Abstract:
A medical probe device of this invention comprising a catheter having a control end and a probe end. The probe end includes a stylet guide housing having at least one stylet port and stylet guide means for directing a flexible stylet outward through at least one stylet port and through intervening tissue to targeted tissues. A stylet is positioned in at least one of said stylet guide means, the stylet comprising a non-conductive sleeve having a RF electrode lumen and an optional a fluid supply lumen and a temperature sensor lumen therein. At least one portion of an opposed surface of the electrode lumen and the electrode can be spaced apart to define a liquid supply passageway for delivery of medicament liquid. The RF electrode enclosed within the non-conductive sleeve has a distal length optionally having at least one current focusing groove means thereon and a distal tip shaped to focus current crowding on its terminal end, whereby Rf current passing therefrom into surrounding tissue forms a lesion extending outward from the groove and tip. The focusing groove means can be a plurality of annular focusing grooves or a spiral focusing groove thereon.

Description:
RELATIONSHIP TO COPENDING APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 08/779,421 filed Jan. 7, 1997, now U.S. Pat. No. 5,895,370, which is a continuation of U.S. patent application Ser. No. 08/470,621 filed Jun. 6, 1995, now U.S. Pat. No. 5,591,125, which is a continuation of U.S. patent application Ser. No. 08/061,647 filed May 13, 1993, now U.S. Pat. No. 5,421,819, which is a continuation-in-part of U.S. patent application Ser. No. 07/929,638 filed Aug. 12, 1992, now abandoned, and U.S. patent application Ser. No. 08/012,379 filed Feb. 2, 1993, now U.S. Pat. No. 5,370,675. A related application is U.S. patent application Ser. No. 08/062,364 filed May 13, 1993, now U.S. Pat. No. 5,435,805. The entire contents of all of the above application are hereby incorporated herein by this reference. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed to a unique device and method for penetrating body tissues for medical purposes such as tissue ablation and fluid substance delivery, for example. The device penetrates tissue to the precise target selected in order to deliver energy to the tissue and/or deliver substances. It limits this treatment to the precise preselected site, thereby minimizing trauma to normal surrounding tissue and achieving a greater medical benefit. This device is a catheter-like device for positioning a treatment assembly in the area or organ selected for medical treatment with one or more stylets in the catheter, mounted for extension from a stylet port in the side of the catheter through surrounding tissue to the tissue targeted for medical intervention. 
     BACKGROUND OF THE INVENTION 
     Treatment of cellular tissues usually requires direct contact of target tissue with a medical instrument, usually by surgical procedures exposing both the target and intervening tissue to substantial trauma. Often, precise placement of a treatment probe is difficult because of the location of targeted tissues in the body or the proximity of the target tissue to easily damaged, critical body organs, nerves, or other components. 
     Benign prostatic hypertrophy or hyperplasia (BPH), for example, is one of the most common medical problems experienced by men over 50 years old. Urinary tract obstruction due to prostatic hyperplasia has been recognized since the earliest days of medicine. Hyperplastic enlargement of the prostate gland often leads to compression of the urethra, resulting in obstruction of the urinary tract and the subsequent development of symptoms including frequent urination, decrease in urinary flow, nocturia, pain, discomfort, and dribbling. The association of BPH with aging has been shown to exceed 50% in men over 50 years of age and increases in incidence to over 75% in men over 80 years of age. Symptoms of urinary obstruction occur most frequently between the ages of 65 and 70 when approximately 65% of men in this age group have prostatic enlargement. 
     Currently there is no proven effective nonsurgical method of treatment of BPH. In addition, the surgical procedures available are not totally satisfactory. Currently patients suffering from the obstructive symptoms of this disease are provided with few options: continue to cope with the symptoms (i.e., conservative management), submit to drug therapy at early stages, or submit to surgical intervention. More than 430,000 patients per year undergo surgery for removal of prostatic tissue in the United States. These represent less than five percent of men exhibiting clinical significant symptoms. 
     Those suffering from BPH are often elderly men, many with additional health problems which increase the risk of surgical procedures. Surgical procedures for the removal of prostatic tissue are associated with a number of hazards including anesthesia related morbidity, hemorrhage, coagulopathies, pulmonary emboli and electrolyte imbalances. These procedures performed currently can also lead to cardiac complications, bladder perforation, incontinence, infection, urethral or bladder neck stricture, retention of prostatic chips, retrograde ejaculation, and infertility. Due to the extensive invasive nature of the current treatment options for obstructive uropathy, the majority of patients delay definitive treatment of their condition. This circumstance can lead to serious damage to structures secondary to the obstructive lesion in the prostate (bladder hypertrophy, hydronephrosis, dilation of the kidney pelves, chronic infection, dilation of ureters, etc.) which is not without significant consequences. In addition, a significant number of patients with symptoms sufficiently severe to warrant surgical intervention are therefore poor operative risks and are poor candidates for prostatectomy. In addition, younger men suffering from BPH who do not desire to risk complications such as infertility are often forced to avoid surgical intervention. Thus the need, importance and value of improved surgical and non-surgical methods for treating BPH is unquestionable. 
     High-frequency currents are used in electrocautery procedures for cutting human tissue especially when a bloodless incision is desired or when the operating site is not accessible with a normal scalpel but presents an access for a thin instrument through natural body openings such as the esophagus, intestines or urethra. Examples include the removal of prostatic adenomas, bladder tumors or intestinal polyps. In such cases, the high-frequency current is fed by a surgical probe into the tissue to be cut. The resulting dissipated heat causes boiling and vaporization of the cell fluid at this point, whereupon the cell walls rupture and the tissue is separated. 
     Destruction of cellular tissues in situ has been used in the treatment of many diseases and medical conditions alone or as an adjunct to surgical removal procedures. It is often less traumatic than surgical procedures and may be the only alternative where other procedures are unsafe. Ablative treatment devices have the advantage of using an electromagnetic energy which is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of circulating fluids and other natural body processes. 
     Microwave, radiofrequency, acoustical (ultrasound) and light energy (laser) devices, and tissue destructive substances have been used to destroy malignant, benign and other types of cells and tissues from a wide variety of anatomic sites and organs. Tissues treated include isolated carcinoma masses and, more specifically, organs such as the prostate, glandular and stromal nodules characteristic of benign prostate hyperplasia. These devices typically include a catheter or cannula which is used to carry a radiofrequency electrode or microwave antenna through a duct to the zone of treatment and apply energy diffusely through the duct wall into the surrounding tissue in all directions. Severe trauma is often sustained by the duct wall during this cellular destruction process, and some devices combine cooling systems with microwave antennas to reduce trauma to the ductal wall. For treating the prostate with these devices, for example, heat energy is delivered through the walls of the urethra into the surrounding prostate cells in an effort to ablate the tissue causing the constriction of the urethra. Light energy, typically from a laser, is delivered to prostate tissue target sites by “burning through” the wall of the urethra. Healthy cells of the duct wall and healthy tissue between the nodules and duct wall are also indiscriminately destroyed in the process and can cause unnecessary loss of some prostate function. Furthermore, the added cooling function of some microwave devices complicates the apparatus and requires that the device be sufficiently large to accommodate this cooling system. 
     Application of liquids to specific tissues for medical purposes is limited by the ability to obtain delivery without traumatizing intervening tissue and to effect a delivery limited to the specific target tissue. Localized chemotherapy, drug infusions, collagen injections, or injections of agents which are then activated by light, heat or chemicals would be greatly facilitated by a device which could conveniently and precisely place a fluid (liquid or gas) supply catheter opening at the specific target tissue. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a device and method for penetrating tissue, through intervening tissues to the precise target tissue selected for a medical action such as tissue ablation and/or substance delivery, limiting this activity to the precise preselected site, thereby minimizing the trauma and achieving a greater medical benefit. 
     It is another object of this invention is to provide a device and method for tissue ablation of body tissues which delivers the therapeutic energy directly into targeted tissues while minimizing effects on its surrounding tissue. 
     It is a still further object of this invention is to provide a device and method for introducing fluid treatment agents such as flowable liquids and gases, with greater precision and ease to a specific location in the body. 
     Another object of this invention is to provide a thermal destruction device which gives the operator more information about the temperature and other conditions created in both the tissue targeted for treatment and the surrounding tissue. In addition, it will provide more control over the physical placement of the stylet and over the parameters of the tissue ablation process. 
     In summary, the medical probe device of this invention comprises a catheter having a control end and a probe end. The probe end includes a stylet guide housing having at least one stylet port and stylet guide means for directing a flexible stylet outward through at least one stylet port and through intervening tissue to targeted tissues. A stylet is positioned in at least one of said stylet guide means, the stylet comprising a non-conductive sleeve having at least two and preferably three lumina therein. An RF electrode lumen terminates at a distal port in the distal end of the non-conductive sleeve, and a radiofrequency electrode is positioned in the RF electrode lumen for longitudinal movement therein through the distal port. Preferably, at least one portion of an opposed surface of the electrode lumen and the electrode are spaced apart to define a liquid supply passageway for delivery of medicament liquid. A second optional fluid passage lumen terminates at a distal port in the distal end of the non-conductive sleeve and comprises means passing fluid therethrough. 
     A temperature sensor third lumen terminates in a sealed closure adjacent the distal end of the non-conductive sleeve. At least one and preferably a plurality of temperature sensing devices such as thermocouples are positioned in the third lumen, the leads extending through the lumen. One preferred embodiment has two temperature sensing devices positioned in the third lumen, one temperature sensing device being positioned within about 1 mm of the distal end of the non-conductive sleeve, and the second temperature sensing device being positioned at least 3 mm and preferably from 3 to 6 mm from the distal end of the non-conductive sleeve. 
     In summary, another embodiment of this invention comprises a catheter having a control end and a probe end, the probe end including a stylet guide housing having at a stylet port and stylet guide means for directing a flexible stylet outward through the stylet port and through intervening tissue to targeted tissues. A stylet is positioned in at least one of said stylet guide means, the stylet comprising an electrical conductor enclosed within a nonconductive sleeve. The electrode has a distal length having at least one current focusing groove means thereon and a distal tip shaped to focus current on its terminal end, whereby RF current passing therefrom into surrounding tissue forms a lesion extending outward from the groove and tip. In one preferred embodiment, the distal length has a plurality of annular focusing grooves or a spiral focusing groove thereon. 
     Preferably at least a part of the electrode is enclosed within a support tube having sufficient strength to maintain electrode linearity when the electrode is directed outward through the stylet port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of an RF ablation catheter embodiment of this invention with an fiber optic viewing accessory. 
     FIG. 2 is a cross-sectional view of a catheter of FIG. 1 showing details of the stylet guide housing. 
     FIG. 3 is a side view of the stylet and lumen assembly of this invention. 
     FIG. 4 is a cross-sectional side view of the of the junction of the stylet and control tube assembly taken along the central axis of the tubing. 
     FIG. 5 is a cross-sectional view of the junction of the stylet and control tube assembly taken along the line  5 — 5  of FIG.  4 . 
     FIG. 6 is a cross-sectional view of a trilumen stylet of this invention taken along the line  6 — 6  in FIG.  3 . 
     FIG. 7 is a cross-sectional side view of the trilumen stylet tip shown in FIG. 3 taken along line  7 — 7  of FIG.  6 . 
     FIG. 8 is a plane view of the annular groove embodiment of the current density focusing electrode of this invention. 
     FIG. 9 is a plane view of the spiral groove embodiment of the current density focusing electrode of this invention. position and the sleeve partially retracted therefrom. 
     FIG. 10 is an exploded view of the RF ablation catheter shown in FIG.  1 . 
     FIG. 11 is an isometric view of the adjuster block and tension tube assembly of the RF ablation catheter shown in FIG.  10 . 
     FIG. 12 is a detailed view “A” of the tension tube connections shown in FIG.  11 . 
     FIG. 13 is an exploded view of the sleeve and electrode slide block assembly of the embodiment shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The device of this invention provides a precise controlled positioning of a treatment stylet in a tissue targeted for treatment, destruction or sampling from a catheter positioned in the vicinity of the target tissue. 
     The term “stylet” as used hereinafter is defined to include both solid and hollow probes which are adapted to be passed from a catheter port through normal tissue to targeted tissues. The stylet is shaped to facilitate easy passage through tissue. It can be a solid wire, thin rod, or other solid shape or it can be a thin hollow tube or other shape having a longitudinal lumen for introducing fluids to or removing materials from a site. The stylet can also be a thin hollow tube or other hollow shape, the hollow lumen thereof containing a reinforcing or functional rod or tube such as a laser fiber optic. The stylet preferably has a sharpened end to reduce resistance and trauma when it is pushed through tissue to a target site. 
     The stylet can be designed to provide a variety of medically desired treatments of a selected tissue. As a radiofrequency electrode or microwave antenna, it can be used to ablate or destroy targeted tissues. As a hollow tube, it can be used to deliver a treatment fluid such as a liquid to targeted tissues. The liquid can be a simple solution or a suspension of solids, for example, colloidal particles, in a liquid. Since the stylet is very thin, it can be directed from the catheter through intervening normal tissue with a minimum of trauma to the normal tissue. 
     The device and method of this invention provide a more precise, controlled medical treatment which is suitable for destroying cells of medically targeted tissues throughout the body, both within and external to body organs. The device and method are particularly useful for treating benign prostate hyperplasia (BPH), and the device and its use are hereinafter described with respect to BPH, for purposes of simplifying the description thereof. It will be readily apparent to a person skilled in the art that the device and method can be used to destroy body tissues in any body cavities or tissue locations that are accessible by percutaneous or endoscopic catheters, and is not limited to the prostate. Application of the device and method in all of these organs and tissues are intended to be included within the scope of this invention. 
     BPH is a condition which arises from the replication and growth of cells in the prostate and the decrease of cell death rate, forming glandular and stromal nodules which expand the prostate and constrict the opening of the prostatic urethra. Glandular nodules are primarily concentrated within the transition zone, and stromal nodules within the periurethral region. Traditional treatments of this condition have included surgical removal of the entire prostate gland, digital removal of the adenoma, as well as transurethral resection of the urethral canal and prostate to remove tissue and widen the passageway. One significant and serious complication associated with these procedures is iatrogenic sterility. More recently, laser treatment has been employed to remove tissue, limiting bleeding and loss of body fluids. Balloons have also been expanded within the urethra to enlarge its diameter, with and without heat, but have been found to have significant limitations. 
     Microwave therapy has been utilized with some success by positioning a microwave antenna within the prostatic urethra and generating heat in the tissue surrounding the urethra with an electromagnetic field. Coolants are sometimes applied within the catheter shaft to reduce the temperature of the urethral wall. This necessitates complicated mechanisms to provide both cooling of the immediately adjacent tissues while generating heat in the more distant prostatic tissue. This technique is similar to microwave hyperthermia. Similarly, radiofrequency tissue ablation with electrodes positioned within the urethra exposes the urethral wall to destructive temperatures. To avoid this, low temperature settings required to protect the urethra must be so low that the treatment time required to produce any useful effect is unduly extended, e.g. up to three hours of energy application. 
     One embodiment of the device of this invention uses the urethra to access the prostate and positions RF electrode stylets directly into the tissues to be destroyed. The portion of the stylet conductor extending from the urethra to targeted tissues is enclosed within a longitudinally adjustable sleeve shield which prevents exposure of the tissue adjacent to the sleeve to the RF current. The sleeve movement is also used to control the amount of energy per unit surface area which is delivered by controlling the amount of electrode exposed. Thus the ablative destruction is confined to the tissues targeted for destruction, namely those causing the constriction. Other aspects of the invention will become apparent from the drawings and accompanying descriptions of the device and method of this invention. It will be readily apparent to a person skilled in the art that this procedure can be used in many areas of the body for percutaneous approaches and approaches through body orifices. 
     FIG. 1 is an isometric view of an RF ablation catheter embodiment of this invention with a fiber optic viewing accessory. The flexible catheter  2 , attached to handle  4 , has a terminal stylet guide  6  with two stylets  8 . The handle has stylet electrode tabs  10  and  11  and sleeve tabs  12  and  13  as will be described in greater detail hereinafter. The handle  4  is also connected to a optical viewing assembly  14  and RF power connector  16 , transponder connector  18  and thermocouple connectors  20 . The portions of the catheter  2  leading from the handle  4  to the stylet guide tip  6  can optionally has a graduated stiffness. For example, the catheter can be designed to be more stiff near the handle and more flexible near the tip, or any other stiffness profiles. The catheter can be constructed of an inner slotted stainless steel tube with outer flexible sleeve such as is described in U.S. Pat. No. 5,322,064, the entire contents of which are incorporated herein by reference. It can also be made of coiled or braided wire to which an outer sleeve is bonded. 
     The fiber optic viewing assembly in this embodiment includes a lens focusing assembly  22 , a lens viewing assembly support connector  24  assembly attached to a male quick disconnect connector  26  by flexible tubing  28 . 
     FIG. 2 is a cross-sectional view of a catheter of FIG. 1 showing details of the stylet guide housing. The stylet guide housing  6  has a curved passageway  28  through which the stylet  8  is extended into the tissue to be treated. Further details of these components are described in copending applications Ser. No. 08/012,370 filed Feb. 2, 1993, now U.S. Pat. No. 5,370,675, and application Ser. No. 08/063,364 filed May 13, 1993, now U.S. Pat. No. 5,435,805. 
     FIG. 3 is a side view of the stylet and lumen assembly of this invention. The key components of the stylet of this embodiment are an insulating sleeve  30  and an electrode  32  extending therethrough. The electrode  32  has a sharpened tip, in this embodiment a broadened spear tip. The proximal end of the electrode and sleeve are connected by respective sleeve connector  334  and electrode connector  338  to handle sleeve and electrode slides described in greater detail hereinafter with respect to FIGS. 10 and 13. An electrode support tube  36  extends from the electrode connector  338  to the area  38  of the sleeve connector  334  to transmit compressive pressure without collapsing the electrode  32 . An insulating sleeve support tube  40  made of shrink tubing extends from the sleeve connector  334  to the beginning or proximal end  42  of the outer tubing  44 . Tubing  44  joins the support tubing to the control tube  46 . The control tube  46  supporting both the electrode and insulating sleeve extends to the junction  48  (see FIG. 4) of the electrode lumen passageway  50  and the electrode  32 . In this manner, support is provided over the length of the stylet extending from the handle to the trilumen tip, preventing collapse or loss of linearity of the highly flexible electrode when it is pushed through the stylet guide housing. 
     FIG. 4 is a side elevational view in section of the junction of the stylet and control tube assembly along the central axis of the tubing, and FIG. 5 is a cross-sectional view of the junction of the stylet and control tube assembly taken along the line  5 — 5  of FIG.  4 . At the junction  48 , the electrode  32  extends through the upper electrode lumen wall  62  and enters the electrode lumen  50 . The outer tubing  52  encloses and supports both the distal ends of the control tubing  46  and a trilumen sleeve tube  54 . 
     Referring to FIG. 5, the space  56  between the control tube  46  and the trilumen sleeve tube  54  can be filled with an adhesive to secure them together. The trilumen sleeve tube  54  includes the electrode lumen  50 , a temperature sensor lumen  58  and a fluid supply lumen  60  for supply of optional fluids such as antibiotics or anesthetics to the area of treatment. 
     FIG. 6 is a cross-sectional view of a trilumen stylet of this invention taken along the line  6 — 6  in FIG.  3 . The trilumen sleeve  30  is an insulating sleeve for the electrode  32  and includes the additional temperature sensor lumen  58  and liquid supply lumen  60 . The inner surface of the electrode lumen  50  can be spaced from the outer surface of the electrode by a distance “h” which can be, for example, from about 1 to 3 mm to define an additional liquid supply conduit with an approximate annular cross-section. 
     FIG. 7 is a cross-sectional side view of the trilumen stylet tip shown in FIG. 6 taken along the line  7 — 7 . The terminal end of the temperature sensor lumen  58  is sealed to protect the electrical components. Thermocouple  64  is placed at the distal end of the sleeve  30  to monitor the temperature of the tissue surrounding the electrode  32  and is preferably less than about 1 mm from the exposed electrode. Thermocouple  66  is placed at least about 3 mm and preferably from about 3 to 6 mm from the tip of sleeve  30  to monitor the temperature of the duct wall (such as the urethra) through which the stylet is extended. This is provided to ensure the duct wall temperature does not reach destructive levels when the RF treatment of tissue surrounding the extended electrode is underway. 
     FIG. 8 is a plane view of the annular groove embodiment of the current density focusing electrode of this invention. In this embodiment, the electrode is ground to a single current focusing sharp tip  68  without secondary corner or other sharp edges which could also focus or crowd current. Additional current focusing can be provided along the electrode surface by the annular grooves  70  and  72 . The temperature of the tissue surrounding the electrode initially increases in initial zones  74 ,  76  and  78 . The elevated temperature zone then extends to two intermediate zones  80  and  82 , as the zones from the grooves merge. Thereafter all of the elevated temperature zones merge to form the single oval zone lesion  84 . Use of these current focusing grooves  70  and  72  produces a more symmetrical lesion. 
     FIG. 9 is a plane view of the spiral groove embodiment of the current density focusing electrode of this invention. In this embodiment, the electrode is also ground to a single current focusing sharp tip  86  without secondary sharp corners or edges which could also focus or crowd current. Additional current focusing can be provided along the electrode surface by at least one spiral or helical groove  88 . The temperature of the tissue surrounding the electrode initially increases in the initial tip zone  90  and spiral zone  92 . The elevated temperature zone then extends to two intermediate zones  94  and  96 , as the spiral zone  92  merges to form a single zone  96 . Thereafter all of the elevated temperature zones merge to form the single oval zone lesion  98 . Use of the spiral focusing groove  88  provides a more symmetrical lesion. 
     FIG. 10 is an exploded view of the RF ablation catheter assembly shown in FIG.  1 . The upper handle plate  276  has two central slots  278  and  280  through which the electrode control slides  10  and  11  are attached to respective left electrode slide block  282  and right electrode slide block  284 . Sleeve control slides  12  and  13  are attached through outer slots  286  and  288  to respective left sleeve slide block  290  and right sleeve slide block  292 . Fiber optic receptor housing  30  is mounted on the proximal surface of the upper handle plate  276 . The electrical receptor  294  is received in respective cavities  296  and  298  in the upper handle plate  276  and lower handle plate  300  attached thereto. The lower handle plate  300  has a central cavity  302  which accommodates the electrode and sleeve slide blocks and associated elements. 
     Microswitch activator blocks  304  (only left sleeve block shown) are connected to the sleeve slide blocks  290  and  292 . They are positioned to actuate the microswitches  306  when the respective sleeve block (and sleeve attached thereto) have been advanced. The microswitches  306  hold the respective RF power circuits open until the respective sleeves are advanced to a position beyond the urethra wall and into the prostate to prevent direct exposure of the urethra to the energized RF electrodes. Extension of the sleeve 5 mm beyond the guide is usually sufficient to protect the urethra. 
     The tension-torque tube assembly  308  (see FIG. 11) is mounted in the distal end of the housing in the receptor  310 . 
     FIG. 11 is an isometric view of the adjuster block and tension tube assembly  308  of the RF ablation catheter shown in FIG.  10 . The torque tube  312  extends from the torque coupler  314  through the twist control knob  316  to the stylet guide  6 . Bending flexure of the torque tube  312  during use lengthens the path from the handle to the guide tip  6 . To prevent a resulting retraction of the stylet sleeve and electrode components when the torque tube  312  is flexed, a tension tube  318  having a fixed length and diameter smaller than the inner diameter of the torque tube  312  is provided. The distal end of the tension tube  318  is securely attached to the stylet guide  6 , and the proximal end  320  is secured to the adjuster block  322 , for example by an adhesive. The axial position of the adjuster block  322  can be adjusted to ensure the stylets  8  are initially positioned just inside the outlet ports in the stylet guide  6 . Torque coupler  314  is mounted on the coupler block  324 . Twist control knob stop pin  326  extends into a grove (not shown) and limits rotation of the control knob  316 . 
     FIG. 12 is a detailed view “A” of the distal end tension tube connections of the tension tube shown in FIG.  11 . The tension tube  318  is securely connected to the proximal end  328  of the stylet guide  6 , for example by a length of shrink tubing  330 . 
     FIG. 13 is an exploded view of the sleeve and electrode slide block assembly of the embodiment shown in FIG.  10 . The right sleeve slide block  292  has a projection  332  which extends inward under the right electrode slide block  284 . Right sleeve connector  334  is mounted to the inner end of the projection  332 , secured to the end of the proximal end of the sleeve  336 . Right electrode connector  338  is attached to an inner surface of the electrode slide block  284  and is secured to the proximal end of electrode  340 . The right sleeve and electrode slide blocks  292  and  284  are slidingly attached to the right friction adjustment rail  342  by screws (not shown) through slots  344  and  345 , the screws being adjustable to provide sufficient friction between the blocks and the rail  342  to provide secure control over the stylet movement. The left sleeve slide block  290  and left electrode slide block  282  are mirror replicas of the right blocks and are similarly mounted on the left friction rail  348 . The left sleeve and electrodes are not shown. 
     Although preferred embodiments of the subject invention have been described in some detail, it is understood that obvious variations can be made without departing from the spirit and the scope of the invention as defined by the appended claims.