Abstract:
A prosthetic tricuspid remodeling annuloplasty ring having two free ends that are upturned in the inflow direction to help avoid unnecessary leaflet abrasion. The free ends are desirably separated across a gap that is large enough to reduce the risk of passing sutures through the conductive system of the heart, yet not too large that support of the septal leaflet of the tricuspid annulus is degraded. The tricuspid ring may have four sequential segments looking from the inflow side and extending in a clockwise direction from a free end located adjacent the antero septal commissure after implant. The ring may define an inflow bulge in the first segment and/or an inflow bulge in the fourth segment that help the ring conform to the natural bulges created by the adjacent aorta, thereby reducing stress and the potential for ring dehiscence. Desirably, the ring has variable flexibility, either gradual and/or between or within different segments, so as to adapt or harmonize its 3-dimensional shape to each individual patient and, therefore, to significantly reduce the constraints on the annulus and adjacent structures, particularly the leaflets and the conduction tissue.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to medical devices and particularly to a tricuspid annuloplasty ring. 
       BACKGROUND OF THE INVENTION 
       [0002]    In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary, and are each mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice. 
         [0003]    Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood through the valve when the valve is closed. Valve disease can be severely debilitating and even fatal if left untreated. 
         [0004]    Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. The most widely used repair technique is remodeling annuloplasty first proposed by the same inventor in which the deformed valve annulus is reshaped by attaching a prosthetic annuloplasty repair segment or ring to the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow. 
       FIELD OF THE INVENTION 
       [0005]    The present invention relates generally to medical devices and particularly to a tricuspid annuloplasty ring. 
       BACKGROUND OF THE INVENTION 
       [0006]    In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary, and are each mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice. 
         [0007]    Heart valve disease is a widespread condition in which one or more of the valves of the heart fails to function properly. Diseased heart valves may be categorized as either stenotic, wherein the valve does not open sufficiently to allow adequate forward flow of blood through the valve, and/or incompetent, wherein the valve does not close completely, causing excessive backward flow of blood through the valve when the valve is closed. Valve disease can be severely debilitating and even fatal if left untreated. 
         [0008]    Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. The most widely used repair technique is remodeling annuloplasty first proposed by the same inventor in which the deformed valve annulus is reshaped by attaching a prosthetic annuloplasty repair segment or ring to the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow. 
         [0009]    The annuloplasty ring typically comprises an inner substrate of a metal such as rods or bands of stainless steel or titanium, or a flexible material such as silicone rubber or Dacron cordage, covered with a biocompatible fabric or cloth to allow the ring to be sutured to the fibrous annulus tissue. Annuloplasty rings may be stiff or flexible, split or continuous, and may have a variety of shapes, including circular, U-shaped, C-shaped, or kidney-shaped. Examples are seen in U.S. Pat. Nos. 5,041,130, 5,104,407, 5,201,880, 5,258,021, 5,607,471 and, 6,187,040 B1. Whether totally flexible, rigid, or semi-rigid, annuloplasty rings have sometimes been associated with a certain degree of arrhythmia or a 10% to 15% incidence at 10 years of ring dehiscence and/or conduction tissue disturbance. The present invention is intended to reduce the complications. 
         [0010]    For the purposes of anatomic orientation, please refer to  FIG. 1 , which is a schematic representation of the AV junctions within the heart and the body in the left anterior oblique projection. The body is viewed in the upright position and has 3 orthogonal axes: superior-inferior, posterior-anterior, and right-left. Traditional nomenclature for the AV junctions derives from a surgically distorted view, placing the valvular rings in a single horizontal plane with antero-posterior and right-left lateral coordinates. The descriptive terms used, however, are anatomically inaccurate. An accurate account of the coordinates of the valvular orifices is provided by the simple expedient of relating appropriately the view obtained in left anterior oblique projection to the supero-inferior and antero-posterior coordinates of the body. 
         [0011]      FIG. 2  is a cutaway view of the heart from the front, or anterior, perspective, with most of the primary structures marked. As is well known, the pathway of blood in the heart is from the right atrium to the right ventricle through the tricuspid valve, to and from the lungs, and from the left atrium to the left ventricle through the mitral valve. The present application has particular relevance to the repair of the tricuspid valve, which regulates blood flow between the right atrium and right ventricle, although certain aspects may apply to repair of other of the heart valves. The tricuspid and mitral valves together define the atrioventricular (AV) junctions. 
         [0012]    As seen in  FIG. 2 , four structures embedded in the wall of the heart conduct impulses through the cardiac muscle to cause first the atria then the ventricles to contract. These structures are the sinoatrial node (SA node), the atrioventricular node (AV node), the bundle of His, and the Purkinje fibers. On the rear wall of the right atrium is a barely visible knot of tissue known as the sinoatrial, or SA node. This tiny area is the control of the heart&#39;s pacemaker mechanism. Impulse conduction normally starts in the SA node. It generates a brief electrical impulse of low intensity approximately 72 times every minute in a resting adult. From this point the impulse spreads out over the sheets of tissue that make up the two atria, exciting the muscle fibers as it does so. This causes contraction of the two atria and thereby thrusts the blood into the empty ventricles. The impulse quickly reaches another small specialized knot of tissue known as the atrioventricular, or AV node, located between the atria and the ventricles. This node delays the impulse for about 0.07 seconds, which is exactly enough time to allow the atria to complete their contractions. When the impulses reach the AV node, they are relayed by way of the several bundles of His and Purkinje fibers to the ventricles, causing them to contract. As those of skill in the art are aware, the integrity and proper functioning of the conductive system of the heart is critical for good health. 
         [0013]      FIG. 3  is a schematic view of the tricuspid valve orifice seen from its inflow side (from the right atrium), with the peripheral landmarks labeled as: antero septal commissure, anterior leaflet, posterior commissure, posterior leaflet, postero septal commissure, and septal leaflet. Contrary to traditional orientation nomenclature, the tricuspid valve is nearly vertical, as reflected by these sector markings. From the same viewpoint, the tricuspid valve  20  is shown surgically exposed in  FIG. 4  with an annulus  22  and three leaflets  24   a ,  24   b ,  24   c  extending inward into the flow orifice. Chordae tendineae  26  connect the leaflets to papillary muscles located in the RV to control the movement of the leaflets. The tricuspid annulus  22  is an ovoid-shaped fibrous ring at the base of the valve that is less prominent than the mitral annulus, but larger in circumference. 
         [0014]    Reflecting their true anatomic location, the three leaflets in  FIG. 4  are identified as septal  24   a , anterior  24   b , and posterior (or “mural”)  24   c . The leaflets join together over three prominent zones of apposition, and the peripheral intersections of these zones are usually described as commissures  28 . The leaflets  24  are tethered at the commissures  28  by the fan-shaped chordae tendineae  26  arising from prominent papillary muscles originating in the right ventricle. The septal leaflet  24   a  is the site of attachment to the fibrous trigone, the fibrous “skeletal” structure within the heart. The anterior leaflet  24   b , largest of the 3 leaflets, often has notches. The posterior leaflet  24   c , smallest of the 3 leaflets, usually is scalloped. 
         [0015]    The ostium  30  of the right coronary sinus opens into the right atrium, and the tendon of Todaro  32  extends adjacent thereto. The AV node  34  and the beginning of the bundle of His  36  are located in the supero-septal region of the tricuspid valve circumference. The AV node  34  is situated directly on the right atrial side of the central fibrous body in the muscular portion of the AV septum, just superior and anterior to the ostium  30  of the coronary sinus  30 . Measuring approximately 1.0 mm×3.0 mm×6.0 mm, the node is flat and oval. The AV node  34  is located at the apex of the triangle of Koch  38 , which is formed by the tricuspid annulus  22 , the ostium  30  of the coronary sinus, and the tendon of Todaro  32 . The AV node  34  continues on to the bundle of His  36 , typically via a course inferior to the commissure  28  between the septal  24   a  and anterior  24   b  leaflets of the tricuspid valve; however, the precise course of the bundle of His  36  in the vicinity of the tricuspid valve may vary. Moreover, the location of the bundle of His  36  may not be readily apparent from a resected view of the right atrium because it lies beneath the annulus tissue. 
         [0016]    The triangle of Koch  30  and tendon of Todaro  32  provide anatomic landmarks during tricuspid valve repair procedures. A major factor to consider during surgery is the proximity of the conduction system (AV node  34  and bundle of His  36 ) to the septal leaflet  24   a . Of course, surgeons must avoid placing sutures too close to or within the AV node  34 . C-shaped rings are good choices for tricuspid valve repairs because they allow surgeons to position the break in the ring adjacent the AV node  34 , thus avoiding the need for suturing at that location. 
         [0017]    A rigid C-shaped ring of the prior art is the Carpentier-Edwards Classic® Tricuspid Annuloplasty Ring sold by Edwards Lifesciences Corporation of Irvine, Calif., which is seen in  FIGS. 5A and 5B . Although not shown, the planar ring  40  has an inner titanium core (not shown) covered by a layer of silicone and fabric. Rings for sizes 26 mm through 36 mm in 2 mm increments have outside diameters (OD) between 31.2-41.2 mm, and inside diameters (ID) between 24.3-34.3 mm. These diameters are taken along the “diametric” line spanning the greatest length across the ring because that is the conventional sizing parameter. A gap G between free ends  42   a ,  42   b  in each provides the discontinuity to avoid attachment over the AV node  34 . The gap G for the various sizes ranges between about 5-8 mm, or between about 19%-22% of the labeled size. As seen in the implanted view of  FIG. 6 , the gap G is sized just larger than the AV node  34 . Despite this clearance, some surgeons are uncomfortable passing sutures so close to the conductive AV node  34 , particularly considering the additional concern of the bundle of His  36 . 
         [0018]    A flexible C-shaped tricuspid ring is sold under the name Sovering™ by Sorin Biomedica Cardio S.p.A. of Via Crescentino, Italy. The Sovering™ is made with a radiopaque silicone core covered with a knitted polyester (PET) fabric so as to be totally flexible. Rings for sizes 28 mm through 36 mm in 2 mm increments have outside diameters (OD) between 33.8-41.8 mm, and inside diameters (ID) between 27.8-35.8 mm. As with other tricuspid rings, a gap between the free ends provides a discontinuity to avoid attachment over the AV node. The gap for the various sizes ranges of the Sovering™ ranges between about 18-24 mm, or between about 60%-70% of the labeled size. Although this gap helps avoid passing sutures close to the conductive AV node  34  and bundle of His  36 , the ring is designed to be attached at the commissures on either side of the septal leaflet and thus no support is provided on the septal side. 
         [0019]    Despite numerous designs presently available or proposed in the past, there is a need for a prosthetic tricuspid ring that better harmonizes with the anatomical and physiologic features of the tricuspid annulus, and in particular for a prosthetic tricuspid ring that better fits the contours of the tricuspid annulus and presents selective flexibility to reduce the stress in the attachment sutures, while at the same time reduces the risk of inadvertently passing a suture through the critical physiologic structures within the heart that conduct impulses. 
       SUMMARY OF THE INVENTION 
       [0020]    The present invention provides a tricuspid annuloplasty ring including a ring body generally arranged in a plane and about an axis along an inflow-outflow direction, the ring body being discontinuous so as to define a first free end and a second free end separated across a gap, the two free ends being bent out of the plane in an inflow direction. Preferably, the two free ends are flexible and can be bent to have an axial height of between about 1-4 mm out of the plane. 
         [0021]    Preferably, the ring body defines a generally asymmetric ovoid shape and extends in a clockwise direction from a first free end located adjacent the antero-septal commissure when implanted, as seen looking at the inflow side thereof, around a first segment, a second segment, a third segment, and a fourth segment that terminates in the second free end at a septal point. In one embodiment the ring body has an arcuate bulge out of the plane toward the inflow side at the first segment to accommodate an anatomical bulge of the aorta into the tricuspid annulus. In a further embodiment, the ring body has an arcuate bulge out of the plane toward the inflow side at the fourth segment to accommodate an anatomical bulge of the aorta into the tricuspid annulus. Still further, the ring body desirably has a varying flexibility and is stiffer adjacent the first free end than adjacent the second free end, or comprises at least one hinge point that is locally more flexible than adjacent segments. In one preferred construction, the ring body comprises a plurality of concentric peripheral bands having an axial dimension which is larger adjacent the first free end than adjacent the second free end. In a preferred embodiment, the ring has a long dimension in millimeters, and the free ends are separated by a distance of between about 40%-50% of the long dimension. 
         [0022]    In accordance with another aspect of the invention, a prosthetic tricuspid annuloplasty ring having a long dimension in millimeters, comprises an asymmetric generally ovoid ring body. The ring body is generally arranged in a plane and about an axis along an inflow-outflow direction and is discontinuous so as to define two free ends. The ring body has a length and shape such that if a first free end is implanted adjacent an antero septal commissure of the tricuspid annulus, the ring body conforms to the tricuspid annulus and a second end is located adjacent a septal leaflet thereof, and the free ends are separated across a gap having a dimension of between about 40%-50% of the long dimension. 
         [0023]    In the ring having a gap of between 40%-50% of the long dimension, the ring body extends in a clockwise direction from the first free end, as seen looking at the inflow side thereof around a first segment, a second segment, a third segment, and a fourth segment that terminates in the second free end at a septal point. In one embodiment the ring body has an arcuate bulge out of the plane toward the inflow side at the first segment to accommodate an anatomical bulge of the aorta into the tricuspid annulus. In a further embodiment, the ring body has an arcuate bulge out of the plane toward the inflow side at the fourth segment. Still further, the ring body desirably has a varying flexibility and is stiffer adjacent the first free end than adjacent the second free end, or comprises at least one hinge point that is locally more flexible than adjacent segments. 
         [0024]    In accordance with a still further aspect of the invention, a prosthetic tricuspid annuloplasty ring comprises an asymmetric generally ovoid ring body generally arranged in a plane and about an axis along an inflow-outflow direction with a first free end located adjacent an antero-septal commissure when implanted and a second free end located at a septal point. The ring body extends in a clockwise direction as seen looking at an inflow side from the first free end around a first segment, a second segment, a third segment, and a fourth segment that terminates in the second free end. The ring body has an arcuate bulge out of the plane toward the inflow side at the first segment so as to accommodate an anatomical bulge of the aorta into the tricuspid annulus. The ring body may also have an arcuate bulge out of the plane toward the inflow side at the fourth segment. Desirably, the ring body has a varying flexibility and the fourth segment is relatively more flexible than the third segment. The first free end may also be stiffer than the second free end. Alternatively, the varying flexibility comprises at least one hinge point that is locally more flexible than adjacent segments. 
         [0025]    In a further embodiment, and prosthetic tricuspid annuloplasty ring is provided that comprises an asymmetric generally ovoid ring body generally arranged in a plane and about an axis along an inflow-outflow direction with a first free end located adjacent an antero-septal commissure when implanted and a second free end located at a septal point. The ring body extends in a clockwise direction as seen looking at an inflow side from the first free end around a first segment, an second segment, a third segment, and a fourth segment that terminates in the second free end. The ring body has a variable flexibility comprising at least one hinge point that is locally more flexible than adjacent segments. Desirably, the hinge point is located at the approximate midpoint of the ring body. Alternatively, there are two hinge points located approximately diametrically opposite one another so that the ring flexes generally in a plane. 
         [0026]    A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]    Features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims, and appended drawings wherein: 
           [0028]      FIG. 1  is a schematic representation of the AV junctions within the heart and the body in the left anterior oblique projection; 
           [0029]      FIG. 2  is a cutaway view of the heart from the front, or anterior, perspective; 
           [0030]      FIG. 3  is a schematic plan view of the tricuspid annulus with typical orientation directions noted as seen from the inflow side; 
           [0031]      FIG. 4  is a plan view of the native tricuspid valve and surrounding anatomy from the inflow side; 
           [0032]      FIGS. 5A and 5B  are plan and septal elevational views, respectively, of a planar tricuspid annuloplasty ring of the prior art; 
           [0033]      FIG. 6  is a plan view of the native tricuspid valve and surrounding anatomy from the inflow side with the annuloplasty ring of  FIGS. 5A-5B  implanted; 
           [0034]      FIGS. 7A-7C  are plan and septal and anterior elevational views, respectively, of an exemplary tricuspid annuloplasty ring of the present invention illustrating its free ends bent toward the inflow side and an antero-superior bulge; 
           [0035]      FIG. 8  is a plan view of the native tricuspid valve and surrounding anatomy from the inflow side with the annuloplasty ring of  FIGS. 7A-7B  implanted; 
           [0036]      FIGS. 9A-9C  are plan and septal and anterior elevational views, respectively, of the exemplary tricuspid annuloplasty ring of  FIGS. 7A-7B  with portions cutaway to show internal details; and 
           [0037]      FIGS. 10A-10D  are sectional views taken along respective section lines in  FIG. 9A . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    The present invention provides an improved tricuspid annuloplasty ring that better conforms to the native annulus and is shaped to protect certain features of the surrounding anatomy. The ring of the present invention is designed to support a majority of the tricuspid annulus without risking injury to the leaflet tissue and heart&#39;s conductive system, such as the AV node  34  and bundle of His  36  (see  FIG. 4 ). Additionally, the present ring is contoured to better approximate the three-dimensional shape of the tricuspid annulus; specifically, the ring is substantially planar but includes a bulge in the inflow direction at the location of the bulge created by the adjacent aorta. The bulge helps reduce stress between the ring and surrounding tissue, and thus the potential for tearing or ring dehiscence. 
         [0039]    Another feature that matches the present tricuspid ring with the physiological features of the annulus is a variable flexibility from a relatively stiff first segment to a relatively flexible fourth segment. This varying flexibility permits the ring to adapt (harmonize) its motion and 3-dimensional shape to that of the annulus, rather than impose its own motion and 3-D geometry thereto which tends to increase the risk of ring dehiscence. In particular, the motion of the tricuspid annulus during systole-diastole is believed to exert some torsional forces on the implanted ring, and the variable flexibility accommodates such torques. Moreover, localized points of flexibility or “hinges” around the ring as described herein may best conform and harmonize the physical properties of the ring to the annulus motion, while at the same time providing the needed corrective support. 
         [0040]    It should also be understood that certain features of the present tricuspid ring might also be applicable and beneficial to rings for other of the heart&#39;s annuluses. For instance, the present ring includes upturned or bent free ends that help reduce abrasion on the adjacent leaflets. The same structure might be used in a discontinuous ring for the mitral valve annulus. 
         [0041]    The term “axis” in reference to the illustrated ring, and other non-circular or non-planar rings, refers to a line generally perpendicular to the ring that passes through the area centroid of the ring when viewed in plan view. “Axial” or the direction of the “axis” can also be viewed as being parallel to the direction of blood flow within the valve orifice and thus within the ring when implanted therein. Stated another way, the implanted tricuspid ring orients about a central flow axis aligned along an average direction of blood flow through the tricuspid annulus. Although the rings of the present invention are 3-dimensional, portions thereof are planar and lie perpendicular to the flow axis. 
         [0042]      FIGS. 7A-7C  illustrate, in plan and septal and anterior elevational views, a tricuspid ring  50  of the present invention having a ring body  52  generally arranged about an axis  54  and being discontinuous so as to define two free ends  56   a ,  56   b . The axis  54  in  FIG. 7A  lies at the centroid of the ring or along of the axis of blood flow through the ring  50  when implanted, and it will be understood that the relative directions up and down are as viewed in  FIG. 7B . Using this convention, the ring  50  is designed to be implanted in a tricuspid annulus such that blood will flow in the downward direction. 
         [0043]    As seen in  FIGS. 7A-7C  and also in  FIGS. 9A-9C , the ring body  52  is substantially asymmetric and ovoid with the first free end  56   a  located adjacent the antero-septal commissure (see  FIG. 3 ). The ring body  52  extends in a clockwise direction, as seen looking at the inflow side in  FIG. 7A , around a first segment  60   a  corresponding to the aortic part of the anterior leaflet, a second segment  60   b  corresponding to the remaining part of the anterior leaflet and ending at the postero septal commissure, a third segment  60   c  from the postero septal commissure to a line  61  part way along the septal leaflet, and a fourth segment  60   d  that terminates in the second free end  56   b  at a septal point. The nomenclature for these segments is taken from the standard anatomical nomenclature around the tricuspid annulus as seen in  FIG. 3 . 
         [0044]    The precise relative dimensions of the segments may vary, but they are generally as indicated in the view of  FIG. 7A . That is, the second segment  60   b  is the largest, followed by the first segment  60   a , and then the smaller third segment  60   c  and fourth segment  60   d . It should be further noted that the term “asymmetric” means that there are no planes of symmetry through the ring body  52  looking from the inflow side, and “ovoid” means generally shaped like an egg with a long axis and a short axis, and one long end larger than the other. 
         [0045]      FIG. 8  shows the tricuspid ring  50  in plan view after having been implanted or otherwise affixed to a tricuspid valve. To quantify relative to the native anatomy, the combined first and second segments  60   a  and  60   b  extend approximately around the tricuspid annulus between the two commissures  28  that bookend the septal leaflet  24   a . Accordingly, a pair of commissure markers  62   a ,  62   b  on the exterior of the ring body  52  facilitate implantation by registering the ring  50  with respect to the commissures  28 . The markers  62   a ,  62   b  are typically radially-oriented colored thread fastened to a fabric covering on the ring. 
         [0046]    A majority of the ring body  52  is planar except for the free ends  56   a ,  56   b  which are upturned and the first segment  60   a  and a part of fourth segment  60   d  that are bowed upward. (To repeat, the “up” direction is merely for purpose of clarity herein and is synonymous with the inflow direction). As with existing rings, sizes 26 mm through 36 mm in 2 mm increments are available having outside diameters (OD) between 31.2-41.2 mm, and inside diameters (ID) between 24.3-34.3 mm. Again, these diameters are taken along the “diametric” line spanning the greatest length across the ring, as seen in  FIG. 5A . It should be mentioned that the present invention is not limited to the aforementioned range of sizes, and larger rings of 38 or 40 mm OD are also possible, for example. 
         [0047]    A gap G′ between the two free ends  56   a ,  56   b  is substantially larger than in certain rings of the prior art to reduce the risk of suturing into the AV node or bundle of His, and to accommodate variations in anatomy and location of the bundle of His. In particular, the gap G′ is preferably between about 40%-50% of the labeled size, preferably between about 43-45%. In one configuration, the gap G′ is about 40% of the size of the long axis of the ring, which is typically the labeled size in millimeters. In absolute terms, the gap G′ is desirably between about 10-18 mm, depending on the labeled size. For instance, the gap G′ is preferably about 13.6 mm for a size 34 ring (about 40% of the labeled size). On the other hand, the gap G′ is not too large to reduce the effective support for the septal leaflet  24   a . Preferably, the fourth segment  60   d  of the ring  50  of the present invention extends at least half of the way around the septal leaflet  24   a.    
         [0048]    In a preferred embodiment, the gap G′ is larger than the gap G in the rigid C-shaped Carpentier-Edwards Classic® Tricuspid Annuloplasty Ring, seen in  FIGS. 5A and 5B . The gap G for the various sizes of Classic® Rings ranges between about 5-8 mm, or between about 19%-22% of the labeled size. At the same time, the gap G′ of the ring of the present invention is larger than the gap in the flexible C-shaped Sovering™ tricuspid ring from Sorin Biomedica Cardio S.p.A. The gap for the various sizes of the Sovering™ ranges between about 18-24 mm, or between about 60%-70% of the labeled size. Therefore, the gap G′ of the ring of the present invention is preferably greater than 8 mm and less than 18 mm, or is between about 23%-59% of the labeled size (typically equal to the dimension in millimeters of the long axis of the ring). 
         [0049]    The free ends  56   a ,  56   b  of the exemplary ring  50  are upturned in the inflow direction so as to help reduce abrasion on the adjacent leaflets (septal, or both septal and antero-superior). Prior rings that are not completely flexible terminate in ends that are extensions of the ring periphery, that is, they do not deviate from the paths that the adjacent segments of the ring follow. As will be explained below, the present ring  50  desirably includes a core member that provides at least some rigidity and structural support for the annulus. The upturned ends  56   a ,  56   b  present curved surfaces that the constantly moving leaflets might repeatedly contact, as opposed to point surfaces so that forcible abrasion of the moving leaflets in contact with the ends of the ring is avoided. 
         [0050]    As seen in  FIGS. 7B and 7C , the exemplary ring  50  also includes an upward arcuate bow or bulge  64  in the first segment  60   a , and another upward bulge  65  in the fourth segment  60   d . The “aortic” bulge  64  accommodates a similar contour of the tricuspid annulus due to the external presence of the aorta and desirably extends from near the first free end  56   a  along first segment  60   a  to a location that corresponds to the end of the aortic part of the anterior leaflet. Prior tricuspid rings are substantially planar, and if at all rigid they necessarily deform the annulus to some extent at this location. The aortic bulge  64  helps reduce stress upon implant and concurrently reduces the chance of dehiscence, or the attaching sutures pulling out of the annulus. The axial height h b  of the aortic bulge  64  above the nominal top surface of the ring body  52 , as indicated in  FIG. 9C , is between about 3-9 mm, preferably about 6 mm. The “septal” bulge  65  conforms to the slight bulging of the septal leaflet attachment in this area. The axial height h s  of the septal bulge  65  above the nominal top surface of the ring body  52 , as indicated in  FIG. 9B , is between about 2 to 4 mm. These two bulges  64 ,  65  provide a “saddle shape” to the ring body  52 . 
         [0051]    Now with particular reference to  FIGS. 9A-9C  and  10 A- 10 D, the tricuspid ring  50  of the present invention is seen partially cutaway and in sections to illustrate further exemplary features. As seen best in the cutaway portion of  FIG. 9B , the ring body  52  preferably comprises an inner core  70  encompassed by an elastomeric interface  72  and an outer fabric covering  74 . 
         [0052]    The inner core  70  extends substantially around the entire periphery of the ring body  52  and is a relatively rigid material such as stainless steel, titanium, Elgiloy (an alloy primarily including Ni, Co, and Cr), Nitinol, and even certain polymers. The term “relatively rigid” refers to the ability of the core  70  to support the annulus without substantial deformation, and implies a minimum elastic strength that enables the ring to maintain its original shape after implant even though it may flex somewhat. Indeed, as will be apparent, the ring desirably possesses some flexibility around its periphery. To further elaborate, the core  70  would not be made of silicone, which easily deforms to the shape of the annulus and therefore will not necessarily maintain its original shape upon implant. 
         [0053]    The elastomeric interface  72  may be silicone rubber molded around the core  70 , or a similar expedient. The elastomeric interface  72  provides bulk to the ring for ease of handling and implant, and permits passage of sutures though not significantly adding to the anchoring function of the outer fabric covering  74 . The fabric covering  74  may be any biocompatible material such as Dacron® (polyethylene terepthalate). As seen in  FIGS. 10A-10C , the elastomeric interface  72  and fabric covering  74  project outwards along the outside of the ring  50  to provide a platform through which to pass sutures. 
         [0054]    As mentioned above, the ring  50  of the present invention may possess a varying flexibility around its periphery. In general, the ring  50  is desirably stiffer adjacent the first free end  56   a  than adjacent the second free end  56   b , and preferably has a gradually changing degree of flexibility for at least a portion in between. For instance, the first segment  60   a  may be relatively stiff while the remainder of the ring body  52  gradually becomes more flexible through the second segment  60   b , third segment  60   c , and fourth segment  60   d . In a preferred embodiment, the fourth segment  60   d  is more flexible than the third segment  60   c.    
         [0055]    With reference to  FIG. 7A , the reader will appreciate that the flexibility of the fourth segment  60   d  accommodates the inward movement of the annulus in that sector from fluid dynamic closing forces on the valve, and therefore reduces the chance of dehiscence. More particularly, radial forces exerted on the ring in the vertical direction, or along the small axis, will act on the flexible fourth segment  60   d  and proportionately bend it inward, as indicated in phantom. This reduction in the antero-septal ring dimension, in turn, will reduce tension on the native valve leaflets that pull inward from valve closing forces. Tests have been conducted to determine the amount of force and movement associated with the septal aspect of the tricuspid annulus in both systole and diastole. Consequently, a preferred flexibility for the fourth segment  60   d  has been determined and quantified in terms of the amount of desirable deformation under a given load. In one embodiment, the flexibility of the fourth segment  60   d  is such that it deforms inward by about 10% of the antero-septal (small axis) ring dimension under maximum load, typically resulting from right ventricular pressures of up to 70 mm Hg. In contrast, left ventricular pressures of up to 120 mm Hg are handled by a more robust mitral annulus. The tricuspid annulus is more fragile and implanted annuluplasty rings are somewhat more prone to dehiscence. 
         [0056]    Another potential configuration of variable flexibility consists of one or more points of localized flexibility, or “hinge points,” that may supplement the aforementioned gradually changing stiffness or be incorporated into an otherwise constant stiffness ring. The locations of the contemplated hinges are best described with reference to  FIGS. 7A and 7B . 
         [0057]    A central hinge created by an area of the ring body  52  that is locally more flexible than adjacent sectors is desirably located mid-way along the second segment  60   b , as indicated by a hinge line  66 . This hinge is located approximately at the center of the length of the ring body  52 , and permits the segments on either side to flex or twist with respect to one another. Alternatively, two generally diametrically-opposed hinge points indicated by hinge lines  61  and  67  may be provided. These hinges are located at the upward bulges  64 ,  65  in the ring body  52 , and provide “saddle” flexibility so that the ring flexes generally in a plane intersecting the bulges. A ring according to the present invention may have one or more of these hinges. Also, as mentioned above, the discrete hinges or points of flexibility may be incorporated into rings having constant or variable flexibility, as described above. Finally, though 3-dimensional rings are shown, the several embodiments of flexibility described herein may also be provided in a flat, planar tricuspid ring, and with or without the increase gap between the free ends. 
         [0058]    In one exemplary construction, the ring body includes a core  70  made of a plurality of concentric peripheral bands having an axial dimension which is larger adjacent the first free end  56   a  than adjacent the second free end  56   b . Sectional  FIGS. 10A-10C  illustrate this embodiment. The core  70  in the first segment  60   a  (and possibly in a portion of the second segment  60   b ) is as seen in  FIG. 10A , with six (6) concentric bands of a material such as Elgiloy. In the section of  FIG. 10B , which is taken through the second segment  60   b , a section of the core  701  still comprises six concentric bands, but its axial height is reduced relative to the height of the core as seen in  FIG. 10A . Finally,  FIG. 10C  shows a section through the third segment  60   c  wherein a further section of the core  70 ″ is further reduced in height but also only comprises four (4) concentric bands, with two of the bands having terminated or tapered off somewhere between sections  10 B and  10 C. Of course, this construction is entirely exemplary and the core  70  could also be made of a single integral member that gradually tapers down in size, among other alternatives. Several other alternatives are disclosed in U.S. Pat. No. 5,104,407 to Lam, et al., the disclosure of which is expressly incorporated herein by reference. 
         [0059]      FIG. 10D  shows the internal structure of the ring body  52  at the second end  56   b . The core  70  is shown bending upward into close proximity with the extreme tip of the free end  56   b , though it is protected by the elastomeric interface  72  and the outer fabric covering  74 . Desirably, the core  70  has its greatest flexibility at this location, which is mid-way around the septal leaflet side of the tricuspid annulus. The upward bend of the core  70  and ring body  52  desirably makes an angle θ of between 45°-90°, preferably greater than 60°. Furthermore, the axial height h e , as indicated in  FIG. 9C , of the free ends  56   a ,  56   b  above the nominal top surface of the ring body  52  is between about 1-4 mm, preferably about 2 mm, and preferably the two free ends project upward the same distance (although such a configuration is not an absolute requirement). Because of the flexibility of the ring body  52  at the second end  56   b , there is a reduction in the antero-septal dimension of the ring depending on the load applied by the annulus in the small axis (vertical) dimension. 
         [0060]    While the foregoing is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Moreover, it will be obvious that certain other modifications may be practiced within the scope of the appended claims.