Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/02—Prostheses implantable into the body
  • A61F2/04—Hollow or tubular parts of organs, e.g. bladders, tracheae, bronchi or bile ducts
  • A61F2/06—Blood vessels
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
  • A61B90/08—Accessories or related features not otherwise provided for
  • A61B2090/0801—Prevention of accidental cutting or pricking
  • A61B2090/08021—Prevention of accidental cutting or pricking of the patient or his organs
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2250/00—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof
  • A61F2250/0058—Additional features; Implant or prostheses properties not otherwise provided for
  • A61F2250/0096—Markers and sensors for detecting a position or changes of a position of an implant, e.g. RF sensors, ultrasound markers
  • A61F2250/0098—Markers and sensors for detecting a position or changes of a position of an implant, e.g. RF sensors, ultrasound markers radio-opaque, e.g. radio-opaque markers

Definitions

• the present invention relates to a tubular sheath for protecting coronary artery bypass grafts such as the internal mammary artery (IMA) and to a method of fabricating an extruded and expanded bio-compatible tubular sheath for this purpose.
• the invention also relates to a surgical procedure in which a tubular sheath is placed over the graft to be protected when performing bypass graft surgery.
• Background Of The Invention The use of the internal mammary artery as a bypass graft to correct a coronary artery obstruction has been an accepted medical procedure for a number of years.
• the internal mammary artery, left in situ attached to the subclavian artery, is anastomosed to the coronary artery beyond the obstruction.
• One of the reasons for use of the IMA in coronary artery bypass procedures is the high patency rate compared with saphenous vein bypass grafts.
• IMA grafts Because of the substantial utilization of IMA grafts, patients who previously have undergone such procedures are undergoing repeat coronary bypass surgery (termed "re-do" surgery).
• the IMA is normally dissected with an IMA pedicle and it is particularly susceptible to adhesion formation because of its location and because of the surrounding muscle and tissue associated with its take-down from the mediastinal fat at the chest wall. Generally, most of the pedicle remains outside the closure of the pericardium.
• Adhesions to the IMA pedicle make it difficult to identify the IMA and render the IMA susceptible to injury during repeat median sternotomy. Damage to these important vessels that supply critical coronary arteries can be very serious. As a result, medical procedures have been developed which allow quick and easy identification of the IMA pedicle and which protect the IMA pedicle from inadvertent injury when repeat median sternotomies are performed. Damage to a patent IMA can be fatal when the left ventricle is completely dependent on the bypass conduit. Current procedure involves cutting a segment of synthetic membrane, preferably porous expanded polytetrafluoroethylene of the type sold under the trademark Gore-Tex® Surgical Membrane, to an appropriate length and width.
• the membrane segment is typically .1 mm thick and is wrapped around the IMA at the end of the operation. Small hemoclips or sutures are then used to hold the edges of the segment together.
• the proximal and distal ends of the wrap are sutured to the proximal pedicle and the epicardium using conventional sutures to prevent the sleeve from migrating.
• Repeat or re-do cardiac surgery in the face of a patent IMA artery bypass graft is very tedious and a potentially dangerous procedure. Inadvertent injury to the IMA can induce ischemia, infarction and death.
• the present invention provides a supple protective covering for the IMA and other coronary artery bypass grafts which is supplied as a preformed tubular sheath which the surgeon may easily slip over the IMA or other Irving blood conduit after dissection and prior to anastomosis of the distal end of the IMA or conduit.
• a tubular sheath is provided of bio-compatible material such as expanded, porous PTFE.
• the sheath is provided in a predetermined wall thickness, typically about 0.4 mm and having a diameter range of approximately 10 to 40 mm.
• the sheath is provided to the surgeon in sterilized package form and it is necessary only for the surgeon to remove the sheath from the package and slip the sheath over the IMA prior to reattachment of the IMA to the coronary artery beyond the obstruction.
• the surgeon at the time of positioning the sheath about the IMA, can trim the sheath to the desired length, if necessary.
• the sheath may be fastened in place by conventional methods such as suturing, clipping, stapling or with the use of adhesives. Once in place, the sheath assists in isolating the IMA preventing formation of adhesions and scar tissue.
• the presence of the sheath makes it much easier for the surgeon to identify the IMA in case of re-do surgery, reducing the possibility of injury to the IMA during repeat median sternotomy and also reducing surgery time.
• the sheath of the invention being flexible and supple, is clampable during re-operation procedures and does not present any seam or suture line along its length.
• the sheath of the present invention is fabricated from a bio-compatible material which is preferably porous PTFE.
• a preferred form is fabricated by extruding and expanding tubular PTFE products to create a tubular article of porous expanded PTFE having a microstructure of nodes interconnected by fibrils.
• the manufacture of porous, expanded PTFE materials is described by U.S. Patent 4,187,390 incorporated by reference herein.
• helical grooves are placed in the extruder tip of the mandrel. The tip is received within a die. The tip is provided with a predetermined back taper which assists in forcing the material into the annular area between the die and tip and into the grooves in the tip.
• PTFE resin is mixed with a liquid lubricant and forced under pressure by a ram through the annular area defined by the tip and the die to form extruded tubing.
• This extrusion method and apparatus is described by U.S. Patent Nos. 4,743,480 and 4,876,051 also incorporated by reference herein.
• the extruded tubing is expanded by stretching it at a controlled rate.
• the stretched tube is longitudinally restrained from shrinking and heat treated in an oven set to above the crystalline melt temperature of PTFE. Once heat treating has been completed, the tube is released from its restraints. It is desirable to have a structure with a fibril length of less than about 5 microns in orderto minimize tissue attachment to the tubular sheath.
• Fibril length is measured by cutting a sample tube lengthwise nd then photographing the desired surface, inner and outer, under sufficient magnification.
• a sufficient number of fibril lengths are measured from the photograph of the sample surface to compute a statistically significant mean fibril length.
• a fibril length is measured from the edge of one node to the edge of an adjacent node.
• the resulting expanded PTFE tube can then be cut into individual sheaths of shorter, predetermined length, as for example 20 cm., and thereafter appropriately packaged and sterilized by conventional sterilization techniques such as autoclaving or gas sterilization.
• Figure 1 is a perspective view of a tubular sheath in accordance with the present invention.
• Figures 2 to 4 are perspective views showing the steps in coronary artery bypass operation illustrating the positioning of the sheath around the IMA pedicle and re-attachment of the IMA to the coronary artery beyond the obstruction;
• Figure 5 is an elevational view of the mandrel portion of the extruder apparatus for extruding sheaths according to the present invention
• Figure 6 is a sectional view of the die
• Figure 7 is a sectional view of the extruder tip taken along line 7-7 of Figure
• Figure 8 is a perspective view of an alternate embodiment of a sheath according to the invention.
• FIG 9 is a view, partly in section, of the assembled extruder; and Figure 10 is a schematic diagram setting forth the steps in the method of forming IMA protective sheaths in accordance with the present invention.
• the sheath of the present invention is generally as indicated by the numeral 10 and is shown in Figure 1 and is for installation over the IMA as shown in Figures 2 to 4.
• Tubular implants have been used in the medical industry as replacements for arteries and veins and are generally referred to as prosthetic grafts.
• the present invention will be described as a tubular sheath as it is not a fluid-carrying conduit but instead serves as a covering about an artery or vein to protect the artery or vein from dissection injury, formation of adhesions and to facilitate identification. While the invention will be described with application to an IMA, it is to be understood that this is a representative description as the sheath may be applied in the same manner in other applications to protect other living blood conduits such as the gastroepiploic artery or saphenous veins.
• the sheath 10 comprises a generally tubular body portion 12 that is open at opposite ends 14 and 16.
• the body is constructed as a tube of material which is inert and bio-compatible and preferably is porous, expanded PTFE.
• the method of fabricating the sheath as an integral tubular structure will be described hereafter.
• the sheath is provided to the surgeon in a sterile condition such as in a sterilized package so that it may be removed from the package and positioned over the internal mammary artery.
• the sheath will have a predetermined length which may vary but typically will be approximately 20 cm. which corresponds to the maximum length of the IMA.
• the internal diameter of the sheath may vary but would be in the range of 10 to 40 mm so that a loose fit exists between the sheath and the artery.
• the sheath is flexible having a wall thickness of about 0.4 mm.
• the purpose of the sheath is to provide a covering about the IMA to protect the IMA and to prevent cellular ingrowth and formation of adhesions around the IMA pedicle and also serves to assist to identify the IMA in the case of re-do surgery. Also, since the sheath is flexible, it can be clamped. The sheath may remain in place during re-do surgery if it is not necessary to repair the area encompassed by the sheath.
• FIGS 2 to 4 illustrate the installation of the sheath of the present invention during coronary artery bypass operation.
• a median sternotomy is initially performed in conventional manner.
• the pericardium is opened and the selected right or left IMA is dissected.
• the left internal mammary artery 25 is shown in
• FIG 2 as being dissected from the retrosternum with soft tissue pedicle attached.
• the sheath 10 according to the present invention has been provided in packaged, sterilized form and is removed from the package and the surgeon cuts the sheath to the desired length.
• the sheath is then slipped about the distal end of the detached IMA, as seen in Figure 3.
• the diameter of the sheath is sufficient to allow the sheath to be loosely positioned about the IMA and also facilitates easy positioning of the sheath about the IMA.
• Re-attachment or anastomosis of the distal end of the IMA at the selected by-pass location is then completed.
• the sheath being flexible and supple, may be retracted to allow visual inspection of the IMA.
• the sheath When the procedure is completed, the sheath is extended along substantially the entire length of the IMA. For example, distal anastomosis to the left anterior descending (LAD) coronary artery is a typical by-pass procedure.
• the sheath may be left in unattached position about the IMA or, if preferred, the surgeon may prefer distal fixation of the sheath to the epicardium using conventional suturing techniques.
• the surgery is completed by closing the sternum with stainless steel wires.
• the subcutaneous tissues and skin are closed in layers with appropriate sutures such as polyglactin sutures.
• IMA's which have been wrapped using prior art techniques have exhibited virtually no adhesions between the chest wall and the IMA pedicle with the IMA remaining patent.
• PTFE membranes have been shown to be relatively impermeable to cellular infiltration, cause minimal adjacent inflammatory response and are resistant to damage by electrocautery.
• the sheath around the IMA pedicle facilitates visual identification of the IMA pedicle during re-do operations and provides an adhesion-free plane of dissection for isolation of the vessel.
• the sheath being flexible is clampable during re-operation procedures.
• the sheath 10A is constructed having perforations 32 at selected locations formed, for example, by conventional laser cutting techniques. The perforations are provided to reheve potential bleeding complications from the interior of the sheath.
• Figure 8 also shows a "tail" 36 attached to the sheath.
• the tail 36 is a string of bio-compatible material attached to the tube 10A and serves to assist the surgeon in locating the sheath and enclosed IMA when performing re-do surgery.
• the tail may be PTFE and may be bonded or fused to the tube, and suitably colored for better visual identification.
• the sheath may be rendered radio-opaque by attaching a radio-opaque material such as a barium strip 38 to the surface of the sheath 10A as shown in Figure 8.
• a radio-opaque material such as a barium strip 38
• the radio-opaque strip may be extruded into the tube when it is fabricated by blending a substance such as barium sulphate into the PTFE resin.
• the starting material is preferably a paste of PTFE which includes PTFE resin with a liquid lubricant.
• a tubular billet is preformed and extruded in the extrusion apparatus as shown in Figures 5, 6, 7 and 9. The apparatus will be described more fully hereafter.
• the extrusion exits the extrusion die in tubular form.
• the extruded tube is stretched to between 1.5 to 2.5 times its original length.
• the extruded tube is held in the stretched condition and thermally locked by heating the material.
• the stretch should proceed at a rate of about 200%/sec.
• the stretched tube is then heated to a temperature above the crystalline melting point of the PTFE, generally at above 327 ⁇ F.
• the material then may be cut to the desired length to form individual sheaths and as indicated; 20 cm. is considered an appropriate length for most graft applications.
• the sheaths may be suitably packaged and sterilized. Sterilization techniques can be conventional techniques such as gas sterilization or autoclaving. 8
• the apparatus for extruding the sheath 10 includes a hollow cylindrical die 50 housing a tip 56 centrally positioned in the barrel.
• the die 50 is of substantially uniform internal diameter along its lower end 59 having a conical section 58 at its upper end into which resin is forced.
• the tip 56 has a slight back taper.
• the tip 56 and die 52 establish an annulus 60 from which the material is extruded.
• a billet of lubricated PTFE is placed in the extruder and a ram, not shown, is activated to force the billet through the annulus 60.
• a ram not shown
• the tip may be smooth, preferably, the surface of the tip is provided with a plurality of helical grooves 62 pitched at an angle of about between 10° and 85° with respect to the longitudinal axis of the tip.
• Example 1 discloses a preferred example of a process for making the IMA sheath according to the present invention and is set forth for purposes of understanding but not intended to limit the scope of the present invention.
• Example 1 Fabrication Of Expanded PTFE Sheath An extruder tip was used as described above with reference to Figures 5, 6 and 9, having six helical grooves.
• PTFE resin (Fluon CD-123 obtained from ICI Americas) was prepared and blended with approximately 120 cc's of Isopar M odorless solvent produced by Exxon Corporation per pound of PTFE to form an extrudate.
• the extruded material was then compressed into a tubular billet heated and extruded into an 18 mm ID tube in a ram extruder as generally described above in Figures 5 to 9.
• the extruder tip had a nominal diameter of 18.69 mm and the die had a nominal diameter of 19.46 mm at the discharge end.
• a back taper of 1 mm per 4.8 cm was provided on the tip. The back taper was provided inwardly from the end of the tip beginning at about 9.53 mm.
• the tip was provided with a 45° right hand helix groove.
• the groove had a radius of 1.19 mm and the grooves were equally spaced around the periphery of the tip and the grooves being approximately 0.25 mm deep.
• the extruded tubing from the die was subsequently processed into individual sheaths as described of porous, expanded PTFE having approximate internal diameter of 17 mm.
• the stretch conditions were maintained at a temperature of approximately 300 °C, a stretch ratio of 2 to 1, with a stretching rate of approximately 200% per second determined by dividing the percentage change in length by the duration of the stretching operation.
• the stretched tubes were longitudinally restrained and then placed in an oven set at 350 °C for about 40 seconds. Individual sheaths were formed by cutting the tube into 20 cm. segments. The sheaths were then ready for packaging and sterihzation procedures to be subsequently performed.
• the present invention provides a sheath for application about grafts such as the IMA which sheath has substantial advantages over the prior art and which provides advantages of protection from dissection, identification and other benefits, particularly important in the event of re ⁇ do bypass surgery.
• the sheath With the sheath, the initial surgery is more expedient and re-do surgery much less complicated as visual identification, protection from dissection injury and an adhesion-free plane for dissection of the vessel is provided.
• the sheath is made of a bio-compatible material, preferably a porous, expanded PTFE produced by an extrusion, expansion and heating process. The material is provided to the surgeon in convenient form to minimize the installation time.
• the sheaths can also be fabricated to provide radio-opacity, if desired. Apertures for relief of potential interior bleeding complications may also be provided.

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• Health & Medical Sciences (AREA)
• Gastroenterology & Hepatology (AREA)
• Pulmonology (AREA)
• Cardiology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Transplantation (AREA)
• Engineering & Computer Science (AREA)
• Biomedical Technology (AREA)
• Heart & Thoracic Surgery (AREA)
• Vascular Medicine (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Prostheses (AREA)
• Materials For Medical Uses (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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Cited By (5)

• 1994
  • 1994-11-01 AU AU11284/95A patent/AU1128495A/en not_active Abandoned
  • 1994-11-01 WO PCT/US1994/012467 patent/WO1995035072A2/fr active Application Filing

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