Abstract:
An implantable device ( 10 ) for assisting the functioning of the heart of a patient. The device ( 10 ) includes compressing means ( 14 ) adapted to be positioned about the aorta ( 12 ) of a patient for externally engaging and compressing the aorta ( 12 ) and means ( 30 ) for releasing the compressing means ( 14 ) from about the aorta ( 12 ). The releasing means ( 30 ) being adapted for releasing in response to intracorporeal input during minimally invasive surgery or in response to intracorporeal input. The device ( 10 ) is connectable to motive means adapted to activate the compressing means ( 14 ). The compressing means ( 14 ) and the releasing means ( 30 ) are fully implantable within the thoracic cavity of the patient.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to counterpulsation heart assist devices, systems and methods.  
         BACKGROUND OF THE INVENTION  
         [0002]    The intra-aortic balloon pump (IABP) was first proposed in the 1960&#39;s as a method of partial support for an acutely failing heart, for example, after heart surgery or heart attack. An IABP comprises a long thin catheter [7-12 Fr] with an elongated balloon at its tip [volume 25-50 ml]. The balloon is inserted via the femoral artery and inflated and deflated in counter-pulsation with the heart beat. Inflation in diastole causes a diastolic pressure pulse with increase in blood flow to the relaxing heart muscle. Deflation of the balloon immediately before the heart ejects (presystole) reduces the pressure head against which the left ventricle has to eject blood, improving cardiac output and reducing the work of the heart. Early investigators determined that the best and most efficient balloon position was closest to the heart, i.e., in the ascending aorta. However, in recent times, the balloon is positioned via the femoral artery in the descending aorta for short term (1-10 days) use.  
           [0003]    IABP counterpulsation has been proven to work very well in the short-term to assist hearts to recover when drugs (ionotropes etc.) are insufficient or inappropriate to support the cardiovascular system.  
           [0004]    IABP&#39;s operating in counterpulsation assist the heart function. When inflated, the balloon propels blood peripherally from within the aorta to improve blood circulation in the patient. Moreover, more blood is forced into the coronary arteries to help nourish and strengthen the heart muscle. However, disadvantages of IABPs that limit their application are: the patient is bedridden and not able to sit or walk; there is very high incidence of limb ischemia and complications; and the IABP are not able to be left in for any period of time greater than 10 days. A further disadvantage is the balloon comes into direct contact with the blood flowing into the aorta, which can cause damage to the blood cells and a risk of thromboembolism. In addition, current IABP systems are inflated by means of a tube passing through the body and directly into a groin vessel, the femoral artery, which results in a high risk of associated leg complications. Additionally, the use of a gas to inflate the balloon is not an entirely safe operation since any leakage of gas from the balloon into the blood stream could cause a gas embolus.  
           [0005]    Aortic compression (periaortic diastolic compression) has also been described as a means to increase coronary blood flow, e.g. U.S. Pat. No. 4,583,523 and U.S. Pat. No. 4,979,936. The Applicant&#39;s international PCT patent application Ser. No. PCY/AU00/00654 (international publication No. WO 00/76288) entitled “Heart Assist Devices Systems and Methods” discloses heart assist devices that can be quickly and totally implanted in a relatively easy manner and with minimum trauma to a patient. The disclosed devices advantageously have no blood contacting surfaces and do not require cardiopulmonary bypass for implantation. Generally speaking, the devices disclosed include and aortic compression means adapted, when actuated, to compress an aorta, a fluid reservoir and a pump means adapted to pump a fluid fro the fluid reservoir to the aortic compression means to actuate same. The fluid reservoir is adapted to be wholly positioned within the chest cavity of the patient.  
         OBJECT OF THE INVENTION  
         [0006]    It would be desirable to have a heart assist device that could be quickly implanted and explanted in a relatively easy manner and with minimum trauma to the patient and to allow ambulation with low risk of complications.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, in a first aspect, the present invention provides an implantable device for assisting the functioning of the heart of a patient, the device including:  
           [0008]    compressing means adapted to be positioned about the aorta of a patient for externally engaging and compressing the aorta; and  
           [0009]    means for releasing the compressing means from about the aorta, said releasing means being adapted for releasing in response to intracorporeal input during minimally invasive surgery or in response to extracorporeal input,  
           [0010]    wherein the device is connectable to motive means adapted to activate the compressing means, and the compressing means and the releasing means are fully implantable within the thoracic cavity of the patient.  
           [0011]    In a second aspect, the present invention provides a device for assisting the functioning of the heart of a patient, the device including:  
           [0012]    inflatable compressing means adapted to be positioned about the aorta of a patient for externally engaging and compressing the aorta;  
           [0013]    means for releasing the compressing means from about the aorta, said releasing means being adapted for releasing in response to intracorporeal input during minimally invasive surgery or in response to extracorporeal input,  
           [0014]    motive means to periodically inflate the compressing means in counterpulsation with the rhythm of the patient&#39;s heart, the motive means being adapted for external location and connection to the compressing means via a percutaneous line,  
           [0015]    wherein the compressing means and the release means are fully implantable within the thoracic cavity of the patient and the compressive means include means adapted for attachment to itself for engaging the aorta and for detachment from itself for intracorporeal or extracorporeal releasing from the aorta.  
           [0016]    Minimally invasive surgery preferably includes endoscopic surgery.  
           [0017]    Preferably, the releasing means is adapted to allow minimally invasive surgical or non-surgical removal of the device from the patient&#39;s thoracic cavity.  
           [0018]    Alternatively, the releasing means is adapted to allow minimally invasive surgical or non-surgical de-activation of the device (to disable compressing of the aorta) and retention in the patient&#39;s thoracic cavity.  
           [0019]    The heart assist device of the present invention allows, at least in preferred embodiments, partial unloading of the heart, augmenting of the cardiac output of the heart, increased coronary artery blood flow and substantial recovery of the heart so that the device could be weaned Further, the device advantageously has no blood contacting surfaces. Additionally, the device does not require cardiopulmonary bypass for implantation and can therefore be turned on and off without significant patient risk.  
           [0020]    After use, it is preferable for the device to be released and removed from the body, advantageously without requiring further surgery. Alternatively, the device can be left in situ, in an inactive state, until needed again. Alternatively, the device can be left in situ for on-demand, spaced-apart sessions of counterpulsation for treatment or relief from chronic myocardial ischaemia and/or heart failure. The provision of releasing means ensures that however the device is used it may be readilly removed at any time without difficulty.  
           [0021]    An advantage of at the least the preferred embodiments of the device and system of the present invention is the risk of limb ischaemia associated with conventional IABP systems is avoided because there is no blood contact with the implanted device—particularly as there is no catheter placed in a small lumen vessel—vessel size is an independent risk factor for limb ischemia using IABP. Patient ambulation is also possible. Additionally, the implantation technique used for the device of the invention is less invasive than those required for other devices. In particular, compared to the arrangement taught in U.S. Pat. No. 4,583,523, the device of the present invention provides a better outcome in term of reduced risk of infection, cosmesis and ease of implant and explant. Another advantage of at the least the preferred embodiments of the device and system of the present invention is that there is little risk to the patient in the event of the device failure. A gas leak may cause a pneumothorax, but would not cause intravascular gas embolism as is known with IABPs. The preferred embodiments of device also have the significant advantage of being able to be weaned and turned off in the event of cardiac recovery. This is not possible with known implantable heart assist devices such as LVADs. If the heart shows signs of recovery, the device can be retrieved by remotely releasing the compressing means and withdrawing the device. However, if the heart shows signs of relapsing back into failure, the device can be switched back on.  
           [0022]    The compressing means of the device of the present invention preferably includes an inflatable cuff or one or more preshaped balloons for positioning against or around a portion of the aorta or for wrapping around a portion of the aorta. Preferably, the balloon(s)/cuff is/are configured longitudinally to fit the curve of the ascending aorta. In a particularly preferred form of the device of the present invention, the cross-section of the balloon(s)/cuff is/are C-shaped, allowing wrapping of the balloon(s)/cuff, preferably with some overlap, around the aorta. In one embodiment of the invention the balloon(s)/cuff is/are shaped such that they concentrically compresses the length of enclosed aorta and spread the compression forces evenly, thereby reducing any wear or fatigue on any one part of the aorta. Alternatively, the balloon(s)/cuff can inflate assymetrically about the aorta. The balloon(s)/cuff is/are enclosed within a flexible and non-elastic outer sleeve wrap or sheath. The sleeve has an elongated “tongue” on one arm of the C-shaped balloon(s)/cuff that is passed around the aorta to be secured by suturing or other means on the outer aspect of the arm of the C-arm to which the wrap is secured, by sutures, staples, or the like. The release mechanism may be part of the securing means or separate from the securing means. Furthermore, the preshaped balloon(s)/cuff and flexible sleeve are particularly designed to create a snug fit and low profile on the aorta, to reduce damage to the aorta and surrounding structures, and to create maximum efficiency of the device.  
           [0023]    The balloon(s)/cuff is/are preferably made from a very thin synthetic plastics material desirably having an inner wall that is elastic or inelastic. If the inner is inelastic, it is preferably so shaped that it can be moved inwardly as the balloon(s)/cuff is/are inflated. The outer wall of the balloon(s)/cuff is/are preferably inelastic. If the wrap extends around the whole balloon(s)/cuff the outer wall could be made of an elastic material. In a further alternative, outfolds or extensions of the inelastic outer wall are used to achieve the wrap without the need for a separate wrap material. In one preferred form, the elastic materials in which the balloon(s)/cuff is/are made include silicones. Relatively inelastic or inelastic plastics (at the operating pressures) in which the balloon(s)/cuff is/are made include polyurethanes, co-polymers of silicones and urethanes, PET and PTFE.  
           [0024]    The balloon(s)/cuff are preferably connected to a catheter which extends out of the body and which is adapted for carrying the inflating fluid into and out of the balloon(s)/cuff. The fluid is preferably a gas, most preferably helium. The catheter is preferably also used to withdraw the balloon(s)/cuff from the patient and is connected to the balloon(s)/cuff sufficiently securely that the force of withdrawal will not detach the catheter from the balloon(s)/cuff.  
           [0025]    In preferred forms, the wrap extends around the whole balloon(s)/cuff and is connected onto itself, or connected to the balloon(s)/cuff at each end, or extends only across the gap between the ends of the balloon(s)/cuff. In the latter case, the wrap is connected at each end to, or integral with, the balloon(s)/cuff.  
           [0026]    In other preferred forms, the wrap is separate from the balloon(s)/cuff, or integral with the balloon(s)/cuff.  
           [0027]    The wrap is desirably as thin and flexible as possible but also sufficiently inelastic so as to not stretch when the balloon(s)/cuff is/are inflated. The wrap is preferably formed of a woven dacron material such as “Twillweave”(regd. Trade Mark) or from a sheet of synthetic plastics film. Suitable synthetic plastics include PET, PTFE and polyurethanes. If the wrap is formed of a woven dacron it is desirably coated in a smooth and low friction plastics material such as PTFE. In another form, the wrap is made of a memory shape plastic, and when it is desired to remove the wrap it is heated or cooled slightly to cause it to shrink into a more compact form.  
           [0028]    The means to secure the ends of the wrap together can be the same means as are involved in the release of the wrap or may be separate from the release means. The securing means preferably comprises a row of suture stitches made by the surgeon when placing the device in the patient. These stitches being placed between the ends of the wrap or between one end of the wrap and a part of the balloon. Stitches allow the surgeon to easily place the cuff with the required tightness around the aorta, some of the other possible securement arrangements may not provide this flexibility. As an alternative to stitches, the securing means can be: an adhesive patch on the wrap which can stick onto a corresponding part of the wrap or the balloon(s)/cuff, the adhesive patch can optionally be covered with a “peel off” strip until used; a sliding clasp fastener; or one or more “bundle tie” type ratchet connectors. Alternatively, an end of the wrap can be sutured, or otherwise connected, to a release thread extending down the catheter, which thread is connected to the balloon(s)/cuff. The two ends of the wrap, or one end of the wrap and one part of the balloon(s)/cuff, being provided with hooks or holes through which a thread can be laced and drawn tight.  
           [0029]    The release mechanism is preferably: a wire which extends down the catheter and may be pulled to release one end of the wrap; a thread extending down the catheter to which one end of the wrap is connected which can be released, an advantage of this arrangement is that the wrap can be tightened or loosened around the aorta during the operation or while it is in place on the patient post operation; a thread extending down the catheter and connected to a sliding clasp connector which can be pulled to release the sliding clasp connector; a thread extending down the catheter and connected to a knife blade positioned relative to sutures or other connecting means so that pulling of the thread causes the knife blade to sever the sutures; an electric wire embedded in the wrap so that passage of a brief electric current along the wire will fuse or melt the connection.  
           [0030]    The release mechanism is preferably adapted such that, after release, the wrap is drawn into a tube adjacent to the catheter, thereby assisting the withdrawal of the device from the patient.  
           [0031]    The placement of the device is typically during an upper mid-line stemotomy. The balloon(s)/cuff is placed around the aorta and the catheter placed to extend transcutaneously. The catheter can be extended downwardly from the aorta and emerge from the patient between the ribs or below the costal margin on the right or left hand side of the patient or extended upwardly to emerge in the region of the supra sternal notch. The device can also be placed thoracoscopically via thoracic ports in the right and/or left chest.  
           [0032]    The removal of the device is effected by releasing the release mechanism and gently withdrawing the balloon(s)/cuff from the patient. If desired, a trocar, possibly with an expandable conical proximal end, is slid down the catheter to assist in the withdrawal of the balloon(s)/cuff through the skin. The trocar being slid down the catheter until it is inside the chest cavity, thereafter its conical end is expanded to form a funnel into which the balloon(s)/cuff is/are drawnIf present the conical end can then be collapsed to compress the cuff. It may be also desirable to actively deflate the balloon to reduce it to the smallest possible cross sectional size. The balloon(s)/cuff can also be formed with fluoroscopic markers so that the removal procedure may be performed under real time fluoroscopy. This alerts the surgeon to any problems which might cause him/her to leave the balloon(s)/cuff in place in the patient or to perform minor surgery to remove the cuff. The physical separation of the balloon(s)/cuff from the aorta and any tissue which has grown around the device is assisted by inflating the balloon(s)/cuff after the wrap has been released from around the aorta.  
           [0033]    In a preferred form of the invention, the device is adapted for compression of the ascending aorta. An upper mid-line stemotomy provides easy surgical access to the ascending aorta and has the further advantage of not being very painful for the patient. A minimum incision is required in this procedure alternatively the device may be placed by minimally invasive surgery between the ribs.  
           [0034]    The cuff has a single inlet/outlet port for the passage of fluid to inflate/deflate the cuff. The fluid used is preferably gas, such as air or helium. The port and connecting tube to the motive means is of sufficient diameter and length to allow rapid emptying and filling of the cuff without generating too high compression pressures. In a preferred mode of use of the device of the invention, the compressing means is preferably adapted to squeeze approximately 15-25 ml of blood form the ascending aorta in each compression cycle. The fluid preferably moves within 0.15 sec for effective counterpulsation action. The compressive force emptying the cuff is the force exerted by the compressed aorta. This is approximately 100 mmHg. A tube lumen of approximately 0.5 cm with a length of 20-30 cm allows 25 ml gas to pass down a gradient of 100 mm Hg in less than 0.15 sec. The compressive force filling the cuff is generated by the motive means, and this pressure gradient is approximately the same (ie the motive means generates approximately 200 mmHg) to allow the fluid to shift into the cuff in less than 0.15 sec.  
           [0035]    The port preferably has a trumpet-shaped or flanged opening into the cuff to spread the fluid more evenly into the cuff during inflation and to assist more rapid deflation. The trumpet shaped port also results in a tapered exterior surface of the cuff which facilitates removal of the device percutaneously via a small incision in the chest wall. A diffuser can also mount within the lumen of the port to reduce the fluid force on the balloon cuff during inflation.  
           [0036]    The motive means of the device of the invention can be any means that is capable of cyclically compressing and decompressing the fluid sac. The motive means can include or be associated with means for detecting speed and completeness of cuff filling and emptying, and of monitoring the fluid pressure within the connector tube, means for measuring arterial blood pressure or flow. The motive means can also act to record the ECG. An example of a suitable motive means is the Datascope 97 IABP console or the Arrow ACAT console. The cuff may also have holes or slits to accommodate coronary artery bypass grafts to the ascending aorta. Alternatively, grafts can be positioned distal or proximal to the cuff.  
           [0037]    In yet a further aspect, the present invention provides a method for improving blood circulation in a subject, the method including the steps of: implanting a device in accordance with the earlier aspects of the invention fully within the thoracic cavity of a subject; actuating the compressing means periodically in synchrony with the diastole period to compress the aorta; and alternating the period of actuation with periods of deactivation of the compressing means thereby allowing the aorta to return to its uncompressed shape.  
           [0038]    The method and device of the invention advantageously allows relief/recovery from heart failure whilst allowing the patient to move around freely, for unlimited periods of time and without the risk of limb complications while allowing the device to be removed easily should that de required or desired. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]    Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which:  
         [0040]    [0040]FIG. 1 is a perspective view of a first embodiment of an implantable device according to the invention positioned around the ascending aorta (release mechanism not shown);  
         [0041]    [0041]FIG. 2 is a side view of the device shown in FIG. 1 (release mechanism not shown):  
         [0042]    [0042]FIG. 3 is a cross-sectional view of the device shown in FIG. 2 along line  3 - 3 .  
         [0043]    [0043]FIG. 4 is a partial perspective view of a first embodiment of a release mechanism (in a close position) suitable for use in embodiments of implantable devices according to the invention;  
         [0044]    [0044]FIG. 5 is a partial perspective view of the mechanism shown in FIG. 4 (in a released position);  
         [0045]    [0045]FIG. 6 is a side view of a second embodiment of an implantable device according to the invention;  
         [0046]    [0046]FIG. 7 is an end view of the device shown in FIG. 6;  
         [0047]    [0047]FIG. 8 is a side view of a third embodiment of an implantable device according to the invention;  
         [0048]    [0048]FIG. 9 is an end view of the device shown in FIG. 8;  
         [0049]    [0049]FIG. 10 is a side view of a balloon used in the device shown in FIG. 8;  
         [0050]    [0050]FIG. 11 is an end view of the balloon shown in FIG. 10;  
         [0051]    [0051]FIG. 12 is a side view of a fourth embodiment of an implantable device according to the invention;  
         [0052]    [0052]FIG. 13 is a further side view of the device shown in FIG. 12;  
         [0053]    [0053]FIG. 14 is an opposite side view to that of FIG. 13 of the device shown in FIG. 12;  
         [0054]    [0054]FIG. 15 is a side view of an embodiment of a balloon suitable for use in implantable devices according to the invention;  
         [0055]    [0055]FIG. 16 is an end view of the device shown in FIG. 15;  
         [0056]    [0056]FIG. 17 a side view of another embodiment of a balloon suitable for use in implantable devices according to the invention;  
         [0057]    [0057]FIG. 18 is an end view of the device shown in FIG. 17;  
         [0058]    [0058]FIG. 19 is a side view of yet another embodiment of a balloon suitable for use in implantable devices according to the invention;  
         [0059]    [0059]FIG. 20 is an end view of the device shown in FIG. 19; and  
         [0060]    [0060]FIG. 21 is a side view of a yet further embodiment of a balloon suitable for use in implantable devices according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0061]    [0061]FIG. 1 shows a schematic perspective view of a first embodiment of a heart assist device  10  in accordance with the invention. The device  10  is suitable for implantation in the thoracic cavity of a patent adjacent the ascending portion of the aorta  12 , as shown. The device  10  includes a flexible hollow inflatable cuff  14  and a percutaneous gas line  16 . The cuff  14  is curved along its length so as to substantially replicate the curve of the aorta  12  adjacent thereto. The cuff has two free ends  18  (only one shown) which are adapted to overlap when the cuff  14  is placed around the aorta  12 .  
         [0062]    As is shown in FIGS. 1 and 2, the cuff  14  is retained adjacent the aorta  12  after implantation by suturing the two free ends together at  20 . A more detailed description of the cuff, its method of implantation and its method of use can be found in the applicant&#39;s above noted international PCT patent application, the relevant portions of which are incorporated herein by cross-reference.  
         [0063]    As best shown in FIG. 2, the gas line  16  exits the body viz a (minor) incision  21  through the skin  22  near the 5 th  anterior intercostal space the cuff  14  is activated (ie. inflated) and deactivated (ie. deflated) in counterpulsation with the heart by the gas line  16  being connected to an external portable IABP console, for example that known as the Datascope 97 (Datascope is a registered trade mark).  
         [0064]    [0064]FIG. 2 also shows a release mechanism in the form of percutaneous line  24  which, when pulled from outside of the patent&#39;s body, in the direction of arrow  26 , removes the sutures  20  securing the two free ends  18  of the cuff  14 , thereby releasing the cuff  14  from engagement from the aorta  12 . Further pulling of the line  24 , again in the direction of arrow  26 , withdraws the device  10  from the patient viz the incision  21 .  
         [0065]    [0065]FIG. 3 shows another embodiment of a heart assist device  10  which is retained adjacent the aorta  12  by a substantially inelastic flexible sheath  28  placed around the cuff  14  and held in place by having the ends of the sheath sutured together by sutures. A more detailed description of the sheath, its method of implantation and its method of use is also found in the Applicant&#39;s above noted international PCT application, the relevant portions of which are incorporated herein by cross-reference. In this embodiment, the release line  24  is adapted to release connectors on two adjacent portions of the sheath  28 , thereby releasing the sheath  28  from around the cuff  14  and disengaging the cuff  14  from the aorta  12 . Again further pulling of the line  24  withdraws the sheath  28  and cuff  14  through a small incision in the patient. In this embodiment of the invention the connectors are separated from the sutures. A different mechanism is thus used to hold the ends of the sheath  28  together as compared with that used to release the sheath  28  from about the aorta  12 .  
         [0066]    [0066]FIGS. 4 and 5 show in detail a release mechanism  30  that is preferably incorporated into the sheath  28  and which is suitable for use in the embodiment of the invention shown in FIG. 3. The mechanism  30  has opposed ends  32  and  34  that are provided with complimentary spaced apart members  36  and  37 . The seven uppermost member members  36  have a plain hole therein. The lower most member  37  has a threaded hole therein which is adapted to engage with a threaded grub screw  38  provided on the end of semi rigid release line  40 . By being semi rigid, the release line  40  is able to bend along its longitudinal axis but not twist about its longitudinal axis when a rotational force is applied to one end. In this way, rotation of the end of the line  40  external the patient causes corresponding rotation of the other end of the line  40  containing the grub screw  38 . It is to be noted that in another embodiment of the invention the mechanism  30  may be used instead of the sutures  20  and serve both the purpose of connecting the ends of the sheath  28  as well as releasing them.  
         [0067]    In use, the sheet  30  is positioned around the cuff and the members  36  brought together to the position shown in FIG. 4. The grub screw  38  is passed through all of the members  36  and then screwed into engagement with the member  37 . When the cuff  14  is to be removed, the line  40  is twisted, as indicated by arrow  42 , until the grub screw  38  is free from engagement with the member  37 , as indicated by arrow  44  to release the sheath  28  from around the cuff  14 , and the cuff  14  from securement around the aorta  12 .  
         [0068]    Other embodiments of release mechanism (not shown) for the cuff or sheath include remotely actuated zipping mechanisms; metal wires with an end which can be heated to melt the cuff or sheath or the sutures, captive blades which may be drawn through the cuff or sheath, releaseable stitching, releaseable clips or VELCRO™ having a release force higher than the forces generated by inflation of the cuff but lower than the force necessary to damage to aorta.  
         [0069]    [0069]FIGS. 6 and 7 show a second embodiment of a heart assist device  50  in accordance with the invention. The device  50  is again suitable for implantation in the thoracic cavity of a patient adjacent the ascending portion of the aorta. The device  50  includes a hollow inflatable balloon  52  and a percutaneous gas line  54  connected to a gas duct  56 . The device  50  also includes a short wrap  58  which extends across the gap between the ends of the balloon  52 . One end  58   a  of the wrap  58  is permanently adhered to the outer surface of the balloon  52  adjacent one of its ends. The other end  58   b  of the wrap  58  has an adhesive patch which is caused to adhere to the other end of the balloon  52  after the device  50  is placed around the aorta of a patient. A releasable join  60  is formed intermediate the ends of the wrap  58  with a series of small open-ended, transversely extending pockets  62 , which interdigitate. A wire  64  extends down a tube  65  and through the aligned and interdigitated pockets  60  to prevent the two parts of the wrap  58  from being separated. When the wire  64  is withdrawn, preferably extracorporeally in a similar manner to that described in relation to the release mechanism  30 , the two parts of the wrap  58  separate allowing the device  50  to be withdrawn from the patient or, alternatively, left in the patient in an inactive state.  
         [0070]    [0070]FIGS. 8 and 9 show a third embodiment of a heart assist device  70  in accordance with the invention. The device  70  is also suitable for implantation in the thoracic cavity of a patient adjacent to the ascending portion of the aorta. FIGS. 10 and 11 show, in isolation, a balloon  72  used in the device  70 . A catheter  76  is connected to the balloon  72 , which has a circular cross section when inflated (see solid lines) and an arcuate one when deflated (see phantom lines). A separate wrap is provided in two parts  74  and  78 , which is made of a thin non-elastic synthetic plastics material. A tube  80  is positioned along the mid-line of the wrap part  78  which extends beyond the wrap part  78  and through the skin of the patient alongside the catheter. A doubled over thread  82  extends down the tube  80  and the mid-point loop  84  of the thread  82  projects through a hole  86  in the tube  80 . To implant, the balloon  72  is positioned on the aorta and the wrap  74 ,  78  placed over it and the free end of the wrap part  78  is loosely sutured to the loop in the thread. To remove, one end of the thread  82  is withdrawn from the tube  80 . This releases the free end of the wrap part  78 . The balloon  72  is then inflated to urge the wrap  74 ,  78  off the aorta. The balloon  72  is then deflated and withdrawn. The wrap  74 ,  78  is then withdrawn separately.  
         [0071]    FIGS.  12  to  14  show a fourth embodiment of a heart assist device  90  in accordance with the invention. In this embodiment, a balloon  92  is provided with a catheter (not shown) which has a dual lumen  96   a  and  96   b . The lumen  96   a  conveys gas to the balloon  92  while the other lumen  96   b  carries both a wire  98  and a looped thread  100 . The wire  98  extends down the catheter to its proximal end and projects through a transverse open end pocket  102  in one end of a wrap  104 . The wire  98  holds the wrap  104  releasively connected to the balloon  92 . The thread  100  projects from an aperture  108  in the lumen  96   b  and is sutured to a free end of the wrap  104 . To remove the device  90 , the wire  98  is withdrawn which released an end of the wrap  104  from the balloon  92 . The thread  100  is then pulled, which draws the wrap  104  in to the lumen  96   b  of the catheter. The balloon  92  and the wrap  104  can then be withdrawn through the patient as described in relation to earlier embodiments.  
         [0072]    [0072]FIGS. 15 and 16, FIGS. 17 and 18, FIGS. 19 and 20 and FIG. 21 respectively show embodiments of balloons suitable for use in embodiments of heart assist devices according to the invention.  
         [0073]    [0073]FIGS. 15 and 16 show an essentially cylindrical balloon  110 , which is depicted deflated in solid lines and inflated in phantom lines. FIGS. 17 and 18 show a balloon  120  having an essentially arcuate cross section, similar to that used in the heart assist device  50 . FIGS. 19 and 20 show an arrangement of smaller individual balloons  130  spread around the aorta and all lying in alignment with the aorta. FIG. 21 shows a single balloon  140  which includes a number of smaller balloon segments  142  therein, which are separated by non-inflated portions  144 . The segments  142  extend along the aorta. In a varaition of this embodiment (not shown), the segments  142  extend around the aorta.  
         [0074]    It will be appreciated that the shape and number of balloons affects the way in which the aorta is compressed. If a single circular balloon is used then the aorta will be compressed from only one side. If the balloon encircles the aorta then the aorta will be inwardly compressed about its whole circumference. To be effective, the balloon is configured to preferably displace from 10-30 ml, more preferably 15-20 ml of blood from the aorta of an adult human.  
         [0075]    The heart assist devices described above can be implanted during surgery only for this purpose. However, a particular advantage of the disclosed devices is that they can be quickly and easily temporarily installed around the patient&#39;s aorta whilst the patient is undergoing surgery for other reasons and then removed as described above without the need for any further surgery to take place. This allows two surgical operations to be avoided.  
         [0076]    The device also allows the patient to abulate and there is no risk of leg ischaemia. If connected to a fixed motive means (eg. the Datascope 97 IABP console) then the patient&#39;s mobility is limited by the percutaneous line. However, this limitation is overcome by use of a portable, miniaturised motive means (eg. a belt mounted, battery powered device).  
         [0077]    The present invention is suitable for short and/or long term treatment for heart failure and/or myocardial ischaemia. The present invention can also provide a suitable bridging device for patient&#39;s awaiting heart transplantation.  
         [0078]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, although the invention has been described in specific reference to compression of the aorta, the devices, systems and methods of the present invention can equally be used for the compression of the pulmonary artery to effectively act as a right ventrical assist device, and the present invention extends to this alternative aspect. Further, the invention extends to all types of devices able to extracorporeally release a cuff or sheath from around the aorta. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.