Abstract:
Catheter curve shape struts for steerable medical devices such as catheters are disclosed. These struts may not only help shape a steerable portion of a medical device (e.g., a distal portion of a catheter), but also may help to return a steered or deflected portion of the medical device to an uncurved configuration when it is no longer desirable or necessary to steer or deflect the medical device. These struts may include first and second pluralities of complementary, staggered cutout regions. When used in a catheter that is deployed via an introducer, at least some configurations of the catheter curve shape strut can enable the catheter to be rotated about its longitudinal axis, even when the distal deflectable section is in a curved configuration and inside of the introducer.

Description:
BACKGROUND 
       [0001]    a. Field 
         [0002]    The instant disclosure relates to components for steerable medical devices. In one particular form, the disclosure relates to a strut comprising part of a distal deflectable section of an electrophysiology catheter to facilitate predictable and repeatable asymmetric and symmetric deflection of the distal deflectable section. 
         [0003]    b. Background Art 
         [0004]    Electrophysiology catheters are used in a variety of diagnostic, therapeutic, and/or mapping and ablative procedures to diagnose and/or correct conditions such as atrial arrhythmias, including for example, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmias can create a variety of conditions including irregular heart rates, loss of synchronous atrioventricular contractions, and stasis of blood flow in a chamber of a heart, which can lead to a variety of symptomatic and asymptomatic ailments and even death. 
         [0005]    Typically, a catheter is deployed and manipulated through a patient&#39;s vasculature to the intended site, for example, a site within a patient&#39;s heart. The catheter typically carries one or more electrodes that can be used for cardiac mapping or diagnosis, ablation, and/or other therapy delivery modes, or both, for example. Once at the intended site, treatment can include, for example, radio frequency (RF) ablation, cryoablation, laser ablation, chemical ablation, high-intensity focused ultrasound-based ablation, microwave ablation, and/or other ablation treatments. In some procedures, the catheter imparts ablative energy to cardiac tissue to create one or more lesions in the cardiac tissue. These lesions disrupt undesirable cardiac activation pathways and thereby limit, corral, or otherwise prevent errant conduction signals that can form the basis for arrhythmias. 
         [0006]    To position a catheter within the body at a desired site, some type of navigation must be used, such as using mechanical steering features incorporated into the catheter (or an introducer sheath). In some examples, medical personnel may manually manipulate and/or operate the catheter using the mechanical steering features. 
         [0007]    In order to facilitate the advancement of catheters through a patient&#39;s vasculature, the simultaneous application of torque at the proximal end of the catheter and the ability to selectively deflect the distal tip of the catheter in a desired direction can permit medical personnel to adjust the direction of advancement of the distal end of the catheter and to selectively position the distal portion of the catheter during an electrophysiological procedure. The proximal end of the catheter can be manipulated to guide the catheter through a patient&#39;s vasculature. The distal tip can be deflected by a pull wire or other tension member attached or anchored at the distal end of the catheter and extending proximally to an actuator in a control handle that controls the application of tension on the pull wire. 
         [0008]    The foregoing discussion is intended only to illustrate the present field and should not be taken as a disavowal of claim scope. 
       BRIEF SUMMARY 
       [0009]    It is desirable to be able to ensure that a deflectable portion of a catheter shaft may be predictably deflected in a preferentially-planer manner whenever desired throughout a medical procedure. It is also desirable to be able to tailor total deflectability of the catheter distal portion and the curve shape of the deflectable portion throughout the full deflection of the catheter shaft. 
         [0010]    In one embodiment, a catheter curve shape strut comprises a longitudinally-extending cylindrical wall, the wall having an outer surface, an outer surface circumference, and an outer surface length measured longitudinally. The wall comprises connected end-to-end cylindrical sections including at least a first cylindrical section and a second cylindrical section. There are a plurality of first slots through the cylindrical wall and sequentially arranged along a first line extending longitudinally along the wall outer surface in both the first cylindrical section and the second cylindrical section. There are a plurality of second slots through the cylindrical wall and sequentially arranged along a second line extending longitudinally along the wall outer surface in both the first cylindrical section and the second cylindrical section. The slots in the plurality of second slots are longitudinally offset from the slots in the plurality of first slot. Also, the plurality of second slots further comprises second slots of a first type and second slots of a second type. The second slots of the first type are sequentially arranged along the second line only along the first cylindrical section, and the second slots of the second type are sequentially arranged along the second line only along the second cylindrical section. In some embodiments, the second slots of the second type are longer in a circumferential dimension than one-half of the outer surface circumference, whereby at least some of the second slots of the second type circumferentially overlap with at least some of the slots in the first plurality of slots. An expansion gap may be present between at least some of the end-to-end cylindrical sections. 
         [0011]    In another embodiment, a catheter curve shape strut is configured to facilitate preferentially-planar, asymmetric deflection of a medical device. The catheter curve shape strut comprises the following: (1) a longitudinally-extending cylindrical wall, the wall having an outer surface, an outer surface circumference, and an outer surface length measured longitudinally, wherein a first line extends longitudinally along the outer surface, wherein a second line extends longitudinally along the outer surface, and wherein the second line is circumferentially offset from the first line by 180 degrees; (2) a plurality of first slots through the cylindrical wall and sequentially present along the first line, wherein each first slot has a first slot length measured circumferentially on the outer surface between first slot ends, wherein each first slot has a first slot width measured longitudinally on the outer surface, and wherein the first slot length is greater than the first slot width; (3) a plurality of first arches, wherein each first arch is present between a pair of longitudinally-adjacent first slots, wherein each first arch has a first arch length measured circumferentially on the outer surface, wherein each first arch has a first arch width measured longitudinally on the outer surface, and wherein the first arch length is greater than the first arch width; (4) a plurality of second slots through the cylindrical wall and sequentially present along the second line, wherein each second slot has a second slot length measured circumferentially on the outer surface between second slot ends, wherein each second slot has a second slot width measured longitudinally on the outer surface, and wherein the second slot length is greater than the second slot width; and; (5) a plurality of second arches, wherein each second arch is present between a pair of longitudinally-adjacent second slots, wherein each second arch has a second arch length measured circumferentially on the outer surface, wherein each second arch has a second arch width measured longitudinally on the outer surface, and wherein the second arch length is greater than the second arch width, wherein at least one of the first slot length and the second slot length is greater than one-half of the outer surface circumference. The catheter curve shape strut may further comprise a plurality of bridges connecting the first arches to the second arches. The plurality of bridges may define first and second diametrically-opposed serpentine backbones. The catheter curve shape strut may further comprise at least two alignment tabs on each longitudinal end of the strut. 
         [0012]    In yet another embodiment, a catheter curve shape strut assembly comprises a curve shape strut, an outer body surrounding the curve shape strut, and an insert component surrounded by the curve shape strut. The outer body may comprise a single polymer layer. The insert component may be formed from an extruded polymer and may comprise three longitudinally-extending lumens, including a central lumen straddled by a pair of pull wire lumens that may be diametrically-opposed. 
         [0013]    In another embodiment, a distal deflectable portion of an ablation catheter comprises a catheter curve shape strut assembly, a tip electrode affixed to the distal end of the catheter curve shape strut assembly, a plurality of ring electrodes affixed to the catheter curve shape strut assembly proximal to the tip electrode, a pull ring affixed to the catheter curve shape strut assembly proximal to the plurality of ring electrodes, a coupler affixed to the proximal end of the catheter curve shape strut assembly, and first and second pull wires, each pull wire having a distal end affixed to the pull ring. The first pull wire may extend proximally from the pull ring through the first pull wire management channel, and the second pull wire may extend proximally from the pull ring through the second pull wire management channel. 
         [0014]    In a further embodiment, a catheter comprises an elongated catheter shaft comprising a distal deflectable section, first and second pull wires (each pull wire having a proximal end and a distal end) extending along the elongated catheter shaft, an actuator operatively coupled to the proximal ends of the first and second pull wires and adapted selectively deflect the distal deflectable section, a curve shape strut assembly comprising part of the distal deflectable section and itself comprising a curve shape strut mounted within an outer jacket, and a pull ring affixed to the distal ends of the first and second pull wires. 
         [0015]    The foregoing and other aspects, features, details, utilities, and advantages of the present disclosure will be apparent by reading the following description and claims, and from reviewing the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  depicts a representative ablation catheter having a distal deflectable section configured to create asymmetric curve shapes when deflected in different directions, as represented by the two curves shown in phantom. 
           [0017]      FIG. 2  is a fragmentary, isometric view of a portion of the distal deflectable section, with sections on each end broken away to reveal various details. 
           [0018]      FIG. 3  is a fragmentary, isometric view of the proximal end of a strut assembly and pull wires, with a portion of an outer body of the strut assembly removed to show various features of a strut and of an insert component comprising part of the strut assembly. 
           [0019]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 3 . 
           [0020]      FIG. 5  is an isometric view of a strut assembly, depicted with a strut shown in phantom within the outer body of the strut assembly, and with the pull wires removed. 
           [0021]      FIG. 6  is a cross-sectional view of the strut assembly depicted in  FIG. 5 , taken along line  6 - 6  of  FIG. 5 . 
           [0022]      FIG. 7  is a cross-sectional view of the strut assembly depicted in  FIG. 5 , taken along line  7 - 7  of  FIG. 5 . 
           [0023]      FIG. 8  is an exploded, isometric, assembly view of the strut assembly depicted in  FIGS. 5-7 , revealing details about the components of the strut assembly. 
           [0024]      FIG. 9  is a cross-sectional view of the insert component, taken along line  9 - 9  of  FIG. 8 . 
           [0025]      FIG. 10  is a side view of a strut according to one embodiment. 
           [0026]      FIG. 11  is an end view of the strut depicted in  FIG. 10 , taken in the direction of line  11 - 11  in  FIG. 10 . 
           [0027]      FIG. 12  is a planar view of a flat, two-dimensional cut pattern that could be used to automate the production of the strut depicted in, for example,  FIG. 10 . 
           [0028]      FIG. 13  is an enlarged view of the circled portion of  FIG. 12 . 
           [0029]      FIG. 14  is a greatly enlarged, fragmentary view of a portion of a cut pattern such as the one depicted in  FIG. 12 , depicting further details about the construction and components of a strut. 
           [0030]      FIG. 15  schematically depicts a representative view of an arch compromising part of a strut, and provides details regarding the parameters used to describe an arch configuration. 
           [0031]      FIG. 16  is an isometric view of a strut according to another embodiment. 
           [0032]      FIG. 17  is an isometric view of another embodiment of a strut, shown adjacent to a representative pull ring. 
           [0033]      FIGS. 18-20  depict different embodiments of two-dimensional cut patterns that could be used to form various strut embodiments, each having stiffness that varies along the longitudinal axis of the strut. 
           [0034]      FIG. 21  is a fragmentary, isometric view of a representative distal deflectable section of an ablation catheter having a flexible, irrigation tip, a strut assembly, and a coupler for attaching the distal deflectable section to a proximal catheter shaft. 
           [0035]      FIGS. 22 and 23  are enlarged, fragmentary views of the distal portion of the distal deflectable section depicted in  FIG. 21 , and provide further details about the placement of various components. 
           [0036]      FIGS. 24 and 25  are enlarged, fragmentary, isometric views of the proximal portion of the distal deflectable section depicted in  FIG. 21 , and show the alignment tabs in position on a tab alignment ring comprising part of one possible embodiment of a coupler. 
           [0037]      FIGS. 26 and 27  are enlarged, isometric views of the coupler that is also depicted in  FIGS. 21, 24, and 25 . 
           [0038]      FIGS. 28-30  schematically depict a distal deflectable section comprising a strut assembly before a severe kink, while having a severe kink, and after recovering from a severe kink. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  depicts a representative catheter  10  compromising a catheter curve shape strut (not directly visible in  FIG. 1 ). In particular, this catheter includes a handle  12  and a catheter shaft  14 . The handle  12  comprises a housing  16  that houses an actuator (not shown). The catheter shaft comprises a proximal section  18  and a distal deflectable section  20  connected at a juncture  22 . As shown in  FIG. 1 , the distal deflectable section  20  is mounted to the distal end of the proximal catheter shaft and includes, in this embodiment, three ring electrodes  24  and a tip electrode. As shown in phantom in  FIG. 1 , the catheter curve shaped strut comprising part of the distal deflectable section  20  facilitates the formation of asymmetric curves upon deflection of the distal section in different directions. Although the phantom lines in this figure schematically depict the curves commencing from the same longitudinal position along the catheter shaft, the curves could each commence at a different longitudinal location along the catheter shaft. Also, and as discussed further below, although  FIG. 1  depicts asymmetric curves, the distal deflectable section could be constructed to deflect symmetrically. 
         [0040]      FIG. 2  is a fragmentary, isometric view of a portion of the distal deflectable section depicted in  FIG. 1 . In  FIG. 2 , however, the ring electrodes and tip electrode have been removed, and the distal deflectable section  20  has been separated from the proximal catheter shaft  18 . In this figure, a portion of the outer body (or outer jacket or outer layer)  28  of the distal deflectable section has been broken away on the distal end (i.e., the left-hand end as oriented in  FIG. 2 ) of the distal deflectable section to reveal a representative pull ring  30 . Similarly, at the proximal end (i.e., the right-hand end as oriented in  FIG. 2 ) of the distal deflectable section  20 , another fragment of the outer body has been broken away to reveal first and second pull wires  32 ,  34 , respectively, entering the proximal end of the distal deflectable section on their way to the pull ring. As shown in  FIG. 2 , first and second tightly-wound compression coils  36 ,  38  may surround the first and second pull wires  32 ,  34 , respectively. Although these compression coils are shown in  FIG. 2  to terminate just proximal to the proximal end of the distal deflectable section, these tightly-wound compression coils, in reality, may extend through the entire length of the proximal catheter shaft  18  to the handle  12 . 
         [0041]      FIG. 3  is an enlarged, fragmentary, isometric view of the proximal end of the distal deflectable section, shown with a portion of the outer body  28  removed to reveal a plurality of cutout regions (or slots or channels or gaps), including a first plurality of cutout regions  40  and a second plurality of cutout regions  42 , formed in the strut  44  comprising part of the strut assembly (see element  46  in  FIG. 5 ). As shown in  FIG. 3 , the strut assembly includes the outer jacket  28 , the strut  44 , and an insert component  48 , which may be, for example, made from an extruded polymer. The strut may be constructed from a super-elastic Nitinol and, in one embodiment, the outer body comprises a single layer of polymer material. The outer body  28  could, however, comprise multiple layers, including layers of different types of materials. As clearly shown in  FIG. 3 , the insert component  48  may comprise a section of tri-lumen tubing, including a single central lumen  50  that is straddled by a pair of diametrically-opposed pull wire lumens  52 ,  54  (see, e.g.,  FIG. 4 ). As discussed further below, these pull wire lumens must be properly oriented relative to a cut pattern (various representative cut patterns are depicted in  FIGS. 12-14  and  FIGS. 18-20 ) in the strut for the distal deflectable section to deflect as desired.  FIG. 4  is a cross-sectional view of the strut assembly  46  depicted in  FIG. 3 , taken along line  4 - 4  of  FIG. 3 . As clearly shown in  FIG. 4 , the insert component  48  includes a large central lumen  50  for wire management, for example, and the two offset pull wire lumens  52 ,  54  (shown as diametrically opposed from each other in this embodiment). 
         [0042]      FIG. 5  is an isometric view of a strut assembly  46 . In this figure, the strut  44  comprising part of the strut assembly is depicted in phantom below the outer body.  FIG. 6  is a lateral cross-sectional view of the strut assembly, taken along line  6 - 6  of  FIG. 5 .  FIG. 7  is a longitudinal cross-sectional view of the strut assembly depicted in  FIG. 5 , taken along line  7 - 7  of  FIG. 5 . 
         [0043]      FIG. 8  shows the components of the strut assembly  46  depicted in  FIGS. 5-7  prior to assembly and a reflow process. As represented by the staggered, serpentine dashed lines in  FIG. 8 , the strut assembly  46  is constructed by placing the insert component  48  into the strut  44 , and then inserting the combined strut and insert component into the outer body  28 . That assembly of the insert component, the strut, and the outer body would then be subjected to a reflow process to help lock the components together into a functional strut assembly. Also clearly visible for the first time in  FIG. 8  are alignment tabs (or pin)  56  on the longitudinal ends of the strut. Although the strut embodiment shown in  FIG. 8  has two alignment tabs on each of its longitudinal ends (note that only one of the two alignment tabs on the right-hand end of the strut as oriented in  FIG. 8  is visible), any number of alignment tabs could be used. Two alignment tabs per end, each tab being approximately 0.01 inches by 0.01 inches, has been found to work well. As explained further below, the alignment tabs help ensure that the pull wires ultimately end up correctly oriented relative to the cutout pattern in the strut, so as to be able to effectuate deflection of the distal deflectable section. The alignment tabs also facilitate torque transfer along the catheter shaft.  FIG. 9  is a cross-sectional view taken along  9 - 9  of  FIG. 8 , and clearly depicts the diametrically-opposed pull wire lumen (or channels)  52 ,  54  and the large central wire management lumen  50 . 
         [0044]      FIG. 10  is a side view of a strut  44   I  according to an embodiment.  FIG. 11  is an end view of the strut depicted in  FIG. 10 , taken in the direction represented by the arrows on line  11 - 11  of  FIG. 10 . In this embodiment, the strut  44   I  includes a distal part  58  and a proximal part  60  that meet at a location represented by a vertical line  62 . Each end of this strut again includes a pair of diametrically-opposed alignment tabs  56 , two of which may be seen in  FIG. 11 . Again, although any number of alignment tabs may be used, it works well to have two alignment tabs that are diametrically opposed from each other as shown to best advantage in  FIG. 11 . As shown in  FIG. 10 , in this embodiment of the strut  44   I , a first plurality of slots  40  are formed in the upper surface of the strut and define a first plurality of arches  64 . A second plurality of slots  42  is cut in the bottom surface of the strut  44   I , creating a second plurality of arches  66 . These slots and arches are explained further below. 
         [0045]    In the embodiment depicted in  FIG. 10 , each slot  40  comprising the first plurality of slots is the same, and each arch  64  comprising the first plurality of arches is the same. The second plurality of slots  42 , however, comprises two types of slots. In particular, the proximal end of the strut (i.e., the right-hand end of the strut as oriented in  FIG. 10 ) includes a plurality of deep (or tall), narrow cuts or slots  42   a,  and the distal portion of the strut includes a plurality of relativity wider and more shallow slots  42   b.  Also, the slots  40  in the top portion of the strut  44   I  are identical to the slots  42   b  in the bottom portion of the strut along the distal portion  58  of the strut  44   I . The differences between the slot configurations in the top of the strut versus the slot configurations in the bottom of the strut along the proximal part of the strut, create asymmetric curves when the catheter is deflected in different directions. In particular, if the distal end of the distal deflectable section is deflected downwardly (i.e., in the direction of arrow  68  depicted in  FIG. 10 ), the deflection curve will tend to commence at the location represented by the vertical line  62 , which, as noted above, is at the junction of the distal part  58  with the proximal part  60  of the strut  44   I . However, if the distal deflectable section is deflected upwardly (i.e., in the direction of arrow  70  depicted in  FIG. 10 ), the resulting curve will tend to commence closer to the proximal end  72  of the strut. 
         [0046]    The strut  44   I  depicted in  FIG. 10  could be created in an automated process. In order to drive the automated process, a cut pattern  74  may be defined from a CAD model of the strut and then information about the design may be loaded into the guidance system for a cutting machine (e.g., a laser cutter—not shown).  FIG. 12  depicts a two-dimensional, flat pattern  74  that could be used to direct the cutting machine to create the strut depicted in  FIG. 10 . In particular, if the flat pattern  74  were formed into a cylindrical configuration (as shown in  FIGS. 10 and 11 ), by joining the top horizontal edge  76  of the pattern depicted in  FIG. 12  with the bottom edge  80  of the pattern, that body would have a configuration similar to that shown in  FIG. 10 . 
         [0047]    The pattern  74  depicted in  FIG. 12  is symmetrical about a longitudinally-extending line  78 , which longitudinally divides the pattern into symmetrical upper and lower halves. That is, the portion of the pattern above the line  78  is a mirror image of the portion of the pattern below the line. This pattern also defines the proximal part  60  (which, in this embodiment, is an asymmetric portion), which is the portion of the pattern to the left of a vertical line  62 ; and the distal part  58  (which, in this embodiment, is a symmetric portion), which is the portion of the pattern to the right of the vertical line  62 . In this embodiment, the first plurality of elliptical slots is longitudinally-arranged (or ‘stacked’) along the line of symmetry  78 . Each elliptical slot  40  in the first plurality of slots is the same. In other words, in the pattern  74  depicted in  FIG. 12 , the elliptical cutouts comprising the first plurality of slots are the same from the proximal end of the strut to the distal end of the strut. 
         [0048]    The pattern depicted in  FIG. 12  also comprises a second plurality of cutout regions (or slots)  42 . It should be kept in mind that  FIG. 12  depicts a ‘flat pattern.’ Thus, half of each slot in the second plurality of slots opens upwardly in the depicted pattern, and the other half of each slot opens downwardly in the depicted pattern. As may be clearly seen in  FIG. 12 , the second plurality of slots  42  are not uniform from one end of the strut to the other. In particular, on the proximal end of the strut pattern (i.e., on the left-hand end of the strut pattern as oriented in  FIG. 12 ), along what will become the asymmetric portion of a strut (i.e., the portion to the left of vertical line  62 ), the second slots  42   a  are of a first type; and, on the distal end of the strut pattern (i.e., on the right-hand end of the strut pattern as oriented in  FIG. 12 ), along the symmetric portion of the strut pattern (i.e., the portion to the right of vertical line  62 ), the second slots  42   b  are of a second type. The second slots of a first type  42   a  are relatively narrow and relatively long compared to the second slots of a second type  42   b  along the symmetric portion of the strut. Further, in the symmetric section, the slots in the first plurality of slots are identical to the second type of second slots. That is, to the right of vertical line  62 , the complementary slots  40 ,  42   b  are the same and are merely staggered longitudinally. 
         [0049]    Moving distally from the proximal end of the strut to the distal end of the strut depicted in  FIG. 12 , the second slots get shorter and wider (e.g., compare slots  42   a  to slots  42   b ). In particular, the second slots of the first type  42   a  are narrow and deep compared to the second slots of the second type  42   b.  As a direct result, the first arches  64  (discussed further below in connection with  FIG. 14 ) get longer as one transitions from the asymmetric portion of the cut pattern to the symmetric portion. Correspondingly, again moving from the proximal end of the strut to the distal end of the strut, the second arches  66  get narrower (e.g., compare arches  66   a  to arches  66   b ). Finally, as one moves from the proximal end of the strut cut pattern  74  depicted in  FIG. 12  to its distal end, the bridges  82  (see  FIGS. 13 and 14 ) that connect the first arches  64  to the second arches  66  get shorter. That is, the bridges in the symmetric deflection portion are shorter than the bridges in the asymmetric deflection portion. Bridges are discussed in detail below in connection with  FIG. 14 . In the configuration depicted in  FIGS. 10 and 12 , the first arches  64  match the second arches  66   b,  and the first slots  40  match the second slots  42   b  in the symmetric portion  58  of the strut. Thus, in the symmetric portion of a strut, deflection is symmetrical.  FIG. 13  is an enlarged view of the circled portion of  FIG. 12 . 
         [0050]    In order to better understand the cut patterns used to form the struts,  FIG. 14  depicts a greatly enlarged portion of the cut pattern  74  depicted in  FIG. 12 . Each strut is formed from a series of longitudinally-offset arches, including a first plurality of arches  64  and a second plurality of arches  66 . The arches comprising the first plurality of arches are arranged in a longitudinally-extending row (or series), as shown to good advantage in  FIG. 12 . Similarly, the arches  64  comprising the second plurality of arches are arranged in a complementary and circumferentially-offset, second longitudinally-extending row. Adjacent arches of said first plurality of arches  64  are separated by circumferentially-extending cutout regions  40  (or slots or channels or gaps). Similarly, adjacent arches  66  comprising the second plurality of arches are separated by circumferentially-extending cutout regions  42 . Each cutout region may have an elliptical configuration as shown in, for example, FIG. 12 - 14 , or a cat-eye or almond configuration, such as shown in, for example,  FIG. 3 . Other symmetrical and asymmetrical slot shapes are contemplated, such as diamonds, rectangles, and triangles. 
         [0051]    Again referring to  FIG. 14 , each of the first arches  64  extends circumferentially a distance L 3  between a third longitudinally-extending line  84  and a fourth longitudinally-extending line  86 . Each of these first arches has a midpoint width  88 . Further, each of the first arches is separated from the next adjacent arch by a first cutout region  40 . Each of the these first cutout regions has its own midpoint width  90 , and extends circumferentially a distance L 2 +L 3 +L 4  between a second longitudinally-extending line  92  and a fifth longitudinally-extending line  94 , as clearly depicted in  FIG. 14 . Referring briefly to  FIG. 15 , each arch (e.g., arch  64 ) shown in Fig. 14  subtends an angle theta (0) and has an arc length L and a span S. Referring back to  FIG. 14 , the depicted cut pattern  74  further comprises a plurality of second arches  66 , each having a mid-point width  100 , separated by a plurality of second cutout regions  42 , each having a mid-point width  102 . Each of the second arches extends circumferentially a distance L 1 +L 5  from the second longitudinally-extending line  92  in  FIG. 14  to the fifth longitudinally-extending line  94 , keeping in mind that the cut pattern  74  depicted in  FIG. 14  is a flat, two-dimensional pattern. Thus, the first longitudinally-extending line  96  and the sixth longitudinally-extending line  98  shown in  FIG. 14  comprise the same line in the cylindrical strut  44   I  formed from the pattern depicted in  FIG. 14 . Thus, the length of the second arches, as discussed above, is the distance L 1  from the second longitudinally-extending line  92  downward (as depicted in  FIG. 14 ) to the first longitudinally-extending line  96 , plus the distance L 5  from the fifth longitudinally-extending line  94  upward (as depicted in  FIG. 14 ) to the sixth longitudinally-extending line  98 . As also shown in  FIG. 14 , the length of each second cutout region  42  in this particular pattern is the sum of L 1 +L 2 +L 4 +L 5 . 
         [0052]      FIG. 14  also clearly depicts the bridges  82  (or links or connectors) that connect the first arches  64  to the second arches  66 . These bridges flexibly interconnect the first plurality of arches to the second plurality of arches. A first plurality of adjacent bridges  82  form a first longitudinally-extending, serpentine backbone (this backbone may be seen in, for example,  FIG. 10  running longitudinally along the vertical midline of the strut  44   I ), which permits and facilitates preferentially-planar deflection of the distal deflectable section  20 , and restrains out-of-plane deflection. When the slots are elliptical as shown in, for example,  FIG. 14 , the arches take the shape of necked-in rectangles in the two-dimensional cut pattern. 
         [0053]      FIG. 16  is an isometric view of a strut  44   II  according to another embodiment. In this figure, the distal end of the strut is on the left, and the proximal end of the strut is on the right. Similar to the strut discussed above, the strut depicted in  FIG. 16  includes a section  58   I  of symmetric cuts and a section  60   I  of asymmetric cuts. In section  58   I , the top cuts  40   I  and bottom cuts  42   b   I  are the same. In contrast, in section  60   I , the top and bottom cuts are different. Looking more carefully at  FIG. 16 , a first plurality of slots  40  separates a first plurality of arches  64 . In section  58   I  of the strut, each arch  64   a   I  has a first width  88   a.  In section  60   I , each arch  64   b   I  has a second width  88   b  that is larger than the first width. 
         [0054]    Looking now more carefully at the slots on the bottom of the strut  44   II  depicted in  FIG. 16 , the slots  42   a   I  in section  58   I  are shallower but wider than the slots  42   b   I  in section  60   I . Thus, moving distally from the proximal end of the strut to the distal end of the strut (i.e., from right to left in  FIG. 16 ), the first slots  40   I  remain constant, the first arches get narrower and longer (i.e., arches  64   a   I  are narrower and longer than arches  64   b   I ) after the transition from section  60   I  to section  58   I  (i.e., after crossing vertical line  62   I ), the second slots get shorter and wider (i.e., slots  42   a   I  are shorter and wider than slots  42   b   I ) after the transition from section  60   I  to section  58   I , the second arches get narrower (compare width  100   b  of arches  66   b   I  to width  100   a  of arches  66   a   I ), and the bridges get shorter (compare longer bridges  82   b  to shorter bridges  82   a ). 
         [0055]      FIG. 17  depicts yet another embodiment of a strut  44   III .  FIG. 17  also shows a pull ring  30  exploded away from the distal end of the strut. The strut depicted in  FIG. 17  has a stiffer proximal portion  60   II  (i.e., the left end of the strut as depicted in  FIG. 17 ) and a softer distal portion  58   II  (i.e., the right end of the strut as depicted in  FIG. 17 ). The strut again comprises a first plurality of arches  64   a   II ,  64   b   II , a first plurality of slots  40   II , a second plurality of arches  66   a   II ,  66   b   II  and a second plurality of slots  42   a   II ,  42   b   II . The first plurality of slots and the first plurality of arches are arranged along a first longitudinally-extending line  104  in  FIG. 17 . In other words the midpoints (or waists) of the first plurality of slots  40   II  and of the first plurality of arches  64   a   II ,  64   b   II  would be aligned along the first longitudinally-extending line  104 . In this particular embodiment, the slots in the first plurality of slots  40   II  remain a constant size for the entire length of the strut  40   III . The slots in the second plurality of slots  42   a   II ,  42   b   II , however, are shorter and wider in the softer section  58   II  of the strut than they are in the stiffer section  60   II  of the strut. In this embodiment, the midpoints of the second plurality of slots  42   a   II ,  42   b   II  and of the second plurality of arches  64   a   II ,  64   b   II  would be aligned along a second longitudinally-extending line (not shown in  FIG. 17 ) that would be circumferentially offset 180 degrees from the first longitudinally-extending line  104 . Since the second slots get shorter in the distal, softer potion of the strut depicted in  FIG. 17  (compare longer slots  42   b   II  to shorter slots  42   a   II  the first arches get longer in the softer, distal portion  58   II . The second arches, however, remain the same size throughout the length of the strut. Finally, as one moves distally and transitions from the stiffer portion  60   II  to the softer portion  58   II , the bridges get shorter. That is, the bridges are shorter in the softer portion of the strut. 
         [0056]    Looking next at  FIGS. 18-20 , some relatively complex strut cut patterns  74   I ,  74   II , 74   III , respectively, each for creating a strut having longitudinally-varying stiffness, are described next. Each of these cut patterns comprises twelve sections (S 1 - 512 —only labeled in  FIG. 18 ) and eight different sub-cut patterns (P 1 -P 8 —only labeled in  FIG. 18 ), but any number of sections and sub-cut pattern combinations could be used. Further, each strut pattern depicted in  FIGS. 18-20  includes a proximal pattern portion  106  (to the left of vertical line  108 ) and a distal pattern portion  110  (to the right of vertical line  108 ). The proximal pattern portion  106  is the same for each of these three strut cut patterns  74   I ,  74   II ,  74   III , and comprises six sections (namely, S 1 -S 6 ) and five sub-cut patterns (namely, P 1 -P 5 ): 
         [0057]    Section S 1  comprises sub-cut pattern P 1 ; 
         [0058]    Section S 2  comprises sub-cut pattern P 2 ; 
         [0059]    Section S 3  comprises sub-cut pattern P 3 ; 
         [0060]    Section S 4  comprises sub-cut pattern P 4 ; 
         [0061]    Section S 5  comprises sub-cut pattern P 4 ; and 
         [0062]    Section S 6  comprises sub-cut pattern P 5 . 
         [0000]    Each of the distal strut pattern portions  110  shown in  FIGS. 18-20  is different from the other two, and each again comprises six sections (namely S 7 -S 12 ), but only three cut patterns (namely, P 6 -P 8 ): 
         [0063]    Section S 7  comprises sub-cut pattern P 6 ; 
         [0064]    Section S 8  comprises sub-cut pattern P 7 ; 
         [0065]    Section S 9  comprises sub-cut pattern P 7 ; 
         [0066]    Section S 10  comprises sub-cut pattern P 7 ; 
         [0067]    Section S 11  comprises sub-cut pattern P 7 ; and 
         [0068]    Section S 12  comprises sub-cut pattern P 8 . 
         [0069]    Continuing to consider  FIGS. 18-20 , the following pairs of adjacent sections are separated by a type one expansion gap (or transition region), G 1 , or a type two expansion gap, G 2  (these gaps G 1 , G 2  are only labeled in  FIG. 18 ): 
         [0070]    Sections S 3  and S 4  are separated by expansion gap G 1 ; 
         [0071]    Sections S 4  and S 5  are separated by expansion gap G 1 ; 
         [0072]    Sections S 5  and S 6  are separated by expansion gap G 1 ; 
         [0073]    Sections S 7  and S 8  are separated by expansion gap G 2 ; 
         [0074]    Sections S 8  and S 9  are separated by expansion gap G 2 ; 
         [0075]    Sections S 9  and S 10  are separated by expansion gap G 2 ; 
         [0076]    Sections S 10  and S 11  are separated by expansion gap G 2 ; and 
         [0077]    Sections S 11  and S 12  are separated by expansion gap G 2 . 
         [0000]    As noted above and as may be clearly seen in these three figures, the G 1  expansion gap is different from the G 2  expansion gap G 2 . 
         [0078]    As already stated, section S 1 -S 6 , which together comprise the proximal strut cut pattern portion  106 , are the same in each of the cut patterns  74   I - 74   III  depicted in  FIGS. 18-20 , respectively. In particular, in the proximal strut cut pattern portion  106 , the slots straddling the longitudinal centerline  112  that bifurcates the pattern horizontally into symmetrical upper and lower portions are long and narrow in the section S 1 (see slots  114   a ), and then wider (longer midpoint width) and shorter in remaining sections S 2 -S 6  (see slots  114   b ). The slots  114   b  in section S 2 -S 6  are the same size in the depicted embodiment. 
         [0079]    On the other hand, the distal portion  110  of the cut patterns depicted in  FIGS. 18-20  is different in each figure. In  FIG. 18 , the first slots, which extend along the longitudinal centerline  112  are the same size in all of sections S 7 -S 12  (in fact, in  FIG. 18 , the first slots are the same size in all of sections S 2 -S 12 ). In contrast, in  FIGS. 19 and 20 , the first slots are not all the same size in sections S 7 -S 12 . In the  FIG. 19  cut pattern, the slots (which are part of the first plurality of slots) in section S 7  through section S 12  are longer (i.e., taller in  FIG. 19 ) than they are in sections S 2 -S 6 . Similarly, in the  FIG. 20  cut pattern, the slots (which are again part of the first plurality of slots) in section S 7  through S 12  are even longer than the corresponding slots in  FIG. 19 . Thus, a strut constructed from the strut cut pattern  74   I  depicted in  FIG. 18  would have the stiffest distal strut portion, a strut constructed from the strut cut pattern  74   III  depicted in  FIG. 20  would have the least stiff distal strut portion, and a strut constructed from the strut cut pattern  74   II  depicted in  FIG. 19  would have a stiffness somewhere between the stiffness of the other two. As should be apparent from reviewing the representative cut patterns depicted in  FIGS. 18-20 , struts created from these patterns can flex section-by-section, mitigating the tendency of the deflectable section to come out of plane during deflection. These cut patterns also result in a preferentially-planar performance. 
         [0080]      FIG. 21  is a fragmentary, isometric view of a distal deflectable section  20  of an ablation catheter, shown with portions removed or displaced to reveal various internal components. In this figure, a flexible, irrigated tip electrode  116  is shown distal of three ring electrodes  24  and a pull ring  30 . Also visible in this figure, at the proximal end of the distal deflectable section  20 , is a coupler  118  that may be used to join the distal deflectable section  20  to the proximal catheter shaft  18 . 
         [0081]      FIGS. 22 and 23  are enlarged, fragmentary isometric views of part of the distal portion of the distal deflectable section shown in  FIG. 21 . As shown on these two figures, the flexible irrigated tip electrode includes a tip irrigation tube  120  with a barb  122  on its proximal end for connection to a shaft irrigation tube (not shown). Three ring electrodes  24  are shown ‘hovering’ in approximately the correct longitudinal position. A respective pull ring  30  is visible in each of these two figures. Also highly visible in each of these two figures are the alignment tabs  56  riding in corresponding tab slots  124  in the pull ring to ensure that the pull wires  32 ,  34  and the pull wire management channels  52 ,  54  are properly aligned with the cut pattern in the strut. 
         [0082]    Referring next to  FIGS. 24-27 , the coupler  118  that is also depicted in  FIG. 21  will be described.  FIGS. 24 and 25  are fragmentary, isometric views of the proximal end of the distal deflectable section depicted in  FIG. 21 . In each of these two figures, it is possible to see a coupler  118  extending from the proximal end of the distal deflectable section. The distal end of the coupler (not shown in  FIGS. 24 and 25 ) would ride adjacent to or against the proximal end of the strut comprising part of the strut assembly. As clearly shown in these figures, the alignment tabs  56  extending proximally from the proximal end of the strut ride in tab slots  126  formed in a tab alignment ring  128  comprising part of the coupler  118 . These tab slots and the tab alignment ring may be clearly seen in  FIG. 26  as well. In  FIGS. 24 and 25 , the pull wires  32 ,  34  are shown schematically entering the pull wire channels  130 ,  132  comprising part of the shaft coupler  118 . These pull wires would be connected on their distal ends to, for example, the pull ring  30 , and would be connected on their proximal ends to an actuator. The pull wire channels  130 ,  132  would align with the similar pull wire channels  52 ,  54  comprising part of the insert component  48  that is part of the strut assembly  46 . Also clearly visible in  FIGS. 24-27  is a barbed section  134  (labeled in  FIG. 27 ) of the coupler  118 . This barbed section comprises a plurality of slopped annular sections  136  and flat annular sections  138 . The barbed section  134  would be inserted into the distal end of the proximal catheter shaft  18  and then would be connected by adhesive or sonic welding or some other means to the proximal catheter shaft. The pull wire channels  130 ,  132  are offset 90 degrees from the tab slots  126 . The end of the coupler  118  opposite the barbed section  134  comprises a smooth section  140 . This smooth section  140  would ride in, and be attached to, the proximal end of the distal deflectable section  20 . 
         [0083]      FIG. 28  schematically shows a distal deflectable section  20 .  FIG. 29  schematically depicts the distal deflectable section of  FIG. 28  with a severe kink  142  formed in it.  FIG. 30  shows that, after the kink has been removed, the distal deflectable section recovers from even such a severe kink when the strut assembly described herein is in place. 
         [0084]    The strut described above, whether constructed from a laser cut Nitinol tube or some other material, can be configured to give control over the deflection characteristics of a catheter, especially asymmetric deflection, while maintaining the orientation of internal components. The design of the cut pattern can be altered to create various asymmetric curve shapes, planar behavior, desired curve sizes, and desired catheter shaft stiffness. 
         [0085]    One of the benefits of this curve strut is that it makes manufacturing of, for example, the distal deflectable section of a catheter easy and repeatable. Current manufacturing practices may introduce potentially undesirable variability in outgoing assemblies due to the difficult and labor-intensive process required to produce a given deflection behavior. The strut describe about is designed to have an inherent deflection behavior that is easy to assemble and lacks the variation in other assembly methods. The strut helps the catheter take that shape in each deflection. This takes much of the variability out of creating a distal deflectable section by creating a structure with which to create the deflection behavior. Additionally, this component provides excellent durability in the body due to the fact that it does not degrade under in vivo conditions and the super elastic nature of the Nitinol provides excellent return to straight ability in a catheter application. 
         [0086]    Embodiments are described herein of various apparatuses, systems, and/or methods. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of all embodiments. 
         [0087]    Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment,” or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment(s) is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment,” or the like, in places throughout the specification, are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional. 
         [0088]    It will be appreciated that the terms “proximal” and “distal” may be used throughout the specification with reference to a clinician manipulating one end of an instrument used to treat a patient. The term “proximal” refers to the portion of the instrument closest to the clinician and the term “distal” refers to the portion located furthest from the clinician. It will be further appreciated that for conciseness and clarity, spatial or directional terms such as “vertical,” “horizontal,” “up,” “down,” “clockwise,” and “counterclockwise” may be used herein with respect to the illustrated embodiments. However, medical instruments may be used in many orientations and positions, and these terms are not intended to be limiting and absolute. 
         [0089]    Joinder references (e.g., affixed, attached, coupled, connected, and the like) are to be construed broadly and may 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. As used herein, joinder references may also include two components that are molded as a single or unitary piece. Changes in detail or structure may be made without departing from the spirit of the disclosure as defined in the appended claims.