Real-Time Electrocardiogram Monitoring During Treadmill Training in Mice

Real-time assessment of marine electrophysiological properties during training has been challenging so far. This protocol provides an approach to overcome this by allowing real-time ECG monitoring before, during and after treadmill training. Combining treadmill training and real-time ECG monitoring allows to gain new insights into the relationship between exercise and arrhythmias, especially in inherited arrhythmia syndromes using transgenic mouse models.

The method in itself is straightforward but needs careful attention during transmitter implantation and electrical lead positioning to ensure good signal to noise ratio. Aparna Chivukula and Kavi Raj Chataut, two PhD students in my lab will demonstrate the procedure. Activate the transmitter by placing the supplied magnet in close proximity.

Following activation, test the signal from the transmitter using a radio device at 530 hertz AM frequency, a sharp and clear beep indicates the transmitter is activated, whereas an inactivated transmitter does not give any signal. Switch on the treadmill. Set the treadmill slope, speed and shock intensity according to the training protocol.

Press on Settings in the control unit and select Grid Test. This opens a grid size selection screen. Select Mice.

Press on Start to begin the shock test. To begin the test, confirm the warning by touching the screen. Place the conductive part of the sponge accessory provided with the treadmill on the grid of the treadmill.

Place it until the word pass"appears on the screen. Test all grids like this. The test will end automatically after all lanes successfully pass it, but can be stopped anytime by the user by pressing the Stop button.

To continue with the cleaning test, press Start and wait for the test to run. Transfer the animal to the running compartment. Place the signal receiver on the transparent box and connect the signal receiver via the connecting cable to the data acquisition system, which consists of a data exchange matrix and a signal interface, which in turn connects to a computer with the acquisition software running to view the ECG signal during the experiment.

Press Start to enter the running mode. Upon completion, remove the signal receiver from the transparent box and place it back underneath the cage as shown. Turn off the treadmill to avoid any unwanted shocks.

Electrocardiogram data with clear P, Q, R, S and T waves in animals during training was obtained. Heart rate increases to around 800 beats per minute when the animal is exercising, and gradually recovers toward baseline after training. PR interval, QRS duration, and QTc intervals shorten under stress, and once the stress is over, return to baseline.

Detection of tachycardia and bradycardia episodes shows sinus rhythm at baseline and sinus tachycardia during training. Heart rate increases during training and gradually returns to baseline post-training. This trend can also be visualized by the median RR interval.

A comparable standard deviation of RR intervals was obtained at baseline and during training by automated RR annotation, demonstrating data quality. One of the most critical steps is the positioning of the signal receiver on the transparent box to ensure good signal to noise ratio.