An improved guide wire brake that is particularly suited to ablative rotational atherectomy devices is disclosed. The guide wire brake ensures that a guide wire is prevented from rotating or moving axially prior to activation of a primary mover such as a turbine. In one embodiment a pressure relief valve delays the activation of the prime mover on start up, and a check valve delays the release of the guide wire brake on shut down. In a second embodiment the guide wire brake is serially connected to the prime mover such that the prime mover is not connected to the pressurized gas source until after the guide wire brake is engaged. In a third embodiment a guide wire is disposed through a flexible tube within a rigid cylinder that is serially connected to the prime mover, such that when pressurized gas is provided to the prime mover the flexible tube will collapse on the guide wire, to prevent guide wire movement. In a fourth embodiment a mechanical brake, in a single action, engages the guide wire prior to opening a flow path between the pressurized gas source and the prime mover. Methods for manually bypassing the guide wire brake are also disclosed.