The assembly has a screw probe (26) with a structure deployed in a left ventricle cavity, where the structure is a microcable (42) with eclectically conductive core diameter between 0.2 and 0.4 mm in an active free part (58) that is a plate loop. The microcable comprises a strand formed of a set of plies with a composite ply including a material presenting mechanical resistance properties to flexural fatigue higher than mechanical resistance properties of the other materials of the ply and radiopaque material.
