The invention generally relates to the “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities. This definition includes, in particular cardiac implants that monitor cardiac activity and generate stimulation, defibrillation or resynchronization pulses, in case of arrhythmia detected by the device. It also includes the neurological devices, the cochlear implants, the drug pumps, implanted the biological sensors, etc.
These devices comprise a housing generally designated as the “generator”, electrically and mechanically connected to one or more intracorporeal “leads” provided with electrodes coming into contact with the tissues to which it is desired to apply stimulation pulses and/or collect an electrical signal: myocardium, nerve, muscle.
The present invention more specifically relates to a detection/stimulation microlead for implantation in venous, arterial and lymphatic networks.
The current principle of electrical stimulation uses a device, usually called “lead”, which is implanted through various venous, arterial or lymphatic vessels, the function of which is to transmit an electrical signal to the target tissue while maintaining the following general properties:                Ease of implantation by the physician in a network of vessels of the patient, and especially easy: to advance the lead into the vessels by pushing, to make the lead follow tortuous branches and pass routes, and transmit torques;        X-ray visibility to allow the physician easy navigation through the network vessels under X rays;        Atraumaticity of the lead in blood vessels, which requires a flexible structure and the absence of rigid transition or sharp edges;        Ability to transmit an electrical signal to the tissues and to stably perform monopolar or multipolar electrical measurements;        Biocompatibility with living tissues to allow long-term implantation tissue;        Biostability, especially corrosion resistance in the living environment and resistance to mechanical stress fatigue related to patient movement and organs;        Ability to withstand sterilization (gamma rays, temperature . . . ) without damage; and        Compatibility with MRI imaging, particularly important in neurology.        
The current architecture of the known leads meeting these requirements can be reduced to a generally hollow structure allowing the passage of a stylet or a guidewire, and comprising components such as insulated conductor cables connected to mechanical electrodes to ensure electrical conductivity, radiopacity, etc. These leads therefore require complex assembly of a large number of parts, of associated wires and insulating parts, creating significant risk of breakage due to long term mechanical stresses to which they are exposed. Examples of such leads are given in U.S. Pat. Nos. 6,192,280 A and 7,047,082 A.
Among the difficulties encountered, the management of stiffness gradients related to the mechanical parts used can be cited, which strongly affect the implantability properties and mechanical strength in the long term (fatigue). Other problems may also arise in terms of fatigue assemblies. Indeed, any stiffness transition zone may induce risks of fatigue, difficulty to sterilize due to the presence of areas of difficult access, and problems of mechanical resistance of conductor junctions at the connection with the electrodes and the connector.
Moreover, the clinical trend in the field of implantable leads is to reduce the size to make them less invasive and easier to handle through the vessels. The current size of implantable leads is typically of the order of 4 to 6 Fr (1.33 to 2 mm). However, it is clear that reducing the size of the leads would increase complexity and impose technical constraints generating risks. However, such a reduction to less than 1.5 French (0.5 mm) or 1 French (0.33 mm), for example, open up prospects for medical applications in various fields, ranging from cardiology to neurology in the presence of a venous, arterial or even lymphatic network, such as the cerebral venous network or the coronary sinus venous network.
Today, the technology of electrical stimulation has led to major advances in the field of neuromodulation, which is to stimulate target areas of the brain for treatment of Parkinson's disease, epilepsy and other neurological diseases. One could imagine, with this type of technology, to address new areas difficult to reach today, by small pacing leads or “microleads”, with great strength to ensure long-term biostability. With small microleads, it is notably possible to consider the passage in deep coronary vessels to disclose for example a device for stimulation of the left ventricle via two distinct areas. Such a technique would also allow a less invasive approach and especially superior efficacy of these treatments.
It would also be possible to connect one or more microleads through the vessel network considered to the target location. Their implantation could be done, because of their small size, by guiding devices currently used in interventional neuroradiology for the release of springs (coils) in the treatment of intracranial aneurysms. In particular, microleads of 1.5 French would allow the use of implantable catheters of an inner diameter of 1.6 French.
With particular regard to the resynchronization of the cardiac rhythm, left leads currently used are placed in or at the entrance of the coronary sinus because the progression is difficult and often limited by the gradual reduction of the diameter of the sinus passage. Monopolar microleads with a section below 1 French or multipolar microleads whose microcables' diameter is also less than 1 French open new opportunities for physicians to consider implanting beyond the coronary sinus and to position the stimulation electrodes in the deep coronary vessels of the left heart.
EP 2455131 A1 and its US counterpart U.S. Pat. No. 8,521,306 (Sorin CRM SAS) disclose a lead constituted in its active distal part by a microcable having a diameter of about 0.5 to 2 French (0.17 to 0.66 mm). This microcable comprises an electrically conductive core cable formed by a strand of a plurality of composite strands, with a polymer insulation layer partially surrounding the core cable and punctually exposed so as to expose the microcable in one or more points constituting an array of electrodes connected in series, the free end of the strand being also provided with a reported distal electrode. This configuration allows multiplication of the points of stimulation in a deep area of the coronary network.
However, this leads to new technical problems. In particular, the veins of the coronary arteries have a very narrow section, and are consequently very thin, thus inducing a risk of perforation by the microleads having a microcable structure. In addition, during manufacturing, various irregularities (hurtful edges, pointy strands, out of isodiameter strands, etc.) are met in the zone the microcable is cut (using a cutter or laser shot) at the distal end of the strands, irregularities which all are potential sources of damage to the vein walls. These leads must thus have the least traumatic possible distal end for the veins during implantation and during the life of the patient. In addition, the cardiac movements (diastole, systole) impose different constraints, by friction or compression of the lead on the venous walls. The risk is perforation of the vein and/or of the pericardial sac possibly causing serious bleeding for the patient.
In another context, the FR 2550454 A1 describes a hollow catheter for injection of contrast. The open free end of the catheter has a peripheral edge with a deformable annular balloon bag or otherwise, to avoid too sudden contact between the end of the flexible catheter sheath and the tissues of the organ where the catheter is inserted.