Patent Publication Number: US-2022218414-A1

Title: Energy generating device and cauterization system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2020/036818 filed on Sep. 29, 2020, which claims priority to Japanese Application No. 2019-179469 filed on Sep. 30, 2019, the entire content of both of which is incorporated herein by reference. 
    
    
     TECHNOLOGICAL FIELD 
     The present disclosure generally relates to an energy generating device that supplies energy to an electrode for cauterization, and to a cauterization system. 
     BACKGROUND DISCUSSION 
     In recent years, a cauterization device has been used which includes an electrode that cauterizes a biological tissue in a living body. Examples of such a cauterization device include a device that cauterizes the vicinity of a through-hole formed in an atrial septum, to maintain a penetrated state, and a device that cauterizes a myocardium to treat arrhythmia. 
     When a biological tissue is cauterized by the aforementioned cauterization device, it can be difficult to detect how much energy is being applied to the biological tissue. For this reason, energy cannot be applied to the biological tissue with relatively high reproducibility, and the treatment effect can vary. 
     For this reason, Japanese Patent Application Publication No. 2013-111332 A discloses a cauterization state notification device that acquires an impedance of a myocardium from an electrode which performs cauterization, and changes notification sound based on a change in the acquired impedance, in order to treat arrhythmia. An operator can rather easily determine the state of cauterization from the notification sound. 
     The cauterization state notification device disclosed in Japanese Patent Application Publication No. 2013-111332 A makes notification about the state of cauterization by notification sound, and the operator needs to make a determination from the notification sound and to continue or stop the cauterization. For this reason, damage levels of a biological tissue may be not uniform, or tissue damage caused by the application of excessive energy or peripheral embolism caused by the formation of blood clots may be generated. 
     SUMMARY 
     An energy generating device and a cauterization system are disclosed, which are capable of uniformly cauterizing a biological tissue at a desired damage level, and reducing the generation of tissue damage or the generation of peripheral embolism caused by the formation of blood clots. 
     A cauterization device which is an energy generating device including: a control unit configured to control an electric energy output to at least one electrode configured to cauterize a biological tissue. The control unit includes an impedance calculation unit configured to calculate an impedance between the at least one electrode and an electrode serving as a return electrode paired with the at least one electrode, and an output adjustment unit configured to cause electric power to the at least one electrode and the electrode serving as a return electrode paired with the at least one electrode to decrease when the impedance calculated by the impedance calculation unit is more than a predetermined threshold value or is the predetermined threshold value or more (i.e., equal to or greater than the predetermined threshold value). 
     A cauterization system is disclosed, which includes: the energy generating device; and a cauterization device including the at least one electrode configured to cauterize the biological tissue. 
     The energy generating device and the cauterization system configured as described above can determine a level of damage to the tissue caused by the electrode, based on an increase in the impedance of the biological tissue caused by the cauterization, and cause the electric power to the electrode to automatically decrease. For this reason, the energy generating device can uniformly cauterize the biological tissue at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     The output adjustment unit may cause the electric power between the at least one electrode and the electrode serving as a return electrode of the at least one electrode, to be maintained substantially constant when the impedance calculated by the impedance calculation unit is equal to or less than the predetermined threshold value. Accordingly, before the impedance reaches the threshold value, the energy generating device can automatically decrease current according to the impedance that gradually increases as the cauterization progresses. For this reason, the energy generating device can facilitate uniform cauterization of the biological tissue at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     The output adjustment unit may cause a voltage between the at least one electrode and the electrode serving as a return electrode of the at least one electrode, to be maintained substantially constant when the impedance calculated by the impedance calculation unit is equal to or less than the threshold value. Accordingly, before the impedance reaches the threshold value, the energy generating device can automatically decrease electric power according to the impedance that gradually increases as the cauterization progresses. For this reason, the energy generating device can facilitate uniform cauterization of the biological tissue at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     The cauterization device may include a pressing mechanism on which the electrode is disposed and by which the electrode is pressable against the biological tissue. Accordingly, the electrode comes into close contact with the biological tissue, and is unlikely to be exposed in blood. For this reason, it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. In addition, since the electrode comes into close contact with the biological tissue, a change in impedance can be accurately detected, so that a damage level of the tissue can be accurately determined. For this reason, the cauterization system can uniformly cauterize the biological tissue at a desired damage level. 
     The cauterization device may include a shaft portion that is elongated. The pressing mechanism may include an expansion body provided at a distal portion of the shaft portion to be expandable and contractable in a radial direction. The expansion body may include a plurality of wire portions connected to the shaft portion, and at least one holding portion formed of at least one wire portion. The holding portion may include a distal side holding portion and a proximal side holding portion between which a separated distance is narrowed when the expansion body expands. The electrode may be disposed on the distal side holding portion and/or on the proximal side holding portion. Accordingly, the cauterization system effectively brings the electrode into close contact with the biological tissue using the expansion body, so that the electrode can be unlikely to be exposed in the blood. For this reason, it is possible to reduce the generation of peripheral embolism caused by the formation of blood clots. 
     The cauterization device may include a shaft portion that is elongated. The pressing mechanism may include a balloon provided at a distal portion of the shaft portion to be inflatable and contractable in a radial direction. The electrode may be disposed on an outer surface of the balloon. Accordingly, the cauterization system effectively brings the electrode into close contact with the biological tissue using the balloon, so that the electrode can be unlikely to be exposed in the blood. For this reason, it is possible to reduce the generation of peripheral embolism caused by the formation of blood clots. 
     The cauterization device may be a device that cauterizes a biological tissue in the vicinity of a through-hole to maintain the through-hole formed in an atrial septum. Accordingly, the cauterization system can uniformly cauterize the biological tissue in the vicinity of the through-hole of the atrial septum at a desired damage level to properly maintain the through-hole. 
     In accordance with an aspect, a method is disclosed for controlling energy to an electrode for cauterization, the method comprising: controlling an electric energy output to at least one electrode configured to cauterize a biological tissue, the control unit including an impedance calculation unit configured to calculate an impedance between the at least one electrode and an electrode serving as a return electrode of the at least one electrode; and causing electric power to the at least one electrode and the electrode serving as the return electrode of the at least one electrode to decrease when the impedance calculated by the impedance calculation unit is equal to or greater than a predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view illustrating an overall configuration of a cauterization system according to a first embodiment. 
         FIG. 2  is an enlarged perspective view of a distal portion of a cauterization device. 
         FIG. 3  is a block diagram of the cauterization system according to the first embodiment. 
         FIG. 4  is a view for describing a treatment method using the cauterization system according to the first embodiment, and is a view for schematically describing a state where an expansion body is disposed in a through-hole of an atrial septum, in which the cauterization device and a biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIG. 5  is a view for schematically describing a state where the expansion body is disposed in the atrial septum, in which the cauterization device and the biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIG. 6  is a view for schematically describing a state where the expansion body is expanded in diameter in the atrial septum, in which the cauterization device and the biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIG. 7  is a flowchart illustrating a flow of control in a control unit. 
         FIG. 8  is a graph to be displayed on a notification unit. 
         FIGS. 9A and 9B  illustrate front views of the vicinities of holding portions of cauterization systems according to modification examples, wherein  FIG. 9A  illustrates a first modification example, and  FIG. 9B  illustrates a second modification example. 
         FIG. 10  is a block diagram illustrating a third modification example of the cauterization system according to the first embodiment. 
         FIG. 11  is a front view illustrating an overall configuration of a cauterization system according to a second embodiment. 
         FIG. 12  is a block diagram of the cauterization system according to the second embodiment. 
         FIG. 13  is a view for describing a treatment method using the cauterization system according to the second embodiment, and is a view for schematically describing a state where an expansion body is disposed in a through-hole of an atrial septum, in which a cauterization device and a biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
         FIGS. 14A and 14B  illustrate views for describing a treatment method using the cauterization system according to the second embodiment, wherein  FIG. 14A  illustrates a state where the balloon is inflated, and  FIG. 14B  is a cross-sectional view taken along line XIVB-XIVB in  FIG. 14A . 
         FIG. 15  is a front view of the vicinity of an expansion body of a modification example. 
     
    
    
     DETAILED DESCRIPTION 
     Set forth below with reference to the accompanying drawings is a detailed description of embodiments of an energy generating device that supplies energy to an electrode for cauterization, and to a cauterization system representing examples of the inventive energy generating device that supplies energy to an electrode for cauterization, and cauterization system. Note that dimensional ratios in the drawings may be exaggerated and different from actual ratios for convenience of description. In addition, in the specification, a side on which a cauterization device  10  is inserted into a biological lumen will be referred to as a “distal side”, and a side on which operation is performed will be referred to as a “proximal side”. 
     First Embodiment 
     As illustrated in  FIG. 4 , a cauterization system  1  according to a first embodiment is configured to be able to expand a through-hole Hh formed in an atrial septum HA of a heart H of a patient and to perform cauterization to maintain the size of the expanded through-hole Hh. The cauterization system  1  includes the cauterization device  10  that is inserted into a living body to cauterize a biological tissue, and an energy generating device  100  that supplies electric energy to the cauterization device  10 . 
     Initially, the cauterization device  10  will be described. As illustrated in  FIGS. 1 and 2 , the cauterization device  10  includes an elongated shaft portion  20 , an expansion body  21  provided at a distal portion of the shaft portion  20 , and an operation unit  23  provided at a proximal portion of the shaft portion  20 . The expansion body  21  is provided with an energy output unit  22  for performing cauterization. 
     The shaft portion  20  includes an outer shaft  31  that holds the expansion body  21  at the distal portion of the outer shaft  31 , and a storage sheath  30  that stores the outer shaft  31 . The storage sheath  30  is movable forward and backward with respect to the outer shaft  31  in an axial direction. In a state where the storage sheath  30  is moved to a distal side of the shaft portion  20 , the storage sheath  30  can store the expansion body  21  inside of the storage sheath  30 . The storage sheath  30  is moved to the proximal side from a state where the expansion body  21  is stored, and thus the expansion body  21  can be exposed. 
     A pulling shaft  33  is stored inside the outer shaft  31 . The pulling shaft  33  is a shaft for pulling to act a compression force on the expansion body  21 . The pulling shaft  33  protrudes from a distal end of the outer shaft  31  to the distal side, and a distal portion of the pulling shaft  33  is fixed to a distal member  35 . A proximal portion of the pulling shaft  33  extends to the proximal side from the operation unit  23 . The distal member  35  to which the distal portion of the pulling shaft  33  is fixed may not be fixed to the expansion body  21 . Accordingly, the distal member  35  can pull the expansion body  21  in a compression direction. In addition, when the expansion body  21  is stored in the storage sheath  30 , the distal member  35  is separated to the distal side from the expansion body  21 , so that the expansion body  21  can be easily moved in an axial direction and storability can be improved. 
     The operation unit  23  includes a housing  40  to be gripped by an operator, an operation dial  41  to be rotationally operable by the operator, a conversion mechanism  42  that operates in conjunction with rotation of the operation dial  41 , and a connector  43  that is connectable to the energy generating device  100 . The pulling shaft  33  is held by the conversion mechanism  42  inside the operation unit  23 . The conversion mechanism  42  can move the held pulling shaft  33  forward and backward along the axial direction with rotation of the operation dial  41 . For example, a rack and pinion mechanism can be used as the conversion mechanism  42 . The connector  43  can be connected to the energy generating device  100 , and receive electric energy from the energy generating device  100 . In accordance with an embodiment, it may be preferable that the connector  43  is attachable to and detachable from the energy generating device  100 . 
     The expansion body  21  includes a plurality of wire portions  50  in a circumferential direction. In the present embodiment, for example, four wire portions  50  are provided in the circumferential direction. The number of the wire portions  50  is not particularly limited. Each of the wire portions  50  is expandable and contractable in a radial direction of the expansion body  21 . In a natural state where no external force acts on the expansion body  21 , the expansion body  21  is in a reference form where the expansion body  21  is deployed in the radial direction. A proximal portion of the wire portion  50  extends from a distal portion of the outer shaft  31  to the distal side. A distal portion of the wire portion  50  extends from a proximal portion of the distal member  35  to the proximal side. The wire portion  50  is inclined such that the size in the radial direction increases from both end portions toward a central portion in the axial direction. In addition, the wire portion  50  includes a holding portion  51  having a valley shape in the radial direction of the expansion body  21 , at the central portion of the wire portion  50  in the axial direction. 
     The holding portion  51  includes a proximal side holding portion  52 , and a distal side holding portion  53  located closer to the distal side than the proximal side holding portion  52 . The holding portion  51  further includes a proximal side outward projection portion  55 , an inward projection portion  56 , and a distal side outward projection portion  57 . It is preferable that in the reference form, an interval between the proximal side holding portion  52  and the distal side holding portion  53  in the axial direction is slightly wider on a radially outward side than on a radially inward side. Accordingly, a biological tissue can rather easily be disposed (i.e., sandwiched) between the proximal side holding portion  52  and the distal side holding portion  53  from the radially outward side. 
     The proximal side holding portion  52  includes a projection portion  54  protruding toward the distal side. The energy output unit  22  is disposed on the projection portion  54 . Note that the proximal side holding portion  52  may not include the projection portion  54 . Namely, the energy output unit  22  may not protrude to the distal side. 
     The proximal side outward projection portion  55  is located on a proximal side of the proximal side holding portion  52 , and is formed in a shape projecting outward in the radial direction. The distal side outward projection portion  57  is located on a distal side of the distal side holding portion  53 , and is formed in a shape projecting outward in the radial direction. The inward projection portion  56  is located between the proximal side holding portion  52  and the distal side holding portion  53 , and is formed in a shape projecting inward in the radial direction. The proximal side outward projection portion  55 , the inward projection portion  56 , and the distal side outward projection portion  57  are stored in the storage sheath  30 , thus being deformable from a projection shape into a shape, for example, close to being flat. 
     In the present embodiment, the energy output unit  22  is provided at the proximal side holding portion  52 , but the energy output unit  22  may be provided at the distal side holding portion  53 . In addition, the energy output units  22  may be provided at both the proximal side holding portion  52  and the distal side holding portion  53 . 
     Each of the wire portions  50  forming the expansion body  21  has, for example, a flat plate shape obtained by cutting a cylinder. A wire forming the expansion body  21  can have a thickness, for example, of 50 μm to 500 μm and a width of 0.3 mm to 2.0 mm. However, a wire forming the expansion body  21  may have dimensions outside these ranges. In addition, the shape of the wire portion  50  is not limited, and may have, for example, a circular cross-sectional shape or other cross-sectional shapes. 
     As illustrated in  FIGS. 2 and 3 , the energy output unit  22  can include a first electrode  22 A, a second electrode  22 B, a third electrode  22 C, and a fourth electrode  22 D. The first electrode  22 A, the second electrode  22 B, the third electrode  22 C, and the fourth electrode  22 D are disposed in order on the wire portions  50  arranged in the circumferential direction of the expansion body  21 . 
     Since the energy output unit  22  is provided at the projection portion  54  of the proximal side holding portion  52 , when the holding portion  51  holds the atrial septum HA, energy from the energy output unit  22  is transmitted from a right atrium side to the atrial septum HA. When the energy output unit  22  is provided at the distal side holding portion  53 , energy from the energy output unit  22  is transmitted from a left atrium side to the atrial septum HA. 
     The energy output unit  22  can be configured as a bipolar electrode that receives electric energy from the energy generating device  100 . The same voltage can be applied to the first electrode  22 A and to the third electrode  22 C. The same voltage can be applied to the second electrode  22 B and to the fourth electrode  22 D. A voltage having a polarity opposite that of the first electrode  22 A and of the third electrode  22 C can be applied to the second electrode  22 B and to the fourth electrode  22 D. Therefore, energization is performed between the first electrode  22 A and the second electrode  22 B, between the second electrode  22 B and the third electrode  22 C, between the third electrode  22 C and the fourth electrode  22 D, and between the fourth electrode  22 D and the first electrode  22 A. Electric energy from the connector  43  connected to the energy generating device  100  is supplied to the energy output unit  22  by a conducting wire  24  coated with an insulating coating material. When the energy output unit  22  is a bipolar electrode, the number of the electrodes, for example, is not particularly limited as long as the number of the electrodes is 2 or more. 
     The wire portion  50  can be made of a metallic material. The metallic material of the wire portion  50 , for example, can be a titanium-based (Ti—Ni, Ti—Pd, Ti—Nb—Sn, or the like) alloy, a copper-based alloy, stainless steel, β-titanium steel, or a Co—Cr alloy can be used. In accordance with an embodiment, an alloy or the like having a spring property such as a nickel-titanium alloy can be used. However, the material for the wire portion  50  is not limited to these metallic materials, and the wire portion  50  may be made of other materials. 
     The shaft portion  20  includes an inner shaft  32  inside the outer shaft  31 , and the pulling shaft  33  is stored inside the inner shaft  32 . A guide wire lumen is formed in the pulling shaft  33  and in the distal member  35  along the axial direction, and a guide wire  11  can be inserted into the guide wire lumen. 
     In accordance with an embodiment, it can be preferable that the storage sheath  30 , the outer shaft  31 , and the inner shaft  32  of the shaft portion  20 , for example, are made of a material having a certain degree of flexibility. Examples of such a material having a certain degree of flexibility can include polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, and a mixture of two or more of the polyolefin such as polyethylene, polypropylene, polybutene, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, and an ionomer, fluororesins such as soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyether blockamide, polyester, polyester elastomer, polyurethane, and polytetrafluoroethylene, polyimide, PEEK, silicone rubber, and latex rubber. 
     The pulling shaft  33  can be made of, for example, an elongate wire such as a metallic material such as stainless steel or a super-elastic alloy such as a nickel-titanium alloy or a copper-zinc alloy, or a resin material having relatively high rigidity. In addition, the pulling shaft  33  may be formed by coating the above material with a resin material such as polyvinyl chloride, polyethylene, polypropylene, ethylene-propylene copolymer, or fluororesin. 
     The distal member  35  can be made of, for example, a metallic material such as stainless steel or a super-elastic alloy such as a nickel-titanium alloy or a copper-zinc alloy, or a resin material having relatively high rigidity. 
     Next, the energy generating device  100  will be described. As illustrated in  FIG. 3 , the energy generating device  100  includes an energy generating unit  110 , a notification unit  120 , and a control unit  130 . 
     The energy generating unit  110  includes a high-frequency oscillation circuit  111 , a transformer  112 , and a current sensor  113 . The energy generating unit  110  can output electric power input from a commercial power supply, which is converted into a high-frequency current by the high-frequency oscillation circuit  111  and then is converted into an arbitrary voltage by the transformer  112 . In addition, the energy generating unit  110  detects values of currents flowing through the electrodes  22 A to  22 D, using the current sensor  113 . 
     The notification unit  120  can be a portion that notifies the operator of a control status. The notification unit  120  can be, for example, a speaker that makes notification by sound or an image monitor that makes notification by an image. The image monitor can display graphs of changes in electric power, impedance, voltage, and current over time, together with a threshold value, or can numerically display electric power, impedance, voltage, current, threshold value, elapsed time, and various other parameters. In addition, the image monitor can display control status, warning, and the like. Note that a display method of the image monitor or an output method of the speaker is not particularly limited. Note that the notification unit  120  may be an external device that is communicably connected to the energy generating device  100 , instead of being configured in the energy generating device  100 . 
     The control unit  130  includes a central processing unit (CPU), a storage circuit, and an operation program. The control unit  130  may be connected to an interface such as a keyboard or a mouse. The control unit  130  can be, for example, a computer. The control unit  130  can include an output adjustment unit  131 , an impedance calculation unit  132 , and an information output unit  133 . 
     The output adjustment unit  131  controls the energy generating unit  110  to adjust an output of a high-frequency current from the energy generating unit  110 . The output adjustment unit  131  can cause the energy generating unit  110  to output a high-frequency current at an arbitrary voltage. 
     The impedance calculation unit  132  acquires an output high-frequency voltage value from the energy generating unit  110  or from the output adjustment unit  131 , and acquires a high-frequency current value detected by the current sensor  113 , from the energy generating unit  110 . The impedance calculation unit  132  divides the high-frequency voltage value by the high-frequency current value, to calculate a biological impedance value of a site to be cauterized. 
     The information output unit  133  transmits information selected from various information such as output electric power, voltage, current, calculated impedance value, threshold value, elapsed time, and operating state of the output adjustment unit  131  to the notification unit  120 . 
     Next, a treatment method using the cauterization system  1  according to the present embodiment will be described. The treatment method is performed on a patient suffering from a heart failure (left heart failure). As illustrated in  FIG. 4 , the treatment method can be performed on a patient suffering from a chronic heart failure in which a myocardium of a left ventricle of the heart H is hypertrophied and increases in stiffness (hardness) to cause an increase in blood pressure in a left atrium HLa. 
     When the operator forms the through-hole Hh, the operator delivers an introducer in which a guiding sheath and a dilator are combined together, to the vicinity of the atrial septum HA. The introducer can be delivered to, for example, a right atrium HRa via an inferior vena cava Iv. In addition, the introducer can be delivered using the guide wire  11 . The operator can insert the guide wire  11  into the dilator, and deliver the introducer along the guide wire  11 . The insertion of the introducer into or the insertion of the guide wire  11  into a living body can be performed using a method such as using an introducer for blood vessel introduction. 
     Next, the operator causes a puncture device and the dilator to penetrate through the atrial septum HA from a right atrium HRa side toward a left atrium HLa side to form the through-hole Hh. For example, a device such as a wire having a sharp distal end can be used as the puncture device. The puncture device is inserted into a dilator  312 , and is delivered to the atrial septum HA. After the guide wire  11  is removed from the dilator, instead of the guide wire  11 , the puncture device can be delivered to the atrial septum HA. 
     Next, the cauterization device  10  is delivered to the vicinity of the atrial septum HA along the guide wire  11  inserted into the left atrium HLa from the right atrium HRa via the through-hole Hh in advance. At this time, a part of a distal portion of the cauterization device  10  passes through the through-hole Hh opened in the atrial septum HA, and reaches the left atrium HLa. When the cauterization device  10  is inserted, the expansion body  21  is in a contracted form where the expansion body  21  is stored in the storage sheath  30 . In the contracted form, the proximal side outward projection portion  55 , the inward projection portion  56 , and the distal side outward projection portion  57  that have a projection shape in a natural state are deformed, for example, into a shape close to being flat, so that the expansion body  21  is contracted in the radial direction. 
     Next, the storage sheath  30  is moved to the proximal side to expose a distal side portion of the expansion body  21  into the left atrium HLa. Accordingly, the distal side portion of the expansion body  21  is deployed in the radial direction inside the left atrium HLa by the restoring force of expansion body  21 . Next, as illustrated in  FIG. 5 , the storage sheath  30  is moved to the proximal side to expose the entirety of the expansion body  21 . Accordingly, a proximal side portion of the expansion body  21  is deployed in the radial direction inside the right atrium HRa by the restoring force of the expansion body  21 . At this time, the inward projection portion  56  is disposed inside the through-hole Hh. Accordingly, the entirety of the expansion body  21  is deployed by the restoring force of the expansion body  21 , and restores to the original reference form or to a form close to the reference form. At this time, the atrial septum HA is disposed between the proximal side holding portion  52  and the distal side holding portion  53 . Note that the expansion body  21  may come into contact with the through-hole Hh, thereby returning to a shape close to the reference form instead of completely returning to the reference form. Note that in this state, the expansion body  21  is not covered with the storage sheath  30  and does not receive a force from the pulling shaft  33 . This form of the expansion body  21  can be defined as being included in the reference form (i.e., close to the original form in a natural state where no external force acts on the expansion body  21 ). 
     Next, the operator operates the operation unit  23  in a state where the atrial septum HA is held by the holding portion  51 , to move the pulling shaft  33  to the proximal side. Accordingly, as illustrated in  FIG. 6 , the expansion body  21  receiving a compression force in the axial direction has an expanded form where the expansion body  21  is more expanded in the radial direction than in the reference form. In the expanded form of the expansion body  21 , the proximal side holding portion  52  and the distal side holding portion  53  approach each other and the atrial septum HA is held (i.e., sandwiched) between the proximal side holding portion  52  and the distal side holding portion  53 . The holding portion  51  additionally expands in a state where the holding portion  51  holds the atrial septum HA, to widen the held through-hole Hh in the radial direction. 
     After the through-hole Hh is expanded, hemodynamics can be confirmed. 
     As illustrated in  FIG. 4 , the operator delivers a hemodynamics confirmation device  300  to the right atrium HRa via the inferior vena cava Iv. For example, an echo catheter can be used as the hemodynamics confirmation device  300 . The operator can cause a display device such as a display to display an echo image acquired by the hemodynamics confirmation device  300 , and confirm the amount of blood passing through the through-hole Hh, based on a display result. 
     Next, the operator performs a maintenance treatment to maintain the size of the through-hole Hh. In the maintenance treatment, energy is applied to an edge portion of the through-hole Hh through the energy output unit  22 , so that the edge portion of the through-hole Hh is cauterized (heated and cauterized) by the energy. Hereinafter, a method of the maintenance treatment using the cauterization system  1  will be described with reference to the flowchart illustrated in  FIG. 7 . 
     As illustrated in  FIGS. 1 and 3 , the operator operates the energy generating device  100  to which the connector  43  of the cauterization device  10  is connected, to start cauterization. Accordingly, the output adjustment unit  131  of the control unit  130  causes the energy generating unit  110  to output a high-frequency current at constant electric power (step S 1 ). Note that electric power may not be strictly constant and may vary slightly. In addition, the output adjustment unit  131  may not cause the energy generating unit  110  to output a constant electric power. The first electrode  22 A and the third electrode  22 C serve as return electrodes of the second electrode  22 B and of the fourth electrode  22 D. For this reason, energization can be performed between the first electrode  22 A and the second electrode  22 B, between the second electrode  22 B and the third electrode  22 C, between the third electrode  22 C and the fourth electrode  22 D, and between the fourth electrode  22 D and the first electrode  22 A at constant electric power. 
     The electrodes  22 A to  22 D are disposed on the projection portions  54  of the proximal side holding portions  52 . For this reason, the maintenance treatment is performed in a state where the electrodes  22 A to  22 D are buried in a biological tissue by pressing the projection portions  54  against the atrial septum HA. Accordingly, the electrodes  22 A to  22 D do not come into contact with the blood during the maintenance treatment, so that it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. 
     When a biological tissue in the vicinity of the edge portion of the through-hole Hh is cauterized through the electrodes  22 A to  22 D, a degenerated portion in which the biological tissue is degenerated is formed in the vicinity of the edge portion. Since the biological tissue in the degenerated portion is in a state where elasticity is lost, the through-hole Hh can maintain a shape when the through-hole Hh is widened by the expansion body  21 . In the cauterized biological tissue, a damage level (degree of cauterization) progresses and the impedance increases. 
     The impedance calculation unit  132  of the control unit  130  acquires information from the energy generating unit  110  and from the output adjustment unit  131  while electric power is output from the energy generating unit  110 , and calculates an impedance (step S 2 ). The information output unit  133  of the control unit  130  transmits information selected from output electric power, voltage, measured current, calculated impedance value, threshold value, elapsed time, and operating state of the output adjustment unit  131 , and the like, to the notification unit  120  (step S 3 ). Accordingly, the notification unit  120  makes notification about the received information using a set method. For example, as illustrated in  FIG. 8 , the set method can be that the notification unit  120  causes the image monitor to display graphs of changes in electric power and impedance over time, together with a threshold value. 
     When the cauterization progresses over time, the biological impedance gradually increases. Since the electric power output by the energy generating unit  110  is maintained at a constant level (i.e., maintained substantially constant), when the impedance increases, the voltage output from the energy generating unit  110  automatically increases, and the current automatically decreases. Further, since the voltage output from the energy generating unit  110  is limited to a voltage value based on an impedance threshold value set in advance, when the impedance is more than the threshold value, the voltage does not change and the current decreases, and as a result, the electric power decreases. For this reason, the atrial septum HA can be uniformly cauterized at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy. In addition, it is possible to suppress the formation of blood clots caused by the application of excessive energy, and it is possible to reduce the generation of peripheral embolism or the like. In addition, when the atrial septum HA is cauterized to the desired damage level, the electric power output from the energy generating unit  110  automatically decreases to the extent that the atrial septum HA cannot be cauterized any more. For this reason, for example, the notification unit  120  may be omitted. 
     The impedance calculation unit  132  of the control unit  130  determines whether or not the calculated impedance is more than the threshold value set in advance (step S 4 ). Note that the impedance calculation unit  132  may determine whether or not the calculated impedance is equal to or more than the threshold value set in advance. 
     When it is determined that the impedance is more than the threshold value, the impedance calculation unit  132  causes the output (electric power) from the energy generating unit  110  to decrease (step S 5 ). For example, the impedance calculation unit  132  causes the output from the energy generating unit  110  to immediately stop or to gradually decrease and stop. Accordingly, the maintenance treatment is completed. In accordance with an embodiment, instead of causing the output from the energy generating unit  110  to stop, the impedance calculation unit  132  may control the energy generating unit  110  to maintain the voltage constant, so that the output decreases more than when the output automatically decreases. 
     Thereafter, the information output unit  133  of the control unit  130  transmits information including that the impedance is more than the threshold value (or the threshold value or more) and that the impedance calculation unit  132  causes the output from the energy generating unit  110  to decrease, to the notification unit  120  (step S 6 ). The notification unit  120  makes notification about the information using, for example, a set method. 
     Note that the control unit  130  can also cause the output from the energy generating unit  110  to stop, using a method different from the aforementioned control flow. For example, the operator may be able to forcibly stop or decrease the output from the energy generating unit  110  on his or her own judgement using input means such as a switch provided in the energy generating device  100  or in the cauterization device  10 . 
     In accordance with an embodiment, when the electrodes  22 A to  22 D are not in contact with a biological tissue, the impedance does not increase to the threshold value, so that the output (electric power) from the energy generating unit  110  does not decrease. For this reason, energy from the energy generating unit  110  continues to be applied, so that a risk of generation of blood clots may increase. Therefore, when the impedance calculated by the impedance calculation unit  132  does not increases to the threshold value within a specified time set in advance, the control unit  130  can cause the notification unit  120  to make notification about warning. Namely, the specified time is a time threshold value. The specified time is not particularly limited and can be, for example, 20 seconds to 40 seconds. Further, when the impedance does not increase to the threshold value within the specified time, the control unit  130  may forcibly cause the output from the energy generating unit  110  to stop. 
     After the maintenance treatment, the operator can confirm hemodynamics again, and when the amount of the blood passing through the through-hole Hh reaches a desired amount, the operator can reduce the expansion body  21  in diameter, stores the expansion body  21  in the storage sheath  30 , and then removes the storage sheath  30  from the through-hole Hh. Further, the operator removes the entirety of the cauterization device  10  out of the living body to end the treatment. 
     Note that as a first modification example, as illustrated in  FIG. 9A , the expansion body  21 , which is a pressing mechanism may include spring elements  58  that bias the energy output unit  22  including the electrodes  22 A to  22 D toward the distal side holding portion  53 , at the proximal side holding portions  52 . The spring element  58  can be, for example, a coil spring or a leaf spring. Accordingly, the energy output unit  22  supported by the spring elements  58  can be buried in the atrial septum HA. For this reason, the electrodes  22 A to  22 D of the energy output unit  22  are unlikely to come into contact with the blood during the maintenance treatment, so that it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. In accordance with an embodiment, when the electrodes  22 A to  22 D are provided at the distal side holding portions  53 , the spring elements  58  can be provided at the distal side holding portions  53 . 
     In addition, as a second modification example, as illustrated in  FIG. 9B , the expansion body  21 , which is a pressing mechanism may include support balloons  59  that support the energy output unit  22  including the electrodes  22 A to  22 D, at the proximal side holding portions  52 . A fluid is supplied to the support balloons  59  via a fluid supply tube  59 A, so that the support balloons  59  can be inflated to move the energy output unit  22  toward the distal side holding portions  53 . A proximal portion of the fluid supply tube  59 A extends from the operation unit  23  and is connectable to a syringe or the like that supplies the fluid. When the support balloons  59  is inflated, the electrodes  22 A to  22 D supported by the support balloons  59  can be buried in the atrial septum HA. For this reason, the electrodes  22 A to  22 D are unlikely to come into contact with the blood during the maintenance treatment, so that it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. Note that when the electrodes  22 A to  22 D are provided at the distal side holding portions  53 , the support balloons  59  are provided at the distal side holding portions  53 . 
     In addition, as a third modification example, as illustrated in  FIG. 10 , the energy output unit  22  may be configured as a monopolar electrode. In this case, the energy generating unit  110  applies the same voltage to the first electrode  22 A, to the second electrode  22 B, to the third electrode  22 C, and to the fourth electrode  22 D. In addition, the energy generating unit  110  also applies a voltage to a return electrode plate  25  that is an electrode serving as a return electrode of the first electrode  22 A, of the second electrode  22 B, of the third electrode  22 C, and of the fourth electrode  22 D. Then, the first electrode  22 A, the second electrode  22 B, the third electrode  22 C, and the fourth electrode  22 D are energized with the return electrode plate  25  affixed to a body surface of a patient. When each of the electrodes  22 A to  22 D is configured as a monopolar electrode, the number of the electrodes  22 A to  22 D excluding the return electrode plate  25  is not particularly limited as long as the number of the electrodes  22 A to  22 D is one (1) or more. In addition, the same voltage can be applied to the first electrode  22 A, to the second electrode  22 B, to the third electrode  22 C, and to the fourth electrode  22 D, but different voltages may be applied to the first electrode  22 A, to the second electrode  22 B, to the third electrode  22 C, and to the fourth electrode  22 D. Namely, the first electrode  22 A, the second electrode  22 B, the third electrode  22 C, and the fourth electrode  22 D may be separately controlled. In this case, the control unit  130  can separately control the first electrode  22 A, the second electrode  22 B, the third electrode  22 C, and the fourth electrode  22 D according to the aforementioned control flow (refer to  FIG. 7 ). 
     As described above, the energy generating device  100  in the first embodiment includes the control unit  130  that controls an electric energy output to at least one of the electrodes  22 A to  22 D that cauterize a biological tissue. The control unit  130  includes the impedance calculation unit  132  that calculates an impedance between an electrode and an electrode serving as a return electrode of the electrode, and the output adjustment unit  131  that causes electric power to the electrodes to decrease when the impedance calculated by the impedance calculation unit  132  is more than a predetermined threshold value or is the threshold value or more (i.e., equal to or greater than the predetermined threshold value). Accordingly, the energy generating device  100  can determine a damage level of the biological tissue based on an increase in the impedance of the cauterized biological tissue, and cause electric power to the electrodes  22 A to  22 D to automatically decrease. For this reason, the energy generating device  100  can uniformly cauterize the biological tissue at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     In addition, when the impedance calculated by the impedance calculation unit  132  is equal to or less than the predetermined threshold value (i.e., is the threshold value or less or is less than the threshold value), the output adjustment unit  131  causes electric power between an electrode and an electrode serving as a return electrode of the electrode, to be maintained substantially constant. Accordingly, the energy generating device  100  can reduce a decrease in tissue cauterization effect caused by a decrease in electric power, before the impedance reaches the threshold value, and facilitates uniform cauterization of the biological tissue at a desired damage level. 
     In addition, the cauterization system  1  according to the present embodiment can include the energy generating device  100 , and the cauterization device  10  including at least one of the electrodes  22 A to  22 D that cauterize a biological tissue. Accordingly, the cauterization system  1  can uniformly cauterize the biological tissue at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     In addition, the cauterization device  10  can include a pressing mechanism on which the electrodes  22 A to  22 D are disposed and by which the electrodes  22 A to  22 D are pressable against the biological tissue. Accordingly, the electrodes  22 A to  22 D come into close contact with the biological tissue, and are unlikely to be exposed in the blood. For this reason, it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. In addition, since the electrodes  22 A to  22 D come into close contact with the biological tissue, a change in impedance can be accurately detected, so that a damage level of the tissue can be accurately determined. For this reason, the cauterization system  1  can uniformly cauterize the biological tissue at a desired damage level. 
     In addition, the cauterization device  10  includes the elongated shaft portion  20 . The pressing mechanism includes the expansion body  21  provided at the distal portion of the shaft portion  20  to be expandable and contractable in the radial direction. The expansion body  21  includes the plurality of wire portions  50  connected to the shaft portion  20 , and at least one holding portion  51  formed of at least one wire portion  50 . The holding portion  51  includes the distal side holding portion  53  and the proximal side holding portion  52  between which a separated distance is narrowed when the expansion body  21  expands. The electrodes  22 A to  22 D are disposed on the distal side holding portions  52  and/or on the proximal side holding portions  52 . Accordingly, the cauterization system  1  effectively brings the electrodes  22 A to  22 D into close contact with the biological tissue using the expansion body  21 , so that the electrodes  22 A to  22 D can be unlikely to be exposed in the blood. 
     In addition, the cauterization device  10  is a device that cauterizes a biological tissue in the vicinity of the through-hole Hh to maintain the through-hole Hh formed in the atrial septum HA. Accordingly, the cauterization system  1  can uniformly cauterize the biological tissue in the vicinity of the through-hole Hh of the atrial septum HA at a desired damage level to properly maintain the through-hole Hh. 
     Second Embodiment 
     As illustrated in  FIGS. 11 and 12 , a cauterization system  200  according to a second embodiment includes a cauterization device  210  different from that of the first embodiment. Note that portions having the same functions as those of the first embodiment are denoted by the same reference signs, and a description of the portions having the same functions as those of the first embodiment will be omitted. 
     The cauterization device  210  includes an elongated shaft portion  220 , a balloon  230  provided at a distal portion of the shaft portion  220 , and a catheter hub  240  connected to a proximal portion of the shaft portion  220 . The balloon  230  is provided with an energy output unit  250  for performing cauterization. 
     The shaft portion  220  includes an outer tube  221  that is a tubular body of which a distal end and a proximal end of the tubular body are open, and an inner tube  222  disposed inside the outer tube  221 . An inflation lumen  223  through which an inflation fluid for inflating the balloon  230  flows is formed between the outer tube  221  and the inner tube  222 . A guide wire lumen  224  into which the guide wire  11  can be inserted is formed inside the inner tube  222 . 
     A distal side of the balloon  230  can be, for example, bonded to the inner tube  222  and a proximal side of the balloon  230  can be bonded to the outer tube  221 . The inside of the balloon  230  communicates with the inflation lumen  223 . A distal side region and a proximal side region of the balloon  230  in the axial direction are high compliance portions  231  that are flexible and are easy to inflate. In addition, a region of an axially central portion of the balloon  230  is a low compliance portion  232  that is hard and difficult to inflate. An imaging marker  233  having an X-ray imaging property (X-ray opacity) is disposed on the low compliance portion  232 . 
     The catheter hub  240  includes a first opening portion  241 , a second opening portion  242 , and the connector  43  that is connectable to the energy generating device  100 . The first opening portion  241  communicates with the inflation lumen  223  of the outer tube  221  to allow the inflow and discharge of the inflation fluid. The second opening portion  242  communicates with the guide wire lumen  224 . 
     The energy output unit  250  is disposed on an outer surface of the low compliance portion  232  of the balloon  230 . The energy output unit  250  includes the first electrode  22 A, the second electrode  22 B, the third electrode  22 C, the fourth electrode  22 D, a fifth electrode  22 E, and a sixth electrode  22 F. The first electrode  22 A, the second electrode  22 B, the third electrode  22 C, the fourth electrode  22 D, the fifth electrode  22 E, and the sixth electrode  22 F are disposed side by side at substantially equal intervals in order on an outer peripheral surface of the low compliance portion  232 . 
     The energy output unit  250  is configured as a bipolar electrode that receives electric energy from the energy generating device  100 . 
     In accordance with an embodiment, the same voltage can be applied to the first electrode  22 A, to the third electrode  22 C, and to the fifth electrode  22 E. The same voltage can be applied to the second electrode  22 B, to the fourth electrode  22 D, and to the sixth electrode  22 F. A voltage having a polarity opposite that of the first electrode  22 A, of the third electrode  22 C, and of the fifth electrode  22 E is applied to the second electrode  22 B, to the fourth electrode  22 D, and to the sixth electrode  22 F. Therefore, energization is performed between the first electrode  22 A and the second electrode  22 B, between the second electrode  22 B and the third electrode  22 C, between the third electrode  22 C and the fourth electrode  22 D, between the fourth electrode  22 D and the fifth electrode  22 E, between the fifth electrode  22 E and the sixth electrode  22 F, and between the sixth electrode  22 F and the first electrode  22 A. Electric energy from the connector  43  connected to the energy generating device  100  is supplied to the energy output unit  250  by the conducting wire  24  coated with an insulating coating material. 
     In accordance with an embodiment, the energy output unit  250  may be configured as a monopolar electrode to be used together with a return electrode plate. 
     In accordance with an embodiment, it may be preferable that the balloon  230  is made of a material having a certain degree of flexibility, and examples of the material of the balloon can include polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, and a mixture of two or more of polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ionomer, thermoplastic resins such as soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyester, polyester elastomer, polyurethane, fluororesin, silicone rubber, and latex rubber. 
     As illustrated in  FIG. 13 , an operator can relatively accurately dispose the low compliance portion  232  in the through-hole Hh of the atrial septum HA while confirming the position of the imaging marker  233  under radioscopy. Thereafter, when the balloon  230  is inflated, as illustrated in  FIGS. 14A and 14B , surfaces on center sides of the high compliance portions  231  face each other while interposing the low compliance portion  232  between the surfaces facing each other on the center sides of the high compliance portions  231 . The surfaces facing each other serve as a proximal side holding portion  234  and a distal side holding portion  235  that interpose the atrial septum HA between the proximal side holding portion  234  and the distal side holding portion  235 . Since the proximal side holding portion  234  and the distal side holding portion  235  interpose the atrial septum HA between the proximal side holding portion  234  and the distal side holding portion  235 , the low compliance portion  232  can be inflated without being displaced from the through-hole Hh, to widen the through-hole Hh. Then, when the low compliance portion  232  is inflated, the electrodes  22 A to  22 F disposed on the low compliance portion  232  can be strongly pressed against the through-hole Hh. Accordingly, in a state where the electrodes  22 A to  22 F are buried in a biological tissue, the maintenance treatment can be performed. Accordingly, the electrodes  22 A to  22 F do not come into contact with the blood during the maintenance treatment, so that it is possible to suppress the generation of blood clots or the like caused by the leakage of a current to the blood. 
     As described above, the cauterization device  210  of the cauterization system  200  according to the second embodiment includes the elongated shaft portion  220 . The pressing mechanism can include the balloon  230  provided at the distal portion of the shaft portion  220  that is inflatable and contractable in the radial direction. The electrodes  22 A to  22 F are disposed on the outer surface of the balloon  230 . Accordingly, the energy generating device  100  effectively brings the electrodes  22 A to  22 F into close contact with the biological tissue using the balloon  230 , so that the electrodes  22 A to  22 D can be unlikely to be exposed in the blood. 
     Note that the disclosure is not limited only to the aforementioned embodiments and various modifications can be made by those skilled in the art without departing from the technical concept of the disclosure. 
     For example, the cauterization system is not limited to a system that maintains the through-hole Hh formed in the atrial septum HA. For example, the cauterization system may be a system that cauterizes a myocardium to treat arrhythmia, a system that cauterizes and cuts sympathetic nerves to treat hypertension, or the like. In addition, the output adjustment unit  131  of the control unit  130  may cause the energy generating unit  110  to output a high-frequency current at a constant voltage. In this case, since the voltage output by the energy generating unit  110  is maintained constant, when the cauterization progresses over time and the impedance increases, the electric power output from the energy generating unit  110  automatically decreases. For this reason, it is possible to decrease energy applied to the atrial septum HA in a high impedance region, and it is possible to suppress the carbonization of tissues caused by rapid heat generation and the generation of bubbles caused by water vapor. Also in this case, when the impedance is equal to or greater than a predetermined threshold value, the output adjustment unit  131  forcibly causes electric power output by the energy generating unit  110 , to decrease. Accordingly, a biological tissue can be uniformly cauterized at a desired damage level. In addition, it is possible to reduce the generation of tissue damage caused by the application of excessive energy, or the generation of peripheral embolism caused by the formation of blood clots. 
     In addition, as a modification example illustrated in  FIG. 15 , the expansion body  21  may be formed in a mesh shape where wire portions are branched and merged together. The expansion body  21  includes a plurality of the holding portions  51  that are recessed portions, and the energy output unit  22  that is an electrode is disposed on the proximal side holding portion  52  of each of the holding portions  51 . In accordance with an embodiment, the position where the energy output unit  22  is disposed is not limited to the proximal side holding portion  52  and may be a position on the distal side holding portion  53  or on the inward projection portion  56 , at which the energy output unit  22  can come into contact with a biological tissue. In the present modification example, a pulling shaft is not provided. Therefore, the expansion body  21  released from the storage sheath  30  expands a puncture hole Hh using only its own expansion force. 
     The detailed description above describes embodiments of an energy generating device that supplies energy to an electrode for cauterization, and to a cauterization system. The invention is not limited, however, to the precise embodiments and variations described. Various changes, modifications and equivalents may occur to one skilled in the art without departing from the spirit and scope of the invention as defined in the accompanying claims. It is expressly intended that all such changes, modifications and equivalents which fall within the scope of the claims are embraced by the claims.