Abstract:
A leadless cardiac pacemaker comprises a housing, a plurality of electrodes coupled to an outer surface of the housing, and a pulse delivery system hermetically contained within the housing and electrically coupled to the electrode plurality, the pulse delivery system configured for sourcing energy internal to the housing, generating and delivering electrical pulses to the electrode plurality. Systems and methods for delivering the leadless cardiac pacemaker with delivery catheters are also provided. In some embodiments, the delivery catheters include first and second coaxial shafts configured to apply rotational torque to the pacemaker. In other embodiments, the pacemaker is held in place on the catheter with a tether.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119 of U.S. Provisional Patent Application No. 61/392,881, filed Oct. 13, 2010, titled “Delivery and Retrieval Catheter Systems and Methods”, which is incorporated herein by reference in its entirety. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications, including patents and patent applications, mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
       FIELD 
       [0003]    The present disclosure relates to leadless cardiac pacemakers, and more particularly, to features and methods by which they are affixed within the heart. More specifically, the present disclosure relates to features and methods for delivering a leadless cardiac pacemaker to tissue. 
       BACKGROUND 
       [0004]    Cardiac pacing by an artificial pacemaker provides an electrical stimulation of the heart when its own natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient for a patient&#39;s health. Such antibradycardial pacing provides relief from symptoms and even life support for hundreds of thousands of patients. Cardiac pacing may also provide electrical overdrive stimulation to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death. 
         [0005]    Cardiac pacing by currently available or conventional pacemakers is usually performed by a pulse generator implanted subcutaneously or sub-muscularly in or near a patient&#39;s pectoral region. Pulse generator parameters are usually interrogated and modified by a programming device outside the body, via a loosely-coupled transformer with one inductance within the body and another outside, or via electromagnetic radiation with one antenna within the body and another outside. The generator usually connects to the proximal end of one or more implanted leads, the distal end of which contains one or more electrodes for positioning adjacent to the inside or outside wall of a cardiac chamber. The leads have an insulated electrical conductor or conductors for connecting the pulse generator to electrodes in the heart. Such electrode leads typically have lengths of 50 to 70 centimeters. 
         [0006]    Although more than one hundred thousand conventional cardiac pacing systems are implanted annually, various well-known difficulties exist, of which a few will be cited. For example, a pulse generator, when located subcutaneously, presents a bulge in the skin that patients can find unsightly, unpleasant, or irritating, and which patients can subconsciously or obsessively manipulate or “twiddle”. Even without persistent manipulation, subcutaneous pulse generators can exhibit erosion, extrusion, infection, and disconnection, insulation damage, or conductor breakage at the wire leads. Although sub-muscular or abdominal placement can address some concerns, such placement involves a more difficult surgical procedure for implantation and adjustment, which can prolong patient recovery. 
         [0007]    A conventional pulse generator, whether pectoral or abdominal, has an interface for connection to and disconnection from the electrode leads that carry signals to and from the heart. Usually at least one male connector molding has at least one terminal pin at the proximal end of the electrode lead. The male connector mates with a corresponding female connector molding and terminal block within the connector molding at the pulse generator. Usually a setscrew is threaded in at least one terminal block per electrode lead to secure the connection electrically and mechanically. One or more O-rings usually are also supplied to help maintain electrical isolation between the connector moldings. A setscrew cap or slotted cover is typically included to provide electrical insulation of the setscrew. This briefly described complex connection between connectors and leads provides multiple opportunities for malfunction. 
         [0008]    Other problematic aspects of conventional pacemakers relate to the separately implanted pulse generator and the pacing leads. By way of another example, the pacing leads, in particular, can become a site of infection and morbidity. Many of the issues associated with conventional pacemakers are resolved by the development of a self-contained and self-sustainable pacemaker, or so-called leadless pacemaker, as described in the related applications cited above. 
         [0009]    Self-contained or leadless pacemakers or other biostimulators are typically fixed to an intracardial implant site by an actively engaging mechanism such as a screw or helical member that screws into the myocardium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0011]      FIGS. 1A-1C  are embodiments of a leadless cardiac pacemaker or biostimulator. 
           [0012]      FIG. 2A  is one embodiment of a delivery system for delivering a leadless biostimulator. 
           [0013]      FIGS. 2B-2C  are close up views of a distal portion of the delivery system of  FIG. 2A . 
           [0014]      FIGS. 2D-2E  are schematic side and cross-sectional views of the delivery system of  FIG. 2A . 
           [0015]      FIG. 2F  is a cutaway view of a handle portion of the delivery system of  FIG. 2A . 
           [0016]      FIG. 3A  is another embodiment of a delivery system for delivering a leadless biostimulator having a tether. 
           [0017]      FIGS. 3B-3C  are close up views of a distal portion of the delivery system of  FIG. 3A . 
           [0018]      FIGS. 3D-3E  are schematic side and cross-sectional views of the delivery system of  FIG. 3A . 
           [0019]      FIG. 3F  is a cutaway view of a handle portion of the delivery system of  FIG. 3A . 
           [0020]      FIG. 3G  is a close up view of a handle portion of the delivery system of  FIG. 3A . 
           [0021]      FIG. 3H  is one embodiment of a handle portion of a delivery system. 
       
    
    
     SUMMARY OF THE DISCLOSURE 
       [0022]    In some embodiments, a delivery catheter is provided comprising a handle having a torque knob, a first shaft configured to attach the delivery catheter to a leadless biostimulator, and a second shaft having a proximal portion coupled to the torque knob and a distal portion configured to engage the leadless biostimulator when it is attached to the delivery catheter, the second shaft configured to apply rotational torque to the leadless biostimulator with actuation of the torque knob, wherein the first shaft is coaxially disposed within the second shaft. 
         [0023]    In some embodiments, the second shaft further comprises a key configured to mate with a slot on the leadless biostimulator. 
         [0024]    In some embodiments, the second shaft further comprises a slot configured to mate with a key on the leadless biostimulator. In one embodiment, the key comprises a shape selected from the group consisting of square, rectangle, triangle, pentagon, hexagon, cross, and “X”. 
         [0025]    In some embodiments, the first shaft further comprises a screw configured to engage a threaded hole in the leadless biostimulator. In another embodiment, first shaft further comprises a threaded hole configured to engage a screw on the leadless biostimulator. 
         [0026]    In one embodiment, the delivery catheter further comprises a second torque knob coupled to the first shaft, wherein actuation of the second torque knob is configured to rotate the first shaft independently of the second shaft. 
         [0027]    A method of delivering a medical device into a patient is also provided, comprising attaching a leadless biostimulator to a delivery catheter, inserting the leadless biostimulator into a patient, advancing the leadless biostimulator to a target tissue, applying torque from a first shaft fully disposed in the delivery catheter to the leadless biostimulator to screw a fixation device of the leadless biostimulator into the target tissue, and unscrewing a second shaft fully disposed in the delivery catheter from the leadless biostimulator to detach the leadless biostimulator from the delivery catheter. 
         [0028]    In some embodiments, the applying torque step comprises rotating the first shaft in a first direction. In another embodiment, the unscrewing step comprises rotating the second shaft in a second direction different than the first direction. 
         [0029]    In some embodiments, the applying torque step further comprises applying torque from a key disposed on the first shaft of the delivery catheter to a slot disposed on the leadless biostimulator. In another embodiment, the unscrewing step further comprises unscrewing a screw disposed on the second shaft from a threaded hole in the leadless biostimulator. 
         [0030]    Another delivery catheter is provided, comprising a shaft configured to apply rotational torque to a leadless biostimulator, lumen disposed within the shaft, the lumen sized and configured to receive a tether of the leadless biostimulator, and a tether lock disposed in the delivery catheter and configured to engage the tether to hold the leadless biostimulator in contact with the delivery catheter. 
         [0031]    In some embodiments, the shaft further comprises a key configured to mate with a slot on the leadless biostimulator. In another embodiment, the shaft further comprises a slot configured to mate with a key on the leadless biostimulator. In one embodiment, the key comprises a shape selected from the group consisting of square, rectangle, triangle, pentagon, hexagon, cross, and “X”. 
         [0032]    In another embodiment, the tether lock comprises a pin. In some embodiments, he tether lock comprises a button and a locking cam. 
         [0033]    A method of delivering a medical device into a patient is provided, comprising applying tension to a tether of a leadless biostimulator to hold the leadless biostimulator in contact with a delivery catheter, inserting the leadless biostimulator into a patient, advancing the leadless biostimulator to a target tissue, applying torque from a shaft of the delivery catheter to the leadless biostimulator to screw a fixation device of the leadless biostimulator into the target tissue, and releasing the tension from the tether to detach the leadless biostimulator from the delivery catheter. 
         [0034]    In some embodiments, the applying torque step comprises rotating the shaft. In another embodiment, the applying torque step further comprises applying torque from a key disposed on the shaft of the delivery catheter to a slot disposed on the leadless biostimulator. In yet another embodiment, the applying torque step further comprises applying torque from a slot disposed on the shaft of the delivery catheter to a key disposed on the leadless biostimulator. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    Various embodiments for delivering system comprising one or more leadless cardiac pacemakers or biostimulators are described. A leadless cardiac pacemaker can communicate by conducted communication, representing a substantial departure from conventional pacing systems. For example, an illustrative cardiac pacing system can perform cardiac pacing that has many of the advantages of conventional cardiac pacemakers while extending performance, functionality, and operating characteristics with one or more of several improvements. 
         [0036]    In some embodiments of a cardiac pacing system, cardiac pacing is provided without a pulse generator located in the pectoral region or abdomen, without an electrode-lead separate from the pulse generator, without a communication coil or antenna, and without an additional requirement on battery power for transmitted communication. 
         [0037]    An embodiment of a cardiac pacing system configured to attain these characteristics comprises a leadless cardiac pacemaker that is substantially enclosed in a hermetic housing suitable for placement on or attachment to the inside or outside of a cardiac chamber. The pacemaker can have two or more electrodes located within, on, or near the housing, for delivering pacing pulses to muscle of the cardiac chamber and optionally for sensing electrical activity from the muscle, and for bidirectional communication with at least one other device within or outside the body. The housing can contain a primary battery to provide power for pacing, sensing, and communication, for example bidirectional communication. The housing can optionally contain circuits for sensing cardiac activity from the electrodes. The housing contains circuits for receiving information from at least one other device via the electrodes and contains circuits for generating pacing pulses for delivery via the electrodes. The housing can optionally contain circuits for transmitting information to at least one other device via the electrodes and can optionally contain circuits for monitoring device health. The housing contains circuits for controlling these operations in a predetermined manner. 
         [0038]    In some embodiments, a cardiac pacemaker can be adapted for delivery and implantation into tissue in the human body. In a particular embodiment, a leadless cardiac pacemaker can be adapted for implantation adjacent to heart tissue on the inside or outside wall of a cardiac chamber, using two or more electrodes located on or within the housing of the pacemaker, for pacing the cardiac chamber upon receiving a triggering signal from at least one other device within the body. 
         [0039]    Self-contained or leadless pacemakers or other biostimulators are typically fixed to an intracardial implant site by an actively engaging mechanism or primary fixation mechanism such as a screw or helical member that screws into the myocardium. Examples of such leadless biostimulators are described in the following publications, the disclosures of which are incorporated by reference: (1) U.S. application Ser. No. 11/549,599, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker System for Usage in Combination with an Implantable Cardioverter-Defibrillator”, and published as U.S.2007/0088394A1 on Apr. 19, 2007; (2) U.S. application Ser. No. 11/549,581 filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker”, and published as U.S.2007/0088396A1 on Apr. 19, 2007; (3) U.S. application Ser. No. 11/549,591, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker System with Conductive Communication” and published as U.S.2007/0088397A1 on Apr. 19, 2007; (4) U.S. application Ser. No. 11/549,596 filed on Oct. 13,2006, entitled “Leadless Cardiac Pacemaker Triggered by Conductive Communication” and published as U.S.2007/0088398A1 on Apr. 19, 2007; (5) U.S. application Ser. No. 11/549,603 filed on Oct. 13,2006, entitled “Rate Responsive Leadless Cardiac Pacemaker” and published as U.S.2007/0088400A1 on Apr. 19,2007; (6) U.S. application Ser. No. 11/549,605 filed on Oct. 13, 2006, entitled “Programmer for Biostimulator System” and published as U.S.2007/0088405A1 on Apr. 19, 2007; (7) U.S. application Ser. No. 11/549,574, filed on Oct. 13, 2006, entitled “Delivery System for Implantable Biostimulator” and published as U.S.2007/0088418A1 on Apr. 19, 2007; and (8) International Application No. PCT/U.S.2006/040564, filed on Oct. 13, 2006, entitled “Leadless Cardiac Pacemaker and System” and published as WO07047681A2 on Apr. 26, 2007. 
         [0040]    In addition to the primary fixation mechanism, such as a helix, some biostimulators may further include a secondary fixation mechanism to provide another feature for keeping the biostimulator in place within the body. Secondary fixation mechanisms can be either active (e.g., the secondary fixation mechanism can actively engage tissue, either within or outside the heart), or can be passive (e.g., the secondary fixation mechanism is not attached to tissue but rather prevents the biostimulator from moving around in the body in the case of accidental detachment). Further details on secondary fixation mechanisms can be found in U.S. application Ser. No. 12/698,969. 
         [0041]    Leadless pacemakers or biostimulators can be delivered to and retrieved from a patient using any of the delivery systems described herein. In some embodiments, a biostimulator is attached or connected to a delivery system and advanced intravenously into the heart. The delivery system can include features to engage the biostimulator to allow fixation of the biostimulator to tissue. For example, in embodiments where the biostimulator includes an active engaging mechanism, such as a screw or helical member, the delivery system can include a docking cap or key configured to engage the biostimulator and apply torque to screw the active engaging mechanism into the tissue. In other embodiments, the delivery system includes clips designed to match the shape of a feature on the biostimulator and apply torque to screw the active engaging mechanism into the tissue. 
         [0042]      FIGS. 1A-1C  show a leadless cardiac pacemaker or leadless biostimulator  100  having an active fixation device or helix  102 . The biostimulators can include a hermetic housing at least one electrode disposed thereon. Further details of a typical leadless biostimulator can be found in the U.S. Patent Publications listed above. Additionally, a biostimulator can further include a proximal cap  104  positioned on or near a proximal end of the biostimulator. In  FIGS. 1A and 1C , the proximal cap  104  can further comprise an indentation or key  106 . The key can be any number of shapes, such as square, triangle, rectangle, hexagon, pentagon, etc, as will be described in further detail below. Referring to  FIG. 1B , the proximal cap can further comprise a taper  108  as it is attached to the biostimulator  100 . The taper can be grasped or connected to a delivery or extraction catheter, as will be discussed below. 
         [0043]      FIG. 2A  illustrates a biostimulator delivery system  20  for delivery of a biostimulator  200  into a patient. The delivery system  20  can include delivery catheter  210 , handle  212 , deflection arm  214 , sheath  216 , catheter shaft  217 , catheter flush port  218 , sheath flush port  220 , and torque knobs  222  and  224 . The deflection arm  214  can be used to steer and guide the catheter during implantation and/or removal of the biostimulator. The catheter flush port  218  and sheath flush port  220  can be used to flush saline or other fluids through the catheter and sheath, respectively. Sheath  216  can be advanced distally over catheter shaft  217  to provide additional steering and support for the delivery catheter during implantation. 
         [0044]      FIG. 2B  is a close-up view of a distal portion of delivery catheter  210  and biostimulator  200 . The biostimulator of  FIG. 2B  includes a helix  202  for attachment of the biostimulator to tissue. The delivery catheter can include a docking cap  226  having a key  228  sized and configured to mate with a proximal end cap  230  disposed on the biostimulator. The delivery catheter can further include a screw  232  configured to couple with the proximal cap of the biostimulator. 
         [0045]      FIG. 2C  is another close-up view of the delivery catheter  210  and biostimulator  200  shown in  FIG. 2B , but from a different perspective to show the proximal portion of the biostimulator. As shown in  FIG. 2C , the proximal end cap  230  includes a cutout or slot  234  sized and configured to mate with the key  228  on catheter  210  (shown in  FIG. 2B ). Furthermore, the proximal end cap  230  can also include a threaded hole  236  sized and configured to accept and couple to screw  232  of the delivery catheter. In  FIGS. 2B-2C , key  228  is shown as a “male” key and slot  234  is shown as a “female” key, but it should be understood that in other embodiments, the “male” key or key  228  can be located on the proximal end cap  230 , and the “female” key or slot  234  can be disposed on the delivery catheter. The same can be said for screw  232  and threaded hole  236 . It should also be appreciated that key  228  and slot  234  can comprise any number of shapes, such as square, rectangle, triangle, pentagon, hexagon, cross, “X”, etc, so long as key  228  fits within and can apply rotational torque to slot  234 . 
         [0046]      FIG. 2D  is a schematic diagram of delivery catheter  210 , showing coaxial shafts  238  and  240  coupled to key  228  and screw  232 , respectively, and extending through the length of the catheter shaft  217 . Since shafts  238  and  240  are arranged in a coaxial configuration within catheter shaft  217 , the key  228  and screw  232  can be rotated independently from one another during implantation and/or removal of the biostimulator into tissue.  FIG. 2E  is a cross sectional view of  FIG. 2D  along line  2 E- 2 E, showing the relative positions and sizes of shafts  238  and  240  within the delivery catheter  210 . 
         [0047]      FIG. 2F  is a cutaway view of handle  212  of delivery catheter  210 , showing how coaxial shafts  238  and  240  (not shown because it is disposed within shaft  238 ) are connected to the handle. As shown in  FIG. 2F , shaft  238  runs from the distal end of the catheter shaft (from key  228  in  FIG. 2B ) and terminates at torque knob  224  in handle  212 . Similarly, shaft  240  (not shown in  FIG. 2F  because it is disposed coaxially within shaft  238 ) runs from the distal end of the catheter shaft (from screw  232  in  FIG. 2B ) and terminates at torque knob  222  in handle  212 . Rotation of torque knob  224  by a user, such as a physician, will cause rotation of shaft  238 . Similarly, rotation of torque knob  222  will cause rotation of shaft  240 . In addition,  FIG. 2F  shows deflection arm lock  242  and catheter strain relief  244 . Deflection arm lock  242  can be used to lock the distal portion of the delivery catheter in place when the catheter has been bent or steered using deflection arm  214 . Catheter strain relief  242  provides a smooth transition between the handle and the catheter shaft so as to prevent kinking at the junction between the shaft and handle. 
         [0048]    Referring to  FIGS. 2A-2F , it can now be understood how biostimulator  200  can be delivered and attached to tissue, and then released from delivery system  20 . In  FIGS. 2B-2C , docking cap  226  of delivery catheter  210  can be advanced over proximal end cap  230  of biostimulator  200  so that key  228  fits within and is mated to slot  234 . Screw  232  can then be inserted into hole  236  and attached to biostimulator  200  by rotating torque knob  222  (and thus rotating shaft  240  and screw  232 ) so as advance and engage the screw  232  into threaded hole  236 . When torque knob  222  is rotated to screw the delivery catheter into the biostimulator, torque knob  224  can be left alone (e.g., not rotated) so that key  228  engages and applies torque to slot  234 . 
         [0049]    Next, the biostimulator and delivery system can be inserted into the patient and advanced to the target location (e.g., the biostimulator can be advanced into the cardiac chamber) as known in the art. 
         [0050]    Upon reaching the target tissue, both torque knobs  222  and  224  can be rotated together to cause helix  202  of biostimulator  200  to engage and become inserted into tissue. By rotating the torque knobs together, both coaxial shafts  238  and  240  (and thus key  228  and screw  232 ) are rotated together, causing the biostimulator and helix  202  to rotate or screw into tissue. Once the helix is fully inserted into tissue, torque knob  224  can be held in place, and torque knob  222  can be unscrewed, causing screw  232  to disengage from threaded hole  236  of biostimulator  200 . Once the delivery catheter  210  is disengaged from the biostimulator, the catheter can be removed from the patient, leaving the biostimulator in place at the target tissue. 
         [0051]      FIG. 3A  illustrates a biostimulator delivery system  30  for delivery of a biostimulator  300  into a patient. The delivery system  30  can correspond to delivery system  20  of  FIGS. 2A-2F , so delivery catheter  310 , handle  312 , deflection arm  314 , sheath  316 , catheter shaft  317 , catheter flush port  318 , sheath flush port  320 , and torque knob  324  of  FIG. 3A  can correspond, respectively, to delivery catheter  210 , handle  212 , deflection arm  214 , sheath  216 , catheter shaft  217 , catheter flush port  218 , sheath flush port  220 , and torque knob  224  of  FIG. 2A . 
         [0052]      FIG. 3B  is a close-up view of a distal portion of delivery catheter  310  and biostimulator  300 . The biostimulator of  FIG. 3B  includes a helix  302  for attachment of the biostimulator to tissue as well as a secondary fixation mechanism or tether  346 . In some embodiments, the tether may be either a conductive or non-conductive material. As described above, a secondary fixation mechanism or tether can be used to provide a second point of attachment between the biostimulator and the patient. The delivery catheter can include a docking cap  326  having a slot  348  sized and configured to mate with a proximal end cap  330  disposed on the biostimulator. 
         [0053]      FIG. 3C  is another close-up view of the delivery catheter  310  and biostimulator  300  shown in  FIG. 3B , but from a different perspective to show the proximal portion of the biostimulator. As shown in  FIG. 3C , the proximal end cap  330  can be sized, shaped, and configured to mate with the slot  348  on catheter  310  (shown in  FIG. 3B ). Furthermore, the proximal end cap  330  can also be the point of attachment of tether  346  to the biostimulator  300 . In  FIGS. 3B-3C , proximal end cap  330  is shown as a “male” key and slot  348  is shown as a “female” key, but it should be understood that in other embodiments, the “male” key can be located on the delivery catheter, and the “female” key can be disposed on or in the proximal end cap. It should also be appreciated that proximal end cap  330  and slot  348  can comprise any number of shapes, such as square, rectangle, triangle, pentagon, hexagon, etc, so long as slot  348  fits around and can apply torque to proximal end cap  330 . 
         [0054]      FIG. 3D  is a schematic diagram of delivery catheter  310 , showing shaft  350  and tether  346  disposed within a lumen inside shaft  350 . Since shaft  350  and tether  346  are arranged in a coaxial configuration within catheter shaft  317 , the shaft  350  and slot  348  can be rotated independently from catheter shaft  317  and tether  346  during implantation and/or removal of the biostimulator into tissue.  FIG. 3E  is a cross sectional view of  FIG. 3D  along line  3 E- 3 E, showing the relative positions and sizes of shaft  350  and tether  346  within the delivery catheter  310 . 
         [0055]      FIG. 3F  is a cutaway view of handle  312  of delivery catheter  310 , showing how shaft  350  and tether  346  are connected to the handle  312 . As shown in  FIG. 3F , shaft  350  runs from the distal end of the catheter shaft (from key slot  348  in  FIG. 3B ) and terminates at torque knob  324 . Tether  346  runs from the biostimulator through the torque shaft  350  and extends beyond the proximal end of handle  312 . Tether  346  is moveable within the catheter and the handle. In one embodiment, tether lock  352  can comprise a pin and tether  346  can extend beyond the handle and wrap around tether lock  352  to hold the tether taut and in place during implantation and/or removal of the biostimulator. Rotation of torque knob  324  by a user, such as a physician, will cause rotation of shaft  350  and slot  348 . 
         [0056]    Referring to  FIGS. 3A-3F , it can now be understood how biostimulator  300  can be delivered and attached to tissue, and then released from delivery system  30 . In  FIGS. 3B-3C , docking cap  326  and slot  348  of delivery catheter  310  can be advanced over proximal end cap  330  of biostimulator  200  so that slot  348  fits over and is mated to end cap  330 . Tension can then be applied to tether  346  to pull and hold biostimulator  300  tight against and in contact with delivery catheter  310 . Referring to  FIG. 3F , the tether can be wound around tether lock  352  to hold tether  346 , and thus biostimulator  300 , in place on the delivery catheter. 
         [0057]    Next, the biostimulator and delivery system can be inserted into the patient and advanced to the target location (e.g., the biostimulator can be advanced into the cardiac chamber), as known in the art. 
         [0058]    Upon reaching the target tissue, torque knob  324  can be rotated to cause helix  302  of biostimulator  300  to engage and become inserted into tissue. By rotating the torque knob, shaft  350  causes slot  348  to engage and apply torque to proximal end cap  330 , forcing the helix to rotate and screw into tissue. Once the biostimulator is fully inserted into tissue, the tether can be removed from tether lock  352 , releasing the tension in tether  346  and causing biostimulator to be free to pull away from delivery catheter  310 . The delivery catheter  310  is free to be disengaged from the biostimulator, and the catheter can be removed from the patient over the tether, leaving the biostimulator in place at the target tissue. The tether  346  can then be attached to the desired tissue to provide a secondary anchor for the biostimulator. 
         [0059]      FIG. 3G  is a close-up view of a proximal portion of handle  312 , including torque knob  324 , shaft  350 , tether lock  352 , torque puck  354 , and tether tension springs  356 . During steering of the delivery catheter, the catheter foreshortens as it is deflected. The length of torque shaft  350  does not change since it is typically made of stainless steel tube and coil. To compensate for the length change between the catheter and the torque shaft during deflection, the distal tip of the torque shaft is fixed at the distal tip of the catheter and the proximal end of the torque shaft is allowed to float inside the handle. Torque puck  354  is attached to the proximal end of the torque shaft  350  to allow the torque shaft to move longitudinally during catheter deflection. The torque puck can include a keyed shape that allows it to move longitudinally but remain able to be rotated radially so as to turn the torque shaft (and thus the key at the distal end of the torque shaft). The tether tension springs can be attached to the tether to keep the tether under tension (and thereby keep the LCP docked to the tip of the delivery catheter) during delivery and navigation of the delivery catheter. 
         [0060]      FIG. 3H  is a close-up view of an alternative embodiment of a proximal portion of handle  312 , in which the tether lock  352  of  FIG. 3G  has been replaced with surface  358  and locking cam  360 . Instead of wrapping the tether around tether lock  352 , as described above, in the embodiment of  FIG. 3H  the tether  346  can be frictionally held in place between surface  358  and cam  360 . The locking cam can include a spring  368  and hinge  364  to cause locking cam  360  to apply a return force against the surface  358  and thus hold the tether in place. Pushing button  366  inwards towards the handle, as indicated by arrows  362 , can cause the locking cam to pivot on hinge  364  to release the tether. 
         [0061]    As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis, for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed.