A monitoring system comprises an implantable intra- vascular support device for positioning against a vessel wall and an implantable sensor-actuator mounted to the support device. The sensor-actuator is drivable between a non-deployed position in which it is against the support device and a deployed position in which it is displaced away from the support device. Sensor signals are generated when in the deployed position. This system is able to monitor flow away from the edge of a vessel by deploying the sensor-actuator towards the center of the vessel. When flow monitoring does not need to take place, it can be non- deployed so that it does not present an occlusion to the flow.
