Background Art

[0004] Radiofrequency (RF) ablation is a treatment modality that uses heat to destroy unwanted tissue. Initially used in the 1980s to treat cardiac arrhythmias, RF ablation has gained clinical application across a wide range of conditions and is now the preferred treatment for certain types of arrhythmias and certain cancers. During RF ablation, electrodes are inserted near a target area under the guidance of medical imaging. The tissue surrounding the electrodes in the target area is destroyed by heating with RF current.

[0005] RF ablation is typically performed at a continuous power level of approximately 20 to 50 watts, with a contact force of approximately 10 g and under irrigation. The ablation time is typically about 1 minute, depending on the size of the lesion to be achieved. Generally speaking, higher power levels reduce the time required to form a specific lesion. However, in prior art systems, higher continuous power values ​​cannot be used because of the risk of steam pop formation.

[0006] US Patent Application 2010 / 0057072 to Roman et al., the disclosure of which is incorporated herein by reference, describes an ablation catheter for performing tissue ablation. This disclosure indicates that RF energy can potentially be safely delivered at wattages up to 100W.

[0007] U.S. Patent No. 7,207,989 to Pike Jr. et al., the disclosure of which is incorporated herein by reference, describes a method for ablating tissue in or around the heart to create enhanced ablation lesions. A distal end of a needle electrode is introduced into tissue. A conductive fluid is infused through the needle electrode and into the tissue. After and / or during the introduction of the fluid into the tissue, the tissue is ablated.

[0008] U.S. Patent Application 2015 / 0272655 to Condie et al., the disclosure of which is incorporated herein by reference, describes a system for preventing unintentional tissue damage caused by unintentional delivery of bipolar radiofrequency energy. The disclosure states that if 100 watts of RF energy is delivered, but only 10 watts are needed to generate the desired electrode temperature, the electrode may be activated for 10% of a given period of time and deactivated for 90% of that duration.

[0009] U.S. Patent No. 8,641,705 to Leo et al., the disclosure of which is incorporated herein by reference, describes a device for controlling lesion size in catheter-based ablation therapy. The device measures the force applied by a contact ablation probe to target tissue and integrates the force over the energized time of the ablation probe. The force-time integral can be calculated and utilized to provide an estimated lesion size (depth, volume, and / or area) in real time.

[0010] U.S. Patent 8,882,761 to Desai, the disclosure of which is incorporated herein by reference, describes a catheter for ablation. The disclosure relates to a commonly practiced ablation procedure and states that in such a procedure, 35 to 50 watts of power are delivered by a temperature-controlled radiofrequency generator at 40 to 50 degrees Celsius, and a saline irrigation fluid rate of 30 ml / min is used during ablation.

[0011] U.S. Patent Application 2011 / 0009857 to Subramaniam et al., the disclosure of which is incorporated herein by reference, describes an open-flow irrigation catheter with turbulent flow. A pressurized fluid is delivered from a fluid lumen within a catheter body to an ablation electrode. The fluid flow within the fluid lumen is generally laminar. The generally laminar fluid flow transitions from the fluid lumen to a turbulent fluid flow within the ablation electrode.

[0012] In an article by Topp et al., entitled "Saline-linked surface radiofrequency ablation: Factors affecting steam popping and depth of injury in the pig liver," Ann. Surg. Vol. 239, No. 4, pp. 518-527 (2004), the authors claim to have identified parameters that predict steam popping and the depth of tissue damage under non-pop conditions. This article is incorporated herein by reference.

[0013] U.S. Patent Applications 15 / 179090, 15 / 179129, 15 / 179167, and 15 / 179196, each entitled “TEMPERATURE CONTROLLED SHORT DURATION ABLATION” and filed on June 10, 2016, the disclosures of which are incorporated herein by reference, describe methods for ablation, including 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 comprising 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 further comprises performing ablation of the tissue by initially using a first power using the selected value, switching to a second power after a predefined time between 3 s and 6 s, and terminating the ablation after a total time of ablation between 10 s and 20 s.

[0014] Documents incorporated by reference into this patent application will be considered an integral part of this patent application, but do not include any terms defined in these incorporated documents in a manner that conflicts with definitions explicitly or implicitly given in this specification, and only the definitions in this specification should be considered. Summary of the Invention

[0015] In some embodiments, a method of ablation comprises:

[0016] Inserting a catheter into a subject, the catheter having an ablation device configured for tissue contact

[0017] electrode;

[0018] performing an ablation session on the tissue for a predetermined total duration, comprising:

[0019] applying radio frequency (RF) power in a range of approximately 75 W-95 W via the electrode, the RF power causing resistive heating for a first duration to form an ablation lesion having a first depth;

[0020] pausing application of RF power to the electrode for a second duration; and

[0021] RF power in the range of approximately 75 W - 95 W is reapplied to the lesion via the electrode for a third duration to increase the lesion to a second depth.

[0022] In some embodiments, the first duration is about 4 seconds.

[0023] In some embodiments, the second duration is no greater than about 10 seconds.

[0024] In some embodiments, the second duration is about 4 seconds.

[0025] In some embodiments, the second duration is about 5 seconds.

[0026] In some embodiments, the third duration is about 4 seconds.

[0027] In some embodiments, the total duration is less than about 18 seconds.

[0028] In some embodiments, the total duration is less than about 13 seconds.

[0029] In some embodiments, the first depth is about 3.5 mm.

[0030] In some embodiments, the second depth is about 4.5 mm.

[0031] In further embodiments, a method of ablation comprises:

[0032] inserting a catheter into a subject, the catheter having an ablation electrode configured for tissue contact;

[0033] performing an ablation session on the tissue for a predetermined total duration, comprising:

[0034] applying resistive heating via the electrode with radio frequency (RF) power in the range of about 75 W-95 W for a first duration to form an ablation lesion having a depth of about 3.5 mm;

[0035] pausing application of RF power to the electrode for a second duration to allow tissue surrounding the lesion to heat by conduction from the lesion; and

[0036] While the tissue surrounding the lesion remains heated by conduction from the lesion, resistive heating is reapplied to the lesion via the electrodes with RF power in the range of approximately 75W-95W for a third duration to increase the depth of the lesion to approximately 4.5 mm.

[0037] In other embodiments, a method of ablation comprises:

[0038] inserting a catheter into a subject, the catheter having an ablation electrode configured for tissue contact;

[0039] performing an ablation session on the tissue for a predetermined total duration of less than about 13 seconds, comprising:

[0040] applying radiofrequency (RF) power in the range of about 75W-95W through the electrodes for about 4 seconds to induce resistive heating, thereby forming an ablation lesion;

[0041] pausing application of RF power to the electrodes for no more than about 5 seconds to allow tissue surrounding the lesion to heat by conduction from the lesion; and

[0042] While the tissue surrounding the lesion remains heated by conduction from the lesion, RF power in the range of about 75W-95W is reapplied to the lesion via the electrodes for about 4 seconds to induce resistive heating, thereby increasing the depth of the lesion.

[0043] In an alternative embodiment, a method of ablation comprises:

[0044] inserting a catheter into a subject, the catheter having an ablation electrode configured for tissue contact;

[0045] performing an ablation session on the tissue for a predetermined total duration of less than about 13 seconds, comprising:

[0046] Radio frequency (RF) power is applied through the electrodes by resistive heating to form a

[0047] Ablation lesion with a depth of 3.5 mm;

[0048] suspending application of RF power to the electrodes to allow tissue surrounding the lesion to heat by conduction from the lesion; and

[0049] While the tissue surrounding the lesion remains heated by conduction from the lesion, RF power is reapplied via the electrodes to increase the depth of the lesion to approximately 4.5 mm by resistive heating.

[0050] In some embodiments, the RF power is about 90W.

[0051] In further embodiments, a method of ablation comprises:

[0052] inserting a catheter into a subject, the catheter having an ablation electrode configured for tissue contact;

[0053] performing an ablation session on the tissue for a predetermined total duration, comprising:

[0054] applying approximately 360 joules of radio frequency (RF) power through the electrode for a first duration of approximately 4 seconds to form an ablation lesion having a first depth of approximately 3.5 mm;

[0055] pausing application of RF power to the electrode for a second duration of no greater than about 10 seconds;

[0056] as well as

[0057] About 360 joules of RF power is reapplied to the lesion via the electrode for a third duration of about 4 seconds to increase the lesion to a second depth of about 4.5 mm.

[0058] In other embodiments, a method of ablation comprises:

[0059] inserting a catheter into a subject, the catheter having an ablation electrode configured for tissue contact;

[0060] performing an ablation session on the tissue for a predetermined total duration, comprising:

[0061] applying about 360 joules of radio frequency (RF) power through the electrode to form an ablation lesion having a first depth of about 3.5 mm by resistive heating;

[0062] pausing application of RF power to the electrode for a second duration to allow the lesion to heat surrounding tissue by conductive heating; and

[0063] When the surrounding tissue contains conductive heating from the lesion, approximately 360 joules of RF power are reapplied to the lesion via resistive heating via the electrodes to a second depth of approximately 4.5 mm.

[0064] The present disclosure will be more fully understood through the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 is a schematic diagram of an ablation system according to an embodiment of the present invention;

[0066] Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D schematically illustrates a distal end of a probe for use in a system according to an embodiment of the present invention;

[0067] Figure 3 is a flow chart of steps performed using the system during an ablation session;

[0068] Figure 4A shows the tissue temperature measured during application of 90 W of RF power for a short duration of 4 seconds;

[0069] Figure 4Bshows the tissue temperature measured during a longer duration of 30 seconds of application of 30 W of RF power;

[0070] Figure 5A shows the lesion surface area and lesion depth resulting from ablation using a single application of high RF power for a short duration; and

[0071] Figure 5B The larger lesion surface area and greater lesion depth resulting from using two applications of high RF power in short duration separated by an interval of RF power pause are shown. DETAILED DESCRIPTION

[0072] Overview

[0073] Radiofrequency (RF) ablation in prior art systems is typically performed at a continuous power level of approximately 20-50 watts, with a contact force of approximately 10 g and under irrigation. The ablation time is typically approximately 1 minute, depending on the size of the lesion to be achieved. Generally speaking, higher power levels reduce the time required to form a particular lesion. However, in prior art systems, higher continuous power values ​​of approximately 100 watts cannot be used because of the risk of steam pop formation.

[0074] The present inventors have discovered that by applying two "pulses" of short duration, high RF power, separated by a predetermined pause interval in the RF power, the lesion created by the first pulse can be improved with a second pulse to have a larger surface area and greater depth. A "sweet spot" without steam popping can be achieved using these two pulses, wherein the first pulse applies high RF power in the range of 75W-95W for a short duration of 4-5 seconds, which results in resistive heating and thermal delay in the lesion, which, during the pause interval in the range of RF power of between 4 and 10 seconds, conducts heat to the surrounding tissue to prepare the surrounding tissue for expansion of the lesion to have a larger surface area and greater depth when the second pulse, also applying high RF power in the range of about 75W-95W for a short duration of 4-5 seconds, is applied. The permissible contact force on the electrode is selected to be in the range of 5g-50g, the maximum permissible temperature of the tissue to be ablated is selected to be in the range of 55°C-65°C, and the irrigation rate for providing irrigation fluid to the electrode is selected to be in the range of 8ml / min-45ml / min.

[0075] In an embodiment of the present invention, during the ablation procedure, the temperature of the tissue to be ablated is carefully monitored and recorded at an extremely high rate. If the monitored temperature exceeds a preset maximum temperature limit, the RF power supplied to the tissue is stopped or reduced.

[0076] The impedance of the RF energy supplied to the ablated tissue is also monitored. If the impedance increases beyond a preset value, the RF energy supply is discontinued.

[0077] Monitoring of temperature and impedance allows embodiments of the present invention to perform tissue ablation at powers of up to 100 W without adversely affecting the tissue during the ablation session. The high power enables ablation sessions to be shortened to typically no more than 10 seconds. DETAILED DESCRIPTION

[0079] Reference Figure 1 , which is a schematic diagram of an invasive medical procedure using an ablation device 12, according to an embodiment of the present invention. The procedure is performed by a physician 14, and by way of example, it is assumed that the procedure in the following description includes ablation of a portion of myocardium 16 of the heart of a human patient 18. However, it should be understood that embodiments of the present invention are not limited to this particular procedure and may also include substantially any ablation procedure on biological tissue.

[0080] To perform ablation by RF ablation, the physician 14 inserts the probe 20 into the patient's lumen so that the distal end 22 of the probe enters the patient's heart. The distal end 22 includes one or more electrodes 24 mounted on the outside of the distal end that contact corresponding locations of the myocardium. The probe 20 has a proximal end 28. Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D The distal end 22 of the probe is described in more detail below. A large ground patch (not shown) is attached to the patient's skin, for example, on the patient's back, abdomen, or thigh. The RF energy delivered by the probe 20 is transferred from the electrode 24 through the patient's body to the large ground patch.

[0081] The device 12 is controlled by a system processor 46, which is located in an operating console 48 of the device. The console 48 includes controls 49 used by the physician 14 to communicate with the processor. During the procedure, the processor 46 generally tracks the position and orientation of the distal end 22 of the probe using any method known in the art. For example, the processor 46 may use a magnetic tracking method in which a magnetic transmitter outside the patient 18 generates a signal in a coil located at the distal end. The device 12 is manufactured by Biosense Webster, of Diamond Bar, CA. The system uses this type of tracking method.

[0082] Software for processor 46 can be downloaded electronically to the processor, for example, over a network. Alternatively or in addition, the software can be provided via non-transitory tangible media such as optical, magnetic, or electronic storage media. Tracking of distal tip 22 is typically displayed on a three-dimensional representation 60 of the patient's heart 18 on screen 62. The progress of ablation performed using device 12 is also typically displayed on screen 62 as a graphic 64 and / or text and numerical data 66.

[0083] To operate the device 12, the processor 46 communicates with a memory 50 having a plurality of modules used by the processor to operate the device. Thus, the memory 50 includes a temperature module 52, a power control module 54, a force module 56, and an irrigation module 58, the functions of which are described below. The modules may include hardware components as well as software components.

[0084] Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D The distal end 22 of the probe 20 is schematically shown according to an embodiment of the present invention. Figure 2A is a cross-sectional view along the length of the probe, Figure 2B It is along Figure 2A A cross-sectional view of the cut IIB-IIB marked in FIG. Figure 2C is a perspective view of a portion of the distal end and Figure 2D is a schematic cross-sectional view of a force sensor 90 incorporated into a proximal portion 92 of the distal end. An insertion tube 70 extends along the length of the probe and is connected at a terminal end at its distal end to a conductive cap electrode 24A, which is used for ablation. The conductive cap electrode 24A is also referred to herein as an ablation electrode. The 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, for example, gold or platinum. The ablation electrode 24A is typically perforated with a series of irrigation holes 72. In one embodiment, there are 36 holes 72, evenly distributed on the electrode 24A.

[0085] Electrical conductors 74 pass through the insertion tube 70 to carry radio frequency (RF) electrical energy from the ablation module 54 ( Figure 1) is transmitted to electrode 24A, thereby energizing the electrode to ablate myocardial tissue in contact with the electrode. As described below, module 54 controls the level of RF power dissipated by electrode 24A. During the ablation procedure, irrigation fluid flowing through hole 72 irrigates the tissue being treated, and the flow rate of the fluid is controlled by irrigation module 58. The irrigation fluid is delivered to electrode 24A by a tube (not shown) within insertion tube 70.

[0086] Temperature sensor 78 is mounted in the conductive top cover electrode 24A at a position arranged axially and circumferentially around the distal end of the probe. In one embodiment disclosed by the present invention considered herein, top cover 24A includes six sensors, wherein a group of three sensors are located at a distal position near the end, and another group of three sensors are located at a slightly more proximal position. This distribution is shown only by way of example, however, a greater or lesser number of sensors can be installed in any suitable position in the top cover. Sensor 78 can include a thermocouple, a thermistor or a miniature temperature sensor of any other suitable type. Sensor 78 is connected by a lead (not shown) running through the length of the insertion tube 70, thereby providing a temperature signal to the temperature module 52.

[0087] In the disclosed embodiment, the top cover 24A includes a relatively thick side wall 73 of approximately 0.5 mm thick to provide the desired thermal insulation between the temperature sensor 78 and the irrigation fluid inside the central cavity 75 of the tip. The irrigation fluid exits the cavity 75 through the hole 72. The sensor 78 is mounted on a rod 77 that fits into a longitudinal aperture 79 in the side wall 73. The rod 77 may comprise a suitable plastic material, such as polyimide, and may be held in place at their distal end by a suitable adhesive 81 (such as epoxy). U.S. patent application 2014 / 0171821 to Govari et al. describes a catheter having temperature sensors mounted in a configuration similar to that described above, which application is incorporated herein by reference. The above arrangement provides a series of six sensors 78, but other arrangements with other numbers of sensors will be apparent to those skilled in the art, and all such arrangements and numbers are within the scope of the present invention.

[0088] In the description herein, it is assumed that distal end portion 22 defines a set of xyz orthogonal axes, wherein axis 94 of the distal end portion corresponds to the z-axis in the set. For simplicity and by way of example, it is assumed herein that the y-axis is in the plane of the paper, the xy plane corresponds to the plane defined by circle 86, and the origin of the xyz axes is the center of the circle.

[0089] Figure 2DFIG2 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, connecting the cap 24A to the proximal end 92. A position sensor 98 is fixed to the distal side of the spring 94 and is assumed herein to include one or more coils coupled to the force module 56 via conductors 100.

[0090] An RF transmitter 102 (typically a coil) is secured to the proximal side of spring 94, and RF energy for the transmitter is provided from force module 56 via conductor 104. The RF energy from the transmitter passes through sensor 98, generating a corresponding signal in conductor 100 of the sensor.

[0091] In operation, when a force is applied to the top cover 24A, the sensor 98 moves relative to the transmitter 102, and this movement causes a change in the sensor signal. The force module 56 uses the change in the sensor signal to provide a measure of the force on the top cover 24A. This measure generally provides the magnitude and direction of the force.

[0092] A more detailed description of sensors similar to sensor 90 is provided in US Patent Application 2011 / 0130648, which is incorporated herein by reference.

[0093] return Figure 1 , the temperature module 52 receives signals from six sensors 78 within the top cover 24A and uses these signals to determine the maximum of six measured temperatures. The temperature module is configured to calculate the maximum temperature at a fixed rate, which is assumed to be every 33 ms in this article, but other embodiments may calculate the maximum temperature at a higher or lower rate. In some embodiments, the maximum temperature is determined at a frequency of at least 30 Hz. The calculated maximum temperature is also referred to as the measured temperature in this article, and the measured temperature is registered as the temperature of the ablated tissue. The temperature module transmits the measured temperature value to the power control module 54.

[0094] The power control module 54 provides RF power to the top cover 24A in the range of 1 W to 100 W. In an embodiment of the present invention, the module can be configured to provide a maximum RF power to the top cover 24A, which can be set in the range of 70 W-100 W.

[0095] The power control module also measures the impedance of the cap 24 A. The impedance is measured at a predetermined rate, herein assumed to be every 500 ms, but other embodiments may measure the impedance at a lower or higher rate.

[0096] The maximum power and the time period for which it is delivered are selected by physician 14. The actual power delivered is determined by the measured temperature received from temperature module 52, as described below.

[0097] Typically, during an ablation treatment, the impedance of cap 24A decreases. Embodiments of the present invention also check whether the impedance has increased by more than a preset value from the previous impedance measurement, assumed herein to be 7Ω, although other embodiments may use a larger or smaller impedance increase value as the preset value. An increase in impedance typically occurs if there are undesirable changes in the ablated tissue, such as charring or steam pop. If the impedance increases by more than the preset value, the power control module is configured to stop delivering RF to cap 24A.

[0098] Despite the power selection by the physician, the power control module is configured to reduce the delivered power, typically by between about 5% and about 95%, if the measured temperature received from the temperature module reaches or exceeds the maximum allowed temperature set by the physician 14 .

[0099] Typically, exceeding the maximum allowable temperature may cause undesirable effects such as charring, condensation on the cap 24A, and / or steam popping in the ablated tissue.

[0100] As described above, force module 56 is capable of measuring the force on cap 24 A. In an embodiment, the allowable force for ablation is in the range of 5g-35g.

[0101] The irrigation module 58 controls the rate at which the irrigation fluid is delivered to the catheter tip. In some embodiments of the present invention, the rate can be set within the range of 8 ml / min to 45 ml / min.

[0102] Figure 3 Flowchart of steps performed during operation of device 12 during an ablation session according to an embodiment of the present invention. In an embodiment of the present invention, an ablation session includes at least three phases: a first phase of a first time period during which a first RF target power is applied; followed by a second phase of a second time period during which the application of RF power is reduced or suspended; and further followed by a third phase of a third time period during which a second RF target power is applied. The target power in each time period is the maximum RF power that can be delivered by power control module 54.

[0103] When high-power RF energy is delivered to the ablation electrode for a predetermined short duration (e.g., 4-5 seconds), in the first phase of the ablation session, the tissue between the electrode and a ground patch elsewhere on the patient's body undergoes resistive heating at a rate proportional to the square of the current density, such that the current density is highest in the tissue immediately adjacent to the electrode because its surface area is relatively small relative to the ground patch. Thus, when the tissue is sufficiently heated to induce necrosis, the tissue immediately surrounding the electrode undergoes resistive heating, thereby forming an ablation lesion within the predetermined short duration.

[0104] In the second phase of the ablation session, RF power to the ablation electrode is reduced or suspended for a predetermined duration (e.g., between about 4 and 10 seconds) so that tissue surrounding the lesion experiences conductive heating from the lesion as resistive heat from the lesion diffuses to surrounding tissue.

[0105] In the third phase of the ablation session, while resistive heat continues to be conducted into the surrounding tissue and before such resistive heat is significantly or completely dissipated, RF energy is applied a second time for a predetermined short duration (e.g., 4 seconds-5 seconds) to produce additional resistive heating in the ablation lesion, resulting in additional conductive heating in the surrounding tissue that causes necrosis, which advantageously increases the size of the ablation lesion in the surrounding tissue, including increased surface area and increased depth.

[0106] According to embodiments of the present invention, tissue subjected to high RF power for a short duration exhibits a thermal delay, wherein the temperature of the ablated tissue continues to increase after the RF ablation at high power subsides. Figure 4A In the present invention, 90W of RF power is applied to the tissue for 4 seconds, during which the tissue temperature increases rapidly at a generally steady rate (i.e., a generally linear slope) to a temperature of 48°C, at which time necrosis begins and initial lesions are formed. Notably, after the RF power is reduced or paused, the tissue temperature continues to increase at approximately the same steady rate to a range of about 72°C–96°C or greater for at least another 2 seconds. The tissue temperature then remains constant at the peak for about 1 second to 2 seconds, after which the tissue temperature begins to decrease at about 4 seconds after the reduction. The tissue temperature decreases at a significantly slower rate than the rate at which the tissue temperature increases during ablation.

[0107] The continued increase in tissue temperature due to resistive heating after ablation subsides advantageously facilitates conductive heating of the tissue surrounding the ablation lesion, which enables or at least prepares and primes the ablation lesion to increase in surface area and depth when further high RF power is applied to the ablation lesion, such as a second application of ablation at 90 W for 4 seconds.

[0108] For a 4-second application of 90 W, the thermal delay in tissue at a depth of 3 mm (as measured by a thermocouple sensor) is approximately 10 seconds. Approximately 90% of the heat in the tissue is dissipated within 4 seconds at a depth of 3 mm. Pausing the RF power for four seconds between the first application of 90 W for 4 seconds and the second application of 90 W for 4 seconds allows for heat dissipation and provides safer conditions for overlapping ablations or ablations of the same lesion.

[0109] In contrast, applying low RF power for a longer duration results in a significant reduction in thermal delay. Figure 4BAs shown, applying RF power at 30 W for 30 seconds results in little, if any, sustained increase in tissue temperature after the RF power is reduced or paused. Although tissue temperature during ablation may peak at a higher temperature, the tissue temperature decreases within approximately 2 seconds after the RF power is reduced. Therefore, there is less thermal delay for conductive heating of the tissue surrounding the ablation lesion to increase surface area or depth.

[0110] Notably, reducing or pausing the RF power between the two short durations or "pulses" of high RF power minimizes the risk of complications due to excessive heating of the tissue (e.g., steam popping and / or charring). Thus, a balance is achieved between excessive heating that causes unintended damage to the tissue and sufficient heating to produce the desired thermal delay in the tissue surrounding the lesion for effective conductive heating to increase the lesion surface area and depth.

[0111] Applying high RF power in short durations or "pulses" of about 4-5 seconds is desirable because the short duration minimizes physician variability in the use and operation of the catheter. The shorter duration can minimize unintended movement of the catheter tip and / or unintended inconsistencies in the pressure applied by the catheter tip to the tissue. In an ablation session that produces a lesion that forms a continuous line of block, such as in a pulmonary vein isolation procedure, the physician's consistency in his or her use of the catheter is an important factor in forming a successful continuous line of block. Therefore, high RF power enables short ablation durations to achieve greater consistency and, therefore, a higher success rate in treating patients.

[0112] It should be understood that thermal energy is measured in joules (J) within the International System of Units (SI). One joule is the amount of energy equivalent to a force of 1 Newton applied over a distance of 1 meter. Thus, this is the energy required to accelerate a mass of 1 kg through a distance of 1 m at a speed of 1 m / s2 in space. 1J=1kg×m2 / s2. Energy is the result of power multiplied by pulse duration (J=W*s), so controlling energy includes controlling two variables: time and power. Therefore, some embodiments of the present invention can also be described as applying a pulse of approximately 360 joules of energy per pulse to the tissue via the electrode, where 360 ​​joules is converted to a power range of 75W over a period of 5 seconds and to a power of 95W over a period of 3.8 seconds to provide resistive heating with sufficient thermal delay.

[0113] Where the ablation electrode is a distal tip electrode, the electrode has a diameter of approximately 2.5 mm, resulting in an ablation lesion having a depth of approximately 3.5 mm, which can be increased to a depth of approximately 4.5 mm using pulses of high RF power for short durations, as described herein.

[0114] refer to Figure 4AIn a range setting step 200, a range is set for each of the above-mentioned variable parameters. In one embodiment, the ranges are set as shown in Table I. Table II below lists additional parameters that may be incorporated into an ablation session, including an irrigation rate ranging from approximately 8 ml / min to 45 ml / min and an allowable force of the ablation electrode on tissue ranging from 5 g to 50 g.

[0115] Table I

[0116]

[0117] Table II

[0118] parameter scope Allowable force 5g–50g Flushing rate 8ml / min–45ml / min

[0119] The range setting step 200 is performed before the physician 14 performs ablation.

[0120] At the beginning of an ablation session, in a probe introduction step 202 , the physician 14 inserts the probe 20 into the desired location in the myocardium 16 using the tracking system incorporated into the device 12 .

[0121] In a select values ​​step 204 , before performing the ablation procedure, physician 14 selects values ​​to be used in the procedure from at least the parameter values ​​listed in Table I (and may include those of Table II) and provides the values ​​to the system using controls 49 .

[0122] In a start RF delivery step 206, an ablation session is initiated by physician 14, thereby initiating operation of device 12. The ablation session uses the parameter values ​​selected in step 204 to perform ablation. Typically, during the ablation session, screen 62 displays to the physician at least the parameter values ​​listed in Table I (or, if not, Table II). Screen 62 can also be configured to display to the physician the progress of RF delivery using methods known in the art. The display of progress can be graphical (such as a simulation of the size of the lesion resulting from the ablation) and / or alphanumeric.

[0123] During the RF delivery procedure, the system uses the power control module to perform several checks on the progress of the procedure, such as Figure 3 This is shown in the flow chart by decision steps 210 , 212 , 216 , 218 , and 224 .

[0124] refer to Figure 3The power control module in step 207 starts a counter, where N = 0. In step 208, the power control module applies a first pulse of high RF power as the first phase of the ablation session. In decision step 210, the power control module checks whether the measured tissue temperature exceeds 100°C, as a safety measure. If the measured tissue temperature is not greater than 100°C, the power control module in decision step 212 checks whether the preset short duration of the first pulse has expired. If not, the first pulse continues to be applied. If so, the power control module in step 213 increments the counter by one and, in step 214, pauses the RF power as the second phase of the ablation session.

[0125] In decision step 216, the power control module checks whether the preset time period of the pause has been reached. If so, the power control module in decision step 218 checks whether the count N=2. If so, the power control module in step 220 provides a prompt (visual and / or audio) to the physician to move the electrode to another tissue location. If not, the power control module returns to step 208 to apply a second pulse of high RF power as the third phase of the ablation session and proceeds through decision steps 210 and 212 as described above until the count N=2 in decision step 218, in which case the power control module in step 220 prompts the physician to move the electrode to another tissue location.

[0126] Whenever the tissue temperature measured in decision step 210 exceeds 100° C., the power control module stops the RF power in step 222 as a safety measure and displays the N count to the physician and asks the physician whether to reset the system in decision step 224. In some embodiments, step 222 may involve reducing the RF power rather than stopping the RF power.

[0127] like Figure 5A and Figure 5B As shown, the ablation lesions formed in the thigh tissue and the beating heart tissue when 90W was applied once for 4 seconds had a smaller width and a smaller depth than the ablation lesions formed in the thigh tissue and the beating heart tissue when 90W was applied “twice” for 4 seconds (which were separated by an ablation pause interval of 4 seconds).

[0128] It should be understood that the above embodiments are cited by way of example only, and the present invention is not limited to what has been specifically shown and described hereinabove. 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.

Claims

1. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration; The instructions further cause the device to: applying radio frequency (RF) power in the range of 75 W-95 W via the electrode, the RF power causing resistive heating for a first duration of 4-5 seconds to form an ablation lesion having a first depth; pausing application of RF power to the electrodes for a second duration of 4-10 seconds to allow tissue surrounding the lesion to heat by conduction from the lesion; and RF power in the range of 75 W - 95 W is reapplied to the lesion via the electrode for a third duration of 4-5 seconds to increase the lesion to a second depth.

2. The apparatus of claim 1, wherein the total duration is less than 18 seconds.

3. The apparatus of claim 1, wherein the total duration is less than 13 seconds. The apparatus of claim 1 , wherein the first depth is 3.5 mm. The apparatus of claim 1 , wherein the second depth is 4.5 mm.

6. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration; The instructions further cause the device to: applying resistive heating via the electrode with radio frequency (RF) power in the range of 75 W - 95 W for a first duration of 4-5 seconds to form an ablation lesion having a depth of 3.5 mm; pausing application of RF power to the electrode for a second duration of 4-10 seconds to allow tissue surrounding the lesion to heat by conduction from the lesion; as well as While the tissue surrounding the lesion remains heated by conduction from the lesion, resistive heating is reapplied to the lesion via the electrodes with RF power in the range of 75W-95W for a third duration of 4-5 seconds to increase the depth of the lesion to 4.5 mm.

7. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration of less than 13 seconds; The instructions further cause the device to: applying radiofrequency (RF) power in the range of 75W-95W through the electrodes for 4 seconds to induce resistive heating, thereby forming an ablation lesion; pausing application of RF power to the electrode for no more than 5 seconds to allow tissue surrounding the lesion to be heated by conduction from the lesion; as well as While the tissue surrounding the lesion remains heated by conduction from the lesion, RF power in the range of 75W-95W is reapplied to the lesion via the electrodes for 4 seconds to induce resistive heating, thereby increasing the depth of the lesion.

8. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration of less than 13 seconds; The instructions further cause the device to: applying radio frequency (RF) power via the electrode for a first duration of 4-5 seconds by resistive heating to form an ablation lesion having a depth of 3.5 mm; pausing application of RF power to the electrode for a second duration of 4-10 seconds to allow tissue surrounding the lesion to heat by conduction from the lesion; as well as While the tissue surrounding the lesion remains heated by conduction from the lesion, RF power is reapplied via the electrodes by resistive heating for a third duration of 4-5 seconds to increase the depth of the lesion to 4.5 mm.

9. The apparatus of claim 8, wherein the RF power is 90 W.

10. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration; The instructions further cause the device to: applying 360 joules of energy at radio frequency (RF) power through the electrode for a first duration of 4 seconds to form an ablation lesion having a first depth of 3.5 mm; pausing application of RF power to the electrode for a second duration of no greater than 10 seconds; as well as Energy of 360 joules at RF power is reapplied to the lesion via the electrode for a third duration of 4 seconds to increase the lesion to a second depth of 4.5 mm.

11. A device for ablation, comprising: a catheter having an ablation electrode configured for tissue contact; processor; a memory having stored thereon instructions that, when executed by the processor, cause the device to perform an ablation session on the tissue for a predetermined total duration; The instructions further cause the device to: applying 360 joules of energy at radio frequency (RF) power through the electrode for a first duration of 4-5 seconds to form an ablation lesion having a first depth of 3.5 mm by resistive heating; pausing application of RF power to the electrode for a second duration of 4-10 seconds to allow the lesion to heat surrounding tissue by conductive heating; as well as When the surrounding tissue contains conductive heating from the lesion, 360 joules of energy are reapplied to the lesion via the electrodes by resistive heating with RF power for a third duration of 4-5 seconds to a second depth of 4.5 mm.

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