Method for anchoring a mitral valve

[0001] The invention relates to minimally invasive cardiac surgery.

[0002] The art of artificial heart valves is well known. Recently there is a strong interest in minimally invasive methods of replacing defective heart valves, an in particular in percutaneous deployment methods. In those procedure, the new valve and all the steps to install it, are delivered via a fairly narrow catheter, typically 8-10 mm diameter.

[0003] Replacing major surgery with the small incision needed for inserting such a catheter is a major step in cardiac surgery.

[0004] The mitral valve is a particularly difficult case as the heart has an unfavorable geometry for anchoring a replacement valve. In conventional cardiac surgery the new valve is sutured to the tissue around the natural valve, which is surrounded by an annular ring of more rigid tissue known as the valve annulus. This procedure is not practical for percutaneous surgery. The main object of the invention is to devise an anchoring method for a replacement mitral valve. A further object is making the method both reversible and percutaneous.

[0005] An artificial mitral valve is anchored in the left atrium by placing the valve between the annulus of the natural mitral valve and an artificial annulus. The artificial annulus is formed by inserting a tool into the coronary sinus, and adjusting the tool to force the wall of the left atrium to form an annulus above the artificial valve, this locking it in place and forming a hemostatic seal. The artificial; valve can be held by compression from above or by circumferential compression from the tool. The compression can be released in order to remove the valve, if desired.

[0013] Referring now to FIG. 1, the cross section of the upper part of the heart shows the left atrium 1, the right atrium 2, pulmonary veins 3 and 4, tricuspid valve 5 and mitral valve 6, interventricular septum 7, atrioventricular septum 8, coronary sinus 10, interartial septum 11, and tendon of Todaro12. An artificial mitral valve 32 is introduced into the left atrium to replace a defective mitral valve 6. The artificial valve is of flexible construction in order to be deployed percutaneously via a catheter 38. For deployment it is compressed into an elongated oval shape. The art of percutaneous deployment is well known in minimally invasive surgery. One way to deploy valve 32 is to pass catheter 38 via septum 11, after entering the right atrium via the superior vena cava. The anchoring tool 9 is shown in FIG. 1 already inside the coronary sinus 10. The periphery of mitral valves 6 is less flexible and forms a shape 39 known as the mitral valve annulus.

[0014] Referring now to FIG. 2, valve 32 is allowed to expand to its normal form. Valve 32 comprises of very flexible leaflets 34, and a less flexible annulus 33. The overall shape of valve 32 is matched to the area above the mitral valve annulus, which is generally “D” shaped. The cross section of the annulus can be round, oval, rectangular or any other shape suitable for forming a hemostatic seal when seated above the annulus 39 of the defective valve 6. Annulus 33 can also be composed of multiple materials, some more rigid to better control the shape and some more flexible to help if forming a hemostatic seal. For example, annulus 33 can be made of soft silicone rubber with a Nitinol wire ring embedded in the annulus to control the shape of the ring. The leaflets 34 can be made of silicone rubber, Dacron or any other thin flexible material which is compatible with the heart. Artificial mitral valves capable of being delivered via a catheter are commercially available from Edwards Life Sciences (www.edwards.com).

[0015] At this stage the anchoring tool 9 is in the coronary sinus but it is left in the relaxed and flexible position, as explained later on.

[0016] After the valve 32 is placed at the final location above the defective valve 3 it has to be anchored into place. Valve 32 is brought into the correct position by using the delivery catheter to push it downwards (this is also aided by the downwards blood flow). To secure it in place, a second annulus, similar to the natural annulus 39 of the mitral valve 6, is created above valve 32 by a ring-like anchoring tool 9 shown in cross section in FIG. 3. When tool 9 is tightened it pulls in the outside wall of left atrium 1 as well as interartial septum 11 to form an almost full ring 36 around the valve annulus 33. This locks valve 32 between the natural annulus 39 of mitral valve 6 and an artificial annulus 36. By further tightening tool 9 a hemostatic seal is established. Since annulus 33 is flexible (as is tool 9) it will conform to the exact shape of the annulus 39. Inside the right atrium, tool 9 is placed against the interartial septum 11 just above tendon of Todaro 12.

[0017] Details of tool 9 are shown in FIG. 4. Tool 9 is made of rigid links 25 connected by two flexible cables 26 and 27. Protrusions or barbs 28 ban be added to increase anchoring in the coronary sinus. A barb 24 is mounted on end piece 23. This barb is covered by tube 21 of adjustment tool 15. When tube 21 is detached from end piece 23, barb 24 springs open and secures the position of tool 9 relative to septum 11 (shown in FIG. 1). The shape of tool 9 is adjusted by tensioning cable 26 by turning screw 22 using matching socket 21 connected to inner flexible tube 19. Both tool 9 and flexible tube 15 have a hole for guide wire 18. Flexible tube 19 can rotate freely inside flexible adjustment tool 15. Both adjustment tool 15 and inner flexible tube are made of metal bellows type hose or of a braided hose, as these type hoses are torsionally stiff but easy to bend. It is desirable to make screw 22 and socket 20 of a ferromagnetic material, and provide a small rare-earth magnet (not shown) inside socket 20. This facilitates locating screw 22 if adjustment tool 15 has to be re-connected to tool 9 inside the heart.

[0018] Referring now to FIG. 5 and FIG. 4, the percutaneous use of the invention is shown. Anchoring tool 9 is attached to flexible adjustment tool 15 and is inserted into the right atrium 2 via catheter 14, typically through the superior vena cava 13 over a guide wire 18. Guide wire 18 is inserted first, via ostium 37, all the way to the end of the coronary sinus 10. Tools 9 and 15 are guided by the wire 18. Tool 9 can be bent into shape by turning knob 17 while holding shaft 16. Turning knob 17 will turn socket 20 and tighten cable 26. To release adjustment tool 15, knob 17 is pressed into shaft 16 causing tool 9 to be ejected from tube 21 and embed barb 24 in septum 11. The operation is fully reversible As long as guide wire 18 is in place. It is even possible to re-adjust or remove tool 9 at a later date, if socket 20 can be lined up with screw 22. This is assisted by magnetic attraction, as explained earlier. The reversibility of the operation is a major advantage should the artificial valve need to be removed.

[0019] The same tool can be used both as an adjustment tool for controlling regurgitation in a natural mitral valve and as a anchoring tool for an artificial valve, This is important as in many cases an adjustment can correct the problem in the natural valve, without need for installing an artificial valve. At a later date an artificial valve may be required. In such a case, tool 9 simply needs to be loosened, an artificial valve installed and tool 9 re-tightened.

[0020] A more detailed view of tool 9 is given in FIG. 6. Each one of links 25 are cut at an angle 31. Angles 31 and length of links 25 determine the final shape of tool 9 when cable 26 is fully tightened. In order to keep links 25 in a single plane, the ends are cut in a V-shape as shown in insert drawing 40, which depicts a side view of links 25. The V shaped cut can be aligned with the longitudinal axis, as shown in 40, or can form an arbitrary angle to it. In such a case tool 9 will acquire a three-dimensional shape when tightened rather than fit in a single plane. Tightening screw 22 pulls nut 30 and tensions cable 26, causing tool 9 to tighten towards the final shape. The cross section of links 25 is designed to allow maximal blood flow in the coronary sinus. Cable 26 is permanently attached to nut 30 and to the last link (not shown), which is the link furthest away from end piece 23. Cable 27 is permanently attacked to the last link but not attached to end piece 23 in order to accommodate the change in length when tool 9 is changing from straight to curved. When cable 26 is loosened tool is very flexible, similar to a chain. When cable 26 is fully tight tool 9 can exert considerable force (a few Kg) in the radial direction.

[0021] By the way of example, tool 9 is made of type 316 stainless steel, with links 25 having a cross section of about 2×3 mm, and a length of about 12 mm each. Each links has three holes about 1 mm diameter each. Cables 26 and 27 are made of stainless steel as well and have an outside diameter of about 0.8 mm. Screw 22 is made of 400 series stainless (to be magnetic) and is 2 mm diameter with 3 mm hex head.

[0022] The term “annulus” in this disclosure has to be broadly interpreted. It need not be a complete circle, as tool 9 encircles the majority of the artificial valve circumference but not all of it, due to the presence of the aortic valve. The term “artificial annulus” should be understood as any arc-like retention feature formed by tool 9. Also, while the preferred embodiment shows the artificial annulus formed above the artificial mitral valve, it is obvious that the artificial annulus can be used to anchor the valve even without being above it. By the way of example, the periphery of the artificial valve can have a groove and the artificial annulus can engage this groove. In a different embodiment the base of the artificial valve can be wider than the top part, thus allowing anchoring by an artificial annulus. It is also clear that the tool 9 need not be made of individual links. It can be made of an elastic material such as Nitinol and rely on the elastic force to form the artificial annulus. While the term “anchoring” in this disclosure implies forming a hemostatic seal between the artificial valve annulus and the existing mitral vale annulus, it is understood that the seal need not be perfect to practice the invention, as any small gaps tend to seal themselves over time due to formation of scar tissue and deposits. A further improvement can be in the form of adding magnets to the artificial valve annulus and adding ferromagnetic material to tool 9. This helps align the valve with the artificial annulus. While the force of the magnets may be insufficient to retain the valve, it is sufficient to hold in the correct position until tool 9 is tightened.

[0023] An alternate way of using the artificial annulus is to use it as an anchoring base for a balloon expandable valve. Balloon expandable valves are well known in the art and are used, for example, as replacement aortic valves. Until now they were not used as mitral valves since there was no sufficiently rigid surface to expand the balloon against. FIG. 7 shows using tool 9 to form a rigid artificial annulus 36, then expanding balloon mounted valve 42, mounted on balloon 41, into the rigid structure that was formed.