An apparatus comprising: a processor circuit, including: an input, configured to receive an intrathoracic electrical response signal obtained from a subject in response to a delivered subcapture electrical test stimulus, the test stimulus delivered and the response signal obtained during both first and second time periods, in which the subject is in different first and second posture positions during the respective first and second time periods; and an evaluation circuit, operatively coupled to the input, the evaluation circuit configured to process information about a change in the response signal between the first and second time periods to compute an indication of electrode displacement within the subject between the first and second time periods; and an output, configured to provide the indication of electrode displacement to a user or an automated process, characterized in that the input of the processor circuit is configured to receive a posture-indicative signal obtained from a subject during the first and second time periods; wherein the processor is configured to declare an electrode displacement occurrence, between the first and second time periods, in response to a decrease in thoracic impedance exceeding a specified threshold value, within a specified period of time, when the patient shifts from a recumbent posture position to an upright posture position between the first and second time periods. a processor circuit, including: an input, configured to receive an intrathoracic electrical response signal obtained from a subject in response to a delivered subcapture electrical test stimulus, the test stimulus delivered and the response signal obtained during both first and second time periods, in which the subject is in different first and second posture positions during the respective first and second time periods; and an evaluation circuit, operatively coupled to the input, the evaluation circuit configured to process information about a change in the response signal between the first and second time periods to compute an indication of electrode displacement within the subject between the first and second time periods; and an output, configured to provide the indication of electrode displacement to a user or an automated process, characterized in that the input of the processor circuit is configured to receive a posture-indicative signal obtained from a subject during the first and second time periods; an input, configured to receive an intrathoracic electrical response signal obtained from a subject in response to a delivered subcapture electrical test stimulus, the test stimulus delivered and the response signal obtained during both first and second time periods, in which the subject is in different first and second posture positions during the respective first and second time periods; and an evaluation circuit, operatively coupled to the input, the evaluation circuit configured to process information about a change in the response signal between the first and second time periods to compute an indication of electrode displacement within the subject between the first and second time periods; and an output, configured to provide the indication of electrode displacement to a user or an automated process, characterized in that the input of the processor circuit is configured to receive a posture-indicative signal obtained from a subject during the first and second time periods; wherein the processor is configured to declare an electrode displacement occurrence, between the first and second time periods, in response to a decrease in thoracic impedance exceeding a specified threshold value, within a specified period of time, when the patient shifts from a recumbent posture position to an upright posture position between the first and second time periods.