Abstract:
An epicardial stimulation lead includes a lead body having a connector at a proximal end for coupling the lead to a generator of an active implantable medical device. The lead also includes a distributor housing at a distal end of the lead body and means for anchoring the distal end of the lead body to the epicardium. The lead also includes an active part having a plurality of microcable conductors, the proximal ends being coupled to the distributor housing, the distal ends being free. Each microcable has a diameter of at most equal to 2 French. Each microcable includes at least one denuded area in the insulating coating forming a stimulation electrode adapted to contact or penetrate an epicardium wall. Each microcable also includes a transverse elongated member extending at an angle relative to the main direction of the microcable for penetrating into the epicardial wall.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/630,482, filed Sep. 28, 2012, which claims the benefit of and priority to French Patent Application No. 11/58882, filed Sep. 30, 2011, both of which are hereby incorporated by reference herein in their entireties. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to “active implantable medical devices” as defined by the Jun. 20, 1990 90/395/CEE directive of the European Community Council, which includes devices that continuously monitor a patient&#39;s cardiac rhythm and deliver to the heart if and as needed electrical pulses for stimulation (pacing), cardiac resynchronization, cardioversion and/or defibrillation in response to a rhythm disorder detected by the device, and more particularly to “epicardial” leads that are directly fixed on the outer wall of the heart, as contrasted with “endocardial” leads which are inserted in a cavity of the heart where they are introduced via the venous system, and “coronary” leads implanted in the heart coronary network. 
         [0003]    The epicardial leads may be prescribed for the stimulation of the left ventricle, as an alternative to pacing leads implanted via the coronary sinus, which require a delicate approach for their implantation and are not without various drawbacks. 
         [0004]    Nevertheless, unlike endocardial leads introduced via the venous network (see for example U.S. Pat. Publication No. 2009/0157136 A1), the implantation of an epicardial lead constitutes a very invasive operation, usually requiring general anesthesia and the use of surgical techniques. It is indeed necessary that a chest surgeon incises the thorax so as to provide access to the pericardial sac (the pericardium being the fibro-serous envelope that surrounds the heart) and the myocardium itself, in order to fix the lead on the external wall of the latter, by suturing or by screwing. 
         [0005]    For this reason, the implantation of an epicardial lead, though representing a known technique, is often seen as a back-up solution in case of failure of implantation of a lead through the coronary sinus. Moreover, an epicardial lead often provides poor results, especially with respect to electrical performance. 
         [0006]    Several types of epicardial leads have been proposed, but all have serious enough drawbacks. A first type of lead uses an electrode pressed against the wall of the epicardium, wherein it is supported by suturing. These leads are very stable, but require broad access to allow the suture by the surgeon, and the possible implantation zone is very limited, as it is restricted to the vicinity of the chest incision. 
         [0007]    A variant of this type of lead is a lead body that is divided into two distinct branches, each branch having a distal end supporting a pacing electrode to be sutured on the cardiac wall. This support is provided by an absorbable suture terminated with a needle: during the procedure, after suturing the electrode to its support on the cardiac wall, the surgeon buries the absorbable suture using the needle, which needle is subsequently removed by cutting the suture. This permanent traction effort provides excellent contact of the electrode, positively biased against the heart wall. The presence of two separate electrodes also allows application of a bipolar stimulation, over a somewhat wider surface area. 
         [0008]    Another type of lead proposed is equipped with an anchoring helical screw for screwing in the myocardium wall. Screwing can be performed directly, but the work area is then limited in the same way as a sutured lead. It can also be performed using a special insertion tool having an articulated head on which the lead is mounted, but the area of possible implantation, although broader, is nevertheless limited by the rigidity and the large diameter of the support tube of the instrument that the surgeon must manipulate in the curved pericardial space. 
         [0009]    Moreover, from the mechanical point of view, the screws of current leads are very generously sized, due to the mechanical stresses exerted on the screw during implantation, arising from the high amplitudes of displacements and the radial tractions that are exerted. These generously sized screws are relatively traumatic to the tissues, with possible creation of local fibrosis reactions. 
         [0010]    One disadvantage which is common to all these leads, besides the highly invasive surgery, is their relatively poor electrical performances, particularly because of the large size of the sutured electrode (which should ensure a satisfactory contact with the heart wall) or because of the large dimensions of the screw (needed to withstand implantation constraints). But a large electrode does not provide a satisfactory current density, which is detrimental to the stimulation efficiency. 
         [0011]    In addition, the stimulation is punctual (only one stimulation site), with two drawbacks: 
         [0012]    A less effective stimulation compared to a multisite configuration, and 
         [0013]    The risk that the chosen site is not the most effective, or that because of cardiac remodeling, the site originally chosen over time become less effective. In this regard, given the invasive nature of the operation, it is not a realistic option to consider further surgery on the patient to try to improve the situation by seeking a possible alternative site that would be more effective than the originally chosen site. 
         [0014]    A final drawback of existing epicardial leads, particularly for screw leads, is that it is almost impossible to extract them once they are implanted. 
         [0015]    For all these reasons, the use of epicardial leads remains undeveloped, and these leads are generally used as a last resort when other techniques are not feasible. 
         [0016]    The U.S. Pat. Publication No. 2007/0043412 A1 proposes a device implementing multiple electrodes (of a conventional type) located in different parts of the epicardium to form a network of electrodes. From an electrical point of view, each electrode is provided with its own connecting conductor, and the respective conductors are connected together to a common conductor connected at its other (proximal) end to the generator. The pacing pulses can thus be simultaneously spread to several electrodes at several points of the myocardium, corresponding to the points of implantation of the electrodes. 
         [0017]    WO 2005/039690 A1 describes a different lead configuration, wherein two screw epicardial electrodes are implanted facing each of the two ventricles, each electrode being connected to the generator by its own conductor. 
         [0018]    With these devices, since the electrodes used are of a conventional type (typically, screw electrodes), the problems mentioned above related to the nature of the electrodes remain, including: difficulty of implantation with the use of complex instruments particularly for in situ screwing after the implantation position is reached; need of a highly invasive intervention, which is traumatic for tissues with possible creation of a local fibrosis reaction of large sized screws because of mechanical constraints; poor electrical performances because of the large size of the electrode, which does not provide a satisfactory current density, to the detriment of the stimulation effectiveness. 
       SUMMARY 
       [0019]    It is, therefore, an object of the present invention to propose an epicardial lead having multiple stimulation points which is simple in construction (and therefore inexpensive to manufacture and with high reliability), and, above all, can also be implemented by operative techniques usually practiced by surgeons. 
         [0020]    The present invention is directed to an epicardial pacing lead whose active part: 
         [0021]    guarantees an excellent and sustainable electrical contact with the tissues to stimulate; and 
         [0022]    improves the stimulation efficiency by multiplying or expanding the stimulation area, allowing (unlike traditional leads) simultaneous stimulation of several regions of the epicardium. 
         [0023]    In this latter regard, it has been found with cardiac resynchronization therapy (CRT) devices that using multiple stimulation points on the left ventricle is a factor that substantially improves the quality of CRT. 
         [0024]    Essentially, the solution of the present invention is to distribute on the surface of the heart muscle, or therein, an array of micro-electrodes that are in turn carried by a plurality of microcables. 
         [0025]    These microcables are very flexible and extend outwardly from, i.e., radiate from a common distributor housing or hub, mounted at the end of an epicardial lead body, ensuring the distribution of current to the various microcables, with the possibility of bipolar pacing and/or of multiplexing of the different microcables. The distributor housing preferably has its own means for attachment to the heart wall (e.g., a suture or screw), and is itself devoid of any electrodes. 
         [0026]    Broadly, the present invention is directed to an epicardial stimulation lead including, as known in the prior art, in particular from U.S. Pat. Publication No. 2007/0043412 A1 referenced above: a lead body made of a sheath of deformable material, enclosing at least one connection conductor; a proximal end including a connector for coupling the epicardial lead to a generator of an active implantable medical device; a distal end including a means for anchoring the epicardial lead to a wall of the epicardium and an active part comprising a plurality of stimulation electrodes, directly coming in contact with, or into, the wall of the epicardium; a distributor housing, placed at or near the distal end of the lead body, and a network of electrically insulated flexible conductors radiating from the distributor housing and extending between a proximal end connected to the distributor housing and a remote and free distal end, the proximal end being electrically connected at or via the distributor housing to an appropriate connection conductor of the lead body. 
         [0027]    Preferably, the flexible conductors are microcable elements having a diameter of at most 2 French (0.66 mm). Each microcable more preferably comprises at least one denuded area, and each of these denuded areas forms one of the stimulation electrodes, such that the stimulation electrodes formed by denuded areas on the same microcable are electrically connected together. Each microcable further comprises at least one transverse elongate member extending at an angle to the main direction of the microcable, for penetrating into the wall of the epicardium. 
         [0028]    In one embodiment, at least one transverse elongated member is a burying loop formed by a curvature of the microcable or a free extension formed on a bypass of the microcable. 
         [0029]    In one embodiment, a radially distal end of said at least one transverse elongate member includes one of said denuded areas, so as to allow the electrode to be buried in the epicardium tissue—below the surface—to provide an in depth stimulation of the epicardium. 
         [0030]    In one embodiment, each microcable comprises a succession of elongated portions extending along the main direction of the microcable, separated by compliance loops extending in a direction transverse to the microcable and providing the microcable flexibility and extensibility in the longitudinal direction. 
         [0031]    In one embodiment, denuded areas of each microcable are formed at one radially distal end of the compliance loops, so as to allow a stimulation of the epicardium surface. 
         [0032]    In one embodiment, the compliance loops and the transverse elongate elements extend in different respective planes forming an angle between them. 
         [0033]    In one embodiment, the length of each microcable, in the deployed state is between 5 and 80 mm. 
         [0034]    In one embodiment, the distributor housing bears the anchoring means to a wall of the epicardium. 
         [0035]    In one embodiment, the total exposed surface of the denuded areas of each microcable is at most 10 mm 2 . 
         [0036]    In one embodiment, the length in the longitudinal direction of each denuded area of each microcable is at most 10 mm. 
         [0037]    In one embodiment, the lead body encloses a connection conductor comprising a plurality of separate connection conductors, and the lead comprises a corresponding plurality of microcables electrically isolated from each other and respectively connected to the plurality of connection conductors, so as to allow a bipolar or multipolar stimulation between denuded areas of different respective microcables. 
         [0038]    In a preferred embodiment, the lead comprises a corresponding plurality of microcables electrically isolated from each other, and the distributor housing comprises a controlled switch means between on the one hand, a microcable selected from a number of the plurality of microcables and, on the other hand, a common connection conductor of the lead body, so as to allow selection from among the denuded areas from different respective microcables. 
         [0039]    In one embodiment, the microcable is formed of a plurality of wires twisted together, wherein at least some of the wires incorporate a core of a radio-opaque material such as platinum-iridium or tantalum wrapped in a mechanically durable sheath of a material such as nitinol (NiTi) or stainless steel (or vice versa). 
         [0040]    Preferably, the microcable comprises a multiwire structure coated by an insulating material, for example, parylene or a sheath of PET or PMMA, wherein the denuded areas are formed by ablation, leaving openings in the insulating layer along the microcable. 
         [0041]    In one embodiment, the distal end of each microcable has a curved needle for stitching and burying of the microcable during implantation of the lead, this needle being subsequently separated from the microcable by cutting (e.g., an absorbable suture may be provided between the needle and the end of the microcable for this purpose). 
         [0042]    In another aspect, there is an epicardial stimulation lead including a lead body having at a distal end a distributor housing, wherein the distributor housing comprises an anchor for anchoring the distal end of the lead body to a patient&#39;s epicardium. The lead also includes an active part comprising a plurality of flexible microcables coupled to the distributor housing at a proximal end and having a free distal end remote from the distributor housing, said microcables being electrically connectable via the distributor housing to a connection conductor of the lead body. Each microcable has a diameter that is smaller than a diameter of the lead body and has a stimulation electrode adapted to contact or penetrate an epicardium wall. Each microcable also includes a transverse elongated member extending at an angle relative to a main direction of the microcable for penetrating into the wall of the epicardium. 
         [0043]    In yet another aspect, there is a method for implanting an epicardial lead at or in a heart wall including attaching a distributor housing to the heart wall, the distributor housing being positioned at a distal end of a lead body, wherein the lead body extends between a connector at a proximal end for connecting the lead to a generator of an active implantable medical device and the distributor housing at the distal end. The method further includes implanting a plurality of microcables on the heart wall such that a stimulation electrode on the microcable is in contact with the heart wall, wherein the plurality of microcables extend from the distributor housing and have a free end distal from the distributor housing. 
     
    
     
       DRAWINGS 
         [0044]    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 annexed drawings, in which; 
           [0045]      FIG. 1  schematically illustrates an epicardial lead according to a first preferred embodiment of the present invention; 
           [0046]      FIG. 2  schematically illustrates an epicardial lead according to a second embodiment of the present invention wherein each microcable has a plurality of stimulation electrodes; 
           [0047]      FIG. 3  schematically illustrates an epicardial lead according to a third embodiment of the present invention implementing a multiplexing system between the different microcables of the lead; 
           [0048]      FIG. 4  illustrates a perspective view of a first representative configuration for a microcable for an epicardial lead of the present invention; 
           [0049]      FIG. 5  illustrates the microcable of  FIG. 4 , seen in projection in two orthogonal planes P 1  and P 2 ; 
           [0050]      FIG. 6  illustrates a variant of  FIG. 5 , with a different positioning of the stimulation electrodes; 
           [0051]      FIG. 7  is a schematic plan view of an epicardial lead according to the present invention, implanted with a microcable configuration such as that illustrated in  FIG. 5 ; 
           [0052]      FIG. 8  is homologous to the epicardial lead of  FIG. 7 , in a cross-sectional view through the heart wall; 
           [0053]      FIG. 9  illustrates a perspective view of a second possible configuration of a microcable for a lead of the present invention; 
           [0054]      FIG. 10  illustrates the microcable of  FIG. 9 , seen in projection in two orthogonal planes P 1  and P 2 ; and 
           [0055]      FIG. 11  is a schematic view, in cross section, through the heart wall, of an epicardial lead according to the present invention, implanted with the microcable configuration of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0056]    With reference to the drawing  FIGS. 1-10 , several exemplary embodiments of an epicardial lead in accordance with the present invention will now be described. 
         [0057]    The epicardial lead  10  according to the present invention essentially comprises a lead body  12  terminated at its proximal end by a connector  14  of conventional type (IS-1 or IS-4). 
         [0058]    At its distal end, lead body  12  has a distributor housing or hub  16  provided with anchoring means of a known type (e.g. a suture or a screw), but which is not stimulating: indeed, the present invention does not expect or require distributor housing  16  to carry a stimulation electrode. Distributor housing  16  preferably includes a perforated foil collar to strengthen the anchoring by development of fibrosis. Distributor housing  16  may, for example, have a flattened cylindrical shape, with a typical diameter of 6 mm and a height of 4 mm. 
         [0059]    In one embodiment, a plurality of microcables  18  is connected to distributor housing  16  by their proximal ends, their other distal ends being free (optionally already provided with a needle attached for the surgeon to use, who removes it once the implantation is performed). Distributor housing  16  includes typically six to eight microcables  18 , but this number is given only as an example and is not intended to be limiting in any way. The length of each microcable  18 , in the deployed state, is typically between 5 and 80 mm. 
         [0060]    Distributor housing  16  ensures the physical connection of each electrical microcable  18  with a corresponding internal conductor of lead body  12 , this conductor extending to connector  14 . 
         [0061]    The term “microcable” should be understood to refer to a very small diameter cable, of at most two French (0.66 mm), preferably about 1 French (0.33 mm). Each microcable is formed of an electrically isolated metallic conductor, except for at least one denuded area  20  or “window”, forming a corresponding stimulation electrode (represented by a star in the Figures). 
         [0062]    In the embodiment illustrated in  FIG. 1 , each microcable  18  includes one denuded area  20 ,  20 ′ forming an electrode (hereinafter, the terms “denuded area”, “electrode” and “window” are interchangeably used). 
         [0063]    A first number of microcables  18  carry electrodes  20  and are connected together in distributor housing  16  to a first conductor of lead body  12 , and a second number of microcables  18  carrying electrodes  20 ′ connected together and to a second conductor of lead body  12 , the second conductor being different from the first conductor. It is thus possible to apply bipolar pacing between, on one hand, electrodes  20  (schematically shown by white stars) and electrodes  20 ′ (schematically shown by black stars). 
         [0064]    With reference to  FIG. 2 , an embodiment is shown in which each microcable  18  carries a plurality of electrodes, for example, two electrodes  20  or two electrodes  20 ′, which thus expands the stimulation area along a same microcable. 
         [0065]    With reference to  FIG. 3 , a third embodiment is illustrated in which microcables  18  respectively include electrodes  20 ,  20 ′,  20 ″,  20 ′″ . . . and wherein each microcable  18  is connected to the input of a multiplexing module having a switch incorporated in distributor housing  16 . An appropriate command sent to the multiplexing module housing is used to select at will via the switch the one or the other set of electrodes  20 ,  20 ′,  20 ″,  20 ″″ . . . to test the possible stimulation sites and choose the one or ones providing the best results from a physiological standpoint. The multiplexing system can be, for example, that described in EP 1938861 A1 (and its counterpart: U.S. Pat. Publication No. 2008/0177343) and EP 2082684 A1 (and its counterpart: U.S. Pat. Publication No. 2009/0192572) (both assigned to Sorin CRM S.A.S., previously known as ELA Medical), which are hereby incorporated herein by reference. Such a multiplexing module allows in particular to implement the concept of “electronic repositioning” to direct or redirect the electric field between different electrodes by selecting, among the various possible configurations, those providing the best efficiency from the electrical and hemodynamic points of view. This technology also helps to manage the behavior of hemodynamic changes (reverse remodeling), simply by reprogramming the generator via telemetry through the skin, without the need for further surgical intervention. 
         [0066]    In a preferred embodiment, to increase the stimulation area a variant of the present invention is to provide, for example, four independent microcables  18  or groups of microcables  18  each connected to four separate conductors within lead body  12 . Connector  14  is then implemented as an appropriate connector, for example, of the IS-4 type, thus benefiting from four independent stimulation areas. 
         [0067]    In all cases, denuded areas  20  of each microcable  18  form a succession of individual electrodes, together constituting a set of electrodes connected in series. This allows multiple points of contact with the heart wall and thus ensures a multi-zone distribution of the stimulation energy at several points in the epicardium and thus the left ventricle. 
         [0068]    Preferably, the individual surface area of each electrode is at most 1 mm 2 , which allows disposing several electrodes on microcable  18  without exceeding a combined total area of 10 mm 2 . Due to the low cumulative surface area, the benefits of a “high current density” lead is achieved, with both more efficient physiological stimulation and reduced energy consumption. Advantageously, this is achieved maximizing the likelihood of physical, therefore electrical, contact between the electrodes and excitable tissue, due to the multiplication of these electrodes. 
         [0069]    Regarding microcable  18  used in these various embodiments, the core of it is advantageously made of nitinol (NiTi alloy) or of MP35N-LT (35% Ni, 35% Co , 20% Cr and 10% Mo stainless steel), materials whose main advantage is their extreme endurance and fatigue resistance, with a coating of platinum-iridium. The result is native corrosion resistance at the electrodes, while ensuring fatigue resistance, which are imperatively required. 
         [0070]    More preferably, the structure of microcable  18  is advantageously a multiwire structure in which each wire strand is preferably consisting of a core of platinum-iridium coated by a thickness of nitinol or MP35N-LT- or vice versa, so as to optimize response to the requirements of both corrosion and fatigue resistance. The wire strands can then be coated with a thin layer of parylene (for example, of C type). In this case, more or less complex windows are arranged along the microcable, for example by plasma ablation, to form electrodes  20 . To improve the electrical performance, these denuded areas can further be coated, for example, with titanium nitride. Alternatively, the wire strands can be enveloped in a polyurethane tube interrupted (i.e., containing apertures) at the locations of electrodes  20 ; or one or more layers made of tubes made of PET (polyethylene terephthalate), fluoropolymer, PMMA (methyl polymethacrylate), PEEK (polyetheretherketone), polyimide or other suitable similar material. 
         [0071]    Such a microcable structure, without any internal lumen and with several microwires braided together, is both enduring (against cardiac movements) and resisting to stress in particular during the implantation. 
         [0072]    Another advantage of this solution, particularly significant, is due to the highly flexible and floating (floppy) property of the microcable, which provides excellent atraumaticity. In chronic implantation, such a microcable is very non traumatic to the tissues and thus preserves the cells in the immediate vicinity of the electrodes: one can therefore expect good electrical performance including in the long term, unlike the traditional epicardial leads, which are far more traumatic. 
         [0073]    These types of braided microcables are available, for example, from Fort Wayne Metals Inc., Fort Wayne, Indiana, USA, and are used in the medical field in particular for the production of defibrillation conductors—but having a different arrangement of materials: in these known applications the structure is a multiwire structure in which each wire includes a core of silver (to improve conductivity) coated by a thickness of stainless steel; these microstructures, isolated or not, are then incorporated into a multi-lumen lead body of classic construction. 
         [0074]    Alternatively, it is nevertheless possible to have a platinum-iridium wire in the center of a 1×7-type multiwire structure, the more fragile wire being then embraced and protected by the more durable outer wires. 
         [0075]    Finally, the platinum-iridium material can be replaced by any radio opaque material such as tantalum. 
         [0076]    Various possible geometric conformations of microcables  18  (preformed at manufacturing), with reference to  FIGS. 4-11 , will now be discussed. 
         [0077]    In  FIGS. 4 and 5 , a first representative configuration is illustrated, wherein microcable  18  comprises a series of alternating corrugated portions  22 ,  24  with one or more transverse elongate members  22  extending in a first plane P 1  and compliance loops  24  extending in a second plane P 2  orthogonal to the plane P 1 , the intersection of these two planes P 1  and P 2  coinciding with the main direction Δ (longitudinal direction) of microcable  18 . 
         [0078]    Transverse elongate members  22  are landfill loops designed to make a penetration in the thickness of the epicardium, with the locally denuded areas  20  forming the stimulation electrodes, which are located on top of landfill loops  22 . 
         [0079]    Compliance loops  24 , for example, formed as two half-periods of a sinusoid or of a similar shape, can prevent the transmission of cyclic stresses, resulting from the beating of the heart, to the stimulating areas formed by the electrodes  20  on top of landfill loops  22 . 
         [0080]    Note that the simplicity of the structure - isolated microcable with occasionally denuded areas forming the electrodes—allows without difficulty having an electrode on top of a (preshaped) ripple (corrugation) of the microcable, which would be much more difficult with conventional structures, for which it is considered that the areas of maximum curvature a priori are the most stressed ones, which leads to avoid locating the electrodes there. 
         [0081]    Furthermore, placing denuded areas  20  at the top of the landfill loops  22  offers the possibility of employing sector electrodes. In this regard, in cross-sectional view, the denuded areas do not span around the entire periphery of microcable  18 , but rather only span over an angular sector located on the side of the outer face of the curvature, that is to say the side facing the tissues with which they come into contact. It is thus possible to keep isolated much of the angular sector, which further limits the stimulating surfaces, resulting in the direct benefits outlined above in terms of increase of the current density. 
         [0082]    The use of a buried electrode corresponding to the configuration of  FIGS. 4 ,  5  and  8  allows in deep stimulation and reduces the risk of phrenic nerve stimulation, and the deep stimulation that it provides ensure better efficiency from the electrical and hemodynamic point of view. 
         [0083]    Alternatively, it is possible to provide a different configuration, such as that illustrated in  FIG. 6 , wherein the electrodes  20  are arranged at the top of the compliance loops  24 . Landfill loops  22  are then only used as anchors of the microcable to the heart wall. With this second configuration, the surface in which the compliance loops  24  extend is preferably a curved surface S 2  ( FIG. 4 ) instead of a plane P 2 , with a curvature directed towards the wall (that is to say in the direction of landfill loops  22 ). This allows forcing the mechanical contact of electrodes  20  with the muscle surface, due to the vertical spring effect of compliance loop  24 , since the curvature of surface S 2  is, in the free state, greater than that of the heart muscle. 
         [0084]    With, in this method, a surface contact with the electrode instead of a buried electrode, the trauma suffered by the tissues is reduced, which increases the electrical performance. To reduce the risk of phrenic nerve stimulation, it is possible to sectorize the surface of stimulation electrodes  20  located at the top of compliance loops  24 , that is to say the side facing the tissues with which they come into contact. It is thus possible to keep isolated much of the angular sector, which further limits the stimulating surfaces, resulting in the direct benefits outlined above in terms of increasing the current density. 
         [0085]      FIGS. 7 and 8  are schematic views, respectively a plan view and a cross section view through the heart wall  26 , of an epicardial lead according to the present invention with a microcable configuration such as that illustrated in  FIG. 5 , in an implanted situation. 
         [0086]    The implantation of the lead according to the invention begins with the attachment of the distribution housing  16  to the heart wall. 
         [0087]    The next step is to successively implant the various microcables on the heart wall, with burial of loop or loops  22  to ensure the continued position of the microcable. These loops  22 , carrying (or not) the stimulation electrodes, may be buried in the muscle by a series of regularly spaced punctures. 
         [0088]    The end of the microcable is equipped for this purpose, as explained above, with a curved needle, preferably factory fitted, to bite/bury the microcable at regular intervals, the needle being cut off after burial. The cut end of the microcable is then isolated by a deposit of biocompatible glue. To minimize the risk of creating an additional electrode at the location of the cut, it is possible to insert an absorbable suture between the needle and the end of microcable, the cut separating the needle being then performed on the absorbable suture. 
         [0089]    It should be understood that the particular configuration of the lead of the invention is particularly well suited to an intervention by robotic microsurgical techniques, taking advantage of the remarkable capabilities of this technology to automatically operate “microsutures” controlled at a distance by the surgeon. 
         [0090]      FIGS. 9 ,  10  and  11  are counterparts of  FIGS. 4 ,  5  and  8 , respectively, for a variant of the microcable in which the one or more transverse elongated elements, instead of being landfill loops, are free extensions  28  substantially straight, bearing at their free end stimulation electrode  20 . These extensions  28  are connected at their other end to microcable  18  running on the surface of the heart muscle (this microcable  18  being of course provided with compliance loops  24  to prevent the transmission of stresses between the free extensions  28 ). 
         [0091]    For implantation, each free extension  28  can be previously housed inside a puncture breakable micro-needle, to achieve the burial of the stimulating free extension  28  by insertion of the needle and subsequent removal of it (thanks to its breakability) once the landfill is made. 
         [0092]    This microcable configuration delivers a deep stimulation of the myocardium, close to endocardial stimulation. 
         [0093]    After surgery, the epicardial emergence of the free end is fixed to the wall by a known attachment method such as suture or deposit of adhesive point  30  of a biocompatible surgical adhesive such as BioGlue (registered trademark) available from Cryolife, Inc. (http://www.cryolife.com/products/biodlue-surqical-adhesive). 
         [0094]    One skilled in the art will appreciate that the present invention can be practiced by embodiments other than those described herein, which are provided for purposes of explanation, and not of limitation.