|Publication number||WO1998015237 A1|
|Publication date||16 Apr 1998|
|Filing date||6 Oct 1997|
|Priority date||7 Oct 1996|
|Also published as||CA2264695A1, EP0957822A1, EP0957822A4|
|Publication number||PCT/1997/18311, PCT/US/1997/018311, PCT/US/1997/18311, PCT/US/97/018311, PCT/US/97/18311, PCT/US1997/018311, PCT/US1997/18311, PCT/US1997018311, PCT/US199718311, PCT/US97/018311, PCT/US97/18311, PCT/US97018311, PCT/US9718311, WO 1998/015237 A1, WO 1998015237 A1, WO 1998015237A1, WO 9815237 A1, WO 9815237A1, WO-A1-1998015237, WO-A1-9815237, WO1998/015237A1, WO1998015237 A1, WO1998015237A1, WO9815237 A1, WO9815237A1|
|Inventors||Mark L. Jenson, William J. Drasler|
|Applicant||Possis Medical, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Non-Patent Citations (1), Referenced by (2), Classifications (4), Legal Events (9)|
|External Links: Patentscope, Espacenet|
CROSS REFERENCES TO CO-PENDING APPLICATIONS
This patent application is a continuation-in-part of Serial No. 08/410,865 filed March 27, 1995, entitled "Vascular Graft" by the same invento .
BACKGROUND OF THE INVENTION 1. Field of the Invention - The present invention is for a vascular graft, and more particularly, pertains to implants used in the body to replace or augment natural blood vessels which supply arterial blood to organs and tissues throughout the body. More particularly, the implants are vascular grafts used to supply blood to the tissue. 2. Description of the Prior Art
Congenital defects, disease, or injury can render a person's blood vessels incapable of serving as an appropriate conduit for blood. Autogenous blood vessels may be relocated from their original site in the person's body and grafted to a new site as a replacement for the diseased or traumatized native vessel. Synthetic or non-autogenous tissue origin vascular grafts may also be implanted in a person to replace diseased or traumatized native vasculature. Infection, aneurysm, thrombosis, hyperplastic tissue response, and stenosis at the anastomoses, are all problems which occur with any known vascular graft whether it be of autogenous or non-autogenous origin. It is commonly held that low velocity of blood flow and low flow rate are major factors which reduce patency of vascular grafts. Conversely then, higher flow rate and higher velocity of flow are major factors which increase patency longevity.
The autogenous saphenous vein and internal thoracic artery are used successfully as vascular conduits for coronary artery revascularization. Although the search for a suitable prosthetic graft for aortocoronary bypass continues, nothing better than the autogenous vessels are available. Surgeons have been reluctant to use synthetic grafts in aortocoronary bypass because of few proved instances of long-term patency.
Although saphenous veins are used in aortocoronary bypass procedures, there are certain disadvantages: (1) unavailability, (2) small size, (3) non-uniform caliber, (4) varicosities, (5) large diameter, (6) sclerosis, (7) obstruction due to intimal hyperplasia, (8) aneurysm formation, (9) considerable time required for harvesting (10) leg discomfort and swelling, and (11) possible leg infection.
A significant number of patients requiring aortocoronary bypass do not have suitable veins, or the veins have been used for previous aortocoronary bypass or for peripheral vascular bypass procedures. On occasion, the need for a graft may have been unforeseen prior to surgery, and the legs not prepared for harvesting of the vein. The cephalic vein from the arm has been used when the saphenous vein is not available. However, it is usually thin-walled and often of poor caliber. Furthermore, the cosmetic effect of harvesting the cephalic vein is unacceptable for some patients. The internal mammary artery is widely accepted as suitable for myocardial revascularization, in that it has an excellent patency rate, but is usually useful only for the left anterior descending and diagonal coronary arteries. Experience with free grafts of the internal mammary and radial arteries has been disappointing, since long-term patency has been poor.
The importance of the velocity of blood flow in autogenous vein grafts has been emphasized. There is evidence of an inverse relationship between the velocity of blood flow in venous grafts and the amount of intimal proliferation observed. Autopsy studies indicate the occlusion of aortocoronary saphenous vein grafts more than one month after operation is most commonly caused by fibrous intimal proliferation. Although the cause of this lesion has not been definitely established, studies would suggest that it is probably related to a low velocity of flow through the graft. This suggests that every effort should be made to achieve a high velocity of flow in coronary artery bypass grafts.
Blood flow through a conduit at high velocity can generate a very large shear stress at the wall of the conduit. If the wall surface is rough and allows platelets to adhere to the surface the continual exposure of the platelets to the high shear stress will cause them to become activated. Platelet activation then leads to the formation of thrombus which in turn results in a narrowing or blockage of the conduit. To prevent this from occurring the conduit should be made with a smooth blood contact surface in the regions where the shear stress can cause platelet activation. Platelet deposit will not be allowed to build up on smooth surfaces; the deposit will instead be released from the surface before it has had a chance to reach a size that could cause a significant narrowing or blockage in the conduit. As the platelet or thrombus deposit begins to adhere and build up on the wall, the shear stress due to the flow will overcome the adhesion force and break the deposit off of the wall such that it cannot build up to a size that can block the fluid pathway.
The prevention of deposit build-up is particularly important in the higher shear stress region found in the restricted passage of the present invention.
Synthetic vascular grafts are generally constructed with a porous structure that will allow some tissue penetration from the outside of the graft to the inside blood flow surface. Typically, grafts made of expanded polytetrafluoroethylene have a porosity that is described by an inter-nodal distance of approximately 30 microns. Other porous grafts may have a fibrous structure with fiber spacing or pore size defined by a permeability of the graft per unit area to a fluid such as water exposed to a driving force of a specific pressure.
Grafts with smaller relative porosity do not allow for tissue penetration through the graft wall as well as grafts with a more open structure with greater porosity. Grafts which do not allow significant tissue penetration through the graft wall generally do not form a complete cellular layer or neointima on the flow surface of the graft. The formation of such a neointima, particularly if the cells in contact with the blood were endothelial cells, would be very desirable. Endothelial cells secrete several substances which help to reduce platelet adhesion, platelet activation, and reduce the incidence and magnitude of a thrombotic event which could easily cause a graft to occlude.
Enlarging the porosity of the graft allows tissue penetration to occur more easily and quickly thereby providing the inner surface with access to endothelial cells. Additional cell types which can penetrate through the graft wall include smooth muscle cells, fibroblasts, and a variety of white cell types. As the tissue penetrates through the graft wall in response to chemotactic, foreign material, electrical, mechanical, and other physiological signals, tissue thickening can occur on the inner blood flow surface of the graft and can lead to graft stenosis and occlusion. The thickness of this excessive tissue buildup is modulated by the flow rate and corresponding shear rate and shear stress found at the inner blood flow surface of the graft. A typical shear stress in a normal arterial conduit can range from 10-100 dynes/cm2 with a median value of approximately 20 dynes/cm2. Under conditions of low shear stress, the ability of tissue to thicken on the inner flow surface is much greater than at high shear stress. At high shear stress the tissue does not become excessively thick but instead forms a thin cellular neointima that will resist platelet deposition and thrombosis.
The present invention provides a high wall shear stress on the inner blood flow surface. The graft wall can then be constructed of a material that will allow for ease of tissue penetration through the wall yet it will not result in an excessively thick tissue buildup on the inner surface. Endothelial cells or a neointima can form on the inner flow surface and impart antithrombotic character to the graft.
A method of bringing the endothelial cells to the surface faster than that which would occur by natural cellular through-growth of cells originating from the tissues surrounding the graft would be to put endothelial cells onto the inner graft surface prior to graft implantation. Such methods are often referred to as endothelial cell seeding or sodding. Other approaches have been used to provide improved surface chemistry or morphology to encourage the natural endothelialization process or to enhance the seeding or sodding techniques; these approaches include deposition of particular biologic or synthetic materials, such as type IV/V collagen, use of extracellular matrix proteins as a graft substrate to encourage healing and endothelialization, and modification of biological response by various drugs. These endothelial cell seeding and sodding techniques have been used with porous vascular grafts with only limited success. Prosthetic vascular grafts currently enjoy some success in large-diameter, high-flow situations; however, the endothelial cell seeding or sodding techniques are generally used to enhance the antithrombotic capacity of a synthetic graft which is exposed to a low blood flow rate and consequential low shear stress. Under these conditions one of two outcomes generally result depending upon the graft porosity. For grafts of low porosity, the endothelial cells generally do not remain stable on the graft surface and are soon sloughed off or washed off of the surface. For grafts of a high porosity that will allow for tissue through-growth, the neointima will become excessively thickened and result in a stenotic graft.
Therefore, the enhancement provided by endothelial seeding or sodding generally does not improve the performance of prosthetic vascular grafts in low-flow situations such as aortocoronary bypass sufficiently to obtain acceptable performance. However, the present invention by use of a controlled arteriovenous shunt converts such typically low-flow situations into high-flow situations, wherein the enhancements of endothelial seeding or sodding can further improve such prosthetic vascular graft performance.
The use of endothelial cell sodding or seeding as part of the graft of this invention where the porosity of the graft wall is high enough to allow for ease of penetration offers several advantages over other synthetic grafts. The sodding or seeding provides an acute antithrombotic activity due to the presence of the endothelium and its secreted chemicals. The porosity of the graft allows for tissue penetration to the inner surface which is then maintained at a thin level due to the high shear stresses provided by the graft. Long-term antithrombotic activity is thereby provided to the graft via the endothelium that was obtained from the tissue that has penetrated the graft wall. Short-term or acute benefit is also obtained from the endothelium due to secretion of active antithrombotic agents and due to physical blockage of graft pores by the tissues used in the sodding process.
Endothelial cell sodding typically involves steps of: obtaining tissue such as microvascular rich tissue from fat tissue, omentum, or intraperitoneal tissue, typically from a human patient; separating the endothelial cells from the tissue and concentrating and purifying the endothelial cells; and applying the endothelial cells onto the graft surface. Endothelial cell seeding typically involves steps of: obtaining endothelial cells from a donor, typically a human patient; mixing endothelial cells with blood; applying the blood and endothelial cell mixture to the graft, typically forcing the material into pores in the graft; and allowing the blood to clot, thereby "pre-clotting" the graft with endothelial cells in the clot.
Synthetic vascular implants are disclosed by Liebig in U.S. Pat. Nos. 3,096,560; 3,805,301 and 3,945,052. These grafts are elongated knit fabric tubes made of yarn, such as polyester fiber. Synthetic tubes of other construction can be used as vascular grafts; for example, ePTFE tubes made according to U.S. Pat. Nos. 3,953,566 and 4,187,390 by Gore. Tubes of biologic origin, such as from human or other animal arteries, veins, or other tissue, have been used as vascular grafts; for example, Dardik in U.S. Pat. No. 3,894,530 discloses the use of an umbilical cord for a vascular graft. Holman et al. in U.S. Pat. No. 4,240,794 disclose a method of preparing human and other animal umbilical cords for use as a vascular replacement. These synthetic and biologic tubes have been used as alternatives to the saphenous vein implant. The ends of the tubes are anastomosed to ends of arteries to bypass diseased or damaged areas of the arteries; they replace the diseased portions of the arteries. Similar implants are also used to connect body vessels, such as an artery and a vein, or to bypass diseased or damaged areas of veins. Methods of and devices for endothelial cell seeding and sodding of standard vascular grafts are disclosed by Williams et al. in U.S. Patent Nos. 4,820,626 and 5,131,907 and by Alchas et al. in U.S. Patent Nos. 5,035,708 and 5,372,945.
The present invention relates to earlier vascular graft and blood supply methods disclosed by Possis in U.S. Patent Nos. 4,601,718; 4,546,499; and 4,562,597 which describe a vascular graft with a flow restrictor. The present invention and disclosure teaches various key aspects and enhancements not taught in the earlier patents but which are of practical value, and which can extend the range of practical application.
SUMMARY OF THE INVENTION The general purpose of the present invention is a vascular graft. The goal of vascular reconstructive surgery is to effectively supply blood to organs and tissues whose blood vessels integrity are compromised by congenital defects or acquired disorders, such as arteriosclerosis, trauma, and other diseases. The invention is a graft and a method employing the graft for supplying blood to organs and tissues throughout the body. The graft can also be used as a venous reconstruction to provide effective outflow from organs or tissues, or to serve as a conduit adjoining two blood vessels or conduits of the body.
The graft can supply blood to vessels which require additional blood flow (blood-requiring vessels) ; more commonly, it is the tissues and organs perfused by the "blood-requiring vessels" which actually need the additional blood flow. Alternatively, the additional blood flow can serve other purpose (s), such as to increase the longevity of patency of the vessels due to the increased blood flow, or to create a convenient means for vascular access for obtaining blood, performing hemodialysis, or infusion of chemicals or medications into the vascular system. Further, a restricted passage can be used to redistribute the blood pressures or flow rates in the body such as to relieve excess pressure, to redistribute oxygenated and non-oxygenated blood as in a
Blalock-Taussig shunt or to otherwise treat a patient.
The graft includes an elongated means for carrying blood from a higher pressure blood supply to one or more blood receivers at a lower pressure. The elongated means has a body providing a first passage for carrying of blood. The body may be connected to one or more blood-requiring vessels via one or more openings in the body for supplying blood to the blood-requiring vessels. The body has an inlet end means adapted to be connected to one or more supplies of blood under pressure, whereby blood flows into the first passage. The flow of blood and pressure of the blood in the first passage is controlled with a restriction means having a restricted second passage connected to the downstream portion of the body remote from the inlet end means. An outlet end means connects the restriction means to blood receiver. The outlet end means may contain a segment downstream from the restrictor (downstream segment) including a third, elongated, passage which conveys blood from the restriction means to the blood receiver, or the outlet end means may comprise means for connecting the restriction means to the blood receiver thereby providing communication facilitating the flow of blood from the second passage to the blood receiver. The third passage also provides a chamber wherein the velocity and velocity gradients of the blood flow are decreased before entering into the receiving vessel. The first and second (and third, when present) passages together form a continuous passage. A pressure differential between the blood supply and the blood receiver maintains continuous and adequate blood flow at a desired pressure and velocity through the first and second passages and provides a continual supply of blood for blood-requiring vessels attached to the body. When used to provide effective outflow from organs or tissues, one or more drainage vessels such as veins or lymph vessels are connected to the third passage via one or more openings in the third passage; flow from these drainage vessels then flows into the third passage since it is at low pressure, being downstream of the restrictor.
The graft is typically used to supply blood to one or more coronary artery branches in a human heart. 5 The heart has two atria for receiving blood from the vena cava and pulmonary veins and is connected to an aorta to carry blood under pressure from the heart. The graft typically includes an elongated tubular means having a continuous longitudinal passage for carrying blood from
1.0 the aorta or other high pressure blood vessel (supply vessel) to the superior vena cava or atrium or other low pressure blood vessel (receiving vessel) . The tubular means has an inlet end sutured or otherwise attached to the aorta forming an anastomosis so that blood under
15 pressure flows from the aorta into the first passage and is discharged through an outlet end into the superior vena cava or other vessel of lower mean pressure than the aorta. The outlet end of the tubular means is sutured or otherwise attached to the tissue around an opening in
20 communication with the superior vena cava.
The flow rate, velocity of flow, and pressure of the blood in the continuous passage is controlled by a restriction. The restricted second passage typically has a reduced cross sectional area and a diameter that is
25 smaller than the first passage, typically less than one-half the diameter of the main body or first passage of the tubular means. The restricted passage is also typically smaller than the third passage in the outlet end of the tubular means. However, the restricted
30 passage can be placed at the outlet end of the graft without a non-restricted region at the outlet; attachment means such as a sewing ring or flange may be used to facilitate connection to the receiving vessel. The flow restrictor can be a smaller-diameter passage of circular cross section, but can be any other feature which restricts flow and maintains a pressure differential between the upstream and downstream ends of the restrictor. For example, the restrictor could be a noncircular passage having smaller effective diameter, an orifice or nozzle, or a combination of restricting areas such as multiple paths which together provide the effect of flow restriction. The restriction can be adjustable, for example, to obtain a particular flow rate desired in the continuous passage or to obtain particular pressures in the continuous passage, or can be positionable, for example, to locate the restriction at a desired location along the continuous passage. The longer the length of restricted second passage, the greater the restriction effect for a given diameter of restricted second passage. The restricted portion will typically have higher fluid shear stress at the surface than other portions of the continuous passage. The pressure differential between the supply vessel and the receiving vessel causes a continuous flow of blood in quantities and at velocities that inhibit thrombosis, and provides a continuous supply of blood at a desired pressure to the arteries connected to the tubular means. The particular dimensions of the graft are chosen to accommodate the particular application. For example, a graft body with an internal diameter in the range of approximately 4 mm to approximately 7 mm, with sufficient length to reach the various vessels as needed, and a restrictor with an internal diameter in the range of approximately 1 mm to approximately 3 mm, can be used advantageously for aortocoronary bypass applications. The present invention includes use of biologic material together with a restricted passage to improve performance of the graft. A variety of biologic materials can be used advantageously, applied to the interior blood-contact surface, the exterior surface, in interstices within the wall of the graft, or a combination of these. For example, endothelial cells applied to the blood-contact surface can reduce thrombosis on the surface, and can supply substances such as prostacyclin or nitric oxide to downstream tissues thereby enhancing the environment and biologic responses or activity of the downstream tissues. In another example, biologic material mixtures including endothelial cells can be placed in the interstices of the graft, providing for migration and propagation of endothelial cells onto the blood-contact surface. In yet another example, biologic materials containing growth factors can be applied to the external surface of a porous graft to optimize tissue ingrowth into interstices and incorporation of the graft. In still another example, biologic materials can be used to fill interstices of the graft thereby preventing leakage through the wall. These and other applications of biologic material can be utilized to enhance the results of the grafting, yet take advantage of the controlled flow present in the restricted passage of the graft to enhance patency and control pressures in the passage. In many applications such as aortocoronary bypass, a conventional graft including such biologic materials would not function acceptably due to thrombosis. Indeed, there can be a synergy wherein a graft with a restricted passage, including biologic material, connected to blood vessels of differing pressure such as one or more arteries and a vein, can function better than either (1) a graft with a restricted passage but without biologic material, (2) a graft with biologic material but without a restricted passage and extend the utility of the combination graft (restricted passage with biologic material) to applications in which neither (1) (graft with restricted passage) or (2) (graft with biologic material) would be useful alone.
In the primary method of use, the tubular means has one or more openings in the body used to provide blood to one or more coronary arteries or branches. The coronary arteries are sutured to the tubular means whereby blood flows through the openings in the tubular means into the coronary artery branches. The graft can also be used to perfuse other non-coronary arteries (blood-requiring vessels) of the body. The inlet end of the tubular means can be anastomosed to any arterial source of blood that has adequate arterial pressure and supply of blood flow volume; for example, the arterial source can be an axillary artery, a femoral artery, or any other convenient artery or more than one arteries. The blood can be discharged into any vessel which is capable of receiving the blood flow rate that is supplied; for example, the receiving vessel can be a femoral vein or one or more convenient veins. The non-coronary blood-requiring vessel (s) that need blood perfusion are anastomosed to the tubular means such that blood flows into these non-coronary blood-requiring vessel (s) from the arterial source via the tubular means. The restricted passage is located downstream from the blood-requiring vessels and is connected to one or more blood-receiving vessels via outlet end means. In another method of use, the graft can be used to create an arteriovenous shunt between a high pressure blood vessel and a low pressure blood vessel without the need for any additional openings in the tubular means. The inlet end is anastomosed onto an artery or other high pressure supply vessel and the outlet end is anastomosed onto a vein or other low pressure receiving vessel. The restriction passage is used to reduce or control the amount of blood flow that is allowed to pass through the graft conduit. When used in this manner to create an arterio-venous shunt, the restriction may be at any location along the graft. There may be advantages to positioning the restriction at particular locations along the graft. For example, positioning the restriction near the upstream end (inlet end) provides a longer region downstream from the restriction (downstream segment) containing a passage (third passage) which is at lower pressure and may be convenient for access to blood via needle puncture into the third passage which is under lower pressure (for example, to reduce bleeding at the puncture sites due to the lower pressure) ; positioning the restriction near the downstream end provides a longer (first passage) region upstream from the restriction which is at higher pressure and may be convenient for obtaining blood from the vascular system via needle puncture, or for access to blood within the first passage via other access method. Positioning the restriction near the mid-portion of the graft can provide regions at higher pressure and at lower pressure which may be convenient, for example, for hemodialysis, in which blood could be obtained from the higher pressure first passage and infused into the lower pressure third passage. The supply vessel and receiving vessel may be native vessels such as arteries, veins, or heart chambers, or they may be saphenous vein or other biologic or synthetic vessel implanted or otherwise connected to a blood vessel or other cavity.
In a first embodiment of the invention, the elongated means is an elongated synthetic or biologic tube (such as a polytetrafluoroethylene tube, a Dacron tube, a silicone tube, or a tube of one or more other synthetic biocompatible material, autogenous saphenous vein, a human umbilical cord, a biological vessel such as a bovine internal mammary artery that has undergone a processing step for strengthening or other reasons, or other tissue tubes of any origin including composites of tissue and synthetic component; the tube may have metallic content) . The tube has a continuous passage and has a flow restriction (such as with higher shear region, a reduced diameter, or reduced cross sectional area, a narrowing in the tube, a separate piece with a narrowed passage which is inserted into the tube, or an externally compressed portion of the tube) near the outlet end of the tube. The flow restriction can be constructed of similar material (s) as the elongated tube, or can be constructed of different biocompatible material. Blood flows from the inlet end, which is attached to a supply of blood such as an artery, along the passage, through the flow restriction, and to the outlet end, which is attached to a blood receiver such as a vein. Between the inlet end and the flow restriction, one or more arteries (such as coronary arteries) which require additional blood perfusion can be connected to the tube so that blood can flow from the tube into those arteries. The diameter of the tube is appropriate for connection to the supply artery and the blood-requiring arteries and the receiving vein; the diameter of the passage is typically reduced at the flow restriction. The flow restriction controls the blood flow and maintains sufficient pressure of the blood at the connections to the blood-requiring arteries so that the arteries are perfused by blood from the tube. The restricted passage also controls the flow and velocity and pressure of blood moving through the outlet end of the tube into the receiving vessel. An optional external sleeve supports the restriction and the outlet end of the tube and the connection to the receiving vein to reduce crushing or kinking. The flow rate along the tube is typically larger than the flow rate supplied to the blood-requiring vessels from the connections to the tube due to the flow which passes through the flow restrictor and into the receiving vein. The larger flow rate reduces the likelihood of thrombosis or clotting of the tube. The blood-contacting surface in the flow restrictor region is smooth in order to reduce the likelihood of thrombotic or cellular deposit in this region. The blood-contacting surface in other regions of the tube has biologic material incorporated therein to aid in healing and incorporation of the graft in the body, encourage neointimal endothelialization, control intimal thickening or reduce thrombosis. Biologic materials such as the following can be used advantageously: collagen, cross-linked collagen, fibronectin, vitronectin, laminin, proteoglycans, amino acid peptides incorporating the arginine-glycine-aspartic acid sequence, other extracellular matrix proteins or vascular intimal basement membrane proteins, integrin-related compounds, fibrin, endothelial cells, or other tissue-derived materials or mixtures or synthetic analogs and derivatives, and can include biologically-active additives such as growth factors or thrombosis modulating factors or chemicals. Thus, a variety of biologic materials, synthetic analogs, and derivatives can be used to obtain enhanced performance of a vascular graft, and still benefit from the restricted flow obtained with the present invention. Interstices of porous grafts can also contain biologic material serving to modulate the performance of or tissue response to the implant.
A second embodiment of the invention is similar to the first, but differs in that the flow restriction is located at the outlet end of the tube. The passage is therefore small in diameter and may be inappropriate for connection to the receiving vein. A sewing ring or flange is provided to facilitate this connection to the receiving vein.
A third embodiment of the invention is similar to the first and the second, but has a branched passage. Multiple branches are connected to supply arteries, and each branch is connected to one or more blood-requiring arteries. The branches join upstream from the flow restriction. In this manner, the tube can be used to supply multiple blood-requiring arteries which are not conveniently located to allow use of a non-branched tube, such as on anterior and posterior surfaces of the heart, but only one flow restriction and only one connection to a receiving vein is required.
In a fourth embodiment of the invention, the elongated means is an elongated synthetic or biologic tube (such as a polytetrafluoroethylene tube, a Dacron tube, a silicone tube, or a tube of one or more other synthetic biocompatible material, a human umbilical cord, a biological vessel such as a bovine internal mammary artery that has undergone a processing step for strengthening or other reasons, or autogenous vessels, or other tissue tubes of any origin including composites of tissue and synthetic component; the tube may have metallic content) . The tube has a continuous passage and has a flow restriction (such as with higher shear region, a reduced diameter, or reduced cross sectional area, a narrowing in the tube, a separate piece with a narrowed passage which is inserted into the tube, or an externally compressed portion of the tube) at some point along the tube. Blood flows from the inlet end, which is attached to a supply of blood such as an artery, along the passage, through the flow restriction, and to the outlet end, which is attached to a lower pressure blood receiver such as a vein or pulmonary artery. The diameter of the tube is appropriate for connection to the supply artery and the receiving vein; the diameter of the passage is typically reduced at the flow restriction. The flow restriction controls the blood flow through the tube and maintains higher pressure of the blood upstream from the flow restriction, and lower pressure of the blood downstream from the flow restriction. An optional external sleeve supports the restriction; optional external support at the outlet end reduces crushing or kinking. The tube can be used, for example, for hemodialysis access to blood via needle puncture, or to mix oxygenated and non-oxygenated blood such as providing controlled blood flow between the aorta and the pulmonary artery.
The foregoing embodiments are meant to illustrate the form and the utility of the invention. Additional embodiments such as inserting flow restrictions into autogenous vessels, or combinations of these illustrative embodiments, can be used advantageously .
The invention includes a method of providing a continuous supply of flowing blood at a desired pressure to one or more blood receiving vessels, such as coronary arteries of a human or other primate. A graft having a blood flow restricting passage is anastomosed to the aorta or other high pressure section of the blood circulatory system. The graft is placed adjacent the heart to locate portions of the graft in proximity to selected coronary branch arteries. Selected portions of the graft are anastomosed to coronary arteries. The outlet end means (which can include a downstream segment with a third passage, downstream from the restricted second passage) form the outlet end of the graft. The outlet end of the graft is anastomosed to the superior vena cava or other low blood pressure section of the blood circulatory system. Blood under pressure continuously flows from the aorta into the graft, since there is a substantial blood pressure difference between the aorta and superior vena cava; there is a continuous flow of blood along the graft, through the restricted passage, and into the superior vena cava. The restricted passage prevents the flow of blood from being excessive and maintains the blood pressure in the portion of the graft upstream from the restricted passage at substantially the same as the aorta blood pressure and controls the pressure and velocity of blood flowing out of the graft to a low pressure receiving vessel such as an atrium or vena cava.
The restricted passage has a blood contact surface that is smooth in order to reduce platelet and other thrombotic or cellular deposit on the surface. Shear-induced platelet activation is dependent upon the magnitude of shear stress as well as time of exposure to these stresses. Fluid shear stresses at the blood-contact surface will typically be larger at one or more portions of the flow restrictor than at one or more other portions of the graft. It is essential that the flow surface of the restricted passage be free of significant platelet deposit or thrombotic deposit. Shear stresses will tend to wash away any tissue buildup on the surface of a smooth restricted passage keeping the surface relatively free of deposit. Therefore, it is important to have a smooth blood-contact surface in the restriction. The shear stresses in the restricted passage can typically range from approximately 300 dynes/cm2 to over 1000 dynes/cm2 depending upon the flow rate through the graft. Platelets exposed to these stresses for extended periods of time will activate and cause thrombosis to occur, leading to graft failure. A blood contact surface that is smooth will not allow thrombotic or cellular deposition to build up on the surface, reducing the likelihood of thrombosis of the graft. The smooth surface will be typically on the order of a 1 microinch finish, such as the smoothness of a polished metal surface, and usually in the range of 0 to approximately 20 microinch, but generally in the range of 0 to approximately 200 microinch, depending on the roughness morphology and the number and distribution of defects. Larger defects such as pits, scratches, or bumps can be considerably larger provided they are relatively infrequent in the largely smooth surface; other factors such as material composition, characteristics of the blood, medication, etc., may influence the smoothness requirements, but in general a restriction with a smoother surface will tend to have less platelet or other tissue buildup. In a flow restriction containing a smaller diameter region for example, increased smoothness is required in the smaller diameter portion; increased smoothness may also be required in adjacent regions such as tapered, converging, or diverging regions, and in any regions which may have disturbed flow, or stagnant or slowly moving blood. Similarly, stagnant regions, steps, parting lines, and other defects at size or shape transitions, especially near the flow restriction, should be minimized in order to avoid undue thrombus or other tissue buildup.
The elongated means which has a body providing a first and third passage for carrying the blood is typically constructed of a porous material in order to allow tissue penetration from the outside of the elongated means to the inner flow surface of the passage. A higher porosity will enhance the tissue penetration and will deliver endothelial cells or a neointima to the inner surface. The relatively higher shear stress found in the passage due to the increased flow rate which exists in the graft of the present invention will reduce the likelihood for tissue thickening on the inner wall leading to stenosis and graft failure. The first and third passage can also be seeded or sodded with endothelial cells to provide acute phase antithrombotic activity. Over time, tissues which have penetrated through the graft wall will help to form a stable neointima on the inner flow surface to provide long term antithrombotic activity. The relatively high rate of shear found with a graft of the present invention will ensure that the neointimal thickness does not become excessive. The presence of a stable neointima can also reduce the problem of anastomotic stenosis which can occur with vascular grafts.
Vascular grafts with high porosity, such as that needed to promote or sustain adequate tissue through-growth or luminal endothelialization, tend to have increased thrombosis, especially in the acute phase, due to the surface morphology. Increased flow by use of a graft of the present invention can help to overcome this acute problem, and allow the enhancements of endothelial cell seeding or sodding to be used, especially in applications where low flow rates would otherwise be encountered. Vascular grafts typically have a relatively uniform porous structure through the wall of the graft, but a restricted passage incorporating biologic material can have other wall structures, and still be used advantageously. For example, the wall may have pores only at the inside or outside surface, have a generally porous structure with an essentially nonporous layer at some point in the wall, have varying dimensions of pores and interstices through the thickness of the wall, or have an essentially nonporous structure. A restricted passage with biologic material can be structured to have large pores at the external surface to facilitate tissue ingrowth into the interstices, but have smaller pores at or near the internal surface to reduce tissue or thrombus buildup, to control tissue through-growth through the wall, or to limit leakage of blood or serum through the wall. For instance, a wall structure with uniform pores larger than the dimensions of a cell, such as in the range of approximately 5 micrometers to approximately 200 micrometers can be used, or a wall structure with varying pore dimensions such as from approximately 5 micrometers to approximately 20 micrometers at or near the inside surface and approximately 10 micrometers to approximately 200 micrometers at or near the outside surface. Some porous materials are characterized by other dimensions, such as with expanded polytetrafluoroethylene in which an internodal distance is specified, in the range of approximately 10 micrometers to approximately 120 micrometers, for example. Any porous structure can be considered in an analogous way by characterizing the structure with an effective equivalent pore diameter range, or using other measures of porosity such as water entry pressure, mean flow pore size, and so forth.
Serum or blood leakage through the wall of the graft can be a problem when utilizing grafts with high porosity. Endothelial cell seeding or sodding, or deposition of collagen or other materials on the graft, will reduce or eliminate the bleed through or weeping which may otherwise occur with implant of a high porosity graft, thus the higher porosity needed to allow for tissue through-growth through the graft wall does not result in serum, blood, or other leakage through the graft wall during or after implant; and, acute phase antithrombotic activity is imparted to the graft that would otherwise tend to be more thrombotic due to the increased porosity and larger pores needed for obtaining the higher porosity. BRIEF DESCRIPTION OF THE DRAWINGS
Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: FIG. 1 illustrates a vascular graft including a flow restrictor attached to members of a heart;
FIG. 2 illustrates a restrictor member aligned over and about one end of a graft;
FIG. 3 illustrates a cross sectional view of the restrictor along lines 3-3 of FIG. 2;
FIG. 4 illustrates a cross sectional view of the restrictor along lines 4-4 of FIG. 2;
FIG. 5 illustrates a cross sectional view of the restrictor along lines 5-5 of FIG. 2; FIG. 6 illustrates the aortic end of the tubular member implanted into the aortic ostium and anastomosed thereto by sutures;
FIG. 7 illustrates the open end of the downstream segment implanted into an ostium open to the superior vena cava and anastomosed thereto by sutures;
FIG. 8 illustrates a graft anastomosed to the coronary branch by sutures;
FIG. 9 illustrates a graft segment having a continuous member restrictor segment; FIG. 10 illustrates a cross sectional view of the continuous restrictor along lines 10-10 of FIG. 9;
FIG. 11 illustrates a cross sectional view of the tubular member along lines 11-11 of FIG. 9; FIG. 12 illustrates an autogenous saphenous vein having a flow restrictor;
FIG. 13 illustrates a cross sectional view of the cylindrical wall along line 13-13 of FIG. 12; FIG. 14 illustrates a cross sectional view of the inlet passage along line 14-14 of FIG. 12;
FIG. 15 illustrates a cross sectional view of the intermediate throat section along line 15-15 of FIG. 12; FIG. 16 illustrates a cross sectional view of the outlet passage along line 16-16 of FIG. 12;
FIG. 17 illustrates a cross sectional view of a flow restrictor sutured to an autogenous saphenous vein;
FIG. 18 illustrates a graft segment having a spiral wrapped tubular body;
FIG. 19 illustrates a graft segment having a plurality of loops about the tubular body;
FIG. 20 illustrates a flow restrictor attached to the vena cava by a sewing ring; FIG. 21 illustrates a cross sectional view of the sewing ring and restrictor member along line 21-21 of FIG. 20;
FIG. 22 illustrates a cross sectional view of the small diameter region along line 22-22 of FIG. 20; FIG. 23 illustrates a vascular graft having multiple segments.
FIG. 24 illustrates a vascular graft having a fiber material tubular member;
FIG. 25 illustrates a cross sectional view along line 25-25 of FIG. 24;
FIG. 26 illustrates a vascular graft having a fiber material tubular member having endothelial cell seeding; FIG. 27 illustrates a cross sectional view along line 27-27 of FIG. 26; and,
FIG. 28 illustrates a vascular graft having a fiber material tubular member having modulating biological material residing in the pores of the fiber material tubular member.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIGS. 1, 2, 3, 4 and 5 there is shown an anterior view of a human heart indicated generally at 10. Heart 10 has a right atrium 11, and superior vena cava 16. Blood from the body flows through vena cava 16 into right atrium 11. The pressure of the blood in right atrium 11 is low as the blood flows into atrium 11. Blood is pumped from the heart to the body tissues via the aorta 23. The pressure differential of the blood between aorta 23 and the superior vena cava 16 is approximately 90 mm Hg. The muscle tissue of the heart is provided with a supply of blood from coronary arteries such as the left coronary artery 24. Left coronary artery 24 extends from aorta 23 along the left side of the heart toward the apex 27. Coronary artery 24 has a number of branches 28, 29 and 30 which supply blood to the muscle tissue. Left coronary artery 24 has a short common stem which bifurcates or trifurcates into branches 28-30. These branches are very small in normal hearts. They may enlarge considerably in persons suffering from coronary arteriosclerosis in whom coronary arterial branches become obstructed or occluded. A right coronary artery also supplies blood to the heart. The graft of the invention can be used to provide an adequate supply of blood to any coronary artery.
Referring to FIGS. 1-5 there is shown a vascular graft of the invention indicated generally at 36. Graft 36 is an elongated tubular member 37 having a continuous passage for carrying blood. Tubular member 37 has a continuous cylindrical wall 38 having an inside surface 39 forming an elongated longitudinal passage 40. Tubular member 37 has an aortic or inlet end 41 and an atrial or outlet end 42. A main body 43 extends from inlet end 41 to a restricted or reduced diameter section 44. Restricted section 44 is connected to a downstream segment 46. Preferably, restricted section 44 is less than about 5 cm from outlet end 42 when it is attached to the heart tissue. This location for the restriction section 44 in near proximity to the outlet end 42 will reduce the amount of tubular member located downstream from the restrictor and reduce the possibility for graft kinking to occur in this low pressure region of the graft.
As shown in FIGS. 2-5 restricted section 44 has a cylindrical wall 47 integral with cylindrical wall 38 of the main body 43 a downstream segment 46. Cylindrical wall 47 surrounds and is joined to a restrictor 12 which contains a throat region 13 and two varying diameter walls 49 and 51. The restrictor provides restriction of flow; typically, as shown in FIGS 3 and 5, by a throat passage 48 having a cross sectional area substantially smaller than the cross sectional area of passage 40. The cross sectional area of passage 40 is preferably more than four times larger than the cross sectional area of throat passage 48. The same restriction of flow could be provided by a non-circular throat region having smaller effective diameter than the effective diameter of passage 40, or by a combination of restricting areas such as multiple paths which together provide the effect of flow restriction. Converging wall 49 is joined to wall 47 at junction 14. Diverging wall 51 is joined to wall portion 47 at junction 15. Wall portion 20 surrounds an outlet passage 52 leading to the outlet end 42. The cross sectional area of outlet passage 52 is substantially the same as the cross sectional area of passage 40 of main body 43. The cross sectional area of outlet passage 52 can be larger or smaller than the cross sectional area of passage 40. Converging and diverging wall portions 49 and 51 each have a longitudinal length and an inside wall surface that has a gradual smoothly-varying diameter to minimize turbulence in the blood flow in the flow restrictor (second passage) and minimize stagnant regions in which deposits could build up. Preferably, cylindrical wall 13 surrounding passage 48 has a longitudinal length that is shorter than the longitudinal length of the wall portions 49 and 51. Other length and size relationships can be used. The longer the length of throat region 13, the greater the blood pressure drop for a given cross sectional area of passage 48. The restrictor is made with a smooth surface finish so that platelet deposition and activation will not result in thrombosis of the restrictor. Interior surface 39 has a biologic material, such as endothelial cells, applied to it; this biologic material typically does not extend into the restrictor region, due to the requirement for smooth surface finish of the blood contact surface of the restrictor, and since the restrictor typically has higher blood velocity and higher fluid shear stress at the blood contact surface which would tend to remove the biologic material. Passage 52 provides a chamber wherein the velocity and velocity gradients of the blood flow are decreased before it flows into the atrium of the heart or superior vena cava. Downstream segment 46 is of a size to permit easy attachment thereof to the heart tissue or blood receiving vessel. An outer sleeve 17 can be joined to wall 47 forming junctions at sites 18 and 19. The outer sleeve helps to hold the downstream segment 46 in an open cylindrical shape that is not kinked such that blood flow through the outlet end 42 is not blocked or restricted due to unwanted kinking. Outer sleeve 17 can have a conformation which closely approximates the geometry of the receiving vessel and further help to hold the receiving vessel open at the outlet end; FIG. 1 shows a beveled conformation. Outer sleeve 17 also provides a protection to the joints 14 and 15 by restrictions any relative motion between the restrictor 12 and the wall 47. The outer sleeve is an enhancement and is not always required. The preferred length of downstream segment 46 is 2 cm or less in order to reduce the likelihood of graft kinking on this low pressure section of graft. The main body of the graft 40 is not as prone to kinking due to the greater pressure of the blood contained within it during use.
Member 37 is a tubular structure, preferably made from a synthetic material such as polytetrafluoroethylene, polyester, silicone, or other polymeric material or a composite consisting of more than one material. The tubular structure can also be made from autologous, heterogeneous, or other biological tissue, including but not limited to a saphenous vein, human umbilical vein or bovine carotid artery. The tubular member can be pre-curved and tapered to form the desired restricted section 44 by processing; in this case, junctions 14 and 15 may be absent due to contiguous construction. The restrictor can be made from but is not limited to silicone, pyrolytic carbon, polytetrafluoroethylene, polyester, polyurethane, titanium, stainless steel, or other biological, polymeric, or non-polymeric materials. The restrictor 12 can be molded into the tubing member 38 using standard liquid polymeric injection or melt injection. In this case the formation of the restrictor 12 and its junctions 14 and 15 to the tubular wall 47 can occur in the same step. Conversely the restrictor 12 can be formed from a separate material and bonded to wall 47 as a separate operation. Alternatively, an insert with the shape of a restrictor can be manufactured separately and simply placed inside of the tubular member at the appropriate site.
Referring to FIG. 1, vascular graft 36 is located adjacent the heart 10. Restricted section 44 and downstream segment 46 are located adjacent superior vena cava 16. As shown in FIG. 6, inlet or aortic end 41 of tubular member 37 is implanted into an aortic ostium 53 and anastomosed thereto with sutures 54. Alternatively, inlet end 41 can be anastomosed to a different convenient high pressure vessel such as a the left subclavian artery or other major artery. As shown in FIG. 7, the open end of downstream segment 46 is implanted into an ostium 56 open to superior vena cava 16 and anastomosed thereto with sutures 57. The restrictor 44 is located close to outlet end 42 . The blood continuously flows through passage 40 of tubular member 37, by reason of the blood pressure difference between aorta 23 and superior vena cava 16. Restriction 44 prevents the flow of blood through passage 40 from being excessive. Alternatively, downstream segment 46 of tubular member 37 can be anastomosed to right atrium 11, left atrium 13, the inferior vena cava, coronary sinus, or other convenient low pressure vessel. The body 43 of graft 36 is located adjacent one or more of the coronary branches 28-30. The surgeon has the option to anastomose and, therefore, perfuse one or more of the coronary branches along the path of the graft 36. Referring to FIG. 8, graft 36 is anastomosed to coronary branch 35 with sutures 58. The cylindrical wall 38 is provided with an opening 59 to allow blood to flow from passage 40 into the coronary artery passage 61. The restricted passage 48 adjacent the outlet end of the graft allows the coronary arteries to be perfused with sufficient quantities of blood at pressures within a few mm Hg of the aortic blood pressure. The flow of blood through restricted passage 48 is laminar and continues as a transitional flow through the passage 52 into superior vena cava 16. There is a minimum of turbulence of the blood in graft 36. The interior surface 39 of the tubular member 37 is preferably smooth and continuous, but may have steps or transitions of geometry or of material, such as when using a separate insert is placed inside the graft to form the restrictor.
Tests indicate that, using a 5 mm diameter tubular graft with a simulated aortic flow of approximately 5000 ml per minute and pressure of 100 mm Hg, approximately 500 to 700 ml per minute will flow through a 2 mm restriction into the superior vena cava or right atrium. The cardiac output will increase about 10 to 15 percent to accommodate the flow to the receiver through the restricted portion of the graft. Excessive flow to the receiver could require too much increase in cardiac output; one of the functions of the flow restrictor is to control the flow to a level which could be normally tolerated by the patient. Each coronary artery supplied with blood will require about 50 to 150 ml per minute of blood for adequate perfusion, with the total resting coronary flow approximately 250 ml/min, combining all coronary arteries. Since an unrestricted 5 mm graft anastomosed to an aorta can provide blood flow well in excess of 2000 ml per minute, an adequate blood supply is available for as many coronary branches as may be required. A surgeon may choose to use an autogenous saphenous vein, a synthetic graft or a biological conduit for the tubular member 37 of the graft.
Referring to FIGS. 9-11, there is shown a segment of graft that contains a restrictor segment 44 as a continuous part of tubular member 37. This graft does not require a joining or bonding of restrictor wall 22 to the wall 38 of the tubular member 37 since they are continuous or formed from the same material. The flow surface 23, 24, and 25 of the restrictor must be smooth and relatively free of defects to prevent thrombotic deposits of adhering to the surface. The interior surface, other than the blood contact surface of the restrictor, has a biologic material, such as endothelial cells, applied to it; this biologic material typically does not extend into the restrictor region, due to the requirement for smooth surface finish of the blood contact surface of the restrictor, and since the restrictor typically has higher blood velocity and higher fluid shear stress at the blood contact surface which would tend to remove the biologic material.
Referring to FIGS. 12-17, there is shown a segment of an autogenous saphenous vein indicated generally at 70 comprising an elongated member 71. Member 71 has a continuous cylindrical wall 72 surrounding a passage or lumen 73 for accommodating flowing blood. The inlet end 74 of member 71 has an opening 75. The saphenous vein 70 follows a path about the heart to reach occluded arteries in the manner of graft 36, as shown in FIG. 1. Lumen 73 has a generally uniform diameter from the inlet end 74 to the outlet end 76. A blood flow restrictor or tubular segment indicated generally at 77 is anastomosed to outlet end 76 of vein 70. Blood flow restrictor 77 has an inlet end section 78 and an outlet end section 79 joined to an intermediate throat section 81. The restrictor contains a smooth inner surface with a surface finish that will not allow platelets or thrombotic deposit to build up on the flow surface of throat section 81. Other portions of the restrictor have a biologic material, such as endothelial cells, applied to the inner surface. A porous or non-smooth surface with general surface finish of 5-10 micron defects in size can result in thrombosis of the restrictor. Flow surfaces in high shear regions of a flow restrictor of approximately 10-30 micron finish will not be swept clean by the shear stresses imposed by the blood flow. Inlet passage 82 communicates with a restricted passage 83 in throat section 81; passage 83 communicates with an outlet passage 84 with outlet end 86. The cross sectional area of outlet passage 84 is substantially the same as the cross sectional area of the inlet passage 82. The size of restricted passage 83 can vary relative to the size of inlet passage 82. Preferably, the diameter of inlet passage 82 is more than twice the diameter of restricted passage 83. The cross sectional area of passage 82 is preferably more than four times the cross sectional area of throat passage 83. Passage 83 allows blood to continuously flow through lumen 73 at a desired blood pressure in lumen 77 so that one or more coronary arteries can be perfused. The outlet end section 79 has an open outlet 86 allowing blood to flow into the superior vena cava when section 79 has been anastomosed to the superior vena cava. In use, the surgeon harvests a section of the saphenous vein from the leg of the patient. A blood flow restrictor 77 having the desired size restricted passage 83 is secured with sutures 87 to outlet end 76 of tubular member 71. The inlet end 74 is anastomosed to aorta 23. Tubular member 71 encircles the heart to locate outlet end 79 of restrictor 77 adjacent the superior vena cava. End 79 is anastomosed to the superior vena cava so that a continuous and adequate flow of blood is maintained through tubular member 70 and restrictor 77. The blood is at a desired pressure so that one or more coronary arteries can be perfused. The surgeon can anastomose one or more coronary arteries along the path of tubular member 70 in a manner, as shown in FIG. 11. This allows the continuous flow of blood under pressure from passage 73 into the lumen of the coronary arteries.
Graft kinking is a major concern for vascular graft implants and can lead to device failure if not properly considered. FIG. 18 shows a graft segment with a restrictor section 44 located near the outlet end 42. The inlet end 41 is typically attached to the aorta thereby putting tubular member 37 under aortic pressure and resistant to kinking. The junction 101 between the restricted section 44 and the tubular body may be prone to kinking due to differences in flexibility of the tubular member and the restricted section. A spiral bead of polymeric material 100 such as silicone, polyolefin, Dacron, polytetrafluoroethylene, or other material can be wrapped around the tubular body 37 in order to reduce the likelihood of graft kinking; the wrapped portion of tubular body 37 can range from approximately 1 cm to the entire length of tubular body 37.
FIG. 19 shows a graft segment with the restrictor 44 located at a distance of more than 1 cm from the outlet end 42; the downstream segment 46 of the graft is prone to kinking since the pressure contained within this segment is similar to the low pressure found in the venous system of the body. In this segment, polymeric loops have been attached to the outer surface of the downstream segment 46. The toroidally shaped loops can be made of a polymeric, metallic, or composite material which holds the downstream segment 46 in a circular cross sectional shape thereby preventing kinking in this region.
Referring to FIGS. 20-22 there is shown a segment of a vascular graft of the invention that contains a restrictor 44 placed at the outlet end of the graft. There is included a sewing ring 110 which provides for attachment to superior vena cava 16; sewing ring 110 is attached at points at or near its external edge 115. Sewing ring 110 has a biologic material, such as endothelial cells, applied to it. The restrictor contains a region 111 having smaller internal diameter and blood-contact surface 113. The smaller internal diameter region extends to superior vena cava 16, and blood-contact surface 113 is continuous with blood-contact surface 112 at sewing ring 110. Blood passes through smaller internal diameter region 111 and flows into superior vena cava 16 as shown at 114.
Referring to FIG. 23 there is shown a vascular graft similar to the graft of FIG. 1, but adapted to provide multiple segments 152 and 153 similar to body 43 of FIG. 1. Segments 152 and 153 can be made of synthetic or biological materials or any combination thereof and can be joined at site 154 so as to provide strength and prevent leakage of the blood contained within. A graft of the invention can be manufactured with multiple branches meeting at point 154, or multiple separate segments may be joined at point 154 using thermal, chemical, or other bonding methods, or the surgeon can attach multiple segments at the desired location 154. Segments 152 and 153 have inlet ends 150 and 151, respectively, shown attached to the aorta. Segments 152 and 153 can be located near coronary artery branches; segment 152 is shown adjacent to and attached at points 155 and 156 to coronary artery branches 28 and 29 on the anterior surface of the heart 10, respectively, and segment 153 is shown adjacent to and attached at point 157 to coronary artery branch 158 on the posterior surface of the heart 10. The graft provides blood to the coronary artery branches 28, 29 and 158. The advantage in having multiple separate segments such as segments 152 and 153 is that it allows connection to artery branches remote from each other, such as on the anterior and posterior surfaces of the heart, without requiring that the graft be extensively looped around from artery to artery, sharply bent, crossed over itself, or otherwise be routed in a poor manner. Segments 152 and 153 join at point 154, and a single flow restrictor 44 controls the flow of blood in the graft. The open outlet end 42 of downstream segment 46 is attached to superior vena cava 16. Referring to FIGS. 24 and 25, vascular graft 160 includes a tubular member 172 having an aortic or inlet end 162 and an outlet end 164 and a restricted section 166 connected to a downstream segment 168. A main body 170 extends from inlet end 162 to the restricted or reduced diameter section 166. Tubular member 172 has a continuous cylindrical graft wall 174 having an interior surface 176 and an external surface 178. The interior surface 176 forms an elongated longitudinal passage 180. The material 182 of which tubular member 172 is constructed may be expanded polytetrafluoroethylene, porous silicone, porous urethane, filamentous dacron, or other porous material or composite structure that can allow for penetration of tissue 181 through the continuous cylindrical graft wall 174 from the external surface 178 to the interior surface 176.
FIG. 25 shows a cross sectional view along line 25-25 of FIG. 24, where all numerals correspond to those elements previously described. The porous structure of the continuous cylindrical graft wall 174 is shown; interconnecting fiber material 182 is indicated. Although the porous structure can be obtained by a plurality of interconnecting pores in a matrix of interconnecting fibers, any structure that will allow penetration of tissue 181 through the continuous cylindrical graft wall 174 from the external surface 178 to the interior surface 176 can be utilized.
Referring to FIGS. 26 and 27, vascular graft 186 includes a tubular member 188 having an aortic or inlet end 190 and an outlet end 192 and a restricted section 194 connected to a downstream segment 196. A main body 198 extends from inlet end 190 to the restricted or reduced diameter section 194. Tubular member 188 has a continuous cylindrical graft wall 200 having an interior surface 202 and an external surface 204. The interior surface 202 forms an elongated longitudinal passage 206. The material 184, of which tubular member 188 is constructed, may be expanded polytetrafluoroethylene, porous silicone, porous urethane, filamentous dacron, or other porous material or composite structure that can allow for penetration of tissue 210 through the continuous cylindrical graft wall 200 from the external surface 204 to the interior surface 202.
FIG. 27 illustrates a view along line 27-27 of FIG. 26 where material 184, of a larger porosity or greater distance between the fibers, with respect to the material 182 of FIG. 25, makes up the structure of the continuous cylindrical graft wall 200 of FIG. 26 has been incorporated. The interior surface 202 has had endothelial cell seeding or sodding 208 applied to it and has resulted in the laydown of tissue 210 on the interior surface 202 subsequent to . penetration through the continuous cylindrical graft wall 200. Cellular tissue 210 can penetrate into the great external surface 204 and migrate through the continuous cylindrical graft wall 200 to reach the interior surface 202. The presence of cellular tissue 210 on the interior surface 202 of the vascular graft 186 imparts a biocompatible aspect to interior surface 202 in the form of reduced platelet adhesion and activity and reduced amount of thrombus formation. This neointima will also reduce the leakage of serum on blood fluids from moving from the interior surface 202 of the vascular graft 186 to the external surface 204 before the continuous cylindrical graft wall 200 has had time for tissue 210 to penetrate into the pores from the external surface 204.
Referring to FIGS. 28 and 29, vascular graft 212 includes a tubular member 214 having an aortic or inlet end 216 and an outlet end 218 and a restricted section 220 connected to a downstream segment 222. A main body 224 extends from inlet end 216 to the restricted or reduced diameter section 220. Tubular member 214 has a continuous cylindrical graft wall 226 having an interior surface 228 and an external surface 230. The interior surface 228 forms an elongated longitudinal passage 232. The material 234, of which tubular member 214 is constructed, may be expanded polytetrafluoroethylene, porous silicone, porous urethane, filamentous dacron, or other porous material or composite structure that can allow for tissue penetration through the continuous cylindrical graft wall 226 from the external surface 230 to the interior surface 228.
FIG. 28 shows an alternate embodiment similar to that of FIGS. 24 and 26 which incorporates a porous graft wall. FIG. 29 shows a partial cross section analogous to that of FIGS. 25 and 27. In this embodiment, the interstices or pores of the continuous cylindrical graft wall 226 contain biologic material 235 which modulates the biologic response to the graft. The biologic material 235 can either fill the pore space, such as pore space 236, or provide a coating 235a onto the fibers 240 or material that comprises the continuous cylindrical graft wall 226. In this case, it is not necessary to sod the blood-contact interior surface 228 with endothelial cells, but instead the biologic material 235 and 235a modulates the natural response by the recipient to provide the needed effects of controlling thrombosis and intimal thickening. For example, the recipients native tissue (not shown) can migrate and proliferate onto interior surface 228 and provide endothelial cells to cover the blood contact surface of the graft. The grafts of the invention can be used to carry blood in other applications such as in peripheral revascularization procedures of the lower extremities. For example, the graft would be interposed between the most outlet arterial anastomosis and the popliteal vein or one of its major branches. The source of blood or blood supply would be the femoral artery and anastomosis would be made from opening (s) in the body of the graft to blood-requiring vessel (s) such as the popliteal artery and/or its outlet branches, the anterior tibial, posterior tibial, or peroneal arteries. The blood flow restricting passage or throat passage located between these arteries and the outlet end of the graft controls the blood flow through the graft. The control of blood flow allows adequate perfusion of blood pressure to these arteries and at the same time insures continuous blood flow to maintain patency of the graft.
While there has been shown and described the preferred embodiments of the graft of the invention, and method of supplying a continuous blood flow to one or more arteries, it is understood that changes in the materials, size, length of the graft, and location of the graft may be made by those skilled in the art without departing from the invention. The invention is defined in the following claims.
10 heart 38 cylindrical wall
11 right atrium 39 inside surface
12 restrictor 40 longitudinal passage
41 aortic or inlet
14 junction end
42 atrial or outlet
16 superior vena cava end
17 outer sleeve 43 main body
18 flow surface 44 restricted or reduced
19 flow surface diameter section
20 flow surface
44a continuous restrictor
21 wall portion segment
22 restrictor wall 44b restrictor
46 downstream segment
24 left coronary artery 47 cylindrical wall portion
48 throat passage
28 branch 29 branch 49 varying diameter wall 30 branch 51 varying diameter wall
34 passage 52 outlet passage
35 coronary branch 53 aortic ostium
36 vascular graft 57 sutures
37 tubular member 59 opening
150 inlet end 61 coronary artery 151 inlet end passage
152 multiple segment
70 autogenous 153 multiple segment saphenous vein
71 elongated member
155 attachment point
72 cylindrical wall 156 attachment point
157 attachment point
73 passage lumen
158 coronary artery
74 inlet end branch
75 opening 160 vascular graft
76 outlet 162 inlet end
77 flow restrictor 164 outlet end
78 inlet end 166 restricted section
79 outlet end 168 downstream segment
81 intermediate 170 main body throat section
172 tubular member
82 inlet passage
83 restricted passage cylindrical graft wall
84 outlet passage
176 interior surface
86 outlet end
178 external surface
102 polymeric loops
103 outer surface
110 sewing ring
111 region 184 material
113 contact surface 186 vascular graft
114 blood flow 188 tubular member
115 external edge 190 inlet end 235 biological material
192 outlet end
236 pore space
196 downstream segment
198 main body
200 continuous cylindrical graft wall
202 interior surface
204 external surface
212 vascular graft
214 tubular member
216 inlet end
218 outlet end
220 restricted section
222 downstream segment
224 main body
226 continuous cylindrical graft wall
228 interior surface
230 external surface
234 fiber material Various modifications can be made to the present invention without departing from the apparent scope hereof.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4562597 *||29 Apr 1983||7 Jan 1986||Possis Medical, Inc.||Method of supplying blood to blood receiving vessels|
|US4601718 *||13 Jul 1984||22 Jul 1986||Possis Medical, Inc.||Vascular graft and blood supply method|
|US4921495 *||24 Mar 1986||1 May 1990||Kanegafachi Kagaku Kogyo Kabushiki Kaisha||Porous artificial vessel|
|1||*||See also references of EP0957822A4|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|EP1339356A2 *||30 Oct 2001||3 Sep 2003||Children's Medical Center Corporation||Tissue-engineered vascular structures|
|EP1339356A4 *||30 Oct 2001||7 Jul 2004||Childrens Medical Center||Tissue-engineered vascular structures|
|International Classification||A61F2/06, A61L27/00|
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