Patent Grant
7850729
This invention relates generally to assisting the natural heart in operation and, more specifically, to components to assist in actuating one or more walls of the natural heart.
The human circulatory system is critical for survival and systematically provides nutrients and oxygen as well as removing harmful waste products from all parts of the body. The heart is a critical component of the circulatory system in that it provides pumping power. Generally the right side of the heart receives blood from the ‘systemic circulation’ (all the body except the lungs) and pumps it into the ‘pulmonary circulation’ (lungs), whereas the left side of the heart receives blood from the lungs and pumps it back into the systemic circulation. Each side comprises an inflow or collecting chamber with a thin muscular wall, its ‘atrium’ and a thicker, more powerful muscular pumping chamber, its ‘ventricle’, which alters volume cyclically due to contraction and relaxation of the muscles in its walls. One-way valves are positioned in the passage way between the left and right atrium and the corresponding ventricle, and between each ventricle and the large arteries, which conduct blood into the systemic or pulmonary circulation, respectively. Because of this arrangement, each atrium may gently contract, causing blood to flow across the ‘atrioventricular’ valve into the ventricle, with that valve then closing to prevent return. Similarly, each ventricle may then forcefully contract, causing blood to flow across the outflow valves into the systemic or pulmonary circulation. A physical ailment or condition which compromises the effective muscular contraction in the walls of one or more chambers of the heart can therefore be particularly critical and may result in a condition which must be medically remedied if the person is to long survive.
More specifically, the muscle of the heart may degrade for various reasons to a point where the heart can no longer provide sufficient circulation of blood to maintain the health of a person at an acceptable level. In fact, the heart may degrade to the point of failure and not been be able to sustain life. To address the problem of a failing natural heart, solutions are offered to maintain the circulation. Some of these solutions involve replacing the heart. Some involve assisting it with mechanical devices. Some are directed to maintain operation of the existing heart.
The heart may be removed and replaced with either a mechanical device (a total artificial heart) or a natural heart from another human or an animal (heart transplant). Artificial heart use has been complicated by consequences of blood clots forming on the internal lining. The most serious consequence is a breaking loose of such clots, which are then propelled into various parts of the circulation. In the event of such a clot being propelled into the brain, a disabling or fatal stroke may result. While human heart transplantation is limited by rejection, a response of the body's immune system, this may usually be controlled by medications to the degree that half of all recipients survive at least ten years, generally with acceptable health and function. However a more serious limitation is numbers of available donors. These are usually accidental death victims whose hearts maintain function despite brain death. Currently these are available for less than 1 to 2 percent of potential beneficiaries (about 2000 per year in the United States for over 200,000 people dying of heart failure annually in the same country, for example).
The heart may be assisted by mechanical auxiliary pumps. These are of three general types: counterpulsators, pulsatile assist systems, and nonpulsatile assist systems. Counterpulsators such as intraaortic balloon pump cyclically remove or displace blood from the arterial system in synchrony with the natural heart's beat and, without valves, may perform substantial work for a weakened heart. Pulsatile assist systems (ventricular assist devices) are similar to artificial hearts except that they are used in addition to one or both sides of the heart rather than instead of the heart. They receive blood from either the atrium or ventricle on one side of the circulation and pump it into that side's arterial system, relieving the ventricle of part of its volume load, pressure load, or both. They consist of a blood chamber with at least partial wall flexibility, inflow and outflow valves, and some means, usually pneumatic, hydraulic, or electric, by which the wall may be moved and volume altered to pump blood. Nonpulsatile assist systems are rotary pumps, either centrifugal, axial flow, or a combination, that similarly pump blood in a steady flow from atrium or ventricle into circulatory systems. All of these mechanical pumps have extensive non-living material surfaces that contact blood. The complications of blood clotting with stroke or other serious aftermaths described with artificial hearts also occur with these mechanical auxiliary pumps.
Because of the severe shortage of human donor hearts for transplant, unsolved immunologic problems of animal donor hearts for transplants and prevalence of serious complications of artificial blood-contacting surfaces of both artificial hearts and auxiliary pumps, means of aiding the actuation of the natural heart walls have been attempted. Both skeletal muscle wraps (‘cardiomyoplasty’) and mechanical compression devices (‘mechanical ventricular actuation’) have been used. In either approach, the external wall surfaces of the heart are compressed and the heart volume altered, thereby pumping blood out of the chambers. Muscle wraps are limited by available space relative to muscle mass required for power, as well as by intrinsic stiffness that compromises re-filling between beats. Both muscle wraps and mechanical compression devices are limited by inability to effectively restrict volume and pressure delivery to one chamber of the heart. This chamber restriction is important because the two sides of the circulation require far different pressures for acceptable function (usually the systemic pressure is 3 to 5 times as high as is the pulmonary pressure). Compressive patterns of either muscle wraps or mechanical devices may also distort heart valves, which can lead to valve leakage.
Therefore, to be effective and safe, mechanical pumping of a person's existing heart, such as through mechanical compression of the ventricles or some other action thereon, must address these issues and concerns in order to effectively and safely pump blood. Specifically, weakened ventricle or ventricles must rapidly and passively refill between beats at low physiologic pressures, and the valve function must be physiologically adequately. The blood flow to the heart muscle must not be impaired by the mechanical device. Still further, the left and right ventricular pressure independence must be maintained within the heart.
Internal stabilizing components to complete the three-dimensional control of a chambers' boundaries, which components are suspended through the substance of heart walls from the external (to the heart) actuating mechanism should be a useful adjunct. These provide a means to facilitate the precise control of actuation—determining the prescribed pattern and distribution needed to (1) prevent valvular distortion, (2) avoid myocardial blood flow compromise, (3) provide a type of shape alteration of the actuated chamber at end-actuation which will facilitate passive refilling during shape restoration, and (4) ensure relative independence of pressure in the various chambers.
Specifically, U.S. Pat. No. 5,957,977, which is incorporated herein by reference in its entirety, discloses an actuation system for the natural heart utilizing internal and external support structures. That patents provides an internal and external framework mounted internally and externally with respect to the natural heart, and an actuator device or activator mounted to the framework for providing cyclical forces to deform one or more walls of the heart, such as the left ventricular free wall. The invention of U.S. patent application Ser. No. 09/850,554, which has issued as U.S. Pat. No. 6,592,619, further adds to the art of U.S. Pat. No. 5,957,977 and that patent is also incorporated herein by reference in its entirety. The application specifically sets forth various embodiments of activator or actuator devices, which are suitable for deforming the heart walls and supplementing and/or providing the pumping function for the natural heart.
While the actuation systems of those patents provide a desirable actuation of the natural heart, it is further desirable to improve upon the interface between the actuation system and the heart.
Specifically, the coupling between the internal and external framework elements of the actuation system occurs across tissue. For example, transmural cords extend between semi rigid internal valve annular rings and an external transverse arc of a yoke coupled to the outside of the heart. Due to over-tightening of the cords when they are positioned, and/or to swelling of the tissue afterward, there may be compression of myocardial tissue and traversing of coronary artery branches.
Also, the coupling between discrete actuating components and discrete framework components, both external to the heart, have potential of damaging or abrading the surface of the heart during motion.
It is further desirable to achieve such goals while still providing sufficient anchoring for the various components of the actuation system. It is still further desirable to provide a counterforce to stabilize the base of the ventricular mass during application of deforming forces to the free walls and/or septum of the ventricle or ventricles.
Still further, it is an objective to provide desirable actuation of the heart to achieve a long-term solution to heart weakening or heart failure. These objectives and other objectives and advantages of the present invention will be set forth and will become more apparent in the description of the embodiments below.
The active jacket is a preferred embodiment of the basal cushion, which extends over the free ventricular wall of one or both ventricles as well as over the ventricular base. In this embodiment, it is a thin (generally 0.5 to 8.0 mm thick), flexurally elastic jacket substantially encompassing the epicardial surface of at least one chamber of the natural heart. ‘Flexurally elastic’ in this description is defined as having a measurable bending stiffness (neither flaccid nor absolutely rigid) in a tangent plane in at least part of the structure. Fabrication methods and materials may be varied as required in any location to meet required specifications. The jacket may also be longitudinally elastic in tension and/or compression in at least one direction at one or more locations.
For the purposes of illustrating the invention, the following parts list corresponds to the Figures listed above and included herewith.
Part Numbers
In one embodiment of the present invention, a cushioned, flexurally elastic jacket is configured to rest on the extracardiac border of at least one cardiac chamber, including the basal margin.
The jacket has an inner, or heart-facing surface [40] and an outer surface [41]. The jacket generally has a free-wall [42] section and a basal section [43] each of which may extend over the left, right, or both sides of the heart—although the illustration in figures shown is for the left ventricle. The free-wall section of the jacket is configured to fit over the free wall of the ventricle, and the basal section over the ventricle's base, surrounding its inflow and outflow valves.
The free-wall section of the jacket [39] may include one or more actuator elements [38], such as mechanical actuator elements, for deforming the free wall section to assist or replace the natural operation of the heart. The actuator element [38] will be coupled to a suitable actuator system [37] for providing the power and control of the actuation, such as to exert a force and empty the heart chamber (systole). The free-wall section of the jacket, whether part of a left, a right, or biventricular device, since it has flexural elasticity as described above, exerts an outward force on pericardium or other tissues surrounding the ventricular free wall during refilling (diastole). This is due to passive elastic recoil derived from energy stored during active ejection(systole). The outward force may be transmitted to the heart wall, and thus assist refilling either by means of a relative vacuum produced between the jacket and heart wall (following chest closure and removal and/or absorption of any air or free fluid) or by means of direct adhesion of the heart wall to the jacket during healing.
While it shares similarities of employing spring strain energy, stored in systole, to assist diastolic filling, these embodiments of the active jacket are distinguished from an embodiment of the ‘spring-loaded ventricle’ concept disclosed through CardioClasp, Inc. in that in all embodiments of that disclosure, restoring force was directly applied to the inside the heart chamber. The active jacket of the present invention is completely outside the ventricle.
The jacket preferably has means provided for egress of tissue fluid that may accumulate, either discrete fenestrations [44] or porosity of at lease part of the structure. The basal portion has either pre-cut apertures for the great vessels and atria or is suited for cutting these as required at operation. In the non-limiting example shown, dashed lines indicate sites of the aperture for the aorta [10] and of the aperture for the left atrium [8].
Mechanical characteristics of the jacket may vary at various sites within the jacket. That is, the jacket may be, but is not necessarily, isotropic and/or homogeneous in structure. The ventricular portion of the jacket is preferably not obstructive to through-flow of tissue fluid, allowing any such fluid accumulating near the heart to exit and thus be more likely to be reabsorbed. The jacket may be fenestrated in multiple places as shown in
A nonlimiting example of an alternate construction in which spring elements make up all of the jacket's structure is shown in
This (the all-spring active jacket) is distinctly different from the structure of some superficial similarity that is taught by International patent publication # WO 01/67985 A1 and precedent US filings, by Lau, assigned to Paracor, Inc. The Paracor filings teach a mesh made up of linked individual spring units in such as way that it purposefully does not have the defined flexural elasticity of the active jacket taught herein, but is instead flaccid to flexion, as is appropriate for it's completely different purpose (anisotropic passive restraint of a dilated heart).
The spring elements may alternatively be made of nonmetallic materials such as glass fibers, carbon fibers, composites of such fibers with matrix materials such as an epoxy or polyester compound, or other materials—either single composition or composite—with similar mechanical and biologic properties.
The spring elements may be of any configuration known to those familiar with mechanical design, such as ribbon, leaf, corrugated sheet, coil, bar, or serpentine wire, with present preference being serpentine wire. Mechanical behavior of either the entire jacket or portions of it may be altered by design by varying the number of spring elements, joining techniques between spring elements, the distribution and orientation of spring elements, thickness or gauge of materials, and spring configuration at any site. In the presently preferred embodiment of serpentine wire metal spring elements, “configuration” in this context means periodicity of undulations, amplitude of undulations, and the pattern (that is, whether the pattern is sinusoidal, continuous link of circular arcs with or without straight segments, and so forth).
The jacket may be partially or totally constructed of soft materials, which contribute all, or part of its flexural elasticity. These soft materials may be polymer fibers (such as polyester) (either unorganized or organized in some fashion such as a braid, weave or knit). In an alternative, these soft materials may be an elastomeric polymer (such as silicone rubber or a polyurethane).
In yet another alternative, the soft material may be a fiber structure such as described above, impregnated with an elastomeric polymer such as also described above, so as to form a fiber-reinforced, elastomeric-matrix composite. The jacket may be comprised of multiple materials such as spring elements of the types described above in a network encased in soft materials such as the polymer fibers, the elastomeric polymer, or the composite of both described above.
A preferred embodiment of composition, shown in a nonlimiting example in
The jacket may have additional cushioning, such as a layer of very low durometer elastomer, over all or part of its inner surface At least part of the jacket's inner surface may be textured so as to encourage adhesion to the heart wall during healing. Regions of the inner surface may have additional cushioning or texturing or both or neither. Texturing with a material such as polyester velour, overlaying or incorporated in all or part of the jacket's inner surface, in intended to encourage secure adherence to heart surface during healing. This is shown in
In the preferred method of seating the jacket on a heart, the needles of the completed circumferential row of sutures or cords, extending from bolsters, framework or other means of interventricular septum stabilization, are, after exiting the ventricular or atrial external surfaces, advanced through the substance of the jacket near its margin, following by lowering the jacket into place and tying in a manner used by and familiar to cardiac surgeons for sewing and seating a prosthetic heart valve. Protective structures, such as those described below, for the great vessel(s) and atrium(or atria) are placed prior to lowering the jacket into position and tying the sutures, which secure the jacket.
In a modified similar method, the sutures are mechanically fixed, rather than tied, to prepared receiving elements in the jacket near its margins.
Because of the risks of tying or fixing these jacket-fixing sutures or cords either excessively loose (i.e., bleeding from the heart surface) or excessively tight (i.e., reduction of blood flow to the heart tissue supplied by any coronary arteries traversing the region), means of measuring or otherwise controlling the tension with which these sutures or cords are placed may be useful. The teaching of this invention includes examples of such means.
An indicator device may be used with, calibrating tightness of tied sutures joining internal structures, such as bolsters or frame struts, through myocardium to jacket. The indicator device may function as a surface tension indicator to allow control of suture tying tightness in which a laminated structure, with alternate laminae translucent and either textured or colored, in such a way that a visible change signals achievement of adequate tightness for control of bleeding. This indicator system may be constructed in such a way that a visible change signals achievement of excessive tightness that, if not reversed, could risk tissue damage.
A specific example of such a system follows, as illustrated in
An alternative means of calibrating suture tying tightness while securing the jacket [61] is the tensile elastic element such as a spring of various configurations or a loop [62] of elastomeric polymer such as shown in the nonlimiting example of
Yet another alternative is use of a tension-calibrating device for fixing sutures which is an adaptation of ratcheted tension-control fastening devices familiar to those in both cardiac surgery and engineering design (e.g. ‘snap-band guns’) configured to work with sutures after penetrating from bolsters and regulate tension at which sutures are mechanically fixed.
The ratcheting and tension limiting features of such devices may be either adapted and incorporated into prefixed openings in the margins of the jacket into which the sutures may be inserted or configured to be used with sutures penetrating the jacket's substance by needles or by other means. An auxiliary structure may be required for stabilization and protection of great vessel origins during and after placement of the jacket. These structures may or may not provide for fixation to the jacket, to the great vessel or to both. For the great vessels, a ‘sleeve’ may be configured for fitting around the base or root of the aorta or pulmonary artery, the sleeve and the vessel which it surrounds being within that vessel's aperture in the basal portion of the active jacket. The sleeve is illustrated in
The sleeve may have a tubular portion [68] that envelopes the aorta or pulmonary artery for approximately 5 to 40 mm starting near the level of the valve commisures, to be placed after separation of the soft tissue joining the pulmonary artery and aorta.
The tubular portion of the sleeve may be of a biocompatible material, that is porous such as expanded polytetraflurethylene (ePTFE) or knitted or woven polyester. Alternatively, the tubular portion of the sleeve may be of a biocompatible material that is nonporous such as solution cast polyurethane. The tubular portion the sleeve may be complete with intent to place over the proximal part of a transected great artery in the case of a complete or partial autotransplantation placement technique. The tubular portion of the sleeve may be separated vertically at one point on the circumference, preferably at the point that will be over the center of the non-coronary cusp of the aortic valve in the case of aortic use.
The sleeve may have a flared portion [69] that extends outward between the great vessel and the part of the jacket that is adjacent the great vessel aperture. The junction of the tubular and flared portions of the sleeve may be smooth and continuous to conform to the underlying tissue surface. The flared portion of the sleeve [69] may be of a biocompatible material that is in two layers joined at the margins, both porous, such as expanded polytetraflurethylene (ePTFE) or knitted or woven polyester, with solid particles, spherical or otherwise, 1 to 5 mm in diameter, loosely packed between the layers in the fashion of a ‘bean bag’ [70] so that it will protect the base of the great vessel against potential abrasion by the margins [71] of the active jacket's great vessel aperture(s). This is believed to be particularly important in a left or biventricular system, as the coronary arteries originate from the aorta, as shown by the right coronary artery [19] in
The flared portion of the sleeve may be composed of a biocompatible material that is in two layers joined at the margins, both nonporous, such as solution cast polyurethane, possibly reinforced with another polymer membrane, with a liquid (such as saline solution or silicone oil) or a gel (such as silicone gel or a biocompatible hydrogel) contained between the layers.
The flared portion of the sleeve may be composed of a biocompatible material that is in two layers joined at the margins, both being asymmetric in the case of the aorta, extending outward in a lobular fashion over the location of the origin of the two main coronary arteries and their more proximal branches in order to protect them from any eroding effect of the margins of the aperture.
An auxiliary structure may be required for stabilization and protection of atrial bases including atrioventricular valve annuli during and after placement of the jacket. These structures may or may not provide for fixation to the jacket, to the atrium, or to both.
For stabilization and protection of atrial wall and atrioventricular valve annulus and fixation of those structures to the jacket, a structure termed a ‘collar’ is taught. A method for preparing the atria for collar placement consists of incising the right atrial wall adjacent the intra-atrial septum and then repairing the resulting defect in the medial right atrial wall with a patch of any material, autologous or prosthetic, which is commonly used for septal defect repair, as illustrated in
A collar is configured for fitting around the base of the left or of the right atrium, the collar and the atrium which it surrounds being positioned within that atrium's aperture in the basal portion of the active jacket described above. The collar is illustrated in
The method of placing the collar is as follows: An annuloplasty ring [31], of standard rigid, semirigid, or flexible type, is fixed onto the mitral annulus using standard operative technique to assure adequate apposition of the posterior leaflet [82] and anterior leaflet [83] of the mitral valve [15]. Then the collar is either slipped over the atrial base intact, in the event of a cardiectomy/autotransplant technique, or separated and reattached in the event of an in situ heart technique. Sutures [84] are placed from the annuloplasty ring through the proximal atrial wall to the collar.
Although the components of the active jacket, the great vessel sleeve, and the atrial collar are each illustrated as individual embodiments, in an alternative embodiment, each of those components might be coupled together. For example, they could be integrally fabricated such that a single structure includes the jacket, the great vessel sleeve, and the atrial incorporated all incorporated in a single element. In another alternative embodiment, while separate pieces, the individual elements might be interlocked such as with interlocking surfaces. For example, mating hook and loop fastening surfaces might be utilized on the heart-facing surface of the jacket for a short distance (a few millimeters) adjacent the aortic aperture and on the away-from-the-heart surface on the flared portion of the aortic sleeve.
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
This application is a continuation of PCT/US2004/018298 filed on Jun. 9, 2004, which claims priority of U.S. Provisional Patent Application No. 60/477,086, filed Jun. 9, 2003. The disclosure of each priority application is hereby incorporated by reference herein in its entirety. This application is also a Continuation-In-Part application of U.S. patent application Ser. No. 10/667,877, filed Sep. 22, 2003 now abandoned and entitled “Basal Mounting Cushion Frame Component to Facilitate Extrinsic Heart Wall Actuation” and also is a Continuation-In-Part application of U.S. patent application Ser. No. 10/197,973, filed Jul. 18, 2002 now abandoned and entitled “A Protective Sheath Apparatus and Method for Use with a Heart Wall Actuation System for the Natural Heart,” both applications of which are hereby incorporated by reference in their entireties.
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| Number | Date | Country | |
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| Parent | PCT/US2004/018298 | Jun 2004 | US |
| Child | 11298428 | US |
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|---|---|---|---|
| Parent | 10667877 | Sep 2003 | US |
| Child | PCT/US2004/018298 | US | |
| Parent | 10197973 | Jul 2002 | US |
| Child | 10667877 | US |
