US 20050113635 A1
This is a support device that prevents, reduces, and delays remodeling of diseased cardiac tissue, and also decreases the impact of such remodeling on collateral tissue is disclosed. The invention further reinforces abnormal tissue regions to prevent over-expansion of the tissue due to increased afterload and excessive wall tension. As a result, the support device prevents phenomenon such as systolic stretch from occurring and propagating. The support structure maintains and restores diastolic compliance, wall motion, and ejection fraction to preserve heart functionality. As such, the support device prevents and treats cardiomyopathy and congestive heart failure.
22. A method of transferring energy from viable heart tissue to less viable or non-viable heart tissue by utilizing a natural motion of a heart, comprising:
positioning a support structure over the viable and the less viable or non-viable heart tissue; and
attaching the support structure to the viable heart tissue and to the less viable or non-viable heart tissue such that the support structure exerts a force against the less viable or non-viable heart tissue in response to the motion of the heart.
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This application claims priority to provisional U.S. patent application Ser. No. 60/231,075, filed Sep. 8, 2000, the entirety of which is hereby incorporated by reference.
This invention is directed towards the transfer of energy from viable tissue regions to less viable or non-viable regions, thereby preventing, compensating for, or treating tissue responses to ischemia, infarction, or other abnormalities. In particular, this invention is directed towards the prevention, reduction, and delay of the remodeling of diseased cardiac tissue and the prevention and treatment of cardiomyopathy and congestive heart failure.
Ischemic injury causes tissue remodeling over time. This produces dyssynchronous, hypokinetic, dyskinetic or akinetic tissue function. One mechanism that perpetuates tissue remodeling (termed systolic stretch) occurs when viable ventricular tissue contracts, producing pressure that causes less viable or non-viable tissue to be forced outward. This bulging of the less viable or non-viable tissue dissipates the pumping force of the heart and adversely impacts cardiac output. The heart attempts to compensate for this decrease in cardiac output by increasing contractility and/or heart rate. However, the degree of systolic stretch progressively increases over time, continuing to reduce cardiac output, enlarge the volume of remodeled tissue, and exacerbate the potential for rupture of the affected tissue.
One condition that can result from such remodeling is cardiomyopathy, a typically chronic disorder of heart muscle that may involve hypertrophy and obstructive damage to the heart. A current approach for treating end-stage cardiomyopathy involves resecting a significant portion of the left ventricular free wall to reduce the size of the left ventricular cavity. The procedure, developed by Randas J. V. Batista, attempts to improve the relationship between volume, mass, and diameter. In reducing the volume of the left ventricle, investigators have observed a decrease in mitral regurgitation but a concomitant decrease in diastolic compliance. This decreases diastolic filling, which adversely impacts the complete cardiac cycle.
Other approaches for treating cardiomyopathy include reshaping the heart chambers using tethers, balloons, external bands, or other tension structures to reduce the end-diastolic diameters of the ventricles. PCT Pamphlets WO 98/29041 entitled “Heart Wall Tension Reduction Apparatus and Method”; WO 99/30647 entitled “Valve to Myocardium Tension Members Device and Method”; WO 00/06026 entitled “Heart Wall Tension Reduction Apparatus and Method”; WO 00/06027 entitled “Stress Reduction Apparatus and Method”; WO 00/06028 entitled “Transventricular Implant Tools and Devices”; WO 00/16700 entitled “External Stress Reduction Device and Method” describe tethers or bands that change the geometry of the heart and restrict the maximum outer diameters of the ventricles. The tethers are positioned inside the heart and extend from one side of the ventricle to the other to exert tension on opposite sides of the heart. The bands are positioned around the epicardial surface of the ventricles and restrict expansion of the ventricles. The tethers and bands only limit local wall tension and maximal end-diastolic diameter; they do not directly assist in systolic ejection or diastolic filling of the heart. Nor do they distribute loading over a large region of heart tissue.
The present invention addresses deficiencies associated with prior approaches of purely reducing the end-diastolic diameter of the heart or preventing over-stressing of cardiac tissue. The approach described by this invention uses a heart support structure to transfer energy, in the form of contraction and expansion, from viable heart tissue to less viable or non-viable heart tissue. This structure prevents, compensates for, or treats tissue responses to ischemia, infarction, or other abnormalities.
The embodiments of the invention maintain diastolic compliance of the cardiac tissue and synchronize the expansion and contraction of the diseased tissue to that of viable tissue in order to restore systolic ejection and diastolic filling. This improves wall motion and better restores normal functionality of the heart. As a result, the embodiments of the invention prevent, reduce, and/or delay remodeling of the diseased tissue, decrease the impact of such remodeling on collateral tissue, and preserve all phases of the cardiac cycle.
The embodiments of the invention are also useful in reinforcing abnormal tissue regions to prevent over-expansion of the tissue due to increased afterload and excessive wall tension. As a result, the dyssynchrony, hypokinesis, dyskinesis or akinesis, which occurs when tissue remodels over time, is inhibited. As such, the embodiments of the invention prevent progressive cardiomyopathy and congestive heart failure.
This invention provides electromagnetic assist devices that take advantage of the characteristics of the heart support structure of the invention to impart contraction and expansion throughout the heart, or along a specific region of the ventricles. The electromagnetic assist device strategically induces magnetic fields throughout individual electromagnets coupled to the support structure, which causes an attraction or repulsion of the electromagnets and imparts a contraction or expansion of the heart support structure, and transfers such energy to cardiac tissue.
The present invention also provides enhancements to the overall system to continue to make positioning and securing the heart support structure amenable to less invasive procedures, such an endoscopic, port access approaches. In addition, the present invention enables catheterization approaches to position and secure the heart support structure.
Further features and advantages of the inventions will be elaborated in the detailed description and accompanying drawings.
The embodiments of the invention are intended to transmit energy from viable tissue regions to less viable or non-viable regions thereby preventing, compensating for, or treating tissue responses to ischemia, infarction, or other abnormalities. Ischemic injury causes tissue remodeling over time and produces dyssynchronous, hypokinetic, dyskinetic or akinetic tissue function. The embodiments of the invention prevent, reduce, and/or delay remodeling of diseased cardiac tissue, and also decrease the impact of such remodeling on collateral tissue. The embodiments of the invention are also useful in reinforcing abnormal tissue regions to prevent over-expansion of the tissue due to increased afterload and excessive wall tension. The embodiments of the invention maintain and/or restore diastolic compliance, wall motion, and ejection fraction to preserve heart functionality. As such, the embodiments of the invention prevent progression of cardiomyopathy and congestive heart failure.
The approach described by this invention, which uses a heart support structure to transfer energy (in the form of artificial contraction and expansion) from viable heart tissue to less viable or non-viable heart tissue, addresses the deficiencies of prior approaches, which purely reduce the end-diastolic diameter of the heart. This invention aids the heart during systolic ejection and diastolic filling to better restore normal functionality of the heart. The heart support structure controls the motion of the heart and synchronizes the contraction and expansion of diseased tissue to that of viable tissue.
The heart support structure also accounts for the natural motion of the heart. As the heart contracts, the cross-sectional diameters of the ventricles decrease and the distance from the mitral valve annulus to the apex of the heart also decreases; as the heart expands, the cross-sectional diameters of the ventricles increase and the distance from the mitral valve annulus to the apex of the heart also increases. The optimal ratios of expansion (and contraction) between the cross-sectional diameters of the ventricles and the distance from the mitral valve annulus to the apex of the heart may be incorporated in the support structure to further preserve heart functionality. The heart support structure therefore preserves the wall motion and prevents remodeling of the diseased tissue by inhibiting over-expansion and maintaining normal actuation of all phases of the cardiac cycle. As a result, the dyssynchrony, hypokinesis, dyskinesis or akinesis, which occurs when tissue remodels over time, is inhibited.
Heart Support Structures
The heart support structure embodiments consist of one or more components designed to exert force against a diseased (e.g., ischemic or infarcted) region of tissue in response to the contraction or expansion of viable tissue. As such, the support structure transfers energy from viable tissue to less viable or non-viable tissue to control and force movement of injured tissue and prevent remodeling that occurs as a response to ischemic injury.
The heart support structures are preferably fabricated from superelastic (pseudoelastic) shape memory alloys, such as nickel titanium. Superelastic materials elastically deform upon exposure to an external force and return towards their preformed shape upon reduction or removal of the external force. Superelastic shape memory alloys are capable of exhibiting stress-induced martensitic behavior; which means they transform from the preshaped austenitic phase to the softer and more ductile martensite phase upon application of stress and transform back toward the stronger and harder austenite phase once the stress is removed. Superelastic shape memory alloys enable straining the material numerous times without plastically deforming the material. Superelastic shape memory alloys are also light in weight, biocompatible, and exhibit excellent tensile strengths such that they may be attached to the heart without substantially adding weight or bulk.
The characteristics of superelastic shape memory alloys described above highlight their utility in providing a support structure for the heart because they withstand continuous and frequent deflections without plastically deforming or observing fatigue failures. Superelastic support structures may also be elastically deflected into small radii of curvature and return towards their preformed configuration once the external force causing the deflection is removed. Although other, more conventional materials such as stainless steel may be used in this application, their geometry is likely to be less fine or compact because their material properties dictate that the total elastic energy stored in a given device is much lower. Other known metal, alloy, and thermoplastic materials plastically deform when deflected into similar radii of curvature, using comparable strains, and are unable to return towards their original configuration. As such, superelastic support structures permit deflections into smaller radii of curvature than other metals, alloys, and polymers resulting in the ability to withstand larger strains without failing; they are also capable of exerting substantial force when deflected.
We prefer that support structures fabricated from shape memory alloys (e.g., nickel titanium) be engineered to form stress-induced martensite (SIM) at body temperature. The composition of the shape memory alloy is preferably chosen to produce martensitic transformation temperatures (Ms and Mf) and austenitic transformation temperatures (As and Af) such that the alloy exhibits stress induced martensite up to a temperature Md, greater than Af
The relative composition of nickel and titanium determines the Af of the shape memory allow. For example, nickel titanium having an atomic ratio of 51.2% Ni and 48.8% Ti exhibits an Af of approximately −20 C; nickel titanium having an atomic ratio of 50% Ni to 50% Ti exhibits an Af of approximately 100 C (Melzer A, Pelton A. “Superelastic Shape-Memory Technology of Nitinol in Medicine” Min Invas Ther & Allied Technol. 2000: 9(2) 59-60).
Preferably the composition and fabrication of the nickel titanium is chosen such that the Af is below 32 C. Such materials are able to withstand strains as high as 10% without plastically deforming. As such, these superelastic materials are capable of elastically exerting force upon deflection.
Superelastic shape memory alloys that do not exhibit stress-induced martensitic behavior at body temperature but enable elastic deformation through the range of motion the material is exposed may alternatively be used. Materials other than superelastic shape memory alloys may be used for the support structures provided they can be elastically deformed within the temperature, stress, and strain parameters required to maximize the elastic restoring force. Such materials include other shape memory alloys, spring stainless steel 17-7, ELGILOY (Elgiloy LP, Elgin, Ill.), superelastic polymers, etc.
Throughout this description, discussions of external force preferably refer to the contraction and/or expansion of viable tissue causing the support structure to respond accordingly unless otherwise specified. Alternatively, another external means, artificial, biological, or a combination of artificial and biocompatible means for compressing and/or expanding the support structure may be used as will be discussed later.
Other materials may be used as a covering to the support structure, including thermoplastics (e.g., polytetrafluoroethylene or PTFE), thermoset plastics (e.g., polyethylene terephthalate, polyester), or silicone. For example, heart support structures fabricated from nickel titanium may be covered with expanded PTFE by sintering layers of expanded PTFE positioned to encompass the support structure material. Alternatively, the support structures may be coated with silicone, which when allowed to cure produces a covering over the support structure.
The heart support structure may be coated with materials such as parylene or other hydrophilic substrates that are biologically inert and reduce the surface friction. To further reduce the surface friction, metallic or metallic alloy fittings may be electropolished. Evidence suggests that electropolishing reduces adhesion because of the smooth surface and low surface tension. Alternatively, the heart support structures may be coated with heparin, thromboresistance substances (e.g., glycoprotein IIb/IIIa inhibitors), antiproliferative substances (e.g., Rapamycin), or other coatings designed to prevent adhesion, thrombosis for blood contacting support structures, hyperplasia, or other tissue response that may adversely impact the functionality of the heart support structure. Alternatively, materials such as platinum, gold, tantalum, tin, tin-indium, zirconium, zirconium alloy, zirconium oxide, zirconium nitrate, phosphatidyl-choline, pyrolytic carbon, or others may be deposited onto the heart support structure surface using electroplating, sputtering vacuum evaporation, ion assisted beam deposition, vapor deposition, silver doping, boronation techniques, a salt bath, or other coating process.
A still further improvement of the heart support structure that is within the scope of the present invention is to include beta or gamma radiation sources on the heart support structure. A beta or gamma source isotope having an average half-life of approximately 15 days such as Phosphorous 32 or Palladium 103 may be placed on the heart support structure using an ion-implantation process, chemical adhesion process, or other suitable method.
The heart support structure embodiments may be fabricated from a sheet of material cut into the desired pattern and formed (e.g., through a heat treatment process) into the desired geometry (planar, conical, elliptical, cylindrical, or other shape). To produce these heart support structures, the raw material may be fabricated into the desired pattern by chemical etching, electron discharge machining (EDM), laser cutting, or other manufacturing process. Heart support structures fabricated from sheet stock are then wrapped or otherwise placed around mandrels having the desired resting three-dimensional profile(s) and the heart support structure is heated until it assumes this configuration. After heating, the support structure is quenched or otherwise allowed to return to room temperature, at which the support structure maintains the preformed shape. If any sides are to be bonded, spot welding, laser welding, or other manufacturing process may be employed.
Alternatively, heart support structure embodiments of the present invention may be fabricated from a tube of material having a desired cross-sectional geometry. The desired pattern of links, anchors, anchor pins, holes, slots, and/or cells may be fabricated on the tubular metal material and may be created using chemical etching, EDM, laser cutting, or other manufacturing process. These heart support structures may be thermally formed into the desired planar or three-dimensional profile depending on the desired shape of the heart support structure.
The support structure embodiment in
Each support link 30 extends from at least one peripheral link 26 located past one end of the injured tissue 24, and attached to viable tissue, to at least one peripheral link 26 located past the opposite end of the injured tissue 24, and attached to viable tissue. An alternative configuration involves individual support links that terminate at the central region 28 and are not attached to the other independent support links throughout the central region 28 or using peripheral links.
Peripheral links 26 and support links 30 in the embodiment of
It should be noted that middle section 32 may be located along central region 28, anywhere between central region 28 and peripheral links 26, and/or along the proximal end of the support structure defined by peripheral links 26. Different middle sections 32 may be positioned at different locations along the tissue surface, depending on the axial stiffness and flexibility requirements of support links 30.
The parameters of each support link 30 (width, wall thickness, total length, and turn length) also influence the stiffness. The stiffness profile of the support structure determines the degree of contraction and expansion transferred from viable tissue to injured tissue 24 throughout the support structure 20. This profile may be optimized depending on the anticipated position of various support links 30 relative to anatomic structures and desired responses.
For example, the apex of the heart contracts and expands at a different degree than the left ventricular free wall; the right ventricle (RV) is much more compliant than the left ventricle. As such, support structure 20 must incorporate such profiles to maximize the restoration of systolic ejection and diastolic filling. More than one target zone of injured tissue may be addressed with a single support structure or multiple support structures by tailoring the stiffness profile(s) of the support structure(s) to ensure the desired contraction and expansion force is transferred and distributed throughout the surface of the targeted tissue surface.
For example, support links 30 positioned along the right ventricle 4 require substantially less stiffness than those positioned along the left ventricle 2 to impart the same amount of contraction and expansion in the right and left ventricle respectively. In addition, the amount of contraction and expansion for the right ventricle differs from that for the left ventricle, thus the stiffness profile of apically positioned support structures must account for the disparity.
As previously stated, individual support links 30 may incorporate different stiffness characteristics to tailor the stiffness profile of the support structure to the physiologic requirements. The proximal ends of the support links 30 are attached to the peripheral links 26 such that the intersection forms anchors 52 or defines an attachment point. Peripheral links 26 are configured significantly more flexible than support links 30 since peripheral links 26 maintain the integrity of support structure 20 but do not transfer energy throughout tissue encompassed by the support structure.
The central zones of the various support structure embodiments discussed above may be integral to support links 30 or alternatively may be comprised of one or more separate components that are attached to the support links. This separate component(s) may be fabricated from the same material as the support links or a different material. For instance, compliant materials such as silicone, urethane, or other biological materials having high percent elongation characteristics may be used.
The characteristics of this support structure are substantially different than the flattened profile of any prior stent or stent-graft. Conventional stents or stent-grafts contract or minimally change in length as the diameter is expanded. Stents or stent-grafts fabricated with the support structure geometry shown in
The support structure embodiment shown in
The support structure embodiment of
Other combinations of cell widths W1 and lengths L1 may be used to tailor the stiffness and degree of ratio of expansion between the width and length for the support structure to the geometry of the heart and the amount of expansion and contraction desired throughout the support structure.
For example, to tailor this support structure embodiment so it may be positioned apically, length A1 of the support structure may be tapered along width B1 such that the length of each cell L1 decreases at specified intervals and/or the length of each horizontal link 38 decreases. Such modifications potentially impact the stiffness profile of the support structure; therefore, cell width T1, horizontal link width T2, vertical link width T3, and/or wall thickness of each cell and link may be decreased as the cells are tapered so as to compensate for the increase in stiffness associated with decreasing the cell dimensions.
Cell width T1, horizontal link width T2, vertical link width T3, and/or wall thickness of each cell and link may alternatively be varied to predefine the stiffness profile of the support structure, accommodate nonlinear expansion or contraction requirements throughout the ventricles, or address anatomic variances that warrant changes in support structure geometry or stiffness.
Positioning and securing support structure 20 to the surface of the heart chamber is preferably performed with the heart at end-diastole and with the support structure in the enlarged orientation (either by preshaping or manually stressing). In certain scenarios, the support structure may be configured to exert some contractile force throughout the cardiac cycle, even during end-diastole. To accomplish this, the support structure is positioned and secured to the tissue surface during end-diastole with the support structure stressed into its expanded orientation. Securing the support structure to the heart during end-diastole ensures better seating against the ventricle and the observed spacing between attachment points 22 ensures optimal transfer of contraction and expansion energy from the support link attachment points to the injured tissue 24.
It should be noted that the steps of positioning and securing support structure 20 to the tissue surface may alternatively be performed at end-systole with support structure 20 in the contracted orientation, or at any phase in the cardiac cycle. It should also be noted that the positioning and design of the support structure may bias the structure such that a continuous contractile force exerted by the elasticity of the support structure is applied even during end-diastole, a continuous expansion force is applied even during end-systole, or a contractile force is applied during relaxation and diastolic filling and an expansion force is applied during contraction and systolic ejection.
The embodiments described above show the support structure attached to the epicardial surface of the ventricles. Alternatively, as shown in
The LV support structure 86 is preferably preshaped to match the end-diastolic geometry and optimal size of the left ventricular cavity. Peripheral links 26 and support links 30 of LV support structure 86 do not interfere with the operation of mitral valve 48, the papillary muscles, or the chordae tendonae. Support links 30 may be fabricated with spaces where the papillary muscles extend into the left ventricular cavity and where the chordae tendonae extend from the papillary muscles and connect to mitral valve 48. Support links 30 are distributed throughout the endocardial surface of the left ventricle extending from the interventricular septum 46 completely around the left ventricular free wall. As such, injured tissue regions extending into or located along the interventricular septum may be covered by support structure 86. Alternatively, the left ventricular support structure 86 may be designed to cover only the interventricular septum, the left ventricular free wall, or other endocardial tissue region.
The RV support structure 88 is preferably preshaped to match the end-diastolic geometry and optimal size of the right ventricular cavity. Peripheral links 26 and support links 30 of RV support structure 88 do not interfere with the operation of the tricuspid valve 50, the papillary muscles, or the chordae tendonae. Support links 30 may be fabricated with spaces where the papillary muscles extend into the right ventricular cavity and where the chordae tendonae extend from the papillary muscles and connect to the tricuspid valve 50. Support links 30 are distributed throughout the endocardial surface of the right ventricle extending from the interventricular septum 46 completely around the right ventricular free wall. As such, injured tissue regions extending into or located along the interventricular septum may be covered by the support structure 86. Alternatively, the right ventricular support structure 86 may be designed to cover only the interventricular septum, the right ventricular free wall, or other endocardial tissue region. For injured tissue isolated within the interventricular septum, the right ventricle is the preferred location to position and secure a support structure against the endocardial surface in which the support structure is designed to solely cause expansion and contraction of injured tissue along the interventricular septum;
Support structures located along the endocardial surface of the right and/or left ventricle may be combined with support structures located along the epicardial surface to enhance the transfer of energy from viable tissue to less viable or non-viable tissue, especially when several injured tissue regions are dispersed throughout the heart. The support structures may be independent such that the endocardial support structures are not attached to the epicardial support structures. Alternatively, individual support links of the endocardial support structures may be inserted through the myocardium and may be connected to epicardial support structures so as to interconnect the expansion and contraction of the endocardial support structures to the epicardial support structures. This is especially relevant when the injured tissue extends from the interventricular septum to the left ventricular free wall and the desired position of the support structure extends from the right ventricular endocardial surface of the interventricular septum through the myocardium of the right ventricle and along the epicardial surface of the left ventricle. Other combinations of endocardially and epicardially positioned support structures may be used to address other indications or injured tissue locations.
The various support structure embodiments described above exhibit isotropic, orthotropic, or anisotropic structural properties. It should be noted that the embodiments of the invention may be modified to exhibit different structural properties (isotropic, orthotropic, or anisotropic) to match the inherent structural properties of the tissue surface to which the support structure encompasses, or to tailor the support structure to specific tissue surface locations. They may also be configured to modify the structural properties of the tissue surface to reduce wall tension,. improve contractility, or otherwise change the functionality of the heart. It should also be noted that the structural properties of the support structures described above may be modified to address other applications as are known to those of skill in the art.
Support Structure Anchoring
The heart support structures described above typically are secured to the epicardial surface and/or endocardial surface at attachment points 22. A variety of bonding methodologies may be employed including adhesives (fibrinogen, etc.), coagulating the surface to the support structure by heating the tissue, or mechanically anchoring the support structure to the tissue surface, a technique that is discussed below. The support structures may incorporate anchors that penetrate into tissue, holes to pass suture, flaps that become entangled in the trabecula of the ventricles for endocardial support structures, or other mechanical securing mechanism with which to attach the heart support structure to the tissue surface. The heart support structure is alternatively secured to the tissue surface using commercially available implantable clips, staples, or other means.
Alternatively, the anchor may be inserted past the first heart surface (epicardium 60 or endocardium 58), through the myocardium 56, and past the second heart surface (endocardium 58 or epicardium 60) such that the anchor pins are constrained by the second heart surface. As shown in
During deployment, anchor pins 54 may be constrained with a delivery tube or may be allowed to deflect into a reduced diameter as the anchor is inserted through the tissue surface (and tissue interface 18, if any). The outward bias of anchor pins 54 causes them to extend radially once positioned within the myocardium and prevent pulling the anchor away from the tissue surface. The anchor shown in
The anchor pin of these embodiments may be configured with alternative geometries to facilitate deployment and/or attachment of the support structure to the tissue surface. For example, a single anchor pin may extend from the anchor as a hook which is capable of being inserted through the tissue surface by angling the anchor pin such that the distal tip penetrates through the tissue surface and advancing the rest of the anchor.
The anchors described previously may also be connected to an electrosurgical generator capable of transmitting radio frequency (RF) energy to tissue contacting the anchors. As such, tissue adjacent the anchors resistively heats in response to exposure to the RF energy, causing the tissue to coagulate to the anchors and enhance the bond between the anchors (and thus the support structure) and the tissue surface.
As shown in
As shown in
Alternatively, tissue interface 18 may be a spacer 90 incorporated in support structure 20 at attachment point 22 to maintain separation between the epicardium 60 or endocardium 58 and the links of support structure 20, as shown in
The support structure does not move relative to the tissue surface 60 or 58 at the anchors and/or attachment points; therefore, the support structure may directly contact the tissue surface at those locations, realizing that the support structure will endothelialize or epithelialize at the locations where the support structure is in intimate tissue contact. For support structures that completely reflect motion of the heart throughout the surface of the support structures, the entire support structure may be placed into intimate contact with the tissue surface 60 or 58 and allowed to epithelialize or endothelialize and become integral with the heart.
The harvested biological material is preferably a section of the pericardium, which may be cut away, sized relative to the heart support structure, and positioned between the support structure and the epicardium. Other tissue such as submucosal tissue (e.g., that obtained from the small intestine or other body organ) may be harvested, formed into the desired geometry, and used as the heart interface. The use of submucosal tissue is described in WO 98/19719 by Geddes, et al, entitled “Myocardial Graft Constructs”, the entirety of which is incorporated herein by reference. Other biological materials such as collagen may alternatively be formed into the desired geometry and used as the heart interface.
The primary advantage of using biological tissue interface materials over currently available synthetic materials is the reduction in adhesions, thrombosis for tissue interfaces that are exposed to blood flow, or other tissue response that may adversely impact the function of the heart support structure. However, the heart support structure embodiments of the invention are equally effective at utilizing all types of tissue interface materials, biological and synthetic.
Synthetic tissue interface materials may be manufactured by extruding, injection molding, weaving, braiding, or dipping polymers such as PTFE, expanded PTFE, urethane, polyamide, polyimide, nylon, silicone, polyethylene, polyester, PET, composites of these representative materials, or other suitable graft material. These materials may be fabricated into a sheet, tubing, or other three-dimensional geometry using one or a combination of the stated manufacturing processes. Tubing materials may be along at least one side to form a flattened profile. The synthetic bypass graft may be coated, deposited, or impregnated with materials, such as parylene, heparin solutions, hydrophilic solutions, thromboresistance substances (e.g., glycoprotein IIb/IIIa inhibitors), antiproliferative substances (e.g., Rapamycin), or other substances designed to reduce adhesions, thrombosis (for heart interfaces exposed to blood flow), or mitigate other risks that potentially decrease the functionality of the heart support structure. In addition, synthetic bypass grafts may be seeded with endothelial cells or other biocompatible materials that further make the inner surface of the bypass graft biologically inert.
Surgical positioning and securing of the heart support structures described above to the epicardial tissue surface 60 involves a relatively large incision through the thoracic cavity to expose the heart. Surgical intervention enables accurate positioning and assures optimal securing of the support structure relative. During open heart surgery, direct access to the epicardial surface of the heart enables suturing or adhesively bonding the support structure to the heart; as such, alternative anchoring mechanisms described above are not necessarily requited. However, such anchoring mechanisms may provide benefit in reducing the time to attach the support structure to the surface of the heart or improve the expanded (or contracted) orientation of the support structure relative to the end-diastolic (or end-systolic) orientation of the heart.
The support structure embodiments discussed in this invention are directly amenable to less invasive (i.e. minimally invasive) surgery involving a thoracostomy or mini median sternotomy to access the heart and endoscopes to visualize the thoracic cavity.
The deployment system for such reduced access surgical applications leverages conventional port access techniques to produce an opening through the thoracic cavity. Trocars are commonly used to gain access into the thoracic cavity after puncturing through the intercostal space. Once the ports into the thoracic cavity are defined, the parietal pericardium is cut and the incision is extended to expose the epicardial surface of the heart. As previously stated, the pericardium may be used as the tissue interface between the support structure and the epicardial surface of the heart.
The support structure is compressed into a reduced diameter by rolling for relatively planar support structures, or folding, stretching, or otherwise bending for more three-dimensional support structures. The compressed support structure is positioned in a delivery sheath designed to feed the support structure past the port. Once inside the thoracic cavity, the support structure is expelled from the delivery sheath, at which point it expands towards its preformed resting shape.
At this point, the support structure is lined up relative to the desired epicardial location and individual anchors are positioned through the tissue surface to secure the support structure to the tissue surface at each attachment point. As previously stated, alternative securing modalities may be used including adhesives, suture, thermal coagulation, implantable clips, staples, or other mechanism.
Conventional forceps, hemostats, and clamps are used to position the anchors. Alternatively, delivery tubes may compress the anchor pins into a reduced diameter for insertion through the tissue surface. In such a case, the delivery tubes are beveled at their distal ends to penetrate through the tissue surface and to provide a conduit to insert the anchor and position the anchor pin or pins into the myocardium.
When positioning the individual anchors at each attachment point, the support structure is continuously lined relative to the epicardial surface and at end-diastole and the anchors are inserted through the tissue surface. This ensures the support structure is positioned in its expanded orientation against the ventricles in their expanded orientation producing a better match between the expansion and contraction properties of the support structure to that of the ventricles. When lining the anchors of the support structure, the support links may need to be stressed or preformed into their expanded orientation to ensure the support links are appropriately lined up relative to the end-diastolic heart. As previously stated, the support structure may alternatively be attached to the heart during end-systole; at which case, the support structure is stressed or preformed into its contracted orientation during the attachment process. Alternatively, the heart may be temporarily stopped while securing sections of the support structure to the epicardial surface.
When positioning the support structures against the endocardial surface, catheters are used to compress the support structure into a reduced diameter. The catheters may be inserted percutaneously into the venous or arterial vasculature and routed to the desired heart chamber. To access the left ventricle, a catheter is routed through the femoral or brachial artery, around the aorta, past the aortic valve and into the left ventricle. Alternatively, the catheter is passed through the femoral or subclavian vein, into the right atrium, past the interatrial septum (by use of a transseptal technique), into the left atrium, past the mitral valve annulus, and into the left ventricle. To access the right ventricle, the catheter is passed through the femoral or subclavian vein, into the right atrium, past the tricuspid valve, and into the right ventricle.
Once in the desired heart chamber, the catheter is positioned at the apex of the ventricle. The support structure is compressed within the catheter by folding, stretching, or otherwise bending the support structure prior to inserting the catheter to the desired heart chamber. The support structure forms a three-dimensional geometry that closely matches the endocardial surface (either at end-diastole or end-systole). The anchors of the support structure may contain flaps intended to become entangled in the trabecula of the ventricles or anchor pins capable of becoming constrained in the myocardium once the anchor has penetrated through the endocardial surface. A plunger, in the form of a second steerable catheter, may be used to urge the anchors into position. Alternatively, the delivery catheter may be used as the plunger.
If any are used, the sheath and dilators of the deployment systems may be constructed from polyethylene, polycarbonate, thermoplastic (such as PEEK, manufactured by Victrex PLC, United Kingdom), other polymer, metal, or metal alloy that may be extruded, injection molded, or swaged into a tube having the desired cross-sectional profile. A taper and radius may be formed in the components of the deployment system by thermally forming the tubing into the desired shape or incorporating such features in the injection molding cast. In addition, the components of the deployment system may incorporate a softer distal tip fabricated by thermally bonding a short section of lower durometer tubing to the sheath or tapering the thickness of the sheath tubing.
To prevent the backflow of blood through deployment sheaths, hemostatic valves may be used. The hemostatic valves prevent blood leakage but permit insertion of the support structure through the sheath.
It is within the scope of this invention to provide electromagnetic assist devices that take advantage of the characteristics of the heart support structure of the invention to impart contraction throughout the heart or along a specific region of the ventricles. These devices strategically induce magnetic fields throughout the heart support structure to impart an expansion or contraction of the heart support structure, which then transfers energy to the heart chambers.
The electromagnetic assist device may function independent from the natural contraction of the heart chambers to completely control the timing of isovolumetric ventricular contraction, systolic ejection, isovolumetric relaxation, and diastolic filling. Alternatively, the electromagnetic assist device may be synchronized to the inherent electrical propagation of the heart, which passes from the SA Node through the atria along the AV Node and through the ventricles. In doing so, the electromagnetic assist device times each phase of the cardiac cycle, as artificially created using the heart support structure, relative to the inherent electrical propagation of adjacent cardiac tissue, thereby preserving the natural motion of the heart and responding to biological stimuli for changing heart rate.
U.S. Pat. No. 6,099,460 to Denker, incorporated herein by reference in its entirety, a heart that is artificially forced to contract in response to magnetic fields induced by electromagnets positioned on the exterior surface of the heart and/or interior of the heart. The '460 patent does not incorporate a support structure to provide optimal contraction and expansion, but relies solely on the attraction of the electromagnets positioned on opposite sides of the heart chambers. In addition the injured or diseased tissue contracts differently than viable tissue thus continuing to propagate the tissue remodeling of the injured or diseased tissue. In addition, the '460 patent does not teach assisting in the diastolic filling of the heart, and therefore excludes one important phase in the cardiac cycle.
Electromagnetic cores 74 are positioned over horizontal links 38 of support structure 20, as shown by an enlarged view of the support structure in
Simultaneously, polarity switching unit 70 changes the OUTB connection from the IN− to the IN+ and vice versa. In switching the positive and negative connections of an electromagnetic coil 72, the induced magnetic field along the electromagnetic coil alters its polarity accordingly. As such, the response of adjacent coils to the specific polarity protocol may be specified to selectively produce an attraction between adjacent electromagnets, thereby causing a contraction of the heart support structure, or to induce a repulsion between adjacent electromagnets thereby causing an expansion of the heart support structure. The ability to switch the polarity of at least one set of electromagnetic coils 72 enables producing both an attraction and a repulsion thereby covering the complete cardiac cycle. The embodiment shown in
The period and amplitude of each pulse transmitted from the electromagnetic source (directly or via the polarity switching unit) to the electromagnetic coils determines the amount and duration of the attraction or repulsion force imparted to heart support structure 20 by the electromagnetic assist device. Support structure 20 is essential to the electromagnetic assist device in that it provides enhanced control to and enables variability in the expansion and contraction throughout the surface of the heart. Changing the stiffness profile of the support structure 20 throughout the surface of the heart is more sensitive and effective than varying the degree of attraction and repulsion between adjacent magnets.
As shown in
Other Artificial Assists
The heart support structure embodiment shown in
One such artificial external force involves attaching a length of skeletal tissue to a section of the support structure and causing the skeletal tissue to contract and relax in response to pacing stimuli. This linear contraction and expansion is transferred throughout the entire support structure to impart the desired three-dimensional contraction and expansion responses.
Another artificial external force involves any type of motor capable of exerting a linear force in response to an electrical current. The motor should be capable of miniaturization to fit inside an implantable device and operate under battery power such that the battery life lasts for years.
This invention has been described and specific examples of the invention have been portrayed. The use of those specific examples is not intended to limit the invention in any way. Additionally, to the extent that there are variations of the invention which are within the spirit of the disclosure and yet are equivalent to the inventions found in the claims, it is our intent that those claims cover those variations as well.