Abstract:
An apparatus for sampling tissue includes a tissue engaging member for engaging and retaining a sample of a tissue structure, and a cutter surrounding the tissue engaging member. The tissue engaging member and cutter are both operative to translate longitudinally with respect to one another, and a mechanism prevents the cutter from moving distally, the mechanism being released and the cutter freed to move distally when the tissue engaging member is in a predetermined position, preferably distal of the cutter. Thereby, out of sequence operation, e.g., premature cutting of the tissue before the tissue engaging member is in position, is prevented.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention relates to the field of medical instruments, and more particularly, to a device for sampling tissue.  
         [0003]     2. Description of Related Art  
         [0004]     Tissue coring devices, e.g., punches, as well as other devices for sampling tissue, such as for biopsies, are used in many surgical applications. For example, in order to perform proximal anastomosis of a bypass graft on to the aorta, it is essential to perform an aortotomy. In such a procedure, a punch is passed through an opening created in the aorta by the punch or a separate instrument. Typically, the punch employs a device to retain the tissue to be cut by the coring knife of the punch such that, following the cut, the excised tissue is retained by the punch. A clean cylindrical aortotomy of the right size is essential to the success of the procedure. Moreover, the aortotomy should be free of tissue damage and embolic events. An embolic event can occur if the donut, i.e., the excised tissue, is lost in the body. The donut can then become an embolus that can travel in the bloodstream until it reaches a constricted region where it blocks blood flow.  
         [0005]     Such a scenario can occur when the coring knife of the punch is used out-of-sequence. For example, where the coring knife is used to core or sample the tissue prior to deployment of a tissue retention device, the retention device can then deployed after the complete coring, pushing the cut donut into the blood stream. The out-of-sequence scenario can be caused by the surgeon&#39;s unfamiliarity with the device or procedure or a simple mental lapse, for example. Furthermore, out-of-sequence use of the punch can result in damage to the instrument and/or to the surrounding tissue.  
         [0006]     Other problems with conventional devices occur where the coring knife is exposed and is damaged during use. A damaged coring knife is undesirable as it produces unreliable aortotomies. In addition, an exposed coring knife can damage the sealing device that may be used in conjunction with the punch. When used in aortotomy, a sealing device maintains a hermetic seal with the aorta after the aortotomy is formed, preventing excessive blood loss. It is known to use a cap to protect the coring knife when it is not being used, as well as during insertion of the punch into the handle. The cap is small, however, and can be dropped easily, as well, potentially damaging the coring knife.  
         [0007]     Another weakness of the prior art is that it is possible with conventional devices to damage the aorta or other organ due to “back-walling,” which occurs where the coring knife strikes the tissue behind the tissue which is desired to be cut. Accordingly, there is a need for a device for sampling or coring tissue that addresses the above and other issues.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     The present invention addresses the shortcomings of the prior art by providing an improved device for sampling or coring tissue. The device is suitable for use with essentially any type of tissue, such as tissue from the aorta, intestines and veins. Generally, the device is suitable for any biopsy or for the cutting and retrieval of tissue from any tissue structure. The device has a robust design that improves safety by positively securing the cut tissue or donut, while also providing a means to prevent out-of-sequence operation. Furthermore, the device can provide positive sensory feedback, e.g., auditory, visual, and/or tactile, regarding the configuration of the device. In one embodiment, the device has a recessed cutter or coring knife to prevent incidental damage and to eliminate the need for an additional cap.  
         [0009]     According to the present invention, an apparatus for sampling tissue includes a tissue engaging for engaging and retaining a sample of a tissue structure, and a cutter surrounding the tissue engaging member. The tissue engaging member and cutter are both operative to translate longitudinally with respect to one another, and a mechanism prevents the cutter from moving distally, the mechanism being released and the cutter freed to move distally when the tissue engaging member is in a predetermined position, preferably distal of the cutter. Thereby, out of sequence operation, e.g., premature cutting of the tissue before the tissue engaging member is in position, is prevented.  
         [0010]     Alternately or additionally, distal movement of the tissue engaging member to a first predetermined position initiates distal movement of the cutter to a second predetermined position, proximal of the tissue engaging member.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     These and other features, advantages and benefits will be made apparent through the following descriptions and accompanying figures, where like reference numerals refer to the same features across the various drawings.  
         [0012]     FIGS.  1 ( a )-( g ) illustrate a sequence of use of a tissue sampling device according to the present invention;  
         [0013]      FIG. 2  illustrates a deployment sequence of a cutter and retention member of a tissue sampling device according to the present invention;  
         [0014]      FIG. 3 ( a ) illustrates a schematic view of a tissue sampling device in a reset position according to the present invention;  
         [0015]      FIG. 3 ( b ) illustrates a schematic view of a tissue sampling device with its retention member deployed according to the present invention;  
         [0016]      FIG. 3 ( c ) illustrates a schematic view of a tissue sampling device with its retention member and cutter deployed according to the present invention;  
         [0017]      FIG. 4 ( a ) illustrates a profile view of a tissue sampling device with its retention member and cutter deployed according to the present invention; and  
         [0018]      FIG. 4 ( b ) illustrates a cross-sectional view of the tissue sampling device of  FIG. 4 ( a ) according to the present invention.  
         [0019]     FIGS.  5 ( a )- 5 ( d ) illustrate the sequence of use of a tissue sampling device according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIG. 3 ( a ) illustrates a schematic view of a tissue-sampling device in a reset position according to one embodiment of the present invention. In the reset position of the device  100 , the retention member  130  and cutter  120  are disposed within the outer sleeve  110  of the body  300 . The device includes various actuating mechanisms, including a plunger  310  that, together with a control assembly  320 , controls the translation of the retention member  130 . The control assembly  320 , shown schematically, preferably includes mechanisms for controlling the translation and rotation of the retention member  130  and cutter  120 . Specifically, a spring  322  biases a block  324  rearward or proximally. The block  324  is linked to a shaft  360  on which the retention member  130  is carried. The plunger  310  includes a push-button spring lock mechanism  312 , shown in  FIG. 3 ( b ), and is connected to the shaft  360 .  
         [0021]     In operation, the plunger  310  is depressed and moves the block  324 , shaft  360  and retention member  130  distally against the force of the compressed spring  322 . When the block  324  moves a predetermined distance in a distal direction, the block  324  forces a distal end of a lever  326  to move clockwise until the block  324  passes the lever  326 , at which time a proximal face of the block  324  opposes a distal portion of the lever  326 , preventing the block  324  from retracting proximally. The lever  326  is preferably pivotally mounted and spring-biased in the counterclockwise direction.  
         [0022]     With the lever  326  opposed to block  324 , the retention member  130  protrudes from the body  300 , locked against proximal movement. Significant further movement in the distal direction is resisted by spring  322 , which is preferably configured to be nearly at its fully compressed position when block  324  is distal to lever  326 .  
         [0023]     Since rotation of the block  324  is not precluded by contact with the lever  326 , rotational movement of the shaft  360  and retention member  130  is allowed. In particular, rotational movement of the plunger  310  results in rotational movement of the shaft  360  and retention member  130 . The retention member  130  can thus be rotated to engage the tissue to be cored. Once the surgeon visually observes that the retention member  130  has engaged the tissue, the surgeon advances knob  328  distally to deploy the cutter  120 . Distal movement of the knob  328  advances the stop key  341 , gears  340  and  342 , and flange  334  distally against the urging of spring  344 . Flange  334  is operatively connected to the cutter  120 , and therefore the cutter is protruded from the body  300 . Flange  334  is advanced until it is secured against proximal retraction by spring-biased lever  332 . Lever  332  is prevented from moving into an engaged position by projection  333  before the distal extension of block  324 . Accordingly, the cutter cannot be latched in a deployed position until the tissue retention member  130  is in a range of distal positions, i.e., in advance of the cutter  120 . Once the cutter is deployed, the surgeon rotates a knob  305  that causes gears  306  and  307  to rotate. The gears  306  and  307  may have a 3:1 ratio, for example. Rotation of the gear  307  causes rotation of shaft  330 .  
         [0024]     As the block  328  moves distally, it contacts a proximal portion of the lever  326 , causing the distal portion of the lever  326  to rotate clockwise to a position where the distal portion of the lever  326  does not contact the block  324 , as shown in  FIG. 3 ( c ). Free from the restraint of lever  326 , spring  322  urges block  324  and retention member  130  proximally. Therefore, the tissue captured by the retention member would be drawn into the body  300  once severed by the cutter  120 . Additionally, as block  328  rides along the top portion of lever  326 , a lower portion of lever  326  engages any of one or more slots  327  disposed on shaft  360 , thereby preventing any rotational movement of shaft  360  and retention member  130 .  
         [0025]     Gears  340 ,  342  are positioned distally within control assembly  320  to control the movement of cutter  120 . Gear  340  is slidably mounted onto shaft  330  such that as knob  305  is rotated, gear  340  rotates. Gear  342  is slideably disposed on shaft  360 , and is engaged with gear  340 . Gear  342  in turn is connected directly to flange  334 , which is connected to the cutter  120  through a shaft  370 . Shaft  370  may be mounted coaxially outside the shaft  360 . The proximal end of gear  340  is attached to a key  341 , which is disposed about shaft  330 . At least a portion of key  341  is disposed between gear  342  and flange  334 . As gear  340  moves distally due to the rotation of knob  305 , key  341  ensures that gear  342  and flange  334  also move distally. Therefore, by turning knob  305 , the surgeon both advances and rotates the cutter  120  to core the tissue engaged by the retention member  130 .  
         [0026]     As is shown in  FIG. 3 ( a ) and described, supra, lever  332  is initially biased against a lower portion of flange  334 . With lever  326  in the position shown in  FIG. 3 ( c ), only the tissue itself prevents the retention member  130 , the shaft  360  and block  324  from retracting proximally into the body  300  under the urging of spring  322 . Therefore, when the cutter  120  completes the coring operation, the retention member  130 , the shaft  360  and block  324  all retract automatically, capturing the tissue donut  195  within the body  300 . Further, block  324  contacts projection  333  provided on lever  332 , causing the lever  332  to pivot downward and out of engagement with the proximal side of flange  334 . Subsequently, flange  334  and cutter  120  retract into the body under the urging of spring  344 . The proximal movement of the cutter  120 , flange  334 , gears  340 ,  342 , and key  341  may be limited by a fixed stop  343  provided within control assembly  320 .  
         [0027]     The return to the reset position proximally within body  300  provides a visual confirmation to the surgeon that the donut  195  has been captured and the coring is complete. The block  328  may protrude outside of the control assembly  320  so that the surgeon can visually ascertain the movement and position of the block  328  and, consequently, the cutter  120 . That is, if the block  328  is positioned at a distal location, the cutter  120  is deployed, and if the block  328  is positioned at a proximal location, the cutter  120  is withdrawn. The distal portion of the device  100  may be disassembled and sterilized for reuse, if desired.  
         [0028]      FIG. 4 ( a ) illustrates a profile view of a tissue-sampling device with its retention member  130  and cutter deployed according to a second embodiment of the present invention.  FIG. 4 ( b ) illustrates a longitudinal cross-section of  FIG. 4 ( a ). The device  400  includes a body  430  having a distal portion  432  that is removable from a control assembly  436  via a handle release  434 . Actuating mechanisms include a perforated or slotted wheel  440  that translates axially and rotates, to engage and rotate, respectively, the cutter  120 . Knob  450  translates axially and rotates to control translation and rotation, respectively, of the retention member  130 .  
         [0029]     In a reset position, the knob  450  is positioned proximally from the control assembly  436 , preferably further than shown. In particular, a shaft  460  is linked to the knob  450 , detent structure  462 , and retention member  130 . When the knob  450  is pushed toward the control assembly  436 , i.e., moved distally, against the force of a spring  422 , a pivoting lever  464 , which is spring biased in the clockwise direction, engages in a detent  466  of the detent structure  462 . This locks the retention member  130  in the deployed position to prevent further axial movement. The engagement of the lever  464  in the detent  466  does not prevent rotation of the retention member  130  in response to rotation of the knob  450 . One or more gear teeth or fins  465  are provided about the shaft  460 . A corresponding cutout in the proximal end wall  467  of the control assembly  436  allows the shaft  460  and the retention member  130  to be withdrawn proximally and locked against rotation. The cutouts may also extend distally from the end wall  467  to resist rotation of the shaft  460  for a longer range of axial motion.  
         [0030]     Perforated wheel  440  is shown in a distal position. In this position, gears  474  engage to allow the perforated wheel  440  to rotate the shaft  472  and ultimately the cutter  120 . Additionally, when pressed distally against a proximal bias, in this case a coil spring, the shaft  472  is pressed distally to expose the cutter  120 . Pivoting lever  470  is spring biased clockwise. In the reset position, lever  470  will not hold the perforated wheel  440  forward if it were advanced. However, when shaft  460  is engaged with latch  464  in a deployed position, proximal protrusion  484  constrains the movement of lever  470 , preventing full rotation. Thereafter, when perforated wheel  440  is pressed distally, lever  470  engages a circumferential ridge  480  in the interior of perforated wheel  440 . Once engaged, lever  470  prevents proximal movement of the perforated wheel  440 , while allowing it to rotate. The shaft  472  may be coaxially outside the shaft  460  that carries the retention member  130 .  
         [0031]     With the retention member  130  deployed, the surgeon pierces and engages the tissue with the retention member  130 . The surgeon may rotate the knob  450  to cause the coil-shaped retention member  130  to securely engage the tissue. If the retention member  130  comprises a barb, hook or other structure that does not require rotation to engage the tissue, the device  400  need not have that capability. Moreover, as mentioned, the entire device  400  can be rotated manually by the surgeon to rotate the retention member  130 .  
         [0032]     The distal movement of the knob  450  to extend the retention member  130  causes a raised structure  476  associated with the shaft  460  to contact the lever  470 . Thus, lever  470  to pivots counterclockwise to the position shown in  FIG. 4 ( b ), where it disengages from the perforated wheel  440 . This permits the surgeon to manually move the perforated wheel  440  distally to extend the cutter  120  from the body  430  of the device  400 . Therefore, the cutter  120  cannot be deployed until after the retention member  130  is deployed. When the perforated wheel  440  is moved distally, a portion of the perforated wheel  440  contacts a portion of the lever  464 , such as the upper portion which extends radially outward and distally, to move it counterclockwise, causing the lever  464  to disengage from the detent  466  in the detent structure  462 . As a result, the retention member  130  is urged back proximally by the spring  422 . However, the retention member  130  with the engaged tissue cannot move proximally under the spring bias because of the resiliency of the tissue. Subsequently, the surgeon manipulates the cutter  120 , e.g., via the perforated wheel  440 , to core and sample the tissue. The perforated wheel  440  is linked via gears  474  to the shaft  472  that controls the cutter  120 .  
         [0033]     As the tissue is being cored, the resiliency in the tissue allows limited proximal movement of the retention member influenced under spring  422 . In a preferred embodiment, once so moved, fins  465  will engage slots  467  to prevent rotation of the shaft  460 . Once the tissue is cored, the retention member  130  retracts proximally into the cutter  120  and body  430 , and fins  465  pass through the corresponding cutout in the end wall  467 . The shaft  460  and consequently the knob  450  are also retracted proximally, providing a visual confirmation to the surgeon that the donut  195  has been captured and the coring is complete. A protrusion  482  on the shaft  460  urges the lever  470  counterclockwise as it passes, freeing the perforated wheel  440  to retract distally, thereby allowing the cutter  120  to retract as well.  
         [0034]     Thus, distal movement of the knob  450  results in locking of the retention member  130  in the deployed position and unlocking of the cutter  120 . Subsequent distal movement of the perforated wheel  440  results in unlocking the retention member  130 . Additional locking mechanisms may be provided as desired, e.g., to maintain the cutter  120  locked in the non-deployed position while the retention member  130  is locked in the deployed position.  
         [0035]     Referring now to FIGS.  1 ( a )- 1 ( g ) and the graph of  FIG. 2 , shown is a sequence of operation for a cutter according to the present invention. Each  FIG. 1 ( a )- 1 ( f ) corresponds approximately to each instant in time t_ 1  through t_ 6 , respectively, while  FIG. 1 ( g ) corresponds to instant t_ 8 . In the graph of  FIG. 2 , the horizontal axis illustrates time, which is not necessarily continuous, and the vertical axis illustrates a relative position of the cutter  120 , retention member  130  and outer sleeve  110  of the body with respect to the tissue wall  190 . In the present example, the units on the vertical axis may be millimeters (mm). A position less than zero on the vertical axis indicates that the outer sleeve  110 , the cutter  120 , or the retention member  130  is outside the surface, or adventita  290 , of the tissue wall  190 , whose position is represented by the line  290 . The inner surface of the tissue wall  190 , or intima  295 , presumes a wall thickness of 5 mm, solely for the purposes of illustration. The position of the outer sleeve  110  is represented by line  210 , while the position of the retention member  130  is represented by line  230 , and the position of the cutter  120  is represented by line  220 . The reset configuration of the device in  FIG. 1 ( a ) is shown at time t_ 1  in  FIG. 2 . In this illustrative example, the cutter  120  is recessed 4 mm inside the end of the outer sleeve  110 , while the retention member  130  is recessed 2 mm inside the end of the outer sleeve  110 . The tissue  190  is 14 mm beyond the end of the outer sleeve  110 .  
         [0036]     The configuration shown in  FIG. 1 ( b ) corresponds with time t_ 2  in  FIG. 2 . Here, the retention member  130  protrudes or extends beyond the end of the outer sleeve  110 , e.g., at a position 7 mm past the outer sleeve  110 . The cutter  120  has not moved during the time between t_ 1  and t_ 2  when the retention member  130  initially protrudes past the end of the outer sleeve  110 . However, following time t_ 2 , the cutter  120  begins to move distally until it protrudes to its fullest extent, e.g., 1 mm past the outer sleeve  110 , at time t_ 3 , as shown in  FIG. 1 ( c ). The retention member  130  also continues to move distally between t_ 2  and t_ 3  until it protrudes fully, e.g., 12 mm past the outer sleeve  110 .  
         [0037]     At time t_ 3 , the surgeon may advance the device  100  toward the tissue  190  until the tip of the retention member  130  pierces the tissue,  FIG. 1 ( d ). The coil-like retention member  130  may also be rotated at this time to further engage and draw the tissue toward cutter  120 . If the retention member  130  is not mounted for rotation with respect to the body of the device, the retention member  130  can be rotated by having the surgeon manually rotated the entire device. If the retention member  130  is mounted for rotation with respect to the body of the device, the retention member  130  can be rotated by rotating or otherwise moving an actuating mechanism, as described supra. Optionally, the retention member may comprise a barb, hook, scoop or other structure that does not require rotation to engage the tissue.  
         [0038]     At time t_ 3 , when the retention member  130  protrudes fully, it may be locked to prevent further axial movement, while permitting the retention member  130  to rotate. Additionally, the cutter  120  may be locked to prevent both translation and rotation with respect to the retention member and/or the outer sleeve  110 . Between time t_ 3  and t_ 4 , the retention member  130  is rotated further to draw the tissue closer to the cutter  120 . At time t_ 4 , the tissue  190  contacts the cutter  120 ,  FIG. 1 ( e ), and rotation of the cutter  120  may be allowed, while the lock against translation is maintained. In particular, the surgeon rotates the cutter  120 , and simultaneously advances it, either manually or through an actuating mechanism, until it cores the tissue  190 ,  FIG. 1 ( f ). The retention member  130  secures the resulting tissue core, or donut  195 , to ensure it is not lost. In addition, a rotational lock on the retention member  130  may be engaged at this time, while any lock against translation has already been or is now disengaged to allow the retention member  130  to start to withdraw proximally, back into the outer sleeve, between time t_ 4  and t_ 5 .  
         [0039]     The retention member  130  may withdraw gradually by movement of an appropriate actuating mechanism. Alternately, the actuating mechanism may have a spring mechanism that exerts a force on the retention member  130  to cause the retention member  130  to snap back when the tissue is cored. The retention member  130  is withdrawn at least into the interior of the cutter  120  and eventually into the interior of the device body.  
         [0040]     At time t_ 6 , the intima of the tissue donut  195  is even with the cutter  120  and thus is fully cored as is represented by the intersection of lines  290  and  210 . Withdrawal of the retention member  130  and the donut  195  continues through time t_ 6  up until time t_ 7  while the cutter  120  remains deployed. At time t_ 7 , when the retention member  130  is fully withdrawn, withdrawal of the cutter  120  begins. At time t_ 8 , the cutter  120  is also fully withdrawn into the outer sleeve  110 ,  FIG. 1 ( g ). If the retention member  130  retracts under the force of a spring mechanism when the donut  195  is free from the surrounding tissue  190 , the time between t_ 6  and t_ 7  is essentially zero.  
         [0041]     Preferably, when using the device, the retention member  130  should be at a position distal to the cutting knife  120  and fully deployed prior to the exposure of the cutting knife  120  beyond the outer sleeve  110 . This ensures that the retention member  130  is fully deployed into the tissue  190  before the tissue  190  contacts the cutter  120 . This configuration is depicted in  FIG. 1 ( e ), where the cutter  120  meets the tissue only after the retention member  130  has pierced and at least a portion of the retention member  130  tissue has passed into the tissue. At this point, a proximal spring bias may be applied to the retention member  130 , and additionally, the retention member  130  may be prevented from rotating with respect to the tissue  190 . Thus, only the cutter  120  is allowed to rotate, thereby coring the tissue as seen in  FIG. 1 ( f ). When the full wall thickness of the aorta or other tissue  190  is cut, the retention member  130  retracts inside the lumen of the cutter  120  along with the captured donut  195 . At this time, the cutter  120  may be retracted so that both the cutter  120  and the retention member  130  retract well within the atraumatic outer lumen or sleeve  110  of the device body at time t 8 , as in the reset position of  FIG. 1 ( a ). Thus, the device  100  is reset.  
         [0042]     Therefore, according to the present invention, the surgeon cannot core or even cut the tissue  190  prior to deploying the retention device  130 , thereby preventing use of the device  100  out-of-sequence.  
         [0043]     Referring now to FIGS.  5 ( a )- 5 ( d ), illustrated is a sequence of use of an example tissue-sampling device with a fixed cutter according to another embodiment of the present invention. A schematic view of the device  500  includes a body  510 , a cutter  520 , a retention member  530 , and an actuating mechanism  560 . The actuating mechanism  560  includes a chamber  532  in which a spring  534  is provided. The chamber is closed at its distal end, in this case by a fixed washer  533 . Spring  534  extends between the fixed washer  533  and a movable plate  538  at the proximal end of the chamber  532 . Plate  538  is fixed to the retention device  530  via shaft  536 .  
         [0044]     Further, plate  538  may be provided with one or more tabs  562 , which project into one or more slots  564  provided along the length of the chamber  532 . As a result, the plate  538  and the retention member  530  are constrained to rotate with the chamber  532 . Tabs  562  and/or slots  564  may also extend to the exterior of the body  510 , to provide a visual indication to the surgeon of the retention member position. Alternately or additionally, the body  510  may be mad transparent in whole or in part in order to make the tabs  562  visible to the surgeon.  
         [0045]     The retention member  530  protrudes distally beyond the cutter  520 . When the retention member  530  is a coil or other design that requires rotation, the surgeon rotates the chamber  532 , or the body  510  if fixed to the chamber  532 , to engage the tissue  525 . Arrow  550  illustrates an example direction of rotation. Rotation continues until the retention member  530  engages the tissue and the cutter  520  begins to contact the tissue  525  ( FIG. 5   b ). Furthermore, the actuating mechanism  530  may be actuated so that the retention member  530  is fed further distally while the spring  534  is compressed ( FIG. 5   c ).  
         [0046]     Once the cutter  520  contacts the tissue  525 , the cutter can be rotated to core or otherwise cut the tissue. The tissue  525  is urged proximally against the cutter  520  by the force of the spring  534  that acts on the retention member  530  ( FIG. 5   c ). When the tissue  525  has been cored, the retention member  530  with the tissue donut  527  secured thereon is free to snap back proximally under the force of the spring  534  ( FIG. 5   d ). The retention member  530  also retracts, at least partly, in the cutter  520 .  
         [0047]     A lever, knob, or other equivalent means may also be provided for positioning and optionally, locking, the retention member  530  in the fully protruding position of  FIG. 5   c , where it protrudes past the cutter  530  to engage the tissue  525 . Once the tissue  525  is engaged, the retention member  530  can be unlocked, at which time the tissue  525  is urged proximally so that the cutter  520  contacts the tissue  525 , as shown in  FIG. 5   b . A proximal user-operable portion may be provided for rotating the cutter  520  as well to allow the cutter  520  to cut the tissue  525 .  
         [0048]     When the retention member  530  is a barb or other element that does not require rotational movement to engage the tissue  525 , the retention member  530  can be mounted translation only with respect to the body  510 . A lever, knob, or other equivalent means may again be provided for locking or otherwise positioning the retention member  530  in the position of  FIG. 5   c . Once the tissue is engaged, the retention member is unlocked and urged proximally so that the tissue  525  is urged against the cutter  520 , as shown in  FIG. 5   c . Again, a proximal user-operable portion may be provided for rotating the cutter  520  to allow the cutter  520  to cut the tissue  525 .  
         [0049]     Advantageously, in the approach of  FIGS. 5   a - 5   d , the device  500  is simplified in construction since the cutter  520  can be fixed against translation relative to the body  510 . It is also possible for the cutter to be fixed against rotation with respect to the body  510 . In this case, the cutter  520  can be rotated by rotating the entire body  510 . At least part of the retention member  530  always protrudes distally past the cutter  520 . A protective cap may be employed when the device  500  is not in use, notwithstanding the disadvantages of a cap as described, supra.  
         [0050]     Specific construction details that are not shown are believed to be within the purview of those of ordinary skill in the art. Moreover, note that any portion or all of the deployment sequence of the device, such as movement of the cutter  120  or retention member  130 , can be automated using appropriate sensors and motorized actuating mechanisms.  
         [0051]     The present invention has been described herein with reference to certain preferred embodiments. These embodiments are offered as illustrative, and not limiting, of the scope of the invention. Certain modifications or alterations may be apparent to those skilled in the art without departing from the scope of the invention, which is defined by the appended claims.