Abstract:
The invention relates to an implantable capsule, particularly an autonomous capsule of cardiac stimulation, including a tubular body provided at the distal end of an anchoring element with a helical screw adapted to penetrate tissue a wall of an organ of a patient, the body housing a set of functional elements of the capsule. It includes, in an annular area surrounding the base of the screw recessed arrangements defining a set of flush tips oriented in a circumferential direction opposite to that of the screwing, to avoid the unscrewing of the capsule.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of and priority to French Patent Application No. 1455896, filed Jun. 25, 2014, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     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 to devices that continuously monitor heart rhythm and deliver to the heart if necessary stimulation, resynchronization and/or defibrillation pulses in cases of arrhythmia detected by the device. 
     The invention relates especially, but is not limited to, those devices that are in the form of an autonomous capsule intended to be implanted in a heart chamber (atrium or ventricle, right or left). These capsules are free of any mechanical connection to an implantable (such as a housing of the stimulation pulse generator) or non-implantable (external device such as programmer or monitoring device for patient remote monitoring) main device. For this reason they are called “leadless capsules” to distinguish them from electrodes or sensors disposed at the distal end of a conventional probe (lead), which is traversed throughout its length by one or more conductors connecting the electrode or sensor to a generator connected to an opposite, proximal end of the lead. 
     EP 2394695 A1 (Sorin CRM),now EP 2394695 B1, describes an autonomous intracardiac capsule, and a method to implant it to the selected detection/stimulation site and reposition it if necessary. 
     Note, however, as will be understood by reading the description, that the autonomous nature of the capsule is not inherently a necessary feature of the invention, and that the latter can be both applied to capsules permanently mounted at the distal end of a lead. 
     An implantable capsule includes a body housing the main components of the device (electronic circuits, power source, stimulation electrodes, etc.) and a base secured to the body and rigidly supporting methods for fixing to the wall. 
     In the case of cardiac leads, two types of fasteners are known and conventionally employed: fixation with “barbs” is the oldest and is still used marginally, but the leads based on a fixing screw have supplanted barb leads and currently represent the majority of the market. They allow a generally robust and effective fixation. 
     The screw is a projecting helical screw extending axially the capsule body and adapted to penetrate the heart tissue by screwing in the implantation site, in the same method as the conventional screw leads. 
     However, the fixing of such devices is still a critical point to the extent that accidental detachment of the capsule would cause the latter to be released into the heart chamber and then transported by the blood in the venous or arterial system. Complication risk to the patient would be extremely high, as well as the risk of cardiac system injury which can be generated by the end of the fastening system or other projecting regions of the implant such as a needle electrode or a projecting ridge. 
     More than a lead device, an autonomous device undergoes stresses and movements generated by the heart wall, as it does not benefit from the axial holding force from the lead body. 
     To fulfill its permanent anchoring function, the fastening system must also include a function of irreversibility. That is to say it can be removed from the heart wall only by the doctor&#39;s voluntary action and according to a predefined method, but in no case by repeated movements or vibrations of the heart, or by modification of heart muscle due to the disease or tissue aging. 
     WO 2012/051235 A1 discloses reverse rotation prevention methods which implement arrangements with protruding spikes formed directly on the screw and oriented in an opposite circumferential direction to the direction of screwing, or protruding spikes penetrating the tissues at the base of the screw. This implies significant damage to all tissues crossed or adjacent during implantation of the implant. 
     SUMMARY 
     One aspect of the present invention provides an autonomous implantable device which allows ensuring good opposition to unscrewing while having a much smaller traumatic effect. 
     This is particularly important to the extent that surrounding tissues are the primary targets of the stimulation method, and it is important to protect these tissues during implantation and during operation of the device, to ensure low pacing thresholds and thus preserve the longevity of the device. 
     More specifically, one embodiment of the invention proposes to this purpose an implantable capsule, including a cardiac stimulation autonomous capsule, including in a manner known per se a tubular body provided at its distal end with a helical anchoring screw member capable of penetrating into a tissue of a wall of an organ of a patient, the body housing a set of functional elements of the capsule. The capsule further includes a set of flush peaks oriented in a circumferential direction opposite to that of the screwing. 
     In one embodiment of the invention, the capsule includes an annular support surface formed in an annular region surrounding the base of the screw in the radial direction; and formed in a flush manner in said annular support surface, hollowed recesses defining said set of peaks. 
     According to various advantageous embodiments:
         The hollowed recesses include oblique recesses formed from a generally continuous annular face of the support so as to form peaks pointing in an opposite circumferential direction to the screwing, in particular with an inclination angle between the recesses between 40° and 60° relative to the surface of the annular face;   The proportion of the surface of the annular face occupied by the recesses is between 20 and 40%, and preferably close to 30%;   The screw anchoring member is formed from a resilient metal wire wound in a helix and terminating in a peak, and able to generate a traction force of said annular region toward said wall, namely with a spacing between the successive turns of the helix which increases between a base of the screw and its tip;   The capsule further includes a tip electrode projecting inside the screw member, this electrode being configured as a harpoon. The electrode may in particular be a revolution part centered on the axis rotation of the capsule during screwing, and/or include a conical head at the free end of a stem narrower than the head;   The capsule further includes a pharmaceutical product diffusion ring disposed within the annular region, the recesses being adapted to facilitate the circulation of the product towards the outside of said region;   The capsule includes a piece of biodegradable material wherein the hollowed recesses defining the set of peaks are formed, the biodegradable material being especially possibly a bioabsorbable biopolymer of the group consisting of: polylactides (PLA), polyglycolides (PGA) and polylactide-co glycolide (PLGA).       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, characteristics and advantages of the present invention will become apparent to a person of ordinary skill in the art from the following detailed description of preferred embodiments of the present invention, made with reference to the drawings annexed, in which like reference characters refer to like elements and in which: 
         FIG. 1  is an overall perspective view of an implantable capsule according to one embodiment of the invention. 
         FIG. 2  is a perspective view and in half-section of a distal region of the capsule of  FIG. 1 . 
         FIG. 3  is a perspective view of an anchoring screw support of the capsule of  FIGS. 1 and 2 . 
         FIG. 4  is a perspective view of a detail of the support of  FIG. 3 . 
         FIG. 5  is a side view of the detail of  FIG. 4 . 
         FIG. 6  is a perspective view and in half-section of a distal region of a capsule incorporating an alternative embodiment. 
         FIG. 7  is a perspective view, in another direction, of that distal region. 
         FIG. 8  is a perspective view of a screw-support assembly according to another aspect of an implantable capsule, the screw being visible in transparency. 
         FIG. 9  is a perspective view of the screw-support assembly of  FIG. 8 . 
         FIG. 10  is a partial perspective view of an alternative embodiment of the support for fixing the screw on the support. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the device of the invention will now be described, along with examples of realization of an implantable capsule. 
     Referring firstly to  FIG. 1 , an implantable capsule  10  is shown, here an autonomous capsule for cardiac stimulation, including a capsule body  12  and an anchoring member of helical screw-type  14 . 
     The screw  14  is formed by a helically wound wire with a right screw pitch and is mounted on a screw support  16  incorporating arrangements ensuring the irreversibility of the anchoring as will be seen hereinafter. 
     The screw  14  is rendered permanently secured to its support  16 , for example by laser welding according to the distributed welding points. 
     The assembly is then permanently secured to the body of the capsule  12  by a laser welding bead. 
     Note that the material of the screw  14  and of its support  16  may be different, for example a platinum/iridium  90 / 10  couple for the screw  14 , and titanium for the support  16 . It is indeed possible, as will be seen below with reference to the embodiment shown in  FIGS. 8  and  9 , to implement an effective method of assembly of these elements even if they are made of heterogeneous materials. 
     The various parts are made, for example, of biocompatible metal alloys such as stainless steel or a titanium alloy, preferably a biocompatible titanium alloy for the capsule body  12  and the support  16 . 
     The arrangements for the irreversibility of fastening include notches or recesses  16   a  formed in the support  16 . 
     The fastener assembly consisting of parts  14 ,  16  has a diameter preferably equal to that of the body of the implant, typically 6 to 7 mm, and a slightly lower axial length, typically between 4 and 6 mm. The screw  14  defines a space occupied by another sub-assembly of the device, here a sub-assembly of stimulation electrodes. 
     The fastening system is designed to secure the implant in a stable and a sustainable manner over time through the helical screw  14  forming a spring with scalable turns and ending in a point capable of puncturing the endothelium and of penetrating muscle tissue. This presses the cardiac wall on the generally annular end face of the support  16 , substantially at the same position (in the axial direction) than the inner bearing surface of the electrode system. 
     In more detail, the screw support  16  presents on said end face  16   c  a series of recesses  16   a  which perform the function of irreversibility once in contact with the endothelium. In this position, the fastening system is unremovable. Under the action of the screw  14  which acts as a tension spring carrying an axial retaining force, the cardiac wall is pressed against the face  16   c  of the screw support  16  and locally anchors in the recesses (here six in number, uniformly distributed) by the above-mentioned spring effect. 
     As will be discussed in more detail later, the six recesses may be defined as sharp, but shallow edges in their (circumferentially) area opposite the direction of screwing of the helix and then provide six punctual anchoring points distributed on the endothelium (mutual spacing of 60° in this example), which provide the irreversibility of screwing to anchor the capsule. 
     Now in more detail and with reference to  FIG. 2 , a stimulation subassembly is observed, constituted by two electrodes  18  and  20  maintained by an electrode support  22  which also supports at its periphery a ring  24  for elution of a steroid product. 
     The support  22  is positioned coaxially with the screw support  16 , inside the latter, and fixed by adhesive or other suitable methods on a wall  12   a  closing the interior of the capsule body  12  at its distal, screw side, end, the support being accurately located thanks to a circular shoulder  12   b  provided on the outer face of said wall. 
     The central pacing tip electrode  18  is fixed (by crimping, bonding, etc.) in the center of the support  22  and electrically connected to the internal electronics of the capsule accommodated in the body  12  via a micro-feedthrough. The second electrode  20  here has the form of a washer positioned and fixed, for example by bonding, on the external face of the support  22  and is also connected through a micro-feedthrough to the internal electronics. 
     The ring  24  is impregnated with a steroid such as dexamethasone and is positioned under the electrode  20 . The steroid product can reduce tissue inflammation during the first weeks after implantation. 
     The electronics associated with the electrodes can implement, in the case of cardiac pacing, functions of sensing and pacing, the described structure ensuring a reliable and permanent contact between the electrodes  18 ,  20  and the tissues. 
     The helix screw  14  is constituted of a metal wire with a diameter of about 0.5 mm, with a winding diameter typically about 5 mm and preferably identical to the body  12  of the device. The screw includes a planar base followed by two adjacent turns and a final turn extending, e.g., approximately on 1.5 turns with an inter-coil space of the same order of magnitude as the diameter of the wire. 
     The free end of the screw  14  is refined, in this case by machining in two mutually orthogonal planes, creating a perforating, but not sharp tip  14   a . The purpose of this tip is to allow crossing the endothelium and then of easily penetrating into the cardiac muscle, while creating minimal tissue damage. The helix screw  14  here is made of implantable and biocompatible stainless steel 316L or of any other equivalent material, which delivers a stiffness of about 0.1 N/mm (linear spring stiffness, as measured by tensile or compression using a dynamometer on a 1 mm stroke). 
     This gives the screw an axial flexibility which gives it a spring effect, operating a tensile effort to maintain firm contact between the support  16  and the cardiac wall. Thus, during the penetration of the screw  14  in the muscle, the screw deforms axially until contact with the free edge  16   c  of the support  16  with the endothelium. The spring effect of the screw will then axially compress the endothelium and the muscle between the coils and create a wedging effect. In addition, the close proximity of the coils and their tensile effect on the endothelium force the input thereof in the anti-unscrewing notches. During this movement, the pacing tip electrode  18  pierces the endothelium and thus comes into contact with the excitable cells of the cardiac wall. 
     Other coil configurations are of course possible, but it is advantageous to provide a spacing between turns which increases from the base of the screw (wherein as we saw the spacing may be zero) and the tip  14   a  of the screw. This helps promote the axial tensile force applying the support  16  against the cardiac wall. 
     Furthermore it is understood that the electrode  18  contributes to the fastening of the capsule while providing reliable and continuous contact with the compressed tissues by the axial force of the screw  14  towards the support  16 . 
     Such a configuration is particularly suitable for low energy stimulation, with a needle length of the order of 1.2 mm and a diameter of the order of 0.4 mm, a surface area of the order of 1 mm 2 . 
     Referring particularly to  FIGS. 3-5 , the support  16  of the screw  14  has as stated a face or support edge  16   c , preferably with a slightly rounded profile, from which six recesses  16   a  for performing six sharp edges  165 , highly localized and highly punctual (see in particular  FIGS. 4 and 5 ) ensuring the irreversibility of the screwing of the capsule made as described above, are formed in an oblique direction. 
     Localized perforation of endothelium is achieved by the sharp edges  165 , the other edges which form the boundaries of the notch being deliberately very rounded so as not to spread or enlarge the piercing of the endothelium during the unscrewing effort. The support surface supporting unscrewing constraints being maximized, the risks of tearing of the endothelium are minimized. 
     Preferably, but not limited to, the relative surface area occupied by the recesses of the support surface  16   c  is from 20 to 40% of this surface, more preferably around 30%, which allows to limit the traumatic effect of the sharp edges  165  by limiting the penetration of tissues into the recesses  16   a , while ensuring a good attachment of said edges  165  in the endothelium, and thus the effectiveness of the anti-unscrewing function. 
     The dimensions of the recesses may vary. For example and with reference particularly to  FIG. 5 , the width l may be of the order of 0.3 to 0.8 mm, the depth or the length L can be between 0.5 and 1 mm, and their inclination a may be between 20 and 60°, and preferably close to 45°. 
     In an advantageous implementation variant, the recesses  16   a  defining the sharp edges  165  are realized in a biodegradable insert on the support  16 . The material used to make this patch may especially be a bioabsorbable biopolymer such as polylactide (PLA), polyglycolide (PGA) and polylactide-co-glycolide (PLGA) or any other equivalent, implantable, absorbable material in body. The anti-unscrewing function is then provided for a predetermined period, for example from 3 to 12 months, during which the fibrosis progressively overlap the base of the capsule. Then, in the long term it will become easier to remove the capsule once the anti-unscrewing function has disappeared. 
     Referring now to  FIGS. 6 and 7 , we will describe an alternative embodiment of the tip electrode  18 . The latter in this case has an enlarged head  18   a , preferably of conical shape, joining at its base, an annular returning shoulder  18   b , a narrower rod  18   c.    
     The shoulder  18   b  has a surface which mechanically strengthens the stability of the capsule on the cardiac wall, participating in the retention of the tissue compressed by the axial force of the screw  14 . 
     In this example, the shoulder  18   b  has a ring width of the order of 0.2 mm. This value can vary depending on requirements and the size of the capsule, typically between 0.05 and 1 mm. 
     The cone angle is in turn included between about 30 and 60°, and typically around 50°. 
     A permanent assembly solution of the screw  14  on its support  16  will now be described, this solution being implemented independently of the anti-unscrewing and attachment characteristics to the cardiac wall, as detailed in the foregoing. 
     The problem solved by this solution is to assemble a screw  14  made of stainless steel or of other not directly sealable material on the titanium housing of the capsule. 
     Thus, referring to  FIGS. 8 and 9 , the support  16  has a configuration including a plurality of through orifices  16   b , having a cross section approximately corresponding to that of the rods or tubes and for example circular, formed in the wall of the support  16 . These orifices receive counterpart rods or tubes  14   b  formed on the periphery of the base of the screw  14 , corresponding angular locations. In this example, two through orifices  16   b , spaced for example by 60°, and two corresponding tubes or rods  14   b , are provided. 
     Specifically, first, the screw  14  slides under slight tightening into the support  16  until the axial abutment against a shoulder formed in the central bore of the support. Several radial through holes  16   b  are arranged in the support  16 , which coincide with the part of the screw with contiguous coil. A rod or a tube  14   b  of the same material as the screw, or a laser-weldable material to the screw material, is then inserted into each of these side holes. In the (preferred) case of a tube, the bore of the tubes then leads to the turns of the screw. A laser shot through these holes then allows direct tube/screw welding ensuring the requirements of a good laser welding, namely: i) material compatibility, ii) direct contact and iii) visual access for shooting and quality control. 
     This welding being done, the screw is locked in translation and rotation in its support by mechanical anchoring and without direct laser welding, which leaves a lot of freedom in the combination of support/screw materials. 
     Other significant advantages of this solution are the small footprint and very low complexity of machining. 
     According to an alternative embodiment illustrated in  FIG. 10  of the drawings, a bayonet-type mounting may be provided between the screw  14  and its support  16 , the screw  14  then having at its base two rods or tubes such as  14   b , preferably diametrically opposed, and the support  16  having in two diametrically opposite regions notches  16   d  in the general form of a L extending from the free face of the support  16 . This allows, prior to laser welding, the mounting of the screw  14  by axial translation for engagement of the rods or tubes in the notches, followed by a rotation for the locking of the rods or tubes at the bottom of the notches. 
     It can exist, in addition to these two notches, other notches  16   d  and/or other circular holes  16   b.    
     In the first case described above, the assembly method of the capsule preferably includes the steps of: 
     a) fixing the support  16  to the body by welding, 
     b) engaging the base of member  14  within said support, 
     c) engaging the rods or tubes  14   b  in the orifices  16   b,    
     d) welding the rods or tubes on the base of member  14 , by laser welding through the inside of the support, and 
     e) welding the rods or tubes in their respective orifices, by laser welding, externally to the support. 
     Note that the “welding” step d) should not be understood in the narrow sense of mechanical welding with melting of the material of two separate pieces, but as an operation to collapse the material of the rod or of the tube within the housing supporting the mechanical connections and to enhance the atraumatic function by removal of the protruding shapes. 
     In the case of the variant of  FIG. 10 , the method preferably includes the steps of: 
     a) fixing the support  16  provided with notches  16   d  to the body by welding, 
     b) welding the rods or tubes on the base of member  14  by laser welding, 
     c) pre-assembling the anchoring element with its base in the support, by bayonet-type mounting involving said rods or tubes and the said notches, and 
     d) welding the rods or tubes in the notches, by laser welding, externally to the support. 
     Advantageously, orifices  16   b  or  16   d  in a greater number to the number of rods or tubes  14   b  of the screw  14  are present. In this method, the orifices  16   b  or  16   d  remaining free facilitate the diffusion of the steroid product delivered by the ring  24  radially towards the cardiac wall. 
     In another variant, it is planned that the notches  16   d  for such a bayonet type mounting are formed to participate in an anti-unscrewing function as described above. 
     The various components and parts described above may be made by machining or other shaping in accordance with conventional techniques. 
     Moreover, it is planned as described above that the support  16  surrounds the base of the anchoring element, but alternatively that the base of the anchoring member surrounds the support, in which case a skilled-in-the-art person will make necessary modifications, in particular with regard to the positioning of rods or tubes  14   b  for fixing between the anchoring element and support. 
     The capsule can be placed by the practitioner according to the method described in particular in EP 2394695 A1, now EP 2394695 B1, and also extracted using a known technique, the proximal portion  12  of the body of the capsule being arranged in an appropriate method. 
     The invention is not limited to the attachment of an autonomous stimulation capsule in a cardiac wall of the human body, but can be implemented in other implantable systems, whether they are autonomous or contained in a lead tip. Depending on the nature of the attachment wall in question, the lengths of the helix and optionally of the electrode can be easily adapted by a skilled in the art person, without degrading the fixing and irreversibility performances.