A conductor assembly for a medical device lead includes a helically coiled conductor including a plurality of turns having a coil pitch and an outer diameter and consisting of one filar having a filar diameter. The coil pitch and outer diameter are selected based on the filar diameter to minimize heating of the helically coiled conductor in the presence of an MRI field. A polymer sheath is formed about the helically coiled conductor such that the coil pitch of the unifilar helically coiled conductor is maintained. The polymer sheath is configured to increase a torque transmitting capacity of the helically coiled conductor.
