An implantable medical system comprising: at least one medical electrical lead (14, 16, 18) including: a plurality of electrodes (20, 22, 26, 30, 32, 34, 36, 40, 42) carried by the at least one medical electrical lead; and a plurality of electrical conductors (62, 64), each of the plurality of electrical conductors electrically connected to a respective one of the plurality of electrodes; an implantable medical device adapted to be coupled to the at least one medical electrical lead, the implantable medical device including: a sensing module electrically coupled to the plurality of electrical conductors when the implantable medical device is coupled to the at least one medical electrical lead, the sensing module configured to sense a cardiac signal using at least one of the plurality of electrodes; and a controller electrically coupled to the sensing module; characterised in that the controller is configured to receive the cardiac signal, determine a slope of the cardiac signal, compare the slope of the cardiac signal to a short circuit threshold, and detect a short circuit event within the medical electrical lead when the slope of the cardiac signal exceeds the short circuit threshold. at least one medical electrical lead (14, 16, 18) including: a plurality of electrodes (20, 22, 26, 30, 32, 34, 36, 40, 42) carried by the at least one medical electrical lead; and a plurality of electrical conductors (62, 64), each of the plurality of electrical conductors electrically connected to a respective one of the plurality of electrodes; an implantable medical device adapted to be coupled to the at least one medical electrical lead, the implantable medical device including: a sensing module electrically coupled to the plurality of electrical conductors when the implantable medical device is coupled to the at least one medical electrical lead, the sensing module configured to sense a cardiac signal using at least one of the plurality of electrodes; and a controller electrically coupled to the sensing module; a plurality of electrodes (20, 22, 26, 30, 32, 34, 36, 40, 42) carried by the at least one medical electrical lead; and a plurality of electrical conductors (62, 64), each of the plurality of electrical conductors electrically connected to a respective one of the plurality of electrodes; an implantable medical device adapted to be coupled to the at least one medical electrical lead, the implantable medical device including: a sensing module electrically coupled to the plurality of electrical conductors when the implantable medical device is coupled to the at least one medical electrical lead, the sensing module configured to sense a cardiac signal using at least one of the plurality of electrodes; and a controller electrically coupled to the sensing module; a sensing module electrically coupled to the plurality of electrical conductors when the implantable medical device is coupled to the at least one medical electrical lead, the sensing module configured to sense a cardiac signal using at least one of the plurality of electrodes; and a controller electrically coupled to the sensing module; characterised in that the controller is configured to receive the cardiac signal, determine a slope of the cardiac signal, compare the slope of the cardiac signal to a short circuit threshold, and detect a short circuit event within the medical electrical lead when the slope of the cardiac signal exceeds the short circuit threshold.