a controller for use with a guidewire , such as a vascular guidewire , provides a mechanism for gripping and applying a torque to the guidewire without the need to thread the guidewire axially through the controller and at a location close to a point of access of the guidewire . in one embodiment , the controller includes a side - access , multi - part assembly including a collett or other gripping element that applies a uniform radially inward force on the guidewire . in another embodiment , for use with guidewires having active electrically controllable elements , the controller integrally or removably incorporates a switch or other mechanism to initiate an energized state . the controller thereby permits , among other advantages , ergonomic , single - handed control of an electronically steerable guidewire , including axially displacing , torquing and steering the guidewire .