Abstract:
Embodiments of a permanent shunt are provided. According to one aspect of the invention, the shunt is a flexible biocompatible fluid directing lumen with first and second ends, with at least one of the first and second ends provided with a shape memory alloy adapted to cause the end to expand in dimension upon application of a predetermined amount of energy to cause fixation of the end of the shunt within an opening in the anatomy. According to another aspect of the invention, the shunt includes open first and second ends, a central portion therebetween, and an access port within said central portion, with the access port being smaller than the first and second ends.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates broadly to surgical methods and surgical devices. More particularly, this invention relates to methods for treating an ischemic heart by permanent perfusion of the coronary sinus and shunts therefor.  
         [0003]     2. State of the Art  
         [0004]     When significant diffuse stenotic coronary artery disease exists, flow through the coronary arteries is diminished. There are two conventional treatments for such a condition. One therapeutic modality to deal with this coronary arterial insufficiency is to deploy metal stents into the coronary arteries at the sites of such stenoses to improve flow. The other treatment is to surgically anastomose a detouring conduit on the coronary artery to bypass the stenosed segment; i.e., coronary artery bypass surgery. In either situation, it is not uncommon for stenoses to again appear below the treatment site, and which again require therapeutic intervention to increase blood flow through coronary arteries to nourish the myocardium.  
         [0005]     The coronary sinus is the confluence and the final conduit for a group of cardiac veins before they empty into the right atrium. Coronary arterial blood, after passing through the myocardial bed is emptied into the right atrium in a deoxygenated state via the coronary sinus. So, in contrast to the high pressure coronary arterial system, the coronary sinus is a low pressure bed.  
         [0006]     Previously, the coronary sinus has been used as a pathway to increase perfusion of the myocardium. An experimental modality of blocking the egress of blood flow from the coronary arterial bed, by tying off the mouth of the coronary sinus as it enters the right atrial cavity, has been employed with limited success because no new blood was delivered to the coronary sinus. Mohl W. et al., “Clinical evaluation of pressure-controlled intermittent coronary sinus occlusion: randomized trial during coronary artery surgery”,  Ann Thorac Surg,  46(2):192-201 (August 1988). In another experimental animal model, anastomosis of a vein conduit (harvested from the leg) from a high pressure location on the aorta to the coronary sinus was performed. See Louis J. Acierno,  The History of Cardiology,  pp. 658-60 (1994) (discussing the ‘Beck I’ operation). The treatment provided long-term retrograde perfusion to the myocardium and blocked egress from the coronary sinus into the atrium. However, the procedure described is highly invasive open heart surgery, and the thinness of the coronary sinus wall is not equipped for graft anastomosis which may lead to complications such as leakage, tearing or hemorrhage.  
         [0007]     In addition, during invasive cardiology procedures, a temporary exterior shunt from the femoral artery to the coronary sinus, accomplished on the cardiologist&#39;s catheterization table by a connecting catheter supported by a pump, has been employed to provide perfusion of the coronary artery. See Kar S et al., “Myocardial protection by diastolic coronary venous retroperfusion during PTCA” [Abstr],  Proceedings of the Third International Symposium on Myocardial Protection via the Coronary Sinus  (June 1988; Boston, USA) and Kar S et al., “Synchronized Coronary Venous Retroperfusion for Support and Salvage of Ischemic Myocardium During Elective and Failed Angioplasty,”  J Amer. Coll. Cardio.,  18(1):271-282 (1991). Similar temporary exterior shunts have also been tried by surgeons in the operating room to augment coronary bed perfusion during coronary bypass surgery. See Harinder S et al., Retrograde Coronary Sinus Perfusion for Management of Coexistent Critical Unstable Carotid and Coronary Artery Disease,  Indian Heart J,  54: 717-719 (2002); Castella M et al., “Reduction of Systolic and Diastolic Dysfunction by Retrograde Coronary Sinus Perfusion During Off-Pump Surgery”,  J Thoracic and Cardiovascular S,  127:1018-1025 (2004); and Harinder S, “Efficacy of Retrograde Coronary Sinus Perfusion In Off-Pump Surgery”,  J Thoracic and Cardiovascular S,  129(2):476-477 (2005).  
       SUMMARY OF THE INVENTION  
       [0008]     It is therefore an object of the invention to provide methods for permanent retrograde perfusion from the aorta to the coronary sinus to provide perfusion to the heart.  
         [0009]     It is also an object of the invention to provide methods which are less invasive than open heart surgery.  
         [0010]     It is a further object of the invention to provide a method for permanent retrograde perfusion from the aorta to the coronary sinus which can be performed percutaneously and methods which can be performed thoracoscopically.  
         [0011]     It is another object of the invention to provide permanently implantable shunts for implantation between the aorta and the coronary sinus.  
         [0012]     It is an additional object of the invention to provide suitable shunts which can be implanted percutaneously and shunts which can be implanted thoracoscopically.  
         [0013]     In accord with these objects, which will be discussed in detail below, in a minimally invasive manner, a permanent shunt is implanted to carry arterial blood from the aorta into the relatively lower pressure venous bed of the coronary sinus. Since egress from the coronary sinus into the right atrium is blocked, the higher pressure arterial blood is forced through the coronary sinus venous bed in a retrograde fashion thus accomplishing perfusion of those arterial beds that are deprived of normal antegrade coronary arterial blood flow on account of coronary arterial stenoses.  
         [0014]     In one embodiment, the shunt is delivered percutaneously via a catheter-based delivery system. A guidewire is introduced from the lumen of the aorta, through the right atrial cavity and into the mouth of the coronary sinus, and the delivery system is delivered thereover.  
         [0015]     In another embodiment, the shunt is delivered in a minimally invasive, preferably thoracoscopic, manner. A scope is inserted through the chest wall to gain access to the right side of the heart, the pericardium is opened, and using guidewires access to the coronary sinus and the aorta is established (from outside the right atrial cavity). The shunt is threaded into the coronary sinus and the aorta, over preferably two guidewires. Thus, most of the body of the shunt comes to lie in the pericardial sac, outside the cavity of the right atrium.  
         [0016]     In each embodiment, the shunt must be anchored at both ends, kink-resistant, and permanently implantable. The shunt will carry high pressure arterial blood into the coronary sinus and normal egress of blood from the coronary sinus into the right atrium will be at least partially blocked resulting in retrograde perfusion of the myocardium.  
         [0017]     Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic view of the heart with a percutaneous shunt delivery system according to the invention with a first embodiment of a shunt;  
         [0019]      FIG. 2  is a schematic view of the heart with the first embodiment of the shunt implanted between the sinus of valsalva in the aorta and the mouth of the coronary sinus;  
         [0020]      FIG. 3  is a side elevation of a second embodiment of a shunt;  
         [0021]      FIG. 4  is a side elevation of an alternate second embodiment of the shunt;  
         [0022]      FIG. 5  is a side elevation of yet another second embodiment of the shunt in a first configuration;  
         [0023]      FIG. 6  is a side elevation of the shunt of  FIG. 5  in a second configuration;  
         [0024]      FIGS. 7-9  illustrate initial steps of a second method of practicing the invention;  
         [0025]      FIG. 10  is a schematic view showing the shunt in prepared for implantation;  
         [0026]      FIGS. 11-13  illustrate later steps of the second method of practicing the invention;  
         [0027]      FIG. 14  is a side elevation of a third embodiment of a shunt of the invention in a first configuration; and  
         [0028]      FIG. 15  is a side elevation of the third embodiment of the shunt of the invention in a second configuration. 
     
    
     DETAILED DESCRIPTION  
       [0029]     In accord with the invention methods are provided for introducing and implanting a permanent shunt between the aorta and the coronary sinus. The shunt then carries arterial blood from the relatively higher pressure aorta into the relatively lower pressure venous bed of the coronary sinus. As discussed in more detail below, in one embodiment, the shunt preferably has an insertion point in the lumen of the aorta and most preferably the sinus of valsalva which has fluid dynamic conditions placing it in substantially more consistent pressure than the upper tubular portion of the aorta from which prior art temporary shunts have extended. Since egress from the coronary sinus into the right atrium is blocked, the higher pressure arterial blood is forced through the coronary sinus venous bed in a retrograde fashion, thus accomplishing perfusion of those arterial beds that are deprived of normal antegrade coronary arterial blood flow on account of coronary arterial stenoses. Upon permanent retrograde perfusion, thebesian veins (micropores) within the right side of the heart become active to perfuse the myocardium of the right side of the heart. In addition, thebesian veins on the left side of the heart, which open only when the coronary sinus is blocked over an extended period of time, also open and perfuse the myocardium of the left side of the heart.  
         [0030]     Referring now to  FIG. 1 , according to a first embodiment of the method in which the shunt between the aorta and the coronary sinus is implanted percutaneously in the heart  10 , access to the lumen of the aorta  12  and the sinus of valsalva  14  is via the femoral, brachial, or other suitable artery. A shunt delivery system includes a guiding catheter  16  with a steerable piercing tip  18 . The guiding catheter  16  is introduced to the right portion  20  or non-coronary portion  22  of the sinus of valsalva  14 , as these locations will provide access to the right atrium  24 . Using the tip  16  of the guiding catheter  16 , the wall  26  of the sinus of valsalva  14  is pierced (in a manner similar to piercing the septum when accessing the left atrium via the right atrium) to place the catheter tip  18  within the right atrium  24 . It is noted that the wall of the sinus of valsalva and the right atrial wall are nearly fused into a single structure at that level. As such, passage from the sinus of valsalva into the right atrial cavity is the straightforward matter of traversing this common wall with the sharp catheter tip.  
         [0031]     The guiding catheter  16  has a channel that allows passage of a guidewire  30 . Under ultrasound, fluoroscopy, or other radiological modality, the guidewire  30  is guided into the mouth  32  and lumen of the coronary sinus  36 .  
         [0032]     A shunt  40  is provided on a delivery catheter  42  within the guiding catheter  16 . The delivery catheter  42  is threaded over the guidewire  30 , into the lumen of the coronary sinus  36 , via the sinus of valsalva  14  and right atrium  24 . Alternately, the entire guiding catheter  16  may be introduced into the coronary sinus  36 , so that an anchoring mechanism, described below, on the distal end  46  of the unexpanded end of the shunt  40  is protected from causing injury to the structures of the heart, as the shunt is threaded over the guidewire.  
         [0033]     Once the appropriate position of the distal end  46  of the shunt  40  is confirmed in the mouth  32  of the coronary sinus  36 , the anchoring mechanism at the distal end is deployed, e.g., by expanding the distal end  46  of the shunt  40 , to cause the distal end of the shunt to completely occupy the inside of the mouth  32  of the coronary sinus  36 . Each of the distal (coronary sinus end) and the proximal (aortic sinus of valsalva end) ends  46 ,  48  of the shunt are equipped with anchoring mechanisms such as barbs  50 , hooks, coils, inflatable cuffs, etc. to allow proximal and distal anchoring of the shunt to the inside of their respective anatomical fixation sites.  
         [0034]     In one embodiment, expansion is effected by self expansion, e.g., accomplished by release of tension on a resilient material as it is advanced out of the catheter sheath. Such resilient materials may be spring metals, shape memory alloys (SMA), polymers, and/or combinations thereof, covered with a polymeric or fabric material to effect a blood carrying conduit. Alternately or additionally, where the shunt has a shape memory alloy (SMA) wound or woven into a fabric or polymeric lumen, the shunt may be expandable upon application of a predetermined amount of energy. In particular, referring to  FIG. 1 , the shunt  40  may include a coil  60 ,  62  of the same shape memory alloy at each of its distal and proximal ends and separate leads  64 ,  66  for activation to cause respective end expansion, or different alloys activatable at different temperatures and a common activation lead or distinct activation leads for the proximal and distal ends. All activation leads preferably terminate at the proximal end for coupling to a energy source coupled to or inserted through or the delivery system. Expansion of the ends of the shunt causes fixation of the ends of the shunt within the sinus of valsalva (in distinction from expansion of the sinus of the valsalva). The central portion of the shunt may also include an SMA coil  68  which can effect expansion of the shunt to maintain lumen patency. As another alternative, the shunt may be mechanically expandable, e.g., via expansion of an internally positioned inflatable balloon which can be advanced on a balloon catheter over the guidewire  30 .  
         [0035]     Referring to  FIG. 2 , once the distal end  46  of the shunt  40  is expanded to effect securement of the distal end of the shunt within the mouth  32  of the coronary sinus  36 , the guiding catheter  16  is then gradually withdrawn from the coronary sinus, back into the sinus of valsalva  14  such that now the proximal end  48  of the shunt is in the sinus of valsalva. The anchoring mechanism of the proximal end of the shunt is now similarly deployed to fix it within the sinus of valsalva in a fluidtight and airtight manner.  
         [0036]     The body  50  of the shunt (that portion between the distal and proximal ends  46 ,  48 ) is preferably designed to be patent once the delivery system is removed. Such may be via the materials used for the shunt, e.g., non-kinking skeletal frames with a polymeric or biologic covering (e.g., PTFE, woven Dacron, cell cultures, albumin, collagen, etc.), or a non-kinking polymeric tubular construct without a skeletal frame. Where a frame is used, it may be self-expanding upon the withdrawal of the catheter sheath, mechanically expandable, or expandable upon the application of a predetermined temperature (e.g., where the frame is constructed of a shape memory alloy (SMA)). Alternatively, the shunt may be an implantable natural construct (human or animal vein, artery, etc.). As yet another alternative, the central portion of the shunt may be balloon expandable and expanded to its full, open configuration after securement of the distal end or the proximal end. The guidewire  30  is removed at the end of the procedure.  
         [0037]     The length of the shunt  40  for a percutaneous approach is preferably approximately 4 to 6 cm, the diameter of a central portion of the shunt of the preferably approximately 3 to 6 mm, the diameter at the distal end, in the expanded state, is approximately 1 to 3 cm, and the diameter at the proximal end, in the expanded state, is approximately 0.6 to 1.5 cm.  
         [0038]     Thus, an unexpanded shunt  40  is deployed percutaneously into the coronary sinus through the aortic sinus via the right atrial cavity and anchored there distally and anchored proximally in the aorta using a catheter-based shunt delivery system. This forms a shunt, from the relatively high pressure sinus of valsalva (80-100 mmHg) with arterial blood, to the lower pressure venous coronary sinus (5-20 mmHg) via the right atrium. The shunt is an internal shunt, lying within the right atrium. Since, the mouth of the coronary sinus is completely occupied by the expanded and anchored distal opening of the conduit, egress from the coronary sinus into the right atrium is blocked.  
         [0039]     In an alternative embodiment, after expansion of the distal end of the shunt, the distal end is secured within the mouth of the coronary sinus but egress from the coronary sinus is only partially blocked. This is advantageous and desirable in certain clinical conditions in order to avoid the temporary edema of the heart tissue that may occur with complete blockage of egress (i.e., until thebesian veins open).  
         [0040]     In another approach a shunt between the aorta and coronary sinus is delivered in a minimally invasive, preferably thoracoscopic manner. Prior to discussing the procedure, the shunt will now be described. Referring to  FIG. 3 , the shunt  100  includes first and second ends  102 ,  104 , and a central portion  106  with a relatively small access port  108 ; i.e., smaller than either of the first and second ends  102 ,  104 . The central portion  106  is preferably constructed to be patent under low pressure conditions. Nevertheless, due to the required aortic implantation location, discussed below, the shunt  100  will be subject to relatively higher pressure (on average 120 mmHg systolic pressure) than in the percutaneous approach (on average substantially constant 100 mmHg in the sinus of valsalva) and the fluid pressure of the blood within the implanted shunt should operate to maintain the patency of the shunt whether or not the shunt is provided with specialized structure specifically intended to maintain shunt patency. The access port  108  in the central portion may include a relatively resilient or rigid rim  110  which facilitates introduction of guidewires therethrough and retention of ligating clips, as discussed below. Each of the first and second ends  102 ,  104  includes structure  112  which can be expanded (as shown in broken lines) within the mouth of the coronary sinus and aorta, respectively, to fix the first and second ends relative thereto upon implantation, as discussed below. The shunt  100  may be any of the constructs discussed above with respect to the percutaneously deployed embodiment; i.e., structural frame in combination with a sheath, a polymeric tubular construct, or a biologic tubular construct.  
         [0041]     With respect to expanding the first and second ends of the shunt, the ends are preferably balloon (or otherwise mechanically) expandable. Alternatively, referring to  FIG. 4 , the ends  202 ,  204  of the shunt  200  may include SMA coils  214   a,    214   b  or another construct with one or more leads  216   a,    216   b  that extend to or adjacent the access port  208 , facilitating activation and expansion of the ends  202 ,  204  (as shown in broken lines) by coupling of the leads to an energy source for application of a predetermined temperature or temperatures to cause reconfiguration (as described above in more detail with respect to shunt  40 ). As yet another alternatively, referring to  FIGS. 5 and 6 , the ends  302 ,  304  of the shunt  300  may be self-expandable, with retractable sleeves  306  coupled over the ends to prevent expansions of the ends during the initial stages of implantation. The sleeves  306  may be provided with loops  308  or other structure to facilitate retraction of the sleeves toward the central portion. After insertion of the ends  302 ,  304  into their respective implantation sites, the sleeves  306  may be retracted to cause the expansion of the ends and effect permanent retention within the implantation sites. As yet another alternative, wherein an anatomical vessel is used, the access port (a hole) will need to be created in the vessel and some means for coupling the ends within the mouth of the coronary sinus and aorta are preferably coupled to the shunt before the introducing the shunt to the implantation site.  
         [0042]     The length of the shunt is preferably approximately 10 to 12 cm, the diameter of a central portion of the shunt of the preferably approximately 4 to 6 mm, the diameter at the distal end, in an expanded state, is approximately 1 to 3 cm, and the diameter at the proximal end, in an expanded state, is approximately 0.6 to 1.5 cm.  
         [0043]     Now, in accord with another minimally invasive, preferably thoracoscopic method of the invention, the patient is anaesthetized and an appropriate amount of heparin is administered to prevent coagulation on the guidewires, the use of which is discussed below. The patient is positioned, prepped and draped. Referring to  FIG. 7 , preferably at the fourth, fifth or sixth intercostal space, a thoracoscope  400 , a first large cannula  402  and optionally a second large cannula (not shown) are inserted through the chest wall to gain access to the right side of the heart  404 . The first cannula  402  is introduced through the pericardium adjacent the right atrial wall  406 . The second cannula is positioned at a distance from the thoracoscope and first cannula to define a triangular work arrangement between the scope and two cannulas and may be used if desired throughout the procedure with non-specific instruments which may facilitate the procedure, e.g., retractors, heart stabilizers, graspers, etc.  
         [0044]     A needle  408  is introduced through the first cannula  402  and the tip of the needle is used to pierce a hole  409  through the right atrial wall  406 . The location of the tip of the needle in the right atrial cavity may be confirmed by aspirating blood through the needle. Once the location is confirmed, a first guidewire  410  is introduced through the needle and directed into the mouth  412  of the coronary sinus  414 . Once confirmation of the distal end of the guidewire  410  is assured, e.g., via echocardiogram, the needle  408  and first cannula  402  are withdrawn leaving the first guidewire  410  in position.  
         [0045]     The first cannula  402  is then reinserted into the chest wall in the same hole  416  as before adjacent the first guidewire  410 . The first cannula  402  is directed toward the lower ascending aorta  418 . This location is chosen because access to the sinus of valsalva  420  is difficult to reach and blocked by the right atrial wall  422 . Thus feeding the coronary sinus from the sinus of valsalva is less practical in a thoracoscopic approach than in a percutaneous approach. The needle  408  is inserted through the first cannula  402  to pierce the ascending aorta  418 . Blood is preferably aspirated to confirm needle location within the aortic lumen. A second guidewire  424  is introduced through the needle  408  and its distal end is positioned within the aorta  418 . The needle  408  and first cannula  402  are withdrawn, leaving the first and second guidewires  410 ,  424  exiting the chest from the same hole  416 , as shown in  FIG. 9 .  
         [0046]     Referring to  FIG. 10 , the proximal ends of the first and second guidewires  410 ,  424  are then threaded through the first and second ends  102 ,  104 , respectively, of the shunt  100  and out the access port  108 . The shunt  100  is preferably folded into a U-shape to facilitate the insertion. The proximal ends of the guidewires ends  410 ,  424  and the folded shunt  100  are then positioned within the distal end of the first cannula  402 , and the first cannula is reintroduced into the same hole  416  in the chest wall.  
         [0047]     Referring to  FIG. 11 , a grasper/pusher instrument  430  is then introduced through the first cannula  402  and used to maneuver the first end  102  of the shunt  100  over the first guidewire  410  and through the hole  409  pierced in the right atrial wall  406  and into the mouth  412  of the coronary sinus  414 . Another instrument inserted through a second cannula may facilitate this maneuver. Once the first end  102  of the shunt  100  is within the coronary sinus  414 , it is expanded to effect retention therein. Where the first end is balloon expandable, a balloon catheter  432  is introduced over the first guidewire  410 , through the access port  108 , and into the first end  102  of the shunt  100  and inflated with fluid to cause permanent expansion of the first end  102  of the shunt ( FIG. 12 ). The balloon catheter  432  is then removed. Where the first end is expandable by reconfiguration of an SMA element, an energy source is coupled to the lead of the first end to cause the SMA element is to reconfigure into a retaining shape/size. Where the first end is self-expandable, a grasper or other tool is used to retract the sleeve (e.g., at loops  308 ,  FIG. 6 ) to allow the first end to expand. Expansion may include deployment of barbs, hooks and/or other tissue engaging structure on the outer surface of the first end of the shunt in addition to or as an alternative to expanding the diameter of the first end of the shunt. Where natural biologic tubular constructs are used, either a tissue coupling means at the first end is activated, e.g. in accord with the above, or an instrument is inserted to the implantation site which can effect the necessary anastomosis between the shunt and the mouth of the coronary sinus. Once the first end  102  of the shunt  100  is coupled within the mouth  412  of the coronary sinus  414 , the first guidewire  410  is removed from the patient.  
         [0048]     The grasper/pusher  430  is then directed to the second end  104  of the shunt  100 . The second end  104  is advanced along the second guidewire  424  and inserted into the hole pierced in the aorta  418 . The second end  104  is then expanded, as discussed above, to effect its retention within the aorta. The second guidewire  424  is then also removed from the patient. It is recognized that the shunt  100  is now an open conduit between the aorta  418  and the mouth  412  of the coronary sinus  414  with blood being forced under pressure in a retrograde manner into the coronary sinus. As such, there may be leakage of blood at the access port  108 . Initially, this provides an avenue for any potential clot to escape. However, the access port  108  must be sealed. Therefore, referring to  FIG. 13 , a clip applier or other suitable ligating instrument is introduced through the first or second cannulas and operated to provide a clip  440  or other ligating element to seal the access port  108 . The rim  110  on the access port  108  of the shunt  100  facilitates retention of the clip  440  or other ligating element on the shunt. Once the access port  108  is closed, the shunt  100  provides a permanent means for retrograde perfusion of the coronary sinus and the myocardium below any coronary blockage.  
         [0049]     Referring to  FIG. 14 , a similar thoracoscopic method is provided using a shunt  500  without an access port. The first and second ends  502 ,  504  of the shunt  500  include retractable sleeves  506  with guidewire loops  508 . The ends of the shunt may be guided on two guidewires  510 ,  512 , as discussed above, to the appropriate location via the loops  508  (instead of through the center of the shunt). Referring to  FIG. 15 , once each end  502 ,  504  of the shunt  500  is in its intended implant location, its sleeve  506  is retracted to allow expansion of the end and retention of the end within the coronary sinus and aorta. Alternately, the shunt may be implanted thoracoscopically, and expanded with percutaneous assist.  
         [0050]     According to an alternative minimally invasive embodiment of the invention, the first end of the shunt is modified such that, upon expansion of the first end, the first end is smaller than the mouth of the coronary sinus. As such, egress from the coronary sinus is only partially blocked. This is advantageous and desirable in certain clinical conditions in order to avoid the temporary edema of the heart tissue that may occur with complete blockage of egress (i.e., until thebesian veins open).  
         [0051]     There have been described and illustrated herein several embodiments of shunts and methods of permanently and minimally invasively implanting shunts between the aorta and the coronary sinus. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular shunt constructs have been disclosed, it will be appreciated that other constructs, including materials, configurations, means for end expansion and tissue retention, etc. can be used as well. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.