Catheter and ablation system

Abstract

A catheter according to the present invention comprises a shaft 10, a plurality of splines 16 that are arranged around the axis of the shaft 10 on the tip end side of the shaft 10, one or more ablation electrodes 18 that are provided to one or more of the splines 16 and are to be used for ablation of biological tissue, and two or more reference electrodes 32 that are each provided to one of the splines 16 so as to be further to the base end side of the shaft 10 than the ablation electrode 18 that is positioned furthest to the base end side and are to be used for measurement of a reference impedance that is a reference point for determining contact of the ablation electrodes 18 with the biological tissue.

Description

Catheter and Ablation Systems

[0001] The present disclosure relates to catheters and ablation systems.

[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.

[0003] Special table 2019-500170 publication

[0004] In ablation procedures, a voltage must be applied to the ablation electrode while it is in contact with the biological tissue so that a lesion of sufficient depth can be formed in the affected biological tissue. Therefore, there is a need to accurately determine whether the ablation electrode is in contact with the biological tissue.

[0005] The present disclosure has been made in light of these circumstances, and its purpose is to provide a technology that assists in determining whether an ablation electrode is in contact with biological tissue.

[0006] One aspect of the present disclosure is a catheter comprising: a shaft, a plurality of splines arranged around the shaft distal end, one or more ablation electrodes disposed on one or more splines and used for ablation of biological tissue, and two or more reference electrodes used for measuring a reference impedance that serves as a reference point for determining contact of the ablation electrodes with biological tissue, each of the two or more reference electrodes being disposed on one of the splines and closer to the proximal end than the ablation electrode located closest to the proximal end of the shaft.

[0007] Another aspect of the present disclosure is an ablation system including the catheter of the above aspect, and a power supply device having 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 voltages to the ablation electrode and the reference electrode.

[0008] Any combination of the above components, and conversion of the expression of the present disclosure into a method, device, system, etc., are also valid aspects of the present disclosure.

[0009] According to the present disclosure, it is possible to provide a technique for assisting in determining whether an ablation electrode is in contact with biological tissue.

[0010] 3A and 3B are schematic diagrams for explaining various deployed shapes of the electrode assembly; and FIG. 3B is a flowchart for determining contact of each ablation electrode.

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

[0012] FIG. 1 is a schematic diagram of an ablation system 1 according to an embodiment. In FIG. 1, some of the components of the ablation system 1 are depicted as functional blocks. At least some of these functional blocks can be realized as a hardware configuration using elements and circuits such as a computer CPU and memory, and as a software configuration using a computer program or the like. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

[0013] The ablation system 1 performs a predetermined ablation on a patient's biological tissue 2. The biological tissue 2 to be treated may be, for example, an organ experiencing arrhythmia. The ablation system 1 can also be used for ablation of other biological tissues 2. The ablation system 1 includes a catheter 4, a return electrode 6, a power supply 8, and a sheath 9.

[0014] The catheter 4, as an example, includes a shaft 10, an electrode assembly 12, and a handle 14. The shaft 10 is formed of a flexible tubular body, and at least the distal end is 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 lead wires and operating wires, as well as an inner tube 22 (see FIG. 2), which will be described later, are inserted into the lumens.

[0015] An electrode assembly 12 is provided on the distal end of the shaft 10. Figure 2 is a perspective view of the electrode assembly 12. The electrode assembly 12 includes a plurality of splines 16, one or more ablation electrodes 18, and two or more reference electrodes 32. Note that Figure 1 illustrates the electrode assembly 12 in a folded state, and Figure 2 illustrates the electrode assembly 12 in a first deployed 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 number of splines 16 is not limited to six and may be any number as long as there is a plurality of splines. In the present disclosure, when there is no need to distinguish the first spline 16a to the sixth spline 16f from one another, they may be simply referred to as "splines 16."

[0017] The splines 16 are arranged at intervals around the axis of the shaft 10. The distal end of each spline 16 is connected to a distal tip 20. The proximal end of each spline 16 is inserted into the shaft 10 from its distal end and fixed to the shaft 10. The distal end of an inner tube 22 is connected to the distal tip 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 retreated toward the distal end and proximal end of the shaft 10 by operating the handle 14.

[0018] When the inner tube 22 is retracted toward the proximal end of the shaft 10 with each spline 16 extending linearly, the distal tip 20 is displaced toward the proximal end of the shaft 10. This causes each spline 16 to curve and bulge outward, and the electrode assembly 12 assumes a basket shape. When the inner tube 22 is pushed toward the distal end of the shaft 10 with each spline 16 curved, the distal tip 20 is displaced toward the distal end of the shaft 10. This causes each spline 16 to become linear, and the electrode assembly 12 is folded. The term "basket shape" comes from the fact that the shape of the multiple splines 16 resembles the curved pattern on the surface of a basketball.

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

[0020] 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, but the number of ablation electrodes 18 provided on each spline 16 is not limited to four. Also, there may be splines 16 on which no ablation electrodes 18 are provided. In the present disclosure, when there is no need to distinguish the first ablation electrode 18a to the fourth ablation electrode 18d from one another, they may be simply referred to as "ablation electrodes 18."

[0021] The reference electrode 32 is an electrode used to measure the reference impedance. The reference impedance is the impedance that serves as a reference point, i.e., zero point, when determining whether the ablation electrode 18 is in contact 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 not in contact with the biological tissue 2. Each reference electrode 32 is disposed on one of the splines 16. The catheter 4 of this embodiment has, as an example, two reference electrodes 32, one on the second spline 16b and one on the fifth spline 16e. Note that the splines 16 on which the reference electrodes 32 are disposed are not particularly limited. One of the reference electrodes 32 is also used to determine whether the ablation electrode 18 is in contact, as described below.

[0022] Each reference electrode 32 is disposed on the spline 16 closer to the proximal end of the shaft 10 than the ablation electrode 18 that is disposed closest to the proximal end of the shaft 10 on the spline 16 on which it is mounted. In the present embodiment, each fourth ablation electrode 18d is disposed closest to the proximal end of the shaft 10 among all the ablation electrodes 18 to which the ablation voltage is applied. Therefore, each reference electrode 32 is disposed closer to the proximal end of the shaft 10 than each fourth ablation electrode 18d. In this way, by disposing the reference electrode 32 closer to the base of the spline 16, it is possible to make it more difficult for the reference electrode 32 to come into contact with the biological tissue 2.

[0023] Preferably, each reference electrode 32 is disposed in a proximal range of not more than half, or even not more 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 disposed so that at least a portion of it overlaps with the shaft 10 when viewed in the axial direction of the shaft 10 when each spline 16 is in its most curved state.

[0024] The distal end of a lead wire (not shown) is connected to each ablation electrode 18 and each reference electrode 32. The lead wire is passed through the lumen of the shaft 10, and the proximal end is connected to a connector (not shown) of the handle 14 shown in Fig. 1. Each lead wire is electrically connected to the power supply unit 8 via the connector of the handle 14.

[0025] The number of reference electrodes 32 may be three or more. However, two reference electrodes 32 are sufficient to measure the reference impedance. Therefore, two reference electrodes 32 are preferable from the viewpoint of suppressing an increase in the number of parts and assembly steps. Furthermore, it is preferable that each reference electrode 32 is arranged on a different spline 16 as in the present embodiment. This makes it easier to arrange each reference electrode 32 in an area where it is difficult for them to come into contact with the biological tissue 2, compared to when each reference electrode 32 is arranged on the same spline 16. Note that it is sufficient that at least some of the multiple reference electrodes 32 are arranged on different splines 16. For example, when 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 another spline 16. Alternatively, the multiple reference electrodes 32 may be arranged on only one spline 16. In other words, all of the reference electrodes 32 of the electrode assembly 12 may be provided on only one spline.

[0026] As shown in Figures 3(A) and 3(B), the electrode assembly 12 can assume a number of deployed shapes in which the degree of curvature of each spline 16 varies. In other words, the basket shape includes shapes with various degrees of expansion. Figures 3(A) and 3(B) are schematic diagrams illustrating the various deployed shapes of the electrode assembly 12. Note that Figures 3(A) and 3(B) illustrate an electrode assembly 12 having eight splines 16 as an example.

[0027] That is, the electrode assembly 12 can be in a first deployed state in which each spline 16 is curved to a predetermined degree, as shown in FIGS. 2 and 3A, and a second deployed state in which each spline 16 is curved more sharply than in the first deployed state, as shown in FIG. 3B. The second deployed state refers to a state in which each spline 16 has a portion with a greater curvature than in the first deployed state. That is, the curvature of the portion with the greatest curvature in the second deployed state is greater than the curvature of the portion with the greatest curvature in the first deployed state. Furthermore, the electrode assembly 12 may be capable of maintaining various deployed states in which the curvature of each spline 16 is gentler than in the first deployed state, more sharply than in the second deployed state, or a curvature between the first and second deployed states, depending on the degree of operation of the handle 14.

[0028] Returning to FIG. 1 , the handle 14 is provided at the proximal end of the shaft 10, and is disposed outside the body when the catheter 4 is in use. The handle 14 has a main body portion that is held by the operator, and an operating portion for advancing and retracting the inner tube 22. The operating portion is, for example, configured as a lever that is slidable in the axial direction of the shaft 10. Operating the operating portion can displace the inner tube 22 toward the proximal end relative to the shaft 10. This causes the electrode assembly 12, which is in a collapsed state, to unfold in a direction intersecting the axis of the shaft 10. Operating the operating portion can also displace the inner tube 22 toward the distal end relative to the shaft 10. This causes the electrode assembly 12, which is in an unfolded state, to collapse. A connector is provided in the main body portion. The catheter 4 may also have an irrigation mechanism that sprays irrigation fluid, such as saline, from the distal end during ablation.

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

[0030] The power supply device 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 configured with, for example, a dial, a button, a touch panel, etc., and is operated by the operator of the ablation system 1. The operator can input various setting values ​​and signals instructing operations to the power supply device 8 via the input unit 24. Note that the various setting values ​​may be set in advance, such as at the time of product shipment, and stored in the power supply device 8. 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 conductors and connectors. The power supply unit 26 supplies an ablation voltage V to the ablation electrodes 18 and the return electrode 6 in accordance with a control signal CTL sent from the control unit 28. ｏｕｔThe power supply unit 26 also applies a voltage for measuring the reference impedance to the two reference electrodes 32 in accordance with the control signal CTL. The power supply unit 26 also applies a voltage for determining contact of the ablation electrodes 18 to one of the reference electrodes 32 and each ablation electrode 18 in accordance with the control signal CTL. The power supply unit 26 is configured with a predetermined power supply circuit, for example, a switching regulator.

[0032] The control unit 28 controls the overall operation of the power supply device 8 and executes predetermined arithmetic processing. The control unit 28 is configured, for example, by a microcomputer. The control unit 28 controls the power supply unit 26 to apply voltages to each ablation electrode 18, the return electrode 6, and each reference electrode 32 by sending a control signal CTL to the power supply unit 26. The control unit 28 also acquires information via the power supply unit 26, including voltage values ​​and current values ​​obtained by applying voltages to each electrode, and can measure the impedance between any two electrodes. The control unit 28 can also 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 configured with a liquid crystal display, a CRT display, an organic EL display, etc. The display unit 30 displays, for example, the results of the determination performed 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 reaches the biological tissue 2 through the inside of the sheath 9.

[0035] Next, a detailed description will be given of how the ablation system 1 according to this embodiment is used. The ablation system 1 according to this embodiment ablates the biological tissue 2 by irreversible electroporation (IRE). Because IRE is non-thermal, it is possible to suppress damage to the tissues and nerves surrounding 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] IRE involves pulsed electric field ablation (PFA). PFA is an ablation technique that kills cells by applying a pulsed electric field generated by applying a high voltage between each ablation electrode 18 and the return electrode 6, i.e., forms a region in the biological tissue 2. The electric field tends to be reflected at the boundaries between tissues. This can prevent damage to adjacent tissues when cauterizing the affected area. Note that a region may also be formed by applying a voltage to any number of ablation electrodes 18 to generate a pulsed electric field between these ablation electrodes 18.

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

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

[0039] In this case, the ablation electrode 18, which is the subject of contact determination, is also used as the reference electrode. Using the ablation electrode 18 as the reference electrode allows for highly accurate contact determination because the two electrodes used to measure the reference impedance are the same as the two electrodes used for contact determination. However, the ablation electrode 18 is an electrode for forming a region in the biological tissue 2. Therefore, the reference electrode 32 is positioned so as not to contact the biological tissue 2, whereas the ablation electrode 18 is positioned so as to contact the biological tissue 2. The reference impedance is measured when the ablation electrode 18 is near the biological tissue 2, i.e., in an environment where ablation is performed. Therefore, 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 the ablation electrode 18 in a non-contact state with the biological tissue 2.

[0040] In contrast, the catheter 4 according to this embodiment includes two reference electrodes 32 as described above. The impedance between the two reference electrodes 32 is used as the reference impedance. Because the reference electrodes 32 are not required to contact the biological tissue 2, they can be placed at positions on the spline 16 where they are unlikely to come into contact with the biological tissue 2. This prevents each reference electrode 32 from coming into contact with 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 determination of the ablation electrode 18. Therefore, the catheter 4 according to this embodiment can assist in contact determination of the ablation electrode 18.

[0041] 4 is a flow diagram of contact determination for each ablation electrode 18. First, the operator of the ablation system 1 inserts the catheter 4 into the sheath 9, which has been inserted into the patient's body beforehand (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. Upon receiving the instruction to start the impedance measurement, the control unit 28 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 value (S103). Electricity flows more easily through blood than through the sheath 9. Therefore, the impedance measured when at least one reference electrode 32 is located within the sheath 9 is greater than the impedance measured when both reference electrodes 32 are exposed from the sheath 9. Therefore, by determining whether the impedance between the two reference electrodes 32 is less than the first threshold value, it is possible to determine whether the two reference electrodes 32 are exposed from the sheath 9.

[0043] Furthermore, it is relatively easy for an operator to determine by X-ray imaging that the spline 16 has been exposed from the sheath 9. On the other hand, because the reference electrode 32 is provided at the base of the spline 16, it is not easy to reliably determine by X-ray imaging that the spline 16 has been exposed from the sheath 9. In contrast, by using the impedance between the two reference electrodes 32 as a determination criterion, it is possible to more accurately determine that the reference electrode 32 has been exposed from the sheath 9. The first threshold value can be set appropriately based on the designer's empirical knowledge or experiments or simulations conducted by the designer, and is set in advance and stored in the control unit 28. The first threshold value is, for example, 500 Ω.

[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 is less than the first threshold value.

[0045] If the impedance between the two reference electrodes 32 is equal to or greater than the first threshold value (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 operator inserts the catheter 4 further into the body, and the exposure of the reference electrodes 32 is determined again. If the impedance between the two reference electrodes 32 is less than the first threshold value (Y in S103), that is, if the two reference electrodes 32 are exposed from the sheath 9, the deployment state of the electrode assembly 12 is confirmed (S104).

[0046] The exposure determination of the two reference electrodes 32 may be performed as follows. That is, the control unit 28 starts measuring the impedance between the two reference electrodes 32 when 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 timing when the insertion of the catheter 4 begins. The control unit 28 repeats this impedance measurement while the catheter 4 is moving within the sheath 9. Then, when the control unit 28 detects that the measured impedance is less than the first threshold value, it displays on the display unit 30 that the two reference electrodes 32 are exposed from the sheath 9. This allows the user to proceed to confirm the deployment state.

[0047] The deployed state is checked, for example, by the operator. The operator can grasp the deployed state of the electrode assembly 12 based on the position of the operation unit provided on the handle 14, etc. The operator inputs the grasped deployed state to the power supply device 8 via the input unit 24. The deployed state of the electrode assembly 12 may be checked by the control unit 28. The deployed state of the electrode assembly 12 may be limited to only two states, the first deployed state and the second deployed state, or may include other deployed states in which the curvature of each spline 16 differs from that of the first deployed state and the second deployed state.

[0048] Next, a reference impedance A in the confirmed deployed state of each spline 16 is set (S105). This setting is initiated, for example, by the control unit 28 detecting an input of the deployed state. For example, the control unit 28 sets the impedance determined to be less than the first threshold value in step S103 as the reference impedance A in the confirmed deployed state in step S104 and stores the set impedance. Note that 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. Alternatively, the reference impedance A may be set by the operator via the input unit 24.

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

[0050] Then, the control unit 28 determines whether the ablation electrode 18 has contacted the biological tissue 2 based on the difference Δ between the reference impedance A and the impedance B. As an example, the control unit 28 determines whether the difference Δ between the reference impedance A and the impedance B is equal to or greater than a predetermined second threshold value (S107). As an 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 the impedance B is equal to or greater than the second threshold value, it is possible to determine whether the ablation electrode 18 has contacted the biological tissue 2.

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

[0052] If the difference Δ is equal to or greater than the second threshold value (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, for example, the display unit 30. If the difference Δ is less than the second threshold value (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, for example, the display unit 30. Then, the control unit 28 determines whether contact determination has been performed for all ablation electrodes 18 to which the ablation voltage is to be applied (S110).

[0053] If contact determination has been performed for all ablation electrodes 18 (Y in S110), the contact determination flow for the ablation electrodes 18 ends. If contact determination 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 determination has not been performed. Note that contact determination may be performed by the 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 checks 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 has been completed, the operator can determine whether or not to start ablation based on the contact state of each ablation electrode 18. For example, when 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, is continuous over the entire circumference, the operator instructs the control unit 28 via the input unit 24 to start ablation.

[0055] As an example, when an ablation electrode 18 in contact with the biological tissue 2 on a certain spline 16 and an ablation electrode 18 in contact with the biological tissue 2 on 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, when the first ablation electrode 18a on the first spline 16a and the first ablation electrode 18a on 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.

[0056] Furthermore, when an ablation electrode 18 in contact with the biological tissue 2 on a certain spline 16 and an ablation electrode 18 in contact with the biological tissue 2 on a spline 16 adjacent to this spline 16 are positioned 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, when a first ablation electrode 18a on a first spline 16a and a second ablation electrode 18b on a 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 controller 28 may correct the reference impedance A depending on 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, one of the two electrodes to which a voltage is applied in measuring the reference impedance A and measuring the impedance B is the same, the reference electrode 32, but the other is different, either the reference electrode 32 or the ablation electrode 18. Therefore, the positional relationship of the two electrodes used in measuring the reference impedance A and measuring the impedance B is different. For this reason, the accuracy of the contact determination based on the reference impedance A measured with the two reference electrodes 32 may be lower than that of the contact determination based on the 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 difference in impedance due to differences in the positional relationship between the two electrodes used. The correction value α can be set appropriately based on the designer's empirical knowledge or experiments or simulations conducted by the designer, and is set in advance and stored in the control unit 28. The correction value α may vary depending on the deployment state of the spline 16. In this case, the correction value α may be determined for each deployment state. Alternatively, the same correction value α may be used uniformly for all ablation electrodes 18.

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

[0060] The embodiments of the present disclosure have been described in detail above. The above-described embodiments merely illustrate specific examples of implementing the present disclosure. The content of the embodiments does not limit the technical scope of the present disclosure, and many design modifications, such as changing, adding, or deleting components, are possible within the scope of the concept of the present disclosure defined in the claims. A new embodiment with design modifications will combine the effects of the combined embodiments and modifications. In the above-described embodiments, the content that allows such design modifications is emphasized by using notations such as "in this embodiment" or "in this embodiment," but design modifications are also permitted even in content without such notation. Any combination of the components included in each embodiment is also valid as an aspect of the present disclosure. Hatching on cross sections in the drawings does not limit the material of the hatched object.

[0061] Embodiments may be identified by the following items: [Item 1] A catheter (4) comprising: a shaft (10); a plurality of splines (16) arranged around the axis of the shaft (10) at the distal end of the shaft (10); one or more ablation electrodes (18) disposed on one or more splines (16) and used for ablation of biological tissue (2); and two or more reference electrodes (32) used for measuring a reference impedance (A) that serves as a reference point for determining contact of the ablation electrodes (18) with the biological tissue (2), each of the two or more reference electrodes (32) being disposed on one of the splines (16) and being disposed closer to the proximal end than the ablation electrode (18, 18d) located closest to the proximal end of the shaft (10). [Item 2] The catheter (4) of item 1, wherein at least a portion of the two or more reference electrodes (32) are disposed on different splines (16). [Item 3] An ablation system (1) comprising: the catheter (4) of item 1 or 2; and a power supply device (8) having 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 a voltage to the ablation electrode (18) and reference electrode (32). [Item 4] The control unit (28) determines whether the ablation electrode (18) has contacted biological tissue (2) based on a difference (Δ) between an impedance (B) measured when a voltage is applied to the reference electrode (32) and the ablation electrode (18), and a reference impedance (A). [Item 5] The ablation system (1) of item 4, in which the control unit (28) corrects the reference impedance (A) depending on 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.[Item 6] The ablation system (1) according to any one of items 3 to 5, wherein the ablation system (1) includes a sheath (9) through which the catheter (4) is inserted, and the control unit (28) determines whether the reference electrodes (32) are exposed from the sheath (9) based on impedance measured when a voltage is applied to the two reference electrodes (32).

[0062] The present disclosure may be utilized in catheters and ablation systems.

[0063] 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. A catheter comprising: a shaft; a plurality of splines arranged around the axis of the shaft at the distal end of the shaft; one or more ablation electrodes arranged on one or more of the splines and used for ablation of biological tissue; and two or more reference electrodes used for measuring a reference impedance that serves as a reference point for determining contact of the ablation electrode with the biological tissue, each of the two or more reference electrodes being arranged on one of the splines and closer to the base end than the ablation electrode that is located closest to the base end of the shaft.

2. The catheter of claim 1, wherein the two or more reference electrodes are positioned on at least some of the splines that are different from one another.

3. An ablation system comprising: a catheter according to claim 1 or 2; a power supply unit electrically connected to the ablation electrode and the reference electrode of the catheter; and a power supply device having a control unit that controls the power supply unit to apply voltages to the ablation electrode and the reference electrode.

4. The ablation system according to claim 3, wherein 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.

5. The ablation system according to claim 4, wherein 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.

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

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