|Title of Invention||
|Abstract||An annuloplasty prosthesis for mitral and tricuspid heart valves in the form of a ring (1) which is either open, or closed apart from a gap, whereby the ring (1) has a core with a sectorally varying bending flexibility on the ring level.|
The invention relates to an annuloplasty prosthesis for mitral and tricuspid heart valves in the form of an open ring or one closed apart from a gap.
Annuloplasty prostheses are inserted in case of heart valve insufficiencies to forego implanting an artificial heart valve. Use of an annuloplasty prosthesis is combined, if necessary, with valve reconstruction, shortening or transpositioning the papillary tendinous fibres or shortening the papillary muscles.
The atrioventricular annulus is a dynamic structure, that undergoes changes in size and form during the heart cycle. During systole the medium annulus diameter of the mitral valve is particularly reduced by posterior annular contraction, while the anterior annular length remains almost unchanged. If there is a systolic anterior motion (SAM) , and moreover, a too large posterior valve leaflet, it can lead to left ventricular outflow tract obstruction (LVOTO).
3elonging to the insufficiencies that can be annuloplastically created, is, above all, loss of systolic discharge which is not due to stenosis, caused by raised systolic reflux of the blood through the mitral or tricuspid valve into the corresponding
vestibule. Chronic causes can bring about these insufficiencies, such as valve prolapse, left and right ventricular dilatation, overdistention of the pulmonary artery or left ventricular valve diseases, that impair the function of the tricuspid valve. These symptoms can be caused, for example, by rheumatic fever, coronary diseases, calcified annulus, Marfan Syndrome, malfunction of the papillary muscles or lupus. However, acute causes can also be responsible for these insufficiencies, such as valve prolapse through ruptured papillary tendinous fibres (myxoma, endocarditis, trauma) and ruptured papillary muscle, (infarction, trauma) as well as a perforated valve leaflet (endocarditis).
The aim of mitral or tricuspid valve reconstruction by implanting an annuloplasty prosthesis is basically to create a co-aptation surface of the valve leaflet that is as wide as possible, and tissue relief during systole as well as good haemodynamics during diastole. This involves correcting the dilatation and/or deformation of the annulus, selectively reducing deformed areas of the valve leaflet as well as preventing recurrent dilatation and deformation. Up until now, rigid or flexible mitral valve reconstruction rings (Carpentier or Duran rings) have been used, which effect a reduction of the mitral valve ring and therefore lead to increased competence. Rigid annuloplasty rings, as revealed, for example, in US-A 3 656 185, are characterised by great dimensional stability. Flexible annuloplasty rings have, in contrast, the advantage of cyclic deformation capability. They display high structural torsion capability and extremely low circumferential expansion. This ensures clear tissue relief of the atrioventricular annuli. Computer simulations and practical measurements with a 3-D echocardiographic procedure have unequivocally verified the advantages of these flexible rings over the rigid annuloplasty rings that have been known for some time. During systole, the entire valve surface subjected to pressure is reduced here, by approx. 25 percent (Kunzelmann K.S. et al.: Flexible versus rigid annuloplasty for mitral valve annular dilatation: a finite element model. J. Heart Valve Dis. 1998; 7, 1: 108-116 and Yamaura Y et al.: Three-dimensional echocardiographic evaluation of configuration and dynamics of the mitral annulus in patients fitted with an annuloplasty ring. J. Heart Valve Dis. 1997; 6, 1: 43-47).
On the other hand, a larger atrioventricular opening surface is available for diastolic ventricle opening, with thus lower influx resistance than with a completely rigid annuloplasty ring. Even the SAM syndrome occurs considerably less frequently after implantation of flexible annuloplasty than subsequent to rigid rings being implanted. However, what is disadvantageous about the annuloplasty rings, which are completely flexible apart from the circumferential length, is that there are periodic folding movements and bulges in the valve leaflets, above all in the area of commissures, after the implantation which has to be carried out on a relieved and arrested annulus.
The present invention is based on the task of creating an annuloplasty prosthesis, which has the advantages of flexible annuloplasty rings, but without their disadvantages.
Accordingly, the present invention provides an annuloplasty prosthesis for mitral and tricuspid heart valves in the form of a ring, that has a core with sectorially varying flexibility in the plane of the ring, namely in the main kinematic plane, characterized in that the ring has the form of an open ring, or has the form of a ring that is closed except for a gap.
While it is true that an annuloplasty prosthesis with areas of varying flexibility is already known from WO 9.7/16135, here, the flexibility is attained by more or less widely opened ring forms. However, the annuloplasty prostheses according to this invention can be both closed rings as well as open rings, still having the required flexibility properties. In this, vein, the core may have high flexural flexibility in the middle area - the area of the posterior mitral valve leaflet - and a high flexural rigidity in the plane of the ring in the area of the valve commissures. This can be attained, for example, by the core having sectors with different cross sections over its length. The different cross sections have steady or non steady transitions between them.
The mechanical deformation properties of the sectoral cross sectioning of the annuloplasty ring core as per invention enable, in a simple manner, the cyclic deformation of the known flexible annuloplasty
rings to be combined with the good dimensional stability of the known rigid annuloplasty rings.
Special advantages are incurred when the core is produced from one uniform material. The core's fracture safety property can then be very much more easily controlled than with jointed cores. Coming into question as materials for the core are particularly metals or metal alloys, preferably a titanium alloy. Here, the core can be preferably produced from round or polyhedral wire. The different core profiles can then be produced by cold-shaping the wire. Cold-shaping the wire causes it to be tougher than in thermal shaping.
The wire can have a basically square cross-section in places, whereby the height and width of the cross-section varies over the length of the wire. Depending on which direction the wire is flattened in, flexibility is changed against force being exerted on the ring level. Should the core be only slightly thick in the radial direction of the annuloplasty ring, then the entire ring in this area can be bent very easily. On the other hand, a core flattened on the ring level will lead to a high radial rigidity in the core, so that the annuloplasty ring can only be bent slightly in these areas. Changing the ratio of the profile height to the profile width enables alterations to be made to the core's geometrical moment of inertia of up to 40 percent over the unmodified profile.
In a preferred form of execution, the core can be surrounded by bio-compatible sheathing, for example, a hose made with expanded polytetrafluoroethylene (ePTFE). A padded layer, for example, made of polyester fabric, may be appointed between the core and sheathing.
Further advantages ensue, when the ring is cambered forwards from the ring level in the direction of blood flow, i.e. in the direction of the vestibule. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS: A preferred form of execution of an annuloplasty ring is described below in detail with the aid of a drawing.
The following is shown:
Fig. 1 a view of the main level of an open annuloplasty ring;
Fig. 2 a view of the annuloplasty ring from Fig. 1 from below;
Fig. 3 a section through the annuloplasty ring from Fig. 1 along line III-III
Fig. 4 a section through the annuloplasty ring from Fig. 1 along line IV-IV
Fig. 5 a section through the annuloplasty ring from Fig. 1 along line V-V
Fig. 6 a representation of the course of the axial geometrical moment of inertia Iz as a function of the H/B ratio;
Fig. 7 a representation corresponding to Fig. 1 of the annuloplasty ring with the heart valve in diastolic form;
Fig. 8 a representation corresponding to Fig. 7 of the annuloplasty ring with the heart valve in systolic form.
The C-shaped annuloplasty ring 1 from Fig. 1 has a symmetrical axis 22, that is vertically intersected through an axis 5, which runs through the area of the largest ring expansion. The axis 5 and the symmetrical axis 22 tension the kinematic main level. The annuloplasty ring 1 is provided with marks on its ends 6, on the points of greatest ring expansion 7 and on the interface 8 of the symmetrical axis 22, for simplified positioning by the heart surgeon. These marks 6, 7, 8 can, for example, be produced from coloured, braided polyester seam material. Line 16 represents the course of the annuloplasty ring's neutral fibres and is not subjected to expansion with elastic form changes. This line is the geometric guide size to calculate the sectorial geometrical moment of inertia of the annuloplasty ring 1.
It is clarified in Fig. 2 that the annuloplasty ring 1 is cambered forwards from the main level in the direction of blood flow, i.e. is convexly pre-formed in the direction of the vestibule. Axis 9 in Fig. 2 is orthogonal to the axes 5 and 2 from Fig. 1 and points in the Z direction, which the geometrical moments of inertia Iz are referred to.
Ring 1 is subdivided into sectors 2, 3, 4 of varying bending flexibility in the kinematic main level as per Fig. l. In the symmetrically appointed sectors 2, ring 1 possesses the greatest rigidity and in area 4 the lowest rigidity. Sectors 3 are areas of medial rigidity. Varying rigidity is attained by a core 10 contained in the inside of ring 1, said core having a different profile in sectors 2, 3 and 4. This is shown in Figures 3 to 5. Core 10 is formed here by a round wire, whereby the round cross-section as per Fig. 4 is maintained unchanged in sectors 3.
Fig. 3 shows sector 2 of the annuloplasty ring 1 (Fig. 1) stiffened against the forces on the kinematic main level in section view. Symmetrical axes 14a and 15a are directed parallel to axis 9 and the main level. They are always orthogonal to the neutral fibre 16 and are intersected in it. The ratio of height H to width B of the core profile 10a of the core 10 of the annuloplasty ring 1, which can, for example, lie between 0.35 and 1, causes a high geometrical moment of inertia Iz relative to the unmodified, circular profile 10b (Fig. 4), as shown in Fig. 6. Therefore there is also greater rigidity against external forces that are exerted inside the main level. In the form of execution displayed, the sectorial-ly profiled core wire 10 is surrounded by a hose 13 made of expanded polytetrafluoroethylene. A polyester fabric can be used as the padded layer 12 under an outer ePTFE sheathing 11.
In Fig. 4, the annuloplasty ring 1 is shown in sector 3 with unmodified core cross-section in section view. Symmetrical axes 14b and 15b are directed parallel to axis 9 (Fig. 2) and the main level (Fig. 1). They also run orthogonally to neutral fibre 16 and are intersected in it. The ratio of height H to width B of the core profile 10b of 1 causes a smaller geometrical moment of in-
ertia Iz (Fig. 6) than in sector 2 and therefore lower rigidity against external forces that are exerted inside the main level.
In Fig. 5, the annuloplasty ring 1 is shown in sector 4 (Fig. 1) of higher flexibility in section view. Symmetrical axes 14c and 15c are once again directed parallel to axis 9 (Fig. 2) and the main level. They likewise run orthogonally to the neutral fibre 16 and are intersected in it. Core profile 10c has a large ratio of height H to width B here, for example, in the range of 1 to 2.86, which causes a lower geometrical moment "of inertia (Iz) and therefore lesser rigidity against external forces that are exerted inside the main level, in comparison to the unmodified profile 10b from Fig. 4.
In Fig. 6, the interpolated course of the axial geometrical moment of inertia (Iz) is shown dependent of the height/width ratio H/B by the execution example of a flattened round core wire with 1.2 mm diameter. The interpolation is based on three measured H/B ratios produced by cold-shaping a round wire (see Points 23, 24, 25 in the diagram from Fig. 6).
For the unmodified round wire in sector 3 (Figures 1 and 4), H = B = core wire diameter, and Iz can be calculated by:
Izcircle =0.049 B4
For the sectorially stiffened core wire in sector 2 (Figures 1 and 3), a minimum ratio H/B = 0.35 can be produced, so that Iz can be stated in good approximation by
Izsquare - 0.083 • H • B3
For the sectorially flexibilised core wire in sector 4 (Figures 1 and 5), a maximum ratio H/B =2.86 can be produced, so that Iz
(Point 25) can likewise be calculated in good approximation as in Point 23.
Geometrical moments of inertia Iz with geometrical cross-sectional transitions from round wire to cold-shaped polyhedral wire can be calculated for 0.35 = H/B = 2.86 and a pre-given wire diameter D of 1.2 mm of the unmodified material by the general interpolation equation (Fig. 6):
Iz = D - (-0.214 + 0.225 e07287 B/H) mm4
With other wire diameters, the parameters of the applied exponential function must be newly calculated through new support points (23, 24, 25).
In Fig. 7, the annuloplasty ring 1 is shown on the annulus of the mitral valve 17 during diastole. The annuloplasty ring 1 is, as at the time of its being implanted, not burdened by forces on the main level and has an undeformed neutral fibre 16.
Fig. 8 shows, on the other hand, the flexible adjustment of a mitral form of execution of the annuloplasty ring 1 as per invention to the systolic form of the anterior 21 and posterior 20 heart valve leaflets therefore allowing an optimum co-aptation line 26. The neutral fibre 16 is flexibly bent into its new form 18. Sector 4 (Fig. 1) undergoes the greatest change of form on the posterior leaflet 20. The annuloplasty ring's 1 greatest rigidity lies in the area of the commissures on either end of the co-aptation line 26 in the opposite sectors 2 (Fig. 1). The upper curve width 19 on either side can be stated by the equation:
As = X • q • 14 / (E • Iz)
whereby E is the elasticity module of the core material, q (1) the circumferential load effective on the main level which is exerted on the ring by the tissue via the seams, 1 the length of the neutral fibre seen from axis 22, and ? a proportionality factor which is dependent on the geometry of the neutral fibre.
WE CLAIM :
1. Annuloplasty prosthesis for mitral and tricuspid heart valves in the form of a ring (1), that has a core (10) with sectorially varying flexibility in the plane of the ring, namely in the main kinematic plane, characterized in that the ring (1) has the form of an open ring (1), or has the form of a ring (1) that is closed except for a gap.
2. Annuloplasty prosthesis as claimed in claim 1, wherein the core (10) has a form that varies sectionally over its long sectors (2,3,4).
3. Annuloplasty prosthesis as claimed in claim 2, wherein the different sectional forms (10a, 10b, 10c) pass over, one into another, either uniformly or non-uniformly,
4. Annuloplasty prosthesis as claimed in one of claims 1 to 3, wherein the core (10) is produced from a uniform material.
5. Annuloplasty prosthesis as claimed in claim 4, wherein the core (10) is produced from a metal or a titanium alloy wire.
6. Annuloplasty prosthesis as claimed in claim 5, wherein the core (10) is produced from a round or multifaceted wire.
7. Annuloplasty prosthesis as claimed in claim 6, wherein the different sectional forms (10a, 10b, 10c) of the core (10) are formed from cold-worked wires.
8. Annuloplasty prosthesis as claimed in claims 6 or 7, wherein, at least in certain areas, the wire has a substantially rectangular, cross-sectional form (10a, 10c), whereby the height (H) and breadth (B) of the cross-sectional form varies over the length of the wire.
9. Annuloplasty prosthesis as claimed in one of claims 1 to 8, wherein the core (10) is surrounded by a biologically compatible casing (11).
10. Annuloplasty prosthesis as claimed in claim 9, wherein the padding (12), made of a polyester chord, is disposed between the core (10) and the casing (11).
11. Annuloplasty prosthesis as claimed in one of claims 1 to 10, wherein the ring (1) arches convexly in the direction of the atrium, in the direction of blood flow, out of the plane of the ring.
12. An annuloplasty prosthesis, substantially as herein described, particularly with reference to the accompanying drawings.
An annuloplasty prosthesis for mitral and tricuspid heart valves in the form of a ring (1) which is either open, or closed apart from a gap, whereby the ring (1) has a core with a sectorally varying bending flexibility on the ring level.
|Indian Patent Application Number||116/CAL/2000|
|PG Journal Number||10/2007|
|Date of Filing||28-Feb-2000|
|Name of Patentee||JOSTRA MEDIZINTECHNIK AG|
|Applicant Address||HECHINGER STRASSE 38, 72145, HIRRLINGEN, GERMANY|
|PCT International Classification Number||A 61 F 2/24|
|PCT International Application Number||N/A|
|PCT International Filing date|