DISPOSABLE CONTROL MECHANISM FOR DIRECTED CATHETERField of the Invention The invention relates to the field of steerable catheters and more particularly to a slidable control mechanism for use with a steerable catheter to minimize the fatigue of control change. BACKGROUND OF THE INVENTION Modern surgical procedures often require localized diagnoses or treatments applied to relatively inaccessible interior body areas. In the past, such procedures usually involved invasive surgery, allowing the physician to visually identify or treat the area of interest having access through a relatively large opening or an incision made in the body. Unfortunately, invasive surgical methods often include undesirable side effects of tissue trauma associated with the procedure. Frequently, the effects of trauma prolong the healing and rehabilitation period for the patient. For minimizing the trauma often associated with invasive surgery, those skilled in the art have developed relatively small catheters to be inserted into the vasculature of the body. Normally, the catheter has access to the body through a small vasculature in a predictable manner, the catheter must be precisely controllable in its position, as examples, the ablation electrodes or imaging probes next to the specific tissues of interest . To allow manipulation of the catheter inside the body, the sliding control wire mechanisms are used to selectively "steer" the distal tip of the catheter while the operator inserts the device into the body. Such mechanisms usually include a pair of control cables that expand the length of the catheter shaft or body. The control wires have respective distal ends anchored to specific locations at the distal tip of the catheter body corresponding to the predetermined deflection movement. The proximal ends of the wires are mounted to a sliding mechanism that responds to the operator in order to place the wires in tension, pulling the end of the catheter for deflection in a first direction, while simultaneously compressing, or flexing the other wire. An example of such a catheter configuration incorporating said control mechanism can be found in the U.S. Patent. No. 5,383,852, assigned to the assignee of the present invention. While such devices generally provide a relatively high degree of deflection direction for the catheter tip, over a relatively short period, the repetitive tension and flexing of the control wires often cause premature fatigue of the control cable. As a result, the operable life time of the device can be substantially shortened.
To address the problem of cable fatigue in a steerable medical device, one proposal (Takahashi USP 4,294,233) describes directing the distal tip of an endoscope by independently manipulating two traction wires by changing an operating quadrant arrow. Means are provided for adjusting the looseness or the flexed portion of the non-tense wire. The disclosed means includes a large slot portion within a release adjustment member to define an escape area for the undirected cable. While the design may be satisfactory for its intended applications in the area of rotary control mechanisms, it does not address the problem of looseness adjustment for slidable control mechanisms. Many operators prefer linearly displaceable slide control mechanisms in particular applications. In addition, the Takahashi design provides only a passive device to minimize compression on an unselected cable. Therefore, those skilled in the art have recognized the need for a slidable control mechanism for manipulating the distal end of a steerable catheter. Additionally, there is a need for a slidable control mechanism to help actively prevent compression on any steering cable. The control mechanisms of the present invention meet these needs.
COMPENDIUM OF THE INVENTION The control mechanism of the present invention extends the operable life of the control wires used to direct the distal tip of a steerable catheter. Life is prolonged by reducing the fatigue of the control wire that results from the compression or bending of the wires during the operation. A further advantage of the present invention involves the active assistance provided by an adjustment mechanism to maintain a slight tension on an unselected wire to ensure an anti-looseness effect. To perform the advantages described above, the control mechanisms of the present invention manipulate a pair of control wires having distal portions anchored to the distal end of a steerable catheter. The control wires extend longitudinally through the catheter and include proximal ends. The control mechanism includes a sliding mechanism coupled to the proximal ends of the control wires and can be moved along a linear path to place a selected one of the wires in tension without placing the other wires in compression. Other aspects and advantages of the present invention will become apparent from the following detailed description when read together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of a steerable catheter that implements a rotary control mechanism according to an embodiment of the present invention; FIGURE 2 is, is a partial cross-sectional view along line 2-2 of Figure 1; FIGURE 3 is a diagrammatic illustration of the control mechanism in a neutral position; FIGURES 4-5 are diagrammatic illustrations showing the activation of the sliding of the control mechanism; and FIGURES 6-8 are diagrammatic illustrations showing the distal flexing movement of the distal end of the catheter corresponding to the actuation of the control mechanism shown in Figures 3-5. DETAILED DESCRIPTION OF THE INVENTION Steerable catheters provide physicians or operators an indispensable tool to conveniently access the interior of the human body without the level of trauma commonly associated with more invasive surgical techniques. As shown for example in Figure 1, a steerable catheter according to an embodiment of the present invention, and generally designated 12, includes a hollow handle 14. The inside of the handle defines a compartment 15 (Figure 2) for housing a control mechanism according to the present invention, generally designated 30. A longitudinal groove 17 formed along the side of the handle defines a linear path for the sliding movement of the control mechanism. Referring now to Figure 1, a narrow flexible arrow 16 projects longitudinally from one end of the handle for intravascular insertion. The arrow is usually formed of a polyurethane material of predetermined stiffness and includes one or more longitudinal extension lumens (not shown) to operate two or more steerable or control wires 18 and 20 (Figures 3-5) through the same In order to precisely address the distal end of the catheter 16 during intravascular insertion, the control wires 18 and 20 run longitudinally through the lumen of the catheter shaft and are mounted respectively to the specific distal points within the shaft. The connection points correspond to the predetermined directional deflections of the arrow in response to the tension forces placed on a selected wire. The steering wires may comprise stainless steel cables having tensile strength of approximately 6.9 kg. Referring now to Figures 2 and 3, the control mechanism of the present invention incorporates a slidable mechanism 32 engaged in the proximal ends of the control wires 18 and 20 and moving along a linear path to place one selected from said wires in tension without placing the other wires in compression.
The slide mechanism 32 includes a rectangular-shaped slide control member 34 formed with a pair of spaced longitudinal passages 36 and 38 arranged in parallel relation. The recessed cavities 40 and 42 are formed at opposite ends offset from the passages to define respective shoulders 44 and 46. A pair of support bolts 48 and 50 are longitudinally aligned and spaced apart (Figure 2) and project laterally from the side of the element and are complementarily formed to slidably engage the groove in the handle 17. A digital control 52 is mounted to the bolts for preventing the element from uncoupling from the slot and responding to manually applied forces to drive the control mechanism linearly along the path of the slot. Referring now to Figure 3, an adjustment device 60 is coupled to the slide mechanism via the control wires 18 and 20 to selectively secure the proximal ends of control wires. The adjustment device comprises a rotating pulley 62 for redirecting the force applied by the sliding element 34 to the control wire 20 and a pair of bypass elements 68 and 70, the pulley includes a peripheral groove (not shown) and is it is rotatably mounted on a shaft 66 mounted on the back inside the handle compartment 16. The shaft is positioned at the rear of the slot 17 and is oriented in such a way that the pulley forms a pulley plane parallel to the path of the pulley. the control wires 18 and 20.
The driving elements 68 and 70 include respective arrows, or hypo-pipes 72 and 74 slidably mounted within the passages 36 and 38. The pipes 72 and 74 include respective larger diameter diameter retainers 76 and 78 at the proximal ends of the ports. pipelines. The pipes are attached to the proximal ends of the respective control wires 18 and 20 through a stamping operation carried out during the assembly of the control mechanism. Referring further to Figure 3, a particularly advantageous aspect of the present invention involves an active anti-loosening function. To accomplish this capability, the driving elements 68 and 70 include respective coil springs 80 and 82 slidably disposed externally of the respective hypo-pipes 72 and 74. The springs are nested in the recessed cavities 40 and 42 formed in passages 36 and 38. When installed, the springs were formed in compression between the shoulders 44 and 56 and the arrow seals 76 and 78. The elasticity constants of the springs 44 springs are of a level capable of extending a slight tension on the wires to adjust any looseness, but below a level in order to cause some deflection of the catheter shaft. The assembly of the control mechanism 30 comprises direct techniques well known to those skilled in the art. In general, with the respective control wires 18 and 20 already anchored to the distal end of the catheter shaft 16, the proximal ends of the proximal wires are measured and cut to different lengths to accommodate the pulley 62. Consequently, the wire 20 is guided around the groove of the pulley and through the lower passage 38 formed in the slidable member 34. The end of the wire is stamped on the arrow of the hypo-pipe 74 with the coil spring 82 already disposed along the same. The wire 18 then engages the slide member by leading it through the upper passage 36 and stamping the other hypo-pipe arrow 72. Following the initial assembly of the control mechanism for the control wires 18 and 20, calibration must be performed of the mechanism with respect to the desired directional deflections. Calibration methods are well known in the art, but generally involve fixing the rail in a neutral positionabout halfway along the groove of the handle 17 and fixing the control wires to a slightly predetermined tension with the arrow in a substantially straight configuration, as illustrated in Figure 6. The adjustment devices (not shown) ) provide correctable tension on the wires 18 and 20 to maintain a constant and relatively equivalent tension on each of the wires to define the neutral position. Once the neutral position has been established, as shown in Figures 2 and 6, the mechanism moves linearly to each of the extreme positions, as shown in Figures 4-5 and 7-8, with slight adjustments made as necessary to effect appropriate deflections. During operation, the catheter assembly 12 will normally be initially fixed to the relaxed or calibrated neutral configuration, as shown in Figures 3 and 6. Visual confirmation of the neutral state can be made by simply referring to the position of the digital control 52 , normally positioned in half along the slot 17. The catheter can then be directed into a relatively small incision formed in the vasculature to access the desired areas of interest. Once inserted into the body, manipulation of the distal tip of the catheter can be accomplished by sliding the digital control forward or backward corresponding to the desired direction of deflection. Referring now to Figure 4, it is applied to the initial backward force applied to the digital control 52 linearly displaces the sliding member 34 to engage back the upper hypo-tubing retainer 76. The continuous backward movement of the sliding member causes The hypo-tubing pulls the wire along the same direction, placing a tension force on the wire and resulting in a directional deflection of the catheter shaft, as shown in Figures 4 and 7. A particularly advantageous aspect of the present invention is shown in Figures 4 and 5. With particular emphasis directed to Figure 4. the proximal movement of the sliding member 34 is not prevented by the lower hypo-tubing 74 because the associated retainer 78 is placed in the distal end. In response to the sliding movement of the element 34 along the lower tube, the compressed coil spring 82 nested within the lower passageway 42 expands as the distance between the shoulder 46 and the stop 78 increases. The overall effect of the spring maintains a positive voltage level on the wire 20, preventing it from bending or compressing at the same time as the other wire 18 deflects the catheter. Because the bending of the wire 20 is prevented, eliminating a common cause of premature fatigue of the control wire, the operational utility of the control wires will be substantially prolonged. The sliding movement of the digital control of the distal direction again compresses the lower spring 82 in the cavity 42. Because the elasticity constant of the spring is lower than that required to exert a deflection on the catheter shaft, the position of the Hypo-pipe 74 remains relatively unchanged. Simultaneously the deflected catheter shaft 16 (of the proximal drive of the digital control) exerts an opposite directed tension force on the upper wire 18 sufficient to keep the upper spring 80 nested in the upper passage cavity 40 until a position is reached. neutral The continuous distal drive of the digital element 52 then directs the sliding member 34 distally to engage copying the lower hypo-tubing retainer 78 and placing the wire 20 at sufficient tension to deflect the tip of the catheter. Figures 5 and 8 illustrate this action, with anti-loosening results of the upper drive element 68 similar to that discussed above for the drive element 70. While the control mechanism of the present invention has been described as the only handling device for the arrow catheter, it will be understood that one or more additional control mechanism can be implemented to complete the invention. For example, the capabilities of the present invention can be supplemented by a rotary control mechanism 80 (Figure 1) disposed close to the digital control 52 to effect a steerable control on the additional control wires driven through the arrow and anchored to the end. distal of the arrow. A suitable rotary control mechanism is described in co-pending applicant application S / N 08 / 818,353. assigned to the assignee of the present invention and incorporated herein by reference. Those skilled in the art will appreciate that many benefits and advantages are given by the control mechanism of the present invention. The capacity of the sliding mechanism has significant importance by placing a selected wire in tension to deflect the arrow of the catheter, without placing the other wire in compression. This extends the operational utility of the control wires by minimizing control wire fatigue due to repetitive flexing of the wires when they are loosened or compressed.
In addition, the implementation of an adjustment device to actively maintain a predetermined tension on each of the wires at all times further increases the anti-loosening capability of the sliding mechanism. While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes can be made in form and detail thereon without departing from the spirit and scope of the invention. .