A therapy assembly configured for at least partial insertion in a living body. At least one fixation structure is attached to the therapy delivery element proximate the electrodes. The fixation structure is configured to collapse radially inward and wrap circumferentially around the therapy delivery element to a collapsed configuration when inserted into a lumen of an introducer. The fixation structures deploy to a deployed configuration when the introducer is retracted. The fixation structure includes major surfaces generally parallel with, and extending radially outward from, a central axis of the therapy delivery element, proximal edge surface oriented toward the proximal end, and a distal edge surface oriented toward the distal end. The proximal and distal edge surfaces provide generally symmetrical resistance to displacement of the therapy delivery element within the living body in either a proximal direction or a distal direction along the central axis.