An electrical parameter value indicative of an impedance of an electrical path between a first medical device implanted within a patient and a second medical device implanted within the patient may be determined by generating and delivering an electrical signal between electrodes connected to the first medical device and sensing the electrical signal with two or more sense electrodes connected to the second medical device. In some examples, the electrical parameter value indicative of the impedance may be used to detect a system integrity issue, such as relative movement between the first and second medical devices, such as between leads connected to the medical devices, or a lead-related condition. In other examples, the determined impedance may indicate a transthoracic impedance of the patient.
