Patent Publication Number: US-6214022-B1

Title: Perfusion device for maintaining blood flow in a vessel while isolating an anastomosis

Description:
This a continuation of application Ser. No. 08/790,827, filed on Jan. 23, 1997, and now U.S. Pat. No. 5,925,054 which is a continuation-in-part of Ser. No. 08/603,415, filed on Feb. 20, 1996, and issued as U.S. Pat. No. 5,769,870 on Jun. 23, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates principally to a perfusion device for use in performing minimally-invasive vascular microsurgeries and in particular to minimally invasive coronary artery bypass grafting (CABG) procedures such as an internal mammary artery (IMA) or vein graft to a coronary artery anastomosis procedure. The device of the invention maintains blood flow distally in a coronary artery such as the LAD during the construction of an anastomosis, thereby preventing ischemia and maintaining a dry anastomosis site to facilitate the procedure. 
     Surgeons are constantly striving to develop advanced surgical techniques resulting in turn in the need for developing advanced surgical devices and instruments to facilitate performance of such techniques. Recent advances in the surgical field are increasingly related to operative techniques which are less invasive and reduce overall patient trauma. To illustrate, in the field of CABG procedures it has been common practice for surgeons to perform a sternotomy where a lengthy incision is made down the middle of the chest to expose the body cavity in the thorax region, wherein retractors are employed to provide the surgeons the access required to perform the necessary bypass surgery. 
     However, more recent surgical techniques employ less invasive CABG procedures, known as “endoscopic” surgery, involving the use of an endoscope instrument which permits the visual inspection and magnification of any cavity in the body, such as the thorax cavity. The procedure involves the insertion of tubes called trocar cannulas through the soft tissue protecting the body cavity. The surgeon then performs diagnostic and therapeutic procedures at the surgical site with the aid of specialized micro-instrumentation designed to fit through the various trocar cannulas that provide the required openings into the body cavity. 
     In such endoscopic techniques, an arterial blood source such as an IMA is dissected from its location, transacted and prepared for attachment at an anastomosis site on a selected coronary artery, commonly the left anterior descending artery (LAD). To this end, a portion of the LAD is exposed and an incision is made in the arterial wall. The distal end of the IMA is then sutured over the incision in the LAD to complete the bypass graft surgery. 
     However, in order to perform the above surgical procedures, heart activity must be arrested. Thus, to maintain the patient, it is necessary first to divert the patient&#39;s blood circulation through an extracorporeal cardiopulmonary bypass system. This is accomplished by isolating the heart at selected arterial locations using selected catheter instruments and occluders to draw the blood into the bypass system for oxygenation thereof via an associated pump oxygenator. The oxygenated blood is returned to the patient to maintain the patient&#39;s systemic circulation during the surgery. The procedure further includes the ligating of vessels by pinching off the vessel with sutures and/or the use of occluder devices in the artery, the functions of which are to prevent the flow of blood through the artery to maintain a dry surgical site during the suturing of the anastomosis. 
     Accordingly, many typical cardiovascular surgical procedures, even many so-called less invasive procedures, include the procedures of placing the patient on a cardiopulmonary bypass system and then inducing cardioplegia arrest of the heart. It follows that the entire anastomosis construction is performed with the heart in the arrested state, and with special precautions taken to prevent any blood flow in the vessel on which the anastomosis surgery is being performed. To this end, an occluder device, which is sometimes inserted in the blood vessel to isolate the anastomosis site, is specifically configured to be impenetrable to the flow of fluid and to thereby prevent the flow of blood through the occluder device at the anastomosis site. 
     The surgical procedures of previous mention experience the disadvantages of increased trauma to the arteries caused by ligatures, to the heart due to the cessation of blood flow to distal portions thereof, and to the patient in general due to the cardiopulmonary bypass and cardioplegia arrest procedures and instruments. Accordingly, it would be highly desirable when performing a bypass surgery to circumvent the problems of previous mention, that is, to obviate the need for a cardiopulmonary bypass procedure and to allow the anastomosis construction to be performed without the occlusion of blood flow through the associated blood vessel and to prevent ischemia while still maintaining a dry anastomosis site to facilitate the suturing procedure. 
     An analogous problem is encountered whenever a surgical procedure penetrates the wall of a vessel. In many instances, the problem is overcome using mechanical means to occlude the vessel, either by externally clamping the vessel closed, or by use of an intravascular occluder as mentioned above. However, both approaches necessarily interrupt blood flow through the vessel, depriving the downstream tissue of oxygenated blood and creating the possibility of ischemia/reperfusion injury. 
     SUMMARY AND DESCRIPTION OF THE INVENTION 
     The present invention overcomes the above problems by enabling a surgeon to perform an anastomosis construction on, for example, a left anterior descending coronary artery (LAD) without occluding the distal flow of blood through the LAD to the heart. The invention thus facilitates the anastomosis construction by keeping the surgical site free of blood while preventing ischemia and reducing overall patient trauma. 
     Although the present invention is described herein in the performance of anastomosis surgery involving a graft of an internal mammary artery (IMA) to a LAD, it is to be understood that the invention and associated techniques are equally applicable to performing anastomosis constructions or surgical grafts on body vessels other than the LAD-IMA example employed herein for purposes of description. 
     Moreover, certain embodiments of the invention may be used in any medical application where a flow of fluid is desired to be maintained past an opening in the fluid conduit. Such applications occur in several surgical settings and other procedures both within the cardiovascular system and elsewhere. 
     The present invention comprises a distal perfusion device, hereinafter termed a “shunt” for ease of description, for use in LAD-IMA surgical procedures and the like. The shunt maintains blood flow in the LAD to prevent ischemia while maintaining a dry or blood free anastomosis site to facilitate a surgeon&#39;s suturing procedure. A shunt also provides support within the LAD if the LAD is ligated via sutures bordering the anastomosis site thereby decreasing trauma to the vessel. The shunt may also be configured with flanges, protruding edges, etc., to help expose the anastomosis to aid the positioning of a needle or otherwise further facilitate the suturing procedure. 
     To this end, the invention provides a microsurgical device, generally including a cylindrical central portion or member formed of a thin-walled, tube-like flexible material which includes a lumen therein to allow the flow of blood or other fluids through the central member. In preferred embodiments, selectively tapered end members are provided on either extremity of the central member, which extremities may be termed the proximal and distal extremities upon insertion in the LAD. The tapered end members include various configurations and perforations in the conical walls and/or in the apexes as well, as necessary to maintain the nominal blood flow through the shunt. The configuration of the opposing tapered ends facilitates the insertion of the shunt into an incision in the LAD, for example, by a surgeon using forceps. Since the shunt must be longer than the incision, that is, the anastomosis site, various shunts are installed in preferred embodiment by first inserting one end, generally of either end of the shunt, into the incision until the opposite end of the shunt clears the respective apex of the incision. The shunt is pressed into full coaxial alignment with the LAD and then is slid in the direction of the opposite end until it is centered within the LAD relative to the anastomosis site. A surgical thread or other filamentary strand may optimally be attached to the shunt at a strategic point or points to aid in the selected insertion of the shunt through the incision and into position in the LAD, as well as to aid in the selected removal of the shunt prior to conclusion of the anastomosis construction. 
     The central member and tapered end members may be integrally formed as by a molding process, or the end members may be individually formed and then coaxially affixed permanently to the extremities of the central member by a suitable bonding, gluing, etc., process. A number of materials are contemplated for use in accordance with the invention, wherein the material used, in part or in total, dictates the structural configuration of the shunt and the associated manner of inserting, expanding and/or contracting the particular shunt. 
     In preferred embodiments, the shunt may include spaced apart annular ridges located generally about the extremities of the central member to provide enlarged diameters for the shunt beyond either extremity of the anastomosis site to enhance the occlusion of blood therefrom. The ridges may be integrally formed about the central member or may comprise expandable members whose diameters are enlarged radially outward when required, generally upon insertion of the shunt in the LAD. Depending upon the material and associated structure, the expandable ridges may, or may not, subsequently be contractible to their initial diameters to facilitate the removal of the shunt. 
     In one configuration, the shunt is manufactured to include a means for providing structural support in at least the central member of the distal perfusion device. Preferably, the structural support means traverses the entire central member to provide increased structural support and to maintain the shape of the shunt when inserted in the vessel. In preferred embodiments of the invention, the structural support means is a coil which is embedded in a flexible material which seals the shunt along its length and the length of the central lumen disposed therein. The coil is inherently flexible and returns to its original shape after being manipulated during insertion into the vessel at the anastomosis. Although a coil is preferred, a braid, mesh, or other rigid structure such as a tube or cylinder may also be incorporated into the central member of the shunt. 
     The manufacture of the preferred coil embodiment may be achieved by embedding the structural support means into a thermoplastic elastomer or other fluid impermeable flexible material to obtain a conformable center section which provides structural integrity around a hollow space (lumen) traversing the center section to permit the flow of fluid, i.e., blood, therein. Preferably a thermoplastic elastomer extrusion can be drawn over a flexible coil and subsequently shrunk onto the coil, i.e., by heat treatment. The coil may also be dipped in silicone to impregnate the structural means. The coil can be formed from several materials generally considered suitable for filaments, including stainless steel, tungsten, aluminum, etc. Additionally, a synthetic coil can be formed from Kevlar and like materials. 
     To form a central member from a coil, particularly where the central member is sized for a typical LAD, the coil is slipped over a teflon beading mandrel with an outside diameter of approximately 0.032″ and a thermoplastic elastomer (such as a polyether block amide PEBA) lumen is slipped over both the coil and mandrel. The PEBA is melted and impregnated into the coil by heating with a hot nozzel or hot dye at approximately the melt temperature for the polymer used (such as 300 at 450° F.) for about 30 seconds to one minute. The shrink tubing is manually removed to yield a reinforced central member assembly made of a coated structural means comprised of an impregnated coil. 
     Alternatively, the reinforced central member assembly can be made using a molding process or an extension process. The molding process can be done by applying short cycles of heat and pressure. A coextrusion process can also be used by simultaneously winding a coil into an extruder to impregnate the coil. The tips of the shunt are made in a similar fashion to the central member. A tapered mandrel is used as the inside of the mold and either a heat shrink tubing or a hot dye is used as the outside mold. Heat and pressure are necessary to flow the thermoplastic elastomer to the proper shape. The tip is drilled or punched with a sharp hypotube to create the perfusion holes. After one tip is made a mandrel is inserted through one of the perfusion holes to form the tip at the other end. Alternatively, the tips with or without holes, can be injection molded of then attached to the central member. 
     The device at the invention may also be expandable and may have expandable members attached to the central member by any convenient method such as by ultraviolet curing of an adhesive, a cyanoacrylate adhesive, or by solvent bonding. Where necessary, the expandable members may be compressed using a mechanical fixture or equivalent during attachment. 
     In preferred embodiments of this configuration, the expandable members are comprised of annular segments of expandable foam which, upon radial expansion, engage the interior walls of the vessel to prevent the flow of blood from passing out through the opening in the vessel. The foam material may be advantageously selected to expand upon contact, or shortly thereafter, with blood or other fluid so that the shunt may be manipulated with the expandable members in a substantially unexpanded state, followed by insertion into the vessel whereupon the members expand to engage the inner walls of the vessel. The expansion of the expandable members may be caused by contact with fluid such as blood by chemical treatment of the shunt, or by constructing the shunt so that insertion into a vessel causes selective exposure of the expandable members to fluid. 
     To provide maximum control over the timing of the expansion of the expandable members and to provide a slippery surface during insertion against the artery wall, all or a portion of the annular ridges, may be covered or surrounded by an associated structure such as a substantially fluid impermeable sheath means which is removed from about the expandable ridges upon positioning of the shunt device. The sheath means are preferably made of C-flex, a styrene ethylene butylene styrene block copolymer and are simultaneously stretched and slipped over and around the expandable members. Once the sheath means are positioned, a thread is arranged to facilitate removal of the sheath means upon placement of the shunt. In the above configurations, the shunt may be positioned such that the central member is coaxial within the vessel prior to removal of the sheath means, or expansion of the expandable members, thereby providing maximum control, minimizing the potential for trauma to the vessel, and providing a more effective seal between the shunt and the interior of the vessel at points beyond the apex of the incision. In a preferred embodiment of this configuration, the sheath means are deployed by manipulating a plurality of threads, which may be surgical sutures, and which are attached to or surround the sheath means. The thread(s) may approach the shunt substantially at the middle of the central member of the shunt (of may be offset) where one or more, and preferably two, suture guides direct the path of the thread to engage the sheath means at either end of the shunt. 
     In this embodiment, the central member of the shunt has associated therewith at least one (and preferably two) threaded guides which are typically offset from the center of the device and are each disposed between the center point of the lumen of the device and the expandable members at either end of the shunt device. The thread guides reduce the possibilities that the threads will become entangled with sutures used in the surgical procedure. Thread or suture guides are also used as covers and capture the sheaths after deployment in a way to minimize interference of the sheaths with sewing needles used to sew the anastomosis. 
     The sheath means and attached thread are preferably associated with a sheath remover which facilitates the selective removal of the sheath means from about the expandable members. The sheath remover is a small length of hollow tubing which should have a diameter less than the central member of the shunt and less than the shunt retriever described elsewhere herein. The sheath remover is traversed by the thread and facilitates the mechanical removal of the sheath means by sliding the sheath remover into abutment with the shunt. The sheaths may then be removed by drawing tension on the thread. After removal of the sheaths, the sheath remover is slid along the thread away from the arteriotomy. 
     In addition, a single ridge of an axial length sufficient to span the anastomosis site may be provided concentrically about the central member. The single ridge configuration preferably is an expandable member which initially is in a contracted condition to facilitate insertion. The expandable member further subsequently may be contracted to facilitate removal from the LAD. 
     In further embodiments, the central member itself, along with the end members which may be tapered accordingly, is selectively expandable radially outward, whereby essentially a portion of the shunt is expanded in diameter upon demand when the shunt is in place, to occlude blood from the thusly isolated anastomosis site. As in the case of the single and dual ridge embodiments of previous discussion, the material used in forming the shunt may dictate the structure of the shunt as well as its associated manner of contraction and/or expansion. Where a separate expandable member is provided in close proximity to the end members, the end members may be tapered from the most distal point backwards such that the abutment with the expandable members is substantially flush, i.e., have substantially equal outer diameters. 
     To illustrate, in the dual or single ridge shunt configuration, the expandable members which are formed, for example, of a hydrophilic polymer material which expands upon being converted to a hydrogel material in the presence of aqueous fluids such as hydrophilic polyurethane. The hydrogel will undergo hydration-dehydration cycles, however since the shunt is in a wet environment the material and thus the expanded ridges may not be contractible subsequently. In an alternative embodiment the ridges may be formed of annular balloons which are both expandable and contractible on demand. The single ridge configuration is provided with a partial cylindrical sheath in the region of the anastomosis to prevent puncture of the balloon by a suture needle. 
     In further embodiments, the central member and the tapered end members themselves are formed of the hydrophilic material which converts to a hydrogel material or hydrophilic polyurethane when wet. Alternatively, the central member is formed of an elongated annular balloon which when expanded still provides the lumen therethrough. In another embodiment, the central member is formed of a cylindrical unfolding spiral of a polymer material such as polyurethane, polyester, polyethylene, PEBA, silicone, latex, a shape memory thermoplastic, or hydrophilic polyurethane which loses a sticky property and expands to a desired diameter of, for example, from I to 6 millimeters (mm), upon being exposed to an aqueous fluid. Such a material and the shunt generally is not contractible after expansion. 
     In a further alternative embodiment, the cylindrical unfolding spiral is formed of two bonded sheets of, for example, a nickel-titanium alloy material having an inherent shape-memory property. One sheet is annealed in the shape of a tightly curled cylinder, while the other sheet is annealed as a flat or less curled sheet. A heating coil is bonded to each sheet. The shunt is formed of the bonded sheets rolled into a spiral cylinder of selected diameter. The application of a small electrical current to one coil causes the shunt to contract, while the application of a small electrical current to the other coil causes the cylindrical spiral to unfold and expand to the desired diameter. 
     In still a further alternative embodiment, the shunt is formed of a cylindrical braided material of selected nominal diameter. The braided material decreases in diameter relative to the nominal diameter when stretched axially, and increases in diameter relative to the nominal when compressed axially. The shunt is formed of the braided material to define a central member with tapered end members integrally formed therewith. A selected length of the central member is impregnated with an elastomer material such as silicon, latex, etc., which is impervious to fluids while still allowing axial and radial flexibility. A thread or other filamentary strand, is attached internally to either tapered end of the shunt, whereby applying a pulling force to the thread causes the braid to contract and expand, while relaxing the pulling force allows the braided material to relax and contract. 
     In other alternative embodiments, various configurations of flexible springs and/or coils are employed as the basic expandable and contractible structures. The coils generally are provided with a loose or compliant cover, for example, a fluid-impermeable, flexible elastomer material to provide the fluid impervious central member required to isolate the anastomosis site. In some embodiments the shunt diameter is controlled by the application of a force to a thread, thin wire, etc., which force in turn alters a natural state of the coil to produce an expansion and/or contraction. 
     In a modification of the various shunt embodiments, a portion is removed from the central member to define a necked-down mid section. This embodiment lends itself to an insertion procedure wherein the shunt is folded at the necked-down mid section via forceps or other insertion instruments and both tapered ends are inserted through an arteriotomy whereupon the shunt is gently unfolded into place in the artery. 
     In a further alternative embodiment, a shunt access member in the general shape of a tube, is formed in the central member of the shunt to extend generally radially therefrom. The tube includes a lumen therethrough which is in communication with the lumen of the shunt. Such an access member may provide support for the distal end of an IMA to facilitate the anastomosis construction and/or to maintain blood flow from the IMA to the artery or other vein or artery from the body or outside the body. Further, the access member provides access to the artery by an introducer implemented in another insertion procedure particularly applicable to such a shunt configuration. 
     The device of certain embodiments of the invention is of a size to fit conformingly within an arterial vessel, especially a coronary artery, and is of an overall length and diameter usually in accord with a vessel occluder rather than a mere tube-type shunt of traditional design which only permits the flow of blood therethrough. Despite the smaller dimensions of the distal-perfusion type shunt of the invention, the shunt has sufficient tensile strength to be manipulated by a surgeon using surgical tools, is flexible enough to be placed within a moving vessel without damaging the vessel or the surrounding tissues, and is structurally durable enough to maintain a shape permitting the flow of blood therethrough. 
     As is apparent from the description herein, the insertion and removal of the device of the invention is achieved in a manner to lessen the possibility of damaging the vessel into which the device is inserted. The shunt may readily be inserted and removed using forceps. For insertion, first, one end member of the device is inserted into the vessel by guiding the tip of one end member through the arteriotomy and then advancing one end of the device into the vessel until the holes in the first end member are within the vessel at a point beyond the incision. Similarly, the expandable members or annular ridges are advanced to a point beyond the apex edge at either end of the incision to effectively seal the device against the inside of the vessel. At this point, the central member is manipulated until the tip of the other end member can also be introduced through the arteriotomy. Once both tips and end members are inserted, the central member of the shunt is positioned within the arteriotomy to prevent the flow of blood out through the arteriotomy while permitting distal perfusion by the flow of blood through the shunt; preferably, the end members of the shunt are roughly equidistant from the center of the arteriotomy. 
     The device may have fixtures or separate apparatus operably associated therewith to aid in deploying and removing the shunt in a surgical setting. As noted above, a thread attached to the device, preferably in the center thereof, aids in removal. Additionally, however, one may use the thread in cooperation with additional associated fixtures to provide a shunt remover for removal and retrieval of the shunt from the vessel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are elevational views, in cross-section, of a small segment of an artery depicting a shunt installed within the artery in accordance with the invention to isolate an anastomosis site while maintaining blood flow distally. 
     FIGS. 3,  4  and  6  are elevational views, in cross-section, of alternative embodiments of the present invention depicting additional configurations and modifications of the invention of FIGS. 1,  2 . 
     FIGS. 4A and 4B are cross-sectional views taken along section lines  4 A and  4 B respectively, of FIG.  4 . 
     FIG. 5 is an elevational view, in cross-section, of a dual balloon configuration such as employed in the shunt embodiment of FIG. 4, illustrating one construction thereof and the manner of assembly about a shunt central member. 
     FIG. 7 is an elevational view, in cross-section, of still a further alternative embodiment of the present invention wherein the central member and tapered ends of the shunt are contractible and expandable. 
     FIG. 7A is a cross-sectional view taken along section line  7 A of FIG.  7 . 
     FIG. 7B is a cross-sectional view of an alternative configuration for the shunt of FIG. 7 employing a folding central member. 
     FIGS. 8 and 9 are partial elevational views, generally in cross-section, of alternative tapered end configurations which may be used in the shunts described herein. 
     FIGS. 10A,  10 B are simplified elevational views of an alternative two-piece embodiment of the invention, further depicting a sequence of steps taken by a surgeon to install the shunt at the anastomosis site. 
     FIG. 11A is an elevational view, in cross-section, of a further alternative embodiment of the invention employing a very flexible coil coated with a flexible material such as silicon, latex, etc. 
     FIG. 11B is an elevational view illustrating a procedure for inserting the shunt of FIG. 11A in place in an artery via an incision. 
     FIGS. 12A,  12 B are elevational views, in partial cross-section, of a modified embodiment of the invention, illustrating a procedure for inserting the shunt in place in an artery via an incision. 
     FIGS. 13A,  13 B,  13 C are elevational views, in cross-section, of a further modified embodiment of the invention, further illustrating a procedure for inserting the shunt in place in an artery via an incision. 
     FIGS. 14A,  14 B,  14 C are elevational views, in partial cross-section, of a further alternative embodiment of the invention, further illustrating a procedure and associated implements for inserting the shunt in place. 
     FIGS. 15A,  15 B and  16 A,  16 B are elevational views of still other alternative embodiments of the invention employing a braided tube and a laminated foil structure, respectively. 
     FIG. 17 is an elevational view, in cross-section, of an asymmetrical shunt configuration, further depicting a gum wrapper thread technique for facilitating shunt removal. 
     FIG. 18 is an elevational view of yet another alternative embodiment of the invention employing an expanding spring structure. 
     FIG. 19 is a cross-sectional view of another alternative embodiment of the invention. 
     FIG. 20 is an embodiment of the invention having two expandable members at either end of the device, surrounded by sheath means positioned with a vessel. 
     FIG. 21 is an embodiment of the invention having expandable members at both ends of the central member and one expandable member shown in an expanded state. 
     FIG. 22 shows an embodiment wherein the sheath means are deployed by manipulation of the thread to permit fluid exposure and complete expansion of the expandable members. 
     FIGS. 23A through 23C are embodiments of the invention having varying configurations of the expandable members relative to the perfusion openings, and optimally permanent and/or semi-permeable sheath means. 
     FIGS. 24A through 24C shows the device having means for retrieving the shunt comprised of a shunt remover operably associated with the suture. 
     FIG. 25 is a preferred embodiment of the invention having rounded end members and which is designed to be manufactured in discrete sizes for selection by the surgeon depending on the interior dimension of the target vessel of the anastomosis. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As may be seen from the following description and accompanying drawings, the present invention contemplates several basic shunt configurations, with a plurality of modifications to the configurations, wherein the modifications for the most part are interchangeably useable in the various basic shunt configurations. Likewise, while several materials are particularly for use with certain shunt configurations as disclosed, the materials discussed herein may generally be used with any of the shunt configurations without departing from the spirit of the invention. 
     FIG. 1 illustrates a basic shunt  20  formed of a central member  22  having a lumen  24  therethrough for passage of blood through the shunt  20  as depicted by arrow  26 . The central member  22  terminates in extremities  28  and is formed of a material such as polyurethane, polyethylene, silicon, etc. The shunt  20  is shown in FIG. 1 installed in place within, for example, an LAD artery  30  of previous mention, and particularly spanning an arteriotomy or incision  32  in the LAD which forms a site for an anastomosis construction. The shunt  20  is of sufficient outside diameter of, for example approximately 1-5 to 6 mm or any value therebetween, such that, when installed, fits snugly within the interior walls of the LAD  30  to thereby maintain the anastomosis site, corresponding to the incision  32 , free from blood while allowing blood flow  26  through the LAD. As depicted, the shunt  20  not only occludes the blood from the LAD, but also occludes blood flow from possible arterial side-branches such as depicted at  34 ,  36 . 
     As is well known, the anastomosis surgery consists of grafting a distal end of, for example, the internal mammary artery (IMA)  38 , to the LAD  30  to encompass the incision  32 . The anastomosis is performed by the surgeon by sequentially passing sutures  40  through the edges of the incision  32  and through the distal end of the IMA  38  until suture loops are made around the confronting circumference, in conventional fashion. Prior to tightening the suture loops about the circumference of the arteriotomy to secure the graft, the shunt  20  is carefully removed from within the LAD either directly or by pulling on a thread or like filamentary strand  42  or suture secured to a selected point or points on the shunt, while guiding the shunt via forceps or tweezers through the incision and adjacent loops of the sutures  40 . The suture loops about the circumference of the arteriotomy are then drawn tight to provide a fluidly sealed anastomosis. 
     By way of example, an arteriotomy may be of the order of 6 to 12 millimeters (mm) and the perfusion devices generally are of the order of 15 to 30 mm and most often 20-25 in length, with an inside diameter generally of 0.5 to 2 mm, and most often 0.65 to 1.0 mm. and the outside diameter generally of from 1.0 to 6.0 mm. and most often 1.5 to 3.5 mm. 
     FIG. 2 depicts a modification to the shunt  20  of FIG. 1, namely the addition of more pronounced tapered end members  44 ,  46  to the extremities  28  of the central member  22 , to form a generally symmetrically tapered shunt  50 . The end members are formed of the same material as the central member  22 , or may be formed separately of a material of different stiffness and then bonded, glued, etc., to the central member  22 . The taper angle of the end members  44 ,  46  may vary from a slight taper with a relatively large apex opening such as in FIG. 1, to a sharp taper extending to a closed apex to form a tip distal to the openings or perforations  52  as in FIG. 2 or to the open apex of FIG.  1 . The tapered end members  44 ,  46  are provided with a selected array of openings on perforations  52 , the number and arrangement of which are variable to provide the nominal blood flow desired for the particular surgical application. 
     FIG. 3 depicts an alternative embodiment of the invention wherein the shunt  50  of FIG. 2 is modified to provide a shunt  60  having annular ridges  62 ,  64  formed about generally the extremities  28  of the central member  22 . The ridges may be integral and formed of the same material as is the central and tapered end members  22 ,  44 ,  46  and as such are formed with pre-selected diameters. Alternatively, the ridges may be expandable members which are formed of other materials and/or of devices which are expandable as well as contractible as further described below in alternative embodiments. To illustrate, the annular ridges  62 ,  64  may be formed of the hydrophilic polymer material such as a soft shape memory thermoplastic that may be activated at body temperature or a hydrophilic polyurethane which, due to its disposition about the extremities  28  of the central member  22 , expands radially outward as it converts to a hydrogel material upon being inserted in the aqueous fluid environment of the LAD. 
     Exposure of the expanding materials to fluid my be achieved by several alternative means including providing a removable covering for the material and generally disposed about the annular ridges  62 ,  64  (in an embodiment of FIG. 2) as described in greater detail below. Alternatively, the central member  22  in end members  44 ,  46  may have an integral opening or channel (not shown) formed therein such that fluid such as blood contacts the expanding materials upon insertion into the vessel, such as the LAD artery  30 . Moreover, the expandable materials may be provided with a covering, such as the sheath means described in greater detail below, which is permanently affixed about the end members and which is permeable or semi-permeable to fluid. This embodiment provides an expandable end member  44 ,  46  for the device whereby the expansion occurs automatically upon insertion of the device into the anastomosis site (incision)  32 . Other triggerable expanding polymer materials may be used as well such as open cell foam, etc. The enlarged ridges provided by the expandable materials provide enhanced contact with the interior wall of the LAD to maximize the isolation of the anastomosis site. Note that the apexes formed at the tips of the tapered end members  44 ,  46  herein are depicted open at  65  to allow added blood flow, if desired, in addition to the openings or perforations  52 . In FIG. 3, the filamentary strand  42  is attached at two spaced apart points of the central member  22  via diverging strands  66 ,  67 . Such a dual-point strand configuration aids in the shunt insertion process, particularly when the surgeon initially inserts, for example, the end member  44  into the incision ( 32 , FIGS. 1,  2 ) by pulling gently on the combined strands  42 ,  67  as depicted by arrow  68  toward the proximal end of the shunt  60  while urging the shunt with forceps. Once the distal end member  46  clears the incision, the shunt  60  is urged distally in the LAD with forceps and by pulling gently on the combined strands  42 ,  66  as depicted by arrow  69 . Such a dual-point filamentary strand connection may be employed in other shunt embodiments described herein if desired or a single strand configuration may be used as described in greater detail herein. 
     FIG. 4 depicts a shunt  70  similar in configuration to the shunt  60  of FIG. 3 but including the modification comprising selectively expandable dual ridges defined by expandable “balloons”  72 ,  74  which herein are integrally formed with the central and tapered end members  22 ,  44 ,  46  as shown. However, the expandable dual ridges may be provided as a separately formed assembly coaxially assembled about generally the central member, as further described in FIG.  5 . As shown further in FIGS. 4A,  4 B, the central member  22  includes an axially extending thickened upper section  76  within which is formed a lumen  78  which extends the length of the central member to open into respective chambers of the expandable balloons  72 ,  74 . The lumen  78  is depicted in communication with a centrally located fluid supply tube  80  through which air, saline fluid, etc., may be supplied on demand to the balloons  72 ,  74  to expand them radially outward to desired diameters  72 ,  74 , shown in phantom line. As may be seen, the dual balloons may be contracted to a reduced diameter on demand by removing the supply of fluid, or by applying a selected source of vacuum. If a centrally located supply tube such as tube  80  is used to supply the fluid on demand to the expandable balloons  72 ,  74 , it is preferable to form the balloons of a non-compliant material, that is, a material which expands to a limit and expands no further even with the introduction of additional pressure. The use of a compliant material, such as silicon or latex, with a single supply tube could result in the expansion of one balloon but not of the other. However, a compliant material may be used if the central lumen  78  is omitted and two supply tubes supply the expansion fluid directly to respective expandable balloons  72 ,  74 . 
     The supply tube  80  may be advantageously used with the device of this invention for several purposes in addition to supplying air, fluid for the selective inflation of balloon members. The supply tube  80  may have open ports (not shown) which allow fluid to flow around the device and the incision  32  of the anastomosis site such as for irrigation, to expose the edges of the arteriotomy, etc. Thus, the supply  80  tube or tubes may perform several functions, and including shunt removals, may, as seen in FIGS. 4A and 4B, be in communication with a lumen  78  which may be integral with the body of the central member  22 . Where the lumen  78  terminates in an open part (not shown) or parts, the location of the open parts is dictated by the desired function. Where the parts facilitate irrigation, the parts will preferably be proximal to the central member  22  of the device, near the edges of the arteriotomy, and open to the external portion of the central member  22  proximal to any structure, such as balloon  72 ,  74  or annular ridges  62 ,  64 , which seal about the interior of the vessel. Likewise, for drug delivery, the opening may be external of the central member  22  or internal to deliver drugs directly into the distal perfusion provided by the device during the surgical procedure. 
     FIG. 5 depicts an alternative construction for providing the expandable dual balloon configuration illustrated in FIG.  4 . The configuration of FIG. 5 is a separate dual balloon assembly  86  in the form of a tube-like structure which can be coaxially slid over a pre-formed shunt, such as shunts  20  and  50  of FIGS. 1 and 2, and bonded, glued, etc., to the exterior cylindrical wall of the shunt (shown herein in phantom line). The assembly  86  is formed of a central member  88  of a selected material such as polyethylene, polyurethane, polyester, etc. Expandable balloons  90 ,  92  formed of the same or a different material are bonded, glued, molded, etc., to respective ends of the central member  88  to define a unitary tube-like structure. An upper axial portion of the cross-section of the central member is thickened to allow the formation therethrough of a lumen  94  which communicates with respective chambers of the balloons  90 ,  92 . A fluid supply tube  96  is formed in communication with the lumen  94  to supply or extract the air or other expansion fluid to the balloons  90 ,  92  on demand. In their expanded condition, the balloons  90 ,  92  expand radially outward to a desired diameter  90 ,  92 , depicted in phantom line. In the example of FIG. 5, the sealed chambers of the balloons  90 ,  92  are formed after the assembly  86  is sealed to a shunt, however the balloons may be formed with respective internal cylindrical walls to define a totally sealed chambers/balloons assembly  86  prior to assembly about a shunt. 
     As may be seen, the configuration of the balloons  90 ,  92 , lumen  94  and supply tube  96  resemble the configuration of the equivalent elements of FIGS. 4,  4 A,  4 B. As discussed previously relative to FIG. 4, the material used to form the balloons  90 ,  92  may be non-compliant or compliant with one or two supply tubes  96 , respectively, coupled thereto, and, optimally, providing the various functions as described above. 
     Indicator and valve mechanisms may be employed to effect a controlled expansion of the outer diameters of the balloons described in conjunction with FIGS. 4 and 5. For example, a low volume syringe may be coupled to fluid supply tubes  80  (FIG. 4) and  96  (FIG. 5) for injecting fluid to expand the respective balloons. The volume of the injected medium may be controlled by means of a indicator integral with the syringe wherein the volume of injected medium directly corresponds to the expansion of the outer diameter of the balloon. A pressure valve, also integral with the syringe, may be employed to measure the pressure of the balloons, and automatically limit the expansion of the balloons so as to prevent over-stretching of the artery wall, which may lead to serious damage to the intimal lining. Such a volume control mechanism is most useful for balloons made of compliant material. For shunts having two supply tubes (one for each balloon), a syringe having an independent supply line, indictor and valve mechanisms for each fluid supply tube may be sued. Alternatively, pressure-sensitive indicator may be used to control the expansion of the balloons. This type of mechanism may be more suitable for lower compliance balloons wherein the rate of expansion is more pressure-controlled. 
     FIG. 6 depicts a shunt  100  generally formed in the manner of the FIG. 4 shunt  70 , wherein however the spaced-apart dual balloon configuration is replaced with a single axially extending cylindrical balloon  102  angularly formed about the exterior cylindrical wall of generally the central member  22 . A fluid supply tube  104  (or tubes) is formed in communication with an annular chamber formed by the single balloon  102  and the central member exterior wall, to supply or extract the fluid to respectively expand or contract the balloon on demand. The expanded balloon is depicted in phantom line at  102 . As previously discussed relative to FIGS. 5 and 4, the single balloon  102  configuration may be formed as a separate single balloon assembly in the form of a tube-like structure which can be coaxially slid over a pre-formed shunt and bonded, glued, etc., thereto to define the balloon chamber. 
     FIG. 7 depicts another embodiment of the invention comprising a shunt  110  formed of a material which is suitably expandable upon demand in response to an inherent property and a stimulus which energizes such property. In this embodiment, the central member and, to some extent, the end members themselves expand to fit snugly within the artery. Such a material may include, for example, the hydrophilic polymer of previous discussion which expands in its hydrogel state, such as a hydrophilic polyurethane, a material having an inherent shape-memory property such as a nickel-titanium alloy, or a soft shape-memory thermoplastic that is actuated at body temperature. The shunt  110  may comprise the previously described configuration of a cylindrical central member  22 , terminated at either extremity with tapered end members  44 ,  46 . Alternatively, the central member may be formed not in a continuous cylinder, but may instead define a central member  112  formed of a sheet of suitable material such as polyethylene, polyurethane, polyester, etc., rolled into a cylindrical spiral with overlapping edges  114  of the sheet, as depicted in cross-section in FIG.  7 A. In the spiral cylindrical configuration, the tapered end members preferably are formed to, or of, the extremities of the central member  112 , and likewise may have overlapping edges. 
     In the expandable cylindrical configuration of FIG. 7, the shunt walls expand radially outward to increase the overall diameter of the shunt on demand such as, for example, after the shunt has been installed in place in the LAD. Depending upon the material, the cylindrical central member  112  may, or may not, be contractible radially inward when removal of the shunt is desired. In the cylindrical spiral configuration of FIG. 7A, the polymer material becomes slippery in the presence of fluids which causes the spiral of material to uncoil as depicted by arrows  116 , thereby increasing the overall diameter of the shunt  110  as depicted in phantom line at  112 . 
     FIG. 7B depicts an alternative configuration for providing a contractible/expandable shunt  110  employing a polymer material and a wire  115  embedded in the central member  112  along its length. A choker tube  117  is attached to a mid point of the member  112  diametrically opposite to a mid point of the wire  115 . A thread  119  attached to the wire mid point extends through the choker tube  117 . The application of a pulling force on the thread  119  while holding the tube  117 , causes the bottom length of the shunt to fold in as depicted in phantom line at  112  of FIG.  7 B. This decreases the dimension of the cross-section of the diameter shunt to facilitate insertion into the arteriotomy or removal from the artery. 
     FIGS. 8 and 9 depict alternative configurations for the end members, sharing specifically tapered end members  118 ,  120 , respectively, which may be used with the shunts described herein in place of the more pointed end members  44 ,  46  of previous description. The end member  118  is sliced preferably at an angle of the order of from 30 to 60 degrees relative to the axial length of the central member  22 , and a perforation or opening  122  of selected size may be formed in the wall of the end member generally coincident with the extended point of the end member  118 . The resulting tapered end of the end member  118  may be formed to curl radially inward around the oval circumference thereof to provide a more rounded end while further decreasing the size of a central opening  123 . 
     The tapered end member  120  of FIG. 9 is shortened in length with a relatively acute taper and a central opening  124 . The shortened end member  120  facilitates insertion of a shunt in an incision where the opposite end of the shunt is inserted initially, since the shortened end member  120  more readily clears the respective end of the incision. The FIG. 9 further depicts an integral stub  126  formed of the shunt material at a location approaching an extremity of the central member  22 . The stub  126  provides a readily grasped portion of the shunt to facilitate the insertion of the shunt via forceps. The stub may include connection for the filamentary strand  42  as shown. As will be readily appreciated by those of skill in the art, although the various embodiment of the invention are described in a symmetrical fashion about the center of the shunt, the ends thereat, and the end members particularly need not be of like configuration and may vary to facilitate the insertion, function, and removal of the device. For example, the end member of the shunt for first insertion into the vessel may have a more blunt end, as the design of the end member  120  of FIG. 9, to avoid inserting the end member  120  into a side branch of the vessel. Alternatively, an end member having a jointed tip distal to the openings or perforations  52  may facilitate easier insertion with a reduced possibility of damage to the vessel. The end of the shunt second inserted may have a finer tip because the second end may necessarily be inserted when the central member  22  is bent during placement in the arteriotomy incision  32 . 
     FIGS. 10A,  10 B depict an alternative embodiment of a two piece shunt  130  which configuration facilitates the initial insertion of the shunt through the incision  32  and into the LAD  30 . The shunt  130  is formed of two shortened central members  132 ,  134 , wherein one central member, for example  132 , has a slightly smaller diameter than the confronting central member, for example  134 . The member  134  of larger diameter has a leading portion thereof somewhat hardened to facilitate the meshing and thus assembly of the two halves into the single piece shunt  130  (FIG.  10 B). The shunt half formed of central member  132  includes a tapered end member  136  formed therewith similar to the more pointed end members  44 ,  46  of FIGS. 2-4,  6 ,  7 . The shunt half formed of central member  134  includes a tapered end member  138  which resembles that of FIG. 9, but which could be otherwise. In this example, the annular ridges  140 ,  142  are shown as non-balloon types such as those of FIG. 3, but could comprise the balloon or other configurations of ridges of description herein. Filamentary strand  144  and an integral stub  126  are secured to respective central members  132 ,  134  respectively. 
     FIG. 10A depicts the separate insertion of each shunt half, where shunt half  132 ,  136  is inserted proximally in the LAD  30  using the strand  144  and forceps to urge the half in the direction shown by arrow  148 . Then shunt half  134 ,  138  is inserted distally in the LAD  30  using an integral stub  126  and forceps to urge the half in the direction of arrow  150 . Then as depicted in FIG. 10B, the two halves are manipulated to provide the single piece shunt  130  by gently pulling the strand  144  and stub  126 , and thus the halves, towards each other as depicted by arrow  152 , while guiding the halves with forceps until the halves are united. As may be seen, the distal half of the shunt  130  has the larger diameter such that the blood flow in the artery passes unobstructed from the smaller, inside diameter to the larger outside diameter in the joined region. 
     FIGS. 11A,  11 B depict a further alternative shunt  160  formed of a lightweight flexible coil  162  formed of, for example, a stainless steel filament. In this embodiment, substantially the entire structural support means of the device is provided by the lightweight flexible coil  162 . As shown in FIG. 11A, the coil  162  may be wound having a substantially uniform diameter along the length of the central member. The dimensions of the spiral of the coil  162  may also be varied to provide the expanded or tapered end members as described in other embodiments of the invention. To selectively alter the dimensions of the coil  162 , the wire of the coil  162  is would around a mandrel having the desired dimension of the coil. Thus, expanded end members, i.e., end members having a smaller diameter than the central member, (not shown), may be formed by wrapping the wire of the coil  162  around a suitably shaped mandrel. With each possible configuration for the central member and end members, the spiral of the coil  162  preferably is tightened at the ends  164 ,  166  thereof to provide decreasing diameters and thus tapered end members  168 ,  170  for facilitating insertion in the artery  30 . The coil  162  is coated with a flexible material such as, for example, silicon, to define an impervious tube having a lumen  24  therethrough. Alternatively, the coating would be interrupted to provide perfusion holes in a portion of the lumen  24 . The resulting shunt is very flexible and is configured with an outside diameter which allows it to fit snugly within a blood vessel such as the LAD  30  while maintaining blood flow through the lumen. The wire of which coil  162  is comprised is shown as a round wire in these exampled, but may be flat or have other configurations as desired. FIG. 11B depicts one manner of installing the shunt in the LAD  30 , wherein the end members  168 ,  170  are pinched towards one another, either separately or simultaneously, passed through the incision  32 , and then urged into respective proximal and distal portions of the LAD as shown by arrows  172 , using the filamentary strand  42  and forceps. In FIG. 11B the central member of the coil shunt  160  is depicted in place within the LAD  30  in phantom line. As noted above, the central member comprised of a coil shunt may be used separately or may be joined with other features of the invention as described herein such as the end members of FIGS. 8-9, the lumen of FIGS. 4,  6 ,  7 , etc. 
     FIGS. 12A,  12 B depict a further modification to a shunt or shunts of previous or following description, which modification lends itself to an alternative technique for insertion of a shunt  180  in place in a blood vessel such as the LAD  30 . The shunt  180  is modified to include a means for attaching a guide such as a guide wire or catheter at a point on the shunt such as a perforation  182  formed in the distal end member  184 . The perforation  182  is adapted to receive a flexible guide wire  188  such as those used for catheters. The guide wire may include a typical helical coil  190  at the tip thereof or may include a balloon device as discussed below. Where the device is inserted through an incision such as arteriotomy  33  insertion of the shunt  180  is initiated as in FIG. 12A by inserting a proximal tapered end member  186  into the LAD  30  and urging the shunt as depicted by arrow  192  by gently pulling on the filamentary strand  42  while guiding and urging the shunt with forceps (not shown). The guide wire  188  is passed through the perforation  182  and thence through the incision  32  and distally into the LAD  30 . As next depicted in FIG. 12B, the guide wire  188  then is used to guide the distal end member  184 . into the LAD  30  while the shunt  180  is urged distally with forceps  194  and the strand  42 , as depicted by arrow  196 . After the shunt  180  is in place, as depicted in phantom line, the guide wire  188  is removed and the anastomosis construction can proceed. To prevent the guide wire  188  from being dislodged from its position distally in the LAD  30 , a balloon device  198  typically employed with catheters may be employed at the end of the guide wire. Expansion of the balloon device  198  as depicted in phantom line secures the end of the guide wire  188  to prevent it from being dislodged while the shunt is being urged distally along the guide wire. 
     Where the shunt is positioned using a catheter (not shown) which passes through the interior of the vessel  30 , the shunt is preferably affixed at one end to the most distal end of a catheter and advanced along with the catheter through the interior of the vessel  30  until the shunt reaches the point at the interior of the vessel  30  where the incision will be made to form the arteriotomy  32 . 
     FIGS. 13A,  13 B,  13 C depict still another alternative embodiment of the invention and a preferred method of installation of a corresponding shunt  200  via the incision  32  of, for example, the LAD  30 . The shunt  200  may be formed generally of one of the various shunt configurations of previous description with a central member  202  and tapered end members  204 ,  206 . However, as depicted in FIG. 13A, the shunt  200  is modified by removing an arcuate portion from the central member  202  to define a necked-down section  208  along a substantial length of the central member  202 , as shown. The arcuate portion which is removed may be of different lengths and/or depths into the central member, as desired. The necked-down section  208  enhances the bending flexibility of the shunt  200 , which configuration thus lends itself to a preferred method of installation of the shunt  200 . To this end, referring to FIG. 13B, the shunt  200  may be folded at its middle in the direction of the necked-down section  208 , and then pinched together as with the forceps  194  or other instrument of FIG. 12B, shown here in cross-section. The tapered end members  204 ,  206 , in their pinched-together configuration, are inserted through the incision  32  and urged in respective proximal and distal directions in to the LAD  30 , as depicted by arrows  210 . Further gentle manipulation of the shunt  200  is made with the forceps  194  in successive stages until the shunt is in a position such as shown in FIG. 13C where each end member  204 ,  206  is fully aligned coaxially in the LAD  30 . The shunt  200  then gently is reciprocated while being pushed down via the forceps into full alignment within the LAD  30 , as shown in previous figures. Upon conclusion of the suturing process but prior to tightening the suture loops, the modified shunt  200  is readily removed by pulling gently on the filamentary strand  42  to raise the necked-out and thus flexible central member  202  sufficiently to enable the surgeon to grasp, and thus pinch together, the shunt via the forceps  194 . Initial and subsequent movement of the shunt  200  also is depicted by FIGS. 13C,  13 B, respectively, if the previous insertion steps of arrows  210  are reversed as depicted by arrow  212 , shown in phantom line. 
     FIGS. 14A,  14 B,  14 C depict yet another alternative embodiment of the invention and another associated method of installation of a corresponding shunt  220  in place in an artery such as the LAD  30 . The shunt  220 , as in FIGS. 13A-13C, in general may comprise one of the shunt configurations of previous description formed of similar material. However, the shunt  220  is modified to include a shunt access member  222  which may be oval in cross-section to generally match the shape of the arteriotomy during the anastomosis construction and which provides an access lumen  224  in communication with the lumen  24  of the shunt  220 . 
     The combination of the lumen  24  and the access lumen  224  creates a substantially T-shaped fluid communication pathway such that blood can be removed from the vessel for analysis or surgical purposes. Alternatively, intravenous fluids, medicines, etc. can be introduced into the vessel via access lumen  224  to allow pharmaceutical intervention at the site of the anastomosis or distally by virtue of the distal perfusion enabled by the device of the invention. The configuration of the shunt  220  is illustrated in FIG. 14C installed in place in an artery such as the LAD  30 . The shunt configuration employing the shunt access member  222  enables an installation procedure utilizing a pair of introducers  226 ,  228  which aid in guiding the shunt  220  into place in the LAD  30 . The introducers are generally similar to dilators used in bypass procedures. In particular, the introducers  226 ,  228  each include a very flexible, or floppy, tube  230 ,  232  of, for example, a polymer material. A guide wire  234 ,  236  of selected firmer flexibility is threaded into respective floppy tubes  230 ,  232  to provide initial support for the tubes, to facilitate the shunt installation, described below. 
     FIG. 14A illustrates initial steps in the procedure of installing the shunt  220 . A first step typically is to install proximal and distal snares  238 ,  240  loosely about the LAD  30  at locations proximal and distal to the arteriotomy or incision  32 . The introducers  226 ,  228  are each threaded through the shunt access member  222 , out through respective tapered end members  242 ,  244 , and thence into the LAD  30  via respective distal and proximal apexes of the arteriotomy  32 . As illustrated in FIG. 14A, the end of the introducer  226  is fed through the distal snare  240  while the end of the introducer  228  is fed through the proximal snare  238 . FIG. 14A depicts the shunt  220  after initial steps of urging the shunt towards the incision  32  along the introducers  226 ,  228 , wherein the tapered end members  242 ,  244  are forced to begin converging together as they are urged along the guiding introducers. 
     As shown in FIG. 14B, the snares  238 ,  240  are tightened before the installation procedure is continued, to secure the introducers in place in the LAD  30 . The support wires  234 ,  236  then are removed from within the respective floppy tubes  230 ,  232  as depicted by arrows  246 , to provide increased flexibility in rotating the shunt  220  while urging the end members  242 ,  244  into the LAD  30 . Forceps  194  or other appropriate instruments are employed to aid in pinching the ends of the shunt  220  together to facilitate their entry through the arteriotomy, as shown in FIG.  14 B. The procedure is continued until the shunt  220  is in place in the LAD  30 , as depicted in partial phantom line in FIG.  14 C. The snares  238 ,  240  are removed and the floppy tubes  230 ,  232  are removed from the shunt as shown by arrows  248 . Alternatively, the snares can be retightened around the shunt as depicted by  238  in FIG. 14C to secure an adequate blood seal for the anastomosis. In one procedure, the shunt access member  222  is ligated with a suture  249 , or with a filamentary strand previously secured about the member  222 . 
     Alternatively, the shunt access member  222  may be replaced by an IMA supporting member such as that shown in FIG.  16 . The distal end of the IMA then is slipped over the IMA supporting member which, together with the shunt  220 , provides support for the anastomosis construction. 
     Although a pair of introducers are depicted in performing the installation procedure of FIGS. 14A-14C, a single introducer may be employed with an installation procedure generally similar to that described relative to FIGS. 12A-12B. That is, an introducer is threaded through the shunt access member  222 , out one end member of the shunt and into the LAD  30 . Then installation is accomplished by first inserting the free end of the shunt into the LAD opposite to the location of the end of the introducer, whereupon the introducer then is used along with forceps to finish the installation as in FIGS. 12A,  12 B. 
     In addition, the ends of the single or dual introducers may include an inflatable balloon device such as balloon device  198  discussed relative to the guide wire  188  of FIG. 12B, to secure the introducer in place within the LAD  30 . Thus, the snares  238 ,  240  may be dispensed with which reduces the arterial trauma which can occur from the pinching effect of the snare. Further, means other than a suture or strand may be employed to seal the shunt access member  222 . For example, surgical clips or an expandable material such as the hydrogel material of previous mention, may be used. 
     FIGS. 15A,  15 B depict a further embodiment of the invention employing a braided tube  252  to form the central member and tapered end members of a shunt  250 . A central portion  254  of the braided tube  252  is coated with an elastomer material to provide an impermeable membrane that stretches when the braided tube  252 , that is, the shunt  250 , is compressed axially. The remaining uncoated end portions of the braided tube  252  provide the tapered end members of previous description as well as the openings to allow the flow of blood through the shunt. A choker tube  256  is integrally secured to a mid point of the central portion  254  of the shunt. Atraumatic tips  258  of soft elastomer or plastic material are formed as end members at the ends of the braided tube  252  to prevent damage to the artery during insertion. A thread  260  is secured to each end of the shunt and thence through the lumen of the central portion and out through the choker tube  256 . 
     The shunt  250  is inserted through the arteriotomy or incision  32  by slipping first one end and then the other therethrough into the LAD  30 , as depicted in FIG.  15 A. As depicted in FIG. 15B, the shunt  250  is expanded radially outward to engage the interior wall of the LAD  30 , by applying a pulling force to the thread  260  while holding the choker tube  256  to compress the braided tube  252  axially. The expanded central portion  254  spans, and thus occludes, the arteriotomy. The shunt is maintained in the expanded condition by pinching the choker tube  256  with locking forceps  262  or other pinching device, to lock the thread  260  therein. 
     FIGS. 16A,  16 B depict still a further embodiment of the invention wherein a coil shunt  270  is formed of a pair of coils  272 ,  274  which are laminated with an elastomer material to provide flexible tubular members about the coils. The elastomer material may also extend between the coils  272 ,  274  to define a tubular center member  276 . The center member  276  is formed about and between the coils by means of, for example, a conventional molding process and may include, in the region of the anastomosis, an inflatable, generally oval shaped balloon device  278  which when inflated exposes the edges of the incision  32  to facilitate the suturing procedure. An IMA supporting member  280  formed of an elastomer material and having a lumen  282  therethrough, is molded at its distal end to the elastomer material extending between the coils  272 ,  274 . The resulting IMA lumen  282  thus is in communication with the lumen  24  of the shunt  270  to allow the flow of blood from the IMA  38  to the LAD  30  if desired. However, the combined shunt structure, including the inflatable balloon device  278 , maintain a dry anastomosis site. In addition, the IMA supporting member  280  may include at its proximal end an enlarged flange  284 , formed of material such as hydrogel or an inflatable balloon, which exposes the distal end of the IMA  38  to further facilitate the suturing procedure. To illustrate, FIG. 16A depicts a suturing needle  286  used in a typical suturing procedure, wherein the procedure is aided by the exposure of the anastomosis by the IMA flange  284  and the balloon device  278  as depicted. 
     As show in FIGS. 16A,  16 B, the proximate ends of the coils  242 ,  244  are accessible via coil removers  288  whereby the coils may be unraveled independently from within the laminated elastomer material, FIG. 16B, to provide an enlarged lumen  24  or to facilitate the removal of the shunt  270 . 
     It is understood that an IMA supporting tube, such as the tube  280  of FIGS. 16A,  16 B, may be employed in the various shunt configurations of description herein if desired, and is not limited to use with the coil configuration as shown and described. Alternatively, the central tube  280  can be connected to other source arteries or veins to provide perfusion and allow drug delivery. These source arteries can be the femoral vein, aorta, medial artery, etc. Alternatively, the T-shaped shunt or standard shunt can be used to provide intermediate blood perfusion to the distal myocardium for cases when the patient is hemodynamically unstable during the operation without necessarily focussing on occlusion. The goal would be to prevent further ischemia damage and to stabilize the patient before beginning an anastomosis. 
     FIG. 17 depicts further alternative modifications to the various shunt configurations described herein, in accordance with the aspect of the invention where an asymmetric construction is used. For example, a central member  292  and associated tapered end members  294 ,  296  may be formed with slightly tapered geometry to define thus an asymmetrical shunt configuration matching the typical decreasing diameter of a coronary artery in the distal direction. In addition, a shunt may include a means for splitting the shunt, either axially along its length of circumferentially, to enhance the collapse of the shunts diameter to facilitate its removal. To this end, in FIG. 17, a thread  298 , flexible wire, etc., is embedded within the wall of the shunt, preferably at least along the central member  292  in the same manner as a gum wrapper package is provided with a filament to split the package wall. The thread  298  may extend from a point  293  along the length of the shunt to a point  295 , and thence in a loose loop to a tear patch  297 . The thread then extends from the shunt as depicted at  299  through, for example, a suitable opening in the diametrically opposed wall of the central member  292 . Thus the thread  298  is used as the means for aiding the insertion of the shunt where gentle pulling does not tear the patch  297  to initiate the splitting action. When the shunt is to be removed, forceps or other appropriate instruments are placed against the shunt and a greater pulling force is applied to tear the patch  297  and cause the thread  298  to slice through the shunt wall. 
     As noted above, the various embodiments described herein may be asymmetrical in design and construction. This extends to the tensile strength of the overall device and to the central member  292  particular. Because one end member of the device is typically introduced first, the central member may have various degrees of stiffness along its length. Preferably, the end designed for first insertion is stiffer to allow the first end to be pushed into the vessel and to avoid undesired flexing of the central member  292  upon insertion. The opposite end designed for second insertion, is more flexible so that it may be more readily bent for insertion when the first end is already in place in the vessel. Having a more flexible section also provides ease of removal at the end of the anastomosis procedure. 
     Similarly, although in the embodiments described herein and shown in the attached figures the central member is generally centrally disposed relative to the circumference of the end members, the central member may be offset such that the shunt device could be positioned within the arteriotomy such that the central member would lie closely along the inner side of the vessel opposite the site of the arteriotomy incision. This configuration maintains the structural portion of the shunt device, which actually rests inside the vessel, out of the way of the suturing procedure whereby the surgeon attaches the vessel to complete the anastomosis. 
     FIG. 18 depicts a further alternative embodiment of the invention, wherein a further coil structure is employed in a shunt  300 . More particularly, thin, flexible wire springs or coils  302 ,  304  are laminated with a coating of a flexible elastomer material, generally as previously depicted in FIGS. 16A,  16 B, to form an impervious central member  305  and generally tapered end members  306 ,  308 . The end members are formed with openings  301 ,  303 . A choker tube  310  is formed with a wall of the central member  304  at generally a midpoint and extends generally normal therefrom. Threads are secured to respective facing ends of the coils  302 ,  304 , are passed through the choker tube  310  as divided threads and extend from the tube as a united thread  312 . As depicted in solid, a pulling force applied to the thread  312  while the choker tube  310  is held axially stretches the coils (herein only coil  302  and laminated coating is shown in a stretched condition). A locking forceps  314  is used to pinch the choker tube  310  against the thread  312  and to maintain the coils and thus the shunt in the extended condition. The small diameter of the unextended shunt  300  allows ready insertion in the artery. Once in place, the forceps  314  are removed and the coils  302 ,  304  return to their natural axially compact state (herein shown by the coil  304  and laminated coating, in phantom line). As may be seen, when the coils  302 ,  304  return to their natural state, the diameters of the shunt  300  at either end expand radially outward to provide snug engagement of the elastomer coating with the interior walls of the LAD  30  proximal and distal to the anastomosis site. 
     FIG. 19 depicts a further alternative embodiment of an expandable shunt  320  wherein a cylindrical unfolding spiral is formed of two bonded sheets  322 ,  324  of, for example, a nickel-titanium alloy material having an inherent shape-memory property. One sheet, for example  324 , is annealed in the shape of a tightly curled cylinder, while the other sheet, for example  322 , is annealed as a flat or less curled sheet. A heating coil  326 ,  328  is bonded to respective sheets  322 ,  324 . The shunt  320  is formed of the bonded sheets rolled into a spiral cylinder of a diameter corresponding to the desired diameter in use. Since the shunt  320  is expandable through most sizes of arteries, the initial diameter of the shunt may be made smaller than the diameter of the smallest arteries. Application of a small electrical current for a short duration to the coil  328  bonded to the tightly curled sheet  324  via, for example, a voltage source  330  and a switch  332 , causes the sheet to contract, facilitating the insertion of the shunt  320  in the artery  30 . Upon insertion of the shunt, another small electrical current is applied for a short duration to the coil  326  of the sheet  322  which is annealed while flat or less curled, causing the cylindrical spiral to unfold to expand the diameter of the shunt. When contraction of the shunt  320  is desired as when the shunt is to be removed, the current is applied to the coil  328  which causes the cylindrical spiral to contract radially inward. 
     Referring to FIG. 20, an embodiment of the invention has a selectively expandable members  350  disposed proximate to each end member  351  and proximal to the openings/perforations  352  for perfusion. Each end member  351  has a tip  353 , distal to the perfusion openings  352 , pointing in opposite directions respectively and generally coaxial with the central member  354 . As shown in FIG. 20, the shunt device has been inserted through arteriotomy  355  formed in vessel  30  and has been positioned such that each expandable member  350  is maintained in a position beyond the apex of the incision forming the arteriotomy  355  and is placed prior to selective expansion at the expandable member(s)  350 . In this embodiment, each expandable member  350  is an annular section of expandable foam that is covered with sheath means  356  to maintain the expandable member  350  in an unexpanded state until the placement and positioning of the shunt is complete. In the embodiment of FIG. 20, each sheath means  356  is attached to a thread  357  for selective removal of the sheath means  356  from about the expandable members  350 . The thread  357  may be a single line which approaches the central member  354  at approximately the mid-point or may be offset, or may have several individual threads, at least one of which is attached to each sheath means and which are interwoven. Thread guides  358  may direct each thread axially along the central member  354  to attach to the sheath means  356 . FIG. 21 shows the relative configurations of the device having one expandable member  350  in an expanded state and one expandable member  350  remaining in an unexpanded state. 
     The thread guides  358  may be rigid plastic fixtures integrally formed with the central member  354  or may be provided by a plurality of annular plastic bands (not shown) which tightly surround the central member  354 . In this configuration, threads  357  pass underneath the annular bands and are connected to the sheath means  356 . Ideally at least two annular bands are provided in a similar fashion to the embodiment shown in FIG. 22, i.e., one each between the point where a thread or threads  357  engage to shunt device and where a thread  357  is attached to the sheath means  356 . Thus, when the sheath means are removed by drawing tension on the threads  357 , the sheath means  356  are tightly gathered and collected next to the annular bands such that the sheath means  356  do not become detached from the device and remain securely attached to the central member  354  while the surgical procedure is completed. 
     Referring to the embodiments of FIGS. 21 through 23C, the central member  354  preferably has a structural support means comprised of a coil  272  to provide a coil-reinforced lumen that provides flexibility without kinking and reduces the overall thickness required for the lumen wall. The coil  272  may be continuous, may have a variable winding frequency, and may also be a square, flat, or triangular shape. For ease of insertion and removal, the coil  272  may be provided in individual segments that have interruptions at one or more points along the length of the central member  354 . Preferably, the interruptions are near the center of the central member  354 , for ready removal for example, at the point at which the central member  354  of the device is affixed to the thread  362 . 
     FIG. 22 shows the embodiment of FIG. 20 after the sheath means  356  have been removed from about the expandable members  350  and drawn towards the center of the shunt by exerting tension on the thread  357  via thread guides  358 . In this configuration, the sheath means  356  are gathered together by the thread  357  when removed from about the expandable members  350  to avoid becoming entangled during the anastomosis procedure. The expandable members  350  expand to contact, in annular fashion, the interior at the vessel  30  to seal the flow of blood to prevent leakage through the arteriotomy  355  while establishing flow into and out of the perfusion holes or perforations  352 , through the central member  354 , and out the opposite perfusion holes to provide perfusion distal to the arteriotomy. 
     Selective expansion may also be provided by a thread  357  which actuates a mechanical means (not shown) for causing the means for providing an enlarged diameter to expand. For example, a proximal collar may be provided having a plurality of outwardly bendable wires or tires that bend outward when tension is exerted on a thread attached to the distal end of the mechanical means. Thus, as tension is drawn on the distal end of the mechanical means, the proximal collar remains in place while the wires or tires bend radially outward forcing a permanent sheath means  356  or other covering to engage the inside of the vessel. 
     Each of the embodiments of the distal perfusion device (shunt) having expandable members may readily be provided by polyvinyl acetate or polyvinyl alcohol foam particularly annular foam sections that are close to or about the end members of the shunt. The rate of expansion if the expandable members may be altered by coating the foam with a hydrophilic or coating that provides lubrication. The coating also aids atraumatic insertion and removal of the shunt and means are not used, facilitates removal of sheath means in certain embodiments. The coating may include heparin or other blood-related products compatible for export to dissolution in the blood stream. Particularly where sheath means are not used, the foam may also be treated with a cured adhesive or coating of silicon or a like substance to retard the fluid permeability of the foam, thereby reducing the rate of expansion and providing additional time to position the shunt during the anastomosis procedure prior to expansion. 
     FIG. 23A shows a preferred configuration for the end members  351  being in close conformity with expandable members  350  such that minimal trauma to the vessel results from insertion of the device. In this configuration, the maximum outer diameter of the expandable members  350 , in their original state, closely approximates the outer diameter of the end member  351  at the point where the end member  351  and the expandable member  350  meet. The expansion of these expandable members  350  may be provided by any of the techniques previously described herein, such as by deployment of a sheath means, a permanent sheath which is permeable or semi-permeable to fluids, or by modifying the design of the end members or central member to provide fluid access to the expandable members. 
     Referring to FIG. 23B, in another embodiment the sheath means  356  is permanently affixed to the exterior of the expandable members  350 . Expansion of the members  350  is likewise achieved by exposure to fluids, however, the fluid source comes from within the central member  354  by openings  352  located beneath the expandable members  350 . Fluid passing through openings  352  encounters the underside of the expandable members  350  causing them to expand such that the sheath means  356  abuts the interior of the vessel. Referring to FIG. 23C, a similar resulting configuration can be provided without the necessity for openings  352  to be in fluid communication with the expandable members by providing a semi-permeable sheath means, preferably formed of a flexible thin polymer sheet that may have a dissolvable coating, such that fluid causes the expandable members to expand by slowly penetrating the sheath means from the exterior thereof. 
     Referring to FIGS. 24A,  24 B, and  24 C, removal of a shunt having a flexible central member  364  from within the arteriotomy may be facilitated by a removal device  365  which is preferably integral with a thread  362  attached to the shunt of the invention. The shunt remover  365  may be comprised of a substantially cylindrical hollow body  360  having a stretchable tapered end portion  361  for easy insertion between sutures. Tapered end portion  361  is also made of a flexible or stretchable material, such as polyurethane, polyester, PEBA, polyethylene, etc. to ease drawing the shunt into the body of the shunt remover. The shunt may be drawn into the body of the shunt remover  365  by applying tension to thread  362  which is attached to the shunt, and is preferably larger in diameter, i.e., double the outer diameter of the central member  364 . Thread  362  is also attached to the shunt at a point off-center (not shown) so that expandable members  350  exit the arteriotomy one at a time, or sequentially, to avoid stretching the arteriotomy and to avoid jamming within shunt remover  365 . At the completion of the use of the shunt, the shunt remover would be advanced to the arteriotomy site and placed against the central member  264  at the point where the thread is attached to the central member. As shown in FIG.  24 B, by contacting the central member  364  of the shunt with the body of the shunt remover  365  and exerting tension on the thread  362 , the central member  364  collapses and is drawn into the body of the shunt remover  365  as shown in FIG.  24 C. By this design and technique, the shunt is readily removed from the vessel through the arteriotomy, in a single step, without the necessity to manipulate the shunt, thereby reducing the possibility of damaging the vessel. 
     The body  360  of the shunt remover  365  may have an opening, preferably formed as a slit  366 , running the length of the cylindrical portion of the body  360  of the remover  365  to ease the insertion and manipulation of the shunt remover  365  about the thread  362 . Alternatively, the slit  366  may extend through only a portion of the cylindrical body  360  of the shunt remover  365 . If desired, a similar device (not shown) can be used as a shunt insertion tool by providing a plunger within the body  360  and by folding an unused shunt and positioning it in the body thereof. By depressing the plunger the shunt is directed into the vessel. A stop may also be positioned at the distal end and placed inside the vessel to direct insertion of the shunt into the vessel by deflecting the tips in either direction. 
     In embodiments where a removable sheath means are used, the sheath remover  365  may have associated therewith a sheath remover  367  preferably traversed by the thread  362  and located intermediate of the shunt and shunt remover  365 . The diameter of the shunt remover is smaller than the diameter of the central member  364 . Using the sheath remover  367 , the sheath means are removed by bringing the sheath remover  367  into contact with the central member  364  at the point of attachment to the thread  362 . Because the inner-diameter of the sheath remover  367  is smaller than the central member  364  of the shunt, by exerting tension on the thread  362 , the sheath means are removed from about the expandable members  350 . 
     Referring to FIG. 25, a preferred embodiment of the invention is shown which is similar to the embodiment of FIG.  3  and has rounded end members  368  to engage the interior surfaces of the vessel, perfusion holes  369  distal to the rounded portion of the end members  368 , and a tip distal to the perfusion holes  369  to facilitate placement of the device in the vessel. This configuration is preferred for ease of manufacture and is specifically contemplated to be manufactured in discrete and varying sizes depending on a clinical assessment of the physiology of an individual patient. Typically, the outer diameter of the device at its maximum point, the point of the maximum diameter of the rounded end members, varies from approximately 1.5 mm to 5.0 mm. In use, the selection of the proper size of the device of the invention may be achieved by visual inspection or by mechanical measurement of the vessel interior at the site of the arteriotomy. The device is preferably provided with a thread line affixed to the central member to facilitate removal of the device. 
     In addition to providing a separate fixture to remove the shunt, a similar, related device can be used to insert the shunt into the vessel through the arteriotomy and to position the shunt in preparation for the anastomosis. As with the body of the shunt remover, the shunt insertion tool has a body which is preferably greater than twice the largest outer diameter of the central member of the shunt. The shunt is placed in the body at the distal end where an opening exists. Within the body of the shunt insertion tool, a slidable member engages the shunt and pushes the shunt out of the body of the insertion tool and into the vessel. Preferably, the shunt is doubled over within the body of the insertion tool such that approximately the mid-point of the shunt is most proximal to the surgeon and the ends of the shunt are most distal and may extend slightly from the opening at the distal end of the shunt insertion tool. To deploy the shunt, the slidable member is moved downward to abut the shunt within the body of the insertion tool such that approximately the mid-point of the shunt is most proximal to the surgeon and the ends of the shunt are most distal and may extend slightly from the opening at the distal end of the shunt insertion tool. To display the shunt, the slidable member is moved downward to about the shunt within the body of the insertion tool to force the shunt out of the insertion tool and into the vessel. While the distal end of the insertion tool may be comprised of a simple opening, the distal end may also have guides to facilitate atraumatic insertion of the shunt into the vessel. 
     Although the invention has been described herein relative to specific embodiments and modifications, various additional features and combinations of those specifically described will be apparent from the description and drawings. Thus the scope of the invention is defined by the following claims and their equivalents.