Abstract:
The present invention comprises a tubular shunt for insertion into a fluid vessel in a living creature constructed of an elastically deformable material that reduces in circumference when stretched longitudinally so that the ends of the shunt may be easily inserted into openings in a blood vessel and where the material expands circumferentially when allowed to axially contract such that the ends of shunt press against the vessel wall to secure the shunt and form a water tight seal to permit fluid to flow through the tubular conduit of the shunt. A method for shunting fluid-flow in a portion of a vessel in a living creature is also disclosed wherein a shunt of the present invention is stretched longitudinally so that the ends of the shunt contract and then inserted into a lumen of a blood vessel. Following insertion of the shunt, the shunt is allowed to return to its relaxed geometry so that it forms a fluid tight seal with the interior of the lumen.

Description:
This is a divisional of application Ser. No. 09/143,995, filed Aug. 31, 1998, now U.S. Pat. No. 6,168,623. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to prosthetic conduits or shunts used in surgery to bypass or reroute the flow of a bodily fluid. More particularly, the invention relates to conduits or shunts which are used temporarily during surgery to allow an uninterrupted flow of blood to tissues whose normal blood supply has been at least partially interrupted by a surgical procedure on a vessel such as an artery. These conduits are frequently used during procedures in which the affected tissue is particularly sensitive to a decreased blood supply. Examples of procedures in which sensitive tissues may benefit from an uninterrupted blood supply include carotid endarterectomy, coronary artery bypass grafting on an arrested, partially arrested or beating heart, and thoraco-abdominal aortic reconstructions. The use of a shunt during each of these procedures protects the brain, the myocardium, and the spinal cord, respectively. 
     BACKGROUND OF THE INVENTION 
     Many different vascular shunts or catheters are currently employed during surgery to maintain blood flow in extremities and tissues served by a blood vessel undergoing a surgical procedure. One example, the Pruitt-Inahara carotid shunt (described in U.S. Pat. No. 3,435,824), includes the use of a tube having inflatable bladders encircling each end of the tube and further includes a duct for the passage of blood. During the surgical procedure, the vessel undergoing the procedure is partially cut through and the ends of the tube inserted into the vessel. The bladders are then inflated to a pressure that causes the ends of the tube to be retained within the vessel but without causing the vessel wall to overextend and rupture due to overinflation of the bladders. Care must be taken to monitor the pressure in the bladders during inflation to limit damage to the vessel though some damage to the endothelium is common. A central portion of the shunt between the ends remains outside the vessel and is commonly looped in a circular manner to prevent crimping of the plastic or silicone rubber tubing which forms the central portion of the shunt. Upon completion of the surgical procedure, the incisions around the ends of the shunt are loosely sutured, the bladders are deflated to permit the ends of the shunt to be withdrawn from the vessel, and the sutures are pulled tight to close the incisions. 
     Moses, U.S. Pat. No. 5,453,084, describes another example of a vascular shunt wherein a tube is inserted into the incised vessel and a ring clamp or purse suture is applied to the vessel wall at the position of each end of the tube to create a water seal between the vessel wall and the shunt tube and to hold the ends in place within the vessel. The tube is fabricated of a transparent material to permit observation of the fluid flowing through the shunt in order to verify that the shunt is functioning. In addition, the tubing material must be flexible enough to permit the tube to be manipulated into position but must also resist crimping so as not to occlude the flow of fluid through the shunt when it is bent. The shunt is removed by removing the ring clamps or loosening the purse sutures holding the shunt in place, withdrawing the shunt through the open incisions. The sutures are then tightened to close the incisions. The use of clamps or sutures to hold the shunt in place can cause neuro-muscular trauma to the vessel in the regions of contact. 
     Black, U.S. Pat. No. 5,129,883, describes a catheter adapted to be inserted into a patient&#39;s circulatory system and threaded through to a portion of the system to be shunted. The catheter includes inflatable cuffs with a conduit that permits blood flow to bypass the region of the vessel between the cuffs. When the cuffs are inflated, blood flow is diverted through the conduit. As with the Pruitt-Inahara shunt above, the inflation pressure in the cuffs must be monitored to limit the amount of damage done to the vessel wall by the inflatable cuffs. Rayhanabad (U.S. Pat. No. 4,712,551) and Miller, Jr. et al. (U.S. Pat. No. 3,991,767) each describe variations on a tubular shunt with an inflatable cuff. 
     Healey, U.S. Pat. No. 4,721,109 describes a single piece device with a center tube and inflatable outer casing wherein the center tube fits into the ends of a damaged blood vessel to reconnect the two ends and conduct blood and the inflatable outer casing expands to secure the device within the vessel. Healey (U.S. Pat. No. 4,753,236) also describes a two piece device wherein each piece has an inflatable outer casing and a tubular internal portion wherein the two tubular portions include connectors adapted to couple to one another. The inflatable casings expand to secure each piece into an opening in a severed vessel and the tubular portions are coupled together to reconnect the ends of the vessel. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide methods and devices for temporarily shunting a fluid-carrying vessel or tubular tissue structure in a living creature to provide uninterrupted flow of fluid through the vessel or tissue structure during a surgical procedure. 
     Another object of the present invention is to provide a shunt apparatus positionable within an incision in a blood vessel such that the shunt provides a substantially bloodless field around the incision site. 
     Another object of the present invention is to provide a shunt apparatus having a tubular structure constructed of an elastically deformable material that reduces circumferentially when axially lengthened and expands circumferentially toward an original, biased circumference when allowed to axially contract. 
     Another object of the present invention is that the circumference of the ends of the shunt apparatus will expand when the ends are released such that the ends securely lodge against the inner walls of a vessel into which the shunt is inserted and hold the shunt apparatus in place within the vessel lumen. 
     Yet another object of the present invention is that the circumference of the ends of the shunt apparatus may be reduced for easy insertion into the openings of an incised vessel. 
     It is a further object of the present invention that the shunt be secured within the vessel without the use of clamps or inflatable bladders. 
     It is an additional object of the present invention that the shunt apparatus may be easily repositioned within the vessel without interrupting the flow of fluid through the shunt apparatus. 
     Accordingly, the present invention provides a shunting device for implantation in a fluid-carrying vessel or tubular tissue structure having an elastically deformable, generally tubular body structure. The body structure has contiguous segments or regions including first and second end portions and a central region therebetween to collectively define a conduit having a longitudinal axis. Stretching at least one end portion of the shunting device along the longitudinal axis results in a reduction in a dimension of the tubular structure which is transverse to the longitudinal axis. The shunting device further includes means associated with the tubular body for facilitating the insertion and positioning of the shunting device within a vessel or tubular tissue structure. Such a means may include a receptacle integrally formed in the tubular body structure to receive a free-standing positioning stylus. Alternately, the means may include a stylus attached to one or both of the end portions of the tubular body with or without a positioning tube. 
     More particularly, the apparatus of the present invention includes a composite tube with a relatively large, relaxed circumference at both ends, and a smaller circumference section in the middle. The tube is constructed such that elongating the tube causes the circumference to reduce by about half. In a first embodiment, the tube is constructed of a tubular braided monofilament, which is then impregnated with an elastomeric material to provide vessel sealing and elasticity. Further, the larger circumference segments taper down to the smaller center segment, and the smaller circumference segment is substantially aligned with the outer aspect of the two larger circumference segments. Preferably, each of the ends of the tube is cut at an oblique angle. 
     Positioned on the outer surface along each the larger circumference segments of the tube is a closed-end positioning receptacle or cavity into which a stylus, such as a pushrod or wire, may be inserted to elongate the tube. This receptacle may extend partially along the larger circumference segment or back and over to the smaller circumference segment. The receptacle or cavity may be positioned on the outside surface of the main shunt tube, or it may be positioned along the inside surface of the tube at the ends and pass through the wall of the tube to the outer surface somewhere along the length of the tube. Ideally, this receptacle is sufficiently flexible that it collapses at least partially when the push rod is removed. This push rod receptacle may be fixed to the wall of the main shunt tube at the ends only or it may be fixed to the wall along the entire length. An advantage of extending the outer tube to the mid section of the shunt is that the shunt may be repositioned without removing the shunt from the vessel. 
     In another embodiment of the present invention, the shunt may have a thin stylus, such as a fine-gauge wire, attached to the tip of the obliquely cut end and extend back to at least the central portion of the shunt. The stylus may be used independently to stretch the shunt or may be used in conjunction with a narrow-lumen positioning sleeve, preferably made of metal or plastic. The position sleeve is passed over the wire to the end of the shunt while pulling on the wire to selectively extend the shunt. The pressure that the sleeve exerts against the end of the shunt causes elongation of the shunt which collapses the tube for easy insertion into a vessel. 
     In another embodiment, the wire stylus may have a sharpened distal end. In use, the sharpened end of the stylus is used to penetrate the outer surface of the end portion of the shunt. The stylus is then used to stretch the shunt so as to decrease the diameter of the shunt for insertion into the vessel. The shunt is preferably configured from a soft silicone or elastomer which allows penetration by the sharpened stylet without compromising the integrity of the blood lumen of the shunt. 
     In another embodiment of the present invention, a shunt positioning tool configured to securely hold and manipulate the shunt is provided. The positioning tool comprises a first and second elongate arm members which may be biased from an open to a closed position so as to securely engage a shunt between first and second semi-cylindrical distal ends of the arms. The shunt positioning tool may include a locking ring which is operable to securely fix the distal ends about the shunt during insertion or manipulation of the shunt. A pair of wire guides may also be included to accurately guide the distal movement of one or more stylets so as to stretch and contract the shunt for installation or manipulation of the shunt. 
     These and other objects, features and advantages will become apparent when considered with reference to the following description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an axial cross-sectional diagram of an embodiment of a shunt apparatus of the present invention in its natural or unstretched condition. 
     FIG. 1B is an axial cross-sectional diagram of the embodiment of FIG. 1A in a stretched or lengthened condition and an embodiment of a stylus of the present invention functionally positioned within a positioning receptacle of the shunt apparatus. 
     FIG. 2 is a diagram showing a vessel being incised to permit insertion of a shunt apparatus of the present invention. 
     FIG. 3 is a diagram of the embodiment of the shunt apparatus of FIGS. 1A and 1B being held by a pair of surgical forceps while being stretched by a stylus of the present invention. 
     FIG. 4A is a diagram showing the stretched end of the shunt apparatus of FIGS. 1A and 1B being inserted into the vessel lumen of the vessel of FIG.  2 . 
     FIG. 4B is a shunt positioning tool of the present invention shown manipulating a shunt device in a target coronary artery of an anastomosis with the left internal mammary artery. 
     FIG. 4C is a shunt positioning tool of the present invention having first and second elongate arm members fixed relative to each other at a distal end of the arm members. 
     FIG. 4D is the shunt positioning tool of FIG. 4C including a pair of curved wire guides fixed to the first and second elongate arm members. 
     FIG. 4E is a shunt positioning tool of the present invention wherein the first and second elongate arm member are hingedly connected at an intermediate point on the arm members. 
     FIG. 4F is a shunt positioning tool of the present invention wherein first and second elongate arm members are slidingly connected relative to each other. 
     FIG. 5 is a diagram showing the other end of the shunt apparatus of FIGS. 1A and 1B being inserted into the vessel lumen on the other side of the incision in the vessel. 
     FIG. 6 is a diagram showing the shunt apparatus of FIGS. 1A and 1B in its functional position within the incised vessel. 
     FIG. 7 shows the shunt apparatus of FIGS. 1A and 1B being repositioned within the vessel during suturing of the incision. 
     FIG. 8 shows the shunt apparatus of FIGS. 1A and 1B being removed from the vessel through a partially sutured incision. 
     FIG. 9 shows the incision in the vessel being clamped and sutured for final closure after removal of the shunt apparatus of FIGS. 1A and 1B. 
     FIG. 10 is a diagram of another embodiment of the shunt apparatus of the present invention wherein the positioning receptacles are located on the inside surface of the ends of the main shunt tube and the central portion of the shunt includes a reinforcing member. 
     FIG. 11 is a diagram of embodiment of the present invention wherein elongated positioning receptacles extend from the inside surface of the ends of the main shunt tube. 
     FIG. 12 is a diagram of yet another embodiment of the present invention wherein short positioning receptacles are located on the outside surface of the ends of the main shunt tube. 
     FIG. 13 is a diagram of another embodiment of the present invention wherein elongated positioning receptacles extend along the outside surface of the ends of the main shunt tube. 
     FIG. 14 is a diagram of another embodiment of the present invention wherein elongated positioning receptacles extend along the outside surface of the ends of the main shunt tube and attach to the outside surface of the central portion of the main shunt tube. 
     FIG. 15A is a diagram of another embodiment of the present invention having a stylus integrally coupled to each end of the shunt. 
     FIG. 15B is a diagram of the shunt of FIG. 15A, wherein elongation of the shunt is accomplished by stretching apart the ends of the shunt by means of the stylets. 
     FIG. 15C is a diagram of the shunt of FIG. 15A, wherein elongation of the shunt is accomplished by means of passing a slender sleeve over the stylus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawings where like reference numbers refer to like elements of the invention, there are shown various embodiments of the shunt apparatus of the present invention. FIGS. 1A and 1B are cross-sectional side views illustrating one embodiment of the shunt apparatus  100  of the present invention in its natural (i.e., unstretched) and lengthened (i.e., stretched) conditions, respectively. Shunt apparatus  100  consists of a continuous tube body  108  defining a longitudinal axis A and having an inner surface  122  and outer surface  124  defining a fluid conduit or lumen  126 . Tube  108  has various contiguous portions or segments, namely, two end portions or segments  102  and  140  and a central portion or segment  130  therebetween. End regions  102  and  140  terminate in tips  104  and  144 , respectively, which preferably have a tapered, pointed, or oblique design to facilitate insertion of shunt  100  into a vessel or tissue structure. 
     From the cross-sectional side view of FIG. 1A, tube  108  can be described as having lower and upper wall portions  132  and  134  about axis A. Lower wall portion  132  is preferably substantially linear for the entire length of the tube so that, when implanted or positioned within a fluid-carrying vessel or tissue structure, lower wall portion  132  fits flush against at least a portion of the inner wall of the vessel or tissue structure. Upper wall portion  134  has tapered areas  106  and  146  which define the inner portions of regions  102  and  140 , respectively, and which, in the view of FIG. 1A, defines a recessed area  128  of central segment  130 . As such, the respective dimensions transverse to axis A (e.g., inner and outer diameters and circumferences) of tube  108  at end segments  102 ,  140 , identified generally about axes B and D, are greater than at central segment  130 , identified generally about axis C. Upon insertion through an incision made in a vessel or the like, recessed area  128  is generally positioned to face outward through the incision to provide a working space within the vessel while minimizing the escape or leakage of blood or other fluid at the surgical site. The working space may facilitate, for example, the removal of plaque in an endarterectomy procedure performed on the vessel or the forming of an anastomosis in a coronary artery bypass graft procedure. 
     Tube body  108  is preferably constructed of a biologically compatible, elastic material that is deformable to be generally conformable, particularly at end regions  102  and  140 , to the vessel wall into which shunt  100  is inserted. The shunt&#39;s elasticity permits at least a portion of tube body  108  to be stretched or lengthened along its length while reducing a dimension of shunt  100  which is transverse or substantially perpendicular to the shunt&#39;s longitudinal axis (such as the internal and external circumferences and diameters of shunt  100 ). More particularly, the tube material is selected so at least the outer circumference and diameter of end regions  102  and  140  can be reduced by about half, when the end region is lengthened or stretched in a direction away from central region  130  along axis A. Additionally, the material of tube  108  is sufficiently flexible and kink-resistant such that tube  108  may be flexed or bent about its width without kinking, and to allow atruamatic insertion of tube  108  into a vessel. Tube  108  is also fluid and gas impermeable to provide a leak-free conduit  126 . 
     Accordingly, the tube material preferably comprises a monofilament material, such as braided polyester, impregnated with an elastomeric material, such as silicone, latex, or other similar materials. A suitable braided polyester material is available from Atkins &amp; Pearce of Covington, Ky. The cross-hatched texture of the woven fabric of the preferred tubing material aids in securing the outer surface of the shunt  100  in the vicinity of the end regions  102  and  140  against the vessel walls. A suitable elastomeric material is available from Nusil Technology of Carpinteria, Calif. It should be understood, however, that any impermeable, elastic material that is biologically compatible and, when formed into a tube, reduces in cross-sectional circumference upon lengthening or stretching of the tube, is suitable for the shunts of the present invention. 
     Referring again to FIGS. 1A and 1B, shunt  100  further includes positioning stylus receptacles  110  and  150  disposed adjacent to end regions  102  and  140 , respectively, of tube body  108  for receiving a stylus  120  (FIG.  1 B), such as a wire or rod, to aid in manipulating shunt  100  into position within a vessel. Generally, positioning receptacles  110  and  150  are at least partially integrally formed with tube body  108  and have a closed end  112  and  152 , respectively, and an open end  116  and  156 , respectively, and closed surfaces therebetween to define a cavity  114  and  154  which may be in the form of a tube, slot, pocket or channel. Positioning receptacles of the present invention may vary in size, length, and position relative to the end and central portions of the shunt tube body  108 . For example, receptacles  110  and  150  of FIGS. 1A and 1B are integrally mounted to and extend substantially linearly along upper wall portion  134  of tube  108  from the respective tips  104 ,  144  to approximately mid-way to respective tapered areas  106 ,  146 . Various other embodiments of positioning receptacles are discussed below with respect to FIGS. 10-14. 
     Shown operatively received within receptacle  110  in FIG. 1B is a hand-held shunt positioning stylus  120 . Stylus  120  may be a pre-formed, substantially rigid rod having a pre-selected bend or angle (see FIG. 3) or curve, as shown in FIG. 1B, and a suitable length, preferably about 10 to 20 cm, to accommodate a particular surgical access site or patient anatomy. Alternately, stylus  120  may consist of a semi-rigid but malleable wire that may be optimally shaped at the time of surgery and thereafter reshaped if needed during the surgery for repositioning the shunt in the same vessel or inserting the shunt in another vessel. Stylus  120  may also have a handle (not shown) to allow better gripping and control of the stylus. 
     The lengthening of tube  108  along its longitudinal axis A and the contraction or reduction of the circumferential dimensions of end regions  102  and  140  when stylus  120  is employed are schematically illustrated in FIG.  1 B. The reduced circumferences and diameters which result when end regions  102  and  140  are lengthened permit oblique tips  104  and  144  of end regions  102  and  140 , respectively, to be inserted through a small incision in a vessel and to be delivered and extended within the lumen of the vessel on either side of the incision. When end regions  102  and  140  are permitted to axially contract to their pre-formed length, as shown in FIG. 1A, end regions  102  and  140  will expand towards their biased, natural circumferential dimensions and press against the interior walls of the shunted vessel to form a fluid-tight seal. 
     Prior to beginning the surgical procedure to install the shunt, a shunt device of appropriate size is selected for the vessel to be shunted. The size of the shunt, and particularly the circumferences of a shunt when in respective relaxed and stretched conditions, are selected based on the inner diameter of the vessel or tissue structure into which the shunt is to be inserted. More specifically, the central region of the shunt, when in a relaxed condition, should have an outer circumference that approximates the circumference of the inner wall of the vessel so that the shunt will fit within the lumen of the target vessel. Furthermore, in such a relaxed condition, the central region of the shunt should have an internal area which will allow blood flow there through to approximate the natural fluid flow volume through the vessel. Additionally, the circumferences of the end regions, when in a relaxed or biased condition, must be large enough so that the end regions, once inserted into the vessel and released, expand to apply sufficient pressure against the vessel wall to form a fluid-tight seal between the outer surface of the shunt and the inside vessel wall. 
     Although suitable for a variety of vascular procedures, the shunt of the present invention is most suitable for a carotid endarterectomy procedure and an anastomosis in a coronary artery bypass graft procedure. Accordingly, shunts of the present invention would be typically sized for such procedures. The following dimensions for shunts, for insertion into coratid and coronary arteries, in intended to be exemplary, with variations. For example, the average internal diameter of human carotid arteries is about 4 mm for external carotid arteries, 6 mm for internal carotid arteries, and 12 mm for common carotid arteries. The average incision length in a carotid artery for performing an endarterectomy procedure is from about 3 to 4 cm, preferably from about 3.4 to about 3.8 cm, and more preferably about 3.6 cm. Thus, a shunt of the present invention for employment in a coratid endarectomy procedure has the following approximate dimensions: an end-to-end length of about 7 to 9 cm; a central portion length of about 2 to 4 cm, an outer diameter of about 4 to 8 mm, and an internal diameter of about 3 to 7 mm for center portion  130 ; an axial length of 1 cm for each tapered region  106 ,  146 ; an axial length of from 1 to 2 cm, an outer diameter of about 4 to 12 mm, and an internal diameter of about 1 to 4 mm for each end region  102 ,  140 ; an internal diameter of from about 0.25 to 0.75 mm for receptacle pockets  114  and  154 ; and an angle of 30 to 60 degrees from the axis defined by the length of the shunt for the oblique cut of each tip  104 ,  144 . 
     The average internal diameter of human coronary arteries is from about 1 to 3.5 mm, and the length of an arteriotomy for an anastomosis in a coronary artery, for example, is from about 3 to 5 mm. Thus, for surgical procedures involving coronary arteries, a shunt of the present invention has the following approximate dimensions: an end-to-end axial length of about 1.5 to 3 cm; an axial length of about 1 to 2.5 cm, an outer diameter of about 1 to 3.5 mm, and an internal diameter of about 0.75 to 3 mm for central region  130 ; an axial length of 0.1 to 0.25 cm for each tapered region  106  and  146 ; an axial length of from 0.25 to 0.5 cm, an outer diameter of about 2 to 5 mm, and an internal diameter of about 1.5 to 4.5 mm for the end regions  102  and  140 ; an internal diameter of about 0.20 to 0.75 mm for receptacle pockets  114  and  154 ; and an angle of 30 to 60 degrees for the oblique cut of tips  104  and  144 . 
     Referring now to FIGS. 2-9 an exemplary method of use of a shunt of the present invention is illustrated and described. Specifically, the implantation and removal of the inventive shunt in a blood vessel is described primarily in the context of an endarterectomy procedure. However, the procedure described herein is intended to be exemplary and in no way limits the devices and methods of the present invention. 
     After a determination is made as to the appropriate incision site on the target vessel  230 , the vessel  230 , as shown in FIG. 2, is then preferably occluded to temporarily arrest the flow of blood while an incision  234 , called an arteriotomy, is made in the target vessel using conventional instruments such as scalpel  225 . There are various means known in the art for temporarily occluding a vessel. One such means are small vascular clamps, which are commonly used in endarterectomy procedures. As shown in FIG. 2, a vascular clamp  233  is placed on each side of incision  234 ; however, one clamp on the proximal side or upstream side of the incision may be sufficient. Another occlusion technique (not shown), which is often used during an anastomosis for coronary artery bypass graft and may be used with the present invention, involves tying a suture around the outside of the target vessel. An incision  234  is then made in vessel  230  to expose the vessel lumen  232  on one end of incision  234  and the vessel lumen  236  at the opposing end of incision  234 . 
     Next, a shunt  300 , such as that illustrated in FIG. 3, is provided which may have its inner and outer surfaces heperinated prior to implantation in the vessel  232  to reduce clotting due to interaction between the patient&#39;s blood and the material of shunt  300 . While grasping the central portion  316  of shunt  300  with a pair of forceps  600 , a shunt positioning tool  342 , or between a thumb and forefinger, a stylus, such as positioning wire  340  shown in FIG. 3, is inserted into a first receptacle  322  in an end portion  318  of shunt  300 . Pushing on wire  340  while pulling or fixing the position of central portion  316 , as indicated by the respective arrows, causes end portion  318  to stretch or lengthen. This elongation in turn reduces the cross-sectional dimensions of end portion  318 . Specifically, the circumference and diameter of the outer surface of end portion  318  is caused to collapse or become reduced to permit insertion of oblique tip  320  into lumen  232 , as shown in FIG.  4 A. The lengthening of end portion  318  should be continued until substantially the entirety of end portion  318  is positioned within blood vessel  232 . Stylus wire  340  may then be withdrawn to permit end region  318  to axially contract along the longitudinal axis of shunt  300  and to circumferentially expand to its natural, biased dimension, lodging itself against the vessel wall of vessel lumen  232 . 
     FIG. 4B shows an alternate means of inserting shunt  300  into a coronary artery in a procedure for bypassing an occluded coronary artery with a fresh supply of blood from the left internal mammary artery using a shunt positioning tool  342 . The shunt positioning tool  342  provides a superior means of grasping and manipulating the shunt  300  within the vessel  232  during the anastomotic procedure than does a simple pair of forceps  600 . In particular, the shunt positioning tool  342  prevents inadvertent rotation or slippage of the shunt  300  during manipulation of the shunt  300 . 
     The construction of a shunt positioning tool  342  of the present invention is shown in detail in FIG.  4 C. The tool  342  is shown in its “opened” and “closed” positions. The tool  342  comprises a first elongate arm  344  and a second elongate arm  346  wherein the first and second arms  344 ,  346  are pivotably fixed at a proximal end of the shunt positioning tool  342  relative to each other. The first and second arms  344 ,  346  include a first and second distal end  348 ,  350  to which is configured to conformingly engage the cylindrical body of the shunt  300  of the present invention when the first and second arms  344 ,  346  are biased to a closed position relative to each other. For the embodiment shown in FIG. 4C, the shunt positioning tool  342  is configured similarly to an elongate pair of tweezer forceps with a special shunt engaging distal end. It can be seen that the pivotable attachment point  351  may be located at an intermediate point on the elongate arm members so that device operates in a scissors-like fashion. A number of other configurations for the shunt positioning tool are also possible without departing from the spirit of the invention. 
     The distal ends  348 ,  350  of the first and second elongate arms  344 ,  346  are configured having a semi-cylindrical configuration which is sized to engage the outer surface of the shunt conformingly. The device may also include a locking ring  360  which may be slid distally along the first and second arms  344 ,  346  to hold the arms in a closed position when grasping the shunt  300 . 
     As seen in FIG. 4B, the axial length of the semi-cylindrical distal ends  348 ,  350  of the shunt positioning tool  342  should be no greater than the length of the center portion  316  of the shunt  300 . Preferably, the axial length should be kept relatively short to prevent interference with the walls of the incision  365 . Keeping the length short will also allow maximum maneuverability of the shunt  300  and the tool  342  within the vessel  332  during the procedure. 
     FIG. 4D shows another shunt positioning tool  342  of the present invention wherein the shunt  300  is securely held in the distal ends  348 ,  350  of the tool  342 . The shunt position tool  342  further includes first and second wire guides  354 ,  356  which are fixed to the first and second arms  344 ,  346  proximal to the distal ends  348 ,  350  of the respective arms. The wire guides  354 ,  356  serve as a means to properly guide a wire or stylus  340  into receptacles  110  or  150 . Preferably, the wire guides are configured from a curved piece of tubing which evenly translates distal movement of the wire  340  into lateral movement of the wire  340 . When the wire  340  is in engagement with the receptacle  110 , for example, lateral movement of the wire will cause axial stretching and contraction of the first end  362  of the deformable shunt  300 . The tool  342  may also further include a thumb tab  361  fixed to the proximal end of one or both wires  340  which allows easy, one-handed longitudinal elongation and contraction of the shunt  300  for emplacement of the device within a vessel. 
     FIG. 4E is an alternate embodiment of the shunt positioning tool  342  wherein it is configured with pivotable attachment point  351  intermediate the distal and proximal ends of the first and second  344 ,  346  elongate arm members. A latching tooth portion  370  is included to securely hold the distal ends  348 ,  350  in a closed position if desired. 
     FIG. 4F is an alternate configuration of a shunt positioning tool  342  of the present invention wherein first and second elongate arm members  344 ,  346  are slidable relative to each other from an “open” to a “closed” position The first and second arms  344 ,  346  may also be provided with handles of thumb knobs  378 ,  380  to aid in the manipulation of the device around a shunt. The device may also be provided with a locking device to lock the tool  342  in place around a shunt. 
     Returning to a description of a method of inserting a shunt of the present invention, FIG. 5 illustrates that, following insertion of the first end  318  of shunt  300  into the vessel lumen  236  using either a traditional grasping method or the shunt positioning tool  342  of the present invention, a wire  340  is then inserted into receptacle  314  and the central portion  316  is grasped to similarly stretch and insert end portion  314  into lumen  236 . After shunt  300  has been acceptably positioned, wire  340  is then removed from receptacle  314  and vascular clamps  233  are removed from vessel  232  to allow blood to flow in its natural direction through shunt  300 . In FIG. 6, end portions  314  and  318  are shown fully deployed within lumens  236  and  232 , respectively, and central portion  316  is nestled into blood vessel  230  in the vicinity of incision  234 . 
     The determination as to whether shunt  300  is first inserted into the portion of vessel which is downstream (i.e., the portion distal to incision  234 ) or upstream (i.e., the portion of vessel proximal to incision  234 ) of the natural direction of flow of the bodily fluid may depend on several factors, including the procedure being performed (e.g., endarterectomy, coronary artery bypass grafting, etc.), the vessel being shunted, the patient&#39;s anatomy, and surgeon preference, and will likely vary from vessel to vessel and from case to case. 
     Should the need arise, shunt  300  may be repositioned during the surgical procedure by reinserting wire  340  into either receptacle  312  or  322  to lengthen and reposition end portions  314  or  318 , respectively, within the vessel  230 , as illustrated in FIG.  7 . Forceps  600  may be required to grasp central portion  316  and hold shunt  300  steady while wire  340  is reinserted and used to stretch the appropriate end portion. Repositioning of the shunt may be performed prior to suturing or as incision  234  is sutured and the incised opening is reduced in size. The shunt positioning device  342  illustrated in FIGS.  4 (B-D) may also be used to rapidly manipulate the shunt as shown in FIG.  4 B. 
     To remove shunt  300 , FIG. 8 demonstrates that the incision  234  is sutured leaving a small opening to permit removal of the shunt. Forceps  600  or other previously discussed positioning tools are then used to grasp shunt  300  by central portion  316  and pull the shunt out through the opening remaining in vessel  230 . In FIG. 9, a side-biting clamp  900  is used to hold closed the remaining opening in incision  234  as suturing needles  910  and  94  are used to suture the remainder of incision  234  shut with sutures  912  and  916 . 
     Examples of other surgical procedures in which the shunt would be implanted in a manner similar to that described above, with minor modifications which can be readily understood and appreciated by those skilled in the art, include, but are not limited to, coronary artery bypass grafting and thoraco-abdominal aortic reconstruction. 
     Turning now to FIGS. 10-15, there are illustrated views of alternate embodiments of the present invention. For example, FIG. 10 illustrates a shunt  1000  having a central portion  1016 , and end regions  1014  and  1018  similar to that of shunt  100  of FIGS. 1A and 1B. The positioning receptacles  1012  and  1022  (illustrated in phantom) of FIG. 10 differ from those of FIGS. 1A and 1B in that they are disposed on the inner, rather than outer, surface of end regions  1014  and  1018  of shunt  1000 . Additionally, the length of receptacles  1012  and  1022  are coincident with the length of end regions  1014  and  1018 , and their respective openings  1013  and  1023  are coincident with the outer surface of the shunt at respective tapered areas  1015  and  1017 . The embodiment of FIG. 10 also employs a reinforcing member, such as a metal ribbon or coil  1002 , disposed along a central region  1016  to prevent the central region from becoming crimped during insertion or repositioning of shunt  1000 , thereby causing the flow of fluid through shunt  1000  to be pinched off. 
     FIG. 11 illustrates another shunt  1100  of the present invention wherein receptacles  1112  and  1122  are disposed along the inner surface of end regions  1114  and  1118 , as in FIG. 10, but are longer than the end regions and extend, in the form of tube portions  1113  and  1123 , respectively, past the outer surface of shunt  1100 , inwardly or proximally with respect to the shunt tube, and over a portion of central region  1116 . Preferably, when shunt  1100  is operatively positioned within a vessel, tube portions  113  and  1123  extend past the respective apexes of the incision and are readily visible and accessible for insertion of a stylus into receptacles  1112  and  1122 . 
     FIGS. 12-14 illustrate further embodiments of the present invention wherein the respective stylus receptacles are disposed along the outer surfaces of at least a portion of the end regions, similar to the embodiment of FIGS. 1A and 1B, and all having closed ends coincident with the tip ends. In FIG. 12 the receptacles  1212  and  1222  are disposed along only about one fourth to less than about one half the length of end regions  1214  and  1218  but may extend over more or less thereof. 
     In the embodiment of FIG. 13, receptacles  1312  and  1322  are disposed along the entire length of end regions  1314  and  1318 , respectively, and, similar to the embodiment of FIG. 11, further comprise tubular extensions  1313  and  1323 , respectively, which extend proximally over at least a portion of recessed area  1317  of central region  1316 . Here, tubular extensions  1313  and  1323  are each shown to extend over about one third of recessed section  1317  but may extend over more or less thereof. 
     FIG. 14 illustrates an embodiment wherein receptacles  1412  and  1422  are disposed on the outer surface of shunt  1400  along the length of end regions  1414  and  1418  and terminate in proximally extending tubular extensions  1413  and  1423 , respectively. Unlike the embodiment of FIG. 13, the ends of tubular extensions  1413  and  1423  are fixed to a portion of the recessed area  1417  of central region  1416 . Enough space remains between the fixed ends  1413  and  1423  so that a stylus may be received in either receptacle  1412  or  1422 . 
     Preferably, the positioning receptacles of the present invention are collapsible so that, if disposed on the outer surface of the shunt, they do not interfere with the fluid tight sealing between the shunt and the vessel wall. On the other hand, if disposed along the inner surface of the shunt, collapsible positioning receptacles will not impede the flow of fluid through the shunt lumen. To this end, the positioning receptacles of the present invention may be made of material similar to that suggested for the shunt body. 
     The embodiment of FIGS. 15A and 15B differ from the others previously described in that shunt  1500  does not have any positioning receptacles, but rather, has stylets  1519  and  1521  integrally coupled at one end thereof to shunt tips  1510  and  1520 , respectively. Stylets  1519  and  1521  may be pre-formed or malleable, and have a selected length suitable for the surgical procedure being performed. Stylets  1519  and  1521  may consist of a wire that is looped through or otherwise fastened to the most distal portion of tips  1510  and  1520 . As illustrated in FIG. 15B, the two stylets may be used in tandem by simultaneously exerting a distally directed force, as indicated by the arrows, on each of them to stretched the respective end regions  1514  and  1518 . Alternatively, as shown in FIG. 15C, a thin positioning tube  1530  may be passed over one of the wire stylets  1519  (not shown),  1521  while gently pulling on the stylet to stretch the respective end region  1514 ,  1518 . 
     In an alternate configuration, the wire stylet may comprise a relatively stiff material which is configured having a sharpened distal end (not shown). In use, the distal end is used to penetrate the body wall of the shunt at one or both ends of the shunt at a relatively oblique angle. The shunt is preferably configured from a relatively soft silicone or elastomer which will allow penetration by the wire stylet yet still remain impermeable to fluid flow should the stylet accidentally completely penetrate the body wall of the shunt. The use of a sharpened stylet eliminates the need for a receptacle disposed on the first and/or second ends of the shunt while still providing a means for longitudinal elongation and contraction of the shunt. 
     The overall shape of the shunt embodiments illustrated in FIGS. 1-15 is that of an irregular cylinder. However, the present invention is not limited to a cylindrical device but can vary significantly within the confines of a generally tubular structure. For instance, the end portions of the shunt may be frustoconical in shape or flared to form a hyperboloid in one sheet with the central portion. Irrespective of shape, the various shunts of the present invention should be elastically deformable so as to be expandable along their lengths and substantially contractible along their widths to facilitate insertion, positioning and removal of the shunt in a vessel, to minimize trauma to the vessel, and to easily conform to the contours of the vessel into which the shunt is implanted. 
     The above-described components of the present invention or a combination thereof may be provided in a surgical kit. Such a kit may include, for example, one or more shunts of varying sizes, with positioning receptacles having various configurations and one or more positioning stylets. It may also include a shunt positioning tool as herein described. In another embodiment, such a kit may include one or more shunts having integrally attached stylets and positioning tubes. 
     Although only certain embodiments have been described in detail, those having ordinary skill in the art will certainly understand that many modifications are possible without departing from the teachings thereof. All such modifications are intended to be encompassed within the following claims.