Abstract:
Surgical construction or bypass grafting of a target vessel includes method and instrumentation and apparatus for forming and inserting a fluid-impervious tubular conduit including a central protrusion through an aperture in the vessel to form a fluid-conducting shunt past the aperture. An anastomosis over the aperture is partially completed with the protrusion of the tubular conduit extending through the partial anastomosis. A removal tube is disposed over the protrusion for applying tensile force thereto relative to the tubular conduit for dissembling the tubular conduit along a continuous path for removal as a single strand from the vessel through the tube and aperture and the partial anastomosis prior to completion of the procedure.

Description:
FIELD OF THE INVENTION 
   This invention relates to temporary conduits for use in vascular surgical procedures, and more particularly to a temporary shunt for easy insertion into, and removal from, a target vessel in a living body. 
   BACKGROUND OF THE INVENTION 
   During arterial reconstruction or bypass procedures, the target artery is generally clamped proximal and distal to an anastomotic site for a brief interval to provide a blood-free field for performing the anastomosis. However, interruption of blood flow in the recipient artery may be dangerous to the patient. Ischemia to the heart during coronary artery bypass may result in myocardial infarction. Similarly, ischemia to the brain during carotid endarterectomy may result in stroke. Consequently, surgeons often place an arterial shunt in the artery undergoing reconstruction, to avoid the potential for ischemic complications. The arterial shunt is a flexible tube that is inserted into the arteriotomy. The outer diameter of the shunt approximates the inner diameter of the artery, so that flow is maintained in the artery and ischemia does not occur as the arterial bypass or endarterectomy is being performed. 
   Presently, it is difficult to remove a shunt following its use. As the anastomosis is being completed, or the artery is being closed following endarterectomy, the last several suture loops at the entry site of the shunt are not cinched down, and the shunt is worked out of the artery. Shunt removal is a delicate process, and it may be difficult to perform without disrupting the anastomosis being formed. The anastomotic suture may be broken, or tension on the suture may cause it to cut through the arterial wall. 
   SUMMARY OF THE INVENTION 
   In accordance with an embodiment of the present invention, a shunt is formed of a coiled strand, with a loop of the strand extending out of the center of the formed shunt. A tube is positioned over the center loop against the shunt to aid in removing the shunt by uncoiling the coiled strand for retrieval through the tube. The distal ends of the shunt may contain bulbous portions formed out of the strand to enhance fluid-tight sealing of the shunt within the inner walls. Alternatively, the coiled strand may form a tapered shunt, with one end of greater diameter than the other end. 
   In use, the shunt is placed into an incision in a vessel, with one end of the shunt contacting the inner wall of the vessel proximal to the incision and the other end of the shunt contacting the inner wall of the vessel distal to the incision. The anastomosis is sewn with only the loop extending out of the anastomotic attachment. A stitch is placed on either side of the loop as it exits the intra-vessel portion of the shunt. At the completion of the anastomosis, before the ends of the suture are tied, the removal tube is brought down to the vessel surface, and held stationary with a pair of curved or right-angled clamps. The loop of the shunt is pulled against the tube to cause the shunt to dissemble and peel away into a strand for removal through the tube. The stationary tube rests against the outer surface of the shunt during the dissembly process to assure that the suture line is not stressed as tensile force is exerted on the loop to unravel and remove the shunt. In this way, substantially all the force required to disassemble the shunt is exerted against the distal end of the tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a flexible tensile element such as a suture coated with a thermoplastic polymer; 
       FIG. 2  is a perspective view of the tensile element of  FIG. 1  being formed around a mandrel; 
       FIG. 3  is a perspective view of the tensile element coiled about the mandrel; 
       FIG. 4  is a perspective view of the shunt formed from the fused tensile element; 
       FIG. 5  is a perspective view of the dissembled shunt as retrieved through a removal tube; 
       FIGS. 6   a – 6   c  are partial plan views of a mandrel for forming bulbous ends on a shunt in accordance with an embodiment of the present invention; 
       FIG. 7  is a flow chart illustrating the process of installing and removing a temporary shunt in accordance with an embodiment of the present invention; and 
       FIG. 8  is a sectional view of the shunt being inserted into an artery. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIGS. 1–4 , there is shown an embodiment of the present invention in which a tubular conduit for use as an arterial shunt is formed as a coil including a plurality of substantially contiguous convolutes  16  of an elongated strand  9  that may be coated with a bioinert and preferably thermoplastic polymer. The strand  9  is wound on a mandrel  17  that has a substantially constant diameter between the ends thereof, with a protruding loop  13  formed intermediate the ends. The strand  9  is constructed from a length of suture or wire that is coated with a material such as polyvinyl chloride, polyurethane, silicone rubber, or the like. The center of the length of strand  9  is formed into the loop  13  of length approximately 5 cm. The two strands at the bottom of the loop  13  may be held together by a tie  15  such as a band heat-sealed to the strands, or by a length of heat shrink tubing, or by a suture winding, or held together by adhesive, or by welding a length of adjacent strands together using heat or solvent bonding, or the like. 
   The strand  9  with its formed center loop  13  is continuously wound around a rod-like mandrel  17 , as shown in  FIGS. 2 and 3 , with adjacent convolutes  16  of the coil substantially in contact with one another. The ends of the strand  9  are temporarily held onto the mandrel  17  using clips, clamps, elastic bands, sutures, or the like, as shown in  FIG. 3 . The adjacent convolutes  16  of the continuously coiled and looped strand  9  are then bonded together by heating and pressing the thermoplastic coating, or by adhesive bonding or solvent bonding or by surface coating, or the like, to form the tubular, liquid-impervious conduit  19  that serves as the arterial shunt, as shown in  FIG. 4 . Expanded bulbous ends may be formed on the distal ends of the conduit or shunt by expanding a corresponding portion of the mandrel  17 , as shown in  FIGS. 6   a – 6   c , prior to winding and bonding of the coiled and looped strand. The ends of the mandrel  17  may then be contracted to allow release of the bonded shunt  19 . 
   The conduit or shunt  19  may also be formed with varying pitch of adjacent convolutes  16  along the tubular length thereof to promote varied flexibility between the ends. As shown, for example, in  FIG. 8 , greater bending occurs near the center and ends as the shunt  19  is inserted into the artery or vessel  29 . Also, the shunt  19  may be formed of the strand wound in opposite directions between the protrusion and each end, or may be formed with tapering cross section between the ends, for example, to establish a selected pressure drop through the shunt where desirable in certain surgical environments. Additionally, shunt  19  may be formed of a strand  9  that is disposed, for example, along a serpentine pattern from end to end, or from center to each end, about the entire periphery of the tubular shunt  19 . Also, the loop  13  may be disposed closer to one of the spaced ends to facilitate easier insertion of the shunt into an artery. In another embodiment, the ends of the strand  9  may be routed through the tubular conduit  19  from the spaced ends to be brought out through a central portion of the tubular conduit  19  as the protrusion on which tensile force is exerted in order to disassemble the shunt inwardly from the spaced ends toward the center. 
   In each such form of the shunt  19 , the region between adjacent convolutes or wraps of the strand constitutes a continuous region of diminished tensile and shear strength whether formed by heating and pressing together of a thermoplastic surface layer, or by surface coating, or by adhesive or welded attachment of the adjacent convolutes in order to assure that disassembly of the tubular shunt occurs along such region, as later described herein. 
   Referring now to the partial plan views of  FIGS. 6   a – 6   c , the expandable end portions of the mandrel  17  may be constructed as lengths of longitudinally split tube  23  with an internally threaded portion  21  proximal to the split portions  23 . Bolts  25  threaded into the ends of the mandrel  17  compress the split portions  23  of the mandrel and cause them to expand. Formation of the mandrel from resilient material allows the mandrel  17  to contract to its natural, undilated position. Upon removal of the threaded bolts  25 , the associated tubular conduit  19  thus formed around such expandable mandrel  17  includes bulbous extreme ends that promote superior liquid sealing against the arterial walls when positioned within the target artery. A removal tube  31  may be captivated overlaying the loop  13  by attaching a ring  33  through the loop  13  of the larger diameter than can pass through the removal tube  31 . 
   In operation, and with reference to the flow chart of  FIG. 7  and the sectional view of  FIG. 8 , the tubular conduit  9  is sufficiently flexible and resilient when formed as previously described to facilitate reasonably easy insertion  36  of the ends through an aperture  27  in a wall of artery or vessel  29 . Then, by manipulating extension of the remote ends of the tubular conduit  19  into upstream and downstream positions  30 ,  32  relative to the vascular aperture  27 , the tubular conduit  19  can be so positioned  38  to serve as a vascular shunt through the region of the aperture  27  to promote continued blood flow through the inside of the convolutes during vascular surgery  40  for the reconstruction or formation of a vascular bypass on the target vessel  29 . The integral loop  13  remains protruding through the vascular aperture  27  and through a partially completed anastomosis  42  (not shown) to facilitate later removal of the shunt  19  from within the vessel  29 . 
   In an arterial bypass anastomosis or arterial reconstruction, and before first and last stitches of the suture are tied off, the central loop  13  remains protruding through the incomplete segment of the anastomosis to facilitate convenient removal of the shunt with minimal disturbance of surrounding tissue. Specifically, a removal tube  31 , as shown in  FIGS. 4 and 8 , is positioned  44  over the central loop  13  against the shunt  19 , with the distal end of the removal tube  31  disposed between first and last stitches in the incomplete segment of the anastomosis. The loop  13  is then tensioned  46  relative to the removal tube  31 , which can be retained in fixed position relative to the artery  29 , in order to unravel the shunt  19  for removal  48  from within the artery through the removal tube  31  as the looped, continuous strand  9 , as shown in  FIG. 5 . Removal of the strand  9  and associated liquid-impervious layer thereon through the removal tube  31  in this manner thus minimizes dissociative forces applied to the target artery  29  or the anastomosis which can then be completed  50  by tightening the sutures and tying off the ends, with resultant minimum loss of blood or interruption of arterial blood flow. 
   Therefore, the method and apparatus of the present invention provide a temporary shunt to facilitate blood flow through a target vessel during vascular reconstruction or bypass surgery. Various configurations of the tubular conduit facilitate insertion and removal of the shunt with minimum blood loss or interruption of blood flow.