Abstract:
A transmyocardial implant includes a hollow conduit having a first portion and a second portion. The first portion is received within the lumen. The first portion has an axial dimension aligned with an axis of the vessel. The second portion is sized to extend from the vessel through the myocardium into the heart chamber. The conduit has open first and second ends on axial ends of respective ones of the first and second portions to define a blood flow pathway within an interior of the conduit between the first and second ends. A collar surrounds an exterior of the artery overlying the first portion at the first open end.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to an implant for passing blood flow directly between a chamber of the heart and a coronary vessel. More particularly, this invention pertains to such an implant with an enhanced design for avoiding damage to a vessel. 
     2. Description of the Prior Art 
     Commonly assigned U.S. Pat. No. 5,755,682 and PCT International Publication No. WO 98/06356 teach an implant for defining a blood flow pathway directly from a chamber of the heart to a lumen of a coronary vessel. An embodiment disclosed in the aforementioned patent and application teaches an L-shaped implant. The implant is a conduit having one leg sized to be received within a lumen of a coronary artery and a second leg sized to pass through the myocardium and extend into the left ventricle of the heart. As disclosed in the above-referenced patent and application, the conduit remains open for blood flow to pass through the conduit during both systole and diastole. The conduit penetrates into the left ventricle in order to prevent tissue growth and occlusions over an opening of the conduit. 
     Commonly assigned and co-pending U.S. patent application Ser. No. 08/944,313 filed Oct. 6, 1997, now U.S. Pat. No. 5,984,956, entitled “Transmyocardial Implant”, and filed in the name of inventors Katherine S. Tweden, Guy P. Vanney and Thomas L. Odland, teaches an implant such as that shown in the aforementioned &#39;356 application and &#39;682 patent with an enhanced fixation structure. The enhanced fixation structure includes a fabric surrounding at least a portion of the conduit to facilitate tissue growth on the exterior of the implant. 
     Implants such as those shown in the aforementioned patent and applications include a portion to be placed within a coronary vessel and a portion to be placed within the myocardium. When placing a portion of the implant in the coronary vessel, the vessel is incised a length sufficient to insert the implant. When placed within the coronary vessel, the implant discharges flow axially into the vessel. 
     When placing an implant, a portion of the coronary artery is dissected. The dissected portion is incised and the vessel portion of the implant is inserted into the lumen. A stay suture secures the artery to the implant. The stay suture is placed around the artery and vessel portion a distanced spaced from the open end of the vessel portion. 
     In a preferred embodiment, the implant is rigid. An artery is flexible. A pulsing and alternating flow of blood through the rigid implant and flexible vessel can result in relative movement between the implant and vessel. As a result of such movement, a rubbing action may occur with the implant causing cellular damage to the vessel. Such damage may proliferate resulting in a fibrotic response which grows to block the implant or artery. 
     SUMMARY OF THE INVENTION 
     According to a preferred embodiment of the present invention, a transmyocardial implant is disclosed for establishing a blood flow path through a myocardium between a heart chamber and a lumen of a coronary vessel residing on an exterior of the heart. The implant includes a hollow conduit having a first portion and a second portion. The first portion is received within the lumen. The first portion has an axial dimension aligned with an axis of the vessel. The second portion is sized to extend from the vessel through the myocardium into the heart chamber. The conduit has open first and second ends on axial ends of respective ones of the first and second portions to define a blood flow pathway within an interior of the conduit between the first and second ends. A collar surrounds an exterior of the artery overlying the first portion at the first open end. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a first embodiment of an implant and collar according to the present invention; 
     FIG. 2 is a cross-sectional view of the collar of FIG. 1; 
     FIG. 3 is a side cross-sectional view of the implant and collar of FIG. 1 following surgical placement; 
     FIG. 3A is an enlargement of a portion of the view of FIG. 3 showing an alternative embodiment with an extension with varying thickness; 
     FIG. 4 is a side elevation view of a second embodiment of an implant and collar according to the present invention; 
     FIG. 5 is a side cross-sectional view of the implant and collar of FIG. 4 secured to a coronary vessel; and 
     FIG. 6 is a perspective view of a third embodiment showing a vessel portion of an implant inserted within an artery and surrounded by a fabric collar. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to FIG. 1, a conduit  10  is shown in the form of an L-shaped rigid tube. The conduit  10  may be formed of titanium or other rigid biocompatible material such as pyrolytic carbon or may be titanium coated with pyrolytic carbon. The material of the conduit  10  is preferably a rigid material in order to withstand contraction forces of the myocardium. By way of example, the tube will have an outside diameter D O  of about 2.5 millimeters and an internal diameter D I  of about 2 millimeters to provide a wall thickness of about 0.25 millimeters. 
     The implant  10  has a first portion (or vessel end)  12  sized to be received within the lumen of a coronary vessel such as the lumen  80  of a coronary artery  82  illustrated in FIG.  3 . The conduit  10  has a second portion (or myocardium end)  14  extending at a right angle to the axis of portion  12 . The second portion  14  is sized to extend from the coronary artery  82  directly through the myocardium  84  and protrude into the left ventricle  86  of a patient&#39;s heart. The second portion  14  is sized to have a length sufficient for the portion  14  to protrude into the left ventricle  86 . 
     The vessel end  12  has a first opening  16 . The myocardium end  14  has a second opening  18  in communication with an interior  19  (shown in FIG. 3) of the implant  10 . Therefore, blood can freely flow through the implant  10  between the left ventricle  86  and the lumen  80  of the coronary artery  82 . Blood flows axially out of opening  16  parallel with the axis of lumen  80 . 
     As discussed more fully in the afore-mentioned commonly assigned and co-pending U.S. patent application Ser. No. 08/944,313, the portion  14  may be provided with tissue-growth inducing material (only shown in the present application in FIG. 6) such as a polyester fabric sleeve to immobilize the implant  10  within the myocardium  84 . 
     The present invention further includes a collar  20 . The collar  20  in the embodiment of FIGS. 1-3 is a tubular member having a thickened cylindrical portion  22  and co-axially aligned thinned cylindrical portion  24 . The thickened and thinned portions  22 ,  24  are joined at a transition point  24 . Preferably, the thickened and thinned portions  22 ,  23  are integrally formed of molded, bio-compatible material such as silicone rubber. 
     The thickened and thinned portions  22 ,  24  have a common internal diameter D sized larger than the outside diameter D O  of the vessel portion  12  by an amount less than or equal to the thickness of the artery  82 . An axial split line  26  is formed through the thickened and thinned portions  22 ,  24  to permit the collar  20  to be axially split open for placement on an artery  82  and implant  10  as will be described. The thickened portion  22  includes an annular groove  28  to receive a suture  30  to hold the collar  20  in place. 
     With respect to the representative dimensions given, the collar  20  has an internal diameter D of 3.0 mm. The thickened portion  22  has an external diameter D T  of 5.0 mm and an axial length L T  of 4.0 mm. The thinned portion  24  has an external diameter D t  of 3.75 mm and an axial length L t  of 3.0 mm. Preferably, the collar  20  is formed of silicon rubber having a Durometer of  30  Shore A. 
     In FIG. 3, the vessel portion  12  is shown residing within a coronary vessel (such as coronary artery  82 ). The longitudinal axis of the vessel portion  12  is aligned with the axis of the lumen  80 . Sutures  15  secure the artery  82  to the vessel portion  12 . The proximal portion of the coronary artery is ligated by sutures  85  distal to an obstruction  87 . 
     When placing an implant  10 , a surgeon dissects a portion of the artery  82  away from the myocardium  84 . The surgeon ligates the artery  82  distal to an obstruction  87  with sutures  85 . The surgeon then forms an incision through the artery  82  distal to the ligating suture  85 . 
     The vessel portion  12  is slipped into the lumen  80  through the open end  82   a  of the artery  82 . A stay suture  15  is placed around the artery  82  overlying the vessel portion  12 . 
     The collar  20  is split open at the part line  26  and placed over the artery  82  at the open end  16  and overlying the vessel portion  12 . The collar  20  is positioned with the thickened portion  22  overlying the vessel portion  12  and with the thinned portion  24  extending distally to the open end  16  and overlying the artery  82 . The transition point  23  between the thickened and thinned portions  22 ,  24  is positioned flush with the open end  16 . A stay suture  30  is placed in groove  28  to hold the collar  20  tightly on the artery  82  and vessel portion  12 . 
     Since the internal diameter D of the thickened portion  22  is only 0.5 mm larger than the external diameter D O  of the vessel portion  12 , the artery  82  (which typically has a wall thickness of 0.25 mm or greater) is crimped onto the vessel portion  12  along the entire axial length L T  of the thickened portion  22 . This crimping prevents relative movement between the implant  10  and any overlying portion of the artery  82 . 
     The thinned portion  24  provides a stiffening along the artery  82  distal to the open end  16 . This reduces relative movement between the artery  82  and vessel portion  12  at the open end  16 . The thinned portion  24 , while stiffer than an artery  82 , is still flexible to create a transition zone between the artery  82  and vessel portion  12 . Effects of a compliance mismatch between the vessel portion  12  and artery  82  are distributed over a length of the artery  82  (represented by the length L t  of the thinned portion  24 ) thereby minimizing arterial injury. Further, the thinned portion distributes forces over the exterior of the artery  82  rather than having such forces impact upon a more fragile interior surface of the artery  82 . 
     Numerous modifications are possible with the embodiment of FIGS. 1-3. For example, as described, the thinned portion  24  has uniform thickness and durometer along its axial length L t . This results in uniform stiffness. The thinned portion  24  can be modified to vary the flexibility of the thinned portion along its length L t  by, for example, varying its thickness (as shown in FIG. 3A in which elements are numbered as before but with triple apostrophes to distinguish the embodiments) or material of construction. Also, while simply placing the thinned portion  24  over an artery  82  is presently preferred, a layer of fibrotic-based adhesive can be placed between the thinned portion  24  and the artery  82 . Adhering the artery  82  to the thinned portion  24  reduces relative movement between the artery  82  and vessel portion  12  and collar  20  when the artery might constrict during diastole. 
     An additional advantage of the embodiment of FIGS. 1-3 is to permit slight axial misalignment between the vessel portion  12  and the artery  82 . The thinned portion  24  urges the artery  82  into such alignment with the resulting forces distributed over the length L t  of the thinned portion  24 . 
     FIGS. 4-5 illustrate an alternative embodiment implant  10 ′ (all similar elements numbered identically with the addition of an apostrophe and not separately described unless modified in the embodiment). In FIGS. 4-5, the thinned portion  24  is eliminated. The thickened portion  22 ′ crimps the artery  82 ′ and is flush with the open end  16 ′. This reduces the relative motion and transfers torque to the artery  82 ′ at a point distal to the open end  16 ′. 
     An additional alternative is to fabricate the collar  20  in situ. For example, any one of a number of polymers in fluid form can be placed around the artery overlying the implant  10 . Such polymers are cured in situ through any one of a variety of means (e.g., exposure to radiation such as light wavelengths selected to cure the polymer). Such polymers are used in practice by the Focal™ company of Massachusetts, United States. The cured polymer acts as a collar with the benefits of the present invention. 
     FIG. 6 illustrates a still further alternative embodiment. In FIG. 6, all elements corresponding to those in FIG. 1 are identically numbered with the addition of a double apostrophe. Structure identical to FIG. 1 is not separately described. In FIG. 6, the second portion  14 ″ of the implant  10 ″ is shown provided with a polyester fabric cuff  15 ″ to facilitate tissue in-growth as described in the afore-mentioned U.S. patent application Ser. No. 08/882,397. The first portion  12  is shown inserted into a coronary artery  82 ″. The collar  20 ″ is a polyester fabric sheet (e.g., a sheet of polyethylene terephthalate). The sheet  20 ″ is formed into a cylinder surrounding the exterior of the artery  82 ″ and overlying the vessel portion  12 ″ at its open end. The sheet  20 ″ preferably extends beyond the open end. The sheet  20 ″ is tightened and secured in place by sutures  30 ′. Tissue may grow into the fabric  20 ″ bonding the fabric  20 ″ to the artery  82 ′. 
     Having disclosed the present invention in a preferred embodiment, it will be appreciated that modifications and equivalents may occur to one of ordinary skill in the art having the benefits of the teachings of the present invention. It is intended that such modifications shall be included within the scope of the claims appended hereto.