Catheter and ablation system

Abstract

This supports the detection of contact between ablation electrodes and biological tissue. [Solution] The catheter comprises a shaft 10, a plurality of splines 16 arranged around the axis of the shaft 10 at the tip of the shaft 10, one or more ablation electrodes 18 arranged on one or more splines 16 and used for ablation of biological tissue, and two or more reference electrodes 32 used for measuring a reference impedance, which is a reference point for determining contact of the ablation electrode 18 with biological tissue, the two or more reference electrodes 32 each located on one of the splines 16 and further proximal to the ablation electrode 18 located furthest proximal to the shaft 10.

Description

Technical Field

[0001] The present disclosure relates to a catheter and an ablation system.

Background Art

[0002] Patent Document 1 discloses an ablation system including an ablation catheter and a pulse waveform generator that delivers voltage pulses to the ablation catheter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In ablation surgery, it is necessary to apply a voltage to an ablation electrode while the ablation electrode is in contact with living tissue so as to form a region (lesion) of sufficient depth in the affected living tissue. Therefore, there is a desire to accurately determine that the ablation electrode is in contact with the living tissue.

[0005] The present disclosure has been made in view of such a situation, and an object thereof is to provide a technique for assisting in determining contact of an ablation electrode with living tissue.

Means for Solving the Problems

[0006] One aspect of the present disclosure is a catheter. The catheter comprises a shaft, a plurality of splines arranged around the axis of the shaft at the tip of the shaft, one or more ablation electrodes arranged on one or more splines and used for ablation of biological tissue, and two or more reference electrodes used for measuring a reference impedance, which is a reference point for determining contact of the ablation electrodes with biological tissue, each of the two or more reference electrodes located on one of the splines and further proximal to the ablation electrode located furthest proximal to the shaft.

[0007] Another aspect of the present disclosure is an ablation system. This ablation system comprises a catheter as described above, a power supply unit electrically connected to the ablation electrode and reference electrode of the catheter, and a power supply unit having a control unit that controls the power supply unit to apply a voltage to the ablation electrode and reference electrode.

[0008] Any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure. [Effects of the Invention]

[0009] This disclosure provides a technology that supports the determination of contact between an ablation electrode and biological tissue. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the ablation system according to an embodiment. [Figure 2] This is a perspective view of the electrode assembly. [Figure 3] Figures 3(A) and 3(B) are schematic diagrams illustrating various unfolded shapes of the electrode assembly. [Figure 4] This is a flowchart illustrating the contact detection process for each ablation electrode. [Modes for carrying out the invention]

[0011] The present disclosure will be described below with reference to the drawings, based on preferred embodiments. The embodiments are illustrative and not limiting, and not all features or combinations thereof described in the embodiments are necessarily essential to the present disclosure. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted where appropriate. The scale and shape of each part shown in each drawing are set for convenience to facilitate explanation and are not to be interpreted restrictively unless otherwise specified. Furthermore, where terms such as "first," "second," etc. are used in this specification or claims, unless otherwise specified, these terms do not indicate any order or importance, but are used to distinguish one configuration from another. In addition, some components that are not important for explaining the embodiments are omitted in each drawing.

[0012] Figure 1 is a schematic diagram of an ablation system 1 according to an embodiment. In Figure 1, some of the components of the ablation system 1 are depicted as functional blocks. At least some of these functional blocks can be implemented as hardware components and circuits, including the CPU and memory of a computer, and as software components, such as computer programs. It will be understood by those skilled in the art that these functional blocks can be implemented in various ways through combinations of hardware and software.

[0013] Ablation system 1 performs a predetermined ablation on the patient's biological tissue 2. Examples of biological tissue 2 to be treated include organs where arrhythmias occur. Ablation system 1 can also be used for ablation of other biological tissues 2. Ablation system 1 comprises a catheter 4, a counter electrode plate 6, a power supply unit 8, and a sheath 9.

[0014] One example catheter 4 comprises a shaft 10, an electrode assembly 12, and a handle 14. The shaft 10 is composed of a flexible tubular body, with at least its tip being inserted into the patient's body. The shaft 10 is made of a known flexible material, including resins such as polyolefin, polytetrafluoroethylene, polyether block amide, and polyamide. The shaft 10 has a multi-lumen structure, for example, having multiple lumens. Various thin wires (not shown), such as conductors and operating wires, and an inner tube 22 (see Figure 2), which will be described later, are inserted through the lumens.

[0015] An electrode assembly 12 is provided at the tip of the shaft 10. Figure 2 is a perspective view of the electrode assembly 12. The electrode assembly 12 comprises a plurality of splines 16, one or more ablation electrodes 18, and two or more reference electrodes 32. Figure 1 shows the electrode assembly 12 in a folded state, while Figure 2 shows the electrode assembly 12 in a first unfolded state.

[0016] Each spline 16 is a linear body extending in the axial direction of the shaft 10 and is made of the same flexible material as the shaft 10. The electrode assembly 12 shown in Figure 2 has, as an example, a first spline 16a, a second spline 16b, a third spline 16c, a fourth spline 16d, a fifth spline 16e, and a sixth spline 16f, but the splines 16 are not limited to six and may be multiple. In this disclosure, when there is no need to distinguish between the first splines 16a to the sixth splines 16f, they may simply be referred to as "spline 16".

[0017] Each spline 16 is arranged at intervals around the axis of the shaft 10. The tip of each spline 16 is connected to the tip chip 20. The proximal end of each spline 16 is inserted into the shaft 10 from the tip of the shaft 10 and fixed to the shaft 10. The tip of the inner tube 22 is connected to the tip chip 20. The inner tube 22 is passed through the lumen of the shaft 10, and its proximal end is connected to the handle 14. The inner tube 22 can be advanced and retracted to the tip side and the proximal end side of the shaft 10 by operating the handle 14.

[0018] When the inner tube 22 is pulled toward the proximal end side of the shaft 10 with each spline 16 extending linearly, the tip chip 20 is displaced toward the proximal end side of the shaft 10. As a result, each spline 16 curves so as to bulge outward, and the electrode assembly 12 forms a basket shape. When the inner tube 22 is pushed out toward the tip side of the shaft 10 with each spline 16 curved, the tip chip 20 is displaced toward the tip side of the shaft 10. As a result, each spline 16 becomes straight, and the electrode assembly 12 is folded. The "basket shape" is derived from the fact that the shapes of the plurality of splines 16 are similar to the curved pattern on the surface of a basketball.

[0019] The ablation electrode 18 is used for ablation of the biological tissue 2. That is, the ablation electrode 18 is an electrode to which a voltage for forming a region in the biological tissue 2, in other words, a voltage for ablation, is applied while being in contact with the biological tissue 2. The ablation electrode 18 is arranged on one or more splines 16. In the present embodiment, a plurality of ablation electrodes 18 are provided on each of all the splines 16. The plurality of ablation electrodes 18 are arranged at predetermined intervals in the longitudinal direction of each spline 16. Each ablation electrode 18 is ring-shaped and is made of a metal having good electrical conductivity such as platinum, gold, silver, copper, aluminum, stainless steel, or an alloy thereof.

[0020] The electrode assembly 12 shown in FIG. 2 has, as an example, a first ablation electrode 18a, a second ablation electrode 18b, a third ablation electrode 18c, and a fourth ablation electrode 18d on each spline 16. However, the number of ablation electrodes 18 provided on each spline 16 is not limited to four. Also, there may be a spline 16 on which no ablation electrode 18 is provided. In the present disclosure, when there is no need to distinguish between the first ablation electrode 18a to the fourth ablation electrode 18d from each other, they may simply be referred to as "ablation electrode 18".

[0021] The reference electrode 32 is an electrode used for measuring the reference impedance. The reference impedance is a reference point, that is, a zero point impedance when determining the contact of the ablation electrode 18 with the biological tissue 2. Therefore, the reference electrode 32 is a reference electrode. The reference impedance can be measured by applying a voltage to two reference electrodes 32 that are in a non-contact state with the biological tissue 2. Each reference electrode 32 is disposed on any one of the splines 16. The catheter 4 of the present embodiment has, as an example, two reference electrodes 32, and one reference electrode 32 is disposed on each of the second spline 16b and the fifth spline 16e. Note that the spline 16 on which the reference electrode 32 is installed is not particularly limited. One of the reference electrodes 32 is also used for determining the contact of the ablation electrode 18 described later.

[0022] Each reference electrode 32 is disposed on the spline 16 and on the proximal end side of the shaft 10 closer to the proximal end than the ablation electrode 18 located on the proximal end side of the shaft 10. In the present embodiment, each fourth ablation electrode 18d is located on the proximal end side of the shaft 1 of all the ablation electrodes 18 to which the ablation voltage is applied. Therefore, each reference electrode 32 is located on the proximal end side of the shaft 10 closer to the proximal end than each fourth ablation electrode

[0023] Preferably, each reference electrode 32 is positioned in a range of less than half, and even less than one-third, of the range from the proximal end of each spline 16 to the fourth ablation electrode 18d closest to the proximal end. Also preferably, each reference electrode 32 is positioned such that, when each spline 16 is in its most curved state, at least a portion of it overlaps with the shaft 10 when viewed from the axial direction of the shaft 10.

[0024] The tip of a wire (not shown) is connected to each ablation electrode 18 and each reference electrode 32. The wire is passed through the lumen of the shaft 10, and its base end is connected to a connector (not shown) on the handle 14 shown in Figure 1. The power supply 8 is electrically connected to each wire via the connector on the handle 14.

[0025] The reference electrodes 32 may be three or more. However, the reference impedance can be measured with just two reference electrodes 32. Therefore, from the viewpoint of suppressing an increase in the number of parts and assembly man-hours, it is preferable to have two reference electrodes 32. Furthermore, it is preferable that each reference electrode 32 be arranged on different splines 16, as in this embodiment. This makes it easier to place each reference electrode 32 in a region that is less likely to come into contact with the biological tissue 2, compared to the case where each reference electrode 32 is arranged on the same spline 16. It is sufficient that at least some of the multiple reference electrodes 32 are arranged on different splines 16. For example, if the electrode assembly 12 has three reference electrodes 32, two reference electrodes 32 may be arranged on the same spline 16 and one reference electrode 32 may be arranged on a different spline 16. Alternatively, multiple reference electrodes 32 may be arranged on only one spline 16. In other words, all the reference electrodes 32 of the electrode assembly 12 may be provided on only one spline.

[0026] Furthermore, as shown in Figures 3(A) and 3(B), the electrode assembly 12 can take on multiple unfolded shapes, each with a different degree of curvature of the spline 16. In other words, the basket shape includes shapes with various degrees of bulging. Figures 3(A) and 3(B) are schematic diagrams illustrating the various unfolded shapes of the electrode assembly 12. Figures 3(A) and 3(B) show an electrode assembly 12 having eight splines 16 as an example.

[0027] In other words, the electrode assembly 12 can take on a first unfolded state in which each spline 16 is curved to a predetermined degree, as shown in Figures 2 and 3(A), and a second unfolded state in which each spline 16 is curved more sharply than in the first unfolded state, as shown in Figure 3(B). The second unfolded state means that each spline 16 has a portion with greater curvature than when it is in the first unfolded state. That is, the curvature of the portion with the maximum curvature in the second unfolded state is greater than the curvature of the portion with the maximum curvature in the first unfolded state. Furthermore, the electrode assembly 12 may maintain various unfolded states in which the curvature of each spline 16 is less pronounced than in the first unfolded state, sharper than in the second unfolded state, or a degree of curvature between the first and second unfolded states, depending on the degree of operation of the handle 14.

[0028] Returning to Figure 1, the handle 14 is located at the proximal end of the shaft 10 and is positioned outside the body when the catheter 4 is in use, and is grasped or operated by the operator. The handle 14 has a main body that is grasped by the operator and an operating part for advancing and retracting the inner tube 22. The operating part is composed of, for example, a lever that can slide in the axial direction of the shaft 10. When the operating part is operated, the inner tube 22 can be displaced toward the proximal end relative to the shaft 10. This causes the folded electrode assembly 12 to unfold in a direction intersecting the axis of the shaft 10. Also, when the operating part is operated, the inner tube 22 can be displaced toward the tip relative to the shaft 10. This causes the unfolded electrode assembly 12 to fold. The connector is provided on the main body. The catheter 4 may also have an irrigation mechanism that sprays an irrigation fluid such as physiological saline from the tip during ablation.

[0029] The counter electrode plate 6 is attached to the patient's body surface during ablation. The counter electrode plate 6 is also electrically connected to the power supply unit 8. During ablation, a voltage is applied to each ablation electrode 18 and the counter electrode plate 6, thereby ablating the biological tissue 2.

[0030] The power supply unit 8 includes, for example, an input unit 24, a power supply unit 26, a control unit 28, and a display unit 30. The input unit 24 is composed of, for example, a dial, buttons, a touch panel, etc., and is operated by the operator of the ablation system 1. The operator can input various setting values ​​and signals to instruct operations to the power supply unit 8 via the input unit 24. The various setting values ​​may be pre-set and stored in the power supply unit 8 at the time of product shipment, etc. Signals indicating the setting values, etc., are sent from the input unit 24 to the control unit 28.

[0031] The power supply unit 26 is electrically connected to each ablation electrode 18 and each reference electrode 32 via wires and connectors. The power supply unit 26 supplies the ablation voltage V to the ablation electrode 18 and the counter electrode plate 6 according to the control signal CTL sent from the control unit 28. outThe power supply unit 26 applies a voltage for measuring the reference impedance to the two reference electrodes 32 according to the control signal CTL. The power supply unit 26 also applies a voltage for determining contact of the ablation electrode 18 to either of the reference electrodes 32 and each ablation electrode 18 according to the control signal CTL. The power supply unit 26 is composed of a predetermined power supply circuit, such as a switching regulator.

[0032] The control unit 28 controls the operation of the entire power supply unit 8 and performs predetermined calculations. The control unit 28 is composed of, for example, a microcomputer. The control unit 28 sends a control signal CTL to the power supply unit 26, thereby controlling the power supply unit 26 to apply voltage to each ablation electrode 18, the counter electrode plate 6, and each reference electrode 32. The control unit 28 also acquires information, including voltage and current values ​​obtained by applying voltage to each electrode, via the power supply unit 26, and can measure the impedance between any two electrodes. Furthermore, the control unit 28 can determine the state of each electrode using the measured impedance.

[0033] The display unit 30 displays various types of information to the outside. The display unit 30 is composed of a liquid crystal display, a CRT display, an organic EL display, etc. The display unit 30 displays, for example, the results of a determination made by the control unit 28.

[0034] The sheath 9 is a flexible tubular body that assists in the insertion of the catheter 4 into the body. The sheath 9 is made of a known flexible material, including resins such as polytetrafluoroethylene and polyether block amide. The sheath 9 is inserted into the body prior to the insertion of the catheter 4 into the patient's body. The catheter 4 is inserted through the sheath 9 and passes through the sheath 9 to reach the biological tissue 2.

[0035] Next, the usage of the ablation system 1 according to this embodiment will be described in detail. The ablation system 1 of this embodiment performs ablation on biological tissue 2 by irreversible electroporation (IRE). Since IRE is non-thermal, it can suppress damage to tissues and nerves located around the biological tissue 2. For example, when performing pulmonary vein dissection to treat atrial fibrillation, it is possible to suppress damage to the esophagus and phrenic nerve around the affected area, thereby suppressing the occurrence of complications such as esophageal fistula and phrenic nerve paralysis.

[0036] In IRE, pulsed electric field ablation (PFA) is performed. PFA is an ablation technique that kills cells by using a pulsed electric field generated by applying a high voltage to each ablation electrode 18 and the counter electrode plate 6, thereby forming a region in the biological tissue 2. The electric field tends to reflect at the boundary between tissues. Therefore, when the affected area is ablated, damage to adjacent tissues can be suppressed. Alternatively, a region may be formed by applying voltage to any number of ablation electrodes 18 and generating a pulsed electric field between these ablation electrodes 18.

[0037] When the ablation voltage is applied to the ablation electrode 18, it is important that the ablation electrode 18 is in contact with the biological tissue 2. Whether or not the ablation electrode 18 is in contact with the biological tissue 2 can be determined by using the impedance between the ablation electrode 18 and one of the reference electrodes 32 as an indicator. In other words, the blood that occupies the space in the body where the electrode assembly 12 is placed conducts electricity more easily than the biological tissue 2. For this reason, the impedance between the ablation electrode 18 and the reference electrode 32 differs depending on whether or not the ablation electrode 18 is in contact with the biological tissue 2.

[0038] Specifically, the impedance when the ablation electrode 18 is in contact with the biological tissue 2 is greater than the impedance when the ablation electrode 18 is not in contact with the biological tissue 2. Therefore, by using the impedance between the ablation electrode 18, which is not in contact with the biological tissue 2, and the reference electrode 32, which is not in contact with the biological tissue 2, as the reference impedance, it can be determined that the ablation electrode 18 is in contact with the biological tissue 2 when the difference between the impedance between the ablation electrode 18 and the reference electrode 32 and the reference impedance is greater than or equal to a predetermined threshold.

[0039] In this case, the ablation electrode 18, which is the target of contact detection, is also used as the reference electrode. By using the ablation electrode 18, which is the target of detection, as the reference electrode, the two electrodes used for measuring the reference impedance and the two electrodes used for contact detection are the same, thus enabling highly accurate contact detection. However, the ablation electrode 18 is an electrode used to form a region in the biological tissue 2. Therefore, while the reference electrode 32 is positioned so as not to contact the biological tissue 2, the ablation electrode 18 is positioned to contact the biological tissue 2. Furthermore, the reference impedance is measured in the vicinity of the biological tissue 2, that is, in the environment in which ablation is performed. For this reason, there is a possibility that the ablation electrode 18 may come into contact with the biological tissue 2 when measuring the reference impedance. Alternatively, it is not easy to measure the reference impedance while maintaining a non-contact state between the ablation electrode 18 and the biological tissue 2.

[0040] In contrast, the catheter 4 according to this embodiment is equipped with two reference electrodes 32 as described above. The impedance between the two reference electrodes 32 is defined as the reference impedance. Since the reference electrodes 32 are not required to come into contact with the biological tissue 2, they can be positioned on the spline 16 in a location that is unlikely to come into contact with the biological tissue 2. Therefore, it is possible to suppress contact between each reference electrode 32 and the biological tissue 2 when measuring the reference impedance. As a result, the measurement accuracy of the reference impedance can be improved, thereby improving the accuracy of contact detection of the ablation electrode 18. Thus, the catheter 4 according to this embodiment can support contact detection of the ablation electrode 18.

[0041] Figure 4 is a flowchart of the contact determination process for each ablation electrode 18. First, the catheter 4 is inserted into the sheath 9, which has been pre-inserted into the patient's body, by the operator of the ablation system 1 (S101). Next, a voltage is applied to the two reference electrodes 32, and the impedance between the two reference electrodes 32 is measured (S102). The start of this impedance measurement is instructed, for example, by the operator via the input unit 24. When the control unit 28 receives the instruction to start the impedance measurement, it controls the power supply unit 26 to apply a voltage to the two reference electrodes 32.

[0042] The control unit 28 then determines whether each reference electrode 32 is exposed from the sheath 9 based on the impedance measured when a voltage is applied to the two reference electrodes 32. The control unit 28 then displays the determination result on the display unit 30. As an example, the control unit 28 determines whether the impedance between the two reference electrodes 32 is less than a predetermined first threshold (S103). Blood conducts electricity more easily than the sheath 9. Therefore, the impedance measured when at least one reference electrode 32 is located inside the sheath 9 is greater than the impedance measured when both reference electrodes 32 are exposed from the sheath 9. For this reason, by determining whether the impedance between the two reference electrodes 32 is less than the first threshold, it is possible to determine whether the two reference electrodes 32 are exposed from the sheath 9.

[0043] Furthermore, the operator can relatively easily determine if the spline 16 is exposed from the sheath 9 by X-ray imaging. On the other hand, since the reference electrode 32 is located at the base of the spline 16, it is not easy to reliably determine if it is exposed from the sheath 9 by X-ray imaging. In contrast, by using the impedance between the two reference electrodes 32 as a criterion, it is possible to determine with higher accuracy whether the reference electrode 32 is exposed from the sheath 9. The first threshold value can be set as appropriate based on the designer's empirical knowledge or experiments and simulations conducted by the designer, and is preset and held in the control unit 28. The first threshold value is, as an example, 500Ω.

[0044] The exposure determination of the two reference electrodes 32 may be performed by the operator. For example, the control unit 28 displays the impedance between the two reference electrodes 32 on the display unit 30. The operator can determine whether the two reference electrodes 32 are exposed from the sheath 9 by checking whether the impedance displayed on the display unit 30 has fallen below a first threshold.

[0045] If the impedance between the two reference electrodes 32 is greater than or equal to the first threshold (N in S103), that is, if the two reference electrodes 32 are located inside the sheath 9, steps S101 to S103 are repeated. That is, the catheter 4 is further inserted into the body by the operator, and the exposure of the reference electrodes 32 is checked again. If the impedance between the two reference electrodes 32 is less than the first threshold (Y in S103), that is, if the two reference electrodes 32 are exposed from the sheath 9, the deployment status of the electrode assembly 12 is checked (S104).

[0046] The exposure determination of the two reference electrodes 32 may be performed as follows: The control unit 28 starts measuring the impedance between the two reference electrodes 32 as soon as the insertion of the catheter 4 into the sheath 9 begins. The start of this measurement is instructed, for example, by the operator via the input unit 24 at the time when the catheter 4 begins insertion. The control unit 28 repeats this impedance measurement while the catheter 4 is moving inside the sheath 9. When the control unit 28 detects that the measured impedance is less than a first threshold, it displays on the display unit 30 that the two reference electrodes 32 have been exposed from the sheath 9. This allows the user to proceed to confirming the deployment status.

[0047] The deployment state can be confirmed, for example, by the operator. The operator can determine the deployment state of the electrode assembly 12 based on the position of the operating part provided on the handle 14. The operator inputs the determined deployment state to the power supply unit 8 via the input unit 24. Alternatively, the control unit 28 may perform the confirmation of the deployment state of the electrode assembly 12. The deployment state of the electrode assembly 12 may consist of only two states, a first deployment state and a second deployment state, or it may include other deployment states in which the curvature of each spline 16 differs from the first and second deployment states.

[0048] Next, a reference impedance A is set for the deployed state of each confirmed spline 16 (S105). This setting is initiated, for example, by the control unit 28 upon detecting the input of the deployed state. For example, the control unit 28 sets and holds the impedance determined to be less than the first threshold in step S103 as the reference impedance A for the deployed state confirmed in step S104. Alternatively, after the confirmation process in step S104 is performed, a voltage may be applied to the two reference electrodes 32, and the measured impedance may be used as the reference impedance A. Furthermore, the setting of the reference impedance A may be performed by the operator via the input unit 24.

[0049] Next, a voltage is applied to one of the reference electrodes 32 and any ablation electrode 18, and the impedance B between the two electrodes is measured (S106). This measurement is started, for example, by the control unit 28 when it detects the setting of the reference impedance A. Note that the measurement of impedance B may also be started by the operator via the input unit 24. The reference electrode 32 used for measuring impedance B can be arbitrarily selected.

[0050] The control unit 28 then determines whether the ablation electrode 18 has come into contact with the biological tissue 2 based on the difference Δ between the reference impedance A and impedance B. For example, the control unit 28 determines whether the difference Δ between the reference impedance A and impedance B is greater than or equal to a predetermined second threshold (S107). For example, the difference Δ is an absolute value. As described above, the impedance when the ablation electrode 18 is in contact with the biological tissue 2 is greater than the impedance when the ablation electrode 18 is not in contact with the biological tissue 2. Therefore, by determining whether the difference Δ between the reference impedance A and impedance B is greater than or equal to the second threshold, it is possible to determine whether the ablation electrode 18 has come into contact with the biological tissue 2.

[0051] The impedance between two electrodes tends to change depending on the relative positions of the two electrodes. Therefore, it is preferable to use different second thresholds depending on the deployment state of the spline 16. Accordingly, the control unit 28 selects a second threshold to be used for contact determination according to the deployment state confirmed in step S104. The second threshold according to the deployment state can be set appropriately based on the designer's empirical knowledge or experiments and simulations conducted by the designer, and is set in advance and held within the control unit 28. For example, the second threshold in the first deployment state is 20Ω, and for example, the second threshold in the second deployment state is 30Ω.

[0052] If the difference Δ is greater than or equal to the second threshold (Y in S107), the control unit 28 determines that the ablation electrode 18 is in contact with the biological tissue 2 (S108), and displays this fact on the display unit 30, for example. If the difference Δ is less than the second threshold (N in S107), the control unit 28 determines that the ablation electrode 18 is not in contact with the biological tissue 2 (S109), and displays this fact on the display unit 30, for example. Then, the control unit 28 determines whether contact determination has been performed for all ablation electrodes 18 to which the ablation voltage is applied (S110).

[0053] If contact detection is performed for all ablation electrodes 18 (Y in S110), the contact detection flow for the ablation electrodes 18 is completed. If contact detection has not been performed for all ablation electrodes 18 (N in S110), steps S107 to S109 are performed for the ablation electrodes 18 for which contact detection has not been performed. Note that contact detection may be performed by an operator. For example, the control unit 28 displays the difference Δ on the display unit 30. The operator selects a second threshold value according to the deployment state and confirms whether the difference Δ displayed on the display unit 30 is equal to or greater than the second threshold value. This makes it possible to determine whether each ablation electrode 18 has come into contact with the biological tissue 2.

[0054] Once contact determination for all ablation electrodes 18 is complete, the operator can decide whether or not to start ablation based on the contact state of each ablation electrode 18. For example, if the contact state of each ablation electrode 18 with the biological tissue 2 is such that the region that can be formed by each ablation electrode 18 is continuous over at least a portion of the circumferential direction of the shaft 10, more preferably continuous over the entire circumference, the operator instructs the control unit 28 to start ablation via the input unit 24.

[0055] For example, if an ablation electrode 18 in contact with biological tissue 2 at a certain spline 16 and an ablation electrode 18 in contact with biological tissue 2 at a spline 16 adjacent to this spline 16 are located at the same position in the axial direction of the shaft 10, the regions formed by these two ablation electrodes 18 are continuous with each other. For example, if the first ablation electrode 18a of the first spline 16a and the first ablation electrode 18a of the second spline 16b are both in contact with biological tissue 2, the regions formed by these two ablation electrodes 18 are continuous with each other.

[0056] Furthermore, if an ablation electrode 18 that contacts the biological tissue 2 at a certain spline 16 and an ablation electrode 18 that contacts the biological tissue 2 at a spline 16 adjacent to this spline 16 are located adjacent to each other in the axial direction of the shaft 10, the regions formed by these two ablation electrodes 18 are continuous with each other. For example, if the first ablation electrode 18a of the first spline 16a and the second ablation electrode 18b of the second spline 16b are both in contact with the biological tissue 2, the regions formed by these two ablation electrodes 18 are continuous with each other.

[0057] The control unit 28 may correct the reference impedance A according to the difference in position between the reference electrode 32 used to measure the reference impedance A and the ablation electrode 18 that is the target of contact determination. That is, in both the measurement of reference impedance A and the measurement of impedance B, the two electrodes to which voltage is applied are common to both, one of which is the reference electrode 32, but the other differs depending on whether it is the reference electrode 32 or the ablation electrode 18. Therefore, the positional relationship of the two electrodes used in the measurement of reference impedance A and the measurement of impedance B is different. For this reason, contact determination based on reference impedance A measured with two reference electrodes 32 may have lower accuracy compared to contact determination based on reference impedance measured using the ablation electrode 18 that is the target of contact determination as the reference electrode.

[0058] Therefore, the control unit 28 increases or decreases the reference impedance A measured by the two reference electrodes 32 by a correction value α so as to reduce the impedance difference due to the difference in the relative positions of the two electrodes used. The correction value α can be set as appropriate based on the designer's empirical knowledge or experiments and simulations conducted by the designer, and is set in advance and held within the control unit 28. The correction value α may differ depending on the deployment state of the spline 16. In this case, a correction value α may be determined for each deployment state. Alternatively, the same correction value α may be uniformly used for all ablation electrodes 18.

[0059] The shapes of the spline 16, ablation electrode 18, and reference electrode 32 are not limited to those described above. Furthermore, the configurations of the catheter 4 and power supply 8 can be modified as appropriate. For example, the catheter 4 may have a shaft 10 tip that can be bent in one or multiple directions by operating the handle 14. Control of the power supply 26 by the control unit 28 may be implemented by hardware (circuit) or by software (program). If implemented by software, the software consists of a group of programs that cause a computer to execute each function. Each program may, for example, be pre-installed in the computer or installed on the computer from a network or recording medium. In this embodiment, the reference electrode 32 is used only for measuring the reference impedance, but the reference electrode 32 may also be used as the ablation electrode 18.

[0060] The embodiments of this disclosure have been described in detail above. The embodiments described above are merely examples of how to implement this disclosure. The content of the embodiments does not limit the technical scope of this disclosure, and many design changes, such as changes, additions, and deletions of components, are possible, as long as they do not deviate from the idea of ​​this disclosure as defined in the claims. A new embodiment with design changes will have the effects of both the combined embodiment and the variation. In the embodiments described above, the content in which such design changes are possible is emphasized with notations such as "of this embodiment" or "in this embodiment," but design changes are also permitted even if there are no such notations. Any combination of components included in each embodiment is also valid as an embodiment of this disclosure. The hatching applied to the cross-section in the drawings does not limit the material of the object to which the hatching is applied.

[0061] The embodiments may be specified by the items described below. [1st item] Shaft (10) and Multiple splines (16) are arranged at the tip of the shaft (10) in the direction of the axis of the shaft (10), One or more ablation electrodes (18) are arranged on one or more splines (16) and used for ablation of biological tissue (2), A set of two or more reference electrodes (32) used to measure a reference impedance (A), which is a reference point for determining contact of the ablation electrode (18) with biological tissue (2), wherein each of the two or more reference electrodes (32) is positioned on one of the splines (16) and is positioned more proximal to the ablation electrode (18, 18d) located furthest proximal to the shaft (10), Catheter (4). [Second item] Two or more reference electrodes (32) are arranged such that at least a portion of them are on different splines (16). The first item is a catheter (4). [3rd item] The catheter (4) of item 1 or item 2, The power supply device (8) includes a power supply unit (26) electrically connected to the ablation electrode (18) and reference electrode (32) of the catheter (4), and a control unit (28) that controls the power supply unit (26) to apply voltage to the ablation electrode (18) and reference electrode (32). Ablation system (1). [4th item] The control unit (28) determines whether the ablation electrode (18) has come into contact with the biological tissue (2) based on the difference (Δ) between the impedance (B) measured when a voltage is applied to the reference electrode (32) and the ablation electrode (18) and the reference impedance (A). The third item is the ablation system (1). [Item 5] The control unit (28) corrects the reference impedance (A) according to the difference in position between the reference electrode (32) used to measure the reference impedance (A) and the ablation electrode (18) that is the target of contact determination. Ablation system (1) of item 4. [Item 6] The ablation system (1) includes a sheath (9) through which a catheter (4) is inserted. The control unit (28) determines whether the reference electrodes (32) are exposed from the sheath (9) based on the impedance measured when a voltage is applied to the two reference electrodes (32). An ablation system according to any of items 3 through 5 (1). [Explanation of Symbols]

[0062] 1 Ablation system, 2 Biological tissue, 4 Catheter, 8 Power supply unit, 9 Sheath, 10 Shaft, 16 Spline, 18 Ablation electrode, 26 Power supply unit, 28 Control unit, 32 Reference electrode.

Claims

1. The shaft and Multiple splines arranged in the direction of the shaft's axis at the tip of the shaft, One or more ablation electrodes arranged on one or more of the splines and used for ablation of biological tissue, A set of two or more reference electrodes used to measure a reference impedance, which is a reference point for determining contact of the ablation electrode with the biological tissue, wherein each of the two or more reference electrodes is located on one of the splines and is positioned closer to the proximal end than the ablation electrode located furthest towards the proximal end of the shaft, catheter.

2. The two or more reference electrodes are arranged on splines that are at least partially different from each other. The catheter according to claim 1.

3. A catheter according to claim 1 or 2, The power supply device comprises a power supply unit electrically connected to the ablation electrode and the reference electrode of the catheter, and a control unit that controls the power supply unit to apply voltage to the ablation electrode and the reference electrode. Ablation system.

4. The control unit determines whether the ablation electrode has come into contact with the biological tissue based on the difference between the impedance measured when a voltage is applied to the reference electrode and the ablation electrode and the reference impedance. The ablation system according to claim 3.

5. The control unit corrects the reference impedance according to the difference in position between the reference electrode used to measure the reference impedance and the ablation electrode that is the subject of contact determination. The ablation system according to claim 4.

6. The ablation system comprises a sheath through which the catheter is inserted. The control unit determines whether the reference electrodes are exposed from the sheath based on the impedance measured when a voltage is applied to the two reference electrodes. The ablation system according to claim 3.

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