An apparatus and a method are described in which a signal is received from a gyroscope sensor mounted on a subject. The gyroscope sensor is configured to measure rotational movement of the subject's heart, the signal being indicative of a left ventricular twist of the subject's heart. A change in the left ventricular twist of the subject's heart caused by occlusion of blood flow by an arterial occlusion device configured to selectively occlude blood flow of the subject is determined.