Abstract:
A system and method for implantation of an autonomous intracardiac capsule. The autonomous capsule includes a cylindrical body with an anchoring screw for penetrating a tissue wall, and at least one coupling finger radially projecting outwards. An implantation accessory includes a lead body and a helical guide, for guiding and driving by rotation the capsule. This helical guide is integral with the lead body, and its inner diameter is sufficient to contain that cylindrical body of the capsule therein. The helix direction of the helical guide is opposite to that of the anchoring screw such that continued rotational motion imparted on the lead body drives the anchoring screw into the target tissue and then emerges the capsule from the helical guide. The helical guide is resiliently compressible in axial direction, and its helix pitch is increased in the free distal end portion.

Description:
RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 13/160,407 filed Jun. 14, 2011, now issued as U.S. Pat. No. 8,548,605, which claims the benefit of French Application No. 10/54699 entitled “Autonomous Intracardiac Capsule And Its Implantation Accessory” and filed Jun. 14, 2010, both of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to “active implantable medical devices” as defined by the 20 Jun. 1990 Directive 90/385/EEC of the Council of the European Communities, particularly to devices that continuously monitor a patient&#39;s heart rhythm and deliver to the heart, if necessary, electrical stimulation, resynchronization, cardioversion and/or defibrillation pulses in response to a rhythm disorder detected by the device, and even more particularly to the implantation of autonomous capsules that are implanted in a heart chamber with no physical, wired connection to a remote device, for remote monitoring of the patient. 
     BACKGROUND 
     Autonomous capsules, also referred to as “leadless capsules,” including without limitation autonomous intracardiac capsules (collectively hereinafter referred to as a “capsule”), are distinguished from wired electrodes and sensors that are placed at the distal end of a lead, and connected by a conductor traversing the length of the lead to a device connected at the opposite (proximal) end of the lead. Such capsules are, for example, described in US Patent Publication No. 2007/0088397 A1 and PCT Publication WO 2007/047681 A2 (Nanostim, Inc.) and US Patent Publication No. 2006/0136004 A1 (EBR Systems, Inc.). 
     These capsules are usually cylindrical structures having a long axis and a diameter. They are usually attached directly to the heart tissue by a projecting helical anchoring screw. The anchoring screw axially extends from the cylindrical body of the capsule and is designed to penetrate the heart tissue by screwing into the implant site. 
     Of course, to enable data exchange with a remote device, such capsules incorporate a transmitter/receiver for wireless communication with the remote device. A remote device in this context may be an active implantable medal device (e.g., a housing of stimulation pulse generator) or an external device such as a programmer or other device for monitoring a patient. 
     The capsule can also incorporate a sensor to locally measure the value of a parameter such as, for example, the oxygen level in the blood and/or the acceleration of the heart wall. These capsules can also be detection/stimulation capsules with means to collect depolarization potentials of the myocardium and/or deliver pacing pulses to the site where the capsule is implanted. Such a detection/stimulation capsule then includes an appropriate electrode, which can be, for example, an active portion of the anchoring screw. 
     In general, the capsule may be an epicardial capsule, attached to the outer wall of the heart, or an endocardial capsule, attached to the inner wall of a ventricular or an atrial cavity. However, It should be understood that the present invention is not limited to a particular type of capsule, and it applies equally to any type of capsule, regardless of its functional purpose. 
     In the case of an endocardial capsule, the difficulty of implantation is increased because the implantation path involves going through the peripheral venous system. With the assistance of fluoroscopy, the capsule may be directed to a selected implant site, a known method that is both precise and perfectly secure. Once the implant site is reached and the capsule is anchored in the wall, the operator may then operate the “release” of the capsule, and disconnect it from an associated implantation accessory. 
     US Patent Publication No. 2009/0204170 A1 (Cardiac Pacemakers, Inc.) describes a capsule for electrical stimulation and an accessory tool for its implantation, in which the capsule is guided by a catheter to the implant site within a directing tube pressed against the heart wall, and then progressively screwed into the heart wall by a driving stylet extending into the lumen of the catheter. 
     The general acceptance by persons of ordinary skill in the art of the use of endocardial capsules relies on an ability to provide a delivery system that is capable of securing the implantation of these capsules, according to the following: 
     An implantation procedure similar to current practice, allowing practitioners to make use of well-known and well-controlled lead manipulation gestures: e.g., subclavian puncture, insertion and manipulation of a catheter through preformed stylets during an approach to the selected implantation site, fixation with screws or tines, etc.; 
     Standard Environment in the Operating Room; 
     Limiting the risk of “carotage” of tissue due to an excessive tightening that may damage or, even worse, puncture the wall (especially in the case of implantation in a thin wall such as the atrial septum); 
     Possibility of postoperatively withdrawing and/or repositioning the capsule in case of problems, even after a release of the capsule from its delivery system; 
     Limiting the consequences of a capsule migration in case of displacement during the acute phase of an intervention; and 
     Certainty of a good anchoring of the capsule before removing the implantation accessory. 
     OBJECT AND SUMMARY 
     The present invention is directed to a system comprising a capsule and an in situ implantation accessory, a combination in itself known, particularly from the US Published Patent Application 2009/0204170 A1, and improvements thereto. In accordance with the present invention, the capsule preferably comprises a tubular cylindrical body having at one end a projecting helical anchoring screw axially extending from the cylindrical body and, at least one coupling finger secured to the cylindrical body that extends radially outward. The helical anchoring screw is configured to penetrate into the tissue of the wall of a cavity, ventricle or atrium, of the heart. The implantation accessory has at its distal end a disconnectable means for supporting and guiding the capsule to the implantation site, and for rotational driving of the capsule to allow simultaneous driving of the anchoring screw and screwing it into the wall of the heart cavity. 
     In accordance with a preferred embodiment, the implantation accessory includes a lead body with a sheath of deformable material having at its distal end a helical guide forming said disconnectable means for supporting, guiding, and rotating the capsule. The helical guide extends axially from the lead body and is attached to the latter in rotation and in translation. The inside diameter of the helical guide is homologous to the outside diameter of the cylindrical body of the capsule so as to house the latter inside, with the at least one coupling finger protruding between the coils of the helical guide. The helix direction of the helical guide is opposite to that of the anchoring screw. 
     In a first embodiment, the helical guide is a projecting helix axially extending from the distal end of the lead body, including a resiliently compressible helix in the axial direction and whose helix pitch is increased in its free distal end portion. 
     Preferably, the capsule comprises two coupling fingers, one located towards the distal end of the capsule and the other located towards the proximal end of the capsule. The spacing between the two coupling fingers along the axial direction of the capsule is selected to provide a compression of the helix when the cylindrical body of the capsule is completely housed inside the helical guide. Advantageously, when the cylindrical body of the capsule is completely housed inside the helical guide, this assembly also includes a protective soluble coating covering the capsule equipped with its anchoring screw within the helical guide. More preferably, the capsule includes a reset ramp extending from the coupling finger located at the distal end. The reset ramp forms a portion of a helical thread with a helix direction opposite to that of helical guide, and is able to contact at its proximal end and engage with free end of the helical guide. 
     In a second embodiment, the distal end of the lead body has a hollow cylindrical tube extending axially and forming a housing for containing the capsule, the helical guide being a helical groove formed in the inner surface of the housing, and means are provided to deploy the capsule anchoring screw by a pin-driven drive. 
     Preferably, the helix pitch of the helical guide is increased in its free distal end portion. Also preferably, in this embodiment, as in the first embodiment, the capsule has two coupling fingers, one towards the distal end and the other towards the proximal end, and the spacing between the two coupling fingers in the axial direction is selected to provide a compression of the helix when the cylindrical body of the capsule is completely housed inside the helical guide. 
     In another embodiment, the system of the present invention may further include a flexible wire disposed within and running along a lumen of the lead body having a distal end, connected to the capsule, and a proximal end, extending out the proximal end of the lead body. The flexible wire preferably has in the vicinity of the connection point to the capsule a portion or length made of a resorbable material. 
     In one embodiment, the capsule can be a capsule for detection/stimulation comprising means for detecting depolarization potentials and/or delivering stimulation pulses and coupled to at least one electrode carried by the capsule, wherein the electrode is an active part of the anchoring screw, and transmitter/receiver wireless communication means for communicating with a remote device. 
    
    
     
       BRIEF DESCRIPTION OF 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 a perspective view of a first embodiment of a system of a capsule and an implantation accessory in accordance with the present invention in a configuration wherein the two elements are separated; 
         FIG. 2  shows the system of  FIG. 1 , in a standalone configuration wherein the capsule is coupled to the implantation accessory before implantation; 
         FIG. 3  shows the system of  FIG. 2 , in a configuration during implantation of the capsule in a heart cavity; 
         FIG. 4  is a perspective sectional view of a second embodiment of an implantation accessory in accordance with the present invention before implantation; 
         FIG. 5  shows the accessory of  FIG. 4 , with the capsule housed in the implantation accessory; 
         FIG. 6  is an enlarged view of the distal portion of the implantation accessory of  FIG. 4 ; 
         FIG. 7  illustrates a third embodiment of a system of a capsule and an implantation accessory in accordance with the present invention including a flexible wire; and 
         FIGS. 8   a  and  8   b  are perspective views, in two different orientations, of the embodiment of  FIG. 1  illustrating a reversibility of the implantation of the capsule. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of preferred embodiments of the present invention will now be described with reference to the drawings. In  FIG. 1 , reference  10  designate a capsule having a cylindrical body  12  having an axis and which is provided at one end with a helical anchoring screw  14  axially extending from the tubular body  12  and secured to it in rotation and translation. Anchoring screw  14  preferably includes a distal portion  16  formed along a length of about 1.5 to 2 mm of non-touching turns for penetrating into the cardiac tissue. Distal portion  16  is connected to tubular body  12  via a transition portion  18  having a mechanical bending flexibility, for example, a part formed of contiguous turns in the absence of any stress on the screw. 
     Anchoring screw  14  may be an electrically active screw. In this regard, at least at its distal end, anchoring screw  14  may serve as a detection and/or stimulation electrode. Alternately, screw  14  may simply be a passive screw only for anchoring the cylindrical body  12  in the wall of the cardiac cavity. 
     The cylindrical body  12  typically includes various control and power circuits, for signal processing and wireless communication to enable the exchange of signals with a remote device, which may or may not be implanted. These aspects are in themselves known, and as they form no part of the present invention, they will not be described in further detail. One skilled in the art is referred to the various publications cited at the beginning of this description for more details on the structure and function of capsules. 
     Cylindrical body  12  is cylindrical and preferably includes at least one coupling finger shaped as an axially projecting protuberance, the function of which is explained below. In the examples shown, capsule  10  preferably comprises two such coupling fingers, finger  20  being distally located, and finger  22  being proximally located, with a spacing or gap between fingers  20  and  22  in the axial direction having a predetermined value (the importance of which is explained below). It should be understood that the form of these coupling fingers  20 ,  22  can be adapted to give them a softened, atraumatic profile. 
     Cylindrical body  12  typically has a length from about 5 to 10 mm and a diameter from about 1 to 2 mm (i.e., 6 French). Proximal end  24  of capsule  10  can be rounded or domed for, on the one hand, making it atraumatic and, on the other hand, facilitating its coupling with the implantation accessory. 
       FIGS. 1-3  further illustrate a first embodiment of the implantation accessory  26  used for the implantation of capsule  10 . 
     Accessory  26  generally comprises a body  28  that is structurally similar to a conventional monopolar lead body in that it includes along its entire length, a coiled conductor  30  that is covered by a sheath  32 . Sheath  32  is typically made of polyurethane to reduce friction when the lead body is inserted into a guide catheter or the venous system, and to provide better sensitivity and better transmission of torque. In the context of the present invention, however, it should be understood that conductor  30  preferably has no electrical function; rather conductor  30  only contributes to the mechanical behavior of lead body  28  provides radio-opacity to aid in detection of the lead body position, e.g. by fluoroscopy. 
     The conductor assembly  30 /sheath  32  cooperate to provide lead body  28  with a torsional rigidity sufficient to transmit a torque from its proximal end to its distal end to rotate the distal end. It is possible, alternatively or in addition, to introduce in the lumen of lead body  28  a screwing stylet, in particular when the sheath  32  does not present a sufficient torsional stiffness, to rotate directly the distal end of the lead body from the proximal end. 
     The distal end of lead body  28  is provided with a tip  34  which is secured to a helical guide  36  formed, in this first embodiment, of a number of turns (helix)  38  of an elastic material (e.g., an alloy of the M35N or nitinol type). As a result, helix  38  is compressible in the axial direction, similar to a helical compression spring. 
     Typically, helix  38  has a reverse pitch compared to the pitch of helical anchoring screw  16  of the capsule, e.g., a left pitch if anchoring screw  16  has a right pitch. In addition, helix  38  has at its free distal end a slightly elongated pitch, for example, on the most distal turn  40 . 
     At the opposite end, helix  38  is connected to tip  34  by a transition portion  42  having a bending flexibility, for example, a portion  42  formed of adjacent turns in the absence of any force acting on helix  38 . 
     During manufacturing, body  12  of capsule  10  is screwed into helix  38 , thus resulting in the configuration shown in  FIG. 2 . The gap between coupling fingers  20  and  22  is sized to ensure, in this configuration, a slight compression of helix  38  when coupling finger  20  engages the distal coil  40  which, as explained above, has an elongated pitch compared to the rest of helix  38 . 
     The entire distal portion is preferably covered with a soluble coating  44 , for example, polyethylene glycol (PEG). Soluble coating  44  is provided to protect anchoring screw  14 , helix  38  and the surrounding tissue during insertion of the system assembly into and through the venous system. To limit the dissolution time, it is possible to provide the soluble coating with a stepped profile, with the result that the coating around anchoring screw  14  is less thick than elsewhere. 
     During implantation, the assembly as shown in  FIG. 2  is introduced to the cavity using a conventional procedure. Lead body  28  being of a standard construction, the practitioner will find its manipulation will have the classic feel of manipulation of a monopolar lead body with respect to, for example, torque, flexibility and slip. 
     Once soluble coating  44  is completely dissolved, the physician positions the tip of anchoring screw  14  against the heart wall, and starts screwing, by clockwise rotation (corresponding to a right pitch of the anchoring screw  14 ). The torque is transmitted from the proximal end of lead body  28  and allows, in a first step, the penetration of the anchoring screw  14  into the tissue of the wall  46  of the cavity of the heart. The corresponding value of torque for this operation is designated as C screwing •  FIG. 3  shows the configuration of the assembly after complete screwing: the front of capsule  10  abuts against heart wall  46  and thus halts the progression of anchoring screw  14 , also generating a significant increase of the reaction torque. 
     With an anchoring screw of a standard lead, as the practitioner continues rotation of the lead body and of the screw, the torque increases and exceeds a limit C coring . Anchoring screw  14  then risks tearing the tissue under the local effect of rotation of the screw without any advance of the screw, causing a laceration to the tissues and, in extreme cases, perforation of the wall with the risk of tamponade. 
     In contrast, in accordance with the present invention: the physician can pursue without risk the rotation, always clockwise in this embodiment, of lead body  28  because the extra torque occurring due to the reaction of screw  14  anchored in tissue  46  is absorbed by the connection between helix  38  and capsule  10 . Specifically, the elasticity in compression of helix  38  is chosen to define a sliding torque C sliding  below the limit C coring . Thus, when the couple C sliding  is reached, further clockwise rotation of lead body  28  starts its rotation around capsule  10 , due to the reversed pitch of helix  38 . The latter then gradually emerges from capsule  10  by unscrewing (due to the reversal of the pitch). Note that the slightly increased pitch size of last turn  40  can generate a compression of the turns of helix  38  between coupling fingers  20  and  22  (arrows  48 ), and hence an increasing supporting force of these coupling fingers, until the release of distal finger  20 , a situation that defines a release torque C release  allowing then the decoupling of capsule  10  and of lead body  28  (arrow  50 ). 
     The geometry of the various elements that make this interaction, as well as the elasticity in compression of helix  38 , are selected to verify the relationship:
 
C screwing &lt;C sliding &lt;C release &lt;C coring  
         C screwing  designating the screwing torque in the tissues,   C sliding  designating the additional torque absorbed by the connection between the helix and the capsule,   C release  designating the couple met for the release of the distal finger, and   C coring  designating the torque limit beyond which the rotation of the anchoring screw may cause a tearing of the tissues of the wall.       

     It should be understood that the release system, located near anchoring screw  14  and thus at the distal end of the assembly, is not dependent on the torsional behaviour of lead body  28 , at the difference, for example, of a system for limiting torque that would be placed proximally. 
     Moreover, it is noted that during the release, the compressed length helix  38  is maximum, which ensures maximum reproducibility of the release torque. 
     The mechanism as described above allows absorbing the gradual rise of the torque due to the reaction of the anchoring screw  14  once it is fully inserted in the wall of the heart chamber, with a double benefit of (i) certainty of complete screwing of capsule  10 , and (ii) removing of any risk of tamponade. 
     Advantageously, the whole operation is transparent to the physician, because a single simple rotational movement from the proximal end of lead body  28  ensures both the complete fixation of the capsule and its release. 
     A second embodiment of the accessory in accordance with the present invention will now be described with reference to  FIGS. 4-6 . The second embodiment is particularly well suited to embodiments wherein lead body  28  is a standard system known as a pin driven system. A pin driven system is one wherein the practitioner holds in one hand the proximal end of the lead body and in the other hand turns, directly or through a tool, the pin extending from the proximal end. Specifically, the plug is secured to the axial conductor  30  extending within lead body  28 , this conductor being then free to rotate relatively to sheath  32  and being connected at its distal end to the tip  34 . 
     In addition, lead body  28  has at its distal end a cylindrical tube  52 . Tube  52  has an inner diameter homologous with the outside diameter of capsule  10  (see  FIG. 5 ) and a length allowing it to contain the capsule, including anchoring screw  14 , inside the hollow tube. 
     This second embodiment advantageously does not require use of a soluble PEG coating to protect the screw, because screw  14  can be retracted within tube  52  for the duration of the intravenous transit. 
     Tube  52  is preferably hollow and provided with a helical groove  54  (seen in particular in the enlarged view of  FIG. 6 ) formed in the inner surface of tube  52  opening into an internal circular recess. Coupling finger  20  thus slides in this helical groove when the connector pin is activated (i.e., employing the pin-driven technique), driving screw  14  out of tube  52 . 
     The helical guide forming a spring is shown at  56 . It is in the form of a flat ribbon  56  in an elastically deformable in compression material with a proximal end  58  secured to the tip  34 . It has a free distal end  60  which has on its last turn a pitch size slightly increased in the same manner as turn  40  described in the first embodiment. 
     The direction of the pitch of helical groove  54  is the same as that of anchoring screw  14  (right pitch), however the pitch of flat spring  56  forming a helical guide is a reversed pitch (left pitch). 
     With this configuration, the rotation of the connector pin at the proximal end of lead body  28  rotates tip  34  and simultaneously capsule  10  and spring  56  in a forward helical movement relative to tube  52 . This results in a gradual deployment of screw  14  from tube  52 , and then a screwing of screw  14  into wall  46  of the heart cavity, until the front of capsule  10  abuts against wall  46 . 
     The further screwing causes, by the action of helical spring  56  on coupling fingers  20  and  22 , the separation of capsule  10  from spring  56 , allowing the gradual release of capsule  10  with the same function of disengagement described above with respect to the first embodiment, which prevents tissue damage by the anchoring screw. 
     Kinematics and stresses on the torque values described in detail for the first embodiment are applicable equally to this second embodiment. 
       FIG. 7  illustrates a preferred embodiment that can be implemented with either of the first or second embodiments described above, and is designed to allow a repositioning, in the short or in the medium term, of capsule  10  after its initial implantation and release. In this embodiment, separate from the connection between the separable lead body  28  and capsule  10 , a flexible wire  62  is connected at its distal end to capsule  10  and passed through the lead body so that its proximal end extends out the proximal end of the lead body (not shown). 
     Once capsule  10  is implanted, its proper functioning is tested, including if appropriate, the proper establishment of wireless communications between capsule  10  and a remote device (not shown). When capsule  10  is secured, and proper functioning is determined, lead body  28  is completely removed, and an excess length of flexible wire  62  is left to protrude outside the patient, under preferably a protective dressing. 
     In this regard, flexible wire  62  may be used to retrieve the capsule in case of a displacement in acute phase, by simply pulling on wire  62 . 
     Flexible wire  62  more preferably comprises a region  64  made of a resorbable material at its point of connection with capsule  10 , for example, over a length of 3 to 5 mm. This then allows the final withdrawal of flexible wire  62  after a suitable time period, by simply pulling, e.g., one month after surgery. 
     All or part of the flexible wire  62  may contain an active DSP agent (e.g., Dexamethasone Sodium Phosphate or a like agent to control tissue inflammation (as known to be used in a conventional pacing lead)), or a surface processing intended to stop any spread of infection between the emerging wire part (under the dressing) and the wire part inserted into the venous system. 
     Further, in the case of a negative functionality test immediately after implantation or in the event of a later malfunction, it is possible to reengage helical guide  36  on the capsule through the guiding of flexible wire  62  and to the rounded shape of rear part  24  of capsule  10 . Capsule  10  can then be unscrewed from wall  46  by rotating lead body  28  in a counterclockwise direction and relocated to another site by applying the same system and principle as described above, by namely a clockwise rotation. 
     Flexible wire  62  can preferably be colored with different colors for each of the implanted capsules in order to more easily identify the relevant capsule (e.g., atrial, ventricular) in the event of an extraction and reimplementation operation. 
     Advantageously, the present invention thus provides two safety functions for the release of the capsule. The first safety function results from the release system that avoids coring of the heart wall. The second safety function arises by giving the practitioner the opportunity, even after a capsule release, to recover, in the short or medium term, the capsule in case of difficulty, using the flexible wire. 
       FIGS. 8   a  and  8   b , illustrate according to two different orientations, an alternate embodiment providing reversibility of the implantation of the capsule, in order if necessary to couple again lead body  28  to capsule  10  so as to unscrew it to remove it and possibly relocate it to another site. 
     Upon replacing the lead body on the capsule, the resetting of helical guide  36  may include to accommodate on capsule  10  in the distal region a compression ramp  66  extending from distal coupling finger  20 . Ramp  66  has, as illustrated in  FIGS. 8   a  and  8   b , a helical shape  68  extending over the length of a fraction of a turn, with a right pitch (opposite the pitch of helix  38 ) and having a proximal side  70  against which free end  72  of helix  38  slides. Compression ramp  66  is necessitated by the fact that, in its absence, helix  38 , uncompressed when docking with the capsule  10  and then screwing on proximal coupling finger  22 , would engage distal coupling finger  20  by its distal end, so that the release mechanism described above would no longer work. 
     One skilled in the art will understand that the present invention can be practiced by other than the embodiments disclosed herein, which are provided for the purposes of illustration only but not of limitation.