Implantable lead for sensing mechanical activity of a human heart. The lead comprises an insulating polymeric tube extending from a proximal end to a distal end of the lead, an electric conductor provided in the lumen of the polymeric tube, and a sensor connected to the conductor at a distal end thereof. The polymeric tube is provided with a conductive surface layer along the interface between the polymeric tube and the electric conductor. Thereby, accumulation of electrical charges between the electric conductor and the polymeric tube is prevented.