The invention relates to the prosthetic heart valve stent used in prosthetic heart valves in treatment of structural heart diseases particularly severe aortic stenosis by a minimally invasive method.

The current solutions in stents used particularly in aortic prosthetic heart valves are characterized by the fact that posts create straight lines after assembling (fig.l - prior art) Such geometry of the stent scaffold cause change of the total length in the compression phase. The posts of length L form an angle with the horizontal line a, and as a result the height H has a smaller value than the length L. After compression straightening of the posts takes place and the height H takes the maximum value which is equal to the length of the post L, and thus changes its total dimension.

The stents known from the patent descriptions W02018026904 (Al), WO2018042439, (EP3315094), US 2003/0153874 Al, US20180185179, US20150272730 have the shape of an open cylinder, positionedin such a way so that its longitudinal axis passing along the cylinder centre is placed in the direction of blood flow from the left heart ventricle to the aorta. Stents have a distal section, the central section and the proximal section. Stents have the form of a flexible net which is constructed in such a way that they can be compressed and delivered by the delivery system and thereafter they are expandedto a resting state. The resting state takes place at the moment of its expanding. Due to this fact stents have two configurations, the first one after compression, ready for the implantation to the patient, and the other one in the expanded state. After expansion the stent net takes shapes similar to "X". In this case during compression and expansion change of the total height of the valve takes place. At the momentof compression and expansionhigher stresses occur in the places of coupling between the stent scaffolds in comparison to other places in the valve stent. In order to reduce these stresses chamfers are necessary.

In stents for aortic valves apart from standard net constructions of "X" type which are cut off from a uniform roller, alternative shapes of stents are tested, known from the patent description US20150057747, called "Stent with alternative cell shapes". There are also stents with irregular shapes, e.g. dilatation stent JPH11319112, with rectangular shapes with roundings and stents with local protrusions which alter in sine function CN2617398.

In the patent description US20180200051 a mechanism comprising posts connected by kinematic pairs ( rotary connections) constitutes the actively controllable stent and it is to enable active regulation of the position in combination with the drive screw and with the proximal and distal drive blocks.

In order to improve nesting in the passing between the aorta and the left heart ventricle micro-anchors are used in stents for aortic prosthetic heart valves in stents known from the patent description US20090259306 Transcatheter heart valve with micro-anchors.

The process of preparing a stent for implantation comprises compressing a stent from the target shape (cut) to the diameter enabling putting on the sheath and its implantation with use of TAVI system, and thereafter its expansion to the original diameter e.g. with use ofballoon angioplasty. During this process in stents with straight posts a change of total length of the post takes place. This effect is called "fore-shortening" and it can negatively affect the precise positioning of the valve stent during TAVI operation. In order to achieve better seating of the stent between the ventricle and the aortic part the effect of "dogboning" is applied. The said effect consists of variable characteristics of expansion of the stent by balloon angioplasty, i.e. in the first phase of the distal and proximal sections, and thereafter in the central section. The said effect is most often caused by use of the balloon with variable stiffness on its length. The alternative solution is to use the shape of the stent scaffold with variable geometrical stiffness.

The invention relates to the stent, particularly for the aortic prosthetic valve made in the form of a cylinder comprising posts and excisions between posts and openings for mounting the system holding the valve leaflets. The posts of the stent in the compressed phase have the shape of a wave described by the smooth function and the said posts together with excisions between adjacent posts have a corrugated structure, favourably in the shape similar to fragments of the trigonometric function sin or cos. A smooth function is a function that has continuous derivatives. In the expanded phase of the stent the posts are twisted lengthwise. In the distal or proximal section there are additional excisions for the change of the stent geometry in the expanded phase. In the stent geometry there are openings for mounting the system holding the valve leaflets. The edges of the stent are rounded and chamfered.

The advantage of the presented stent is the specific geometry of the stent scaffold, which ensures lack of the length change within a defined scope during the process of expansion and compression, more even distribution of stresses during compression and expansion of the stent, and also lengthwise twisting of the posts during expansion which improves adhesion of the stent/valve to the walls of blood vessels, to the aorta (fig.10) and also improves tightness in the valve. Such effect ensures application of the smooth function (smooth function is a function that has continuous derivatives up to desired order over some domain) describing the corrugated construction of the stent with use of e.g. trigonometric function sin/cos. During expansion the effect "dog-bone" is created by applying variable geometric stiffness of the stent resulting from usage of additional excisions or of a variable number of posts in the stent. The stent can constitute an element of the prosthetic heart valve expanded with use of e.g. a balloon or it can be self-extendible, and the hidden sheath or a another setting mechanism can be configured for maintaining the stent scaffold in the decreased configuration during delivery. Expanding the stent scaffold in the native annulus of the aortic valve can comprise a balloon expansion of the scaffold stent or enabling self— expansion.

The presented shape can be applied in the systems for replacing a native aortic valve, mitral valve, tricuspid valve or pulmonary valve.

The invention is shown in the examples of execution in the picture, where fig.l shows the geometry of the currently used stents during the process of compression, fig.2 shows the difference in length of a straight post and a post with corrugated structure (described by the smooth function in the compressed phase), fig. 2b shows the comparison of the shape of the post described by the function cos, sin and the straight line, fig. 3 a,b,c,d,e, - examples of shapes of the geometry of the stent scaffolding in the compressed phase, fig.4 - the construction form of the compressed valve with fig.3a, fig.5 - shows the geometry of the stent scaffold I) in the compressed phase II) in the expanded phase, fig.6 - the construction form of the compressed valve with fig.b, fig.7 - the construction form of the compressed valve with fig. 3c, fig. 8 - the construction form of the compressed valve with fig. 3d fig. 9 - the construction form of the compressed valve with fig. 3e and fig. 10 shows the stents in the axial view.

The invention consists of applying in the stent in the compressed phase posts with corrugated structure, whose geometry can be described by the smooth function (functions which have continuous derivatives up to some desired order over some domain) Trigonometric functions sin/cos are examples of such functions.

The stent shown in the picture in the compressed state consists of posts with the shape of a corrugated construction 1 and excisions 2 enabling expansion of the stent in a balanced way. Furthermore, it is possible to make additional recesses 3 in the distal and proximal sections of the valve stent in order to accelerate the process of expansion and obtaining the dogboningeffect, making openings 4 for mounting the valve leaflets, introducing roundings and chamfering in the stent 5 in order to avoid sharp edges. Minor longitudinal twistings of the posts are the characteristic feature of this stent during expansion, marked no 6 in fig. 10

Such geometry of the stent scaffold ensures lack of the length change within a defined scope during the process of expansion and compression. Additionally, the corrugated construction form causes lower stress concentration during compression and expansion. Fig. 2 shows the stent with suggested geometry ensuring the constant value of the total length during processes of expansion/compression.

The length of the post in the function cos can be determined from the following formula:

Where the function f(x) is the function describing the corrugated construction expressed e.g. with use of the function L =

Where the parameter a increases/decreases the amplitude of the wave, the parameter c increases/decreases the frequency of the wave. The amplitude describes the height which is reflected in the value on the axis of ordinates (y-axis), the frequency refers to the speed of the repetition of the wave form on the axis ob abscissa (x-axis).

Examples of the stent parameters:

• The diameter of the whole stent in expanded state from 19 to 29 mm

• The total height of the stent from 20 to 30 mm

• The post in the expanded state has the following properties:

• The height of the post H in the range from 2 to 5 mm

• The length of the post L in the range from 2 to 8 mm

• The width between ends S in the range from 0 to 6 mm

Fig 3 shows a number of stent forms with various additional features. In the solutions from a) to e) the compressed stent has the shape of a wave similar to the function sin/cos, which causes lack of the effect "fore-shortening". In the variations d) and e) the geometrical stiffness in the distal section was changed by making an excision, which causes its earlier expansion. The characteristic shape "dogboning" is created without using a balloon with variable stiffness. In the variants c) and e) there are openings for mounting the commissures of the valve leaflets.

The geometry of the stent scaffold in the expanded phase is created as a result of dynamic loads during the process of balloon angioplasty (fig.2). It causes lack of possibility to describe the said geometry in an unambiguous manner with use of the function and mathematical parameters, so the ultimate shape is dependent on the dynamics of the above mentioned process, used materials and the features of the applied balloon. However the shape of the stent after compression, the examples are shown in fig.3-9. In the solution a) middle free ends of the posts can be used as hooks for the leaflets or for the material sealing the valve. The contact between the posts instead of straight lines is spread on the curves, whose length is bigger than the length of straight lines.

Other proposed variants of the stent with corrugated structure similar to the function sin are shown below, they include additional openings and excisions. No. 1 is the corrugated construction of posts in the stent, no. 2 are excisions, no.3 are additional excisions of the material in order to obtain a proper shape during expansion (dogboning), no. 4 are openings for mounting the valve leaflets in the places where a commissure is formed for a proper coaptation, no.5 are rays of a rounding and of a chamfer of the stent.