Rotational atherectomy device with frictional clutch having magnetic normal force

An embodiment is a rotational atherectomy system, comprising: an elongated, rotatable, flexible drive shaft having a distal end for insertion into a vasculature of a patient and having a proximal end opposite the distal end remaining outside the vasculature of the patient; a motor for rotating the drive shaft; and a clutch having a characteristic threshold torque, comprising: a motor plate rotationally connected to the motor; and a drive shaft plate rotationally connected to the drive shaft, the motor plate and the drive shaft plate being parallel and coaxial, being disposed directly longitudinally adjacent to each other, and being held together longitudinally by a magnetic attractive force between the motor plate and the drive shaft plate. Torques between the motor and the drive shaft less than the threshold torque are transmitted completely between the motor plate and the drive shaft plate, which remain held together rotationally by static friction. Torques between the motor and the drive shaft greater than the threshold torque cause the motor plate and the drive shaft plate to slip rotationally past each other. Torques between the motor and the drive shaft greater than the threshold torque cause a residual torque to be transmitted between the motor and the drive shaft, the residual torque being less than the threshold torque and being determined by a kinetic coefficient of friction between the motor plate and the drive shaft plate.