Abstract:
An electrosurgical hand piece device is configured to cut tissue with monopolar RF energy to extract a medical lead submersed in fluid. The device includes an electrode surrounded by an electrically insulating coating that can be exposed from a distal edge of the electrode when power is supplied to the device, thereby focusing the energy at the distal edge and enabling tissue to be more easily and safely cut from around the medical lead while in fluid.

Description:
PRIORITY 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Application No. 62/369,472, filed Aug. 1, 2016. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a medical lead extraction device, and in particular, an electrosurgical hand piece configured to cut tissue with monopolar radiofrequency (“RF”) energy to extract a medical lead submersed in fluid. 
       BACKGROUND 
       [0003]    Cardiac pacemakers and implantable cardioverter defibrillators (ICDs) are devices implanted within patients&#39; bodies to treat various cardiac conditions. These devices include a power source that sends electrical signals down a cardiac lead that extends from the power source to a patient&#39;s heart. The cardiac leads can be epicardial leads, which are leads with electrodes attached to the outside of the heart, or endocardial leads, which are leads that are inserted through a vein and guided into a chamber of the heart through the vein. 
         [0004]    Although implanted cardiac leads typically have a useful life of many years, at some point leads may become inoperative, another type of lead may be needed or the corresponding pacemaker or ICD may be removed. Although cardiac leads can be left in the heart, doing so can lead to serious medical complications for the patient. It is therefore often desirable to surgically remove such leads. In addition, there are circumstances that make removal of the lead a medical necessity, such as infection or vein obstruction. 
         [0005]    Complicating removal of an endocardial lead extending through a patient&#39;s vein is the fact that over time, the lead tends to become encapsulated against the wall of the vein by fibrotic tissue. The fibrotic tissue can make separation and removal of the lead from the vein difficult, and severe damage can be caused removing the lead, including possible dissection or perforation of the vein. 
         [0006]    A number of methods and devices have been developed for removing cardiac leads encapsulated by fibrotic tissue from veins of patients. One exemplary device is disclosed in U.S. Pat. No. 5,980,515 to Tu. This device includes a cylindrical, non-conductive delivery catheter with a conductive electrode at its distal end. A conducting wire connected to an external radiofrequency (RF) energy source is secured to the electrode to deliver RF energy to the electrode. In use, the electrode and delivery catheter are advanced over an implanted cardiac lead. The RF energy source is activated and a sharp edge of the electrode is advanced into the fibrotic tissue encapsulating the lead, such that the fibrotic tissue is removed by a combination of the RF energy and mechanical cutting by the sharp edge of the electrode. As the fibrotic tissue is cut away, the cardiac lead can be removed from the vein. 
         [0007]    Studies have found that devices employing bipolar RF energy can cause harm to patients including in some cases death and therefore monopolar RF energy is generally safer and preferred. Current monopolar RF-based lead extraction devices, however, face challenges for use in in vivo fluid environments such as when immersed in blood within a vein. Specifically, it has been a challenge for electrodes to fire or deliver sufficient RF energy to dissect tissue when completely submersed in a fluid such as blood. This is significant because modern RF electrosurgery technology leverages plasma generation by ionizing air to cause tissue dissection. When an RF electrode is completely submersed in blood as opposed to air, current density drops because the exposed surface of the electrode is in contact with the blood, which is a conductive medium, resulting in a lower impedance around the electrode. Moreover, because of the lower impedance in liquids, creating plasma in such an environment is challenging. If plasma is not created, then RF dissection/ablation becomes ineffective and the device is unable to dissect the tissue to remove the lead. 
       SUMMARY 
       [0008]    The present invention advantageously provides an electrosurgical hand piece device configured to cut tissue with monopolar RF energy to extract a medical lead submersed in fluid. The device includes an electrode surrounding by an electrically insulating coating that can be exposed from a distal edge of the electrode when power is supplied to the device, thereby focusing the energy at the distal edge and enabling tissue to be more easily and safely cut from around the medical lead while in fluid. 
         [0009]    In an exemplary embodiment, a medical lead extraction system includes a hollow flexible elongate catheter, a handle attached to a proximal end of the catheter, and a hollow electrode attached to a distal end of the catheter. The hollow electrode can have a distal cutting edge and be configured to be advanced over a cardiac lead disposed within a blood vessel of a patient. A conductor can extend along the catheter and attach to the hollow electrode to transmit electrical energy from a power source to the hollow electrode. An electrically insulating coating can surround the hollow electrode with the coating configured to degrade from and expose the distal cutting edge of the hollow electrode when the electrical energy is transmitted to the hollow electrode. This enables the distal cutting edge to transmit the electrical energy to aid in dissecting tissue to remove the cardiac lead. 
         [0010]    In an exemplary embodiment, a method of removing a cardiac lead from within a blood vessel of a patient can include inserting a hollow flexible elongate catheter into a blood vessel of a patient. The catheter can include a hollow electrode attached to a distal end of the catheter that is advanced over a medical lead disposed in the blood vessel to contact a distal cutting edge of the hollow electrode with tissue surrounding the medical lead. Electrical energy can be provided to the hollow electrode that can cause a coating surrounding the hollow electrode to degrade from and expose the distal cutting edge of the hollow electrode. The tissue surrounding the medical lead can then be removed with the distal cutting edge of the hollow electrode. 
         [0011]    Various embodiments of systems, devices and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the present invention. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, implantation locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily obtained by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
           [0013]      FIG. 1  is a side cross-sectional view of an exemplary electrosurgical medical device constructed in accordance with the principles of the present application; 
           [0014]      FIG. 2  is a partial side view of the medical device of  FIG. 1 ; 
           [0015]      FIG. 3  is a zoomed in view of the electrode tip of  FIG. 2  showing an example of a coating process; 
           [0016]      FIG. 4  is a partial side view of another embodiment of an electrosurgical medical device; 
           [0017]      FIG. 5  is a partial side cross-sectional view of the medical device of  FIG. 4 ; and 
           [0018]      FIG. 6  is a zoomed in view of a portion of the medical device of  FIG. 5 . 
           [0019]      FIGS. 7A-7C  depict an exemplary embodiment of a coating and removal process for an electrode tip according to an embodiment of the present disclosure. 
           [0020]      FIGS. 8A-8B  depicts an exemplary electrosurgical medical device constructed in accordance with the principles of the present application in use to remove a medical lead from a patient. 
       
    
    
       [0021]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
       DETAILED DESCRIPTION 
       [0022]    Referring now to the drawings in which like reference designators refer to like elements,  FIG. 1  depicts an exemplary electrosurgical medical device  10  constructed in accordance with the principles of the present application. The medical device  10  can include a hand piece including a handle  12  with a connector  13  extending proximally therefrom for connection to an electrosurgical unit  16  configured to generate and provide monopolar radiofrequency (RF) energy to the device  10 . The device  10  can include one or more finger switch buttons (not shown) for activating the device  10  and can include an actuator for providing selective torque to a distal portion of the device  10 . Moreover, a return electrode (not shown), e.g. a back plate, can also be included to provide a pathway for monopolar ablation from the device  10  to a patient. 
         [0023]    An elongate flexible catheter can extend from the distal end of the handle  12 . The elongate flexible catheter  14  can define a proximal end  17  and a distal end  18  and at least one lumen  20  there through. In an exemplary configuration, the elongate catheter  14  is a non-conductive catheter at least partially composed of a flexible material, such as nylon or Pebax®. The catheter  14  can further include a lubricious liner  22  which coats the inner surface of the catheter  14  to reduce friction as the catheter  14  is advanced over the lead to provide smoother lead removal with improved tactile feel. In one configuration, the elongate catheter  14  includes an electrically insulating material within the inner diameter of the lumen  20  and can include heat shrink tubing or other insulative coating or material on its exterior surface to further discourage or prevent the transmission of energy out of the catheter. The elongate catheter  14  can in various embodiments be a catheter having a size between, for example, 8 Fr. and 16 Fr., can have varying (e.g., increasing) flexibility along its major longitudinal axis from its proximal end  17  to its distal end  18 , and can have one or more inflexible or malleable sections along such axis so as to assist the user in inserting, navigating or advancing catheter  14  into position. 
         [0024]    A conductor  24  configured to provide power from the electrosurgical unit  16  to the distal end  18  of the elongate catheter  14  can be disposed in or within catheter  14 , e.g., within lumen  20 . In one configuration, the conductor  24  can be configured as a wire coiled along the length of the elongate catheter  14  such that the conductor  24  is in contact with the inner diameter of the elongate catheter  14  from the proximal end  17  to the distal end  18  of the elongate catheter  14 . In another configuration, the conductor  24  can be embedded within the wall of the elongate catheter  14 . In various embodiments, the catheter  14  can have non-preferential bending characteristics such that elongate catheter  14  does not more easily bend in a particular direction or along a particular plane, but instead can easily bend in multiple directions. Due to the ability to easily bend in multiple directions, a configuration that does not have preferential bending enables the elongate catheter  14  to be advanced within the body around tortuous areas with greater control and less risk of unwanted tissue damage. In an exemplary configuration, the conductor  24  is surrounded by a non-conductive coating or structure (e.g., a non-conductive braid, which may be flat or round), that insulates the conductor  24  from the remainder of the elongate catheter  14  and reduces capacitive leakage. Use of a non-conductive structure around the conductor extending along the catheter is significant because without such a structure the conductor would case the catheter to become capacitively coupled to the body, causing significant leaking of the RF energy along the catheter and leading to lower power at the electrode edge. 
         [0025]    An electrode  26  configured to deliver monopolar (RF) energy to a target tissue region can be coupled to the distal end  18  of the elongate catheter  14 . In an exemplary configuration shown in  FIG. 2 , the electrode  26  includes a first portion  28  extending away from the distal end  18  of the elongate catheter  14  having a first outer diameter and a second portion  30  extending into the elongate catheter  14  having a second outer diameter less than the first outer diameter. This enables the conductor  24  to make contact with the electrode  26 , and transmit energy thereto, with a conductive contact (e.g., a solder joint) positioned within the catheter, preferably providing a liquid tight, insulated connection. In one configuration, the first portion  28  of the electrode  26  is a hollow metallic substantially cylindrical element with an opening  29  sized to receive a medical lead. The second portion  30  of the electrode can also be a substantially cylindrical, hollow, metallic element that likewise is sized to receive the lead. In one configuration the first portion  28  includes a cutting edge  32  that is sharpened (e.g., serrated as shown in  FIG. 4 ) at its distal end to enhance the ability of the edge  32  to cut calcified tissue. In other configurations, the distal end of the first portion  28  has a smooth cylindrically uniform cutting edge that is thinly sharpened. In operation, such a uniform cutting edge is generally sufficient to remove most tissue adhesions by advancing the electrode without rotation. For more challenging procedures involving calcified tissue, a non-uniform cutting edge (e.g., a serrated edge) can be used to employ mechanical cutting by rotating the serrated edge in addition to the RF energy. In various embodiments, the cutting edge  32  can be a continuous edge extending circumferentially around the distal edge of the electrode. In the context of the cylindrical electrode depicted, such a continuous, circumferential edge is generally circular. However, the cutting edge can have various other geometrical configurations, such as, for example, oval, square, etc. 
         [0026]    Referring to  FIGS. 4-6 , the electrode  26  can include a barb  34  or other projecting portion extending outwardly from the second portion  30  of the electrode  26 . The barb  34  can be shaped to extend circumferentially around the electrode  26  and can be configured to function as a coupling point of the elongate catheter  14  to the electrode  26 . In one configuration, the barb  34  is press fit into the catheter  14  such that the barb  34  engages and captures the interior of the catheter  14  to hold the electrode  26  in place relative to the catheter  14 . In some embodiments, a heat shrink tubing can then be applied to the exterior of the catheter  14  adjacent the location of the barb  34  to further retain the electrode  26  therein. The barb  34  can if desired be formed of a conductive material. In one configuration, the barb  34  can provide a welding site at which the conductor  24  is coupled to the electrode  26 . In other configurations, the conductor  24  can be welded to a welding site  36  elsewhere on the electrode  26 . For example, the welding site  36  can in one configuration be approximately 0.015″ in diameter at a location distal to the barb  34  and proximal to the distal end  18  of the catheter  14 , as shown in, for example,  FIG. 5 . In other configurations, the welding site  36  can be positioned anywhere between the barb  34  and the transition between the first portion  28  of the electrode  26  and the second portion  30  of the electrode  26 . The welding site  36  can provide a single connection at which electrical energy is transferred from the conductor  24  to the electrode  26 . So long as the welding site is suitably positioned within the catheter  14 , it can be insulated from the exterior conductive blood surrounding the device. The welding site  36  can be covered with an insulator such as a heat shrink  38  to minimize leakage conductance. 
         [0027]    In one configuration, the electrode  26  is coated with an insulative material such as a ceramic or glass enamel coating that insulates substantially covered portions of the electrode  26  from transmitting RF energy. As shown in Section A-A and Detail B of  FIG. 3 , the entirety of the electrode  26  can initially be coated. This can be done by, for example, dipping the electrode  26  in a suitable dielectric coating material. Suitable dielectric coating materials will be insulative and capable of withstanding high temperatures. Suitable dielectric coating materials desirably also will be capable of bonding to the electrode (which may for example be made from a material such as stainless steel, tungsten, molybdenum, tantalum, titanium, etc.). In addition, suitable dielectric coating materials desirably will have a viscosity such that when the coating cures or otherwise hardens on the electrode, the coating will provide a thin layer of coating in areas where the radius of curvature of the electrode is small (e.g., at the distal cutting edge of the electrode as will be described in more detail below). In certain exemplary embodiments, the insulative material is a ceramic or glass enamel coating made from one or more inorganic oxides such as K 2 O, Na 2 O, ZnO, MgO, CaO, SrO, BaO, Al 2 O 3 , SiO 2 , B 2 O 3 , La 2 O 3 , MnO 2 , and CoO. Additional exemplary coatings for the electrode  26  are disclosed in U.S. Pat. Nos. 7,458,972, 7,736,361, and 8,211,105, and U.S. Patent Publication No. 2010/0069904, the entirety of which are expressly incorporated by reference herein. In further embodiments, the insulative material need not be a ceramic or glass enamel coating, but can be formed of any other material capable of insulating the electrode body from transmitting energy and withstanding the power transmitted by and the heat produced when operating the device. 
         [0028]    As can be seen in Detail B of  FIG. 3 , the wall of the first portion  28  of the electrode  26  can taper in width as the first portion  28  extends distally from the distal end  18  of the elongate catheter  14  and the first portion  28  of the electrode  26  can also have a decreasing radius of curvature. Due to the decreasing radius of curvature of the electrode  26  as it extends distally, a smaller thickness of the coating material is deposited on the surface of the electrode  26  toward the distal end  18  of the electrode  26 , including the cutting edge  32 . In various embodiments, a Teflon® or other non-stick coating can be applied over the coating on the exterior of the electrode  26 . 
         [0029]    When the device  10  is initially activated, the energy provided by the RF power source can cause, in various embodiments, the thinner layer of coating at the cutting edge  32  to degrade. Because the coating is thicker around the cylindrical body of the electrode  26 , the coating generally will not degrade from other portions of the electrode. Therefore, the RF energy transmitted by the electrode will be focused only at its cutting edge  32 . Limiting the active electrode surface area by use of the coating (e.g., the exposed metal) in this manner results in higher impedance and higher current density at the distal, cutting end of the electrode  26  that better facilitates the generation of plasma when the electrode  26  is disposed in a conductive medium such as blood as opposed to non-coated cylindrical electrodes, which were found to not generate sufficient plasma for tissue dissection. In addition, confining the generation of plasma to this smaller surface area lowers the operating temperature of the electrode such that less power is required to create plasma. In some embodiments, the device  10  can be activated following insertion into the region of the body in which it is being used, e.g., within a vein, but prior to contacting the tissue to be dissected. In other embodiments, the device  10  can be activated at the time resistance in the body is encountered in the form of the tissue to be dissected. 
         [0030]    In one configuration, when the device is activated with as little as 3 W of power delivered to the electrode  26  in an aqueous environment such as blood, the coating may degrade from the surface of the cutting edge  32  of the electrode  26  due to the thinness of the coating at that location, for example, when the edge radius on the electrode  26  is less than 0.005″. Depending on the particular coating, the coating may, for example, degrade when the temperature of the electrode reaches between 500-800° Celsius for an edge radius less than 0.005″. In other configurations, the coating may be etched, grinded, or otherwise mechanically removed from the distal end of the electrode  26  following the coating process. 
         [0031]    In an exemplary use of the device  10 , the reduced capacitance leakage and higher current density at the distal end of the electrode  26  provided by coating a cylindrical electrode with the distal cutting end exposed, or with a thin degradable coating, can facilitate the generation of plasma when the electrode  26  is disposed in a conductive medium such as blood, enhancing the ability of the device  10  to cut tissue and remove a medical lead without damaging surrounding tissue. In a particular application shown in  FIGS. 8A-8B , the opening  29  in the electrode  26  may be advanced over a medical lead  40 , for example an ICD lead or CRT device lead previously disconnected from the device and extending through a blood vessel  42  of a patient and coupled to the heart in, for example, the right ventricle. As the electrode  26  is advanced over the lead  40 , power provided by the RF power source enables the electrode  26  to generate plasma and cut tissue  44 , such as, for example, scar tissue, fibrous tissue, and calcium surrounding the lead  40  with the cutting edge  32 . Although primarily described herein as being used to remove leads from within blood vessels of a patient, it should be noted that lead removal devices according to the present application could also be used to remove leads from other areas of a patient. For example, the devices described herein could also be used to remove leads placed in the extravascular sub-sternal space (sub-sternal leads). 
         [0032]    An exemplary waveform of the energy used for generating plasma with the device  10  in an aqueous environment is a low voltage and constant duty cycle waveform, for example, a pure CUT duty cycle sinusoidal waveform that is always on when activated. This waveform has been tested on a porcine model at various key anatomical locations including the jugular vein, the superior vena cava, the right atrium and the apex of the heart (up to 20 W and 600V) and did not introduce any adverse physiological side effects. In one embodiment, the frequency of the waveform is 470 kHz. The waveform has proven effective to enable the device to dissect soft tissue at 10 W or greater power. A low voltage, constant duty cycle waveform is desirable because waveforms with high peak voltage create the potential for arcing through the lead and conducting currently directly to the myocardium where the lead is fixed. Also, waveforms with a low duty cycle may result in power being delivered on a low carrier frequency (e.g., 300 Hz) which can cause cardiac fibrillation. Another exemplary waveform can be used with monopolar Transcollation® technology, which uses RF energy, with the waveform having a low impedance power curve at, for example, 50 W to 90 W. Optionally, saline may be added to the system. The monopolar Transcollation waveform has also been tested in-vivo on a sheep model at between 50-90 W. Various electrosurgical units  16  can be utilized to generate and provide the desired voltage and waveform to the device  10 . Example electrosurgical generators include the Medtronic AEX generator or the Medtronic Pulsar generator available from Medtronic, Inc. of Minneapolis, Minn. and the Bovie generator available from Bovie Medical Corporation of Clearwater, Fla. 
         [0033]    In an exemplary embodiment, an electrosurgical medical device  10  includes an elongate catheter  14  having a proximal end  17 , a distal end  18 , and at least one lumen  20  there through. The catheter  14  is sized to receive a medical lead within the lumen  20 . A lubricious liner  22  can coat the interior of the elongate catheter  14 . A hollow cylindrical electrode  26  is coupled to the distal end  18  of the elongate catheter  14 , the electrode  26  including a first portion  28  extending distally away from the distal end  18  of the catheter  14  and a second portion  30  disposed within the lumen  20  of the catheter  14 . The electrode  26  is configured to deliver monopolar RF energy configured to cut tissue. The first portion  28  of the electrode  26  can be tapered in thickness as it extends distally away from the catheter  14 . The electrode  26  can initially be entirely coated or otherwise covered with a dielectric material configured to prevent the transmission of monopolar radiofrequency energy at a predetermined coating thickness of the dielectric material. A coiled conductor  24  is disposed within the elongate catheter  14  and coupled to the second portion  30  of the electrode  26  at a coupling location proximal to the distal end  18  of the catheter  14 . The coupling location can include an insulating material covering the coiled conductor  24  at the coupling location. When energy is provided to the electrode  26  from an RF power source via the conductor  24 , the energy can cause the dielectric coating material to degrade from a cutting edge  32  at the distal end of the electrode  26 . This provides reduced capacitance leakage and higher current density at the distal end of the electrode for cutting tissue to remove a lead. 
         [0034]    In order to remove a given lead, the opening  29  in the electrode  26  has to be advanced over the lead. If the opening is not advanced over the lead, such as because the lead is too large for the opening or the opening is not properly aligned with the lead, the device will push against the lead and cause the lead and insulation to bunch together rather than cutting away tissue and freeing the lead. This issue, sometimes referred to as “snowplowing,” causes the lead to become further stuck in the tissue potentially leading to significant damage to the vasculature or other region of the body and making removal even more difficult. In various embodiments, the system described herein can be utilized to identify when snowplowing is occurring by monitoring the impedance encountered by the system while in operation. Either a sharp increase in impedance over a short time period (e.g., from 300 ohms to 1500 ohms) or a gradual increase to a higher than expected impedance (e.g., over 3000 ohms) may be indicative of snowplowing. In some embodiments, the system can be configured to automatically provide an alert or warning to a user when potential snowplowing is detected. An alert or warning can be provided when a rate of change of impedance exceeds a threshold, when the detected impedance exceeds a threshold value, or both. The alert or warning can be auditory, visual, or both and could be provided by the electrosurgical unit or a separate monitoring/display device. In some embodiments, a plurality of lead removal devices having electrodes of varying diameters can be provided, such that when snow plowing is detected with one lead removal device, a second device having a larger diameter more likely to fit over the lead can be employed. 
       Example 1 
       [0035]    Electrodes from lead extraction devices such as those described above were removed and compared for both activated (n=3) and non-activated (n=3) devices. The electrodes  26  were potted and sectioned for analysis via digital microscopy. By matching the CTE of the metal electrode with the CTE of the dielectric coating, the propensity of the coating to degrade or breakdown after exposure to high temperatures during use is reduced. As such, various metals and various coatings could be used. To activate the devices, a pure CUT duty cycle 20 W waveform was applied for 5 seconds. Post activation, the ceramic coating on the distal cutting edge  32 B of the activated electrodes was shown to be completely removed from the circumference of the cutting edge  32 B, as shown in  FIG. 7C . Measuring from the inner diameter of the cylindrical electrode. This correlates to an average active cutting surface area of about 0.0024 square inches. 
       Example 2 
       [0036]    Lead extraction devices as described herein were used to remove leads from live sheep and were found to successfully cut away tissue and remove leads without harming the sheep. Leads were first pulled by hand using a force gauge to verify that the leads contained tissue ingrowth and were adhered in place. Force gauge readings demonstrated that the leads could not be removed with 3 kilogram-force (6.61 pound-force). Both vascular and sub-sternal leads were removed. Successful lead extraction was accomplished with a low impedance power curve with monopolar Transcollation® at 50 W. Impedance around the electrode during successful extraction was in a range of 70 ohms to 200 ohms. Pure cut (at 50 W), blend (at 50 W), 5% coagulation, 10% coagulation, and monopolar Transcollation® (at 90 W) waveforms were all further tested without harm to the sheep. Histological analysis of the sheep post mortem showed that the lead extraction tool did not cause noteworthy vascular injury as evidenced by the lack of significant hemorrhage or hematoma formation around the vasculature. The intravascular/intima surface is challenging to evaluate grossly for the presence of tool-induced intimal lesions as the tissue sheaths around the leads blended in with the intima/vessel wall. In most cases, there was no evidence of lead extraction tool induced injury inside the heart. In one case the heart had only a small focus of acute myocardial injury due to the lead extraction of the vascular leads. The small myocardial injury would be inconsequential for the heart function. 
         [0037]    Although specific and in some cases preferred embodiments have been illustrated and described, it will be appreciated by those of ordinary skill in the art that a variety of alternate or equivalent embodiments calculated to achieve the same purposes may be substituted for the specific embodiments shown and described above. This application is intended to cover any such adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.