An implantable medical lead configured for active fixation in the vasculature of a patient includes an elongated lead body having a central lumen and a distal tip. Disposed within the central lumen are a fixation helix and an elongated member, such as a lead coil, coupled to the fixation helix. The elongated member is adapted to rotate the fixation helix, thereby causing it to advance or retract within the central lumen of the lead body. The lead body includes a window along a portion of its length through which the fixation helix may be affixed to a blood vessel of the patients vasculature.
