Patent Publication Number: US-2021161658-A1

Title: Prosthetic Heart Valve for Transfemoral Delivery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to U.S. Provisional Application 60/978,794, filed Oct. 10, 2007, entitled, “Prosthetic heart valve specially adapted for transfemoral delivery,” which is assigned to the assignee of the present application and is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to prosthetic heart valves, and specifically to prosthetic heart values configured for transfemoral delivery. 
     BACKGROUND OF THE INVENTION 
     Aortic valve replacement in patients with severe valve disease is common surgical procedure. The replacement is conventionally performed by open heart surgery, in which the heart is usually arrested and the patient is placed on a heart bypass machine. In recent years, prosthetic heart valves have been developed which are implanted using minimally invasive procedures such as transapical or percutaneous approaches. These methods involve compressing the prosthesis radially to reduce its diameter, inserting the prosthesis into a delivery tool, such as a catheter, and advancing the delivery tool to the correct anatomical position in the heart. Once properly positioned, the prosthesis is deployed by radial expansion within the native valve annulus. 
     PCT Publication WO 05/002465 to Schwammenthal et al., which is assigned to the assignee of the present application and is incorporated herein by reference,  describes prosthetic devices for treating aortic stenosis. 
     PCT Publication WO 06/070372 to Schwammenthal al., which is assigned to the assignee of the present application and is incorporated herein by reference, describes a prosthetic device having a single flow field therethrough, adapted for implantation in a subject, and shaped so as to define a fluid inlet and a diverging section, distal to the fluid inlet. 
     US Patent Application Publication 2006/0149360 to Schwammenthal et al., which is assigned to the assignee of the present application and is incorporated herein by reference, describes a prosthetic device including valve-orifice attachment member attachable to a valve in a blood vessel and including fluid inlet, and a diverging member that extends from the fluid inlet, the diverging member including a proximal end near the fluid inlet and a distal end distanced from the proximal end to distal portion of the diverging member has a larger cross-sectional area for fluid flow therethrough than a proximal portion thereof. 
     US Patent Application Publication 2004/0236411 to Sarac et al., which is incorporated herein by reference, describes a prosthetic valve for replacing a cardiac valve, which includes an expandable support member and at least two valve leaflets made of a first layer of biological material selected from peritoneal tissue, pleural tissue or pericardial tissue. A second layer of biological material is attached to the support member. The second layer is also made from peritoneal tissue, pleural tissue or pericardial tissue. The second layer includes a radially inwardly facing surface that defines a conduit for directing blood flow. The valve leaflets  extend across the conduit to permit unidirectional flow of blood through the conduit. Methods for making and implanting the prosthetic valve are also described. 
     US Patent Application Publication 2006/0259136 to Nguyen et al,, which is incorporated herein by reference, describes a heart valve prosthesis having a self-expanding multi-level frame that supports a valve body comprising a skirt and plurality of coapting leaflets. The frame transitions between a contracted delivery configuration that enables percutaneous transluminal delivery, and an expanded deployed configuration having an asymmetric hourglass shape. The valve body skirt and leaflets are constructed so that the center of coaptation may be selected to reduce horizontal forces applied to the commissures of the valve, and to efficiently distribute and transmit forces along the leaflets and to the frame. Alternatively, the valve body may be used as a surgically implantable replacement valve prosthesis. 
     The following patents and patent application publications, all of which are incorporated herein by reference, may be of interest: 
     US Patent Application Publication 2005/0197695 to Stacchino et al. 
     U.S. Pat. No. 6,312,465 to Griffin et al. 
     U.S. Pat. No. 5,908,451 to Yeo 
     U.S. Pat. No. 5,344,442 to Deac 
     U.S. Pat. No. 5,354,330 to Hanson 
     US Patent Application Publication 2004/0260389 to Case et al. 
     U.S. Pat. No. 6,730,118 to Spencer et al.  
     U.S. Pat. No. 7,018,406 to Sequin et al. 
     U.S. Pat. No. 7,018,408 to Bailey et al. 
     U.S. Pat. No. 6,455,153 and US Patent Application Publication 2003/0023300 to Bailey et al. 
     US Patent Application Publication 2004/0186563 to Lobbi 
     US Patent Application Publication 2003/0130729 to Paniagua et al. 
     US Patent Application Publication 2004/0236411 to Sarac et al. 
     US Patent Application Publication 2005/0075720 to Nguyen et al. 
     US Patent Application Publication 2006/0058872 Salahieh et al. 
     US Patent Application Publication 2005/0137688 to Salahieh at al. 
     US Patent Application Publication 2005/0137690 to Salahieh at al. 
     US Patent Application Publication 2005/0137691 to Salahieh et al. 
     US Patent Application Publication 2005/0143809 to Salahieh et al. 
     US Patent Application Publication 2005/0182483 to Osborne et al. 
     US Patent Application Publication 2005/0137695 to Salahieh et al. 
     US Patent Application Publication 2005/0240200 to Bergheim 
     US Patent Application Publication 2006/0025857 to  Bergheim et al. 
     US Patent Application Publication 2006/0025855 to Lashinski et al. 
     US Patent Application Publication 2006/0047338 to Jenson et al. 
     US Patent Application Publication 2006/0052867 to Revuelta et al. 
     US Patent Application Publication 2006/0074485 to Realyvasquez 
     US Patent Application Publication 2003/0149478 to Figulla et al. 
     U.S. Pat. No. 7,137,184 to Schreck 
     U.S. Pat. No. 6,296,662 to Caffey 
     U.S. Pat. No. 6,558,418 to Carpentier et al. 
     U.S. Pat. No. 7,267,686 to DiMatteo et al.  
     SUMMARY OF THE INVENTION 
     In some embodiments of present invention, a prosthetic heart valve prosthesis comprises a collapsible support frame and a prosthetic valve. The support frame is shaped so as to define three commissural posts to which the prosthetic valve is coupled, an upstream skirt, and a plurality of downstream axial support extensions, commissural posts are arranged circumferentially around a central longitudinal axis of the valve prosthesis, and extend in a downstream direction at a first angle with respect to the central longitudinal axis. The upstream skirt includes a plurality cells that extend outward in an upstream direction. The skirt is configured to apply an axial force in a downstream direction on an upstream side of the native annulus and left ventricular outflow tract (LVOT). 
     The downstream axial support extensions join a downstream side of the skirt, and extend in a downstream direction at a second angle with respect to the central longitudinal axis, which second angle is greater than the first angle between the commissural posts and axis. Because of this greater angle, the downstream axial support extensions (a) apply an upstream axial force to a downstream side the native leaflet tips, (b) do not touch the leaflets of the prosthetic valve when the prosthetic valve is in its open position, (c) provides stability to the support frame. 
     In some embodiment of the present invention, the support frame is shaped so as to define a plurality of upper sinus support elements, which extend in a downstream direction. The upper sinus support elements are configured to rest against the upper aortic sinuses (i.e., the downstream portion of the aortic sinuses) upon  implantation of the valve prosthesis, so as to provide support against tilting of the prosthesis with respect to the central longitudinal axis thereof. For some applications, the support frame is shaped so as to define exactly three downstream axial support extensions and exactly six upper sinus support elements. 
     In some embodiments of the present invention, a prosthetic heart valve prosthesis is provided that is similar to the prosthesis described above, except as follows. A portion of cells of the support frame of the prosthesis are shaped to define a plurality of outwardly-extending short axial support arms, which extend radially outward and upstream from the central longitudinal axis of the prosthesis. The shape of the support frame allows the valve prosthesis to be implanted such that an upstream section of the prosthesis is positioned upstream to the native annulus of the patient, while the axial support arms are protrude over the tips of the native leaflets, and collectively define an outer diameter that is greater than the diameter of the tips of the native leaflets. The axial support arms are distributed around the circumference of the frame such that, depending on the rotational orientation of the valve prosthesis, the arms engage and rest against either a native valve commissure (riding astride the commissure) or a leaflet tip, such that the valve prosthesis is anchored axially regardless of the rotational orientation of the prosthesis. The axial support arms are sized so as to not extend to the floors of the aortic sinuses. This configuration applies an axial force to the native valve complex from below and above the complex, anchoring the valve prosthesis in place, and inhibiting migration of the prosthetic valve both upstream and downstream. This  configuration also allows the valve prosthesis to apply outward radial force to the native valve. 
     There is therefore provided, in accordance with an embodiment of the present invention, apparatus including a valve prosthesis for attachment to a native valve complex of a subject, the prosthesis including: 
     a prosthetic heart valve; and 
     a support frame, which is shaped so as to define:
         two or more commissural posts, to which the prosthetic heart valve is coupled, which posts are arranged circumferentially around a central longitudinal axis of the valve prosthesis, and extend in a downstream direction at a first angle with respect to the central longitudinal axis,   a bulging upstream skirt, and   a plurality of downstream axial support extensions, which join a downstream side of the upstream skirt, which extend in a downstream direction at a second angle with respect to the central longitudinal axis, the second angle greater than the first angle, and which are configured to apply an axial force to a downstream side of native leaflet tips of the native valve complex.       

     In an embodiment, the support frame is shaped so as to define a plurality of upper sinus support elements, which extend in a downstream direction, and which are configured to rest against native upper aortic sinuses. 
     The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which:  
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic illustrations of a valve prosthesis, in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic illustration of a delivery system for delivering the valve prosthesis of  FIG. 1  to a target site and implanting the prosthesis at the site, in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic cross-sectional illustration of a front end of a catheter of the delivery system of  FIG. 2 , in accordance with an embodiment of the present invention; 
         FIGS. 4A-L  schematically illustrate a procedure for implanting the valve prosthesis of  FIG. 1  using the delivery system of  FIG. 2 , in accordance with an embodiment of the present invention; 
         FIGS. 5A-C  axe schematic illustrations of three different possible rotational orientations of the valve prosthesis of  FIG. 1  with respect to the native valve upon deployment, in accordance with an embodiment of the present invention; 
         FIGS. 6A-D  are schematic illustration of another valve prosthesis, in accordance with an embodiment of the present invention; 
         FIGS. 7A-D  schematically illustrate a portion of a procedure for implanting the valve prosthesis of  FIGS. 6A-C  using the delivery system of  FIG. 2 , in accordance with an embodiment of the present invention; 
         FIGS. 8A-C  show the valve prosthesis of  FIGS. 6A-D  in place within the native aortic valve of the patient, in accordance with an embodiment of the present  invention; 
         FIG. 9  is a schematic illustration of a catheter tube, in accordance with an embodiment of the present invention; and 
         FIG. 10  is a schematic illustration of a shaped balloon, in accordance with an embodiment of the present invention.  
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS. 1A and 1B  are schematic illustrations of a valve prosthesis  30 , in accordance with an embodiment of the present invention.  FIG. 1B  shows the prosthesis including a prosthetic valve  21  and a skirt  31 , as described below, while  FIG. 1A  shows the prosthesis without these elements for clarity of illustration. Valve prosthesis  30  comprises a collapsible support frame  40 , which typically comprises exactly three commissural posts  34 , arranged circumferentially around a central longitudinal axis  16  of valve prosthesis  30 . Valve prosthesis  30  further comprises prosthetic downstream valve  2  coupled to commissural posts  34 . Valve  21  typically comprises a pliant material. The pliant material is configured to collapse inwardly (i.e., towards central longitudinal axis  16 ) during diastole, in order to inhibit retrograde blood flow, and to open outwardly during systole, to allow blood flow through the prosthesis. 
     Valve prosthesis  30  is configured to be implanted in a native diseased valve of a patient, such as a native stenotic aortic or pulmonary valve, using a minimally-invasive approach, such as a beating heart endovascular retrograde transacrtic, e.g. transfemoral, procedure. Support frame  40  is typically collapsed or crimped so that its diameter is reduced in order to facilitate loading onto a catheter or cannula for delivery to the native valve site during a minimally-invasive delivery procedure, as described hereinbelow with reference to  FIGS. 2, 3, and 4A -L. Support frame  40  is configured such that application of radial forces thereon radially compress the frame, reducing the frame&#39;s outer diameter. Upon removal of the radial forces, the frame assumes its  earlier diameter and shape. The prosthesis, while the frame is in its compressed state, is loaded into a tube sufficiently small to allow transluminal delivery to the patient&#39;s native valve site. Support frame  40  comprises a suitable material that allows mechanical deformations associated with crimping and expansion of valve prosthesis  30 , such as, but not limited to a superelastic material, such as nitinol, or a stainless steel alloy (e.g., AISI 316). 
     Support frame  40  is typically shaped to define an upstream section  22 , a throat section  24 , and a downstream section  26 . The cross-sectional area of upstream section  22  gradually decreases from an upstream end thereof to a downstream end adjacent to throat section  24 . The diameter of throat section  24  is typically larger than that of the aortic annulus of the intended patient. The cross-sectional area of downstream section  26  gradually increases to an area greater than that of throat section  24 . Thus the cross-sectional areas of both the upstream and downstream sections are greater than that of the throat section. Throat section  24  is configured to be placed within the leaflet section of the native valve, slightly above the aortic annulus at the ventriculo-aortic border, such that downstream section  22  is located in the aorta, such as in the aortic sinuses. 
     Typically, support frame is elastic, and is shaped so as to define a plurality of collapsible cells. For example, the support frame may be fabricated by cutting a solid tube. The cells may be diamond-shaped, parallelogram-shaped, or otherwise shaped to be conducive to crimping the frame. Downstream section  26  is typically shaped so as to define bulging upstream skirt   31 , which is configured to apply an axial force directed toward the ascending aorta. Optionally, skirt  31  is shaped so as to define one or more barbs  32  positioned circumferentially such that the barbs pierce the native vale annulus in order to provide better anchoring. Typically, valve prosthesis  30  further comprises a skirt covering  35  which is coupled to upstream skirt  31 , such by sewing the covering within the skirt (configuration shown in  FIG. 1B ) or around the skirt (configuration not shown). Skirt covering  35  may comprise, for example, polyester or a processed biological material, such as pericardium. Support frame  40  thus defines a central structured body for flow passage that terminates in an upstream direction in a flared inlet (upstream skirt  31 ) that is configured to be seated within an LVOT immediately below an aortic annulus/aortic valve. 
     Typically, a portion of the cells of support frame are shaped to define a plurality of outwardly-extending short axial support arms  33 , which extend radially outward and upstream from central longitudinal axis  16 . Axial support arms  33  are distributed around the circumference of the frame at a predetermined height from the upstream end of the frame, and may be either evenly (as shown in  FIGS. 1A and 1B ) or unevenly distributed (not shown in the figures) around the circumference. Support frame  40  typically is shaped to define at least three axial support arms  33 , such as greater than three arms. For some applications, the number of support arms is a multiple of three, such as six (as shown in  FIGS. 1A and 1B ). 
     The shape of support frame  40  allows valve prosthesis  30  to be planted such that upstream section positioned upstream to the native annulus of the  patient, while axial support arms  33  protrude over the tips of the native leaflets, and collectively define an outer diameter D that is greater than the diameter of the tips of the native leaflets. Axial support arms  33  flare out latera in an upstream direction during deployment at an angle β with central longitudinal axis  16  valve prosthesis  30 . Axial support arms  33  are radially distribute around the frame such that, depending on the rotational orientation of valve prosthesis  30 , the axial support arms engage and rest either a native valve commissure (riding astride the commissure) or a leaflet such that the valve prosthesis is anchored axially regardless of the rotational orientation of the prosthesis, as described in more detail hereinbelow with reference to  FIGS. 5A-C . Axial support arms  33  are sized so as to not extend to the floors of the aortic sinuses. This configuration applies an axial force to the native valve complex from below and above the complex, anchoring valve prosthesis  30  place, and inhibiting mi ration of the prosthetic valve both upstream and downstream. This configuration also allows the valve prosthesis to apply outward radial force to the native valve. 
     Although exactly three commissural posts  34  shown an the figures, for some applications valve prosthesis  30  comprises fewer or more posts  34 , such as two posts  34 , or four or more posts  34 . It is noted that approximately 90% of humans have exactly three aortic sinuses. The three posts provided in most embodiments correspond to these three aortic sinuses. For implantation in the approximately 10% of patients that have exactly two aortic sinuses, prosthesis typically includes exactly two posts.  
       FIG. 2  is a schematic illustration of a delivery system  50  for delivering valve prosthesis  30  to a target site and implanting the prosthesis at the site, in accordance with an embodiment of the present invention. Delivery system  50  comprises a catheter  100 , which comprises an inner neutral tube  103  which is concentric with an outer tube  101 . The diameter of outer tube  101  typically varies along catheter  100 . Neutral tube  103  is fixed with respect to neutral tube holder  51  and a handle  52 . A tip  102  of catheter  100  is located at a downstream end of neutral tube  103 , such that outer tube  101  abuts against tip  102  when catheter  100  is in a closed position, as shown in  FIG. 2 . Delivery system  50  is used to effect the release of valve prosthesis  30  (the prosthesis is not shown in  FIG. 2 ) by moving the tubes  101  and  103  with respect to one another. Delivery system further comprises an outer tube holder  51  and a delivery body  53 , which can move with respect to neutral tube holder  51  and handle  52 . To open the catheter, outer tube holder  51  is pulled backwards, while handle  52  and neutral tube holder  51  are held stationary. As a result, outer tube  101  moves in a backward direction with respect to neutral tube  103 , and the catheter opens. The downstream end of outer tube  101  is fixed to the upstream end of tip  102 . 
       FIG. 3  is a schematic cross-sectional illustration of a front end of catheter  100 , in accordance with an embodiment of the present invention. Valve prosthesis  30  is shown within the catheter in the prosthesis&#39;s compressed state, held in a valve holder  104  and compressed between neutral tube  103  and outer tube  101 . The catheter is in its closed state, such that the  downstream end of outer tube  101  rests against the upstream end of tip  102 . 
       FIGS. 4A-L  schematically illustrate a procedure for implanting valve prosthesis  30  using delivery system  50 , in accordance with an embodiment of the present invention. Although these figures show the implantation of the prosthesis in an aortic position, these techniques, as appropriately modified, may also be used to implant the prosthesis in other locations, such as in a pulmonary valve. 
     As shown in  FIG. 4A , delivery catheter  100  is inserted into a body lumen  15 . For seine applications, body lumen  15  is a femoral artery. The catheter is inserted into body lumen  15 , and is guided over a guidewire  200  through the ascending aorta and over an aortic arch  10 . Optionally, stenotic aortic valve  310  is partially dilated to about 15-20 mm (e.g., about 16 mm), typically using standard valvuloplasty balloon catheter. 
     As shown in  FIG. 4B , catheter  100 , which rides over guidewire  200 , is passed over aortic arch  10  towards a native aortic valve  202 . The tip of guidewire  200  passes into a left ventricle  11 . 
     As shown in  FIG. 4C , catheter tip  102  is advanced toward the junction of native aortic valve leaflets  12  towards left ventricle  11 , while the catheter continues to ride over the guidewire. 
     As shown in  FIG. 4D , catheter tip  102  is brought past native aortic valve leaflets  12  into left ventricle  11 . Outer tube  101  of catheter  100  is located between native aortic leaflets  12 .  
     As shown in  FIG. 4E , catheter tip  102  is further advanced, past aortic leaflets  12  and deeper into left ventricle  11 . Outer tube  101  of catheter  100  is still located between native aortic leaflets  12 . 
     As shown in  FIG. 4F , outer tube  101  is withdrawn a Predetermined distance to expose upstream skirt  32  of valve prosthesis  30 . Outer tube  101  moves with respect to inner tube  103 , such that valve prosthesis  30  and inner tube  103  are partially exposed from the catheter. Skirt  31  is positioned within left ventricle  11 . At this point during the implantation procedure, skirt  31  may not yet have come in contact with the ventricular side of native aortic leaflets  12 . 
     As shown in  FIG. 4G , catheter  100  is withdrawn until skirt  31  abuts firmly against the ventricular side of the aortic annulus and/or aortic valve leaflets  12 . If provided, barbs  32  may pierce the native annulus, or may rest against the ventricular side of the valve complex. 
     As shown in  FIG. 4H , outer tube  101  is further withdrawn until the tube is located just upstream of the ends of commissural posts  34  of valve prosthesis  30 , such that the commissural posts are still held firmly by cuter tube  101 . 
       FIG. 4I  shows valve prosthesis  30  immediately upon release from outer tube  101 . Support frame  40 , which is typically superelastic, rapidly expands to its fully opened position, pushing native valve leaflets  12  radially outward. 
       FIG. 4J  shows the opening of valve prosthesis  30  to its fully expanded shape. Axial support arms  33  protrude over the tips of the native leaflets  12 , so that they provide axial support to prosthetic valve  30 , and prevent  the valve from being forced into the ventricle  11  through native leaflets  12  during the cardiac cycle. Prosthetic valve  30  is thus released with the outer tube being moved in only one direction during the entire procedure, which facilitates the implantation procedure significantly. 
       FIG. 4K  shows catheter  100  in its closed position, with cuter tube  101  resting firmly against catheter tip  102 . Catheter  100  is withdrawn over the aortic arch, still riding on guidewire  200 . 
       FIG. 4L  is a schematic illustration of prosthetic valve  30  in the aortic position, in accordance with an embodiment of the present invention. Skirt  31  is positioned within ventricle  11  such that the throat section.  24  of support frame  40  is located in close proximity to the native annulus between native leaflets  12 . Commissural posts  34  of valve prosthesis  30  generally define a diverging shape, and are located on the arterial side of the native valve. Native valve leaflets  12  generally follow the contour of valve prosthesis  30 . Axial support arms  33  protrude over the tips of the native leaflets, and provide axial support to prevent device embolism into ventricle  11 . It is noted that in the configuration shown, valve prosthesis  30  does not include barbs  32 , described hereinabove with reference to  FIGS. 1A and 1B . 
       FIGS. 5A-C  are schematic illustrations of three different possible rotational orientations of valve prosthesis  30  with respect to the native valve upon deployment, in accordance with an embodiment of the present invention. All of these rotational orientations, as well as intermediate rotational orientations not shown, provide proper axial fixation of the valve prosthesis. For clarity of illustration, in  FIGS. 5A-C   only support frame  40  of the valve prosthesis is shown, without prosthetic downstream valve  21  or skirt covering  35  of skirt  31 . The valve prosthesis is deployed within the aortic root, which includes aortic sinuses, coronary ostia  14 , and native valve commissures  15 . Upon implantation, valve prosthesis  30  provides axial anchoring on both sides (ventricular and arterial) of the native valve annulus. Skirt  31  extends radially below the annulus, providing an axial force applied in the arterial direction to the underside of the annulus, while axial support arms  33  exert an axial force in the ventricular direction by resting against the tips of native leaflets  12  or native commissures  13 . 
       FIG. 5A  shows a first possible rotational orientation of valve prosthesis  30 , in which commissural posts  34  of the prosthesis are aligned with native commissures  15 , allowing axial support arms  33  to rest against the tips of native leaflets  12 . 
       FIG. 5B  shows another possible rotational orientation of prosthetic valve  30  within the native valve complex, in which commissural posts  34  of the prosthesis are positioned at a rotational offset of about 60 degrees with respect to native commissures  15 , with axial support arms  33  extending over the tips of native leaflets  12 . As can be seen in  FIG. 5B , axial support arms  33  provide axial anchoring, regardless of the rotational orientation of the prosthesis with respect to the native valve. As can be seen, axial support arms  33 , which are circumferentially distributed around prosthetic valve  30 , obviate tine need to rotationally align prosthetic valve  30  with any anatomical feature of the native valve complex, since axial support arms  33  are generally guaranteed to be located between native  commissures  15 , or riding astride the native commissures 
       FIG. 5C  shows yet another possible rotational orientation of prosthetic valve  30  within the native valve complex upon deployment, in which commissural posts  34  of the prosthesis are offset with respect to native valve commissures  15  by about 30 degrees. Even in this particular rotationally asymmetric position, axial support arms  33  engage the tips of native leaflets  12 , or native valve commissures  15 , effectively applying a downward axial force to the native structure, obviating the need for deliberate rotational positioning prosthetic valve  30  during the implantation process. 
     For some applications, prosthesis  30  is implanted using some of the techniques described with reference to  FIGS. 9A-G  in U.S. application Ser. No. 12/050,628, filed Mar. 18, 2008, entitled, “Valve suturing and implantation procedures,” which is incorporated herein by reference. 
     Reference is now made to  FIGS. 6A-D , which are schematic illustration of a valve prosthesis  130 , in accordance with an embodiment of the present invention.  FIG. 6A  shows the prosthesis including a prosthetic downstream valve  118  and a skirt covering  135  of a skirt  131 , while  FIGS. 6B, 6C, and 6D , for clarity of illustration, shows only a support frame  140  of the valve prosthesis, without prosthetic downstream valve  118  or skirt covering  135  of skirt  131 .  FIGS. 6A-C  are side views, while  FIG. 6D  is a top view of the valve prosthesis (viewed from the downstream side). Skirt covering  135  may comprise, for example, polyester or a processed biological material, such as pericardium. 
     Other than as described heteinbelow, valve  prosthesis  130  is generally similar to valve prosthesis  30 , described hereinabove with reference to  FIGS. 1, 4A -L, and  5 A-C. For example, as described hereinabove with respect to valve prosthesis  30 , valve prosthesis  130  comprises support frame  140 , which is shaped so as to define three commissural posts  134  to which prosthetic valve  118  is coupled, and upstream skirt  131 . The commissural posts are arranged circumferentially around a central longitudinal axis  116  of the valve prosthesis. The upstream skirt includes a plurality of cells  137  that extend outward in an upstream direction. The skirt is configured to apply an axial force in a downstream direction on an upstream side of the native annulus and left ventricular outflow tract (LVOT). Unlike valve prosthesis  30 , valve prosthesis  130  typically does not comprise short axial support arms  33 . 
     Support frame  140  is shaped so as to define a plurality of downstream axial support extensions  128 . The downstream axial support extensions join a downstream side of upstream skirt  131 , and extend in a downstream direction at an angle ø with respect to central longitudinal axis  116  of valve prosthesis  130 , while commissural posts  131  extend in a downstream direction at an angle α with respect to axis  116  (the angles are shown in  FIG. 6A ). Angle n is greater than angle α. Because of this greater angle, downstream axial support extensions  128 : (a) apply an upstream axial force to a downstream side of the native leaflet tips, (b) do not touch the leaflets of the prosthetic valve when the prosthetic valve is in its open position, and (c) provide stability to support frame  140 . Angle ø may, for example, be between about 15 and about 45 degrees, such as about 30 degrees, while angle α may, for example, be  between about 1 and about 15 degrees, such as about 8 degrees. 
     For some applications, an upstream-most portion of each downstream axial support extension  128  joins the downstream site of upstream skirt  131 , and two lateral portions of each extension join respective cells of the frame that extend in an upstream direction from respective commissural posts  134 . 
     In an embodiment of the present invention, support frame  140  is shaped so as to define a plurality of upper sinus support elements  136 , which extend in a downstream direction. Upper sinus support elements  136  are configured to rest against the upper aortic sinuses (i.e., the downstream portion of aortic sinuses  13 ) upon implantation of valve prosthesis  130 , so as to provide support against tilting of the prosthesis with respect to central longitudinal axis  16  thereof. Typically, the downstream-most portions of upper sinus support elements  136  are bent toward central longitudinal axis  16  of the prosthesis to avoid damage to the walls of the upper sinuses. For some applications, support frame  140  is shaped so as to define exactly three downstream axial support extensions  128  and exactly six upper sinus support elements  136 . 
     For some applications, as seen clearly in  FIG. 6C , each upper sinus support element  136  has two upstream-most portions  142  and  144 . Upstream-most portion  142  joins a downstream-most portion  146  of one of downstream axial support extensions  128 , and upstream-most portion  144  joins one of commissural posts  134 . For some applications, as shown in  FIG. 6C , upstream-most portions  142  of two of upper sinus support elements  136  join a single downstream-most portion  145  of one of downstream  axial support extensions  128 , such that two of upper sinus support elements  136  are circumferentially positioned between each pair or two of commissural posts  134 . 
       FIGS. 7A-D  schematically illustrate a portion of a procedure for implanting valve prosthesis  130 , configured as described hereinabove with reference to  FIGS. 6A-D , using delivery system  50 , accordance with an embodiment of the present invention. The first steps of the procedure are performed as described hereinabove with reference to  FIGS. 4A-G , until skirt  131  abuts firmly against the ventricular side of the aortic annulus and/or aortic valve leaflets  12 . After these steps, outer tube  101  is further withdrawn until the tube is located just upstream of the ends of commissural posts  134  of valve prosthesis  130 , as shown in  FIG. 7B . The commissural posts are still held firmly by outer tube  101 . 
     The physician performing the procedure withdraws the delivery system until he or she feels significant. resistance as skirt  131  comes in contact with the upstream side of the native annulus and/or the LVOT, as shown in  FIG. 7C . 
     As shown in  FIG. 7D , support frame  140  gently further deployed further until bulges  120  defined by downstream axial support extensions  128  on the side of the prosthesis snap above the native leaflets, providing tactile feedback that the correct anatomical location has been reached. The prosthesis is now completely released from outer tube  101 . 
       FIGS. 8A-C  show valve prosthesis  130  in place within the native aortic valve of the patient, in accordance with an embodiment of the present invention.  FIGS. 8A   and  8 C are side views, and  FIG. 8B  is a too view of the valve prosthesis (viewed from the downstream side). Commissural posts  134  and downstream axial support extensions  128  may or may not touch the walls of the sinuses. Typically, the downstream-most portions of upper sinus support elements  136  are bent toward central longitudinal axis  16  of the prosthesis to avoid damage to the walls of the upper sinuses. 
       FIG. 9  is a schematic illustration of a catheter tube  200 , in accordance with an embodiment of the present invention. Catheter tube  260  comprises feelers  261  which align themselves with the sinuses, thereby guiding the delivery catheter in both radial and axial directions. Feelers  261  are initially located within an outer tube  244 , and extend out through slits  262  defined by the outer tube. Slits  262  may be arrange circumferentially around the catheter tube. Feelers  261  may be extended and retracted by the physician, so that the feelers are in a retracted position while the catheter is advanced through the vasculature, and are extended before the delicate placement stage of the implantation procedure. 
       FIG. 10  is a schematic illustration of a shaped balloon  271 . In accordance with an embodiment or the present invention. The balloon is used to plastically deform support structure  40  of valve prosthesis  30  or  130 , and to give the structure a non-cylindrical shape. In this embodiment, support structure  40  or  140  may comprise a stainless steel alloy which is plastically deformed during crimping, thereby reducing the valve diameter, and mounted onto the balloon prior to implantation. When the delivery catheter is in place in the patient, shaped balloon  271  is used to open the crimped prosthesis into place, and to give it a non-cylindrical  shape. 
     In the present patent application, including in the claims, the word “downstream” means near or toward the direction in which the blood flow is moving, and “upstream” means the opposite direction. For embodiments in which the valve prosthesis is implanted at the aortic valve, the aorta is downstream and the ventricle is upstream. As used in the present patent application, including in the claims, the “native valve complex” includes the native semilunar valve leaflets, the annulus of the valve, the subvalvular tissue on the ventricular side, and the lower half of the semilunar sinuses. As used in the present application, including in the claims, a “native semilunar valve” is to be understood as including: (a) native semilunar valves that include their native leaflets, and (b) native semilunar valves, the native leaflets of which have been surgically excised or are otherwise absent. 
     For some applications, techniques described herein are performed in combination with techniques described in a US provisional patent application filed on even date herewith, entitled, “Prosthetic heart valve having identifiers for aiding in radiographic positioning,” which is assigned to the assignee of the present. application and is incorporated herein by reference. 
     The scope of the present invention includes embodiments described in the following applications, which are assigned to the assignee of the present application and are incorporated herein by reference. In an embodiment, techniques and apparatus described in one or more of the following applications are combined with techniques and apparatus described herein: 
         U.S. patent application Ser. No. 11/024,905, filed Dec. 30, 2004, entitled, “Fluid flow prosthetic device,” which issued as U.S. Pat. No. 7,201,772;   International Patent Application PCT/IL2005/001399, filed Dec. 29, 2005, entitled, “Fluid flow prosthetic: device,” which published as POT Publication WO 06/070372;   International Patent Application PCT/IL2004/000601, filed Jul. 6, 2004, entitled, “Implantable prosthetic devices particularly for transarterial delivery in the treatment of aortic stenosis, and methods of implanting such devices,” which published as POT Publication WO 05/002466, and U.S. patent application Ser. No. 10/563,384, filed Apr. 20, 2006, in the national stage thereof, which published as US Patent Application Publication 2006/0259134;   U.S. Provisional Application 60/845,728, filed Sep. 19, 2006, entitled, “Fixation member for valve”;   U.S. Provisional Application 60/852,435, filed Oct. 16, 2006, entitled, “Transapical delivery system with ventriculo-arterial overflow bypass”;   U.S. application Ser. No. 11/728,253, filed Mar. 23, 2007, entitled, “Valve prosthesis fixation techniques using sandwiching”;   International Patent Application PCT/IL 2007/001237, filed Oct. 16, 2007,  entitled, “Transapical delivery system with ventriculo-arterial overflow bypass,” which published as PCT Publication WO 2008/04754; and/or   U.S. application Ser. No. 12/050,628, filed Mar. 18, 2008, entitled, “Valve suturing and implantation procedures.”       

     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well a variations and modifications thereof that are non in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.