Technical Field

The present invention relates to a device for the treatment of mitral valve prolapse. The mitral valve in a human being is a bicuspid valve located between the left atrium and left ventricle of the heart. The mitral valve is designed to allow blood flow from the left atrium into the left ventricle when the ventricular pressure is lower than the atrial pressure, and to close to prevent backflow from the ventricle into the atrium when the ventricle contracts and thus increases the blood pressure in the ventricle. Any damage to the mitral valve can allow blood to regurgitate i.e. to flow back into the left atrium when the left ventricle contracts. This significantly decreases the efficiency of the heart.

Each half of the mitral valve consists of a leaflet formed of flexible material which is anchored by cords (the chordae tendineae) located at several points around its perimeter, to the controlling papillary muscles in the left ventricle. As shown in Figure 1 , each half of the mitral valve may diagrammatically be visualised as a parachute 10, with the leaflet as the parachute canopy 11 , the cords as the parachute lines 12, and a parachute load as the papillary muscles 13.

Figure 2 illustrates diagrammatically the manner in which the mitral valve seals:- the two leaflets (shown as parachute canopies 11) are expanded by the increased blood pressure in the left ventricle so that the leaflets are pushed into the lower part of the left atrium and contact each other to form a seal. In this position, the cords 12 are taut.

The most common type of damage to a mitral valve is degeneration or damage to the cords:- the cords can stretch and slacken so that they no longer hold the leaflets correctly, or can rupture entirely. Either of these problems can result in what is known as a "flail leaflet" where the leaflet can move out of its correct position because it is not properly anchored, and thus fail to form an effective seal. A flail leaflet is shown diagrammatically in figure 3 as leaflet portion 11 a with a broken cord 12a attached.

Background Art

A number of techniques have been developed for the repair of a damaged mitral valve: e.g. the entire valve can be replaced with an artificial valve;

the broken or stretched cord can be replaced with an artificial cord or with a chordal transplant;

the flail portion of the leaflet can be tethered to another leaflet.

It will be appreciated that all of these techniques require invasive surgery.

A transcatheter technique has been developed, which uses a mitral valve clip to tether the flail section to an adjacent leaflet. However, this technique is suitable only for some valve failures and it also requires a high level of skill and is time-consuming.

Disclosure of the Invention

An object of the present invention is the provision of a device which will allow effective treatment of a mitral valve prolapse without invasive surgery and which is comparatively simple to position correctly.

The present invention provides a device for the treatment of mitral valve prolapse, said device comprising an openwork body capable of being collapsed sufficiently to permit transcatheter delivery and of being expanded when in position in the left atrium; the size and shape of said device being such that a surface of the expanded openwork body supports a mitral valve in the closed position; wherein said openwork body provides a series of apertures such that blood can flow through said body in use.

As used herein, the term "openwork" refers to open cage work, or lattice, i.e. a plurality of elongated members interconnected to form a structure with a plurality of apertures. The apertures are sufficiently small to adequately support the mitral valve in the closed position, but are sufficiently large to avoid the risk of occlusion when in situ. The apertures need not be uniform in size or spacing, but typically each side of an aperture would be in the size range 6 millimetres - 14 millimetres, preferably in the size range 6 millimetres - 10 millimetres.

The openwork body may be any of a wide variety of regular or irregular shapes:- the sole requirements are that the body is of an openwork material, that it is capable of being collapsed and then expanded, and that it provides one or more surfaces which, when the body is correctly positioned in the left atrium, are capable of re-establishing the closure plane of the mitral valve. In the preferred embodiment, the surface of the expanded body is a convex surface and forms part of the surface of the sphere. However, the surface need not be a curved surface and, if curved, need not be a regularly curved surface.

Examples of suitable shapes are a sphere, an ovoid, and a truncated cube. In practice, a patient requiring a device in accordance with the present invention would have a scan, (e.g. CT scan or ultrasound scan) of the mitral valve region carried out, to check the size and shape of the left atrium, and a device in accordance with the present invention would then be sized and shaped to provide a good fit.

The present invention further provides a method for the treatment of mitral valve prolapse which includes the steps of:

providing a device as described above;

collapsing the device so as to permit transcatheter delivery;

inserting the device by means of a selected blood vessel into the left atrium; expanding the device so as to occupy a major portion of the left atrium, such that a surface of the device provides an openwork surface or surfaces lying over the mitral valve, so as to support the mitral valve in the closed position.

It is envisaged that the device could be made of a variety of suitable biologically compatible materials such as nitinol (nickel/titanium alloy) or titanium; biologically compatible plastics materials also could be used.

Techniques for constructing a device which can be collapsed so as to permit transcatheter delivery are well-known in medical technology, and any of a range of suitable techniques may be used in constructing the device of the present invention. For example, the device may be constructed such that the elongated members forming the device can be slid between a collapsed and an expanded condition and/or the device may be made of a shape metal (memory metal) such as a nickel titanium alloy, (e.g. Nitinol) in the same manner as self expandable metallic stents.

Brief Description of the Drawings

By way of example only, a preferred embodiment of the present invention is described in detail, with reference to the accompanying drawings in which:-

Figure 1 is a diagrammatic representation of part of a mitral valve; Figure 2 is a diagrammatic representation of a mitral valve when closed;

Figure 3 is a diagrammatic representation of a damaged mitral valve;

Figure 4 is a section through a human heart showing the left atrium and the left ventricle;

Figure 5 is a section through a human heart showing the left atrium and the left ventricle, with a device according to the present invention positioned in the left atrium; and

Figures 6 and 7 are diagrammatic views of two other possible shapes of devices. Best Mode for Carrying out the Invention

Referring in particular to Figure 4, a human heart 15 is shown, including the left ventricle 16 and a left atrium 17. A mitral valve 18 is formed from a pair of leaflets 19, 20 which are supported by two sets of spaced cords 21 , 22 which extend between the respective leaflets 19, 20 and the corresponding papillary muscles 23, 24.

When the mitral valve 18 is closed (as shown in Figure 4) the sets of cords 21 , 22 are taut and the two adjacent surfaces, 19a, 20a of the leaflets 19, 20 are pressed together to close the valve. As described above, if some or all of the cords of a leaflet of stretched or broken, the corresponding portion of the associated leaflet can flail as illustrated diagrammatically in Figure 3, with the result that the valve fails to close.

To overcome this problem and to assist a damaged valve to close correctly, a device 25 in accordance with the present invention is inserted in the left atrium, as shown in Figure 5. The device 25 occupies a substantial proportion of the left atrium - this automatically positions the device 25 correctly, and ensures that the device cannot move away from the mitral valve 18. When the device 25 is position in the left atrium, part of the surface of the device 25 overlies and supports the leaflets 19, 20 of the mitral valve 18 when the valve is in the closed position; this prevents a flail leaflet from moving out of position and ensures a satisfactory closure of the valve 18.

The device 25 is an openwork sphere made of a biologically compatible material as discussed above. The device 25 need not be a true sphere (see above), but it must provide a surface or surfaces against which the leaflets of the mitral valve 18 can close. The apertures 26 of the device 25 need not be a specific size or shape, nor do they need to be regularly spaced. However, it is important that the apertures 26 are sufficiently small that when the device 25 is in position, it provides adequate support to the leaflets i.e. that it re-establishes the closure plane of the mitral valve. In addition, it is important that the apertures 26 are sufficiently large that they do not encourage occlusion when in position, because it is essential that blood can flow freely through the device 25, and thus through the left atrium. It is believed that apertures having sides in the size range 6 millimetres - 14 millimetres will be suitable in practice.

If it is possible to position the device in a particular orientation in the atrium, then it would be feasible to have smaller apertures 26 immediately adjacent the mitral valve, for increased support of the leaflets, and larger apertures elsewhere on the device.

Figures 6 and 7 show two other possible shapes for the device:- Figure 6 shows an ovoid shape, Figure 7 shows a truncated cube shape. For clarity, Figure 7 shows the truncated cube as a solid, rather than openwork, but the device is of course openwork. The shape and size of the left atrium varies considerably from one person to another, and the best practice would be to carry out a scan, (e.g. CT scan or ultrasound scan) of the patient to establish the size and shape of the left atrium as accurately as possible, and then either custom make the device to the required size and shape or select the best fit from a range of pre-made devices.

The device 25 is positioned by collapsing the device so that it is suitable for transcatheter insertion, and then inserting the catheter plus device 25 through the femoral vein, into the right atrium and then through the septum into the left atrium. The insertion can be guided in known manner using x-ray and/or ultrasound scanning; accurate scanning will enable the device to be turned to a specified orientation before expanding the device to the position shown in Figure 5. However, the device 25 can be designed such that it will operate satisfactorily in any orientation.

It will be appreciated that the above described device and insertion method offers a significantly less invasive solution to the problem of mitral valve failure. In addition, the insertion method requires a lower skill level than either invasive surgery or the use of a mitral valve clip. The device can be removed if necessary.