A fastener for attaching a device to a catheter used to mediate a procedure in a patient's body, the fastener dimensioned so that it and the device can be introduced into the patient's body with the catheter and comprising: a clutch controllable to lock the fastener onto and to unlock the fastener from the catheter; and a controller operable to control the clutch selectively to lock onto and unlock from the catheter when the catheter and fastener are inside a body of a patient.
