Patent Publication Number: US-2022211431-A1

Title: Medical device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2020/036817 filed on Sep. 29, 2020, which claims priority to Japanese Application No. 2019-178330 filed on Sep. 30, 2019, the entire content of both of which is incorporated herein by reference. 
    
    
     TECHNOLOGICAL FIELD 
     The present disclosure relates to a medical device that expands and maintains a hole of a biological tissue. 
     BACKGROUND DISCUSSION 
     Chronic heart failure is one of known heart diseases. The chronic heart failure is broadly classified into a systolic heart failure and a diastolic heart failure, based on a cardiac function index. In a patient suffering from diastolic heart failure, a myocardium is hypertrophied and increases in stiffness (hardness), so that the blood pressure in a left atrium increases and the pumping function of a heart is decreased. Accordingly, the patient shows a heart failure symptom such as a pulmonary edema. There is also a heart disease in which the blood pressure on a right atrium side increases due to pulmonary hypertension or the like, and the pump function of a heart is decreased, thereby showing heart failure symptoms. 
     In recent years, for the patients suffering from a heart failure, attention has been paid to a shunt treatment in which a shunt (through-hole) serving as an escape route for increased atrial pressure is formed in an atrial septum, thereby being able to reduce heart failure symptoms. In the shunt treatment, the atrial septum is accessed using a transvenous approach method, and a through-hole of a desired size is formed. Then, a method has been known in which a shunt hole is subjected to energy to be cauterized, thereby maintaining the shunt hole. 
     In addition, for example, Japanese Patent No. 6013186 discloses a device that brings an expansion body including a plurality of wires having a cauterization function, into contact with a renal artery wall and cauterizes renal sympathetic nerves adjacent to the renal artery wall, as a treatment for hypertension. 
     When the expansion body including the plurality of wires is contracted, the position of the expansion body with respect to a shaft located at a center of the plurality of wires may be displaced. In a case where the positions of the contracted wires are displaced with respect to the shaft, when the expansion body is stored in a tubular member, the expansion body may be damaged or may be difficult to store in the tubular member. 
     SUMMARY 
     A medical device is disclosed, which is capable of suppressing damage to an expansion body that expands a biological tissue, or suppressing the difficulty in storing the expansion body in a tubular member when the expansion body is stored in the tubular member. 
     A medical device is disclosed, which includes: a shaft portion that is elongate; and an expansion body provided at a distal portion of the shaft portion to be expandable and contractable in a radial direction. The shaft portion includes a central shaft extending along an axis of the expansion body. The expansion body includes a plurality of wire portions that are expandable and contractable in the radial direction. Each of the wire portions includes a contact portion that comes into contact with the central shaft, when contracted. An opening portion is formed in at least one of the contact portion and the central shaft. A protruding portion is formed in at least one of the contact portion and the central shaft. When the expansion body is contracted, at least a part of the protruding portion enters an inside of the opening portion, and comes into contact with the opening portion. 
     In the medical device configured as described above, when the expansion body is stored in a tubular member, it is possible to suppress the displacement of the contact portion of the expansion body to contract, from the central shaft. For this reason, it is possible to suppress damage to the expansion body or to suppress the difficulty in storing the expansion body in the tubular member when the expansion body is stored in the tubular member. 
     The opening portion and/or the protruding portion may extend in an axial direction. Accordingly, even when the axial positions of the contact portion of the expansion body to contract and of the central shaft are changed, it is possible to suppress the displacement of the contact portion from the central shaft. In a case where one of the opening portion and the protruding portion extends in the axial direction, even when the other does not extend in the axial direction, the opening portion and the protruding portion are slidable on each other without being displaced from each other. Note that both the opening portion and the protruding portion may extend in the axial direction. 
     When the expansion body is contracted, the contact portion or the central shaft may come into contact with the opening portion so as to be slidable in an axial direction. Accordingly, in the medical device, when the expansion body is stored in the tubular member, the contact portion of the expansion body to contract is slidable in the axial direction without being displaced from the central shaft. For this reason, it is possible to suppress damage to the expansion body or to suppress the difficulty in storing the expansion body in the tubular body when the expansion body is stored in the tubular member. 
     The wire portion may include a proximal side outward projection portion protruding outward in the radial direction, a distal side outward projection portion located closer to a distal side than the proximal side outward projection portion, to protrude outward in the radial direction, and an inward projection portion protruding inward in the radial direction between the proximal side outward projection portion and the distal side outward projection portion. The contact portion may be formed in the inward projection portion. Accordingly, when the proximal side outward projection portion is contracted and stored in the tubular member from a proximal side, the contact portion of the inward projection portion can come into contact with the central shaft. At this time, since the protruding portion can enter and come into contact with the opening portion, when the proximal side outward projection portion is stored in the tubular member, it is possible to suppress the displacement of the contact portion from the central shaft. 
     The medical device may further include an energy transmission element disposed on the wire portion to output energy. Accordingly, it is possible to suppress the displacement of the contact portion of the wire portion on which the energy transmission element is disposed, from the central shaft. 
     The opening portion may be a through-hole. Accordingly, the structure of the medical device can be simplified to reduce the diameter and to reduce the cost. 
     The opening portion may be a non-through recessed portion. Accordingly, the opening portion does not penetrate through the contact portion or through the central shaft in which the opening portion is provided, to an opposite side. For this reason, it is possible to suppress interference of the opening portion with other members. 
     An axially orthogonal cross section of an outer peripheral surface of the central shaft may be a substantially circular shape, and the protruding portion may be a part of the outer peripheral surface of the central shaft. Accordingly, the outer peripheral surface of the central shaft can serve as the protruding portion, so that the structure of the medical device can be simplified to reduce the diameter and to reduce the cost. In addition, since the protruding portion is smooth due to the outer peripheral surface of the central shaft serving as the protruding portion, it is possible to suppress interference of the protruding portion with other members. 
     The protruding portion may be a member protruding outward in the radial direction from an outer peripheral surface of the central shaft. 
     Accordingly, the protruding portion protruding from the outer peripheral surface of the central shaft can reliably enter the inside of the opening portion of the contact portion, and come into contact with the opening portion. For this reason, the protruding portion can effectively suppress the displacement of the protruding portion that has entered the inside of the opening portion, from the opening portion. 
     The opening portion may be formed of two opening side protruding portions arranged at an interval. Accordingly, the opening side protruding portions can effectively suppress the displacement of the protruding portion that has entered the inside of the opening portion, from the opening portion. 
     In accordance with an aspect, a medical device comprising: an elongated shaft; an expansion body on at a distal portion of the shaft, the expansion body configured to be expandable and contractable in a radial direction, the shaft includes a central shaft extending along an axial direction of the expansion body; the expansion body includes four wire portions configured to be expandable and contractable in the radial direction, the four wire portions include a contact portion that comes into contact with the central shaft when contracted; an opening portion is formed in at least one of the contact portion and the central shaft; a protruding portion is formed in at least one of the contact portion and the central shaft; and when the expansion body is contracted, at least a part of the protruding portion enters an inside of the opening portion, and comes into contact with the opening portion. 
     In accordance with another aspect, a method for treatment method, the method comprising: expanding a through-hole formed in an atrial septum to allow a right atrium and a left atrium of a heart failure patient to communicate with each other; confirming hemodynamics of blood flow in a vicinity of the through-hole; performing maintenance treatment for maintaining a size of the through-hole with a medical device comprising an elongated shaft portion, and an expansion body provided at a distal portion of the shaft portion, the expansion body configured to be expandable and contractable in a radial direction, the expansion body includes a plurality of wire portions configured to be expandable and contractable in the radial direction, each of the wire portions includes a contact portion that comes into contact with a central shaft, when contracted, an opening portion is formed in at least one of the contact portion and the central shaft, a protruding portion is formed in at least one of the contact portion and the central shaft; and contracting the expansion body such that at least a part of the protruding portion enters an inside of the opening portion and comes into contact with the opening portion. 
       FIG. 1  is a front view illustrating an overall configuration of a medical device according to the present embodiment. 
       FIG. 2  is an enlarged perspective view of the vicinity of an expansion body. 
       FIG. 3  is a front view illustrating a state where one wire portion is flattened. 
       FIG. 4  is a view for describing a treatment method using the medical device according to the present embodiment, and is a view for schematically describing a state where the expansion body is disposed in a through-hole of an atrial septum, in which the medical 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 medical 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 the atrial septum, in which the medical device and the biological tissue are illustrated in a front view and in a cross-sectional view, respectively. 
       FIGS. 7A and 7B  are cross-sectional views illustrating a state where the expansion body is stored in a storage sheath,  FIG. 7A  illustrates a state where a proximal portion of the expansion body is stored, and  FIG. 7B  illustrates a state where the entirety of the expansion body is stored. 
       FIG. 8  is a cross-sectional view taken along line VIII-VIII in  FIG. 7A . 
       FIG. 9  is a perspective view illustrating a state where the proximal portion of the expansion body is stored in the storage sheath. 
       FIGS. 10A-10D  illustrates cross-sectional views of the vicinities of contact portions of medical devices according to modification examples,  FIG. 10A  illustrates a first modification example,  FIG. 10B  illustrates a second modification example,  FIG. 10C  illustrates a third modification example, and  FIG. 10D  illustrates a fourth modification example. 
    
    
     DETAILED DESCRIPTION 
     Set forth below with reference to the accompanying drawings is a detailed description of embodiments of a medical device that expands and maintains a hole of a biological tissue representing examples of the inventive medical device that expands and maintains a hole of a biological tissue. The dimensional ratios on the drawings may be exaggerated or different from the actual dimensions or actual ratios for convenience of description and illustration. In addition, in the specification, a side on which a medical 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”. 
     As illustrated in  FIG. 4 , the medical device  10  according to the present 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 a maintenance treatment to maintain the size of the expanded through-hole Hh. 
     As illustrated in  FIG. 1 , the medical device  10  according to the present embodiment can include a shaft portion  20  that is elongate, 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 transmission element  22  for performing the aforementioned maintenance treatment. 
     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 central shaft  33  is stored inside the outer shaft  31 . The central shaft  33  is a shaft for pulling to cause a compression force to act on the expansion body  21 . An axially orthogonal cross section of an outer peripheral surface of the central shaft  33  is a substantially circular shape. The central shaft  33  protrudes from a distal end of the outer shaft  31  to the distal side, and a distal portion of the central shaft  33  is fixed to a distal member  35 . A proximal portion of the central shaft  33  extends to the proximal side from the operation unit  23 . The distal member  35  to which the distal portion of the central 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 extended in a stretching 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, and a conversion mechanism  42  that operates in conjunction with rotation of the operation dial  41 . The central shaft  33  can be held by the conversion mechanism  42  inside the operation unit  23 . The conversion mechanism  42  can move the held central 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 expansion body  21  will be described in more detail. As illustrated in  FIGS. 2 and 3 , the expansion body  21  includes a plurality of wire portions  50  in a circumferential direction. In the present embodiment, four wire portions  50  are provided in the circumferential direction. Note that 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  can be 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  can include 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 be rather easily disposed 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 transmission element  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 transmission element  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 proximal side outward projection portion  55  is stored in the storage sheath  30 , thus being deformable from a projection shape into a shape close to being flat. 
     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 proximal side outward projection portion  55  is stored in the storage sheath  30 , thus being deformable from a projection shape into a shape close to being flat. 
     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. A contact portion  58  that can come into contact with the central shaft  33  is formed on a radially inner side of the inward projection portion  56 . The contact portion  58  includes an opening portion  59  that can face the central shaft  33 , and two outer edge portions  60  interposing the opening portion  59  in a width direction. The width direction is a direction orthogonal to the axial direction of the expansion body  21 , and is a direction orthogonal to the radial direction of the expansion body  21 . In the present embodiment, the opening portion  59  is a through-hole penetrating through the inward projection portion  56  in the radial direction of the expansion body  21 . The opening portion  59  may be formed not only in the inward projection portion  56  but also to the proximal side holding portion  52  or to the distal side holding portion  53 . The inward projection portion  56  in which the opening portion  59  is provided has low flexural rigidity. For this reason, the inward projection portion  56  is easily deformed into a shape projecting inward in the radial direction, and is easily deformed into a shape close to being flat. 
     In the present embodiment, the energy transmission element  22  is provided at the proximal side holding portion  52 , but the energy transmission element  22  may be provided at 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 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. 
     Since the energy transmission element  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 transmission element  22  is transmitted from a right atrium side to the atrial septum HA. When the energy transmission element  22  is provided at the distal side holding portion  53 , energy from the energy transmission element  22  is transmitted from a left atrium side to the atrial septum HA. 
     The energy transmission element  22  is configured as, for example, a bipolar electrode that receives electric energy from an energy supply device that is an external device. In this case, energization is performed between the energy transmission elements  22  disposed on the wire portions  50 . The energy transmission element  22  and the energy supply device are connected to each other by a conducting wire coated with an insulating coating material. The conducting wire extends to the outside via the shaft portion  20  and via the operation unit  23 , and is connected to the energy supply device. 
     Alternatively, the energy transmission element  22  may be configured as a monopolar electrode. In this case, energization is performed between the energy transmission element  22  and a counter electrode plate prepared outside a living body. In addition, the energy transmission element  22  may be a heating element (electrode chip) that receives high-frequency electric energy from the energy supply device to generate heat. In this case, energization is performed between the energy transmission elements  22  disposed on the wire portions  50 . Further, the energy transmission element  22  can be configured as an element capable of applying energy to the through-hole Hh, such as an element that exerts a heating or cooling action using microwave energy, ultrasound energy, coherent light such as laser, a heated fluid, a cooled fluid, or a chemical medium, an element that generates frictional heat, or a heater including an electric wire or the like, and a specific form of the energy transmission element  22  is not particularly limited. 
     The wire portion  50  can be made of a metallic material. As to the metallic material of the wire portion  50 , for example, 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, it may preferable to use an alloy or the like having a spring property such as a nickel-titanium alloy. However, the material for the wire portion  50  is not limited to these 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 central shaft  33  is stored inside the inner shaft  32 . A guide wire lumen is formed in the central 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. 
     It is preferable that the storage sheath  30 , the outer shaft  31 , and the inner shaft  32  of the shaft portion  20  are made of a material having a certain degree of flexibility. Examples of the material of the storage sheath  30 , the outer shaft  31 , and the inner shaft  32  of the shaft portion  20  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 polyolefins such as polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, 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 central 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 central shaft  33  may be formed by coating the above disclosed metallic materials 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, a treatment method using the medical device  10  according to the present embodiment will be described. The treatment method is performed on a patient suffering from a heart failure (left heart failure). More specifically, as illustrated in  FIG. 4 , the treatment method is 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 . Note that the insertion of the introducer into or the insertion of the guide wire  11  into a living body can be performed using a known 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 the dilator, 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 medical 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 medical device  10  passes through the through-hole Hh opened in the atrial septum HA, and reaches the left atrium HLa. When the medical 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 into a shape close to being flat, and thus the expansion body  21  is contracted in the radial direction. 
     Next, as illustrated in  FIG. 7A , 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 the 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 . 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. In this state, the expansion body  21  is not covered with the storage sheath  30  and does not receive a force from the central shaft  33 , and wherein this form of the expansion body  21  can be defined as being included in the reference form. 
     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 central 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 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  100  to the right atrium HRa via the inferior vena cava Iv. For example, an echo catheter can be used as the hemodynamics confirmation device  100 . The operator can cause a display device such as a display to display an echo image acquired by the hemodynamics confirmation device  100 , 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 transmission element  22 , so that the edge portion of the through-hole Hh is cauterized (heated and cauterized) by the energy. When a biological tissue in the vicinity of the edge portion of the through-hole Hh is cauterized through the energy transmission element  22 , 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 addition, the energy transmission element  22  is disposed on the projection portion  54  of the proximal side holding portion  52 . For this reason, the maintenance treatment is performed in a state where the energy transmission element  22  is buried in the biological tissue by pressing the projection portion  54  against the atrial septum HA. Accordingly, the energy transmission element  22  does 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. 
     After the maintenance treatment, hemodynamics can again be confirmed, and when the amount of the blood passing through the through-hole Hh reaches a desired amount, the operator reduces the expansion body  21  in diameter. The operator moves the storage sheath  30  with respect to the expansion body  21  in a distal end direction. Accordingly, the expansion body  21  is gradually stored in the storage sheath  30  from the proximal side. As illustrated in  FIGS. 7A, 8, and 9 , when the proximal side outward projection portion  55  of the expansion body  21  is stored in the storage sheath  30 , the proximal side outward projection portion  55  is deformed into a shape close to being flat. At this time, the contact portion  58  of the inward projection portion  56  is pressed against the outer peripheral surface of the central shaft  33  by a reaction of the proximal side outward projection portion  55  that is elastically deformed into a shape close to being flat. Then, the contact portion  58  of the inward projection portion  56  slides on the outer peripheral surface of the central shaft  33  in a contact state, and moves to the distal side with respect to the central shaft  33 . At this time, the outer peripheral surface of the central shaft  33  having a cylindrical shape is curved to project outward in the radial direction, so that the outer peripheral surface forms a protruding portion  34 . For this reason, the protruding portion  34  that is a part of the outer peripheral surface of the central shaft  33  enters a space surrounded by the opening portion  59  of the contact portion  58 . The protruding portion  34  in the outer peripheral surface of the central shaft  33  extends in the axial direction. For this reason, as indicated by an alternate long and short dashed lines in  FIG. 8 , the displacement of the inward projection portion  56  including the contact portion  58  from the outer peripheral surface of the central shaft  33  is suppressed. In a case where the inward projection portion  56  is displaced from the outer peripheral surface of the central shaft  33 , when the expansion body  21  is stored in the storage sheath  30 , the expansion body  21  may be damaged due to receiving an excessive load or may be difficult to store in the storage sheath  30 . However, in the present embodiment, since the inward projection portion  56  is unlikely to be displaced from the outer peripheral surface of the central shaft  33 , it is possible to suppress damage to the expansion body  21  or to suppress the difficulty in storing the expansion body  21  in the storage sheath  30  when stored in the storage sheath  30 . 
     The operator additionally moves the storage sheath  30  to the distal side with respect to the expansion body  21 . Accordingly, as illustrated in  FIG. 7B , the inward projection portion  56  and the distal side outward projection portion  57  of the expansion body  21  are gradually stored in the storage sheath  30  from the proximal side. When the distal side outward projection portion  57  of the expansion body  21  is stored in the storage sheath  30 , the distal side outward projection portion  57  is deformed into a shape close to being flat. At this time, the contact portion  58  of the inward projection portion  56  is pressed against the outer peripheral surface of the central shaft  33  by a reaction of the distal side outward projection portion  57  that is elastically deformed into a shape close to being flat. However, since the protruding portion  34  of the central shaft  33  enters the space surrounded by the opening portion  59  of the contact portion  58 , the displacement of the inward projection portion  56  including the contact portion  58  from the outer peripheral surface of the central shaft  33  is suppressed. For this reason, it is possible to suppress damage to the expansion body  21  or to suppress the difficulty in storing the expansion body  21  in the storage sheath  30  when stored in the storage sheath  30 . 
     The configuration where the contact portion  58  of the expansion body  21  stored in the storage sheath  30  includes the opening portion  59  that the protruding portion  34  of the outer peripheral surface of the central shaft  33  enters is also effective when the expansion body  21  is released from the storage sheath  30  and is expanded. Namely, the inward projection portion  56  including the contact portion  58  is unlikely to be displaced from the outer peripheral surface of the central shaft  33 , so that the expansion body  21  can be relatively smoothly expanded. 
     After the operator stores the expansion body  21  in the storage sheath  30 , the operator additionally removes the entirety of the medical device  10  out of the living body to end the treatment. 
     As described above, the medical device  10  according to the aforementioned embodiment includes the shaft portion  20  that is elongate; and the expansion body  21  provided at the distal portion of the shaft portion  20  to be expandable and contractable in a radial direction. The shaft portion  20  includes the central shaft  33  extending along an axis of the expansion body  21 . The expansion body  21  includes the plurality of wire portions  50  that are expandable and contractable in the radial direction. Each of the wire portions  50  includes the contact portion  58  that comes into contact with the central shaft  33 , when contracted. The opening portion  59  is formed in the contact portion  58 . The protruding portion  34  is formed in the central shaft  33 . When the expansion body  21  is contracted, at least a part of the protruding portion  34  can enter an inside of the opening portion  59 , and come into contact with the opening portion  59 . For this reason, when the expansion body  21  is stored in the storage sheath  30 , the medical device  10  can help suppress the displacement of the contact portion  58  of the expansion body  21  to contract, from the central shaft  33 . For this reason, it is possible to suppress damage to the expansion body  21  or to suppress the difficulty in storing the expansion body  21  in the storage sheath  30  when the expansion body  21  is stored in the storage sheath  30 . 
     In addition, the opening portion  59  and/or the protruding portion  34  extend in the axial direction. Accordingly, even when the axial positions of the contact portion  58  of the expansion body  21  to contract and of the central shaft  33  are changed, the displacement of the contact portion  58  from the central shaft  33  can be suppressed. 
     In a case where one of the opening portion  59  and the protruding portion  34  extends in the axial direction, even when the other does not extend in the axial direction, the opening portion  59  and the protruding portion  34  are slidable on each other without being displaced from each other. Note that both the opening portion  59  and the protruding portion  34  may extend in the axial direction. 
     In addition, when the expansion body  21  is contracted, the contact portion  58  or the central shaft  33  comes into contact with the opening portion  59  so as to be slidable in the axial direction. Accordingly, in the medical device  10 , when the expansion body  21  is stored in the storage sheath  30 , the contact portion  58  of the expansion body  21  to contract is slidable in the axial direction without being displaced from the central shaft  33 . For this reason, it is possible to suppress damage to the expansion body  21  or to suppress the difficulty in storing the expansion body  21  in the storage sheath  30  when the expansion body  21  is stored in the storage sheath  30 . 
     In addition, the wire portion  50  includes the proximal side outward projection portion  55  protruding outward in the radial direction, the distal side outward projection portion  57  located closer to the distal side than the proximal side outward projection portion  55 , to protrude outward in the radial direction, and the inward projection portion  56  protruding inward in the radial direction between the proximal side outward projection portion  55  and the distal side outward projection portion  57 . The contact portion  58  is formed in the inward projection portion  56 . Accordingly, when the proximal side outward projection portion  55  is contracted and stored in the storage sheath  30  from the proximal side, the contact portion  58  of the inward projection portion  56  can come into contact with the central shaft  33 . At this time, since the protruding portion  34  can enter and come into contact with the opening portion  59 , when the proximal side outward projection portion  55  is stored in the storage sheath  30 , the displacement of the contact portion  58  from the central shaft  33  can be suppressed. In addition, also when the inward projection portion  56  and the distal side outward projection portion  57  are stored in the storage sheath  30 , since the protruding portion  34  can enter and come into contact with the opening portion  59 , the displacement of the contact portion  58  from the central shaft  33  can be suppressed. For this reason, it is possible to suppress damage to the expansion body  21  or to suppress the difficulty in storing the expansion body  21  in the storage sheath  30  when the expansion body  21  including the proximal side outward projection portion  55 , the inward projection portion  56 , and the distal side outward projection portion  57  is stored in the storage sheath  30 . 
     In addition, the medical device  10  includes the energy transmission element  22  that is disposed on the wire portion  50  to output energy. Accordingly, it is possible to suppress the displacement of the contact portion  58  of the wire portion  50  on which the energy transmission element  22  is disposed, from the central shaft  33 . 
     In addition, the opening portion  59  is a through-hole. Accordingly, the structure of the medical device  10  can be simplified to reduce the diameter and to reduce the cost. 
     In addition, the axially orthogonal cross section of the outer peripheral surface of the central shaft  33  is a substantially circular shape, and the protruding portion  34  is a part of the outer peripheral surface of the central shaft  33 . Accordingly, the structure of the medical device  10  can be simplified to reduce the diameter and to reduce the cost. In addition, since the protruding portion  34  is smooth due to the outer peripheral surface of the central shaft  33  serving as the protruding portion  34 , it is possible to suppress the hooking of other instruments or of other portions of the medical device  10  on the protruding portion  34 . 
     Note that the disclosure is not limited only to the aforementioned embodiment and various modifications can be made by those skilled in the art without departing from the technical concept of the disclosure. 
     For example, as in a first modification example illustrated in  FIG. 10A , the opening portion  59  may be a recessed portion not penetrating through the inward projection portion  56  in the radial direction of the expansion body  21 . Accordingly, the opening portion  59  is not penetrated to a side opposite a side on which the contact portion  58  of the inward projection portion  56  is provided. For this reason, it is possible to suppress interference of the opening portion  59  with other instruments or with other portions of the medical device  10 . 
     In addition, as in a second modification example illustrated in  FIG. 10B , the protruding portion  34  may be a member that is fixed to the outer peripheral surface of the central shaft  33  to protrude outward in the radial direction from the outer peripheral surface. Accordingly, the protruding portion  34  protruding from the outer peripheral surface of the central shaft  33  can reliably enter the inside of the opening portion  59  of the contact portion  58 , and come into contact with the opening portion  59 . For this reason, the protruding portion  34  can effectively suppress the displacement of the protruding portion  34  that has entered the inside of the opening portion  59 , from the opening portion  59 . 
     In addition, as in a third modification example illustrated in  FIG. 10C , the central shaft  33  may be provided with the opening portion  59 , and the inward projection portion  56  of the expansion body  21  may be provided with the protruding portion  34 . In addition, the central shaft  33  may be provided with both an opening portion and a protruding portion, and the inward projection portion  56  may be provided with a protruding portion that comes into contact with the opening portion of the central shaft  33 , and with an opening portion that comes into contact with the protruding portion of the central shaft  33 . 
     In addition, as in a fourth modification example illustrated in  FIG. 10D , the opening portion  59  may be formed of two opening side protruding portions  36  that are arranged at an interval on the outer peripheral surface of the central shaft  33 . Accordingly, the opening side protruding portions  36  can effectively suppress the displacement of the protruding portion  34  of the inward projection portion  56  that has entered the inside of the opening portion  59 , from the opening portion  59 . 
     In addition, the central shaft  33  which faces the contact portion  58  and in which the opening portion  59  or the protruding portion  34  is formed may not be a shaft for pulling to cause a compression force to act on the expansion body  21 . 
     The detailed description above describes embodiments of a medical device that expands and maintains a hole of a biological tissue. 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.