Patent Publication Number: US-2022211430-A1

Title: Medical Device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/JP2020/036816 filed on Sep. 29, 2020, which claims priority to Japanese Application No. 2019-178331 filed on Sep. 30, 2019, the entire content of both of which is incorporated herein by reference. 
    
    
     TECHNOLOGICAL FIELD 
     This disclosure relates to a medical device for applying energy to a biological tissue. 
     BACKGROUND DISCUSSION 
     Chronic heart failure is a known heart disease. 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, myocardial hypertrophy appears, and stiffness (hardness) increases, so that blood pressure increases in a left atrium, and a cardiac pumping function is degraded. In this manner, the patient may show heart failure symptoms such as a pulmonary edema. In addition, another heart disease of the patient who shows the heart failure symptom because blood pressure increases on a right atrium side due to pulmonary hypertension, and the cardiac pumping function is degraded. 
     In recent years, shunt treatments have attracted attention in which, for the patients who suffer from heart failure, a shunt (through-hole) serving as an escape route for increased atrial pressure is formed in an atrial septum, thereby enabling heart failure symptoms to be alleviated. In the shunt treatment, the atrial septum is accessed using an intravenous approaching method, and the through-hole is formed to have a desired size. For example, a medical device disclosed in U.S. Pat. No. 8,882,697 is used as one of medical devices for performing the shunt treatment on the atrial septum. 
     In the medical device of U.S. Pat. No. 8,882,697, a shunt hole is enlarged using a balloon serving as an expansion body that is provided in a distal portion of a shaft portion, and the shunt hole is maintained by an electrode provided in the balloon. In this medical device, the electrode (energy transfer element) is exposed to blood, so that energy is provided into the blood and an unintended site, which may cause variations in the degree of cauterization, formation of a thrombus, generation of tissue damage and the like. 
     SUMMARY 
     A medical device is disclosed that can reduce variations in the degree of cauterization by an energy transfer element, and can suppress generation of thrombus formation, tissue damage, and the like due to the cauterization. 
     A medical device is disclosed that can include: an elongated shaft portion; and an expansion body that is provided in a distal portion of the shaft portion, and can expand and contract in a radial direction, in which the expansion body includes a plurality of wire portions that are linked with the shaft portion, and at least one clamping portion that is formed by at least one of the wire portions, the clamping portion includes an energy transfer element that outputs energy, and a back support portion, the back support portion includes a receiving surface that can face the energy transfer element when the expansion body expands, and the receiving surface is configured to be inclined so as to be approximately parallel to the energy transfer element, when the energy transfer element moves toward the back support portion. 
     With the medical device configured as the above, the receiving surface is approximately parallel to the energy transfer element in accordance with the movement of the energy transfer element, so that the energy transfer element can come into close contact with the biological tissue that is clamped between the energy transfer element and the receiving surface. Therefore, variations in the degree of cauterization by the energy transfer element can be reduced. Moreover, the energy transfer element can be prevented from locally floating from the biological tissue. Therefore, the energy transfer element can be prevented from supplying energy into blood and an unintended site, and generation of thrombus formation, tissue damage, and the like due to the cauterization can be suppressed. 
     The at least one clamping portion may include two outer peripheral portions on both sides in a width direction that is a direction orthogonal to an axis direction of the expansion body, and a direction orthogonal to the radial direction of the expansion body, relative to the back support portion. In this manner, the outer peripheral portions effectively guide the energy transfer element that moves toward the back support portion, to the back support portion that is positioned between the outer peripheral portions. Therefore, the energy transfer element can press the biological tissue supported by the two outer peripheral portions, and can press the biological tissue against the back support portion that is disposed between the two outer peripheral portions. Therefore, the energy transfer element comes into close contact with the biological tissue and is relatively hard to float from the biological tissue, and the position of the energy transfer element relative to the biological tissue is stably maintained by the two outer peripheral portions. 
     The two outer peripheral portions each may have a convex shape to an outer side in the width direction. In this manner, between the two outer peripheral portions, a wide region in which the back support portion is disposed can be secured. Moreover, the two outer peripheral portions in the width direction can support the biological tissue in the wide region, so that the energy transfer element and the receiving surface that clamp the biological tissue between the two outer peripheral portions can be rather easily maintained in the suitable positions. 
     The two outer peripheral portions each may have a circular arc shape that smoothly projects to the outer side in the width direction. In this manner, the outer peripheral portions is configured to be stored in an inner surface of a storage sheath without being caught on the inner surface of the storage sheath, which is a tubular member that stores the expansion body so as to be releasable, for example. Accordingly, the outer peripheral portions can be smoothly stored in the storage sheath, and can be smoothly released from the storage sheath. 
     Moreover, a maximum width of the outer peripheral portions that sandwich the back support portion between the two outer peripheral portions in the width direction may be larger than a maximum width of the energy transfer element in the width direction. In this manner, the outer peripheral portion easily guides a press direction of the energy transfer element so as to head for the back support portion. 
     The back support portion may move larger than the two outer peripheral portions due to a force in the axis direction to be received from the energy transfer element. In this manner, the back support portion can flexibly receive the biological tissue that is pressed by the energy transfer element while moving rearward larger in the press direction of the energy transfer element than the outer peripheral portion. Therefore, the energy transfer element comes into close contact with the biological tissue and is hard to float from the biological tissue. 
     The expansion body may include an inner projection portion between the energy transfer element and the back support portion, and the maximum width between the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions in the width direction may be larger than a maximum width of the inner projection portion in the width direction. In this manner, while maintaining the flexibility of the inner projection portion, a structure in which the width between the two outer peripheral portions is widened can be obtained. 
     The back support portion may have a cantilever beam shape that extends from the wire portion. In this manner, the back support portion can warp flexibly by receiving a force. 
     The back support portion may be a member that is supported by at least one flexible support wire that extends from the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions. In this manner, the back support portion can move lager than the outer peripheral portions due to a force in the axis direction. 
     The back support portion may be at least one flexible back support wire that extends from the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions. In this manner, the back support portion can warp more flexibly than the outer peripheral portions due to a force in the axis direction. 
     The back support portion may be a mesh-like member that extends from the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions. In this manner, the back support portion can warp more flexibly than the outer peripheral portions due to a force in the axis direction. 
     The back support portion may be a film body that extends from the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions. In this manner, the back support portion can warp more flexibly than the outer peripheral portions due to a force in the axis direction. 
     In accordance with an aspect, a medical device is disclosed comprising: an elongated shaft portion; and an expansion body that is provided in a distal portion of the shaft portion, and is configured to expand and contract in a radial direction, wherein the expansion body includes a plurality of wire portions that are linked with the shaft portion, and at least one clamping portion that is formed by at least one of the wire portions, the clamping portion includes an energy transfer element configured to output energy, and a back support portion, the at least one clamping portion includes two outer peripheral portions on both sides in a width direction, the back support portion includes at least one flexible back support wire that extends from the two outer peripheral portions that sandwich the back support portion between the two outer peripheral portions, and the receiving surface is configured to be inclined to be approximately parallel to the energy transfer element, when the energy transfer element moves toward the back support portion. 
     In accordance with another aspect, a method for treatment, 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 that is provided in a distal portion of the shaft portion, the expansion body configured to expand and contract in a radial direction, wherein the expansion body includes a plurality of wire portions that are linked with the shaft portion, and at least one clamping portion that is formed by at least one of the wire portions, the clamping portion includes an energy transfer element configured to output energy, and a back support portion, and wherein the back support portion includes a receiving surface; expanding the expansion body in the through hole so that the receiving surface faces the energy transfer element; and moving the energy transfer element toward the back support portion so that the receiving surface is approximately parallel to the energy transfer element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view illustrating an overall configuration of a medical device according to an embodiment. 
         FIG. 2  is an enlarged perspective view illustrating the vicinity of an expansion body. 
         FIG. 3  is a front view illustrating a state where one of wire portions is extended to be flat. 
         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 is illustrated in a front view and a biological tissue is illustrated in a cross-sectional view, respectively. 
         FIG. 5  is a view for schematically describing a state where a distal portion of the medical device is inserted into the atrial septum, in which a part of the medical device is illustrated in a front view, and a storage sheath and the biological tissue are illustrated in a cross-sectional view, respectively. 
         FIG. 6  is a view for schematically describing a state where a site on a distal side of the expansion body is developed on a left atrium side, in which the medical device is illustrated in a front view and the biological tissue is illustrated in a cross-sectional view, respectively. 
         FIG. 7  is a view for schematically describing a state where the expansion body is disposed in the atrial septum, in which the medical device is illustrated in a front view and the biological tissue is illustrated in a cross-sectional view, respectively. 
         FIG. 8  is a view for schematically describing a state where a diameter of the expansion body is increased in the atrial septum, in which the medical device is illustrated in a front view and a biological tissue is illustrated in a cross-sectional view, respectively. 
         FIGS. 9A and 9B  are cross-sectional views illustrating the atrial septum and the expansion body, and wherein  FIG. 9A  illustrates a state before the atrial septum is clamped by a distal side clamping portion and a proximal side clamping portion, and  FIG. 9B  illustrates a state where the atrial septum is clamped by the distal side clamping portion and the proximal side clamping portion. 
         FIGS. 10A and 10B  are cross-sectional views illustrating the atrial septum and the expansion body, and wherein  FIG. 10A  is a cross-sectional view taken along XA-XA line in  FIG. 9A , and  FIG. 10B  is a cross-sectional view taken along XB-XB line in  FIG. 9B . 
         FIG. 11  is a view for schematically describing a state where the through-hole of the atrial septum is enlarged by the expansion body, in which the medical device is illustrated in a front view and a biological tissue is illustrated in a cross-sectional view, respectively. 
         FIG. 12  is an enlarged perspective view illustrating the vicinity of an expansion body of a medical device according to a first modification example. 
         FIGS. 13A to 13D  are enlarged perspective views each illustrating the vicinity of a distal side clamping portion of a medical device according to modification examples, and wherein  FIG. 13A  illustrates a second modification example,  FIG. 13B  illustrates a third modification example,  FIG. 13C  illustrates a fourth modification example, and  FIG. 13D  illustrates a fifth modification example. 
     
    
    
     DETAILED DESCRIPTION 
     Set forth below with reference to the accompanying drawings is a detailed description of embodiments of a medical device for applying energy to a biological tissue representing examples of the inventive medical device for applying energy to a biological tissue. The size ratios on the drawings may be exaggerated or different from the actual ratios for convenience of description and illustration. Moreover, in the present specification, a side of a medical device  10  to be inserted into a lumen of a living body is referred to as a “distal side”, and a side at which the medical device  10  is operated is referred to as a “proximal side”. 
     The medical device  10  according to the present embodiment is configured, as shown in  FIG. 4 , such that a through-hole Hh formed in an atrial septum HA of a heart H of a patient can be enlarged, and further, a maintenance treatment can be performed that maintains the through-hole Hh having been enlarged to the increased sized. 
     As shown in  FIG. 1 , the medical device  10  according to the present embodiment includes an elongated shaft portion  20 , an expansion body  21  that is provided in a distal portion of the shaft portion  20 , and an operation unit  23  that is provided in a proximal portion of the shaft portion  20 . In the expansion body  21 , an energy transfer element  22  for performing the aforementioned maintenance treatment is provided. 
     The shaft portion  20  includes an outer shaft  31  that holds the expansion body  21  in a 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 rearward in an axis direction (or axial direction) relative to the outer shaft  31 . The storage sheath  30  in a state of having moved to a distal side of the shaft portion  20  can store the expansion body  21  in an inside of the storage sheath  30 . The storage sheath  30  is moved to a proximal side in a state where the expansion body  21  is stored to enable the expansion body  21  to be exposed. 
     A pulling shaft  33  is stored in an inside of the outer shaft  31 . The pulling shaft  33  protrudes from a distal end of the outer shaft  31  to the distal side, and has a distal portion that is fixed to a distal member  35 . A proximal portion of the pulling shaft  33  extends to the proximal side of the operation unit  23 . The distal member  35  to which the distal portion of the pulling shaft  33  is fixed does not need to be fixed to the expansion body  21 . In this manner, the distal member  35  can pull the expansion body  21  in a contracting direction. Moreover, when the expansion body  21  is stored in the storage sheath  30 , the distal member  35  can be separated from the expansion body  21  to the distal side, so that movement of the expansion body  21  in an extending direction becomes relatively easy to enable the storage capability to be improved. 
     The operation unit  23  can include a housing  40  to be gripped by an operator, an operation dial  41  that can be rotationally operated by the operator, and a conversion mechanism  42  that is operated in conjunction with the rotation of the operation dial  41 . The pulling shaft  33  is held by the conversion mechanism  42  in the inside of the operation unit  23 . The conversion mechanism  42  can move the pulling shaft  33  that is held by the conversion mechanism  42  forward and rearward along the axis direction in conjunction with the rotation of the operation dial  41 . The conversion mechanism  42  can be, for example, a rack and pinion mechanism. 
     The expansion body  21  will be described in more details. As shown in  FIGS. 2 and 3 , the expansion body  21  can include a plurality of wire portions  50  in a circumferential direction. In the present embodiment, the four wire portions  50  are provided in the circumferential direction. Note that, the number of the wire portions  50  is not specially limited. The wire portions  50  can respectively expand and contract in a radial direction of the expansion body  21 . In a natural state where no external force acts, the expansion body  21  becomes in a reference form in which the expansion body  21  is developed 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 to increase in the radial direction from both end portions to a central portion in an axis direction (axial direction) of the expansion body  21 . Moreover, the wire portion  50  can include a clamping portion  51  having a valley shape in an axial central portion, in the radial direction of the expansion body  21 . 
     The clamping portion  51  can include a proximal side clamping portion  52  and a distal side clamping portion  53 . The clamping portion  51  further includes a proximal side outer projection portion  55 , an inner projection portion  56 , and a distal side outer projection portion  57 . An interval between the proximal side clamping portion  52  and the distal side clamping portion  53  is preferably opened slightly larger in the axis direction (axial direction) on an outer side than on an inner side in the radial direction, in the reference form, which helps make it relatively easy to dispose a biological tissue between the proximal side clamping portion  52  and the distal side clamping portion  53 , from the outer side in the radial direction. 
     The proximal side outer projection portion  55  is positioned on a proximal side of the proximal side clamping portion  52 , and is formed in a convex shape toward the outer side in the radial direction. 
     The inner projection portion  56  is positioned between the proximal side clamping portion  52  and the distal side clamping portion  53 , and is formed in a convex shape toward the inner side in the radial direction. A central through-hole  59  is formed in the inner projection portion  56  such that the inner projection portion  56  bends rather easily. 
     The distal side outer projection portion  57  is positioned on a distal side of the distal side clamping portion  53 , and is formed in a convex shape to the outer side in the radial direction. In the wire portion  50 , one distal side through-hole  60  is formed in the vicinity of the distal side outer projection portion  57  and the distal side clamping portion  53 . The distal side through-hole  60  penetrates into the radial direction of the expansion body  21 . In this manner, the distal side outer projection portion  57  has low flexural rigidity. Therefore, the distal side outer projection portion  57  rather easily deforms to have a convex shape toward the outer side in the radial direction, and easily deforms such that the convex shape becomes flat. Note that, the number of the distal side through-holes  60  is not specially limited. Accordingly, the number of the distal side through-holes  60  may be two or more. 
     The proximal side clamping portion  52  includes a projection portion  54  that protrudes toward the distal side. The energy transfer element  22  is disposed in the projection portion  54 . 
     The distal side clamping portion  53  can include two outer peripheral portions  61  that are provided on both outer sides in a width direction, and a back support portion  62  that is provided between the two outer peripheral portions  61 . The width direction is a direction orthogonal to the axis direction (axial direction) of the expansion body  21 , and a direction orthogonal to the radial direction of the expansion body  21 . The back support portion  62  includes a receiving surface  63  that can face the energy transfer element  22  that is disposed in the distal side clamping portion  53  when the expansion body  21  expands. 
     Each of the outer peripheral portions  61  can have a circular arc shape that projects toward the outer side in the width direction. Therefore, between the two outer peripheral portions  61 , a relatively wide region in which the back support portion  62  and the distal side through-hole  60  are disposed can be secured. In addition, an outer side of the outer peripheral portion  61  in the width direction becomes relatively smooth, so that the outer peripheral portion  61  can be prevented from being caught on an inner surface of the storage sheath  30 , which stores the expansion body  21  inside the storage sheath  30 . A maximum width L 1  between the outer peripheral portions  61  in the width direction is greater than a maximum width L 2  of the inner projection portion  56  in the width direction. Therefore, while maintaining the easiness of bending of the inner projection portion  56 , the outer peripheral portions  61  can be formed in a shape expanding in the width direction. Moreover, a maximum width L 5  of the receiving surface  63  in the width direction is not specially limited, but is preferably the same as or slightly larger (or greater) than a maximum width L 3  of the energy transfer element  22  in the width direction. In this manner, the receiving surface  63  can appropriately receive a biological tissue that is pressed by the energy transfer element  22 . Moreover, the maximum width L 1  between the outer peripheral portions  61  in the width direction is not specially limited, but is preferably larger (or greater) than the maximum width L 3  of the energy transfer element  22  in the width direction. Moreover, a maximum width L 4  of the distal side through-hole  60  in the width direction is not specially limited, but is preferably larger (or greater) than the maximum width L 3  of the energy transfer element  22  in the width direction. 
     The back support portion  62  protrudes between the two outer peripheral portions  61  from a site on a side of the inner projection portion  56  of the distal side clamping portion  53  toward a side of the distal side outer projection portion  57 . The back support portion  62  is disposed between the two outer peripheral portions  61  to be spaced from the two outer peripheral portions  61 . An end portion of the back support portion  62  on the side of the distal side outer projection portion  57  is a free end (i.e., not connected to other portions). Accordingly, the back support portion  62  has a cantilever beam-like form in which a proximal portion of the back support portion  62  is fixed, and warps (i.e., bends) relatively easily. Therefore, the back support portion  62  can relatively easily warp (i.e., bend) than each of the outer peripheral portions  61  due to a force toward the distal side that is received by the receiving surface  63 . The back support portion  62  is disposed so as to be clamped by the two outer peripheral portions  61 , but does not necessarily need to be strictly positioned in the space positioned between the two outer peripheral portions  61 . The back support portion  62  may be disposed so as to be clamped by the two outer peripheral portions  61  at a position slightly shifted from the space positioned between the two outer peripheral portions  61 . At least a part of the back support portion  62  is preferably disposed in the space positioned between the two outer peripheral portions  61 . 
     In the back support portion  62 , one back support through-hole  64  is formed on the proximal side, in other words, on a side close to the inner projection portion  56 . The back support through-hole  64  penetrates into the radial direction of the expansion body  21  (the thickness direction of the wire portions  50 ). In this manner, the back support portion  62  has low flexural rigidity on a side close to the inner projection portion  56 . Therefore, the back support portion  62  can rather easily warp (i.e., bend) due to a force that is received by the receiving surface  63 . The number of the back support through-holes  64  is not specially limited. Accordingly, the number of the back support through-holes  64  may be two or more. Moreover, no back support through-hole  64  may be formed in the back support portion  62 . 
     In the present embodiment, the energy transfer element  22  is provided in the proximal side clamping portion  52  and the back support portion  62  is provided in the distal side clamping portion  53 , and alternatively, the energy transfer element  22  may be provided in the distal side clamping portion  53  and the back support portion  62  may be provided in the proximal side clamping portion  52 . 
     The wire portion  50  forming the expansion body  21  can have a flat plate shape cut from a cylinder, for example. The wire forming the expansion body  21  can have, for example, a thickness of 50 μm to 500 μm and a width of 0.3 mm to 2.0 mm. However, the wire forming the expansion body  21  has a size outside this range. Moreover, the shape of the wire portion  50  is not limited, and may have a circular shape in a cross section or other shapes in a cross section, for example. 
     The energy transfer element  22  is provided in the projection portion  54  of the proximal side clamping portion  52 , so that when the clamping portion  51  clamps the atrial septum HA, the energy from the energy transfer element  22  is transferred to the atrial septum HA from the right atrium side. In a case where the energy transfer element  22  is provided in the distal side clamping portion  53 , the energy from the energy transfer element  22  is transferred to the atrial septum HA from the left atrium side. 
     The energy transfer element  22  can be configured to include, for example, a bipolar electrode that receives electric energy from an energy supply device serving as an external device. In this case, electricity is supplied among the energy transfer elements  22  disposed in the respective wire portions  50 . The energy transfer element  22  and the energy supply device are connected to each other by a conductive wire coated with an insulating coating material. The conductive wire extends to the proximal side of the medical device and outside of the medical device via the shaft portion  20  and the operation unit  23 , and is connected to the energy supply device. 
     Alternatively, the energy transfer element  22  may be configured as a monopolar electrode. In this case, the electricity is supplied between the energy transfer element  22  and a counter electrode plate prepared outside the body. Moreover, the energy transfer element  22  may be a heating element (electrode chip) that generates heat by receiving high-frequency electric energy from the energy supply device. In this case, electricity is supplied among the energy transfer elements  22  disposed in the respective wire portions  50 . In addition, the energy transfer element  22  can be configured to include an element that can apply energy to the through-hole Hh, such as an element that provides heating or cooling operation by 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, and a specific form of the energy transfer element  22  is not specially limited. 
     The wire portion  50  can be formed of a metal material. As the metal material, 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, an alloy having a spring property such as a nickel titanium alloy may be more preferably used. However, a material for the wire portion  50  is not limited to the materials disclosed, and the wire portion  50  may be formed of other materials. 
     The shaft portion  20  can include an inner shaft  32  in the inside of the outer shaft  31 , and the pulling shaft  33  is stored in an inside of the inner shaft  32 . A guide wire lumen is formed in the pulling shaft  33  and the distal member  35  along the axis direction, and a guide wire  11  can be inserted through the guide wire lumen. 
     The storage sheath  30 , the outer shaft  31 , the inner shaft  32  of the shaft portion  20  are preferably formed of a material having a certain degree of flexibility. Examples of the materials of the storage sheath  30 , the outer shaft  31 , and the inner shaft  32  of the shaft portion  20  can include polyolefin such as polyethylene, polypropylene, polybutene, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, an ionomer, or a mixture of two or more of polyolefin such as polyethylene, polypropylene, polybutene, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, and an ionomer, soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyester, polyester elastomer, polyurethane, fluorine resin such as polytetrafluoroethylene, polyimide, PEEK, silicone rubber, and latex rubber. 
     The pulling shaft  33  can be formed of, for example, an elongated wire material including a super elasticity alloy such as a nickel-titanium alloy and a copper-zinc alloy, a metal material such as stainless steel, and a resin material having comparatively high rigidity. Moreover, the pulling shaft  33  may be formed of the abovementioned wire material coated with a resin material such as polyvinyl chloride, polyethylene, polypropylene, an ethylene-propylene copolymer, or fluorine resin. 
     The distal member  35  can be formed of, for example, a super elasticity alloy such as a nickel-titanium alloy and a copper-zinc alloy, a metal material such as stainless steel, and a resin material having comparatively 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 shown in  FIG. 4 , the treatment method is performed on the patient suffering from chronic heart failure, who has a high blood pressure in a left atrium HLa due to myocardial hypertrophy appearing in a left ventricle of the heart H and increased stiffness (hardness). 
     When the through-hole Hh is formed, an operator delivers an introducer in which a guiding sheath and a dilator are combined with each other to the vicinity of the atrial septum HA. The introducer can be delivered to a right atrium HRa via an inferior vena cava Iv, for example. The introducer can be delivered using the guide wire  11 . The operator can insert the guide wire  11  into the dilator, and can deliver the introducer along the guide wire  11 . The insertion of the introducer, the insertion of the guide wire  11 , and the like to a living body can be performed by using a method such as using an introducer for blood vessel introduction. 
     Next, the operator causes a puncture device and the dilator to penetrate from the right atrium HRa side toward the left atrium HLa side, thereby forming the through-hole Hh. As for the puncture device, for example, a device such as a wire having a sharp distal end can be used. The puncture device is inserted into the dilator, and is delivered to the atrial septum HA. The puncture device can be delivered to the atrial septum HA instead of the guide wire  11 , for example, after the guide wire  11  is extracted from the dilator. 
     Next, as shown in  FIG. 4 , the operator delivers the medical device  10  to the vicinity of the atrial septum HA along the guide wire  11  inserted in advance into the left atrium HLa from the right atrium HRa via the through-hole Hh. Further, as shown in  FIG. 5 , 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 in which the expansion body  21  is stored in the storage sheath  30 . In the contracted form, the proximal side outer projection portion  55 , the inner projection portion  56 , and the distal side outer projection portion  57  having convex shapes in a natural state deforms into a shape close to a relatively flat shape, so that the expansion body  21  contracts in the radial direction. 
     Next, as shown in  FIG. 6 , the storage sheath  30  is moved to the proximal side, thereby exposing a portion on a distal side of the expansion body  21  in the left atrium HLa. In this manner, the portion on the distal side in the expansion body  21  is developed in the radial direction in the left atrium HLa due to a self-restoring force. Next, as shown in  FIG. 7 , the storage sheath  30  is moved to the proximal side, thereby exposing the entire expansion body  21 . In this manner, the portion on the proximal side in the expansion body  21  is developed in the radial direction in the right atrium HRa due to a self-restoring force. In this process, the inner projection portion  56  is disposed to an inner side of the through-hole Hh. In this manner, the entire expansion body  21  is developed due to the self-restoring force, and is recovered to an original reference form or a form close to the reference form. In this case, the atrial septum HA is disposed between the proximal side clamping portion  52  and the distal side clamping portion  53 . In a clamping direction of the biological tissue, the atrial septum HA is disposed between the energy transfer element  22  and the back support portion  62 . The expansion body  21  is brought into contact with the through-hole Hh, and thus is not completely returned to the reference form but may be returned to a shape close 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 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 ). 
     Each of the outer peripheral portions  61  has a circular arc shape that projects to the outer side in the width direction. Therefore, it can be difficult for the outer peripheral portion  61  to be caught on the inner surface of the storage sheath  30 . Accordingly, the expansion body  21  including the outer peripheral portions  61  can be smoothly released from the storage sheath  30 . 
     Next, the operator operates the operation unit  23  in a state where the clamping portion  51  holds the atrial septum HA, thereby moving the pulling shaft  33  to the proximal side. In this manner, as shown in  FIG. 8 , the expansion body  21  that receives a contracting force in the axis direction becomes in an expanded form in which the expansion body  21  has expanded more in the radial direction than in the reference form. The expansion body  21  becomes in the expanded form, so that the proximal side clamping portion  52  and the distal side clamping portion  53  come closer to each other, and the atrial septum HA is clamped between the proximal side clamping portion  52  and the distal side clamping portion  53 . In this process, the energy transfer element  22  and the back support portion  62  face each other. The clamping portion  51  in the state of clamping the atrial septum HA further expands to widen the through-hole Hh in the radial direction. 
     As shown in  FIG. 9A  and  FIG. 10A , when the proximal side clamping portion  52  and the distal side clamping portion  53  come closer to each other from the state where the proximal side clamping portion  52  and the distal side clamping portion  53  are separated from each other, as shown in  FIG. 9B  and  FIG. 10B , the atrial septum HA is clamped between the proximal side clamping portion  52  and the distal side clamping portion  53 . Further, the energy transfer element  22  presses the atrial septum HA to the distal side. In this process, the distal side clamping portion  53  causes the back support portion  62  to warp (i.e., bend) to the distal side between the two outer peripheral portions  61 , and receives the atrial septum HA that is pressed by the energy transfer element  22 , between the two outer peripheral portions  61 . The receiving surface  63  of the back support portion  62  receives a force via the atrial septum HA from the energy transfer element  22 , and warps (bends) so as to be approximately parallel to the energy transfer element  22 . Further, the back support portion  62  causes, while flexibly warping (bending), a repulsion force in a reverse direction of a press-in direction of the energy transfer element  22  to act on the atrial septum HA that is pressed by the energy transfer element  22 . In this manner, the energy transfer element  22  comes into close contact with the atrial septum HA. In addition, the energy transfer element  22  can be prevented from locally floating from the atrial septum HA. 
     In addition, when the energy transfer element  22  is brought into contact with the atrial septum HA, the two outer peripheral portions  61  that sandwich the back support portion  62  between the two outer peripheral portions  61  effectively guide the energy transfer element  22  to the back support portion  62  that is positioned between the outer peripheral portions  61 . In this manner, the energy transfer element  22  can press the atrial septum HA that is supported by the two outer peripheral portions  61  while coming into contact with the atrial septum HA, and can press the atrial septum HA against the back support portion  62  that is disposed between the two outer peripheral portions  61 . Therefore, the energy transfer element  22  comes into close contact with the atrial septum HA and is relatively difficult to float (or move) from the atrial septum HA, and a position of the energy transfer element  22  relative to the atrial septum HA is stably maintained between the two outer peripheral portions  61 . 
     The atrial septum HA is clamped between the energy transfer element  22  and the back support portion  62 , while being clamped in an uneven structure of the projection portion  54  and the distal side through-hole  60 . In this process, the back support portion  62  warps (bends), so that the atrial septum HA is rather easily clamped in the uneven structure of the projection portion  54  and the distal side through-hole  60 . In this manner, the proximal side clamping portion  52  and the distal side clamping portion  53  support with each other in a circumferential direction of the expansion body  21 , so that a position shift of the expansion body  21  in the circumferential direction can be suppressed between the proximal side clamping portion  52  and the distal side clamping portion  53 . Therefore, an expanding force of the expansion body  21  can be reliably transferred to the biological tissue. The proximal side clamping portion  52  and the distal side clamping portion  53  clamp the biological tissue when the expansion body  21  expands. When the expansion body  21  expands indicates any one of the middle of the expansion of the expansion body  21 , the instant when the expansion body  21  completely expands, and the time from when the expansion body  21  completely expands to when the expansion body  21  contracts. 
     Further, the maximum width L 1  between the outer peripheral portions  61  in the width direction is greater than the maximum width L 2  of the inner projection portion  56  in the width direction. Therefore, while flexibly maintaining the inner projection portion  56 , a region in which the back support portion  62  is disposed is rather easily secured between the two outer peripheral portions  61 . Moreover, the maximum width L 1  between the outer peripheral portions  61  in the width direction is greater than the maximum width L 3  of the energy transfer element  22  in the width direction. Therefore, the outer peripheral portions  61  rather easily guide the press direction of the energy transfer element  22  towards the back support portion  62 . Moreover, the maximum width L 4  of the distal side through-hole  60  in the width direction is greater than the maximum width L 3  of the energy transfer element  22  in the width direction. Therefore, the outer peripheral portions  61  rather easily guide the press direction of the energy transfer element  22  towards the back support portion  62 . In addition, the energy transfer element  22  can easily enter between the outer peripheral portions  61 , so that a force in which the proximal side clamping portion  52  including the energy transfer element  22  and the distal side clamping portion  53  including the outer peripheral portions  61  support with each other in the circumferential direction of the expansion body  21  easily acts between the proximal side clamping portion  52  and the distal side clamping portion  53 . 
     After the through-hole Hh has been enlarged, the hemodynamics is confirmed. As shown in  FIG. 11 , the operator delivers a hemodynamics confirming device  100  to the right atrium HRa via the inferior vena cava Iv. As for the hemodynamics confirming device  100 , for example, an echo catheter can be used. The operator can cause an echo image acquired by the hemodynamics confirming device  100  to be displayed on a display apparatus such as a display, and can confirm a blood volume passing through the through-hole Hh based on a display result of the echo image. 
     Next, the operator performs maintenance treatment for maintaining 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 transfer element  22 , thereby cauterizing (heating and cauterizing) the edge portion of the through-hole Hh by using the energy. When the biological tissue in the vicinity of the edge portion of the through-hole Hh is cauterized through the energy transfer element  22 , a degenerated portion having the degenerated biological tissue is formed in the vicinity of the edge portion. The biological tissue in the degenerated portion is in a state where elasticity is lost, so that the through-hole Hh can maintain a shape widened by the expansion body  21 . 
     The medical device  10  includes the back support portion  62 , so that the energy transfer element  22  comes into close contact with the atrial septum HA. Therefore, variations in the degree of cauterization by the energy transfer element  22  can be reduced. Moreover, the energy transfer element  22  can be prevented from locally floating (or moving) from the atrial septum HA. Therefore, the energy transfer element  22  is prevented from supplying energy into blood and an unintended site, and generation of thrombus formation, tissue damage, and the like can be suppressed. 
     Moreover, the energy transfer element  22  is disposed in the projection portion  54  of the proximal side clamping portion  52 . Therefore, the projection portion  54  is pressed against the atrial septum HA, whereby the maintenance treatment is performed in a state where the energy transfer element  22  is embedded in the biological tissue. In this manner, the energy transfer element  22  is prevented from supplying energy into blood and an unintended site, and generation of thrombus formation, tissue damage, and the like can be suppressed. 
     After the maintenance treatment, the hemodynamics are confirmed again, and in a case where the volume of blood passing through the through-hole Hh reaches a desired amount, the operator decreases the diameter of the expansion body  21 , and stores the expansion body  21  in the storage sheath  30  and then extracts the expansion body  21  from the through-hole Hh. The outer peripheral portion  61  has a circular arc shape that projects to the outer side in the width direction, and thus it is difficult for the outer peripheral portion  61  to be caught on the inner surface of the storage sheath  30 . Accordingly, the expansion body  21  including the outer peripheral portions  61  is smoothly stored in the storage sheath  30 . In addition, the operator extracts the entire medical device  10  to the outside of the living body, and ends the treatment. 
     As in the foregoing, the medical device  10  according to the abovementioned embodiment includes: the elongated shaft portion  20 , and the expansion body  21  that is provided in a distal portion of the shaft portion  20  and can expand and contract in a radial direction, in which: the expansion body  21  includes a plurality of wire portions  50  that are linked with the shaft portion  30 , and at least one clamping portion  51  that is formed by at least one wire portion  50 ; the clamping portion  51  includes the energy transfer element  22  that outputs energy, and the back support portion  62 ; the back support portion  62  includes the receiving surface  63  that can face the energy transfer element  22  when the expansion body  21  expands; and the receiving surface  63  can be inclined so as to be approximately parallel to the energy transfer element  22  when the energy transfer element  22  moves toward the back support portion  62 . In this manner, in the medical device  10 , the receiving surface  63  is approximately parallel to the energy transfer element  22  in accordance with the movement of the energy transfer element  22 , so that the energy transfer element  22  can come into close contact with the biological tissue between the energy transfer element  22  and the receiving surface  63 . Therefore, variations in the degree of cauterization by the energy transfer element  22  can be reduced. Moreover, the energy transfer element  22  can be prevented from locally floating from the biological tissue. Therefore, the energy transfer element  22  can be prevented from supplying energy into blood and an unintended site, and generation of thrombus formation, tissue damage, and the like due to the cauterization can be suppressed. In the present embodiment, the back support portion  62  is inclined by warping (or bending) due to a force in the axis direction. Note that, the back support portion  62  can be inclined without warping (or bending) by being supported by another deformable member, as shown in a second modification example (see  FIG. 13A ), which is described later, for example. 
     Moreover, at least one clamping portion  51  may include the two outer peripheral portions  61  on both sides in a width direction that is a direction orthogonal to the axis direction of the expansion body  21 , and a direction orthogonal to the radial direction of the expansion body  21 , relative to the back support portion  62 . In this manner, the outer peripheral portions  61  effectively guide the energy transfer element  22  that moves toward the back support portion  62  to the back support portion  62  that is positioned between the outer peripheral portions  61 . Therefore, the energy transfer element  22  can press the biological tissue supported by the two outer peripheral portions  61 , and press the biological tissue against the back support portion  62  that is disposed between the two outer peripheral portions  61 . Therefore, the energy transfer element  22  comes into close contact with the biological tissue and can be difficult to float (or move) from the biological tissue, and the position of the energy transfer element relative to the biological tissue can be stably maintained by the two outer peripheral portions  61 . 
     In addition, the two outer peripheral portions  61  each have a convex shape to the outer side in the width direction. In this manner, between the two outer peripheral portions  61 , a relatively wide region in which the back support portion  62  is disposed can be secured. In addition, the two outer peripheral portions  61  in the width direction can support the biological tissue in the relatively wide region, so that the energy transfer element  22  and the receiving surface  63  that clamp the biological tissue between the two outer peripheral portions  61  are rather easily maintained in the suitable positions. 
     In addition, the two outer peripheral portions  61  each have a circular arc shape that smoothly projects to the outer side in the width direction. In this manner, the outer peripheral portion  61  can be stored without being caught on the inner surface of, for example, the storage sheath  30  for storing the expansion body  21  so as to be releasable. Accordingly, the outer peripheral portions  61  can be smoothly stored in the storage sheath  30 , and can be smoothly released from the storage sheath  30 . 
     In addition, the maximum width L 1  between the outer peripheral portions  61  that sandwich the back support portion  62  between the outer peripheral portions  61  in the width direction is greater than the maximum width L 3  of the energy transfer element  22  in the width direction. In this manner, the outer peripheral portions  61  rather easily guide the press direction of the energy transfer element  22  toward the back support portion  62 . 
     In addition, the back support portion  62  moves more than the two outer peripheral portions  61  due to a force in the axis direction to be received from the energy transfer element  22 . In this manner, the back support portion  62  can flexibly receive the biological tissue that is pressed by the energy transfer element  22  while moving retracting more than the outer peripheral portion  61  in the press direction of the energy transfer element  22 . Therefore, the energy transfer element  22  comes into close contact with the biological tissue, and it is difficult to float (or move) the energy transfer element  22  from the biological tissue. 
     In addition, the expansion body  21  includes the inner projection portion  56  that projects to the inner side in the radial direction, between the energy transfer element  22  and the back support portion  62 , and the maximum width L 1  between the outer peripheral portions  61  that sandwich the back support portion  62  between the outer peripheral portions  61  in the width direction is greater than the maximum width L 2  of the inner projection portion  56  in the width direction. In this manner, while maintaining the flexibility of the inner projection portion  56 , a structure in which the width between the two outer peripheral portions  61  is widened can be obtained. The inner projection portion  56  is flexible to enable the expansion body  21  to be stored in the storage sheath  30 , for example. In addition, the inner projection portion  56  is flexible to make it easy to bring the energy transfer element  22  and the back support portion  62  that sandwich the inner projection portion  56  between the energy transfer element  22  and the back support portion  62  such that the energy transfer element  22  and the back support portion  62  can be moved close to or separate from each other. 
     In addition, the back support portion  62  can have a cantilever beam shape that extends from the wire portion  50 . In this manner, the back support portion  62  can flexibly warp (bend) by receiving a force. 
     In addition, this disclosure further provides a treatment method. The treatment method is a cauterization method of cauterizing a biological tissue, in which: a cauterization device is inserted into a right atrium, the cauterization device including the elongated shaft portion  20 , and the expansion body  21  that is provided in a distal portion of the shaft portion  20  and can expand and contract in a radial direction, in which the expansion body  21  includes a plurality of wire portions  50  that are linked with the shaft portion  20 , and at least one clamping portion  51  that is formed by at least one wire portion  50 , the clamping portion  51  includes the energy transfer element  22  that outputs energy, and the back support portion  62 , and the back support portion  62  includes the receiving surface  63  that can face the energy transfer element  22  when the expansion body  21  expands; a distal portion of the expansion body  21  contracted in the radial direction is inserted into the left atrium via the through-hole Hh opened in the atrial septum HA; the distal portion of the contracted expansion body  21  is developed in the left atrium due to a self-restoring force, and a proximal portion of the contracted expansion body  21  is developed in the right atrium HRa due to a self-restoring force, whereby a biological tissue in the vicinity of the edge portion of the through-hole Hh in the atrial septum HA is disposed between the energy transfer element  22  and the back support portion  62 ; the developed expansion body  21  is expanded in the radial direction, whereby the through-hole Hh is widened while clamping the biological tissue by the clamping portion  51 ; with the expansion of the through-hole Hh, the biological tissue is pressed toward the back support portion  62  by the energy transfer element  22 ; the receiving surface  63  of the back support portion  62  is caused to warp so as to be approximately parallel to the energy transfer element  22 ; a repulsion force from the receiving surface  63  of the back support portion  62  is caused to act on the biological tissue, whereby the energy transfer element  22  is brought into close contact with the biological tissue; and the biological tissue is cauterized by the energy to be output from the energy transfer element  22  having brought into close contact with the biological tissue. 
     In the cauterization method configured as the above, in accordance with the movement of the energy transfer element  22 , the receiving surface  63  becomes approximately parallel to the energy transfer element  22 , so that the energy transfer element  22  can be brought into close contact with the biological tissue between the energy transfer element  22  and the receiving surface  63 . Therefore, variations in the degree of cauterization by the energy transfer element  22  can be reduced. In addition, the energy transfer element  22  can be prevented from locally floating (or moving) from the biological tissue. Therefore, the energy transfer element  22  can be prevented from supplying energy into blood and an unintended site, and generation of thrombus formation, tissue damage, and the like due to the cauterization can be suppressed. 
     Note that, this disclosure is not limited to the above-described embodiment, but various changes by those skilled in the art can be made within the technical scope of the present disclosure. For example, as a first modification example shown in  FIG. 12 , the outer peripheral portion  61  does not need to be formed in a convex shape to the outer side in the width direction. 
     In addition, the form of the back support portion  62  is not limited. For example, as the second modification example shown in  FIG. 13A , the back support portion  62  does not need to have a cantilever beam-like form, but may be supported, for example, by at least one, preferably a plurality of flexible support wires  65  that extend from the two outer peripheral portions  61 . The support wire  65  is thinner and more flexible than the outer peripheral portion  61 . A constituent material for the support wire  65  is not specially limited as long as it can flexibly deform, and for example, a super elasticity alloy such as a nickel-titanium alloy and a copper-zinc alloy, a metal material such as stainless steel, polyolefin such as polyethylene, polypropylene, polybutene, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer, an ionomer, or a mixture of two or more of materials disclosed above, soft polyvinyl chloride resin, polyamide, polyamide elastomer, polyester, polyester elastomer, polyurethane, fluorine resin such as polytetrafluoroethylene, and a resin material such as polyimide, PEEK, silicone rubber, or latex rubber can be preferably used. The back support portion  62  is linked with the outer peripheral portions  61  only by the support wires  65 . Therefore, the back support portion  62  can be inclined relatively easier by receiving a force in the axis direction (axial direction), than the outer peripheral portion  61 . A plurality of the support wires  65  may be provided and disposed approximately in parallel to each other. In addition, a plurality of the support wires  65  may be provided and disposed in a mesh shape. 
     Moreover, as a third modification example shown in  FIG. 13B , the back support portion  62  may include at least one, preferably a plurality of back support wires  66  having both ends that are fixed to the outer peripheral portions  61 . A constituent material for the back support wire  66  is not specially limited as long as it can flexibly deform, and for example, the above-mentioned material applicable to the support wire  65  can be used suitably. The receiving surface  63  of the back support portion  62  is formed by the plurality of the back support wires  66  with gaps. 
     Moreover, as a fourth modification example shown in  FIG. 13C , the back support portion  62  may be a mesh-like member that is disposed between the two outer peripheral portions  61 . The mesh-like member may include, for example, a plurality of fine lines, or a flexible member having a large number of holes being formed in the flexible member. A constituent material for the mesh-like member is not specially limited as long as it can flexibly deform, and for example, the above-mentioned material applicable to the support wire  65  can be used suitably. 
     Moreover, as a fifth modification example shown in  FIG. 13D , the back support portion  62  may be an elastically deformable film body that is disposed between the two outer peripheral portions  61 . As a constituent material for the film body, for example, resin such as fluorine resin, polyethylene, and polypropylene, thermoplastic elastomer, rubber, or the like can be used suitably. 
     The detailed description above describes embodiments of a medical device for applying energy to 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.