A therapy assembly configured for at least partial insertion in a living body. A plurality of fixation structures are disposed radially around the therapy delivery element proximate the electrodes. The fixation structures include wires having a diameter in a range between about 0.004 inches and about 0.020 inches. The wires have a first end attached to the therapy delivery element and a second end attached to a sliding member configured to slide along the therapy delivery element. The fixation structures are configured to collapse inward to a collapsed configuration when inserted into a lumen of an introducer and to deploy to a deployed configuration when the introducer is retracted. A fitting is located at proximal end of the introducer that releasably locks the therapy delivery element to the introducer, such that torque applied to the fitting is substantially transmitted to the distal end of the therapy assembly.