Mitral Valve Device Using Conditioned Shape Memory Alloy

Abstract

A mitral valve annulus reshaping device includes at least a portion that is formed of a biocompatible shape memory alloy SMA having a characteristic temperature, A f , that is preferably below body temperature. The device is constrained in an unstable martensite (UM) state while being introduced through a catheter that passes through the venous system and into the coronary sinus of the heart. The reshaping device is deployed adjacent to the mitral valve annulus of the heart as it is forced from the catheter. When released from the constraint of the catheter, the SMA of the device at least partially converts from the UM state to an austenitic state and attempts to change to a programmed shape that exerts a force on the adjacent tissue and modifies the shape of the annulus. The strain of the SMA can be varied when the device is within the coronary sinus.

1 . A device adapted to be inserted into a coronary sinus within a body of a patient, for use in modifying an annulus of a mitral valve of the patient to treat a mitral valve pathology, comprising: (a) a structure having at least a portion thereof comprising a shape memory alloy, said shape memory alloy having a characteristic temperature, A f , selected to be no greater than a normal temperature of a body of a patient in which the device will be used, and having a programmed shape to which the shape memory alloy returns when substantially converted to an austenitic state; and (b) a restraint that mechanically maintains the shape memory alloy in a deformed state while the structure is being inserted info a coronary sinus of a patient, said restraint being controlled to enable the shape memory alloy to return to its austenitic state, causing the shape memory alloy to try to assume its programmed shape with a coronary sinus, said programmed shape being selected and said structure being disposed at a desired orientation within a coronary sinus by the restraint so as to apply a force against a mitral valve to modify an annulus of the mitral valve. 
     
     
         2 . The device of  claim 1 , wherein the shape memory alloy includes titanium and nickel. 
     
     
         3 . The device of  claim 1 , wherein the shape memory alloy is super-elastic, so that the shape memory alloy is adapted to produce a force directed against a mitral valve annulus from within a coronary sinus, as the shape memory alloy super-elastically changes from the deformed shape to the programmed shape. 
     
     
         4 . The device of  claim 3 , wherein the super-elastic properties of the shape memory alloy are directed outwardly when the shape memory alloy is allowed to change from the deformed shape to the programmed shape, to provide a force adapted to anchor the device at a desired position within a coronary sinus. 
     
     
         5 . The device of  claim 1 , wherein the shape memory alloy has a reduced curvature when in the deformed state, compared to that of the programmed state. 
     
     
         6 . The device of  claim 1 , wherein the shape memory alloy has a greater curvature when in the deformed state, compared to that of the programmed state. 
     
     
         7 . A device adapted to be inserted into a coronary sinus within a body of a patient, for use in modifying an annulus of a mitral valve of the patient to treat a mitral valve pathology, comprising: (a) a venous deliverable component having at least a portion that is formed of a shape memory alloy, said shape memory alloy being selected to have a characteristic temperature, A f , that is no greater than a normal body temperature of a patient with which the device is used, said shape memory alloy being further characterized by being capable of reversibly changing between a martensite state and an austenitic state within a body of a patient, while remaining at substantially a constant temperature, said changes between the martensite state and austenitic state corresponding to a change in shape of the shape memory alloy; and (b) at least a portion of the device comprising a selectively configurable force applying component to apply a force directed against an interior surface of a coronary sinus, causing a modification of an annulus of a mitral valve within a body of a patient. 
     
     
         8 . The device of  claim 7 , wherein the shape memory alloy comprises nickel and titanium. 
     
     
         9 . The device of  claim 7 , wherein the force applying component applies an outwardly directed force relative to a longitudinal axis of the device, said outwardly directed force being selectively produced as a result of a change in shape of the shape memory alloy and used to anchor the device at a desired position within a coronary sinus. 
     
     
         10 . The device of  claim 7 , wherein the shape memory alloy reversibly changes between the martensite state and the austenitic state as a function of a strain applied to the shape memory alloy. 
     
     
         11 . The device of  claim 10 , further comprising a constraint applied to the shape memory alloy to maintain the shape memory alloy in the martensite state, said constraint being selectively released to enable the shape memory alloy to change toward the austenitic state. 
     
     
         12 . The device of  claim 10 , wherein a change from the martensite state to the austenitic state by the shape memory alloy causes an increased curvature of the device. 
     
     
         13 . The device of  claim 10 , wherein a change from the martensite state to the austenitic state by the shape memory alloy causes a decreased curvature of the device. 
     
     
         14 . The device of  claim 10 , further comprising a spring formed of the shape memory alloy and an adjustment tether that is adapted to extend outside a body of a patient when the device is disposed within a coronary sinus, said adjustment tether being used to modify a tension applied to the spring, changing a strain experienced by the shape memory alloy comprising the spring, causing the shape memory alloy to reversibly change between the austenitic state and the martensite state. 
     
     
         15 . The device of  claim 14 , wherein the spring comprises an arched leaf spring. 
     
     
         16 . The device of  claim 14 , wherein the spring comprises a helical coil spring. 
     
     
         17 . The device of  claim 14 , wherein the adjustment tether adjusts a stiffness and length of the spring, adapting the spring to reshape a mitral valve annulus. 
     
     
         18 . The device of  claim 14 , wherein the adjustment tether elongates the spring as the shape memory alloy reversibly changes between martensite and austenite. 
     
     
         19 . The device of  claim 18 , wherein the spring comprises an arched leaf spring. 
     
     
         20 . The device of  claim 18 , wherein the spring comprises a helical coil spring.