Abstract:
Flexible annuloplasty ring having internal close coiled helical spring embodied, inter alia, in a mitral ring having a curved semi-flexible stiffener member in the anterior segment to maintain intertrigonal distance during implantation, the plane of the anterior segment lying at an arc configuration of about 30°-75° to the plane of the posterior segment, arcing up across the anterior leaflet to prevent outflow tract obstruction.

Description:
FIELD OF THE INVENTION 
     This invention relates to prosthetic annuloplasty rings for use in the surgical correction of some defects of the two atrio-ventricular valves in the human heart. 
     BACKGROUND OF THE INVENTION 
     The mitral valve lies in the left side of the heart and the tricuspid valve in the right. These valves, especially the mitral valve, if significantly damaged require repair or replacement. The normal mitral and tricuspid valves have different anatomy the annulus of mitral valve is somewhat “D” shaped, while the annulus of the tricuspid valve is more nearly circular. Valve dysfunction can lead to stenosis a restriction to flow or regurgitation, or both. 
     A surgically repairable valve often has a dilated annulus. This dilatation may prevent full coaptation of valve leaflets, while an asymmetrical annular dilatation may result in incomplete leaflet coaptation and hence leakage of the valve. Consequently, most repair procedures involve remodeling and stabilization of the annulus by implanting an annuloplasty ring to reduce in the overall size of the valve annulus. When repairing the mitral repairs it is necessary to preserve the normal distance between the two fibrous trigones located adjacent to the anterior leaflet. In this region a definitive annulus is absent. Alteration of the inter-trigonal distance could lead to distortion of the aortic valve with possible aortic regurgitation or left ventricular outflow obstruction. Thus an effective annuloplasty ring should ensure that the natural inter-trigonal distance is neither increased nor diminished by the valve repair procedure. 
     The prior art regarded as most pertinent to the present invention is incorporated herein by reference to provide a comprehensive background setting to enable better understanding of the present invention and its advantages. The incorporated prior art is tabulated hereinafter, and the features of the prior art considered most closely related to the problems faced in the prior art that are overcome by the present invention are discussed in some detail hereinafter. 
     Various prostheses have been described for use in conjunction with mitral or tricuspid valve repair. Each has disadvantages. The ring developed by Dr. Alain Carpentier U.S. Pat. No. 3,656,185 is rigid and flat. Although widely used, criticism of its inflexibility preventing the normal alteration in size and shape of the mitral annulus with the cardiac cycle has been widespread. The complication of left ventricular outflow tract obstruction has been described in association with this device. This complication can take the form of a decrease in the dimensions of the left ventricular outflow tract, or systolic anterior motion of the anterior leaflet of the valve. Both complications were reported by Geller M, Kronzon I, Slater J et al. “Long-term follow-up after mitral valve reconstruction: incidence of postoperative left ventricular outflow obstruction”. Circulation 1986;74 supp. I I-99-103. They implanted Carpentier rings in sixty-five patients. All sixty surviving patients were restudied 1-55 months postoperatively. All showed a significant decrease in the dimensions of the left ventricular outflow tract, and 6 patients 10% also had systolic anterior motion SAM. Another complication of the Carpentier ring has been inflow obstruction. This complication associated with its use in tricuspid valves was reported by Carpentier et al. in nine of seventeen patients Carpentier A, Deloche A, Hanania G, et al. “Surgical management of acquired tricuspid valve disease”. J Thorac Cardiovasc Surg 1974;67:53-65. In addition, the Carpentier ring has the disadvantage of not being of adjustable size. Thus the surgeon has to accurately judge the correct size of ring needed to reduce the annulus size and produce a competent valve. 
     An open ring valve prosthesis was described in U.S. Pat. No. 4,164,046 comprising a uniquely shaped open ring valve prosthesis having a special velour exterior for effecting mitral and tricuspid annuloplasty. This ring was not adjustable in size during or following implantation. The fully flexible annuloplasty ring described by Carlos D. Duran and Jose Luis M. Ubago, “Clinical and Hemodynamic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction” Annals of Thoracic Surgery, No.5, 458-463, November 1976 could only be shortened in the posterior segment by the placement of plicating sutures. The judgement of the position, size and spacing of these sutures requires skill and experience. However, inappropriate suture placement in the anterior segment could cause undesirable intra-trigonal shortening. Adjustable annuloplasty rings were described by Dr. William Angell U.S. Pat. No. 4,042,979 and Dr. Miguel Puig-Massana U.S. Pat. No. 4,290,151. Both incorporate draw-strings capable of reducing the size of the posterior portion of the ring. The former contains a rigid or flexible member in the anterior leaflet portion of the ring. The latter ring is also adjustable but fully flexible. With this device the use of a continuous implantation suture was recommended rather than the more generally used interrupted sutures. With the Puig-Massana ring the use of interrupted sutures would be likely to interfere with the internal drawstrings. However, should a continuous suture be used for implantation, and the ring then contracted by the internal drawstrings, loosening of the continuous suture would be caused by the reduction in the circumference of the annulus. A further disadvantage of Puig-Massana&#39;s ring is that following the tightening of the drawstrings, a bulky knot is formed on the atrial surface of the ring. Hence, the knot lies in the direct blood flow path into the inflow of the valve. Should a thrombus form on the knot it could later embolize. In addition, should the surplus drawstrings be cut too close to the knot, there is the danger of the knot becoming undone. Conversely, should significant surplus drawstrings tails remain, abrasion of the valve leaflets could occur. The adjustable ring by Dr. Ali Ahmadi has the disadvantage of being circular, which is not an appropriate shape, particularly for the mitral annulus. 
     The rigid rings described above were probably conceived on the assumption that the mitral annulus is “D” shaped and lies in a single flat plane. That this was a misconception was shown by Levine, R. A., Triulzi, M. O., Harrigan P., and Weyman,A. E. “The relationship of mitral annular shape to the diagnosis of mitral valve prolapse”, Circulation 75, No. 4, 756-767, 1987. This work shows that the mitral valve annulus is a complex and mobile structure and demonstrated that the mitral valve takes the form of a central, elliptical portion of a hyperbolic paraboloid or saddle shaped surface. It is clear that imposing a flat ring or even a segment of a flat ring would distort the annulus and could cause left ventricular outflow tract obstruction. 
     Wright and Elliott, U.S. Pat. No. 5,674,279, describe annuloplasty and suture rings in the form of adjustable, flexible tricuspid and tricuspid annuloplasty rings having internal drawstrings that merge from the rings on the annular faces so that the drawstring knots are out of the bloodstream. The drawstrings are contained in clearly marked channels. The mitral ring has a curved semi-flexible stiffener member in the anterior segment to maintain intertrigonal distance during implantation. While the Wright and Elliott device solved many of the problems inherent in the prior art devices, there remains a need for flexible tricuspid and tricuspid annuloplasty rings that assure that the orifice defined by the ring remains substantially constant in cross-section without undue interference with the movement of the surrounding tissue. 
     The present invention is embodied in annuloplasty ring structure that in large measure overcome the disadvantages of the prior art and provides improved performance and reliability. 
     It is an objective of this invention to provide a fully flexible, annuloplasty rings specific for use in mitral and tricuspid valve repair. 
     It is a further objective of this invention to provide a mitral annuloplasty ring in which the inter-trigonal distance and anterior segment is maintained during implantation. 
     It is a further objective of this invention to provide an annuloplasty ring which is flexible yet which resists plication (puckering) by the action of the implantation sutures. 
     It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible in an undulating manner so as to follow the change in shape of the mitral annulus, in the plane of the annulus. 
     It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible about the posterior portion of its circumference, and that prevents restriction of the left ventricular outflow tract. 
     It is a further objective of this invention to provide a mitral annuloplasty ring that is flexible about the anterior portion of its circumference, and that prevents restriction of the left ventricular outflow tract. 
     It is a further objective of this invention to provide an annuloplasty ring that is technically easy to use. 
     Other objectives and advantages of this invention will be more apparent from the detailed description of the device which follows. 
     SUMMARY OF THE INVENTION 
     This invention relates to flexible atrio-ventricular annuloplasty ring incorporating a circumferential string and one or more light, closely wound helical metallic spring members through which said string passes. In a preferred embodiment of the invention, one spring is situated in a substantial portion of one segment of the ring, and other like springs are situated in the second and third segments of the ring. When such ring is implanted in the mitral annulus, the first segment of the ring containing the spring will correspond to the anterior segment of the annulus. Likewise the second and third segments of the ring containing like springs will be implanted such that said second and third segments correspond to right and left segments of the posterior annulus respectively. When said ring is implanted in the tricuspid annulus, the first segment of the ring will be implanted in the posterior segment of the tricuspid annulus. 
     In an alternative embodiment of the invention, one spring is situated in a substantial portion of the first segment, and elastomeric radiopaque members are situated in the second and third respectively through which said string pass. When such a ring is implanted in the mitral annulus, the first segment of the ring containing the spring will correspond to the anterior segment of the annulus. Likewise the second and third segments of the ring containing radiopaque members in said second and third segments will be implanted such that said second and third ring segments correspond to right and left segments of the posterior mitral annulus respectively. When said alternative embodiment of said ring is implanted in the tricuspid annulus, the first segment of the ring containing the spring will correspond posterior segment of the tricuspid annulus. In mitral valve surgery, the first segment spring member serves to prevent shortening intratrigonal and anterior leaflet distance by plication of the ring, and hence of the annulus, during implantation. The anterior segment of the ring is intended to be sutured in a curved arc across the sub-aortic curtain of the atrial wall of the aortic outflow tract. In a preferred embodiment of the invention the close coiled springs contained in the said second and third segments of the ring will also prevent shortening of the annulus by plication. 
     In one preferred embodiment of the invention the flexible body of the ring is of an symmetrical biocompatible tube formed from extruded and expanded polytetrafloroethylene. In an alternative embodiment the flexible body of the ring is of a asymmetrical biocompatible tube formed from extruded and expanded polytetrafloroethylene. In a further alternative embodiment of the invention the biocompatible body is formed of braided, knitted or woven DACRON® polyethylene teraphthalate, or other biocompatible fibrous material, formed into tubular form. The body of the further alternative embodiment of the invention may be substantially circular or oval in cross-section. 
     The preferred annuloplasty ring comprises an elongate tube of suturable material, an elongate tubular flexible non-contractile member, preferably in the form of a close coiled biocompatible spring member in tube, the spring member having first and second ends and defining a passage there through, a string extend through passage in the spring and means securing the string proximate said ends of the for preventing extension of the. The spring and string are configured and constructed and secured together to allow the ring define an arc corresponding, in use, to the curved anterior segment of the mitral valve annulus and to permit the shape to vary during the cardiac cycle without extension or compression of the arc length. The annuloplasty ring is suitable for use in repair a patient&#39;s mitral valve annulus, said mitral valve annulus comprising anterior and posterior segments., the tube and spring being configured and constructed to encompass, in use, at least a substantial part of the anterior segment of the mitral valve annulus. In a preferred embodiment, the spring and string are configured and constructed and secured together to define an arc configuration corresponding, in use, to the curved anterior segment of the mitral valve annulus and to permit said arc configuration to vary during the cardiac cycle without extension of the. 
     Generally, the annuloplasty ring may comprise an elongate tube of suturable material, an elongate tubular flexible non-contractile member configured and constructed to define a passage there through in said tube, said member having first and second ends and defining a passage there through, a string extend through said passage in said non-contractile member, and means securing the string proximate said ends of said non-contractile member for preventing extension of said elongate tubular flexible non-contractile member. The elongate tubular flexible non-contractile member and string are configured and constructed and secured together to define an arc configuration corresponding, in use, to the curved anterior segment of the mitral valve annulus and to permit said arc configuration to vary during the cardiac cycle without extension of said elongate tubular flexible non-contractile member. The valve may be configured and constructed to be used in the repair of a patient&#39;s mitral valve annulus that comprises anterior and posterior segments, the annuloplasty ring comprising an elongate tube of suturable material, an elongate tubular flexible, non-contractile member configured and constructed to define a passage there through in said tube, said elongate tubular flexible non-contractile member having first and second ends and defining a passage there through, a string extend through said passage, and means securing the string proximate said ends of said elongate tubular flexible non-contractile member for preventing extension of said elongate tubular flexible non-contractile member, said tube and elongate tubular flexible non-contractile member being configured and constructed to encompass, in use, at least a substantial part of the anterior segment of the mitral valve annulus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood and the advantages will become apparent to those skilled in the art by reference to the accompanying drawings, wherein like reference numerals refer to like elements in the several Figures, and wherein: 
     FIG. 1 shows a plan view from the atrial aspect of the closed ring. 
     FIG. 2 shows a side elevation view of the closed ring., i.e., the closed ring of FIG. 1 viewed from the right side as depicted in the drawing. 
     FIG. 3 shows a cross-sectional view of a preferred embodiment of the closed ring taken along line  3 — 3  of FIG.  2 . 
     FIG. 4 shows a cross-sectional view of a preferred embodiment of the closed ring taken along line  4 — 4  of FIG.  1 . 
     FIG. 5 shows a cross-sectional view of a preferred embodiment of the closed ring taken along line  5 — 5  of FIG.  1 . 
     FIG. 6 shows a cross-sectional view of an alternative embodiment of the closed ring invention, the cross-section corresponding to the cross-section taken in a plane corresponding to that shown in FIG.  3 . 
     FIG. 7 shows a cross-sectional view of the alternative embodiment of the closed ring depicted in FIG. 6, taken along lines  7 — 7  of FIG.  6 . 
     FIG. 8 shows a cross-sectional view of the alternative embodiment of the closed ring depicted in FIG. 6, taken along lines  8 — 8  of FIG.  6 . 
     FIG. 9 shows a plan view from the atrial aspect of a further alternative embodiment is which the ring is intended to support the posterior segment of the valve orifice. 
     FIG. 10 shows a side elevation view of the open ring shown in FIG.  9 . 
     FIG. 11 shows a cross-sectional view the open ring depicted in FIGS. 9 and 10, taken along lines  11 — 11  of FIG.  10 . 
     FIG. 12 shows an enlarged partial cross-sectional view of the open ring shown in FIG. 11, the cross-section corresponds to the cross-sectional view of FIG. 11, enlarged. 
     FIG. 13 shows a cross-sectional view another alternative embodiment of the closed ring, similar in overall configuration to that shown in FIG. 9, the cross-section corresponding to the cross-section taken in a plane corresponding to that shown in FIG.  11 . 
     FIG. 14 shows an enlarged partial cross-sectional view of the further alternative embodiment of the open ring shown in FIG. 13, the cross-section correspond to the cross-sectional view of FIG. 13, enlarged. 
     FIG. 15 shows a cross-sectional view of another alternative embodiment of the annuloplasty rings of this invention, showing and alternative suturing structure, sutured into the annulus of an atrio-ventricular valve. 
     FIG. 16 shows a cross-sectional view of a different alternative embodiment of the annuloplasty rings of this invention, showing and alternative suturing structure, the suture knots being located on the outermost periphery of the annuloplasty ring, the ring being shown sutured into the annulus of an atrio-ventricular valve. 
     FIG. 17 shows a cross-sectional view of yet another alternative embodiment of the annuloplasty rings of this invention, showing and alternative suturing structure, the suture knots being located on an outer, thinner peripheral portion of the annuloplasty ring, the ring the ring being shown sutured into the annulus of an atrio-ventricular valve. 
     FIG. 18 shows a cross-sectional view of the alternative embodiment of the annuloplasty rings shown in FIG. 17, further improved by the addition of a very fine layer of biocompatible fabric to encourage tissue attachment to the annuloplasty ring of this invention, showing and alternative suturing structure, on an outer, thinner peripheral portion of the annuloplasty ring, the ring being shown sutured into the annulus of an atrio-ventricular valve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This invention is directed to a fully flexible, atrio-ventricular annuloplasty ring containing a circumferential internal string which passes though the lumen of a substantially non-compressive close coiled helical spring member which is located in a least one segment of the ring. 
     In a preferred embodiment of the invention, when used in the mitral valve, one flexible but in expansible and incompressible portion of the prosthesis is formed to fit about the base of the anterior leaflet of the valve, and second and third portions flexible but in expansible portions of the prosthesis are formed to fit about the base of the left and right segments of the posterior annulus leaflet of the valve. A flexible close coiled helical spring member located in the anterior portion of the prosthesis is to maintain the natural geometry of the anterior segment during and following implantation. The flexible nature of the spring allows the anterior segment containing the spring to follow a curved path on an inclined plane on the sub aortic curtain above the so called annulus of the anterior leaflet, and to follow any natural motion of the base of the aortic valve. Colored marking sutures in the anterior segment of the device serve to mark the two locations of the ring that are intended to lie adjacent to the natural tissue trigons of the anterior portion of the natural annulus. These colored marking sutures may, in an alternative embodiment of the device, serve to anchor and stabilize an internal string of the device. 
     The flexible member that is non-compressive and rendered inextendable by an internal string, knotted at either end of the helical spring. The close coiled helical spring forms a radiopaque member. The string maintains the natural geometry of the intra-trigonal and/or intra-commisural anterior leaflet distance when said ring is implanted in the mitral position. At the same time the annuloplasty ring provides adequate strength and flexibility and limited tissue in growth potential yet permits a low needle penetration force for convenience of implantation. A particular advantage of this construction is that there are no portions of the extruded and expanded material of the body that might fray, and that the joint line is so placed within the ring is not subject to stresses. The body is substantially circular in cross- section. 
     The flexible body of the ring is of a biocompatible material, preferably of an extruded and expanded polyethertetraphylate tubular material. The construction of the annuloplasty ring is such that it is relatively simple to manufacture. The ring contains radiopaque materials so that postoperative radiopaque assessment is simplified. 
     Referring now to FIG.  1  and FIG. 2, the device  10  is composed of a single flexible cylindrical tube  11 , which has its ends  12 ,  13  sewn together by suture  14  to form a flattened ring having an inner periphery  15  and an outer periphery  16 . The ring has three segments  17 ,  18 ,  19 . The following nomenclature will apply to the ring as it is to be implanted in the mitral annulus of a patient. Segment  17  is designated as the anterior segment, segment  18  the right posterior segment, and segment  19  the left posterior segment. At the junction of the anterior segment  17  and the right posterior segment  18  is a colored marker  20 . This mark is intended to lie adjacent to the natural tissue of the right commissural portion of the natural annulus. At the junction of the anterior segment  17  and the left posterior segment  19  is a colored marker  21 . This mark is intended to lie adjacent to the natural tissue of the left commissural portion of the natural annulus. Approximately 3 mm from the right commissural marker  20  and in the anterior segment  17  is located a colored suture  22  which forms the right trigon marker. Approximately 3 mm from the left commissural marker  21  and in the anterior segment  17  is located a colored suture  23  which forms the left trigon marker. 
     Referring now to FIG. 4 it will be noted that tubular body  11  has inner wall  24 , defining inner space  25 . Contained in the space  25  within inner wall  24  is a close coiled helical springs  26 . This spring is preferably wound from a biocompatible metal such an Carpenter NP35N alloy. The spring is preferably wound using 0.010-0.012 inch diameter wire, although other wire diameters in the range 0.005-0.020 inches are possible. Spring  26  lies in the anterior segment  17  of the ring. Anterior segment spring  26  has an outer diameter  29  and an inner diameter  30 . The inside diameter is approximately 0.035 inches, and the outside diameter is approximately 0.055 inches. 
     Referring now to FIG. 5 it will be seen that spring  27 , which is a close coiled helical spring such as the spring  26  just described, lies in the right posterior segment  18  of the ring. A mirror image of the structure shown in FIG. 5 is found on the left of the structure depicted in FIGS. 1-3, wherein a like spring  28  lies in the left posterior segment  19  of the ring. 
     Likewise, right and left posterior springs  27  and  28  have an outer diameter and an inner diameter preferably corresponding to like diameters of spring  26 . A single string  35 , monofilament or multifilament, lies within the inner diameters of springs  26 ,  27 ,  28  respectively. This string  35 , which is preferably of a size  1  braided polyester surgical suture, is terminated in a secure knot  36 . The string also has two simple knots preferably “Figure of eight knots”  37 ,  38 . String termination knot  36  lies approximately straddling tube ends  12 ,  13  within tube seam formed by suture  14 , and between one end  39  of right posterior segment spring  27  and one end  40  of left posterior segment spring  28 . The overall diameter of termination knot  36  is larger than the inner diameter  32  of right posterior segment spring  27  and larger than the inner diameter  34  left posterior segment spring  28 . The simple knot preferably “a Figure of eight knot”  37  of string  35  lies immediately adjacent and between end  41  of right posterior segment spring  27  and end  43  of anterior segment spring close coiled helical spring  26 . Likewise the simple knot preferably “a Figure of eight knot”  38  of string  35  lies immediately adjacent and between end  42  of left posterior segment spring  28  and end  44  of anterior segment spring close coiled helical spring  25 . The overall diameter of simple knots  37 ,  38  are larger than the inner diameter  30  of anterior segment spring  26  and inner diameters  32  of right posterior segment spring  27  and inner diameter  34  left posterior segment spring  28 . 
     Right trigon suture marker  22  passes internally through tube  11  and through internal string  35  at  45  adjacent to knot  37  and likewise left trigon suture marker  23  passes internally through tube  11  and through internal string  35  adjacent to knot  38  at  46 . Thus the overall size of knots  36 ,  37 ,  38  relative to the inner diameter  30  of anterior segment spring  26  and inner diameter  32  of right posterior spring  27  and inner diameter  34  left posterior spring  28 , combined with right and left trigon sutures engaging with string  35  at points  45 ,  46  prevent radial migration of string  35  and spring  26  relative to tube  11 , and also prevent radial migration towards the anterior segment  17  of right segment spring  27  and left segment spring  28  towards the anterior segment  17  of ring  10 . 
     Reference is now made to FIGS. 6,  7  and  8 , tubular body  111  has inner wall  124 , defining inner space  125 . Contained in the space  125  within inner wall  124  in the anterior segment  117  is a close coiled helical springs  126 , preferably wound from a fatigue resistant, biocompatible metal such as Carpenter MP35N. The spring is preferably wound using 0.010-0.012 inch diameter wire, although other wire diameters in the range 0.005-0.020 inches are possible. Anterior segment spring  126  has an outer diameter  129 , preferable of approximately 0.055 inches, and an inner diameter  130 , preferable of approximately 0.035 inches. Contained in the space  125  within inner wall  124  in the right and left posterior segment  118 ,  119  are elongate tubular flexible non-contractile members such as flexible radiopaque tubes  127 ,  128 , preferably of silicon elastomer impregnated with barium sulfate. Right posterior tube  127  has an outer diameter  131  preferably of approximately 0.055 inches and an inner diameter  132  preferably of approximately 0.035 inches, and left posterior tube  128  has an outer diameter  133  and an inner diameter  134 . The inner and outer diameters of left posterior tube  128  is the same as that of right posterior tube  127 . Lying within the inner diameter  130  of spring  126  and inner diameters  132 ,  134  of tubes  127 ,  128  is provided a single string  135 . This string  135 , which is preferably of a size  1  braided polyester surgical suture, is terminated in a secure knot  136 . The string also has two simple knots preferably “Figure of eight knots”  137 ,  138 . String termination knot  136  lies approximately straddling tube ends  112 ,  113  within tube seam formed by suture  114 , and between one end  139  of right posterior segment tube  127  and one end  140  of left posterior segment tube  128 . The overall diameter of termination knot  136  is larger than the inner diameter  132  of right posterior segment tube  127  and larger than the inner diameter  134  left posterior segment tube  128 . The simple knot preferably “a Figure of eight knot”  137  of string  135  lies immediately adjacent and between end  141  of right posterior segment tube  127  and end  142  of anterior segment spring close coiled helical spring  126 . Likewise the simple knot preferably “a Figure of eight knot”  138  of string  135  lies immediately adjacent and between end  142  of left posterior segment tube  128  and end  144  of anterior segment spring close coiled helical spring  126 . The overall diameter of simple knots  137 ,  138  are larger than the inner diameter  130  of anterior segment spring  126  and inner diameters  132  of right posterior segment tube  127  and inner diameter  134  left posterior segment tube  128 . Right trigon suture marker  122  passes internally through tube  111  and through internal string  135  at  145  adjacent to knot  137  and likewise left trigon suture marker  23  passes internally through tube  111  and through internal string  135  adjacent to knot  138  at  146 . Thus the overall size of knots  136 ,  137 ,  138  relative to the inner diameter  130  of anterior segment spring  126  and inner diameter  132  of right posterior tube  127  and inner diameter  134  of left posterior tube  128 , combined with right trigon suture  122  and left trigon suture  123 , engaging with string  135  at points  145 ,  146  prevent radial migration of string  135  and anterior springs  126  relative to tube  111 , and also prevent radial migration towards the anterior segment  117  of right segment tube  127  and left segment tube  128  towards the anterior segment  117  of ring. 
     Referring now to FIGS. 9 through 12, a open suture ring of substantially similar construction is shown. The ring  200  comprises a tubular member  210  generally of the type previously described terminated at its respective ends by plugs  212  and  214 . Colored sutures  230  and  232  are provided for identification and orientation. The plugs  212  and  214  are secured in position in the ends of the tube and provide securement of the ends by way of knots  216  and  218 , respectively, as shown in FIG. 11, the right end, as depicted in FIG. 11, being shown in enlarged detail in FIG.  12 . The plugs  212  and  214  may be of any suitable biocompatible material that can be punctured with a needle or formed in situ. Resilient polymers of many formulations can be used. The preferred material is self-vulcanizing silicone rubber, often referred to as RTV (room temperature vulcanizing) silicon rubber, which is easily and quickly formed in situ during fabrication. Enclosed inside the tube, in generally the same arrangement as described, is a non-expansible coiled spring  226  constrained non-extendably in the tube by string  235  as described in reference to the previous embodiments. An end cap, such as shown at  228 , captures the end of the spring and rests against the end plug  214 , like structure being found at the other end of the ring as well. 
     The alternative embodiment of the ring  300  depicted in FIGS. 13 and 14 is structurally the same with the parts tube  310 , plugs  312  and  314 , knots  316  and  318  being substantially as described with the analogous structures in FIGS. 11 and 12. In this embodiment, however, the member  326 , held by end caps  328  and secured by string  335  is a flexible radiopaque tubes, preferably of silicon elastomer impregnated with barium sulfate, of the type described in reference to FIGS. 6 and 8. 
     Reference is made now to FIG. 15 which shows an enlarged cross-section view of a further alternative embodiment of the invention which may be embodied in rings of the type shown in any of preceding figures, differing only with respect to the outer tube construction. In suture rings  400  of this alternative embodiment, the outer ring  410  of the structure is formed in a “D” shape to provide additional material to be used in suturing the ring to the tissue T as shown, for example, by suture S. A reinforcing pledgit R may be used on the other side of the tissue T at the option of the surgeon. The suture knots may be positioned entirely outside the blood flow path, e.g. to the right of the “D” cross-sectional shaped ring  410  as shown in FIG.  15 . As in the other embodiments, the ring comprises a non-extendable coil spring  426  secured against extension by a string  435 . The ring is preferably made of expanded poly- tetra-flouro-ethylene in “D” shaped in cross-section, the face to the left in the Figure being, in use, the inner face forming the inside of ring, the opposing face forming the outside of ring  400 . The cylindrical recess through which the non-expandable spring extends is radially displaced inwards towards the center of ring such that the outer wall thickness along the central axis is greater than inner wall thickness. As shown in FIG. 15,  5  the cylindrical recess contains the internal components of the ring previously described, such as close coiled helical spring  426  and string  435 . The cylindrical recess is somewhat larger in diameter than that of the close coiled helical spring  426  to allow the internal components to slide into place without due interference with tubular body, and is preferable of approximately 0.060 inches diameter. The asymmetrical “D” shaped cross-section allows additional space for the needle of the implanting suture to pass on the portion of tube, relative to the use of the cylindrical member shown in the previously described embodiments. This additional material through which the implanting suture passes provides greater suture pull-out strength, and hence provides additional improved safety to the device. This is illustrated in FIG. 15, which shows the ring sutured onto the annulus of an atrio-ventricular valve of the heart. by a multiplicity of sutures, a portion of one of which is shown at S passing through the upper face of tube, through outer wall, through lower face and annulus, and typically into a reinforcing pledgit, lying adjacent to ventricular wall, thence back up through the ring to be secured by a knot. 
     FIG. 16 depicts an annuloplasty ring  500  generally to the type shown in FIG. 15, components numbers  510 ,  526  and  535  corresponding components numbered  410 ,  426  and  435  shown in FIG.  15 . Components R, S and T being as previously described. Note that the knot in the Suture S is on the outer periphery of the annuloplasty ring. 
     FIG. 17 depicts an annuloplasty ring  600  generally to the type shown in FIG. 15, components numbers  610 ,  626  and  635  corresponding components numbered  410 ,  426  and  435  shown in FIG. 15, except that the ring is constructed and configured to define the cross section  610  as comprising a thinner peripheral portion through which the suture extends. Components R, S and T being as previously described. Note that the knot in the Suture S is on the thinner periphery of the annuloplasty ring. 
     FIG. 18 depicts an annuloplasty ring  700  generally to the type shown in FIG. 15, components numbers  710 ,  726  and  735  corresponding components numbered  410 ,  426  and  435  shown in FIG. 15, except that the ring is constructed and configured to define the cross section  710  as comprising a thinner peripheral portion through which the suture extends, such as depicted in FIG. 17, with the addition of a very thin layer  780  of biocompatible fabric, e.g. of DACRON® polyester fabric, over the TEFLON® expanded polytetrafluoroethylene (PTFE) of which the outer tube of the annuloplasty ring is made. This layer of fabric causes gives rise to tissue in growth and reduces the likelihood that thin layers of tissue may grow on the Expanded PTFE and slough off into the blood stream. Components R, S and T being as previously described. Note that the knot in the Suture S is on the thinner periphery of the annuloplasty ring. The annuloplasty ring of this embodiment is formed of an elongate tube of suturable expanded polytetrafluoroethylene material configured and constructed to define in cross-section an inner annular periphery having a first thickness and an outer annular periphery having a second thickness, the second thickness being substantially less than the first thickness, the thickness of the tube gradually diminishing from the inner periphery to the outer periphery. 
     The method of use of is as follows. The chest is opened to expose the heart, appropriate cannulae are place and cardiopulmonary bypass established using conventional techniques. The left atrium is opened to expose the mitral valve. An appropriate repair procedure to the valve leaflets or chordae is then carried out. 
     The annuloplasty ring will then be implanted as part of the repair procedure to stabilize the annulus. The appropriate size ring is chosen using sizers supplied for this purpose. Interrupted sutures are placed at the fibrous trigones, between the trigones, and around the remaining circumference of the annulus. The sutures are passed through corresponding portions of the annuloplasty ring, outside the portion containing the spring. The ring is then gently pushed down the sutures until it lies on the annulus. Each interrupted suture is tied and cut. Mitral valve competency is then checked, and if satisfactory the atrium is closed, air is removed from the heart. After the heart starts to beat the patient is slowly removed from cardiopulmonary bypass and the chest closed. Implantation of the tricuspid ring follows a similar course with variations appropriate to the different anatomy. 
     Incorporated Prior Art 
     References Cited 
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     Publications 
     Tsakiris AG. “The physiology of the mitral valve annulus”. in The mitral valve—a pluridisciplinary approach. ed Kalmanson D. Publishing Sciences Group, Acton, Ma., pg 21, 1976. 
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     Industrial Application 
     This invention is useful in the surgical instrument industry.