Abstract:
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.

Description:
FIELD OF THE INVENTION  
       [0001]    The invention relates to cardiac surgery, and in particular to methods of treating heart failure such as congestive heart failure and diastolic dysfunction by percutaneous surgery. 
       BACKGROUND OF THE INVENTION  
       [0002]    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. 
         [0003]    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 of 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 correct for any rigid internal reinforcement. 
         [0004]    It is the object of the present invention to provide a system to assist diastolic function, the system being able to fit through a catheter and be installed percutaneously. A further object is to have the system also limit the enlargement of the left ventricle, thus solve two major problem of congestive heart failure in a single percutaneous procedure. Further objects and advantages of the system will become clear by studying the disclosure and the drawings. 
       SUMMARY OF THE INVENTION  
       [0005]    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. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0006]      FIG. 1  is a cross section of the heart showing the deployment of the invention. 
           [0007]      FIG. 2A  is a cross section of the left ventricle with the device still in catheter. 
           [0008]      FIG. 2B  is a cross section of the left ventricle after deployment. 
           [0009]      FIG. 3  is a perspective view of the invention. 
           [0010]      FIG. 4  is a cross section of the left ventricle showing the device being retrieved. 
           [0011]      FIGS. 5A ,  5 B,  5 C and  5 D show different styles of construction. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    The invention comprises of an elastic structure that it introduced into the left ventricle 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 to the ventricular wall. At this point the invention 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 and ventricular wall. 
         [0013]      FIG. 1  shows a typical deployment of the invention, via a catheter  1  inserted through the aorta into left ventricle  2  of 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 required by the invention 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 elastic device  4 . 
         [0014]      FIG. 2A  shows device  4  still inside catheter  1 . Device  4  is held by flexible cable  7  which is used to push device through catheter  1 , typically via a hemostatic seal outside the body (not shown). Typically a guide wire  11  is used to guide the catheter into the left ventricle. 
         [0015]      FIG. 2B  shows the device after deployment. Device  4  expands elastically to fill the ventricle. Ventricular contractions help embed barbs  8  into ventricular wall  6 . Over time, scar tissue  6 ′ forms a permanent bond between device  4  and wall  6 . The maximum opening of 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 rather than between adjacent arms (as shown by  10 ) as this allows the cross member to clear the papillary muscles, allowing the device to cover a larger part o the left ventricle. As seen in  FIG. 2B , the papillary muscles can fit between two elastic members of device  4 . 
         [0016]      FIG. 3  gives a more detailed view of the invention. Device  4  has two pairs of elastic arms  4 ′ and  4 ″. The arms are equipped with barbs  8  and cross members  9  and  10 . The arms 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 the apex of device  4  a connector  12 , such as a thread, is used for temporary attachment to flexible cable  7  via 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 and stop ventricular enlargement (after members  4 ′ and  4 ″ bonded to ventricle wall by scar tissue). 
         [0017]    The number of flexible members of device  4  and number of cross members can vary, the preferred embodiment having from 3 to 12 elastic members. Cross members can connect adjacent elastic members as members  10  do, or connect opposing members as members  9  do. The arrangement shown in  FIG. 3  is desired in order to allow members  4 ′ and  4 ″ to extend beyond the papillary muscles without cross members  9  touching muscles or mitral valve cords. Like any spring, the force members  4 ′ and  4 ″ exert on ventricle wall 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 k is selected not to interfere with systolic function while still helping diastolic filling. By the way of example, the total force the ventricular wall is capable of exerting on each one of the elastic members 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 of wire forming members  4 ′ and  4 ″ is determined by k. It is typically in the range of 0.5-1 mm. 
         [0018]    In order to place device  4  correctly relative to the papillary muscles the orientation of the device inside the left ventricle needs to be known. This can be done by fluoroscopy, ultrasound or by other location methods such as magnetizing 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). 
         [0019]    The design of device  4  allows aborting the deployment at any stage and retrieving the device. This is shown in  FIG. 4 . A flexible cable  7  terminating in a hook  16  is introduced. 
         [0020]    Cross members  9  are snagged by hook  16  and device is pulled back into catheter  1 . If retrieval is desirable the two cross members  9  should be permanently joined at the cross-over point  18 . This allows the hook to self-center regardless of the point it snagged cross members  9  and regardless whether it snagged one or both. Obviously the retrieval is much more difficult once scar tissue has developed. 
         [0021]      FIG. 5  offers a more detailed close-up view of the device construction.  FIG. 5A  shows elastic elements  4  made of spring wire, cross members  10  made of thin stainless steel cable and barb  8  made of steel wire spot welded to  4 . If needed, a load spreading structure  17  can be added. It can be made of bent wire, spot welded to  4  as shown, or as a polymeric strip. The complete device can be coated with an anti-coagulant coating, drug eluting coating or any beneficial coating well known from the art of stents. An alternate embodiment, cut out from a single sheet of elastic material and bent to shape is shown in  FIG. 5B . This mode of construction particularly advantageous when device is made of Nitinol, as Nitinol is difficult to join. As before, an optional load spreading structure  17  can be added. 
         [0022]      FIG. 5C  shows an embodiment not using discrete barbs but providing elastic members  4  with a special surface finish to promote rapid bonding with ventricular wall. 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, 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. 
         [0023]      FIG. 5D  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 layer  18  is hemostatic the invention can also seal an aneurysm or puncture in the ventricular wall, while still providing the other stated benefits. This is particularly desirable when the ventricular wall is already significantly thinned by enlargement. 
         [0024]    While the examples shown use a catheter to enter the left ventricle via the mitral valve, it is obvious that the invention is independent of the method of deployment. The device can be installed in the left ventricle also via the aortic valve, by piercing the apex of the left ventricle or by an incision at any convenient point. It can be used percutaneously or during conventional cardiac surgery.