An endovascular device, including an elongated flexible sheath defining a lumen with an inner opening sized for enabling selective advancement of an endovascular instrument therethrough, the sheath having at least a first region and a second region; an electrode within the first region of the sheath; and a constrictor associated with the first region of the sheath, the constrictor being configured, while at least the first region and the second region of the sheath are positioned within a body and in response to an input received from outside the body, to reversibly narrow the lumen of the sheath in an area adjacent the electrode to thereby bring the electrode into contact with an adjacent portion of the endovascular instrument.