Patent Publication Number: US-2022226135-A1

Title: Handle for two-stage deployment of a stent

Description:
FIELD OF THE INVENTION 
     The present invention relates to the deployment of stents and other expandable devices within a body of a subject. 
     BACKGROUND 
     U.S. Pat. No. 9,867,701 describes a delivery device for a collapsible prosthetic heart valve, including an operating handle and a catheter assembly. The operating handle may include a housing defining a movement space therein, a carriage assembly moveable in a longitudinal direction within the movement space, a deployment actuator coupled to the housing and rotatable relative to the housing, and a coupling assembly rotationally fixed to the deployment actuator. The catheter assembly may include a first shaft around which a compartment is defined and a distal sheath operatively connected to the carriage assembly. Movement of the carriage assembly in the longitudinal direction in the movement space may move the distal sheath between the closed condition and the open condition. The coupling assembly may have an engaged position in which rotation of the deployment actuator moves the carriage assembly, and a disengaged position in which rotation of the deployment actuator does not move the carriage assembly. 
     U.S. Pat. No. 9,198,788 describes a delivery system to deliver and deploy a prosthesis in a body lumen, and methods of use thereof. The delivery system allows for operation of the delivery system with one hand while maintaining accuracy in delivery and deployment of the prosthesis. An exemplary embodiment of the delivery system includes a first sheath control on a housing so as to be accessible from the exterior of the housing, wherein the first sheath control is operatively engaged with the sheath and controls movement of the sheath axially proximally with respect to the housing, thereby releasing at least a portion of the prosthesis. 
     U.S. Pat. No. 5,591,196 describes a method for intraluminal delivery and deployment of an expandable prosthesis at a site within a body lumen. The method comprises the steps of placing the prosthesis over a support having at least two movable wings mounted on a catheter, delivering the prosthesis to the desired location by moving the catheter through the body passageway, and moving the wings radially outwardly to thereby deploy the prosthesis within the body passageway. 
     U.S. Pat. No. 7,976,574 describes a delivery system utilizing a handle assembly including an actuating mechanism capable of initially providing sufficient mechanical advantage to overcome static friction when initiating deployment of the medical device. The actuating mechanism includes components which help to increase the speed of deployment as the physician continues to manipulate the actuating mechanism. 
     U.S. Pat. No. 10,327,927 describes a vascular intervention device delivery system including a catheter with a proximal end attached to a handle, and a distal carrier segment for mounting a vascular intervention device thereon. A retractable sheath is movable from a first position covering the distal carrier segment to a second position retracted proximally uncovering the distal carrier segment. A pull is attached to the retractable sheath and extends proximally from the retractable sheath toward the handle. A majority of the length of the pull has a cross sectional shape with a concave side that faces the longitudinal axis and is opposite to a convex side that faces away from the longitudinal axis. The cross sectional shape has a width that is greater than a thickness. 
     US Patent Application Publication 2009/0138023 describes an actuator handle for use with an implantable medical device deployment system. The actuator handle includes a first actuator and a second actuator for manipulating and controlling first and second retaining members of the deployment system to effectuate release of a medical device from the deployment system. 
     SUMMARY OF THE INVENTION 
     There is provided, in accordance with some embodiments of the present invention, an apparatus for retracting a sheath from over an expandable medical device. The apparatus includes a shell, configured to couple to a longitudinal element, a carriage disposed within the shell and configured to couple to the sheath, and a lever protruding from the shell and configured to retract the sheath while a distal end of the longitudinal element contacts the expandable medical device, by rotating proximally so as to move the carriage proximally by a first distance, and, subsequently to rotating proximally, sliding proximally so as to move the carriage proximally by a second distance. 
     In some embodiments, the carriage is configured to couple to the sheath via one or more other longitudinal elements. 
     In some embodiments, 
     the carriage is shaped to define:
         a port configured to receive a distal end of a syringe, and   a lumen in fluid communication with the port, and       

     the carriage is configured to couple to the sheath by gripping the sheath, or another longitudinal element coupled to the sheath, within the lumen, such that fluid injected from the syringe flows through the sheath via the lumen. 
     In some embodiments, 
     the shell is shaped to define a slit, and 
     the lever is configured to rotate proximally, and to slide proximally, within the slit. 
     In some embodiments, 
     the shell includes a distal arcuate portion and a proximal straight portion, 
     the lever is configured to rotate proximally while protruding from the distal arcuate portion, and 
     the lever is configured to slide proximally while protruding from the proximal straight portion. 
     In some embodiments, the first distance is between 5 and 10 mm. 
     In some embodiments, 
     the carriage is an inner carriage, 
     the apparatus further includes an outer carriage, and 
     the lever is rotatably coupled to the outer carriage such that the lever is configured to move the inner carriage proximally with respect to the outer carriage by the first distance, and to move the inner carriage, together with the outer carriage, proximally by the second distance. 
     In some embodiments, the apparatus further includes a stopper within the shell, 
     the shell is configured to couple to the longitudinal element by virtue of the stopper being coupled to an inside of the shell and to a proximal end of the longitudinal element, and 
     the lever is configured to move the carriage proximally until movement of the carriage is stopped by the stopper. 
     In some embodiments, an axial position of the stopper is adjustable. 
     In some embodiments, a base of the lever is shaped to define at least one outwardly-protruding protrusion, and an inner wall of the shell is shaped to define at least one inwardly-protruding protrusion aligned with the outwardly-protruding protrusion while the lever is rotating proximally such that, while the lever is rotating proximally, the inwardly-protruding protrusion inhibits the base of the lever from sliding proximally. 
     In some embodiments, 
     the lever is shaped to define at least one protrusion, and 
     the carriage is shaped to define at least one depression configured to receive the protrusion following the rotation of the lever. 
     In some embodiments, 
     the carriage is shaped to define a distal L-shaped protrusion, and 
     the lever includes two legs that straddle the distal L-shaped protrusion such that, prior to the rotation of the lever, a vertical proximally-facing face of the distal L-shaped protrusion contacts the lever. 
     There is further provided, in accordance with some embodiments of the present invention, a method for retracting a sheath from over an expandable medical device. The method includes rotating a lever, which protrudes from a shell of a handle, proximally, such that the lever proximally moves, by a first distance, a carriage disposed within the shell and coupled to the sheath. The method further includes, subsequently to rotating the lever, sliding the lever proximally such that the lever moves the carriage proximally by a second distance. 
     In some embodiments, 
     the carriage is shaped to define a port and a lumen in fluid communication with the port, 
     the carriage is configured to couple to the sheath by gripping the sheath, or another longitudinal element coupled to the sheath, within the lumen, and 
     the method further includes, prior to rotating the lever, flushing the sheath by:
         inserting a distal end of a syringe into the port, and   injecting fluid from the syringe into the port or the lumen such that the fluid flows through the sheath via the lumen.       

     There is further provided, in accordance with some embodiments of the present invention, a method including coupling a sheath to a carriage disposed within a shell of a handle, placing an expandable medical device within the sheath, and coupling a proximal end of a longitudinal element to a stopper disposed within the shell proximally to the carriage. The method further includes, subsequently to placing the expandable medical device within the sheath and coupling the proximal end of the longitudinal element to the stopper, moving the stopper distally until a distal end of the longitudinal element contacts the expandable medical device, and, subsequently to moving the stopper distally, fixing the stopper in place. 
     In some embodiments, an inner wall of the shell is shaped to define one or more tracks, and moving the stopper distally includes sliding the stopper distally along the tracks. 
     In some embodiments, a proximal end of the shell is shaped to define an opening, and moving the stopper distally includes pushing the stopper distally using a pushing element inserted through the opening. 
     In some embodiments, fixing the stopper in place includes fixing the stopper in place by screwing the stopper to the shell. 
     The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a system for treatment of a subject, in accordance with some embodiments of the present invention; 
         FIGS. 2-3  are schematic illustrations of a handle, in accordance with some embodiments of the present invention; 
         FIG. 4  is a schematic illustration of a portion of a handle, including a carriage and a lever, in accordance with some embodiments of the present invention; 
         FIG. 5  is a schematic illustration of a lever and a shell, in accordance with some embodiments of the present invention; and 
         FIG. 6  is a schematic illustration of a longitudinal cross-section through a distal portion of a handle, in accordance with some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Typically, to deploy an expandable medical device such as a stent, a sheath is retracted from over the device, thus exposing the device such that the device expands. However, the amount of static friction between the sheath and the device may be relatively large, particularly if the device was compressed within the sheath for an extended period of time. As a result, it may be difficult to retract the sheath in a controlled and steady manner. 
     To address this challenge, embodiments of the present invention provide a handle configured to deploy an expandable medical device in a two-stage process. The handle comprises a lever and a carriage, which is coupled directly or indirectly to the sheath. In the first stage of deployment, the lever is rotated so as to move the carriage proximally by a first, relatively small distance. Subsequently, in the second stage of deployment, the lever is slid proximally, thus moving the carriage proximally by a second, larger distance. 
     Advantageously, the mechanical advantage provided by the lever during the first deployment stage facilitates overcoming the friction force between the sheath and the device. Moreover, due to the limited movement of the carriage during the first deployment stage, the first deployment stage does not expose the device; rather, the device is exposed, in a controlled and steady manner, only during the second stage of deployment. 
     System Description 
     Reference is initially made to  FIG. 1 , which is a schematic illustration of a system  20  for treatment of a subject, in accordance with some embodiments of the present invention. 
     System  20  comprises a sheath  24 . As shown in the inset portion  25  of  FIG. 1 , which shows the contents of sheath  24 , the sheath is configured to contain an expandable medical device  38  in a crimped (unexpanded) configuration. Device  38  may comprise, for example, a stent (e.g., a mesh stent or a covered stent), a flow diverter, an aneurysm graft, or a heart valve. 
     System  20  further comprises a handle  22  for deploying device  38  from sheath  24  within a body cavity, such as a blood vessel, of the subject. Handle  22  comprises a shell  44 , which may be made from a plastic or any other suitable material, and a lever  40 , which protrudes from shell  44 . When using the handle, a user, such as a physician, typically grips shell  44  with one hand, with the thumb of the hand placed over the head  94  of the lever. (Optionally, head  94  may be shaped to define bumps, which inhibit the thumb from slipping off the head.) Alternatively, the user may grasp head  94  with his other hand. 
     Reference is now additionally made to  FIG. 2 , which is a schematic illustration of handle  22 , in accordance with some embodiments of the present invention. A portion of shell  44  is hidden from view in  FIG. 2 , so as to expose components of the handle contained within the shell. 
     Handle  22  comprises a carriage  48  disposed within shell  44  and configured to couple to sheath  24 . As further described below, by manipulating lever  40 , the user moves the carriage proximally, thus retracting sheath  24  from over device  38  such that the device expands within the body cavity. 
     Typically, the carriage is not coupled directly to the sheath, but rather, is coupled to the sheath via one or more longitudinal elements. For example, the inner wall of the sheath may be coupled to a rapid exchange tube  32 , which in turn may be coupled to a flexible tube  30 . Flexible tube  30 , in turn, may be coupled to a reinforced tube  36 , which is coupled to the carriage. For example, as shown in  FIG. 6  (described below), reinforced tube  36  may be gripped within a lumen of the carriage, e.g., by virtue of being glued to the wall of the lumen. Typically, flexible tube  30  has a length between 20 cm and 1.5 m, so as to extend from the exterior of the subject to the site at which the expandable device is to be deployed. 
     Shell  44  is configured to couple to a longitudinal element  26 . As the lever retracts the sheath by moving the carriage proximally relative to shell  44 , the distal end of longitudinal element  26  remains in contact with the expandable medical device. Thus, longitudinal element  26  inhibits retraction of the expandable medical device (i.e., the longitudinal element provides a distal counterforce to the device), such that the sheath is retracted from over the expandable medical device. 
     Typically, longitudinal element  26  comprises a flexible wire  27 , which is distally coupled to a distal tube  28 . Typically, flexible wire  27  has a length between 20 cm and 1.5 m. 
     Prior to deploying the expandable medical device, the sheath (together with the expandable device disposed therein) is navigated, typically under fluoroscopy, to the site at which the device is to be deployed. In some embodiments, the sheath is navigated over a guidewire. The guidewire may be passed through a guidewire tube  34 , which runs through rapid exchange tube  32  and distal tube  28 . 
     Typically, shell  44  is shaped to define a slit  50 , and lever  40  is configured to move proximally within slit  50 . In some embodiments, system  20  further comprises a safety tab  42 , which fits into the slit proximally to lever  40  so as to lock the lever in place, i.e., inhibit any unintended movement of the lever. Prior to deploying the expandable medical device, tab  42  is removed from the handle. 
     Deploying the Expandable Medical Device 
     Advantageously, as described above in the Overview, handle  22  facilitates a two-stage deployment of device  38 . 
     During the first stage, lever  40  is rotated proximally, as indicated in  FIG. 2  by a rotation indicator  52 . (In the context of the present application, including the claims, a “proximal rotation” of the lever refers to a rotation of the lever in which head  94  of the lever moves proximally.) The rotation of the lever moves the carriage proximally by a first distance d 1 , which in some embodiments is between 5 and 10 mm. Advantageously, the mechanical advantage provided by the lever facilitates overcoming the friction between the sheath and the expandable device. 
     Typically, during the first stage of deployment, the lever is rotated until the lever contacts the top face  96  of carriage  48 , such that the carriage inhibits further rotation of the lever. 
     During the second stage, the lever is slid proximally, as indicated in  FIG. 2  by a sliding indicator  54 . The sliding of the lever moves the carriage proximally by a second distance d 2 . 
     Typically, shell  44  is coupled to longitudinal element  26  via a stopper  46 , in that stopper  46  is coupled to the inside of the shell (e.g., via a screw  57 , as described below) and to the proximal end of longitudinal element  26  (e.g., via glue inserted through the shell). (Stopper  46  may comprise a piece of material, such as a piece of plastic, having any suitable shape.) During the second stage of deployment, carriage  48  is moved proximally until the movement of the carriage is stopped by stopper  46 , e.g., by virtue of a protrusion  56 , which protrudes upwardly from the carriage, fitting into a complementary depression in the underside of the stopper. 
     Typically, the axial position of stopper  46 —i.e., the position of the stopper along an axis running between the proximal and distal ends of the handle—is adjustable. For example, the inner wall of the shell may be shaped to define one or more tracks  47 , and the stopper may be configured to slide along tracks  47 . During the assembly of system  20 , the sheath is coupled to the carriage, the expandable medical device is placed within the sheath, and the proximal end of the longitudinal element is coupled to the stopper. (The latter three steps may be performed in any suitable order.) Stopper  46  is then moved distally until the distal end of longitudinal element  26  contacts the expandable device. For example, the proximal end of the shell may be shaped to define an opening  60 , and the stopper may be pushed distally by a pushing element (e.g., a finger or a tool) inserted through opening  60 . Subsequently, the stopper is fixed in place, e.g., by inserting screw  57  through a screw-hole  58  in shell  44  and, using the screw, screwing the stopper to the shell. 
     In general, the expandable device is placed within the sheath such that the distance separating the distal end of the device from the distal end of the sheath is greater than d 1  but less than d 2   min -L, d 2   min  being the minimum expected value of d 2  following the adjustment of the stopper, and L being the length of the expandable device (e.g., 20, 30, 40, or 60 mm). By virtue of the distance being greater than d 1 , the device does not exit the sheath (even partly) during the first stage of deployment, even in a case of minimal friction between the sheath and the device, in which case the sheath is retracted by d 1 . By virtue of the distance being less than d 2   min -L, the device exits the sheath during the second stage of deployment even in a case of maximal friction between the sheath and the device, in which case the sheath is not retracted at all during the first stage. 
     Typically, the shell comprises a distal arcuate portion  62  and a proximal straight portion  64 . The lever is configured to rotate proximally while protruding from distal arcuate portion  62 , typically with head  94  being situated a small distance (e.g., 1-5 mm) from the distal arcuate portion. The lever is further configured to slide proximally while protruding from proximal straight portion  64 , typically with head  94  being situated a small distance (e.g., 1-5 mm) from the proximal straight portion. 
     Advantageously, distal arcuate portion  62  helps the user ascertain the moment at which the first deployment stage ends and the second stage begins. Furthermore, the distal arcuate portion may facilitate locking the lever prior to deployment, e.g., using safety tab  42 . 
     Reference is now made to  FIG. 3 , which is another schematic illustration of handle  22 , in accordance with some embodiments of the present invention. (As in  FIG. 2 , a portion of shell  44  is hidden from view so as to expose the interior of the handle.) Reference is also made to  FIG. 4 , which is a schematic illustration of a portion of handle  22 , including carriage  48  and lever  40 , in accordance with some embodiments of the present invention. 
     Typically, the lever comprises a neck  41 , which extends along the longitudinal axis of the lever, along with two legs  72 , which extend along the longitudinal axis of the lever between neck  41  and the base  71  of the lever. (Neck  41  thus joins legs  72  to head  94 .) Typically, legs  72  are disposed at opposite sides of neck  41 , such that neck  41  is aligned with slit  50  ( FIG. 1 ) while legs  72  are disposed beneath the shell at opposing sides of the slit. Thus, during the second stage of deployment, the shell inhibits the lever from rotating distally. 
     In some embodiments, legs  72  straddle a distal L-shaped protrusion  16  of carriage  48 . Prior to the rotation of the lever, the vertical proximally-facing face  17  of protrusion  76  contacts the lever, such that the lever inhibits carriage  48  from sliding proximally. 
     In some embodiments, the lever is shaped to define at least one protrusion  90 , such as a respective protrusion  90  on each leg  72  of the lever. Additionally, the carriage (in particular, top face  96 ) is shaped to define at least one depression  92  configured to receive protrusion  90  following the rotation of the lever. For example, the carriage may be shaped to define two depressions  92 , each depression  92  aligned with a respective leg  72  such that the depression is configured to receive the protrusion on the leg. By virtue of the protrusions fitting into the depressions, the carriage does not slide proximally away from the lever during the second stage of deployment. 
     Typically, carriage  48  is shaped to define one or more distal protrusions  68  that contact lever  40 ; for example, the carriage may be shaped to define two protrusions  68 , each of which contacts a different respective leg  72  of the lever. As the lever is rotated, the lever pushes against protrusions  68 , thus moving the carriage proximally. Distance d 1 —the distance by which carriage  48  is moved during the first stage of deployment—may be adjusted by varying the distance d 3  between the axis of rotation of the lever and protrusions  68 ; as d 3  is increased, d 1  increases. (It is noted that the mechanical advantage d 4 /d 3  of the lever, where d 4  is the distance from the axis of rotation to the top of the head of the lever, also varies with d 3 .) 
     Alternatively or additionally to protrusions  68 , the carriage may be shaped to define one or more distally-protruding racks, and the base  71  of the lever—comprising, for example, the respective bases of legs  12 —may be shaped to define one or more partial pinions that contact the racks. As the lever rotates, the pinions may move the racks proximally, thus moving the carriage. 
     It is noted that, in addition to the distance between the axis of rotation and the point of contact between the lever and the carriage, distance d 1  is a function of the angle by which the lever is rotated. In some embodiments, this angle is between 25 and 90 degrees. 
     Typically, handle  22  further comprises an outer carriage  66 . In such embodiments, lever  40  is rotatably coupled to outer carriage  66  such that the lever is configured to move carriage  48 —which may be referred to, in such embodiments, as an “inner carriage”—proximally with respect to the outer carriage by distance d 1  ( FIG. 2 ) during the first stage of deployment. Subsequently, during the second stage of deployment, the lever moves the inner carriage, together with the outer carriage, proximally by distance d 2 . 
     In some embodiments, as shown in  FIGS. 3-4 , outer carriage  66  comprises a first carriage wall  66   a  and a second carriage wall  66   b  joined to one another by a distal carriage bottom  70 . Alternatively, the outer carriage may comprise a single carriage wall joined to carriage bottom  70 . In either case, lever  40  is typically coupled to carriage bottom  70 . For example, the carriage bottom may comprise respective pins  74  on opposite sides of the carriage bottom (or a single pin passing through the carriage bottom), and the respective bases of legs  72  may be fitted over pins  74  such that the pins define the axis of rotation of the lever. 
     In some embodiments, as shown in  FIG. 3 , outer carriage  66  is shaped to define at least one groove  78 , and inner carriage  48  is shaped to define at least one protrusion  80  configured to slide within groove  78  while, during the first stage of deployment, the lever moves the inner carriage proximally with respect to the outer carriage. For example, each of first carriage wall  66   a  and second carriage wall  66   b  may be shaped to define a respective groove  78 , and the inner carriage may be shaped to define two protrusions  80  on opposite sides of the inner carriage such that each of the protrusions slides within a different respective groove  78 . Alternatively or additionally, the inner carriage may be shaped to define at least one groove, and the outer carriage may be shaped to define at least one protrusion configured to slide within the groove during the first stage of deployment. Advantageously, the aforementioned grooves and protrusions guide the movement of the inner carriage within the outer carriage. 
     Similarly, shell  44  may be shaped to define at least one groove  82 , and outer carriage  66  may be shaped to define at least one protrusion  84  configured to slide within groove  82  while, during the second stage of deployment, the lever moves the inner and outer carriages proximally with respect to the shell. Alternatively or additionally, the outer carriage may be shaped to define at least one groove  86 , and the shell may be shaped to define at least one protrusion  88  configured to slide within groove  86  during the second stage of deployment. For example, each of first carriage wall  66   a  and second carriage wall  66   b  may be shaped to define a respective protrusion  84 , along with a pair of grooves  86  on opposite sides of the protrusion. Complementarily, each wall of the shell may be shaped to define a groove  82 , within which a protrusion  84  of one of the carriage walls slides, along with a pair of protrusions  88  on opposite sides of the groove, which slide within grooves  86  of the wall. Advantageously, the aforementioned grooves and protrusions guide the movement of the outer carriage within the shell. 
     In alternate embodiments, the handle does not comprise an outer carriage. Rather, carriage  48  comprises a proximal portion, a distal portion, and a compressible middle portion (comprising a spring, for example) that joins the proximal portion to the distal portion. During the rotation of the lever, the distal portion of the carriage is moved toward the proximal portion of the carriage as the middle portion is compressed. Subsequently, the entire carriage is moved proximally by the sliding of the lever. 
     Reference is now made to  FIG. 5 , which is a schematic illustration of lever  40  and shell  44 , in accordance with some embodiments of the present invention. (Other components of the handle, such as the carriages, are omitted from  FIG. 5 .) 
     In some embodiments, base  71  is shaped to define at least one outwardly-protruding arcuate protrusion  98 , and the inner wall of the shell is shaped to define at least one inwardly-protruding arcuate protrusion  99 . During the first deployment stage, protrusion  99  is aligned with protrusion  98  such that, while the lever is rotating, protrusion  99  inhibits the base of the lever from sliding proximally. For example, the base of each leg  72  may be shaped to define a respective protrusion  98 , each of which is aligned with a different respective protrusion  99  during the first deployment stage. As the lever completes its rotation, protrusion  98  drops below protrusion  99 , such that the base of the lever is free to slide proximally during the second deployment stage. 
     Flushing the Sheath 
     Reference is now made to  FIG. 6 , which is a schematic illustration of a longitudinal cross-section through a distal portion of handle  22 , in accordance with some embodiments of the present invention. 
     Typically, carriage  48  is shaped to define a port  100 , such as a female Luer port, configured to receive (e.g., via an opening  106  in the shell) the distal end of a syringe  102 . (It is noted that the bottom of port  100  is shown in  FIG. 4 .) Typically, carriage  48  is further shaped to define a lumen  104  in fluid communication with port  100 . 
     In such embodiments, as described above with reference to  FIGS. 1-2 , the carriage is configured to couple to sheath  24  ( FIG. 1 ) by gripping the sheath, or another longitudinal element (such as reinforced tube  36 ) coupled to the sheath, within lumen  104 . Thus, prior to the deployment of the device, the sheath may be flushed with a fluid, such as saline, injected from syringe  102 . In particular, the fluid may be injected into port  100  (and/or directly into lumen  104 ) such that the fluid flows through the sheath via the lumen. For example, the fluid may flow through the sheath via lumen  104 , reinforced tube  36 , flexible tube  30 , and rapid exchange tube  32 , which, as described above with reference to  FIG. 1 , is coupled to the inside of the sheath. 
     In some embodiments, as shown in  FIG. 6 , longitudinal element  26  passes through lumen  104 . In such embodiments, a seal  108 , such as an O-ring, may be placed around the longitudinal element within lumen  104  and proximally to port  100 , so as to inhibit the flow of fluid through the proximal end of the lumen. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of embodiments of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.