GB2398245A - Valve Prosthesis and Implantation - Google Patents

Abstract

An implant implantation unit (2), for inplanting at a determined position in the tubular element (51) with a wall comprising a cavity (50), is pushed there by a catheter (60) and the unit comprises deformable feelers (31) to, under the control of remote activation elements (42), change from a stowed form to a deployed functional form, to detect the cavity (50) and position itself there with reference to the position of the cavity. The unit has at least one marker for tagging it, to allow the limit to be imaged by an imaging device.

Description

VALVE PROSTHESIS AND IMPLANTATION

The current invention relates to an implant implantation unit and to a procedure for fitting the unit in a tubular element.

The problem at the origin of the invention concerns the implantation of heart valves. Until recently this necessitated open heart surgical operations, with stages such as stopping the heart, the implementation of extra bodily blood circulation and restarting the heart after the implantation of replacement heart valves. These surgical operations are difficult and delicate and present mortal risks related to operating shocks.

Document US 5 824 063 thus describes a unit carrying replacement heart valves, the unit comprising a tubular implant in synthetic material carrying internally a replacement valve in natural material.

Documents US 5 855 601 and US 5 868 783 describe new heart valve implantation methods, which offer the advantage of avoiding open heart surgery. These methods provide the implantation, by movement through the blood circulation system, of a heart valve replacement unit comprising a radially expandable intra-vascular cylinder carrying a biological valve internally. An inflatable part of a balloon catheter is placed inside the carrier cylinder and the implantation is done by introduction into a vein and movement as far as the failed valve using a catheter. A two dimensional image screen display allows the detection that the carrier cylinder has reached the required position and the cylinder is then dilated by inflating the balloon through the catheter and maintains its expanded shape.

The balloon is then deflated and withdrawn with the catheter.

The carrier cylinder presents a sealed casing, which is thus forced against the artery wall, so as to avoid the blood flow bypassing the replacement valve.

However, when the aorta is involved this procedure is not applicable because the coronary arteries open close to the failed native valves, so that the carrier cylinder is likely to block them, provoking the death of the patient.

For percutaneous implantation of a valve prosthesis, such as a coronary valve prosthesis, the proper orientation of the valve is important to avoid the possibility of the valve obstructing one of the coronary orifices. This would have disastrous consequences.

The inventor of the present application has previously thought of providing two corresponding openings in the wall of the carrier cylinder casing. However, so that these openings will be placed opposite the two coronaries, the position ofthe carrier cylinder in the aorta must be completely controlled. Monitoring on the screen allows the progress, or axial position, of the carrier cylinder to be checked, but the angular position will be neither visible nor controlled.

The inventor has therefore found a solution, described below, allowing the angular position, as well as the translational position, o f the carrier cylinder to be controlled.

He has therefore thought about the resolution of the more general problem of positioning an implant unit or transport vehicle in a tubular element with difficult access. The field of application could thus concern other fields than the medical, such as the petroleum or nuclear industries, for installing sensors, valves and other items. The scope of the present application must therefore not be considered as limited to the resolution of the original problem. In a more general way, the invention aims to allow, the placing, in a difficult to access location of a tubular element, of a unit intended to carry an implant, whatever the function of the implant.

To this end, the invention concerns in the first place a unit for the implantation in a determined position of a tubular element with a wall comprising a cavity, the unit being arranged to cooperate with means for driving the unit in the tubular element, a unit characterized by the fact that it comprises deformable feelers arranged so that, under the control of means for remote activation, it passes from a stowed to a deployed functional shape, to detect the cavity and position itself there with reference to the position of the cavity, and at least one marker on the unit for tagging the unit to permit the unit to be imaged by an imaging device when the unit is implanted in the cavity.

Thus, the unit can be made to advance blind and the feelers allow the automatic detection ofthe cavity and positioning at it.

The final required position can also be reached even through a contraction of the tubular element for example an access artery leading to an artery of larger diameter.

The invention also concerns a process, which is not surgical and without therapeutic aim, for implantation of the inventive unit, at a predetermined position in a tubular element presenting a wall comprising a cavity which procedure is characterized by the fact that, a user inserts the unit through an open end ofthe tubular element he activates drive means to make the unit advance to a position before the determined position, he commands the feeler remote activation means and, with the advance continuing, he stops the action of the drive means when he detects a blockage of the advance, indicating that the feeler means are positioned in the cavity, and he detects the orientation of the unit in the cavity by means of an imaging device which images at least one marker on the unit for tagging the unit and the cavity.

The present invention also provides a valve prosthesis adapted to be implanted percutaneously, the valve prosthesis including a stent and at least one marker on the stent for tagging the stent to permit the position of the stent to be imaged by an imaging device.

The imaging device may be a three dimensional imaging device, such as an echocardiograph, a magnetic resonance imager or a computerized tomography scanner.

The characteristics and advantages of the present invention will appear more clearly with the aid of the following description of a particular form of the realization of the inventive unit and a variant, as well as the procedure for using it, with reference to the attached drawing, in which: Figure 1 is a lateral cross section of the inventive unit, representing the feeler positioning and anchoring elements, associated with a cylinder carrying a valve prosthesis, the whole being covered by two removable concentric activation casings, Figure 2 corresponds to figure 1, the feeler positioning and anchoring elements having been deployed radially by axial withdrawal of the external casing, Figure 3 corresponds to figures 1 and 2, with the carrier cylinder surrounded by positioning and anchoring feeler elements having been deployed radially after axial withdrawal of the internal casing, Figure 4 is a lateral view of the carrier cylinder and the positioning and anchoring feeler elements, Figure 5 is a lateral perspective view of the positioning and anchoring feeler elements, Figure 6 is a schematic face view of the inventive unit, and Figure 7 is a schematic lateral section of the variant.

As shown in figure 1, the present implementation example corresponds to the medical problem, explained at the beginning, of implanting a functioning replacement valve for the native aorta valve. The valve implantation unit 10 comprises a carrier element 20 to hold the implant, joined to a plurality of feeler, or palpation, elements or fingers 30, 31, here regularly spaced angularly all around, for positioning and anchoring relative to relief features, specifically a cavity in the aorta wall, unit 10 being linked removably to a positioning catheter 60. Unit 10 is associated with two concentric sleeves 41, 42 for successive remote activation, by radial expansion, of feeler elements 30, 31 then the carrier element 20. The direction of movement of unit 10 is therefore towards the left in figures 1 to 3. Reference 62 represents an axis of symmetry and the drive direction of unit l O and catheter 60.

The implantation valve forms a prosthesis 1 comprising valve units 2 of the valve whose shape and size correspond perfectly, in the operating position, to those of the native aorta valves 50 (fig. 2). The prosthesis 1 is fixed to the implant holding carrier vehicle element 20, here comprising a cylindrical mesh in a big-compatible material such as steel, gold alloys and for preference as here, nitinol, which comprises a shape memory nickel titanium alloy offering the ability to regain its shape after initial deformation, here by radial compression. The fixing of prosthesis 1 to the cylindrical nitinol mesh is made in well defined locations leaving free those regions that correspond to the valve units 2 after deployment from the stowed position of figure 2, as illustrated below in respect of figure 3.

Figure 4 represents the cylindrical mesh 20 in the deployed form, carrying the valve units 2 also deployed internally, on which are connected the feeler elements 30, 31, here in the form of a generally cylindrical exterior ring of wire loops of which one (31) at least, here in fact three, protrudes laterally and towards the front, opposite the catheter 60. In this example, the loops 31 extend, in the deployed position, in a direction inclined at about 30 degrees towards the front (direction of movement towards the target position) relative to the axis 62 of the mesh 20 and the ring 30. The feeler elements 30, 31 are joined to the cylindrical mesh 20 in such a way that their axial and angular positions relative to it are perfectly defined. The assembly, cylindrical mesh 2 and feeler elements 30, 31, is here composed of the auto expandable big-compatible material mentioned above.

The cylindrical carrier mesh 20 is here covered with an impermeable lateral casing intended to tee pressed against the aorta wall to avoid bypassing by brood circulation.

Figure 5 shows the feeler elements 30, 31 in perspective. Figure 6 is a schematic view, along the unit 10 axial direction, showing the three loops 31 protruding laterally from the tubular grid 20 that carries them, while the 2 valve units of the valve to be implanted are fixed internally to the carrier cylinder 20.

In addition, if necessary, an inflatable balloon, joined to the catheter 60, can here be placed inside the carrier cylinder 20, to be fed with liquid under pressure through catheter pipe 60 so as to cause or assist the radial expansion of the carrier cylinder 20 to the required deployed form.

As the feeler elements 30, 31 are made in a self expanding material such as nitinol, or an equivalent element forming an elastically protruding foot or finger, unit 10 is covered with an inhibition sleeve 42 to hold the feeler elements 30, 31 in a stowed position, the loops 31 being folded on the ring 30 and thus also on the mesh 20. Sleeve 42 extends to cover the catheter 60. A second sleeve 41, effectively the same length and without effect on the feeler elements 30, 31, is here similarly provided to hold the carrier cylinder in the stowed position, so as to avoid unplanned deployment even in the absence of inflation of the balloon 3. The two sleeves 41, 42, are mounted concentrically on the catheter 60. The sleeves 41 and 42 are accessible from the end of catheter 60 opposite to the unit 10.

Elements 3, 41, 42, and 60 comprise a functional catheter assembly separable from the unit 10, for the positioning and switching on this latter and the payload (2).

The two sleeves 41, 42 inhibit the radial deployment of the structure 20, 30, 31 until the latter reaches the region of the native aorta valve 50 to be functionally replaced, and thus allow the introduction of unit 10 into the blood circulation system, such as a reduced diameter incised artery.

As indicated, the catheter 60, with balloon 3, is detachably joined to the implantation unit so as to allow an axial advance of the implantation unit lO in the blood circulation system up to the implantation location, and the withdrawal of the catheter assembly 3, 41, 42,60.

To free itself, the catheter 60 comprises, in this example, at the fixed end of carrier cylinder 20, a spring effect clamp (not shown), with remotely controlled teeth fitted to rotate radially, for connection to the unit 10 and has a sliding central remote control metal wire to axially push back the claw branches or teeth so as to separate them radially and so free the catheter 60 of the implantation unit 10 according to the sugar claw principle.

When the cylindrical mesh 20 is deployed, the pressure on the aorta internal wall is provided by the shape memory effect, which thus ensures the radial dilation of the prosthesis 1. The failed native valve unit 50 is flattened by being pressed by the tubular grid 20 against the aorta internal wall, each of the three loops 31 protruding laterally having previously been engaged in one, specifically, of the three native valve units 50 and being similarly pressed to confirm its anchorage. The valve units 50 are thus clamped between the mesh 20,30 and the respective loops 31.

As shown schematically in Figure 1, at least one, or a plurality, or each feeler element 30,31 is provided with a marker 100 for tagging the unit to permit the unit to be imaged by an imaging device when the unit is implanted. The marker(s) are provided in such a manner that the angular orientation of the valve can be determined when the marker(s) is or are imaged. The imaging device is preferably a three-dimensional imaging device, such as an echocardiograph device, a magnetic resonance imager or a computer tomography scanner. However, other three dimensional imaging devices and techniques may be employed. The material employed to tag the stent would depend on specific imaging tools, and such materials for associated imaging tools are known in the art. The marker may be applied (for example as a coating) to the feeler element(s), either wholly or partially over the feeler element(s), or may compose the feeler element. Therefore the marker may comprise a coating, a non structural part or a structural part of the valve, for example of the feeler element of the valve. In other embodiments of a valve prosthesis embodying the invention, when feeler elements are absent, one marker is present or a plurality of markers are present on the stent to enable the position and angular orientation of the stent to be imaged by the same imaging tool and process employed to image the artery into which the valve prosthesis is percutaneously implanted.

In accordance with the invention, tagging can be done in a way that the tags are related so that the safest way of implantation would by aligning the tags to the coronary orifice.

Alternatively, tags could be placed so that the zones of risk where a coronary orifice could be blocked would be identified. By tagging of the stent with material which is easily seen by the imaging techniques, this allows safer deployment of the stent, because an operator would not only have good visualization of the coronary orifices by the imaging technique but also the stent, and in particular its translational position and angular orientation.

The implantation procedure for the unit 10 described above, according to the preferred method of implementation, comprises the following steps. After insertion of the implantation unit 10 into the circulatory system, and after having pushed it using the catheter 60 to a position above the final target position, here precisely where the unit 10 arrives in the aorta, and so that a large diameter space is thus offered to it, the following stage consists of freeing the lateral loops 31, initially pressed against the stowed mesh 20, 30. The release of the loops 31 is done by withdrawing the external retention sleeve 42 (figure 2), that is to say withdrawn whilst maintaining the thrust on the catheter 60. The forward movement of the unit 10 continuing, the loops 31, being then protruded laterally towards the front with respect to the axial direction of forward movement, in opposition to the catheter 60, they form a sort of tripod and simultaneously penetrate the three respective native valves 50, effectively identical, comprising an arrangement of connection pockets in a complete ring with each extending over 120 degrees, filling in total the whole of the perimeter of the aorta internal wall 51. Each native valve unit 50 offers a rounded base.

Each lateral protrusion 31, turned towards the front, presses against the base of the native valve unit 50 concerned, in general in a point distant from the "lowest" point of the base, that is to say, the furthest from the catheter 60. This is therefore a partial stop because the axial advance of the unit 10 continues by thrust from the catheter 60, the axial thrust of the unit 10 causing it to slide to the lowest point. The bottom of the valve unit SO thus comprises a sort of inclined plane guidance track (not orthogonal to the axis (62) of the aorta) which, in reaction to the axial forward force, creates a circumferential reaction force causing the rotation of the unit 10 until the feeler loop considered 31 reaches the lowest point, which corresponds to a complete end wall (with tangential plane orthogonal to the axis (62) of the aorta 51), and thus corresponds to the final axial and angular position sought for the unit 10.

Each lateral protrusion 31, with rounded ends, here as a loop, so as to be able to slide in the bottom of the valve unit SO, thus comprises, by continuous cooperation with the variable depth rounded base of the native valves 50, means for rotational drive of the feeler elements 30, 31 and thus also of the cylindrical mesh 20, to which it is joined.

However if the lateral protrusions 31 by chance bump against a native valve unit 50 commissure, the implantation unit 10 can be slightly withdrawn and the operator twists the catheter 60 so that it pivots angularly to be able to restart the positioning and anchoring operation.

The assembly, feeler elements 30, 31 and cylindrical mesh 20, being positioned axially and at an angle with respect to the specific relief of the aorta comprising the native valve units 50, it is then automatically positioned with respect to the two coronary openings (52) for which the axial and angular position with respect to the valve units 50 is determined and known, the valve unit - coronary axial distance evidently depending on the size of the patient.

In the case considered here in which the three native valves 50 form a circular circumference to the aorta wall extending over 360 degrees, a single lateral protrusion is sufficient to module 120 degrees positioning and anchoring the cylindrical mesh 20. As stated above, in a general case, there could only be one feeler 30, 31 working with a row of cavities or pockets covering all the circumference of the tubular element, or even a single pocket of cavity 50 only occupying a sector of the circumference and a plurality of feelers 30, 31 all around the unit 10 so that one of them fits in the cavity.

It will be noted that, in the present example, module 120 degrees positioning can be tolerated because the two coronaries (52) naturally effectively show this angle. If this was not the case, it would be necessary laterally to enlarge two openings or serrations 22 provided in the casing 21 so that they were positioned opposite the coronaries (52) (fig. 4 and position marked on figure 3.), or again to feel, using the feelers 31, the coronaries (52) themselves, which also comprise cavities in the aorta 51, and not to sense the native valve units 50. This case corresponds to the variant described below.

In the positioning step, both the angular orientation of the valve and the aorta are imaged by a common 3D imaging technique such as echocardiography, magnetic resonance imaging or computerized tomography scanning so that the valve is implanted percutaneously in the correct orientation without obstructing one of the coronary orifices.

Positioning thus having been effected, the following stage, as show in figure 3 consists, of deploying the cylindrical mesh 20 carrying internally the valve units 2 by withdrawing the internal retaining sleeve 41, to consolidate the anchorage and change the valve units 2 to their operational forth. For the clarity of the drawing, in particular the protrusions 31, the mesh 20 has been represented with a relatively small diameter, whereas in fact it matches that of the aorta 51, with a slight increase to ensure the required lateral pressure. In the same way, two protrusions 31 have been represented, although in fact they are separated by 120 degrees, with the plane of figure 3 only in reality cutting one. For this reason, only a single coronary has been drawn (52).

The three loops 31 protruding however provide by themselves a basic anchorage in the bottom of the pockets comprising the native valves 50 and ensure the positional stability of the prosthesis 1. After a few weeks, fibrous tissue will cover the prosthesis 1, combining with the lateral protrusions 31 to further improve the fixing.

It will be noted however that, in the deployed position of the feeler elements 31, it is not necessary that their free ends should be firmly pressed against the aorta 51 wall. It is sufficient that their radial extension should be sufficient that they hook, in passing, onto the valve units 50. Because ofthis, when the feeler elements 31 are deployed, before the final position, the later axial translation of the unit 10, up to this position, is done without "hard" rubbing under pressure, ofthe part of the loops 31 on the aorta wall 5 1. The latter thus does not run any risk of damage due to scratching or piercing, the loops 31 being feelers, that follow the aorta wall 51 to detect the valve units 50. As described above, rounded feet or lugs can also be suitable.

The feeler loops 31 thus do not here have very firm anchoring of the unit 10 in the aorta 51 as their main function, because they do not aim to exert a large radial anchoring pressure.

As indicated above, this is only a basic anchoring. It is then the radial deployment of the mesh 20 that creates, by shape memory, a definitive radial anchoring pressure that forces the mesh 20 under pressure against the aorta wall 51 and thus blocks any relative movement, such as the withdrawal of the unit 10 that could be due to blood flow, in a direction opposite to the insertion of the unit 10. The feeler elements 11 are then functionally superfluous. They however contribute to maintaining position by pinching the valve units 2. As the mesh offers a relatively high contact surface with the aorta 51, any risk of damaging the latter is excluded. The shape memory material allows the radial pressure exerted on the aorta 51 to be precisely determined, the diameter ofthe latter thus increased being then perfectly defined, which eliminates all risk of excessive radial stress.

The inventive procedure can be implemented in non-surgical manner and without therapeutic aims, to implant the unit 10 (or equivalent) in a determined position in a tubular elements offering a wall including a cavity, the procedure comprising the following stages: a user inserts the unit (10) into an open end to the tubular element, the user activates the drive means (60) (catheter, external magnet or other) to move the unit (10) up to a position upstream the determined position, the user commands the feeler element (30,31) activation means (42) and, the forward motion continuing, the user stops the activation of the drive means (60) when he detects a blockage of the advance, due to the fact that the feeler means (30,31) are position in the cavity.

To ease the drive of the unit 10, this one can be associated with a type of precursor rostrum 61 (fig. 1 to 3) forming a guide, in the form of a cylindrical element of a limited diameter, joined to the catheter 60.

It will be noted that the implantation unit according to the invention can, first, be implanted alone, without implant or payload, the latter being implanted later on the implantation unit according to the same principle. In a similar case, the inventive unit comprises means for receiving the second support, to come, of the implant, said means being arranged to ensure the position and anchorage, both axially, by stopping, and radially, with angular error correction means such as a finger or cavity provided to fit with an element of matching shape in the second support.

In the variant shown in figure 7, the implantation unit has the reference 110 and comprises functional elements similar to those of unit 10, with the same references preceded by the hundred 1, which have not however all been represented, with the aim of clarity. The cylindrical carrier element 120 is joined to a feeler element 131 which protrudes laterally and which has the same type of construction as the carrier element 120. In precise fashion, the feeler element 131 appears in the form of a cylinder, stowed radially in the rest position. When the unit 110 is pushed by the catheter 160, towards the bottom in figure 7, from a position above that shown, it engages in the coronary 52 when the free end is thus released from contact with the internal wall of the aorta 51.

The unit llO thus comprises a type of fork that locks by stopping in the bifurcation between the aorta 51 and the coronary 52. When the end position is reached the two elements 120, 131 are deployed by two balloons respectively and form a type of two fingered glove.

Thus, during the positioning phase, the feeler 131 presents a radially stowed form, thus with reduced diameter not risking blocking the coronary 52. Then the feeler 131 is deployed, by inflation of the associated remote control balloon, and constitutes a lining, or internal 'casing', pressed against the internal wall of the coronary 52 in accordance with the principle explained above for the carrier cylinder 20.

It will be noted that, as 120 and 131 each occupy a particular branch S1, 52, they can be considered as functionally equivalent, with the two principle functions if required. Each of them can in effect be a payload (2) carrier and can also be considered as being a feeler, because the aorta 51 can be considered (functionally in the context of the present invention) as being a cavity or branch with respect to the coronary 52. Thus the feeler means comprise a cylindrical element 131 arranged to change from a stowed form to a radially deployed form, supported against a wall of the cavity, here the coronary 52, under the influence of remote control means (balloon and catheter 160).

To avoid the risks of movement of the feeler 131 into the coupling position to the coronary 52, due to an angular error that necessitates several attempts, it can be arranged for a guide wire to be passed into the coronary 52 and the upper part of the aorta 51, the unit 110 being threaded above it across the feeler 131 that is thus angularly oriented towards the coronary 52. Another guide wire can at the same time guide cylinder 120 into the aorta 51.

Claims (12)

1. CLAIMS: 1. Unit for implantation of an implant (2) at a determined

   position in a tubular element (51) with a wall comprising a cavity (50,52), the unit (10) being arranged to work with driving means (60) to drive the unit into the tubular element (51), the unit characterised by the fact that it comprises deployable feeler means (30, 31, 131) arranged to, under the control of remote control means (42), change from a stowed form to a functional deployed form, to detect the cavity (50, 52) and position themselves there with reference to the position ofthe cavity (50, 52), and at least one marker (100) on the unit for tagging the unit to permit the unit to be imaged by an imaging device when the unit is implanted in the cavity.
2. 2. A unit in accordance with claim 1, in which the feeler means (30, 31) are made from a shape memory material.
3. 3. A unit in accordance with one of the claims 1 and 2, in which the remote control means are detachable and comprise a retaining sleeve (42) to hold the feeler means (30, 31) in the stowed form, said sleeve extending over the feeler means (30, 31) to free them by relative withdrawal of the sleeve relative to a wire unit thrust drive element (60).
4. 4. A unit in accordance with one of the claims I to 3, in which the feeler means (30, 31) comprise a ring, of generally cylindrical form with a radial direction, of loops (31) made of a wire with a limited stiffness in the radial direction, at least one of the loops (31) being arranged to protrude laterally so as to make a feeler.
5. 5. A unit in accordance with one of the claims I to 4, in which the feeler means (30, 31) comprise a plurality of feeler fingers (31) regularly spaced angularly and arranged so that, in the deployed form, they extend in respective inclined directions, at acute angles to a longitudinal drive axis (G2) forward from the unit towards the cavity (50).
6. 6. A unit according to one of claims 1 to 5, in which the feeler means (30,31) are joined to deformable means (20), to hold an implant (2), arranged so that, under the action of release means (41), it changes from a stowed form to a radially deployed form, pressed against the wall of the tubular element (51) and bringing the implant (2) into use.
7. 7. A unit according to claims 3 and 6 together, in which the means (20) to receive the implant (2) comprise a mesh in a generally cylindrical form having an axial direction, to carry the implant, with a limited rigidity in the axial direction, and the release means include a moveable sleeve (41) to retain the carrier mesh (20) in the stowed position, extending axially above the mesh to release it by a relative axial withdrawal of the sleeve (42) connected to a wire unit thrust drive element (60), the retention and holding sleeves (41, 42) being concentric.
8. 8. A unit in accordance with one of the claims 6 and 7, in which the implant reception means (20) are covered with a lateral sealing sleeve (21) intended to be pressed against the wall of the tubular element (51) by said implant reception means (20) and the sleeve sealing casing (21) occupies an angular position determined relative to the feeler means.
9. 9. A unit in accordance with one of claims 1 to 8, in which the feeler means (131) comprise a cylindrical element arranged to change from a stowed form to a radially deployed form arranged for pushing against a wall of the cavity (52) under the effect of remote control means.
10. lO. A procedure, non surgical and with non therapeutic aims, of implanting a unit (10) according to claim 1, in a determined position in a tubular element with a wall (51) comprising a cavity (50, 52), the procedure characterized by the fact that: a user inserts the unit (10) by an open end ofthe tubular element, the user activates the drive means (60) to make the unit (10) move forward to a position upstream the determined position, the user commands the feeler means (30, 31, 131), remote control means (42), and with the forward motion continuing, the user stops the activation of the drive means (60) when he detects that the motion is blocked, due to the fact that the feeler means (30, 31, 131) are positioned in the cavity (50, 52), and the user detects the orientation of the unit in the cavity (50,52) by means of an imaging device which images at least one marker (100) on the unit for tagging the unit and the cavity (50,52).
11. 11. A valve prosthesis adapted to be implanted percutaneously, the valve prosthesis including a stent and at least one marker on the stent for tagging the stent to permit the position of the stent to be imaged by an imaging device.
12. 12. A method of percutaneous implantation of a valve prosthesis according to claim 11, the method including the step of imaging the at least one marker while the valve is being implanted so that the orientation of the valve prosthesis in the artery is imaged.