Abstract:
The present invention provides a novel bifurcated stent for providing retrograde flow of oxygenated blood from the left ventricle to the myocardium via the coronary sinus without a significant or deleterious left-to-right shunt. The present invention includes a main covered stent and a side limb, generally contemplating a Y or a T shaped bifurcated stent.

Description:
BACKGROUND  
         [0001]    I. Field of Invention  
           [0002]    The present invention contemplates a bifurcated stent for supplying oxygenated blood retrogradely from the left ventricle to the myocardium through the coronary sinus. The percutaneously-delivered stent directs blood from the left ventricle to the coronary sinus. By controlling the amount of blood flowing into the bifurcated stent and the right atrium, blood is directed retrogradely through the side limb of the present invention to the heart tissue.  
           [0003]    II. Description of Related Technology  
           [0004]    Retrograde perfusion of the heart through the coronary sinus has long been known for treating end-stage heart disease. Previous methods, among others, have attempted to connect the aorta to the coronary sinus during open-heart surgery using a graft of the jugular vein, the internal mammary artery, or the carotid artery. Alternatively, an occlusion balloon has been used for a short period of time.  
           [0005]    Nelson et al. (U.S. Pat. No. 5,824,071, 1998) discloses an apparatus and method for providing retrograde perfusion directly from the left ventricle to the coronary sinus. Although Nelson requires a pressure sensitive valve that prevents pressure build-up inside the coronary sinus from rising above 60 mm Hg, Nelson does not teach how such a valve may be constructed. Nelson does not teach or describe the features or components of such a pressure sensitive valve. Further, it is unlikely that such a device may be introduced percutaneously and will likely require invasive surgery.  
           [0006]    In 2000, Patel et al. conducted an experiment for percutaneous arterialization of the coronary sinus using a stent. See Patel et al.,  Percutaneous Transmyocardial Intracardiac Retroperfusion Shunts: Technical Feasibility in a Canine Model,  JVIR 2000, 11:382-390. The stent employed by Patel, et al., however, results in a significant shunting of oxygenated blood from the left ventricle to the right atrium (hereinafter “left-to-right shunt”). These shortcomings in the prior art are solved by the present invention.  
         SUMMARY OF INVENTION  
         [0007]    The present invention incorporates by reference application Ser. No. 09/796,528, titled A STENT FOR ARTERIALIZATION OF CORONARY SINUS AND RETROGRADE PERFUSION OF THE MYOCARDIUM, filed Mar. 2, 2001, and application Ser. No. ______, TWO-PIECE STENT COMBINATION FOR PERCUTANEOUS ARTERIALIZATION OF THE CORONARY SINUS AND RETROGRADE PERFUSION OF THE MYOCARDIUM, filed Jan. 7, 2002.  
           [0008]    It is an object of the present invention to provide a novel covered stent for providing retrograde flow of oxygenated blood from the left ventricle to the myocardium via the coronary sinus without a significant or deleterious left-to-right shunt. The present invention includes a main covered stent and a side limb, generally contemplating a Y or a T shaped bifurcated stent.  
           [0009]    In a preferred embodiment, the bifurcated stent has a main covered stent and a side limb. The main covered stent preferably has a tubular shape with a passageway therethrough and has a leading end and a trailing end. The main covered stent preferably has a smaller cross-sectional area or passageway at the leading end and the trailing end in comparison to the remainder of the main covered stent. Also, the main covered stent has a main stent, which is covered with a graft. Optionally, the leading end portion of the main stent may not be covered. The main covered stent also has an opening about the middle portion of its length.  
           [0010]    The side limb of the bifurcated stent is preferably either attached about the opening or fits within the opening to complete the T or Y shape. Thus, the side limb is in contact with the main covered stent about said opening. The side limb has a side stent and a cuff that is optional. The cuff, when present, is preferably attached to the graft of the main covered stent or is continuous with the main covered stent. A side stent, however, may or may not be attached (e.g., pre-attached or attached by being woven in a continuous manner to the main stent or by being stitched to the main stent) to the main stent. Thus, the side limb, which has a side stent and an optional cuff, provides a passageway for blood flow retrogradely to the myocardium.  
           [0011]    Various embodiments are contemplated in the present invention. In one embodiment, the side limb may include both a cuff and a side stent, wherein the side stent is not attached to the main stent. In this embodiment, after the main covered stent is first delivered, the side stent is delivered to fit within the cuff. In another embodiment, the side limb may include the side stent but not the cuff, and the side stent is pre-attached to the main stent by being stitched or weaved (in a continuous fashion) to the main stent. In this embodiment, both the main covered stent and the side limb are delivered at the same time. In yet another embodiment, the side limb only has a side stent without the cuff, wherein the side stent is not attached to the main stent. In this embodiment, after the main covered stent is delivered, the side stent is delivered to fit within the opening.  
           [0012]    For delivery, the main covered stent and the side limb may be compressed to fit within a catheter for percutaneous delivery into desired position. Upon delivery, the main covered stent may self expand to form a friction fit within the coronary sinus. The leading end is preferably positioned in the left ventricle, and the majority of the main covered stent fits substantially within the coronary sinus. The trailing end of the main covered stent may be in the right atrium or within the coronary sinus, preferably near the coronary ostium.  
           [0013]    In delivering the present invention percutaneously, the opening or side limb is preferably aligned to face the upstream portion of the coronary sinus. All other lengths and placements preferably correlate to this placement. The side limb is positioned so that it preferably fits within the upstream portion of the coronary sinus and opens toward the myocardium. For fluoroscopic positioning, the opening is preferably marked with a ring made of radio-opaque material, such as platinum or gold.  
           [0014]    Blood from the left ventricle flows through the leading end and into the main covered stent. Because of the graft, blood then flows either out into the right atrium through the trailing end or into the upstream portion of the coronary sinus through the opening and the side stent. Some blood may also flow back into the left ventricle. Thus, the size of the passageway at the leading end controls the amount of blood flowing into the main covered stent; the size of the passageway at the trailing end controls the amount of blood flowing into the right atrium (“left-to-right shunt”); and the size of passageway of the side limb controls the amount of blood flowing into the upstream portion of the coronary sinus. These three sizes are interrelated, and therefore interdependently control the amount of retrograde flow. For example, diminishing the amount of left-to-right shunt increases the pressure in the coronary sinus while directing more blood flow through the side limb. Some amount of blood flow into the right atrium, however, is necessary to prevent excessive pressure build-up in the coronary sinus. Preferably, the sizes of the three passageways work together to prevent the coronary sinus pressure from rising above a suitable level, e.g., of about 50 mm Hg or in the alternative of about half systemic pressure, while at the same time avoiding excessive left-to-right shunting.  
           [0015]    The present invention also contemplates a percutaneous method of delivery of the bifurcated stent of the present invention to allow blood flow from the left ventricle to the coronary sinus. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0016]    [0016]FIG. 1A shows a preferred embodiment of a bifurcated stent according to the present invention, wherein the side stent is not attached to the main stent.  
         [0017]    [0017]FIG. 1B shows a preferred embodiment of a bifurcated stent according to the present invention, wherein the side stent is attached to the main stent and the cuff is not present in the side limb.  
         [0018]    [0018]FIG. 1C shows a preferred embodiment of a bifurcated stent according to the present invention, wherein the side stent is not attached to the main stent and the cuff is not present in the side limb.  
         [0019]    [0019]FIG. 2 represents a preferred placement of the bifurcated stent according to the present invention in a schematic diagram of the heart.  
         [0020]    [0020]FIG. 3 shows an apparatus for percutaneously delivering the bifurcated stent of the present invention.  
         [0021]    [0021]FIG. 4 shows an alternative embodiment of a bifurcated stent having flaring ends with constrictions near the trailing end and the leading end. 
     
    
     DETAILED DESCRIPTION  
       [0022]    A preferred embodiment of a bifurcated stent  101  according to the present invention is illustrated in FIG. 1A. The bifurcated stent  101  generally has a main covered stent  107  and a side limb  132 . The main covered stent  107  generally has a tubular shape with a passageway therethrough, having a leading end  103  and a trailing end  105 . The main covered stent  107  may have a slight bend or may otherwise be straight along its extent.  
         [0023]    The main covered stent  107  generally refers to a combination of an underlying main stent  113  (bare stent) and a graft  111  (covering). The graft  111  is preferably inside the main stent  113 , but may also be outside the main stent  113 . In another embodiment, the stent  113  may be sandwiched between an outer graft and an inner graft (not pictured). The graft  111  is made from any of a number of commercially available materials such as PET, PTFE, or other suitable material as known in the art. Hereinafter, the combination of the graft  111  and the main stent  113  will be referred to as the main covered stent  107 .  
         [0024]    The bifurcated stent  101  also has a side limb  132 , which forms the short limb of the Y or T shaped stent. The side limb  132  includes a side stent  131  and an optional cuff  123 . The cuff  123 , when present, is attached to the graft  111  of the main covered stent  107 . The side stent  131 , which is always present, however, may or may not be attached to the main stent  113  of the main covered stent  107 . The side stent  131  may be attached to the main stent  113  by stitching or weaving. In an alternative embodiment, the side sent may also be attached by being a continuous weave of the main stent. Various preferred embodiments are shown in FIGS. 1A, 1B, and  1 C.  
         [0025]    In the embodiment shown in FIG. 1A, the side limb  132  includes both the cuff  123  and the side stent  131 . Although the cuff  123  is pre-attached to the graft  111 , the side stent  131  is not attached to the main stent  113  of the main covered stent  107 . In this embodiment, the main covered stent  107  is first delivered to fit substantially within the coronary sinus, with the opening  125  facing the upstream portion of the coronary sinus. After delivering the main covered stent  107 , the side stent  131  is delivered to fit within the cuff  123 . The side stent  131  may also optionally fit within the opening  125 .  
         [0026]    In the embodiment shown in FIG. 1B, the side limb  147  includes the side stent  143  but does not contain a cuff. In further contrast to the embodiment in FIG. 1A, the side stent  143  is attached to the main stent  148 , e.g., by being connected or stitched or by being a continuous weave with the main stent  148 . The side stent  143  is preferably pre-attached, but may optionally be attached after delivery. The side stent  143  in this embodiment is relatively short and ranges in length from about 0.25 cm to about 1.0 cm. In this embodiment, the main covered stent  145  and the side limb  147  are delivered simultaneously since they are attached to form a single unit. The side limb  147  is preferably delivered to face the retrograde portion of the coronary sinus. In the embodiment shown in FIG. 1B, the portion of the main stent  148  near the leading end, preferably about 0.5 cm in length, is not covered with the graft  149 .  
         [0027]    In the embodiment shown in FIG. 1C, the side limb  156  includes only the side stent  151 . There is no cuff in this embodiment. Furthermore, the side limb  156  is not attached to the main stent  155  of the main covered stent  158 . In this embodiment, the main covered stent  158  is first delivered with the opening  154  facing the upstream portion of the coronary sinus. Because there is no cuff as in FIG. 1A, the side stent  151  is then positioned to fit within the opening  154 . In FIGS.  1 A- 1 C, the side limbs are in contact with the main covered stent about said opening. Other embodiments and variations, not specifically disclosed but obvious to one of ordinary skill in the art, are also contemplated in the present invention. Thus, FIGS.  1 A- 1 C as preferred embodiments are not meant to be exhaustive or limiting.  
         [0028]    Referring back to FIG. 1A, the opening  125  is preferably circular in shape and is located in the main covered stent  107  about the mid portion along its length. (The length between the leading end  103  and the opening  125  is preferably chosen to represent the distance between the left ventricle and the coronary sinus.) The opening  125  is preferably lined with a ring  121 , which is preferably made of radio-opaque material, such as platinum or gold, to facilitate placement during percutaneous delivery.  
         [0029]    Referring to the side limb  132 , the cuff  123  is made of the similar material as the graft  111  discussed above. In a preferred embodiment, the cuff  123  has a constant cross-sectional diameter equal to that of the opening  125 . In another embodiment, the cross-sectional diameter of the cuff  123  varies along its length.  
         [0030]    For the main covered stent,  107 , the cross-sectional diameter varies along its length. The main covered stent  107  generally has the smallest cross-sectional diameters (or passageway) at the trailing end  105  and at the leading end  103 . Thus, traveling from the trailing end  105  to the leading end  103 , the cross-sectional diameter of the main covered stent  107  increases until it reaches a maximum diameter. The maximum diameter may continue, may thereafter increase or decrease, but will eventually decrease down toward the leading end  103 . In a preferred embodiment as shown in FIG. 1, the main covered stent  107  has a shape that tapers in cross-sectional diameter toward the trailing end  105  and toward the leading end  103 .  
         [0031]    Referring to preferred dimensions, the length of the main covered stent  107  from the trailing end  105  to the leading end  103  is preferably from about 2 cm to about 6 cm, and more preferably from about 2 cm to about 5 cm. More particularly, the length of the main covered stent  107  from the trailing end  105  to the opening  125  is preferably from about 1 cm to about 4 cm, and more preferably about 2 cm. The length of the main covered stent  107  from the leading end  103  to the opening  125  is preferably from about 0.5 cm to about 3 cm in length, and more preferably about 1 cm.  
         [0032]    As for the preferred diameter of the cross-sectional area (or passageway), the trailing end  105  has a diameter of from about 1 mm to about 6 mm, and more preferably from about 2 mm to about 5 mm. The diameter of the passageway at the leading end  103  is preferably from about 1 mm to about 6 mm, and more preferably from about 2 mm to about 5 mm. The opening  125  also has a cross-sectional diameter of from about 1 mm to about 6 mm, and more preferably from about 2 mm to about 5 mm. The cross-sectional diameter of the side limb  132  may either be constant or may vary along its length. In the embodiment shown in FIG. 1A, the cross-sectional diameter of the side limb  132  is approximately the same as the cross-sectional diameter of the opening  125 .  
         [0033]    As discussed above, the side limb  132  may include a side stent  131 , which may or may not be attached to the main stent  113 . For example, as shown in FIG. 1B, if the side stent  143  is attached (by being connected, e.g., stitched to, or by being a continuous weave with) the main stent  148 , both the side limb  147  and the main covered stent  145  are allowed to expand after delivery. The side limb  147  is positioned to point toward the retrograde portion of the coronary sinus. In a preferred embodiment, the attached side stent  143  is from about 0.25 cm to about 1.0 cm in length. As shown in FIGS. 1A and 1C, however, the side stent  131  or  151 , which is not attached to the main stent  113  or  155 , is preferably from about 0.5 cm to about 2 cm in length.  
         [0034]    Referring back to FIG. 1A as an example, the side stent  131  is made preferably of surgical grade stainless steel or nitinol in woven design, and may be of any other configuration or material as known in the art or as commercially available. The side stent  131  also has a tubular shape with a passageway therethrough. The side stent  131  has a cross-sectional diameter after expansion of preferably from about 1 mm to about 6 mm, and more preferably from about 2 mm to about 5 mm.  
         [0035]    Although the cuff  123  is optional, it is advantageous in that it allows for a greater margin of error in inserting the side stent  131  into the retrograde portion of the coronary sinus. The cuff  123  allows the side stent  131  to be inserted in a more forgiving manner should the opening  125  not be aligned perfectly with the retrograde portion of the coronary sinus. In an alternative embodiment, the side stent  131  may protrude through opening  125  as a bare stent without the cuff  123 .  
         [0036]    The main stent  113  and side stent  131  are preferably made of a flexible material that can withstand bending without kinking to allow fluid passageway therethrough. The main stent  113  and side stent  131  also allow compression and expansion cross-sectionally. A number of suitable commercially available stents with these desired characteristics may be employed in practicing the present invention. Metallic stents as well as non-metallic stents may be used in the construction. Non-metallic stents, for example, may be made of a suitable plastic material. Suitable designs include various wire mesh designs and weave configurations as known in the art. In one embodiment, the main stent  113  and side stent  131  may have a coiled construction as known in the art.  
         [0037]    Referring now to FIG. 2, the bifurcated stent  101  of FIG. 1 is positioned in a schematic diagram of the human heart  200 . The heart  200  generally has a left ventricle  202 , a left atrium  206 , a right ventricle  222 , and a right atrium  210 . The left ventricle  202  is primarily responsible for delivering oxygenated blood to the body. The left atrium  206  receives oxygenated blood from the lungs, which is then delivered to the left ventricle  202 . The right atrium  210  is primarily responsible for receiving deoxygenated blood from the body. Deoxygenated blood then flows into the right ventricle  222  before being sent to the lungs for oxygenation. After perfusing the heart, blood from the coronary arteries normally drains to the coronary sinus  218  and into the right atrium  210 . The coronary ostium  226  connects the right atrium  210  to the coronary sinus  218 .  
         [0038]    In a preferred embodiment as shown in FIG. 3, the bifurcated stent  102 , which is compressed onto a catheter  143  and covered by a retractable sheath  141 , is introduced and placed into position before removing the sheath to expose the bifurcated stent  101 . The method used by Patel et al. may be employed in delivering the stent according to present invention. Patel et al.,  Percutaneous Transmyocardial Intracardiac Retroperfusion Shunts: Technical Feasibility In a Canine Model,  JVIR 2000, 11:382-390. Patel, et al. modifies the stent delivery method as described by Rosch, et al. in Rosch, et al.,  Coaxial Catheter, Needle System for Transjugular Portal Vein Entrance,  JVIR, Vol. 4, No. 1, pp. 145-147, 1993.  
         [0039]    Referring back to FIG. 2, a sheath is introduced into the jugular vein percutaneously, through which the coronary sinus  218  is catheterized and a wire is introduced. Once the catheter is removed, a stiff needle guide combination is passed over the wire as known in the art. The needle guide is aimed at the left ventricle  202  (marked with a percutaneously introduced pigtail catheter) and pierced through the coronary sinus wall into the left ventricle  202 . A guide wire is passed into the aorta (not pictured) and the needle guide is removed to leave a hole  301 . The hole  301  may be widened with a balloon catheter. The hole punctured allows for the main covered stent  107  to fit therebetween, and therefore blood flows from the left ventricle  202  into the passageway of the main covered stent  107 .  
         [0040]    Delivery involves placing the bifurcated stent  101  within a retractable sheath  141  as seen in FIG. 3 around catheter  143 . Catheter  143  also has a tip  145  which is guided by the guide wire  147 . After positioning, the retractable sheath  141  of the catheter  143  is removed, and the bifurcated stent  101  is allowed to expand, if the stent  101  is a self-expanding stent.  
         [0041]    Before removing the retractable sheath  141 , however, the catheter  143  is preferably rotated about the guide wire  147  to align the opening or the ring  121  with the upstream portion of the coronary sinus  218 . A catheter placed in the coronary sinus  218  for contrast injection may aid in aligning the ring  121  with the coronary sinus  218 . Referring back to FIG. 1, the opening  125  is bordered by the ring  121 , and the ring  121  is made of radio-opaque material, such as platinum or gold, to aide in the alignment of the opening  125  with the coronary sinus  218 . Thus, under fluoroscopic control, the ring  121  is aligned with the opaque or marked element in the upstream portion of the coronary sinus  218 . By occluding the trailing end  105  of the main covered stent  107  with a balloon catheter, blood flow will open the cuff  123  into the upstream portion of the coronary sinus  218  for alignment with the coronary sinus  218 . The cuff  123  is then reinforced with a side stent  131 , if the side stent  131  is not already attached to the main stent  113 .  
         [0042]    During delivery, the opening  125  or the side limb  132  is preferably aligned with the retrograde portion of the coronary sinus  218  as accurately as possible. After the opening  125  is aligned with the coronary sinus  218 , however, an additional extension stent (not pictured) as known in the art may be coupled to the main covered stent  107  at the leading end  103  so that the leading end  103  will be located within the left ventricle  202 .  
         [0043]    Once the ring  125  is aligned with the coronary sinus, the retractable sheath  141  is pulled back, and the bifurcated stent  101  is allowed to expand. The main covered stent  113  (see FIG. 1) and/or the side stent  131  is preferably self expanding, which expands upon introduction into the body. If the stent is not self expanding or has not fully expanded, a balloon catheter as known in the art may be used to expand the main covered stent  107  of the invention.  
         [0044]    Referring again to FIG. 2, the leading end  103  is positioned preferably within the left ventricle  202 . If the leading end  103  is not in the left ventricle  202 , an additional extension stent (not pictured), as discussed above, may be used to further elongate the leading end  103  portion of the stent  113 . The main covered stent  107  is positioned to lie primarily within the coronary sinus  218 . The trailing end  105  is preferably placed within the right atrium  210 . If the main covered stent  107  is too short for the trailing end  105  to reach the right atrium  210 , an extension (not pictured) as known in the art may be used. Alternatively, the main covered stent  107  may be within the coronary sinus  218 , preferably near the coronary ostium  226 . To help gauge the approximate length of the main covered stent  107 , a guide wire with radio-opaque marking every 1 cm may be used to measure the various relevant distances between the left ventricle  202  and the coronary ostium  226 . In another embodiment, the trailing end  105  may be positioned within the coronary sinus  218 .  
         [0045]    As the main covered stent  107  expands after release from the retractable sheath  141 , it expands to form a friction fit within the inner wall of the coronary sinus  218 . This friction fit keeps the main covered stent  107  stationary to prevent axial rotation and migration and therefore keeps the ring  121  or the side limb  132  in alignment with the retrograde portion of the coronary sinus  218 . The graft  111  of the main covered stent  107  directs blood flowing into the coronary sinus to flow through the passageway at the trailing end  105  or through the passageway of the side limb  132 . Some amount of blood in the main covered stent may also flow into the left ventricle through the leading end  103 .  
         [0046]    The amount of blood flow through the side limb  132  is generally inversely related to the amount of left-to-right shunting. Blood flowing from the left ventricle  202  into the main covered stent  107  flows out through the opening  125  and the side limb  132  to provide retrograde perfusion to the myocardium. The size of the diameter of the passageway at the trailing end  105  influences the amount of shunt. For example, decreasing the size of the passageway at the trailing end  105  increases the retrograde perfusion of the myocardium. If the flow rate to the passageway at the trailing end  105  is too great, the heart tissue would not adequately be perfused. Too small a diameter, however, may increase the pressure within the coronary sinus  218  to dangerous levels. Thus, the passageway at the trailing end  105  should be large enough to prevent excess pressure build-up, but at the same time be restrictive enough to allow the heart to be supplied with oxygenated blood. The size of the three passageways, at the leading end  103 , the trailing end  105 , and the opening  125 , are interrelated and balanced to influence the left-to-right shunt and the coronary sinus pressure. As an illustrative example only, and not as a limitation, the amount of shunting may preferably be less than approximately a one-and-a-half to one shunt ratio. In a preferred embodiment, the pressure within the coronary sinus  218  does not exceed about 50 mm Hg. In an alternative embodiment, the pressure within the coronary sinus  218  does not exceed about half systemic pressure.  
         [0047]    Coronary sinus pressure may also be controlled by the amount of blood flowing from the left ventricle  202  into the main covered stent  107 . Thus, the size of the passageway at the leading end  103  may be chosen in relation to the size of the passageway at the trailing end  105  to provide efficient retrograde perfusion of heart tissue without excessive pressure build-up.  
         [0048]    In an alternative embodiment, as seen in FIG. 4, the smallest cross-sectional diameter of the stent  501  may not be at the leading end  505  and the trailing end  509 , but may be approximately 1 mm to about 1 cm from the leading end  505  and the trailing end  509 . Thus, the stent  101  would have one or two flaring ends. The smallest cross-sectional area would be at constriction  520 , which is near the leading end  505 , and at constriction  522 , which is near the trailing end  509 . The cross-sectional area from the constriction  520  to the leading end  505  or the trailing end  509  may also be constant.