Abstract:
A cardiac assist device and method of use for assisting the function of a heart. The assist device includes a compressor positioned against the epicardial wall of the heart and a field generator for driving a fluid coupled to the compressor to exert pressure on the heart. The field generator may be a magnetic field generator and the fluid coupled to the compressor may be a ferrofluid. The compressor may include two containment regions containing ferrofluid on opposite sides of the heart, and a pair of compression portions coupled to the containment regions. The filled generator may be electromagnetic which includes two electromagnets having corresponding core portions and corresponding coils. The electromagnets may be disposed with their north and south poles in alignment and separated by a gap to allow relative movement. The electromagnets may be external or internal to the body.

Description:
BACKGROUND OF THE INVENTION 
     The present invention deals with a ventricular assist device. More particularly, the present invention deals with cardiomyoplasty using a ferro fluid or other similar fluid. 
     A number of different types of coronary disease can require ventricular assist. Present ventricular assist devices (VADs) employ mechanical pumps to circulate blood through the vasculature. These pumps are typically plumbed between the apex of the left ventricle and the aortic arch (for LVADs), and provide mechanical assistance to a weak heart. These devices must be compatible with the blood, and inhibit thrombus formation, due to the intimate contact between the pump components and the blood. 
     Cardiomyoplasty is a form of ventricular assist which includes squeezing the heart from the epicardial surface to assist the ejection of blood from the ventricles during systole. This form of ventricular assist does not require contact with blood or surgical entry into the cardiovascular system. It has been expressed in several embodiments over the years. The first involves an approach which is drastically different from the mechanical pump approach discussed above. The approach uses a muscle in the patient&#39;s back. The muscle is detached and wrapped around the epicardium of the heart. The muscle is then trained to contract in synchrony with the ECG pulse, or other pulse (which may be generated by a pacemaker). Since the back muscle does not contact blood, many of the issues faced by conventional LVADs are avoided. However, this approach also suffers from disadvantages, because operation of the muscle tissues is poorly understood and largely uncontrolled. 
     A number of other methods are also taught by prior references. Some such references disclose balloons or bellows which squeeze on the exterior surface of the heart in synchrony with the ECG signal. U.S. Pat. No. 3,455,298 to Anstadt discloses an air pressure source which is used to inflate a balloon about a portion of the external surface of the heart, in order to provide a squeezing pressure on the heart. 
     Other references disclose similar items which are inflated using fluid inflation devices. Still other references disclose mechanical means which apply pressure radially inwardly on the epicardial surface of the heart. For instance, U.S. Pat. No. 4,621,617 to Sharma discloses an electromechanical mechanism for applying external pressure to the heart. 
     The air and fluid inflation devices exhibit certain advantages in that they use conformable fluids to provide an atraumatic squeezing force on the surface of the heart, as opposed to mechanical and electromechanical devices which use rigid surfaces, which contact the heart, in order to exert the squeezing force. However, one disadvantage of the fluid devices is the need for a pump which delivers fluid from a reservoir. The pump and the associated electronics is generally bulky, and can be too large and cumbersome to be implanted within the patient. Thus, such devices often require the patient to remain in bed while the device is in use. 
     Further, while the human muscle wrap approach does address some of these problems, it requires radical surgery plus the training of the muscle, which may not always be accomplished successfully. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a cardiac assist device for assisting the function of a heart. The assist device includes a compressor positioned against the epicardial wall of the heart and a field generator for driving a fluid coupled to the compressor to exert pressure on the heart. The pressure exerted against the heart improves heart function. 
     The field generator may be a magnetic field generator and the fluid coupled to the compressor may be a ferrofluid. The magnetic field generator may include an electromagnet having a core and an energizeable coil disposed thereabout. The ferrofluid may be disposed proximate a gap in the electromagnet such that the compressor exerts a force against the heart wall by generation of a magnetic field in the gap. 
     The compressor may include two containment regions containing ferrofluid on opposite sides of the heart, and a pair of compression portions coupled to the containment regions. The electromagnet may include two electromagnets having corresponding core portions and corresponding coils. The electromagnets may be disposed with their north and south poles in alignment and separated by a gap to allow relative movement. The electromagnets may be external or internal to the body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a partial sectional view of a human heart and its associated proximate vascular system. 
     FIG. 2 is a diagrammatic illustration, in partial schematic form, of an assist device in accordance with one aspect of the present invention. 
     FIG. 3 is a top view of the device shown in FIG.  2 . 
     FIGS. 4A-4C illustrate an assist device in accordance with another aspect of the present invention. 
     FIGS. 5A-5C illustrate an assist device in accordance with another aspect of the present invention. 
     FIGS. 6A-6C illustrate an assist device in accordance with another aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a partially sectioned view of a human heart  20 , and its associated vasculature. The heart  20  is subdivided by muscular septum  22  into two lateral halves, which are named respectively right  23  and left  24 . A transverse constriction subdivides each half of the heart into two cavities, or chambers. The upper chambers consist of the left and right atria  26 ,  28  which collect blood. The lower chambers consist of the left and right ventricles  30 ,  32  which pump blood. The arrows  34  indicate the direction of blood flow through the heart. The chambers are defined by the epicardial wall of the heart. 
     The right atrium  28  communicates with the right ventricle  32  by the tricuspid valve  36 . The left atrium  26  communicates with the left ventricle  30  by the mitral valve  38 . The right ventricle  32  empties into the pulmonary artery  40  by way of the pulmonary valve  42 . The left ventricle  30  empties into the aorta  44  by way of the aortic valve  46 . 
     The circulation of the heart  20  consists of two components. First is the functional circulation of the heart  20 , i.e., the blood flow through the heart  20  from which blood is pumped to the lungs and the body in general. Second is the coronary circulation, i.e., the blood supply to the structures and muscles of the heart  20  itself. 
     The functional circulation of the heart  20  pumps blood to the body in general, i.e., the systematic circulation, and to the lungs for oxygenation, i.e., the pulmonic and pulmonary circulation. The left side of the heart  24  supplies the systemic circulation. The right side  23  of the heart supplies the lungs with blood for oxygenation. Deoxygenated blood from the systematic circulation is returned to the heart  20  and is supplied to the right atrium  28  by the superior and inferior venae cavae  48 ,  50 . The heart  20  pumps the deoxygenated blood into the lungs for oxygenation by way of the main pulmonary artery  40 . The main pulmonary artery  40  separates into the right and left pulmonary arteries,  52 ,  54  which circulate to the right and left lungs, respectively. Oxygenated blood returns to the heart  20  at the left atrium  26  via four pulmonary veins  56  (of which two are shown). The blood then flows to the left ventricle  30  where it is pumped into the aorta  44 , which supplies the body with oxygenated blood. 
     The functional circulation, however, does not supply blood to the heart muscle or structures. Therefore, functional circulation does not supply oxygen or nutrients to the heart  20  itself. The actual blood supply to the heart structure, i.e., the oxygen and nutrient supply, is provided by the coronary circulation of the heart, consisting of coronary arteries, indicated generally at  58 , and cardiac veins. Coronary artery  58  resides closely proximate the endocardial wall of heart  24 . The coronary artery  58  includes a proximal arterial bed  76  and a distal arterial bed  78  downstream from the proximal bed  76 . 
     In order to assist the heart, the present invention provides a fluid either partially surrounding the heart, or completely surrounding the heart, wherein the fluid can be influenced by electric or magnetic fields. The fluid is located closely proximate the epicardial surface of the heart and is influenced by the application of an electric or magnetic field in order to assist the heart. 
     FIG. 2 is a diagram, in partial schematic form, illustrating cardiomyoplasty system  100  which is used, in accordance with one aspect of the present invention, in order to assist the heart  20 . In system  100 , heart  20  is illustrated surrounded by a bag  102  which is substantially, or partially, filled with a ferrofluid (shown in FIG.  3 ). System  100  also includes electromagnet sections  104  and  106  which are coupled, through switches  108  and  110 , to a power supply  112 . Switches  108  and  110  are controlled by controller  114  which, in one preferred embodiment, receives an ECG input signal from heart rate sensor or monitor  116 . 
     In one preferred embodiment, bag  102  is formed of a non-compliant balloon material which is preferably attached to portions of the heart by sutures, indicated generally at  118 . Bag  102  is filled with a ferrofluid which, in one preferred embodiment, is paramagnetic in that it becomes magnetic in the presence of an applied magnetic field. Such fluids are commercially available from Ferrof luidics Corporation, 40 Simon Street, Nashua, N.H. 03061, and Lord Corporation, 405 Gregson Drive, Cary, N.C. 27511. The fluid is preferably biocompatible and includes suspensions of small, ferromagnetic particles. In zero applied field, the fluid is non-magnetic. However, the fluid becomes magnetized when an external magnetic field is applied. The maximum magnetization which can occur in the fluid is referred to as the saturation induction, and is typically achieved in applied fields of about 1000 Oersteds, and has typical values of about 1000 Gauss. Applied fields in this range, and higher, can be achieved with electromagnets using conventional core materials and fairly modest electrical power. 
     The ferrofluids surrounding the heart are energized by magnetic fields which can originate from electric currents or permanent magnets situated either within or outside the body. For example, the magnetic fields in FIG. 2 are generated by electromagnets  104  and  106  located outside the body. Electromagnets  104  and  106  each include a coil  120  and  122 , respectively which is formed, illustratively, of insulated copper wire. Coils  120  and  122  are wound around thin sheets of magnetic material  124  and  126 , respectively. The material  124  and  126 , in one preferred embodiment, is commercially available under the commercial designation Hiperco, from Carpenter Metals, of Reading, Pa. In the embodiment illustrated in FIG. 2, electromagnets  104  and  106  are generally semi-circular in shape, and are each configured as half torroids set up in a repulsion configuration. 
     Coils  120  and  122  are coupled to power supply  112  (which in one preferred embodiment is a battery) through switches  108  and  110 , which are controlled by controller  114 . A bipolar ECG lead  130  is attached at a point on the patient&#39;s chest and provides a signal to heart rate sensor  116  which, in turn, provides a signal to controller  114  indicative of the activity of heart  20 . Controller  114  controls switches  108  and  110  to selectively energize coils  120  and  122  during systole. 
     When current is passed through coils  120  and  122 , in the direction indicated, a magnetic field is directed through the chest of the patient from the north poles (indicated by the letter N in FIG. 2) to the south poles (indicated by the letter S in FIG. 2) of coils  120  and  122 . This field magnetizes the ferrofluid within bag  102  and forces it to a center line (designated by dashed line  132 ) between electromagnets  104  and  106 , in the direction indicated by arrows  134  and  136 . Energization of electromagnets  104  and  106  also forces the ferrofluid in bag  102  toward the north and south poles in the direction generally indicated by arrows  138  and  140 . Bag  102  reacts in this way because a force develops which pulls the ferrofluid to the point of the strongest field concentration within system  100 . 
     As the field is applied, bag  102 , under the force of the ferrofluid driven by the magnetic field, is squeezed inwardly and flattened. The force is proportional to the area of the ferrofluid. Only a few pounds per square inch (psi) are required to pump the blood from within heart  20 . This can be achieved when only a few Watts of power are delivered to coils  120  and  122 . The amplitude of the coil current controls the pressure exerted by the bag  102  of ferrofluid. Of course, the magnitude of the current can be adjusted until the patient&#39;s blood pressure is within a normal range. 
     In one illustrative embodiment, electromagnets  104  and  106  are contained within a vest worn about the chest of the patient. Also, magnetic shields  142  are provided to cover the region of the gap between the semi-circular magnets, both on the North Pole and South Pole ends, and reside on the outside surface, away from the patient. Magnetic shield  142  confines the high magnetic field to a region within the patient&#39;s chest. 
     FIG. 3 is a top view of a portion of system  100  shown in FIG.  2 . In FIG. 3, bag  102  is shown as having a pair of generally oppositely disposed pouches  146  and  148  which are connected by bands  150  and  152  which extend about, and are sutured to heart  20 . Pouches  146  and  148  contain the ferrofluid material. Thus, when the magnetic field is applied, pouches  146  and  148  are pulled in generally opposite directions toward the north and south poles, respectively. This tends to flatten bag  102  about heart  20 . Since pouches  146  and  148  generally reside closer to the north and south poles, this provides more efficient magnetic coupling between those poles and the ferrofluid residing in pouches  146  and  148 . 
     Of course, a wide variety of other bag configurations can be used as well. For example, instead of having two discrete pouches, bag  102  can be formed having a single pocket which extends about the entire periphery of heart  20 , bag  102  can be formed having a number of separately divided pockets which extend about the periphery of heart  20 . Further, bag  102  may preferably be formed with seams  119  which are disposed about regions having larger coronary vessels  121  in order to avoid compressing those vessels during energization of the coil. Other, different bag configurations can be used as well. 
     FIGS. 4A-4C illustrate a cardiac assist system  200  in accordance with another aspect of the present invention. A number of other items in system  200  are similar to those in system  100  illustrated in FIGS. 2 and 3, and are similarly numbered. However, system  200  is substantially entirely implantable. System  200  includes a plurality of electromagnets  202 ,  204 , and  206 . Each electromagnet includes a core  208  surrounded by a coil  210 . Each of the coils  210  is coupled to a corresponding switch  212 ,  214 , or  216 , which is controlled by controller  114  based on an ECG or other suitable signal, and selectively couples coils  210  to battery  112 . As with system  100 , the cores  208  of the electromagnets are preferably a Hiperco or other suitable core material surrounded by coils  210 , which is preferably formed of insulated silver or gold wire. All circuitry is preferably implantable, and battery  112  is preferably inductively recharged from outside the body. 
     The plurality of electromagnets  202 ,  204  and  206  are separated by gaps  220 . Thus, the electromagnets form torroids which substantially surround the heart, but which are split into a plurality of sections which define magnetic gaps  220 . Each of the gaps contains two bags  222  and  224 , which are separated by a septum  226 . In one preferred embodiment, bags  222  are disposed in a direction radially toward the epicardial wall of heart  20 , while bags  224  are disposed in an opposite direction. 
     Bags  222  are filled with non-magnetic fluid, while bags  224  are filled with ferrofluid. When current is applied to the torroidal coils during systole, each ferrofluid bag  224  is drawn into a corresponding gap  220 , thus exerting an inwardly directed force on bags  222  and thus on the epicardial wall of heart  20 . This force displaces the non-magnetic fluid against the heart wall. During diastole, the coils are de-energized and expansion of heart  20  advances bag  222  back into gaps  220  and thus displaces the ferrofluid in bag  224 , out of gap  220 . Bags  222  and  224  thus mimic the action of fingers performing heart massage. 
     In accordance with one aspect of the present invention, gaps  220  are narrower at the apex of heart  20  and wider toward the top of the heart  20 . Since the gaps are narrower at the apex, the magnetic field in the narrower gap region is stronger than at the top of heart  20 . This causes pressure to build, once the coils are energized, from the apex upward in a natural progression to assist displacement of blood from left ventricle  30 . In addition, as illustrated in FIG. 4A, bags  222  and  224  are formed in gaps  220  substantially about the left ventricle  30  of heart  20 , while no gaps are preferably defined by the electromagnets about right ventricle  32 . This preferentially exerts pressure to assist in displacement of blood from left ventricle  30 . 
     FIGS. 4B and 4C illustrate the action of one set of bags  222  and  224  under the influence of the magnetic field exerted by the electromagnets  204  and  206 . It will be appreciated that similar action will take place in each of the gaps  220 . FIG. 4B illustrates that the coils on electromagnets  204  and  206  are energized during systole to create a magnetic field in gap  220 . The magnetic field draws the ferrofluid in bag  224  into the gap, thus displacing the non-magnetic fluid in bag  222  inwardly toward heart  20 . By contrast, when the magnets are de-energized during diastole, the heart chambers fill thus exerting a pressure on bag  222  which displaces the ferrofluid in bag  224  from gap  220 , radially outwardly, to allow expansion of the heart  20 . 
     FIGS. 5A-5C illustrate a portion of another assist system  300  in accordance with another aspect of the present invention. As with systems  100  and  200 , a heart rate monitor  116 , a controller  114 , a plurality of switches, and implantable battery  112  are preferably provided in system  300 , although they are not illustrated for the sake of clarity. In system  300 , a torroidal electromagnet  302  includes a core member  304 , which is preferably formed of Hiperco material, and winding  306 , which is preferably formed of insulated silver or gold wire. To improve flexibility of the electromagnet, the core may consist of a flat bag of ferrofluid. Core member  304  is disposed about the epicardial layer of heart  20  and defines a gap  308  between ends thereof. Core member  304  is also preferably sutured to heart  300  in two or more locations generally indicated by numeral  310 . The areas at which core  304  is sutured to the epicardial wall of heart  20  are preferably proximate left ventricle  30 . 
     System  300  also preferably includes a bag  312  of ferrofluid material. Bag  312  includes a plurality of separate pouches  314 , each of which form an elongate finger containing ferrofluid material. Bag  312  is preferably sutured to the epicardial layer of heart  20  in gap  308 . The current in coil  306  is preferably driven by an implanted battery, and is switched on during the heart&#39;s systolic phase. The beginning of systole can be sensed in several different ways, including by using the QRS complex on an ECG electrode planted on the heart, by using the heart sound produced when the aortic valve opens and sensed by an implanted microphone, or by using a preset pressure threshold as measured on or in the left ventricle. The current through coil  306  is switched off when the T-wave of the ECG signal is identified, when the aortic valve is heard closing, or when the pressure drops below a valve closing threshold. 
     When coil  306  is energized, the end portions of core  304  tend to move toward one another in the directions generally indicated by arrows  316  and  318 , in order to close gap  308 . This causes a squeezing on heart  20  in the direction indicated by arrows  316  and  318 . 
     In addition, pouches  314 , containing ferrofluid, are preferably centered longitudinally in gap  308 , but are radially displaced on the left ventricle  30  outward from the plane of gap  308  when not under the influence of a magnetic field. The ferrofluid in pouches  314  is positioned to partially close the magnetic circuit in gap  308 . Thus, when coil  306  is energized, the ferrofluid is drawn radially inward, in the direction indicated by arrows  320 , as gap  308  is closing generally tangentially. Thus, left ventricle  30  is receiving a squeezing force in two directions, which enhances the efficiency of the cardiac assist. 
     It should also be noted that sutures  310  are preferably formed in a region of left ventricle  30 , or approximately on a line dividing left ventricle  30  from right ventricle  32 . Thus, only left ventricle  30  is squeezed. The sutures maintain a gap between electromagnet  302  and the epicardial wall of heart  20  in the area of right ventricle  32 . Thus, right ventricle  32  does not receive any of the squeezing force. Of course, without sutures  310 , both left ventricle  30  and right ventricle  32  could be squeezed. 
     FIGS. 5B and 5C are top views of system  300  illustrating the operation thereof. In FIG. 5B, coil  306  is de-energized, such that gap  308  is larger and pouches  314  are radially displaced, somewhat, from gap  308 . However, upon energization of coil  306 , gap  308  tends to close in the direction indicated by arrows  316  and  318 , and pouches  314  tend to move radially inwardly, into gap  308 , in the direction indicated by arrows  320 . FIG. 5C illustrates system  300  after coil  306  is energized. Note that gap  308  has closed somewhat, and pouches  314  are now more closely drawn within gap  308 , thus squeezing left ventricle  30 . 
     It should be noted that, in FIGS. 5A-5C, and in accordance with one aspect of the present invention, core  304  is made from a plane of individual Hiperco wires overwound with AWG #25 copper wire. This entire structure is only approximately 0.048 inches thick, and is quite flexible, especially when held together by a flexible adhesive, such as urethane. The structure is wrapped around heart  20 , and sutured. The ends defining gap  308  are softened with a urethane coating. Flexibility can also be achieved by making the magnetic core from a flat bag of ferrofluid. Alternatively, the torroid is made of a more rigid structure which is shaped to fit snugly about heart  20 , without sutures. In such an embodiment, only the magnetically permeable material in bag  312  moves under the influence of the magnetic force, while the ends of the torroid do not close. 
     Also, in the embodiment shown in FIGS. 5A-5C, the coil resistance of the torroidal coil is approximately 6.5 ohms with a maximum current rating of 1 amp. The average heat dissipation required to generate desirable compressive force is approximately 3.3 watts, with an efficiency of 55% (i.e., 4 watts of pumping power). 
     FIGS. 6A-6C illustrate another system  400  in accordance with another aspect of the present invention. System  400  includes a rigid structure or frame  402 , which has a bag  404  partially filled with ferrofluid material, supported thereby. In one embodiment, bag  404  is adhered to structural frame  402 . The structural frame  402  is formed of non-magnetic material, such as structural plastic, and structure  402  and bag  404  are overwound with a copper coil  406 . 
     The density of the windings is greater in a region proximate left ventricle  30  than in the region proximate right ventricle  32 . In one preferred embodiment, the density in the region of left ventricle  30  is double that in the region of right ventricle  32 . For example, in a region of structure  402  proximate right ventricle  32 , coil  406  includes N windings per unit length. However, in a region of structure  402  proximate left ventricle  30 , coil  406  includes more windings, such as 2N windings. It should also be noted that bag  404  is disposed on the outside of rigid structure  402  in the area proximate right ventricle  32 , but is disposed on the inside surface of structure  402  in the area proximate left ventricle  30 . In accordance with one aspect of the present invention, structure  402  includes a transition section  408  which forms a gap between two longitudinally separated rails  410  and  412 . The bag passes from the outer surface of structure  402  to the inner surface thereof through gap  408 . 
     The conductive windings, in one embodiment, are physically attached to the surface of bag  404 , and the wires are quite flexible. In another embodiment, where the wires are more rigid, the wires are not attached to the surface of balloon  404 , but are instead simply draped over the surface of bag  404 . Further, in addition, the windings of coil  406  are physically attached to the outside of structure  402  in the area proximate left ventricle  30 , and are physically attached to the inside of structure  402  in the area proximate right ventricle  32 . 
     As with previous embodiments, one or more switches are provided to alternately couple coil  406  to a power supply  112  under the control of a controller  114 . In addition, a heart rate sensor  116  can also be provided to provide an input to the control circuitry such that the coil can be energized in synchronicity with the heart action. 
     Initially, balloon  404  is evacuated and partially re-filled with ferrofluid. When coil  406  is energized, the ferrofluid is forcibly moved within balloon  404  to the region around left ventricle  30 , because the greater density of windings in coil  406  in that region produces a stronger magnetic field. This preferentially fills balloon  404  proximate left ventricle  30  and thereby exerts a compression force on the epicardial surface of heart  20  in the region of left ventricle  30 . However, even when the coil is energized, there is still enough ferrofluid in the remainder of balloon  404  in the region around right ventricle  32  to complete the torroidal magnetic circuit throughout the entire circumference of heart  20 . 
     During diastole, the left ventricle  30  expands, and coil  406  is de-energized. The ferrofluid within balloon  404  is thus displaced from the left ventricle side of balloon  404  to the right ventricle side of balloon  404  where it occupies space outside of the volume of heart  20 . When the right ventricle side of balloon  404  is fully inflated, there is still enough ferrofluid left on the left ventricle side of balloon  404  to make a complete magnetic circuit, once coil  406  is re-energized. 
     FIGS. 6B and 6C are top views of system  400  shown in FIG.  6 A. In FIG. 6B, system  400  is shown with coil  406  energized during systole. It can be seen that balloon  404  preferentially fills on the side of heart  20  proximate left ventricle  30 , to exert compressive force in the direction generally indicated by arrow  420  on the epicardial surface of heart  20 . However, during diastole, and as shown in FIG. 6C, left ventricle  30  fills thus displacing ferrofluid from the left ventricle side of bag  404 , causing it to be displaced to a position outside structure  402  to the right ventricle side of balloon  404 . 
     It should also be noted that, system  400  shown in FIGS. 6A-6C can be sutured to the epicardial surface of heart  20  at any desirable location. For example, structure  402  can be sutured to a region of epicardial surface of heart  20  proximate the division between left ventricle  30  and right ventricle  32 . In this way, as balloon  404  fills, it exerts a backpressure on the rigid structure causing balloon  404  to expand inwardly and thus compress left ventricle  30 , without exerting any pressure on right ventricle  32 . In addition, during diastole, the ferrofluid falls under the force of gravity to the region of balloon  404  proximate the apex of the heart, and to the lower, posterior side of the heart, which is tilted back in the chest cavity. When current is applied to coil  406 , the apex region of the heart will be squeezed first, forcing the blood up and out of the heart in a natural contractile motion. 
     Thus, it can be seen that the present invention provides significant advantages over prior systems. The present invention need not be as compatible and deal with thrombus formation issues as required by systems which are deployed within the heart. Similarly, the present invention does not require external fluid sources for selectively filling a bag or pouch with fluid in order to exert compression on the heart. In addition, the present invention does not deal with natural muscle fibers wrapped around the heart, and thus does not encounter the difficulties associated with such techniques. Also, the present invention exerts a pressure on the heart with a pliable fluid filled surface which yields an atraumatic compressive force on the heart, as opposed to a traumatic compressive force encountered during compression with a rigid mechanical structure. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.