This system includes a conductor microcable and an insulating microcatheter, including a hollow tube housing the microcable with the possibility of relative axial translation therebetween. The microcatheter is suitable for permanent implantation. The microcatheter, in its distal portion, includes at least one lateral window formed by a through orifice formed on the wall of the hollow tube. The window forms a stimulation site defined on the wall of the target vein facing the window of the microcatheter, and provides for a region of the microcable surface located at the window to form a stimulation electrode. In its distal portion, the microcable is not isolated at least in the region of the window of the microcatheter. The microcatheter is telescopically moveable on the microcable, so as to modify the position of the stimulation site of the target vein.