SYSTEM FOR IMPROVING DIASTOLIC DYSFUNCTION

[0001] This application is a continuation of U.S. patent application Ser. No. 11/497,309, now allowed, which has a filing date of Aug. 2, 2006 which is incorporated herein by reference in its entirety.

[0002] This application relates to cardiac surgery, and in particular to methods of treating heart failure such as congestive heart failure and diastolic dysfunction by percutaneous surgery.

[0003] Diastolic dysfunction (i.e., insufficient expansion of the left ventricle during the diastolic phase) and general deterioration of the left ventricular performance are very common problems, affecting about 5 million people in the US alone. The problems can be triggered by a myocardial infraction or develop slowly over time. More background data on congestive heart failure can be found on the internet at: http://healthlink.mcw.edu/article/928348606.html and many other medical sources.

[0004] Prior art treatment can be classified generally into three methods: surgery to change the shape of the left ventricle, wrapping the heart in an elastic net, or introducing a reinforcing structures via a catheter into the left ventricle. The first two methods require extensive surgery. The prior art minimally invasive or percutaneous procedures such as disclosed by US patent applications 2005/0015109; 2004/0243170; 2004/0249408 and 2006/0025800 addressed the need of strengthening the heart wall to resist remodeling and enlargement due to systolic pressure, but do not improve diastolic expansion to allow better filling of the left ventricle with blood. In many cases prior art methods actually sacrifice diastolic function in exchange for preventing the abnormal enlargement of the left ventricle that often follows myocardial infraction. For example, wrapping the heart in an elastic net will assist systolic action and will limit left ventricle enlargement, but will interfere with diastolic function as it will require more force to expand the left ventricle and stretch the net. The same is true for any rigid internal reinforcement.

[0005] As taught herein a system may assist diastolic function, the system being able to fit through a catheter and be installed percutaneously. The system may also limit the enlargement of the left ventricle, thus solving two major problem of congestive heart failure in a single percutaneous procedure. Further advantages will become clear by studying the disclosure and the drawings.

[0006] An elastic structure is introduced percutaneously into the left ventricle and attached to the walls of the ventricle. Over time the structure bonds firmly to the walls via scar tissue formation. The structure helps the ventricle expand and fill with blood during the diastolic period while having little affect on systolic performance. The structure also strengthens the ventricular walls and limits the effects of congestive heart failure, as the maximum expansion of the support structure is limited by flexible or elastic members.

[0013] Various embodiments of a cardiac device comprise an elastic structure that it introduced into a left ventricle of a heart and assists diastolic function by gently trying to expand the left ventricle. The elastic force is a small fraction of the force during systolic contraction, thus the device has little effect on the systolic pressure or ejected volume. It is well known that diastolic dysfunction is a major cause of cardiovascular failure, as it is far more common than systolic dysfunction. After some time (weeks to months) scar tissue permanently binds the elastic structure of the device to the ventricular wall. At this point the device also prevents ventricular enlargement, acting as reinforcement to the ventricular wall and limiting the maximum size of the left ventricle. Since the enlargement of the left ventricle as a result of congestive heart failure or infarct is gradual, scar tissue will have a chance to form before full bond strength is required between the elastic structure of the device and the ventricular wall.

[0014] FIG. 1 shows a typical deployment of a cardiac device 4 according to one illustrated embodiment of the invention. Deployment is performed via a catheter 1 inserted through the aorta into a left ventricle 2 of a heart 3. Any method of accessing the left ventricle can be used, such as trans-septal or via the apex of the left ventricle. The catheter size is in the same range as other percutaneous cardiac procedures, using sizes in the range of 18 Fr to 28 Fr (about 6 to 9 mm). The cross section also shows the papillary muscles 5 and device 4.

[0015] FIG. 2-A shows the device 4 still inside catheter 1. Device 4 is held by flexible cable 7 which is used to push the device 4 through the catheter 1, typically via a hemostatic seal outside the body (not shown). Typically a guide wire 11 is used to guide the catheter 1 into the left ventricle 2.

[0016] FIG. 2-B shows the device 4 after deployment in the left ventricle 2 of a heart 3. The device 4 expands elastically to fill the left ventricle 2. Ventricular contractions help embed a number of barbs 8 into a ventricular wall 6. Over time, scar tissue 6′ forms a permanent bond between the device 4 and the ventricular wall 6. The maximum opening of the device 4 is limited not only by the ventricular wall 6 but by flexible cross-members 9 and 10. It is desired to connect members 9 across the device 4 rather than between adjacent arms (as shown by reference numeral 10) as this allows the cross member to clear the papillary muscles, allowing the device 4 to cover a larger part o the left ventricle 2. As seen in FIG. 2B, the papillary muscles 5 can fit between two elastic members of device 4.

[0017] FIG. 3 provides a more detailed view of the device of FIGS. 1, 2-A and 2-B. The cardiac device 4 has two pairs of elastic arms 4′ and 4″. The arms 4′ and 4″ are equipped with barbs 8 and cross members 9 and 10. The arms 4′ and 4″ can be made from any durable elastic material such Nitinol, spring tempered stainless steel, plated beryllium copper or polymeric material. For added elasticity small loops 12 can be added. At an apex of the device 4 a connector 14, such as a thread, is used for temporary attachment to the flexible cable 7 via a thread 13. Cross members 9 and 10 can be flexible steel cables, polymeric cables, flexible ribbons or similar flexible members. The purpose of members 9 and 10 is to limit the maximum dilation of the ventricle 2 and stop ventricular enlargement (after members 4′ and 4″ bond to ventricle wall 6 by scar tissue 6′).

[0018] The number of flexible members 4′ and 4″ of device 4 and number of cross members 9, 10 can vary, the preferred embodiment having from three to twelve elastic members 9, 10. Cross members 9, 10 can connect adjacent elastic members 4′ and 4″ as members 10 do, or connect opposing members 4′ and 4″ as members 9 do. The arrangement shown in FIG. 3 is desired in order to allow elastic members 4′ and 4″ to extend beyond the papillary muscles 5 without cross members 9 touching the papillary muscles 5 or mitral valve cords (also known as chordae tendineae). Like any spring, the force that elastic members 4′ and 4″ exert on ventricle wall 6 is F=k(x+a), “k” being the spring constant, “a” the preload (amount of spring preload beyond the fully dilated position) and “x” the ventricular wall movement. The spring constant k is selected not to interfere with systolic function while still helping diastolic filling. By the way of example, a total force the ventricular wall 6 is capable of exerting on each one of the elastic members 4′ and 4″ is about 20-30 Nt (about 2-3 Kg) and the average movement during contraction is about 1-2 cm. In order to limit the effect on systolic operation the total force is chosen to be below 10% of systolic force, or about 2 Nt. If a preload of 2 cm is chosen, the spring constant can be calculated from the equation: 2 Nt=k(0.02 m+0.02 m), k=50 Nt/m. The size (i.e., diameter) of wire forming elastic members 4′ and 4″ is determined by the spring constant k. The size is typically in the range of 0.5-1 mm.

[0019] In order to place the device 4 correctly relative to the papillary muscles 5 the orientation of the device 4 inside the left ventricle 6 needs to be known. This can be done by fluoroscopy, ultrasound or by other location methods such as magnetizing elastic members 4′ but not 4″. This creates a north and south pole 15 which can be detected from outside the body by a magnetometer (or even a very sensitive magnetic compass).

[0020] The design of the device 4 allows aborting the deployment at any stage and retrieving the device 4. This is illustrated in FIG. 4. A flexible cable 7 terminating in a hook 16 is introduced via a catheter 1.

[0021] Cross members 9 are snagged by the hook 16 and the device 4 is pulled back into the catheter 1. If retrieval is desirable the two cross members 9 should be permanently joined at a cross-over point 18. This allows the hook 16 to self-center regardless of the point at which the hook 16 snagged cross members 9 and regardless whether the hook 16 has snagged one or both cross members 9. Obviously the retrieval is much more difficult once scar tissue 6′ has developed.

[0022] FIGS. 5-A through 5-D offer a more detailed close-up view of the construction of the device 4. FIG. 5-A shows the elastic elements 4′ and 4″ of the device 4 made of spring wire, cross members 10 made of thin stainless steel cable and barb 8 made of steel wire spot welded to the remainder of the device 4. If needed, a load spreading structure 17 can be added. The load spreading structure 17 can be made of bent wire, spot welded to remainder of the device 4 as shown, or can take the form of a polymeric strip. The complete device 4 can be coated with an anti-coagulant coating, drug eluting coating or any beneficial coating well known from the art of stents.

[0023] FIG. 5-B shows an alternate illustrated embodiment, cut out from a single sheet of elastic material and bent to shape. This mode of construction particularly advantageous when device 4 is made of Nitinol, as Nitinol is difficult to join. As before, an optional load spreading structure 17 can be added.

[0024] FIG. 5-C shows an embodiment of a device 4 that does not use discrete barbs but providing elastic members 4 with a special surface finish to promote rapid bonding with ventricular wall 6. Some examples of such finishes are: porous surfaces, surfaces coated with biological adhesives, surfaces coated with miniature barbs similar to the well known Velcro® fastener (generically termed hook and loop fastener), growth-promoting drug coating etc. It is known in the art that velour-like finishes promote tissue infiltration and greatly increase bonding strength. Test results are listed in U.S. Pat. No. 4,164,046 hereby incorporated by reference.

[0025] FIG. 5-D shows an embodiment in which the cross members are replaced with a continuous layer of a flexible mesh or flexible hemostatic material 18, such as Dacron fabric. When the layer 18 is hemostatic the device 4 can also seal an aneurysm or puncture in the ventricular wall 6, while still providing the other stated benefits. This is particularly desirable when the ventricular wall 6 is already significantly thinned by enlargement.

[0026] While the examples shown use a catheter 1 to enter the left ventricle 6 via the mitral valve, it is obvious that various other techniques may be employed to deploy the device 4. The device 4 can be installed in the left ventricle 6 also via the aortic valve, by piercing an apex of the left ventricle 6 or by an incision at any convenient point. It can be used percutaneously or during conventional cardiac surgery.