Abstract:
An assembly includes a medical device provided with an anchoring member adapted to penetrate tissue of a cavity of the heart. The assembly further includes an implantation accessory including an elongated tubular element provided with a fastening mechanism for handling and guiding the medical device to an implantation site. The fastening mechanism includes an elastic deformable component cooperating with a rigid component, that is able to disconnect the medical device from the tubular element under the effect of a rotation exerted to the tubular element. The elastic deformable component cooperates with the rigid component such that the elastic deformable component exerts on the latter a radial constriction effect, and the elastic component and the rigid component being disconnected under the combined effect of a torsion torque and a traction exerted to the elastic deformable component, to thereby reduce the radial constriction until release of the rigid component.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to French Patent Application No. 1356021, filed Jun. 24, 2013. French Patent Application No. 1356021 is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The invention relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implants to continuously monitor heart rhythm and deliver, if necessary, electrical pulses to the heart for stimulation, resynchronization and/or defibrillation in case of rhythm disorder detected by the device. 
         [0003]    The invention relates, in general, to the in situ implantation of such devices provided at the distal end with an anchoring device adapted to penetrate the tissue of a body wall at the chosen implantation site. 
         [0004]    A typical example of such an anchoring member is a projecting helical screw axially extending from the medical device body and adapted to penetrate the heart tissue by a screwing motion at the implantation site. However, this anchoring arrangement is not limitative of the invention, which also applies to other types of anchoring members, for example by implementation of needles, hooks, barbs, etc., penetrating tissue for permanently fixing the medical device. 
         [0005]    According to a first aspect, the invention more particularly relates to those devices that are in the form of an autonomous capsule implanted in a heart chamber (ventricle, atrium or even arterial left heart chamber). The device will be hereinafter referred to as “autonomous capsule” or “leadless capsule” (the autonomous character of the capsule, albeit not intrinsically, being a necessary feature of the invention). These autonomous capsules are devoid of any physical connection to a main implanted device (such as the housing of a stimulation pulse generator) or not implanted device (external device such as a programmer or monitoring device for remote monitoring of the patient). Accordingly, the capsules are referred to as “leadless capsules”, to distinguish them from electrodes or sensors located at the distal end of a conventional lead, which is traversed throughout its length with one or more conductors galvanically connecting the electrode or sensor to a connected generator at an opposite, proximal, end to the lead. 
         [0006]    It will be seen that, according to a second aspect, the invention can be generalized to the “delivery”. That is to say the implantation in the selected site of implantation of other types of medical devices. In one example, such devices may be stimulation leads in the form of a tubular body having at its distal end an anchoring mechanism for anchoring to a heart wall and an active portion provided with detection/stimulation electrodes, and at its proximal end, mechanical and electrical connection to the housing of a generator that is remotely implanted from the site of application of the pulses. The invention can be applied to still other types of implantable devices, for example to capsules intended for release in situ of an active pharmacological agent. 
         [0007]    When the leadless capsules are endocardial capsules (capsules attached to the inner wall of an atrial or ventricular chamber, as opposed to epicardial capsules fixed to the external wall of the heart), the implantation constraints are increased because of the surgery approach. The approach for endocardial implantation involves going through the peripheral venous system and directs, under image intensifier, the capsule to the selected implantation site. This in a both precise and perfectly secure method. It is only once the site is reached and the capsule is firmly attached in the heart wall that the operator may proceed to the “release” of the capsule, or more particularly, its disconnection from the implantation accessory. 
         [0008]    U.S. 2012/0095539 A1 discloses an implantation accessory for an endocardial electrostimulation leadless capsule. This accessory includes a steerable catheter carrying the capsule. The steerable catheter houses in its inner lumen at its end a wire which is distally connected to the capsule and which is operable in translation and rotation from the proximal end by a handle provided for the practitioner. In a first embodiment, the capsule is mounted to the catheter tip by a system of male/female nesting and the wire end is screwed to the back of the capsule. The retention wire keeps the two elements of the coupling system fitted into each other by a slight tension on the wire, the latter being locked in translation in the manipulation handle. In a second embodiment, the wire remains attached to the capsule after it has been separated from the catheter, so as to act as a safety wire in case it is necessary to reoperate on the capsule after implantation. 
         [0009]    EP 2394695 A1 (Sorin CRM SAS) discloses another autonomous intracardiac capsule assembly with an implantation accessory. The capsule holds on the sidewall of the tubular body coupling fingers cooperating with a helical guide carried by the distal end of the implantation accessory. The direction of helix of the helical guide is opposite to that of the anchoring screw of the capsule, so as to transmit the screwing torque of the anchoring screw in the heart wall. Then after the front face of the capsule is coming to bear against this wall, the progressive separation of the capsule with the implantation accessory occurs by further screwing of the catheter causing the coupling fingers to slide between the turns of a helical compression spring. The torque limiter effect is thus being obtained by the compression of this helical spring. 
         [0010]    The acceptance by practitioners of the technique of endocardial leadless capsules involves being able to offer a delivery system that is able to secure the implementation of these capsules in meeting all of the following requirements:
       Procedure similar to the current practice, which makes use of well-known and mastered practitioners gestures: subclavian or femoral puncture, insertion and manipulation of a catheter via preformed stylets during the approach phase of the selected implantation site, fastening of the screw or barb type, catheter manipulation of the electrophysiology type, etc.;   Standard environment of the operating room;   Limiting the risk of coring of the tissues due to excessive tightening which may damage the wall or worse, puncture it (especially in the case of implantation into a thin wall as the atrial septum or the apical region the right ventricle);   Possibility of intraoperatively or postoperatively removing and/or repositioning in case of problems, even after release of the capsule;   No risk of migration of the capsule during the acute phase response;   Certainty of a good fixation of the capsule before removing the implantation accessories, this constraint being the most critical of all;   System natively designed for a femoral approach (see below);   For vessels and heart chambers, no risk of damage by the anchoring member (screw, hook, needle, etc.) throughout the implantation method, including the navigation in the venous network and the approach phase to the selected implantation site;   Quick procedure, with an implantation target time of approximately 30 minutes ‘skin-to-skin’, comparable to that of the implantation of a generator and a conventional ventricular lead;   Safe operation, including in the case of: i) improper handling, with in this case inability to jettison the capsule if screwing of the anchoring member is incomplete, and/or ability to recover the capsule during the procedure, and ii) premature discontinuation of the procedure;   Low cost of manufacturing of the complete implantation system, notably through the use of proven technologies and components in similar applications.       
 
         [0022]    A further difficulty arises with the current leadless capsules due to their relatively large dimensions, with a typical diameter of about 4-7 mm and a length of 15-40 mm. Indeed, to reach a heart chamber, and in particular to reach the apex of the right ventricle, with an object of this size there is no routine procedure by high approach, that is to say via the subclavian vein. It is therefore necessary to use a different approach, from a femoral puncture then to go back in the inferior vena cava to the heart. 
         [0023]    Such a femoral approach is recognized as more difficult, especially because of the large angle between the inferior vena cava and the axis of the right ventricle. Indeed, in the case of a high approach, at the arrival in the atrium, the distal portion of the implantation catheter is naturally oriented towards the apex of the right ventricle. At this point, one just has to push the catheter through the tricuspid valve and reach the bottom of the ventricle, wherein the anchoring member may be screwed to the wall after landing. However, in the case of a femoral approach, once the atrium is reached it is necessary to perform a turning maneuver of the distal end of the catheter to guide the latter towards the ventricle and allow it to pass through the tricuspid valve and continue to progress in the right direction, towards the apex of the ventricle. 
         [0024]    For this purpose, well-known steerable catheters exist, the tip of which is operated from the proximal handle so that it can perform such a reorientation maneuver in the atrium under image intensifier. But a final challenge remains in the final approach phase, as part of the steerable catheter may be too short or poorly shaped to allow docking with the wall of the ventricular apex. 
         [0025]    There is therefore the need to have an implantation accessory for fine adjustment and precise approach of the implantation site with large differences in myocardium anatomy. 
       SUMMARY 
       [0026]    The invention discloses, in a first aspect, to use a steerable catheter and to extend it distally by a projecting cylindrical tip containing the capsule to be implanted. This capsule is maintained in the retracted position in the tip via a sub-catheter inserted into the inner lumen of the first catheter, the capsule and the sub-catheter being temporarily linked by a single disconnectable mechanism fixed on the sub-catheter and allowing a complete screwing of the capsule in the tissue before release. The telescopic configuration of the sub-catheter allows projecting the capsule out of the protection tip and beyond the latter on several centimeters, permitting in all cases a complete and accurate approach of the capsule to the bottom of the ventricle. 
         [0027]    According to a second, more general, aspect the invention discloses a simple switchable mechanism provided between a implantation accessory and a medical device (corresponding, respectively, to the sub-catheter and to the leadless capsule in the previous particular case). This mechanism may include of an elastic deformable component used in radial compression, that is to say for its pinch effect and not for its axial tensile/compression effect. Such an elastic component may be a coil spring, and can play both the role of a releasable connection and of torque limiter against excessive tightening action which could result in a coring of the tissues. 
         [0028]    More specifically, according to the aforementioned first aspect, the invention discloses a set of intracardiac capsules with its in situ implantation accessory. This disclosure describes an autonomous capsule with a cylindrical tubular body provided at its distal end by an anchoring member adapted to penetrate a tissue wall of a cavity of the heart, and an implantation accessory of this capsule. The implantation accessory includes a catheter with an inner lumen, extended at its distal end by a tubular protection tip defining an interior volume capable of housing the capsule, and disconnectable mechanisms for supporting and guiding the capsule to the implantation site. 
         [0029]    The catheter is a remotely steerable catheter. The implantation accessory further includes a sub-catheter housed within the lumen of the remotely steerable catheter, and having a degree of freedom in translation and a degree of freedom in rotation relative to the remotely steerable catheter. The sub-catheter and the capsule are telescopically extendable with respect to the remotely steerable catheter between i) a retracted position wherein the capsule and its anchoring member are completely housed inside the tubular protection tip, and ii) a position wherein the capsule is deployed out of the tubular protection tip and is carried by the distal end of sub-catheter. Finally, the distal end of the sub-catheter and the proximal region of the capsule are provided with a first fastening mechanism for mutually securing in translation and in rotation. The fastening mechanism may be disconnectable under the effect of a rotation applied to the sub-catheter from the proximal end thereof. 
         [0030]    In a preferred embodiment, the implantation accessory further includes a retaining wire housed in a lumen of the sub-catheter that links the capsule to the proximal end of the sub-catheter. The retaining wire is movable within the lumen of the catheter so as to allow removal of the latter, thereby leaving the capsule and the retaining wire in place. The proximal region of the capsule and the distal end of the retaining wire are provided with a second disconnectable fastening mechanism for securing in translation and in mutual rotation. 
         [0031]    The retention wire may be a particular wire adapted to transmit rotational torque from its proximal end to its distal end, and the second fastening mechanism includes a rotational connection separable under the effect of said torque applied to the retaining wire, including a threaded element formed at the distal end of the retaining wire and cooperating with a threaded part formed at the proximal end of the capsule, or vice versa. 
         [0032]    In a preferred embodiment, the first disconnectable fastening mechanism includes a deformable elastic component, such as a helical spring which cooperates with a rigid object, such as a central core on the capsule. The spring extends around the core such that it exerts on the latter a radial constriction effect, the spring and the core being configured to be disengaged under the effect of a torque applied to the spring at one end thereof, having the effect to reduce said radial constriction to release the core. 
         [0033]    Preferably, the proximal end of the spring is secured to the distal end of the sub-catheter. The distal end of the spring is preferably free. The core is preferably an axial lashing rod carried by the proximal end of the capsule and secured in rotation with the latter. 
         [0034]    When the capsule includes an anchoring screw, the direction of the coil spring is the same as that of the anchoring screw. The value of the torque applied to the spring that is effective to reduce said radial constriction to release of the core is determined. This torque value depends on the geometry of the spring and of the elasticity of the material which constitutes it, so as to be always lower that a predetermined limit value that is corresponding to a limit holding torque of the anchoring screw in the tissue of the implantation site, without coring of this tissue. 
         [0035]    Furthermore, to allow the introduction of the assembly, it is possible to use a guidewire. In such embodiments, the protection tip then includes in the thickness of its peripheral wall a lateral lumen extending axially and opening at both the distal and proximal sides of the tip. This lumen being adapted to receive the guidewire and to allow the sliding thereon of the implantation accessory with the capsule housed in the protection tip. Finally, the protection tip preferably has at least one vent hole, and at least one radiopaque marker. 
         [0036]    According to an exemplary embodiment, a medical device may include, at its distal end, an anchoring member capable penetrating a tissue wall of a body, and an in situ implantation accessory of the medical device. The implantation accessory according to the present invention includes a deformable elongate tubular member having a disconnectable mechanism for support of the medical device and guiding of the medical device to a site of implantation. The disconnectable mechanism includes a helical spring cooperate with a central core and is suitable for securing in translational and in mutual rotation the tubular element of the implantation accessory and the medical device, and able to decouple the medical device with the tubular member of the implantation accessory under the effect of a rotation applied to the tubular member from the proximal end thereof. 
         [0037]    Typically, the spring extends around the core with an adjustment such that it exerts on the latter a radial constriction effect, the spring and the core being capable of disengagement under the effect of a combined torque and traction applied to the spring at one end thereof, being effective to reduce said radial constriction to release the core. 
         [0038]    Preferably, the proximal end of the spring is secured to the distal end of the tubular member of the implantation accessory, the distal end of the spring is free, and the core is an axial lashing rod carried by a proximal end of the medical device and secured in rotation to the latter. 
         [0039]    When the medical device bears an anchoring screw, the direction of the coil spring is the same as that of the anchoring screw. The value of said torque applied to the spring that is effective to reduce said radial constriction to release of the core is determined. The torque value depends on the geometry of the spring and the elasticity of the material which constitutes it, so as to be always lower to a predetermined limit value, corresponding to a holding torque limit of the anchoring screw in the tissue of the implantation site, without coring of this tissue. Finally, the distal end of the spring is advantageously a rounded end. 
         [0040]    According to another aspect of the invention, a method for implanting a medical device includes introducing a medical device provided at its distal end with an anchoring member adapted to penetrate tissue of a wall of a cavity of a heart to a target location in a cavity of the heart, wherein a proximal end of the medical device is coupled to a distal end of an elongated tubular element with a fastening mechanism. The fastening mechanism comprises an elastic deformable component cooperating with a rigid component. The method further includes rotating the elongated tubular element to cause rotation of the medical device and engage the anchoring member with the tissue of the cavity of the heart to implant the anchoring member into the tissue. After implantation, rotation of the elongated tubular element is continued in the same direction so as to generate an excess torque to thereby release the fastening mechanism and decouple the elongated tubular member from the medical device. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0041]      FIG. 1  illustrates the implantation accessory of the invention and its capsule, in position, with a schematic representation of the femoral approach and of the chambers of the heart. 
           [0042]      FIG. 2  shows the distal end of a remotely steerable catheter provided with its protection tip, in the retracted position of the leadless capsule. 
           [0043]      FIG. 3  is an enlarged, sectional view of  FIG. 2 , showing the general configuration of the various internal elements and the leadless capsule housed inside the protection tip. 
           [0044]      FIG. 4  is an enlarged view of the sectional view of  FIG. 3 , in the region of the connection with the proximal end of the leadless capsule. 
           [0045]      FIG. 5  separately shows the radial compression coil spring mounted on the end of the sub-catheter. 
           [0046]      FIG. 6  is a sectional view corresponding to  FIG. 5 . 
           [0047]      FIG. 7A  is a sectional view showing a socket of a hollow cylinder housing a lamella. 
           [0048]      FIG. 7B  is a sectional view corresponding to  FIG. 7A . 
           [0049]      FIG. 7C  is a sectional view of a non-deformable axis inserted into the hollow cylinder housing of  FIG. 7A . 
           [0050]      FIG. 7D  is a sectional view corresponding to  FIG. 7C . 
           [0051]      FIG. 8  shows the distal end of the remotely steerable catheter provided with its protection tip mounted on a coiled guidewire used to advance this tip from the femoral puncture until the selected implantation site. 
           [0052]      FIG. 9  shows the distal end of the remotely steerable catheter provided with its protection tip, with the leadless capsule partially emerged of this tip. 
           [0053]      FIG. 10  is an enlarged, sectional view of  FIG. 9 , showing the general configuration of the different internal elements. 
           [0054]      FIG. 11  is an enlarged and sectional homologous view of  FIG. 10 , once the capsule is implanted in the chosen site, after removal of the sub-catheter and with the retaining wire still in place. 
           [0055]      FIG. 12  shows the final configuration of the capsule and the implantation accessory in the situation corresponding to that of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0056]    An exemplary embodiment of the device of the invention will now be described.  FIG. 1  illustrates a schematic representation of the femoral access route and the chambers of the heart, and depicting the implantation accessory according to the present invention bearing an autonomous capsule of the leadless type  10 . 
         [0057]    Such a leadless capsule (shown in more detail in particular in  FIG. 11 ) includes a tubular body  12  provided at one of its ends with a projecting helical anchoring screw  14  axially extending from the tubular body and integral with it in rotation. The anchoring screw  14  includes in its distal portion a length of the order of 1.5 to 2 mm of non-contiguous turns, adapted to penetrate the heart tissue so as to secure the capsule there. The screw  14  can be an electrically active screw, comprising the detection/stimulation electrode at least at its distal end, or it can be a passive screw serving only to the anchoring of tubular body  12  in the wall of the heart chamber. In the latter case, the capsule is provided with an axial conductive needle  16  acting as a detection/stimulation electrode in contact with the myocardial tissue. Alternatively, it is also possible to provide a surface electrode. 
         [0058]    The tubular body  12  includes various power supply circuits and methods for signal processing and wireless communication for the exchange of signals with a remote master device, implanted or not. These aspects are in themselves known, and since they are not part of the invention, they will not be described. 
         [0059]    At its proximal end  18 , the tubular body  12  of the capsule  10  includes an axial lashing rod  20  with a rounded end, the function of which will be described later in the implantation procedure. This lashing rod  20  is smooth on its outer face and has an internal threaded axial hole, a structure which will be explained in more detail with the description of  FIG. 4  below. 
         [0060]    The leadless capsule  10  is intended to be implanted in the right ventricle  22 , especially at the bottom of the ventricle, in the region of the apex  24 . For a conventional stimulation lead (connected to a remote generator), the location would typically be performed via the subclavian vein  26 , as illustrated in dashed lines at  28 , so that the end of the lead would be approximately oriented in the ΔRV axis of the right ventricle and thus could easily pass through the tricuspid valve and reach the apex of the ventricle  24 . However, as mentioned in the introduction, this implantation approach is not feasible for implantation of leadless capsules, the dimensions and, in particular, the external diameter, being far superior to those of the head of a conventional lead. 
         [0061]    It is therefore necessary to access, via the vena cava  30 , from a femoral puncture  32 . But in this case, the axis of approach, that is to say the ΔVC axis of the vena cava, has a strong angulation (angle  34 ) with the axis ΔRV of the right ventricle. Therefore, it is necessary to form a curvature  36  at the right atrium  38  in order to pass the implantation accessory emerging from the sinus  40  of the vena cava to the tricuspid valve  42  to then reach the cavity  22  of the right ventricle. Similar difficulties arise for implantation into the left ventricle, the implantation access then involving an arterial femoral puncture and the passage of the aortic arch. 
         [0062]    Such a maneuver can be performed through a “steerable” catheter, with a catheter tube  44  handled from the proximal end by an operating handle  46  available to the practitioner. Using the handles  48 ,  48 ′ the latter can create and adjust a curvature  50  to guide the distal end  52  of catheter  44  accurately, typically with an orientation up to  180 ° in both directions with a variable radius of curvature, of the order of 5 to 60 cm. The handle  46  is also provided with a purge drain lateral track  54  and of a valve  56 , features which are in themselves entirely conventional. 
         [0063]    With a conventional steerable catheter, if it is possible to precisely adjust the curvature  50 , it is not possible to change the area of the catheter wherein, along its length, the curvature is formed. However, in the particular case illustrated with a femoral approach, with the objective of reaching the bottom of the right ventricle, this limitation can be troublesome with some specific morphologies with very elongated cavity. Indeed, the distal portion  52  of the steerable catheter located beyond the curvature of the region  50  may be too short to reach the region of the apex  24 . Embodiments of the present invention address this difficulty, as will be explained hereinafter, so that the implementation of the invention is possible using a marketed, pre-existing, steerable conventional catheter to reduce the cost of the implantation accessory of the invention. 
         [0064]      FIGS. 2 to 4  show, in enlarged views, the distal end of the steerable catheter  44 , with the different characteristic elements of the invention. The steerable catheter  44  is provided at its distal end with a tubular protection tip  58  having a central recess  60  ( FIG. 3 ) for housing the capsule  10  in a configuration called “retracted position”, corresponding to  FIGS. 2-4 . The main function of the tip  58  is to protect the capsule, including the anchoring screw  14 , during the intravenous passage of curves, angulations, valves, etc. Conversely, the cap protects the tissue from the risk of stripping potentially caused by the movement of translation of the screw. 
         [0065]    The outer diameter of the steerable catheter  44  is typically between 10 and 15 French (6.6 to 10 mm), for an inner lumen diameter of between 8 and 12 French (2.66 mm to 4 mm). The tubular tip  58  must be able to house the capsule and therefore have an inside diameter of about 21 French (7 mm). Furthermore, a catheter of this size must necessarily move into the venous system while being guided by a coiled guidewire previously introduced into the vasculature. 
         [0066]    As in the illustrated design, the central canal of the catheter  44  is blocked by the capsule. To allow the introduction of a guidewire, the tubular tip is provided with an eccentric lateral lumen  62  extending axially the length of the tip and opening at the distal  64  and proximal  66  sides, preferably extending over the entire length of the tip  58 . The inner diameter of the lateral lumen  62  allows for the introduction of a conventional coiled guidewire of a diameter of 3 French (1 mm), and the sliding of the tip, and therefore of the entire steerable catheter  44 , through the vasculature (this configuration is notably shown in  FIG. 8 , wherein the reference  98  designates the coiled guidewire). Alternatively, the eccentric lateral lumen  62  may be extended along the body of the steerable catheter  44  to facilitate the pushing of the coiled guidewire and prevent any curling phenomenon thereof. 
         [0067]    Note that the eccentricity of the lumen  62  combined to the beveled profile of the tip allows easy progression into the venous system by a “sidewire” technique. In addition, the front panel  68 , the most distal area of the tip  58 , is shaped to have a minimum front bearing surface to avoid any risk of perforation in case of accidental operation without the coiled guide. 
         [0068]    In addition, a radiopaque marker  70  is provided in front of the tubular tip  58  on the most distal surface of this tip, to more efficiently identify the capsule outlet if the tip is made of a radio-transparent material. Finally, one or more drain holes  72  are disposed proximal to the tip, to prevent piston effect upon injection of contrast medium, which otherwise would result in pushing the capsule  10  out of the protection tip  58 . 
         [0069]    The catheter  44  is formed with a reinforced structure, such as a wire mesh or a coil embedded in the thickness of the catheter wall, so as to provide a torque transmission capability exerted on the proximal handle to the distal end (reinforced structure  74 ). 
         [0070]    The implantation accessory of the invention further includes, typically, a sub-catheter  76 , introduced into the central lumen of the steerable catheter  44 , and movable in rotation and in translation relative to the latter. The function of this sub-catheter  76  is to ensure the deployment of the capsule out of the protection tip and to advance the capsule to the implant site by a translation movement over a sufficient length, typically from to 2 to 6 cm depending on the anatomy of the patient. In the figure, arrow  78  indicates the translation of the sub-catheter  76  within the steerable catheter  44 , and arrow  80  indicates the translation of the capsule  10  out of the protection tip  58 . The sub-catheter  76  also has the function of ensuring the transmission of torque from the proximal end (at the operating handle) to its distal end, and is provided for this purpose of a reinforced structure  82 . 
         [0071]    It is possible to use as the sub-catheter  76  a conventional guide catheter sized from 4 to 6 French (1.33 to 2 mm), which is an existing, simple and cost-saving device meeting the current constraints torque transmission, low coefficient of friction inside and outside, flexibility, etc. Sub-catheter  76  may have a proximal “Luer-Lok” connection for the rapid mounting of a multifunction adapter such as a rotational hemostasis valve or other adapter compatible with this sealed connection standard. Alternatively, the sub-catheter  76  can be used to inject a contrast to the back of the capsule  10  so as to accurately monitor the operation under fluoroscopy. 
         [0072]    A fastening mechanism according to the present invention is directed to the coupling of an implantation device including a hollow or not elongated tubular member (such as a catheter) with an autonomous (such as a leadless capsule) or not (such a probe head of a pacing lead) medical device, said device being provided at its distal end with an anchoring mechanism adapted to penetrate a cardiac or else body tissue. The fastening mechanism according to the invention employs an elastic deformable component, such as helical spring  84 , which is not used for its properties of elasticity in axial traction/compression (effect resulting from the elongation or the reconciliation of the coils of the spring), but for its radial compression properties, that is to say for the pinch or throttle effect can such a spring can exert around a rigid component, such as a core inserted into the helical form. In other embodiments, the elastic deformable component may be a lamella that provides radial compression about the core. 
         [0073]    The geometry of the elastic deformable component, such as a spring, and the elasticity of the material which constitutes it are chosen so as to produce between the elastic component and the core, in the absence of external stress, an interference fit (caused by the radial compression resulting from the pinch effect). In the illustrated example of  FIG. 4  of the leadless capsule  10 , the core is constituted by the lashing rod  20  with rounded end, located axially on the proximal portion  18  of the capsule  10  and outwardly oriented. This lashing rod  20  may be shaped to optimize the disengagement function. 
         [0074]    The spring  84  is shown in detail and in isolation in  FIGS. 5 and 6 . The spring  84  is secured to the distal end of the sub-catheter  76  by turns  86 . This securing in translation and in rotation, for example by welding or gluing, must be kept regardless of the degree of stress normally applied to the sub-catheter  76  and to the spring  84 . 
         [0075]    The turns  88  located distally of the spring  84  are free turns, which are surrounding the lashing rod  20  but which are not mechanically fastened to the latter by connection mechanisms other than interference fit with tightening obtained in the static configuration of these two elements. In addition, the distal end of the spring  84  is preferably a rounded end to prevent tissue injury and hang at various manipulations. The inactive turns  86  and/or the active turns  88  may be either touching or not contiguous. 
         [0076]    Once the capsule  10  is fixed to the implant after complete penetration of the anchoring screw  14  to the front face of the capsule, the practitioner continues to make the sub-catheter  76  turn, thereby generating an excess torque. The excess torque has the effect of reducing the force exerted by the free turns  88  on the lashing rod  20 , to cause rotational sliding of these turns on this same rod. By combining this rotational movement to a slight tensile load, the compression spring  84  is released from the lashing rod  20 , by longitudinal sliding of the turns on the rod, thus releasing the capsule  10  from the spring  84 , and thus from the sub-catheter  76 . 
         [0077]    In an alternative embodiment of the first fastening mechanism, shown in  FIGS. 7A-7D , the deformable plastic member is a lamella  184  that is positioned in a socket created by a hollow cylinder  186 . The lamella  184  is radially deformable relative to the cylinder axis. The rigid component is provided in the form of a non-deformable plug element  188  configured to be introduced into the socket of the hollow cylinder  186 . The introduction causes deformation of the lamella  184 , thereby producing a radial force between the plug element  188  and the lamella  184 , as shown in  7 D. Relative rotational movement between the hollow cylinder  186  and the plug element  188  generates a tangential calibrated friction and therefore creates a limitation in the torque applied to the components of the system. 
         [0078]    The radial compression spring  84  or lamella  184  thus act as torque limiter. Indeed, with the anchoring screw of a standard leadless capsule, if the practitioner continued rotation of the sub-catheter  76  and therefore of the capsule  10 , the torque would increase and exceed a limit C coring . This increases the risk of the anchoring screw locally tearing the tissues under the effect of the rotation of the screw advance thereof, causing a tearing of the tissues and, in the extreme, a perforation of the wall, with the risk of tamponade. This is not the case with the device and methods provided by the invention. The practitioner may indeed safely continue rotating the sub-catheter  76 , always in the same direction (usually clockwise), because the extra torque due to the reaction of the anchoring screw anchored in the tissue is absorbed by the connection between, for example, the spring  84  and the lashing rod  20  (phenomenon of sudden increase of the torque when the front face of the capsule contacts the cardiac tissue). More specifically, the geometry and elasticity of the spring  84  are chosen so as to define a predefined torque C release  lower to the coring limit, C coring , corresponding to a limit holding torque of the anchoring screw in this tissue, without coring of the tissue, while providing a full screw (tissue contacting the front face of the capsule). Thus, when the C release  torque is reached, the further rotation of the sub-catheter  76  in the clockwise direction causes, in combination with a slight traction force, the gradual release of the spring  84  with the lashing rod  20  by longitudinal sliding of the turns of the radial spring along the rod. In case of any excess torque, the turns of the radial spring slide in rotation on the securement ring therefore no longer transmit torque elevation. The clutch release torque C release  is adjusted to a typical value of about 0.01 to 0.05 N·cm. 
         [0079]    Furthermore, in a static configuration, the pinch force of the free portion  88  of the spring  84  on the lashing rod  20  is selected so as to prevent accidental disassembly by a traction force (axially directed force) lower to a sufficient threshold, typically a threshold which provides holding even for a traction exerted on the sub-catheter  76  under a force of up to 20 N. 
         [0080]    Note also that if it is desirable to unscrew the capsule, for example because after a first implantation it is found that the electrical performance of the site are not satisfactory, the coupling system by the spring  84  will have no release effect during unscrewing. Since the spring will then be driven in reverse rotation (usually counterclockwise), this will further increase the effect of the tightening of the turns  88  of the lashing rod  20 . 
         [0081]    Another advantage of the spring  84  is after the release of the capsule, the implantation device is present with a screw at its end in the form illustrated in  FIGS. 5 and 6 . In particular, the free turns  88  of the spring  84  form a screw. In case of reoperation intraoperative, that is to say, if it is desirable to secure the new sub-catheter  76  to the capsule, the screw formed by the spring  84  will have the advantage of requiring no angular adjustment to secure the lashing rod  20  of the capsule to be retrieved (unlike the systems using a male/female connector which require positioning to allow the interlocking of the two elements). 
         [0082]    Finally, note that the torque limiter comprising spring  84  is conveniently located in the chain of transmission of forces. Specifically, any loss of fidelity in the transmission of torque between the proximal end of the sub-catheter  76  (that is to say from the handle manipulated by the practitioner) and its distal end (the location of the coupling spring  84 ) has no effect on the maximum or minimum torque at the interface between the anchoring screw and the tissue, which is a guarantee of complete fixation. This is not the case for a detachable system that would be located further upstream, typically in the operating handle  46 . Note also that all of these features are obtained via a very economical component of very simple and compact design. 
         [0083]    The release of the capsule may thus be effected by a combined screwing and traction movement in two steps. First, screwing of the capsule in the heart wall, by clockwise rotation of the sub-catheter  76  (e.g. 10 rpm) under a slight push. Second, release of the capsule by a further clockwise rotation of the sub-catheter  76  (e.g. 5 turns) under slight tension to allow removal of the sub-catheter after release of the spring  84 . To obtain this result, the direction of the turns of the spring is of course selected in the same direction as that of the anchoring screw, preferably with a right-engaging thread, so that the screwing of the capsule and then its release correspond to a rotation of the sub-catheter  76  in the clockwise direction, the most conventional one. 
         [0084]    Advantageously, the implantation kit also includes a security thread or retainer  90  of “breadcrumb” wire-type connected to the capsule  10  on the distal side, extending over the entire length of the sub-catheter  76  and exceeding it proximally, that is to say on the side of the operating handle  46 . 
         [0085]    As shown in  FIGS. 11 and 12 , once the capsule  10  is implanted and dropped, its operation is tested, including the establishment of good wireless communication between the capsule and the remote master device as well as the stimulation electrical performance. 
         [0086]    Once the steerable catheter  44  and the sub-catheter  76  are completely removed, the retaining wire allows for intraoperatively retrieving the capsule, with reintroduction of the implantation accessory by making it slide along the retaining wire until the protection tip  58  caps the capsule. The latter can then be re-coupled to the sub-catheter by a clockwise rotation (the clutch-limiter functionality being always effective). The capsule can then be unscrewed from the wall  100  by a counterclockwise rotation and repositioned at another site by the same principle as what has been described above, by a clockwise rotation of the sub-catheter. 
         [0087]    The retaining wire is for example a wire of 1 French diameter (0.43 mm) having at its distal end  92  a thread  94  able to cooperate with a mating internal thread  96  formed in a threaded axial bore of the stowage axis  20  ( FIG. 4 ). This retaining wire is preferably sufficiently flexible in its distal part (6 to 8 cm), while being able to transmit to the distal end  92  an unscrewing torque resulting from a rotation exerted from the proximal end, at the operating handle. Note that, because of the very small diameter of the screwing system  94 ,  96 , the torque to be exerted to produce the unscrewing is very small (of the order of 0.02 N·cm), and may not in any way exert trigger a rotation movement of the capsule  10  which is firmly secured to the heart wall by the anchoring screw. The retention wire may be colored in different colors for each of the implanted capsules, so as to more easily identify the appropriate capsule in the event of reoperation. 
         [0088]    The technique of the invention therefore provides triple security through the release system which allows at the release of the capsule:
       To ensure complete screwing of the capsule in the tissue;   To prevent coring of the heart wall; and   To ensure the practitioner to recover the capsule after dropping in case of difficulty, through the retaining wire.       
 
         [0092]    The procedure for setting up the leadless capsule through the implantation accessory as described above comprises the following steps, each of which is relatively conventional and can be easily performed by a practitioner without requiring special skills or additional maneuvers:
       Right or left femoral puncture, in order to access the inferior vena cava  30 ;   Optional percutaneous introduction of a 23 French haemostatic introducer (7.66 mm);   Insertion of the steerable catheter  44  on a spiral guidewire (illustrated at  98  in  FIG. 8 ), typically a 3 French (1 mm) guidewire on which the tubular tip  58 , and thus the steerable catheter  44  will slide and move to the right atrium  38 ;   Turning maneuver of the tip of the steerable catheter  44  (as shown at  36  in  FIG. 1 ) and introduction of the tip  58  in the right ventricle;   Release of the capsule  10  to the apex of the ventricle by translation of the sub-catheter  76  in the steerable catheter  44  (configuration shown in  FIG. 10 );   Visualization of the cardiac walls by injection of contrast medium through the sub-catheter;   Fine positioning of the capsule to the selected target site, with the possibility of translation once in the cardiac cavity by a more or less important deployment of the sub-catheter  76  from the steerable catheter  44 , allowing fine adjustment to suit a wide variety of anatomies;   Screwing of the capsule in the heart wall to the release of the radial compression spring  84 ;   Separation of the sub-catheter  76  with the capsule  10 , and removing of the sub-catheter  76  out of the steerable catheter  44  (configuration shown in  FIG. 11 );   Electrical test of the capsule;   Complete removal of steerable catheter  44  and of the sub-catheter  76 ;   Final release of the capsule, with withdrawal of the retaining wire  90  by low torque unscrewing; and   Closure of the puncture site.