US20010016700A1 - Transmyocardial implant with flow reduction - Google Patents

Abstract

A transmyocardial implant establishes a blood flow path through a heart wall between a heart chamber and a lumen of a coronary vessel on the heart wall. The implant includes a hollow conduit having an open first end and an open second end. The conduit is dimensioned so as to extend at least from the vessel through said heart wall and into said chamber. The conduit has a conduit wall defining a blood flow pathway within an interior of said conduit between the first and second ends. The first and second ends are mutually positioned for the first end to reside within the vessel and opposing a wall of the vessel when the conduit is placed within the heart wall with the second end protruding into the chamber. The conduit wall is formed of a material sufficiently rigid to resist deformation and closure of the pathway in response to contraction of the heart wall. A flow restriction is formed in the pathway for reducing a discharge velocity of blood flow discharged from the first end.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0001]
• 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 reducing a likelihood of damage to a coronary vessel from a high -velocity blood flow discharge.[0002]
• 2. Description of the Prior Art[0003]
• 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 conduit 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.[0004]
• 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 '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.[0005]
• 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. A portion of an interior surface of the implant portion in the vessel acts as a deflection surface to prevent direct impingement of high velocity blood flow on a vessel wall.[0006]
• The L-shaped implant described in the foregoing is preferably placed through a surgical procedure (open chest or minimally invasively). The suitability of an implant for minimally invasive or percutaneous procedures is influenced, at least in part, by the external size and shape of the implant. The size can be reduced and shape enhanced by elimination of the vessel portion of the foregoing designs.[0007]
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 heart wall between a heart chamber and a lumen of a coronary vessel on the heart wall. The implant includes a hollow conduit having an open first end and an open second end. The conduit is dimensioned so as to extend at least from the vessel through said heart wall and into said chamber. The conduit has a conduit wall defining a blood flow pathway within an interior of said conduit between the first and second ends. The first and second ends are mutually positioned for the first end to reside within the vessel and opposing a wall of the vessel when the conduit is placed within the heart wall with the second end protruding into the chamber. The conduit wall is formed of a material sufficiently rigid to resist deformation and closure of the pathway in response to contraction of the heart wall. A flow restriction is formed in the pathway for reducing a discharge velocity of blood flow discharged from the first end.[0008]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic cross-sectional view of an implant according to the present invention in place in a heart wall to define a blood flow path from a left ventricle to a coronary artery distal to an obstruction.[0009]
DESCRIPTION OF THE PREFERRED EMBODIMENT
• With reference to FIG. 1, an implant[0010]10 is shown including a straight elongate, generally cylindrical tube or conduit11. The conduit11 may be formed of titanium or other rigid biocompatible material such as pyrolytic carbon or may be titanium coated with pyrolytic carbon. Preferably, theinterior wall13 of the conduit11 is polished to a high degree of polish to reduce the likelihood of thrombus formation on the wall. The material of the conduit11 is preferably a rigid material in order to withstand contraction forces of the heart wall, as will be described.
• In the preferred embodiment, the tube[0011]11 will have an outside diameter Do of about 1 to 3 millimeters and an internal diameter D1 of about 0.5 to 2.5 millimeters to provide a wall thickness of about 0.5 millimeters. By way of non-limiting example, a specific D_omay be 2.5 millimeters and a specific D1 may be 2.0 millimeters.
• The size range given permits insertion of the conduit into a coronary vessel to be bypassed. Commonly, such vessels in an adult human have internal diameters of 1 to 3 millimeters when under the influence of normal pressurized blood flow.[0012]
• The tube[0013]11 has a firstopen end12 which is sized to be received within the lumen of a coronary vessel such as thelumen100 of acoronary artery102 illustrated in FIG. 1. As used in this application, the term “vessel” refers to veins or arteries. The present invention is described with reference to bypassing a coronary artery with blood from a left ventricle. The invention is equally applicable to forming a blood flow path from other heart chamber to any other coronary vessel.
• The conduit[0014]11 has a secondopen end14. The conduit11 is sized to extend from thecoronary artery102 directly through theheart wall104 and protrude into theleft ventricle106 of a patient's heart. Preferably, theend14 protrudes at least about 5 millimeters from aninner surface103 of theheart wall104 during maximum heart wall thickness during systole. Heart wall thickness varies from patient to patient and among locations on the heart. In a preferred embodiment of forming a flow path from the left ventricle to a coronary artery of an adult human, the length L of the conduit (measured as the axial distance betweenends12 and14) will be between about 10 and 30 millimeters. With the foregoing specific example, for aheart wall104 having a maximum systolic thickness of 20 millimeters, the length L of the conduit11 is25 millimeters.
• The[0015]openings12,14 communicate with aninterior20 of the conduit11. Therefore, blood can freely flow through the conduit11 between theleft ventricle106 and thelumen100 of thecoronary artery102.
• At[0016]first opening12, the conduit11 is outwardly flared at22 to act as a stop to limit insertion of the implant10 into theheart wall104. Further, theflaring22 acts as a smooth flow path for guiding blood flow out ofend12.
• As mentioned, the tube[0017]11 is preferably formed of titanium or other smooth biocompatible material in order to resist thrombus formation on theinner surface13 of the conduit11. Titanium is a presently preferred material due its long-term use in the cardiovascular industry. Further, titanium is sufficiently rigid to withstand deformation forces caused by contraction of theheart wall104 to avoid deformation of the tube11 so that the tube11 remains open during both diastole and systole. Also, the tube11 is solid on its cylindricalinner surface13. Therefore, highly thrombogenic material from theheart wall104 cannot pass into and contaminate theinterior20 of the conduit11.
• While tissue will adhere to titanium, the adhesion may be inadequate when subjected to the shearing contracting forces of the[0018]heart wall104 due to the relative smoothness of extruded titanium. Therefore, a completed implant10 includes asleeve24 of tissue growth-inducing material secured to an exterior surface of the conduit11. Thesleeve24 is attached to the conduit11 by asuture23 tightly surrounding both thesleeve24 and conduit11.
• The[0019]sleeve24 surrounds the exterior surface of the tube11 and is recessed back from both ofends12,14 so that after placement thesleeve24 resides solely in the heart wall104 (although slight protrusion ofsleeve24 into the left ventricle can be tolerated). It is desired the sleeve not be so closely positioned near open ends12,14 such that tissue growth on thesleeve24 can grow over and occlude the open ends12,14. It is anticipated that tissue growth on and into thesleeve24 could result in a buildup of tissue beyond thesleeve24 to a thickness of about at least 1 millimeter. It is desirable that such tissue growth does not extend over ends12,14. Accordingly, thesleeve24 is spaced from ends of the tube11 by a distance greater than an anticipated thickness of tissue growth extension beyond thesleeve24.
• The[0020]sleeve24 is selected to induce tissue growth and attachment. Preferably, thesleeve24 is formed of a fabric having biocompatible fibers defining interstitial spaces to receive tissue growth. An example of such a fabric is polyethylene terephthalate (such as polyester fabric sold by DuPont Company under the trademark Dacron). Such a fabric permits rapid tissue integration into the fabric thereby anchoring the fabric and, hence, the tube11 to the patient's tissue.
• While a fabric tissue growth inducing material is illustrated, other materials could be used. For example, the tissue growth inducing material could be sintered metal on the external surface of the tube[0021]11. Sintered metal results in a porous surface to receive tissue growth. The area of the sintered metal will be spaced from ends12,14 to prevent tissue accumulation on the sintered area from growing over and blocking12,14. Alternatively, the exterior surface of the tube11 can be roughened. The roughening can be in the form of a knurling or other roughened surface due to sandblasting or the application of sinter beads. The roughening results in surface protrusions and pitting, around which tissue may grow.
• The implant[0022]10 is placed with thefirst end12 placed within theartery lumen100 distal to anobstruction105. Normal nourishing blood flow is in the direction of arrow A. The implant10 passes through theheart wall104 with thesecond end14 positioned within theleft ventricle106 and spaced from theinner surface103 of theheart wall104 by5 millimeters during periods of maximum heart wall thickness. Thesleeve24 is positioned opposing theheart wall104 so that tissue from theheart wall104 can grow into thesleeve24.
• With the positioning thus described, the[0023]first opening12 opposes awall102aof theartery102. As a result, blood discharged from theopening12 impinges directly upon thearterial wall102a.
• The[0024]artery wall102ais a fragile layer of cells and fibers. Direct impingement of blood flow on thewall102acan damage theartery wall102a. As a healing response to such damage, a cellular matrix may develop and proliferate to such an extent that opening12 orlumen100 could occlude.
• The present invention reduces the velocity of blood flow through the[0025]opening12. Specifically, a flow restriction in the form of a narrowing30 is placed within the conduit11. Therestriction30 reduces blood flow below a velocity which would otherwise cause occluding trauma to theartery wall102a.
• With the specific example given, the[0026]restriction30 results in a narrow interior diameter D of about0.5 millimeters. Thenarrow restriction30 is positioned about8 millimeters fromend14. Therestriction30 is formed by a venturi constriction formed within the conduit11adjacent end14. The venturi may be formed by machining the conduit11 from a solid blank of titanium. Theventuri30 has ashallow ramp31 on a downstream side to avoid turbulence. Since an upstream side33 isadjacent end14, turbulence during reverse flow is not a serious concern.
• With the[0027]restriction30 as described, flow velocity out ofend12 is reduced below a level which would otherwise cause occluding trauma to theartery wall102a. By avoiding such trauma, a straight implant10 can be provided which is more susceptible to minimally invasive and percutaneous implantation as well as being suitable for traditional surgical approaches.
• Preferably, the blood flow velocity from[0028]end12 is reduced to a velocity of normal blood flow within an artery102 (about 30 ml/min.). Since theleft ventricle106 has a high maximum pressure, the pressure differential between theventricle106 andartery lumen100 results in a higher than normal blood flow rate in the absence of therestriction30.
• 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, in the preferred embodiment shown, the tube[0029]11 is a cylinder with circular cross-section. The tube11 could have an oval cross-section atend12 to provide a larger flow area and further reduce flow velocity. Also, while the tube11 is preferably straight, the tube11 could be bent so that the direction of blood flow fromend12 is not perpendicular to the arterial blood flow direction A.

Claims (12)

What is claimed:

1. A transmyocardial implant for establishing a blood flow path through a heart wall between a heart chamber and a lumen of a coronary vessel on said heart wall, said implant comprising:

a hollow conduit having an open first end and an open second end, said conduit sized to extend at least from said vessel through said heart wall and into said chamber, said conduit having a conduit wall defining a blood flow pathway within an interior of said conduit between said first and second ends;

said first and second ends mutually positioned for said first end to reside within said vessel and opposing a wall of said vessel when said conduit is placed within said heart wall with said second end protruding into said chamber;

said conduit wall formed of a material sufficiently rigid to resist deformation and closure of said pathway in response to contraction of said heart wall;

a flow restriction formed in said pathway for reducing a discharge velocity of blood flow discharged from said first end.

2. A transmyocardial implant according to

claim 1

wherein said flow restriction is selected for said discharge velocity to be less than an occluding trauma inducing velocity.

3. A transmyocardial implant according to

claim 1

wherein said restriction is a narrowing in said pathway positioned between enlarged crosssectional areas of said pathway.

4. A transmyocardial implant according to

claim 3

wherein said pathway has a substantially straight longitudinal axis between said first and second ends.

5. A transmyocardial implant according to

claim 1

wherein said conduit is sized for said first end to extend into said chamber beyond said heart wall.

6. A transmyocardial implant according to

claim 1

further comprising a tissue growth inducing material surrounding said conduit wall.

7. A transmyocardial implant according to

claim 6

wherein said tissue growth inducing material includes a plurality of fibers defining a plurality of interstitial spaces for receiving tissue growth and said tissue growth inducing material is biocompatible.

8. A transmyocardial implant according to

claim 7

wherein said tissue growth inducing material is a polyester fabric.

9. A transmyocardial implant according to

claim 6

wherein said tissue growth inducing material include a porous layer on said exterior of said conduit.

10. A transmyocardial implant according to

claim 9

wherein said tissue growth inducing material includes a sintered layer.

11. A transmyocardial implant according to

claim 6

wherein an external area of said conduit surrounded by said tissue growth inducing material is abraded.

12. A method for establishing a blood flow path through a heart wall between a heart chamber and a lumen of a coronary vessel on said heart wall, said method comprising:

forming a blood flow path from said vessel through said heart wall and into said chamber;

maintaining said blood flow path open during both systole and diastole;

restricting blood flow through said pathway to reducing a discharge velocity of blood flow discharged into said vessel.

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