Patent Application
20060178551
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 passageway between the left and right atrium and the corresponding ventricle, and between each ventricle and the large arteries that 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 10 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, the 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 that 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 security and safety of means of attaching hardware to the heart.
It is still further desirable to modify devices so that they are suitable for placement through small operations (minimally invasive operative access). It is yet still further desirable to provide devices and methods that make possible safe access to the heart for future operations, such as coronary bypass.
Part Numbers
A series of ‘bolsters’ [1], soft, and smooth contoured, shown in
Balled tips [6] either may be pre-fixed on or may be placed on point [7] of needles to facilitate their safe passage through myocardium, lessening the likelihood of damage to vessels or other structures. The ball tips may be mounted on a cylindrical segment of metal hypodermic tubing [8] that may be placed on the needle tip before or at operation and removed when required.
A method of placement of bolsters comprises pressing the ball-protected needle tip against the inner lining tissue of the heart (the ‘endocardium’) [9], optionally with a preparatory ‘knick’ in the local endocardium, and pressing, optionally with a gentle vibratory motion, as it advances in and through the heart wall, generally at or near the junction of the right ventricle [10] and the left ventricle [11], as in
An optional elongated needle (similar configuration, several times as long) allows the method of placement to be modified for access other than ventricular incision, variably configured for use through a ventricular free wall puncture, an atrial puncture, or a venous puncture, with use of fluoroscopy or other imaging guidance as required.
The provisions described here for placement may be augmented by preliminary or coincident visualization by epicardial ultrasound or other means of identifying vulnerable structures such as coronary arteries.
In the preferred method of seating the one particular wall actuating component, an ‘active jacket’ [13], the needles of the completed circumferential row of bolsters, exiting the ventricular or atrial external surfaces, are advanced through the substance of the jacket near its margin (
This creates a series of cords [21] across the myocardium such as illustrated in
A ‘stringing’ material [22], such as braided polyester suture, ePTFE (expanded polytetraflurethylene) or braided polyester ribbon, is pre-prepared for use, in one or more segments, to link bolsters across the septum, thus creating a ‘snow-shoe-like’ network so that the septum is supported from the bolsters and thus indirectly by the jacket margins to which the bolsters have been anchored across the heart walls. Access for stringing is generally direct vision through one or more small (2 to 4 cm long) incisions (‘ventriculotomies’) [23] in the right ventricular free wall [24] as in
As shown in
An indicator device may be used with this method, calibrating tightness of tied sutures joining bolsters through myocardium to jacket [13]. Such an indication is disclosed in a related patent application entitled “Deforming Jacket for a Heart Actuation Device” and filed on Jun. 9, 2004 as a PCT application, which application is incorporated herein by reference.
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 tension-calibrating device for fixing sutures may be 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 adapted and incorporated into prefixed openings in the margins of the jacket into which the sutures may be inserted. 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 for 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
This structure will provide an indicator of the compressive force of a tied penetrating suture loop. The mechanism is that a certain degree of compressive stress will cause sufficient thinning of the second layer [30] that the initially visible yellow surface layer [29] color becomes green as it becomes compressed against the blue layer [31], and then brownish gray as the three layers are all closely compressed. In the lined variant, thinning of the second layer [30] with pressure causes the non-lined appearance of the surface layer [29] to transform locally to the left-to-right crosshatching as layer 3 becomes visible through it, and by a similar process at higher tying pressure then transforms to a grid pattern as the fifth layer [33] also becomes visible from the surface in the immediate vicinity of the suture being tightened. Thus a desirably compressed region [34] and/or any excessively compressed region [35] will be readily recognizable. As will be apparent, for either variant construction parameters may be selected such that the yellow to green (or clear to lined) transition occurs at a compressive stress which in the underlying tissue is expected to arrest bleeding, while the green to brownish-gray (or lined to gridded) occurs at a stress somewhat lower than one at which tissue ischemia is risked. This may be calibrated based on experimental assessment to a level where tying ‘tight enough but not too tight’ is readily achieved by visual guidance.
a is an ‘exploded’ view of laminar construction as described in the prior paragraph.
b illustrates the first transition where single direction cross hatch marks are visible, representing achievement of the ‘safe and necessary’ pressure, whereas the grid cross hatching in
An alternative means of calibrating suture tying tightness while securing the jacket [13] is the tensile elastic element such as a spring of various configurations or a loop [36] 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.
Yet another means of tension control is a miniature but very secure suture clamp of the type shown in
Such a clamp is temporarily mounted on an applicator. In the nonlimiting example shown here the applicator [47] is cast or machined from a rigid material, preferably a solid polymer such as polyethylene or polypropylene. It has a handle [48] contiguous with a body [49], with the body connected to a stage [50]. In the body there is a cavity [51] open on one side; the cavity has an upper margin [52] and a lower margin [53]. In use, the clamp is positioned on a stage [50] and held open by an instrument while pin [46] is lifted by another instrument. In the setting of a surgical operation these maneuvers could be readily done using hemostats or a hemostat and a forceps, respectively. With a similar instrument, the clamp is moved into position so that the pin [46], until released, holds the clamp open as shown in
After loading, traction may be exerted on the cord [3] by the operator. This is generally done manually, holding the handle 48 in the nondominant hand and the cord [3] in the dominant hand. It is important that the wrist of the handle-holding hand be relaxed so that the stage [50] rests freely on the heart surface [12] or jacket [13] surface. The tension generated in the cord exerts an upward force on sliding pulley [56] and thus on piston [59] and compression spring [62]. The spring constant of spring [62] and its longest permitted configuration (i.e., its length when piston is resting on the channel constriction) are selected so that the spring will be compressed further upon achievement of a targeted minimum tension in the cord [3] and be compressed sufficient to withdraw the pin [46] completely into the channel [60] with tension no greater than ˜120% of this value. At that point, jaws [43] are released and grasp cord [3]. Upon sensing this, generally by means of hearing a clicking noise, the operator releases the cord, removes it from the applicator, and cuts excessive length. It will be apparent that simple additions to the design would permit an optional cutting blade to automatically divide the cord above the clamp immediately after closure.
Note that effective tension is that between cord and applicator. If applicator is held with any substantial force away from the heart (i.e., if it does not rest freely on the heart surface) the clamp could be released with tension in the cord at heart exit lesser than the minimum desired. Thus an alternative design omits stage [50]. This necessitates care in positioning the clamp so that its grip on pin [46] alone assures proper angulation as it is brought into contact with the heart surface and tension commenced. Note also in a no-stage applicator, the minimum tension selected may be modestly lower than in an applicator that does have a stage. This is because applicator removal in a staged applicator will add the thickness of the stage (generally 1-2 mm) to intramyocardial cord length, lessening tension slightl.
A means of potentially improving access to and visibility of individual transventricular fixation points is illustrated in
Still yet another embodiment provides devices and techniques permitting construction of a sling or net to mechanically control the ventricular septum, and to suspend that sling or net from the portion of an active jacket on the heart surface, through only punctures, without incisions in the right or left ventricle. First, styli [66] (shown in
A minimum of five needle paths, which will subsequently be cord paths, are required, as illustrated in
Entrance and exit sites are targets only. Depending on anatomy, for example, an entrance that is approximately a few millimeters removed from that outlined may be chosen due to pattern of coronary vessels—both arteries and the coronary sinus and its tributaries. Typical paths are outlined below as projections [71] to [75], corresponding to the numbers in the left column of the table] on the surface of the right ventricle [10] In the preferred technique, each stylus is passed and then withdrawn, generally by one of the two methods to be described following the table, leaving a strand of flexible porous material extending along its path and joining the entrance and the exit points.
Again, this is a nonlimiting illustration of patterns of placement, from which many deviations in number of stylus paths, their course, or both, are possible. Entrances and exits may be interchanged depending on operative access and visibility. For one example of an alteration, the posterior extreme of path [72], [74], and [75], now adjacent one another, could be separated with that of path [75] changed to a more basal and that of path [74] to a more apical location.
Methods for Placement of Strands for Septal Supporting Net Along Paths of Styli
There are two general methods, each derived from commonly used surgical techniques for passing flexible members (e.g., vascular grafts, pacemaker wires, various types of conduits) through closed spaces, and both given as non-limiting examples.
For strands already equipped with or intended to be attached to a bolster that has been placed against the endocardial surface by direct vision, securing by tying or otherwise fixing the external end to either the jacket wall or to a separate button as described above may be sufficient. For strands placed by the methods described immediately above—via punctures, not incisions-special methods may be required.
First is a method in which the heart is removed similarly to the technique for removing a donor heart for transplant, has atria separated and right ventriculotomies made, and then is fitted with annuloplasty ring (s), atrial collar(s), great artery sleeve(s), septal rim bolsters, left-side jacket/actuator (if left-only or biventricular system) or, right-side jacket/actuator (unless left-only system), and septal splint, and then reimplanted following closure of the ventriculotomies
Second is a method in which the heart is left in site with atrial separation performed through an approach similar to that used for open mitral valve access, bolsters placed through an approach similar to that used for ventricular septal defect repair, annuloplasty ring placed by standard left atriotomy, jacket rim by ‘parachute suture’ and sequentially lowering and tying similarly to valvular prosthesis placement, collar sleeve and jacket base by separating and reattaching about intact structures, and finally suture closure of atriotomy and ventriculotomies.
Devices and Methods to Facilitate Reoperation
Means have been developed for separation of jacket from heart wall for re-operation, particularly for coronary artery procedures and to protect coronary arteries and conduits after reassembly and reactivation of the active jacket.
The interface between the jacket and the heart surface may be configured to allow removal at subsequent operations for coronary artery disease or other purpose.
The interface of may be achieved by an inner layer [89] that is configured to encourage tissue ingrowth and biologic adhesion, such as polyester velour, and an easily separable bonding [90] of that layer to the remainder of the jacket [13]. (
The easily separable bonding may be achieved by a hook and loop interface similar to the mechanism of ‘Velcro’. The easily separable bonding may be achieved by low strength polymer adhesive. Sharp dissection of a heart-adhering layer and the remainder of the jacket may be facilitated by contrasting colors. For a non-limiting example, the heart-adhering layer may be white and the facing portions of the remainder of the jacket a bright blue. Metallic components of the jacket may also be incorporated to establish a clear plane of dissection. This helps to guide a sharp dissection, facilitating removal of essentially the full thickness of at least selected regions of a jacket, leaving only a soft polymer fabric adherent to the heart. A non-limiting example is a thin titanium mesh.
The jacket may be fabricated in several modules of which one or more may be removed for access to coronary arteries or other otherwise obscured parts of cardiac anatomy at re-operation, following by replacement and secure mechanical fixation after the intervention.
The method of coronary artery intervention in the presence of an adherent mesh after jacket removal generally includes localization and assessment of native coronary arteries through direct surface ultrasonic imaging using techniques familiar in cardiac surgery. A gel-filled or bead-filled cushion may be fabricated in an assortment of sizes and shapes to be placed around, over, or beside a coronary artery conduit, such as an internal thoracic graft, to protect it in the manner of naturally occurring coronary fat pads. These protect the conduit from compression and abrasion after replacement and activation of the jacket. (
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/US2004/018299 filed on Jun. 9, 2004, which claims priority of U.S. Provisional Patent Application No. 60/477,078, filed Jun. 9, 2003. The disclosure of each priority application is hereby incorporated by reference herein in its entirety. This application is a Continuation-In-Part application of U.S. patent application Ser. No. 10/667,877, filed Sep. 22, 2003 and entitled “Basal Mounting Cushion Frame Component to Facilitate Extrinsic Heart Wall Actuation” which application is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60477078 | Jun 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US04/18299 | Jun 2004 | US |
| Child | 11299197 | Dec 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10667877 | Sep 2003 | US |
| Child | 11299197 | Dec 2005 | US |
