Abstract:
A steerable elongated medical device adapted to be advanced through a tortuous pathway to a desired location in a body includes an outer tube extending between an outer tube proximal segment and an outer tube distal segment, having an outer tube wall forming an outer tube lumen and an elongated outer tube slot through the outer tube wall to the outer tube lumen. The elongated outer tube slot has a first portion and a second portion and is formed between an outer tube slot proximal end and an outer tube slot distal end and extending axially along the outer tube distal segment through an outer tube slot length to define a cutaway portion of the outer tube. A reinforcing sleeve is positioned within the outer tube lumen and extends between a reinforcing sleeve proximal end and a reinforcing sleeve distal end, and the reinforcing sleeve forms a reinforcing sleeve slot portion aligned with and extending along the first portion of the outer tube slot and includes a reinforcing sleeve overlap portion extending over the second portion of the outer tube slot.

Description:
FIELD OF THE INVENTION 
     The present invention pertains to the permanent or temporary implantation of elongated medical instruments in the body or used to access a site in the body to facilitate introduction of a further medical device, and particularly to elongated steerable medical devices, such as a steerable stylets, for steering the distal end and imparting curves in distal segments of such medical instruments to facilitate implantation. 
     BACKGROUND OF THE INVENTION 
     A wide variety of elongated medical instruments are currently available that are adapted to be permanently or temporarily implanted in the mammalian body, usually the body of a human patient, or used to access a site in the body to facilitate introduction of a further implantable medical device or delivery of a therapeutic or diagnostic agent. Such elongated medical instruments have an instrument body extending between instrument body proximal and distal ends, and a distal segment of the instrument body is advanced to a remote site in the body. 
     In many cases, the introduction of such elongated medical instruments to a remote site in the body is effected through a skin incision accessing an incision into a blood vessel, whereby the instrument body is advanced through a pathway until the distal segment or the instrument body distal end are located at the remote site. Such advancement is often through a tortuous pathway having twists and turns requiring the capability to impart a curve or deflect the instrument body distal end to facilitate advancement. Therefore, the introduction of such elongated medical instruments through vascular pathways or other tortuous pathways in the body is facilitated by a wide variety of techniques and mechanisms that have been developed to impart curves in the distal segment of the instrument body or to deflect or steer the instrument body distal end. 
     Currently, endocardial cardiac pacing leads used in association with a pacemaker implantable pulse generator (IPG) and/or cardioversion/defibrillation leads used in association with implantable cardioverter/defibrillator (ICD) IPGs are introduced into a vein either via a cut down or percutaneous sheath introduction. Such cardiac leads are advanced under fluoroscopy into either the right atrium, right ventricle (or both in the case of a dual chamber pacemaker or ICD implantation) or into a cardiac vessel, e.g., the coronary sinus and great vein. Generally speaking, it is highly desirable that such cardiac leads be so flexible through their length that they are capable of flexing with the movement of the heart and other muscular movement so as to void the fracture of the lead body due to its cumulative stressing. Such cardiac lead bodies are generally too limp to be advanced axially on their own through the vascular pathway to the desired site in a heart chamber or vessel. 
     It has been commonplace for many years to employ thin wire, stiffening stylets extended down a lumen of the lead body to stiffen the entire assembly so that it can be pushed axially through the venous pathway. Then, the distal pace/sense electrodes or cardioversion/defibrillation electrodes (herein “cardiac electrodes”) must be fixed at the preferred site in the heart chamber or vessel to operate most efficaciously and to prevent dislodgement. The introduction and fixation of these cardiac leads is the most time consuming and difficult aspect of the implantation. 
     At the outset, a straight or slightly curved stiffening stylet wire is first extended into the lead body lumen within the cardiac lead in order to give the cardiac lead sufficient column strength and rigidity to be pushed through the tributary veins and typically into the subclavian vein. The stylet wire may be left straight or provided with a certain degree of curvature to facilitate the introduction through these veins and through the initial curvatures thereof. Thereafter, and from time to time, as the physician directs the distal tip of the cardiac lead in a tortuous path leading to the right heart through the superior vena cava (SVC), it may be necessary to withdraw the stylet and either substitute a new stylet wire or impart a different curvature to the distal portion of the stylet wire, reinsert the stylet wire, and advance the distal portion of the lead a bit further until another obstacle to advancement is encountered. 
     When the distal cardiac electrodes are to be placed in the right ventricle, the physician manually fashions a curve at the tip of another stylet wire that is inserted into the lead body lumen to advance the assembly through the tricuspid valve into the right ventricle. Most physicians continue advancing the lead with the curved tip stylet in place into the pulmonary artery outflow track to confirm right ventricle access and to rule out the possibility of entrance into the coronary sinus or coronary vein, which can mimic the appearance of a right ventricle placement under fluoroscopy. The conventional practice requires the physician to then remove the curved stylet and partially re-advance the original or another straight stylet into the lead body lumen, once the physician has confirmed that the lead is in fact in the pulmonary outflow track. The cardiac lead is then carefully pulled back under direct fluoroscopic observation until the lead body distal segment drops from the proximal portion of the pulmonary artery to the floor of the right ventricle. The physician then advances the stylet to its fully advanced position within the lead body lumen and advances the lead distal end into the right ventricular apex. Passive or active fixation mechanisms at the lead body distal end then effect fixation with the trabeculae or the myocardium to acutely maintain the cardiac electrode electrode(s) at the operative site. 
     In the case of atrial lead placement, the lead body distal end is typically lodged or affixed in the right atrial appendage which results in the lead body extending into the right atrium via the SVC and then bent through about a 180° or greater bend. Over the years, many atrial cardiac lead designs and atrial cardiac lead introduction tools and techniques have been proposed or clinically used to both achieve this orientation and to fix the cardiac lead body distal end within the atrial appendage and avoid dislodgement. Initially, such atrial cardiac leads were formed with a permanent “J”-shaped bend to facilitate both the positioning and the retention of the atrial electrode in the patient&#39;s atrial appendage as taught, for example, in U.S. Pat. No. 4,136,703. Insertion of these “J”-shaped leads is greatly facilitated through the use of a straight solid inner stylet which, in this case, straightens the bend normally fixed within the distal end of the lead itself to the extent that the stylet is advanced into or retracted from the lead body lumen. Such J-shaped atrial leads have largely been abandoned in favor of reduced diameter lead bodies that cannot accommodate shape-forming structures and the use of the straightening stylet as described above. Today, the small diameter cardiac lead body is normally straight, and the lead body distal end is typically aimed into the atrial appendage employing multiple insertions of relatively straight and curved stylets. The electrode bearing lead body distal end is fixed in the atrial appendage by means of an active fixation screw or passive fixation tines. However, dislodgements can occur before the fixation is effected when a stylet is withdrawn proximally as the stylet may bind against the lead body lumen in the region of the bend. 
     Similar techniques and multiple stylets are avoided to advance a cardiac lead distal segment into the coronary sinus and great vein. 
     Thus, there are multiple exchanges of straight stylet wires and curved stylet wires which have been bent according to the physician&#39;s choice in a typical cardiac lead implantation in the right atrium and ventricle. Stylets are typically formed of solid wire, typically about 0.014-0.018 inches in diameter. During handing, such stylets can easily become bent or kinked, and thereafter cause great difficulty when an attempt is made to reinsert them through the narrow inner diameter of the lead body lumen, which may only be 0.019 inch in the case of a stylet of 0.018 inch diameter, thereby providing no more than 0.0005 inch clearance around the circumference. The continual withdrawal and reintroduction of stylets is time consuming and offers the potential of damaging the lead in the process. 
     Moreover, it is undesirable to contaminate the lead body lumen with blood during this process because drying blood can form a strong adhesive bond between the stylet and the lumen wall, making stylet removal impossible and rendering the lead unusable. Because the surgeon is working through an open wound, even the most fastidious surgeon will have blood on his gloves that can be transferred to the stylet. The blood congeals, and because of the small clearance, even a few drops of blood are sufficient to causing jamming of the stylet inside the lead body lumen. When the stylet jams in the lead body lumen, kinking of the stylet within the lead can occur, which kinks, in turn, will create new jams or problems with the insertion and retraction of the stylet from the lead body lumen. In some cases, the jamming is so severe that the cardiac lead must be removed from the heart for fear of insulation puncture, discarded, and a new lead implanted, thereby at least doubling the lead cost used in the procedure as well as operative time. The overall result of such difficulties is that operative time is greatly increased, which results in increased time delay, associated cost, and prolonged X-ray exposure to the patient under continuous fluoroscopy as well as prolonged scattered X-ray exposure to the operating room staff due to procedural time delays. These problems with the use of multiple stiffening stylets have been recognized in the art and many proposals have therefore been advanced to reduce the number of stylets and the consequent number of times that stylet removal and re-insertion are needed. 
     In addition, the complexity of cardiac leads, the number of cardiac leads implanted in a common path, and the advancement of coronary sinus leads deep in a coronary vein have led to efforts to at least not increase and optimally to decrease the overall diameter of the cardiac lead body without sacrificing reliability and usability. More recently, it has been proposed to diminish the lead body by eliminating the lumen for receiving the stiffening stylet and by reducing the gauge and coil diameter of the coiled wire conductor or replacing it with highly conductive stranded filament wires or cables. In bipolar or multi-polar leads, each such cable extends through a separate lumen of the lead body to maintain electrical isolation. 
     Over the last 30 years, it has become possible to reduce endocardial lead body diameters from 10 to 12 French (3.3 to 4.0 mm) down to 2 French (0.66 mm) presently through a variety of improvements in conductor and insulator materials and manufacturing techniques. The lead bodies of such small diameter, 2 French, endocardial leads must possess little if any column strength that could cause the lead distal end fixation mechanism and electrode to perforate through the myocardium during implantation and if the lead body were to become axially force-loaded during chronic implantation. As a result, the small diameter lead bodies lack “pushability”, that is the ability to advance the lead distal end axially when the lead proximal end is pushed axially, particularly when the lead body extends through the tortuous transvenous pathway. 
     Commonly assigned U.S. Pat. Nos. 6,280,433 and 6,379,346 disclose steerable catheters that are employed to access a blood vessel through a percutaneous incision and to be advanced to a site within the vascular system or a heart chamber so that such a small diameter cardiac lead can be implanted through a delivery lumen of the catheter. A bilumen catheter body is disclosed that includes a relatively large diameter delivery lumen and a smaller diameter stylet lumen that is blocked at its distal end. The deflection mechanism in this case includes a stiffening stylet that can be selectively introduced into and removed from the stylet lumen from a proximal hub or handle. The stiffening stylet is advanced distally until the stylet distal end abuts the closed stylet lumen distal end to stiffen the catheter body to aid its introduction and advancement. The stylet distal end can be shaped when outside the stylet lumen opening to impart a curve to the catheter body when inserted into the lumen to assist in steering the catheter body distal end through the pathway. The stylet lumen is preferably lined with a wire coil sheath, and the handle and delivery lumen are preferably slittable by a slitting tool to aid in removing the introducer catheter from an electrical medical lead introduced through the delivery lumen. The delivery lumen exit port and the closed end of the stylet lumen are both located at the bitumen catheter body distal end. 
     A variety of deflectable or steerable stylets have been proposed and in some cases clinically introduced to aid in direct implantation of a cardiac lead having a lead lumen or to aid in the deflection and steering of a bilumen guide catheter. One approach has been to employ deflectable stylets wherein the stylet distal segment can be deflected or curved while within the lead body lumen from the proximal end thereof. Two-piece stylets that include a straight, tubular outer member and a curved inner member received within the outer member lumen enabling relative movement of the inner and outer members are disclosed in U.S. Pat. Nos. 4,136,703, 4,381,013 and 5,728,148. The outer tubular member of the &#39;013 patent enables the transmission of torque applied by the implanting physician at the proximal end to be transmitted to a fixation helix located at the lead body distal end lead to screwed the helix into endocardial tissue. Alternatively, two-piece stylets comprising a curved outer member and a relatively straight inner member are also known to the art, as disclosed in U.S. Pat. Nos. 4,676,249 and 5,040,543. In such composite stylets, the relative position of the inner member with respect to the outer member determines the degree to which the curved member (inner or outer) is allowed to display its preset curvature. 
     A common approach to providing controllable deflection of the distal end segments of catheters, guidewires, and stylets employs a generally straight outer sheath or tube and a pull or push or push-pull wire extending through a lumen of the outer sheath to an attachment point at the sheath distal end. The wire is pushed or pulled on at its proximal end typically through a handle that is permanently or removably attached to the catheter or guidewire proximal end. The proximal retraction or distal advancement of the pull or push wire, respectively, causes at least a distal segment of the outer sheath to bend or deflect. Examples of such deflection mechanisms in catheters can be found in U.S. Pat. Nos. 4,815,478, 4,898,577, 4,940,062, 5,545,200 and 6,251,092. U.S. Pat. Nos. 4,815,478 and 4,940,062 disclose the use of push-pull wires extending through guidewire lumens for deflecting a guidewire distal end by manipulating a handle at the guidewire proximal end. 
     Deflectable stylets intended to be inserted into cardiac lead body lumens employing this type of deflection mechanism are disclosed in U.S. Pat. Nos. 5,170,787, 5,327,906, 5,439,006, 5,662,119, 6,027,462, 6,059,739, and 6,146,338. Such deflectable stylets include an elongated stylet body or tube extending from a stylet body proximal end to a stylet body distal end, a handle coupled to the stylet body proximal end, and a traction wire or pull wire extending through a stylet lumen of the stylet body of tube from the handle to the stylet body distal end. Many of these patents disclose steerable stylet handles at the stylet body proximal end that are manipulated by one hand operation to induce a bend in a distal segment of the stylet body. 
     Several embodiments of deflectable stylets are disclosed in the &#39;119 patent that employ an elongated metal tube having a stylet tube lumen through which a traction or pull wire extends to a distal wire end. In each case, a distal portion of the pull wire is exposed along a like distal portion of the metal tube in such a way that traction applied to the pull wire proximal end causes the distal portion of the tube to bow or bend. The exposure of the distal portion of the pull wire extending alongside the metal tube is created in several ways. 
     In one embodiment depicted in  FIGS. 1 and 2  (FIGS. 12 and 13 of the &#39;119 patent), an elongated cutaway portion  11 ′ of the tube wall  15 ′ of tube  10 ′ is formed extending between cuts  18 ′ and  20 ′ proximal to tube distal end  22 ′. The cutaway portion  11 ′ extends about half way through the tube wall  15 ′ exposing a distal portion of the pull wire  12 ′ extending proximally and distally through the tube lumen  13 ′. The pull wire  12 ′ terminates in ball-shaped distal end element  23  having a diameter greater than the inside diameter of the tube lumen  13 ′ that bears against the tube distal end  22 ′ when pulled proximally. 
     In another embodiment depicted in  FIG. 3  ( FIG. 8  of the &#39;119 patent), one side of the tube wall  15  is indented against the other side of the tube wall  15  between two openings  18  and  20  proximal to the tube distal end  22  to form a bendable indented portion  11  of the tube  10 . The pull wire  12  is threaded out of the tube lumen  13  through the proximal opening  18  and back into the tube lumen  13  through the distal opening  20 , whereby a distal portion of the pull wire  12  is exposed extending alongside the indented portion of the tube wall  15 . The distal end of the pull wire  12  is crimped to the tube distal end  22  in this case. 
     The tube  10  is preferably formed of stainless steel hypodermic needle tubing having an outside diameter in the range of 0.012 to 0.016 inches. Pull wire  12  is preferably formed of high tensile strength stainless steel wire having a diameter in the range of 0.005 to 0.007 inches. The distance between the proximal openings  18 ,  18 ′ and the distal openings  20 ,  20 ′ is stated to be between 2 to 4 inches. 
     In a variation of these embodiments, a tubular retainer formed of a thin tube of polyimide, stainless steel or Nitinol is fitted over the tube  10  to extend across the indented portion  11  and the cutaway portion  11 ′ to restrict the outward movement of the pull wire  12  when it is tensioned, which could exert excessive friction against the coiled conductors defining the cardiac lead lumen that the tube  10  is inserted into. 
     In use, the tube  10  is normally relatively straight when the pull wire  12  is relaxed. A curve or bend is effected in the distal portion of the tube  10  at the indented portion  11  or the cutaway portion  11 ′ when the pull wire  12  is pulled proximally. The induced curve or bend stresses the tube wall  15  along the indented portion  11  and the cutaway portion  11 ′. It is stated in the &#39;119 patent that prototypes of the cutaway tube embodiment of  FIGS. 1 and 2  were found in testing to be inferior to the indented tube embodiment of  FIG. 3  in resistance to kinking, and that the indented embodiment of  FIG. 3  was easier to manufacture than the cutaway embodiment of  FIGS. 1 and 2 . 
     However, It can be difficult to indent thin wall stainless steel or shape memory alloy tubes to achieve the uniform indentation depicted in the &#39;119 patent. It can also be difficult to precisely form uniform diameter proximal and distal holes as depicted in the &#39;119 patent. Poor torque transmission and uneven bending characteristics can result particularly at the proximal end of the indented portion  11  that is weakened both by indentation and formation of the hole through the tube wall. 
     Thus, despite these improvements, there is still a perceived need for steerable stylet having a small diameter stylet body that is simple and inexpensive to manufacture, resists kinking, and that can be manipulated to control the deflection of and impart a wide degree of dynamic curvature in a distal segment of the stylet body. 
     SUMMARY OF THE INVENTION 
     The invention is therefore directed to improvements in a steerable elongated medical devices, adapted to be advanced through a tortuous pathway to a desired location and having a small diameter body that is simple and inexpensive to manufacture, resists kinking, and that can be manipulated easily to control the deflection of and impart a wide degree of dynamic curvature in a distal segment of the device. 
     In accordance with the present invention, a steerable elongated medical device adapted to be advanced through a tortuous pathway to a desired location in a body includes an outer tube extending between an outer tube proximal segment and an outer tube distal segment, having an outer tube wall forming an outer tube lumen and an elongated outer tube slot through the outer tube wall to the outer tube lumen. The elongated outer tube slot has a first portion and a second portion and is formed between an outer tube slot proximal end and an outer tube slot distal end and extending axially along the outer tube distal segment through an outer tube slot length to define a cutaway portion of the outer tube. A reinforcing sleeve is positioned within the outer tube lumen and extends between a reinforcing sleeve proximal end and a reinforcing sleeve distal end, and the reinforcing sleeve forms a reinforcing sleeve slot portion aligned with and extending along the first portion of the outer tube slot and includes a reinforcing sleeve overlap portion extending over the second portion of the outer tube slot. 
     According to an embodiment of the present invention, a steerable elongated medical device adapted to be advanced through a tortuous pathway to a desired location in a body includes an outer tube extending between an outer tube proximal segment and an outer tube distal segment, and having an outer tube wall forming an outer tube lumen and an elongated outer tube slot through the outer tube wall to the outer tube lumen. The elongated outer tube slot has a first portion and a second portion and is formed between an outer tube slot proximal end and an outer tube slot distal end and extends axially along the outer tube distal segment through an outer tube slot length to define a cutaway portion of the outer tube. A reinforcing sleeve is positioned within the outer tube lumen and extends between a reinforcing sleeve proximal end and a reinforcing sleeve distal end. The reinforcing sleeve forms a reinforcing sleeve slot portion aligned with and extending along the first portion of the outer tube slot and includes a reinforcing sleeve overlap portion extending over the second portion of the outer tube slot. A handle is coupled to the outer tube proximal end, and a pull wire is positioned within the outer tube lumen and extends between a pull wire proximal end coupled to the handle and a pull wire distal end coupled to the device along the outer tube distal end. The pull wire extends through the reinforcing sleeve lumen and the outer tube lumen, and the pull wire proximal end is adapted to be manipulated to separate the pull wire proximal end from the outer tube proximal end to induce a bend in the cutaway portion. The outer tube proximal segment is formed of a first material having a first flexibility and the outer tube distal segment is formed of a second material having a second flexibility different from the first flexibility 
     In a preferred embodiment, the reinforcement sleeve has a reinforcement sleeve length that exceeds the length of the outer tube slot and is fitted into the outer tube lumen so that a reinforcement sleeve proximal segment extends proximally from the outer tube slot and a reinforcement sleeve distal segment extends distally from the outer tube slot. In a further feature of this embodiment, the reinforcement sleeve proximal segment is adhered to the outer tube lumen wall. In a still further feature of this embodiment, an elongated reinforcement sleeve intermediate segment extends the length of the outer tube slot. In yet another feature of this embodiment, at least a portion of the reinforcement sleeve intermediate segment is cut away to form an elongated reinforcement sleeve slot, and the outer tube slot and the reinforcement sleeve slot are aligned. 
     Preferably, a polymeric sleeve is fitted over the outer tube to extend over the aligned outer tube slot and reinforcement sleeve slot to retain the pull wire when the pull wire is retracted to form a bend in the nested outer tube and reinforcement sleeve walls. 
     Optionally, the pull wire can be formed having a taper along its length whereby the pull wire diameter extending through the aligned outer tube slot and reinforcement sleeve slot is less than the pull wire diameter proximal to the aligned outer tube slot and reinforcement sleeve slot. 
     Advantageously, the inclusion of the reinforcement sleeve resists the buckling encountered in testing the prior art steerable stylet design illustrated in  FIGS. 1 and 2 . Moreover, fabrication is simplified compared with the fabrication of prior art steerable medical devices. 
     The above-described steerable medical devices of the present invention advantageously facilitate the direct implantation of elongated cardiac leads having stylet lumens or the introduction and steering of guide catheters to a site of implantation of such cardiac leads or other medical devices or therapeutic or diagnostic substances. The features of the present invention can advantageously be incorporated into steerable stylets that impart or enhance torqueability and impart steerability to guide catheter distal ends. 
     This summary of the invention has been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other advantages and features of the present invention will be more readily understood from the following detailed description of the preferred embodiments thereof, when considered in conjunction with the drawings, in which like reference numerals indicate identical structures throughout the several views, and wherein: 
         FIG. 1  is a simplified top view of a distal segment of a stylet body formed having a cutaway tube wall portion in accordance with the prior art; 
         FIG. 2  is a simplified side view of the distal segment of a stylet body of  FIG. 1  formed having a cutaway tube wall portion in accordance with the prior art; 
         FIG. 3  is a simplified top view of a distal segment of a stylet body formed having a crushed tube wall portion in accordance with the prior art; 
         FIG. 4  is a simplified perspective view of a steerable stylet in which the present invention can be incorporated; 
         FIG. 5  is a simplified top view of a distal segment of a stylet body formed having an elongated outer tube slot reinforced with an inner reinforcement sleeve in accordance with a first embodiment of the present invention; 
         FIG. 6  is a simplified side view of the distal segment of the stylet body of  FIG. 5 ; 
         FIG. 7  is a simplified side view of a distal segment of a stylet body formed having an elongated outer tube slot reinforced with an inner reinforcement sleeve in accordance with a second embodiment of the present invention; 
         FIG. 8  is a cross-section view taken along lines  8 — 8  in  FIG. 7 ; and 
         FIG. 9  is a cross-section view taken along lines  9 — 9  in  FIG. 4  of a preferred stylet handle. 
     
    
    
     The figures are not necessarily to scale. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description, references are made to illustrative embodiments for carrying out the invention. It is understood that other embodiments may be utilized without departing from the scope of the invention. Although the present invention is described as preferably being applied to a steerable stylet, the aspects of the present invention are not intended to be limited to use in steerable stylets. Rather, it is understood that the present invention could be utilized in elongated medical devices other than steerable stylets, such as sheaths or catheters, for example. The preferred embodiments of the steerable stylets of the present invention can be employed within the lumens of endocardial cardiac leads, particularly endocardial pacing and/or cardioversion/defibrillation leads, but it will be understood that the steerable stylets of present invention can be utilized in any elongated medical instruments of the types described or mentioned herein and equivalents that may presently exist or come into existence in the future. 
     Moreover, the steerable stylets of the present invention can advantageously be fabricated in a relatively large diameter for use in directing introducers or guide catheters through tortuous pathways as described in the above-referenced &#39;433 and &#39;346 patents, for example, for implanting cardiac leads that do not have lead lumens. Steerable stylet bodies for insertion into cardiac lead lumens typically have a stylet body outer diameter of about 0.016 inches. Larger diameter steerable stylets having an outer diameter of 0.022 inches, for example, (incorporating the reinforcing sleeve construction of the present invention) can advantageously be employed in guide lumens of such bilumen catheters having a guide lumen diameter exceeding the typical cardiac lead body lumen diameter. It is easier to form smaller radii bends in the bendable distal sections of larger diameter (e.g., 0.022 inches) steerable stylet bodies than in smaller diameter (e.g., 0.016 inches) steerable stylets that are robust enough to bend the guide catheter shaft or body to substantially the same radii. Moreover, the larger diameter steerable stylet has sufficient torqueability to increase torqueability of certain guide catheter shafts or bodies or to impart torquebility to a guide catheter shaft or body lacking any torqueability. In addition, it is inherently easier and less expensive to fabricate such larger diameter steerable stylet bodies insertable into a guide lumen of a catheter body than to fabricate smaller diameter steerable stylets providing the same performance. 
     According to the present invention, an elongated medical instrument, such as a steerable stylet  100 , that includes a handle  150  and an elongated stylet body  102  in which the embodiments and features of the present invention can advantageously be combined in various combinations is depicted in FIG.  4 . The stylet body  102  extends a predetermined length between a stylet body proximal end  104  coupled to handle  150  and a stylet body distal end  106 . The stylet body  102  further includes a stylet body proximal segment  108  and a stylet body distal segment  109 . The stylet body  102  encloses an elongated pull wire  112 / 212  extending between a pull wire proximal end coupled to handle  150  and a pull wire distal end affixed at or near the stylet body distal end  106  or abutting a shoulder of the stylet body distal end  106 . For example, the pull wire distal end is coupled to cylindrical distal pull wire stops  123 / 223  that abut a shoulder of the stylet body distal end  106  as described further below. 
     The stylet handle  150  includes a proximal handle portion  152  and a distal handle portion  154  that are movable from close proximity as depicted in  FIG. 4  to separated apart positions to induce a bend in the stylet body distal segment  109 . For example, the pull wire proximal end is coupled to the proximal handle portion  152  and the stylet body proximal end  104  is coupled to the distal handle portion  154 . The pull wire extends distally to a stylet wire distal end that is coupled with the stylet body distal end  106 . The user can grasp the proximal handle portion  152  with the thumb and index finger gripping the flattened sides of the distal handle portion  154 . The distal handle portion  154  can be rotated with the fingers of the other hand to be moved away from the proximal handle portion  152 . The pull wire attached to the proximal handle portion  152  is tensioned (but not twisted), and a bend, e.g., the 180° bend depicted in broken lines depicted in  FIG. 4 , can be induced in the stylet body distal segment  109  in a plane defined by the cutaway portion  111 / 211 . While the term “pull wire” is used herein, it can be seen that in practice, the stylet body proximal end is pushed away from the pull wire proximal end. The induced bend remains even if the grip on the proximal and distal handle portions  152  and  154  is released. 
     A first preferred embodiment of the stylet body  102  is depicted in  FIGS. 5 and 6 . In this embodiment, an outer tube  110  extends the full length of the stylet body  102  through the proximal and distal segments  108  and  109  to an outer tube distal end  122 . The outer tube  110  is preferably formed of stainless steel, hypodermic needle or “hypotube” or a shape memory alloy, e.g., NITi alloy or Nitinol alloy, having an outer diameter of 0.022 inches and an outer tube wall thickness, preferably 0.005 inches, providing an outer tube lumen  113  having an outer tube lumen diameter of 0.012 inches. 
     An elongated portion of the outer tube wall is cut away through an arc of 180° along a cutaway portion  111  near the stylet body distal end between outer tube slot proximal end  118  and outer tube slot distal end  120  to form an elongated outer tube slot  115 , e.g., by grinding or EDM techniques. A reinforcement tube or sleeve  124  is fitted into the outer tube lumen  113  extending at least partly through the length of the outer tube slot  115 . The reinforcement sleeve  124  has a reinforcement sleeve length extending between a reinforcement sleeve proximal end  132  and a reinforcement sleeve distal end  134 , the length of the reinforcement sleeve  124  exceeding the length of the outer tube slot  115 . The reinforcement sleeve  124 , which is preferably formed of a shape memory alloy, forms a reinforcing sleeve lumen  127  so that reinforcing sleeve  124  has an outer diameter D 1  of approximately 0.011 inches, for example, to fit the dimensions of the outer tube lumen  113 , and an inner diameter D 2  of approximately 0.008 inches, for example. 
     The reinforcement sleeve  124  is fitted into the outer tube lumen  113  so that a reinforcement sleeve proximal segment  142  extends proximally within outer tube lumen  113  from the proximal end  118  of the outer tube slot  115  and a reinforcement sleeve distal segment  146  extends distally within the outer tube lumen  113  from the distal end  120  of the outer tube slot  115 . An elongated reinforcement sleeve intermediate segment  144  therefore extends the length of the outer tube slot  115 . At least a portion  148  of the reinforcement sleeve intermediate segment  144  is cut away through 180° to form an elongated reinforcement sleeve slot  125  extending between reinforcement sleeve slot proximal end  128  and reinforcement sleeve slot distal end  130 . The outer tube slot  115  and the reinforcement sleeve slot  125  are aligned, and the reinforcement sleeve proximal segment  142  is adhered to the wall of the outer tube lumen  113  to maintain the alignment. The adhesion can be effected employing Hysol® epoxy. The adhesion of the reinforcement sleeve proximal segment  142  to the wall of the outer tube lumen  113  allows the reinforcement sleeve intermediate and distal segments  144  and  146  free to slide along a wall of the outer tube lumen  113  when a bend is induced along the cutaway portion  111 , such as by applying tension to the pull wire, for example. An overlap portion  117  of the reinforcement sleeve proximal to the reinforcement sleeve slot proximal end  128  and that extends within the outer tube slot  115  between reinforcement sleeve slot proximal end  128  and outer tube slot proximal end  118 , provides strain relief bridging the outer tube slot proximal end  118  where buckling would otherwise likely take place. 
     In one example, the length of the reinforcement sleeve proximal segment  142  is approximately 0.100 inches, the length of the reinforcement sleeve intermediate segment  144  is approximately 0.750 inches, and the length of the reinforcement sleeve distal segment  146  is approximately 0.050 inches. The length of the reinforcement sleeve slot  125  is approximately 0.300 inches. The reinforcement sleeve distal end  134  is, at a minimum, approximately 0.100 inches from the outer tube distal end  122 . The length dimensions and ratio of the length of the reinforcement sleeve slot  125  to the length of the reinforcement sleeve intermediate segment  144  and the outer tube slot  115  are be dependent upon the outer diameters, wall thicknesses, and materials of the outer tube and the reinforcement sleeve. 
     The ratio of the lengths of the solid wall reinforcement sleeve segments  142  and  146  and the ratio of the cut away reinforcement sleeve segment  148  with respect to the length of the outer tube slot  115  provide the optimal bending characteristics and resistance to kinking along the length of the outer tube slot  115 . Stylet bodies having varying flexibility and possible shapes formed in the distal segments thereof can be achieved by controlling the dimensions of the outer tube slot  115  and the reinforcement sleeve slot  125 . Generally, longer and deeper dimensions of the slots  115  and  125  increase flexibility but reduce rigidity in the cutaway portion  111 . Thus, the dimensions of the slots  115  and  125  may be adjusted to provide the desired flexibility and rigidity of the cutaway portion  111  for the intended use. 
     In the illustrated embodiment, the slots  115  and  125  are shown to extend around the periphery of the outer tube  110  and the reinforcement sleeve  124  in an about 180° arc leaving intact arcuate tube walls of the outer tube  110  and reinforcement tube  124 . The arc of the arcuate tube walls of the outer tube  110  and reinforcement tube  124  can differ from 180° and can differ from one another to achieve the desired flexibility and resulting bend shape. 
     The pull wire  112  extends through the reinforcement sleeve lumen  127  and the outer tube lumen  113  to a cylindrical distal pull wire stop  123 . The distal end of the pull wire  112  is crimped into a lumen of a proximal extension of the distal pull wire stop  123  that fits into the outer tube lumen  113 . The cylindrical distal pull wire stop  123  has an outer diameter approximately equal to the diameter of the outer tube  120 , so that the cylindrical distal pull wire stop  123  bears against the outer tube distal end  122  when stressed. In this way, the pull wire distal end is “coupled” to the outer tube distal end  122  at the stylet body distal end  106  as indicated in FIG.  4 . Optionally, the pull wire  112  can be formed having a taper along its length, whereby the pull wire diameter extending through the aligned outer tube slot  115  and reinforcement sleeve slot  125  is less than the pull wire diameter proximal to the aligned outer tube slot  115  and reinforcement sleeve slot  125 . For example, the pull wire  112  can have a proximal wire diameter of 0.010 inches that is tapered to a distal wire diameter of 0.006 inches. 
     The shortened length of the cutaway portion  111  achieved by use of the reinforcement sleeve  124  also shortens the exposed length of the pull wire  112  so that it cannot extend as far away from the outer tube  110  when the outer tube  110  bows outward upon tensioning of the pull wire  112 . Optionally, a polymeric outer sleeve  140  is fitted over the outer tube  110  to extend over the aligned outer tube slot  115  and reinforcement sleeve slot  125  to retain the pull wire  112  generally within the reinforcement sleeve lumen  127  when the pull wire  112  is retracted to form a bend in the nested outer tube and reinforcement sleeve walls. The polymeric outer sleeve  140  is formed of polyimide or PEEK, for example, that is fitted or adhered over the outer tube  110 . 
     In these ways, the reinforcement sleeve  124  reinforces the wall of the outer tube  110  through at least a portion of the length of the outer tube slot  115  to prevent buckling when a bend is induced in the outer tube  115  and the reinforcement sleeve  124 . In this way, when the elongated medical instrument includes a pull wire, a bend can be safely induced in the remaining arcuate section of the outer tube wall when the pull wire  112  extending through the outer tube lumen  113  is retracted with respect to the outer tube  110  (or the outer tube  110  is pushed distally with respect to the pull wire  112 ) by manipulation of the handle  150 . 
     Referring again to  FIG. 4 , it is also possible to employ the principles of the present invention in a distal segment  109  of a stylet body  102  that is formed differently than the proximal segment  108  (or an intermediate segment) of the stylet body  102 . The outer tube  110  can be replaced by a proximal outer tube segment and a distal outer tube segment formed of the same or differing materials, and having the same or differing wall outer tube diameters, wall thicknesses, and bending characteristics. The proximal and distal outer tube segments are joined together end-to-end, and the outer tube slot is formed in the tube wall of the distal tube segment. 
     For example, the proximal segment  108  of stylet body  102  is formed as shown in  FIGS. 7 and 8  from a proximal outer tube  200  of stainless steel, e.g., 304W stainless steel alloy, that is joined at a junction  208  with a distal outer tube  210  that is formed of a shape memory alloy, e.g., Nitinol. Or the proximal segment  108  can be formed of a wire braid reinforced polymer tube. 
     In the depicted embodiment, the junction  208  is effected by an elongated distal counterbore  202  of the tube wall of the proximal outer tube  200  formed of stainless steel into which a proximal segment of the distal outer tube  210  is fitted and adhered employing epoxy cement or the like. A proximal outer tube lumen  204  is thereby axially aligned with a distal outer tube lumen  214 . The proximal outer tube  200  preferably has an outer diameter of nominally 0.022 inches and an outer tube wall thickness of nominally 0.005 inches, providing an outer tube lumen  204  having a nominal outer tube lumen diameter of 0.012 inches. The counterbore diameter is preferably nominally 0.017 inches to receive a distal outer tube  210  having an outer diameter of nominally 0.016 inches and a distal outer tube lumen nominal diameter of 0.011 inches. 
     An elongated portion of the distal outer tube wall is cut away through 180° near the stylet body distal end between distal outer tube slot proximal end  218  and distal outer tube slot distal end  220  to form an elongated outer tube slot  215 . Thus, an intact proximal tubular portion of the distal outer tube  210  extends proximally from the distal outer tube slot proximal end  218 , and an intact distal tubular portion of the distal outer tube  210  extends distally from distal outer tube slot distal end  220 . 
     A tubular distal reinforcement tube or sleeve  224  is fitted into the distal outer tube lumen  214  extending at least partly through the length of the distal outer tube slot  215 . The reinforcement sleeve  224  is preferably formed of a shape memory alloy and has an outer sleeve outer diameter of 0.016 inches, for example, and a reinforcement sleeve lumen  227  inner sleeve lumen diameter of 0.105 inches, for example. 
     The reinforcement sleeve  224  has a reinforcement sleeve length extending between a reinforcement sleeve proximal end  232  and a reinforcement sleeve distal end  234 . In this embodiment, the reinforcement sleeve  224  is tubular and does not have an elongated slot cut away leaving an arcuate section of the tubular wall. And, the reinforcement sleeve  224  does not exceed the length of the outer tube slot  215 , whereby the reinforcement sleeve distal end  234  is disposed intermediate the distal outer tube slot proximal end  218  and distal outer tube slot distal end  220 . For example, the distal outer tube slot  215  can have a nominal length of 1.500 inches, and the reinforcement sleeve distal end  234  is disposed nominally at 0.375 to 0.750 inches from the distal outer tube slot proximal end  218  and distal outer tube slot distal end  220 . 
     The pull wire  212  extends through the reinforcement sleeve lumen  227 , the distal outer sleeve lumen  214  and the proximal outer sleeve lumen  204  to a cylindrical distal pull wire stop  223 . The distal end of the pull wire  212  is crimped into a lumen of the distal pull wire stop  223 . The cylindrical distal pull wire stop  223  has an outer diameter that exceeds the distal outer tube lumen  214  and bears against the distal outer tube distal end  216  when stressed. Optionally, the pull wire  212  can be formed having a taper along its length, whereby the pull wire diameter extending through the distal outer tube slot  215  and reinforcement sleeve lumen  227  is less than the pull wire diameter within the proximal outer tube lumen  204 . For example, the pull wire  212  can have a proximal wire diameter of 0.010 inches that is tapered to a distal wire diameter of 0.006 inches. 
     Optionally, a polymeric outer sleeve  240  is fitted over the distal outer tube  210  to extend over the aligned distal outer tube slot  215  and the reinforcement sleeve  224  to retain the pull wire  212  generally within the distal outer tube lumen  214  when the pull wire  212  is retracted to form a bend in the distal outer tube  210  and the reinforcement sleeve  224  in the cutaway portion  211 . The polymeric outer sleeve  140  can comprise polyimide or PEEK that is fitted or adhered over the outer tube  110 . 
     In these ways, the reinforcement sleeve  224  reinforces the wall of the distal outer tube  210  across the outer tube slot proximal end  218  and through at least a portion  246  of the full length  244  of the distal outer tube slot  215  to prevent buckling when a bend is induced in the distal outer tube  210  and the reinforcement sleeve  224  in the cutaway portion  211 . A bend can be safely induced in the arcuate section of the distal outer tube wall when the pull wire  212  extending through the aligned lumens is retracted with respect to the proximal and distal outer tubes  200  and  210  (or the outer tubes  200  and  210  are pushed distally with respect to the pull wire  212 ) by manipulation of handle  150 . 
     Again, the characteristics of the induced bend can be altered by the selection of the length  244  of the cutaway portion  211 , and the ratio of the segment length  246  to the full length  244  of the cutaway portion  211 . It should be noted that the reinforcement sleeve  224  can be shaped in the same manner as slotted reinforcement sleeve  124  described above with respect to  FIGS. 5 and 6 . 
     Referring again to  FIG. 4 , the stylet handle  150  can take any form that enables the application of tension between and to separate the proximal end of the pull wire  112 / 212  and the stylet body proximal end  104  apart to steer the stylet body distal end  106  and induce a bend along the cutaway portions  111 / 211 . 
     A particular configuration of the stylet handle  150  is shown in FIG.  9 . The distal handle portion  154  has a tubular distal projection  156  into which the stylet body  104  is inserted and attached by adhesive. A distal handle portion lumen  158  extends through the distal handle portion  154 . The proximal handle portion  152  is tubular and threaded internally within proximal handle portion lumen  172  at its distal end to receive a handle end cap  160  and threaded more proximally to receive the threads on the distal projection  168  of a handle insert  162  to enable the handle insert  162  to be moved proximally to release tension or distally to increase tension on the pull wire  112 / 212 . The proximal end opening of the proximal handle portion  152  receives a tubular proximal projection  164  of the distal handle portion  154 . The handle insert  162  comprises a handle insert proximal projection  166  extending into the distal handle portion lumen  158  and a threaded handle insert distal projection  168  that is attached to the internal threads of the proximal handle portion  152 . The pull wire  112 / 212  is inserted through a handle insert lumen  170  that is axially aligned with the distal handle portion lumen  158  extending through the tubular distal projection  156 . The proximal end of the pull wire  112 / 212  is attached to the handle insert  162 . 
     One side of the handle insert distal projection  166  is flattened and bears against a guide pin  174  extending across the proximal handle lumen  172 . A groove  176  is formed around the tubular proximal projection  164  to track a further guide pin (not shown). The user grips the sides of the distal handle portion  154  and rotates the proximal handle portion  152  to rotate the internal screw threads around lumen  172  with respect to the mating screw threads around handle insert distal projection  168  to move handle insert  162  proximally. The proximal movement tensions the pull wire  112 / 212  and induces the bend  111 / 211  as described above. Advantageously, the handle  150  is light in weight, and the tension and induced bend remains in place even if the handle  150  is released so that the user can manipulate the guide catheter handle without having to focus on manually maintaining the bend. 
     The above-described steerable stylets advantageously facilitate the direct implantation of elongated cardiac leads having stylet lumens or the introduction and steering of guide catheters to a site of implantation of such cardiac leads or other medical devices or therapeutic or diagnostic substances. 
     All patents and publications referenced herein are hereby incorporated by reference in their entireties. 
     It will be understood that certain of the above-described structures, functions and operations of the above-described preferred embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. It will also be understood that there may be other structures, functions and operations ancillary to the typical operation of steerable stylets with elongated medical leads or guide catheters or other elongated medical instruments that are not disclosed and are not necessary to the practice of the present invention. 
     In addition, it will be understood that specifically described structures, functions and operations set forth in the above-referenced patents can be practiced in conjunction with the present invention, but they are not essential to its practice. 
     It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention.