Detecting electrode contact using absolute and relative thresholds

Abstract

A medical device includes a probe configured for insertion into a body of a patient and including three or more electrodes arranged along a distal portion of the probe and configured to contact tissue within the body. An electrical signal generator configured to apply a signal between a selected pair of electrodes, the signal having an amplitude sufficient to ablate tissue contacted by the pair of electrodes. A controller configured to measure a current flowing through at least one of the electrodes not included in the selected pair while the signal is applied, and to issue a notification indicating that the tissue is not sufficiently ablated if the measured current exceeds a preset threshold.

Description

Technical Field

[0001] This invention relates generally to medical devices, and more particularly to equipment and methods for electroablation of tissues. Background Technology

[0002] Irreversible electroporation (IRE) and radiofrequency ablation (RFA) are soft tissue ablation techniques that are typically performed by inserting a catheter or thin probe into the tissue and applying a high-frequency current from the end of the catheter or probe into the tissue.

[0003] In intracellular respiration (IRE), short pulses of a strong electric field are applied to create permanent and therefore lethal nanopores in the cell membrane, thereby disrupting cellular homeostasis (internal physical and chemical conditions). Typical pulse widths range from 0.5 μs to 5 μs, pulse frequencies from 50 kHz to 1 MHz, and pulse amplitudes from 200 V to 2000 V. Cell death following IRE is induced by apoptosis (programmed cell death) and non-necrosis (cell damage, which leads to cell destruction through the action of its own enzymes), as in other heat- and radiation-based ablation techniques. IRE is commonly used for tumor ablation in areas where the precision and preservation of the extracellular matrix, blood flow, and nerves are crucial.

[0004] In radiofrequency ablation (RFA), a high-power alternating current is applied to tissue, causing the tissue to ablate due to the heat generated by the current. RFA is used to ablate electrical conduction pathways in tissues such as the heart, tumors, and other dysfunctional tissues. RFA typically uses currents with amplitudes ranging from 0V to 200V and frequencies ranging from 350kHz to 500kHz. Summary of the Invention

[0005] The embodiments of the present invention described below provide improved systems and methods for electroablation of tissues.

[0006] According to an embodiment of the invention, a medical device is provided, comprising a probe configured for insertion into a patient's body, and including three or more electrodes arranged along a distal portion of the probe and configured to contact tissue within the body. An electrical signal generator is configured to apply a signal between a selected pair of electrodes, the signal having an amplitude sufficient to ablate tissue contacted by the pair of electrodes. A controller is configured to measure a current flowing through at least one electrode not included in the selected pair when the signal is applied, and to issue a notification indicating that the tissue has not been sufficiently ablated if the measured current exceeds a preset threshold.

[0007] In some embodiments, the controller is configured to issue a first notification indicating that the tissue has not been sufficiently ablated if the measured current exceeds a first threshold, and a second notification indicating parasitic current between at least one of the electrodes and one of a selected pair of electrodes when the measured current does not exceed the first threshold but exceeds a second threshold below the first threshold. In the disclosed embodiments, the second threshold is less than half of the first threshold. Alternatively, the second threshold can be adjusted by the user.

[0008] Typically, the controller is configured to measure and monitor the corresponding current flowing through multiple electrodes that are not in the selected pair.

[0009] In the disclosed embodiments, the amplitude of the signal is sufficient to cause irreversible electroporation (IRE) of the tissue contacted by the selected pair of electrodes.

[0010] Alternatively or in addition, the distal portion is flexible and configured for insertion into the patient's heart. In one embodiment, the distal portion is configured to form a loop within the heart.

[0011] According to an embodiment of the invention, a method for medical treatment is also provided, the method comprising inserting a probe into a patient's body, wherein the probe includes three or more electrodes arranged along a distal portion of the probe. At least a selected pair of electrodes of the probe are brought into contact with tissue within the body. A signal with an amplitude sufficient to ablate the tissue contacted by the selected pair of electrodes is applied between the selected pair of electrodes. A current flowing through at least one electrode not included in the selected pair is measured while the signal is applied. If the measured current exceeds a preset threshold, a notification indicating that the tissue has not been sufficiently ablated is issued. Attached Figure Description

[0012] The invention will be more fully understood through the following detailed description of embodiments thereof, taken in conjunction with the accompanying drawings, wherein:

[0013] Figure 1 This is a schematic diagram of a medical device during a medical ablation procedure according to an exemplary embodiment of the present invention;

[0014] Figure 2A and Figure 2B This is a schematic diagram of the distal portion of a catheter according to an exemplary embodiment of the present invention.

[0015] Figure 3 This is a graph of the parasitic current flowing through the electrode over time during an ablation procedure according to an exemplary embodiment of the present invention, which schematically illustrates the threshold of the leakage current. Detailed Implementation

[0016] In medical electroablation, an electric current is driven through the patient's tissue. In IRE, the current creates nanopores in cell membranes, while in RFA, the current heats the tissue. The current is injected into the tissue, for example, through electrodes mounted on a catheter inserted into the patient's body. The electrodes are connected to a current source; when the electrodes contact the desired portion of the tissue, the current source is activated, and ablation occurs. Both IRE and bipolar RFA utilize paired electrodes, such that the ablation current flows into the tissue through one electrode and returns through the other. In unipolar RFA, the ablation current flows into the tissue from one electrode in the catheter, as in bipolar RFA, but returns through the patient's body via a common electrode attached to the patient's skin.

[0017] When using flexible catheters with multiple electrodes, such as catheters with a distal portion configured to form a collar, etc. or The catheter (manufactured by Biosense Webster Inc. (Irvine, California)) may have some electrodes that are unintentionally too close to other electrodes, and may even be in contact with each other. Specifically, if a given pair of electrodes is used for ablation, and a third electrode is too close to either of the electrodes in that pair, a significant portion of the ablation current can be shunted to the third electrode, thereby reducing or possibly even eliminating the intended effect of the ablation. The physician performing the ablation may not be aware of this effect on the ablation and therefore will not recognize the need for correction. This problem is particularly pronounced in IRE, where insufficient current can lead to irreversible electroporation; however, it can also occur in other types of treatment, such as RFA.

[0018] The embodiments of the invention described herein address this problem by monitoring the current flowing through those catheter electrodes that are not involved in ablation at any given time during the procedure. These embodiments provide a medical device comprising a probe, an electrical signal generator, and a controller. The probe (such as a catheter) comprises three or more electrodes arranged along the distal portion of the probe and configured to contact tissue within the body. The electrical signal generator applies an electrical signal between a selected pair of electrodes, the signal having an amplitude sufficient to ablate the tissue contacted by that pair of electrodes.

[0019] To ensure that the current actually flows through the tissue and is not shunted to other electrodes, the controller measures the current flowing through these other electrodes when a signal is applied. The current can be measured directly or indirectly, for example, by measuring the voltage on the electrodes as an indicator of the current flowing through them; and the reference to "measuring current" in this specification and claims should be understood to cover any and all measurement methods known in the art, whether direct or indirect. If the measured current exceeds a preset threshold, the controller issues a notification indicating that the tissue may not have been adequately ablated. This notification prompts the operator of the device to check and adjust the placement of the distal portion of the probe in the body, after which ablation can be performed as needed.

[0020] In the disclosed embodiments, one or more current thresholds can be set. A single threshold can be used on its own to alert a physician to the possibility of inadequate ablation, but using two thresholds provides a finer level of guidance. For example, a first threshold can be set at a high level such that current flowing through a given electrode exceeding the threshold indicates that the electrode may be in physical contact with one of the ablation electrodes in the pair. A second threshold can be set at a lower level to indicate that a given electrode is close enough to one of the ablation electrodes in the pair to draw parasitic current flowing through a third electrode, which can have a significant impact on the desired ablation current, even if the third electrode is not in physical contact with the ablation electrode. For example, the second threshold can be set at half the first threshold or possibly a smaller value.

[0021] Based on notifications from the controller, the physician performing the ablation can decide on further actions. If the current to a given electrode exceeds a first threshold, the physician is notified, and it can be assumed that the ablation has been insufficient. In this case, the physician will typically take actions such as adjusting the catheter and repeating the ablation. If the current to a given electrode is less than the first threshold but exceeds a second threshold, the physician is notified. This notification allows the physician to accept or refuse ablation, and also allows them to adjust the second threshold or leave it as is.

[0022] Figure 1 This is a schematic illustration of a medical device 20 during a medical ablation procedure according to an exemplary embodiment of the present invention. A physician 22 performs the procedure on a patient 24 using an ablation catheter 26, the distal portion 28 of which includes a plurality of ablation electrodes 30. The ablation procedure may include an irreversible IRE procedure or a bipolar RFA procedure, or possibly a combination of both.

[0023] In the illustrated embodiment, physician 22 is performing a cardiac ablation procedure using medical device 20. To begin the procedure, physician 22 inserts catheter 26 into the body of patient 24 and then uses control handle 32 to navigate the catheter to an appropriate site inside or outside the patient's heart 34. The physician then contacts the distal portion 28 with tissue 36 of the heart 34 (such as myocardial or epicardial tissue). Physician 22 selects a pair of electrodes 30a and 30b for ablation. Physician 22 then actuates an electro-signal generator (SIGGEN) 38 to generate an ablation signal 40, wherein signal parameters are selected, for example, to be used as an IRE signal or an RFA signal or a combination of both. Signal 40 is carried through catheter 26 to the ablation electrodes 30a and 30b via different corresponding channels, such that an ablation current flows from one of the electrodes in the pair through the patient's tissue 36 and returns through the other electrode in the pair.

[0024] The medical device 20 also includes a controller (CTRL) 44. Before and / or during an ablation procedure, the controller 44 receives setup parameters 46 for the procedure from the physician 22 (or other user). For example, using one or more suitable input devices, such as a keyboard, mouse, or touchscreen, the physician 22 defines the ablation mode (IRE, RFA), parameters of the ablation signal (e.g., power, duration), and the electrode pair used for ablation. The physician 22 may also define a first threshold and a second threshold for detecting parasitic leakage of the ablation current pair to any electrode not included in the selected electrode pair.

[0025] Physician 22 can also use the aforementioned input device to input additional setting parameters 46 for the ablation signal 40, such as maximum power, maximum current amplitude, maximum voltage amplitude, signal duration, and / or any other relevant parameters. In response to receiving the setting parameters 46, controller 44 communicates with signal generator 38, causing the signal generator to generate signal 40 according to the setting parameters. Additionally, controller 44 can display the setting parameters on display 48 (which may include the aforementioned touchscreen).

[0026] During the procedure, the controller 44 uses any suitable tracking technology to track the corresponding position of the ablation electrode 30 within the subject's body. For example, the distal portion 28 may include one or more electromagnetic position sensors (not shown) that output signals that vary with the sensor's position in the presence of an external magnetic field generated by one or more magnetic field generators 50. Based on these signals, the controller 44 can determine the electrode's position. Alternatively, for each electrode, the controller 44 can determine the corresponding impedance between the electrode and a plurality of external electrodes 52 at various locations on the subject's body surface, and then calculate the ratio between these impedances to locate the electrode position. Alternatively, the controller 44 may use both electromagnetic tracking and impedance-based tracking, as described, for example, in U.S. Patent No. 8,456,182, the disclosure of which is incorporated herein by reference.

[0027] In some implementations, the controller 44 determines which of the ablation electrodes 30 contacts the subject's tissue and applies the ablation signal 40 through those electrodes and not others. In other words, the controller 44 selects a subgroup of signals that directs to those electrodes that are in contact with the tissue, and then directs the signal 40 over the selected subgroup of channels, but not over other channels.

[0028] In some embodiments, the controller 44 displays relevant images 54 of the subject's anatomy on a display 48, annotated, for example, showing the current position and orientation of the distal portion 28. Alternatively or additionally, based on signals received from relevant sensors disposed on the distal portion 28, the controller 44 may track the temperature and / or impedance of the tissue 36 and control a signal generator 38 in response to such signals. Alternatively or additionally, the controller 44 may perform any other relevant functions to control or otherwise facilitate the execution of procedures.

[0029] The controller 44 and signal generator 38 are typically located within the console 56, and each may comprise one or more units. The conduit 26 is connected to the console 56 via an electrical interface 58 (such as a port or socket). The signal 40 is thus carried to the distal portion 28 via the interface 58. Similarly, signals for tracking the position of the distal portion 28 and / or for tracking the temperature and / or impedance of the tissue may be received by the controller 44 via the interface 58. The magnetic field generator 50 and the external electrode 52 are connected to the console 56 via cables 60 and 62, respectively.

[0030] Controller 44 typically includes both analog and digital components. Therefore, controller 44 may include multiple analog-to-digital converters (ADCs) for receiving analog signals from conduit 26 and signal generator 38. Controller 44 may also include multiple digital-to-analog converters (DACs) for transmitting analog control signals to signal generator 38 and other system components. Alternatively, these control signals may be transmitted digitally, provided that signal generator 38 is configured to receive digital control signals. Controller 44 typically includes digital filters for extracting signals at a given frequency from the received signals.

[0031] Typically, the functionality of the controller 44 as described herein is implemented at least in part in software. For example, the controller 44 may include a programmable digital computing device, which includes at least a central processing unit (CPU) and random access memory (RAM). Program code (including software programs and / or data) is loaded into the RAM for execution and processing by the CPU. For example, the program code and / or data may be downloaded to the controller electronically via a network. Alternatively or otherwise, the program code and / or data may be provided and / or stored on a non-transitory tangible medium, such as magnetic, optical, or electronic memory. When such program code and / or data are provided to a processor, they create a machine or special-purpose computer configured to perform the tasks described herein.

[0032] although Figure 1 The document illustrates specific types of cardiac ablation procedures, but the principles of the implementation schemes described herein can be applied to any suitable type of ablation procedure.

[0033] Figure 2A and Figure 2B The distal portion 28 of the catheter 26 according to an embodiment of the present invention is shown in two shapes. (Compared to...) Figure 1 Similar items are labeled with the same tags. The catheter 26 is of the "lasso" type and has multiple electrodes 30 mounted on the distal portion 28.

[0034] exist Figure 2A In the middle, the distal portion 28 forms a collar, but none of the electrodes 30 are in contact with or adjacent to any of the other electrodes. Figure 2B In the middle, the distal portion 28 forms a ratio Figure 2A A tighter ring is formed in which electrode 30c is in contact with or adjacent to electrode 30b. Ablation using this pair of electrodes 30a and 30b will cause at least some of the current flowing through electrode 30b to parasitically leak through electrode 30c. Ablation between electrodes 30a and 30b may be insufficient due to the reduced power actually applied to the tissue.

[0035] Figure 3This is a graph 100 showing the parasitic current flowing through the electrode over time during an ablation procedure according to an embodiment of the invention, schematically illustrating the threshold of the leakage current. The electrode under consideration is assumed to be one of the electrodes 30 on the catheter 26, such as electrode 30c in the aforementioned figure, which is not part of the electrode pair through which the ablation current is intended to flow.

[0036] Graph 100 shows the first threshold I marked by line 102. th 1 and the second threshold I marked by line 104 th 2. Furthermore, graph 100 shows the second threshold I. th The adjustment range of 2 is 106, within which the physician 22 can set a second threshold. The vertical axis of graph 100 indicates the current I. i The subscript i refers to two electrodes that are not selected for ablation (such as...). Figure 1 and Figure 2B Any electrode 30 of one of the electrodes in 30a and 30b). For simplicity, only one graph is shown, but for example for a catheter 26 with ten electrodes 30, there will be eight electrodes that do not participate in ablation.

[0037] For illustration, two example currents I are shown. i Currents 108 and 110. In the first example, current 108 exceeds the first threshold I at time t1. th 1. At this point, the controller 44 issues a notification that a short circuit may have occurred between the indicator electrode i and one of the ablation electrodes. The physician 22 may assume that the ablation has been insufficient, and he / she may take actions such as adjusting the catheter 26 and repeating the ablation.

[0038] In the second example, the current 110 exceeds the second threshold I at time t2. th 2. At this point, the controller 44 issues a notification indicating that parasitic current has been detected, potentially leading to insufficient tissue ablation. This notification allows the physician 22 to accept or refuse ablation, for example, by testing whether the current block has been established in the tissue at the ablation site. If the physician 22 determines that ablation is insufficient, he / she can repeat the ablation as needed. The physician 22 can also adjust the second threshold I within the range 106. th 2. Or leave it at its current value. For example, if it is found that ablation is sufficient despite notification, physician 22 may choose to reduce I. th 2. In order to avoid further false alarms.

[0039] It should be understood that the above embodiments are cited by way of example, and the invention is not limited to the specific content shown and described above. Rather, the scope of the invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications thereof, which should be apparent to those skilled in the art upon reading the above description, and which are not disclosed in the prior art.

Claims

1. A medical device for performing ablation, comprising: A probe configured for insertion into a patient’s body, and comprising three or more electrodes arranged along the distal portion of the probe and configured to contact tissues within the body; An electrical signal generator configured to apply a signal between a selected pair of electrodes, the signal having an amplitude sufficient to ablate tissue contacted by the pair of electrodes; as well as A controller configured to measure the current flowing through at least one electrode not included in a selected pair of electrodes when the signal is applied, and to issue a notification indicating that the tissue has not been adequately ablated if the measured current exceeds a preset threshold.

2. The device according to claim 1, wherein, The controller is configured to issue a first notification indicating that the tissue has not been sufficiently ablated if the measured current exceeds a first threshold, and to issue a second notification indicating the parasitic current between the at least one electrode and one of the selected pair of electrodes when the measured current does not exceed the first threshold but exceeds a second threshold below the first threshold.

3. The device according to claim 2, wherein, The second threshold is less than half of the first threshold.

4. The device according to claim 2, wherein, The second threshold can be adjusted by the user.

5. The device according to claim 1, wherein, The controller is configured to measure and monitor the corresponding current flowing through multiple electrodes that are not in the selected pair of electrodes.

6. The device according to claim 1, wherein, The amplitude of the signal is sufficient to cause irreversible electroporation (IRE) of the tissue in contact with the selected pair of electrodes.

7. The device according to claim 1, wherein, The distal portion is flexible and configured for insertion into the patient's heart.

8. The device according to claim 7, wherein, The distal portion is configured to form a loop within the heart.

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