ECG records the electrical activity generated by heart muscle depolarizations (a negative change in the electric charge), which propagates as pulsating electrical waves towards the skin.

How is ECG signal generated?

Electrical signals are produced by contractions in the heart walls which drive electrical currents and create different potentials throughout the body. By placing electrodes on the skin, one can detect and record this electrical activity in an ECG.

How is an ECG measured?

The ECG is measured by placing a series of electrodes on the patient’s skin – so it is known as the ‘surface’ ECG. The wave of electrical depolarisation spreads from the atria down though the IVS to the ventricles. So the direction of this depolarisation is usually from the superior to the inferior aspect of the heart.