Soft-Tissue Depth-Finding Tool

Abstract

A tissue anchor (20) comprises a helical tissue-coupling element (30) disposed about a longitudinal axis (32) thereof and having a distal tissue-penetrating tip (34). The helical tissue-coupling element (30) has: a first axial stiffness along a first axial portion (60) of the helical tissue-coupling element (30); a second axial stiffness along a second axial portion (62) of the helical tissue-coupling element (30) more distal than the first axial portion (60), which second axial stiffness is greater than the first axial stiffness; and a third axial stiffness along a third axial portion (64) more distal than the second axial portion (62), which third axial stiffness is less than the second axial stiffness. Other embodiments are also described.

1 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, wherein the helical tissue-coupling element has:
 a first axial stiffness along a first axial portion of the helical tissue-coupling element,   a second axial stiffness along a second axial portion of the helical tissue-coupling element more distal than the first axial portion, which second axial stiffness is greater than the first axial stiffness, and   a third axial stiffness along a third axial portion more distal than the second axial portion, which third axial stiffness is less than the second axial stiffness.   
     
     
         2 . The apparatus according to  claim 1 , wherein the helical tissue-coupling element has:
 a first axial yield strength along the first axial portion of the helical tissue-coupling element,   a second axial yield strength along the second axial portion of the helical tissue-coupling element, which second axial yield strength is greater than the first axial yield strength, and   a third axial yield strength along the third axial portion, which third axial yield strength is less than the second axial yield strength.   
     
     
         3 . The apparatus according to  claim 1 ,
 wherein the first and the second axial portions are shaftless helical portions of the helical tissue-coupling elements, and   wherein the helical tissue-coupling element has:   a first axial thickness along the first axial portion, and   a second axial thickness along the second axial portion, which second axial thickness is greater than the first axial thickness, the first and second axial thicknesses being measured along the axis.   
     
     
         4 . The apparatus according to  claim 3 , wherein the helical tissue-coupling element has a third axial thickness along the third axial portion, which third axial thickness is less than the second axial thickness, the third axial thickness being measured along the axis. 
     
     
         5 . The apparatus according to any one of  claims 1 - 4 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and wherein the first axial portion extends to the head. 
     
     
         6 . The apparatus according to any one of  claims 1 - 5 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         7 . The apparatus according to  claim 1 ,
 wherein the distal tissue-penetrating tip is at a distal end of the tissue anchor, and the tissue anchor is shaped so as to define a longitudinal channel extending from a proximal end of the anchor to the distal end, and   wherein the apparatus further comprises a depth-finding tool, which comprises a radiopaque bead shaped so as to define a hole therethrough, which bead is positioned within the channel, such that the bead is slidable along the channel.   
     
     
         8 . The apparatus according to  claim 7 , wherein the depth-finding tool further comprises a shaft that is removably positioned within the channel, such that the shaft passes through the hole of the bead, and such that the bead is slidable along the shaft and along the channel. 
     
     
         9 . The apparatus according to  claim 8 , wherein a distal tip of the shaft is sharp. 
     
     
         10 . The apparatus according to  claim 8 , wherein the helical tissue-coupling element is shaped so as to define a distal stopper that prevents the radiopaque bead from advancing distally off of the shaft. 
     
     
         11 . The apparatus according to any one of  claims 7 - 10 ,
 wherein the tissue anchor is shaped so as to define a head at the proximal end thereof,   wherein the helical tissue-coupling element is shaped so as to define and radially surround an empty space that extends along at least 75% of an axial length of the helical tissue-coupling element,   wherein a distal portion of the channel coincides with the empty space,   wherein a proximal portion of the channel is defined by the head,   wherein the distal portion of the channel is wider than the proximal portion of the channel, and   wherein the bead is positioned within the distal portion of the channel, in the empty space.   
     
     
         12 . The apparatus according to any one of  claims 7 - 10 , wherein the depth-finding tool further comprises a wire, which is at least partially disposed within the channel, and which couples the bead to the a proximal portion of the tissue anchor, thereby preventing the bead from exiting the distal end of the tissue anchor. 
     
     
         13 . The apparatus according to  claim 12 , wherein the wire is shaped as a helical spring. 
     
     
         14 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, wherein the helical tissue-coupling element has:
 a first axial yield strength along a first axial portion of the helical tissue-coupling element,   a second axial yield strength along a second axial portion of the helical tissue-coupling element more distal than the first axial portion, which second axial yield strength is greater than the first axial yield strength, and   a third axial yield strength along a third axial portion more distal than the second axial portion, which third axial yield strength is less than the second axial yield strength.   
     
     
         15 . The apparatus according to  claim 14 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and wherein the first axial portion extends to the head. 
     
     
         16 . The apparatus according to any one of  claims 14  and  5 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         17 . Apparatus comprising:
 a tissue anchor, which (a) comprises a helical tissue-coupling element which has a distal tissue-penetrating tip at a distal end of the tissue anchor, and (b) is shaped so as to define a longitudinal channel extending from a proximal end of the anchor to the distal end; and   a depth-finding tool, which comprises a radiopaque bead shaped so as to define a hole therethrough, which bead is positioned within the channel, such that the bead is slidable along the channel.   
     
     
         18 . The apparatus according to  claim 17 , wherein the depth-finding tool further comprises a shaft that is removably positioned within the channel, such that the shaft passes through the hole of the bead, and such that the bead is slidable along the shaft and along the channel. 
     
     
         19 . The apparatus according to  claim 18 , wherein a distal tip of the shaft is sharp. 
     
     
         20 . The apparatus according to  claim 18 , wherein the helical tissue-coupling element is shaped so as to define a distal stopper that prevents the radiopaque bead from advancing distally off of the shaft. 
     
     
         21 . The apparatus according to any one of  claims 17 - 20 ,
 wherein the tissue anchor is shaped so as to define a head at the proximal end thereof,   wherein the helical tissue-coupling element is shaped so as to define and radially surround an empty space that extends along at least 75% of an axial length of the helical tissue-coupling element,   wherein a distal portion of the channel coincides with the empty space,   wherein a proximal portion of the channel is defined by the head,   wherein the distal portion of the channel is wider than the proximal portion of the channel, and   wherein the bead is positioned within the distal portion of the channel, in the empty space.   
     
     
         22 . The apparatus according to any one of  claims 17 - 20 , wherein the depth-finding tool further comprises a wire, which is at least partially disposed within the channel, and which couples the bead to the a proximal portion of the tissue anchor, thereby preventing the bead from exiting the distal end of the tissue anchor. 
     
     
         23 . The apparatus according to  claim 22 , wherein the wire is shaped as a helical spring. 
     
     
         24 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, wherein the helical tissue-coupling element has:
 a first axial thickness along a first axial portion of a shaftless helical portion of the helical tissue-coupling element, and   a second axial thickness along a second axial portion of the shaftless helical portion more distal than the first axial portion, which second axial thickness is greater than the first axial thickness, the first and second axial thicknesses being measured along the axis.   
     
     
         25 . The apparatus according to  claim 24 , wherein the helical tissue-coupling element has a third axial thickness along a third axial portion more distal than the second axial portion, which third axial thickness is less than the second axial thickness, the third axial thickness being measured along the axis. 
     
     
         26 . The apparatus according to any one of  claims 24  and  25 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         27 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, wherein the helical tissue-coupling element is configured to rotate in a first rotational direction when being advanced into tissue, and has:
 a first surface along a first axial portion of a shaftless helical portion of the helical tissue-coupling element, which first surface has a first surface characteristic, and   a second surface along a second axial portion of the shaftless helical portion different from the first axial portion, which second surface has a second surface characteristic that is configured to (a) inhibit rotation of the helical tissue-coupling element to a greater extent than does the first surface characteristic, and (b) inhibit rotation of the helical tissue-coupling element in the first rotational direction to a lesser extent than in a second rotational direction opposite the first rotational direction,   wherein the first and the second surfaces face in a same spatial direction.   
     
     
         28 . The apparatus according to  claim 27 , wherein the second axial portion is more proximal than the first axial portion. 
     
     
         29 . The apparatus according to  claim 27 , wherein the second axial portion is more distal than the first axial portion. 
     
     
         30 . The apparatus according to  claim 27 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and wherein the first axial portion extends to the head. 
     
     
         31 . The apparatus according to  claim 27 , wherein the spatial direction is proximal, and wherein the first and the second surfaces face proximally. 
     
     
         32 . The apparatus according to  claim 27 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         33 . The apparatus according to any one of  claims 27 - 32 ,
 wherein the helical tissue-coupling element has a third surface along a third axial portion of the helical tissue-coupling element more distal than the second axial portion, which third surface has a third surface characteristic that is configured to inhibit the rotation of the helical tissue-coupling element to a lesser extent than does the second surface characteristic, and   wherein the first, the second, and the third surfaces face in the same spatial direction.   
     
     
         34 . The apparatus according to  claim 16 , wherein the first and third surface characteristics are configured to inhibit the rotation of the helical tissue-coupling element to a same extent. 
     
     
         35 . The apparatus according to any one of  claims 27 - 32 , wherein the second surface is sawtooth-shaped so as to provide the second surface characteristic. 
     
     
         36 . The apparatus according to  claim 35 , wherein the sawtooth-shaped second surface does not define any cutting surfaces. 
     
     
         37 . The apparatus according to  claim 35 , wherein the spatial direction is proximal, and wherein the first and the second surfaces face proximally. 
     
     
         38 . The apparatus according to any one of  claims 27 - 32 , wherein the second surface characteristic is surface roughness. 
     
     
         39 . The apparatus according to  claim 38 , wherein the spatial direction is proximal, and wherein the first and the second surfaces face proximally. 
     
     
         40 . The apparatus according to any one of  claims 27 - 32 , wherein an axial length of the first axial portion is at least 10% of an axial length of the helical tissue-coupling element. 
     
     
         41 . The apparatus according to  claim 40 , wherein the axial length of the first axial portion is no more than 30% of the axial length of the helical tissue-coupling element. 
     
     
         42 . Apparatus comprising a tissue anchor, which comprises:
 a radiopaque bead shaped so as to define a hole therethrough; and   a helical tissue-coupling element, which includes a shaftless helical portion that (a) is disposed about a longitudinal axis thereof, (b) has a distal tissue-penetrating tip, and (c) has an axial length of at least 3 mm, and   wherein the shaftless helical portion passes through the hole of the bead, such that the bead is slidable along the shaftless helical portion.   
     
     
         43 . The apparatus according to  claim 42 , wherein the axial length is less than 10 mm. 
     
     
         44 . The apparatus according to  claim 42 , wherein the shaftless helical portion extends along at least 75% of the axial length of the helical tissue-coupling element. 
     
     
         45 . The apparatus according to  claim 42 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         46 . The apparatus according to any one of  claims 42 - 45 , wherein the radiopaque bead comprises a plurality of radiopaque beads shaped so as to define respective holes therethrough, and wherein the helical tissue-coupling element passes through the holes of the beads such that the beads are slidable along the helical tissue-coupling element. 
     
     
         47 . The apparatus according to  claim 46 ,
 wherein the helical tissue-coupling element is disposed about a longitudinal axis thereof, and has:
 a first surface along a first axial portion of the shaftless helical portion, which first surface has a first surface characteristic, and 
 a second surface along a second axial portion of the shaftless helical portion different from the first axial portion, which second surface has a second surface characteristic that is configured to inhibit rotation of the helical tissue-coupling element to a greater extent than does the first surface characteristic, 
   wherein a first one of the beads is initially positioned distal to the second axial portion, and   wherein a second one of the beads is initially positioned proximal to the second axial portion.   
     
     
         48 . The apparatus according to  claim 46 , wherein the radiopaque beads comprise exactly two radiopaque beads. 
     
     
         49 . The apparatus according to any one of  claims 42 - 45 ,
 wherein the helical tissue-coupling element is disposed about a longitudinal axis thereof, and has:
 a first surface along a first axial portion of the shaftless helical portion, which first surface has a first surface characteristic, and 
 a second surface along a second axial portion of the shaftless helical portion different from the first axial portion, which second surface has a second surface characteristic that is configured to inhibit rotation of the helical tissue-coupling element to a greater extent than does the first surface characteristic, and wherein the bead is initially positioned distal to the second axial portion. 
   
     
     
         50 . The apparatus according to  claim 49 ,
 wherein the helical tissue-coupling element is configured to rotate in a first rotational direction when being advanced into tissue, and   wherein the second surface characteristic is configured to inhibit rotation of the helical tissue-coupling element in the first rotational direction to a lesser extent than in a second rotational direction opposite the first rotational direction.   
     
     
         51 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element, which is disposed about a longitudinal axis thereof, has a distal tissue-penetrating tip, and includes at least:
 a shaftless single-helix axial portion, which is shaped so as to define a single helical element, and   a shaftless double-helix axial portion joined to the shaftless single-helix axial portion at a junction along the helical tissue-coupling element.   
     
     
         52 . The apparatus according to  claim 51 , wherein the helical tissue-coupling element has an axial length of at least 3 mm, and wherein the shaftless single- and double-helix portions collectively extend along at least 75% of the axial length of the helical tissue-coupling element. 
     
     
         53 . The apparatus according to  claim 51 , wherein the shaftless double-helix portion is shaped so as to define two helical elements rotationally offset from each other by between 160 and 200 degrees. 
     
     
         54 . The apparatus according to  claim 51 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         55 . The apparatus according to  claim 51 ,
 wherein the shaftless single-helix axial portion has a single-helix axial thickness at a first location on the shaftless single-helix axial portion at a distance of 250 microns from the junction, the distance measured circumferentially around the helical tissue-coupling element,   wherein the shaftless double-helix axial portion, including the two helical elements and the axial gap, has a double-helix axial thickness at a second location on the shaftless double-helix axial portion at the distance from the junction, the single-helix and double-helix axial thicknesses being measured along the axis, and   wherein the double-helix axial thickness equals between 75% and 120% of the single-helix axial thickness.   
     
     
         56 . The apparatus according to  claim 51 , wherein the shaftless double-helix portion is shaped so as to define two helical elements axially offset from each other, separated by an axial gap. 
     
     
         57 . The apparatus according to any one of  claims 51 - 56 , wherein an axial yield strength of the shaftless single-helix axial portion is greater than an axial yield strength of the shaftless double-helix axial portion. 
     
     
         58 . The apparatus according to  claim 57 , wherein the axial yield strength of the shaftless single-helix axial portion is at least 120% of the axial yield strength of the shaftless double-helix axial portion. 
     
     
         59 . The apparatus according to any one of  claims 51 - 56 , wherein the shaftless double-helix axial portion is proximal to the shaftless single-helix axial portion. 
     
     
         60 . The apparatus according to  claim 59 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and wherein the shaftless double-helix axial portion extends to the head. 
     
     
         61 . Apparatus comprising a tissue anchor, which comprises a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, the helical tissue-coupling element comprising a wire which (a) is shaped as a helix, (b) has a non-circular cross section, and (c) is twisted about its longitudinal axis, so as to define a ridged surface. 
     
     
         62 . The apparatus according to  claim 61 , wherein the wire is twisted about its longitudinal axis at between 1 and 5 twists per cm of a length the wire before it is shaped into the helix. 
     
     
         63 . The apparatus according to  claim 61 , wherein the cross section is shaped as a polygon. 
     
     
         64 . The apparatus according to  claim 61 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and the apparatus further comprises a flexible longitudinal member, which is coupled to the head. 
     
     
         65 . The apparatus according to any one of  claims 61 - 64 , wherein the helical tissue-coupling element has:
 a first axial stiffness along a first axial portion of the helical tissue-coupling element,   a second axial stiffness along a second axial portion of the helical tissue-coupling element more distal than the first axial portion, which second axial stiffness is greater than the first axial stiffness, and   a third axial stiffness along a third axial portion more distal than the second axial portion, which third axial stiffness is less than the second axial stiffness.   
     
     
         66 . The apparatus according to  claim 65 , wherein the tissue anchor is shaped so as to define a head at a proximal end thereof, and wherein the first axial portion extends to the head. 
     
     
         67 . Apparatus for use with a tissue anchor, the apparatus comprising a delivery system, which comprises:
 an anchor-deployment tube;   a flexible connecting element selected from the group consisting of: a spring, a braid, a mesh, and a cut tube;   a radiopaque marker, which is coupled to a distal end of the anchor-deployment tube by the flexible connecting element,   wherein the radiopaque marker and the flexible connecting element are arranged radially surrounding the tissue anchor, such that the radiopaque marker is axially moveable along the tissue anchor with respect to the distal end, and   wherein the flexible connecting element is arranged so as to axially compress as the marker moves toward the distal end.   
     
     
         68 . The apparatus according to  claim 67 , wherein the radiopaque marker is shaped as a disc. 
     
     
         69 . The apparatus according to any one of  claims 67 - 68 , wherein flexible connecting element comprises the spring. 
     
     
         70 . The apparatus according to any one of  claims 67 - 68 , wherein the flexible connecting element comprises the braid. 
     
     
         71 . A method comprising:
 providing a tissue anchor, which includes a helical tissue-coupling element disposed about a longitudinal axis thereof and having a distal tissue-penetrating tip, wherein the helical tissue-coupling element has (a) a first axial yield strength along a first axial portion of the helical tissue-coupling element, (b) a second axial yield strength along a second axial portion of the helical tissue-coupling element more distal than the first axial portion, which second axial yield strength is greater than the first axial yield strength, and (c) a third axial yield strength along a third axial portion more distal than the second axial portion, which third axial yield strength is less than the second axial yield strength; and   advancing the helical tissue-coupling element into soft tissue.   
     
     
         72 . The method according to  claim 71 ,
 wherein providing the tissue anchor comprises providing the tissue anchor in which the helical tissue-coupling element has (a) a first axial yield strength along the first axial portion of the helical tissue-coupling element, and (b) a second axial yield strength along the second axial portion of the helical tissue-coupling element, which second axial yield strength is greater than the first axial yield strength, and   wherein the method further comprises:   applying tension to a proximal head of the tissue anchor; and   sensing elongation of the first axial portion while applying the tension.   
     
     
         73 . The method according to  claim 71 , wherein providing the tissue anchor comprises providing the tissue anchor in which the helical tissue-coupling element has (a) a first axial stiffness along the first axial portion of the helical tissue-coupling element, (b) a second axial stiffness along the second axial portion of the helical tissue-coupling element, which second axial stiffness is greater than the first axial stiffness, and (c) a third axial stiffness along the third axial portion, which third axial stiffness is less than the second axial stiffness. 
     
     
         74 . The method according to  claim 71 , wherein providing the tissue anchor comprises providing the tissue anchor in which (i) the first and the second axial portions are shaftless helical portions of the helical tissue-coupling elements, and (ii) the helical tissue-coupling element has (a) a first axial thickness along the first axial portion, and (b) a second axial thickness along the second axial portion, which second axial thickness is greater than the first axial thickness, the first and second axial thicknesses being measured along the axis. 
     
     
         75 . The method according to  claim 74 , wherein providing the tissue anchor comprises providing the tissue anchor in which the helical tissue-coupling element has a third axial thickness along the third axial portion, which third axial thickness is less than the second axial thickness, the third axial thickness being measured along the axis. 
     
     
         76 . The method according to  claim 71 , further comprising applying tension to a proximal head of the tissue anchor. 
     
     
         77 . The method according to  claim 76 , wherein applying the tension comprises sensing elongation of the first axial portion while applying the tension. 
     
     
         78 . The method according to  claim 77 , wherein sensing the elongation comprises sensing the elongation using imaging. 
     
     
         79 . The method according to  claim 77 , wherein sensing the elongation comprises sensing the elongation using tactile feedback. 
     
     
         80 . The method according to  claim 76 , wherein applying the tension comprises pulling on a flexible longitudinal member that is coupled to the proximal head. 
     
     
         81 . The method according to  claim 71 , wherein advancing the helical tissue-coupling element into the soft tissue comprises advancing the second and the third axial portions completely into the soft tissue, and leaving at least a portion of the first axial portion outside of the soft tissue. 
     
     
         82 . The method according to  claim 81 , wherein leaving the at least a portion of the first axial portion outside of the soft tissue comprises leaving the first axial portion entirely outside of the soft tissue. 
     
     
         83 . The method according to  claim 71 , wherein providing the tissue anchor comprises providing the tissue anchor shaped so as to define a head at a proximal end thereof, and wherein the first axial portion extends to the head. 
     
     
         84 . The method according to  claim 71 ,
 wherein providing the tissue anchor comprises providing the tissue anchor (a) in which the distal tissue-penetrating tip is at a distal end of the tissue anchor, and (b) which is shaped so as to define a longitudinal channel extending from a proximal end of the anchor to the distal end,   wherein the method further comprises providing a depth-finding tool, which includes a radiopaque bead shaped so as to define a hole therethrough, which bead is positioned within the channel, such that the bead is slidable along the channel, and   wherein advancing the helical tissue-coupling element into the soft tissue comprises advancing the helical tissue-coupling element into the soft tissue, such that the bead comes into contact with and remains at a surface of the soft tissue.   
     
     
         85 . The method according to  claim 84 , wherein providing the depth-finding tool comprises providing the depth-finding tool further including a shaft that is removably positioned within the channel, such that the shaft passes through the hole of the bead, and the bead is slidable along the shaft and along the channel. 
     
     
         86 . The method according to  claim 85 , further comprising proximally withdrawing the shaft from the channel, leaving the bead in the channel. 
     
     
         87 . The method according to  claim 85 , wherein providing the depth-finding tool comprises providing the depth-finding tool in which a distal tip of the shaft is sharp. 
     
     
         88 . The method according to  claim 87 , further comprising advancing the shaft into the soft tissue while advancing the helical tissue-coupling element into the soft tissue. 
     
     
         89 . The method according to  claim 88 , further comprising, after fully advancing the helical tissue-coupling element into the soft tissue, proximally withdrawing the shaft from the channel, leaving the bead in the channel. 
     
     
         90 . The method according to  claim 87 , further comprising, before advancing the helical tissue-coupling element into the soft tissue, inserting the sharp distal tip of the shaft into the soft tissue slightly, in order to prevent sliding of the depth-finding tool and the anchor on a surface of the soft tissue before advancing the anchor into the tissue. 
     
     
         91 . The method according to  claim 84 , further comprising:
 viewing the bead and a proximal portion of the soft tissue anchor using imaging; and   assessing a depth of penetration of the helical tissue-coupling element into the soft tissue by estimating a distance between the bead and the proximal portion of the tissue anchor.   
     
     
         92 . The method according to  claim 84 , wherein providing the depth-finding tool comprises providing the depth-finding tool further including a wire, which is at least partially disposed within the channel, and which couples the bead to the a proximal portion of the tissue anchor, thereby preventing the bead from exiting the distal end of the tissue anchor. 
     
     
         93 . The method according to  claim 92 , wherein providing the depth-finding tool comprises providing the depth-finding tool in which the wire is shaped as a helical spring. 
     
     
         94 . The method according to  claim 84 ,
 wherein providing the tissue anchor comprises providing the tissue anchor in which:
 the tissue anchor is shaped so as to define a head at the proximal end thereof, 
 the helical tissue-coupling element is shaped so as to define and radially surround an empty space that extends along at least 75% of an axial length of the helical tissue-coupling element, 
 a distal portion of the channel coincides with the empty space, 
 a proximal portion of the channel is defined by the head, and 
 the distal portion of the channel is wider than the proximal portion of the channel, and 
   wherein providing the depth-finding tool comprises providing the depth-finding tool in which the bead is positioned within the distal portion of the channel, in the empty space.