Abstract:
A transmyocardial implant establishes 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 coronary portion sized to be received within the vessel. A myocardial portion is sized to pass through the myocardium into the heart chamber. A transition portion connects the coronary and myocardial portions for directing blood flow from the myocardial portion to the coronary portion. The coronary portion and the myocardial portion have an open construction for permitting tissue growth across a wall thickness of the coronary portion and the myocardial portion. The myocardial portion includes an agent for controlling a coagulation cascade and platelet formation.

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 enhance design for promoting a healed layer of cells on an interior of the implant. 
     2. Description of the Prior Art 
     Commonly assigned U.S. Pat. No. 5,755,682 issued May 26, 1998 and commonly assigned and co-pending U.S. patent application Ser. No. 08/882,397 filed Jun. 25, 1997, entitled “Method and Apparatus for Performing Coronary Bypass Surgery”, and filed in the name of inventors Mark B. Knudson and William L. Giese (published as PCT International Application Publication No. WO 98/06356) both teach an implant for defining a blood flow conduit directly from a chamber of the heart to a lumen of a coronary vessel. In one embodiment, an L-shaped implant is received within a lumen of a coronary artery and passed through the myocardium to extend into the left ventricle of the heart. The conduit is rigid and 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. The &#39;682 patent and &#39;397 application also describe an embodiment where a portion of the implant passing through the heart wall is an open structural member lined by polyester (e.g., Dacron). A further embodiment discloses a portion of the implant in a coronary vessel as being an open cell, balloon-expandable stent. 
     U.S. Pat. No. 5,429,144 to Wilk dated Jul. 4, 1995 teaches implants which are passed through the vasculature in a collapsed state and expanded when placed in the myocardium so as not to extend into either the coronary artery or the left ventricle. The described implants close once per cycle of the heart (e.g., during diastole in the embodiment of FIGS. 7A and 7B or during systole in the embodiment of FIGS.  2 A and  2 B). Either of these two designs may be lined with a graft. 
     Commonly assigned and co-pending U.S. patent application Ser. No. 08/944,313 filed Oct. 6, 1997, 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;397 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. 
     PCT International Application Publication No. WO 98/08456 describes a protrusive stent to form a passageway from the heart to a coronary vessel. The stent is described as wire mesh or other metal or polymeric material and may be self-expanding or pressure expandable. The application describes the stent may be covered by a partial or complete tubular covering of material including polyester, woven polyester, polytetraflouroethylene, expanded polytetraflouroethylene, polyurethane, silicone, polycarbonate, autologous tissue and xenograft tissue. 
     Biocompatibility is an important design feature. Solid metal implants are formed of material (e.g., titanium or pyrolytic carbon) with low incidents of thrombus and platelet activation. While such materials are proven in use in a wide variety of products (e.g., heart valve components), they do not facilitate fall healing. By “healing”, it is meant that over time, the patient&#39;s cells grow over the material of the implant so that blood flowing through the implant is exposed only (or at least primarily) to the patient&#39;s cells rather than to a foreign material. 
     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 coronary portion sized to be received with the vessel. A myocardial portion is sized to pass through the myocardium into the heart chamber. A transition portion connects the coronary and myocardial portions for directing blood flow from the myocardial portion and into the coronary portion. The coronary portion and the myocardial portion have an open construction for permitting tissue growth across a wall thickness of the coronary portion and the myocardial portion. The myocardial portion includes an agent for controlling the coagulation cascade and platelet activation, and promoting healing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side-elevation view of a transmyocardial implant according to the present invention shown in place defining a blood flow path from a left ventricle to a coronary artery; 
     FIG. 2 is a cross-sectional view of the implant of FIG. 1; 
     FIG. 3 is a view of an alternative embodiment of the implant of FIG. 1 illustrating a portion of the implant expandable within a coronary artery; 
     FIG. 4 is a view similar to FIG. 3 showing a transition portion of open cell construction; 
     FIG. 5 is a side section view of an alternative embodiment of FIG. 3 showing a balloon catheter admitted into the implant through an access port; and 
     FIG. 6 is a side sectional view of an expandable implant with a balloon catheter removable through a myocardial portion of the catheter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With initial reference to FIG. 1, a conduit  10  is shown in the form of an L-shaped tube. The conduit  10  may be formed of titanium or other biocompatible material. The material of the conduit  10  is preferably radially rigid material in order to withstand contraction forces of the myocardium. By way of non-limiting example, the tube will have an outside diameter D O  of about 3 millimeters and an internal diameter D I  of about 2.5 millimeters to provide a wall thickness of about .25 millimeters. 
     The tube  10  has a coronary portion  12  sized to be received within the lumen of a coronary vessel such as the lumen  80  of a coronary artery  82  distal to an obstruction  81  as illustrated in FIG.  1 . The conduit  10  has a myocardial portion  14  extending at a right angle to the axis of portion  12 . The myocardial portion  14  is sized to extend from the coronary artery  82  directly through the myocardium  84  and protrude into the left ventricle  83  of a patient&#39;s heart. 
     The coronary portion  12  has a first opening  16 . The myocardial portion  14  has a second opening  18  in communication with an interior  20  of the implant  10 . Therefore, blood can freely flow through the implant  10  between the left ventricle  83  and the lumen  80  of the coronary artery  82 . Blood flows axially out of opening  16  parallel with the axis of lumen  80 . 
     The longitudinal axis of the coronary portion  12  is aligned with the axis of the lumen  80 . Sutures  24  secure the artery  82  to the coronary portion  12 . The proximal portion  82   a  of the coronary artery is ligated by sutures  85 . 
     The coronary and myocardial portions  12 ,  14  have an open lattice construction  12   a ,  14   a  to define a plurality of open cells  12   b ,  14   b  extending through the wall thickness of the implant  10 . Preferably, the coronary and myocardial portions  12 ,  14  are joined by a transition portion  13  in a 90° bend between portions  12 ,  14 . While transition portion  13  can have an open lattice construction as portions  12 ,  14 , transition portion  13  will preferably have smaller open areas in such an open construction or, as illustrated, will be of solid construction. Such construction permits the transition portion to deflect high velocity blood flows from the myocardial portion  14  into the coronary portion  12 . A lattice construction with large open cells in the transition portion could result in the high velocity flow damaging tissue (not shown) overlying the transition portion. 
     Any one or all of the coronary portion  12 , transition portion  13  and myocardial portion  14  could be formed in final size as rigid units or could be formed in small diameter sizes which are subsequently expanded to full size. For example, FIG. 3 illustrates a coronary portion  12 ′ which is formed tapering from the transition portion  13 ′ to a reduced diameter open end  16 ′. The taper permits ease of insertion into a coronary artery. Following such insertion, the tapered coronary portion  12 ′ may be expanded to full size illustrated by the phantom lines in FIG.  3 . Such expansion can be performed using balloon-tipped catheters as is conventional in stent angioplasty. A collapsed and subsequently expanded implant  10  where all portions  12 ,  13  and  14  are expanded can permit use as a percutaneously deployed implant. The present drawings illustrate a presently preferred surgically deployed implant. In the surgical application, the artery is ligated. The implant  10  is passed through the epicardium and myocardium on a side of the artery  82 . 
     FIG. 5 illustrates a balloon  100  placed in a tapered coronary portion  12 . A lead  102  from the balloon  100  is passed through an opening  113 ′ in the transition portion  13 ′. The opening  113 ′ can be closed with a plug  115 ′ after the balloon  100  and lead  102  are withdrawn through the opening  113 ′. 
     Alternatively, in a transition portion  13 ″ with open cell construction (FIG.  4 ), the balloon lead can be passed through the openings of the transition portion  113 ″. FIG. 6 illustrates passing the lead  102  through opening  18  of the myocardial portion. The lead  102  can be pulled upwardly from the exterior of the heart to remove the balloon  100 . Alternatively, the lead  102  can be pulled through a catheter (not shown) adjacent end  18  in the left ventricle. 
     In either percutaneous or surgical implants, a flexible transition portion  13  (as would be achieved with a stent lattice construction) permits relative articulation between the coronary and myocardial portions  12 ,  14  to ensure the coronary portion is axially aligned with the lumen  80 . Absent such articulation, such axial alignment is achieved by accurately controlling the position of the myocardial portion  14  such that the coronary portion  12  is axially aligned with the lumen  80  following implantation. 
     The open cell construction of the coronary and myocardial portions  12 ,  14  permit tissue growth through the open cells  12   b ,  14   b  following implant. The healing procedure in the coronary portion  12  is the same as that in coronary stents. Vascular endothelial cells grow over to coat the structural material  12   a  of portion  12 . 
     In portion  14 , myocardial tissue, if not obstructed, will grow through the cells  14   b . Furthermore, the myocardium is highly thrombogenic. Therefore, uncontrolled contact between the myocardium  82  and the implant interior  20  can result in thrombosis of the implant  10 . Further, it is believed that the epicardium (i.e., outer layer of the myocardium) has a greater density of myocardial growth cells which contribute to healing. 
     To control growth in the myocardial portion  14 , a liner  30  is provided in the myocardial portion  14 . The liner  30  is any porous material for accepting tissue growth and, preferably, is a polyester fabric (e.g., Dacron). The porous liner  30  has interstitial spaces smaller than the open cells  12   c ,  14   c . The liner  30  is shown on an interior of the myocardial portion  14  but could also or alternatively surround the exterior. 
     The liner  30  has an upper end  32  secured through any suitable means (e.g., sutures not shown) to the upper end of the myocardial portion  14 . A lower end  34  is folded over the opening of the myocardial portion  14  and secured to the exterior of the portion  14  by sutures  36 . The myocardial portion  14  is sized to protrude into the left ventricle  83  with only the folded over liner material exposed to the interior of the left ventricle  83 . 
     The liner  30  acts as a porous substrate into which tissue may grow. To prevent thrombus, the liner  30  is impregnated with an agent for controlling coagulation cascade and platelet activation and adhesion. An example of such an agent is heparin but could be any anticoagulant or anti-platelet. Also, an agent such as a basic fibroblast growth factor could be used to accelerate healing. 
     The agent permits structural cells to grow on the liner by limiting thrombus formation which, uncontrolled, would occlude the implant. Due to the open construction, the structural, healing cells of the epicardium can grow onto the liner. Subsequently, endothelial cells can grow on the structural cells. 
     Therefore, the structure described promotes a three-stage healing process: 
     1. the drug agents control healing by minimizing coagulation and platelet activation which would otherwise be stimulated by agents from the myocardium; and 
     2. structural cells grow into and on the liner  30  now lined with the thrombus to initially heal and form a vascular bed; and 
     3. endothelial cells grow over the structural cells. 
     In the transition portion  13 , an open cell structure will permit tissue growth as in the coronary portion  12 . Such growth may also occur in the solid construction. Alternatively, the liner  30  can be extended into the transition portion  13 . Additionally, the open cell structure in the transition portion  13  can permit articulation between the coronary portion and the myocardial portion. Such a structure is shown in FIG.  4 . The open transition portion  13 ″ is formed by a coil  13   a ″ between the coronary portion  12 ″ and the myocardial portion  14 ″. This structure permits bending at the transition portion. As a result, the coronary portion can be axially aligned in the artery without first accurately positioning the myocardial portion. 
     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. For example, the liner  30  can take many constructions including PTFE, expanded-PTFE, polyurethane, polypropylene or any biologically compatible paving material (e.g., a biologically compatible coating such as hydrogel coatings, for example, polyethylene oxide) or natural tissue. Further, restenosis of the coronary portion  12  can be prevented with radioactivity therapy (such as providing the coronary portion with a short half-life beta emitter). Also, the liner  30  may be either a resorbable or non-resorbable material. Genetically engineered cells can be transformed to secrete anticoagulants and other agents to keep the blood fluid (such as tissue plasminogen activator and smooth muscle cells altered to express nitric acid).