Abstract:
A heart assist device in which an inflatable balloon or chamber is held against an outside surface of a curved arterial vessel by a wrap ( 20 ) formed from a flexible sheet-like material. The wrap ( 20 ) having a first end portion ( 22 ), a second end portion ( 30 ) and an intermediate portion ( 26 ) connecting together the first and second end portions ( 22, 30 ). The intermediate portion ( 26 ) comprising at least three separate elongate sections ( 26   a - c ) arranged in side by side array each connected at each end to a respective one of the end portions ( 22, 30 ) of the wrap ( 20 ). The improvement in that the laterally outer ones ( 26   a,b ) of the elongate sections are longer than the central one ( 26   c ) of them. As a result, if the wrap ( 20 ) was laid on a planar surface, the central ( 26   c ) one of the elongate sections would lie substantially in that plane and the laterally outer ones ( 26   a,b ) of the elongate sections would, intermediate their ends, project above that plane.

Description:
TECHNICAL FIELD 
     The present invention relates to an improved wrap generally for a heart assist device and, more particularly, for a counterpulsation heart assist device. 
     The invention has been developed as an improvement over the type of wrap disclosed in the Applicant&#39;s International Patent Application No. PCT/AU2004/001484 (WO 2005/041783), hereafter “the wrap PCT application”, and for use with the type of balloon actuators disclosed in the Applicant&#39;s International PCT Patent Application No. PCT/AU2004/001487 (WO 2005/044338), hereafter “the actuator PCT application”. However, it will be appreciated that the improved wrap is also suitable for use with other heart assist devices that use inflatable actuators. 
     BACKGROUND OF THE INVENTION 
     The wrap disclosed in the wrap PCT application is formed from an elongate piece of woven polyester (or similar non-absorbable bio-stable and bio-compatible material). When laid on a planar surface, the wrap is substantially flat or planar. The wrap includes an opening for a fluid tube to be connected to the inflatable balloon or chamber of a heart assist device. The wrap also includes a thinned portion with a pair of curved longitudinal slits which assist in preventing the wrap from kinking, folding or pleating in the thinned portion when wrapped around a curved portion of an aorta. 
     Parts of the side of the wrap disclosed in the wrap PCT application have a series of spaced apart slits, which are substantially normal to the longitudinal axis of the wrap. The purpose of the slits is to make those parts of the wrap sides more elastic or stretchable than the intermediate central portion of the wrap. As a result, when the wrap disclosed in the wrap PCT application is placed around a curved arterial vessel, such as an ascending aorta, and tightened to a snug fit, less tension is placed in the sides or edges of the wrap than in the centre. This avoids the depression/kinking, and associated high strain levels, associated with earlier wraps without such slits. 
     OBJECT OF THE INVENTION 
     It is an object of the present invention to provide an improved wrap compared to that disclosed in the wrap PCT application, and in a preferred form, a wrap that provides a better anatomical fit around the actuator of a heart assist device and the aorta or other arterial vessel to which it is applied. 
     SUMMARY OF THE INVENTION 
     Accordingly, in a first aspect, the present invention provides, in a heart assist device in which an inflatable balloon or chamber is held against an outside surface of a curved arterial vessel by a wrap formed from a flexible sheet-like material, the wrap having a first end portion, a second end portion and an intermediate portion connecting together the first and second end portions, the intermediate portion comprising at least three separate elongate sections arranged in side by side array each connected at each end to a respective one of the end portions of the wrap, the improvement in that the laterally outer ones of the elongate sections are longer than the central one of them. 
     As a result, if a wrap according to the first aspect of the invention defined above was laid on a planar surface, a central one of the elongate sections would lie substantially in that plane and the laterally outer ones of the elongate sections would, intermediate their ends, project above that plane. 
     In a second aspect, the present invention provides, in a heart assist device in which an inflatable balloon or chamber is held against an outside surface of a curved arterial vessel by a wrap formed from a flexible sheet-like material, the wrap having an inside surface and an outside surface and having a first end portion, a second end portion and an intermediate portion connecting together the first and second end portions, the intermediate portion comprising at least three separate elongate sections arranged in side by side array each connected at each end to a respective one of the end portions of the wrap, the improvement in that the laterally outer ones of the elongate sections are longer than the central one of them. 
     Preferably, the laterally outer edges of the elongate sections are longer than the laterally inner edges of the respective elongate sections. If such a wrap were laid on a planar surface the outer edges of each outer elongate section would project above that surface more than the corresponding inner edge. 
     It is also preferable that the three elongate sections each have a longitudinal axis and the axes of the two laterally outer elongate sections diverge from one another and from the central elongate section along their length from the intermediate portion to each end portion. 
     In a third aspect, the present invention provides, in a heart assist device in which an inflatable balloon or chamber is held against an outside surface of a curved arterial vessel by a wrap formed from a flexible sheet-like material, the improvement whereby if the wrap were laid on a planar surface it would include a dome-like portion extending away from that surface. 
     The dome-like shape is preferably at least partially formed by heat setting of the sheet-like material adjacent an end of the wrap, most preferably by heat setting between corresponding convexly and concavely shaped mould surfaces. The dome-like shape is preferably at least partially formed by removing substantially triangular sections of the to material and then joining edges of the material the adjacent removed portions, most preferably joining by gluing and/or suturing. 
     In a fourth aspect, the present invention provides an improved wrap for a heart assist device, 
     the heart assist device includes an inflatable balloon or chamber adapted for placement against a curved arterial vessel, 
     the wrap being of flexible, substantially non-elastic construction and adapted to, when encircling the balloon/chamber and the arterial vessel to locate the balloon/chamber against the artery at a tension lower than would substantially deform the vessel, adopt a shape substantially conforming to the exterior surfaces of the inflated balloon/chamber and arterial vessel in contact with the wrap. 
     The arterial vessel is preferably curved in two planes and the wrap substantially conforms to the two plane curvature. 
     The wrap is preferably a fabric weave and has some elastic properties due to it being cut on the bias, most preferably at 45 degrees to the warp/weft of the fabric weave. 
     The wrap preferably adopts said shape substantially conforming to the exterior surface of the balloon/chamber and artery substantially without wrinkles or folds. 
     The wrap preferably includes one or more cutouts and/or overlapping portions configured to allow it to substantially conform, in use, to the exterior surface of the balloon/chamber and arterial vessel. The wrap is preferably shaped to substantially conform, in use, to the exterior surface of the balloon/chamber and a curved arterial vessel. The wrap is preferably shaped to substantially conform, in use, to the exterior surface of the balloon/chamber and the ascending aorta, most preferably with the balloon/chamber positioned on the outer, convex side of the ascending aorta. 
     The wrap is preferably generally elongate with two sides and two ends, and includes: a relatively wide suture tab at one of the ends; and a relatively narrow pull tab on the other of its ends. The wrap preferably includes: a first relatively wide portion adjacent the suture tab, adapted to conform to the surface of the balloon/chamber remote the arterial vessel; a second relatively wide portion adjacent the pull tab, adapted to conform to the surface of the arterial vessel substantially adjacent the balloon/chamber; and a relatively narrow portion between the first and second relatively wide portions, adapted to conform to the surface of the arterial vessel not in contact with the balloon/chamber. 
     The first relatively wide portion and the relatively narrow portion preferably include spaced apart slits along their outer sides or edges. 
     The wrap preferably includes a buckle initially positioned on the suture tab, the buckle being adapted to receive therethrough the relatively narrow pull tab during positioning of the wrap and balloon/chamber around the arterial vessel. 
     The pull tab is preferably formed from two layers of the wrap material, most preferably from two layers of a single piece of wrap material that are folded and bonded to one another. 
     The heart assist device preferably includes a fluid inlet/outlet port and the wrap preferably includes a port opening. The port opening is preferably surrounded by a substantially domed surface, most preferably a truncated, ovular domed surface, that tapers outwardly away from the port opening. The port opening is preferably in the first relatively wide section of the wrap. Preferably, the domed surface has one edge longer than the other and a central axis that is concave towards the suture tab. 
     The wrap preferably includes two substantially longitudinal, curved cutouts in the relatively narrow portion between the first and second relatively wide portions. 
     In a fifth aspect, the present invention provides a method of forming an improved wrap for a heart assist device, 
     the heart assist device includes an inflatable balloon or chamber adapted for placement against a curved arterial vessel, 
     the method including forming a flexible, substantially non-elastic material into a shape that, when the wrap is positioned encircling the balloon/chamber and the arterial vessel to locate the balloon/chamber against the arterial vessel at a tension lower than would substantially deform the vessel, substantially conforms to the exterior surfaces of the inflated balloon/chamber and the arterial vessel in contact with the wrap. 
     The method preferably includes forming one or more cutouts and/or overlapping portions in the wrap, such cutouts/portions being configured to allow the wrap to substantially conform to the exterior surface of the balloon/chamber and artery, most preferably without wrinkles or folds. 
     The heart assist device preferably includes a fluid inlet/outlet port and the method preferably includes forming a port opening in the wrap that is surrounded by a substantially domed surface, most preferably a truncated, ovular domed surface, that tapers outwardly away from the port opening. 
     In a sixth aspect, the present invention provides an improved wrap for a heart assist device, 
     the heart assist device includes an inflatable balloon or chamber adapted for placement against a curved arterial vessel, 
     the wrap being of flexible, substantially non-elastic construction which, when developed along its longitudinal direction, includes a substantially domed surface. 
     The domed surface is preferably in the form of a truncated, ovular domed surface that tapers inwardly away from the remainder of the wrap. The domed surface preferably includes a fluid inlet/outlet port opening therein, most preferably at the apex of the dome. The domed surface is preferably formed in a relatively wide portion of the wrap. 
     The wrap preferably also includes a suture tab adjacent one side of the domed surface. 
     The wrap preferably also includes a relatively narrow portion with longitudinally extending, curved slits therein, on the other side of the domed surface. In the relatively narrow portion, the wrap material that is between the side of the wrap and the slits is preferably longer in the longitudinal direction than the wrap material between the two slits. 
     The wrap preferably includes a further relatively wide portion adjacent the side of the relatively narrow portion that is remote the domed surface. The wrap preferably also includes a pull tab adjacent the further relatively wide section, with the pull tab forming one end of the wrap and the suture tab forming the other end of the wrap. 
     In a particularly preferred embodiment of the invention the wrap is cut from a single piece of a flexible sheet-like material at a 45 degree bias. A blank is preferably cut from the sheet-like material including a first end portion, a second end portion and an intermediate portion comprising at least three separate elongate sections arranged in side by side array with at least the central one of those elongate sections connecting the first and second end portions and the laterally outer ones of the elongate sections being only connected to an end portion at one of their ends. In addition the blank preferably includes at least one extension piece that can be folded back over an end portion and connected the free end of at least one of the laterally outer elongate sections so that the length of that laterally outer elongate section is longer than the central one of the elongate sections. 
    
    
     
       BRIEF. DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of an example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a developed plan view of an embodiment of an improved wrap; 
         FIG. 2  is a plan view of a cutting template for the wrap shown in  FIG. 1  atop a piece of wrap material; 
         FIG. 3  is an enlarged detail view of the pull tab end of the wrap shown in  FIG. 1  prior to adhesive bonding; 
         FIG. 4  is a plan view of an adhesive template atop the cut piece of fabric used to form the wrap shown in  FIG. 1 ; 
         FIG. 5  is a perspective view of the wrap of  FIG. 1  with one end undergoing gluing and clamping; 
         FIG. 6  is a plan view of the wrap shown in  FIG. 1  upon removal from an adhesive clamp; 
         FIG. 7  is a partial detail view of the wrap shown in  FIG. 1  beneath an adhesive template; 
         FIG. 8  is an enlarged detailed view of the wrap/template shown in  FIG. 7  gluing operation; 
         FIG. 9  is a plan view of the wrap/template shown in  FIG. 8  subsequent to the gluing operation; 
         FIG. 10  shows the wrap of  FIG. 9  being clamped after the gluing operation; 
         FIG. 11  shows two views of the wrap of  FIG. 1  during suturing adjacent to fluid inlet/outlet port opening; 
         FIG. 12  shows the wrap of  FIG. 11  positioned in a clamp prior to a heat setting operation; 
         FIG. 13  shows the wrap of  FIG. 12  with adhesion locations highlighted; 
         FIG. 14  shows the wrap of  FIG. 13  after the gluing operation and adjacent the male part of an adhesive clamp; 
         FIG. 15  shows the wrap of  FIG. 14  during a clamping operation adjacent the fluid inlet/outlet port opening. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning firstly to  FIG. 1 , there is shown an embodiment of an improved wrap  20  for use with, for example, a heart assist device of the type shown in the actuator PCT application. The wrap  20  is formed from an elongate piece of woven polyester, or similar non-absorbable, bio-stable and bio-compatible material. In contrast to the wrap disclosed in the wrap PCT application, the wrap  20 , when developed or extended along its longitudinal direction (as shown), is not substantially planar but instead includes three dimensional portions which will be described in more detail below. 
     The wrap  20  is generally comprised of five portions namely: a relatively wide suture tab  22 ; a relatively wide domed portion  24 ; a relatively narrow slotted portion  26 ; a relatively wide planar section  28 ; and a pull tab  30 . The planar section  28  also acts as a suture tab as it mates with the tab  22  after encircling the vessel, which will be described in more detail below. 
     The suture tab  22  includes a buckle  32  at its proximal end. The buckle  32  is of the type shown in the Applicant&#39;s International PCT Patent Application No. PCT/AU2004/001488 (WO 2005/041781), hereafter “the buckle PCT application”. The buckle  32  receives the pull tab  30  therethrough during the implantation of a heart assist device, as is described in the buckle PCT application. The relevant contents of the buckle PCT application are incorporated herein by cross reference. 
     When the wrap  20  is laid on a planar surface, the domed surface  24  curves outwardly away from that plane. The domed surface  24  has a generally ovular cross-sectional shape and an inlet/outlet port opening  34  at its apex or geometric centre. The domed surface  24  tapers outwardly away from the opening  34  to the remainder of the wrap  20 . The fluid inlet/outlet tube of an actuator is positioned through the opening  34  prior to implantation of a heart assist device. The domed shape of the surface  24  substantially corresponds to the exterior shape of an inflated balloon/chamber type actuator, when implanted on an arterial vessel. The domed surface  24  also has a curvature to fit the secondary radius of the aorta. The steps included in forming of the domed surface  24  will be described in more detail below. 
     The portion  26  includes a pair of longitudinally extending curved openings or slits  36   a  and  36   b , similar to the slits  32  shown in the wrap PCT application. The slits  36   a  and  36   b  divide the portion  26  into three parts or strips, namely: two outer strips  26   a  and  26   b , which are between the side of the wrap  20  and each of the slits  36   a  and  36   b ; and also a central strip  26   c  which is between the slits  36   a  and  36   b . The laterally outer strips  26   a  and  26   b  are longer than the central strip  26   c . When the wrap  20  is laid on a planar surface, the central strip  26   c  lies substantially in that plane, whereas the laterally outer strips  26   a  and  26   b , being longer, project out of that plane. If the material of the wrap is is relatively stiff the outer strips  26   a  and  26   b  will curve upwardly out of the plane. If the material is softer and more flexible then the projection out of the plane will be more in the nature of crumpling of the material above the plane. Further, the laterally outer edges of the outer strips  26   a  and  26   b  curve, intermediate their ends, more upwardly out of that plane than the laterally inner edges of the outer strips  26   a  and  26   b . It is also to be noted that the longitudinal axes of the strips  26   a  and  26   b  diverge from one another, and from the central strip  26   c , as they extend from the central portion  26  (relatively narrow) to the planar portion  28  and domed portion  24 . 
     The strips  26   a  and  26   b  are longer than the strips  26   c  in the longitudinal direction of the wrap  20 . As a result, when the wrap  20  encircles a curved arterial vessel (e.g. an ascending aorta) with the slits  36   a ,  36   b  positioned against the inner concave surface of the vessel, at a tension lower than would substantially deform the vessel, the strips  26   a ,  26   b  and  26   c  gather together in a manner substantially conforming to the adjacent surface of the vessel without kinking or folding. Moreover, the strips  26   a ,  26   b  and  26   c  conform to the adjacent surfaces of the vessel more closely than the equivalent components of the wrap disclosed in the wrap PCT application, which all had a corresponding length in the longitudinal direction of the wrap. The different lengths of the strips  26   a ,  26   b  and  26   c  also allows for the maintenance of the same elastic properties at each location normal to the longitudinal axis of the vessel. The manufacture of the outer strips  26   a  and  26   b  shall be described in more detail below. 
     The pull tab  30  is formed from two layers of the wrap material, as opposed to the one layer that forms the remainder of the wrap  20 , in order to increase its rigidity. This makes the pull tab  30  easier to handle and position by a surgeon during implantation of a heart assist device. 
     The external edges or sides of the portions  24  and  26  include a series of spaced apart slits  38 . The slits  38  result in those parts of the sides of the wrap  20  being more elastic or stretchable than the intermediate central portion of the wrap  20 . As a result, when the wrap is placed around the aorta and tightened to a snug fit, less tension is placed in the sides or edges of the wrap  20  than in the centre. This avoids the depression/kinking, and associated high strain levels, associated with earlier wraps, as is discussed in the wrap PCT application. 
     The wrap  20  also includes two small slots  40  and  42  and a large slot  44 . The slots  40 ,  42  and  44  are used as location points during the manufacture of the wrap, as will be discussed in more detail below. Slot  44  is used for allis clamps or forceps during implant to allow the wrap to be tensioned using standard length surgical instruments. The slots  40  and  42  also provide areas to enable revascularization or improved blood supply under the wrap  20  when implanted. 
     The wrap  20  also includes one, two or three size identification markings, in the form of one or more dots  46  adjacent the pull tab  30 . One dot indicates a ‘small’ size wrap. Two dots indicate a ‘medium’ size wrap. Three dots indicate a ‘large’ size wrap. 
     The manufacture of the wrap  20  shall now be described with reference to  FIGS. 2 to 15 . All steps in the manufacture of the wrap  20  are performed in a controlled environment room (CER) with all of the operator&#39;s material and tools being cleaned to applicable standards. 
       FIG. 2  shows a stainless steel cutting template  50  adjacent a piece of wrap material  52 . The first stage in the production of the wrap  20  is to iron the wrap material  52 . The ironing is conducted at a linen/dry heat setting. The material  52  in the template&#39;s five central openings  54   a ,  54   b    54   c ,  54   d  (2 of) is then cut and removed in order to form the openings  34 ,  40 ,  42  and  44  respectively. The material  52  exterior to the wrap template  50  is then cut and removed. The material  52  is cut on its bias, at 45 degrees to the warp/weft of the fabric weave. This allows the warp and weft fibres to change angle relative to one another and therefore increase and decrease longitudinally when force is applied or removed, which improves the ability of the wrap  20  to conform to the aorta. The C shaped cut out  30   c  between the tail ends  30   b  ensures only a single layer of material is in the suturing region. This single layer also reduces the stiffness of the wrap when conforming to the aorta. 
     With reference to  FIG. 3 , the right hand end of the wrap material  52  is folded over itself to align the two openings  54   d  that form the large slot  44  in order to form the pull tab  30 . The fold at the distal end of the pull tab  30  is then ironed with tail ends  30   b  aligned with the ends of the slits  36  to create a smooth transition between these parts. This folding also provides a portion for attaching the adjacent ends of the strips  26   a  and  26   b , as will be described in more detail below, whilst also conveniently permitting the wrap  20  to be produced from a single piece of material. 
     As shown in  FIG. 4 , the folded wrap material  52  is then positioned under an adhesive template  56 . The template  56  includes alignment holes  58  and  60 . The alignment hole  58  is aligned with the small slot  40 . The alignment hole  60  is aligned with the size identification markings  46 . The holes  58 ,  60  thus provide references to enable the wrap material to be accurately positioned in relation to the template  56  and ensure the correct size template is used. The exposed edge of the wrap material  52  is then traced with adhesive in the three locations indicated by arrows  62 . The template  62  is then removed and the wrap material  52  is folded to the position shown in  FIG. 3  and clamped under a load  64 , as shown in  FIG. 5 , until the adhesive cures. The load  64  is then removed leaving the wrap material  52  shown in  FIG. 6 . 
       FIG. 7  shows the wrap material of  FIG. 6  clamped beneath an adhesive template  66  (with the strips  26   a  and  26   b  folded out of the way towards the suture tab  22 ). The template  66  is aligned with the wrap material  52  at the three locations indicated by arrows  68 . Adhesive is then applied along the exposed edges  70  of the pull tab  30 . As shown in  FIG. 8 , the outer strips  26   a  and  26   b  then have their edges  72  positioned in contact with the adhesive  70 . The edge  72  is attached to the wrap material closer to the pull tab end of the wrap  20  compared to from where it was cut and on a 30 deg angle from it&#39;s original cut edge. This longitudinal repositioning results in the outer strips  26   a  and  26   b , intermediate their ends, curving away from the remainder of the wrap  20  when the wrap  20  is positioned on a flat surface. The edge  72  is also attached more outwardly than compared to from where it was cut. This lateral repositioning results in the laterally outer edges of the outer strips  26   a  and  26   b , intermediate their ends, curving away more from the remainder of the wrap  20  than the laterally inner edges of the outer strips  26   a  and  26   b . In addition, the laterally outer edge of strips  26   a  and  26   b  when positioned on edge  72  provide a straight section  28  with edges parallel to the central longitudinal axis of the wrap  20  providing suture region adjustable for within a defined range of vessel diameters 
     As shown in  FIG. 9 , an additional clamping template  74  is then positioned over the overlapping surfaces  70  and  72  being glued together. As best shown in  FIG. 10 , a load  76  (similar to the load  64 ) is then applied to the clamped surfaces until the adhesive has cured. 
     As shown in  FIG. 11 , the wrap material  52  has a substantially triangular section removed at  78  either side of the opening  34 . The edges  80  and  82  either side of the removed section are then overlapped, to form a slot at the edge, and initially held in this position by a suture  84  passing through location  86  and  88 . A similar procedure is performed on the opposite side of the wrap material  52 . This forms the basis for producing the domed surface  24 . 
     As shown in  FIG. 12 , the sutured wrap material  52  is then positioned within a mould  90  with an outwardly concave or female recess with an arc on its main axis corresponding in shape an inflated actuator for a heart assist device. The wrap material  52  adjacent the domed surface  24  is then heat shaped by applying a male outwardly convex dome to apply heat consistently across the surface, adding folds in the correct location and heat shaping the remainder. The heat is provided by an iron applied to the mould parts whilst they are clamped together. The ironing is conducted at a linen/dry heat setting for approximately 20 to 30 seconds. The overlapped material and the deformation caused by the moulding and the iron&#39;s heat produces the smooth domed surface  24 . 
     As shown in  FIG. 13 , the sutures  84  are then removed and the overlapped parts of the wrap material  52  are separated so that adhesive can be applied where indicated by arrows  92 . As shown in  FIG. 14 , the previously overlapped parts of the wrap material  52  are then repositioned in contact with one another and placed over a male mould part  94 . As shown in  FIG. 15 , a corresponding female mould part  96  is then used to clamp the overlapping surfaces until the adhesive cures. 
     The use of the wrap  20  in the implantation of a heart assist device is substantially identical to that descried in the buckle PCT application. The relevant contents of which are incorporated herein by cross reference. 
     The wrap  20  formed by the above process, will, when implanted encircling the balloon or chamber of a heart assist device and a curved arterial vessel (eg. the ascending aorta) at a tension lower than would substantially deform the vessel, will substantially conform to the adjacent exterior surfaces of the balloon, chamber and arterial vessel that are in contact with the wrap. More particularly, the wrap  20  will substantially conform to the exterior surface of the balloon, chamber and arterial vessel substantially without wrinkles or folds, whereby the application of force from actuation of the balloon/chamber will be effectively translated normal to the axis of the vessel at any location along the vessel. 
     Although the invention has been described with reference to a preferred embodiment, it will be appreciated that the invention is not limited to this particular embodiment and may be embodied in many other forms.