Abstract: A lead assembly comprises a lead body extending from a lead proximal end portion to a lead distal end portion with at least one conductor disposed therein. A lead lumen extends within the lead body and is dimensioned and configured to removably and rotatably seat a driver therein. The driver includes a driver body extending from a driver proximal end to a driver distal end and having a stylet or guidewire lumen disposed therein. An extendable and retractable active fixation mechanism is disposed at the lead distal end portion. The active fixation mechanism is actuatable by rotation of the driver. In one example, the at least one conductor includes a first conductor and a second conductor, in which the first conductor is co-radial with the second conductor. In another example, the driver distal end includes a portion extractably engagable with the lead distal end portion.