Patent Document

STATEMENT OF INCORPORATION BY REFERENCE 
     This non-provisional U.S. patent application claims the benefit of and priority to provisional U.S. patent application No. 61/411,694 filed 9 Nov. 2010 (the &#39;694 application) relates to U.S. patent application Ser. No. 12/760,337 filed 14 Apr. 2010 (the &#39;337 application). The entire contents of the &#39;694 and the &#39;337 applications are hereby incorporated as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     a. Field of the Invention 
     The disclosure relates to electrophysiology (EP) catheters for use in medical procedures. In particular, the disclosure relates to a family of catheters for use in diagnostic and therapeutic procedures in and around a patient&#39;s cardiac anatomy, such as the ostium of a pulmonary vein. 
     b. Background Art 
     Catheters are used for an ever-growing number of procedures. For example, catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, the catheter is manipulated through the patient&#39;s vasculature and to the intended site, for example a site within the patient&#39;s heart. 
     A typical EP catheter includes an elongate shaft and one or more electrodes on the distal end of the shaft. The electrodes can be used for diagnostic mapping, or ablation the like. Oftentimes, these electrodes are ring electrodes that extend about the entire circumference of the catheter shaft. 
     One specific use of an EP catheter is to map the atrial regions of the heart, and in particular the pulmonary veins, which are often origination points or foci of atrial fibrillation. Such EP mapping catheters typically have at least a partial loop shape at their distal end in order to surround the pulmonary vein ostia. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is the present disclosure relates to a family of EP catheters having highly enhanced deflection capability to effectively access a particular subject&#39;s individual anatomy while at the same time rapidly collecting EP diagnostic data from said subject with a distal portion with an offset shaft-to-loop axis (or junction) and having a single shallow helical fixed-diameter loop. 
     Another embodiment described and depicted herein relates to EP catheters that allow the single shallow helical fixed-diameter loop at the distal end to deflect 180 degrees relative to the remainder of the catheter body in an incredibly small space (e.g., on the order of 50 mm), which is ideal for performing cardiac diagnostic mapping of the atria, for example. In an embodiment, the single shallow helical fixed-diameter loop has an outer-loop diameter of between about 15 mm and about 25 mm, although other dimensions are not excluded. The outer diameter of the catheter body (expressed in units known as French abbreviated as 4 F, for example, each unit of which equals ⅓ of a millimeter, or mm) can vary. For example a majority of the catheter body, the proximal portion, can be on the order of about 7 F and an adjacent neck region can include structure, including an anchoring location for an activation wire, transitions the outer diameter to about 4 F such that the single shallow helical fixed-diameter loop distal portion is 4 F or other uniform outer diameter throughout. 
     In some embodiments, the single shallow helical fixed-diameter loop distal portion includes 20 electrodes, including a relatively longer distal tip electrode (e.g., 19 discrete 1 mm wide ring-type electrodes and a single 2 mm long distal tip electrode). In one form, 20 electrodes are distributed in a paired bi-polar mapping configuration wherein each pair is equally separated from each other pair (e.g., 2.5 mm apart) and each individual pair is closely situated (e.g., 1 mm apart—including the tip electrode to the most-distal ring-type electrode). Such closely spaced bi-polar pairs tend to reduce so-called far field effects in an in-chamber electrocardiogram (EGM) signal. In another form, 10 discrete electrodes (9 ring-type electrodes and one tip electrode) couple to the single shallow helical fixed-diameter loop distal portion to sense EGM signals and are typically evenly-spaced (e.g., 3 mm, 4 mm, 5 mm, 7 mm, or the like) although that is not a requirement as they may be paired in bi-polar pairs as described above. That is, a 1 mm spacing could be following by a 7 mm spacing (in what can be referred to as a 1-7-1 arrangement). In this form the initial spacing between a tip electrode and the next ring-type electrode might be a different value, for example, 2 mm or some other value. 
     Accordingly, this disclosure describes EP catheters including: a tubular catheter body having a proximal region, a neck region, and a distal portion predisposed into a single shallow helical fixed-diameter loop distal portion; a plurality of electrodes disposed on the distal portion (e.g., as noted above, 10 or 20—or more or less—also known as deca- and duo-deca pole or polar electrode arrangement—with unipolar and bipolar pairing provided via suitable switching, as desired); a handle joined to the proximal region (for deflecting the distal part of the shaft portion); and a first activation wire extending through at least a portion of the proximal region of the catheter body. 
     The activation wire deflects the neck region of the catheter body in a common plane. Alternatively, they can deflect the proximal region, the neck region, and/or the looped-portion of the catheter body in different planes. In general, the activation wire couples to a first element (e.g., a round or flat wire, a thread of fiber such as Kevlar, or the like) such that forces are transferred to the shaft proximal of the loop (or the neck portion) via a deflection mechanism such as a rotary knob or a push-pull handle as is known in the EP art. 
     In yet another aspect, the present invention provides a method of manufacturing an EP catheter. The method generally includes the steps of: joining a proximal portion of a shaft portion of an EP catheter to a deflection mechanism and a distal portion to a proximal region of a peripheral edge (or off-axis arrangement) of a distal single shallow helical fixed-diameter loop region having a plurality of electrodes disposed thereon; joining the deflection mechanism to a wire coupled to a distal portion of a segment of flat wire near the neck region and passing through a lubricious tube fastened to the segment of flat wire (thus the flat wire serving as an anchor structure adapted to deflect the neck region of the EP catheter in a planar manner). A method of delivering therapy via a catheter manufactured according to the foregoing includes: introducing the EP catheter into a patient&#39;s body proximate an ostium of interest; actuating the deflection mechanism to deflect the proximal region of the catheter in order to deflect the neck region of the catheter, and advancing or otherwise deploying the single shallow helical fixed-diameter loop portion relative to the ostium of interest. 
     An advantage of EP catheters designed, built, and implemented according to the present disclosure is that the distal portion thereof (the single shallow helical fixed-diameter loop portion) can be efficiently deflected relative to the remainder of the catheter body and thus can efficiently map various surfaces of a heart via the 10 or 20 (or other number) of electrodes. 
     Thus, an EP catheter according to this disclosure includes a tubular catheter body having a proximal region, a neck region, and a distal portion predisposed into an single shallow helical fixed-diameter loop configuration and including mapping electrodes arranged in diverse spacings therebetween. In deflectable embodiments, at least one activation wire extends through at least a portion of the proximal region of the catheter body and is adapted to deflect the distal portion (e.g., approximately 180 degrees) relative to the proximal region. The catheter can be operated manually by a clinician or via a clinician-surrogate such as a computer processor-controlled surgical system. In addition, a variety of localization, visualization, and/or orientation-specific elements can be incorporated into the proximal region, neck region, and proximal portion (e.g., metallic coil members, active impedance emitting or receiving electrodes, fluoroscopically opaque materials, and the like) for use in conjunction with an electroanatomical system, for example. 
     The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view including a partially exploded depiction of an exemplary EP catheter having a distal single shallow helical fixed-diameter loop cardiac mapping portion with EP electrodes disposed in a preconfigured manner, with the partially exploded depiction illustrating the catheter in both a deflected and an undeflected configuration. 
         FIG. 1B  is a plan view of the exemplary EP catheter illustrated in  FIG. 1A  in an undeflected configuration. 
         FIG. 1C  is an enlarged view of the distal single shallow helical fixed-diameter loop cardiac mapping portion of the exemplary EP catheter of  FIG. 1A ; namely, an illustration of a pair of electrodes residing a segment of the offset shaft-to-loop axis cardiac mapping portion. 
         FIG. 1D  is an elevational side view in partial cross section of a neck portion formed just proximal of the distal single shallow helical fixed-diameter loop cardiac mapping portion of the exemplary EP catheter depicted in  FIGS. 1A and 1B . 
         FIG. 2A  is a close up isometric view of the distal single shallow helical fixed-diameter loop cardiac mapping portion of the exemplary EP catheter of  FIGS. 1A and 1B  (with a perspective view of connecting elements within interior portions of the catheter body, or shaft, illustrated) according to some embodiments of the present invention. 
         FIG. 2B  is an enlarged isometric fragmented view of the interior details of the ends of the connecting elements within the interior of the catheter body shown in  FIG. 2A . 
         FIG. 2B ′ is an enlarged isometric fragmented view of the interior details of the ends of the various connecting elements within the interior of the catheter body of  FIG. 2A . 
         FIG. 2C  is an enlarged fragmented plan view of the interior details of the ends of the connecting elements within the interior of the catheter body shown in  FIG. 2A . 
         FIG. 2C ′ is a plan view of a polymer (PEEK) tube having a flattened end to promote adhesive effectiveness at its proximal end to a flat wire (deflection) subassembly that is used to contain a segment of nitinol shape memory wire that forms the single shallow helical fixed-diameter loop distal end of the present family of EP catheters. 
         FIG. 3  is an elevational view showing exemplary dimensions of the distal single shallow helical fixed-diameter loop cardiac mapping portion of the exemplary EP catheter of  FIGS. 1A and 1B  according to an embodiment of the present disclosure (at the perspective illustrated the off-axis junction with the shaft is not apparent). 
         FIG. 4A  depicts the distal single shallow helical fixed-diameter loop cardiac mapping portion of the exemplary EP catheter of  FIGS. 1A and 1B  (with cross references to details shown in  FIG. 4C ). 
         FIG. 4B  is an enlarged fragmentary view in partial cross section and partial cut-away of the distal tip electrode and two ring electrodes and flat wire subassembly connection within the catheter body, respectively, shown in  FIG. 4A . 
         FIG. 4C  is an enlarged cross sectional view of the catheter body near the neck region shown in  FIG. 4A   
         FIG. 5  is a cross-sectional view of the EP catheter illustrated in  FIG. 4C  taken along line A-A as shown in  FIG. 4C . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described with reference to an EP catheter utilized in cardiac EP studies, such as the AFocus II EB diagnostic catheter of St. Jude Medical, Atrial Fibrillation Division, Inc., which can provide access to difficult-to-reach portions of atrial anatomy, in particular the right superior and inferior pulmonary veins. The catheter described, depicted and claimed herein also provides relatively faster cardiac activity data collection (especially in duodecapolar configurations) by rapidly providing the necessary detail to efficiently diagnose complex cardiac arrhythmias. It should be understood, however, that the present teachings can be applied to good advantage in other contexts as well, such as radiofrequency (RF) ablation catheters or other diagnostic cardiac catheters. 
     Referring now to the drawings,  FIGS. 1A and 1B  depict an EP catheter  10  according to a first aspect of the present invention. 
       FIG. 1A  is a plan view including a partially exploded depiction of an exemplary EP catheter  10  having a distal single shallow helical fixed-diameter loop cardiac mapping portion  16  with EP diagnostic, or mapping, electrodes  20  (as depicted herein arranged in an exemplary decapolar configuration), with the partially exploded depiction illustrating the catheter  10  in both a undeflected and a deflected configuration (denoted as “C” and “D” respectively). The off-axis, or peripheral, junction of the single shallow helical fixed-diameter loop to the neck region of the catheter allows 180 degree deflection in on the order of 50 mm (as illustrated in said “D” configuration). 
       FIG. 1B  is a plan view of the exemplary EP catheter  10  illustrated in  FIG. 1A  in an undeflected configuration (i.e., configuration “C” of  FIG. 1A ).  FIG. 1B  shows an approximate minimum length for the catheter body of on the order of about 110 cm, although other lengths can be employed according to this disclosure. 
       FIG. 1C  is an enlarged view of the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  of the exemplary EP catheter  10  of  FIG. 1A ; namely, an illustration of a pair of electrodes  20  residing on a segment  16 ′ of the offset shaft-to-loop axis, single shallow helical fixed-diameter loop cardiac mapping portion  16 . The lateral edges  20 ′ of electrodes  20  are bonded to the adjacent relatively smaller (e.g., 4F) diameter biocompatible tubing (e.g., PTFE or the like) of portion  16  with a biocompatible material such as a polyurethane matrix composed of Polycin 936 and Vorite 689 (mixed 52:48 percent, as an example) produced by CasChem Inc. of Bayonne, N.J. 
       FIG. 1D  is an elevational side view in partial cross section of a neck portion  18  formed just proximal of the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  of the exemplary EP catheter  10  depicted in  FIGS. 1A and 1B . As shown, an extended braid tube/spring assembly  50  surrounds a variety of subcomponents of catheter  10  and is itself wrapped by a relatively smaller diameter biocompatible tubing  18  that covers the neck region and transitions the outer diameter to the about  4 F distal single shallow helical fixed-diameter loop cardiac mapping portion  16 . Where the extended braid tube/spring assembly  50  terminates at its distal edge a small amount of medical grade adhesive polymer  20 ″ (e.g., like the polymer  20 ′ used at the edges of electrodes  20 ) can be applied. A polyimide tube  56 ′ passes through the assembly  50  (and neck region  18 ) and into the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  and isolates a plurality of elongate conductive strands  70 ′ (shown in  FIG. 4B ) that couple the electrodes  20 ,  46  to remote circuitry via a handle ( 22  as shown in  FIGS. 1A and 1B ) having a mass termination where the conductors  70  pass through the handle to couple to an EP recording system or other diagnostic equipment, for example. A flat wire subassembly  52 , which includes segment of flat wire  59 , is coupled to an activation wire  54  and is adapted to impart and release tension to deflect the proximal end  16  in a plane defined by the flat wire subassembly  52  (via manipulation of the handle, such as by rotation or linear actuation members, and the like). The flat wire subassembly  52  is sometimes described as a planarity member or element because it promotes such planar deflection. A short segment of polyimide tubing  56 ′ surrounds a junction of several components; namely, a lubricous tubing member  58  (e.g., PEEK tubing) that receives a proximal end of an elongate shape memory member  30  (formed of nitinol, for example) that is preformed into a desired dimension and configuration for distal portion  16 . In one embodiment, the distal portion  16  has an overall outer diameter of about 15 mm (i.e., for the outermost loop) with a  4 F dimension for portion  16 ′ and 1 mm (wide) platinum electrodes  20  and a 2 mm (long) tip electrode  46 . In this embodiment, the electrodes  20  can be spaced apart in bipolar pairs or evenly (e.g., about 3 mm, 5 mm or other nominal spacing between them). In a bipolar pair configuration the electrode spacing can vary, of course, although in on embodiment the spacing for 1 mm (wide) ring-type electrodes is 1 mm per bipolar pair with 2.5 mm between pairs. In this embodiment the spacing between the tip electrode  46  to the most distal ring-type electrode  20  can be 1 mm or 2 mm or other value. In the embodiments depicted herein the diameter of the outer loop of the distal portion  16  is fixed (e.g., at about 15, mm, 20 mm or less than about 33 mm, or more, if desired). At the junction of the flat wire subassembly  52  with the nitinol wire  30  wrapped in, for example, PEEK tubing urethane adhesive (denoted by reference numeral  26  in  FIG. 2B ) can be applied between, above, and around the components within the polyimide tubing  56 ′ to encapsulate same. Similarly, urethane adhesive  26  can be impregnated into the interstices of the neck region  18  and distal portion  16  to reduce or eliminate any migration of the nitinol wire  30  or PEEK tubing  58  or polyimide tube  60  (surrounding conductor  70 ′) during use. 
     In general, EP catheter  10  can include an elongate catheter body  12 , which, in some embodiments, is tubular (e.g., it defines at least one lumen therethrough). Catheter body  12  includes a proximal region  14 , a distal portion  16 , and a neck region  18  between proximal region  14  and distal portion  16 . One of ordinary skill in the art will appreciate that the relative lengths of proximal region  14 , distal portion  16 , and neck region  18  depicted in  FIGS. 1A and 1B  are merely illustrative and can vary without departing from the spirit and scope of the present invention but likely should not have a magnitude of less than about 110 cm. Of course, the overall length of catheter body  12  should be long enough to reach the intended destination within the patient&#39;s body. 
     Catheter body  12  will typically be made of a biocompatible polymeric material, such as polytetrafluoroethylene (PTFE) tubing (e.g., TEFLON® brand tubing). Of course, other polymeric materials, such as fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxyethylene (PFA), poly(vinylidene fluoride), poly(ethylene-co-tetrafluoroethylene), and other fluoropolymers, can be utilized. Additional suitable materials for catheter body  12  include, without limitation, polyimide-based thermoplastic elastomers (namely poly(ether-block-amide), such as PEBAX®), polyester-based thermoplastic elastomers (e.g., HYTREL®), thermoplastic polyurethanes (e.g., PELLETHANE®, ESTANE®), ionic thermoplastic elastomers, functionalized thermoplastic olefins, and any combinations thereof. In general, suitable materials for catheter body  12  can also be selected from various thermoplastics, including, without limitation, polyamides, polyurethanes, polyesters, functionalized polyolefins, polycarbonate, polysulfones, polyimides, polyketones, liquid crystal polymers and any combination thereof. It is also contemplated that the durometer of catheter body  12  can vary along its length. In general, the basic construction of catheter body  12  will be familiar to those of ordinary skill in the art, and thus will not be discussed in further detail herein. 
     Referring now to  FIG. 2A  which is a close up isometric view of the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  of the exemplary EP catheter  10  of  FIGS. 1A and 1B  (with a perspective view of connecting elements within interior portions of the catheter body, or shaft, illustrated) according to some embodiments of the present invention. As illustrated, the proximal and distal ends of the flat wire subassembly  52  (e.g., implemented to promote planarity during deflection) are emphasized. 
       FIG. 2B  is an isometric illustration of the neck region  18  and the single shallow helical fixed-diameter loop distal portion  16 , polyimide tubing  56 , and the flat wire subassembly  52 . 
       FIG. 2B ′ is an enlarged isometric fragmented view of the interior details of the ends of the various connecting elements within the interior of the catheter body  14 , 18  of  FIG. 2A . As depicted, the proximal end of a flattened PEEK tube  58  that contains the nitinol wire  30  is adhered with urethane adhesive  26  (or other suitable medical grade adhesive) to segment of flat wire  59  of the flat wire subassembly  52  and wrapped in polyimide tubing  56 ′ for containment. The proximal end of the flat wire subassembly  52  couples via a segment of polyimide tubing  56  filled with urethane adhesive  26  that also encapsulates the smaller diameter polyimide tubing  61  where the activation wire  54  resides. A gap of about 1-2 mm between the tubing  56  and the distal end of extended braid/spring subassembly  50  should be optionally maintained (as depicted) and the activation wire  54  and conductor wires  70  (within polyimide tube  60 ) are conveyed through braid/spring subassembly  50  to a handle or other remote location. 
       FIG. 2C  is an enlarged fragmented plan view of the interior details of the ends of the connecting elements within the interior of the catheter body shown in  FIG. 2A . As depicted, the flattened section of the PEEK tubing  58  disposed within the polyimide tubing  56 ′ can comprise a 1 mm segment to promote adhesion to the urethane adhesive  26  impregnated therein and thus to the flat wire subassembly  52 , including segment of flat wire  59 . Similarly, the proximal end of the flat wire subassembly  52  can be surrounded by polyimide tubing  56  and impregnated with urethane adhesive (not shown) to promote mechanical coupling to the adjacent extended braid/spring subassembly  50 . A suitable biocompatible compound  20 ″ (e.g., such as polymer  20 ′) can be applied to the junction between the outer covering for distal portion  16 ′ and the neck region  18 . 
       FIG. 3  is an elevational view showing exemplary dimensions of the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  of the exemplary EP catheter  10  of  FIGS. 1A and 1B  according to an embodiment of the present disclosure. For example, the “plane” of the single shallow helical fixed-diameter loop distal portion  16  can be on the order of 2 mm to the neck region  18 , although other dimensions can be used if desired. Whatever dimension is used the wire support length therefrom should be a reasonable length. 
       FIG. 4A  depicts the distal single shallow helical fixed-diameter loop cardiac mapping portion  16  of the exemplary EP catheter  10  of  FIGS. 1A and 1B  (with cross references to details shown in  FIGS. 4B and 4C ). In the illustrated embodiment the single shallow helical fixed-diameter loop distal portion  16  includes evenly-spaced ten-pole electrodes  20  with a nominal separation between adjacent electrodes  20 . Of course, other dimensions can be used for the electrodes  20  and the spacing therebetween. At the proximal end of the catheter body  12  (not specifically shown) a plurality of individually electrically insulated elongate conductors  70  emerge and are adapted to be individually coupled to mass termination terminal  72  within a handle for ultimate electrical communication with an EP recording system, an electroanatomical localization and visualization system (e.g., such as the ENSITE system of St. Jude Medical, Inc. operating the ONEMAP facility or other similar systems for monitoring cardiac activity and providing one or more visual representations of same). 
       FIG. 4B  is an enlarged fragmentary view in partial cross section and partial cut-away of the distal tip electrode  46  and two ring-type electrodes  20  and flat wire subassembly  52  connection within the catheter body  12 , respectively, shown in  FIG. 4A . Each electrode  20 , 46  couples via an elongate conductor  70 ′ in  FIG. 4B  to remote EP recording and/or localization and visualization equipment. A biocompatible adhesive  21  (e.g., LOCTITE adhesive) can be applied to the junction of the biocompatible tubing  16  of the distal portion  16  and the electrode  46  to eliminate body fluid ingress therein. A so-called safety wire (or element)  71  can couple to the electrode  46  and a proximal location to reduce or eliminate the chance that the electrode  46  might separate from the catheter assembly  10 . 
       FIG. 4C  is an enlarged fragmentary view in partial cross section of the catheter body near the neck region shown in  FIG. 4A  and indicates a cross sectional view along lines A-A therein which is reflected in  FIG. 5  hereinbelow described. The dimensions indicated on  FIG. 4C  are merely exemplary and illustrative and not intended as limiting in any way. 
       FIG. 5  is a cross-sectional view of the EP catheter  10  illustrated in  FIG. 4C  taken along line A-A as shown in  FIG. 4C . The biocompatible tubing overlaying next region  18  includes (electrode  20 ) conductor wires, denoted by reference numeral  70  in  FIG. 5 , surrounded by polyimide tubing  60  and nominally spaced from nitinol wire  30  by a space impregnated with urethane adhesive  26 . 
     One of ordinary skill in the art will appreciate that electrodes  20  can be ring-type electrodes or any other electrodes suitable for a particular application of EP catheter  10 . For example, where EP catheter  10  is intended for use in a contactless EP study, electrodes  20  can be configured as described in U.S. application Ser. No. 12/496,855, filed 2 Jul. 2009, which is hereby incorporated by reference as though fully set forth herein. Of course, in addition to serving sensing purposes (e.g., cardiac mapping and/or diagnosis), electrodes  20  can be employed for therapeutic purposes (e.g., cardiac ablation and/or pacing). 
     Referring again to the present disclosure in general, various handles and their associated actuators for use in connection with deflecting EP catheters are known, and thus handle  22  will not be described in further detail herein except that is has a means for imparting tension (e.g., push-pull knob  24  depicted in  FIGS. 1A and 1B , although other biasing structures can of course be used) to an activation wire. 
     In use, EP catheter  10  is introduced into a patient&#39;s body proximate an area of interest, such as a pulmonary vein ostium. Of course, EP catheter can be introduced surgically (e.g., via an incision in the patient&#39;s chest) or non-surgically (e.g., navigated through the patient&#39;s vasculature to a desired site). Activation wire  54  can be actuated in order to deflect proximal region  14  of catheter body  12  such that distal portion  16  is oriented generally towards the ostium of interest. Electrodes  20  can then be employed for diagnostic or therapeutic purposes. 
     All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and can include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. 
     It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure can be made without departing from the invention as defined in the appended claims.

Technology Category: 1