Abstract:
A stimulation lead is disclosed. This lead comprises a lead body having a lumen housing an inner conductor, the conductor being axially and rotationally movable within the lumen, and coupled to a generator of an active implantable medical device. The lead also has a helical anchoring screw extending from a distal end configured to penetrate target tissue, and a stimulation needle electrically coupled to the conductor and comprising at its distal end an active free portion with at least one stimulation electrode for application of pacing pulses to the target tissue. The stimulation needle is axially movable between a retracted position inside the tubular body, and a deployed position with the active free portion of the needle emerging out of the tubular body, utilizing an actuating mechanism for moving the needle from its retracted position to its deployed position under the effect of rotary movement relative to the lead body.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to French Patent Application No. 1259760, filed Oct. 12, 2012, which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    The invention relates to intracardiac leads for pacing of the left ventricle. The invention is in the general context of “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities, including implants to continuously monitor heart rhythm and deliver as necessary to the heart electrical stimulation, resynchronization or defibrillation pulses. 
         [0003]    Intracardiac “stimulation” leads refers to leads for the delivery of low-energy pulses used for bradycardia or resynchronization therapies. The invention also applies to intracardiac leads for cardioversion/defibrillation intended to deliver a high energy electric shock to the heart to try to terminate a tachyarrhythmia. “Stimulation lead (or electrode)” or “stimulation/defibrillation lead” may refer to any kind of lead used for these or other similar purposes. 
         [0004]    For stimulation of the right ventricle, the implantation of an endocardial lead through the right peripheral venous network is sufficient. However, to stimulate the left ventricle, the situation is more complex. The most commonly adopted solution is to introduce a lead, not into the cavity to stimulate, but in the coronary network, the lead being provided with an electrode applied against the wall facing the epicardium and oriented in direction of the left ventricle. These leads stimulate the heart muscle via one or more point electrodes, the position of which is a function of the predefined trajectory of the cannulated vein. A lead of this type is for example the Situs LV model marketed by Sorin CRM (Clamart, France) and described in EP 0993840 A1 (ELA Medical). The introduction of such a lead is made via the coronary sinus, because of its opening in the right atrium. The lead is then pushed and oriented along the network of coronary veins to the selected site. Once the target vein is reached, the surgeon looks for a satisfying stimulation site, and with a good electrical contact of the stimulation electrode against the tissue of the epicardium. This contact is maintained despite various variations or stresses over time. This implantation technique is not always feasible, especially when the shape of the coronary sinus is too rough, or in case of thrombosis. Indeed, the precise positioning of the electrode(s) to stimulate the left ventricle through the myocardial wall is a critical parameter, and it is not always possible to reach effective stimulation sites. 
         [0005]    Another more difficult and much more invasive technique involves an implantation of epicardial electrodes on the outer wall of the myocardium, in one or more suitable sites facing the cavity of the left ventricle. A variant of this technique, described in EP 2308550 A1 (Sorin CRM), involves the implantation of the electrode, formed by the conductive helical screw of a screw lead, via a bent catheter inserted into the pericardial sac. However, these techniques are relatively invasive and also generally irreversible, since it is very difficult to change the implantation site initially chosen, and to explant, if necessary, the lead at a later stage. 
         [0006]    Another approach, to which the invention pertains, is to stimulate the left ventricle by applying pacing pulses to the wall of the interventricular septum (the wall separating the left ventricle and the right ventricle) by means of a lead inserted into the right ventricle using a traditional approach. This technique involves the drilling of the atrial or ventricular septum, then the introduction of a lead through this septum until it comes into contact with a point on the wall of the left ventricle. The stimulation pulses are then applied directly to the left endocardial site thus selected. For an example of a controlled transeptal puncture technique, one may refer to EP 1516644 A1 (ELA Medical), which describes a guiding accessory having one end closed by an anchoring screw to the right wall of the septum, and in which a piercing stylet is inserted for initiating a puncture of the septum. After withdrawal of the piercing stylet, a guiding stylet is inserted in the accessory, to form an axial guide in which the pacing lead, provided with its electrodes, is then introduced in the left cavity after removal of the accessory. 
         [0007]    Another technique for making a transeptal puncture, described by EP 2327366 A1 (Sorin CRM) is to anchor a screw to the septum wall, and then to apply to this screw radiofrequency energy to progressively sink into the septum wall until it passes through the latter. The puncture can also be performed by a guide-wire supplied with the RF energy, which is pushed to cross from one side to the other the septum. 
         [0008]    These techniques have several drawbacks, mainly due to the fact that they require making a puncture in the septal wall of a diameter sufficient to insert a guide-catheter for establishing a communication between the right and left cavities through the wall, to then insert the left endocardial stimulation lead. Because the element opening into the left ventricle element is a hollow catheter, this results in significant risk of air embolism. To avoid this risk, it is imperative to take many precautions when handling haemostatic valves, meeting purge equipment procedures, etc. However, given the highly invasive nature of the procedure, uncertainties remain about the behavior in the long-term blood circulation, which involves anticoagulation to prevent thromboembolism postoperatively. Finally, subsequent extraction of the lead is practically impossible, because of the excessive risks that would be incurred at the crossing of the septum. 
         [0009]    In any case, these techniques are very difficult to implement and require great skill of the practitioner, who, before crossing the septum, must always ensure perfect positioning of the piercing needle on the wall, crossing the septum having to be undertaken only if there is not any doubt left about the position of the needle, to avoid accidental dissection of the walls by a sudden movement of the needle piercing the septum—hence the development of specific drilling kits, such as those described in EP 1516644 A1 and EP 2327366 A1 above. 
         [0010]    Yet another technique designed to reduce these risks is described by EP 2457612 A1 and EP 2384784 (Sorin CRM). The basic idea is to remove the guide catheter associated to a lead crossing the septum, and replace this set by a conventional lead screwed onto the wall of the right ventricle at the septum, extending the lead by a transeptal microcable, partially isolated and pushed into the left ventricle to come into contact against a target located in this ventricle, for example against the free wall of the latter (that is to say the wall located opposite to the septal wall). 
         [0011]    Due to the extreme thinness of the puncture (the size of which being that of the microcable diameter), this technique greatly reduces the risks associated with previous techniques. However, insofar as the microcable is freely deployed in the left ventricle, it is difficult to control the delivery of pacing pulses at specific sites, and to ensure adequate and continuous contact between the electrodes of this free part and the wall of the left ventricle because of the physical instability of the microcable on the free wall resulting from the very high flexibility of the microcable. In addition, the transmission of the puncture push via the microcable can be difficult: indeed, the need for mechanical endurance requires great flexibility for the microcable, flexibility that is not compatible with the necessary requirement of “pushability” (ability to transmit axial pushing forces applied from the proximal end) during the puncture step. 
       SUMMARY 
       [0012]    In some embodiments of the invention, to overcome these various drawbacks and limitations, the following step is provided: extending a screw lead anchored on the right wall of the interventricular septum, with a very fine telescopic needle, so as to be minimally invasive. The needle is extended so as to puncture the septum thickness, but without or almost without emerging of the left side wall. The screw is in principle passive (it has only a mechanical role) but the tip of the needle is active, with one or more electrodes that can precisely reach the left branch of the His bundle: this branch is indeed a rapid conduction line, and effective and without delay for the stimulation of the left ventricle even in case, for example, of a local left block. As will be seen, the lead is provided with means for precise adjustment of puncture depth, to achieve the desired target area according to a perfectly gradual and controlled method, in addition involving only the usual conventional operative procedures for the practitioner. 
         [0013]    A technique such as that taught by EP 2457612 A1 and EP 2384784 above, which is intended to implant a microcable pushed through the septum into the left ventricle to come into contact against a target in the ventricle (e.g. against the free wall of the latter, located opposite the septal wall) is however not applicable in the present case, of an intraseptal—and not a transeptal—stimulation needle. 
         [0014]    Indeed, insofar as the stimulation must occur at the septum, the position of the tip of the needle may be finely adjusted. The active part bearing the stimulation electrode(s), may be finely adjusted to lie within the thickness of the septum after implantation. This is not possible with a technique of simply pushing a microcable in a sheath, a technique that is inadequate to ensure millimeter precision required for intraseptal implantation. WO 2012/073097 A2 and U.S. 2001/0023367 A1 describe mechanisms of insertion of needles in different, not relating to cardiac pacing, contexts. 
         [0015]    In an exemplary embodiment, a lead body with a flexible hollow sheath is provided. The lead body includes a central lumen housing an inner conductor axially and rotationally mobile within the lumen. On a proximal end, an electrical connector is connected to the generator of an active implantable medical device, said connector having at least one central pin connected to the inner conductor. On the distal end, a lead head with a tubular body integral with the sheath is provided. The lead head includes a distally extended anchoring helical screw. The lead head extends into the cavity of the right ventricle and the anchoring screw penetrates into the right ventricular septal wall under the effect of a screwing movement of the sheath of the lead body from the proximal end of the lead. 
         [0016]    The lead further comprises a stimulation needle, electrically connected to the inner conductor and comprising at its distal end an active free part with at least one stimulation electrode for application of the stimulation pulses. This needle is an axially movable telescopic needle between a retracted position inside the tubular body, and a fully or partially deployed position with the free active portion of the needle emerging out of the tubular body. 
         [0017]    To enable intraseptal stimulation by the needle, wherein said pulses are applied to the septum in a region near the left wall of the region thereof, the lead further comprises an actuating mechanism for production of a controlled movement of the needle from its retracted position to its partially or fully extended position under the effect of a movement of relative rotation of the connector pin relative to the lead body, this movement being transmitted to the pin from the proximal end of the lead. The actuating mechanism comprises a guiding core secured to the needle in rotation and in translation and movable in translation and in rotation inside the tubular body, and means of coupling of the core to the tubular body, for conversion of a relative rotation movement of the core to the tubular body in an axial translation movement of the core inside the tubular body. 
         [0018]    According to various embodiments: 
         [0019]    The means of coupling may be screw-nut means having an internal helical thread of the tubular body member cooperating with a conjugate element that engages with the thread of the tubular body, in particular a helical thread carried by an outer surface of the core; 
         [0020]    The inner conductor may be a coiled conductor arranged in a peripheral region of the hollow sheath; 
         [0021]    The amplitude of the axial translation movement of the core inside the tubular body may be between 10 and 15 mm; 
         [0022]    The length of the protruding part of the needle in the extended position may be between 0 and 15 mm, and has a diameter of 1.5 French (0.5 mm); 
         [0023]    The outer surface of the needle may be electrically insulated, except for at least one exposed area, located in the active free portion, forming said at least one stimulation electrode; 
         [0024]    The free active portion may comprise at least one exposed area extending over no more than 6 mm from the free distal end of the needle; 
         [0025]    The lead may comprise a plurality of exposed distinct zones successively extending along the active free part and separated by not exposed insulating spacers zones; 
         [0026]    The total area of the exposed zone(s) of the active part may be no more than 6 mm 2 ; 
         [0027]    At its proximal portion, the needle may be extended by a rod to which it is integral and which is welded to the inner conductor; 
         [0028]    The anchoring screw and/or the tubular body may be electrically inactive. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0029]      FIG. 1  is a schematic sectional view of the myocardium, showing its different cavities and the main electrical conduction paths. 
           [0030]      FIGS. 2 and 3  are sectional views of the lead head, respectively, in the retracted position and the extended position of the stimulation needle. 
           [0031]      FIGS. 4   a - 4   e  illustrate the various stages of implantation in the wall of the interventricular septum of the lead of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIG. 1  is a schematic sectional view of the myocardium  10  with the right ventricle  12  and the left ventricle  14  separated by the interventricular septum  16 . It has a typical thickness of about 10 to 15 mm and constitutes a significant portion of the cardiac mass. 
         [0033]    The depolarization waves that originate in the sinoatrial node  18  are transmitted to the atrioventricular node  20  and the His bundle  22 , which is divided into two branches extending along the septum  16 , with a straight branch  24  in the region the right septal wall  26  and a left branch  28  in the region of the left septal wall  30 . 
         [0034]    In particular, the left branch  28  is a line of fast longitudinal electrical conduction (arrow  32 ), with a speed of about 4 m/s. However, the conventional techniques implementing retractable screw leads can stimulate the right wall  26 , so that to stimulate the left ventricle  14 , the waves of depolarization must cross the septum  16  (arrow  34 ), but with a speed of cross conduction relatively low, on the order of 0.4 m/s. This introduces a delay of about 30 ms between the application of the pulse on the right portion  26  and the excitement of the left branch  28  leading to contraction of the left ventricle  14 . 
         [0035]    Moving the point of stimulation of the right wall of the septum (conventional technique) to the left wall of the septum, close to the left branch  28  of the His bundle (technique of the invention), can significantly contribute to reduce the time between the application of the pulse and the actual contraction of the left ventricle, and/or mitigate the effects of a local left block. According to the invention, a lead  36 , implanted in a conventional manner in the right cavities, with a lead head  38  anchored against the right wall  26  of the septum  16 , is used for this purpose. The lead head  38  is extended by a telescopic needle whose distal end  40  carries the stimulation electrodes. A gradual and controlled puncture of the septum  16  allows placement of the end  40  of the needle in the vicinity of the left wall  30  without passing through the septum  16 , or only barely opening of this wall, so as to directly stimulate the left branch  28  of the His bundle exactly in the area of rapid conduction, thereby providing a direct and immediate stimulation of the left ventricle  14 . 
         [0036]      FIGS. 2 and 3  more particularly illustrate, respectively in the retracted position and the extended position of the telescopic needle, the structure of the lead head  38  located at the distal end of the lead  36 , and intended to abut against the right septal wall. The lead body  42  includes an insulated flexible hollow sheath  44 , for example of a material such as polyurethane which has very good sliding properties when the sheath is inserted into a delivery catheter, and “torquability”, that is to say, the ability to transmit to the distal end a torque from the proximal end of the lead. The inner lumen of the hollow sheath  44  houses one or more internal conductors, such as in the example shown, a coiled conductor  46  disposed in a peripheral region of the hollow sheath so as to leave a free central space, notably for the insertion of a guiding and/or stiffening stylet within the sheath. If the sheath has a number of internal conductors, the configuration can be advantageously “coradial”, wherein two (or more) conductors are side-by-side coiled insulated conductors in a peripheral region of the inner lumen of the hollow sheath  44  and forming a coil of single radius on one unique thickness. 
         [0037]    The sheath  44  of the lead is extended to its distal end by a tubular body  48  having an outer diameter of about 7 French (2.33 mm). This tubular body  48  carries at its distal end a helical anchoring screw  50 , which can project over an axial length of about 2 mm. Said helical screw is secured to the tubular body  48  which, at its opposite proximal end is secured at a location  52  to the hollow sheath  44 . Thus, any rotational movement of the lead body under the effect of a particular torque applied from the proximal end of the lead by the practitioner will be fully transmitted to the helical screw  50  via the tubular body  48 , the three elements being integral with each other. 
         [0038]    A lead screw implanted similar to what has just been described is generally used as detection/stimulation lead after anchoring of the screw at the site of endocardial stimulation. 
         [0039]    In the case of the invention this is not the case: the function of the screw is here to serve as means for supporting and guiding a stimulation needle punctured in the wall of the septum. For the implementation of the invention, the screw  50  and the tubular body  48  are not (or not necessarily) electrically active elements. 
         [0040]    The tubular body  48  houses, in the retracted position ( FIG. 2 ), a telescopic stimulation needle  54  which is axially movable in translation relative to the tubular body  48 , between the retracted position of  FIG. 2  and an extended position illustrated in  FIG. 3 . Proximally, the telescopic needle  54  is extended by an axial rod  56 , for manoeuvre, welded proximal side to the distal end of the inner conductor  46 , so that any axial or rotation movement of this inner conductor  46  is fully transmitted to the needle  54 . In addition, the needle  54  is not only mechanically but also electrically connected to the inner conductor  46 . 
         [0041]    The proximal end of the inner conductor  46  is connected to a pin  58  of a connector  60  for coupling to the housing of a pulse generator. This is, for example, a standard IS-1 connector or the like, with a pin  58  movable in rotation relative to the connector body  60 , so as to allow pin-driven manipulation, in which the practitioner holds in one hand the body of the connector  60  (integral with the sheath  44  of the lead body  42 ) and applies rotation with the other hand, directly or via a tool, the pin  58  of the connector. The pin  58  is integral with the axial conductor  46 , itself free in rotation within the hollow sheath  44 , the movement of the pin directly transmitted to the spindle  56  and to the telescopic needle  54 . 
         [0042]    The telescopic needle  54  is a solid needle, so as not to present any hollow element in the left ventricle in case the needle crosses through the septum, therefore not creating any risk of air embolism. 
         [0043]    The guiding and the deployment of the telescopic needle  54  are controlled by a movable member  62  within the tubular body  48  and forming a guiding and driving core. This core  62 , integral with the rod  56 , is coupled to the tubular body, for example by an external thread  64  integral with the core  62 , cooperating with an internal thread  66  integral with the tubular body  44 . Thus, a movement of relative axial rotation of the rod  56  relative to the tubular body  48  (resulting from a corresponding movement of relative rotation of the pin  58  relative to the connector  60  proximal side) results in an axial translation of the driving core  62 , and thus of the telescopic needle  54  relative to the tubular body  48 . 
         [0044]    The magnitude of this axial displacement is typically of the order of 10 to 15 mm and has a value significantly greater than that of a conventional deployment mechanism of the screw of a retractable screw lead. 
         [0045]    Flexible bearings  68  and  70  are respectively provided distal and proximal side of the tubular body  48  for guiding of the needle and for sealing of the interior volume of the tubular body and of the lumen of the hollow sheath  44 . 
         [0046]    In the retracted state ( FIG. 2 ), the needle  54  is entirely housed inside the tubular body  48 , from which only the helical anchoring screw  50  protrudes, which is fixed relative to the tubular body  48 . 
         [0047]    In the fully deployed state ( FIG. 3 ), the telescopic needle  54  emerges from the tubular body on a length of about 15 mm. The needle may be deployed in a controlled manner between any of these extreme positions, thus on the length between 0 and 15 mm, in a method adjustable by the practitioner. 
         [0048]    The telescopic needle  54  may be made of a conductor material and may have a diameter of 1 French (0.33 mm). The material can be a stainless alloy such as MP35N, or can be constituted by a composite structure, for example with a core in MP35N and a peripheral biocompatible and radiopaque, such as platinum or a platinum alloy, coating. 
         [0049]    Alternatively, the intraseptal stimulation needle  54  may be made from a microcable having a diameter of about 1.5 F (0.5 mm), which allows it to benefit from the relative flexibility of the latter compared with a monofilament configuration of the same diameter, with thus better fatigue resistance. Such a microcable may include a core comprising a plurality of composite wires stranded together, e.g. with a central strand surrounded by six peripheral strands. Each composite strand is itself made up of a wire the core of which is of platinum-iridium (for radiopacity) surrounded by a plurality of also composite wires providing the required mechanical and electrical properties, for example with a core of silver (for electrical conductivity) wrapped by nitinol (for the properties of resistance to mechanical stress). These different wires are commercially available, for example from the Fort Wayne Metals Company Inc., Fort Wayne, USA, and are used in the medical field in particular to manufacture defibrillation conductors. 
         [0050]    The telescopic stimulation needle  54  is coated with an electrically insulating material, such as parylene. To form the active free part  40 , the insulating coating of the needle is locally removed in order to make one or more denuded regions  72  separated by insulating regions  74 . Advantageously, the active free part  40  having these denuded areas  72  extends over a length of about 6 mm, the surface of the denuded regions being at most 6 mm 2  to limit the stimulating surface. 
         [0051]    Having a plurality of electrodes  72  on a relatively important length (6 mm) offers the possibility to compensate for variations in the thickness of the septum which contracts during a cardiac cycle, and thus to maintain a stimulating surface vis-à-vis the tissue. 
         [0052]    From an electrical point of view, the anchoring screw  50  and the tubular body  48  are in principle inactive, and coated with an insulating material such as Parylene on their entire surface. In specific configurations, however, it is possible to make electrically the anchoring screw  50  and/or all or part of the tubular body  48  active, for example to allow simultaneous stimulation at the anchoring screw (right wall of the septum) and of the active free part  40  of the telescopic needle (left wall of the septum). 
         [0053]    The method to implant the lead just described above will now be made with reference to  FIGS. 4   a  to  4   e.    
         [0054]    The lead can be inserted into a conventional catheter  76 , for the pre-positioning of the lead head against the wall of the ventricular septum. This catheter has a typical outside diameter of 9 French (3 mm). The use of a catheter allows protection of the anchoring screw  50  (which is not a telescopic screw) during the passage through the vessels and the crossing of the tricuspid valve. Examples of suitable catheters allowing access to the right wall of the interventricular septum are described for example in EP 2135638 A1 (pre-shaped catheter, self-adjustable in the direction of the septum wall) and in FR 2932688 A1 (bimaterial catheter whose end is conformable at will), both on behalf of Sorin CRM S.A.S., previously known as ELA Medical. 
         [0055]    The first phase is to identify the anchoring site, by handling the lead-catheter assembly for introduction into the superior vena cava, the right atrium and the right ventricle  12  until it abuts against the right wall  26  of the interventricular septum  16 . 
         [0056]      FIG. 4   a  illustrates the configuration reached when the catheter  76  is brought into abutment against the right wall of the septum  16 , with the lead head  38  placed inside the catheter  76  to the vicinity of this wall  26 . 
         [0057]    The next step, illustrated in  FIG. 4   b , is to give to the sheath  44  of the lead body a rotation movement (arrow  78 ) from the proximal end of the lead body. This rotation causes the screw  50  to penetrate into the tissue of the septum  16  on a relatively small depth (of the order of 2 mm), thereby anchoring the tubular body  48 , to which the screw is integral with, against the right wall  26  of the septum. Full screwing is tactilely detected by the practitioner by the opposed resistance to the rotation. 
         [0058]    The reached site is confirmed by radiographic examination according to different impacts; if the position is not satisfactory, the practitioner can unscrew the lead head and move it under control to another point and then test the new site. 
         [0059]    Once the tubular body  48  is thus anchored to the wall of the septum, the practitioner imparts a rotation to pin  58  of connector  60 . This rotation transmitted by the inner conductor  46  (arrow  80 ,  FIG. 4   c ) is applied to the operating rod  56  which, consequently, causes the gradual penetration of the telescopic stimulation needle  54  into the thickness of the septum  16 , since the lead body, and thus the sheath  44  and the tubular body  48 , are held stationary during this deployment. 
         [0060]    This handling is performed under fluoroscopy in order to visualize the position of the active portion  40  relative to the walls of the septum (which can optionally be visualized by injection of contrast medium through the catheter  76 ). The practitioner can also make at this stage a mapping or electrical testing to verify the effectiveness of the chosen site, in order to determine the optimum positioning of the active portion  40  of the needle, that is to say, the degree of deployment thereof. 
         [0061]    If the site originally chosen is not satisfactory, it is possible to operate one or more repositionings. Indeed, the anchoring of the screw  50  in a relatively small thickness (about 2 mm for a typical thickness of the interventricular septum of 10 to 15 mm) and the very small diameter of the puncture (due to the very small diameter of the needle  55 , in the order of 0.3 mm) are used to remove the lead without causing irreversible damage to the septum—and this contrasts to a conventional transeptal approach, less tolerant to error due to the size of the remaining puncture (corresponding to a catheter of a diameter, typically about 9 French or 2.3 mm). 
         [0062]    The more or less important deployment of the telescopic needle  54  allows taking into account not only the septum thickness variations according to the region of implantation, but also to reflect the fact that the lead can be positioned in a position more or less perpendicular to the wall of the septum (which, in cross section, has a convex shape). 
         [0063]    Once the final site and the degree of deployment of the telescopic needle are selected, the practitioner removes the catheter  76 , resulting in the final configuration of the lead head. 
         [0064]    In the configuration shown in  FIG. 4   d , the distal end  54  of the needle (with the active part  40 ) does not emerge from the left wall  30  of the septum. 
         [0065]    However, as shown in  FIG. 4   e , in certain instances the needle can be caused to pass completely through the septum to position the free end  40  of the needle  54  so that it slightly emerges in the cavity of the left ventricle. This avoids the effect of shelling of the end of the needle to the target tissue, which can lead to their destruction and therefore to a loss of capture during pacing.