Measuring Heart Rate in Freely Moving Mice

Measuring autonomic parameters like heart rate in behaving mice is not only a standard procedure in cardiovascular research but is applied in many other interdisciplinary research fields. With an electrocardiogram (ECG), the heart rate can be measured by deriving the electrical potential between subcutaneously implanted wires across the chest. This is an inexpensive and easy-to-implement technique and particularly suited for repeated recordings of up to eight weeks. This protocol describes a step-by-step guide for manufacturing the needed equipment, performing the surgical procedure of electrode implantation, and processing of acquired data, yielding accurate and reliable detection of heartbeats and calculation of heart rate (HR). We provide MATLAB graphical user interface (GUI)-based tools to extract and start processing the acquired data without a lot of coding knowledge. Finally, based on an example of a data set acquired in the context of defensive reactions, we discuss the potential and pitfalls in analyzing HR data. Key features • Next to surgical steps, the protocol provides a detailed description of manufacturing custom-made ECG connectors and a shielded, light-weight patch cable. • Suitable for recordings in which signal quality is challenged by ambient noise or noise from other recording devices. • Described for 2-channel differential recording but easily expandable to record from more channels. • Includes a summary of potential analysis methods and a discussion on the interpretation of HR dynamics in the case study of fear states.