Patent Publication Number: US-7905892-B2

Title: Suture cutter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 09/940,384, filed Aug. 27, 2001, now U.S. Pat. No. 6,733,509, which also claims the benefit of U.S. Provisional Application Serial No. 60/228,267, filed Aug. 25, 2000, now abandoned, the entirety of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to suturing incisions, and more specifically, to the use of sutures for closing incisions in vessels and organs within a body, and cutting the ends of a suture once it has drawn together tissue portions. 
     2. Description of the Related Art 
     Surgeons frequently encounter the need to close incisions, wounds, or otherwise join tissue portions with a suture. After passing the suture through the tissue portions, the surgeon must tie the suture to draw the tissue portions together and prevent them from separating. When sutures are tied in a region having restricted access, such as the end of a tissue tract leading to an artery, the surgeon is presented with special challenges. Typically, the knot is formed outside the patient and then is pushed towards those tissue portions to be joined together. 
     Once a knot has been positioned against tissue portions such that they are securely fastened together, however, the surgeon must cut back the ends of the suture. This procedure can be difficult when using conventional instruments, particularly where access is limited. A reliable suture cutting procedure is needed whereby a surgeon can rapidly and accurately trim back the strands from a knot. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, there is provided a method of severing end portions of a suture which extend from a sutured tissue portion. The method includes holding the suture end portions, and positioning an elongate member such that a distal portion of the elongate member is adjacent the sutured tissue portion. The method further includes positioning the suture end portions within at least one receptacle disposed at the distal portion of the elongate member, and severing the suture while the suture end portions are within said at least one receptacle by activating a severing element disposed adjacent the receptacle. 
     According to another aspect of the invention, there is provided an apparatus which includes a receptacle for juxtaposing portions of a suture to be connected to each other. The apparatus further includes a collar configured to surround the juxtaposed portions and a compression element positioned to compress the collar against the suture portions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-7  illustrate a first suture cutter embodiment, in which: 
         FIGS. 1 and 2  are end views of the suture cutter; 
         FIGS. 3A ,  4 A, and  5 A are side elevation views of the suture cutter; 
         FIGS. 3B ,  4 B, and  5 B correspond to the side elevation views of  FIGS. 3A ,  4 A, and  5 A, and show the suture cutter being used with a suture; 
         FIG. 6  illustrates the suture cutter pushing a knot into a patient through a catheter sheath introducer (CSI); 
         FIG. 7A  shows the suture ends drawn across the suture cutter in preparation for cutting the suture ends; 
         FIG. 7B  illustrates the suture ends being cut as the suture cutter is rotated about its longitudinal axis, thereby forcing the suture ends against a cutting element; and 
         FIG. 7C  shows the suture cutter and the suture ends after the suture ends have been cut. 
         FIGS. 8-15  illustrate a second suture cutter embodiment, in which: 
         FIGS. 8 and 9  show perspective views of the distal end of the suture cutter; 
         FIGS. 10 and 11  show side views of the distal end of the suture cutter; 
         FIG. 12  shows the full length of the suture cutter including the handle; 
         FIGS. 13 and 14  show the suture cutter with a suture, before and after the suture is thermally cut, respectively; and 
         FIG. 15  shows the suture cutter being used to twist the suture ends. 
         FIGS. 16-24  illustrate a third suture cutter embodiment, in which: 
         FIG. 16  shows a first cylindrical member, which has one end that acts like a knot pusher and another end that includes blade members for cutting suture material; 
         FIG. 17  is a view of the knot pusher end of the first cylindrical member; 
         FIG. 18  is a view of the blade member end of the first cylindrical member; 
         FIG. 19  shows a second cylindrical member, which at one end has an extension member for rotating the second member, and at the other end has blade members for cutting suture material; 
         FIG. 20  is a view of the blade member end of the second cylindrical member; 
         FIG. 21  shows the assembled suture cutter, in which the second cylindrical member has been slid over the first cylindrical member; 
         FIG. 22  shows the blade member end of the assembled suture cutter; and 
         FIGS. 23 and 24  show the suture cutter with a suture, before and after the suture is cut, respectively, in which the suture is cut by rotating the second cylindrical element with respect to the first cylindrical element. 
         FIGS. 25-28  illustrate a fourth suture cutter embodiment, in which: 
         FIG. 25  shows an expanded, isometric view of the distal end of the suture cutter; 
         FIG. 26  is a cutaway which shows a welding element and a cutting element housed inside a compression tip for pressing a suture cylinder against ends of a suture; 
         FIG. 27  shows a lump of suture material (which functions as a knot) which is formed when the suture and the suture cylinder are acted upon by the suture cutter; 
         FIG. 28  shows another expanded, isometric view of the distal end of the knot pusher; 
         FIGS. 29-33D  illustrate a fifth suture cutter embodiment, in which: 
         FIG. 29  is a perspective view showing how the suture cutter captures ends of a suture with a lasso; 
         FIG. 30  is a cross sectional view of the cutter as it is configured in  FIG. 29 ; 
         FIG. 31  shows the lasso having drawn the suture ends though and out of a hypotube; 
         FIG. 32  is a cross sectional view of the cutter as it is configured in  FIG. 31 ; 
         FIGS. 33A-D  illustrate sequentially how a suture collar positioned in the cutter is used to form a fused portion in the suture which then acts like a knot. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Preferred embodiments of the invention are shown and described with respect to the accompanying figures. The suture cutters herein may be used to cut the free ends of a suture extending from a knot that has closed up an incision within a patient (e.g., an incision in an organ or a vessel), or more generally, two tissue portions that have been drawn together. 
     An end view of a first suture cutter embodiment is shown in  FIG. 1 . The suture cutter comprises an elongated, rod-shaped member  100  which includes an elongate recess  106  that extends longitudinally along opposed sides of the member  100  and transversely across the distal end  112  of the member  100 . The recess  106  thus includes a first longitudinal recessed portion  104 , a transverse recessed portion  110  at the distal end  112  of the elongate member  100 , and a second longitudinal recessed portion  116  shown in  FIG. 2 , in which the member  100  has been rotated 180 degrees about its longitudinal axis with respect to its orientation in  FIG. 1 . The second recessed portion  116  is somewhat shallower and narrower than the recessed portions  104 ,  110 . The longitudinal portions  104 ,  116  gradually taper from the distal end  112  of the elongate member  100  into the exterior surface of the member  100 . The recessed portions  104 ,  110  and  116  are shaped as channels having semi-circular or semi-elliptical cross sections, such that ends extending from a surgical knot can be effectively guided within the recessed portions  104 ,  116  and the knot can be pushed by the recessed portion  110  of the member  100 . 
     An angled recess  120  extends between the first and second recessed portions  104 ,  116  along a side of the elongate member  100  at an angle relative to the longitudinal axis of the member  100 . The recess  120  intersects the recessed portion  104  near the juncture of the portion  104  with the transverse portion  110 . The recess  120  intersects the portion  116  at a location which is a significant distance proximal of the distal end  112 . As indicated in  FIGS. 1 and 2 , a cutting element  124  is provided at the end of the recess  120  that is next to the transverse portion  110 . The cutting element  124  comprises a cutting edge that is directed proximally and is formed by a recess  121  that extends generally orthogonal to the recess  120  and between the recess  120  and the recessed portion  116 . The recesses  120  and  121 , as well as the cutting element  124  are more clearly shown in  FIGS. 3A ,  4 A, and  5 A, which are oriented at 120 degrees (about the longitudinal axis) with respect to each other. 
       FIGS. 3B ,  4 B, and  5 B show the member  100  used with a suture  140  which has been tied into a self cinching knot  144 . The member  100  is oriented so that respective end segment portions  140   a ,  140   b  of the suture are disposed resting along and within the longitudinal recessed portions  104 ,  116 , respectively, with the transverse portion against the knot  144 . The knot  144  may be formed as described in Applicant&#39;s copending application entitled “Knot Pusher”, Ser. No. 09/571,759 filed on May 15, 2000 which is hereby incorporated by reference herein. In one embodiment, the suture  140  is a monofiliment suture having a diameter of about 0.010″. It may be introduced into the patient as described in U.S. Pat. No. 5,860,990 entitled “Method and apparatus for suturing” and Applicant&#39;s copending application Ser. No. 09/524,211 filed Mar. 13, 2000 entitled “Suturing device and method”, both of which are hereby incorporated by reference herein. As described in more detail in the aforementioned copending application entitled “Knot Pusher”, the practitioner may form a knot  144  utilizing a variety of knot tying techniques. One example is to tie two consecutive half hitches of the same orientation (e.g., two right hitches or two left hitches). One end segment of the suture  140  (e.g., the end segment  140   b ) remains loosely hanging off to the side while the practitioner pushes the distal end  112  of the elongate member  100  against the knot  144 , with the knot  144  in the recessed portion  110 . The member  100  fits snugly (e.g., 0.010″ clearance) within a catheter sheath introducer (CSI) which has been introduced through an external incision  174  in the skin of the patient. The knot  144  is pushed through the CSI  170 , as shown in  FIG. 6 . The other end segment  140   a  is held firmly in the hand of the practitioner. In this manner, the two half hitches are pushed towards and up to an internal incision in the patient. Next, a single half hitch of the same type is formed (e.g., if two right half hitches were initially used, then a single right half hitch is formed) and pushed towards and up to the internal incision with the member  100 , but with the practitioner now holding both end segments  140   a ,  140   b  securely in one hand. All consecutive loops are advanced in an analogous fashion towards the internal incision and are likewise of the same type, except for the last loop. The last loop is a half hitch of the other type, e.g., if the previous loops were all right half hitches, then a left half hitch is used, thereby creating a square knot, i.e., a tightened knot. 
     As mentioned, other types of knots and knot tying approaches may be used to form a tightened knot. Once a tightened knot has been formed against the internal incision, the practitioner cuts both end segments  140   a ,  140   b  so that no strands are left dangling outside of the patient&#39;s external incision  174 . This is accomplished most easily by first removing the elongated member  100  completely from the patient while leaving the CSI  170  in place. The practitioner then pulls both end segments  140   a ,  140   b  taut and places both segments within the first longitudinal recessed portion  104 . The elongate member  100  is reintroduced into the patient through the CSI  170  and pushed towards the tightened knot (at the internal incision) until the distal end portion  112  of the elongate member  100  butts up against the tightened knot.  FIG. 7A  shows the relationship between the elongated member  100 , the suture  140 , and the tightened knot  144   a  at this point. Next, the practitioner rotates the elongated member  100  so that the suture  140  falls into the angled recess  120 , where the suture is contacted by the cutting element  124 , as shown in  FIG. 7B . While holding the suture end segments  140   a ,  140   b  taught, the practitioner continues to rotate the tubular member  100 , while pulling the member  100  proximally, the force of the cutting element  124  against the suture cuts both end segments  140   a ,  140   b , so that only short, stubby segments  140   c ,  140   d  of the suture remain joined to the tightened knot  144   a , as shown in  FIG. 7C . At this point the loose end segments  140   a ,  140   b  are removed from the patient, along with the CSI  170 . The external incision  174  is then sutured closed. 
     A second suture cutter embodiment  200  is shown in  FIG. 8 . A recessed, transverse, channel-shaped portion  204  at a distal end  202  of the suture cutter  200  extends from one side of the cutter  200  to the other. The portion  204  is configured for guiding suture strands and optionally for pushing knots. Two side resistive heater elements  210 ,  211  (e.g., copper) are located on either side of the suture cutter  200  within the channel-shaped portion  204  at respective ends thereof and about 1 cm longitudinally from the tip of the distal end of the cutter. The side resistive heater elements  210 ,  211  are electrically connected to respective electrically insulated lead lines  214   a ,  215   a  which pass through the cutter  200  and are visible through respective grooves  216   a ,  217   a . A centrally located resistive heater element  220  (shown in dashed lines), disposed in the center of the portion  204  at the tip of the distal end  202 , is likewise connected to an electrically insulated lead line  222   a  which is visible through a groove  224   a . The resistive heater element  220  resides within the cutter  200  near the recessed portion  204  and is not exposed to the outside environment.  FIG. 9  shows the cutter  200  rotated by 180 degrees about its longitudinal axis and illustrates that the resistive heater elements  210 ,  211  are electrically coupled to electrically insulated lead lines  214   b ,  215   b , respectively, which, together with lead lines  214   a ,  215   a,  complete the circuit through the resistive heater elements  210 ,  211 . Likewise, the centrally located resistive heater element  220  is electrically coupled to an electrically insulated lead line  222   b  which, with the lead line  222   a , form an electrical circuit. The lead lines  214   b,    215   b ,  222   b  are located in respective grooves  216   b ,  217   b ,  224   b . Side views of the second suture cutter embodiment  200  are illustrated in  FIGS. 10 and 11 . 
     A full length view of the suture cutter  200  is shown in  FIG. 12 . The suture cutter  200  includes a handle  230  at its proximal end. The handle  230  includes a three-position switch  234  coupled to an LED  238  which indicates whether the switch  234  is off, in the first on-position (for heating the centrally located resistive heater element  220 ), or in the second on-position (for heating the side resistive heater elements  210 ,  211 ). The handle  230  further includes a charging battery  242  (shown in dashed lines). The battery  242  supplies power to the resistive heater elements  210 ,  211 ,  220  as controlled by the switch  234 . 
     The suture cutter  200  may be used to push a knot in a fashion analogous to that of the first suture cutter embodiment described above. In particular, the recessed portion  204  may advantageously engage a knot which is then pushed by the practitioner through a CSI and towards an internal incision in a patient. Although a tightened knot may be formed, for example, by repeatedly pushing half hitches through the CSI as described above, the suture cutter  200  offers alternatives to this approach. For example, once a knot (or even crossed suture end segments) has been positioned just proximal to the internal incision, power may be supplied to the centrally located resistive heater element  220 . As illustrated in  FIG. 13 , this causes the element  220  to heat up. Sufficient heat is applied to plastically deform the suture material in the knot, by partially melting the suture material to join the end segments together. However, the heat is not so great as to sever the suture material. Next, the two end segments  140   a ,  140   b  of the suture  140  are held taut by the practitioner within the channel portion  204  so that they contact the resistive heater elements  210 ,  211 , respectively. Power is then supplied to the elements  210 ,  211  located on either side of the suture cutter  200 . Referring to  FIG. 14 , the resistive heater elements  210 ,  211  supply sufficient heat to cause the suture to be severed by melting, leaving short segments  140   c ,  140   d  of suture material adjoining the formed knot  250 . The end segments  140   a ,  140   b  and the suture cutter  200  can then be removed from the patient along with the CSI. 
     In an alternative method, the two end segments  140   a ,  140   b  may be held taut on respective sides of the suture cutter  200  by the practitioner, and the suture cutter  200  is pushed towards the internal incision. When the distal end  202  of the suture cutter  200  is near the internal incision, the suture cutter  200  is rotated about its longitudinal axis, so that the end segments  140   a ,  140   b  contact and twist about each other, as shown in  FIG. 15 . The practitioner may then apply power to the centrally located resistive heater element  220  to fuse the twisted suture and thereby prevent it from unraveling. The twisted suture effectively becomes a knot that is held together by fused suture material. The end segments  140   a ,  140   b  may be severed by melting using the side resistive heater elements  210 ,  211  as described previously. The end segments  140   a ,  140   b  and the suture cutter  200  can then be removed from the patient along with the CSI. 
     A third suture cutter embodiment is shown in  FIGS. 16-24 .  FIG. 16  shows a side view of a first cylindrical member  300  which at one end  302  includes a channel-shaped, recessed, transverse portion  304  for engaging and pushing a knot. An end view of the recessed portion  304  is shown in  FIG. 17 . At the other end  306  of the cylindrical member  300  is a dome shaped element  308  and four elongate blade members  310  which are circumferentially arranged around the cone-shaped element  308 . The end  306  of the cylindrical member  300  is seen more clearly in the end view of  FIG. 18 . Each of the blade members  310  projects longitudinally and terminates in a terminal end  314  which is rounded or otherwise sufficiently dull that it can not damage tissue. The blade members  310  have longitudinal edges  318 , disposed on the outward side thereof, which are sharp so that they can cut through suture material. 
     A second cylindrical tubular member  322 , illustrated in  FIG. 19 , has an interior passage sized so that it can be slid over the first cylindrical member  300 . At one end  324  of the second cylindrical member  322 , four longitudinally extending, elongate blade members  326  are provided which likewise terminate in flattened or rounded ends  330  that are dull. The blade members  326  have longitudinal edges  334  on the inward side thereof which are sharpened for cutting suture material. An end view of the second cylindrical member  322  is shown in  FIG. 20 . The cylindrical member  322  further includes a extension member  338  such as a hexagonal nut for rotating the second cylindrical member  322 . 
     The first and second cylindrical members  300 ,  322  are operably coupled to form a suture cutter  342  by sliding the second cylindrical member  322  over the first cylindrical member  300 , as shown in  FIG. 21 . The cylinders  300 ,  322  are rotatable relative to each other, and the blade members  310 ,  326  are configured so that the sharpened edge  334  of the blade members  326  and the sharp edges  318  of the blade members  310  pass immediately adjacent to each other during rotation. The tolerance between the blade members  310  and the blade members  326  is such that a suture extending between the blade members  310 ,  326  will be cut when the sharp edges  318  and  334  move past each other. An end view of the device  342  showing the blade members  310 ,  326  is shown in  FIG. 22 . The spaces between each pair of blade members  310  form respective slots for receiving a segment of suture. 
     In operation, the practitioner may use the end  302  of the first cylindrical member  300  to push a knot through a CSI towards an incision within a patient and form a tightened knot just proximal to the internal incision, as discussed in connection with the other methods disclosed herein. The device  342  is then retracted from the patient and turned around so that the end of the device with the blade members  310 ,  326  faces the CSI. Each of the end segments  140   a ,  140   b  of a suture is placed into different suture receiving slots formed by the blade members  310 , as illustrated in  FIG. 23 . The device  342  is reinserted into the patient and pushed through the CSI towards the knot (which is proximal to the internal incision) until the dome shaped element  308  contacts the knot. At this point, the practitioner rotates the second (outer) cylindrical member  322  with respect to the first (inner) cylindrical member  300  by grasping and turning the extension member  338 . As a result of this rotation, the suture material is cut between the blade members  310 ,  326 , as shown in  FIG. 24 . 
     A fourth embodiment is shown and described with respect to  FIGS. 25-28 . The device functions both as a knot former and suture cutter. An exploded, isometric view of the distal end  404  of the device is shown in  FIG. 25 . The two end segments  140   a ,  140   b  of a loop of the suture  140  pass through a suture collar or cylinder  408  which is preferably made of the same material as the suture itself, e.g., monofilament polypropylene. The two end segments  140   a ,  140   b  also pass through a welding element  412 , a cutting element  416 , a compression tip  420 , a lumen  422  in a multi-lumen inner tube  424 , a side hole  426  ( FIG. 28 ) in the inner tube, and a side slot  427  in an outer compression tube  428  which registers with the hole  426 . As illustrated most clearly in the cutaway of  FIG. 26 , the welding element  412  and the cutting element  416  are configured such that they make a good mechanical contact with the inside of the compression tip  420 . Prior to actuation, the suture collar  408  is placed within the welding element  412  so that the proximal end of the suture collar is flush with the proximal end of the welding element, whereas the distal end of the suture collar  408  extends slightly beyond the distal end of the welding element. 
     The compression tip  420  is integrally joined to the inner multi-lumen tube  424 , which may be the same material as the compression tip (e.g., plastic), or alternatively, the compression tip may be metal with the inner tube  424  being plastic. The outer compression tube  428  is slidably mounted on the inner tube  424  and the compression tip  420 . The compression tip  420  has a pair of relief slots which allow its distal end portion to flex inwardly. When the outer compression tube  428  is slidably forced over the compression tip  420 , the compression tip flexes and presses the suture collar against the end segments  140   a,    140   b . The suture collar  408  and the end segments  140   a ,  140   b  may then be fused together by activating the welding element  412  to apply heat to the suture collar  408 . Sufficient heat is applied by the welding element  412  to plastically deform the collar and partially melt the suture material to cause the suture ends and suture collar to fuse together. The heat, however should not be so great as to sever the suture. Such fusion forms a bulb or fused mass  430  in the suture  140  which effectively acts as a knot, as shown in  FIG. 27 . The end segments  140   a ,  140   b  proximal to the suture collar  408  may then be severed from the suture collar by activating the cutting element  416  to apply sufficient heat to the suture ends so that they are severed. The cutting element  416  is spaced proximally from the suture collar so that such cutting leaves behind short, stubby segments  140   c ,  140   d  of suture material attached to the mass  430  (see  FIG. 27 ). The welding element  412  and the cutting element  416  comprise resistive elements that generate heat when electrical current is supplied. In the case of the welding element  412 , heat is transferred to the suture collar  408  and the end segments  140   a,    140   b , so that the suture cylinder and the suture strands meld or fuse together. On the other hand, the heat applied by the cutting element  416  to the end segments  140   a ,  140   b  is sufficient to melt through the strands. After the welding element  412  and the cutting element  416  have been activated in turn and the mass  430  is formed, the suture cutter  400  may be cleaned and reused or simply discarded in favor of a new suture cutter. 
     Electrical current is supplied to the welding element  412  and to the cutting element  416  through respective pairs of lead lines (not shown), which pass through lumens  432 ,  434  in the inner extrusion tube  424  and lumens  436 ,  438  in the compression tip  420 . The lumens  436 ,  438  are shown in  FIG. 28 . When the inner extrusion tube  424  and the. compression tip  420  are joined during the fabrication process, the lumens  432 ,  434  are aligned with the lumens  436 , 438 , respectively, so that the lumens  432 ,  436  form one continuous lumen, as do the lumens  434 ,  438 . The lumen pair  432 ,  436  may be used to carry lead lines to the welding element  412 , whereas the lumen pair  434 ,  438  may be used to carry lead lines to the cutting element  416 . (The lumen  422  in the inner extrusion tube  424  and a lumen  446  in the compression tip  420  are used to receive the end segments  140   a ,  140   b .) A power supply (not shown) connected to the lead lines may be advantageously programmed so that the welding element  412  and the cutting element  416  are supplied with the appropriate amount and duration of current. 
     The end segments  140   a ,  140   b  may be loaded into the suture cutter  400  by drawing them through the suture collar  408  (which is surrounded by the welding element  412 ), the cutting element  416 , the compression tip  420 , the lumen  422  in the inner extrusion  424 , the hole  426  in the inner extrusion  424 , and the slot  427  in the outer compression tube  428 . For this purpose, a suture leader comprising a wire  440  having a grasping portion  441  (see  FIG. 25 ) at its distal end for holding the end segments  140   a ,  140   b  may be used, such as that described in Applicant&#39;s copending Application Ser. No. 09/571,759 entitled “Knot Pusher”, filed on May 15, 2000. The wire  440  is passed through the slot  427  and is pushed distally until the grasping portion exits the suture collar  408 . The end segments  140   a ,  140   b  are then inserted into a loop of wire at the grasping portion to secure the segments to the wire  440 . The wire is then retracted back through the distal end  404  of the suture cutter  400 . The slot  427  may be 1-2 cm in length and is aligned with the hole  426 , so that when the outer compression tube  428  is urged forward (say, 5 mm) to compress the compression tip  420 , the end segments  140   a ,  140   b  are not caught between the inner extrusion  424  and the outer compression tube  428 . 
     It will be understood by those skilled in the art that embodiments similar to the one shown in  FIGS. 25-28  may be employed which rely either on (i) compression forces alone (without the use of a thermal element) to secure the suture collar  408  to the suture end segments  140   a ,  140   b , or alternatively, (ii) a thermal element alone (without the use of a compression tip) to fuse the suture collar  408  to the suture end segments  140   a ,  140   b.    
       FIGS. 29-33D  illustrate a fifth embodiment  500  which acts as a suture cutter while effectively forming a knot as well. As illustrated, the cutter  500  comprises a hypotube  506  that extends from a main body  515 . A carriage member  512  is slidably mounted to ride over the hypotube  506 . As shown in  FIGS. 29 and 30 , a lasso  504  comprised of a loop of flexible line, such as a strand or string, has end portions  504   a ,  504   b  that are attached to the carriage member  512 . When the carriage is at the distal end of the hypotube  506 , the loop is open and extends forward of the hypotube so as to receive and surround end segments  140   a ,  140   b  of a suture  140 . By way of example, the lasso  504  may be comprised of a 0.006″ diameter silk strand. 
     As best shown in  FIG. 30 , the end portions  504   a ,  504   b  of the lasso  504  extend through an opening in the distal end of the hypotube  506  and out of a side window  505  of the hypotube. The terminal ends of the portions  504   a ,  504   b  may be secured within a recess  507  of the carriage member  512  with a bonding material such as cyanoacrylate. Secured within the hypotube  506  is a tubular member that includes a proximal tubular portion  508   a  and a distal tubular portion  508   b  which have been bonded together. The proximal portion  508   a  may be plastic, and the distal portion  508   b  is preferably a high temperature plastic. A plunger  528  is mounted to slide longitudinally within the lumen of the tubular members  508   a ,  508   b . A suture collar  532  comprising a generally cylindrical tubular member is mounted distal to the plunger  528 , in spaced relationship thereto, and within a distal portion  524  of the hypotube  506 . The plunger  528  is sized to apply force to the proximal end of the suture collar  532 . Thus, the lasso  504  extends from the carriage  512  through the window  505 , between the plunger  528  and suture collar  532 , through the central bore of the suture collar  532 , and out of the distal end of the hypotube  506 . 
     The carriage member  512  slides over the hypotube  506 , so that the practitioner may retract (or advance) the carriage member with respect to the hypotube. As mentioned above, when the carriage  512  is advanced to the distal end of the hypotube  506 , the lasso  504  is fully open so as to receive suture end segments  140   a ,  140   b . As the carriage member  512  is retracted, the end portions  504   a ,  504   b  of the lasso  504  are pulled in a proximal direction, so that the size of the loop progressively decreases and the lasso  504  tightens around the suture end segments  140   a ,  140   b , with the lasso pulling the segments  140   a ,  140   b  into the distal end of the hypotube  506 . As the practitioner continues to retract the carriage member  512 , the lasso  504  is pulled through the window  505 , and the suture end segments  140   a ,  140   b  are carried by the lasso through and out of the window  505  in a proximal direction. As shown in  FIG. 31 , the carriage member  512  may be completely retracted until it reaches a detent member  516  (seen in  FIG. 29 ) which holds the carriage member in a proximal position. At this point, the entire lasso  504  has been pulled from the window  505  such that the lasso is free to enlarge and is no longer tightly holding the proximal ends of the suture end portions  140   a ,  140   b  which now hang loosely outside the hypotube  506 , as illustrated both in  FIG. 31  and the cross sectional view of  FIG. 32 . 
     Referring to  FIGS. 33A ,  33 B,  33 C, and  33 D, the practitioner then holds the ends of the suture and advances the hypotube  506  into the patient and toward the suture site through a catheter sheath introducer (CSI)  170 . The distal portion  524  of the hypotube  506  is positioned at the suture site next to tissue portions  526   a ,  526   b  within the patient through which the suture  140  passes, so as to draw the tissue portions  526   a ,  526   b  together. Referring to  FIG. 33A , the plunger  528 , which may be comprised of a hard, high temperature plastic, is then moved distally by applying force to a handle  520  ( FIG. 31 ). Such distal movement drives the plunger against the suture collar  532  which surrounds the suture end segments  140   a ,  140   b.    
     As illustrated in  FIG. 33B , a coiled heating element  536  surrounds the suture collar  532 . The collar  532  melts or deforms when subjected to heat and may be comprised of the same material as the suture  140 , e.g., polypropylene. As the plunger  528  is advanced distally against the suture collar, the heating element is activated to soften the suture collar  532 . The distal end of the hypotube has an annular inward projection which forms an opening that is significantly smaller than the diameter of the suture collar  532  so that application of longitudinal force to the collar  532  by the plunger  528  compresses the heated collar against the annular projection. Such compression causes the collar to plastically deform inwardly around and against the suture ends  140   a ,  140   b , so as to close the opening through the collar  532 . In this way, the suture collar  532  is effectively extruded out the distal portion  524  of the hypotube  506 . As illustrated in  FIG. 33C , such extrusion causes the collar  532  and suture end segments  140   a ,  140   b  to fuse together into a fused mass  534  which effectively acts as a knot (similar to the fused portion  430  of  FIG. 27 ) to keep together the tissue portions  526   a ,  526   b  that have been sutured. To this end, the distal end of the fused mass  534  is preferably adjacent the tissue portions  526   a ,  526   b.    
     After the fused mass  534  is formed, the portions of the free ends of the suture that extend from the mass will be adjacent to and exposed to the coiled heating element  536  (since the fused mass  534  is now outside the hypotube—see  FIG. 33C ). The heating element  536  is activated to sever the end segments  140   a ,  140   b  from the rest of the suture  140 . The practitioner may then withdraw the device  500  from the CSI  170  and out of the patient, leaving the fused mass  534  behind in the patient, as shown in  FIG. 33D . While the preferred embodiment utilizes both heat and compression to cause the collar  532  to lock the suture end portions together, it will be appreciated that other embodiments may use only compression, without heat, and still other embodiments may use only heat, without compression. 
     Although this invention has been described with reference to specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.