Abstract:
Improved stented grafts for coupling vascular members, and for use in surgical implantation during coronary bypass operations. The stented graft of the present invention comprises a plurality of graft link segments, each having a lumen for accommodating blood flow, and with at least one graft link segment being secured to one end of a vascular stent forming a junction between a supply lumen and a delivery lumen. The delivery lumen is arranged to be inserted into the patient&#39;s vascular system downstream from blockage in the coronary artery. In order to provide ease of access for the attachment of a second graft link segment to the stent assembly, the individual tubular element or elements defining the dual lumen assembly are axially offset, one from the other, in order to expose the free end of the stent for receiving a second graft link segment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of my co-pending application Ser. No. 09/491,566, filed Jan. 26, 2000, entitled “STENTED GRAFTS FOR COUPLING VASCULAR MEMBERS”, and assigned to the same assignee as the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to an improved vascular graft system, and in particular to a stented vascular graft system incorporating improved stents and grafts designed to provide flow transfer from an aortic source to a branch flow path for coronary bypass procedures. In accordance with the present invention, graft material is appropriately secured to the stent structure so as to facilitate this step in the coupling of the graft system to the vasculature of the patient, thereby expediting the surgical procedure while at the same time reducing the number of suturing steps necessary in the procedure. The features of the present invention are set forth in greater detail hereinafter. 
     Coronary bypass surgery has become a common procedure, and is normally indicated for conditions requiring replacement and/or reconfiguration due to blockage of the coronary blood flow within a patient. Apparatus and techniques are also disclosed herein for selectively monitoring the flow through a graft. The present invention involves use of a stented graft, and particularly wherein the stent is utilized to receive the graft and also for modifying the flow pattern through coupling to relevant portions of the vasculature. Two forms of stented grafts are utilized in a typical surgical procedure, with a first form being employed for introduction into a coronary artery downstream from a blockage site, and with the second form of stented graft being employed to couple the distal end of the graft network to a point of relatively lower flow pressure, and to serve as a terminus for the grafted structure. In the second form of stented graft, means are provided for suturing the stent to a selected location, typically at the right atrium or superior vena cava. The utilization of stented grafts facilitates and expedites the procedure while reducing the number of necessary steps, all of this being achieved without compromising the efficacy of the overall procedure. 
     In a typical bypass procedure, a section of the vascular system in a patient&#39;s body that has become impaired or inoperative through disease or other defect may be treated so as to improve flow to those portions previously being given an inadequate or limited supply of blood. In order to create the graft network, biocompatible graft material may be employed, such as, for example, Gortex™, with this being a polytetrafluoroethylene-based material normally being accepted by the patient&#39;s body. Thus, such graft material is frequently and typically utilized in bypass as well as in other procedures such as, for example, as a joint reinforcing material, such as a brace interposed across the knee. 
     Because of the physical properties of the biocompatible graft material, stent suturing, while possible, is frequently difficult to complete. The procedure is one which requires great dexterity, and when done at the site, is frequently in a zone with limited accessibility. In the design of the stent portion of the stented grafts, a certain degree of axial offset is provided in order to more fully and completely expose a portion of the stent to which a graft must be applied during the surgical procedure. Because of this greater accessibility and visibility, the stented graft device of the present invention is highly desirable. 
     Coronary bypass procedures are frequently undertaken with patients whose coronary arteries have been partially or almost completely blocked, thereby impeding and disrupting the proper flow of blood through the vascular system. While bypass procedures have been undertaken for some period of time, one meticulous and time consuming step is that of suturing the vascular graft elements. The time required for completing each such suture is reduced significantly through providing a pre-attached or stented graft in accordance with the present invention. 
     As a further feature of the present invention, means can be provided in combination with the vascular assembly for monitoring blood flow through various branches of the graft configuration. In particular, flow rate monitoring may be achieved through utilization of devices functioning in response to temperature variations resulting by introducing a temperature energy signal into the bloodstream, and measuring and/or detecting the thermal response at a downstream location. Another technique suitable for use in connection with the present invention is based upon the use of ultrasonic signals, wherein the system comprises one or more signal generators in communication with the blood flow (transducers) along with detection means, normally an array transducer exposed to the signal. Doppler techniques may be employed to determine flow rate and volume. Such systems are known in the art, with a thermal response system being disclosed in U.S. Pat. No. 5,989,192, and with ultrasonic systems being disclosed in U.S. Pat. No. 5,967,989; 5,807,258 and 5,588,436. 
     In order to evaluate the condition of an individual graft, determinations of flow velocity and overall blood volume provide a good indicator. A determination of pressure differentials between opposed ends of a graft will provide valuable information as well. Obviously, as deposits collect along the interior wall of a graft, pressure differentials will increase along with a corresponding decrease in velocity and flow volume. The utilization of the stented grafts in accordance with the present invention reduces some of the potential for buildup within certain other graft structures, this being accomplished by tailoring the configuration of the flow channel through the stent so as to preserve flow patterns, and also preserve and/or reduce the tendency for any increase in the Reynold&#39;s number within the blood flow through the graft network. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a family of stented grafts are provided for each bypass procedure. In addition to the terminal stent to be described hereinafter, at least one branch stent is provided for each procedure, with the branch stent comprising biocompatible material and including a feature for cross-flow from the supply channel which communicates with the aorta to a location in the coronary artery where flow correction is needed. This location is typically downstream of the blockage necessitating the bypass procedure. These stent devices are typically dual lumen with a cross-flow channel being provided between the lumens, thus permitting a portion of the blood from the main supply to be utilized for flow to the blockage site. In the dual lumen structure, a relatively large diameter lumen is employed for that portion of the graft which is in direct communication with the aorta, with the second lumen typically being of somewhat lesser overall diameter and being designed for insertion into a slit formed in the coronary artery requiring bypass. For many applications, a lumen diameter of approximately 2 mm. is desirable and useful, although lumens of slightly larger and/or smaller diameter may be appropriately considered. 
     The stented grafts also include a terminal or distal stent structure which is designed to be coupled directly to the terminus of the graft network, such as at the right atrium or superior vena cava. This terminal member includes a biocompatible body having a channel or bore therethrough which is provided with a suture flange at one end, and with a graft being secured to the other. As indicated above, the configuration of the bore is such that the flow rate is maintained consistent with that through the balance of the supply network, with the Reynold&#39;s number being held well within the laminar area. 
     In each instance, the graft material is pre-attached to the stent and is of a length which is more than ample for the contemplated use. Thus, the surgeon is able to cut the graft to a desired and required length in the course of the procedure, while at the same time, not having to disturb the integrity of the previously prepared secure junction between the stent and the graft. In the course of the overall procedure, therefore, the distal end of the bypass network including the graft segment along with an appropriate clamping network is secured in place at the vena cava or other low-pressure site, while continuing the process in the direction of the source, normally the aorta. The attachments are made in accordance with the conventional protocol fashion. The first stent is coupled through a slit formed in the pertinent vessel to provide bypass flow through a terminal stent to be described hereinafter. Thereafter, the graft portion of a second stented graft is cut to length, and thereafter sutured to the upstream side of the supply channel of the stent. When there is need for a bypass to one or more additional coronary arteries, an additional or second stent will be attached to each further diseased artery in the same fashion as indicated above. Finally, the stented graft utilizing the stent to be coupled to the upstream side of the supply channel is cut to length and appropriately secured and sutured to the right atrium and/or superior vena cava. 
     Therefore, it is a primary object of the present invention to provide an improved stented graft which is designed for use in graft networks for bypass procedures, and wherein the graft network is surgically implanted within the body of a patient, typically within the thorax. 
     It is a further object of the present invention to provide an improved stented graft wherein the graft is securely attached and coupled to the upstream end of the supply channel of a dual lumen stent, and wherein an internal cross-over is provided which permits metered flow of blood from the supply lumen to the coronary artery at a zone adjacent the diseased or impaired area of the artery. 
     It is a further object of the present invention to provide a family of dual stents which incorporate a supply lumen or channel portion along with a delivery lumen or channel portion, and wherein a separate cross-over lumen is provided for enabling blood flow from the supply channel to the delivery channel, and wherein the configuration of the stent is such that the end of the stent where suture attachment of a graft is required is axially positioned so as to be reasonably accessible to the surgeon so as to enable and facilitate suture attachment. 
     Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims, and accompanying drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is a front perspective view of a graft network employing the stented graft devices of the present invention, with this figure illustrating the stented grafts in place; and with the shaded areas showing where the stent has been inserted in the network for delivery of blood to a diseased coronary artery; 
     FIG. 2 is a front elevational view of one stent structure, illustrating a supply lumen together with a branch lumen, and with the cross-over between supply and branch lumens being shown as well, with the graft portion having been removed; 
     FIG. 3 is a front elevational view of a modified form of the cross-over of FIG. 2, and illustrating further the manner in which the graft is secured in place on the stent; 
     FIG. 4 is a front elevational view similar to FIG.  2  and illustrating a still modified form of stent, and with the graft portion being removed; 
     FIG. 5 is a front elevational view of a still further configuration for a stent, and being shown with the graft removed; 
     FIG. 6 is a top plan view of a stent designed for use at the distal end of the artificial graft, with a graft shown attached to the small end of the stent, with FIG. 6 being on a slightly reduced scale; 
     FIG. 7 is a side elevational view of the stent illustrated in FIG. 6, and shown with the graft portion removed; 
     FIG. 8 is a top plan view of a stent similar to that of FIG. 6, but with an oval configuration being employed for attachment to the aorta or vena cava; 
     FIG. 9 is a side elevational view of the stent apparatus of FIG. 8; and 
     FIG. 10 is a front perspective view of an alternate form of stented graft device of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In accordance with the preferred embodiment of the present invention, and with particular attention being directed to FIG. 1 of the drawings, the graft network generally designated  10  includes a graft segment  11  attached by suture to the aorta as at  12 , and with segment  11  being, in turn, affixed to a stent in place in the system as at  13 . Because of limitations of draftsmanship, the stent device does not appear in detail, but is in place with the branch lumen being in place in angularly disposed relationship along the shaded areas in coronary artery  14 . A second graft segment is provided as at  16 , which is operatively coupled and joined to the downstream supply side of stent  13 , with the distal end of graft  16  having been previously coupled to stent shown at  18 . Again, because of limitations of draftsmanship, stent  18  is in place between the shaded areas of coronary artery  19 . 
     A further graft segment is provided as at  21 , with graft segment  21  being sutured or otherwise secured to the distal end of the supply channel of stent  18 . Stent  23 , which has previously been affixed to graft  21 , is appropriately secured to the surface of the superior vena cava and is utilized to provide a suitable means for receiving that portion of the blood flow from the network  10  which does not otherwise pass from the network to coronary arteries  14  and  19 . 
     By way of example, the stents utilized in the example given above and interposed at  13  and  18  may be of a design selected from one of the stents illustrated in FIGS. 2,  3 ,  4  or  5 . By way of explanation, and with attention being directed to FIG. 2 of the drawings, stent generally designated  30  is a dual lumen device which comprises a pair of lumens arranged in parallel axial relationship within tubular members  31  and  32 . Member  31  functions as a supply lumen with tubular member  32  as a delivery member. Cross-over  33  is provided to meter an appropriate amount of blood flowing within supply tube  31  to tube  32 . A graft, not shown, is permanently attached to stent  30 , of a type as illustrated at  35  in FIG.  3 . Sutures as shown at  36  are utilized, in place, in order to couple or otherwise secure graft  35  to the proximal end of member  31 A. As is apparent from FIG. 1, an annular groove is formed within tubular members  31  and  32 , particularly as shown at  38 , in order to properly receive and retain suturing means therewithin. 
     It will be observed that tubular members  31  and  32  are offset, in an axial direction, one from the other. In this arrangement, the end shown adjacent annular groove  38  is arecessed and/or positioned beneath the corresponding suturing ring  39  in the delivery portion of stent  30 . In this arrangement, therefore, the opposed ends of tubular member  31  projects beyond the corresponding terminal end of delivery tube  32 , such as at  40  about the smaller delivery tube  32 . Also, annular groove  41  is provided to accommodate suture attachment of the next adjacent graft segment, with the suture operation being undertaken in the course of the actual procedure. It will be observed that the axial positioning of the tubular members  31  and  32 , one with respect to the other, is such that there is a significantly greater accessibility to end  40 , than to the opposed end. 
     Inasmuch as the configurations of the individual stents illustrated in FIGS. 3,  4  and  5  are essentially the same as those of FIG. 2, similar reference numerals and identical suffixes will be employed. For example, reference numerals  31 A,  32 A,  39 A, and  41 A designate structure similar to that described in connection with FIG. 2 without the alphabetical suffix. The primary distinction between the structures of FIGS. 2 and 3 lies in the configuration of the cross-over member  43 , with this member being positioned in angular relationship at an acute angle to the flow direction, rather than at a right angle as in the device of FIG.  2 . 
     FIG. 4 is likewise similar in its structure to that of FIG. 2, with the exception being that in the arrangement of the cross-over to a branch lumen utilizing a separate conduit, a bore is formed between the juncture points of supply lumen  50  and delivery lumen  51 , with the port being positioned securely within the juncture point, as at  52 . The orifice size is such that appropriate flow may be achieved. Also, as indicated in connection with FIG. 3, similar structural features found in FIG. 4 are designated with the alphabetical suffix “B” as corresponding to those numeric elements of FIG. 2, including elements  38 B,  40 B, and  41 B. 
     FIG. 5 is again similar in structure and function to that of FIG. 2, with the exception of the cross-over member shown at  55 . Cross-over member  55  blends into delivery member  56 , with flow being the same as that as illustrated and described in FIG.  2 . 
     In the arrangement illustrated in FIG. 5, it will be noted that the axial length and positioning of the members  56  and  57  are generally coincidental, one with the other. Because of the axial offset provided as at  55 , some limited relief is possible to enable the surgeon to suture a graft onto end  58 , with a graft (not shown) already having been affixed and secured to end  59 . 
     In certain applications, it may be appropriate to utilize tubular members which are arranged angularly, one to the other. In such an arrangement, the axial offset may be accomplished through the angular relationship of the individual tubular members. Such a configuration is present in the arrangement of FIG.  1 . 
     With attention now being directed to the embodiments illustrated in FIGS. 6-9, it will be observed that a distal or terminal end of the artificial graft is provided in stent generally designated  60  (FIG.  6 ), with stent  60  including a body member  61  having a configured bore formed therein illustrated in phantom as at  62 . Graft  63  is shown secured in place within annular groove  64  formed within the blood-receiving end of stent  61 . Stent  61  is designed to be secured by conventional suture to the wall of the atrium or superior vena cava, with suture retaining flange  65  being provided for that purpose. 
     The stent generally designated  70  illustrated in FIG. 8 is similar to that of stent  60 , with the exception of the configuration of the distal end  71 . It will be observed that distal end  71  is of oval configuration, with this configuration making it possible for attachment to a vessel having an angular configuration to flow, with the oval configuration being designed to preserve the laminar flow which is desirably achieved throughout the extent of the graft network. As is illustrated in FIG. 9, sewing flange  72  is provided around the circumference of stent  70 . 
     With attention now being directed to FIG. 10, the embodiment of the stented graft generally designated  80  includes a pair of individual tubular members  81  and  82  which are disposed in right angular relationship, one to the other. A graft  83  is coupled to one end of the tubing for the advantageous reasons as set forth above. Communication between tubing elements  81  and  82  is achieved through an appropriately positioned flow channel which communicates between the bores of members  81  and  82 . 
     In performing procedures with the stented grafts of the present invention, the surgeon forms a longitudinal slit in the coronary artery where blockage is known to be present, with the slit being formed downstream from the point of blockage. Thereafter, one end of the tubular stent element is introduced into the coronary artery, and thereafter upon appropriate manipulation, the opposed end is introduced through the same slit. Thereafter, a suture needle is passed through the tissue under the stent, and in alignment with the recess formed in the outer surface of the stent, with the suture then being brought up and ultimately tied. In certain instances, the suture procedure may include forming a continuous loop around the artery wall, and within the annular recess. 
     BIOCOMPATIBLE MATERIALS 
     As has been indicated, biocompatible materials are, of course, utilized in forming any and all of the components of the present invention. In fabricating the components for the present invention, and as previously indicated, biocompatible materials are selected. For the stent component, suitable materials may be selected from the group consisting of titanium, stainless steel, or plastics such as polytetrafluoroethylene, polyurethane, polyethylene, or the like. In certain instances, when a metal is employed, those portions of the stent which are exposed may be coated with a suitable biocompatible coating. 
     As previously indicated, the graft portion may comprise a suitable biocompatible material such as, for example, Gortex™, a well-known and frequently utilized polytetrafluoroethylene-based material. Such materials are, of course, commercially available. 
     STENT CONFIGURATION 
     In most situations and for most applications, orifices and lumens in the delivery side are typically in the range of about 2 millimeters in diameter, although the requirements of individual patients may indicate slightly larger or smaller diameters. This diameter range has been found to preserve laminar flow, with this preservation being a desirable feature for maintaining continuity of blood flow. The lumen on the supply side of the stent is typically of greater diameter, with this diameter being adequate to accommodate the necessary blood flow. Also, in order to preserve the pressure throughout the supply network, the diameters of the lumens on the delivery side should remain in the range set forth above. 
     It will be appreciated, therefore, that the features of the present invention enable the surgeon to more effectively and expeditiously complete the preparation and attachment of a graft network to the vasculature of a patient, and with the design and configuration of the features of the present invention, in particular, being helpful in this enablement. 
     It will be further appreciated that the specific examples provided herein are for purposes of illustration only, and are not to be construed as a limitation upon the scope to which the present invention is entitled.